Is accutane Vitamin A?
Vitamin A
Vitamin A, and more specifically, retinoic acid, appears to maintain normal skin health by switching on genes and differentiating keratinocytes (immature skin cells) into mature epidermal cells. Exact mechanisms behind pharmacological retinoid therapy agents in the treatment of dermatological diseases are being researched.
For the treatment of acne, the most prescribed retinoid drug is 13-cis retinoic acid (isotretinoin). It reduces the size and secretion of the sebaceous glands. Although it is known that 40 mg of isotretinoin will break down to an equivalent of 10 mg of ATRA — the mechanism of action of the drug (original brand name Accutane) remains unknown and is a matter of some controversy. Isotretinoin reduces bacterial numbers in both the ducts and skin surface. This is thought to be a result of the reduction in sebum, a nutrient source for the bacteria. Isotretinoin reduces inflammation via inhibition of chemotactic responses of monocytes and neutrophils. Isotretinoin also has been shown to initiate remodeling of the sebaceous glands; triggering changes in gene expression that selectively induce apoptosis. Isotretinoin is a teratogen with a number of potential side-effects. Consequently, its use requires medical supervision.
Ionone
The carotenes α-carotene, β-carotene, γ-carotene, and the xanthophyll, and β-cryptoxanthin, can all be metabolized to β-ionone, and thus have vitamin A activity because they can be converted by plant-eating animals to retinol and retinal. Carotenoids that do not contain the β-ionone moiety cannot be converted to retinol, and thus have no vitamin A activity.
Hand eczema
In the last couple of years an internal medicine has been approved for the first time for the treatment of chronic hand eczema. This involves a derivative of vitamin A, called alitretinoin, which is also naturally present in the human body. Alitretinoin can be used to treat all forms of severe chronic hand eczema which have not reacted to external cortisone preparations. The effectiveness of this form of treatment has been tested extensively in clinical study programs and proven prior to its approval. The trial results showed that two thirds of patients did not suffer a recurrence 6 months after application of the medication, and that re-treatment is effective if hand eczema reoccurs. The duration of alitretinoin treatment is 3 to 6 months. During treatment and one month prior to beginning and one month after completion, women of childbearing-age must use contraceptives and also test for pregnancy each month since, as with all derivatives of vitamin A, the substance involved is teratogenic. Side effects mainly include temporary headaches during the initial days of treatment, as well as a possible increase in blood fat and cholesterol values. Regular laboratory tests of blood values are recommended to monitor this.
Umami
Professor Shintaro Kodama, a disciple of Ikeda, discovered in 1913 that dried bonito flakes contained another umami substance. This was the ribonucleotide IMP. In 1957, Akira Kuninaka realized that the ribonucleotide GMP present in shiitake mushrooms also conferred the umami taste. One of Kuninaka's most important discoveries was the synergistic effect between ribonucleotides and glutamate. When foods rich in glutamate are combined with ingredients that have ribonucleotides, the resulting taste intensity is higher than would be expected from merely adding the intensity of the individual ingredients.
Withaferin A
Withaferin A is a steroidal lactone, derived from Acnistus arborescens, Withania somnifera (Indian Winter cherry or Ashwagandha in Sanskrit) and other members of Solanaceae family. It has been traditionally used in ayurvedic medicine. It is the first member of the withanolide class of ergostane type product to be discovered. This natural product has wide range of pharmacological activities including cardioprotective, anti-inflammatory, immuno-modulatory, anti-angiogenesis, anti-metastasis and anti-carcinogenic properties.
Vitamin A
All forms of vitamin A have a beta-ionone ring to which an isoprenoid chain is attached, called a "retinyl group". Both structural features are essential for vitamin activity. The orange pigment of carrots (beta-carotene) can be represented as two connected retinyl groups, which are used in the body to contribute to vitamin A levels. Alpha-carotene and gamma-carotene also have a single retinyl group, which give them some vitamin activity. None of the other carotenes have vitamin activity. The carotenoid beta-cryptoxanthin possesses an ionone group and has vitamin activity in humans.
Cat food
Vitamin A is a crucial nutritional component in the maintenance of feline skin and coat health. In addition to its many other functions, vitamin A plays an important role in the keratinization of the skin, hair and nails along with assisting in the development of various epithelial tissues throughout the body. The cells making up the epithelial tissues of the skin, respiratory and gastrointestinal tracts rely on vitamin A to successfully complete the process of mitosis in order preserve these tissues and repair any damages. The mucous secreting cells of the respiratory and gastrointestinal epithelium also specifically require vitamin A to successfully produce a specialized protein referred to as mucoproteins which aid in maintaining the health of these tissues. Unlike most other mammals, the cat is unique in that they are unable to transform B-carotene to vitamin A and therefore explicitly require active forms of vitamin A which are only found in animal products. This difference in metabolism is due to very low levels of activity of the enzyme B-carotene 15, 15’ dioxygenase in feline species. The nutrient profiles developed by AAFCO currently advise a minimum of 3332 IU/kg of vitamin A on a dry matter basis included in adult diets and 6668 IU/kg in the diets of growing kittens as well as pregnant or lactating female cats. Common ingredients which help to incorporate the proper levels of vitamin A into feline diets include various types of liver as well as fish oils.
Alitretinoin
It is a CYP3A4 substrate and hence any inhibitor or inducer of this enzyme may alter plasma levels of alitretinoin. It should not be given to patients with excess vitamin A in their system as there is a potential for its actions on the retinoid X receptor to be exacerbated. It may also interact with tetracyclines to cause benign intracranial hypertension.
Stargardt disease
Alkeus Pharma is evaluating the potential of deuterated vitamin A as the drug ALK-001. The hope is that the deuterated vitamin A will reduce the build-up of toxic vitamin A metabolites in the retina and therefore slow rate of visual deterioration. To create deuterated vitamin A some of the hydrogen atoms are replaced with the isotope  deuterium which has an extra neutron and is therefore twice the standard atomic weight of hydrogen. Patients taking this drug will need to have a diet with very low levels of naturally occurring Vitamin A. A Phase II clinical trial is taking place using ALK-001 that should report in January 2019.
Apocarotenal
Apocarotenal, or "trans"-β-apo-8'-carotenal, is a carotenoid found in spinach and citrus fruits. Like other carotenoids, apocarotenal plays a role as a precursor of vitamin A, even though it has 50% less pro-vitamin A activity than β-carotene. The empirical chemical formula for apocarotenal is CHO.
Leukoplakia
Many different topical and systemic medications have been studied, including anti-inflammatories, antimycotics (target Candida species), carotenoids (precursors to vitamin A, e.g. beta carotene), retinoids (drugs similar to vitamin A), and cytotoxics, but none have evidence that they prevent malignant transformation in an area of leukoplakia.Vitamins C and E have also been studied with regards a therapy for leukoplakia. Some of this research is carried out based upon the hypothesis that antioxidant nutrients, vitamins and cell growth suppressor proteins (e.g. p53) are antagonistic to oncogenesis. High doses of retinoids may cause toxic effects. Other treatments that have been studied include photodynamic therapy.
Nicotinamide
Nicotinamide (NAM), also known as niacinamide, is a form of vitamin B3 found in food and used as a dietary supplement and medication. As a supplement, it is used by mouth to prevent and treat pellagra (niacin deficiency). While nicotinic acid (niacin) may be used for this purpose, nicotinamide has the benefit of not causing skin flushing. As a cream, it is used to treat acne.
Side effects are minimal. At high doses liver problems may occur. Normal amounts are safe for use during pregnancy. Nicotinamide is in the vitamin B family of medications, specifically the vitamin B3 complex. It is an amide of nicotinic acid. Foods that contain nicotinamide include yeast, meat, milk, and green vegetables.
Nicotinamide was discovered between 1935 and 1937. It is on the World Health Organization's List of Essential Medicines, the most effective and safe medicines needed in a health system. Nicotinamide is available as a generic medication and over the counter. In the United Kingdom a 60 g tube costs the NHS about £7.10. Commercially nicotinamide is made from either nicotinic acid or 3-cyanopyridine. In a number of countries grains have nicotinamide added to them.
Vitamin A
Vitamin A promotes the proliferation of T cells through an indirect mechanism involving an increase in IL-2. In addition to promoting proliferation, Vitamin A, specifically retinoic acid, influences the differentiation of T cells. In the presence of retinoic acid, dendritic cells located in the gut are able to mediate the differentiation of T cells into regulatory T cells. Regulatory T cells are important for prevention of an immune response against "self" and regulating the strength of the immune response in order to prevent host damage. Together with TGF-β, Vitamin A promotes the conversion of T cells to regulatory T cells. Without Vitamin A, TGF-β stimulates differentiation into T cells that could create an autoimmune response.
Tocopherol
The amounts of alpha-tocopherol, other tocopherols and tocotrienols that are components of dietary vitamin E, when consumed from foods, do not appear to cause any interactions with drugs. Consumption of alpha-tocopherol as a dietary supplement in amounts in excess of 300 mg/day may lead to interactions with aspirin, warfarin, tamoxifen and cyclosporine A in ways that alter function. For aspirin and warfarin, high amounts of vitamin E may potentiate anti-blood clotting action. One small trial demonstrated that vitamin E at 400 mg/day reduced blood concentration of the anti-breast cancer drug tamoxifen. In multiple clinical trials, vitamin E lowered blood concentration of the immuno-suppressant drug, cyclosporine A. The US National Institutes of Health, Office of Dietary Supplements, raises a concern that co-administration of vitamin E could counter the mechanisms of anti-cancer radiation therapy and some types of chemotherapy, and so advises against its use in these patient populations. The references it cited reported instances of reduced treatment adverse effects, but also poorer cancer survival, raising the possibility of tumor protection from the oxidative damage intended by the treatments.
Bleach and recycle
Vitamin A must be consumed in the diet, as it is not synthesisable by the body. It may, however, be consumed indirectly, in the form of carotenoids such as beta carotene, which can be cleaved to form two retinol molecules. It is absorbed in the gut and is transported around the body via two pathways. In the first, and most predominant, it is esterified with a fatty acid to form a retinyl ester, and packaged into a chylomicron. In the second minor pathway, it is bound to Retinol Binding Protein (RBP) and Transthyretin, which prevents its filtration in the glomeruli. It is via this RBP-Transthyretin pathway that the retina receives most of its retinoids.
Plicatin A
Plicatin A is a hydroxycinnamic acid found in "Psoralea plicata".
Golden rice
It is well known that beta carotene is found and consumed in many nutritious foods eaten around the world, including fruits and vegetables. Beta carotene in food is a safe source of vitamin A. In August 2012, Tufts University and others published research on golden rice in the "American Journal of Clinical Nutrition" showing that the beta carotene produced by golden rice is as effective as beta carotene in oil at providing vitamin A to children. The study stated that "recruitment processes and protocol were approved". In 2015 the journal retracted the study, claiming that the researchers had acted unethically when providing Chinese children golden rice without their parents' consent.
Arnold Orville Beckman
Development of the spectrophotometer also had direct relevance to the war effort. For example, the role of vitamins in health was being studied, and scientists wanted to identify Vitamin A-rich foods to keep soldiers healthy. Previous methods involved feeding rats for several weeks, then performing a biopsy to estimate Vitamin A levels. The DU spectrophotometer yielded better results in a matter of minutes. The DU spectrophotometer was also an important tool for scientists studying and producing the new wonder drug penicillin. By the end of the war, American pharmaceutical companies were producing 650 billion units of penicillin each month. Much of the work done in this area during World War II was kept secret until after the war.
Acne
Retinoids are medications which reduce inflammation, normalize the follicle cell life cycle, and reduce sebum production. They are structurally related to vitamin A. The retinoids appear to influence the cell life cycle in the follicle lining. This helps prevent the accumulation of skin cells within the hair follicle that can create a blockage. They are a first-line acne treatment, especially for people with dark-colored skin, and are known to lead to faster improvement of postinflammatory hyperpigmentation.
Hypervitaminosis A
Hypervitaminosis A results from excessive intake of preformed vitamin A. A genetic variance in tolerance to vitamin A intake may occur. Children are particularly sensitive to vitamin A, with daily intakes of 1500 IU/kg body weight reportedly leading to toxicity.
Rose hip seed oil
The oil contains provitamin A (mostly beta-Carotene). It has been wrongly said to contain retinol (vitamin A) which is a vitamin solely made by animals from provitamin A. It does however contain levels (up to .357 ml/L) of tretinoin or all-trans retinoic acid, a vitamin A acid that retinol converts to.
Prunus
Similar to the plum, peaches and nectarines also have higher TAC in the skin than in the flesh. They also contain moderate levels of carotenoids and ascorbic acid. Peaches and nectarines are orange and yellow in color which can be attributed to the carotenoids present. Ascorbic acid is important in hydroxylation reactions, such as collagen synthesis and de novo synthesis of bone and cartilage, and wound healing. Ascorbic acid is also a precursor of Vitamin C, which is essential for repairing tissues and absorbing iron.
Retinol
Excess vitamin A has also been suspected to be a contributor to osteoporosis. This seems to happen at much lower doses than those required to induce acute intoxication. Only preformed vitamin A can cause these problems, because the conversion of carotenoids into vitamin A is downregulated when physiological requirements are met. An excessive uptake of carotenoids can, however, cause carotenosis.
Souvenaid
Souvenaid is a medical food in the form of a thick, yogurt-like drink that is marketed as helping people with Alzheimer's disease. It contains a mixture of docosahexaenoic acid, eicosapentaenoic acid, phospholipids, choline, uridine monophosphate, vitamin E (alpha-tocopherol equivalents), selenium, vitamin B, vitamin B, and folic acid; this mixture is branded as Fortasyn Connect. As of 2017, the product had failed to show a significant effect in decreasing the rate of cognitive decline or delaying progression of Alzheimer's disease, but appeared to cause minor improvement in verbal memory in some people in the very early stages of the disease. The clinical trials that had been conducted were in people with very early Alzheimers and excluded people who ate recommended amounts of food that included fish oil.
Vitamin A
A sample vegan diet for one day that provides sufficient vitamin A has been published by the Food and Nutrition Board (page 120). Reference values for retinol or its equivalents, provided by the National Academy of Sciences, have decreased. The RDA (for men) established in 1968 was 5000 IU (1500 μg retinol). In 1974, the RDA was revised to 1000 RE (1000 μg retinol). As of 2001, the RDA for adult males is 900 RAE (900 μg or 3000 IU retinol). By RAE definitions, this is equivalent to 1800 μg of β-carotene supplement dissolved in oil (3000 IU) or 10800 μg of β-carotene in food (18000 IU).
Retinyl acetate
World Health Organization recommendation on Maternal Supplementation During Pregnancy states that "health benefits are expected for the mother and her developing fetus with little risk of detriment to either, from a daily supplement not exceeding 10,000IU [preformed] vitamin A (3000mcg RE) at any time during pregnancy." Preformed Vitamin A refers to retinyl palmitate and retinyl acetate.
Retinyl palmitate
Retinyl palmitate is a synthetic alternate for retinyl acetate in vitamin A supplements, and is available in oily or dry forms. It is a common vitamin supplement, available in both oral and injectable forms for treatment of vitamin A deficiency, under the brand names Aquasol A, Palmitate A and many others. It is a constituent of intra ocular treatment for dry eyes at a concentration of 138 µg/g (VitA-Pos) by Ursapharm. It is a pre-formed version of vitamin A; therefore, the intake should not exceed the Recommended Dietary Allowance (RDA). Overdosing preformed Vitamin A forms such as retinyl palmitate leads to adverse physiological reactions (hypervitaminosis A).
Castalagin
The flavono-ellagitannin known as acutissimin A is created when the oak tannin vescalagin interacts with a flavonoid in wine.
Granatin A
Granatin A is an ellagitannin found in the pericarp of "Punica granatum" (pomegranate). It is a weak carbonic anhydrase inhibitor.
Pantothenic acid
Pantothenic acid, also called vitamin B (a B vitamin), is a water-soluble vitamin. Pantothenic acid is an essential nutrient. Animals require pantothenic acid in order to synthesize coenzyme-A (CoA), as well as to synthesize and metabolize proteins, carbohydrates, and fats. The anion is called pantothenate.
Isotretinoin
As of 2017 isotretinoin was marketed under many brand names worldwide: A-Cnotren, Absorica, Accuran, Accutane, Accutin, Acne Free, Acnecutan, Acnegen, Acnemin, Acneone, Acneral, Acnestar, Acnetane, Acnetin A, Acnetrait, Acnetrex, Acnogen, Acnotin, Acnotren, Acretin, Actaven, Acugen, Acutret, Acutrex, Ai Si Jie, Aisoskin, Aknal, Aknefug Iso, Aknenormin, Aknesil, Aknetrent, Amnesteem, Atlacne, Atretin, Axotret, Casius, Ciscutan, Claravis, Contracné, Curacne, Curacné, Curakne, Curatane, Cuticilin, Decutan, Dercutane, Effederm, Epuris, Eudyna, Farmacne, Flexresan, Flitrion, I-Ret, Inerta, Inflader, Inotrin, Isac, Isdiben, Isoacne, Isobest, Isocural, Isoderm, Isoface, IsoGalen, Isogeril, Isolve, Isoprotil, Isoriac, Isosupra, Isosupra Lidose, Isotane, Isotina, Isotinon, Isotren, Isotret, Isotretinoin, Isotretinoina, Isotretinoína, Isotretinoine, Isotretinoïne, Isotrétinoïne, Isotretinoinum, Isotrex, Isotrin, Isotroin, Izotek, Izotziaja, Lisacne, Locatret, Mayesta, Myorisan, Neotrex, Netlook, Nimegen, Noitron, Noroseptan, Novacne, Oralne, Oraret, Oratane, Piplex, Policano, Procuta, Reducar, Retin A, Roaccutan, Roaccutane, Roacnetan, Roacta, Roacutan, Rocne, Rocta, Sotret, Stiefotrex, Tai Er Si, Teweisi, Tretin, Tretinac, Tretinex, Tretvita, Tufacne, Zenatane, Zerocutan, Zonatian ME, and Zoretanin.
Fluclorolone acetonide
Fluclorolone acetonide (INN, or flucloronide, USAN, trade names Cutanit, Topicon) is a corticosteroid for topical use on the skin.
Liquid oxygen (supplement)
Vitamin O is a dietary supplement marketed and sold by Rose Creek Health Products and its sister company The Staff of Life (doing business as R-Garden) since 1998. Despite its name, the product is not recognized by nutritional science as a vitamin. In 1999, the Federal Trade Commission fined the manufacturer for making false statements claiming health benefits resulting from the use of the product. The manufacturer had claimed that taking the supplement had beneficial effects on a wide variety of ailments, including angina, anaemia, and various forms of cancer, and that it also increased vigor and provided for a more positive state of mind. The company states that Vitamin O is "a special supplemented oxygen taken in liquid form and produced through electrical-activation with a saline solution from the ocean," and that the substance increases the amount of oxygen present in the blood.
Inflammatory cytokine
Blocking IL-1 or TNF-α has been highly successful in helping patients with rheumatoid arthritis, inflammatory bowel disease, or graft-vs-host disease. However, the strategy has not yet been successful in humans with sepsis. Therapeutic effects of acupuncture may be related to the body's ability to suppress a range of proinflammatory cytokines such as tumor necrosis factor alpha, IL1B, interleukin 6, and interleukin 10.
Vitamin A
Vitamin A metabolic inhibition as a result of alcohol consumption during pregnancy is the elucidated mechanism for fetal alcohol syndrome and is characterized by teratogenicity closely matching maternal vitamin A deficiency.
Chemotherapy-induced peripheral neuropathy
A 2013 systematic review of the use of acetyl-L-carnitine, glutamine, vitamin E, glutathione, vitamin B6, omega-3 fatty acids, magnesium, calcium, alpha lipoic acid and n-acetyl cysteine as anti-CIPN adjuvants concluded that "currently no agent has shown solid beneficial evidence to be recommended for the treatment or prophylaxis of CIPN."
Lettuce
Depending on the variety, lettuce is an excellent source (20% of the Daily Value, DV, or higher) of vitamin K (97% DV) and vitamin A (21% DV) (table), with higher concentrations of the provitamin A compound, beta-carotene, found in darker green lettuces, such as Romaine. With the exception of the iceberg variety, lettuce is also a good source (10-19% DV) of folate and iron (table).
Vitamin A
Because the conversion of retinol from provitamin carotenoids by the human body is actively regulated by the amount of retinol available to the body, the conversions apply strictly only for vitamin A-deficient humans. The absorption of provitamins depends greatly on the amount of lipids ingested with the provitamin; lipids increase the uptake of the provitamin.
Xerophthalmia
The damage to the cornea in vitamin A associated xerophthalmia is quite different from damage to the retina at the back of the globe, a type of damage which can also be due to lack of vitamin A, but which is caused by lack of other forms of vitamin A which work in the visual system. Xerophthalmia from "hypovitaminosis A" is specifically due to lack of the hormone-like vitamin A metabolite retinoic acid, since (along with certain growth-stunting effects) the condition can be reversed in vitamin A deficient rats by retinoic acid supplementation (however the retinal damage continues). Since retinoic acid cannot be reduced to retinal or retinol, these effects on the cornea must be specific to retinoic acid. This is in keeping with retinoic acid's known requirement for good health in epithelial cells, such as those in the cornea.
Retinol
Vitamin A is essential to maintain intact epithelial tissues as a physical barrier to infection; it is also involved in maintaining a number of immune cell types from both the innate and acquired immune systems. These include the lymphocytes (B-cells, T-cells, and natural killer cells), as well as many myelocytes (neutrophils, macrophages, and myeloid dendritic cells).
Retinol
In the intestine, vitamin A is protected from being chemically changed by vitamin E. Vitamin A is fat-soluble and can be stored in the body. Most of the vitamin A consumed is stored in the liver. When required by a particular part of the body, the liver releases some vitamin A, which is carried by the blood and delivered to the target cells and tissues.
Adaptation (eye)
Although many aspects the human visual system remain uncertain, the theory of the evolution of rod and cone photopigments is agreed upon by most scientists. It is believed that the earliest visual pigments were those of cone photoreceptors, with rod opsin proteins evolving later. Following the evolution of mammals from their reptilian ancestors approximately 275 million years ago there was a nocturnal phase in which complex colour vision was lost. Being that these pro-mammals were nocturnal they increased their sensitivity in low luminescence settings and reduced their photopic system from tetrachromatic to dichromatic. The shift to a nocturnal lifestyle would demand more rod photoreceptors to absorb the blue light emitted by the moon during the night. It can be extrapolated that the high ratio of rods to cones present in modern human eyes was retained even after the shift from nocturnal back to diurnal.Vitamin A is necessary for proper functioning of the human eye. The photopigment rhodopsin found in human rod cells is composed of retinal, a form of vitamin A, bound to an opsin protein. Upon the absorption of light rhodopsin was decomposed into retinal and opsin through bleaching. Retinal could then have one of two fates: it could recombine with opsin to reform rhodopsin or it could be converted into free retinol. The American scientist George Wald was the first to recognize that the visual system expends vitamin A and is dependent upon diet for its replacement.
Vitamin A serves many functions in the human body outside of healthy vision. It is vital in maintaining a healthy immune system as well as promoting normal growth and development. The average adult male and female should consume 900 and 700 micrograms of vitamin A per day, respectively. Consumption above 3000 micrograms per day is referred to as vitamin A toxicity and is usually caused by accidental ingestion of supplements.
Coenzyme A
Coenzyme A is naturally synthesized from pantothenate (vitamin B5), which is found in food such as meat, vegetables, cereal grains, legumes, eggs, and milk. In humans and most living organisms, pantothenate is an essential vitamin that has a variety of functions. In some plants and bacteria, including "Escherichia coli", pantothenate can be synthesised "de novo" and is therefore not considered essential. These bacteria synthesize pantothenate from the amino acid aspartate and a metabolite in valine biosynthesis.
Vitamin A deficiency
Decreasing night blindness requires the improvement of vitamin A status in at-risk populations. Supplements and fortification of food have been shown to be effective interventions. Supplement treatment for night blindness includes massive doses of vitamin A (200,000 IU) in the form of retinyl palmitate to be taken by mouth, which is administered two to four times a year. Intramuscular injections are poorly absorbed and are ineffective in delivering sufficient bioavailable vitamin A. Fortification of food with vitamin A is costly, but can be done in wheat, sugar, and milk. Households may circumvent expensive fortified food by altering dietary habits. Consumption of yellow-orange fruits and vegetables rich in carotenoids, specifically beta-carotene, provides provitamin A precursors that can prevent VAD-related night blindness. However, the conversion of carotene to retinol varies from person to person and bioavailability of carotene in food varies.
Vitamer
For instance, vitamin A has at least six vitamer chemicals that all qualify as "vitamin A", each with slightly different properties. In such a system, "vitamin A" is termed the "generic descriptor" of the vitamin, which is defined by its biological properties in a vitamin-deficient organism, not by its chemical structure. In the "vitamin A" system, four of those found naturally in plant origin foods are chemically carotenoids (three carotenes and one is a xanthophyll). However, the retinol and retinal forms, which occur in animal-based foods, are several times as effective in humans, per microgram, than are the plant-based forms. In some cases these differences are extreme: for example the carotenoid forms of vitamin A cannot be absorbed by cats or ferrets at all, and therefore do not have vitamin A activity in these species. The retinoids are pharmaceutical forms of vitamin A.
Nutritional neuroscience
Vitamin A is an essential nutrient for mammals which takes form in either retinol or the provitamin beta-Carotene. It helps regulation of cell division, cell function, genetic regulation, helps enhance the immune system, and is required for brain function, chemical balance, growth and development of the central nervous system and vision.
Vitamin
For the most part, vitamins are obtained from the diet, but some are acquired by other means: for example, microorganisms in the gut flora produce vitamin K and biotin; and one form of vitamin D is synthesized in skin cells when they are exposed to a certain wavelength of ultraviolet light present in sunlight. Humans can produce some vitamins from precursors they consume: for example, vitamin A is synthesized from beta carotene; and niacin is synthesized from the amino acid tryptophan. The Food Fortification Initiative lists countries which have mandatory fortification programs for vitamins folic acid, niacin, vitamin A and vitamins B1, B2 and B12.
Nicotinamide
Nicotinamide occurs in trace amounts mainly in meat, fish, nuts, and mushrooms, as well as to a lesser extent in some vegetables. It is commonly added to cereals and other foods. If one would want to take it orally, it is present in many multivitamins, and there are around 20–30 mg in each. It is also available as a standalone vitamin, in much higher quantities around 500 mg.A 2015 trial found nicotinamide to reduce the rate of new nonmelanoma skin cancers and actinic keratoses in a group of people at high risk for the conditions.
Commercial sorghum
Sorghum is a good source of B-complex vitamins. Some varieties of sorghum contain β-carotene which can be converted to vitamin A by the human body; given the photosensitive nature of carotenes and variability due to environmental factors, scientists claim sorghum is likely to be of little importance as a dietary source of vitamin A precursor. Some fat-soluble vitamins, namely D, E and K, have also been found in sorghum grain in detectable, but insufficient, quantities. Sorghum as it is generally consumed is not a source of vitamin C.
Isotretinoin
Isotretinoin was first marketed as Accutane by Hoffmann-La Roche. It sold well for many years, but in 2009, Roche decided to remove Accutane from the US market after juries had awarded millions of dollars in damages to former Accutane users over inflammatory bowel disease claims. The American College of Gastroenterologists has released a position paper stating that people with inflammatory bowel disease should not be precluded from having their acne treated with isotretinoin. It then became generic and as of 2017 was marketed under many brand names worldwide.
Isotretinoin is used primarily for severe cystic acne and acne that has not responded to other treatments. Many dermatologists also support its use for treatment of lesser degrees of acne that prove resistant to other treatments, or that produce physical or psychological scarring. Isotretinoin is not indicated for treatment of prepubertal acne and is not recommended in children less than 12 years of age.
Beta-Carotene
The proportion of carotenoids absorbed decreases as dietary intake increases. Within the intestinal wall (mucosa), β-carotene is partially converted into vitamin A (retinol) by an enzyme, dioxygenase. This mechanism is regulated by the individual's vitamin A status. If the body has enough vitamin A, the conversion of β-carotene decreases. Therefore, β-carotene is considered a safe source of vitamin A and high intakes will not lead to hypervitaminosis A.
Thomas Burr Osborne (chemist)
Osborne and Mendel discovered Vitamin A in 1913 in butter fat – independently discovered by Elmer McCollum and Marguerite Davis, who submitted their publication first, with both papers appearing in the same issue of the "Journal of Biological Chemistry" – as well as water-soluble vitamin B in milk. Osborne and Mendel showed, for example, that a lack of Vitamin A in the diet led to xerophthalmia. They also established the importance of lysine and tryptophan in a healthy diet.
Vitamin A
A 2012 systematic review found no evidence that beta-carotene or vitamin A supplements increase longevity in healthy people or in people with various diseases. A meta-analysis of 43 studies showed that vitamin A supplementation of children under five who are at risk of deficiency reduced mortality by up to 24%. However, a 2016 Cochrane review concluded there was not evidence to recommend blanket Vitamin A supplementation for all infants between one and six months of age, as it did not reduce infant mortality or morbidity in low- and middle-income countries. The World Health Organization estimated that vitamin A supplementation averted 1.25 million deaths due to vitamin A deficiency in 40 countries since 1998. In 2008, it was estimated that an annual investment of US$60 million in vitamin A and zinc supplementation combined would yield benefits of more than US$1 billion per year, with every dollar spent generating benefits of more than US$17.
Vitamin A
Vitamin A is found in many foods, including the following list.
Acemannan
Acemannan is a D-isomer mucopolysaccharide in aloe vera leaves. This compound has been known to have immunostimulant, antiviral, antineoplastic and gastrointestinal properties.
Vitamin A
The European Food Safety Authority (EFSA) refers to the collective set of information as Dietary Reference Values, with Population Reference Intake (PRI) instead of RDA, and Average Requirement instead of EAR. AI and UL defined the same as in United States. For women and men ages 15 and older the PRIs are set at 650 and 750 μg/day, respectively. PRI for pregnancy is 700 μg/day, for lactation 1300/day. For children ages 1–14 years the PRIs increase with age from 250 to 600 μg/day. These PRIs are similar to the U.S. RDAs. The European Food Safety Authority reviewed the same safety question as the United States and set a UL at 3000 μg/day.
DU spectrophotometer
Development of the spectrophotometer had direct relevance to World War II and the American war effort. The role of vitamins in health was of significant concern, as scientists wanted to identify Vitamin A-rich foods to keep soldiers healthy. Previous methods of assessing Vitamin A levels involved feeding rats a food for several weeks and then performing a biopsy to estimate ingested Vitamin A levels. In contrast, examining a food sample with a DU spectrophotometer yielded better results in a matter of minutes. The DU spectrophotometer could be used to study both vitamin A and its precursor carotenoids, and rapidly became the preferred method of spectrophotometric analysis.
Gamma-Carotene
γ-Carotene is a carotenoid, and is a biosynthetic intermediate for cyclized carotenoid synthesis in plants. It is formed from cyclization of lycopene by lycopene cyclase epsilon. Along with several other carotenoids, γ-Carotene is a vitamer of vitamin A in herbivores and omnivores. Carotenoids with a cyclized, beta-ionone ring can be converted to vitamin A, also known as retinol, by the enzyme Beta-carotene 15,15'-dioxygenase; however, the bioconversion of gamma-carotene to retinol has not been well-characterized.
Retinoic acid
Retinoic acid is responsible for most of the activity of vitamin A, save visual pigment effects that require retinal (retinaldehyde), and cell metabolism effects that may require retinol itself. Also, some biochemical functions necessary for fertility in vitamin A deficient male and female mammals originally appeared to require retinol for rescue, but this is due to a requirement for local conversion of retinol to retinoic acid, as administered retinoic acid does not reach some critical tissues unless given in high amounts. Thus, if animals are fed only retinoic acid but no vitamin A (retinol or retinal), they suffer none of the growth-stunting or epithelial-damaging effects of lack of vitamin A (including no xerophthalmia—dryness of the cornea). They do suffer retina degeneration and blindness, due to retinal (retinaldehyde) deficiency.
Vitamin A
The discovery of vitamin A may have stemmed from research dating back to 1816, when physiologist François Magendie observed that dogs deprived of nutrition developed corneal ulcers and had a high mortality rate. In 1912, Frederick Gowland Hopkins demonstrated that unknown accessory factors found in milk, other than carbohydrates, proteins, and fats were necessary for growth in rats. Hopkins received a Nobel Prize for this discovery in 1929. By 1913, one of these substances was independently discovered by Elmer McCollum and Marguerite Davis at the University of Wisconsin–Madison, and Lafayette Mendel and Thomas Burr Osborne at Yale University who studied the role of fats in the diet. McCollum and Davis ultimately received credit because they submitted their paper three weeks before Mendel and Osborne. Both papers appeared in the same issue of the "Journal of Biological Chemistry" in 1913. The "accessory factors" were termed "fat soluble" in 1918 and later "vitamin A" in 1920. In 1919, Harry Steenbock (University of Wisconsin–Madison) proposed a relationship between yellow plant pigments (beta-carotene) and vitamin A. In 1931, Swiss chemist Paul Karrer described the chemical structure of vitamin A. Vitamin A was first synthesized in 1947 by two Dutch chemists, David Adriaan van Dorp and Jozef Ferdinand Arens.
Cat skin disorders
Cats cannot synthesize vitamin A from plant beta-carotene, and therefore must be supplemented with retinol from meat. A deficiency in vitamin A will result in a poor coat, with hair loss, with scaly and thickened skin. However an excess of vitamin A, called hypervitaminosis A, can result from over feeding cod liver oil, and large amounts of liver. Signs of hypervitaminosis A are overly sensitive skin, and neck pain causing the cat to be unwilling to groom its self, resulting in a poor coat. Supplementing vitamin A with retinol to a deficient cat, and feeding a balanced diet to a cat with hypervitaminosis A will treat the underlying nutritional disorder.
Pimple
Severe acne usually indicates the necessity of prescription medication to treat the pimples. Prescription medications used to treat acne and pimples include isotretinoin, which is a retinoid. Historically, antibiotics such as tetracyclines and erythromycin were prescribed. While they were more effective than topical applications of benzoyl peroxide, the bacteria eventually grew resistant to the antibiotics and the treatments became less and less effective. Also, antibiotics had more side effects than topical applications, such as stomach cramps and severe discoloration of teeth. Common antibiotics prescribed as of 2001 by dermatologists included doxycycline and minocycline. For more severe cases of acne dermatologists might recommend accutane, a retinoid that is the most potent of acne treatments. However, accutane can cause various side effects including vomiting, diarrhea, and birth defects if taken during pregnancy.
Astaxanthin
The structure of astaxanthin by synthesis was described in 1975. Astaxanthin is not converted to vitamin A in the human body so it is completely nontoxic if given orally.
Spironolactone
The combination of spironolactone with a birth control pill in the treatment of acne appears to have similar effectiveness to a birth control pill alone and the combination of a birth control pill with cyproterone acetate, flutamide, or finasteride. However, this was based on low- to very-low-quality evidence. Spironolactone may be more effective than birth control pills in the treatment of acne, and the combination of spironolactone with a birth control pill may have greater effectiveness for acne than either alone. In addition, some clinical research has found that flutamide is more effective than spironolactone in the treatment of acne. In one study, flutamide decreased acne scores by 80% within 3 months, whereas spironolactone decreased symptoms by only 40% in the same time period. However, the use of flutamide for acne is limited by its liver toxicity. Bicalutamide is a potential alternative to flutamide for acne as well. Spironolactone can be considered as a first-line treatment for acne in those who have failed other standard treatments such as topical therapies and under certain other circumstances, although this is controversial due to the side effects of spironolactone and its teratogenicity.
Retinyl palmitate
World Health Organization recommendation on Maternal Supplementation During Pregnancy states that "health benefits are expected for the mother and her developing fetus with little risk of detriment to either, from a daily supplement not exceeding 10,000 IU [preformed] vitamin A (3000 µg RE) at any time during pregnancy." Preformed Vitamin A refers to retinyl palmitate and retinyl acetate.
Golden rice
In 2009, results of a clinical trial of golden rice with adult volunteers from the US were published in the "American Journal of Clinical Nutrition". The trial concluded that "beta carotene derived from golden rice is effectively converted to vitamin A in humans". A summary for the American Society for Nutrition suggested that "Golden Rice could probably supply 50% of the Recommended Dietary Allowance (RDA) of vitamin A from a very modest amount — perhaps a cup — of rice, if consumed daily. This amount is well within the consumption habits of most young children and their mothers".
Carotene
β-Carotene is composed of two retinyl groups, and is broken down in the mucosa of the human small intestine by β-carotene 15,15'-monooxygenase to retinal, a form of vitamin A. β-Carotene can be stored in the liver and body fat and converted to retinal as needed, thus making it a form of vitamin A for humans and some other mammals. The carotenes α-carotene and γ-carotene, due to their single retinyl group (β-ionone ring), also have some vitamin A activity (though less than β-carotene), as does the xanthophyll carotenoid β-cryptoxanthin. All other carotenoids, including lycopene, have no beta-ring and thus no vitamin A activity (although they may have antioxidant activity and thus biological activity in other ways).
Retinol
Although the vitamin A was not identified until the 20th century, written observations of conditions created by deficiency of this nutrient appeared much earlier in history. Sommer (2008) classified historical accounts related to vitamin A and/or manifestations of deficiency as follows: "Ancient" accounts; 18th- to 19th-century clinical descriptions (and their purported etiologic associations); early 20th-century laboratory animal experiments, and clinical and epidiomologic observations that identified the existence of this unique nutrient and manifestations of its deficiency.All retinoid forms of vitamin A are used in cosmetic and medical applications applied to the skin. Retinoic acid, termed Tretinoin in clinical usage, is used in the treatment of acne and keratosis pilaris in a topical cream. An isomer of tretinoin, isotretinoin is also used orally (under the trade names "Accutane" and "Roaccutane"), generally for severe or recalcitrant acne.
Acne
Topical and oral preparations of nicotinamide (the amide form of vitamin B) have been suggested as alternative medical treatments. It is thought to improve acne due to its anti-inflammatory properties, its ability to suppress sebum production, and by promoting wound healing. Topical and oral preparations of zinc have similarly been proposed as effective treatments for acne; evidence to support their use for this purpose is limited. The purported efficacy of zinc is attributed to its capacity to reduce inflammation and sebum production, and inhibit "P. acnes". Antihistamines may improve symptoms among those already taking isotretinoin due to their anti-inflammatory properties and their ability to suppress sebum production.
Photoaging
The skin contains several antioxidants, including vitamin E, coenzyme Q10, ascorbate, carotenoids, superoxide dismutase, catalase, and glutathione peroxidase. These antioxidants provide protection from reactive oxygen species produced during normal cellular metabolism. However, overexposure to UV rays can lead to a significant reduction in the antioxidant supply, thus increasing oxidative stress. Hence, these antioxidants are essential in the skin's defense mechanism against UV radiation and photocarcinogenesis.
Dog food
Skin and coat health is important in all dogs, but especially becomes important as dogs age. An important nutrient to look for in senior dog foods to support coat health is linoleic acid which can be found in corn and soybean oil. Another important nutrient is vitamin A which helps with keratinization of hair. Good sources of vitamin A for skin and coat health include egg yolk and liver.
Vitamin E
A Cochrane review published in 2017 on antioxidant vitamin and mineral supplements for slowing the progression of age-related macular degeneration (AMD) identified only one vitamin E clinical trial. That trial compared 500 IU/day of alpha-tocopherol to placebo for four years and reported no effect on the progression of AMD in people already diagnosed with the condition. Another Cochrane review, same year, same authors, reviewed the literature on alpha-tocopherol preventing the development of AMD. This review identified four trials, duration 4–10 years, and reported no change to risk of developing AMD. A large clinical trial known as AREDS compared beta-carotene (15 mg), vitamin C (500 mg) and alpha-tocopherol (400 IU) to placebo for up to 10 years, with a conclusion that the anti-oxidant combination significantly slowed progression. However, because there was no group in the trial receiving only vitamin E, no conclusions could be drawn as to the contribution of the vitamin to the effect.
Vitamin A
Retinyl palmitate has been used in skin creams, where it is broken down to retinol and ostensibly metabolised to retinoic acid, which has potent biological activity, as described above. The retinoids (for example, 13-cis-retinoic acid) constitute a class of chemical compounds chemically related to retinoic acid, and are used in medicine to modulate gene functions in place of this compound. Like retinoic acid, the related compounds do not have full vitamin A activity, but do have powerful effects on gene expression and epithelial cell differentiation. Pharmaceutics utilizing mega doses of naturally occurring retinoic acid derivatives are currently in use for cancer, HIV, and dermatological purposes. At high doses, side-effects are similar to vitamin A toxicity.
Artificial rice
Researchers assessed the stability of Ultra Rice's vitamins as the rice is stored; ascorbate, saturated fat and antioxidants were found to be keep the vitamin A intact during storage in high humidity. Another study found that vitamin A losses would stabilize after six months and that the loss of vitamin A during cooking could be predicted.
Vitamin A deficiency
The richest animal sources of vitamin A (retinol) are livers (beef liver - one ounce provides around 8,000 IUs ) and cod liver oil - one teaspoon provides around 4,500 IUs ).
Acne
Flutamide, a pure antagonist of the androgen receptor, is effective in the treatment of acne in women. It has generally been found to reduce symptoms of acne by 80 or 90% even at low doses, with several studies showing complete acne clearance. In one study, flutamide decreased acne scores by 80% within 3 months, whereas spironolactone decreased symptoms by only 40% in the same time period. In a large long-term study, 97% of women reported satisfaction with the control of their acne with flutamide. Although effective, flutamide has a risk of serious liver toxicity, and cases of death in women taking even low doses of the medication to treat androgen-dependent skin and hair conditions have occurred. As such, the use of flutamide for acne has become increasingly limited, and it has been argued that continued use of flutamide for such purposes is unethical. Bicalutamide, a pure androgen receptor antagonist with the same mechanism as flutamide and with comparable or superior antiandrogenic efficacy but without its risk of liver toxicity, is a potential alternative to flutamide in the treatment of androgen-dependent skin and hair conditions in women.
Vitamin A
Due to the unique function of retinal as a visual chromophore, one of the earliest and specific manifestations of vitamin A deficiency is impaired vision, particularly in reduced light – night blindness. Persistent deficiency gives rise to a series of changes, the most devastating of which occur in the eyes. Some other ocular changes are referred to as xerophthalmia. First there is dryness of the conjunctiva (xerosis) as the normal lacrimal and mucus-secreting epithelium is replaced by a keratinized epithelium. This is followed by the build-up of keratin debris in small opaque plaques (Bitot's spots) and, eventually, erosion of the roughened corneal surface with softening and destruction of the cornea (keratomalacia) and leading to total blindness. Other changes include impaired immunity (increased risk of ear infections, urinary tract infections, Meningococcal disease), hyperkeratosis (white lumps at hair follicles), keratosis pilaris and squamous metaplasia of the epithelium lining the upper respiratory passages and urinary bladder to a keratinized epithelium. In relation to dentistry, a deficiency in vitamin A may lead to enamel hypoplasia.
Juice Plus
Concerns have been raised that the nutrients in Juice Plus+ capsules may not be bioavailable or effectively absorbed by the human body, and that some of the nutrients claimed to be in the products may not be present in significant amounts. Studies on nutrient absorption showed that subjects taking Juice Plus had elevated blood levels of folate and β-carotene, but the effects on blood levels of vitamin E and vitamin C were inconsistent. Some studies have shown significant increases in vitamin E and C levels, while other studies have shown much weaker effects on vitamin E and C levels, and that the levels of vitamin E and vitamin C are not significantly increased. Juice Plus was found to increase blood lycopene levels in several studies, while other studies have indicated that Juice Plus does not raise blood levels of lycopene or other phytochemicals in fresh fruits and vegetables such as lutein, zeaxanthin, and β-cryptoxanthin.
Cat
Preformed vitamin A is required in the cat for retinal and reproductive health. Vitamin A is considered to be a fat-soluble vitamin and is seen as essential in a cat's diet. Normally, the conversion of beta-carotenes into vitamin A occurs in the intestine (more specifically the mucosal layer) of species, however cats lack the ability to undergo this process. Both the kidney and liver are contributors to the use of vitamin A in the body of the majority of species while the cats liver does not produce the enzyme Beta-carotene 15,15'-monooxygenase which converts the beta-carotene into retinol (vitamin A). To summarize: cats do not have high levels of this enzyme leading to the cleavage and oxidation of carotenoids not taking place.
Vitamin E
The amounts of alpha-tocopherol, other tocopherols and tocotrienols that are components of dietary vitamin E, when consumed from foods, do not appear to cause any interactions with drugs. Consumption of alpha-tocopherol as a dietary supplement in amounts in excess of 300 mg/day may lead to interactions with aspirin, warfarin, tamoxifen and cyclosporine A in ways that alter function. For aspirin and warfarin, high amounts of vitamin E may potentiate anti-blood clotting action. One small trial demonstrated that vitamin E at 400 mg/day reduced blood concentration of the anti-breast cancer drug tamoxifen. In multiple clinical trials, vitamin E lowered blood concentration of the immuno-suppressant drug, cyclosporine A. The US National Institutes of Health, Office of Dietary Supplements, raises a concern that co-administration of vitamin E could counter the mechanisms of anti-cancer radiation therapy and some types of chemotherapy, and so advises against its use in these patient populations. The references it cited reported instances of reduced treatment adverse effects, but also poorer cancer survival, raising the possibility of tumor protection from the intended oxidative damage by the treatments.
Nutritional neuroscience
Eating foods high in vitamin A or taking dietary supplements, retinol or retinal will prevent a deficiency. The foods highest in vitamin A are any pigmented fruits and vegetables and leafy green vegetables also provide beta-Carotene.
There can be symptoms of fat loss and a reduction of any weight gain that would be considered normal for an individual, especially developmental weight gains such as in infants which would occur if the infant was deprived of vitamin A in utero and/or if it was deprived postnatal for an extensive period of time. The deficiency can also cause conditions such as blindness or night blindness, also known as nyctalopia. Night blindness is due to the inability to regenerate rhodopsin in the rods which is needed in dim light in order to see properly.
A treatment of supplements of retinoic acid which is a part of vitamin A can help replenish levels and help bring learning to normal, but after 39 weeks this is ineffective even if the treatment is daily because it will not bring the retinoid hypo-signalling back to normal.
Retinol
Retinol, also known as Vitamin A, is a vitamin found in food and used as a dietary supplement. As a supplement it is used to treat and prevent vitamin A deficiency, especially that which results in xerophthalmia. In areas where deficiency is common, a single large dose is recommended to those at high risk a couple of times a year. It is also used to prevent further issues in those who have measles. It is used by mouth or injection into a muscle.
Retinol at normal doses is well tolerated. High doses may result in an enlarged liver, dry skin, or hypervitaminosis A. High doses during pregnancy may result in harm to the baby. Retinol is in the vitamin A family. It or other forms of vitamin A are needed for eyesight, maintenance of the skin, and human development. It is converted in the body to retinal and retinoic acid through which it acts. Dietary sources include fish, dairy products, and meat.
Retinol was discovered in 1909, isolated in 1931, and first made in 1947. It is on the World Health Organization's List of Essential Medicines, the most effective and safe medicines needed in a health system. Retinol is available as a generic medication and over the counter. The wholesale cost in the developing world is about US$0.02–0.30 per 50,000 units. In the United States it is not very expensive.
Acitretin
Acitretin (trade names Soriatane and Neotigason) is a second-generation retinoid. It is taken orally, and is typically used for psoriasis.
Vitamin A
Vitamin A deprived rats can be kept in good general health with supplementation of retinoic acid. This reverses the growth-stunting effects of vitamin A deficiency, as well as early stages of xerophthalmia. However, such rats show infertility (in both male and females) and continued degeneration of the retina, showing that these functions require retinal or retinol, which are interconvertible but which cannot be recovered from the oxidized retinoic acid. The requirement of retinol to rescue reproduction in vitamin A deficient rats is now known to be due to a requirement for local synthesis of retinoic acid from retinol in testis and embryos.
Aphanizomenon flos-aquae (dietary supplement)
" Aphanizomenon flos-aquae" has been shown to contain varying amounts at least 13 vitamins: vitamin A (beta-carotene), vitamin C (ascorbic acid), vitamin E, vitamin K, and many of the B-complex vitamins including B (thiamin), B (riboflavin), B (pyridoxine), choline, biotin, niacin, folic acid, pantothenic acid, and B (cobalamin). However, "Aphanizomenon flos-aquae" contains pseudovitamin B which can block absorbtion of true B and is therefore not suitable for use as a B source for humans.
Glutamate-glutamine cycle
Since diffusion and transport of free ammonia across the cell membrane will affect the pH level of the cell, the more attractive and regulated way of transporting ammonia between the neuronal and the astrocytic compartment is via an amino-acid shuttle, of which there are two: leucine and alanine. The amino acid moves in the opposite direction of glutamine. In the opposite direction of the amino acid, a corresponding molecule is transported; for alanine this molecule is lactate; for leucine, α-ketoisocaproate.
Fenretinide
Fenretinide (4-hydroxy(phenyl)retinamide; 4-HPR) (INN) is a synthetic retinoid derivative. Retinoids are substances related to vitamin A. It has been investigated for potential use in the treatment of cancer, as well as in the treatment of cystic fibrosis, rheumatoid arthritis, acne, psoriasis, and has been found to also slow the production and accumulation of a toxin that leads to vision loss in Stargardt's patients.
Retinol
Estimates have changed over time of the rate at which β-carotene is converted to vitamin A in the human body. An early estimate of 6:1 was revised to 12:1 and from recent studies and experimental trials carried out in developing nations it was revised again to 21:1. The implication of the reduced estimate is that larger quantities of β-carotene are needed to yield the necessary dietary requirement of vitamin A. This means that more continents are affected by the deficiency of vitamin A than was previously thought. Changing dietary choices in Africa, Asia, and South America will not be sufficient, and agricultural practices on those continents will need to change.
Urolithin A
Urolithin A is a metabolite compound resulting from the transformation of ellagitannins by the gut bacteria. It belongs to the class of organic compounds known as benzo-coumarins or dibenzo-α-pyrones. Its precursors – ellagic acids and ellagitannins – are ubiquitous in nature, including edible plants, such as pomegranates, strawberries, raspberries, and walnuts. Since the 2000s, urolithin A has been subject of preliminary studies regarding its possible biological effects.
Retinal
catalyzed by a beta-carotene 15,15'-monooxygenase
or a beta-carotene 15,15'-dioxygenase.
Just as carotenoids are the precursors of retinal, retinal is the precursor of the other forms of vitamin A. Retinal is interconvertible with retinol (ROL), the transport and storage form of vitamin A
Vitamin A
Vitamin A deficiency can occur as either a primary or a secondary deficiency. A primary vitamin A deficiency occurs among children and adults who do not consume an adequate intake of provitamin A carotenoids from fruits and vegetables or preformed vitamin A from animal and dairy products. Early weaning from breastmilk can also increase the risk of vitamin A deficiency.
Vitamin
A vitamin is an organic molecule (or related set of molecules) that is an essential micronutrient that an organism needs in small quantities for the proper functioning of its metabolism. Essential nutrients cannot be synthesized in the organism, either at all or not in sufficient quantities, and therefore must be obtained through the diet. Vitamin C can be synthesized by some species but not by others; it is not a vitamin in the first instance but is in the second. The term "vitamin" does not include the three other groups of essential nutrients: minerals, essential fatty acids, and essential amino acids. Most vitamins are not single molecules, but groups of related molecules called vitamers. For example, vitamin E consists of four tocopherols and four tocotrienols. The thirteen vitamins required by human metabolism are: vitamin A (retinols and carotenoids), vitamin B (thiamine), vitamin B (riboflavin), vitamin B (niacin), vitamin B (pantothenic acid), vitamin B (pyridoxine), vitamin B (biotin), vitamin B (folic acid or folate), vitamin B (cobalamins), vitamin C (ascorbic acid), vitamin D (calciferols), vitamin E (tocopherols and tocotrienols), and vitamin K (quinones).
Retinene
The Retinenes (Retinene and Retinene) are chemical derivatives of the dietary supplement vitamin A (see retinol) formed through oxidation reactions.
Retinol
There are two sources of dietary vitamin A. Active forms, which are immediately available to the body are obtained from animal products. These are known as retinoids and include retinaldehyde and retinol. Precursors, also known as provitamins, which must be converted to active forms by the body, are obtained from fruits and vegetables containing yellow, orange and dark green pigments, known as carotenoids, the most well-known being β-carotene. For this reason, amounts of vitamin A are measured in Retinol Equivalents (RE). One RE is equivalent to 0.001 mg of retinol, or 0.006 mg of β-carotene, or 3.3 International Units of vitamin A.
Vitamin A receptor
Vitamin A receptor (also known as "Stimulated by retinoic acid 6," or STRA6 protein) was originally discovered as a transmembrane cell-surface receptor for retinol-binding protein. STRA6 is unique as it functions both as a membrane transporter and a cell surface receptor, particularly as a cytokine receptor. In fact, STRA6 may be the first of a whole new class of proteins that might be known as "cytokine signaling transporters." STRA6 is primarily known as the receptor for retinol binding protein and for its relevance in the transport of retinol to specific sites such as the eye (Vitamin A). It does this through the removal of retinol (ROH) from the holo-Retinol Binding Protein (RBP) and transports it into the cell to be metabolized into retinoids and/or kept as a retinylester. As a receptor, after holo-RBP is bound, STRA6 activates the JAK/STAT pathway, resulting in the activation of transcription factor, STAT5. These two functions—retinol transporter and cytokine receptor—while using different pathways, are processes that depend on each other.
Retinyl acetate
Retinyl acetate (retinol acetate, vitamin A acetate) is a natural form of vitamin A which is the acetate ester of retinol. It has potential antineoplastic and chemopreventive activities.
Skin whitening
Glutathione can be combined with many other agents like Vitamin C to increase its absorption, N-acetyl cysteine to boost its level, and other antioxidants like Vitamin E. Oral intake of glutathione could be harmful when combined with other skin whitening agents such as hydroquinone, which is a carcinogenic element, and monobenzone, which causes irreversible depigmentation.
Carotenoid oxygenase
Carotenoid oxygenases are a family of enzymes involved in the cleavage of carotenoids to produce, for example, retinol, commonly known as vitamin A. This family includes an enzyme known as RPE65 which is abundantly expressed in the retinal pigment epithelium where it catalyzed the formation of 11-cis-retinol from all-trans-retinyl esters.
Alitretinoin
Pregnancy is an absolute contraindication as with most other vitamin A products, it should also be avoided when it comes to systemic use in any women that is of childbearing potential and not taking precautions to prevent pregnancy. Toctino (the oral capsule formulation of alitretinoin) contains soya oil and sorbitol. Patients who are allergic to peanut, soya or with rare hereditary fructose intolerance should not take this medicine. It is also contraindicated in nursing mothers. The oral formulation of alitretinoin is contraindicated in patients with:
Glucuronic acid
Glucuronic acid is a precursor of ascorbic acid (vitamin C, formerly called as L-hexuronic acid). Ascorbate can be biosynthesized by higher plants, algae, yeast and most animals. An adult goat produces ~13 g of vitamin C per day. This ability is lacking in some mammals (including humans and guinea pigs) and also in insects, invertebrates and most fishes. These species require external ascorbate supply, because they lack the biosynthetic enzyme -gulonolactone oxidase.
Vitamin A
The role of vitamin A in the visual cycle is specifically related to the retinal form. Within the eye, 11-"cis"-retinal is bound to the protein "opsin" to form rhodopsin in rods and iodopsin (cones) at conserved lysine residues. As light enters the eye, the 11-"cis"-retinal is isomerized to the all-"trans" form. The all-"trans" retinal dissociates from the opsin in a series of steps called photo-bleaching. This isomerization induces a nervous signal along the optic nerve to the visual center of the brain. After separating from opsin, the all-"trans"-retinal is recycled and converted back to the 11-"cis"-retinal form by a series of enzymatic reactions. In addition, some of the all-"trans" retinal may be converted to all-"trans" retinol form and then transported with an interphotoreceptor retinol-binding protein (IRBP) to the pigment epithelial cells. Further esterification into all-"trans" retinyl esters allow for storage of all-trans-retinol within the pigment epithelial cells to be reused when needed. The final stage is conversion of 11-"cis"-retinal will rebind to opsin to reform rhodopsin (visual purple) in the retina. Rhodopsin is needed to see in low light (contrast) as well as for night vision. Kühne showed that rhodopsin in the retina is only regenerated when the retina is attached to retinal pigmented epithelium, which provides retinal. It is for this reason that a deficiency in vitamin A will inhibit the reformation of rhodopsin and lead to one of the first symptoms, night blindness.