Overconsumption of beta-carotene can only cause carotenosis, a harmless and reversible cosmetic condition in which the skin turns orange. Preformed vitamin A absorption and storage in the liver occur very efficiently until a pathologic condition develops. When ingested, 70–90% of preformed vitamin A is absorbed and used. Sources of toxicity
Diet – Liver is high in vitamin A. The liver of certain animals, including the polar bear, bearded seal, fish, walrus, and moose, are particularly toxic (see Liver (food) § Poisoning). It has been estimated that consumption of 500 grams of polar bear liver would result in a toxic dose for a human. Supplements – Dietary supplements can be toxic when taken above recommended dosages. Types of toxicity
Acute toxicity occurs over a period of hours or a few days, and is less of a problem than chronic toxicity. Chronic toxicity results from daily intakes greater than 25,000 IU for 6 years or longer and more than 100,000 IU for 6 months or longer. Mechanism
Absorption and storage in the liver of retinol occur very efficiently until a pathologic condition develops. Delivery to tissues
Absorption
When ingested, 70–90% of preformed vitamin A is absorbed and used.According to a 2003 review, water-miscible, emulsified, and solid forms of vitamin A supplements are more toxic than oil-based supplement and liver sources. Storage
80–90% of the total body reserves of preformed vitamin A are in the liver (with 80–90% of this amount being stored in hepatic stellate cells and the remaining 10–20% being stored in hepatocytes).
Administration of deferoxamine after acute intoxication may color the urine a pinkish red, a phenomenon termed "vin rosé urine". Apart from iron toxicity, deferoxamine can be used to treat aluminium toxicity (an excess of aluminium in the body) in select patients. In US, the drug is not FDA-approved for this use. Deferoxamine is also used to minimize doxorubicins cardiotoxic side effects and in the treatment of a patient with aceruloplasminemia. Deferoxamine maybe effective for improving neurologic outcomes in persons with intracranial hemorrhage, although the evidence supporting the efficacy and safety for this indication was weak.Some published manuscripts suggesting the use of deferoxamine for patients diagnosed with COVID-19 because of the high level of ferritin among them. Adverse effects
It is unclear if use during pregnancy is safe for the baby.Chronic use of deferoxamine may increase the risk of hearing loss in patients with thalassemia major.Chronic use of deferoxamine may cause ocular symptoms, growth retardation, local reactions and allergy. Mechanism
Deferoxamine is produced by removal of the trivalent iron moiety from ferrioxamine B, an iron-bearing sideramine produced by the actinomycetes, Streptomyces pilosus. Its discovery was a serendipitous result of research conducted by scientists at Ciba in collaboration with scientists at the Swiss Federal Institute of Technology in Zurich and the University Hospital in Freiburg, Germany Deferoxamine acts by binding free iron in the bloodstream and enhancing its elimination in the urine. By removing excess iron from persons with hemochromatosis, the agent reduces the damage done to various organs and tissues, such as the liver.