Curcumin [1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadien-3,5-dione] is a hydrophobic polyphenol derivative which is a potent antioxidant derived from the spice turmeric. Commercial curcumin contains approximately, 77% diferuloylmethane, 17% demethoxycurcumin, and 6% bisdemethoxycurcumin. Curcumin is a major active ingredient of Curcuma Longa which has been used since time immemorial. Curcuma longa (turmeric) is a well known indigenous herbal medicine. It is known for its diverse biological actions and pharmacological activities including anti-inflammatory, antioxidant, antiproliferative, antimicrobial, anticarcinogenic and antiangiogenic properties.
Major depression, a debilitating psychiatric disorder, today is considered as one of the most prevalent human illness. It may be caused by numerous reasons which include persistence of social, occupational, financial and interpersonal difficulties. A person with depression usually exhibits a state of sadness of mood and aversion to usual activities which generally affect a person's thoughts, behaviour, feeling and physical well being.
Various antidepressants have been prescribed for alleviating the symptoms of depression. Currently used drugs mainly include monoamine oxidase inhibitors (MAOIs), tricyclic antidepressants (TCAs), tetracyclic antidepressants (TeCAs), selective serotonin reuptake inhibitors (SSRIs), and Norepineprine dopamine reuptake inhibitors (NDRIs). Some of the blockbuster drugs indicated for treatment of depression which are available in the market are sold under the brands Prozac, Norpramin, Effexor, Serzone, Remeron, Desyrel, Zolsoft, paxil, Pamelor, Aventyl, Surmontil etc. Nuetraceutical products such as St Johns Wort have also been widely used for depression.
However, the therapeutic benefits of the aforementioned drugs are often accompanied by unwanted side effects and the precise mechanisms of action are not well understood. The plethora of associated side effects include nausea, insomnia, anxiety, restlessness, decreased sex drive, dizziness, weight gain or loss, tremors, sweating, sleepiness, fatigue, dry mouth, diarrhoea, constipation, headaches etc. Owing to these side effects and failure of some patients to respond to the already existing drugs, emphasizes the need for safer and efficacious drugs for treatment of major depression.
Therefore, it would be useful to identify a composition from traditional herbs or of herbal origin that would specifically address issues of safety and efficacy, thereby alleviating depressive symptoms. Curcumin is one such molecule that has shown promising efficacy in various animal models of major depression. Although the mechanism of the antidepressant effect of curcumin is not fully understood, it is hypothesized to act through inhibiting the monoamine oxidase enzyme and modulating the release of serotonin and dopamine. Moreover, evidences have shown that curcumin enhances neurogenesis, notably in the frontal cortex and hippocampal regions of the brain. (S K Kulkarni et al. Potentials of Curcumin as an Antidepressant; Scientific World Journal 2009 Nov. 1; 9:1233-41).
Another study confirmed the antidepressant effects of curcumin in the forced swim test which suggested that the antidepressant effects may be mediated by actions in the central monoaminergic neurotransmitter systems. Curcumin doses of 1.25, 2.5, 5 and 10 mg/kg P.O. were used in the forced swim test on rats and chronic treatment with curcumin for 14 days showed to have reduced the immobility time in the forced swim test (Ying Xu et al. Antidepressant effects of curcumin in the forced swim test and olfactory bulbectomy models of depression in rats. Pharmacology Biochemistry and behaviour. 82 (1) 2005. pp. 200-206).
Oral administration of aqueous turmeric extracts (140 to 560 mg/kg P.O.) for 14 days has shown reduction in immobility in tail suspension and forced swim tests. Results suggest that turmeric extract had specific antidepressant effects in vivo (Z F Yu, L D Kong and Y Chen. Antidepressant activity of aqueous extracts of Curcuma longa in mice. Journal of ethnopharmacology. 83 (1-2) 2002. pp. 161-165).
Studies show that stress induced damage to hippocampal neurons may contribute to the pathophysiology of depression. Curcumin administration (10 and 20 mg/kg, P.O.) increased hippocampal neurogenesis in chronically stressed rats, it shows similar activity of classic antidepressant imipramine treatment (Ying Xu et al. Curcumin reverses impaired hippocampal neurogenesis and increases serotonin receptor 1A mRNA and brain-derived neurotrophic factor expression in chronically stressed rats. Brainsearch. 1162 (2007) 9-18).
Another study investigates the involvement of monoaminergic systems in the antidepressant activity of curcumin and the effect of piperine, a bioavailability enhancer, on the bioavailability and the biological effects of curcumin. The study indicates that curcumin dose inhibited the immobility period, increases serotonin (5-HT) as well as dopamine levels and inhibited the monoamine oxidase enzymes in mice. The coadministration of piperine with curcumin resulted in the potentiation of pharmacological, biochemical and neurochemical activities (S K Kulkarni et al. Antidepressant activity of curcumin: involvement of serotonin and dopamine system. Psychopharmacology (2008) 201: 435-442).
AC-cAMP second messenger pathway has recently been suggested to play an important role in depression. Therefore, a compound that regulates the signal pathway may have potential as an antidepressant. Effects of chronic unpredictable mild stress (CUMS) and curcumin on behaviours/serotonergic receptor-coupled AC-cAMP signal pathway have been studied in rats. Curcumin enhanced AC activity and c-AMP levels in platelet and various brain regions, and up-regulated mRNA expressions of AC subtypes AC 2, AC 8 and cAMP response element binding protein (CREB) in the hippocampus, cortex and hypothalamus of the CUMS rats. The potent antidepressant property of curcumin might be attributed to its improvement of AC-cAMP pathway as well as CREB via suppressing central 5-HT (1A/1B/7) receptors in the CUMS rats (Y C Li et al. Antidepressant-like effects of curcumin on serotonergic receptor-coupled AC-cAMP pathway in chronic unpredictable mild stress of rats. Prog Neuropsychopharmacol Biol Psychiatry. 2009 Apr. 30; 33(3): 435-49).
In addition to the above, there are a number of clinical studies dealing with the efficacy of curcumin in humans. Despite the clinical data showing a strong intrinsic activity suggesting the potential of curcumin being used as a therapeutic agent, the use of curcumin in clinics for the treatment for a number of ailments including major depression is limited due to its poor gastrointestinal absorption.
The reasons for reduced bioavailability of any agent within the body may be attributed to low intrinsic activity, poor absorption, high rate of metabolism, inactivity of metabolic products and/or rapid elimination and clearance from the body. Studies on curcumin relating to absorption, distribution, metabolism and excretion of curcumin have revealed poor absorption and rapid metabolism of curcumin severely curtails its bioavailability.
WO2007/103435 discloses curcuminoid formulations having enhanced bioavailability comprising of a curcuminoid, antioxidant, glucuronidation inhibitor, and water-soluble, pharmaceutically acceptable inhibitor which are useful for treating Alzheimer's disease and other age-related disorders.
WO2008/113177 discloses various compounds and compositions comprising polyunsaturated fatty acid monoglycerides and derivatives thereof. These compounds have been indicated as useful for enhancing solubility of various active agents and enhancing their bioavailability.
Indian application no. 1776/DEL/2008 discloses a pharmaceutical composition of curcuminiods with higher drug loading ability, improved bioavailability having adequate physical and chemical stability as a self nanoemulsifying composition.
Yet another Indian patent application no. 1827/DEL/2008 provides for curcumin nanoparticles and curcumin bound to chitosan nanoparticles and methods of producing the same. The bioavailability of curcumin in these formulations was shown to improve by more than 10 fold.
There are several limitations of these compositions such as excessive damage to curcumin in the intestine through cytochromes, reduction of curcumin level in serum due to continuous metabolism in liver resulting in the formation of less potent curcumin glucuronide and sulphates, and difficulty in crossing the blood brain barrier. For these reasons, none of the current technologies have been successful commercially as a remedy for mental depression or as a mood elevator.
Currently used antidepressant drugs have many limitations. Apart from being prescription drugs, requiring a continuous medical supervision during treatment, they have serious side effects. Selective serotonin reuptake inhibitors have side effects such as nausea, diarrhea, agitation, loss of sexual drive, etc. Tricyclic inhibitors have side effects such as dry mouth, blurred vision, dizziness, tremors, etc., Monoamino oxidase inhibitors have side effects such as hepatitis, heart attack, stroke, seizures, etc. Curcumin being from dietary source is free from such serious side effects.