Issues with Human Bioavailability Determinations of Bioactive Curcumin
Journal Title: Biomedical Journal of Scientific & Technical Research (BJSTR) - Year 2019, Vol 12, Issue 4
Abstract
The health benefits of curcumin which is extracted from turmeric (Curcuma longa) are well known. However, curcumin is poorly absorbed in the gastrointestinal tract and undergoes rapid metabolism to inactive forms. The free form of curcumin is more bioactive than its conjugates. Various formulations have been developed to increase curcumin bioavailability. Most curcumin pharmacokinetic studies measure and report total (free plus conjugated) curcumin, not free, bioactive curcumin as a result of enzymatic hydrolysis of plasma samples prior to extraction and analysis. Hydrolysis results in approximately a 10-fold over-estimation of the amount of total curcuminoids in plasma and greater than a 10-fold over-estimation of free, bioactive curcumin, therefore producing a misrepresentation of the results. As a consequence, caution is warranted in interpreting published pharmacokinetic results and claims involving curcumin products.Curcumin is the active polyphenolic constituent in turmeric from the rhizomes of Curcuma longa, and exhibits anti-inflammatory, antioxidant, metabolism regulating, chemoprotective, immuno-modulating, antibacterial, antiviral, anti-fungal, antineoplastic, and anti-depressant properties [1-11]. However, unformulated [regular] curcumin is poorly absorbed and exhibits poor bioavailability, limiting its effects and usefulness. Therefore, various formulations have been developed to enhance curcumin bioavailability, including formulations with micelles, liposomes, interaction with macromolecules such as gelatin and various polysaccharides, and nano-particulate preparations including nano-emulsions, nano-micelles, Nano-gels, dendrimers, polymers, conjugates and solid dispersions [12,13].Orally consumed curcumin is rapidly conjugated in the small intestine, liver and kidneys to curcumin glucuronide and curcumin sulfate which undergo rapid excretion in the urine and feces [4-7,11-16]. Curcumin occurs in the blood primarily as these physiologically and pharmacologically inactive conjugates with relatively little free, bioactive curcumin. Curcumin also undergoes extensive metabolic reduction to dihydrocurcumin, tetrahydro curcumin and hexahydro curcumin by intestinal microorganisms [5,11-17]. However, these metabolites also undergo conjugation, converting them into physiologically inactive constituents that are excreted in the urine and feces [5,11-17]. Curcumin is more physiologically active as compared to its conjugated forms, and therefore free curcumin reflects its bio-efficacy as compared to conjugated metabolites [5,11-14]. Pharmacokinetic studies have been conducted with various curcumin formulations. The major pharmacokinetic index used for determining extent of absorption of various curcumin products is a plot of blood plasma concentration of the active constituent(s) against time, yielding the area under the curve (AUC). Data from pharmacokinetic studies of various products can be compared by normalization of the results on the basis AUC/mg curcumin administered.
Authors and Affiliations
Stohs SJ, Ray SD
Keywords
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- EP ID EP593804
- DOI 10.26717/BJSTR.2019.12.002289
- Views 153
- Downloads 0
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