TETRAHYDROCURCUMINOIDS:
BIOACTIVE ANTIOXIDANT COMPOUNDS FROM CURCUMINOIDS
Lakshmi Prakash, Ph.D. & Muhammed Majeed, Ph.D.
Introduction
Tetrahydrocurcuminoids (THC)*is a colorless
hydrogenated product derived from the yellow curcuminoids, the biologically active
principles from the rhizomes of Curcuma longa (Turmeric), function as efficient
antioxidant compounds. The superior antioxidant property of THC, combined with the lack of
yellow color, render this product useful in achromatic food and cosmetic applications that
currently employ conventional synthetic antioxidants1.
Curcuminoids are reported to be potent
antioxidant compounds by virtue of their molecular structure1. THC have also
shown significant antioxidant action in a number of in vitro and preclinical
studies. Tetrahydrocurcuminoids are valued as the ultimate metabolites of the Curcuminoids
in vivo 2. The poor circulating bioavailability3 of the
parent curcuminoids, often attributed to their limited uptake due to poor water
solubility, often impairs their biological effects in vivo. If supplied as their
ultimate metabolites, this problem could be overcome. Substantial beneficial effects could
be achieved with lower levels of these active metabolites as compared to the parent
compounds. Several independent studies reported the significant antioxidant effects of the
tetrahydrocurcuminoids 4,5,6.
Metabolism
of curcumin
In an early study which elucidated the
metabolic disposition of curcumin in rats, Curcumin labeled with deuterium and tritium was
prepared. Oral and intraperitoneal doses of [3H]curcumin led to the fecal
excretion of most of the radioactivity. The major biliary metabolites were glucuronides of
tetrahydrocurcumin and hexahydrocurcumin. A minor biliary metabolite was dihydroferulic
acid together with traces of ferulic acid. Metabolites were identified using chemical
ionization mass spectrometry7.
A recent study2 investigated the
pharmacokinetic properties of curcumin in mice and further clarified the nature of the
metabolites of curcumin. Curcumin (0.1 g/kg) was administered intraperitoneally to mice
and about 2.25 micrograms/ml appeared in the plasma in the first 15 minutes. Treatment of
the plasma with beta-glucuronidase resulted in a decrease in the concentrations of two
putative conjugates and the concomitant appearance of tetrahydrocurcumin (THC) and
curcumin, respectively. To investigate the nature of these glucuronide
conjugates in vivo, the plasma was analyzed by electrospray technique.
* Patent Granted, U.S. Patent #5,861,415,
and additional U.S. and Worldwide Patents Pending |