Bioavailability

As a metabolite, the Tetrahydrocurcuminoids have a distinct advantage of having higher bioavailability than the regular curcuminoids. Mechanistically the regular curcuminoids once ingested reach to intestine, where they need to pass through the absorption barrier to enter the biological system. Further the reductase system at the cellular level then converts the curcumin to tetrahydrocurcumin. Tetrahydrocurcumin is an active metabolite of the curcumin as investigations in its activity reveals.

In order to study the distribution of the curcumin and its metabolite Tetrahydrocurcumin in the biological system, Okada et al in 2001 performed an animal study, involving feeding a diet containing o.5% curcumin and 0.5% tetrahydrocurcumin to two different groups of mice for 1 month.

After sacrificing the mice, the analysis was carried out on the content of curcumin and THC in the liver as well serum in mice in both groups.

The results showed that in 0.5% curcumin diet group, the mice showed only a small amount of curcumin and its conjugate in serum, whereas in the liver tissue curcumin was undetected. (Table 1)

In the 0.5% Tetrahydrocurcumin diet group, mice showed not only higher concentration of Tetrahydrocurcumin and its conjugate in the serum but also in the liver tissue. (Table 2).

Further in mice fed with 0.5% curcumin, Tetrahydrocurcumin was detected in the liver as well as serum. This is in agreement to the later finding of the Hassaninasab et al (2011) who discovered the curcumin converting enzyme from commensal microbe E. coli in the human gut.

The researchers concluded that Tetrahydrocurcumin has better absorption properties than curcumin.(3)


Ref3: K Okada, C Wangpoengtrakul, T Tanaka, S Toyokuni, K Uchida, T Osawa. Curcumin and especially tetrahydrocurcumin ameliorate oxidative stress-induced renal injury in mice. J. of Nutr. 2001; 31: 2090-95

This can be due to lower resistance towards tetrahydrocurcumin in passing through the gut as compared to curcumin. Further it is also known that Tetrahydrocurcumin has better stability at physiological pH than curcumin itself (figure 1), which may also be aiding its transportation in the biological system (4).

pH stability of curcumin and Tetrahydrocurcumin (adapted from Pan et al 1999, Drug Metabolism and Disposition)

Figure 1. pH stability of curcumin and Tetrahydrocurcumin (adapted from Pan et al 1999, Drug Metabolism and Disposition)


Ref 4: MH Pan, TM Huang, JK Lin. Biotransformation of curcumin through reduction and glucuronidation in mice. Drug Metab and dispos. 1999; 27(1); 486-94.

Absorption characteristics: Curcumin Vs Tetrahydrocurcumin,

Distribution of Curcumin and THC in Blood serum and Liver:

In an animal study on the amelioration of oxidative stress induced renal injury, two separate groups of mice (n=6) were fed with diet containing 0.5% of Curcumin and 0.5% of THC for 1 month. The distribution of Curcumin and THC was determined in blood serum and liver tissue at the end of the study.

Table 1: Distribution of Curcuminoids in liver and blood serum of mice fed with Curcumin

Table 2: Distribution of Curcuminoids in liver and blood serum of mice fed with THC

The concentration of THC in liver and serum was higher than Curcumin in both groups (Table 1 & 2), thus providing proof that orally ingested Curcumin is converted to THC and that THC is more easily absorbed from gastrointestinal tract.