Studies on the in vitro absorption of spice principles – Curcumin, capsaicin and piperine in rat intestines

A comparative evaluation of the absorbability of three structurally similar and physiologically active spice principles in an in vitro
system consisting of everted rat intestinal sacs was made. When everted sacs of rat intestines were incubated with 50–1000 lg of curcumin
in 10 ml incubation medium, absorption of the spice principle was maximum at 100 lg concentration. The amount of absorbed curcumin
present in the serosal fluid was negligible. This and the comparatively lower recovery of the original compound suggested that curcumin
to some extent undergoes a modification during absorption. For similar concentrations of added piperine, about 44–63% of piperine
disappeared from the mucosal side. Absorption of piperine which was maximum at 800 lg per 10 ml was about 63%. The absolute
amounts of piperine absorbed in this in vitro system exceeded the amounts of curcumin. The absorbed piperine could be traced in both
the serosal fluid and in the intestinal tissue, indicating that piperine did not undergo any metabolic change during the process of absorption.
7–12% of the absorbed piperine was found in the serosal fluid. When everted sacs of rat intestines were incubated with 10–500 lg of
capsaicin, a maximum of 82–88% absorption could be seen in the lower concentrations, and the amount of absorbed capsaicin did not
proportionately increase at higher concentrations. A relatively higher percentage of the absorbed capsaicin could be seen in the serosal
fluid as compared to curcumin or piperine. When these spice active principles were associated with mixed micelles, their in vitro intestinal
absorption was relatively higher. Curcumin absorption in everted intestinal sac increased from 48.7% to 56.1% when the same was
present in micelles. In the case of capsaicin and piperine, increase in absorption was 27.8–44.4% and 43.4–57.4%, respectively, when they
were present in micelles as compared to its native form.