Bioavailability Studies of Carotenoids Using Human Exfoliated Colonic Epithelial Cells*

As described before, anumber offactors affect the bioavailability ofvitamin A and provitamin A carotenoids such as their conversion to vitamin A, rate ofabsorption, transport, chemical nature ofthe provitamin A, and also the fat content in the diet. The type of food matrix in which carotenoids are located is a major factor affecting the bioavailability ofprovitamin A carotenoids; bioavailability ofp-carotene from vegetable in particular has been shown to be low compared to that ofpurified p-carotene added to a simple matrix, whereas for lutein the difference is much less (Van het Hofet ai., 2000). As indicated before, vitamin A status is assessed at different levels; however routine measurement ofplasma vitamin A may not be agood indicator as vitamin A level in the plasma is often 'buffered' and the best indicator is the liver level ofvitamin A. Invasive sampling ofblood and liverbiopsies are not practically feasible in field investigations and there are no non-invasive methods to assess the provitamin AI vitamin A status in a target population. Stool is one ofthe major excretory products ofall higher animals and it consists ofamixture oflmdigested food residues, microflora, endogenous secretions and cellular components exfoliated from the gastro intestinal tract (Iyengar et ai., 1991); this excretory product is generated with predictable regularity. It is reported that about 55% ofthe stool mass on dry weight basis is contributed by microbial flora (Stephen et ai., 1980). Recovery and characterisation ofexfoliated intestinal tract cells from human stools has been reported by Albaugh et al. (1992) using cOlmtercurrent centrifugal elutriation. The gastro intestinal tract sheds about 2 x 1011 cells per day as estimated from DNA-loss-