Nutrient interactions in human and Caco-2 cells

R.I. Kushak, Ph.D., DSc., H.S. Winter, MD

MassGeneral Hospital for Children, Harvard Medical School, Boston, MA

Nutrient absorption and drug pharmacokinetics may be regulated by other nutrients. Aim: To study peptide-lipid, peptide-carbohydrate and carbohydrate-lipid interactions in human, human intestinal transplants, and human colon carcinoma cells (Caco-2 line). Methods: Specimens of human intestine were obtained from discarded human fetus after prostaglandin-saline abortion and from children at the time of bowel resection with informed consent. Segments of fetal intestine were xenografted subcutaneously on the back of athymic mice and were used in experiments in 26-62 days after transplantation. Caco-2 cells were grown to confluency on standard medium with 4.5 g/L glucose. Homogenates of intestinal mucosa cells, their brush border fraction, isolated enzymes and ultrasonicated Caco-2 cells were used to study peptidases (dipeptidase, tripeptidase, aminopeptidase N (ApN), carboxypeptidase) and carbohydrases (sucrase, maltase) activity in presence and absence (controls) of different nutrients (modifiers). Enzyme activities were tested biochemically using specific substrates. Modifiers were represented by various carbohydrates (lactose, sucrose, maltose), lipids (tributyrin, triolein, natural oils) and products of their hydrolysis (glycerin, short-chain fatty acids). Results: Carbohydrates and most lipids did not affect most of peptidases in the small intestine and colon; however, trybutyrin and butyric acid significantly (P<0.05) inhibited ApN activity. The same effect of tributyrin was demonstrated in experiments with enterocyte brush borders and purified ApN. The effect of tributyrin on purified enzyme was related to an increase in Km rather than changes in Vmax (Compar Biochem Physiol 1999;124:191). ApN inhibition by tributyrin was observed also in intestinal xenografts. In Caco-2 cells tributyrin inhibited sucrase but stimulated maltase activity. Conclusion: Nutrient interaction should be taken into consideration when evaluating nutrient and drug absorption.

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Paper presented at the International Symposium on Predictive Oncology and Intervention Strategies; Paris, France; February 9 - 12, 2002; in the section on Dietary Influences.