BASAL NUTRITION PROMOTES HUMAN INTESTINAL EPITHELIAL (CACO-2) PROLIFERATION, BRUSH-BORDER ENZYME-ACTIVITY, AND MOTILITY

Objectives: Provision of nutrients to the apical membrane of intestina l epithelial cells by the enteral route is critical for normal gut muc osal function and for the sheet migration required for mucosal healing . The present work attempts to determine whether supplemental nutrient delivery to the basal epithelial surface is important for intestinal epithelial biology. Since attempts to regulate intestinal epithelial c ell biology by manipulation of parenteral nutrition solutions have met with some success, we hypothesized that basally delivered nutrients m ight also be important for intestinal epithelial biology. Design: To t est this hypothesis, we compared the brush border enzyme activity, pro liferation, and motility of human intestinal epithelial (Caco-2) cells cultured on a type I collagen substrate either on cell culture dishes with culture medium above the apical side of the cell monolayer or in culture inserts on 0.45-mu semipermeable membranes with culture mediu m beneath the monolayers as well as above them. Proliferation was asse ssed by serial hematocytometric counts over 13-day period. Doubling ti mes were calculated by logarithmic transformation of cell counts 48 hr s apart. The specific activity of the brush border enzymes, dipeptidyl dipeptidase and alkaline phosphatase, was assayed by the digestion of synthetic chromogenic substrates in protein-matched aliquots of cell lysates. Sheet migration was quantitated by the expansion of Caco-2 mo nolayers across collagen. Motility was dissociated from the proliferat ive component of monolayer expansion by blocking proliferation with mi tomycin C. Setting: Laboratory for gastrointestinal mucosal biology. S ubjects: A well-differentiated subclone of cells derived from the esta blished human Caco-2 colonic epithelial cell line. Measurements and Ma in Results: Basal nutrient delivery promoted Caco-2 proliferation, bru sh border enzyme activity, monolayer expansion, and cell motility. Pro liferation was actually increased by 694 +/- 9.89% (n = 90, p < .0001) in cells nourished apically and basally compared with a 314 +/- 3.31% increase (n = 90, p < .0001) in those cells receiving only apical nut rition. The addition of basal nutrient delivery to the cell culture sy stem augmented both alkaline phosphatase and dipeptidyl dipeptidase sp ecific activity by 116 +/- 5.4% and 256 +/- 14.0%, respectively (p < . 0001, n = 6 for each group). The effects of basal nutrient delivery we re maintained after mitomycin blockade of proliferation for both alkal ine phosphatase (392 +/- 89.8% of control, n = 3, p < .0005) and dipep tidyl dipeptidase (374 +/- 79.1% of control, n = 3, p < .005), suggest ing that the increased digestive enzyme-specific activity reflected di fferentiation rather than indirect effects of slowing of proliferation . Epithelial sheet migration increased by 389 +/- 8.8% and proliferati on-blocked cell motility also increased by 76.5 +/- 1.56% (p < .0005, n = 12 for each) compared with apical nutrient delivery only. Conclusi ons: These results suggest that although apical nutrition may be criti cal for intestinal epithelial cell biology, nutrient delivery to the b asal surface of intestinal epithelial cell membranes may also promote intestinal epithelial differentiation, proliferation, and mucosal heal ing.