Faculty Bibliography

Previous studies from this laboratory have demonstrated a striking difference in rat intestinal glycolipids between differentiated villus cells and immature crypt cells. Villus cells contained proportionally greater amounts of glucosylceramide and hematoside while crypt cells were deficient in hematoside, but contained proportionally greater amounts of trihexosylceramide. In order to further elucidate possible differences between villus and crypt cell glycolipids, a study of the sphingosine and fatty acids of rat intestinal glycolipids was conducted. Villus and crypt cells were separated from rat intestine and the glycolipids purified. Fatty acids and long chain bases of the three major glycolipids (glucosylceramide, trihexosylceramide, hematoside) extracted from these cells were characterized. Phytosphingosine accounted for 63-73% of the total long chain bases in all glycolipids whether from villus or crypt cells. Hydroxy fatty acids represented 70% of total fatty acids in the glucosylceramide and in the hematoside but accounted for only 30% in the trihexosylceramide. In addition, trihexosylceramide contained a larger percentage of fatty acids with 20-carbon atoms than glucosylceramide and hematoside isolated from villus cells. These fatty acids were more concentrated in crypt cells than in villus cells glycolipids. These results suggest that hematoside and trihexosylceramide, respectively abundant in villus and in crypt cells, may be derived from a different lactosylceramide precursor and further underscore differences in villus and crypt cell glycolipid synthesis

Indirect immunofluorescence techniques were employed to determine the distribution within intestinal epithelial cells of apolipoprotein B, a protein essential for the normal transport of fat. Isolated intestinal cells were prepared from rats either during active lipid absorption or after biliary diversion. Specific immunofluorescence from an antiserum to apolipoprotein B was detected in the apical portion of epithelial cells from bile-diverted animals, demonstrating that a pool of apolipoprotein B is present in the nonabsorptive epithelial cell and may be a component of intestinal cell membranes. During lipid absorption in normal rats, an early and sustained increase in immunofluorescence was demonstrated, consistent with an increase synthesis of apolipoprotein B during lipid absorption. This study demonstrates the presence of apolipoprotein B within intestinal epithelium and provides evidence for the participation of this apoprotein in intestinal lipid transport

Intestinal epithelial cells were isolated from rat intestine and grouped into villus and crypt cell fractions. Glycolipids were purified from each cell fraction and quantitated by fluorimetric determination of glycolipid sphingosine. Significant quantities of ceramide were found in all cell fractions and accounted for approximately 15% of total glycolipid sphingosine. While villus and crypt cell fractions quantitatively contained differing amounts of sphingosine, all cell fractions contained proportionally similar quantities of sphingosine when compared to cellular cholesterol or phospholipid. Individual glycolipids, however, showed significant differences in distribution between villus and crypt cells. Hematoside and glucosylceramide were proportionally increased in villus cells, while crypt cells showed an increase in trihexosylceramide and ceramide content. The rate of UDPglucose : hydroxy fatty acid ceramide glucosyltransferase was higher in villus cells while the rate of UDPgalactose : lactosylceramide galactosyltransferase was 3--4 times increased in crypt cells. These studies demonstrate that significant differences in both the distribution and biosynthesis of individual glycolipids occur in crypt and villus cells of rat intestine and are of possible importance in the process of intestinal cell differentiation

The possibility that microtubules might be involved in intestinal lipoprotein formation or secretion was studied by determining the effect of colchicine, a known microtubule inhibitor, on intestinal lipid absorption. The effect of colchicine (0.5 mg per 100 g) in the lymphatic absorption of [14C]oleic acid was studied in rats with indwelling mesenteric lymph cannulas. Colchicine-treated animals showed a marked delay as well as a decrease in the lympatic absorption of [14C]oleic acid. Chylomicrons from colchicine-treated animals showed no difference in apoprotein content when examined on sodium dodecyl sulfate polyacrylamide gels. Micellar lipid absorption was next studied from in situ jejunal loops in animals pretreated with colchicine. Colchicine administration was associated with a 3-fold increase in residual mucosal lipid when compared with controls. Thin layer chromatography of residual lipid demonstrated that residual lipid was largely present as triglyceride, suggesting that the impairment in lipid transport induced by colchicine was at a site distal to triglyceride resynthesis. Electron microscopic examination of intestine from colchicine-treated animals revealed that most residual lipid was present within the endoplasmic reticulum and Golgi in numerous particles the size of chylomicrons (0.2 to 0.4 mu). These results suggest that the impairment in lipid transport induced by colchicine is distal and, in part, may represent an 'exit block'. These results suggest a possible role for microtubules in intestinal lipid transport. However, further studies are required to demonstrate directly the participation of microtubules in chylomicron secretion

The major sialic acid containing glycolipid has been isolated from rat intestinal mucosa. Characterization of this ganglioside by thin layer and gas chromatographic analysis indicates that it is an hematoside (GM3) with the major portion of the sialic acid in the N-glycolyl form. The distribution of this ganglioside was determined in villus and crypt cells isolated from rat intestine. The hematoside content of crypt cells was found to be significantly decreased when compared to villus cells. CMP-sialic acid:lactosylceramide sialyltransferase, responsible for the sialylation of lactosylceramide, was measured in differentiated villus and undifferentiated crypt cells and found to be greatly reduced in the crypt cell fraction. The present study demonstrates that marked differences in ganglioside content and biosynthesis occur in contiguous populations of cells in varying states of differentiation when isolated from normal rat intestine