Seymour M. Sabesin

Intestinal lipid absorption: evidence for an intrinsic defect of chylomicron secretion by normal rat distal intestine.

Intracellular triglyceride accumulation and delayed chylomicron secretion were demonstrated in distal but not in proximal rat intestine following prolonged steady state fat absorption. After 1 and 4 hr of intraduodenal triolein infusion, the mucosal triglyceride content in distal intestinal segments was greatly increased compared with proximal segments. Electron microscopy at each time interval disclosed greater quantities of lipid droplets within the distal cells and these were much larger than the intracellular droplets in the proximal cells, some attaining an enormous size (9000 mμ). When proximal and distal cells were compared at intervals after cessation of a 4 hr triolein infusion, the differences in intracellular lipid accumulation were also evident because, even after 6 hr the distal cells were still filled with large droplets, whereas the proximal cells were almost devoid of fat. These results indicate a basic cellular difference between proximal and distal intestine in the processing of fat and, in contrast to current concepts, suggest that defective chylomicron secretion is not necessarily associated with limited B-apoprotein availability.

Hepatic triglyceride lipase deficiency in liver disease

The activity of post-heparin lipases in patients with alcoholic hepatitis and viral hepatitis was evaluated. Lipoprotein lipase and hepatic triglyceride lipase were differentiated by assay under high and low salt conditions and also by separation on heparin-agarose affinity chromatography columns. The mean activity of hepatic triglyceride lipase in the sera of liver disease patients was only 21–24% of the mean of controls, but lipoprotein lipase in patients’ sera was not different from normal levels. Hepatic triglyceride lipase deficiency may partially account for the accumulation of a triglyceride-rich low density lipoprotein in liver disease.

The Role of Lecithin:Cholesterol Acyltransferase Deficiency in the Apoprotein Metabolism of Alcoholic Hepatitis

In alcoholic hepatitis a severe but reversible LCAT deficiency provides a model to investigate the role of LCAT in lipoprotein metabolism. Serial changes in the lipid and apoprotein composition of the plasma lipoproteins were investigated throughout the illness of patients with alcoholic hepatitis. In severe alcoholic hepatitis, LCAT and cholesteryl esters were greatly reduced or undetectable in plasma. Lipoproteins were isolated by sequential ultracentrifugation of fasting plasma. VLDL was normal in triglyceride and phospholipid content but deficient in cholesteryl esters. Polyacrylamide gel electrophoresis of this fraction revealed greatly increased apo B (≈97%) as tetra-methylurea insoluble protein with traces of apo C and apo E, a composition compatible with nascent VLDL of hepatic origin. LDL was rich in triglyceride but deficient in cholesteryl esters. HDL was enriched in phospholipid but deficient in cholesteryl esters. Polyacrylamide gel electrophoresis demonstrated only apo B in LDL. The predomin...

Lipoprotein lipase and hepatic lipase deficiencies associated with impaired chylomicron clearance in D-(+) galactosamine hepatitis☆

D-(+) galactosamine (GaIN) produces a reversible from of hepatic injury in the rat, accompanied by alterations in morphology and composition of plasma lipoproteins in the fasting state. Lipoprotein lipase (LPL) and hepatic lipase (HL) activities were measured in fasting control and GaIN rats 24 hr after GaIN injection and initiation of fasting. Significant (p less than 0.001) deficiencies of both enzymes were noted in GaIN animals as compared to controls with LPL activity decreasing to 37.6% and HL activity to 23.2% of control values in GaIN animals. Serial enzyme determinations performed in both GaIN and control animals after gastric fat loading revealed an early persistent HL deficiency (p less than 0.025) at 9 hr after GaIN injection and initiation of fasting which persisted after the fat loading at 15 hr, and a later appearing LPL deficiency (p less than 0.025) was noted at 24 hr after GaIN injection and at 9 hr after fat loading. Serial compositional studies of plasma lipoproteins in pooled specimens after a gastric fat load revealed a marked chylomicronemia in GaIN animals compared to controls which reached a maximum at 12 hr after fat loading. A slight increase in VLDL (very low density lipoprotein) triglyceride and total cholesterol (CH) and a late-appearing (16 hr after fat loading) LDL (low density lipoprotein) CH peak, consisting mostly of unesterified CH, were also noted in GaIN rats as compared to control animals. These data demonstrate a defect in chylomicron (CM) catabolism in GaIN hepatopathy in the rat which is probably secondary to the observed severe LPL and HL deficiencies, although other factors such as activator deficiency, plasma inhibitory substances, and a defective CM particle may be important.

Ultrastructural features of regional differences in chylomicron secretion by rat intestine

Abstract An electron microscopic study of the effects of prolonged intraduodenal triolein perfusion on intestinal fat absorption was performed to investigate the ultrastructural features of regional differences in chylomicron secretory capacity in the rat small intestine. Utilizing conditions in which intraluminal triolein concentrations were high enough to saturate the mechanism for fat uptake it was demonstrated that the proximal segments reach a steady state of uptake and chylomicron secretion within one hour whereas triglycerides accumulate progressively in the distal epithelial cells. After one or four hours perfusion with [1- 14 C]triolein the mucosal triglyceride content was much greater in distal than in proximal segments and electron microscopy disclosed many more and larger intracellular fat droplets in the distal absorptive cells. Six hours after stopping the 4 hr perfusion many distal cells were still filled with large fat droplets whereas the proximal cells were devoid of fat. In comparison to proximal intestine, triglycerides accumulated in distal segments following direct segmental triolein perfusion and electron microscopy disclosed large intracellular fat droplets similar to those observed after intraduodenal triolein perfusion. The ultrastructural observations suggest that fat accumulation, in the distal segments, is due to a relatively decreased capacity for chylomicron release. These studies suggest an intrinsic difference between proximal and distal intestine in fat absorption, which may reflect regional differences in cellular function such as membrane availability for the final assembly and secretion of chylomicrons.

Quantitative, multicomponent analysis of fatty acids from cholesteryl esters by chemical ionization reconstructed mass chromatography

Reconstructed mass chromatography using methane as a carrier and reagent gas for chemical ionization gas chromatography-mass spectrometry of the derived methyl esters allows rapid, quantitative microdeterminations of complete cholesteryl ester fatty acid profiles. The sensitivity of this method is consistent with completely specific, multicomponent assay at the picomole level. Introduction of two homologues as internal standards, one into the intact biological specimen and the other after derivatization, provides a measure of the net efficiency of the processes of extraction and derivatization. This procedure may be extended readily to the determination of fatty acid profiles in most biological fluids.

d-Galactosamine hepatotoxicity: V. Role of free fatty acids in the pathogenesis of fatty liver

Abstract The role of free fatty acids (FFA) in the pathogenesis of fatty liver was investigated in female rats who received a single ip injection of d -galactosamine-HCl, (GalN), 750 mg/kg body weight. Groups of rats were either fasted for 14 hr prior to GalN injection and then fasted for the duration of the experiment or were fed ad libitum prior to and after GalN administration. Plasma FFA were determined in groups of fasting or fed rats sacrificed at intervals between 0 and 24 hr after GalN administration. The results revealed a progressive increase in plasma FFA in GalN-injected fasted rats (0 hr, 0.40 μmol/ml; 24 hr, 1.09 μmol/ml) whereas in fed animals only a modest increase in plasma FFA concentrations occurred. Hepatic triglyceride content was determined in groups of fasted and fed rats at 6 and 24 hr after GalN administration. Hepatic triglycerides, in fasted rats, were increased 7-fold at 6 hr (22.4 ± 8.5 mg/g) and were markedly increased at 24 hr (114.8 ± 18.4 mg/g). In contrast, feeding protected the rats from the development of fatty liver since hepatic triglycerides were only twice controls at 6 hr and 4-fold increased 24 hr after GalN. Ultrastructural studies were performed at 15, 24, and 48 hr after GalN in fed and fasted rats. Electron microscopy disclosed hepatocellular necrosis and profound fat accumulation in the fasted animals; however, feeding afforded marked protection against the development of fatty liver and hepatic injury. The results of these studies indicate that the GalN-induced fatty liver is associated with a sustained elevation of plasma FFA. The increase in plasma FFA can be prevented by feeding the animals prior to and after GalN administration suggesting that a stimulus for FFA elevation may be the alterations in carbohydrate metabolism known to be induced by GalN in rat liver.

Effects of acetoxycycloheximide on the metabolism of hepatic triglycerides in the rat

Abstract Acetoxycycloheximide (ACH), the most potent inhibitor of protein synthesis in mammalian tissues, was administered to female rats in order to investigate the relationship of hepatic protein synthesis inhibition to the pathogenesis of fatty liver. Groups of animals were sacrificed at intervals between 1.5 and 24 hr after receiving ACH, by ip injection, in concentrations of either 0.25 or 0.50 mgm/kgm body weight. Blood samples were analyzed for triglyceride and free fatty acid (FFA) content, and hepatic triglycerides were determined. ACH produced neither an increase in hepatic triglyceride content, a depression of plasma triglycerides nor an elevation of FFA. Electron microscopy of the liver failed to demonstrate lipid accumulation. The plasma lipoproteins of ACH-treated rats had normal triglyceride and protein contents. These resutls demonstrate that hepatic protein synthesis inhibition alone is not sufficient to produce liver triglyceride accumulation and emphasize the importance of FFA mobilization in the pathogenesis of fatty liver.