Karen Comai

Rapid separation of neutral lipids, free fatty acids and polar lipids using prepacked silica sep-Pak columns

A method is described for the separation of neutral lipid, free fatty acid and polar lipid classes using small (600 mg), prepacked silica Sep-Pak columns. Combinations of hexane and methyltertiarybutylether were used to progressively elute cholesteryl ester first then triglyceride from the column. After column acidification, fatty acids were eluted followed by cholesterol. Recoveries of these lipids were 96% or greater. Polar lipids were eluted from the column using combinations of methyltertiarybutylether, methanol and ammonium acetate. Phospholipid classes could not be separated completely from each other. Phosphatidylethanolamine and phosphatidylinositol eluted together, whereas the more polar phosphatidylcholine, sphingomyelin and lysophosphatidylcholine were eluted as a second fraction. Recoveries of each phospholipid was greater than 98%.

Separation of neutral lipid free fatty acid and phospholipid classes by normal phase hplc

Normal phase high performance liquid chromatography methods are described for the separation of neutral lipid, fatty acid and five phospholipid classes using spectrophotometric detection at 206 nm. Separations were accomplished in less than 10 min for each lipid class. A mobile phase consisting of hexane/methyltertiarybutylether/acetic acid (100∶5∶0.02) proved effective in separating cholesteryl ester and triglyceride with recoveries of 100% for radiolabeled cholesteryl oleate and 98% for radiolabeled triolein. Free fatty acid and cholesterol were separated by two different mobile phases. The first, hexane/methyltertiarybutylether/acetic acid (70∶30∶0.02) effectively separated free fatty acids and cholesterol, but did not separate cholesterol from 1,2-diglyceride. A mobile phase consisting of hexane/isopropanol/acetic acid (100∶2∶0.02) effectively separated free fatty acid, cholesterol, 1,2-diglyceride and 1,3-diglyceride. Recoveries of oleic acid and cholesterol were 100% and 97%, respectively. Five phospholipid classes were separated using methylteriarybutylether/methanol/aqueous ammonium acetate (pH 8.6) (5∶8∶2) as the mobile phase. The recoveries of phosphatidylinositol, phosphatidylethanolamine, phosphatidylcholine, sphingomyelin and lysophosphatidylcholine were each greater than 96%.

Analyses of renal medullary lipid droplets from normal, hydronephrotic, and indomethacin treated rabbits

Lipid droplets isolated from rabbit renal medullary tissue were analyzed and found to be composed of triglyceride and free fatty acids in a ratio of 2.9∶1. These triglycerides were unique when compared to triglycerides of other rabbit tissues examined, in that they contained high percentages of octadecanoic acid (stearic acid, 9.8%), 5,8,11,14-eicosatetraenoic acid (arachidonic acid, 6.8%), and 7,10,13,16-docosatetraenoic acid (adrenic acid, 10%). Lipid droplet triglycerides were found to increase during experimental hydronephrosis and after administration of indomethacin, a prostaglandin synthetase and phosphodiesterase inhibitor. From gas liquid chromatography of fatty acid methyl esters of these triglycerides, it was determined that they were enriched further in their percent composition of 9,12-octadecadienoic acid (linoleic acid) and arachidonic acid, a prostaglandin precursor. The inverse relationship between lipid droplets and prostaglandin content in the inner medulla suggested a significant role of lipid droplet triglycerides as storage pools for prostaglandin precursors.

Comparative effects of amphetamine and fenfluramine on lipid biosynthesis and absorption in the rat.

Abstract The effects of amphetamine and fenfluramine on lipid biosynthesis and intestinal absorption of triglycerides in the rat were observed independently of the anorectic activity of these drugs. Amphetamine and fenfluramine significantly reduced de novo lipogenesis and cholesterogenesis from 3 H 2 O and [ 14 C] alanine in isolated hepatocytes. Fenfluramine was four times more potent an inhibitor than amphetamine. At high concentrations (above 2 mM), fenfluramine inhibited 14 CO 2 production from [ 14 C] alanine in isolated hepatocytes while amphetamine stimulated 14 CO 2 production at all concentrations tested (0.25 to 8 mM). Lipogenesis in liver and adipose tissue was not reduced in vivo by the acute administration of amphetamine. It, however, reduced lipogenesis in the small intestine. Fenfluramine significantly depressed in vivo lipogenesis in liver, small intestine and adipose tissue at 10 and 20 mg/kg, i.p. Hepatic cholesterogenesis was depressed significantly in vivo by both drugs. Fenfluramine increased serum free fatty acids while amphetamine produced no change. Triglycerides were increased significantly by fenfluramine only. Serum cholesterol and phospholipids were unchanged. Fenfluramine at 40 and 60 mg/kg, p.o., diminished significantly the intestinal absorption of triglycerides and depressed the accumulation of lipid in the liver. Analogous effects were not observed with amphetamine. Amphetamine was a weak inhibitor of rat pancreatic lipase (EC 3.1.1.3) ( K i = 21 mM) and fenfluramine was a stronger inhibitor ( K i = 3.3 mM).

Caloric compensatory responses to diets containing either nonabsorbable carbohydrate or lipid by obese and lean Zucker rats

The effects on food intake and body weight in lean and obese Zucker rats were evaluated following substitution in the diet with either 1) poorly absorbable lipid (hydrogenated soybean oil) for corn oil, or 2) nonabsorbable carbohydrate (fiber) for glucose. Lean Zucker rats compensated for the reduced caloric availability of the high-fiber and hydrogenated oil diets by increasing food consumption. In contrast, obese rats did not respond significantly to these dietary alterations and failed to attain caloric balance during the 16-day study. These differences in caloric compensatory responses were reflected in body weight gains. There were no differences in the amount of weight gained by lean rats fed either the high-or low-fiber diets because of compensatory hyperphagia in the high-fiber group. Lean rats fed the hydrogented oil diets gained less weight than controls fed corn oil diets, even in the presence of compensatory hyperphagia, because of the enhanced fecal excretion of water and metabolites caused by the poorly absorbed fat diet. As a result of a delayed and incomplete response to reduced caloric availability, obese rats fed the high-fiber and hydrogenated oil diets gained significantly less weight than the obese rats fed low-fiber and corn oil diets.

In vivo meal model for the evaluation of agents which affect the absorption of triglyceride and cholesterol

Abstract A meal model in which rats were trained to consume within 2 hr a high fat meal containing glycerol tri[1- 14 C]oleate and [ 3 H]cholesterol was compared to the corn oil bolus model. In the meal model, dietary triglyceride was absorbed from the small intestine faster during the first 6–8 hr and more completely than intubated corn oil, as determined by analysis of intestinal contents, serum radioactivity, serum triglycerides, adipose tissue and liver lipids. The effects of Cholestyramine, Colestipol and Pluronic L-101 (1% dietary admixes) on these variables were evaluated for 5 days in the meal model. Lipid absorption during a 72-hr period was reduced by all compounds. The per cent excretion of glycerol tri[1- 14 C]oleate was increased significantly by Pluronic L-101 (10-fold), Cholestyramine (5.7-fold) and Colestipol (2.7-fold). The excretion of [ 3 H]cholesterol was enhanced significantly by Cholestyramine (1.6-fold) and Colestipol (1.3-fold). The following observations were made 4hr after the initiation of the meal. Pluronic L-101 increased significantly the retention of glycerol tri[1- 14 C]oleate and [ 3 H]cholesterol in stomach (380 and 375 per cent, respectively), and of glycerol tri[1- 14 C]oleate in the small intestine (1100 per cent). The percent of intestinal lipid remaining as triglyce-ride from the intestinal lumen was increased significantly by Pluronic L-101 (160 per cent). Pluronic L-101 reduced significantly [ 14 C]lipid and [ 3 H]cholesterol in liver; Cholestyramine and Colestipol suppressed only [ 3 H]cholesterol. In adipose tissue, Pluronic L-101 treatment reduced significantly [ 14 C]lipid content only; Cholestyramine and Colestipol suppressed selectively [ 3 H]cholesterol. After 5 days of treatment, only Pluronic L-101 treatment resulted in significantly reduced serum triglycerides (32 per cent), cholesterol (21 per cent) and glucose (15 per cent). These data suggest that this in vivo meal-feeding model provides a physiological technique for evaluating agents affecting lipid absorption.