Effects of serpasil on lipids,lipoprotein lipase and lipogenic enzymes in alloxan diabetic rats

Diabetes intensifies the development of atherosclerosis. Treatment with antihypertensive drug, serpasil, arrested the progression of atherosclerosis in alloxan diabetic rats by significantly decreasing the concentration of cholesterol, phospholipids and triglycerides of serum, liver, kidney and aorta. Serpasil also decreased fasting blood sugar and urine sugar levels in these rats. Serpasil administration remarkably altered the deranged lipid metabolism in alloxan diabetic rats by nearly restoring the lipolytic and lipogenic enzyme activity to that of the normal     

Experimental hyperthyroidism in man: effects on plasma lipoproteins, lipoprotein lipase and hepatic lipase

We have studied the effects of triiodothyronine administration (20-40 micrograms three times daily over one week) in six healthy young men, on the activities of lipoprotein lipase and hepatic lipase and on plasma lipoprotein concentrations. Hepatic lipase activity in post-heparin plasma rose by 46 +/- 25% (p less than 0.025), whereas the activity of lipoprotein lipase did not change significantly. Plasma cholesterol concentrations decreased by about 20% (p less than 0.025), whereas there was no change in plasma triglyceride levels. The fall in plasma cholesterol could be accounted for by a reduction of HDL cholesterol (-11%, p less than 0.025) as well as LDL cholesterol (-27%, p less than 0.025). The data emphasize the role of hepatic lipase in the lipoprotein alterations associated with thyroid dysfunction.     

Plasma lipoproteins,postheparin plasma lipoprotein lipase activity intralipid half-life,triglyceride secretion rate and liver lipids in the mouse fed different cholesterol diets

Mice (SC), fed a semipurified diet containing cholesterol, cholic acid and sucrose, exhibited, in comparison to control animals (S), an increase in cholesterol, phospholipid and protein of VLDL, LDL₁ and LDL₂, but triglyceride of the same lipoproteins decreased, as did total plasma triglycerides. Postheparin plasma lipoprotein lipase activity of SC animals was 1.72 times that of S mice. At the same time Intralipid half-life in SC mice was decreased by 52%. Triglyceride secretion rate, after Triton WR 1339 treatment, and liver triglyceride content were reduced in SC animals. HDL mass was decreased in SC mice. Mice (AC) fed a standard diet containing cholesterol showed, in comparison to normal fed animals (A), an increase in cholesterol of VLDL, LDL₁ and LDL₂ but triglyceride of the same lipoproteins decreased as did total plasma triglycerides. Postheparin plasma lipoprotein lipase activity of AC animals was unmodified as was Intralipid half-life. In AC animals triglyceride secretion rate, after Triton WR 1339 treatment, was reduced but in a less extent than in SC mice. Liver triglyceride was unmodified. HDL mass was decreased in AC mice.     

Binding of low density lipoproteins to lipoprotein lipase is dependent on lipids but not on apolipoprotein B

Lipoprotein lipase (LPL) efficiently mediates the binding of lipoprotein particles to lipoprotein receptors and to proteoglycans at cell surfaces and in the extracellular matrix. It has been proposed that LPL increases the retention of atherogenic lipoproteins in the vessel wall and mediates the uptake of lipoproteins in cells, thereby promoting lipid accumulation and plaque formation. We investigated the interaction between LPL and low density lipoproteins (LDLs) with special reference to the protein-protein interaction between LPL and apolipoprotein B (apoB). Chemical modification of lysines and arginines in apoB or mutation of its main proteoglycan binding site did not abolish the interaction of LDL with LPL as shown by surface plasmon resonance (SPR) and by experiments with THP-I macrophages. Recombinant LDL with either apoB100 or apoB48 bound with similar affinity. In contrast, partial delipidation of LDL markedly decreased binding to LPL. In cell culture experiments, phosphatidylcholine-containing liposomes competed efficiently with LDL for binding to LPL. Each LDL particle bound several (up to 15) LPL dimers as determined by SPR and by experiments with THP-I macrophages. A recombinant NH(2)-terminal fragment of apoB (apoB17) bound with low affinity to LPL as shown by SPR, but this interaction was completely abolished by partial delipidation of apoB17. We conclude that the LPL-apoB interaction is not significant in bridging LDL to cell surfaces and matrix components; the main interaction is between LPL and the LDL lipids.     

Effects of probucol on plasma lipids, lipoproteins and parameters of high density lipoprotein metabolism.

Eight patients with primary hypercholesterolemia were treated with probucol for 17 weeks. Plasma total cholesterol, low density lipoprotein (LDL)-cholesterol, and high density lipoprotein (HDL)-cholesterol decreased by 16.6, 15.0 and 25.7%, respectively, in response to probucol treatment. Plasma levels of apolipoprotein B and apolipoprotein A-I also decreased, while apolipoprotein A-II concentrations were unchanged. The decrease in HDL-cholesterol levels was associated with a reduction in HDL particle size. No changes in the plasma lecithin:cholesterol acyltransferase activity or mass occurred in response to probucol treatment. In contrast, a significant 25% increase in plasma cholesteryl ester and triglyceride transfer activity occurred following probucol treatment. There was a positive correlation (R = 0.94) between cholesterol ester and triglyceride transfer. We propose that the increase in lipid transfer activity may in part explain the changes in HDL concentration and size, as well as the previously reported effect probucol has on reducing atherosclerosis in animal models.     

Tissue lipoprotein lipase,serum, and urinary lipids and lipoproteins in experimental glomerulonephritis of rats (Heymann's nephritis)

Serum and urinary cholesterol, triglycerides, high-density lipoproteins, and tissue lipoprotein lipase levels were measured in a group of rats in which experimental glomerulonephritis (EGN) was induced by an injection of renal tubular antigen in Freund's complete adjuvant. Progressively increasing proteinuria beginning after approximately the eighth week was associated with a progressive increase in the levels of serum cholesterol, triglycerides, and high-density lipoprotein cholesterol. Significant lipiduria occurred at the ninth week. Lipoprotein electrophoresis of concentrated urine showed the presence of a band with alpha lipoprotein (high-density lipoprotein) mobility. Eleven weeks after disease induction, the rats were killed and the tissue levels of lipoprotein lipase were measured. A homogenized preparation of the heart, liver, adipose tissue, and skeletal muscle using [¹⁴C]triolein as substrate was used. Nephrotic rats had less than half the myocardial lipoprotein lipase levels of controls (2099 ± 420 and 962 ± 142 (mean ± SD) nm free fatty acids/mg tissue/hr, respectively; P < 0.05). Hepatic, skeletal muscle, and adipose tissue lipoprotein lipase levels were not significantly different in the two groups of rats.These results document the potential usefulness of the rat (EGN) model for further studies in lipoprotein metabolism in nephrotic syndrome. The significance and pathogenesis of reduced myocardial lipoprotein lipase requires further investigation.     

Interaction between diet, exercise and lipids or lipoproteins

Diet can influence the changes in plasma lipoprotein concentrations that occur with exercise. Dietary factors alone, however, probably do not account for the lipoprotein profiles of physically active people. Whether exercise or diet exerts the dominant effect on lipids and lipoproteins depends largely on the level of exercise achieved and the total energy balance. More well designed research is required to examine the effect of diet on lipids and lipoproteins in people of different levels of physical fitness taking part in a variety of physical activities.     

Effects of exercise cessation on lipids and lipoproteins in distance runners and power athletes

The purpose of this study was to determine the effects of short-term exercise cessation on lipid and lipoprotein profile and insulin sensitivity in highly trained runners (n=12; mean age 19.9 years) and power athletes (n=12; mean age 24.4 years). Following 14 days of exercise cessation, running time to exhaustion and maximal oxygen uptake decreased by 9.2% and 4.8% (P < 0.05) in the runners, while in the power athletes one repetition maximum squat and bench press did not change (P>0.05). No changes occurred in body composition. Data from a 2-h oral glucose tolerance test revealed an impairment of the glycemic state in all athletes (P<0.05). In contrast, exercise cessation did not significantly (P>0.05) alter plasma levels of cholesterol, triglycerides, and low density (LDL) and high density lipoprotein (HDL). No changes were observed in HDL₂, HDL_2b, and HDL₃ subfractions, LDL diameter, and qualitative LDL pattern (P>0.05). These data thus suggest that despite a decrease in insulin sensitivity, short-term exercise cessation, independent of exercise mode, was insufficient to alter plasma lipid and lipoprotein profiles in well-trained athletes.     

Heparin binding to lipoprotein lipase and low density lipoproteins

Heparin was fractionated on an affinity column of bovine milk lipoprotein lipase (LpL) immobilized to Affi-Gel-15. The bound heparin, designated high-reactive heparin (HRH), enhanced LpL activity, presumably by stabilizing the enzyme against denaturation. The unbound heparin fraction had no observable effect on the initial rate of enzyme activity. However, at longer times of incubation there was inhibition of LpL activity. LpL-specific HRH also showed a high, Ca²⁺-dependent precipitating activity towards human plasma low density lipoproteins (LDL). Since LpL and LDL both bind to heparin-like molecules at the surface of the arterial wall, we suggest that their similar heparin-binding specificity may have physiological consequences as it relates to the development of atherosclerosis.

Heparin binding Lipoprotein lipase LDL Apolipoprotein Lipolysis     

Differential binding of triglyceride-rich lipoproteins to lipoprotein lipase.

In comparison to very low density lipoprotein (VLDL), chylomicrons are cleared quickly from plasma. However, small changes in fasting plasma VLDL concentration substantially delay postprandial chylomicron triglyceride clearance. We hypothesized that differential binding to lipoprotein lipase (LPL), the first step in the lipolytic pathway, might explain these otherwise paradoxical relationships. Competition binding assays of different lipoproteins were performed in a solid phase assay with purified bovine LPL at 4 degrees C. The results showed that chylomicrons, VLDL, and low density lipoprotein (LDL) were able to inhibit specific binding of (125)I-labeled VLDL to the same extent (85.1% +/- 13.1, 100% +/- 6.8, 90.7% +/- 23.2% inhibition, P = NS), but with markedly different efficiencies. The rank order of inhibition (K(i)) was chylomicrons (0.27 +/- 0.02 nm apoB) > VLDL (12.6 +/- 3.11 nm apoB) > LDL (34.8 +/- 11.1 nm apoB). By contrast, neither triglyceride (TG) liposomes, high density lipoprotein (HDL), nor LDL from patients with familial hypercholesterolemia were efficient at displacing the specific binding of (125)I-labeled VLDL to LPL (30%, 39%, and no displacement, respectively). Importantly, smaller hydrolyzed chylomicrons had less affinity than the larger chylomicrons (K(i) = 2.34 +/- 0.85 nm vs. 0.27 +/- 0.02 nm apoB respectively, P < 0.01). This was also true for hydrolyzed VLDL, although to a lesser extent. Chylomicrons from patients with LPL deficiency and VLDL from hypertriglyceridemic subjects were also studied. Taken together, our results indicate an inverse linear relationship between chylomicron size and K(i) whereas none was present for VLDL. We hypothesize that the differences in binding affinity demonstrated in vitro when considered with the differences in particle number observed in vivo may largely explain the paradoxes we set out to study.     

Plasma lipids and lipoprotein lipase activating property in women on three different combinations of estrogens and progestins

Total plasma lipoprotein lipase (LPL) activating property, triglycerides, cholesterol, low-density lipoprotein cholesterol (LDL-C), and high-density lipoprotein cholesterol (HDL-C) were measured in 24 normal Venezuelan females and in 71 healthy women (20–35 years) who received one of three different combinations of ethinylestradiol and d-norgestrel for at least 6 months.Group I received a low dose combination of 30 μg ethinylestradiol plus 250 μg d-norgestrel; Group II received a high dose of 50 μg ethinylestradiol plus 250 μg d-norgestrel, and Group III received 50 μg ethinylestradiol plus a high dose of 500 μg d-norgestrel. Groups I and II had significantly elevated total plasma cholesterol and LDL-C compared to controls. In Group II total plasma LPL activator property was significantly lower (65.0 ± 18.4 u/ml; mean ± SD) than controls (78.1 ± 21.4 u/ml) Group II also had significantly higher total plasma triglycerides (145.8 ± 51.7 mg/dl) compared to controls (96.8 ± 21.8 mg/dl). Compared to Group II, women in Group III had significantly lower total plasma triglycerides (113.1 ± 48.8 mg/dl) and higher LPL activating property (82.1 ± 22.1 u/ml) than women in Group II.These data extend previous reports on the effects of oral contraceptives on plasma lipids and lipoproteins and suggest that sex steroids may affect plasma triglycerides by influencing apolipoproteins that modulate lipoprotein lipase activity.     

Glucose tolerance, plasma lipoproteins and tissue lipoprotein lipase activities in body builders

Oral glucose tolerance, insulin binding to erythrocyte receptors, serum lipids, and lipoproteins, and lipoprotein lipase activities of adipose tissue and skeletal muscle were measured in nine body builders (relative body weight (RBW) 118 +/- 4%), eight weight-matched (RBW 120 +/- 5%) and seven normal-weight controls (RBW 111 +/- 3%). The body builders had 50% higher relative muscle mass of body weight (% muscle) and 50% smaller relative body fat content (% fat) than the two other groups (P less than 0.005). Maximal aerobic power was comparable in the three groups. In the oral glucose tolerance test (OGTT), blood glucose levels, and plasma insulin levels were lower (P less than 0.05) in the body builders than in weight-matched controls. Insulin binding to erythrocytes was similar in each group. On the basis of multiple linear regression analysis, 87% of the variation in plasma insulin response could be explained by body composition (% muscle and % fat) and VO2max. Plasma total cholesterol, low-density lipoprotein (LDL) cholesterol, and very low-density lipoprotein (VLDL) triglyceride concentrations were significantly lower in the body builders than in weight-matched controls. In comparison with the normal-weight group, the body builders had a lower total cholesterol level. High density lipoprotein (HDL) cholesterol, its subfractions (HDL2 and HDL3 cholesterol) and lipoprotein lipase (LPL) activities of adipose tissue and skeletal muscle were comparable in all three groups. Partial correlation analysis showed a positive relationship between plasma total triglyceride, total cholesterol and LDL cholesterol on the other hand and the % fat on the other.(ABSTRACT TRUNCATED AT 250 WORDS)     

Activation and inhibition of lipoprotein lipase. Studies with artificial lipoproteins.

Human plasma very low density apolipoproteins C-I, C-II and C-III were recombined in vitro with triolein. The lipid-protein complexes were analyzed by ultracentrifugal flotation, agarose gel electrophoresis, immunoelectrophoresis and electron microscopy. Maximal protein/triolein ratios for apoprotein C-I, C-II, C-III-1 and C-III-2 were 50, 45, 95 and 55 microgram/mg, respectively. Electron micrographs exhibited spherical particles with diameters ranging from 200--2000 A comparable to native VLDL and chylomicrons. On agarose gel electrophoresis these complexes showed alpha-mobility. Kinetics of triolein hydrolysis by purified human plasma lipoprotein lipase were studied using these artificial lipoprotein substrates with different apoprotein/triolein ratios. The reaction followed the Michaelis-Menten equation. With increasing amounts of apo C-II, the apparent Km decreased from 0.60 to 0.11 mM. Incubation of the substrate with either rabbit anti-apo C-II gamma-globulins or digestion with trypsin prior to hydrolysis reversed this lowering effect on apparent Km. V was not altered significantly. Increasing amounts of apo C-I, apo C-III-1 or apo C-III-2 without apo C-II caused inhibition of triolein hydrolysis. In the presence of apo C-II, however, similar kinetic parameters were obtained as described above.     

Effects of threonine-poor apolipoproteins on post-heparin plasma hepatic triacylglycerol lipase and lipoprotein lipase

Whole-irradiated rabbit pre-heparin plasma had an important inhibitory effect on hepatic triacylglycerol lipase and lipoprotein lipase activities, whereas control rabbit pre-heparin plasma slightly inhibited hepatic triacylglycerol lipase activity at a high concentration and enhanced lipoprotein lipase activity. As some apolipoproteins were known to modulate these two lipolytic enzymes, the inhibitory effects of irradiated rabbit plasma were investigated in apolipoproteins. Three apolipoproteins, with isoelectric points of about 6.58, 6.44 and 6.12, characterized by their low content in threonine (threonine-poor apolipoproteins) were produced in high concentrations in rabbit VLDL and HDL after irradiation. The effects of these apolipoproteins on control rabbit post-heparin plasma hepatic triacylglycerol lipase and extrahepatic lipoprotein lipase were studied. Threonine-poor apolipoproteins substantially inhibited the hepatic triacylglycerol lipase activity and enhanced the apolipoprotein C-II-stimulated activity of lipoprotein lipase. The amounts of these apolipoproteins in triacylglycerol-rich lipoprotein particles may determine the lipolytic activity of lipoprotein lipase and hepatic triacylglycerol lipase in triacylglycerol hydrolysis. The existence of another inhibitor of lipoprotein lipase remains to be determined.     

Release of endothelial cell lipoprotein lipase by plasma lipoproteins and free fatty acids

Lipoprotein lipase (LPL) bound to the lumenal surface of vascular endothelial cells is responsible for the hydrolysis of triglycerides in plasma lipoproteins. Studies were performed to investigate whether human plasma lipoproteins and/or free fatty acids would release LPL which was bound to endothelial cells. Purified bovine milk LPL was incubated with cultured porcine aortic endothelial cells resulting in the association of enzyme activity with the cells. When the cells were then incubated with media containing chylomicrons or very low density lipoproteins (VLDL), a concentration-dependent decrease in the cell-associated LPL enzymatic activity was observed. In contrast, incubation with media containing low density lipoproteins or high density lipoproteins produced a much smaller decrease in the cell-associated enzymatic activity. The addition of increasing molar ratios of oleic acid:bovine serum albumin to the media also reduced enzyme activity associated with the endothelial cells. To determine whether the decrease in LPL activity was due to release of the enzyme from the cells or inactivation of the enzyme, studies were performed utilizing radioiodinated bovine LPL. Radiolabeled LPL protein was released from endothelial cells by chylomicrons, VLDL, and by free fatty acids (i.e. oleic acid bound to bovine serum albumin). The release of radiolabeled LPL by VLDL correlated with the generation of free fatty acids from the hydrolysis of VLDL triglyceride by LPL bound to the cells. Inhibition of LPL enzymatic activity by use of a specific monoclonal antibody, reduced the extent of release of 125I-LPL from the endothelial cells by the added VLDL. These results demonstrated that LPL enzymatic activity and protein were removed from endothelial cells by triglyceride-rich lipoproteins (chylomicrons and VLDL) and oleic acid. We postulate that similar mechanisms may be important in the regulation of LPL activity at the vascular endothelium.     

Effects of training and a single session of exercise on lipids and apolipoproteins in hypercholesterolemic men

Crouse, Stephen F., Barbara C. O'Brien, Peter W. Grandjean,Robert C. Lowe, J. James Rohack, and John S. Green. Effects oftraining and a single session of exercise on lipids and apolipoproteins in hypercholesterolemic men. J. Appl.Physiol. 83(6): 2019-2028, 1997.To differentiatebetween transient (acute) and training (chronic) effects of exercise attwo different intensities on blood lipids and apolipoproteins (apo), 26 hypercholesterolemic men (cholesterol = 258 mg/dl, age = 47 yr, weight = 81.9 kg) trained three times per week for 24 wk, 350 kcal/session athigh (80% maximal O₂ uptake,n = 12) or moderate (50% maximalO₂ uptake, n = 14) intensity. Serum lipid andapolipoprotein (apo) concentrations (plasma volume adjusted) weremeasured before and immediately, 24, and 48 h after exercise on fourdifferent occasions corresponding to 0, 8, 16, and 24 wk of training.Data were analyzed using three-way repeated-measures multivariateanalysis of variance followed by analysis of variance and Duncan'sprocedures ( = 0.05). A transient 6% rise inlow-density-lipoprotein cholesterol measured before training at the24-h time point was no longer evident after training. Triglyceridesfell and total cholesterol, high-density-lipoprotein cholesterol(HDL-C), HDL₃-C, apo A-I, and apoB rose 24-48 h after exercise regardless of training or intensity.Total cholesterol, HDL₃-C, apoA-I, and apo B were lower andHDL₂-C was higher after trainingthan before training. Thus exercise training and a single session ofexercise exert distinct and interactive effects on lipids andapolipoproteins. These results support the practice of training atleast every other day to obtain optimal exercise benefits.