Postheparin Plasma Lipoprotein Lipase Research Articles

Transgenic mice expressing human lipoprotein lipase driven by the mouse metallothionein promoter. A phenotype associated with increased perinatal mortality and reduced plasma very low density lipoprotein of normal size.

We have produced transgenic mice expressing human lipoprotein lipase (LPL) driven by the mouse metallothionein I promoter. We found that integration of the LPL gene construct was associated with a high perinatal mortality. Animals that survived the first 2 weeks of life grew normally afterwards. Compared with controls, transgenic animals had higher post-heparin plasma LPL and tissue LPL activities. Immunoreactive human LPL was detected in their post-heparin plasma but not in controls. Transgenic animals had significantly lower plasma very low density lipoprotein (VLDL) while on a regular laboratory chow. By electron microscopic analysis and nondenaturing polyacrylamide gradient gel electrophoresis, the size and morphology of the plasma VLDL were very similar in transgenic and control animals, which suggests that VLDL particles acted on by the increased tissue LPL in the transgenic animals were mostly taken up by the cell without being released back into circulation. The hypertriglyceridemia and elevated VLDL in response to sucrose feeding were completely abolished in transgenic animals. They also had lower VLDL lipids compared with control animals when they were fed a high-fat, high-cholesterol diet. Feeding the mother of transgenic mice a high-fat diet during pregnancy completely reversed the high perinatal mortality associated with the integrated transgene, which suggests that the deleterious effect of LPL overexpression may be related to the depletion of some essential lipid nutrient.

Alteration of lipid profiles in plasma of transgenic mice expressing human lipoprotein lipase

Lipoprotein lipase (LPL) is a key enzyme required for the hydrolysis of triglyceride-rich particles. To assess the effects of increased plasma LPL on lipoprotein levels, transgenic mice expressing human LPL (hLPL) were produced. Abundant hLPL transcripts were detected in RNA from different tissues of transgenic mice which resulted in an increase in post-heparin plasma LPL activity of approximately 154%. On rodent chow (p = 0.01) and after a 16-h fast (p = 0.001), plasma triglycerides in transgenic mice were decreased by approximately 50% as compared to littermate controls. Gel filtration chromatography showed a 2-3-fold decrease in very low density lipoprotein triglycerides and cholesterol enrichment of low density lipoprotein. Transgenic mice maintained on a high carbohydrate diet exhibited a 78% (p = 0.03) lowering of low density lipoprotein and very low density lipoprotein cholesterol levels, in addition to a 68% (p = 0.01) lowering of total to high density lipoprotein cholesterol (TC/HDL-C) ratios compared to controls. The distribution of apoA-I and A-II were similar in the transgenics and their non-transgenic littermates, while the apoE distribution was mildly altered in the plasma from the transgenic mice. These data demonstrate that moderate increases in total LPL activity are associated with significant changes in lipoprotein levels and altered composition of lipoprotein particles.

Hyperlipidemia in streptozocin-diabetic hamsters as a model for human insulin-deficient diabetes: Comparison to streptozocin-diabetic rats

Characteristics of the lipoprotein profile and metabolism of triglyceride-rich lipoproteins in diabetic hamsters were investigated to assess their suitability as a model for human diabetic hyperlipidemia. Diabetes was induced in the hamsters by intraperitoneal injection of streptozocin (30 mg/kg) for 3 days and compared with the results in streptozocin-diabetic rats (50 mg/kg intravenously). Similar degrees of hyperglycemia and hypoinsulinemia were observed 8 to 10 days after the final streptozocin injection in both groups. Fasting plasma lipid concentrations were about 2.5 times greater in hamsters than in rats. Plasma cholesterol was principally associated with high-density lipoprotein (HDL) in both rodents, although the distribution in very-low-density lipoprotein (VLDL) and low-density lipoprotein (LDL) was significantly greater in hamsters (44%) than in rats (13%). Diabetes increased the concentrations of triglyceride, cholesterol, and phospholipid 5.6- to 7.8-fold in hamsters, whereas it increased them only 1.3- to 1.6-fold in rats. Diabetic hamsters have a plasma lipoprotein profile similar to that of diabetic man, ie, triglyceride-rich lipoproteins are increased and HDL cholesterol is decreased. The concentration of HDL cholesterol was inversely correlated with the severity of hypertriglyceridemia ( r = .76, P < .005). This combination of events does not occur in diabetic rats. Hamsters had a low level of apoprotein B-48-containing triglyceride-rich lipoproteins, although diabetes increased the estimated concentration by fourfold. In rats apoprotein B-48 is the predominant form, but diabetes did not alter the relative proportion of apoprotein B isoforms. The hypertriglyceridemia in both diabetic animals was solely due to a reduction in the clearance of triglyceride-rich lipoproteins, because the output of triglyceride as determined by the Triton WR1339 method was halved and the fractional catabolic rate of radiolabeled VLDL triglyceride was remarkably decreased. Lipoprotein lipase and hepatic lipase activities in postheparin plasma were lower in hamsters than in rats, and diabetes decreased lipoprotein lipase activity by half in hamsters, but not in rats. These results suggest that hamsters may be a more useful model than rats for delineating the disturbance in lipid metabolism that occurs as a result of insulin-deficient diabetes.

Mechanism of hypertriglyceridemia in dahl salt-sensitive rats, an animal model of spontaneous nephrotic syndrome

It has been reported that focal and segmental glomerulosclerosis (FSGS) with pronounced proteinuria rapidly develop in Dahl salt-sensitive hypertensive (DS) rats fed a high-salt diet. We found that even when they are fed a standard rat chow (0.3% NaCl), DS rats, especially males, exhibit marked proteinuria, hypoalbuminemia, and hypertriglyceridemia without marked hypertension at 32 to 38 weeks of age. The nephrosis was associated with spontaneously developed FSGS. We therefore investigated the mechanism of hypertriglyceridemia in nephrotic animals. Plasma triglyceride (TG) and apoprotein (apo) B levels were markedly increased in DS rats compared with Sprague-Dawley (SD) rats, and this was mainly attributable to an increase in the concentration of very-low-density lipoprotein (VLDL). The TG secretion rate estimated by the Triton WR1339 method was significantly greater in DS rats. VLDL-TGs isolated from both the DS and SD rats were endogenously radiolabeled with different isotopes, and a mixture of these was then injected into DS and SD recipients. The half-life of VLDL-TG was about three times longer in DS recipients, regardless of the source of VLDL. In SD recipients, VLDL from DS rats was cleared at a slower rate than VLDL from SD rats. The activity of lipoprotein lipase in postheparin plasma was substantially decreased in DS rats. Isoelectric focusing gel electrophoresis (IEF) showed that the ratio of apo E C or apo C-II C-III in VLDL was markedly decreased and the ratio of apo E or apo C to apo A1 in high-density lipoprotein (HDL) was slightly decreased in DS rats. These results suggest that the mechanism of hypertriglyceridemia is multifactorial in spontaneous nephrotic rats and is a result of both overproduction and impaired catabolism of VLDL-TG. Abnormal properties of lipoproteins may play an important role in the catabolic defect, as well as the reduced lipoprotein lipase activity, in the nephrotic animals.

High density lipoproteins with differing apolipoproteins: relationships to postprandial lipemia, cholesteryl ester transfer protein, and activities of lipoprotein lipase, hepatic lipase, and lecithin: cholesterol acyltransferase.

To gain insight into metabolic determinants of high density lipoproteins (HDL) containing apolipoproteins A-I and A-II (LpA-I/A-II) and those containing A-I, but devoid of A-II (LpA-I), the plasma concentration of LpA-I and LpA-I/A-II within the HDL2 and HDL3 density spectrum was measured in 14 normolipidemic male subjects on a standardized diet. Apolipoprotein plasma concentrations of HDL subspecies were compared with the magnitude of postprandial lipemia, activities of lipoprotein lipase and hepatic lipase in postheparin plasma, plasma lecithin:cholesterol acyltransferase (LCAT) activity, and cholesteryl ester transfer protein (CETP) mass. Plasma levels of LpA-I/A-II were 2.5 times higher than levels of LpA-I (123 +/- 20 vs. 48.3 +/- 22.1 mg protein/dl) and the partition of LpA-I and LpA-I/A-II between HDL2 and HDL3 differed in that the proportion of LpA-I associated with HDL2 was greater than that of LpA-I/A-II (23 +/- 19 vs. 6 +/- 6%, P < 0.002). With increasing levels of HDL2, the proportion of LpA-I in HDL2 increased (P < 0.002). Furthermore, levels of LpA-I and LpA-I/A-II were strongly correlated within the HDL2 but not within the HDL3 density region. Plasma levels of LpA-I, but not LpA-I/A-II, were inversely correlated with the magnitude of postprandial lipemia. However, activities of lipoprotein lipase and hepatic lipase tended to show stronger associations with the partition of LpA-I/A-II between HDL2 and HDL3 than with that of LpA-I. Within the HDL3, but not the HDL2 density spectrum, LpA-I/A-II exhibited a positive association with plasma LCAT activity, while LpA-I displayed an inverse association with plasma CETP mass. These results are consistent with differences in substrate properties of LpA-I and LpA-I/A-II for lipoprotein modifying enzymes and imply different, but overlapping metabolic pathways of LpA-I and LpA-I/A-II.

ヒト肝性トリグリセリドリパーゼ(HTGL)の生理作用の解明

The purpose of this study is to evaluate changes in hepatic triglyceride lipase (HTGL) and lipoprotein lipase (LPL) as a cause of dyslipoproteinemia in hypothyroidism. Hypothyroidism is associated with pronounced hypercholesterolemia and moderate hypertriglyceridemia. Recent studies suggest that such changes in serum lipids result from the decrease in LDL-receptors and also HTGL and/or LPL activities. In order to accurately evaluate the correlation between both lipases and lipoprotein abnormalities in patients with hypothyroidism, we measured LPL and HTGL mass concentrations in postheparin plasma by means of a sandwich-enzyme immunoassay (EIA) using two distinct monoclonal antibodies before and after treatment with thyroid hormone.Seven patients with untreated hypothyroidism and euthyroid normal controls (n=76) were studied. Hypothyroidism group (H) consisted of 3 males and 4 females (age 60±5 years) and the control group (N) of 46 males and 30 females (age 42±13 years). The plasma cholesterol (C) and triglyceride (TG) levels were significantly increased in the H group compared to the N group: 327±27 vs. 192±27ma/dl and 145±24 vs 88±33mg/dl, respectively. There was no difference in HDL-C (61.2±5.7 vs. 63.1±6.6mg/dl). HTGL was markedly reduced (79%) in the H group (264±57 vs. 1, 252±55ng/ml), while LPL was only slightly reduced (16%) (153±17 vs. 182±5ng/ml). The H group showed a hyperlipidemia of IIa (n=5) or IIb (n=2) as a WHO phenotype. After the patients were treated with thyroid hormone, HTGL level was drastically increased from 264±57ng/ml to 858±115ng/ml, and the LPL level also increased from 153±17ng/ml to 201±29ng/ml. Plasma C level decreased from 327±27 to 234±3mg/dl, and TG from 145±24 to 78±13mg/dl. By plotting all the patient data before and after the treatment, HTGL showed a positive correlation with FT3 (r=0.86) and negative correlation with TSH (r=-0.66). HTGL showed significant inverse correlations with LDL-TG/apoB (r=-0.74) and HDL-TG/apoA (r=-0.74). Our data indicates that HTGL mass concentration is regulated by thyroid hormone level leading us to conclude that HTGL is closely related to the metabolism of triglyceride-rich LDL and HDL particles.

Activation of coagulation factor VII during alimentary lipemia.

Dietary studies have established a connection between plasma lipoproteins and coagulation factor VII. The present study was undertaken to specifically examine whether factor VII is activated during alimentary lipemia and to investigate the relations of factor VII mass and activity state with fasting and postprandial lipoproteins and free fatty acids (FFAs). Factor VII levels were therefore determined in plasma samples taken before and after intake of a standardized, oral fat load of a mixed-meal type in 33 men (mean age +/- SD, 48.8 +/- 3.2 years) with a previous myocardial infarction at a young age and 10 healthy, age-matched control subjects. A panel of methods for factor VII determination was used to ensure that changes in all potentially existing forms of the factor during alimentary lipemia would be included. Substantial activation of factor VII was found to occur during alimentary lipemia, whereas the number of factor VII molecules remained constant or even appeared to decrease after the test meal. Activation of factor VII was more pronounced in control subjects than patients, and the proportion of activated factor VII molecules was higher in control subjects. Interestingly, factor VII activation, which correlated quantitatively with the degree of postprandial triglyceridemia, seemed to be related to FFA production during lipolysis of triglyceride-rich lipoproteins that were generated in response to fat intake. Postheparin plasma lipoprotein lipase activity was lower in patients, which could offer one explanation why factor VII activity was lower during alimentary lipemia in these subjects despite their exaggerated postprandial triglyceridemia. Thus, activation of coagulation factor VII during alimentary lipemia may result in a procoagulant state that is likely to promote the formation of a coronary thrombus in individuals with established coronary artery disease.

Parathyroid hormone is not an inhibitor of lipoprotein lipase activity

The reduced lipoprotein lipase (LPL) activities in uraemia are reflected by increased serum triglyceride concentrations and reduced HDL cholesterol concentrations. Both hyperparathyroidism and circulating inhibitor(s) of LPL have been associated with the disturbances of lipid metabolism in uraemia. The aim of the present study was to investigate if parathyroid hormone (PTH) had an inhibitory effect on LPL activity. Plasma post-heparin LPL activities, plasma LPL inhibitory activities, serum PTHintact and serum PTHC-terminal concentrations were analysed in 20 patients on haemodialysis and 20 healthy controls. The effects of purified, human PTHintact and a carboxyterminal fragment of PTH (PTH39-84) on LPL activities in post-heparin plasma from healthy individuals and on the enzyme activity of purified, bovine milk LPL, activated with apolipoprotein CII, were studied. Patients had significantly higher plasma LPL inhibitory activities than controls, but there was no correlation between plasma LPL inhibitory activities and serum PTH concentrations. Neither PTHintact nor PTH39-84 had a significant effect on LPL activities in vitro. Thus there was no evidence of a direct inhibition of LPL activity by PTH under the present in-vivo or in-vitro conditions.

Hypertriglyceridemia and lowered apolipoprotein C-II/C-III ratio in uremia: Effect of a fibric acid, clinofibrate

We examined the effects of a fibric acid, clinofibrate, on lipoprotein metabolism in 12 hyperlipidemic patients with uremia treated on continuous ambulatory peritoneal dialysis during a 24 week treatment. Daily dose of clinofibrate was 200 mg for the initial four weeks, 400 mg for the second four weeks, and 600 mg for the subsequent 16 weeks. Serum and very-low density lipoprotein (VLDL) triglyceride were decreased by 36% and 48%, respectively. Neither total cholesterol nor apolipoprotein B changed significantly, whereas cholesterol was decreased in VLDL and increased in low (LDL) and high density lipoprotein (HDL) fractions. Post-heparin plasma lipoprotein lipase (LPL) before treatment was not lower than the normal value, and we found no change in LPL activity following clinofibrate. Hepatic triglyceride lipase also did not change. Apolipoprotein (apo) C-II/C-III ratio was low as compared to the normal value before treatment, and the ratio was increased by 38% after the treatment. Decrease in VLDL triglyceride was associated with increase in apo C-II/C-III ratio in all the cases. Abnormal enrichment with triglyceride of LDL and HDL fractions was improved by clinofibrate. Although one patient had a transient and asymptomatic elevation of serum creatine phosphokinase, no patient had muscle pain. There was no accumulation of the drug in the 24 week trial. These results suggest that clinofibrate is an effective and safe approach to the management of dyslipidemia in CAPD patients.

Lipoprotein lipases, lipoprotein density gradient profile and LDL receptor activity in miniature pigs fed fish oil and corn oil

The effects of fish oil and corn oil on plasma lipoprotein concentrations, the lipolytic enzymes, lipoprotein lipase and hepatic triacylglycerol lipase, the density distribution of the plasma lipoproteins and LDL receptor activity were studied. These experiments were designed, in part, to define the mechanism(s) responsible for the increased conversion of plasma VLDL apolipoprotein B to LDL and a decreased LDL apolipoprotein B fractional catabolic rate described in previous apolipoprotein B kinetic studies. Miniature pigs were fed diets for 3 to 6 weeks containing supplements of corn oil or fish oil as Maxepa. Triacylglycerol and cholesterol in plasma and VLDL were significantly reduced by the fish oil diet. LDL and HDL cholesterol were not significantly changed. The fish oil diet significantly reduced post-heparin plasma lipoprotein lipase and hepatic triacylglycerol lipase activities, which may be an adaptive response to the low concentration of substrates (triacylglycerol-rich lipoproteins) for these enzymes. No differences were observed in the density of VLDL, LDL or HDL as determined by density gradient ultracentrifugation with the fish oil diet. No major changes in percent lipid composition of VLDL, LDL and HDL were observed. No differences were found with respect to LDL uptake by J774 macrophages. Receptor mediated clearance of LDL in vivo, as assessed by measuring the difference in fractional catabolic rate of native vs. methylated LDL decreased significantly by 17% ( P < 0.032). We conclude that the increased conversion of VLDL apolipoprotein B to LDL in miniature pigs fed fish oil is not related to an increase in lipolytic enzymes or density distribution of VLDL, but may be due in part to a decrease in LDL receptor activity.

Determinants of fasting hypertriglyceridemia in ventromedial hypothalamic obesity in rats.

The present study investigated the mechanism of fasting hypertriglyceridemia in ventromedial hypothalamic (VMH) obesity by measurement of post-heparin plasma lipoprotein lipase (LPL) activity, triglyceride secretion rate (TGSR), and plasma insulin. One week after VMH lesions, when the lesioned rats were gaining weight rapidly (the dynamic phase), they showed normal plasma triglyceride levels with increased plasma LPL activity and TGSR. There was a positive correlation between hyperinsulinemia and elevated plasma LPL activity or TGSR in VMH-lesioned rats, while no correlation was observed in control rats. Ten weeks after VMH lesions, when the rats had become obese and reached a steady-state weight gain (the static phase), they showed hypertriglyceridemia with increased plasma LPL activity and TGSR. There was, again, a positive correlation between hyperinsulinemia and elevated plasma LPL activity or TGSR in VMH-lesioned rats. These results suggest a possible mechanism of fasting hypertriglyceridemia in these rats; in the dynamic phase adipose tissue adequately takes up circulating triglyceride because the tissue has sufficient take-up capacity and hence hypertriglyceridemia does not develop. In the static phase the tissue cannot adequately take up circulating triglyceride because of a limitation of its capacity, resulting in hypertriglycemia despite enhanced triglyceride secretion and increased LPL activity in both phases.

Mechanism of poloxamer 407-induced hypertriglyceridemia in the rat

One 300 mg i.p. injection of the nonionic surfactant poloxamer 407 (Pluronic® F-127) produces a significant increase above control of both circulating cholesterol and triglyceride (TG) concentrations. The present study was conducted to determine the effect of poloxamer 407 (P-407) on the capacity to hydrolyze circulating TG by lipoprotein lipase (LPL) in an attempt to determine the mechanism of action of P-407. The concentration of TG in the rat following a single 300 mg i.p. injection of P-407 was marked, increasing from 84 ± 10 to 3175 ± 322 mg/dL at 24 hr. The maximal rate of TG accumulation (5.74 mg/dL/min) in the plasma of P-407-injected rats occurred between 2 and 4 hr post-injection. In vitro incubation of LPL with P-407 significantly inhibited enzyme activity with an inhibitory concentration at which 50% of the enzymatic activity was lost of approximately 24 μM. Concentrations of P-407 exceeding 350 μM in vitro completely inhibited LPL activity. The effects of P-407 on the enzymatic activity of LPL in post-heparin plasma obtained following a single 300 mg dose of P-407 to rats demonstrated greater than 95% suppression of LPL activity 3 hr post-injection compared with controls. Inhibition of LPL activity was greater than 90% as long as 24 hr following a single i.p. injection of P-407. However, while the heparin-releasable fraction of capillary-bound LPL was inhibited in the plasma, LPL activity significantly increased in cardiac and skeletal muscle in poloxamer-injected animals compared with sham-injected controls. Although there was no significant change in LPL activity in adipose tissue, testes, and lung resulting from P-407 treatment, LPL activity increased by 37% in myocardium, 69% in soleus, and 66% in gastronemius muscle in P-407-injected rats when compared with controls. Our studies would suggest that the predominant mechanism by which P-407 induced an increase in circulating TG was by a reduction in the rate at which TG was hydrolyzed due to inhibition of heparin-releasable LPL by the surfactant.

Regulation of apolipoprotein A-I-containing lipoproteins in IDDM.

In IDDM patients, serum high-density lipoprotein cholesterol concentrations have been reported to be normal or elevated. The spectrum of high-density lipoprotein particles is highly heterogeneous, but no data are available on the subpopulations of high-density lipoprotein in IDDM. We, therefore, studied the spectrum of high-density lipoprotein particles in 86 IDDM patients (51 men and 35 women) 37 +/- 10 yr of age and in 74 sex-, age-, and body mass index-matched healthy nondiabetic subjects. The concentrations of high-density lipoprotein and HDL2 cholesterol were higher in the IDDM group than in the control subjects (P < 0.01). The apoA-I-to-apoA-II ratio was higher in the IDDM patients than in the nondiabetic subjects (P < 0.001) because of an increased concentration of LpA-I particles (61 +/- 17 vs. 53 +/- 15, P < 0.01). LpA-I particles correlated positively with high-density lipoprotein and HDL2 cholesterol in the two groups. Postheparin plasma lipoprotein lipase activity was significantly higher in the IDDM group than in the control group (P < 0.001), whereas postheparin plasma hepatic lipase activities were similar in both groups. Plasma cholesteryl ester transfer protein activity was estimated in an in vitro isotopic assay using exogenous labeled donor (low-density) and acceptor (high-density) lipoproteins in the absence of native lipoproteins. We observed no difference in cholesteryl ester transfer protein activity between the groups, and no significant correlations existed between cholesteryl ester transfer protein activity and high-density lipoprotein subpopulations.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of gemfibrozil on high density lipoprotein subspecies in non-insulin dependent diabetes mellitus. Relations to lipolytic enzymes and to the cholesteryl ester transfer protein activity

Twenty patients (18 men, 2 women) with non-insulin dependent diabetes mellitus (NIDDM) were randomized to receive either gemfibrozil 1200 mg daily or placebo for 3 months in a double-blind study. The effect of gemfibrozil on plasma HDL subfraction distribution was studied with sequential and density gradient ultracentrifugation and in gradient gel electrophoresis. The concentrations of apo A-I, apo A-II, Lp A-I and Lp A-LA-11 particles were measured. Postheparin plasma lipoprotein lipase (LPL) and hepatic lipase (HL) activities and plasma cholesteryl ester transfer protein (CETP) activities were also determined. Gemfibrozil increased the concentration of HDL cholesterol ( P < 0.01), which was due to the rise of HDL3 cholesterol (+16%), while in the placebo group these values remained unchanged. Gemfibrozil increased the concentrations of apo A-I(+12.6%, NS), apo A-II (+28.2%, P < 0.01) and Lp A-I:A-II particles (+21.6%, P < 0.06) but there were no changes in the placebo group. Neither gemfibrozil nor placebo had any effect on the concentration of Lp A-I particles. As determined by density-gradient ultracentrifugation, gemfibrozil increased the concentration of cholesterol in the most dense HDL fractions (mean density 1.193 g/ml, +22%, P < 0.05 and mean density 1.158 g/ml, +19.3%, P < 0.05). In gradient gel electrophoresis, the gemfibrozil-induced elevations of the cholesterol and protein were most pronounced in the HDL3,, (8.8−8.2 nm) region. Gemfibrozil increased LPL and HL activities by 14.7% ( P < 0.05) and by 18.8% ( P < 0.01), respectively, while in the placebo group LPL and HL activities remained unchanged. Plasma CETP activity was also increased during gemfibrozil treatment while in the placebo group it remained unchanged. We conclude that gemfibrozil causes multiple changes in plasma HDL metabolism. The gemfibrozil-induced elevation of HDL 3 and dense HDL subpopulations may reflect the concerted action of LPL, HL and CETP on plasma HDL metabolism.

Verapamil Prevents Chronic Renal Failure-Induced Abnormalities in Lipid Metabolism

Hypertriglyceridemia is common in chronic renal failure (CRF); this derangement is due to decreased peripheral removal of triglycerides. Certain data indicate that the state of secondary hyperparathyroidism of CRF is, at least in part, responsible for derangements in lipid metabolism. It has been proposed that chronic excess of parathyroid hormone exerts its deleterious effects on many organs through its ability to raise basal levels of cytosolic calcium. Prevention of the latter by a calcium channel blocker is followed by the correction of organ dysfunctions. The present study examined the effect of treatment of CRF rats with verapamil on several parameters of lipid metabolism. Chronic renal failure rats displayed hypertriglyceridemia, fat intolerance, reduced postheparin plasma lipoprotein and hepatic lipase activities, decreased hepatic lipase in liver homogenate, and elevated calcium content in liver and epididymal fat. Treatment of the CRF rats with verapamil prevented all these derangements in lipid metabolism. These effects of verapamil were similar to those produced by parathyroidectomy of CRF rats. The data are consistent with the formulation that chronic excess of parathyroid hormone increases the calcium burden of liver and adipose tissue and consequently impairs the synthesis and/or release of lipoprotein and hepatic lipases. Reduced availability of these enzymes in plasma results in impared peripheral removal of triglycerides, leading to hypertriglyceridemia.

High density lipoprotein subfractions, apolipoprotein A‐I containing lipoproteins, lipoprotein (a), and cholesteryl ester transfer protein activity in alcoholic women before and after ethanol withdrawal

We studied 11 female alcoholics before and after ethanol withdrawal of 2 weeks and 10 healthy normolipidaemic, nonalcoholic women of similar age. In alcoholic women the HDL2 mass was increased by 63% (P < 0.01) on admission and normalized (P < 0.01) during abstention. The concentrations of HDL3 cholesterol and its mass remained unchanged throughout the study. Consistently with the fall of HDL2 gradient gel electrophoresis analyses also demonstrated decrease of the cholesterol concentration of HDL2b and HDL2a (P < 0.05) during alcohol withdrawal. On admission the apo A-II concentration was increased by 48% (P < 0.01) and it was normalized (P < 0.001) during abstention. Among apo A-I containing lipoproteins the most prominent change occurred in Lp A-I:A-II, which fell by 32% (P < 0.01) during 1 week's alcohol withdrawal. During abstention the lipoprotein (a) concentration increased in 10 out of 11 women. In patients cholesteryl ester transfer (CETP) activity increased by 35% (P < 0.01) during 1 week of ethanol withdrawal. On admission postheparin plasma lipoprotein (LPL) and hepatic lipase activities were increased by 25% (P = NS); during 1 week's abstention they both returned to the control level (P < 0.05- < 0.01). In conclusion, chronic alcoholic women display multiple changes of lipoprotein metabolism which are rapidly reversed during abstinence. In contrast to alcoholic men, studied previously by us using the same study design and methods, there was no significant elevation of HDL3 cholesterol and apo A-I. The data suggest that alcohol interferes with several regulatory steps of HDL metabolism which are partly gender dependent.

Impaired chylomicron remnant clearance in familial combined hyperlipidemia.

Postprandial chylomicron remnant clearance was studied in six patients with familial combined hyperlipidemia (FCH) and seven control subjects by using an oral retinyl palmitate (RP) fat-loading test. The chylomicron remnant clearance (Sf < 1,000 fraction), expressed as the area under the RP curve (AUC-RP), was delayed in FCH subjects (65.05 +/- 12.84 hours x [mg/L]) compared with control subjects (25.1 +/- 5.4 hours x [mg/L]; p = 0.01). Postprandial lipoprotein particle size and composition in the Sf > 1,000 fraction were different between FCH and control subjects as analyzed by molecular-sieve chromatography. Fasting high density lipoprotein cholesterol was lower in FCH patients (0.54 +/- 0.09 mmol/L) than in control subjects (0.89 +/- 0.05 mmol/L; p < 0.01). Mean plasma postheparin lipoprotein lipase and hepatic lipase activities were similar between FCH patients (94 +/- 25 and 427 +/- 57 milliunits/mL, respectively) and control subjects (126 +/- 16 and 362 +/- 33 milliunits/mL, respectively). In FCH, a 54% reduction (p < 0.05) of plasma triglycerides to 2.63 +/- 0.41 mmol/L by drug treatment resulted in an enhanced, but not normalized, clearance of chylomicron remnants (39.4 +/- 6.0 hours x [mg/L]). Univariate regression analysis revealed that in FCH subjects the changes in fasting plasma apolipoprotein C-III concentrations after therapy were significantly associated with the changes in chylomicron remnant AUC-RP (r = 0.87; p = 0.02). Delayed elimination of atherogenic chylomicron remnants may contribute to the increased risk of premature atherosclerosis in FCH.

Simvastatin improves chylomicron remnant removal in familial combined hyperlipidemia without changing chylomicron conversion

It is unknown whether the clearance of atherogenic chylomicron remnants and the postprandial lipoprotein metabolism in general can be improved by 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors in subjects with familial combined hyperlipidemia (FCH). Therefore, the postprandial chylomicron remnant clearance was studied in nine normolipidemic untreated controls and seven FCH patients before and after treatment with simvastatin using an oral vitamin A-fat load (24 hours, 50 g/m 2). Treatment with simvastatin reduced plasma cholesterol level by 16% (mean ± SEM, 8.1 ± 0.8 v 6.8 ± 0.8 mmol/L; P < .05) and plasma apolipoprotein (apo) B level by 19% (1.6 ± 0.2 v 1.3 ± 0.2 g/L; P < .05). Plasma apo E level (89.6 ± 21.0 mg/L) was reduced by 29% (63.5 ± 14.1 mg/L; P < .05). High-density lipoprotein cholesterol (HDL-C) and low-density lipoprotein cholesterol (LDL-C) levels did not change; consequently, the reductions seen had been due to a decrease in very-low-density lipoprotein (VLDL) levels. Fasting plasma triglyceride (30% reduction) and plasma apo C-II (31% reduction) levels did not change significantly. Mean postheparin plasma lipoprotein lipase (LPL) activity increased by 13% after treatment (90.4 ± 19.8 v 102.6 ± 20.3 mU/mL; P < .05), but hepatic lipase (HL) activity was not altered. The clearance of chylomicrons (Sf > 1,000), expressed as the area under the 24-hour retinyl palmitate curve, did not change with simvastatin (52.8 ± 12.9 v 51.8 ± 13.4 h · mg −1/L). In contrast, chylomicron remnant (Sf < 1,000) clearance (62.9 ± 11.1 h · mg −1/L) improved after treatment (53.3 ± 11.3 h · mg −1/L; P = .02). In conclusion, the reduction in plasma apo E concentration and the improvement in retinyl palmitate kinetics indicated enhanced chylomicron remnant removal in FCH subjects by simvastatin. An increased activity of LPL was the most likely factor contributing to the increased chylomicron remnant clearance. The atherosclerosis risk profile in FCH improved during simvastatin treatment as evidenced by decreased plasma VLDL cholesterol and apo B levels and increased chylomicron remnant removal.

Lipoprotein heterogeneity in end-stage renal disease

Fifteen patients on chronic maintenance hemodialysis without any additional known cause for dyslipidemia were arbitrarily divided into two groups based on fasting plasma triglyceride levels. The hypertriglyceridemic patients (plasma triglyceride levels above 170 mg/dl, N = 7) also had decreased high density lipoprotein (HDL) cholesterol levels and decreased post-heparin plasma lipoprotein lipase activity compared to the normotriglyceridemic patients (N = 8). All lipoprotein fractions collected by density gradient ultracentrifugation were triglyceride-enriched in the hypertriglyceridemic patients. Both groups of patients had elevated intermediate density lipoprotein levels, heterogeneity in the distribution of low density lipoproteins (LDL) and apoprotein-specific HDL subpopulations, and abnormalities in the size and composition of both LDL and HDL. The described alterations tended to be more marked in hypertriglyceridemic patients and are not detected by the usual laboratory evaluation of lipoproteins. These lipoprotein abnormalities have been shown to be atherogenic in patients without renal disease and are likely to contribute to the high prevalence of premature atherosclerosis in end-stage renal disease.

Composition of human low density lipoprotein: Effects of postprandial triglyceride-rich lipoproteins, lipoprotein lipase, hepatic lipase and cholesteryl ester transfer protein

A preponderance of small, dense low density lipoprotein (LDL) particles has been linked to increased risk of myocardial infarction, and a dense and protein-rich LDL has proved to be a characteristic of patients with manifest coronary heart disease (CHD). The present study focused on metabolic determinants of the LDL subfraction distribution with the emphasis placed on alimentary lipaemia. The relations of plasma levels and composition of light (1.019 < d < l.040 kg/l) and dense (1.040 < d < 1.063 kg/l) LDL subfractions to postprandial triglyceride-rich lipoproteins (TGRL), postheparin plasma lipase activities and the activity of cholesteryl ester transfer protein (CETP) were studied in 32 men with angiographically ascertained premature coronary atherosclerosis (age 48.8 ± 3.2 years) and in 10 age matched healthy control men. LDL subfractions were separated by equilibrium density gradient ultracentrifugation of fasting plasma drawn before participants were subjected to an oral fat tolerance test of a mixed meal type. The response of TGRL to the oral fat load was determined by measuring plasma triglycerides, and the apolipoprotein (apo) B-48 and apo B-100 content of Sf 60–400 and Sf 20–60 lipoprotein fractions. At a second visit plasma samples were taken for determination of postheparin plasma lipoprotein lipase (LPL) and hepatic lipase (HL) activities and for measurement of CETP activity. Hypertriglyceridaemic patients had a preponderance of dense LDL particles compared with normotriglyceridaemic patients and controls. The magnitude of the response of TGRL to the oral fat load showed a positive association with the dense LDL apo B concentration ( r = 0.32−0.52, P < 0.05), whereas the LPL activity correlated positively with the free ( r = 0.50, P < 0.001) and esterified cholesterol (= 0.45, P < 0.01) and apo B ( r = 0.42, P < 0.01) content of the light LDL fraction. The HL activity was found to be inversely associated with the plasma level of light LDL triglycerides ( r = −0.38, P < 0.05). In contrast, no relations were noted between CETP activity and plasma concentrations of LDL constituents. Multiple stepwise linear regression analysis with the proportion of total LDL apo B contained in the dense LDL subfraction (% dense LDL apo B) used as the dependent variable indicated that the combined effect of LPL activity and postprandial plasma levels of TGRL (areas under the curve for plasma triglycerides or Sf 60–400 apo B-48) accounted for around 50% of the variability in the distribution of LDL particles between light and dense subfractions. The present data suggest that LPL activity and the response of TGRL to fat intake are major determinants of LDL heterogeneity.