Differential effect of fenofibrate and atorvastatin on in vivo kinetics of apolipoproteins B-100 and B-48 in subjects with type 2 diabetes mellitus with marked hypertriglyceridemia

The specific impact of 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors and fibrates on the in vivo metabolism of apolipoprotein (apo) B has not been systematically investigated in patients with type 2 diabetes mellitus with high plasma triglyceride (TG) levels. Therefore, the objective of this 2-group parallel study was to examine the differential effects of a 6-week treatment with atorvastatin or fenofibrate on in vivo kinetics of apo B-48 and B-100 in men with type 2 diabetes mellitus with marked hypertriglyceridemia. Apolipoprotein B kinetics were assessed at baseline and at the end of the intervention using a primed constant infusion of [5,5,5-D(3)]-l-leucine for 12 hours in the fed state. Fenofibrate significantly decreased plasma TG levels with no significant change in plasma low-density lipoprotein cholesterol (LDL-C) and apo B levels. On the other hand, atorvastatin significantly reduced plasma levels of TG, LDL-C, and apo B. After treatment with fenofibrate, very low-density lipoprotein (VLDL) apo B-100 pool size (PS) was decreased because of an increase in the fractional catabolic rate (FCR) of VLDL apo B-100. No significant change was observed in the kinetics of LDL apo B-100. Moreover, fenofibrate significantly decreased TG-rich lipoprotein (TRL) apo B-48 PS because of a significant increase in TRL apo B-48 FCR. After treatment with atorvastatin, VLDL and IDL apo B-100 PSs were significantly decreased because of significant elevations in the FCR of these subfractions. Low-density lipoprotein apo B-100 PS was significantly lowered because of a tendency toward decreased LDL apo B-100 production rate (PR). Finally, atorvastatin reduced TRL apo B-48 PS because of a significant decrease in the PR of this subfraction. These results indicate that fenofibrate increases TRL apo B-48 as well as VLDL apo B-100 clearance in men with type 2 diabetes mellitus with marked hypertriglyceridemia, whereas atorvastatin increases both VLDL and IDL apo B-100 clearance and decreases TRL apo B-48 and LDL apo B-100 PR.     

Effects of atorvastatin on postprandial plasma lipoproteins in postinfarction patients with combined hyperlipidaemia

Enhanced and prolonged postprandial lipaemia is implicated in coronary and carotid artery disease. This study assessed the effects of atorvastatin, a 3-hydroxy-3-methylglutaryl-CoA reductase inhibitor, on postprandial plasma concentrations of triglyceride-rich lipoproteins (TRLs). Sixteen middle-aged men with combined hyperlipidaemia (baseline low density lipoprotein (LDL) cholesterol and plasma triglyceride concentrations (median (interquartile range) of 4.54 (4.17-5.26)) and 2.66 (2.04-3.20) mmol/l, respectively) and previous myocardial infarction were randomised to atorvastatin 40 mg or placebo once daily for 8 weeks in a double-blind, cross-over design. The apolipoprotein (apo) B-48 and B-100 contents were determined in subfractions of TRLs as a measure of chylomicron remnant and very low density lipoprotein (VLDL) particle concentrations (expressed as mg apo B-48 or apo B-100 per litre of plasma), in the fasting state and after intake of a mixed meal. Atorvastatin treatment reduced significantly the fasting plasma concentrations of VLDL cholesterol, LDL cholesterol and VLDL triglycerides (median% change) by 29, 44 and 27%, respectively, and increased high density lipoprotein (HDL) cholesterol by 19%, compared with baseline. The postprandial plasma concentrations of large (Svedberg flotation rate (Sf) 60-400) and small (Sf 20-60) VLDLs and chylomicron remnants were almost halved compared with baseline (mean 0-6 h plasma concentrations were reduced by 48% for Sf 60-400 apo B-100, by 46% for Sf 60-400 apo B-48, by 46% for Sf 20-60 apo B-100 and by 27% for Sf 20-60 apo B-48), and the postprandial triglyceridaemia was reduced by 23% during active treatment. In conclusion, atorvastatin 40 mg once daily causes profound reductions of postprandial plasma concentrations of all TRLs in combined hyperlipidaemic patients with premature coronary artery disease.     

Atorvastatin monotherapy vs. combination therapy in the management of patients with combined hyperlipidemia

BACKGROUND: Mixed hyperlipidemia is a common disorder characterized by elevated VLDL and LDL levels. Patients with this syndrome usually are in need of combination therapy, comprising a fibric acid derivate with a statin drug in order to achieve LDL and triglyceride target values. Atorvastatin is a hydroxymethylglutaryl coenzyme A (HMG-CoA) reductase inhibitor demonstrated to be effective in reducing both cholesterol (CHOL) and triglyceride (TG) levels in humans. We examined the efficacy of atorvastatin as monotherapy in achieving a better or the same lipid profile in patients with mixed hyperlipidemia treated with combination therapy. DESIGN: We compared atorvastatin with a combination of a fibric acid derivate and a statin drug (other than atorvastatin) in a 24-week, prospective randomized, open-label study of 27 patients with mixed hyperlipidemia. METHODS: All 27 patients had been treated with statin-fibrate therapy in different regimens for at least a year. Atorvastatin at a daily dose of 20 mg was substituted for statin-fibrate therapy. Lipid and safety profiles were assessed. RESULTS: Atorvastatin significantly reduced total cholesterol, LDL-C, and HDL-C compared to statin-fibrate therapy. In contrast, TG and glucose levels were significantly elevated with atorvastatin. Target LDL-C and TG was achieved in 10 patients with the single therapy of atorvastatin vs. 6 patients under statin-fibrate. In 16 patients, atorvastatin was at least as effective as, or better than, the combination therapy, and was recommended for continuation of treatment. CONCLUSION: Atorvastatin is an adequate monotherapy for many mixed hyperlipidemia patients. We recommend atorvastatin be considered for every patient suffering from mixed hyperlipidemia.     

The effect of 25-hydroxycholesterol on the regulation of apolipoprotein E mRNA levels and secretion in the human hepatoma HepG2.

The human hepatoma cell line, HepG2, was cultured with 25 OH cholesterol, a potent inhibitor of HMG-CoA reductase, in order to examine the effect of the oxysterol on apo E synthesis and secretion. Treatment of cells with oxysterol (2.5 microM) resulted in a greater than 90% inhibition of HMG-CoA reductase activity and a 3-fold reduction in its cognate mRNA level. However, apo E mRNA level and secretion were not affected after 24 h of drug treatment. This drug treatment was associated with a reduction in both cellular free and esterified cholesterol levels by 50% and 40%, respectively. Exposure of HepG2 cells to an ACAT inhibitor, the Sandoz compound (58-035) for 24 h, at a concentration of 5 micrograms/ml, resulted in a 30% increase and 70% decrease in the intracellular levels of free and esterified cholesterol, respectively. Under this regimen of drug treatment, the level of apo E mRNA was increased by approximately 70%, while HMG-CoA reductase mRNA level was decreased by 35%. When the cells were exposed to the combination of the ACAT inhibitor and 25 OH cholesterol, the cellular levels of free and esterified cholesterol were reduced by 30% and 80%, respectively. This combination of drugs had no effect on apo E mRNA; however, the level of HMG-CoA reductase mRNA was decreased by 3.5-fold. Taken together, the data suggested that reduction in the intracellular levels of either free or esterified cholesterol had no effect on apo E mRNA level. By contrast, a small increment in cellular free cholesterol content was associated with a significant induction in apo E mRNA level. Furthermore, 25 OH cholesterol caused a significant redistribution (50%) of apo E from the HDL fraction to the d greater than 1.21 g/ml infranatant. By using high performance liquid chromatography and molecular sieve columns, it was found that the appearance of a lipid-poor apo E particle was not an artifact of ultracentrifugation. This particle contained 85 wt% protein and 15 wt% of free cholesterol and phospholipid. The results suggested that a lipid-poor apo E particle was secreted by the HepG2 cells under certain circumstances.     

NK-104, a potent 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor, decreases apolipoprotein B-100 secretion from Hep G2 cells.

Intracellular cholesterol biosynthesis may play a key role in supplying cholesterol (as cholesteryl ester) for the neutral core of very low density lipoprotein (VLDL), thus modulating the secretion of apolipoprotein B-100 (apo B-100) from hepatocytes. The effect of compound NK-104 was studied, a new competitive inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG CoA-reductase), on apo B-100 synthesis and secretion from the human hepatoma cell line Hep G2. Cells were preincubated with NK-104 (0.01-5 microM) in the presence or absence of oleate (0.8 mM). Apo B-100 in the medium was determined by an enzyme-linked immunosorbent assay (ELISA). Incubation of Hep G2 with NK-104 resulted in a marked inhibition of cholesterogenesis (up to 95%), determined as incorporation of [14C]acetate into sterols, and decreased in a dose-dependent manner apo B-100 secretion, both in basal conditions (from 110 to 82 ng/mg cell protein, P < 0.01) and after incubation with oleate (from 227 to 165 ng/mg cell protein, P < 0.01). Density gradient for distribution of apo B-100 secreted, showed that this decrease was essentially due to a reduction of apo B-100 associated with lipoproteins in the density range of low density lipoproteins (LDL). Pulse chase experiment demonstrated that NK-104 did not affect the synthetic rate of apo B-100 but increased intracellular degradation of newly synthesized protein. The compound had only marginal effect on the mass of intracellular triglyceride but significantly decreased intracellular mass of free cholesterol and cholesteryl ester (P < 0.01). It is speculated that the ability of compound NK-104 to decrease apo B-100 secretion from Hep G2 cells is due to a decreased intracellular cholesterol availability.     

Decreased intracellular degradation and increased secretion of apo B-100 in Hep G2 cells after inhibition of cholesteryl ester synthesis

Control of apolipoprotein B (apo B) secretion in hepatocytes occurs partly at the post-translational level. The key step in this process appears to be intracellular degradation of newly synthesized apo B. The aim of this paper was to investigate the mechanisms that regulate apo B secretion by Hep G2 cells, in response to the inhibition of Acyl-CoA Acyltransferase (ACAT) by the compound Sandoz 58035 (S-58035). S-58035 (20 μM) reduced cholesteryl ester synthesis from [¹⁴C]oleate by 95%, and increased significantly, in a dose-dependent manner, (2–100 μM) apo B secretion, either in control conditions (from 78±4.3 to 126±6.1 ng apo B-100/mg cell protein/4 h) or upon stimulation of apo B secretion by oleate (from 134±4.23 to 177±4.3 ng apo B/mg cell protein/4 h). This increased secretion of newly synthesized apo B-100 was confirmed by pulse experiments and by gradient ultracentrifugation of the media. Moreover pulse-chase experiments showed that the addition of S-58035 reduced intracellular degradation of apo B-100, both in control conditions and in the presence of oleate. S-58035 (20 μM) did not affect total cellular cholesterol content, but free cholesterol increased with a concomitant decrease of cholesteryl ester (−20%). S-58035 increased cellular triglyceride mass, which was observed in basal conditions (from 12.8±1.09 to 22.7±2.7 μg TG/mg cellular protein) and also in presence of oleate (from 48±0.53 to 59±6.3 μg TG/mg cellular protein). This effect is due to a stimulation of triglyceride synthesis, as determined by incorporation of [³H]glycerol into cellular triglycerides. From these data we conclude that, under our experimental conditions, triglyceride synthesis and/or availability is likely to control intracellular degradation of apo B.     

Atorvastatin markedly improves type III hyperlipoproteinemia in association with reduction of both exogenous and endogenous apolipoprotein B-containing lipoproteins

Remnant lipoproteins are known to promote atherosclerosis especially in patients with type III hyperlipoproteinemia (HLP). In the current study, the effects of atorvastatin were investigated with special reference to the exogenous and endogenous apolipoprotein (apo) B-containing lipoprotein metabolism in type III HLP. Four Japanese male patients with type III HLP associated with homozygous apoE2 were studied. One-month administration of atorvastatin (20 mg once daily), after a 4-week dietary run-in, strikingly reduced serum total cholesterol and triglyceride (TG) levels by 52 (P<0.01) and 56% (P<0.05), respectively. Atorvastatin further decreased remnant-like particle (RLP)-cholesterol by 73% and RLP-TG by 65% (P<0.05), respectively. Distribution analysis by polyacrylamide gel disc electrophoresis clearly showed that atorvastatin diminished very low-, intermediate- and low-density lipoprotein particles. The relative particle diameter of intermediate-density lipoprotein became smaller after atorvastatin treatment (P<0.01). Furthermore, ultracentrifugal analysis demonstrated that atorvastatin significantly decreased cholesterol, TG and phospholipid concentrations in all apoB-containing lipoprotein fractions and very low-density lipoprotein (VLDL)-cholesterol/serum TG ratio (P<0.05), implying atorvastatin-induced reduction of beta-VLDL. Finally, newly developed assays of apoB-48 and apoB-100 revealed that atorvastatin markedly reduced these apolipoproteins by 43 and 52%, respectively (P<0.01), suggesting that atorvastatin decreased the number of both exogenous and endogenous apoB-containing lipoproteins. Taken together, atorvastatin improves remnant lipoprotein metabolism in type III HLP both in quality and in quantity. Atorvastatin can be one of the optimal options for the treatment of patients with type III HLP.     

Effects of atorvastatin on triglyceride-rich lipoproteins, low-density lipoprotein subclass, and C-reactive protein in hemodialysis patients

Dyslipidemia is an important risk factor for cardiovascular disease in patients with chronic renal failure (CRF). We evaluated the safety and efficacy of atorvastatin in patients with dyslipidemia associated with CRF who were undergoing hemodialysis (HD). Thirty-five patients who were receiving HD were given atorvastatin (10 mg/d) for 3 months. Chylomicron (CM), light and dense very-low-density lipoprotein (VLDL), intermediate-density lipoprotein (IDL), and light and dense low-density lipoprotein (LDL) were separated by ultracentrifugation. Apolipoprotein (apo) B was measured by electroimmunoassay. Mean LDL particle diameter was measured by gradient gel electrophoresis. Atorvastatin therapy reduced LDL-cholesterol (C) by 36% and remnant-like particle (RLP)-C by 58%. Atorvastatin significantly reduced apo B, apo CIII, and apo E in VLDL by 40% to 46% and IDL-apo B by 66%. Atorvastatin also significantly reduced cholesterol in CM, light VLDL, and dense VLDL without consistently affecting triglyceride (TG) in these lipoproteins. Atorvastatin similarly reduced both light and dense LDL-apo B by 38%. LDL particle size in the HD patients significantly increased during atorvastatin treatment from 25.7 +/- 0.4 to 26.2 +/- 0.6 nm. High sensitive C-reactive protein (HS-CRP) was halved by atorvastatin decreasing from 0.08 +/- 0.05 to 0.04 +/- 0.03 mg/dL. Atorvastatin treatment did not affect the creatinine kinase level, and no classical adverse effects were observed during the study. These results suggest that atorvastatin is safe and effective for the management of dyslipidemia in patients with CFR who are receiving HD, which may help to suppress the development of atherosclerosis.     

The magnitude of decrease in hepatic very low density lipoprotein apolipoprotein B secretion is determined by the extent of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibition in miniature pigs.

It has been postulated that the rate of hepatic very low density lipoprotein (VLDL) apolipoprotein (apo) B secretion is dependent upon the activity of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase. To test this hypothesis in vivo, apoB kinetic studies were carried out in miniature pigs before and after 21 days treatment with high-dose (10 mg/kg/day), atorvastatin (A) or simvastatin (S) (n = 5). Pigs were fed a diet containing fat (34% of calories) and cholesterol (400 mg/day; 0.1%). Statin treatment decreased plasma total cholesterol [31 (A) vs. 20% (S)] and low density lipoprotein (LDL) cholesterol concentrations [42 (A) vs. 24% (S)]. Significant reductions in plasma total triglyceride (46%) and VLDL triglyceride (50%) concentrations were only observed with (A). Autologous [131I]VLDL, [125I]LDL, and [3H]leucine were injected simultaneously, and apoB kinetic parameters were determined by triple-isotope multicompartmental analysis using SAAM II. Statin treatment decreased the VLDL apoB pool size [49 (A) vs. 24% (S)] and the hepatic VLDL apoB secretion rate [50 (A) vs. 33% (S)], with no change in the fractional catabolic rate (FCR). LDL apoB pool size decreased [39 (A) vs. 26% (S)], due to reductions in both the total LDL apoB production rate [30 (A) vs. 21% (S)] and LDL direct synthesis [32 (A) vs. 23% (S)]. A significant increase in the LDL apoB FCR (15%) was only seen with (A). Neither plasma VLDL nor LDL lipoprotein compositions were significantly altered. Hepatic HMG-CoA reductase was inhibited to a greater extent with (A), when compared with (S), as evidenced by 1) a greater induction in hepatic mRNA abundances for HMG-CoA reductase (105%) and the LDL receptor (40%) (both P < 0.05); and 2) a greater decrease in hepatic free (9%) and esterified cholesterol (25%) (both P < 0.05). We conclude that both (A) and (S) decrease hepatic VLDL apoB secretion, in vivo, but that the magnitude is determined by the extent of HMG-CoA reductase inhibition.     

Effect of pravastatin sodium, a new inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase, on very-low-density lipoprotein composition and kinetics in hyperlipidemia associated with experimental nephrosis

The effect of Pravastatin sodium (CS-514), a new inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-CoA R) on very-low-density lipoprotein (VLDL) composition and kinetics was studied in normal and experimental nephrotic rats under fasting conditions. Nephrotic rats, induced by a single intraperitoneal injection of puromycin aminonucleoside (100 mg/kg body weight), had significantly higher plasma lipids and apoprotein (apo) B concentrations than controls. The hypertriglyceridemia associated with nephrosis was mainly due to a markedly elevated VLDL-triglyceride (TG) concentration. Pravastatin sodium was administrated as a 0.04% solution in drinking water for 7 days to normal control and nephrotic rats. Plasma TG concentration in both control and nephrotic rats was significantly reduced by the treatment with Pravastatin, but plasma cholesterol levels were not reduced by the treatment in either group of rats. TG, cholesterol, phospholipid, and apo B concentrations in nephrotic VLDL were significantly reduced by Pravastatin treatment, whereas only TG was decreased in control VLDL. Pravastatin reduced the apo B 100 + 95/48 ratio in nephrotic VLDL. Pravastatin did not alter the lipid concentration of low-density lipoprotein (LDL) and high-density lipoprotein (HDL) in control and nephrotic rats. VLDL-TG turnover studies showed that TG secretion rate was significantly suppressed by Pravastatin administration without affecting its removal in both groups of rats. These suggested that Pravastatin, an inhibitor of cholesterol biosynthesis, can reduce VLDL concentration by rectifying the overproduction of VLDL exhibited in nephrotic rats.     

Atorvastatin treatment does not affect gonadal and adrenal hormones in type 2 diabetes patients with mild to moderate hypercholesterolemia

Atorvastatin, a second generation synthetic 3-hydroxy 3-methylglutaryl-coenzyme-A (HMG-CoA) reductase inhibitor used in the treatment of hypercholesterolemia, reduces both intracellular cholesterol synthesis and serum cholesterol levels, and this could have a potential negative impact on gonadal and adrenal steroidogenesis. Hypercholesterolemia in type 2 diabetes, even when mild, must be treated in an aggressive way, due to the more strict therapeutic goals than in the non diabetic population. Since the wide use of 3-hydroxy 3-methylglutaryl-coenzyme-A (HMG-CoA) reductase inhibitor (statins) in type 2 diabetes, the main aim of our study was to evaluate the effects of "therapeutic" doses of atorvastatin on gonadal and adrenal hormones in 24 type 2 diabetic patients (16 males and 8 postmenopausal females), with mild to moderate hypercholesterolemia (LDL-cholesterol = 150.1 +/- 32.0 and 189.9 +/- 32.9 mg/dl, respectively) studied before and after a 3 months treatment with atorvastatin (20 mg/day). In all patients, lipids and serum cortisol, dehydroepiandrosterone sulphate (DHEA-S), androstendione and sex hormone binding globulin (SHBG) were measured, with the addition, only in males, of testosterone and free testosterone index. After atorvastatin treatment a significant decrease in total and LDL cholesterol was observed (p < 0.05), while HDL-cholesterol did not significantly change ( p = N.S.), as no significant difference was found between steroid hormones measured before and after atorvastatin either in male and females. In conclusion, our data suggest that, in type 2 diabetic patients, the use of atorvastatin has no clinically important effects on either gonadal or adrenal steroid hormones.     

Intestinal rather than hepatic microsomal triglyceride transfer protein as a cause of postprandial dyslipidemia in diabetes

Postprandial dyslipidemia may be a major cause of atherosclerosis in diabetes. Microsomal triglyceride transfer protein (MTP) is essential for the synthesis of the chylomicron particle in the intestine and very low-density lipoprotein (VLDL) in the liver. The purpose of the present study was to examine the effect of diabetes on MTP mRNA expression in a rabbit model of diabetes, which develops atherosclerosis. Male New Zealand white rabbits were fed a 0.5% cholesterol diet. Diabetes was induced with alloxan monohydrate. The lymphatic duct was cannulated and lymph collected for isolation of chylomicrons by ultracentrifugation. Apolipoprotein B48 (apo B48) and apo B100 were separated by polyacrylamide gradient gel electrophoresis and quantified by densitometry. MTP mRNA was determined in liver and intestine by RNase protection analysis, and MTP activity was measured. Diabetic animals had significantly increased plasma triglyceride and decreased high-density lipoprotein (HDL) cholesterol (P <.05). They also secreted more lymph chylomicron apo B48 and apo B100 (P <.05) and more lymph chylomicron total and esterified cholesterol/h (P <.05). Lymph chylomicron particles in the diabetic animals contained significantly less lipid/apo B (P <.05). Intestinal MTP activity and mRNA were significantly higher in diabetic compared with control rabbits (0.07 +/- 0.01 v 0.04 +/- 0.015 fluorescent units/microg microsomal protein and 66 +/- 21 v 37 +/- 11 amol MTP mRNA/microg total RNA (P <.005). There was no difference in MTP activity or mRNA expression in the liver. This study suggests that MTP may play an important role in the postprandial dyslipidemia of diabetes.     

Hepatic cholesterol and bile acid synthesis, low-density lipoprotein receptor function, and plasma and fecal sterol levels in mice: effects of apolipoprotein E deficiency and probucol or phytosterol treatment

We compared hepatic cholesterol metabolism in apolipoprotein (apo) E-knockout (KO) mice with their wild-type counterparts. We also investigated the effects of treatment with phytosterols or probucol on the activity of hepatic 3-hydroxy-3-methyl-glutaryl coenzyme A (HMG-CoA) reductase (cholesterol synthesis), cholesterol 7 alpha-hydroxylase and sterol 27-hydroxylase (bile acid synthesis), and low-density lipoprotein (LDL) receptor function in this animal model of atherogenesis. These findings were then related to treatment-induced changes in plasma, hepatic, and fecal sterol concentrations. Mouse liver membranes have binding sites similar to LDL receptors; the receptor-mediated binding represents 80% of total binding and is LDL concentration-dependent. These binding sites have higher affinity for apo E-containing particles than apo B only-containing particles. Deletion of apo E gene was associated with several-fold increases in plasma cholesterol levels, 1.5-fold increase in hepatic cholesterol concentrations, 50% decrease in HMG-CoA reductase activity, 30% increase in cholesterol 7 alpha-hydroxylase and 25% decrease in LDL receptor function. Treatment of apo E-KO mice with either probucol or phytosterols significantly reduced plasma cholesterol levels. Phytosterols significantly increased the activity of hepatic HMG-CoA reductase, and probucol significantly increased cholesterol 7 alpha-hydroxylase activity. Neither treatment significantly altered hepatic LDL receptor function. Phytosterols, but not probucol, significantly increased fecal sterol excretion and decreased hepatic cholesterol concentrations. Plasma cholesterol lowering effects of phytosterols and probucol are due to different mechanisms: stimulation of cholesterol catabolism via increased bile acid synthesis by probucol and decreased cholesterol absorption by phytosterols. In the absence of apo E, hepatic LDL receptors could not be upregulated and did not contribute to the cholesterol lowering effects of either agent.     

Lipid and apolipoprotein levels and distribution in patients with hypertriglyceridemia: effect of triglyceride reductions with atorvastatin

Atorvastatin is a new hepatic hydroxymethyl glutaryl coenzyme A (HMG-CoA) reductase inhibitor that has been demonstrated to be efficacious in reducing both triglyceride (TG) and cholesterol (CHOL) levels in humans. Twenty-seven (N = 27) patients with primary hypertriglyceridemia (TG > 350 mg/dL) were studied before and after 4 weeks on atorvastatin treatment at a dosage of either 20 (n = 16) or 80 (n = 11) mg/d. The present report examines changes in the plasma levels of several apolipoproteins, including apolipoprotein C-II (apoC-II), apoC-III, and apoE, after atorvastatin. Dose-dependent reductions in both CHOL (20.3% v 43.1%) and TG (26.5% v 45.8%) for the low and high dose, respectively, have been reported in these individuals. In addition to the reductions in apoB commonly associated with the use of HMG-CoA reductase inhibitors, significant reductions in apoE (37% and 49%), apoC-II (28% and 42%), and apoC-III (18% and 30%) were observed with this agent at the 20- and 80-mg/d dosage, respectively. Using fast protein liquid chromatography (FPLC) to fractionate whole plasma according to particle size, the effect of atorvastatin on lipid and apolipoprotein distribution in 20 lipoprotein fractions was also determined. Our results indicate that after 4 weeks on atorvastatin, (1) there was a 2-fold increase in the CHOL content as assessed by the CHOL/apoB ratio for 13 subfractions from very-low-density lipoprotein (VLDL) to small low-density lipoprotein (LDL); (2) there was a statistically significant reduction in the percentage of plasma apoB associated with VLDL-sized particles (30.5% v 26.8%); (3) there was a preferential reduction in plasma apoE from non-apoB-containing lipoproteins with treatment; (4) the losses of apoC-II and apoC-III, on the other hand, were comparable for all lipoprotein fractions; and (5) the fraction of plasma TG associated with HDL was increased after treatment. These changes in lipids and apolipoproteins did not depend on the dose of atorvastatin. There was, on the other hand, a dose-dependent reduction in cholesteryl ester transfer protein (CETP) activity, defined as the percentage of 3H-cholesteryl oleate transferred from high-density lipoprotein (HDL) to LDL. CETP activity was reduced by 10.3% and 26.4% with the low and high dose of atorvastatin. Together, these composition data would be consistent with a net reduction in the number of TG-rich lipoproteins that may be explained by (1) a reduction in VLDL synthesis, (2) a preferential removal of VLDL without conversion to LDL, and (3) a preferential accelerated removal of a subpopulation of LDL.     

Atorvastatin treatment beneficially alters the lipoprotein profile and increases low-density lipoprotein particle diameter in patients with combined dyslipidemia and impaired fasting glucose/type 2 diabetes

Diabetic dyslipidemia is featured by hypertriglyceridemia, low high-density lipoprotein (HDL) cholesterol levels, and elevated low-density lipoprotein (LDL) cholesterol commonly in the form of small, dense LDL particles. First-line treatment, fibrates versus statins or both, of dyslipidemia in diabetic patients has been the focus of debate. We investigated the potential hypolipidemic effects of atorvastatin, a 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor with good triglyceride lowering properties, in patients with combined dyslipidemia and evidence of impaired fasting glucose or type 2 diabetes. Twenty patients were recruited for the study, and after a 60-day wash out period, baseline measurements of lipoprotein parameters, LDL particle diameter, and apolipoprotein B (apoB) degradation fragments were obtained. The group was then randomized, in a double-blinded manner, into 2 subgroups. Group A received atorvastatin (80 mg) and group B received placebo daily for 60 days. After the first treatment period, all patients were reanalyzed for the above parameters. The treatment regime then crossed over for the second treatment period in which group A received placebo and group B received atorvastatin (80 mg) daily for 60 days. All parameters were remeasured at the end of the study. Treatment with atorvastatin resulted in a statistically significant reduction in total cholesterol (41%), LDL cholesterol (55%), triglycerides (TG) (32%), and apoB (40%). Mean LDL particle diameter significantly increased from 25.29 +/- 0.24 nm (small, dense LDL subclass) to 26.51 < 0.18 nm (intermediate LDL subclass) after treatment with atorvastatin (n = 20, P <.005). At baseline, LDL particles were predominantly found in the small, dense subclass; atorvastatin treatment resulted in a shift in the profile to the larger and more buoyant LDL subclass. Atorvastatin treatment did not produce consistent changes in the appearance of apoB degradation fragments in plasma. Our results suggest that atorvastatin beneficially alters the atherogenic lipid profile in these patients and significantly decreases the density of LDL particles produced resulting in a shift from small, dense LDL to more buoyant and less atherogenic particles.     

Effect of gemfibrozil on apolipoprotein B secretion and diacylglycerol acyltransferase activity in human hepatoblastoma (HepG2) cells

The mechanism of action of a widely used drug gemfibrozil to reduce triglycerides (TG) and apolipoprotein B (apo B) is incompletely understood. Using human hepatoblastoma (HepG2) cells, we examined the effect of gemfibrozil on apo B secretion and TG synthesis catalyzed by diacylglycerol acyltransferase (DGAT), primary processes associated with the secretion of LDL. Gemfibrozil significantly decreased apo B secretion by HepG2 cells. It decreased oleate-induced stimulation of apo B secretion, suggesting that gemfibrozil-mediated inhibition of apo B secretion may be dependent on the synthesis of TG catalyzed by DGAT. Pre-incubation of HepG2 cells with gemfibrozil (200-400 micromol/l for 48 h) significantly inhibited microsomal DGAT activity. When added directly to the DGAT assay system containing control microsomes, gemfibrozil significantly inhibited the activity of DGAT by 14-25%. Gemfibrozil (200-400 micromol/l) inhibited TG synthesis by 47-50% as measured by the incorporation of 3H-oleic acid into TG. The data indicate that gemfibrozil inhibits DGAT activity resulting in decreased synthesis of TG and its availability for apo B lipidation rendering it susceptible to intracellular apo B degradation leading to the decreased secretion. These in-vitro data suggest a novel additional mechanism by which gemfibrozil lowers plasma TG and atherogenic apo B lipoproteins in dyslipidemic patients.     

Effect of atorvastatin on apolipoprotein B48 metabolism and low-density lipoprotein receptor activity in normolipidemic patients with coronary artery disease

We aimed to examine postprandial dyslipidemia in normolipidemic patients with coronary artery disease (CAD) and the effects of treatment with an hydroxymethyl glutaryl coenzyme A (HMG-CoA) reductase inhibitor (atorvastatin). Subjects with angiographicaly established CAD were randomized to treatment for 12 weeks with 80 mg/d atorvastatin or placebo and the effects on markers of postprandial lipoproteins and low-density lipoprotein (LDL)-receptor binding determined. LDL-receptor binding was determined in mononuclear cells, as a surrogate for hepatic activity. Fasting levels of cholesterol (P <.001), LDL-cholesterol (P <.001), apolipoprotein (apo)B(48) (P =.019), remnant-like particle-cholesterol (RLP-C) (P =.032), and total postprandial apoB(48) area under the curve (AUC) (P =.013) significantly decreased with atorvastatin compared with placebo. Atorvastatin also significantly increased LDL-receptor binding activity (P <.001), and this was correlated with changes in fasting apoB(48) (r =.80, P =.01). We report that aberrations in chylomicron metabolism in normolipidemic CAD subjects are correctable with atorvastatin by a mechanism involving increased LDL-receptor activity. This effect may, in part, explain the cardiovascular benefit of statins used in clinical trials of CAD patients with normal lipid levels.     

Effect of a statin on hepatic apolipoprotein B-100 secretion and plasma campesterol levels in the metabolic syndrome

OBJECTIVE: We aimed to study the effect of atorvastatin, a statin, on cholesterol synthesis and absorption and VLDL-apoB metabolism in obese men with the metabolic syndrome. METHODS: A total of 25 dyslipidaemic obese men were randomized to atorvastatin (n=13) (40 mg/day) or matching placebo (n=12) for 6 weeks. Hepatic secretion and fractional catabolic rate (FCR) of VLDL-apoB was measured using an intravenous bolus of d(3)-leucine before and after treatment. ApoB isotopic enrichment was measured using GCMS and multicompartmental modelling. Plasma lathosterol: cholesterol and campesterol:cholesterol ratios were determined to assess cholesterol synthesis and cholesterol absorption, respectively. RESULTS: Compared with placebo, atorvastatin significantly decreased (P<0.05) total cholesterol, triglyceride, LDL-cholesterol and VLDL-apoB. Plasma lathosterol:cholesterol ratio decreased from 26.4+/-2.4 to 8.8+/-0.8, while the campesterol:cholesterol ratio increased from 26.5+/-4.4 to 38.6+/-5.8 (P<0.01). Atorvastatin also increased VLDL-apoB FCR from 3.82+/-0.33 to 6.30+/-0.75 pools/day (P<0.01), but did not significantly alter VLDL-apoB secretion (12.8+/-1.7 to 13.8+/-2.0 mg/kg/day). CONCLUSIONS: In obesity, atorvastatin inhibits cholesterogenesis but increases intestinal cholesterol absorption. The increased cholesterol absorption may counteract the inhibitory effect on hepatic VLDL-apoB secretion, but it does not apparently influence enhanced catabolism of VLDL-apoB.     

Niacin accelerates intracellular ApoB degradation by inhibiting triacylglycerol synthesis in human hepatoblastoma (HepG2) cells

The mechanism by which the potent drug niacin decreases apoB-containing atherogenic lipoproteins and prevents coronary disease is unclear. Utilizing human hepatoblastoma (HepG2) cells as an in vitro model, we have examined the effect of niacin on intracellular degradation of apoB and the regulatory mechanisms involved in apoB processing. Niacin significantly increased apoB degradation in a dose- and time-dependent manner. Treatment of HepG2 cells with calpain inhibitor I [N-acetyl-leucyl-leucyl-norleucinal (ALLN), an inhibitor of certain protease-mediated apoB degradation], did not alter niacin-induced apoB degradation. Niacin decreased inhibition of oleate-mediated apoB degradation. Niacin dose-dependently inhibited the synthesis of both fatty acids and triacylglycerol (TG) by 20% to 40% as determined by the incorporation of 14C-acetate and 3H-glycerol into fatty acids and TG, respectively. Incubation of HepG2 cells with niacin significantly inhibited (by 12% to 15%) fatty acid esterification to produce TG as assessed by the incorporation of 3H-oleic acid into TG. 14C-acetate incorporation into cholesterol and phospholipids was unchanged. The activity of microsomal triglyceride transfer protein (MTP), a carrier protein for lipids, was not altered by pretreatment of cells with niacin. ApoB mRNA expression and 125I-LDL protein uptake were also unchanged. These data indicate that niacin accelerates hepatic intracellular post-translational degradation of apoB by selectively reducing triglyceride synthesis (through inhibiting both fatty acid synthesis and fatty acid esterification to produce TG) without affecting ALLN-inhibitable protease- or MTP-mediated intracellular apoB processing, resulting in decreased apoB secretion and hence lower circulating levels of the atherogenic lipoproteins.     

Treatment with atorvastatin ameliorates hepatic very-low-density lipoprotein overproduction in an animal model of insulin resistance, the fructose-fed Syrian golden hamster: evidence that reduced hypertriglyceridemia is accompanied by improved hepatic insulin sensitivity

A novel animal model of insulin resistance, the fructose-fed Syrian golden hamster has been previously documented to exhibit considerable hepatic very-low-density lipoprotein (VLDL) overproduction concomitant with the development of whole body insulin resistance. Here, we investigated whether hepatic lipoprotein overproduction can be ameliorated by treatment with a hydroxymethyl glutaryl conenzyme A (HMG-CoA) reductase inhibitor, atorvastatin, using a series of ex vivo experiments. Hamsters were fed a fructose-enriched diet for 14 days to induce a state of insulin resistance, and then continued on a fructose-enriched diet supplemented with or without 40 mg/kg atorvastatin per day for 14 days. Fructose feeding in the first 2 weeks caused a significant increase in plasma total cholesterol and triglyceride levels. There was a significant decline in plasma triglyceride levels following supplementation with the inhibitor (50% to 59%; P <.05). Experiments with primary hepatocytes revealed a decreased VLDL-apolipoprotein B (apoB) production (37.4% +/- 10.4%; P <.05) in hamsters treated with atorvastatin. Interestingly, atorvastatin treatment partially attenuated (by 23%) the elevated hepatic level of microsomal triglyceride transfer protein (MTP) induced by fructose feeding. There was molecular evidence of improved hepatic insulin sensitivity with atorvastatin treatment based on assessment of the phosphorylation status of the insulin receptor and the expression of protein tyrosine phosphatase-1B. The improvement in insulin signaling was not mediated by a change in hepatic triglyceride accumulation as no significant difference was observed in liver triglyceride levels. Taken together, these data suggest that statins can ameliorate the VLDL-apoB overproduction state observed in a fructose-fed, insulin-resistant hamster model, and may potentially contribute to an enhanced hepatic insulin sensitivity.