Marc J.T.M. Mol

EFFECTS OF SYNVINOLIN (MK-733) ON PLASMA LIPIDS IN FAMILIAL HYPERCHOLESTEROLAEMIA

The effects of synvinolin (MK-733), a competitive inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase, were investigated in 43 patients with heterozygous familial hypercholesterolaemia in a double-blind, placebo-controlled, dose-finding study. Synvinolin was given in doses ranging from 2.5 mg to 80 mg per day for 4 weeks. 8 patients received placebo. Low-density-lipoprotein cholesterol fell on average by 18% on 2.5 mg/day and 42% on 80 mg/day. The drug was as effective whether it was given once or twice daily. Serum high-density-lipoprotein cholesterol tended to increase and serum triglycerides to decrease on the higher doses. The drug was tolerated well. Except for a slight rise in alanine aminotransferase in 3 patients no objective side-effects were observed.

Plasma levels of lipid and cholesterol oxidation products and cytokines in diabetes mellitus and cigarette smoking: effects of vitamin E treatment

To evaluate the role of both oxidation and inflammation in atherosclerosis, we compared LDL oxidizability, in vivo lipid and cholesterol oxidation, and basal and lipopolysaccharide (LPS)-stimulated production of various cytokines in normolipidemic patients with diabetes mellitus (DM: n = 11), cigarettes smokers (n = 14). In addition, the effects of vitamin E (600 I.U./day for 4 weeks) on these parameters were evaluated. Initial LDL oxidation characteristics before and after vitamin E were identical in the 3 groups. Plasma thiobarbituric acid reactive substances were higher in DM and smokers versus controls (0.77 +/- 0.22, 0.74 +/- 0.14 versus 0.62 +/- 0.10 mumol malondialdehyde equivalents/l, respectively; P versus controls < 0.05) and normalized after vitamin E supplementation. Total plasma oxysterols were higher in smokers versus controls (354 +/- 104 versus 265 +/- 66 nmol/l, P < 0.05) and unaffected by vitamin E. The basal and LPS-stimulated levels of interleukin-1 beta and tumour necrosis factor alpha (TNF alpha) and the basal level of interleukin-1-receptor antagonist (IL-1RA) were identical for the 3 groups. LPS-stimulated IL-1RA was higher in DM versus controls (10.7 +/- 2.0 versus 8.1 +/- 1.7 pmol/l, P < 0.05). After vitamin E, TNF alpha dropped in controls and smokers, and IL-1RA in smokers only. Results suggest increased in vivo oxidative stress and inflammation in DM and smoking, which is partly overcome by vitamin E.

Influence of apo E polymorphism on the response to simvastatin treatment in patients with heterozygous familial hypercholesterolemia

In a group of 120 patients with heterozygous familial hypercholesterolemia (FH) the influence of the apolipoprotein E (apoE) polymorphism on pre-treatment plasma lipid levels and on the response to treatment with simvastatin was studied. The apoE phenotype distribution did not differ significantly between the FH group and a sample group of the Dutch population. Differences in pre-treatment lipid levels were not related to the apoE polymorphism in this FH population. After 12 weeks use of a daily dose of 40 mg simvastatin, the plasma total cholesterol, low density lipoprotein (LDL)-cholesterol and plasma triglyceride levels were reduced on average by 33%, 38% and 19%, respectively. At the same time high density lipoprotein (HDL)-cholesterol concentration increased on average by 7%. In the combined FH patient group (males and females) a considerable interindividual variation in response to simvastatin was observed, but was not related to the apoE polymorphism. However, considering males and females separately, we found that female FH patients with the apoE3E3 phenotype responded better on simvastatin treatment with respect to LDL-cholesterol than male FH patients with the apoE3E3 phenotype.

Simvastatin (MK-733): a potent cholesterol synthesis inhibitor in heterozygous familial hypercholesterolaemia

Simvastatin (MK-733), a new inhibitor of 3-hydroxy-3-methylglutaryl-coenzyme A reductase, was administered to 38 patients with heterozygous familial hypercholesterolaemia for 24 weeks. A dose of 40 mg per day produced a mean reduction in low density lipoprotein cholesterol of 43-45% and in triglycerides of 21-31%. Mean high density lipoprotein cholesterol increased significantly by 10-13%. There were no major differences in response whether the drug was taken in one or two doses. MK-733 was tolerated well. Adverse effects were infrequent and limited to slight increases of alanine aminotransferase, creatine phosphokinase and bilirubin. This drug appears to be a potent inhibitor of cholesterol synthesis and has produced the largest therapeutic response as monotherapy in patients with familial hypercholesterolaemia.

Efficacy and tolerability of simvastatin (MK-733)

The efficacy of simvastatin, a new inhibitor of cholesterol biosynthesis, was studied in patients with familial hypercholesterolemia. A mean reduction in low-density lipoprotein cholesterol of 38 percent was observed after eight weeks of treatment with 20 mg of simvastatin; a 42 percent reduction was seen after the next 16 weeks with 40 mg. There was no difference in response whether the drug was taken in one or two doses. In another study, simvastatin (40 mg per day) was compared with cholestyramine (8 to 16 g per day). After 12 weeks, low-density lipoprotein cholesterol was reduced 43 percent by simvastatin and 29 percent by cholestyramine. Combination therapy caused a reduction in low-density lipoprotein cholesterol of 54 percent. Simvastatin appeared also to be a potent hypolipidemic drug in 10 patients with familial dysbetalipoproteinemia. The drug was well tolerated. Adverse effects were primarily composed of increases in serum transaminases and creatine phosphokinase. No effects of simvastatin on the production of steroid hormones were observed.

Some metabolic characteristics of low-density lipoprotein subfractions, LDL-1 and LDL-2: in vitro and in vivo studies

Two low-density lipoprotein subfractions, LDL-1 and LDL-2, with density ranges of respectively 1.023-1.034 and 1.036-1.041 g/ml, were isolated by aspiration after density gradient ultracentrifugation of human pooled serum. In vitro interactions of both LDL subfractions with the LDL receptor of human cultured fibroblasts, human hepatoma cell line Hep G2 and human hepatocytes were compared. No difference in association (binding and internalization) nor in degradation between LDL-1 and LDL-2 by these cells was found. However, kinetic studies in guinea pigs showed that LDL-2 disappeared faster from the circulation and accumulated to a greater extent in the liver, compared to LDL-1. Thus, we were unable to show a difference in the LDL receptor-mediated uptake of both LDL subfractions by various cells in vitro. The results obtained in vivo suggest that LDL-1 is more atherogenic than LDL-2, because its longer half-life renders the particle more susceptible to uptake by the scavenger LDL receptor on macrophages.

Low-density lipoprotein catabolism in WHHL rabbits after partial ileal bypass surgery

The effect of partial ileal bypass surgery (PIB) on lipoprotein concentrations and compositions and on the catabolism of low-density lipoproteins (LDL) was studied in Watanabe heritable hyperlipidemic (WHHL) rabbits. After PIB, total serum cholesterol was 65% lower (6.22 +/- 1.58 vs. 17.24 +/- 3.22 mmol/l) and LDL cholesterol 81% lower (2.02 +/- 0.95 vs. 10.90 +/- 3.60 mmol/l) than in control WHHL rabbits; cholesteryl esters, expressed as percentage of mass, were 55% lower in the very-low and intermediate-density lipoprotein (VLDL + IDL) fractions, and 45% lower in LDL, whereas triacylglycerols were 89% higher in VLDL + IDL and 121% higher in LDL. The fractional catabolic rate (FCR) of LDL protein (apoLDL) from operated animals was 10% higher than that from controls in all animals (0.55 +/- 0.10 vs. 0.50 +/- 0.10 pools/day; P less than 0.01). The FCR of autologous apoLDL in PIB rabbits was 50% higher than that of autologous apoLDL in control rabbits (0.63 +/- 0.05 vs. 0.42 +/- 0.06 pools/day); this was not caused by induction of receptor-mediated clearance of LDL. The production rate of apoLDL after PIB in PIB rabbits was 50% lower compared to control apoLDL in controls (26.0 +/- 6.7 vs. 51.7 +/- 16.4 mg/kg per day). We conclude that PIB lowers LDL cholesterol in WHHL rabbits by a decreased production of LDL, by an increased non-specific clearance of LDL and by compositional changes, which lead to LDL particles containing less cholesterol.

Effects of Partial Ileal Bypass Surgery on Low-Density Lipoprotein Metabolism in Watanabe Heritable Hyperlipidemic Rabbits

Partial ileal bypass (PIB) in Watanabe heritable hyperlipidemic rabbits (WHHL) causes a reduction in plasma cholesterol (chol) of approximately 50%. We have previously performed turnover studies of radiolabeled native and methylated LDL, which showed a reduction in the absolute catabolic rate (ACR) of LDL of 50% after PIB, whereas the fractional catabolic rate (FCR) was unchanged. Furthermore, the receptor-mediated clearance of LDL after PIB remained essentially zero. Use was made of nonautologous LDL from control (C) WHHL. We have now used LDL both from PIB WHHL and C WHHL to study the possible influence of PIB on the composition and kinetics of LDL; for this purpose, LDL was isolated from pooled serum of five WHHL (age 40 ± 4 weeks) 17 weeks after PIB and from pooled serum of five C WHHL (age 46 ± 2 weeks), labeled with 125I and 131I, respectively, and injected simultaneously into each of the ten animals and into one New Zealand white rabbit (NZW). Plasma radioactivities were followed for 72 hr. In PIB WHHL, the plasma pools of LDL-chol and apo LDL were considerably lower ( -82% and -67% versus C WHHL, respectively). Composition studies of LDL showed a significant decrease in cholesteryl esters (% mass) of 46% and a significant increase of triglycerides (% mass) of 120%. In contrast to our previous study, a significantly higher FCR of C LDL in PIB versus C WHHL was found. In addition, the FCR of PIB LDL was significantly higher than that of C LDL in both PIB and C animals. The FCR of PIB LDL in PIB WHHL was 1.5 times higher than the FCR of C LDL in C WHHL. The ACR of PIB LDL in PIB WHHL was 50% lower than the ACR of C LDL in C WHHL, confirming a decreased production rate of LDL after PIB. Our conclusions are: (1) PIB reduced the production rate of LDL, which is in accordance with the results of our previous studies; (2) PIB increased FCR of LDL, which was even more pronounced for PIB LDL (+ 507c) than for C LDL (+ 38%). The dual effect of PIB on production rate and FCR explains the large reduction in LDL. The increase in FCR is apparently caused by an increased uptake of LDL by the liver after PIB and also by intrinsic changes in the structure of LDL. In vitro studies are currently underway to investigate the mechanism of this enhanced uptake.