The mechanism of comparable serum cholesterol lowering effects of pravastatin sodium, a 3-hydroxy-3-methylglutaryl coenzyme A inhibitor, between once- and twice-daily treatment regimens in beagle dogs and rabbits

The History of the WHHL Rabbit, an Animal Model of Familial Hypercholesterolemia (II) - Contribution to the Development and Validation of the Therapeutics for Hypercholesterolemia and Atherosclerosis

A number of effective drugs have been developed through animal experiments, contributing to the health of many patients. In particular, the WHHL rabbit family (WHHL rabbits and its advanced strains (coronary atherosclerosis-prone WHHL-CA rabbits and myocardial infarction-prone WHHLMI rabbits) developed at Kobe University (Kobe, Japan) contributed greatly in the development of cholesterol-lowering agents. The WHHL rabbit family is animal models for human familial hypercholesterolemia, coronary atherosclerosis, and coronary heart disease. At the end of breeding of the WHHL rabbit family, this review summarizes the contribution of the WHHL rabbit family to the development of lipid-lowering agents and anti-atherosclerosis agents. Studies using the WHHL rabbit family demonstrated, for the first time in the world, that lowering serum cholesterol levels or preventing LDL oxidation can suppress the progression and destabilization of coronary lesions. In addition, the WHHL rabbit family contributed to the development of various compounds that exhibit lipid-lowering and anti-atherosclerotic effects and has also been used in studies of gene therapeutics. Furthermore, this review also discusses the causes of the increased discrepancy in drug development between the results of animal experiments and clinical studies, which became a problem in recent years, and addresses the importance of the selection of appropriate animal models used in studies in addition to an appropriate study design.

Pharmacological profile of SMP-797, a novel acyl-coenzyme a: cholesterol acyltransferase inhibitor with inducible effect on the expression of low-density lipoprotein receptor

We investigated the pharmacological profile of SMP-797, a novel hypocholesterolemic agent. SMP-797 showed inhibitory effects on acyl-coenzyme A: cholesterol acyltransferase (ACAT) activities in various microsomes and in human cell lines, and hypocholesterolemic effects in rabbits fed a cholesterol-rich diet and hamsters fed a normal diet. In hamsters, the reduction of total cholesterol level by SMP-797 was mainly due to the decrease of low-density lipoprotein (LDL) cholesterol level rather than that of very low-density lipoprotein (VLDL) cholesterol level. Interestingly, SMP-797 increased the hepatic low-density lipoprotein receptor expression in vivo when it decreased the low-density lipoprotein cholesterol level. SMP-797 also increased low-density lipoprotein receptor expression in HepG2 cells like atorvastatin, an HMG-CoA reductase inhibitor, although other acyl-coenzyme A: cholesterol acyltransferase inhibitor had no effect. In addition, SMP-797 had no effect on cholesterol synthesis in HepG2 cells. These results suggested that the increase of low-density lipoprotein receptor expression by SMP-797 was independent of its acyl-coenzyme A: cholesterol acyltransferase inhibitory action and did not result from the inhibition of hepatic cholesterol synthesis. In conclusion, these results suggest that SMP-797 is a novel hypocholesterolemic agent showing a cholesterol-lowering effect in which the increase of hepatic low-density lipoprotein receptor expression as well as the inhibition of acyl-coenzyme A: cholesterol acyltransferase is involved.

Regulation of hepatic high density lipoprotein binding protein, HB2, expression after administration of simvastatin to rabbits

HB2 a candidate HDL receptor, is quite distinct from other HDL receptors in its structure. However, while changes in cellular cholesterol content, or a reduction in cholesterol biosynthesis accompany corresponding changes in HB2 expression, the level at which these changes occur have not been determined and the regulation and the function of HB2 remain uncertain. In order to further investigate the regulation of HB2, we administered simvastatin to rabbits to reduce cholesterol biosynthesis and follow changes in HB2 mRNA in various tissues. Six rabbits were given 15 mg/kg of simvastatin by oral administration daily and another six rabbits were given the same volume of saline as a control, for 21 days. They were then sacrificed to obtain samples of blood, liver, lung, jejunum and brain. Simvastatin reduced plasma total cholesterol by 47% and free cholesterol concentrations in liver and lung by 25 and 10%, respectively. Northern blot analysis showed that simvastatin lowered the expression of HB2 significantly in the liver and lung by 54% and 42% respectively but not in the jejunum or brain. These results support the findings of a previous study showing that HDL binding activity of both HB1 and HB2, which was determined by ligand blotting using HDL3 as a ligand, were reduced after administering cholesterol lowering agents. (Arteriosclerosis, 10: 1045-1050,1990). The present study suggests that simvastatin down-regulated HB2 at the transcriptional stage. Although the complete physiological function of HB2 is unclear, it appears to play some role in the cholesterol metabolism, warranting further studies to elucidate the nature of this interaction.

[Atorvastatin (Lipitor): a review of its pharmacological and clinical profile]

Hypercholesterolemia is a major risk factor for the development of coronary heart disease. HMG-CoA reductase inhibitors have been used as first-line drugs because of both their superior cholesterol lowering effect and reliable safety profile. Since there are many patients whose plasma cholesterol level does not reach the therapeutic target even if reductase inhibitors are available, more effective drugs have been strongly required for a long time. Atorvastatin, one of the most recently introduced statins, produces greater plasma LDL-cholesterol reductions than other statins. This pronounced effect of atorvastatin seems to be due to its long-lasting action, presumably a reflection of longer residence time of atorvastatin and its active metabolites in the liver. Clinical trials of atorvastatin have also demonstrated marked plasma triglyceride reductions. The triglyceride reduction with atorvastatin seems to stem from the following two indirect mechanisms, limiting VLDL secretion from the liver and increase in clearance of triglyceride-rich lipoprotein via induced LDL receptors from plasma. Eleven clinical trials of atorvastatin, which have been developed in Japan, clearly demonstrated its ability to reduce LDL-C levels more strongly and in significantly more patients to LDL-C treatment goals than other reductase inhibitors with similar safety profiles. Therefore, atorvastatin adds a new dimension to the effective management of hypercholesterolemia and combined hyperlipidemia.

Pravastatin restored the infarct size-limiting effect of ischemic preconditioning blunted by hypercholesterolemia in the rabbit model of myocardial infarction

OBJECTIVES

We tested to find out whether pravastatin restores the infarct size (IS)-limiting effect of ischemic preconditioning (IP) and if it has any effect on the IP-induced activation of adenosine producing enzyme ecto-5'-nucleotidase which plays a key role in the IP-induced cardioprotection.

BACKGROUND

The IS-limiting effect of IP is blunted by hypercholesterolemia. Recently, HMG-CoA reductase inhibitors are shown to have direct cytoprotective effects.

METHODS

Rabbits were fed with a normal or cholesterol (1%) added diet with or without pravastatin (5 mg/kg/day) treatment. Infarct size was measured after 30 min occlusion and 3 h reperfusion of circumflex coronary artery with or without the IP procedure (5 min occlusion and 10 min reperfusion). Additionally, ecto-5'-nucleotidase activities of ischemic and nonischemic myocardium were measured immediately after IP procedure.

RESULTS

This dose of pravastatin did not normalize the increased level of serum cholesterol. The IS-limiting effect of preceding IP (IS reduced from 36.7% to 9.6%, p < 0.001) was abolished by hypercholesterolemia (from 46.1% to 31.3%, p = NS) and restored by pravastatin treatment (from 35.2% to 9.4%, p < 0.001). Pravastatin treatment did not affect IS or the effect of IP under normocholesterolemia. The activation of ecto-5'-nucleotidase presented as the activity ratio of ischemic to nonischemic myocardium (3.1-fold in normocholesterolemia) was blunted by hypercholesterolemia (1.8-fold, p < 0.05) and restored by pravastatin treatment (2.9-fold).

CONCLUSIONS

Pravastatin, at the dose serum cholesterol was not normalized, restored the IS-limiting effect of IP and IP-induced ecto-5'-nucleotidase activation, which were both blunted by hypercholesterolemia. The activation of ecto-5'-nucleotidase may be worth further investigation as a possible mechanism for the hypercholesterolemia-induced retardation and pravastatin-mediated restoration of the cardioprotective effect of IP.