Pravastatin inhibited the cholesterol synthesis in human hepatoma cell line Hep G2 less than simvastatin and lovastatin, which is reflected in the upregulation of 3-hydroxy-3-methylglutaryl coenzyme A reductase and squalene synthase.

Griffioen M.

Gaubius Laboratory IVVO-TNO, Leiden, The Netherlands.

The possible difference between lovastatin (mevinolin, MK-803), simvastatin (MK-733) and pravastatin (CS-514), all chemically-related competitive inhibitors of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase, were tested in the human hepatoma cell line Hep G2, which is often used as a model for the human hepatocyte. After an 18-hr incubation of the cells with the drugs, pravastatin (IC50 = 1900 nM) was less potent than simvastatin and lovastatin (IC50 = 34 and 24 nM, respectively) in inhibiting the sterol synthesis. As a consequence of this inhibition, the HMG-CoA reductase mRNA levels and squalene synthase activity, both negatively-regulated by sterols, were increased equally by simvastatin and lovastatin, whereas the induction by pravastatin was much less. In contrast, there were fewer differences between the compounds in inhibiting HMG-CoA reductase activity, when assayed directly in Hep G2 cell homogenates (IC50 values = 18, 61 and 95 nM for simvastatin, lovastatin and pravastatin, respectively). Moreover, in experiments with human hepatocytes in primary culture the IC50 values for inhibition of the cholesterol synthesis by simvastatin and pravastatin were of the same order of magnitude (23 and 105 nM, respectively). The results are therefore explained as follows: the three drugs act in the same way within the Hep G2 cell in terms of inhibiting HMG-CoA reductase and their subsequent effect on the feedback regulation of the cholesterol synthesis, i.e. increasing squalene synthase and HMG-CoA reductase mRNA. However, pravastatin seems to be less able to enter the cells compared with simvastatin and lovastatin, possibly because of the higher hydrophobicity of the latter compounds. The observation with human hepatocytes suggests that in Hep G2 cells a specific hepatic transporter is missing. On one hand the human hepatoma cell line Hep G2 has proved to be a good model for the study of the feedback regulation of enzymes of the cholesterol biosynthetic pathway such as HMG-CoA reductase and squalene synthase, but, on the other hand seems to be less suitable as a model for the study of specific uptake of drugs, e.g. the vastatins, in human hepatocytes.

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Effects of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors on mitochondrial respiration in ischaemic dog hearts.

Ichihara K.

Department of Pharmacology, Hokkaido College of Pharmacy, Otaru, Japan.

1. Effects of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors, pravastatin and simvastatin, on the myocardial level of coenzyme Q10, and on mitochondrial respiration were examined in dogs. 2. Either vehicle (control), pravastatin (4 mg kg-1 day-1), or simvastatin (2 mg kg-1 day-1) was administered orally for 3 weeks. First, the myocardial tissue level of coenzyme Q10 was determined in the 3 groups. Second, ischaemia was induced by ligating the left anterior descending coronary artery (LAD) in anaesthetized open chest dogs, pretreated with the inhibitors. After 30 min of ischaemia, nonischaemic and ischaemic myocardium were removed from the left circumflex and LAD regions, respectively, and immediately used for isolation of mitochondria. The mitochondrial respiration was determined by polarography, with glutamate and succinate used as substrates. 3. Simvastatin significantly decreased the myocardial level of coenzyme Q10, but pravastatin did not. 4. Ischaemia decreased the mitochondrial respiratory control index (RCI) in both groups. Significant differences in RCI between nonischaemic and ischaemic myocardium were observed in the control and simvastatin-treated groups. 5. Only in the simvastatin-treated group did ischaemia significantly decrease the ADP/O ratio, determined with succinate. 6. The present results indicate that simvastatin but not pravastatin may cause worsening of the myocardial mitochondrial respiration during ischaemia, probably because of reduction of the myocardial coenzyme Q10 level.

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Lovastatin and simvastatin--inhibitors of HMG CoA reductase and cholesterol biosynthesis.

Alberts AW.

Department of Biochemical Regulation, Merck Sharp & Dohme Research Laboratories, Rahway, NJ 07065-0900.

The microsomal enzyme 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase is a key rate-controlling step early in the cholesterol biosynthetic pathway that catalyzes the conversion of HMG CoA to mevalonic acid. Since this enzyme plays a significant role in regulating cholesterol synthesis, it is a rational target for pharmacologic intervention. The first potent, specific inhibitor of HMG CoA was mevastatin (compactin, ML-236B), which was discovered in 1976 by Endo et al. [J Antibiot 1976:29:1346-1348]. Subsequently, lovastatin, a novel, more active fungal metabolite was isolated from a strain of Aspergillus terreus. Lovastatin, the first of this class of agents to be approved for clinical use, was chemically modified to form simvastatin. Simvastatin is superior to lovastatin in intrinsic inhibitory potency. Both are inactive lactone prodrugs that must be converted to their respective dihydroxy open-acid forms to elicit inhibitory activity. Pharmacologic characterization of lovastatin and simvastatin has demonstrated that these potent inhibitors of HMG CoA reductase specifically inhibit cholesterol synthesis in animal cells, as well as in vivo after oral administration of the agents. Oral administration of either lovastatin or simvastatin to dogs in the presence or absence of the bile acid sequestrant cholestyramine results in a marked, sustained lowering of plasma cholesterol. Associated with the cholesterol lowering is a decrease in urinary and plasma levels of mevalonic acid, the end product of the HMG CoA reductase reaction. The target organ for inhibitors of HMG CoA reductase is the liver, the primary site of cholesterol biosynthesis. Both lovastatin and simvastatin are preferentially extracted by this organ.(ABSTRACT TRUNCATED AT 250 WORDS)

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Biochemical changes and morphological alterations of the liver in guinea-pigs after administration of simvastatin (HMG CoA reductase-inhibitor).

Harvengt C.

Laboratory of Pharmacotherapeutics, Catholic University of Louvain, Bruxelles, Belgium.

Simvastatin is a potent competitive inhibitor of the 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-CoA reductase) which is the rate-limiting enzyme of cholesterol synthesis. In guinea-pigs, administration of a high oral dose of simvastatin (125 mg/kg/day at the beginning of the study) during 18 days had a major hepatotoxic effect whereas a lower oral dose (30 mg/kg/day) did not seem to cause any liver damage. A significant reduction in microsomal Cyt P 450 content was only observed on a high dose of simvastatin whereas HMG CoA reductase activity was reduced in the group with the low simvastatin dose. The hepatic microsomal aminopyrine N-demethylase activity remained unchanged in all groups. The liver lesion was hepatocellular necrosis accompanied in some animals by a biliary duct proliferation. It was associated with a 10-fold elevation in serum aspartate and alanine aminotransferase activities, as well as a great reduction in daily food intake and body weight (28%). The hepatotoxicity of simvastatin could result from the low basal content of HMG-CoA reductase in guinea-pig liver, the prolonged inhibition of mevalonate synthesis and probably, from the absence of HMG-CoA reductase enzyme de novo synthesis.

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Clinical benefits and cost-effectiveness of lowering serum cholesterol levels: the case of simvastatin and cholestyramine in The Netherlands.

Ascoop CA.

Institute for Medical Technology Assessment, Erasmus University, Rotterdam, The Netherlands.

To assess the cost-effectiveness of cholesterol-reducing therapy with cholestyramine and simvastatin in the primary prevention of coronary artery disease in The Netherlands, a model of coronary artery disease incidence was used based on multivariate logistic risk functions from the Framingham study. For men with initial cholesterol levels of 8 mmol/liter, the cost per year of life saved of cholestyramine, expressed in Dutch guilders (NLG; 1 NLG = $0.50), ranges from approximately NLG 208,000 to NLG 483,000, depending on the patient's age at initiation of therapy. For simvastatin, cost-effectiveness ranges from NLG 46,000 to NLG 98,000 per year of life saved among this group of men. Similar differences between simvastatin and cholestyramine therapy prevail among women, although the costs per year of life saved for both agents are considerably higher. These results suggest that (1) simvastatin is substantially more cost effective than is cholestyramine; (2) simvastatin therapy compares favorably with other generally accepted medical practices, especially if treatment is initiated at an early age; and (3) as its long-term safety record becomes more established, simvastatin may become accepted as a drug of first choice in the treatment of persons with elevated serum cholesterol levels.

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A selected ion monitoring method for quantifying simvastatin and its acid form in human plasma, using the ferroceneboronate derivative.

Hata S.

Drug Metabolism, Banyu Pharmaceutical Co. Ltd. Tokyo, Japan.

Simvastatin, a pro-drug lactone, forms the open carboxylic acid as a major metabolite that inhibits the activity of 3-hydroxy-3-methylglutaryl coenzyme A reductase. Simvastatin and the acid in plasma were quantified by a gas chromatography/mass spectrometry/selected ion monitoring (GC/MS/SIM) method. These drugs were separated by solid-phase extraction and independently converted into a 1,3-diol-type compound. This compound reacted with ferroceneboronic acid to yield the cyclic boronate that gave satisfactory mass spectra for GC/MS/SIM measurements. The serum was dominated by the molecular ion appearing as the base peak, thereby leading to a sensitive and selective assay. The calibration curves for simvastatin and the acid were linear in their concentration range of 0.1-10 ng ml-1, where the values of coefficient of variation for both drugs were below 8%, except for the value of 11% for simvastatin at a concentration of 0.1 ng ml-1. The quantification limit for both drugs was 0.1 ng ml-1 on the basis of a signal-to-noise ratio of 4:1.

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