atorvastatin Lipitor
Development, validation, and interlaboratory comparison of an HMG-CoA reductase inhibition assay for quantitation of atorvastatin in plasma matrices.

Shum YY, Huang N, Walter G, Black A, Sekerke C, Chang T, Whitfield LR.

Pharmacokinetics/Drug Metabolism Department, Parke-Davis Pharmaceutical Research, Division of Warner-Lambert Company, Ann Arbor, Michigan 48105, USA.

An HMG-CoA reductase inhibition assay was developed and validated for quantitation of atorvastatin in human, dog, rat, and mouse plasma. Atorvastatin was isolated from plasma by protein precipitation. Rat-liver microsomes were used to provide the reductase enzyme. The method was validated by assaying calibration standards and quality controls in triplicate on each of the 3 days. A customized computer program was used for data calculation. Quantitation of the assay ranged from 0.36 to 16 ng/ml of atorvastatin in different plasma matrices. Assay precision and accuracy, based on the coefficient of variation and percent relative error, respectively, of quality controls were 10.4% to 14.5% and within +/- 6.25% in human; 4.89% to 10.6% (+/- 8.13%) in dog; 2.68% to 8.62% (+/- 5.00%) in rat; and 3.68% to 8.96% (+/- 5.38%) in mouse plasma. The method has been applied to pharmacokinetic studies of atorvastatin in human and toxicokinetic studies in dog, rat, and mouse after atorvastatin administration. Atorvastatin equivalent concentrations in a set of plasma samples from subjects receiving single and multiple doses of atorvastatin were determined by validated HMG-CoA reductase inhibition assays at four different laboratories. Results were compared using linear regression and concordance correlation statistical procedures. Good agreements among these data indicated that results from different laboratories with the same validated method can be used interchangeably.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9485553&dopt=Abstract atorvastatin Lipitor



atorvastatin Lipitor
Pre- and postnatal toxicity of the HMG-CoA reductase inhibitor atorvastatin in rats.

Henck JW, Craft WR, Black A, Colgin J, Anderson JA.

Department of Pathology and Experimental Toxicology, Parke-Davis Pharmaceutical Research Division, Warner-Lambert Company, Ann Arbor, Michigan 48105, USA.

Atorvastatin is a potent inhibitor of the enzyme 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase, which catalyzes the conversion of HMG-CoA to mevalonate and constitutes the rate-limiting step in the biosynthesis of cholesterol. Steroid hormones derived from cholesterol, as well as mevalonate and its isoprenoid derivatives, provide important contributions to the maternal animal during pregnancy and lactation, as well as to the growth and development of the offspring; these contributions may potentially be influenced by inhibition of HMG-CoA reductase. To investigate the effects of atorvastatin on various aspects of reproduction and development, female Sprague-Dawley rats received 0, 20, 100, or 225 mg/kg daily by gavage from gestation day 7 through lactation day 20. Maternal toxicity, characterized by morbidity/mortality (13%), reduced body weight gain and food consumption, and pathologic lesions in the nonglandular mucosa of the stomach, occurred at 225 mg/kg. Offspring survival at birth and during the neonatal period at 225 mg/kg was reduced relative to control by up to 45%, and 28% of litters had no viable offspring by 10 days postpartum. Additional effects on offspring included reduced body weight during the neonatal and maturation periods (100, 225 mg/kg), delayed appearance of pinnae detachment and incisor eruption (225 mg/kg), impaired rotorod performance (females only; 100, 225 mg/kg), reduced acoustic startle responding (males only; 20, 100, 225 mg/kg), and transient effects on shuttle avoidance (females only; 225 mg/kg). No treatment-related effects were observed on offspring reproduction. In a separate experiment, a single dose of 10 mg/kg atorvastatin administered to female Wistar rats on gestation day 19 or lactation day 13 provided evidence of placental transfer and excretion into the milk. Results of this study indicate that pre- and postnatal administration of atorvastatin to female rats produces developmental toxicity in their offspring via in utero and/or lactational exposure, and in the presence or absence of maternal toxicity.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9520344&dopt=Abstract atorvastatin Lipitor



atorvastatin Lipitor
Renal dysfunction does not alter the pharmacokinetics or LDL-cholesterol reduction of atorvastatin.

Stern RH, Yang BB, Horton M, Moore S, Abel RB, Olson SC.

Department of Clinical Pharmacology, Parke-Davis Pharmaceutical Research Division of Warner-Lambert Company, Ann Arbor, Michigan, USA.

The objective of this study was to determine the effects of renal dysfunction on the steady-state pharmacokinetics and pharmacodynamics of atorvastatin, a 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor. Nineteen subjects with calculated creatinine clearances ranging from 13 mL/min to 143 mL/min were administered 10 mg atorvastatin daily for 2 weeks. Pharmacokinetic parameters and lipid responses were analyzed by regression on calculated creatinine clearance. Correlations between steady-state atorvastatin pharmacokinetic or pharmacodynamic parameters and creatinine clearance were weak and, in general, did not achieve statistical significance. Although the elimination rate constant, lambda z (0.579), was significantly correlated with creatinine clearance, neither maximum plasma concentration (Cmax, -0.361) nor oral clearance (Cl/F, 0.306) were; thus, steady-state exposure is not altered. Renal impairment has no significant effect on pharmacodynamics and pharmacokinetics of atorvastatin.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9549635&dopt=Abstract atorvastatin Lipitor



atorvastatin Lipitor
Effects of atorvastatin on the intracellular stability and secretion of apolipoprotein B in HepG2 cells.

Mohammadi A, Macri J, Newton R, Romain T, Dulay D, Adeli K.

Department of Chemistry and Biochemistry, University of Windsor, Ontario, Canada.

We investigated the effects of atorvastatin, a new 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor, on the biogenesis of apolipoprotein B (apoB) in intact and permeabilized HepG2 cells. Intact cells were pretreated either with single or multiple doses of atorvastatin (0.1 to 20 micromol/L) for periods of 6 to 20 hours and pulsed with [35S]methionine. In some cases the cells were permeabilized with digitonin. Experiments were performed to investigate the effects of atorvastatin on (1) the rates of lipid synthesis and secretion, (2) the synthesis and accumulation of apoB, (3) the intracellular stability of apoB, (4) the amount of apoB-containing lipoprotein particles assembled in HepG2 microsomes, and (5) the secretion and accumulation of apoB into the culture medium. ApoB synthesis, degradation, and secretion were measured by pulse-chase experiments with [35S]methionine in both intact and permeabilized HepG2 cells. Lipid synthesis was assessed by pulse-labeling experiments with [3H]acetate or [3H]oleate bound to bovine serum albumin. Comparisons were made under basal conditions and in the presence of oleate (0.36 micromol/L). Atorvastatin acutely inhibited the synthesis of cholesterol and cholesterol ester but did not have a significant effect on triglyceride or phospholipid synthesis. Atorvastatin did not affect the uptake of [35S]methionine by the cells nor did it influence the synthesis of apoB or a control protein, albumin. However, atorvastatin reduced the secretion of apoB into the culture medium, apparently by enhancing the degradation of apoB in the cell under basal and induced conditions with oleate. The stability of apoB associated with the lipoprotein particles was also significantly lowered by atorvastatin. The stimulated degradation of apoB in atorvastatin-treated cells was sensitive to MG132, a proteasome inhibitor. The net effect of atorvastatin was a reduction in the number of apoB-containing lipoprotein particles of different sizes isolated from microsomes and a reduction in apoB secretion into the culture medium. The data suggest that atorvastatin may impair the translocation of apoB into the lumen of the endoplasmic reticulum, thus increasing the amount of apoB degraded intracellularly. It is hypothesized that atorvastatin alters these parameters primarily as a result of inhibiting cholesterol synthesis and limiting the availability of cholesterol and/or cholesterol ester for the normal assembly of apoB-containing lipoprotein particles.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9598838&dopt=Abstract atorvastatin Lipitor



atorvastatin Lipitor
Effect of hypolipidemic drugs on key enzyme activities related to lipid metabolism in normolipidemic rabbits.

Alegret M, Verd JC, Diaz C, Hernandez G, Adzet T, Sanchez RM, Laguna JC.

Dept. Farmacologia y Quimica Terapeutica, Facultad de Farmacia, Nucleo Universitario de Pedralbes, Barcelona, Spain.

The effect of atorvastatin (3 mg kg(-1) day(-1)), simvastatin (3 mg kg(-1) day(-1)) and bezafibrate (100 mg kg(-1) day(-1)) administered for 4 weeks to male New Zealand white rabbits on enzyme activities related to lipid metabolism has been studied. Only the statins reduced plasma cholesterol values, while none of the drugs modified plasma triglyceride or high density lipoprotein (HDL)-cholesterol concentrations, nor the activity of enzymes such as hepatic diacylglycerol acyltransferase, lipoprotein lipase or hepatic lipase, directly involved in triglyceride metabolism. Both statins elicited similar increases in the hepatic microsomal 3-hydroxy-3-methyl-glutaryl Coenzyme A (CoA) reductase activity (147 and 109% induction for simvastatin and atorvastatin, respectively), and none of the drugs assayed modified hepatic acyl-coenzyme A:cholesterol acyltransferase activity significantly. Only bezafibrate induced a significant 57% reduction in the activity of hepatic microsomal cholesterol 7alpha-hydroxylase. Regarding the rate limiting enzyme of phosphatidylcholine biosynthesis, CTP:phosphocholine cytidylyl transferase, atorvastatin and bezafibrate behaved similarly, decreasing the enzyme activity in the liver by 45% and 54%, respectively; simvastatin induced no modification of this activity. The reduction of CTP:phosphocholine cytidylyl transferase activity is not caused by a direct inhibition of the enzyme by bezafibrate and atorvastatin. Further, the inhibitory effect of atorvastatin appears to be unrelated to the inhibition of 3-hydroxy-3-methyl-glutaryl CoA reductase elicited in vivo.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9653895&dopt=Abstract atorvastatin Lipitor



atorvastatin Lipitor
Atorvastatin and gemfibrozil metabolites, but not the parent drugs, are potent antioxidants against lipoprotein oxidation.

Aviram M, Rosenblat M, Bisgaier CL, Newton RS.

The Lipid Research Laboratory, Technion Faculty of Medicine, The Rappaport Family Institute for Research in the Medical Sciences and Rambam Medical Center, Haifa, Israel. aviram tx.technion.ac.il

Increased atherosclerosis risk in hyperlipidemic patients may be a result of the enhanced oxidizability of their plasma lipoproteins. We have previously shown that hypocholesterolemic drug therapy, including the 3-hydroxy-3-methyl-glutaryl CoenzymeA (HMG-CoA) reductase inhibitors, and the hypotriglyceridemic drug bezafibrate, significantly reduced the enhanced susceptibility to oxidation of low density lipoprotein (LDL) isolated from hyperlipidemic patients. Although this antioxidative effect could not be obtained in vitro with all of these drugs, the active drug metabolites, which are formed in vivo, could affect lipoprotein oxidizability. We thus sought to analyze the effect of atorvastatin and gemfibrozil, as well as specific hydroxylated metabolites, on the susceptibility of LDL, very low density lipoprotein (VLDL), and high density lipoprotein (HDL) to oxidation. LDL oxidation induced by either copper ions (10 microM CuSO4), by the free radical generator system 2'-2'-azobis 2-amidino propane hydrochloride (5 mM AAPH), or by the J-774A.1 macrophage-like cell line, was not inhibited by the parent forms of atorvastatin or gemfibrozil, but was substantially inhibited (57-97%), in a concentration-dependent manner, by pharmacological concentrations of the o-hydroxy and the p-hydroxy metabolites of atorvastatin, as well as by the p-hydroxy metabolite (metabolite I) of gemfibrozil. On using the atorvastatin o-hydroxy metabolite and gemfibrozil metabolite I in combination an additive inhibitory effect on LDL oxidizability was found. Similar inhibitory effects (37-96%) of the above metabolites were obtained for the susceptibility of VLDL and HDL to oxidation in the oxidation systems outlined above. The inhibitory effects of these metabolites on LDL, VLDL, and HDL oxidation could be related to their free radical scavenging activity, as well as (mainly for the gemfibrozil metabolite I) to their metal ion chelation capacities. In addition, inhibition of HDL oxidation was associated with the preservation of HDL-associated paraoxonase activity. We conclude that atorvastatin hydroxy metabolites, and gemfibrozil metabolite I possess potent antioxidative potential, and as a result protect LDL, VLDL, and HDL from oxidation. We hypothesize that in addition to their beneficial lipid regulating activity, specific metabolites of both drugs may also reduce the atherogenic potential of lipoproteins through their antioxidant properties.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9690910&dopt=Abstract atorvastatin Lipitor