Pharmacology of 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors (statins), including rosuvastatin and pitavastatin

Cholesterol lowering and beyond: role of statins in Alzheimer’s disease

Alzheimer’s disease (AD), the most common form of dementia, is a major health problem with increasing prevalence associated with the increase in life span. Unfortunately, drugs currently used to treat this disorder have only modest therapeutic efficacy. Therefore, there is an urgent need to develop new pharmacological strategies to prevent or delay the onset of AD. As it has been suggested that there is a link between cholesterol and the development of AD, one such strategy could be the inhibition of cholesterol synthesis using HMG-CoA reductase inhibitors (statins). In addition to their cholesterol-lowering properties, statins exert multiple lipid-independent (pleiotropic) effects that may explain some of their beneficial actions. The aim of this article is to summarize the current knowledge on the effects of statins on AD and the mechanisms involved, based on data from in vitro, in vivo and clinical studies, and to provide an overview of the future perspectives in this field.

Therapeutic potential of statins in multiple sclerosis: immune modulation, neuroprotection and neurorepair

Statins as inhibitors of 3-hydroxy-3-methyl glutaryl coenzyme A reductase are widely used as cholesterol-lowering drugs. Recent studies provide evidence that the anti-inflammatory activity of statins, which is independent of their cholesterol-lowering effects, may have potential therapeutic implications for neuroinflammatory diseases such as multiple sclerosis (MS), Alzheimer's disease and brain tumors, as well as traumatic spinal cord and brain injuries. Studies with animal models of MS suggest that, in addition to immunomodulatory activities similar to the ones observed with approved MS medications, statin treatment also protects the BBB, protects against neurodegeneration and may also promote neurorepair. Although the initial human studies on statin treatment for MS are encouraging, prospective randomized clinical studies will be required to evaluate their efficacy in the larger patient population.

Atorvastatin: pharmacological characteristics and lipid-lowering effects

By inhibiting 3-hydroxy-3-methylglutaryl coenzyme-A (HMG-CoA) reductase, the statins reduce hepatocyte cholesterol levels, which results in up-regulation of low-density lipoprotein (LDL) receptors and, consequently, increased clearance of LDL-cholesterol (LDL-C) from the plasma. Structural differences among the available statins partially account for differences in their capacity to inhibit HMG-CoA reductase and their lipid-lowering efficacy, and for variability in other biological properties, such as their pharmacokinetic characteristics and their tolerability and propensity to interact with other drugs. In terms of pharmacokinetic properties, the synthetic (type II) HMG-CoA analogue atorvastatin exhibits a number of characteristics that are different to those of other members of the class, including a longer plasma half-life and metabolites that have an ability to inhibit HMG-CoA reductase equivalent to that of the parent drug. These characteristics are postulated to be responsible for a more prolonged inhibition of HMG-CoA reductase, and, hence, for the greater efficacy of atorvastatin in decreasing total and LDL-C levels relative to other statins (with the exception of rosuvastatin) noted in clinical trials in patients with dyslipidaemias. From the available clinical trial data, atorvastatin can be considered one of the most effective statins, not only by taking into account its effects on LDL-C and ability to meet recommended treatment guidelines for this parameter, but also its effect on triglyceride levels and capacity to modify lipoprotein composition in a non-atherogenic manner. Clinical studies with atorvastatin have also shed some light on the question as to whether it is better to focus on obtaining maximal reduction of LDL-C in at-risk patients or on cardiovascular outcomes. Cardiovascular event rates have been shown to be substantially lower in patients attaining LDL-C levels between 1.0 and 1.6 mmol/L (40-60 mg/dL) or < or =1.0 mmol/L (< or =40 mg/dL) compared with higher levels (>2.1-2.6 mmol/L [>80-100 mg/dL]). This finding reinforces the update of the National Cholesterol Education Programme's clinical practice guidelines, which recommend LDL-C levels <2.6 mmol/L (100 mg/dL) to be the goal of antihyperlipidaemic drug therapy in high-risk patients with CHD, with an optional therapeutic target of <1.8 mmol/L (70 mg/dL) in patients at very high risk.

Usefulness of hydrophilic vs lipophilic statins after acute myocardial infarction: subanalysis of MUSASHI-AMI

BACKGROUND

Statins are widely used to reduce blood levels of low-density lipoprotein-cholesterol (LDL-C). Each statin has unique pharmacokinetic properties; lipophilicity is one such property and relates to tissue selectivity.

METHODS AND RESULTS

The Multicenter Study for Aggressive Lipid-lowering Strategy by HMG-CoA Reductase Inhibitors in Patients with Acute Myocardial Infarction (MUSASHI-AMI) trial evaluated the effect of discretional statin treatment initiated within 96 h after onset of acute myocardial infarction (AMI) in Japanese patients. To clarify whether statin lipophilicity affects prognosis, a post hoc analysis of the MUSASHI-AMI database was performed. Patients who were assigned to receive statin were separated into 2 groups according to the lipophilicity of the statins they were administered: lipophilic statins (atorvastatin, fluvastatin, pitavastatin and simvastatin; LS group; n=131) or hydrophilic statins (pravastatin; HS group; n=110). There was no difference in baseline LDL-C concentrations between the 2 groups. Although LDL-C was decreased more potently in the LS than HS groups (-34% vs -19%; p=0.0069), acute coronary syndrome events tended to occur less frequently (3.6% vs 9.9%; p=0.0530) and the incidence of new Q-wave appearance in electrocardiogram was significantly lower (75% vs 89%; p=0.0056) in the HS than LS groups.

CONCLUSIONS

In normocholesterolemic Japanese patients after AMI, hydrophilic pravastatin could be superior to lipophilic statins at preventing new Q-wave appearance and reducing cardiovascular events.

Prevention of stroke and dementia by statin therapy: Experimental and clinical evidence of their pleiotropic effects

Stroke and dementia are major causes of disability in most countries. Epidemiological studies have demonstrated that statins (3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors) are likely to reduce the risk for developing these formidable disorders. The favorable outcomes in statin users may be attributable to not only cholesterol-dependent actions, but also various cholesterol-independent actions called "pleiotropic effects." Several clinical trials have suggested that statins decrease the incidence of stroke, especially ischemic stroke. Statins improve endothelial function, inhibit platelet activation, reduce blood coagulability, and suppress inflammatory reactions, all of which may contribute to the beneficial effects of the therapy. Statins also reduce the risk of vasospasm caused by subarachnoid hemorrhage (SAH). In addition, statins might inhibit the development and progression of Alzheimer's disease (AD), the dominant type of dementia in most industrialized countries, upstream of the amyloid cascade. In vitro studies have shown that statins modulate the metabolism of the beta-amyloid precursor protein (APP) and reduce the extracellular level of its proteolytic product, amyloid-beta (Abeta). The aggregated Abeta is cytotoxic, leading to formation of neurofibrillary tangles and neuronal loss in the brain. Inflammatory processes are active in AD and may contribute significantly to AD pathology. We review the experimental background regarding the pleiotropic effects of statins and summarize clinical trials that examined the preventative effects of statin therapy on stroke and dementia. We include current trials in which statin therapy is initiated within 24 hr of onset of acute ischemic stroke.

Statins and myotoxicity: a therapeutic limitation

Hydroxymethylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors represent the most successful class of drugs for the treatment of hypercholesterolaemia and dyslipidaemia implicated in the pathogenesis of coronary heart disease and atherosclerosis. However, the popular profile of statins in terms of efficacy has been maligned by its adverse events. The myotoxicity, ranging from mild myopathy to serious rhabdomyolysis, associated with HMG-CoA reductase inhibitors, during treatment of hypercholesterolaemia is of paramount importance. Rhabdomyolysis is a rare but idiosyncratic muscle wasting disorder of different etiologies. Statin-associated rhabdomyolysis causes skeletal muscle injury by self-perpetuating events leading to fatal irreversible renal damage through a series of biochemical reactions. Preferential distribution and action of statins in liver could be the key to minimise myotoxicity concerns. Hepato-specific distribution of statins is governed by various factors such as physicochemical properties, pharmacokinetic properties and selective transporter-mediated uptake in liver rather in extrahepatic cells. The interactions of statins with concomitant drugs of different classes merit attention for their safety profile. Although pharmacokinetic as well as pharmacodynamic interactions have been implicated in pathophysiology of statin-induced muscle wasting, the underlying mechanism is not clearly understood. Besides, pharmacokinetic and phramcodynamic factors, statin-associated myotoxcity may also implicate pharmacogenomic factors. The pharmacogenomics characterised by CYP polymorphism and other genetic factors is responsible for inter-individual variations to efficacy and tolerability of statins. The pathophysiological mechanisms may include statin-induced differences in cholesterol:phospholipid ratio, isoprenoid levels, small GTP binding proteins and apoptosis. However, the present understanding of pathophysiological mechanisms, does not offer a reliable approach to address the same at preclinical level. Although statin-associated myotoxicity affects compliance, quality of life of patient and discontinuation rate, yet the low incidence of myotoxicty including rhabdomyolysis and less severity of commonly occurring myopathy and myalgia do not raise doubts about the clinical efficacy and tolerability of statins. Medical management of myotoxicity seems to be pivotal for the proper compliance of patients with statin treatment. The appropriate and judicious use of drugs would substantially reduce the likelihood of developing clinically important myopathy.

Comparison of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) as inhibitors of cytochrome P450 2C8

Statins are involved in different types of drug interactions. Our objective was to study the effect of statins on cytochrome P450 (CYP) 2C8-mediated paclitaxel 6 alpha-hydroxylation by incubating paclitaxel and statins (0--100 microM) with pooled human liver microsomes. Simvastatin, lovastatin, atorvastatin and fluvastatin were the most potent inhibitors of CYP2C8 activity with K(i) (IC(50)) values of 7.1 (9.6) muM, 8.4 (15) microM, 16 (38) microM and 19 (37) microM, respectively. Cerivastatin, simvastatin acid and lovastatin acid were less potent inhibitors with K(i) (IC(50)) values ranging from 32 to 55 (30--67) microM. Rosuvastatin and pravastatin showed no appreciable effect on CYP2C8 activity even at 100 microM. In conclusion, all the statins tested, except rosuvastatin and pravastatin, had a significant inhibitory effect on the activity of CYP2C8 in vitro. Because many of the statins accumulate in the liver and because also their metabolites may inhibit CYP2C8 activity, in vivo studies are needed to investigate a possible interaction of simvastatin, lovastatin, atorvastatin and fluvastatin with CYP2C8 substrate drugs.

Statins: can the new generation make an impression?

Although large-scale statin trials have demonstrated significant reductions in cardiovascular risk, there are many patients who have a cardiovascular event despite receiving statin therapy. There is increasing evidence that larger reductions in low-density lipoprotein cholesterol (LDL-C) are associated with greater improvements in cardiovascular morbidity and mortality, which highlights the need for more efficacious statins. This article will review the lipid-altering effects of two new statins, rosuvastatin and pitavastatin. Rosuvastatin represents an advance in the pharmacological and clinical properties of other available agents. The large LDL-C reductions observed with rosuvastatin, even at the start dose of 10 mg and in patients switched from other statins to rosuvastatin 10 mg, should help to improve goal attainment, while reducing the need for dose titration. The ability of rosuvastatin to improve other elements of the lipid profile, such as high-density lipoprotein cholesterol (HDL-C), triglycerides and non-HDL-C, may be of utility in patients with diabetes and the metabolic syndrome. Increases in HDL-C, along with the greater efficacy of rosuvastatin for reducing LDL-C and non-HDL-C, may obviate the need for combination therapy. Results of a number of outcome studies with rosuvastatin are expected over the next 5 years, which will contribute to the evidence base for statin therapy and cardiovascular disease prevention.

Cholesterol-independent effects of statins and new therapeutic targets: ischemic stroke and dementia

The 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors, or "statins", are used as cholesterol-lowering agents worldwide. Statins inhibit cholesterol biosynthesis, leading to enhanced uptake of low-density lipoprotein (LDL) from the circulation via LDL receptors. This strong cholesterol-lowering action contributes to the beneficial effects of statins. For example, large clinical trials have demonstrated that statins significantly reduce cardiovascular risk. Recent research has shown that statins have other multiple actions involved in endothelial function, cell proliferation, inflammatory response, immunological reactions, platelet function, and lipid oxidation. These "pleiotropic actions" of statins probably provide a significant contribution to the reduction of cardiovascular events. This review summarizes the pleiotropic actions of statins in both basic and clinical studies. It also considers the potential for statin therapy in the treatment of stroke and dementia.

Pitavastatin

The growing number of trials that have highlighted the benefit of intensive lowering of total- and low density lipoprotein (LDL)-cholesterol levels especially with statins has created a need for more efficacious agents. Pitavastatin is a new synthetic 3-hydroxy-3-methyl glutaryl coenzyme A reductase inhibitor, which was developed, and has been available in Japan since July 2003. Metabolism of pitavastatin by the cytochrome P450 (CYP) system is minimal, principally through CYP 2C9, with little involvement of the CYP 3A4 isoenzyme, potentially reducing the risk of drug-drug interactions between pitavastatin and other drugs known to inhibit CYP enzymes. To date, human and animal studies have shown pitavastatin to be potentially as effective in lowering LDL-cholesterol levels as rosuvastatin; although, head-to-head studies are yet to be conducted.

New drugs for the treatment of hypercholesterolaemia

Endogenous and exogenous pathways determine plasma levels of cholesterol and lipoproteins. Plasma cholesterol levels and coronary heart disease risk can be reduced pharmacologically by decreasing cholesterol synthesis, increasing its elimination and/or reducing its absorption from the intestine. The more profound knowledge about cholesterol homeostasis has allowed the development of several lipid-lowering drugs with different mechanisms of action, with the purpose of reducing both morbidity and mortality associated with coronary heart disease. Two new and more potent 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins), also called superstatins (rosuvastatin and pitavastatin), are being studied for their ability to improve lipid profiles. Rosuvastatin is a potent, hepato-selective and relatively hydrophilic statin with a low propensity for muscle toxicity and drug interactions. Pitavastatin is another statin with a high oral bioavailability and minimal propensity for cytochrome p450-mediated drug interactions. Rosuvastatin seems to be more potent than other available statins while pitavastatin presents with a similar potency to that of atorvastatin. Another promising approach for lowering total and low-density lipoprotein cholesterol levels is inhibition of cholesterol absorption. A wide variety of new agents with the capacity for inhibiting the intestinal cholesterol absorption is currently being investigated. Ezetimibe is a selective cholesterol absorption inhibitor whose clinical efficacy has been recently demonstrated both in monotherapy and in combination with other lipid-lowering drugs. Colesevelam, a new bile acid sequestrant, has shown a clinical efficacy similar to that of other resins, with minimal gastrointestinal side effects, improving tolerability and patient compliance. Other lipid-lowering drugs with the ability to act at the enterocyte level, such as avasimibe and implitapide, are currently being investigated in humans.

Pitavastatin: efficacy and safety profiles of a novel synthetic HMG-CoA reductase inhibitor

The use of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors, statins, has been shown to reduce major cardiovascular events in both primary and secondary prevention, and statins became one of the most widely prescribed classes of drugs throughout the world. Previously, statins have been well tolerated and have shown favorable safety profiles. However, the voluntary withdrawal of cerivastatin from the market because of a disproportionate number of reports of rhabdomyolysis-associated deaths drew attention to the pharmacokinetic profile of statins, which may possibly have been related to serious drug-drug interactions. Pitavastatin (NK-104, previously called itavastatin or nisvastatin, Kowa Company Ltd., Tokyo) is a novel, fully synthetic statin, which has a potent cholesterol-lowering action. The short-term and long-term lipid-modifying effects of pitavastatin have already been investigated in subjects with primary hypercholesterolemia, heterozygous familial hypercholesterolemia, hypertriglyceridemia, and type-2 diabetes mellitus accompanied by hyperlipidemia. Within the range of daily doses from 1 to 4 mg, the efficacy of pitavastatin as a lipid-lowering drug seems to be similar, or potentially superior, to that of atorvastatin. According to the results of pharmacokinetic studies, pitavastatin showed favorable and promising safety profile; it was only slightly metabolized by the cytochrome P450 (CYP) system, its lactone form had no inhibitory effects on the CYP3A4-mediated metabolism of concomitantly administered drugs; P-glycoprotein-mediated transport did not play a major role in its disposition, and pitavastatin did not inhibit P-glycoprotein activity. It could be concluded that pitavastatin could provide a new and potentially better therapeutic choice for lipid-modifying therapy than do the currently available statins. The efficacy and safety of higher dose treatment, as well as its long-term effects in the prevention of coronary artery disease, should be further investigated.

Rosuvastatin: a new HMG-CoA reductase inhibitor for the treatment of hypercholesterolemia

Because of their excellent tolerability and their positive impact on lipid parameters, 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) have become the drugs of first choice for many patients with dyslipidemia. Rosuvastatin is an investigational statin in the U.S. with a number of favorable characteristics, which include low lipophilicity, high hepatocyte selectivity, minimal metabolism, and a low propensity for cytochrome P450 drug interactions. Rosuvastatin has been studied at doses ranging from 1 to 80 mg. In comparative clinical trials, rosuvastatin given at 5 to 10 mg/day reduced low-density lipoprotein cholesterol to a significantly greater extent than atorvastatin 10 mg/day, pravastatin 20 mg/day, and simvastatin 20 mg/day. In addition, rosuvastatin exhibited beneficial effects on other lipid parameters such as high-density lipoprotein cholesterol and triglycerides. Rosuvastatin's safety profile was demonstrated to be similar to those of other statins. Given its favorable pharmacokinetic and pharmacodynamic characteristics, rosuvastatin is likely to become a valuable addition to the statin drug class. The author reviews the pharmacologic and pharmacokinetic properties of this new statin.