Mechanistic studies on metabolic interactions between gemfibrozil and statins

Drug-drug interactions between pemafibrate and statins on pharmacokinetics in healthy male volunteers: Open-label, randomized, 6-sequence, 3-period crossover studies

Elevated triglyceride levels are associated with an increased risk of cardiovascular events despite guideline-based statin treatment of low-density lipoprotein cholesterol. Peroxisome proliferator-activated receptor α (PPARα) agonists exert a significant triglyceride-lowering effect. However, combination therapy of PPARα agonists with statins poses an increased risk of rhabdomyolysis, which is rare but a major concern of the combination therapy. Pharmacokinetic interaction is suspected to be a contributing factor to the risk. To examine the potential for combination therapy with the selective PPARα modulator (SPPARMα) pemafibrate and statins, drug-drug interaction studies were conducted with open-label, randomized, 6-sequence, 3-period crossover designs for the combination of pemafibrate 0.2 mg twice daily and each of 6 statins once daily: pitavastatin 4 mg/day (n = 18), atorvastatin 20 mg/day (n = 18), rosuvastatin 20 mg/day (n = 29), pravastatin 20 mg/day (n = 18), simvastatin 20 mg/day (n = 20), and fluvastatin 60 mg/day (n = 19), involving healthy male volunteers. The pharmacokinetic parameters of pemafibrate and each of the statins were similar regardless of coadministration. There was neither an effect on the systemic exposure of pemafibrate nor a clinically important increase in the systemic exposure of any of the statins on the coadministration although the systemic exposure of simvastatin was reduced by about 15% and its open acid form by about 60%. The HMG-CoA reductase inhibitory activity in plasma samples from the simvastatin and pemafibrate combination group was about 70% of that in the simvastatin alone group. In conclusion, pemafibrate did not increase the systemic exposure of statins, and vice versa, in healthy male volunteers.

Neuroprotective effects of gemfibrozil in neurological disorders: Focus on inflammation and molecular mechanisms

BACKGROUND

Gemfibrozil (Gem) is a drug that has been shown to activate PPAR-α, a nuclear receptor that plays a key role in regulating lipid metabolism. Gem is used to lower the levels of triglycerides and reduce the risk of coronary heart disease in patients. Experimental studies in vitro and in vivo have shown that Gem can prevent or slow the progression of neurological disorders (NDs), including cerebral ischemia (CI), Alzheimer's disease (AD), Parkinson's disease (PD), and multiple sclerosis (MS). Neuroinflammation is known to play a significant role in these disorders.

METHOD

The literature review for this study was conducted by searching Scopus, Science Direct, PubMed, and Google Scholar databases.

RESULT

The results of this study show that Gem has neuroprotective effects through several cellular and molecular mechanisms such as: (1) Gem has the ability to upregulate pro-survival factors (PGC-1α and TFAM), promoting the survival and function of mitochondria in the brain, (2) Gem strongly inhibits the activation of NF-κB, AP-1, and C/EBPβ in cytokine-stimulated astroglial cells, which are known to increase the expression of iNOS and the production of NO in response to proinflammatory cytokines, (3) Gem protects dopamine neurons in the MPTP mouse model of PD by increasing the expression of PPARα, which in turn stimulates the production of GDNF in astrocytes, (4) Gem reduces amyloid plaque pathology, reduces the activity of glial cells, and improves memory, (5) Gem increases myelin genes expression (MBP and CNPase) via PPAR-β, and (6) Gem increases hippocampal BDNF to counteract depression.

CONCLUSION

According to the study, Gem was investigated for its potential therapeutic effect in NDs. Further research is needed to fully understand the therapeutic potential of Gem in NDs.

The Role of Triglyceride-rich Lipoproteins and Their Remnants in Atherosclerotic Cardiovascular Disease

Atherosclerotic cardiovascular disease (ASCVD) is the world's leading cause of death. ASCVD has multiple mediators that therapeutic interventions target, such as dyslipidaemia, hypertension, diabetes and heightened systemic inflammatory tone, among others. LDL cholesterol is one of the most well-studied and established mediators targeted for primary and secondary prevention of ASCVD. However, despite the strength of evidence supporting LDL cholesterol reduction by multiple management strategies, ASCVD events can still recur, even in patients whose LDL cholesterol has been very aggressively reduced. Hypertriglyceridaemia and elevated levels of triglyceride-rich lipoproteins (TRLs) may be key contributors to ASCVD residual risk. Several observational and genetic epidemiological studies have highlighted the causal role of triglycerides within the TRLs and/or their remnant cholesterol in the development and progression of ASCVD. TRLs consist of intestinally derived chylomicrons and hepatically synthesised very LDL. Lifestyle modification has been considered the first line intervention for managing hypertriglyceridaemia. Multiple novel targeted therapies are in development, and have shown efficacy in the preclinical and clinical phases of study in managing hypertriglyceridaemia and elevated TRLs. This comprehensive review provides an overview of the biology, pathogenicity, epidemiology, and genetics of triglycerides and TRLs, and how they impact the risk for ASCVD. In addition, we provide a summary of currently available and novel emerging triglyceride-lowering therapies in development.

Inhibition of CYP2C8 by Acyl Glucuronides of Gemfibrozil and Clopidogrel: Pharmacological Significance, Progress and Challenges

The lipid-regulating drug gemfibrozil is a useful medication for reducing high cholesterol and triglycerides in the blood. In addition to oxidation, it undergoes extensive glucuronidation to produce gemfibrozil acyl glucuronide, which is a known mechanism-based inactivator of cytochrome P450 (CYP) 2C8. Such selective and time-dependent inhibition results in clinically important drug–drug interactions (DDI) with the drugs metabolized by CYP2C8. Similarly, the acyl glucuronide of clopidogrel, a widely used antiplatelet agent, is a potent time-dependent inhibitor of CYP2C8 that demonstrated significant DDI with the substrates of CYP2C8. Current progress in atomic-level understanding mostly involves studying how different drugs bind and undergo oxidation in the active site of CYPs. It is not clear how an acyl glucuronide metabolite of the drug gemfibrozil or clopidogrel interacts in the active site of CYP2C8 and selectively inhibit the enzyme. This mini-review summarizes the current knowledge on some of the important clinical DDI caused by gemfibrozil and clopidogrel due to the inhibition of CYP2C8 by acyl glucuronide metabolites of these drugs. Importantly, it examines recent developments and potential applications of structural biology tools to elucidate the binding and orientation of gemfibrozil acyl glucuronide and clopidogrel acyl glucuronide in the active site near heme that contributes to the inhibition and inactivation of CYP2C8.

CYP3A5*3 and SLCO1B1 c.521T>C Polymorphisms Influence the Pharmacokinetics of Atorvastatin and 2-Hydroxy Atorvastatin

There is a large variability in individual responses to atorvastatin administration. This study assessed the pharmacogenetic effects of solute carrier organic anion transporter family member 1B1 (SLCO1B1, c.388A>G and c.521T>C) and cytochrome P450 3A5 (CYP3A5, CYP3A5*3) genetic polymorphisms on the pharmacokinetics of atorvastatin and its active metabolite, 2-hydroxy (2-OH) atorvastatin, in 46 individuals who were administered a clinically used single oral dosage of 80 mg. The Cmax and AUC of atorvastatin in CYP3A5*3/*3 carriers were 2.6- and 2.8-fold higher, respectively, than those in CYP3A5*1/*1 carriers, and similar results were observed for 2-OH atorvastatin pharmacokinetics. SLCO1B1 c.521T>C also increased the AUC of atorvastatin and 2-OH atorvastatin. The AUC ratio of atorvastatin and 2-OH atorvastatin were not affected by SLCO1B1 c.388A>G or c.521T>C, whereas CYP3A5*3 reduced the AUC ratio. In an analysis evaluating the simultaneous effect of the SLCO1B1 c.521T>C and CYP3A5*3 polymorphisms, SLCO1B1 c.521TT/CYP3A5*1/*1 carriers showed lower Cmax and AUC values for atorvastatin and 2-OH atorvastatin than in individuals with the SLCO1B1 c.521T>C and/or CYP3A5*3 genotypes. Among the participants with the SLCO1B1 c.521TT genotype, the CYP3A5*3 carriers had a higher systemic exposure to atorvastatin and 2-OH atorvastatin than the CYP3A5*1/*1 carriers. Thus, SLCO1B1 c.521T>C and CYP3A5*3 polymorphisms affect the pharmacokinetics of atorvastatin and 2-OH atorvastatin.

Comparison of Sweated and Non-Sweated Ethanol Extracts of Salvia miltiorrhiza Bge. (Danshen) Effects on Human and rat Hepatic UDP-Glucuronosyltransferase and Preclinic Herb-Drug Interaction Potential Evaluation

BACKGROUND

The ethanol of Danshen (DEE) preparation has been widely used to treat cardiac-cerebral disease and cancer. Sweating is one of the primary processing methods of Danshen, which greatly influenced its quality and pharmacological properties. Sweated and non-sweated DEE preparation combining with various synthetic drugs, adding up the possibility of herbal-drug interactions.

OBJECTIVE

This study explored the effects of sweated and non-sweated DEE on human and rat hepatic UGT enzymes expression and activity and proposed a potential mechanism.

METHODS

The expression of two processed DEE on rat UGT1A, UGT2B and nuclear receptors including pregnane X receptor (PXR), constitutive androstane receptor (CAR), and peroxisome proliferator-activated receptor α (PPARα) were investigated after intragastric administration in rats by Western blot. Enzyme activity of DEE and its active ingredients (Tanshinone I, Cryptotanshinone, and Tanshinone I) on UGT isoenzymes was evaluated by quantifying probe substrate metabolism and metabolite formation in vitro using Ultra Performance Liquid Chromatography.

RESULTS

The two processed DEE (5.40 g/kg) improved UGT1A (P<0.01) and UGT2B (P<0.05) protein expression, and the non-sweated DEE (2.70 g/kg) upregulated UGT2B expression protein (P<0.05), compared with the CMCNa group. On day 28, UGT1A protein expression was increased (P<0.05) both in two processed DEE groups, meanwhile the non-sweated DEE significantly enhanced UGT2B protein expression (P<0.05) on day 21, compared with the CMCNa group. The process underlying this mechanism involved with the activation of nuclear receptors CAR, PXR, and PPARα; In vitro, sweated DEE (0-80 μg/mL) significantly inhibited the activity of human UGT1A7 (P<0.05) and rat UGT1A1, 1A8, and 1A9 (P<0.05). Non-sweated DEE (0-80 μg/mL) dramatically suppressed the activity of human UGT1A1, 1A3, 1A6, 1A7, 2B4, and 2B15, and rat UGT1A1, 1A3, 1A7, and 1A9 (P<0.05); Tanshinone I (0-1 μM) inhibited the activity of human UGT1A3, 1A6, and 1A7 (P<0.01) and rat UGT1A3, 1A6, 1A7, and 1A8 (P<0.05). Cryptotanshinone (0-1 μM) remarkably inhibited the activity of human UGT1A3 and 1A7 (P<0.05) and rat UGT1A7, 1A8, and 1A9 (P<0.05). Nonetheless, Tanshinone IIA (0-2 μM) is not a potent UGT inhibitor both in humans and rats; Additionally, there existed significant differences between two processed DEE in expression of PXR, and the activity of human UGT1A1, 1A3, 1A6, and 2B15 and rat UGT1A3 and 2B15 (P<0.05).

CONCLUSION

The effects of two processed DEE on hepatic UGT enzyme expression and activity were different. Accordingly, the combined usage of related UGTs substrates with DEE and its monomer components preparations may call for caution, depending on the drug's exposure-response relationship and dose adjustment. Besides, it is vital to pay attention to the distinction between sweated and non-sweated Danshen in clinic, which exerted an important influence on its pharmacological activity.

Addition of statins to the standard treatment in patients with cirrhosis: Safety and efficacy

This review summarizes the safety and efficacy of statins in patients with cirrhosis. Due to concerns about the safety of statins in patients with impaired liver function, they have recently been investigated as a potential treatment option in cirrhosis. The most clinically significant adverse event is statin-related myopathy, and this may be related to the high serum statin concentrations in the setting of severely impaired liver function. Rhabdomyolysis is the most serious and potentially life-threatening manifestation. It has recently been demonstrated that the recommended dose of simvastatin in patients with decompensated cirrhosis would be 20 mg/d because higher values, such as 40 mg/d, are associated with many adverse events, especially muscle injury. Likewise, simvastatin should not be administered to patients with Model for End-stage Liver Disease score > 12 and/or Child-Pugh class C because of the high risk of severe muscle injury. Due to the pleiotropic effects, the focus on statins has shifted from being considered harmful to something useful. Through these effects, statins could prevent liver-related morbidity and mortality in cirrhotic patients. Observational studies in large populations of patients with cirrhosis have shown that treatment with statins to decrease high cholesterol levels was associated with a reduced risk of hepatic decompensation, hepatocellular carcinoma development and death. The few randomized controlled trials in patients with cirrhosis and portal hypertension showed that statins lower portal pressure, quite likely through a reduction in hepatic resistance. Another large randomized controlled trial in patients with variceal bleeding showed that simvastatin in addition to standard of care did not prevent rebleeding but improved survival rate. Despite these encouraging outcomes, the quality of the evidence regarding the use of statins is low or very low due to the observational characteristics of most of the studies involved. Therefore, it is advisable to perform further randomized controlled trials on a large series of patients with hard clinical endpoints, using different statin types and varying doses. The objectives would be to prevent liver-related morbidity and mortality rather than treating cirrhosis complications to take additional information that makes it possible to add statins to the standard of care of these patients.

New Perspectives on Atherogenic Dyslipidaemia and Cardiovascular Disease

Over the past few decades, atherogenic dyslipidaemia has become one of the most common phenotypic presentations of lipid abnormalities, being strongly and unequivocally associated with an increased risk of cardiovascular (CV) disease. Despite the excellent results achieved from statin and non-statin management of LDL cholesterol and CV events prevention, there still remains a significant residual risk, associated with the prevalence of non-LDL cholesterol lipid patterns characterised by elevated triglyceride levels, low HDL cholesterol, a preponderance of small and dense LDL particles, accumulation of remnant lipoproteins and postprandial hyperlipidaemia. These qualitative and quantitative lipid modifications are largely associated with insulin resistance, type 2 diabetes and obesity, the prevalence of which has grown to epidemic proportions throughout the world. In this review, we analyse the pathophysiology of this particular dyslipidaemia, its relationship with the development of atherosclerotic CV disease and, finally, briefly describe the therapeutic approaches, including changes in lifestyle and current pharmacological interventions to manage these lipid alterations aimed at preventing CV events.

Tendon rupture associated with concomitant simvastatin and gemfibrozil use: Biological and pharmacokinetic implications

Tendon or muscle rupture is a rare complication of statins that could potentially be disabling and result in a significant burden to patients. The co-administration of statin and gemfibrozil should warrant prescribers' awareness of tendon-related complications of statin use, particularly in high-risk populations with poor renal function or musculoskeletal comorbidities.

The UDP-Glycosyltransferase (UGT) Superfamily: New Members, New Functions, and Novel Paradigms

UDP-glycosyltransferases (UGTs) catalyze the covalent addition of sugars to a broad range of lipophilic molecules. This biotransformation plays a critical role in elimination of a broad range of exogenous chemicals and by-products of endogenous metabolism, and also controls the levels and distribution of many endogenous signaling molecules. In mammals, the superfamily comprises four families: UGT1, UGT2, UGT3, and UGT8. UGT1 and UGT2 enzymes have important roles in pharmacology and toxicology including contributing to interindividual differences in drug disposition as well as to cancer risk. These UGTs are highly expressed in organs of detoxification (e.g., liver, kidney, intestine) and can be induced by pathways that sense demand for detoxification and for modulation of endobiotic signaling molecules. The functions of the UGT3 and UGT8 family enzymes have only been characterized relatively recently; these enzymes show different UDP-sugar preferences to that of UGT1 and UGT2 enzymes, and to date, their contributions to drug metabolism appear to be relatively minor. This review summarizes and provides critical analysis of the current state of research into all four families of UGT enzymes. Key areas discussed include the roles of UGTs in drug metabolism, cancer risk, and regulation of signaling, as well as the transcriptional and posttranscriptional control of UGT expression and function. The latter part of this review provides an in-depth analysis of the known and predicted functions of UGT3 and UGT8 enzymes, focused on their likely roles in modulation of levels of endogenous signaling pathways.

Assessment of the Risk of Rhabdomyolysis and Myopathy During Concomitant Treatment with Ticagrelor and Statins

The introduction of ticagrelor, one of the first directly-acting oral antiplatelet drugs, provided new possibilities in the prevention of thrombotic events in patients with acute coronary syndromes (ACS). Current guidelines recommend ticagrelor in dual antiplatelet therapy with aspirin over clopidogrel for prevention of stent thrombosis in patients with ACS. Moreover, in the management of ACS, lipid-lowering treatment with high-intensity statin therapy is advised for secondary prevention of cardiovascular events over the long term. Despite the apparent advantages of combined antiplatelet and lipid-lowering treatments, a possible interaction between statins and ticagrelor may lead to myopathy and rhabdomyolysis. In this review, relevant information was gathered on the ticagrelor-statin interaction that might lead to this life-threatening condition. This review focuses on the most widely used statins—simvastatin, atorvastatin, and rosuvastatin. Possible mechanisms of this interaction are discussed, including CYP3A4 isoenzymes, organic anion transporter polypeptide (OATPs), P-glycoprotein and glucuronidation. PubMed database was searched for relevant case reports and all data gathered from the introduction of ticagrelor to March 2018 are presented and discussed. In summary, co-administration of statins and ticagrelor was found to be relatively safe in routinely prescribed doses. However, caution should be exercised, especially in elder populations.

Rhabdomyolysis after co-administration of a statin and fusidic acid: an analysis of the literature and of the WHO database of adverse drug reactions

Following a severe case of rhabdomyolysis in our University Hospital after a co-administration of atorvastatin and fusidic acid, we describe this interaction as this combination is not clearly contraindicated in some countries, particularly for long-term treatment by fusidic acid. All cases of rhabdomyolysis during a co-administration of a statin and fusidic acid were identified in the literature and in the World and Health Organization database, VigiBase^® . In the literature, 29 cases of rhabdomyolysis were identified; mean age was 66 years, median duration of co-administration before rhabdomyolysis occurrence was 21 days, 28% of cases were fatal. In the VigiBase^® , 182 cases were retrieved; mean age was 68 years, median duration of co-administration before rhabdomyolysis was 31 days and 24% of cases were fatal. Owing to the high fatality associated with this co-administration and the long duration of treatment before rhabdomyolysis occurrence, fusidic acid should be used if there is no appropriate alternative, as long as statin therapy is interrupted for the duration of fusidic acid therapy, and perhaps a week longer. Rarely will interruption of this sort have adverse consequences for the patient.

Inhibitory Effect of Sauchinone on UDP-Glucuronosyltransferase (UGT) 2B7 Activity

Herb-drug interaction (HDI) limits clinical application of herbs and drugs, and inhibition of herbs towards uridine diphosphate (UDP)-glucuronosyltransferases (UGTs) has gained attention as one of the important reasons to cause HDIs. Sauchinone, an active lignan isolated from aerial parts of Saururus chinensis (Saururacease), possesses anti-oxidant, anti-inflammatory, and anti-viral activities. In pharmacokinetics of sauchinone, sauchinone is highly distributed to the liver, forming extensive metabolites of sauchinone via UGTs in the liver. Thus, we investigated whether sauchinone inhibited UGTs to explore potential of sauchinone-drug interactions. In human liver microsomes (HLMs), sauchinone inhibited activities of UGT1A1, 1A3, 1A6, and 2B7 with IC₅₀ values of 8.83, 43.9, 0.758, and 0.279 μM, respectively. Sauchinone also noncompetitively inhibited UGT1A6 and 2B7 with K_i values of 1.08 and 0.524 μM, respectively. In in vivo interaction study using mice, sauchinone inhibited UGT2B7-mediated zidovudine metabolism, resulting in increased systemic exposure of zidovudine when sauchinone and zidovudine were co-administered together. Our results indicated that there is potential HDI between sauchinone and drugs undergoing UGT2B7-mediated metabolism, possibly contributing to the safe use of sauchinone and drug combinations.

In Vitro Comparative Study of the Inhibitory Effects of Mangiferin and Its Aglycone Norathyriol towards UDP-Glucuronosyl Transferase (UGT) Isoforms

Mangiferin (MGF), the predominant constituent of extracts of the mango plant Mangifera Indica L., has been investigated extensively because of its remarkable pharmacological effects. In vitro recombinant UGTs-catalyzed glucuronidation of 4-methylumbelliferone (4-MU) was used to investigate the inhibition of mangiferin and aglycone norathyriol towards various isoforms of UGTs in our study, which evaluated the inhibitory capacity of MGF and its aglycone norathyriol (NTR) towards UDP-glucuronosyltransferase (UGT) isoforms. Initial screening experiment showed that deglycosylation of MGF into NTR strongly increased the inhibitory effects towards almost all the tested UGT isoforms at a concentration of 100 μM. Kinetic experiments were performed to further characterize the inhibition of UGT1A3, UGT1A7 and UGT1A9 by NTR. NTR competitively inhibited UGT1A3, UGT1A7 and UGT1A9, with an IC₅₀ value of 8.2, 4.4, and 12.3 μM, and a Ki value of 1.6, 2.0, and 2.8 μM, respectively. In silico docking showed that only NTR could dock into the activity cavity of UGT1A3, UGT1A7 and UGT1A9. The binding free energy of NTR to UGT1A3, 1A7, 1A9 were −7.4, −7.9 and −4.0 kcal/mol, respectively. Based on the inhibition evaluation standard ([I]/Ki < 0.1, low possibility; 0.1 < [I]/Ki < 1, medium possibility; [I]/Ki > 1, high possibility), an in vivo herb–drug interaction between MGF/NTR and drugs mainly undergoing UGT1A3-, UGT1A7- or UGT1A9-catalyzed metabolism might occur when the plasma concentration of NTR is above 1.6, 2.0 and 2.8 μM, respectively.

Statin-Associated Side Effects

Hydroxy-methyl-glutaryl-coenzyme A (HMG-CoA) reductase inhibitors or statins are well tolerated, but associated with various statin-associated symptoms (SAS), including statin-associated muscle symptoms (SAMS), diabetes mellitus (DM), and central nervous system complaints. These are "statin-associated symptoms" because they are rare in clinical trials, making their causative relationship to statins unclear. SAS are, nevertheless, important because they prompt dose reduction or discontinuation of these life-saving mediations. SAMS is the most frequent SAS, and mild myalgia may affect 5% to 10% of statin users. Clinically important muscle symptoms, including rhabdomyolysis and statin-induced necrotizing autoimmune myopathy (SINAM), are rare. Antibodies against HMG-CoA reductase apparently provoke SINAM. Good evidence links statins to DM, but evidence linking statins to other SAS is largely anecdotal. Management of SAS requires making the possible diagnosis, altering or discontinuing the statin treatment, and using alternative lipid-lowering therapy.

Peroxisome Proliferator-Activated Receptor α Activation Suppresses Cytochrome P450 Induction Potential in Mice Treated with Gemfibrozil

Gemfibrozil, a peroxisome proliferator-activated receptor α (PPARα) agonist, is widely used for hypertriglyceridaemia and mixed hyperlipidaemia. Drug-drug interaction of gemfibrozil and other PPARα agonists has been reported. However, the role of PPARα in cytochrome P450 (CYP) induction by fibrates is not well known. In this study, wild-type mice were first fed gemfibrozil-containing diets (0.375%, 0.75% and 1.5%) for 14 days to establish a dose-response relationship for CYP induction. Then, wild-type mice and Pparα-null mice were treated with a 0.75% gemfibrozil-containing diet for 7 days. CYP3a, CYP2b and CYP2c were induced in a dose-dependent manner by gemfibrozil. In Pparα-null mice, their mRNA level, protein level and activity were induced more than those in wild-type mice. So, gemfibrozil induced CYP, and this action was inhibited by activated PPARα. These data suggested that the induction potential of CYPs was suppressed by activated PPARα, showing a potential role of this receptor in drug-drug interactions and metabolic diseases treated with fibrates.

The Toxicology of HMG—CoA Reductase Inhibitors: Prediction of Human Risk

The discovery that 3-hydroxy-3-methyglutaryl coenzyme A reductase was a rate-determining step in the biosynthesis of cholesterol led to the discovery of inhibitors of this enzyme. To support the development of these agents (statins) as potential hypocholesterolemic drugs, a variety of preclinical studies were conducted in several animal species. Not unexpectedly due to the central role played by mevalonic acid and its products including cholesterol in development and maintenance of cellular homeostasis, administration of high dosage levels of these agents led to the expression of a broad variety of adverse effects in many different tissues. Using the tools of toxicologic pathology and classical risk assessment, these varied toxicities were evaluated by many groups relative to the conditions of use in human therapy and a perspective was developed on potential human risk. These approaches of mechanism-based risk assessment predicted that most of the adverse effects observed in animals would not be seen under conditions of human use and supported the successful introduction of one of the most important classes of human medicines.

In Vitro Metabolism of Montelukast by Cytochrome P450s and UDP-Glucuronosyltransferases

Montelukast has been recommended as a selective in vitro and in vivo probe of cytochrome P450 (P450) CYP2C8 activity, but its selectivity toward this enzyme remains unclear. We performed detailed characterization of montelukast metabolism in vitro using human liver microsomes (HLMs), expressed P450s, and uridine 5'-diphospho-glucuronosyltransferases (UGTs). Kinetic and inhibition experiments performed at therapeutically relevant concentrations reveal that CYP2C8 and CYP2C9 are the principal enzymes responsible for montelukast 36-hydroxylation to 1,2-diol. CYP3A4 was the main catalyst of montelukast sulfoxidation and stereoselective 21-hydroxylation, and multiple P450s participated in montelukast 25-hydroxylation. We confirmed direct glucuronidation of montelukast to an acyl-glucuronide. We also identified a novel peak that appears consistent with an ether-glucuronide. Kinetic analysis in HLMs and experiments in expressed UGTs indicate that both metabolites were exclusively formed by UGT1A3. Comparison of in vitro intrinsic clearance in HLMs suggest that direct glucuronidation may play a greater role in the overall metabolism of montelukast than does P450-mediated oxidation, but the in vivo contribution of UGT1A3 needs further testing. In conclusion, our in vitro findings provide new insight toward montelukast metabolism. The utility of montelukast as a probe of CYP2C8 activity may be compromised owing to involvement of multiple P450s and UGT1A3 in its metabolism.

In Vivo and in Vitro Study on Drug-Drug Interaction of Lovastatin and Berberine from Pharmacokinetic and HepG2 Cell Metabolism Studies

Background: We assumed that the pharmacokinetics of lovastatin could be changed by the induction effect of berberine. Methods: An UPLC-MS/MS method was developed and validated for the pharmacokinetics tudy of lovastatin to investigate the in vivo drug-drug interactions between lovastatin and berberine. SD male rats were random divided into lovastatin group and berberine induced prior to lovastatin group for the in vivo pharmacokinetic studies. Meanwhile HepG2 cells were induced by berberine for three days to study the metabolism of lovastatin. Results: The AUC (p < 0.01) and C_max (p < 0.01) could be significantly decreased in the berberine-induced group in vivo, and the metabolic activity of HepG2 cell ccould be increased by berberine induction in vitro. The metabolism parameters of lovastatin such as CL, V_max and K_m were increased after the induction of berberine. From the pharmacokinetic study of lovastatin induced with berberine, we obtained pharmacokinetic parameters which are compliance with the metabolic parameters of lovastatin in HepG2 cells with berberine induction in vitro. Conclusions: From the in vivo pharmacokinetics study and the HepG2 cell metabolism study in vitro, berberine could be an inducer for the metabolism of lovastatin according to our previous research on berberine induction effects on HepG2 cells, which may be relevant to the fact that berberine possesses induction effects through the CYP 450 3A4 enzyme.

Antilipidemic Drug Therapy Today and in the Future

The armamentarium for the treatment of dyslipidemia today comprises six different modes of action with overall around 24 different drugs. The treatment of lipid disorders was revolutionized with the introduction of statins which have become the most important therapeutic option available today to reduce and prevent atherosclerosis and its detrimental consequences like cardiovascular diseases and stroke. With and optimized reduction of elevated LDL levels with statins, the risk for cardiovascular diseases (CVD) can be reduced by 30%, indicating a residual remaining risk of 70% for the development and progression of CVD notifying still a high medical need for more effective antilipidemic drugs. Consequently, the search for novel lipid-modifying drugs is still one of the most active areas in research and development in the pharmaceutical industry. Major focus lies on approaches to LDL-lowering drugs superior to statins with regard to efficacy, safety, and patient compliance and on approaches modifying plasma levels and functionality of HDL particles based on the clinically validated inverse relationship between high-plasma HDL levels and the risk for CVD. The available drugs today for the treatment of dyslipidemia are small organic molecules or nonabsorbable polymers for binding of bile acids to be applied orally. Besides small molecules for novel targets, biological drugs such as monoclonal antibodies, antisense or gene-silencing oligonucleotides, peptidomimetics, reconstituted synthetic HDL particles and therapeutic proteins are novel approaches in clinical development are which have to be applied by injection or infusion. The promising clinical results of several novel drug candidates, particularly for LDL cholesterol lowering with monoclonal antibodies raised against PCSK9, may indicate more than a decade after the statins, the entrance of new breakthrough therapies to treat lipid disorders.

ω-3 carboxylic acids for hypertriglyceridemia

INTRODUCTION

ω-3 carboxylic acids (ω3 CA), also called ω3 free fatty acids (ω3 FFA), with the trade name Epanova™ is a new formulation of eicosapentaenoic acid (EPA) + docosahexaenoic acid (DHA) approved for the treatment of severe hypertriglyceridemia. The FFA form of EPA and DHA is associated with higher bioavailability than other forms of ω3 fatty acids, potentially resulting in efficacy at lower doses and less dependence on meal relationship.

AREAS COVERED

The efficacy and safety of ω3 CA from clinical trials as well as PK and PD data will be reviewed. The mechanism of action of ω3 fatty acids in the lowering of triglycerides (TG) will be discussed and comparison is made with ω3 ethyl ester compounds.

EXPERT OPINION

ω3 CA are a unique form of ω3 fatty acids that appear safe and effective in lowering serum TG and offer the possibility of better patient compliance due to lower-dose efficacy and the ability to take with or without food. ω3 CA lowered TG by 26 and 31% for the 2 and 4 g/day doses, respectively, and Apo CIII was also lowered 11 and 14%, respectively, as well.

Transcriptional regulation of human UDP-glucuronosyltransferase genes

Glucuronidation is an important metabolic pathway for many small endogenous and exogenous lipophilic compounds, including bilirubin, steroid hormones, bile acids, carcinogens and therapeutic drugs. Glucuronidation is primarily catalyzed by the UDP-glucuronosyltransferase (UGT) 1A and two subfamilies, including nine functional UGT1A enzymes (1A1, 1A3-1A10) and 10 functional UGT2 enzymes (2A1, 2A2, 2A3, 2B4, 2B7, 2B10, 2B11, 2B15, 2B17 and 2B28). Most UGTs are expressed in the liver and this expression relates to the major role of hepatic glucuronidation in systemic clearance of toxic lipophilic compounds. Hepatic glucuronidation activity protects the body from chemical insults and governs the therapeutic efficacy of drugs that are inactivated by UGTs. UGT mRNAs have also been detected in over 20 extrahepatic tissues with a unique complement of UGT mRNAs seen in almost every tissue. This extrahepatic glucuronidation activity helps to maintain homeostasis and hence regulates biological activity of endogenous molecules that are primarily inactivated by UGTs. Deciphering the molecular mechanisms underlying tissue-specific UGT expression has been the subject of a large number of studies over the last two decades. These studies have shown that the constitutive and inducible expression of UGTs is primarily regulated by tissue-specific and ligand-activated transcription factors (TFs) via their binding to cis-regulatory elements (CREs) in UGT promoters and enhancers. This review first briefly summarizes published UGT gene transcriptional studies and the experimental models and tools utilized in these studies, and then describes in detail the TFs and their respective CREs that have been identified in the promoters and/or enhancers of individual UGT genes.

HDL and cognition in neurodegenerative disorders

High-density lipoproteins (HDLs) are a heterogeneous group of lipoproteins composed of various lipids and proteins. HDL is formed both in the systemic circulation and in the brain. In addition to being a crucial player in the reverse cholesterol transport pathway, HDL possesses a wide range of other functions including anti-oxidation, anti-inflammation, pro-endothelial function, anti-thrombosis, and modulation of immune function. It has been firmly established that high plasma levels of HDL protect against cardiovascular disease. Accumulating evidence indicates that the beneficial role of HDL extends to many other systems including the central nervous system. Cognition is a complex brain function that includes all aspects of perception, thought, and memory. Cognitive function often declines during aging and this decline manifests as cognitive impairment/dementia in age-related and progressive neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis. A growing concern is that no effective therapy is currently available to prevent or treat these devastating diseases. Emerging evidence suggests that HDL may play a pivotal role in preserving cognitive function under normal and pathological conditions. This review attempts to summarize recent genetic, clinical and experimental evidence for the impact of HDL on cognition in aging and in neurodegenerative disorders as well as the potential of HDL-enhancing approaches to improve cognitive function.

Dyslipidemia in women: etiology and management

Dyslipidemia is highly prevalent among women. The management of dyslipidemia is a cornerstone in the prevention of both primary and secondary cardiovascular events, such as myocardial infarction, ischemic stroke, and coronary death. All major international guidelines on the treatment of dyslipidemia recommend similar approaches to the management of dyslipidemia in both men and women. Estrogen replacement therapy should not be considered as a therapeutic option for managing dyslipidemia in women. The reduction of atherogenic lipoprotein burden (reducing low-density lipoprotein cholesterol and non-high-density lipoprotein cholesterol based on risk-stratified thresholds and treatment targets) provided the framework for managing dyslipidemia in the US, Europe, Canada, and elsewhere in the world. Very recently, new guidelines in the US have changed this paradigm, whereby rather than focusing on treatment targets, risk now defines the intensity of treatment with statin therapy, with no specific goals for what level of low-density lipoprotein cholesterol should be attained. It is not clear if this will lead to changes in lipid guidelines in other parts of the world. In the meantime, region-specific guidelines should be followed. Lipid lowering with statin therapy does correlate with reductions in cardiovascular event rates in women. The clinical impact of treating dyslipidemias in women with nonstatin drugs (eg, fibrates, nicotinic acid, bile acid-binding resins, omega-3 fish oils) is as yet not determined.

Drug-Drug, Drug-Dietary Supplement, and Drug-Citrus Fruit and Other Food Interactions: What Have We Learned?

Serious drug-drug interactions have contributed to recent U.S. market withdrawals and also recent nonapprovals of a few new molecular entities. Many of these interactions involved the inhibition or induction of metabolizing enzymes and efflux transporters, resulting in altered systemic exposure and adverse drug reactions or loss of efficacy. In addition to drug-drug interactions, drug-dietary supplement and drug-citrus fruit interactions, among others, could also cause adverse drug reactions or loss of efficacy and are important issues to consider in the evaluation of new drug candidates. This commentary reviews (1). the current understanding of the mechanistic basis of these interactions, (2). issues to consider in the interpretation of study results, and (3). recent labeling examples to illustrate the translation of study results to information useful for patients and health care providers.

Individualized risk for statin-induced myopathy: current knowledge, emerging challenges and potential solutions

Skeletal muscle toxicity is the primary adverse effect of statins. In this review, we summarize current knowledge regarding the genetic and nongenetic determinants of risk for statin induced myopathy. Many genetic factors were initially identified through candidate gene association studies limited to pharmacokinetic (PK) targets. Through genome-wide association studies, it has become clear that SLCO1B1 is among the strongest PK predictors of myopathy risk. Genome-wide association studies have also expanded our understanding of pharmacodynamic candidate genes, including RYR2. It is anticipated that deep resequencing efforts will define new loci with rare variants that also contribute, and sophisticated computational approaches will be needed to characterize gene-gene and gene-environment interactions. Beyond environment, race is a critical covariate, and its influence is only partly explained by geographic differences in the frequency of known pharmacodynamic and PK variants. As such, admixture analyses will be essential for a full understanding of statin-induced myopathy.

Dyslipidemia: Management Using Optimal Lipid-Lowering Therapy

Objective:

To evaluate current approaches and explore emerging research related to dyslipidemia management.

Data Sources:

MEDLINE (2004-April 2012) was searched for randomized controlled trials using the terms dyslipidemia and lipid-lowering therapy or statin (>1000 hits). Separate searches (MEDLINE, Google) identified meta-analyses (2010–2011), disease prevalence statistics, and current consensus guidelines (2004–July 2011). Additional references were identified from the publications reviewed.

Study Selection and Data Extraction:

English-language articles on large multi-center trials were evaluated.

Data Synthesis:

National Cholesterol Education Program Adult Treatment Panel III guidelines for the reduction of cardiovascular risk recommend the attainment of specific low-density lipoprotein cholesterol (LDL-C) and non–high-density lipoprotein cholesterol (non–HDL-C) target values, based on an individual's 10-year risk of coronary heart disease or global risk. For most patients unable to achieve recommended lipid level goals with therapeutic lifestyle changes, statins are the first option for treatment. Results of large, well-controlled clinical trials have demonstrated that statins are effective in primary and secondary prevention of cardiovascular disease in diverse populations, including patients with diabetes and the elderly, and that intensive statin therapy provides more effective lipid goal attainment and significantly greater risk reduction in patients with coronary artery disease. Stalin therapy is generally well tolerated but may increase the risk of myopathy. Statin use has been associated with increases in hepatic transaminases and an increased risk of diabetes, although the absolute risk of diabetes is low compared with the risk reduction benefit. Combination therapy including a statin may be appropriate for certain populations, but the risk reduction benefits of combination therapy remain unclear. Ezetimibe is an important treatment option for patients with hypercholesterolemia who do not tolerate intensive statin therapy. Although fibrates or niacin improves overall lipid profiles in patients with hypertriglyceridemia or dyslipidemia who are receiving statin therapy, their efficacy in reducing cardiovascular risk remains questionable and their use raises safety and tolerability concerns.

Conclusions:

Intensifying lifestyle changes and statin dose should be utilized first in patients not achieving their LDL-C and non-HDL-C goals.

Pediatric pharmacogenomics: a systematic assessment of ontogeny and genetic variation to guide the design of statin studies in children

The dose-exposure-response relationship for drugs may differ in pediatric patients compared with adults. Many clinical studies have established drug dose-exposure relationships across the pediatric age spectrum; however, genetic variation was seldom included. This article applies a systematic approach to determine the relative contribution of development and genetic variation on drug disposition and response using HMG-CoA reductase inhibitors as a model. Application of the approach drives the collection of information relevant to understanding the potential contribution of ontogeny and genetic variation to statin dose-exposure-response in children, and identifies important knowledge deficits to be addressed through the design of future studies.

Systemic exposure to atorvastatin between Asian and Caucasian subjects: a combined analysis of 22 studies

The aim of the present study was to determine whether there is a differing pattern of systemic exposure to atorvastatin in Asian versus Caucasian subjects by comparison of data obtained from completed pharmacokinetic studies. Pharmacokinetic data were analyzed from completed single-dose (10-80 mg) studies in Asian and Caucasian subjects. Dose normalized area under the concentration-time curve (AUC) and maximum observed concentration (Cmax) (AUC(dn) and Cmax(dn)) were obtained by dividing each value by the administered dose. Dose-per-bodyweight normalized AUC and Cmax (AUC(dn,wt) and Cmax,(dn,wt)) were obtained by dividing each value by the administered dose per unit bodyweight. Mean difference and 90% confidence intervals for Asian versus Caucasian comparisons were calculated for atorvastatin pharmacokinetic values based on the t statistic and expressed as ratios using Caucasians as the reference. Data were analyzed from 310 Asians and 579 Caucasians from 22 studies. AUC(dn) (Asian = 2.35, Caucasian = 2.06 [ng·hr·mL(-1)]/mg) and Cmax(dn) (Asian = 0.39, Caucasian = 0.40 Cmax(dn,wt)) and the equivalent dose-per-bodyweight normalized values for atorvastatin (AUC(dn,wt): Asian = 157.5, Caucasian = 156.4 [ng·hr·mL(-1)]/[mg·kg(-1)]; Cmax(dn,wt): Asian = 26.2, Caucasian = 30.3 [ng·mL(-1)]/[mg·kg(-1)]) were similar in both ethnic groups. Mean differences and 90% confidence interval for the differences fell within the limits (0.8-1.25) except for Cmax(dn,wt), for which the lower limit was slightly below 80%. No differences were noted in the systemic exposure to atorvastatin between Asian and Caucasian subjects. These data therefore demonstrate that dosing considerations in the current labels for atorvastatin are similar for Asian compared with Caucasian subjects.

Current understanding of hepatic and intestinal OATP-mediated drug-drug interactions

At present, many patients are medicated with various drugs, which are, at the same time, associated with an increased risk of drug-drug interactions (DDIs). Detailed analysis of mechanisms underlying DDIs is the basis of a better prediction of adverse drug events caused by drug interactions. In the last few decades, an involvement of transporters in such processes has been more and more recognized. Indeed, uptake transporters belonging to the organic anion-transporting polypeptide (OATP) family have been shown to interact with a variety of drugs in clinical use. Particularly, the subfamily of OATP1B transporters has been extensively studied, identifying several clinical significant DDIs based on those hepatic uptake transporters. By contrast, the role of OATP2B1 in this context is rather underestimated. Therefore, in addition to known interactions based on OATP1B transporters, we have focused on DDIs probably based on OATP2B1 inhibition in the liver and those possibly owing to the inhibition of OATP2B1-mediated drug absorption in the intestine.

Persistent use of against-label statin-fibrate combinations from 2003-2009 despite United States Food and Drug Administration dose restrictions

STUDY OBJECTIVE

To describe the prevalence of prescribing against-label statin-fibrate combination therapy.

DESIGN

Retrospective cohort study.

DATA SOURCE

Medstat MarketScan Commercial Claims and Encounter database.

PATIENTS

Adults (aged 18-89 yrs) who were prescribed statin-fibrate combination therapy between January 1, 2003, and June 30, 2009, had pharmacy claims demonstrating two or more concurrently filled prescriptions for a statin and a fibrate, and had continuous insurance enrollment for at least 12 months.

MEASUREMENTS AND MAIN RESULTS

Claims data were used to identify patients with dyslipidemia based on International Classification of Diseases, Ninth Revision, Clinical Modification diagnosis codes. National Drug Codes were used to describe concurrent statin-fibrate combination therapy. The primary outcome was recent use of against-label statin-fibrate combination therapy, defined as use during the last 18 months (January 1, 2008-June 30, 2009) of the study period. Patients were stratified according to statin and dosage to identify against-label combination use (e.g., simvastatin > 10 mg/day with gemfibrozil). Within the recent-use period, 131,394 patients were prescribed concurrent statin-fibrate combination therapy; of these patients, 13,420 (10.2%) had against-label therapy. Simvastatin-gemfibrozil accounted for 8978 (66.9%) of all against-label combinations. Of all 9877 simvastatin-gemfibrozil combinations prescribed in the recent-use period (both on-label and against-label use), 8978 (90.9%) were against label. The secondary outcome was prevalence of against-label statin-fibrate combination therapy on an annual basis: 15.5% in 2003, 18.7% in 2004, 9.1% in 2005, 8.3% in 2006, 9.2% in 2007, and 9.8% in 2008.

CONCLUSION

Against-label statin-fibrate combination therapy continues to be prescribed despite established United States Food and Drug Administration (FDA) dose restrictions. Nearly every time the simvastatin-gemfibrozil combination was prescribed, it was against label because simvastatin exceeded the maximum dose restriction. Updated simvastatin labeling in June 2011 includes additional maximum dose restrictions and new contraindications, which include gemfibrozil. Different approaches in clinical practice are needed to ensure adherence with the revised FDA labeling.

Simvastatin interactions with other drugs

INTRODUCTION

Statins, the mainstay of lipid-lowering therapy, are among the most commonly used drugs due to their beneficial effects in cardiovascular morbidity and mortality. Simvastatin, one of the most well-studied statins, is available in several generic forms both as monotherapy and with ezetimibe and is frequently prescribed worldwide. Despite its overall favorable risk profile, several previously stated concerns regarding high-dose simvastatin were recently formalized by the Food and Drug Administration (FDA).

AREAS COVERED

This paper discusses the interactions between simvastatin and other drugs and presents the latest FDA recommendations regarding the safe use of this statin. Relevant articles were identified through a PubMed search (up to December 2011). Furthermore, the latest FDA warning (June 2011) regarding simvastatin use was taken into account.

EXPERT OPINION

Simvastatin may have serious side effects particularly when used in high doses and in combination with certain drugs. Physicians need to adjust the recent recommendations made by the FDA in clinical practice in order to prevent treatment complications.

Induction of P450 3A1/2 and 2C6 by gemfibrozil in Sprague-Dawley rats

Fibrates are a group of peroxisome proliferator-activated receptor α agonists used in the treatment of dyslipidemia; however, they have been reported to cause species-related hepatocarcinogenesis and clinical myotoxicity. Gemfibrozil is one of the most commonly used fibrates, and it shows the highest risk for myotoxicity among the fibrates. The inhibitory drug-drug interaction mechanism associated with gemfibrozil has been explored recently, and the induction of human P450 3A4 and 2C8 has been reported. In this study, in vivo induction of rat P450 by gemfibrozil was studied in Sprague-Dawley rats. After the rats were dosed with gemfibrozil by oral gavage, microsomes were prepared. The metabolic activities of P450 3A1/2, 2C6, and 2D2 were assayed using probe substrates, and the systemic concentration of gemfibrozil during its administration was determined. P450 3A1/2 and 2C6 activities were induced 32-77% in the rats by gemfibrozil when the exposure concentration was in the clinical range. These data indicate that the inducibility of homologous P450 isoforms by gemfibrozil is similar in Sprague-Dawley rats and in humans. Inductive drug-drug interactions and inhibitory actions are involved in the co-administration of gemfibrozil with other drugs, which suggests the relevance for a fibrate-toxicology investigation.

Repaglinide-gemfibrozil drug interaction: inhibition of repaglinide glucuronidation as a potential additional contributing mechanism

AIM

To further explore the mechanism underlying the interaction between repaglinide and gemfibrozil, alone or in combination with itraconazole.

METHODS

Repaglinide metabolism was assessed in vitro (human liver subcellular fractions, fresh human hepatocytes, and recombinant enzymes) and the resulting incubates were analyzed, by liquid chromatography-mass spectrometry (LC-MS) and radioactivity counting, to identify and quantify the different metabolites therein. Chemical inhibitors, in addition to a trapping agent, were also employed to elucidate the importance of each metabolic pathway. Finally, a panel of human liver microsomes (genotyped for UGT1A1*28 allele status) was used to determine the importance of UGT1A1 in the direct glucuronidation of repaglinide.

RESULTS

The results of the present study demonstrate that repaglinide can undergo direct glucuronidation, a pathway that can possibly contribute to the interaction with gemfibrozil. For example, [³H]-repaglinide formed glucuronide and oxidative metabolites (M2 and M4) when incubated with primary human hepatocytes. Gemfibrozil effectively inhibited (∼78%) both glucuronide and M4 formation, but had a minor effect on M2 formation. Concomitantly, the overall turnover of repaglinide was also inhibited (∼80%), and was completely abolished when gemfibrozil was co-incubated with itraconazole. These observations are in qualitative agreement with the in vivo findings. UGT1A1 plays a significant role in the glucuronidation of repaglinide. In addition, gemfibrozil and its glucuronide inhibit repaglinide glucuronidation and the inhibition by gemfibrozil glucuronide is time-dependent.

CONCLUSIONS

Inhibition of UGT enzymes, especially UGT1A1, by gemfibrozil and its glucuronide is an additional mechanism to consider when rationalizing the interaction between repaglinide and gemfibrozil.

Statin Myopathy: Significant Problem With Minimal Awareness by Clinicians and no Emphasis by Clinical Investigators

High cardiovascular risk patients need reduction of low-density-lipoprotein cholesterol (LDL-C) to <70 mg/dL (1.8 mmol/L). Statins are optimal treatment but myopathy can be a limitation to their use. The incidence of statin-related myopathy is difficult to determine but up to 10.5% appears an appropriate estimate. Short-term trials report lower incidence than long-term trials. Statin-related myopathy may be influenced by genetics and tends to be dose-dependent. Ezetimibe can contribute to LDL-C reduction allowing a lower dose of statin to be used. Another approach is to administer rosuvastatin twice weekly. Statins have been shown to interfere with the cellular role of coenzyme Q10. Coenzyme Q10 supplementation may decrease or prevent statin myopathy, but this has not been proven. The occurrence of the most serious complication of myopathy—rhabdomyolysis—is very rare, but awareness of the problem, risks, and prevention are essential.

Biphasic regulation of intracellular calcium by gemfibrozil contributes to inhibiting L6 myoblast differentiation: implications for clinical myotoxicity

Gemfibrozil is the most myotoxic fibrate drug commonly used for dyslipidemia, but the mechanism is poorly understood. The current study revealed that gemfibrozil inhibits myoblast differentiation through the regulation of intracellular calcium ([Ca(2+)]i) as revealed in L6 myoblasts by use of laser scan confocal microscopy and flow cytometry using Fluo-4 AM as a probe. Gemfibrozil at 20-400 μM, could regulate [Ca(2+)]i in L6 cells in a biphasic manner, and sustained reduction was observed when the concentration reached 200 μM. Inhibition of L6 differentiation by gemfibrozil was concentration-dependent with maximal effect noted between 200 and 400 μM, as indicated by creatine kinase activities and the differentiation index, respectively. In differentiating L6 myoblasts, gemfibrozil at concentrations below 400 μM led to no significant signs of apoptosis or cytotoxicity, whereas differentiation, inhibited by 200 μM gemfibrozil, was only partially recovered. A good correlation was noted between gemfibrozil concentrations that regulate [Ca(2+)]i and inhibit L6 myoblasts differentiation, and both are within the range of total serum concentrations found in the clinic. These data suggest a potential pharmacodynamic effect of gemfibrozil on myogenesis as a warning sign, in addition to the complex pharmacokinetic interactions. It is also noteworthy that mobilization of [Ca(2+)]i by gemfibrozil may trigger complex biological responses besides myocyte differentiation. Information revealed in this study explores the mechanism of gemfibrozil-induced myotoxicity through the regulation of intracellular calcium.

Evidence-based management of statin myopathy

Statin-associated muscle symptoms are a relatively common condition that may affect 10% to 15% of statin users. Statin myopathy includes a wide spectrum of clinical conditions, ranging from mild myalgia to rhabdomyolysis. The etiology of myopathy is multifactorial. Recent studies suggest that statins may cause myopathy by depleting isoprenoids and interfering with intracellular calcium signaling. Certain patient and drug characteristics increase risk for statin myopathy, including higher statin doses, statin cytochrome metabolism, and polypharmacy. Genetic risk factors have been identified, including a single nucleotide polymorphism of SLCO1B1. Coenzyme Q10 and vitamin D have been used to prevent and treat statin myopathy; however, clinical trial evidence demonstrating their efficacy is limited. Statin-intolerant patients may be successfully treated with either low-dose statins, alternate-day dosing, or using twice-weekly dosing with longer half-life statins. An algorithm is presented to assist the clinician in managing myopathy in patients with dyslipidemia.