Metabolism and drug interactions of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors in transplant patients: are the statins mechanistically similar?

Asian Pacific Association for the Study of the Liver clinical practice guidelines on liver transplantation

Liver transplantation is a highly complex and challenging field of clinical practice. Although it was originally developed in western countries, it has been further advanced in Asian countries through the use of living donor liver transplantation. This method of transplantation is the only available option in many countries in the Asia-Pacific region due to the lack of deceased organ donation. As a result of this clinical situation, there is a growing need for guidelines that are specific to the Asia-Pacific region. These guidelines provide comprehensive recommendations for evidence-based management throughout the entire process of liver transplantation, covering both deceased and living donor liver transplantation. In addition, the development of these guidelines has been a collaborative effort between medical professionals from various countries in the region. This has allowed for the inclusion of diverse perspectives and experiences, leading to a more comprehensive and effective set of guidelines.

Modeled Hepatic/Plasma Exposures of Fluvastatin Prescribed Alone in Subjects with Impaired Cytochrome P450 2C9*3 as One of Possible Determinant Factors Likely Associated with Hepatic Toxicity Reported in a Japanese Adverse Event Database

Fluvastatin is a 3-hydroxy-3-methylglutaryl CoA reductase inhibitor that competitively inhibits human cytochrome P450 (P450) 2C9 in vitro. Drug interactions between a variety of P450 2C9 substrates/inhibitors and fluvastatin can increase the incidence of fluvastatin-related hepatic or skeletal muscle toxicity in vivo. In this survey, the prescribed dosage of fluvastatin was reduced or discontinued in 133 of 164 patients receiving fluvastatin alone, as recorded in the Japanese Adverse Drug Event Report database of spontaneously reported events. The median days to onset of fluvastatin-related disorders were in the range 30-35 d in the 87 patients. Therefore, we aimed to focus on fluvastatin and, using the pharmacokinetic modeling technique, estimated the virtual plasma and hepatic exposures in subjects harboring the impaired CYP2C9*3 allele. The plasma concentrations of fluvastatin modeled after a virtual oral 20-mg dose increased in homozygotes with CYP2C9*3; the area under the plasma concentration curve was 4.9-fold higher than that in Japanese homozygotes for wild-type CYP2C9*1. The modeled hepatic concentrations of fluvastatin in patients with CYP2C9*3/*3 after virtual daily 20-mg doses for 7 d were 31-fold higher than those in subjects with CYP2C9*1/*1. However, heterozygous Chinese patients with CYP2C9*1/*3 reportedly have a limited elevation (1.2-fold) in plasma maximum concentrations. Virtual hepatic/plasma exposures in subjects harboring the impaired CYP2C9*3 allele estimated using pharmacokinetic modeling indicate that such exposure could be a causal factor for hepatic disorders induced by fluvastatin prescribed alone in a manner similar to that for interactions with a variety of co-administered drugs.

High hepatic and plasma exposures of atorvastatin in subjects harboring impaired cytochrome P450 3A4∗16 modeled after virtual administrations and possibly associated with statin intolerance found in the Japanese adverse drug event report database

Drug interactions between atorvastatin and cytochrome P450 (P450) 3A substrates/inhibitors lead to an increased incidence of skeletal muscle or hepatic toxicity. However, in this survey, among 483 Japanese subjects administered atorvastatin alone, more than half (258) experienced statin intolerance and were unable to continue using the drug. Although many factors underly atorvastatin toxicity, the intrinsic clearance rate might be a contributing causal factor. The impaired P450 3A4 p.Thr185Ser variant, CYP3A4∗16 (rs12721627), has been identified in East Asians with an allele frequency of 2.2%. Pharmacokinetically modeled plasma concentrations of atorvastatin increased after a virtual oral dose of 40 mg in CYP3A4∗16 homozygotes; the maximum concentration and area under the concentration curve, respectively, were 3.3-fold and 4.2-fold those in subjects homozygous for CYP3A4∗1. In subjects with CYP3A4∗16/∗16, the virtual hepatic concentrations of atorvastatin after daily doses of 10 mg for a week were similar to or higher than the plasma concentrations. These results suggest that the estimated high virtual plasma and hepatic exposures obtained by pharmacokinetic modeling in subjects harboring impaired allele CYP3A4∗16 may be one of the causal factors for statin intolerance in a manner similar to the well-known drug interactions caused by co-administrations of CYP3A inhibitors.

Current Evidence, Challenges, and Opportunities of Physiologically Based Pharmacokinetic Models of Atorvastatin for Decision Making

Atorvastatin (ATS) is the gold-standard treatment worldwide for the management of hypercholesterolemia and prevention of cardiovascular diseases associated with dyslipidemia. Physiologically based pharmacokinetic (PBPK) models have been positioned as a valuable tool for the characterization of complex pharmacokinetic (PK) processes and its extrapolation in special sub-groups of the population, leading to regulatory recognition. Several PBPK models of ATS have been published in the recent years, addressing different aspects of the PK properties of ATS. Therefore, the aims of this review are (i) to summarize the physicochemical and pharmacokinetic characteristics involved in the time-course of ATS, and (ii) to evaluate the major highlights and limitations of the PBPK models of ATS published so far. The PBPK models incorporate common elements related to the physicochemical aspects of ATS. However, there are important differences in relation to the analyte evaluated, the type and effect of transporters and metabolic enzymes, and the permeability value used. Additionally, this review identifies major processes (lactonization, P-gp contribution, ATS-Ca solubility, simultaneous management of multiple analytes, and experimental evidence in the target population), which would enhance the PBPK model prediction to serve as a valid tool for ATS dose optimization.

Pravastatin and Simvastatin Pretreatment in Combination with Pyrimethamine and Sulfadiazine Reduces Infection Process of Toxoplasma gondii Tachyzoites (RH Strain) in HeLa Cells

PURPOSE

Toxoplasma gondii is a protozoan from phylum Apicomplexa, which causes the toxoplasmosis infection; this one exhibits an apicoplast organelle which assists in the metabolism of isoprenoids and other pivotal mediators for the parasite survival. Statins are drugs that inhibit cholesterol synthesis, blocking the conversion of the substrate HMG-CoA to mevalonate, thus preventing the initial processes of the biosynthesis of these precursors, both in humans and parasite. Our goal was to verify whether the Toxoplasma gondii (RH strain) tachyzoites form pretreated with pravastatin and simvastatin in association with pyrimethamine and sulfadiazine at low concentrations could affect the infection processes, suggesting direct action on protozoa intracellular proliferation through the inhibition of isoprenoids in the parasite's apicoplast.

METHODS

To have the adhesion, infection, and parasite proliferation during experimental infection investigated, HeLa cells (10⁵) were subjected to a 24-hour infection by T. gondii tachyzoites forms of RH strain (5 × 10⁵) pretreated for 30 min with pravastatin and/or simvastatin combined or not with pyrimethamine and sulfadiazine.

RESULTS

Combined with conventional drugs at low concentrations pravastatin and simvastatin inhibit the adhesion, invasion, and intracellular proliferation of T. gondii in HeLa cells which are similar to the positive control.

CONCLUSION

Pravastatin and simvastatin in association with pyrimethamine and sulfadiazine at low concentrations can be regarded as a promising, effective alternative to toxoplasmosis treatment with reduced side effects.

Statins and the Brain: More than Lipid Lowering Agents?

BACKGROUND

Statins represent a class of medications widely prescribed to efficiently treat dyslipidemia. These drugs inhibit 3-βhydroxy 3β-methylglutaryl Coenzyme A reductase (HMGR), the rate-limiting enzyme of mevalonate (MVA) pathway. Besides cholesterol, MVA pathway leads to the production of several other compounds, which are essential in the regulation of a plethora of biological activities, including in the central nervous system. For these reasons, statins are able to induce pleiotropic actions, and acquire increased interest as potential and novel modulators in brain processes, especially during pathological conditions.

OBJECTIVE

The purpose of this review is to summarize and examine the current knowledge about pharmacokinetic and pharmacodynamic properties of statins in the brain. In addition, effects of statin on brain diseases are discussed providing the most up-to-date information.

METHODS

Relevant scientific information was identified from PubMed database using the following keywords: statins and brain, central nervous system, neurological diseases, neurodegeneration, brain tumors, mood, stroke.

RESULTS

315 scientific articles were selected and analyzed for the writing of this review article. Several papers highlighted that statin treatment is effective in preventing or ameliorating the symptomatology of a number of brain pathologies. However, other studies failed to demonstrate a neuroprotective effect.

CONCLUSION

Even though considerable research studies suggest pivotal functional outcomes induced by statin therapy, additional investigation is required to better determine the pharmacological effectiveness of statins in the brain, and support their clinical use in the management of different neuropathologies.

Retinal Cholesterol Content Is Reduced in Simvastatin-Treated Mice Due to Inhibited Local Biosynthesis Albeit Increased Uptake of Serum Cholesterol

Statins, a class of cholesterol-lowering drugs, are currently being investigated for treatment of age-related macular degeneration, a retinal disease. Herein, retinal and serum concentrations of four statins (atorvastatin, simvastatin, pravastatin, and rosuvastatin) were evaluated after mice were given a single drug dose of 60 mg/kg body weight. All statins, except rosuvastatin, were detected in the retina: atorvastatin and pravastatin at 1.6 pmol and simvastatin at 4.1 pmol. Serum statin concentrations (pmol/ml) were 223 (simvastatin), 1401 (atorvastatin), 2792 (pravastatin), and 9050 (rosuvastatin). Simvastatin was then administered to mice daily for 6 weeks at 60 mg/kg body weight. Simvastatin treatment reduced serum cholesterol levels by 18% and retinal content of cholesterol and lathosterol (but not desmosterol) by 24% and 21%, respectively. The relative contributions of retinal cholesterol biosynthesis and retinal uptake of serum cholesterol to total retinal cholesterol input were changed as well. These contributions were 79% and 21%, respectively, in vehicle-treated mice and 69% and 31%, respectively, in simvastatin-treated mice. Thus, simvastatin treatment lowered retinal cholesterol because a compensatory upregulation of retinal uptake of serum cholesterol was not sufficient to overcome the effect of inhibited retinal biosynthesis. Simultaneously, simvastatin-treated mice had a 2.9-fold increase in retinal expression of Cd36, the major receptor clearing oxidized low-density lipoproteins from Bruch's membrane. Notably, simvastatin treatment essentially did not affect brain cholesterol homeostasis. Our results reveal the statin effect on the retinal and brain cholesterol input and are of value for future clinical investigations of statins as potential therapeutics for age-related macular degeneration.

An update on efflux and uptake transporters as determinants of statin response

INTRODUCTION

Statins are used in the treatment of dyslipidemia promoting primary and secondary prevention against detrimental cardiovascular events. ATP-binding cassette (ABC) and solute carrier (SLC) membrane transporters transport statins across the cell membrane. Differences in drug transporter tissue expression and activity contribute to variability in statin pharmacokinetics (PK) and response. Areas covered: The purpose of this review is to discuss factors impacting transporter expression and the effect this has on statin efficacy and safety. Previous studies have demonstrated that genetic polymorphisms, drug-drug interactions (DDI), nuclear receptors, and microRNAs affect statin PK and pharmacodynamics. Expert opinion: Genetic variants of ABCG2 and SLCO1B1 transporters affect statin PK and, as a result, the intended lipid-lowering response. However, the effect size is small, limiting its applicability in clinical practice. Furthermore, genetic variants do not totally explain the observed intervariability in statin response. Thus, it is likely that transcriptional and post-transcriptional regulation of drug transporters are also highly involved. Further studies are required to understand the contribution of each of these new factors in statin disposition and toxicity.

Effect of polymorphisms in CYP3A4, PPARA, NR1I2, NFKB1, ABCG2 and SLCO1B1 on the pharmacokinetics of lovastatin in healthy Chinese volunteers

AIM

This study examined whether gene polymorphisms (CYP3A4, ABCG2, SLCO1B1, NR1I2, PPARA and NFKB1) influenced the pharmacokinetics of lovastatin in Chinese healthy subjects.

PATIENTS & METHOD

Plasma concentrations of lovastatin and lovastatin acid were quantified using LC/MS/MS.

RESULTS

PPARA c.208+3819 G allele carriers had approximately twofold higher AUC_0-∞ and C_max of lovastatin than wild-type (PPARA c.208+3819 AA) subjects. After adjustment for the PPARA variants, subjects with the SLCO1B1 521TT genotype had approximately 50% lower AUC_0-∞ of lovastatin acid than those with 521TC/CC genotypes, while the AUC_0-∞ of lovastatin lactone in NFKB1-94 DD wild-type carriers was twofold higher than in mutant homozygotes carriers.

CONCLUSION

Gene polymorphisms of PPARA, SLCO1B1 and NFKB1 affected the pharmacokinetics of lovastatin.

The independent contribution of miRNAs to the missing heritability in CYP3A4/5 functionality and the metabolism of atorvastatin

To evaluate the independent contribution of miRNAs to the missing heritability in CYP3A4/5 functionality and atorvastatin metabolism, the relationships among three levels of factors, namely (1) clinical characteristics, CYP3A4/5 genotypes, and miRNAs, (2) CYP3A4 and CYP3A5 mRNAs, and (3) CYP3A activity, as well as their individual impacts on atorvastatin metabolism, were assessed in 55 human liver tissues. MiR-27b, miR-206, and CYP3A4 mRNA respectively accounted for 20.0%, 5.8%, and 9.5% of the interindividual variations in CYP3A activity. MiR-142 was an independent contributor to the expressions of CYP3A4 mRNA (partial R(2) = 0.12, P = 0.002) and CYP3A5 mRNA (partial R(2) = 0.09, P = 0.005) but not CYP3A activity or atorvastatin metabolism. CYP3A activity was a unique independent predictor of variability of atorvastatin metabolism, explaining the majority of the variance in reduction of atorvastatin (60.0%) and formation of ortho-hydroxy atorvastatin (78.8%) and para-hydroxy atorvastatin (83.9%). MiR-27b and miR-206 were found to repress CYP3A4 gene expression and CYP3A activity by directly binding to CYP3A4 3'-UTR, while miR-142 was found to indirectly repress CYP3A activity. Our study indicates that miRNAs play significant roles in bridging the gap between epigenetic effects and missing heritability in CYP3A functionality.

CYP3A4*22 and CYP3A5*3 are associated with increased levels of plasma simvastatin concentrations in the cholesterol and pharmacogenetics study cohort

Objective

Simvastatin is primarily metabolized by CYP3A4. A combined CYP3A4/5 genotype classification, combining the decrease-of-function CYP3A4*22 and the loss-of-function CYP3A5*3, has recently been reported. We aim to determine whether CYP3A4*22 and CYP3A5*3 alleles are associated with increased plasma concentrations of simvastatin lactone (SV) and simvastatin acid (SVA). This is the first report evaluating associations between in-vivo simvastatin concentrations and CYP3A4*22, alone or in a combined CYP3A4/5 genotype-defined classification.

Participants and methods

Genotypes and simvastatin concentrations were determined for 830 participants (555 Whites and 275 African-Americans) in the Cholesterol and Pharmacogenomics clinical trial with 40 mg/day simvastatin for 6 weeks. Concentrations were determined in 12-h postdose samples. Associations between simvastatin concentrations and CYP3A4*22 and CYP3A5*3 alleles were tested separately and in a combined CYP3A4/5 genotype-defined classification system.

Results

In Whites, CYP3A4*22 carriers (n=42) had 14% higher SVA (P=0.04) and 20% higher SV (P=0.06) compared with noncarriers (n=513). CYP3A5*3 allele status was not significantly associated with SV or SVA in Whites. In African-Americans, CYP3A4*22 carriers (n=8) had 170% higher SV (P<0.01) than noncarriers (n=267), but no significant difference was detected for SVA. African-American CYP3A5 nonexpressors (n=28) had 33% higher SV (P=0.02) than CYP3A5 expressors (n=247), but no significant difference was detected for SVA. For both races, SV appeared to decrease across the rank-ordered combined CYP3A4/5 genotype-defined groups (poor, intermediate, and extensive metabolizers); however, similar trends were not observed for SVA.

Conclusion

Genetic variation in CYP3A4 was associated with plasma simvastatin concentrations in self-reported Whites. Genetic variations in CYP3A4 and CYP3A5 were associated with plasma simvastatin concentrations in self-reported African-Americans.

Safety events in kidney transplant recipients: results from the folic Acid for vascular outcome reduction in transplant trial

BACKGROUND

Kidney transplant recipients are at increased risk for adverse safety events related to their reduced renal function and many medications.

METHODS

We determined the incidence of adverse safety events based on previously defined Agency for Healthcare and Research Quality (AHRQ) International Classification of Diseases-9 (ICD-9) code-derived patient safety indicators (PSI) in the Folic Acid for Vascular Outcome Reduction in Transplant trial participants who had a hospitalization stratified by tertiles of estimated glomerular filtration rate (GFR). We also examined the frequency of Micromedex defined two precautionary drug-drug interactions, and two medications whose use may be contraindicated because of reduced GFR from the Folic Acid for Vascular Outcome Reduction in Transplant trial medication thesaurus at baseline, and annually among 4,110 participants. Logistic regression was used to examine the relationship between patient safety events and baseline demographic and clinical variables at a participant level. Event rates were estimated at participant and visit levels.

RESULTS

Of the 2,514 patients with a hospitalization, 978 (38.9%) experienced an AHRQ PSI. Factors which were associated with more common AHRQ PSI included: U.S. location, history of cardiovascular disease or diabetes, and lower tertile of estimated GFR. At a participant level, 2,524 of the 4,110 participants (61.4%) were taking calcineurin inhibitor and statin, 378 (9.2%) were taking azathioprine and an angiotensin-converting enzyme inhibitor, 171 (12.9%) were taking a sulfonylurea), 45 (3.4%) were taking metformin despite a baseline GFR below 40 mL per min per 1.73 m.

CONCLUSION

We conclude that patient safety events are not uncommon in kidney transplant recipients. Careful monitoring is necessary to prevent adverse outcomes.

Characterisation of selected active agents regarding pKa values, solubility concentrations and pH profiles by SiriusT3

The aim of this work was to determine pKa values and solubility properties of 34active agents using the SiriusT3 apparatus. The selected drug substances belong to the groups of ACE-inhibitors, β-blockers, antidiabetics and lipid lowering substances. Experimentally obtained pKa and intrinsic solubility values were compared to calculated values (program ACD/ChemSketch) and pKa values to published data as well. Solubility-pH profiles were generated to visualise the substance solubility over the gastrointestinal pH range. The relationship between the solubility characteristic of a substance, its bioavailability and categorisation according to the Biopharmaceutics Classification System (BCS) was examined as well. The results showed a good agreement between experimentally obtained, calculated and published pKa values. The measured and calculated intrinsic solubility values indicated several major deviations. All solubility-pH profiles showed the expected shape and appearance for acids, bases or zwitterionic substances. The obtained results for the pKa and solubility measurements of the examined active agents may help to predict their physicochemical behaviour in vivo, and to understand the bioavailability of the substances according to their BCS categorisation. The easy and reproducible determination of pKa and solubility values makes the SiriusT3 apparatus a useful tool in early stages of drug and formulation development.

Modeling the effects of commonly used drugs on human metabolism

Metabolism contributes significantly to the pharmacokinetics and pharmacodynamics of a drug. In addition, diet and genetics have a profound effect on cellular metabolism with respect to both health and disease. In the present study, we assembled a comprehensive, literature-based drug metabolic reconstruction of the 18 most highly prescribed drug groups, including statins, anti-hypertensives, immunosuppressants and analgesics. This reconstruction captures in detail our current understanding of their absorption, intracellular distribution, metabolism and elimination. We combined this drug module with the most comprehensive reconstruction of human metabolism, Recon 2, yielding Recon2_DM1796, which accounts for 2803 metabolites and 8161 reactions. By defining 50 specific drug objectives that captured the overall drug metabolism of these compounds, we investigated the effects of dietary composition and inherited metabolic disorders on drug metabolism and drug-drug interactions. Our main findings include: (a) a shift in dietary patterns significantly affects statins and acetaminophen metabolism; (b) disturbed statin metabolism contributes to the clinical phenotype of mitochondrial energy disorders; and (c) the interaction between statins and cyclosporine can be explained by several common metabolic and transport pathways other than the previously established CYP3A4 connection. This work holds the potential for studying adverse drug reactions and designing patient-specific therapies.

Translational insight into statin-induced muscle toxicity: from cell culture to clinical studies

Statins are lipid-lowering drugs used widely to prevent and treat cardiovascular and coronary heart diseases. These drugs are among the most commonly prescribed medicines intended for long-term use. In general, statins are well tolerated. However, muscular adverse effects appear to be the most common obstacle that limits their use, resulting in poor patient compliance or even drug discontinuation. In addition, rare but potentially fatal cases of rhabdomyolysis have been reported with the use of these drugs, especially in the presence of certain risk factors. Previous reports have investigated statin-induced myotoxicity in vivo and in vitro using a number of cell lines, muscle tissues, and laboratory animals, in addition to randomized clinical trials, observational studies, and case reports. None of them have compared directly results from laboratory investigations with clinical observations of statin-related muscular adverse effects. To the best of our knowledge this is the first review article that combines laboratory investigation with clinical aspects of statin-induced myotoxicity. By reviewing published literature of in vivo, in vitro, and clinically relevant studies of statin myotoxicity, we aim to translate this important drug-related problem to establish a clear picture of proposed mechanisms that explain the risk factors and describe the diagnostic approaches currently used for evaluating the degree of muscle damage induced by these agents. This review provides baseline novel translational insight that can be used to enhance the safety profile, to minimize the chance of progression of these adverse effects to more severe and potentially fatal rhabdomyolysis, and to improve the overall patient compliance and adherence to long-term statin therapy.

Methodological issues of retrospective studies assessing health outcomes of potential clopidogrel-statin interaction

OBJECTIVE

Clopidogrel and statins have been commonly coprescribed to patients with atherosclerotic diseases. Clopidogrel-statin interaction was initially described by ex vivo studies, but was not well supported by studies examining health outcomes. This personal view article aims to discuss methodological issues of these studies, especially the retrospective studies assessing health outcomes.

METHODS

A comprehensive literature search was conducted to identify journal articles of clopidogrel-statin interaction that were published in English since January 2003.

KEY FINDINGS

The limitations of retrospective studies include lack of central blinded adjudication of clinical events, incomplete assessment of confounders, inadequate comparison groups and inconsistent use of medication dosage.

CONCLUSION

A well-designed retrospective study may better understand potential clopidogrel-statin interaction and its clinical impacts.

Artemisia scoparia extract attenuates non-alcoholic fatty liver disease in diet-induced obesity mice by enhancing hepatic insulin and AMPK signaling independently of FGF21 pathway

OBJECTIVE

Nonalcoholic fatty liver disease (NAFLD) is a common liver disease which has no standard treatment. In this regard, we sought to evaluate the effects of extracts of Artemisia santolinaefolia (SANT) and Artemisia scoparia (SCO) on hepatic lipid deposition and cellular signaling in a diet-induced obesity (DIO) animal model.

MATERIALS/METHODS

DIO C57/B6J mice were randomly divided into three groups, i.e. HFD, SANT and SCO. Both extracts were incorporated into HFD at a concentration of 0.5% (w/w). Fasting plasma glucose, insulin, adiponectin, and FGF21 concentrations were measured.

RESULTS

At the end of the 4-week intervention, liver tissues were collected for analysis of insulin, AMPK, and FGF21 signaling. SANT and SCO supplementation significantly increased plasma adiponectin levels when compared with the HFD mice (P<0.001). Fasting insulin levels were significantly lower in the SCO than HFD mice, but not in SANT group. Hepatic H&E staining showed fewer lipid droplets in the SCO group than in the other two groups. Cellular signaling data demonstrated that SCO significantly increased liver IRS-2 content, phosphorylation of IRS-1, IR β, Akt1 and Akt2, AMPK α1 and AMPK activity and significantly reduced PTP 1B abundance when compared with the HFD group. SCO also significantly decreased fatty acid synthase (FAS), HMG-CoA Reductase (HMGR), and Sterol regulatory element-binding protein 1c (SREBP1c), but not Carnitine palmitoyltransferase I (CPT-1) when compared with HFD group. Neither SANT nor SCO significantly altered plasma FGF21 concentrations and liver FGF21 signaling.

CONCLUSION

This study suggests that SCO may attenuate liver lipid accumulation in DIO mice. Contributing mechanisms were postulated to include promotion of adiponectin expression, inhibition of hepatic lipogenesis, and/or enhanced insulin and AMPK signaling independent of FGF21 pathway.

Topical anti-inflammatory effect of hypocholesterolaemic drugs

OBJECTIVES

The topical anti-inflammatory effect of simvastatin, atorvastatin, pravastatin, ezetimibe and combined ezetimibe + simvastatin was investigated, using the croton oil model of ear oedema in mice.

METHODS

Simvastatin, atorvastatin, pravastatin, ezetimibe and ezetimibe + simvastatin combination (dissolved in 20 µl of 70% acetone) were topically applied simultaneously with croton oil (200 µg/ear, dissolved in 20 µl of 70% acetone) at the inner surface of each ear. Ear oedema and myeloperoxidase activity, indicative of polymorphonuclear cell migration, were assessed 6 h after inflammatory stimuli.

KEY FINDINGS

It was found that statins can act as topical anti-inflammatories, but the pharmacological effect is dependent on statin polarity. At 0.3 mg/ear inhibition of ear oedema was 79%, 67% and 40% for simvastatin, atorvastatin and pravastatin, respectively. Simvastatin and atorvastatin also remarkably diminished myeloperoxidase activity, even at low concentrations (0.03 mg/ear). Pravastatin, the most polar statin, however, did not cause any reduction in ear oedema or myeloperoxidase activity at low doses. The order of topical anti-inflammatory activity was pravastatin < < < atorvastatin ≤ simvastatin. Ezetimibe, another hypocholesterolaemic drug, also presented anti-inflammatory effects, inhibiting ear oedema by 64% at 0.3 mg/ear. However, when used in combination with simvastatin, no further beneficial effect was observed.

CONCLUSIONS

These results consistently support current evidence showing that statins can be used for treatment of dermatological disorders. Polarity of the molecule, however, is a factor that should be considered before recommending use.

A systems biology approach to dynamic modeling and inter-subject variability of statin pharmacokinetics in human hepatocytes

Background

The individual character of pharmacokinetics is of great importance in the risk assessment of new drug leads in pharmacological research. Amongst others, it is severely influenced by the properties and inter-individual variability of the enzymes and transporters of the drug detoxification system of the liver. Predicting individual drug biotransformation capacity requires quantitative and detailed models.

Results

In this contribution we present the de novo deterministic modeling of atorvastatin biotransformation based on comprehensive published knowledge on involved metabolic and transport pathways as well as physicochemical properties. The model was evaluated on primary human hepatocytes and parameter identifiability analysis was performed under multiple experimental constraints. Dynamic simulations of atorvastatin biotransformation considering the inter-individual variability of the two major involved enzymes CYP3A4 and UGT1A3 based on quantitative protein expression data in a large human liver bank (n = 150) highlighted the variability in the individual biotransformation profiles and therefore also points to the individuality of pharmacokinetics.

Conclusions

A dynamic model for the biotransformation of atorvastatin has been developed using quantitative metabolite measurements in primary human hepatocytes. The model comprises kinetics for transport processes and metabolic enzymes as well as population liver expression data allowing us to assess the impact of inter-individual variability of concentrations of key proteins. Application of computational tools for parameter sensitivity analysis enabled us to considerably improve the validity of the model and to create a consistent framework for precise computer-aided simulations in toxicology.

Cyclosporin A--a review on fermentative production, downstream processing and pharmacological applications

In present times, the immunosuppressants have gained considerable importance in the world market. Cyclosporin A (CyA) is a cyclic undecapeptide with a variety of biological activities including immunosuppressive, anti-inflammatory, antifungal and antiparasitic properties. CyA is produced by various types of fermentation techniques using Tolypocladium inflatum. In the present review, we discuss the biosynthetic pathway, fermentative production, downstream processing and pharmacological activities of CyA.

Influence of fluvastatin on cardiac function and baroreflex sensitivity in diabetic rats

AIM

To investigate whether fluvastatin is able to ameliorate the impaired cardiac function or baroreflex sensitivity (BRS) in rats with type 1 diabetes.

METHODS

Type 1 diabetic rats were induced by intraperitoneal injection of streptozotocin (STZ) and then administered fluvastatin (1.5, 3.0, and 6.0 mg·kg(-1)·d(-1)) for 30 d. Food and drink intake was recorded every day. Fasting blood glucose (FBG) level, blood lipid level, cardiac function and BRS were measured in diabetic rats after fluvastatin treatment for 30 d.

RESULTS

The polydipsia, polyphagia and abnormal biochemical indexes of blood were significantly ameliorated by the the 3.0- and 6.0-mg doses of fluvastatin in STZ-induced diabetic rats. FBG was decreased in diabetic rats after fluvastatin treatment for 30 d. The left ventricular systolic pressure (LVSP) and the maximum rate of change of left ventricular pressure in the isovolumic contraction and relaxation period (±dp/dt(max)) were elevated, and left ventricular diastolic pressure (LVEDP) was decreased by fluvastatin. The attenuated heart rate responses to arterial blood pressure (ABP) increase induced by phenylephrine (PE) and ABP decrease induced by sodium nitroprusside (SNP) were reversed by the 3.0-mg dose of fluvastatin.

CONCLUSION

Fluvastatin regulates blood lipid levels and decreases the FBG level in diabetic rats. These responses can protect the diabetic heart from complications by improving cardiac function and BRS.

Statin Therapy Associated with Fatal Rhabdomyolysis

A 54-year-old man was admitted to the intensive care unit six weeks after a myocardial infarction suffering from metabolic derangement secondary to rhabdomyolysis. There was no obvious precipitant for his condition, though he had recently had his atorvastatin dose increased from 10 mg to 80 mg and a number of new medications commenced. Extensive investigations failed to identify other causes of rhabdomyolysis and it was concluded that his condition related to a combination of statin therapy with other medications, namely the anti-staphylococcal agent fucidic acid. Despite discontinuation of his statin therapy, rhabdomyolysis persisted and the patient died from sepsis related to a prolonged ICU stay. This case highlights the potential risks of statin therapy, particularly in the critically ill patient population, where there may be significant interactions between statins and other co-prescribed medications. Such interactions can lead to impaired statin metabolism, potentially increasing the risks of rhabdomyolysis and other serious side effects.

P-glycoprotein related drug interactions: clinical importance and a consideration of disease states

IMPORTANCE OF THE FIELD

P-glycoprotein (P-gp) is the most characterized drug transporter in terms of its clinical relevance for pharmacokinetic disposition and interaction with other medicines. Clinically significant P-gp related drug interactions appear restricted to digoxin. P-gp may act as a major barrier to current and effective drug treatment in a number of diseases including cancer, AIDS, Alzheimer's and epilepsy due to its expression in tumors, lymphocytes, cell membranes of brain capillaries and the choroid plexus.

AREAS COVERED IN THIS REVIEW

This review summarizes the current understanding of P-gp structure/function, clinical importance of P-gp related drug interactions and the modulatory role this transporter may contribute towards drug efficacy in disease states such as cancer, AIDS, Alzheimer's and epilepsy.

WHAT THE READER WILL GAIN

The reader will gain an understanding that the clinical relevance of P-gp in drug interactions is limited. In certain disease states, P-gp in barrier tissues can modulate changes in regional distribution.

TAKE HOME MESSAGE

P-gp inhibition in isolation will not result in clinically important alterations in systemic exposure; however, P-gp transport may be of significance in barrier tissues (tumors, lymphocytes, brain) resulting in attenuated efficacy.

Drug interactions in transplant patients: what everyone should know

PURPOSE OF REVIEW

Adverse events due to drug-drug interactions remain a challenge in the postsurgical care of transplant recipients. A combination of potent and selective immunosuppressive drugs, which have a narrow therapeutic index, with medications for the treatment of comorbidities such as dyslipidemia, infection, psychiatric conditions, and hypertension, can lead to life-threatening drug-drug interactions.

RECENT FINDINGS

There are a number of important drug-drug interactions which are important for physicians to consider. It is critical to understand the pharmacodynamics and pharmacokinetics of drug-drug interactions, their potential impact on patient care, and the management strategies.

SUMMARY

Close therapeutic drug monitoring and evaluation of drug-specific side effects continue to be an important key to minimize adverse events due to drug-drug interactions.

The use of ciclosporin in psoriasis

Ciclosporin is a cyclic undecapeptide discovered in the 1970s to possess a potent inhibitory action on T lymphocytes. The subsequent discovery, in 1979, that it was remarkably effective in treatment of psoriasis transformed thinking about the nature of the disease, which subsequently became generally recognized as autoimmune in nature. Ciclosporin remains one of the most effective and rapidly acting treatments currently available for psoriasis. Virtually all the diverse manifestations of this disease can respond. The main side effects are nephrotoxicity and hypertension. There is considerable variation between individuals in susceptibility to these so careful monitoring is required. Ciclosporin should be used in single or intermittent short courses for all except the most severe cases as this is safer than continuous treatment. The rate of improvement depends very much on the dose, which ranges from 2 to 5.0 mg/kg/day. Ciclosporin can be combined with any topical treatment and a useful dose-sparing effect can be achieved in this way if patients are compliant. In severe cases ciclosporin is often used in combination with other systemic antipsoriatic drugs in order to spare the dose of each agent and reduce toxicity. Concurrent or intercurrent use of ultraviolet therapy is discouraged due to the increased risk of non-melanoma skin cancer. This article reviews the mode of action, pharmacokinetics, indications, contraindications, side effects, dosage regimens, pretreatment screening and monitoring, drug interactions, and use of treatment combinations with ciclosporin in the management of psoriasis.

Impact of genetic polymorphisms on the efficacy of HMG-CoA reductase inhibitors

Although pharmacologic treatment for cholesterol reduction represents an advance in cardiovascular and atherosclerosis treatment, the benefits of such therapy are still limited because of interindividual variability in the response to these drugs. Disease severity, treatment adherence, physiologic conditions, biologic conditions, and the patient's genetic profile could be cited as important factors in the evaluation of interindividual variability. In regard to the latter consideration, three large groups of genes could be investigated: (i) genes that code for proteins involved in metabolism and/or drug transport, thereby influencing the pharmacokinetics of these compounds; (ii) genes that code for proteins involved in the mechanism of action and/or in the metabolic pathway of drug action, and which therefore influence pharmacodynamics; and (iii) genes that code for proteins involved in direct development of the disease or in intermediate phenotypes. In this review we discuss pharmacogenetic studies of the HMG-CoA reductase inhibitors (statins) and the implications of pharmacogenetic considerations for predicting treatment efficacy and reducing the adverse effects of these drugs. Once new studies have been performed and most of the genetic variability associated with drug action has been revealed, the great challenge will be to apply this knowledge in clinical medicine.

Toxicological Significance of Mechanism-Based Inactivation of Cytochrome P450 Enzymes by Drugs

Cytochrome P450 (P450) enzymes oxidize xenobiotics into chemically reactive metabolites or intermediates as well as into stable metabolites. If the reactivity of the product is very high, it binds to a catalytic site or sites of the enzyme itself and inactivates it. This phenomenon is referred to as mechanism-based inactivation. Many clinically important drugs are mechanism-based inactivators that include macrolide antibiotics, calcium channel blockers, and selective serotonin uptake inhibitors, but are not always structurally and pharmacologically related. The inactivation of P450s during drug therapy results in serious drug interactions, since irreversibility of the binding allows enzyme inhibition to be prolonged after elimination of the causal drug. The inhibition of the metabolism of drugs with narrow therapeutic indexes, such as terfenadine and astemizole, leads to toxicities. On the other hand, the fate of P450s after the inactivation and the toxicological consequences remains to be elucidated, while it has been suggested that P450s modified and degraded are involved in some forms of tissue toxicity. Porphyrinogenic drugs, such as griseofulvin, cause mechanism-based heme inactivation, leading to formation of ferrochelatase-inhibitory N-alkylated protoporphyrins and resulting in porphyria. Involvement of P450-derived free heme in halothane-induced hepatotoxicity and catalytic iron in cisplatin-induced nephrotoxicity has also been suggested. Autoantibodies against P450s have been found in hepatitis following administration of tienilic acid and dihydralazine. Tienilic acid is activated by and covalently bound to CYP2C9, and the neoantigens thus formed activate immune systems, resulting in the formation of an autoantibodydirected against CYP2C9, named anti-liver/kidney microsomal autoantibody type 2, whereas the pathological role of the autoantibodies in drug-induced hepatitis remains largely unknown.

Potential of pharmacokinetic profiling for detecting herbal interactions with drugs

The issue of herb-drug interactions has generated significant concern within the pharmaceutical industry and among regulatory authorities in recent years. Therefore, accurate models of predicting metabolic herb-drug interactions would be useful tools in efforts to avoid toxic adverse events. However, the majority of pharmacokinetic interactions listed for herbal medicinal products are based on theoretical predictions of the in vitro pharmacological effects of known constituents, which do not necessarily have to be the active ingredients. The prediction of herb-drug interactions is further complicated by the fact that pharmacokinetic data on active or (at least) known ingredients are often not available. The present article discusses the potential of pharmacokinetic profiling for detecting herb-drug interactions, using the most frequently cited interactions in the literature as examples. In particular, common mechanisms of herb-drug interactions are summarized, and the available experimental methods for detecting such interactions, as well as the limitations of these models, are critically evaluated. In addition, we discuss the question of whether the existing methods of detecting herb-drug interactions correlate with the clinical relevance. Effective screening tools that accurately predict metabolic herb-drug interactions would offer a tremendous advantage because it is not possible to study all potential herb-drug interactions in clinical trials.

Metabolic properties of the acid and lactone forms of HMG-CoA reductase inhibitors

To gain a better understanding of the metabolic properties between the open acid and lactone form of HMG-CoA reductase inhibitors (statins), the paper focused primarily on characterizing the metabolic properties of statins. We compared the metabolism of the acid and lactone forms of several statins, including atrovastatin, simvastatin, cerivastatin fluvastatin, pitavastatin and rosuvastatin with respect to metabolic clearance, CYP enzymes involved and drug-drug interactions. A remarkable increase in metabolic clearance was noted for all lactones compared with all acids except for pitavastatin lactone. The metabolic clearances of the atrovastatin, simvastatin, cerivastatin, fluvastatin and rosuvastatin lactones were 73-, 70-, 30-, 7- and 64-fold higher, respectively, than those of the corresponding acids. CYP2Cs were critically involved in the metabolism of cerivastatin, fluvastatin and pitavastatin acids. In contrast, CYP2Cs were not involved in the metabolism of the corresponding lactones and CYP3A4 was mainly involved. Moreover, a substantial difference in the metabolic inhibition of statins was found between acids and lactones. Overall, the study demonstrates that CYP-mediated metabolism of lactones is also a common metabolic pathway for statins and that the CYP3A4-mediated metabolism of the lactone forms clearly will need to be taken into account in assessing mechanistic aspects of drug-drug interaction involving statins.

Oxidative in vitro metabolism of liquiritigenin, a bioactive compound isolated from the Chinese herbal selective estrogen beta-receptor agonist MF101

Liquiritigenin [2,3-dihydro-7-hydroxy-2-(4-hydroxyphenyl)-(S)-4H-1-benzopyran-4-one] is one of the major active compounds of MF101, an herbal extract currently in clinical trials for the treatment of hot flashes and night sweats in postmenopausal women. MF101 is a selective estrogen receptor beta agonist but does not activate the estrogen receptor alpha. Incubation with pooled human liver microsomes yielded a single metabolite. Its structure was elucidated using tandem mass spectrometry in combination with analysis of the fragmentation patterns. The metabolite resulted from the loss of two hydrogens and rearrangement to the stable 7,4'-dihydroxyflavone. The structure was also confirmed by comparison with authentic standard material. Maximum apparent reaction velocity (V(max)) and Michaelis-Menten constant (K(m)) for the formation of 7,4'-dihydroxyflavone were 32.5 nmol/g protein/min and 128 microM, respectively. After correction for protein binding (free fraction = 0.84), the apparent intrinsic clearance (CL(int)) for 7,4'-dihydroxyflavone formation was 0.3 ml/g/min. Liquiritigenin was almost exclusively metabolized by CYP3A enzymes. Comparison of liquiritigenin metabolism in human liver microsomes isolated from 16 individuals showed 9.5-fold variability in metabolite formation (3.4-32.2 nmol/g protein/min). An estrogen receptor luciferase assay indicated that the metabolite was a 3-fold more potent activator of the estrogen receptor beta than the parent compound and did not activate the estrogen receptor alpha.

Repression of BK virus infection of human renal proximal tubular epithelial cells by pravastatin

BACKGROUND

BK virus (BKV), a human polyomavirus, causes BKV nephritis, which often leads to graft loss after renal transplantation. Currently, the only efficient therapy against BKV nephritis seems to be a reduction or change of immunosuppressive agents, but this may increase the inherent risk of rejection. Here, we report the ability of 3-hydroxy-3-methyl-glutaryl coenzyme A reductase inhibitor (statin), which is routinely used to treat hypercholesterolemia, to repress BKV entry pathways in human renal proximal tubular epithelial cells (HRPTEC) and, correspondently, prevent BKV infection.

METHODS

HRPTEC were co-incubated with BKV and pravastatin. Then the percentage of HRPTEC infected with BKV by immunofluorescent analysis and large T-antigen expression which suggested BKV infection by Western blots was assessed in the absence and presence of pravastatin. The distribution of purified and labeled BKV particles in the presence and absence of pravastatin was also investigated.

RESULTS

Both the percentage of BKV infected cells and the large T-antigen expression were significantly decreased in HRPTEC pretreated and co-incubated with pravastatin. However, when pravastatin was added 72 hr after BKV infection it failed to decrease percentage of BKV infected cells. It is likely, that pravastatin's inhibitory effect is explained by depletion of caveolin-1, a critical element of caveolae. BKV enters HRPTEC by caveolar-mediated endocytosis. We provide evidence that pravastatin dramatically decreased caveolin-1 expression in HRPTEC and interfered with internalization of labeled BKV particles.

CONCLUSIONS

Our data suggest that pravastatin, acting through depletion of caveolin-1, prevented caveolar-dependent BKV internalization and repressed BKV infection of HRPTEC.

Statins do not adversely affect post-interventional residual platelet aggregation and outcomes in patients undergoing coronary stenting treated by dual antiplatelet therapy

AIMS

There are growing data suggesting a clinical relevance of residual platelet aggregation (RPA) in patients undergoing PCI. Drug-drug interaction of statins and clopidogrel has been controversially discussed in ex vivo studies and clinical trials. The aim of the present study was to investigate the effects of peri-procedural statin medication on the metabolization of aspirin and clopidogrel with regard to platelet aggregation and clinical outcome in patients undergoing coronary intervention.

METHODS AND RESULTS

Patients with coronary stenting for symptomatic coronary artery disease are routinely evaluated by platelet function analysis in a monocentre registry, and for the present study, a consecutive cohort of 1155 patients were analysed. About 87.7% of the patients were treated with statins at the time of platelet function analysis. Residual platelet activity assessed by adenosine diphosphate (20 micromol/L)-induced platelet aggregation was not significantly influenced by statin treatment. Nor the significant effects of CYP3A4-metabolization pathway on post-treatment aggregation were recorded, although there was even a trend to lower RPA values in patients treated with CYP3A4-metabolized statins. Further, in an inter-individual analysis comparing patients treated with CYP3A4- and non-CYP3A4-metabolized statins, no time-dependent difference of clopidogreĺs anti-aggregatory effects was observed. Clinical follow-up of major adverse events (myocardial infarction, ischaemic stroke, death) in 991 patients within 3 months revealed no significant adverse effects of statin treatment on clinical outcome. Instead, statin treatment was independently associated with lower incidence of composite events (HR 0.44, 95% confidence interval 0.23-0.83, P = 0.01).

CONCLUSION

Peri-procedural co-administration of statins does not increase the post-interventional RPA in cardiovascular patients treated with dual antiplatelet therapy and does not worsen the clinical prognosis of these patients.