Simran Maggo

Clinical Implications of Pharmacogenetic Variation on the Effects of Statins

The last decade has seen an increase in the trend of HMG-CoA reductase inhibitor (statin) usage in the Western world, which does not come as a surprise noting that the latest American Heart Association heart and stroke statistics indicate an alarming prevalence of 80 million Americans (one in three) with one or more forms of diagnosed cardiovascular disease (CVD). Meta-analysis of several large-scale, randomized clinical trials has demonstrated statins to be efficacious in significantly reducing CVD-associated mortality in both primary and secondary prevention. Despite their proven efficacy, statins have also gained attention with respect to adverse drug reactions (ADRs) of muscle myopathy, derangements in hepatic function and even ADRs classified as psychiatric in nature. The depletion of cholesterol within the myocyte cell wall and/or the depletion of key intermediates within the cholesterol synthesis pathway are hypothesized as possible mechanisms of statin-associated ADRs. However, pharmacogenetic variability may also be a risk factor for ADRs and can include, for example, enzymes, transporters, cell membrane receptors, intracellular receptors or components of ion channels that contribute to the pharmacokinetics or pharmacodynamics of response to a particular drug. The cytochrome P450 (CYP) enzymatic pathways that comprise the polymorphic genes, CYP2D6, CYP3A4 and CYP3A5, and also a hepatic transporter, solute carrier organic anion transporter (SLCO1B1), which is a single nucleotide polymorphism discovered to be associated with statin-induced myopathy through a genome-wide association study, are discussed with respect to their effect on altering the pharmacokinetic profile of statin metabolism. Variants of the Apolipoprotein E (APO-E) gene, polymorphisms in the cholesteryl ester transfer protein (CETP) gene, the HMG-CoA reductase gene and other proteins are discussed with respect to altering the pharmacodynamic profile of statins. Pharmacogenetics and its application in medicine to individualize drug therapy has been previously shown to be clinically and economically beneficial through quality-adjusted life-year assessment. Therefore, polymorphisms affecting the pharmacokinetic and pharmacodynamic profiles of statins, which are widely used in therapy, with their potential application in the personalized prescribing of statin therapy, need further research. In this review, we update the recent literature with respect to genetic polymorphisms that may influence the pharmacokinetics and pharmacodynamics of statin therapy, and consider the relevance of these findings to the efficacy of treatment, prevention of ADRs and what this may mean for patient tolerance and compliance.

Cardiovascular Events in Patients taking Varenicline

AbstractBackground: The smoking cessation medicine varenicline has been associated with an increased risk of cardiovascular adverse events compared with placebo in clinical trials. Cases of cardiovascular events, including myocardial infarction (MI) and cardiac dysrhythmias, have been noted from spontaneous reporting systems. Objective: The aim of this study was to summarize and describe cardiovascular adverse reactions identified in a general population during intensive postmarketing surveillance of varenicline in New Zealand. Methods: Observational prospective cohort study using prescription event monitoring methods. The patient cohort was established from pharmacy dispensing data sent directly to the Intensive Medicines Monitoring Programme (IMMP) for all New Zealand patients prescribed varenicline. Adverse cardiovascular events were identified from follow-up questionnaires completed by doctors, spontaneous reports and by record linkage to national datasets. Cardiovascular events were organized into clinical groupings for further clinical assessment, and key cases were identified. Results: All New Zealand patients dispensed a prescription for varenicline from 1 April 2007 to 30 November 2010 were included in this study. At 31 January 2011, the IMMP varenicline events dataset included a total of 172 adverse events in the IMMP circulatory System Organ Class. There were 48 reports of myocardial ischaemia, including 12 reports of MI and 8 reports of angina. Two key cases of myocardial ischaemia suggested that this may have been induced by coronary artery spasm secondary to varenicline treatment. There were 50 reports of hypotensive events, with two key cases having documented hypotension associated with chest pain/tightness, and a further 27 reports of dysrhythmia events, including two unexplained sudden deaths. Conclusions: This paper presents a series of cases of cardiovascular events in patients taking varenicline. Whilst there were multiple confounding factors in some patients, key cases were identified that suggested a possible mechanism of dysregulation of blood pressure leading to vasospasm or hypotension.

Effects of HMG-CoA reductase inhibitors on learning and memory in the guinea pig

Statins reduce the risk of death from cardiovascular disease in millions of people worldwide. Recent pharmacovigilance data has suggested that people taking statins have an increased risk of psychiatric adverse events such as amnesia and anxiety. This study aimed to investigate the possibility of statin-induced amnesia through animal models of memory and learning. We conducted extracellular field recordings of synaptic transmission in area CA1 of hippocampal slices to examine the effects of acute cholesterol lowering with lipid lowering drugs. We also assessed the effect of six weeks of simvastatin (2mg/kg/d) and atorvastatin (1mg/kg/d) treatment using the Morris water maze. Long Term Potentiation (LTP) was significantly diminished in the presence of 3µM atorvastatin or simvastatin and by the cholesterol sequestering agent methyl-β-cyclodextrin (MBCD). The effects were reversed in the MBCD but not the statin treated slices by the addition of cholesterol. In the water maze, statin treatment did not cause any deficits in the first five days of reference memory testing, but statin treated guinea pigs preformed significantly worse than control animals in a working memory test. The deficits observed in our experiments in water maze performance and hippocampal LTP are suggestive of statin induced changes in hippocampal plasticity. The effects on LTP are independent of cholesterol regulation, and occur at concentrations that may be relevant to clinical use. Our results may help to explain some of the behavioural changes reported in some people after beginning statin treatment.

Neuroprotective effect of hydroxypropyl-β-cyclodextrin in hypoxia-ischemia.

Neonatal cerebral ischemic injury is a common and debilitating pathology for which there is currently no known purely pharmacological treatments that are effective when delivered immediately after injury. Cyclodextrins are cyclic oligosaccharides that can remove cholesterol from cell membranes and thereby affect receptor function. Cyclodextrins have previously been shown to be neuroprotective in vitro. We showed that hydroxypropyl-&bgr;-cyclodextrin is neuroprotective in rats in vivo when delivered by intraperitoneal injection 30 min following hypoxia-ischemia, when assessed 15 days after surgery. A single dose of 1 g/kg hydroxypropyl-&bgr;-cyclodextrin reduced brain infarction size by 28.57% compared with control (P<0.001). We also report that the same compound reduces neuronal excitability in hippocampal slices and propose that hydroxypropyl-&bgr;-cyclodextrin is neuroprotective by reducing excitotoxicity in the delayed phase of brain damage.

The effect of statins on performance in the Morris water maze in guinea pig.

Statins play a crucial role in reducing the risk of death from cardiovascular disease in millions of people worldwide. Recently, pharmacovigilance data has suggested that statin drugs may have rare but significant adverse psychiatric effects, such as amnesia, anxiety and even aggression. In order to investigate the effects of statins on cognitive function in an animal model, we studied the effect of 6 weeks of daily administration of oral simvastatin (1 mg/kg) or atorvastatin (0.5mg/kg) in guinea pig on performance in the Morris water maze (MWM). Animals were also re-tested in the MWM, 2 weeks after drug cessation, to test for any changes in performance as a result of drug de-challenge. Guinea pigs treated with either statin showed a significant (P<0.001) decrease in total cholesterol and low density lipoprotein-cholesterol (LDL-C), which remained partially reduced after the 2 week drug washout period. Guinea pigs receiving either statin did not show any difference in latency to reach the platform, nor any difference in total distance travelled during testing. Also, analysis of probe trials revealed no significant differences between drug and vehicle groups. However, both groups spent a significantly (P<0.01) greater proportion of time in the outer zone of the maze (indication of increased anxiety) and showed an increase in swimming speed (P<0.05) compared with the vehicle group. Differences between groups for swimming speed, and time spent in the outer zone, were not retained in the drug de-challenge phase. Our results show that low dose treatment with statins can induce mild but significant anxiety in guinea pigs.

Impact of New Genomic Technologies on Understanding Adverse Drug Reactions

It is well established that variations in genes can alter the pharmacokinetic and pharmacodynamic profile of a drug and immunological responses to it. Early advances in pharmacogenetics were made with traditional genetic techniques such as functional cloning of genes using knowledge gained from purified proteins, and candidate gene analysis. Over the past decade, techniques for analysing the human genome have accelerated greatly as knowledge and technological capabilities have grown. These techniques were initially focussed on understanding genetic factors of disease, but increasingly they are helping to clarify the genetic basis of variable drug responses and adverse drug reactions (ADRs). We examine genetic methods that have been applied to the understanding of ADRs, review the current state of knowledge of genetic factors that influence ADR development, and discuss how the application of genome-wide association studies and next-generation sequencing approaches is supporting and extending existing knowledge of pharmacogenetic processes leading to ADRs. Such approaches have identified single genes that are major contributing genetic risk factors for an ADR, (such as flucloxacillin and drug-induced liver disease), making pre-treatment testing a possibility. They have contributed to the identification of multiple genetic determinants of a single ADR, some involving both pharmacologic and immunological processes (such as phenytoin and severe cutaneous adverse reactions). They have indicated that rare genetic variants, often not previously reported, are likely to have more influence on the phenotype than common variants that have been traditionally tested for. The problem of genotype/phenotype discordance affecting the interpretation of pharmacogenetic screening and the future of genome-based testing applied to ADRs are also discussed.

Personalised prescribing in psychiatry: Has pharmacogenomics delivered on its promise?

Australian & New Zealand Journal of Psychiatry, 50(6) Advances in genetic technology in the past two decades promised to transform the way drug treatments are matched to individual patients. However, the anticipated shift towards genetically informed personalised prescribing for mental disorders has not yet occurred. To understand the potential future benefits of pharmacogenomics to psychiatry, it is useful to reflect on results to date. In 2005, the United States Federal Drug Administration approved use of the AmpliChip CYP450 Test (Roche Molecular Systems, Inc.), heralding a new era of personalised drug prescribing. The AmpliChip test was designed to identify common variants in the CYP2D6 and CYP2C19 genes, which encode two cytochrome P450 (CYP) enzymes influencing hepatic drug metabolism. The test was made available for less than US

Epistaxis and other haemorrhagic events associated with the smoking cessation medicine varenicline: a case series from two national pharmacovigilance centres

1000, bringing cutting edge genetics technology within the reach of patients in routine treatment settings. Since then, genomic technology has progressed enormously and costs have fallen dramatically. Now the main barrier to using pharmacogenetic technology is clinical utility rather than cost. Genetic factors influencing the pharmacokinetics of common psychiatric drugs are increasingly well understood. Most psychotropic drugs are metabolised in the liver by enzymes of the CYP family. CYP2D6 (responsible for metabolising about 25% of all drugs, including several antidepressants and antipsychotics) and CYP2C19 (about 10% of drugs, including tricyclic antidepressants, selective serotonin re-uptake inhibitors [SSRIs] and serotonin–norepinephrine reuptake inhibitors [SNRIs]) are particularly important. CYP enzymes are highly polymorphic, and genetic variation contributes greatly to drug metabolism and therefore total drug exposure. Consequently, it is logical CYP polymorphisms would also influence drug response and the liability to adverse effects, although demonstrating this has been surprisingly difficult. For example, in the Sequenced Treatment Alternatives to Treat Depression (STAR*D) study, common known polymorphisms in genes relevant to citalopram metabolism, including CYP2D6, CYP2C19, CYP3A4 and CYP3A5, did not predict retention of subjects in the trial, final citalopram dosage or depression response (Peters et al., 2008). There are several obvious reasons why identifying genetic determinants of pharmacokinetics has not greatly impacted prescribing practices for mental disorders. First, most commonly used psychotropic drugs have a wide therapeutic index, meaning increased drug exposure does not invariably lead to more adverse effects. Furthermore, many drugs with a narrow therapeutic index, including tricyclic antidepressants, are routinely monitored with plasma drug assays; this negates much of the benefit of pharmacogenetic testing. Second, for most drugs used to treat mental disorders, the correlation between drug exposure and clinical response is low. Third, many psychotropic drugs are metabolised by multiple breakdown pathways, meaning complete loss of functioning in one enzyme system may not greatly reduce drug clearance. Despite the disappointing results noted above, individual case reports have highlighted the potential benefits of genetic testing in selected patients with unusual adverse reactions or patterns of drug response. As an example, deficient CYP2D6 and CYP2C19 enzyme activity has been reported in patients experiencing adverse effects from antidepressants while excessive CYP enzyme activity has been reported in association with inadequate clinical response (Dinama et al., 2014). Genetic factors influencing the transport of psychotropic drugs across the blood brain barrier have also attracted attention. In particular, ABCB1, which encodes P-glycoprotein, has been closely studied in relation to antidepressant response. Although results for ABCB1 have been mixed, a Personalised prescribing in psychiatry: Has pharmacogenomics delivered on its promise?

Long fragment polymerase chain reaction

PurposeTo present a case series of haemorrhagic events associated with varenicline identified from the New Zealand (NZ) and Netherlands national pharmacovigilance centres and propose a possible mechanism for these adverse events.MethodsReports of epistaxis and other haemorrhagic events (in all system organ classes excluding gynaecological) associated with varenicline were identified and assessed in both the NZ Intensive Medicines Monitoring Programme (IMMP) and the Netherlands Pharmacovigilance Centre Lareb (Lareb). Additional reports were identified from the World Health Organisation Uppsala Monitoring Centre (WHO-UMC) datasets, and these also underwent causality assessment.ResultsA total of 30 reports of haemorrhagic events were identified by the NZ IMMP (16 reports) and Lareb (14 reports). Six cases of epistaxis were identified, and four patients had a positive dechallenge on withdrawal of varenicline, suggesting a causal association. Another five reports of gingival bleeding were identified, with three patients having a positive dechallenge. Another patient who experienced haemoptysis while taking varenicline had a positive dechallenge and a positive rechallenge. In the WHO datasets, a further 49 reports of epistaxis, 39 reports of haemoptysis and 21 reports of thrombocytopenia were identified. A plausible mechanism for haemorrhagic events associated with varenicline may be a result of interaction with the serotonin (5-HT) receptor system and transporter.ConclusionsThis is the first specific investigation of haemorrhagic events associated with varenicline. The results of our assessment of reports identified by two national pharmacovigilance centres suggest that there may be causal relationship between varenicline and these adverse events.

Relationship between metabolic phenotypes and genotypes of CYP1A2 and CYP2A6 in the Nigerian population

Polymerase chain reaction (PCR) is an oft-used preparatory technique in amplifying specific DNA regions for downstream analysis. The size of an amplicon was initially limited by errors in nucleotide polymerization and template deterioration during thermal cycling. A variant of PCR, designated long-range PCR, was devised to counter these drawbacks and enable the amplification of large fragments exceeding a few kb. In this chapter we describe a protocol for long-range PCR, which we have adopted to obtain products of 6.6, 7.2, 13, and 20 kb from human genomic DNA samples.