Symptomatic interventions for patients with dementia involve anti-dementia drugs to improve cognition, psychotropic drugs for the treatment of behavioral disorders (BDs), and different categories of drugs for concomitant disorders. Demented patients may take >6–10 drugs/day with the consequent risk for drug–drug interactions and adverse drug reactions (ADRs >80%) which accelerate cognitive decline. The pharmacoepigenetic machinery is integrated by pathogenic, mechanistic, metabolic, transporter, and pleiotropic genes redundantly and promiscuously regulated by epigenetic mechanisms. CYP2D6, CYP2C9, CYP2C19, and CYP3A4/5 geno-phenotypes are involved in the metabolism of over 90% of drugs currently used in patients with dementia, and only 20% of the population is an extensive metabolizer for this tetragenic cluster. ADRs associated with anti-dementia drugs, antipsychotics, antidepressants, anxiolytics, hypnotics, sedatives, and antiepileptic drugs can be minimized by means of pharmacogenetic screening prior to treatment. These drugs are substrates, inhibitors, or inducers of 58, 37, and 42 enzyme/protein gene products, respectively, and are transported by 40 different protein transporters. APOE is the reference gene in most pharmacogenetic studies. APOE-3 carriers are the best responders and APOE-4 carriers are the worst responders; likewise, CYP2D6-normal metabolizers are the best responders and CYP2D6-poor metabolizers are the worst responders. The incorporation of pharmacogenomic strategies for a personalized treatment in dementia is an effective option to optimize limited therapeutic resources and to reduce unwanted side-effects.

Pharmacogenomics of Cognitive Dysfunction and Neuropsychiatric Disorders in Dementia.

UDP-glucuronosyltransferases (UGTs) are involved in phase II conjugation reactions of xenobiotics and differences in their isoform activities result in interindividual kinetic differences of UGT probe substrates. Here, extensive literature searches were performed to identify probe substrates (14) for various UGT isoforms (UGT1A1, UGT1A3, UGT1A4, UGT1A6, UGT1A9, UGT2B7 and UGT2B15) and frequencies of human polymorphisms. Chemical-specific pharmacokinetic data were collected in a database to quantify interindividual differences in markers of acute (Cmax) and chronic (area under the curve, clearance) exposure. Using this database, UGT-related uncertainty factors were derived and compared to the default factor (i.e. 3.16) allowing for interindividual differences in kinetics. Overall, results show that pharmacokinetic data are predominantly available for Caucasian populations and scarce for other populations of different geographical ancestry. Furthermore, the relationships between UGT polymorphisms and pharmacokinetic parameters are rarely addressed in the included studies. The data show that UGT-related uncertainty factors were mostly below the default toxicokinetic uncertainty factor of 3.16, with the exception of five probe substrates (1-OH-midazolam, ezetimibe, raltegravir, SN38 and trifluoperazine), with three of these substrates being metabolised by the polymorphic isoform 1A1. Data gaps and future work to integrate UGT-related variability distributions with in vitro data to develop quantitative in vitro-in vivo extrapolations in chemical risk assessment are discussed.

/pdf/human-variability-in-isoform-specific-udp-1y8njywscg.pdf

Human variability in isoform-specific UDP-glucuronosyltransferases: markers of acute and chronic exposure, polymorphisms and uncertainty factors

AIMS To investigate the impact of glucuronidation enzyme (UGT1A4*3 142T>G, UGT1A4*2 70C>A, UGT2B7 -161C>T) and transporter (MDR1/ABCB1 1236C>T, ABCG2 421C>A) polymorphisms on steady-state disposition of lamotrigine and on the lamotrigine-valproate interaction. METHODS Adults with epilepsy on lamotrigine monotherapy (n = 131) or lamotrigine + valproate treatment (n = 74) were genotyped and steady-state lamotrigine and valproate morning troughs were determined as a part of routine therapeutic drug monitoring. RESULTS No effect of UGT and MDR1/ABCB1 polymorphisms was observed. In the entire cohort, ABCG2 421A allele had no effect however an interaction between the variant allele and valproate was observed: (i) in lamotrigine-only patients, variant allele (vs. wild type homozygosity) was independently (adjustments: age, sex, body mass index, lamotrigine dose, other polymorphisms) associated with mildly lower lamotrigine troughs [geometric means ratio (GMR) = 0.76, 95% confidence interval (CI) 0.59-0.98], whereas in lamotrigine + valproate patients it was associated with higher troughs (GMR = 1.72, 95%CI 1.14-2.62); (ii) valproate cotreatment was overall associated with markedly higher troughs vs. lamotrigine monotherapy (GMR = 3.49, 95%CI 2.73-4.44), but more so in variant allele carriers (GMR = 5.24, 95%CI 3.38-8.15) than in wild type homozygotes (GMR = 2.32, 95%CI 1.89-2.83); (iii) variant allele effects in two treatment subsets and valproate effects in two genotype subsets differed by 2.36-fold (95%CI 1.39-3.67); (iv) increase in lamotrigine troughs associated with increasing valproate troughs was greater in variant allele carriers than in wild type homozygotes, i.e. variant allele effect increased with increasing valproate troughs. CONCLUSION This study is first to indicate a potentially relevant interaction between ABCG2 421C>A polymorphism and valproate in their effects on lamotrigine disposition.

https://bpspubs.onlinelibrary.wiley.com/doi/pdf/10.1111/bcp.13646

Interaction between ABCG2 421C>A polymorphism and valproate in their effects on steady-state disposition of lamotrigine in adults with epilepsy.

Pharmacogenomics can identify polymorphisms in genes involved in drug pharmacokinetics and pharmacodynamics determining differences in efficacy and safety and causing inter-individual variability in drug response. Therefore, pharmacogenomics can help clinicians in optimizing therapy based on patient's genotype, also in psychiatric and neurological settings. However, pharmacogenetic screenings for psychotropic drugs are not routinely employed in diagnosis and monitoring of patients treated with mood stabilizers, such as carbamazepine and valproate, because their benefit in clinical practice is still controversial. In this review, we summarize the current knowledge on pharmacogenetic biomarkers of these anticonvulsant drugs.

Pharmacogenetics of Carbamazepine and Valproate: Focus on Polymorphisms of Drug Metabolizing Enzymes and Transporters.

Population pharmacokinetics of valproic acid in epileptic children: Effects of clinical and genetic factors.

Background The association between CYP2D6 metabolizer status and clinical outcomes of venlafaxine was extensively investigated previously, but no widely accepted conclusion has been reached so far. To obtain a more precise estimation of the association, a systematic review by meta-analysis was conducted in the present study. Methods The PubMed, EMBASE, Cochrane Library, Chinese National Knowledge Infrastructure, Technology of Chongqing, and Wan Fang Database were searched for eligible studies up to August 2018. Results Fourteen related studies involving 1035 patients were finally included. Significant associations were found among 3 CYP2D6 phenotypes (NM, IM, and PM) and most pharmacokinetic parameters of venlafaxine. However, CYP2D6 phenotypes were not associated with Hamilton Depression Rating Scale response of venlafaxine. In addition, we also found no significant association between CYP2D6 phenotype and overall rate of adverse events. Conclusions CYP2D6 metabolizer status had significant influence on venlafaxine pharmacokinetics, but insufficient evidence demonstrated that CYP2D6 metabolizer status was associated with its therapeutic effects and overall rate of adverse events, which provided further evidence regarding the relationship between CYP2D6 metabolizer status and venlafaxine.

The Associations Between CYP2D6 Metabolizer Status and Pharmacokinetics and Clinical Outcomes of Venlafaxine: A Systematic Review and Meta-Analysis.

Valproic acid (VPA) is one of the most widely used antiepileptic drugs. Recently, increasing evidence suggested that polymorphisms in UGT2B7 gene were associated with VPA pharmacokinetics, but results remained controversial. Therefore, a meta-analysis was performed to derive a more precise evaluation between C802T, C161T, and G211T polymorphisms and plasma concentration of VPA. The PubMed, EMBASE, and the Cochrane library databases were searched for eligible studies. Articles meeting the inclusion criteria were comprehensively reviewed, and the available data were accumulated. The mean difference (MD) and 95% confidence interval (CI) were applied to assess the strength of the relationship. A total of 12 studies involving 1996 related East Asia epilepsy patients were assessed. We found that the UGT2B7 G211T polymorphism was associated with adjusted plasma VPA concentration (GG versus TT: P = 0.01, I
 2 = 97%; GG versus GT: P < 0.00001, I
 2 = 0%). Additionally, we also observed a significantly association between the C161T polymorphism and adjusted plasma VPA concentration (CC versus CT: P = 0.01, I
 2 = 77%). Nevertheless, the pooled analysis showed that the C802T polymorphism had no significant effect on adjusted serum concentration of VPA. The results of this meta-analysis demonstrated that UGT2B7 G211T and C161T polymorphisms were able to affect the pharmacokinetics in epilepsy patients treated with VPA, which provide further evidence for genetic effects of UGT2B7 gene on pharmacokinetics and pharmacodynamics of VPA. Epilepsy patients with these genotypes may be necessary to increase (or decrease) VPA dose to ensure its therapeutic effect.

Effect of UGT2B7 genotypes on plasma concentration of valproic acid: a meta-analysis

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The Associations Between CYP2D6 Metabolizer Status and Pharmacokinetics and Clinical Outcomes of Venlafaxine: A Systematic Review and Meta-Analysis.

Effect of UGT2B7 genotypes on plasma concentration of valproic acid: a meta-analysis