The Potential Role of POR*28 and CYP1A2*F Genetic Variations and Lifestyle Factors on Clozapine and N-DesmethylClozapine Plasma Levels in Schizophrenia Patients.

BACKGROUND: Despite its advantages over other antipsychotics, for treatment-resistant schizophrenia, clinical use of Clozapine (CLZ) is challenging by its narrow therapeutic index and potentially life-threatening dose-related adverse effects. RESEARCH DESIGN AND METHODS: As the potential role in CLZ metabolism is assigned to CYP1A2 enzyme and consequently Cytochrome P450 oxidoreductase (POR) their genetic variations might help to determine CLZ levels in schizophrenia patients. For this purpose, 112 schizophrenia patients receiving CLZ were included in the current study. Plasma CLZ and N-desmethylclozapine (DCLZ) levels were analyzed by using HPLC and genetic variations were identified with the PCR-RFLP method. RESULTS: The patients' CYP1A2 and POR genotypes seemed to not affect plasma CLZ and DCLZ levels whereas in the subgroup analysis, POR *28 genotype significantly influenced simple and adjusted plasma CLZ and DLCZ levels concerning smoking habit and caffeine consumption. CONCLUSIONS: The findings of the present study highlight the importance of both genetic and non-genetic factors (smoking and caffeine consumption) for the individualization of the CLZ treatment. In addition to that, it suggests that the added utility of not only the CLZ metabolizing enzymes but also POR, which is crucial for proper CYP activity, to guide CLZ dosing might be useful for clinical decision-making.

The Influence of Genetic Variations and Drug Interactions Based on Metabolism of Antidepressants and Anticonvulsants.

BACKGROUND: The variability in drug response is highly complex and can be attributed to the polymedication, genetic polymorphisms modulating drug-metabolizing enzyme activities (cytochromes P450, CYP), physiological and environmental factors." sentence could be revised as "The variability in drug response is highly complex and can be attributed to the polymedication, genetic polymorphisms modulating drugmetabolizing enzyme activities (cytochromeP450s (CYP)), physiological and environmental factors. OBJECTIVE: The main objective of this review is to deeply discuss the role of biotransformation in the occurrence of antidepressant and anticonvulsant induced inter individual variabilities with the focus on genetic variations and drug interactions. METHODS: An extensive search of the literature has been conducted related to biotransformation of the antidepressant and anticonvulsant agents on relationships between genetic differences and drug interactions on available databases. Following keywords are used for relevant articles: "metabolic enzyme", "pharmacokinetic", "antidepressant", "anticonvulsant", "genetic variations", "enzyme inhibition", "enzyme induction" and also with a list of all included antidepressant and anticonvulsants. RESULTS: In the present review, we provided an overview of documented clinically significant pharmacokinetic drug interactions, physiological and environmental differences. We further discuss the significance of genetic variations in drug metabolizing enzymes to underline the need for using the information on both genotype and drug interactions towards implementing better clinical outcomes through personalized medicine in neurology and psychiatry. CONCLUSION: The present review clearly illustrates that interindividual differences in the biotransformation (including genetic variability of the drug metabolizing enzymes, age, sex, diet) of the antidepressant and anticonvulsant drugs, which are commonly prescribed medications globally, has a crucial role in the occurrence of adverse effects and various drug responses. Therefore, the potential results of the drug-drug interactions and individual genetic characteristics should always be considered to make pharmacotherapy safer and more effective, as they have major clinical implications.

The relationship between plasma levels of clozapine and N-desmethyclozapine as well as M1 receptor polymorphism with cognitive functioning and associated cortical activity in schizophrenia.

Studies that examined the effect of clozapine on cognitive functions in schizophrenia provided contradictory results. N-desmethylclozapine (NDMC) is the major metabolite of clozapine and have procognitive effects via agonistic activity in the M1 cholinergic receptors. The rs2067477 polymorphism in the M1 receptors may play role in cognitive profile in schizophrenia. We investigated the association of plasma clozapine (PClz), NDMC (PNdmc) levels and the rs2067477 polymorphism with cognitive functions and cortical activity measured by functional near infrared spectroscopy during the N-Back task in subjects with schizophrenia (N = 50) who are under antipsychotic monotherapy with clozapine. We found that PClz and PNdmc levels were negatively, PNdmc/PClz ratio was positively correlated with immediate recall score in the Rey Auditory Verbal Learning Test. PNdmc/PClz ratio was positively correlated with cortical activity during the N-back task. M1 wild-type group (CC: wild-type) produced higher cortical activity than M1 non wild-type group (CA: heterozygote / AA: mutant) in cortical regions associated with working memory (WM). These results suggest that individual differences in clozapine's effect on short term episodic memory may be associated with PClz and PNdmc. Higher activity in the M1 wild-type group may indicate inefficient use of cortical resources and/or excessive use of certain cognitive strategies during WM performance.

The Association of CYP2D6*4 and POR*28 Polymorphisms on Mirtazapine Plasma Level in Subjects with Major Depressive Disorder and Anxiety Disorders.

AIMS AND OBJECTIVE: The plasma level of mirtazapine (MIR) varies between individuals primarily depending on the differences in metabolism during pharmacotherapy. CYP2D6 takes the role as a major enzyme in MIR metabolism and POR enzyme donates an electron to CYP2D6 for its activity. Single nucleotide polymorphisms in the genes encoding pharmacokinetic enzymes may cause changes in enzyme activity, leading to differences in metabolism of the drug. Our aim was to assess the influence of CYP2D6*4 and POR*28 polymorphisms on MIR plasma levels in Turkish psychiatric patients. MATERIALS AND METHODS: The association between genetic variations and plasma level of MIR was investigated on 54 patients. CYP2D6*4 and POR*28 polymorphisms were analysed using Polymerase Chain Reaction- Restriction Fragment Length Polymorphism (PCR-RFLP) and plasma MIR levels were measured using HPLC. RESULTS: Allele frequencies of CYP2D6*4 and POR*28 were 0.11 and 0.39, respectively in the study population. The results showed that CYP2D6*4 allele carriers have higher C/D MIR levels while POR*28 allele carriers have lower C/D MIR levels. Combined genotype analyses also revealed that individuals with CYP2D6*1/*1 - POR*28/*28 genotype have a statistically lower C/D MIR level (0.95 ng/ml/dose) when compared with individuals with CYP2D6*1/*1 - POR*1/*1 genotype (1.52 ng/ml/dose). CONCLUSION: Our results indicate that CYP2D6*4 and POR*28 polymorphisms may have a potential in the explanation of differences in plasma levels in MIR treated psychiatric patients. A combination of these variations may be beneficial in increasing drug response and decreasing adverse drug reactions in MIR psychopharmacotherapy.

A Novel Genotyping Method for Detection of the Muscarinic Receptor M1 Gene rs2067477 Polymorphism and Its Genotype/Allele Frequencies in a Turkish Population.

OBJECTIVES: Gene variation in the cholinergic muscarinic receptor 1 (CHRM1) has potential to become a candidate biomarker in the development of several disorders as well as drug response. In this study, a novel polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assay was developed to determine the C to A single nucleotide polymorphism at position 267 in the CHRM1 gene. MATERIALS AND METHODS: A new reverse primer and a mismatched forward primer were designed to obtain 125 bp PCR products. The PCR products were then digested with the Hae III restriction enzyme to detect the rs2067477 polymorphism that comprises a C to A base change. The novel assay developed was tested in 51 Turkish schizophrenia patients. RESULTS: The genotyping assay was successfully performed in patients with schizophrenia in order to confirm the accuracy and validity of this method. The frequency of CC, CA, and AA genotypes was 72.5%, 25.5%, and 2%, respectively. On the basis of these findings, the allele frequency of C was 0.85 and the allele frequency of A was 0.15. CONCLUSION: This genotyping assay is practical for screening the CHRM1 C267A polymorphism in pharmacogenetic studies. The present polymorphism may be used as a candidate biomarker to determine genetic susceptibility to related diseases and may contribute to the implementation of individualized drug therapy for M1-related diseases.

A Novel PCR-RFLP Method for Detection of POR*28 Polymorphism and its Genotype/Allele Frequencies in a Turkish Population.

BACKGROUND: The Cytochrome P450 (CYP) enzymes are involved in the metabolism of many endogenous and exogenous substances. They need electrons for their activity. CYP mediated oxidation reactions require cytochrome oxidoreductase (POR) as an electron donor. A common genetic variation identified in the coding region of POR gene (POR*28) leads to an alteration in POR activity by causing amino acid change. The current study aimed to determine the allele and genotype frequencies of POR*28 in a healthy Turkish population by using a novel genotyping assay. METHODS: A novel PCR-RFLP assay was developed for the detection of POR*28 (rs1057868) polymorphism and the obtained frequencies were compared with the data established in various ethnic groups. RESULTS: Genotypic analysis revealed that of 209 healthy, unrelated individuals tested for POR*28 polymorphism, 55.5% of the studied subjects were homozygous for the CC genotype, 34.9% were heterozygous for the CT genotype and 9.6% were homozygous for the TT genotype. The allele frequencies were 0.73 (C) and 0.27 (T). The present results were in accordance with the Hardy- Weinberg equilibrium. The distribution of POR*28 allele varies between populations. The frequency of the T allele among members of the Turkish population was similar to frequencies in Caucasian populations but was lower than in Japanese and Chinese populations. CONCLUSIONS: In this study, a novel method was developed, which could be applied easily in every laboratory for the genotyping of POR *28 polymorphism. The developed genotyping method and documented allele frequencies may have potential in understanding and predicting the variations in drug response/adverse reactions in pharmacotherapy and susceptibility to diseases in POR-mediated metabolism reactions.