Cytochrome P450 2D6 genotyping: potential role in improving treatment outcomes in psychiatric disorders

CYP2D6 Allelic Variants *34, *17-2, *17-3, and *53 and a Thr309Ala Mutant Display Altered Kinetics and NADPH Coupling in Metabolism of Bufuralol and Dextromethorphan and Altered Susceptibility to Inactivation by SCH 66712

Metabolic phenotype can be affected by multiple factors, including allelic variation and interactions with inhibitors. Human CYP2D6 is responsible for approximately 20% of cytochrome P450-mediated drug metabolism but consists of more than 100 known variants; several variants are commonly found in the population, whereas others are quite rare. Four CYP2D6 allelic variants-three with a series of mutations distal to the active site (*34, *17-2, *17-3) and one ultra-metabolizer with mutations near the active site (*53), along with reference *1 and an active site mutant of *1 (Thr309Ala)-were expressed, purified, and studied for interactions with the typical substrates dextromethorphan and bufuralol and the inactivator SCH 66712. We found that *34, *17-2, and *17-3 displayed reduced enzyme activity and NADPH coupling while producing the same metabolites as *1, suggesting a possible role for Arg296 in NADPH coupling. A higher-activity variant, *53, displayed similar NADPH coupling to *1 but was less susceptible to inactivation by SCH 66712. The Thr309Ala mutant showed similar activity to that of *1 but with greatly reduced NADPH coupling. Overall, these results suggest that kinetic and metabolic analysis of individual CYP2D6 variants is required to understand their possible contributions to variable drug response and the complexity of personalized medicine.

Developing a Risk Score to Guide Individualized Treatment Selection in Attention Deficit/Hyperactivity Disorder

OBJECTIVE

To develop a risk score for treatment failure that could potentially be used to individualize treatment selection between lisdexamfetamine dimesylate (LDX) and osmotic-release oral system methylphenidate (OROS-MPH) in children and adolescents with attention deficit/hyperactivity disorder (ADHD).

METHODS

The study used data from patients with ADHD receiving LDX (N = 104) or OROS-MPH (N = 107) in a phase III randomized clinical trial. A prediction model was developed to estimate risk scores for failing OROS-MPH, where treatment failure was defined as less than 25% improvement in the ADHD Rating Scale IV total score from baseline. Patients were ranked by their predicted risks of OROS-MPH failure to define high-risk subpopulations. Outcomes of LDX and OROS-MPH were compared within subpopulations.

RESULTS

The prediction model for OROS-MPH failure selected seven predictors (age, disease duration, and five ADHD Rating Scale IV item scores) and had an in-sample C statistic of 0.860. Among all patients, LDX had a 17% (95% confidence interval 7.1%-27.8%) lower treatment failure rate than that of OROS-MPH; differences in failure rates ranged from 17% to 43% across subpopulations, increasingly enriched for high-risk patients. Similar heterogeneity across subgroups was observed for other efficacy measures.

CONCLUSIONS

In the overall trial population, LDX was associated with a lower rate of treatment failure compared with OROS-MPH in patients with ADHD. A more pronounced benefit of LDX over OROS-MPH was observed among subpopulations with a higher predicted risk of failing OROS-MPH. The present study showed the feasibility of individualizing treatment selection. Future research is needed to prospectively verify these results.

Pharmacogenomic testing for neuropsychiatric drugs: current status of drug labeling, guidelines for using genetic information, and test options

Advancements in pharmacogenomics have introduced an increasing number of opportunities to bring personalized medicine into clinical practice. Understanding how and when to use this technology to guide pharmacotherapy used to treat psychiatric and neurological (neuropsychiatric) conditions remains a challenge for many clinicians. Currently, guidelines exist to assist clinicians in the use of existing genetic information for drug selection and/or dosing for the tricyclic antidepressants, carbamazepine, and phenytoin. Additional language in the product labeling suggests that genetic information may also be useful for determining the starting and target doses, as well as drug interaction potential, for a number of other drugs. In this review, we outline the current status of pharmacogenomic testing for neuropsychiatric drugs as it pertains to information contained in drug labeling, consensus guidelines, and test panels, as well as considerations related to obtaining tests for patients.

Length of psychiatric hospitalization is correlated with CYP2D6 functional status in inpatients with major depressive disorder

AIM

This study aimed to determine the effect of the CYP2D6 genotype on the length of hospitalization stay for patients treated for major depressive disorder.

METHODS

A total of 149 inpatients with a diagnosis of major depressive disorder at the Institute of Living, Hartford Hospital (CT, USA), were genotyped to detect altered alleles in the CYP2D6 gene. Prospectively defined drug metabolism indices (metabolic reserve, metabolic alteration and allele alteration) were determined quantitatively and assessed for their relationship to length of hospitalization stay.

RESULTS

Hospital stay was significantly longer in deficient CYP2D6 metabolizers (metabolic reserve <2) compared with functional or suprafunctional metabolizers (metabolic reserve ≥2; 7.8 vs 5.7 days, respectively; p = 0.002).

CONCLUSION

CYP2D6 enzymatic functional status significantly affected length of hospital stay, perhaps due to reduced efficacy or increased side effects of the medications metabolized by the CYP2D6 isoenzyme. Functional scoring of CYP2D6 alleles may have a substantial impact on the quality of care, patient satisfaction and the economics of psychiatric treatment.

Importance of pharmacogenetics in the treatment of children with attention deficit hyperactive disorder: a case report

This case report highlights the importance of pharmacogenetic testing in the treatment of attention deficit hyperactive disorder (ADHD). A 6-year-old boy diagnosed with ADHD was prescribed methylphenidate 5 mg twice daily (7 am and noon) and the family was compliant with administration of this medication. On the first day of treatment, the patient had an adverse reaction, becoming disobedient, more mischievous, erratic, resistant to discipline, would not go to sleep until midnight, and had a poor appetite. The All-In-One PGX (All-In-One Pharmacogenetics for Antipsychotics test for CYP2D6, CYP2C19, and CYP2C9) was performed using microarray-based and real-time polymerase chain reaction techniques. The genotype of our patient was identified to be CYP2D6*2/*10, with isoforms of the enzyme consistent with a predicted cytochrome P450 2D6 intermediate metabolizer phenotype. Consequently, the physician adjusted the methylphenidate dose to 2.5 mg once daily in the morning. At this dosage, the patient had a good response without any further adverse reactions. Pharmacogenetic testing should be included in the management plan for ADHD. In this case, cooperation between the medical team and the patients’ relatives was key to successful treatment.

Physiogenomic analysis of CYP450 drug metabolism correlates dyslipidemia with pharmacogenetic functional status in psychiatric patients

AIMS

To investigate associations between novel human cytochrome P450 (CYP450) combinatory (multigene) and substrate-specific drug metabolism indices, and elements of metabolic syndrome, such as low density lipoprotein cholesterol (LDLc), high density lipoprotein cholesterol (HDLc), triglycerides and BMI, using physiogenomic analysis.

METHODS

CYP2C9, CYP2C19 and CYP2D6 genotypes and clinical data were obtained for 150 consecutive, consenting hospital admissions with a diagnosis of major depressive disorder and who were treated with psychotropic medications. Data analysis compared clinical measures of LDLc, HDLc, triglyceride and BMI with novel combinatory and substrate-specific CYP450 drug metabolism indices.

RESULTS

We found that a greater metabolic reserve index score is related to lower LDLc and higher HDLc, and that a greater metabolic alteration index score corresponds with higher LDLc and lower HLDc values. We also discovered that the sertraline drug-specific indices correlated with cholesterol and triglyceride values.

CONCLUSIONS

Overall, we demonstrated how a multigene approach to CYP450 genotype analysis yields more accurate and significant results than single-gene analyses. Ranking the individual with respect to the population represents a potential tool for assessing risk of dyslipidemia in major depressive disorder patients who are being treated with psychotropics. In addition, the drug-specific indices appear useful for modeling a variable of potential relevance to an individual's risk of drug-related dyslipidemia.

Antidepressant drugs

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Does the medication pattern reflect the CYP2D6 genotype in patients with diagnoses within the schizophrenic spectrum?

BACKGROUND

Cytochrome P450 2D6 enzyme (CYP2D6) is an important metabolic pathway for many antipsychotics. Its genetic polymorphism causes pharmacokinetic variability that might lead to adverse drug reactions or treatment failure unless countered by appropriate dose adjustments or shift to CYP2D6-independent antipsychotics.

PURPOSE

To investigate the clinical impact of CYP2D6 genotype in patients with a diagnosis within the schizophrenic spectrum using medication pattern as proxy for therapeutic and side effect.

METHODS

The study was conducted in patients genotyped during an inpatient stay (N = 576). Continuous antipsychotic, adjuvant, and anticholinergic drug regimens were registered retrospectively in a cross-sectional manner before genotyping. Antipsychotics were divided into CYP2D6 dependent and independent, and dose equivalents were calculated as chlorpromazine equivalents (CPZEq).

RESULTS

Poor metabolizers and ultrarapid metabolizers were treated with significantly higher median CPZEq doses (625.8; inter quartile range [IQR], 460.4-926.7; and 550; IQR, 199.8-1049) than extensive metabolizers (EMs) and intermediate metabolizers (IMs) (384; IQR, 150-698; and 446; IQR, 150-800) (P = 0.018). Logistic regression showed no association between anticholinergic treatment and CYP2D6 genotype or concomitant treatment with CYP2D6 inhibitors (P = 0.79 and P = 0.46, respectively).

CONCLUSIONS

Our results indicate that CYP2D6 genotype has no sufficient clinical impact that poor metabolizers and ultrarapid metabolizers are easily clinically identified with.

Translating biomarkers to clinical practice

Biomarkers are the measurable characteristics of an individual that may represent risk factors for a disease or outcome, or that may be indicators of disease progression or of treatment-associated changes. In general, the process by which biomarkers, once identified, might be translated into clinical practice has received scant attention in recent psychiatric literature. A body of work in diagnostic development suggests a framework for evaluating and validating novel biomarkers, but this work may be unfamiliar to clinical and translational researchers in psychiatry. Therefore, this review focuses on the steps that might follow the identification of putative biomarkers. It first addresses standard approaches to characterizing biomarker performance, followed by demonstrations of how a putative biomarker might be shown to have clinical relevance. Finally, it addresses ways in which a biomarker-based test might be validated for clinical application in terms of efficacy and cost-effectiveness.

Pharmacogenetics and the pharmacological management of depression

Depression is a chronic disease seen in many healthcare settings. Current pharmacological treatment options are successful in two-thirds of patients. One CYP450 enzyme, CYP2D6, is responsible for the metabolism of 30% of all drugs including many antidepressants. Phenotypes of metabolizer status affect antidepressant treatment outcomes and adverse drug reactions.

Biomarkers in development of psychotropic drugs

Biomarkers have been receiving increasing attention, especially in the field of psychiatry. In contrast to the availability of potent therapeutic tools including pharmacotherapy, psychotherapy, and biological therapies, unmet needs remain in terms of onset of action, stability of response, and further improvement of the clinical course. Biomarkers are objectively measured characteristics which serve as indicators of the causes of illnesses, their clinical course, and modification by treatment. There exist a variety of markers: laboratory markers which comprise the determination of genetic and epigenetic markers, neurotransmitters, hormones, cytokines, neuropeptides, enzymes, and others as single measures; electrophysiological markers which usually comprise electroencephalography (EEG) measures, and in particular sleep EEG and evoked potentials, magnetic encephalography, electrocardiogram, facial electromyography, skin conductance, and others; brain imaging techniques such as cranial computed tomography, magnetic resonance imaging, functional MRl, magnetic resonance spectroscopy, positron emission tomography, and single photon emission computed tomography; and behavioral approaches such as cue exposure and challenge tests which can be used to induce especially emotional processes in anxiety and depression. Examples for each of these domains are provided in this review. With a view to developing more individually tailored therapeutic strategies, the characterization of patients and the courses of different types of treatment will become even more important in the future.

Genetic polymorphisms of cytochrome P450 enzymes and antidepressant metabolism

INTRODUCTION

The cytochrome P450 (CYP) enzymes are the major enzymes responsible for Phase I reactions in the metabolism of several substances, including antidepressant medications. Thus, it has been hypothesized that variants in the CYP network may influence antidepressant efficacy and safety. Nonetheless, data on this field are still contradictory. The authors aim to give an overview of the published studies analyzing the influence of CYP highly polymorphic loci on antidepressant treatment in order to translate the acquired knowledge to a clinical level.

AREAS COVERED

The authors collected and compared experimental works and reviews published from the 1980s to the present and included in the Medline database. The included studies pertain to the effects of CYP gene polymorphisms on antidepressant pharmacokinetic parameters and clinical outcomes (response and drug-related adverse effects), with a focus on applications in clinical practice. The authors focused mainly on in vivo studies in humans (patients or healthy volunteers).

EXPERT OPINION

Great variability in antidepressant metabolism among individuals has been demonstrated. Thus, with the current interest in individualized medicine, several genetic tests to detect CYP variants have been produced. They provide a potentially useful way to anticipate some clinical outcomes of antidepressant treatment, although they will only be extensively used in clinical practice if precise and specific treatment options and guidelines based on genetic tests can be provided.