Human liver expression of CYP2C8: gender, age, and genotype effects

Personalized glucose-lowering effect of chiglitazar in type 2 diabetes

Chiglitazar (carfloglitazar) is a peroxisome proliferator-activated receptor pan-agonist presenting non-inferior glucose-lowering efficacy with sitagliptin in patients with type 2 diabetes. To delineate the subgroup of patients with greater benefit from chiglitazar, we conducted a machine learning-based post-hoc analysis in two randomized controlled trials. We established a character phenomap based on 13 variables and estimated HbA1c decline to the effects of chiglitazar in reference to sitagliptin. Out of 1,069 patients, 63.3% were found to have greater reduction in HbA1c levels with chiglitazar, while 36.7% showed greater reduction with sitagliptin. This distinction in treatment response was statistically significant between groups (pinteraction<0.001). To identify patients who would gain the most glycemic control benefit from chiglitazar, we developed a machine learning model, ML-PANPPAR, which demonstrated robust performance using sex, BMI, HbA1c, HDL, and fasting insulin. The phenomapping-derived tool successfully identified chiglitazar responders and enabled personalized drug allocation in patients with drug-naïve diabetes.

Role of Genetic Polymorphisms in Drug-Metabolizing Enzyme-Mediated Toxicity and Pharmacokinetic Resistance to Anti-Cancer Agents: A Review on the Pharmacogenomics Aspect

The inter-individual differences in cancer susceptibility are somehow correlated with the genetic differences that are caused by the polymorphisms. These genetic variations in drug-metabolizing enzymes/drug-inactivating enzymes may negatively or positively affect the pharmacokinetic profile of chemotherapeutic agents that eventually lead to pharmacokinetic resistance and toxicity against anti-cancer drugs. For instance, the CYP1B1*3 allele is associated with CYP1B1 overexpression and consequent resistance to a variety of taxanes and platins, while 496T>G is associated with lower levels of dihydropyrimidine dehydrogenase, which results in severe toxicities related to 5-fluorouracil. In this context, a pharmacogenomics approach can be applied to ascertain the role of the genetic make-up in a person's response to any drug. This approach collectively utilizes pharmacology and genomics to develop effective and safe medications that are devoid of resistance problems. In addition, recently reported genomics studies revealed the impact of many single nucleotide polymorphisms in tumors. These studies emphasized the importance of single nucleotide polymorphisms in drug-metabolizing enzymes on the effect of anti-tumor drugs. In this review, we discuss the pharmacogenomics aspect of polymorphisms in detail to provide an insight into the genetic manipulations in drug-metabolizing enzymes that are responsible for pharmacokinetic resistance or toxicity against well-known anti-cancer drugs. Special emphasis is placed on different deleterious single nucleotide polymorphisms and their effect on pharmacokinetic resistance. The information provided in this report may be beneficial to researchers, especially those who are working in the field of biotechnology and human genetics, in rationally manipulating the genetic information of patients with cancer who are undergoing chemotherapy to avoid the problem of pharmacokinetic resistance/toxicity associated with drug-metabolizing enzymes.

Cytochrome P450 enzymes in the pediatric population: Connecting knowledge on P450 expression with pediatric pharmacokinetics

Cytochrome P450 enzymes play an important role in the pharmacokinetics, efficacy, and toxicity of drugs. Age-dependent changes in P450 enzyme expression have been studied based on several detection systems, as well as by deconvolution of in vivo pharmacokinetic data observed in pediatric populations. The age-dependent changes in P450 enzyme expression can be important determinants of drug disposition in childhood, in addition to the changes in body size and the other physiological parameters, and effects of pharmacogenetics and disease on organ functions. As a tool incorporating drug-specific and body-specific factors, physiologically-based pharmacokinetic (PBPK) models have become increasingly used to characterize and explore mechanistic insights into drug disposition. Thus, PBPK models can be a bridge between findings from basic science and utilization in predictive science. Pediatric PBPK models incorporate additional system specific information on developmental physiology and ontogeny and have been used to predict pharmacokinetic parameters from preterm neonates onwards. These models have been advocated by regulatory authorities in order to support pediatric clinical trials. The purpose of this chapter is to highlight accumulated knowledge and findings from basic research focusing on P450 enzymes, as well as the current status and future challenges of expanding the utilization of pediatric PBPK modeling.

Effects of the total flavonoid extracts and the monomers of Daphne genkwa on CYP2C8 activity

1. This study aimed to assess the effects of total flavonoid extracts (TFDG) and the monomers of Daphne genkwa on the CYP2C8 activity in vitro and in vivo.2. The 50% inhibitory concentration (IC₅₀) values were used to determine the inhibitory effect of TFDG and its four monomers for the CYP2C8 activity by recombinant human CYP2C8 (RHCYP2C8) yeast microsome system in vitro, and the volume per dose index (VDI) was predicted the potential inhibition in vivo. The effects of multiple-dose administration of TFDG on the pharmacokinetic parameters of rosiglitazone in rats were evaluated.3. The IC₅₀ values of apigenin, luteolin, hydroxy-genkwanin, genkwanin, and TFDG were 7.27μmol/L, 11.9μmol/L, 28.1μmol/L, 127μmol/L, and 13.4μg/mL, respectively. The VDI values of apigenin and TFDG were 2.15L and 6.60L. In vivo study, compared with the control group, the elimination phase half-life and mean residence time in the TFDG treatment group were significantly increased by 96.9% and 106.8% (p < 0.05), respectively.4. Apigenin showed a moderate inhibitory effect on the CYP2C8 activity in vitro, while the other three monomers were weak inhibitors. TFDG had a strong inhibitory effect on CYP2C8 in vitro and in vivo, and also inhibited the metabolism of rosiglitazone in rats.

Physiologically-based pharmacokinetic model predictions of inter-ethnic differences in imatinib pharmacokinetics and dosing regimens

AIMS

This study implements a physiologically-based pharmacokinetic (PBPK) modelling approach to investigate inter-ethnic differences in imatinib pharmacokinetics and dosing regimens.

METHODS

A PBPK model of imatinib was built in the Simcyp Simulator (version 17) integrating in vitro drug metabolism and clinical pharmacokinetic data. The model accounts for ethnic differences in body size and abundance of drug-metabolising enzymes and proteins involved in imatinib disposition. Utility of this model for prediction of imatinib pharmacokinetics was evaluated across different dosing regimens and ethnic groups. The impact of ethnicity on imatinib dosing was then assessed based on the established range of trough concentrations (C_ss,min ).

RESULTS

The PBPK model of imatinib demonstrated excellent predictive performance in describing pharmacokinetics and the attained C_ss,min in patients from different ethnic groups, shown by prediction differences that were within 1.25-fold of the clinically-reported values in published studies. PBPK simulation suggested a similar dose of imatinib (400-600 mg/d) to achieve the desirable range of C_ss,min (1000-3200 ng/mL) in populations of European, Japanese and Chinese ancestry. The simulation indicated that patients of African ancestry may benefit from a higher initial dose (600-800 mg/d) to achieve imatinib target concentrations, due to a higher apparent clearance (CL/F) of imatinib compared to other ethnic groups; however, the clinical data to support this are currently limited.

CONCLUSION

PBPK simulations highlighted a potential ethnic difference in the recommended initial dose of imatinib between populations of European and African ancestry, but not populations of Chinese and Japanese ancestry.

Gephyrin and CYP2C9 Genetic Polymorphisms in Patients with Pharmacoresistant Epilepsy

Purpose

Gephyrin (GPHN) is an essential protein in the regulation of inhibitory postsynaptic density and polymorphism in the corresponding gene may have a role in the development of pharmacoresistant epilepsy (PRE). For the first time, we aimed to evaluate the association of rs928553T/C variants with PRE susceptibility. Moreover, we have analyzed the genetic polymorphism affecting CYP2C9 “rs12782374G/A” in the same population to detect the effect of SNP on the drug-metabolizing ability of patients with PRE.

Patients and Methods

This case-control study enrolled 100 patients (group A) and 100 healthy, age and sex-matched controls, unrelated to patients (group B). TaqMan™ assays using real-time PCR were run for genotyping of rs928553T/C and rs12782374G/A in all participants.

Results

GPHN T>C polymorphism revealed significant risk association with occurrence of PRE using dominant, recessive and codominant models as follows: TT vs (TC+CC): OR 0.23, 95%CI: 0.13–0.43, P<0.001. In addition, (TT+TC vs CC): OR 0.38, 95%CI: 0.18–0.77, P<0.001. Also, T vs C (OR 0.34, 95%CI: 0.22–0.51, P=<0.001). Similarly, CYP2C9 G>A polymorphism showed a significant increased risk of PRE (GG vs (GA+AA): OR 0.11, 95%CI: 0.05–0.23, P<0.001). Furthermore, (GG+GA vs AA): OR 0.18, 95%CI: 0.084–0.39, P<0.001. Also, G vs A (OR 0.24, 95%CI: 0.15–0.366, P=<0.001).

Conclusion

Mutation of both GPHN (rs928553) and CYP2C9 (rs1278237) genes may be implicated as a genetic mediators of resistance in patients with PRE.

In vitro effects of 95% khat ethanol extract (KEE) on human recombinant cytochrome P450 (CYP)1A2, CYP2A6, CYP2B6, CYP2C8, CYP2C19, CYP2E1, CYP2J2 and CYP3A5

OBJECTIVES

Khat, a natural amphetamine-like psychostimulant plant, are widely consumed globally. Concurrent intake of khat and xenobiotics may lead to herb-drug interactions and adverse drug reactions (ADRs). This study is a continuation of our previous study, targeted to evaluate the in vitro inhibitory effects of khat ethanol extract (KEE) on human cytochrome (CYP) 1A2, CYP2A6, CYP2B6, CYP2C8, CYP2C19, CYP2E1, CYP2J2, and CYP3A5, major human drug metabolizing enzymes.

METHODS

In vitro fluorescence enzyme assays were employed to assess CYPs inhibition with the presence and absence of various KEE concentrations.

RESULTS

KEE reversibly inhibited CYP2A6, CYP2B6, CYP2C8, CYP2C19, CYP2E1, CYP2J2 and CYP3A5 but not CYP1A2 with IC₅₀ values of 25.5, 99, 4.5, 21, 27, 17, and 10 μg/mL respectively. No irreversible inhibition of KEE on all the eight CYPs were identified. The K_i values of CYP2A6, CYP2B6, CYP2C8, CYP2C19, CYP2E1, CYP2J2 and CYP3A5 were 20.9, 85, 4.8, 18.3, 59.3, 3, and 21.7 μg/mL, respectively. KEE inhibited CYP2B6 via competitive or mixed inhibition; CYP2E1 via un-competitive or mixed inhibition; while CYP2A6, CYP2C8, CYP2C19, CYP2J2 and CYP3A5 via non-competitive or mixed inhibition.

CONCLUSIONS

Caution should be taken by khat users who are on medications metabolized by CYP2A6, CYP2B6, CYP2C8, CYP2C19, CYP2E1, CYP2J2, and CYP3A5.

Ontogeny of Hepatic Transporters and Drug-Metabolizing Enzymes in Humans and in Nonclinical Species

The liver represents a major eliminating and detoxifying organ, determining exposure to endogenous compounds, drugs, and other xenobiotics. Drug transporters (DTs) and drug-metabolizing enzymes (DMEs) are key determinants of disposition, efficacy, and toxicity of drugs. Changes in their mRNA and protein expression levels and associated functional activity between the perinatal period until adulthood impact drug disposition. However, high-resolution ontogeny profiles for hepatic DTs and DMEs in nonclinical species and humans are lacking. Meanwhile, increasing use of physiologically based pharmacokinetic (PBPK) models necessitates availability of underlying ontogeny profiles to reliably predict drug exposure in children. In addition, understanding of species similarities and differences in DT/DME ontogeny is crucial for selecting the most appropriate animal species when studying the impact of development on pharmacokinetics. Cross-species ontogeny mapping is also required for adequate translation of drug disposition data in developing nonclinical species to humans. This review presents a quantitative cross-species compilation of the ontogeny of DTs and DMEs relevant to hepatic drug disposition. A comprehensive literature search was conducted on PubMed Central: Tables and graphs (often after digitization) in original manuscripts were used to extract ontogeny data. Data from independent studies were standardized and normalized before being compiled in graphs and tables for further interpretation. New insights gained from these high-resolution ontogeny profiles will be indispensable to understand cross-species differences in maturation of hepatic DTs and DMEs. Integration of these ontogeny data into PBPK models will support improved predictions of pediatric hepatic drug disposition processes. SIGNIFICANCE STATEMENT: Hepatic drug transporters (DTs) and drug-metabolizing enzymes (DMEs) play pivotal roles in hepatic drug disposition. Developmental changes in expression levels and activities of these proteins drive age-dependent pharmacokinetics. This review compiles the currently available ontogeny profiles of DTs and DMEs expressed in livers of humans and nonclinical species, enabling robust interpretation of age-related changes in drug disposition and ultimately optimization of pediatric drug therapy.

Anatomical distribution and expression of CYP in humans: Neuropharmacological implications

The cytochrome P450 (CYP450) superfamily is responsible for the metabolism of most xenobiotics and pharmacological treatments generally used in clinical settings. Genetic factors as well as environmental determinants acting through fine epigenetic mechanisms modulate the expression of CYP over the lifespan (fetal vs. infancy vs. adult phases) and in diverse organs. In addition, pathological processes might alter the expression of CYP. In this selective review, we sought to summarize the evidence on the expression of CYP focusing on three specific aspects: (a) the anatomical distribution of the expression in body districts relevant in terms of drug pharmacokinetics (liver, gut, and kidney) and pharmacodynamics, focusing for the latter on the brain, since this is the target organ of psychopharmacological agents; (b) the patterns of expression during developmental phases; and (c) the expression of CYP450 enzymes during pathological processes such as cancer. We showed that CYP isoforms show distinct patterns of expression depending on the body district and the specific developmental phases. Of particular relevance for neuropsychopharmacology is the complex regulatory mechanisms that significantly modulate the complexity of the pharmacokinetic regulation, including the concentration of specific CYP isoforms in distinct areas of the brain, where they could greatly affect local substrate and metabolite concentrations of drugs.

Identifying the Dominant Contribution of Human Cytochrome P450 2J2 to the Metabolism of Rivaroxaban, an Oral Anticoagulant

PURPOSE

Rivaroxaban, an oral anticoagulant, undergoes the metabolism mediated by human cytochrome P450 (CYP). The present study is to quantitatively analyze and compare the contributions of multiple CYPs in the metabolism of rivaroxaban to provide new information for medication safety.

METHODS

The metabolic stability of rivaroxaban in the presence of human liver microsomes (HLMs) and recombinant CYPs was systematically evaluated to estimate the participation of various CYP isoforms. Furthermore, the catalytic efficiency of CYP isoforms was compared via metabolic kinetic studies of rivaroxaban with recombinant CYP isoenzymes, as well as via CYP-specific inhibitory studies. Additionally, docking simulations were used to illustrate molecular interactions.

RESULTS

Multiple CYP isoforms were involved in the hydroxylation of rivaroxaban, with decreasing catalytic rates as follows: CYP2J2 > 3A4 > 2D6 > 4F3 > 1A1 > 3A5 > 3A7 > 2A6 > 2E1 > 2C9 > 2C19. Among the CYPs, 2J2, 3A4, 2D6, and 4F3 were the four major isoforms responsible for rivaroxaban metabolism. Notably, the intrinsic clearance of rivaroxaban catalyzed by CYP2J2 was nearly 39-, 64-, and 100-fold that catalyzed by CYP3A4, 2D6, and 4F3, respectively. In addition, rivaroxaban hydroxylation was inhibited by 41.1% in the presence of the CYP2J2-specific inhibitor danazol, which was comparable to the inhibition rate of 43.3% by the CYP3A-specific inhibitor ketoconazole in mixed HLMs. Furthermore, molecular simulations showed that rivaroxaban is principally bound to CYP2J2 by π-alkyl bonds, carbon-hydrogen bonds, and alkyl interactions.

CONCLUSION

CYP2J2 dominated the hydroxylation of rivaroxaban, which may provide new insight into clinical drug interactions involving rivaroxaban.

Gender differences in the efficacy of pioglitazone treatment in nonalcoholic fatty liver disease patients with abnormal glucose metabolism

Background

Pioglitazone is a promising therapeutic method for nonalcoholic fatty liver disease (NAFLD) patients with or without type 2 diabetes. However, there is remarkable variability in treatment response. We analyzed our previous randomized controlled trial to examine the effects of gender and other factors on the efficacy of pioglitazone in treating Chinese nonalcoholic fatty liver disease (NAFLD) patients with abnormal glucose metabolism.

Methods

This is a post hoc analysis of a previous randomized, parallel controlled, open-label clinical trial (RCT) with an original purpose of evaluating the efficacy of berberine and pioglitazone on NAFLD. The total population (n = 185) was randomly divided into three groups: lifestyle intervention (LSI), LSI + pioglitazone (PGZ) 15 mg qd, and LSI + berberine (BBR) 0.5 g tid, respectively, for 16 weeks. The study used proton magnetic resonance spectroscopy (¹H-MRS) to assess liver fat content.

Results

As compared with LSI, PGZ + LSI treatment further decreased liver fat content in women (− 15.24% ± 14.54% vs. − 8.76% ± 13.49%, p = 0.025), but less decreased liver fat content in men (− 9.95% ± 15.18% vs. − 12.64% ± 17.78%, p = 0.046). There was a significant interaction between gender and efficacy of pioglitazone before and after adjustment for age, smoking, drinking, baseline BMI, BMI change, treatment adherence, baseline liver fat content, and glucose metabolism.

Conclusion

The study recommends pioglitazone plus lifestyle intervention for Chinese NAFLD female patients with abnormal glucose metabolism.

Trial registration

Role of Pioglitazone and Berberine in Treatment of Non-Alcoholic Fatty Liver Disease, NCT00633282. Registered on 3 March 2008, https://register.clinicaltrials.gov.

How Can Drug Metabolism and Transporter Genetics Inform Psychotropic Prescribing?

Many genetic variants in drug metabolizing enzymes and transporters have been shown to be relevant for treating psychiatric disorders. Associations are strong enough to feature on drug labels and for prescribing guidelines based on such data. A range of commercial tests are available; however, there is variability in included genetic variants, methodology, and interpretation. We herein provide relevant background for understanding clinical associations with specific variants, other factors that are relevant to consider when interpreting such data (such as age, gender, drug-drug interactions), and summarize the data relevant to clinical utility of pharmacogenetic testing in psychiatry and the available prescribing guidelines. We also highlight areas for future research focus in this field.

Pharmacogenetics of Statin-Induced Myotoxicity

Statins, a class of lipid-lowering medications, have been a keystone treatment in cardiovascular health. However, adverse effects associated with statin use impact patient adherence, leading to statin discontinuation. Statin-induced myotoxicity (SIM) is one of the most common adverse effects, prevalent across all ages, genders, and ethnicities. Although certain demographic cohorts carry a higher risk, the impaired quality of life attributed to SIM is significant. The pathogenesis of SIM remains to be fully elucidated, but it is clear that SIM is multifactorial. These factors include drug-drug interactions, renal or liver dysfunction, and genetics. Genetic-inferred risk for SIM was first reported by a landmark genome-wide association study, which reported a higher risk of SIM with a polymorphism in the SLCO1B1 gene. Since then, research associating genetic factors with SIM has expanded widely and has become one of the foci in the field of pharmacogenomics. This review provides an update on the genetic risk factors associated with SIM.

A dual functional probe for assessing human CYP450 3A5 and 3A enzymes bioactivities

Aim: CYP3A5 plays a vital role in the drug metabolism, it displays varied expression levels among individuals and is easily influenced by genetic polymorphisms and some diseases. Methodology & results: A dual function probe isobutyryl-11-keto-β-boswellic acid (IKBA) was developed; it possessed a high selectivity toward CYP3A5 and CYP3A enzymes for its two individual metabolites, respectively. The probe has the high accuracy and wide applicability in measuring the real activity of CYP3A5. Finally, IKBA was successfully used for the evaluation of the activity of CYP3A5 and CYP3A enzymes in various bio samples. Conclusion: IKBA could serve as a useful tool for exploring the physiology and pathology functions of CYP3A5 and give some useful guidance for the rational use of clinical drugs.

Responses of CYP450 in the mussel Perna viridis after short-term exposure to the DSP toxins-producing dinoflagellate Prorocentrum lima

Diarrhetic shellfish poisoning (DSP) toxins are key shellfish toxins that cause diarrhea, vomiting and even tumor. Interestingly, bivalves such as Perna viridis have been reported to exhibit some resistances to alleviate toxic effects of DSP toxins in a species-specific manner. Nevertheless, the molecular mechanisms underlying the resistance phenomenon to DSP toxins, particularly the mechanistic role of CYP450 is scant despite its crucial role in detoxification. Here, we exposed P. viridis to Prorocentrum lima and examined the expression pattern of the CYP450 and our comprehensive analyses revealed that P. lima exposure resulted in unique expression pattern of key CYP450 genes in bivalves. Exposure to P. lima (2 × 10⁵ cells/L) dramatically orchestrated the relative expression of CYP450 genes. CYP2D14-like mRNA was significantly down-regulated at 6 h in gill, but up-regulated at 2 h in digestive gland compared with control counterparts (p < 0.05), while CYP3A4 mRNA was increased at 12 h in gill. After exposure to P. lima at 2 × 10⁶ cells/L, the expression of CYP3A4 mRNA was significantly increased in digestive gland at 2 h and 12 h, while CYP2D14-like was up-regulated at 6 h. Besides, CYP3L3 and CYP2C8 also exhibited differential expression. These data suggested that CYP3A4, CYP2D14-like, and even CYP3L3 and CYP2C8 might be involved in DSP toxins metabolism. Besides, provision of ketoconazole resulted in significant decrement of CYP3A4 in digestive gland at 2 h and 12 h, while the OA content significantly decreased at 2 h and 6 h compared to control group without ketoconazole. These findings indicated that ketoconazole could depress CYP3A4 activity in bivalves thereby altering the metabolic activities of DSP toxins in bivalves, and also provided novel insights into the mechanistic role of CYP3A4 on DSP toxins metabolism in bivalves.

Effect of pterostilbene on in vitro drug metabolizing enzyme activity

Pterostilbene is a natural polyphenol compound found in small berries that is related to resveratrol, but has better bioavailability and a longer half-life. The purpose of this study was to assess the potential inhibitory effect of pterostilbene on in vitro drug metabolism. The effect of pterostilbene on cytochrome P450 (CYP) and UDP-glucuronosyltransferase (UGT) enzyme activities were studied using the enzyme-selective substrates amodiaquine (CYP2C8), midazolam (CYP3A4), estradiol (UGT1A1), serotonin (UGT1A6) and mycophenolic acid (UGT1A8/9/10). The IC₅₀ value was used to express the strength of inhibition. Further, a volume per dose index (VDI) was used to estimate the potential for in vivo interactions. Pterostilbene significantly inhibited CYP2C8 and UGT1A6 activities. The IC50 (mean ± SE) values for CYP2C8 and UGT1A6 inhibition were 3.0 ± 0.4 µM and 15.1 ± 2.8 µM, respectively; the VDI exceeded the predefined threshold of 5 L/dose for both CYP2C8 and UGT1A6, suggesting a potential for interaction in vivo. Pterostilbene did not inhibit the metabolism of the other enzyme-selective substrates. The results of this study indicate that pterostilbene inhibits CYP2C8 and UTG1A6 activity in vitro and may inhibit metabolism by these enzymes in vivo. Clinical studies are warranted to evaluate the in vivo relevance of these interactions.

Complete Substrate Inhibition of Cytochrome P450 2C8 by AZD9496, an Oral Selective Estrogen Receptor Degrader

AZD9496 ((E)-3-(3,5-difluoro-4-((1R,3R)-2-(2-fluoro-2-methylpropyl)-3-methyl-2,3,4,9-tetrahydro-1H-pyrido[3,4-b]indol-1-yl)phenyl)acrylic acid) is an oral selective estrogen receptor degrader currently in clinical development for treatment of estrogen receptor-positive breast cancer. In a first-in-human phase 1 study, AZD9496 exhibited dose nonlinear pharmacokinetics, the mechanistic basis of which was investigated in this study. The metabolism kinetics of AZD9496 were studied using human liver microsomes (HLMs), recombinant cytochrome P450s (rP450s), and hepatocytes. In addition, modeling approaches were used to gain further mechanistic insights. CYP2C8 was predominantly responsible for biotransformation of AZD9496 to its two main metabolites whose rate of formation with increasing AZD9496 concentrations exhibited complete substrate inhibition in HLM, rCYP2C8, and hepatocytes. Total inhibition by AZD9496 of amodiaquine N-deethylation, a specific probe of CYP2C8 activity, confirmed the completeness of this inhibition. The commonly used substrate inhibition model analogous to uncompetitive inhibition fit poorly to the data. However, using the same model but without constraints on the number of molecules occupying the inhibitory binding site (i.e., nS₁ES) provided a significantly better fit (F test, P< 0.005). With the improved model, up to three AZD9496 molecules were predicted to bind the inhibitory site of CYP2C8. In contrast to previous studies showing substrate inhibition of P450s to be partial, our results demonstrate complete substrate inhibition of CYP2C8 via binding of more than one molecule of AZD9496 to the inhibitory site. As CYP2C8 appears to be the sole isoform catalyzing formation of the main metabolites, the substrate inhibition might explain the observed dose nonlinearity in the clinic at higher doses.

Pharmacogenetics: Applications to Pediatric Patients

Individual genomic differences may affect drug disposition and effects of many drugs, and identification of biomarkers are crucial to personalize dosage and optimize response. In children, developmental changes associated with growth and maturation translate into different relationships between genotype and phenotype and different responses to treatment compared to adults. This review aims to summarize some developmental aspects of pharmacogenetics, based on practical examples.

Prediction of olanzapine exposure in individual patients using physiologically based pharmacokinetic modelling and simulation

AIM

The aim of the present study was to predict olanzapine (OLZ) exposure in individual patients using physiologically based pharmacokinetic modelling and simulation (PBPK M&S).

METHODS

A 'bottom-up' PBPK model for OLZ was constructed in Simcyp® (V14.1) and validated against pharmacokinetic studies and data from therapeutic drug monitoring (TDM). The physiological, demographic and genetic attributes of the 'healthy volunteer population' file in Simcyp® were then individualized to create 'virtual twins' of 14 patients. The predicted systemic exposure of OLZ in virtual twins was compared with measured concentration in corresponding patients. Predicted exposures were used to calculate a hypothetical decrease in exposure variability after OLZ dose adjustment.

RESULTS

The pharmacokinetic parameters of OLZ from single-dose studies were accurately predicted in healthy Caucasians [mean-fold errors (MFEs) ranged from 0.68 to 1.14], healthy Chinese (MFEs 0.82 to 1.18) and geriatric Caucasians (MFEs 0.55 to 1.30). Cumulative frequency plots of trough OLZ concentration were comparable between the virtual population and patients in a TDM database. After creating virtual twins in Simcyp®, the R2 values for predicted vs. observed trough OLZ concentrations were 0.833 for the full cohort of 14 patients and 0.884 for the 7 patients who had additional cytochrome P450 2C8 genotyping. The variability in OLZ exposure following hypothetical dose adjustment guided by PBPK M&S was twofold lower compared with a fixed-dose regimen - coefficient of variation values were 0.18 and 0.37, respectively.

CONCLUSIONS

Olanzapine exposure in individual patients was predicted using PBPK M&S. Repurposing of available PBPK M&S platforms is an option for model-informed precision dosing and requires further study to examine clinical potential.

Clinical Pharmacokinetics and Pharmacodynamics of Antihyperglycemic Medications in Children and Adolescents with Type 2 Diabetes Mellitus

The incidence of type 2 diabetes mellitus (T2DM) among children and adolescents has been rising. This condition is associated with obesity, and it's prevalence is higher among minority or female youth. Lifestyle modification including diet and exercise is only successful in a small proportion of patients; therefore, pharmacotherapy approaches are needed to treat T2DM among youth. Currently, in the USA, only metformin and insulin are approved for the treatment of T2DM in children. However, several antihyperglycemic agents including exenatide, glimepiride, glyburide, liraglutide, pioglitazone, and rosiglitazone are also used off-label in this population. Moreover, a number of clinical trials are ongoing that are aimed at addressing the safety and efficacy of newer antihyperglycemic agents in this population. Little is known about the safety, efficacy, or pharmacokinetics of antihyperglycemic agents in children or adolescents. Our ability to predict the pharmacokinetics of these agents in youth is hampered first by the lack of information about the expression and activity of drug-metabolizing enzymes and transporters in this population and second by the presence of comorbid conditions such as obesity and fatty liver disease. This article reviews the prevalence of obesity and T2DM in children and adolescents (youth). We then summarize published studies on safety and effectiveness of antihyperglycemic medications in youth. Drug disposition may be affected by age or puberty and thus the expression and activity of different pathways for drug metabolism and xenobiotic transporters are compared between youth and adults followed by a summary of pharmacokinetics studies of antihyperglycemic agents currently used in this population.

Physiologically Based Pharmacokinetic Modeling to Predict Drug-Drug Interactions with Efavirenz Involving Simultaneous Inducing and Inhibitory Effects on Cytochromes

BACKGROUND

Antiretroviral drugs are among the therapeutic agents with the highest potential for drug-drug interactions (DDIs). In the absence of clinical data, DDIs are mainly predicted based on preclinical data and knowledge of the disposition of individual drugs. Predictions can be challenging, especially when antiretroviral drugs induce and inhibit multiple cytochrome P450 (CYP) isoenzymes simultaneously.

METHODS

This study predicted the magnitude of the DDI between efavirenz, an inducer of CYP3A4 and inhibitor of CYP2C8, and dual CYP3A4/CYP2C8 substrates (repaglinide, montelukast, pioglitazone, paclitaxel) using a physiologically based pharmacokinetic (PBPK) modeling approach integrating concurrent effects on CYPs. In vitro data describing the physicochemical properties, absorption, distribution, metabolism, and elimination of efavirenz and CYP3A4/CYP2C8 substrates as well as the CYP-inducing and -inhibitory potential of efavirenz were obtained from published literature. The data were integrated in a PBPK model developed using mathematical descriptions of molecular, physiological, and anatomical processes defining pharmacokinetics. Plasma drug-concentration profiles were simulated at steady state in virtual individuals for each drug given alone or in combination with efavirenz. The simulated pharmacokinetic parameters of drugs given alone were compared against existing clinical data. The effect of efavirenz on CYP was compared with published DDI data.

RESULTS

The predictions indicate that the overall effect of efavirenz on dual CYP3A4/CYP2C8 substrates is induction of metabolism. The magnitude of induction tends to be less pronounced for dual CYP3A4/CYP2C8 substrates with predominant CYP2C8 metabolism.

CONCLUSION

PBPK modeling constitutes a useful mechanistic approach for the quantitative prediction of DDI involving simultaneous inducing or inhibitory effects on multiple CYPs as often encountered with antiretroviral drugs.

Concentration-dependent response to pioglitazone in nonalcoholic steatohepatitis

BACKGROUND

Pioglitazone is a safe and effective option to manage patients with type 2 diabetes and nonalcoholic steatohepatitis (NASH). However, there is marked variability in treatment response.

AIM

To evaluate the relationship between concentrations of pioglitazone and its active metabolites and treatment outcomes in patients with NASH.

METHODS

Pioglitazone concentrations were measured in patients with NASH treated with pioglitazone 45 mg/day for 18 months; liver biopsy samples were obtained at baseline and after treatment. The primary outcome was a ≥2-point reduction in NAFLD activity score (NAS) with at least one-point improvement in more than one liver histology category and without worsening of fibrosis. A novel marker, the pioglitazone exposure index, was calculated to consider the concentrations of pioglitazone as well as the two active metabolites.

RESULTS

The response to pioglitazone was concentration-dependent as evidenced by the significant relationship between both pioglitazone concentration and pioglitazone exposure index with changes in NAS (r=.48, P=.0002 and r=.51, P<.0001, respectively), steatosis (r=.41, P=.002 and r=.46, P=.0005), and inflammation (r=.44, P=.0009 and r=.40, P=.0003). The pioglitazone exposure index was also associated with a change in ballooning (P=.04). The pioglitazone exposure index was higher in patients with NASH resolution (2.85±1.38 vs 1.78±1.48, P=.018). A predictive model for the primary outcome was developed that incorporated baseline NAS and pioglitazone exposure index (AUC=0.77).

CONCLUSIONS

This study demonstrates the importance of pioglitazone exposure to variable response in patients with NASH, and indicates potential factors that may identify patients most likely to benefit from chronic pioglitazone treatment.

The effect of milk thistle (Silybum marianum) and its main flavonolignans on CYP2C8 enzyme activity in human liver microsomes

Milk thistle is a widely-consumed botanical used for an array of purported health benefits. The primary extract of milk thistle is termed silymarin, a complex mixture that contains a number of structurally-related flavonolignans, the flavonoid, taxifolin, and a number of other constituents. The major flavonolignans present in most extracts are silybin A, silybin B, isosilybin A and isosilybin B, silydianin, silychristin and isosilychristin. Silymarin itself has been reported to inhibit CYP2C8 activity in vitro, but the effect of the individual flavonolignans on this enzyme has not been studied. To investigate the effects of milk thistle extract and its main flavonolignans (silybin A, silybin B, isosilybin A and isosilybin B) on CYP2C8 activity at relevant concentrations, the effect of milk thistle extract and the flavonolignans on CYP2C8 enzyme activity was studied in vitro using human liver microsomes (HLM) incorporating an enzyme-selective substrate for CYP2C8, amodiaquine. Metabolite formation was analyzed using liquid chromatography-tandem mass spectrometry (LC/MS-MS). The concentration causing 50% inhibition of enzyme activity (IC50) was used to express the degree of inhibition. Isosilibinin, a mixture of the diastereoisomers isosilybin A and isosilybin B, was found to be the most potent inhibitor, followed by isosilybin B with IC50 values (mean ± SE) of 1.64 ± 0.66 μg/mL and 2.67 ± 1.18 μg/mL, respectively. The rank order of observed inhibitory potency after isosilibinin was silibinin > isosilybin A > silybin A > milk thistle extract > and silybin B. These in vitro results suggest a potentially significant inhibitory effect of isosilibinin and isosilybin B on CYP2C8 activity. However, the observed IC50 values are unlikely to be achieved in humans supplemented with orally administered milk thistle extracts due to the poor bioavailability of flavonolignans documented with most commercially available formulations.

In vitro metabolism of exemestane by hepatic cytochrome P450s: impact of nonsynonymous polymorphisms on formation of the active metabolite 17β-dihydroexemestane

Exemestane (EXE) is an endocrine therapy commonly used by postmenopausal women with hormone‐responsive breast cancer due to its potency in inhibiting aromatase‐catalyzed estrogen synthesis. Preliminary in vitro studies sought to identify phase I EXE metabolites and hepatic cytochrome P450s (CYP450s) that participate in EXE biotransformation. Phase I metabolites were identified by incubating EXE with HEK293‐overexpressed CYP450s. CYP450s 1A2, 2C8, 2C9, 2C19, 2D6, 3A4, and 3A5 produce 17β‐dihydroexemestane (17β‐DHE), an active major metabolite, as well as two inactive metabolites. 17β‐DHE formation in pooled human liver microsomes subjected to isoform‐specific CYP450 inhibition was also monitored using tandem mass spectrometry. 17β‐DHE production in human liver microsomes was unaffected by isoform‐specific inhibition of CYP450s 2A6, 2B6, and 2E1 but decreased 12–39% following inhibition of drug‐metabolizing enzymes from CYP450 subfamilies 1A, 2C, 2D, and 3A. These results suggest that redundancy exists in the EXE metabolic pathway with multiple hepatic CYP450s catalyzing 17β‐DHE formation in vitro. To further expand the knowledge of phase I EXE metabolism, the impact of CYP450 genetic variation on 17β‐DHE formation was assessed via enzyme kinetic parameters. Affinity for EXE substrate and enzyme catalytic velocity were calculated for hepatic wild‐type CYP450s and their common nonsynonymous variants by monitoring the reduction of EXE to 17β‐DHE. Several functional polymorphisms in xenobiotic‐metabolizing CYP450s 1A2, 2C8, 2C9, and 2D6 resulted in deviant enzymatic activity relative to wild‐type enzyme. Thus, it is possible that functional polymorphisms in EXE‐metabolizing CYP450s contribute to inter‐individual variability in patient outcomes by mediating overall exposure to the drug and its active metabolite, 17β‐DHE.

Determination of Human Hepatic CYP2C8 and CYP1A2 Age-Dependent Expression to Support Human Health Risk Assessment for Early Ages

Predicting age-specific metabolism is important for evaluating age-related drug and chemical sensitivity. Multiple cytochrome P450s and carboxylesterase enzymes are responsible for human pyrethroid metabolism. Complete ontogeny data for each enzyme are needed to support in vitro to in vivo extrapolation (IVIVE). This study was designed to determine age-dependent human hepatic CYP2C8 expression, for which only limited ontogeny data are available, and to further define CYP1A2 ontogeny. CYP2C8 and 1A2 protein levels were measured by quantitative Western blotting using liver microsomal samples prepared from 222 subjects with ages ranging from 8 weeks gestation to 18 years after birth. The median CYP2C8 expression was significantly greater among samples from subjects older than 35 postnatal days (n = 122) compared with fetal samples and those from very young infants (fetal to 35 days postnatal, n = 100) (0.00 vs. 13.38 pmol/mg microsomal protein; p < 0.0001). In contrast, the median CYP1A2 expression was significantly greater after 15 months postnatal age (n = 55) than in fetal and younger postnatal samples (fetal to 15 months postnatal, n = 167) (0.0167 vs. 2.354 pmol/mg microsomal protein; p < 0.0001). CYP2C8, but not CYP1A2, protein levels significantly correlated with those of CYP2C9, CYP2C19, and CYP3A4 (p < 0.001), consistent with CYP2C8 and CYP1A2 ontogeny probably being controlled by different mechanisms. This study provides key data for the physiologically based pharmacokinetic model-based prediction of age-dependent pyrethroid metabolism, which will be used for IVIVE to support pyrethroid risk assessment for early life stages.

Role of Cytochrome P450 2C8 in Drug Metabolism and Interactions

During the last 10-15 years, cytochrome P450 (CYP) 2C8 has emerged as an important drug-metabolizing enzyme. CYP2C8 is highly expressed in human liver and is known to metabolize more than 100 drugs. CYP2C8 substrate drugs include amodiaquine, cerivastatin, dasabuvir, enzalutamide, imatinib, loperamide, montelukast, paclitaxel, pioglitazone, repaglinide, and rosiglitazone, and the number is increasing. Similarly, many drugs have been identified as CYP2C8 inhibitors or inducers. In vivo, already a small dose of gemfibrozil, i.e., 10% of its therapeutic dose, is a strong, irreversible inhibitor of CYP2C8. Interestingly, recent findings indicate that the acyl-β-glucuronides of gemfibrozil and clopidogrel cause metabolism-dependent inactivation of CYP2C8, leading to a strong potential for drug interactions. Also several other glucuronide metabolites interact with CYP2C8 as substrates or inhibitors, suggesting that an interplay between CYP2C8 and glucuronides is common. Lack of fully selective and safe probe substrates, inhibitors, and inducers challenges execution and interpretation of drug-drug interaction studies in humans. Apart from drug-drug interactions, some CYP2C8 genetic variants are associated with altered CYP2C8 activity and exhibit significant interethnic frequency differences. Herein, we review the current knowledge on substrates, inhibitors, inducers, and pharmacogenetics of CYP2C8, as well as its role in clinically relevant drug interactions. In addition, implications for selection of CYP2C8 marker and perpetrator drugs to investigate CYP2C8-mediated drug metabolism and interactions in preclinical and clinical studies are discussed.

Systematic tracking of disrupted modules identifies significant genes and pathways in hepatocellular carcinoma

The objective of the present study is to identify significant genes and pathways associated with hepatocellular carcinoma (HCC) by systematically tracking the dysregulated modules of re-weighted protein-protein interaction (PPI) networks. Firstly, normal and HCC PPI networks were inferred and re-weighted based on Pearson correlation coefficient. Next, modules in the PPI networks were explored by a clique-merging algorithm, and disrupted modules were identified utilizing a maximum weight bipartite matching in non-increasing order. Then, the gene compositions of the disrupted modules were studied and compared with differentially expressed (DE) genes, and pathway enrichment analysis for these genes was performed based on Expression Analysis Systematic Explorer. Finally, validations of significant genes in HCC were conducted using reverse transcription-quantitative polymerase chain reaction (RT-qPCR) analysis. The present study evaluated 394 disrupted module pairs, which comprised 236 dysregulated genes. When the dysregulated genes were compared with 211 DE genes, a total of 26 common genes [including phospholipase C beta 1, cytochrome P450 (CYP) 2C8 and CYP2B6] were obtained. Furthermore, 6 of these 26 common genes were validated by RT-qPCR. Pathway enrichment analysis of dysregulated genes demonstrated that neuroactive ligand-receptor interaction, purine and drug metabolism, and metabolism of xenobiotics mediated by CYP were significantly disrupted pathways. In conclusion, the present study greatly improved the understanding of HCC in a systematic manner and provided potential biomarkers for early detection and novel therapeutic methods.

Cytochrome P450 and Non-Cytochrome P450 Oxidative Metabolism: Contributions to the Pharmacokinetics, Safety, and Efficacy of Xenobiotics

The drug-metabolizing enzymes that contribute to the metabolism or bioactivation of a drug play a crucial role in defining the absorption, distribution, metabolism, and excretion properties of that drug. Although the overall effect of the cytochrome P450 (P450) family of drug-metabolizing enzymes in this capacity cannot be understated, advancements in the field of non-P450-mediated metabolism have garnered increasing attention in recent years. This is perhaps a direct result of our ability to systematically avoid P450 liabilities by introducing chemical moieties that are not susceptible to P450 metabolism but, as a result, may introduce key pharmacophores for other drug-metabolizing enzymes. Furthermore, the effects of both P450 and non-P450 metabolism at a drug's site of therapeutic action have also been subject to increased scrutiny. To this end, this Special Section on Emerging Novel Enzyme Pathways in Drug Metabolism will highlight a number of advancements that have recently been reported. The included articles support the important role of non-P450 enzymes in the clearance pathways of U.S. Food and Drug Administration-approved drugs over the past 10 years. Specific examples will detail recent reports of aldehyde oxidase, flavin-containing monooxygenase, and other non-P450 pathways that contribute to the metabolic, pharmacokinetic, or pharmacodynamic properties of xenobiotic compounds. Collectively, this series of articles provides additional support for the role of non-P450-mediated metabolic pathways that contribute to the absorption, distribution, metabolism, and excretion properties of current xenobiotics.

Peroxisome proliferator-activated receptor alpha, PPARα, directly regulates transcription of cytochrome P450 CYP2C8

The cytochrome P450, CYP2C8, metabolizes more than 60 clinically used drugs as well as endogenous substances including retinoic acid and arachidonic acid. However, predictive factors for interindividual variability in the efficacy and toxicity of CYP2C8 drug substrates are essentially lacking. Recently we demonstrated that peroxisome proliferator-activated receptor alpha (PPARα), a nuclear receptor primarily involved in control of lipid and energy homeostasis directly regulates the transcription of CYP3A4. Here we investigated the potential regulation of CYP2C8 by PPARα. Two linked intronic SNPs in PPARα (rs4253728, rs4823613) previously associated with hepatic CYP3A4 status showed significant association with CYP2C8 protein level in human liver samples (N = 150). Furthermore, siRNA-mediated knock-down of PPARα in HepaRG human hepatocyte cells resulted in up to ∼60 and ∼50% downregulation of CYP2C8 mRNA and activity, while treatment with the PPARα agonist WY14,643 lead to an induction by >150 and >100%, respectively. Using chromatin immunoprecipitation scanning assay we identified a specific upstream gene region that is occupied in vivo by PPARα. Electromobility shift assay demonstrated direct binding of PPARα to a DR-1 motif located at positions –2762/–2775 bp upstream of the CYP2C8 transcription start site. We further validated the functional activity of this element using luciferase reporter gene assays in HuH7 cells. Moreover, based on our previous studies we demonstrated that WNT/β-catenin acts as a functional inhibitor of PPARα-mediated inducibility of CYP2C8 expression. In conclusion, our data suggest direct involvement of PPARα in both constitutive and inducible regulation of CYP2C8 expression in human liver, which is further modulated by WNT/β-catenin pathway. PPARA gene polymorphism could have a modest influence on CYP2C8 phenotype.

Gender-Specific Effect of CYP2C8*3 on the Risk of Essential Hypertension in Bulgarian Patients

We conducted a case-control study to determine the contribution of polymorphisms in CYP2C8 (CYP2C8*3) and CYP2J2 (CYP2J2*7) to increased risk of coronary artery disease and essential hypertension in Bulgarians. The current analysis included 192 unrelated hypertensive patients, 261 patients with angiographically documented CAD (153 with myocardial infarction and 108 without myocardial infarction), and 496 population controls. The CYP2C8*3 and CYP2J2*7 polymorphisms were genotyped by TaqMan SNP Genotyping Assay. PLINK version 1.07 was used for the statistical analysis. No overall association was observed for the studied polymorphisms with coronary artery disease and essential hypertension. The frequency of -50T mutant allele of CYP2J2*7 was significantly higher in male with coronary artery disease without history of myocardial infarction (OR 2.16 95% CI 1.04-4.48 p = 0.035) compared to population control group, but this association did not survive after Bonferroni correction (p adj = 0.07). A significant association of CYP2C8*3 allele with increased risk of essential hypertension has found in men (OR 2.12 95% CI 1.18-3.81 p = 0.015) and this relationship remained significant after adjustment for multiple comparisons (p adj = 0.03). This is the first study showing significant gene-sex interaction for CYP2C8*3 with twofold increase in the relative risk of essential hypertension and a similar tendency for CYP2J2*7 associated with coronary artery disease without myocardial infarction in Bulgarian males. The association is not seen in females and in the whole group of patients. This result could be partly explained by the effect of estrogens on the vascular tone of coronary arteries and CYP2C8 gene expression.

Genetic markers in the EET metabolic pathway are associated with outcomes in patients with aneurysmal subarachnoid hemorrhage

Preclinical studies show that epoxyeicosatrienoic acids (EETs) regulate cerebrovascular tone and protect against cerebral ischemia. We investigated the relationship between polymorphic genes involved in EET biosynthesis/metabolism, cytochrome P450 (CYP) eicosanoid levels, and outcomes in 363 patients with aneurysmal subarachnoid hemorrhage (aSAH). Epoxyeicosatrienoic acids and dihydroxyeicosatetraenoic acid (DHET) cerebrospinal fluid (CSF) levels, as well as acute outcomes defined by delayed cerebral ischemia (DCI) or clinical neurologic deterioration (CND), were assessed over 14 days. Long-term outcomes were defined by Modified Rankin Scale (MRS) at 3 and 12 months. CYP2C8*4 allele carriers had 44% and 36% lower mean EET and DHET CSF levels (P=0.003 and P=0.007) and were 2.2- and 2.5-fold more likely to develop DCI and CND (P=0.039 and P=0.041), respectively. EPHX2 55Arg, CYP2J2*7, CYP2C8*1B, and CYP2C8 g.36785A allele carriers had lower EET and DHET CSF levels. CYP2C8 g.25369T and CYP2C8 g.36755A allele carriers had higher EET levels. Patients with CYP2C8*2C and EPHX2 404del variants had worse long-term outcomes while those with EPHX2 287Gln, CYP2J2*7, and CYP2C9 g.816G variants had favorable outcomes. Epoxyeicosatrienoic acid levels were associated with Fisher grade and unfavorable 3-month outcomes. Dihydroxyeicosatetraenoic acids were not associated with outcomes. No associations passed Bonferroni multiple testing correction. These are the first clinical data demonstrating the association between the EET biosynthesis/metabolic pathway and the pathophysiology of aSAH.

Interspecies variability in expression of hepatobiliary transporters across human, dog, monkey, and rat as determined by quantitative proteomics

We quantified, by liquid chromatography tandem mass spectrometry, transporter protein expression of BSEP, MATE1, MRP3, MRP4, NTCP, and OCT1 in our human liver bank (n = 55) and determined the relationship between protein expression and sex, age and genotype. These data complement our previous work in the same liver bank where we quantified the protein expression of OATPs, BCRP, MDR1, and MRP2. In addition, we quantified and compared the interspecies differences in expression of the hepatobiliary transporters, corresponding to the above human transporters, in liver tissue and hepatocytes of male beagle dogs, cynomolgus monkeys, Sprague-Dawley rats, and Wistar rats. In all the species, the sinusoidal OATPs/Oatps were the most abundant hepatic transporters. However, there were notable interspecies differences in the relative abundance of the remaining transporters. For example, the next most abundant transporter in humans and monkeys was OCT1/Oct1, whereas it was Mrp2 and Ntcp in dogs/Wistar rats and Sprague-Dawley rats, respectively. In contrast, the protein expression of the efflux transporters BCRP/Bcrp, MDR1/Mdr1, MRP3/Mrp3, MRP4/Mrp4, and MATE1/Mate1 was much lower across all the species. For most transporters, the expression in the liver tissues was comparable to that in the unplated cryopreserved hepatocytes. These data on human liver transporter protein expression complete the picture of the expression of major human hepatobiliary transporters important in drug disposition and toxicity. In addition, the data on expression of the corresponding hepatobiliary transporters in preclinical species will be helpful in interpreting and extrapolating pharmacokinetic, pharmacological, and toxicological results from preclinical studies to humans.

Personalizing medicine in geriatric oncology

Minimizing toxicity while maximizing efficacy is a common goal in the treatment of any condition but its importance is underscored in the discipline of oncology because of the serious nature of many chemotherapeutic toxicities and the risk of cancer recurrence or disease progression. The challenge of achieving an optimal therapeutic index is especially augmented in the elderly population because of age-related metabolism changes and interacting concurrent medications. Additional factors, such as germline mutations in drug-metabolizing enzymes and other pharmacogenomic alterations, may have more pronounced effects in elderly patients, given their predisposition to altered pharmacokinetics and pharmacodynamics with resulting increased risk of toxicity. Examples of the possible interplay of these factors will be discussed using tamoxifen, paclitaxel, codeine, and fluorouracil as starting points. Limited participation of the elderly in many cancer trials, especially trials assessing drug exposure, makes much knowledge on the interaction of these patient and environmental factors speculative in nature but presents an opportunity for future research to achieve better optimization of chemotherapeutic agents in the elderly.

Cytochrome P450 single nucleotide polymorphisms in an indigenous Tanzanian population: a concern about the metabolism of artemisinin-based combinations

BACKGROUND

Artemisinin-based combinations currently recommended for treatment of uncomplicated Plasmodium falciparum malaria in many countries of sub-Saharan Africa are substrates of CYP enzymes. The cytochrome enzyme system is responsible for metabolism of about 80-90% of clinically used drugs. It is, therefore, important to obtain the pharmacogenetics of the population in the region with respect to these combinations and thereby enable practitioners to predict treatment outcomes. The aim of this study was to detect and determine allelic frequencies of CYP2C8*2, CYP2C8*3, CYP3A4*1B, CYP3A5*3 and CYP2B6*6 variant alleles in a Tanzanian indigenous population.

METHODS

Genomic DNA extraction from blood obtained from 256 participants who escorted patients at Karume Health Centre in Mwanza Tanzania, was carried out using the Gene JET™ Genomic DNA purification kit (Thermo Scientific). Genotyping for the cytochrome P450 variant alleles was performed using predesigned primers. Amplification was done by PCR while differentiation between alleles was done by restriction fragment length polymorphism (PCR-RFLP) (for CYP2C8*2, CYP2C8*3) and sequencing (for CYP2B6*6, CYP3A5*3 and CYP3A4*1B).

RESULTS

CYP2C8*2, CYP2C8*3, CYP3A5*3, CYP3A4*1B and CYP2B6*6 variant allelic frequencies were found to be 19,10,16,78 and 36% respectively.

CONCLUSION

Prevalence of CYP2C8*2, CYP3A5*3, CYP3A4*1B and CYP2B6*6 mutations in a Tanzanian population/subjects are common. The impact of these point mutations on the metabolism of anti-malarial drugs, particularly artemisinin-based combinations, and their potential drug-drug interactions (DDIs) needs to be further evaluated.

CYP2C8 and CYP2C9 mRNA expression profile in the human fetus

CYP2C8 and CYP2C9 are involved in the inactivation of several non-steroidal anti-inflammatory drugs, including ibuprofen. CYP2C9 is the major form in human liver whereas CYP2C8 has been proposed to be the main CYP2C enzyme in fetal liver. The protein expression of CYP2C9 in the first trimester is low, only about 1% of the adult values, whereas the mRNA levels of CYP2C8/9 have not been determined at the fetal stage. In this study the mRNA expression levels of CYP2C8 and CYP2C9 were determined in 20 adult and 60 fetal liver tissue specimens. The expression profiles in fetal kidneys (n = 43), adrenals (n = 46), and lungs (n = 37) were also determined. Moreover the activity against ibuprofen hydroxylation was determined in fetus and adult liver microsomes. Adult liver samples expressed 140 and 400 times higher levels of CYP2C8 and CYP2C9 mRNA, respectively, as compared to fetal liver samples. Consistent with this, the hydroxylation of ibuprofen was 40 times higher in the adult liver microsomes. Hepatic CYP2C8 mRNA was three times more abundant than CYP2C9 mRNA in the fetus. Moreover, CYP2C8 were consistently expressed in all fetal tissues investigated, whereas CYP2C9 gene expression was confined to the liver in fetuses. Our results indicate that CYP2C8 plays a more important physiological role than CYP2C9 in the first trimester.

Cytochrome P450 enzymes in drug metabolism: regulation of gene expression, enzyme activities, and impact of genetic variation

Cytochromes P450 (CYP) are a major source of variability in drug pharmacokinetics and response. Of 57 putatively functional human CYPs only about a dozen enzymes, belonging to the CYP1, 2, and 3 families, are responsible for the biotransformation of most foreign substances including 70-80% of all drugs in clinical use. The highest expressed forms in liver are CYPs 3A4, 2C9, 2C8, 2E1, and 1A2, while 2A6, 2D6, 2B6, 2C19 and 3A5 are less abundant and CYPs 2J2, 1A1, and 1B1 are mainly expressed extrahepatically. Expression of each CYP is influenced by a unique combination of mechanisms and factors including genetic polymorphisms, induction by xenobiotics, regulation by cytokines, hormones and during disease states, as well as sex, age, and others. Multiallelic genetic polymorphisms, which strongly depend on ethnicity, play a major role for the function of CYPs 2D6, 2C19, 2C9, 2B6, 3A5 and 2A6, and lead to distinct pharmacogenetic phenotypes termed as poor, intermediate, extensive, and ultrarapid metabolizers. For these CYPs, the evidence for clinical significance regarding adverse drug reactions (ADRs), drug efficacy and dose requirement is rapidly growing. Polymorphisms in CYPs 1A1, 1A2, 2C8, 2E1, 2J2, and 3A4 are generally less predictive, but new data on CYP3A4 show that predictive variants exist and that additional variants in regulatory genes or in NADPH:cytochrome P450 oxidoreductase (POR) can have an influence. Here we review the recent progress on drug metabolism activity profiles, interindividual variability and regulation of expression, and the functional and clinical impact of genetic variation in drug metabolizing P450s.

Interindividual variability in the hepatic expression of the human breast cancer resistance protein (BCRP/ABCG2): effect of age, sex, and genotype

Breast cancer resistance protein (BCRP), an efflux transporter expressed at the bile canalicular membrane, is responsible for the biliary clearance of many drugs. Data on the interindividual variability of hepatic BCRP expression are needed for in vitro to in vivo extrapolation of the biliary clearance of a BCRP substrate drug. Therefore, we measured the expression of BCRP in human livers (n = 65) by liquid chromatography coupled with tandem mass spectrometry. A calibration curve was generated using a synthetic signature peptide (SSLLDVLAAR) as the calibrator and the corresponding synthetic stable isotope-labeled peptide as the internal standard. The analytical method was accurate and precise. BCRP expression in 50 livers, where it was measurable, was 137.9 ± 42.1 atmol/µg of membrane protein (range 69.7-246.4 atmol/µg of membrane protein). BCRP expression was not associated with age (7-70 years), sex, or mRNA expression. BCRP expression in livers with the variant C421A (rs2231142) allele (14 heterozygotes, two homozygotes; among these, eight livers were below lower limit of quantification) was significantly lower than that in the wild-type livers (p < 0.002). Integration of these data with data on the hepatic expression of other transporters will allow refinement of physiologically based pharmacokinetic models to predict the pharmacokinetics, hepatic exposure, and drug-drug interactions of drugs (and/or their metabolites).