P450 (Cytochrome) Oxidoreductase Gene (POR) Common Variant (POR*28) Significantly Alters CYP2C9 Activity in Swedish, But Not in Korean Healthy Subjects

The effect of the association between CETP variant type and alcohol consumption on cholesterol level differs according to the ALDH2 variant type

Alcohol consumption is associated with a high increased lipid profile and this association may depend on genetic risk factors. In this study, we aimed to assess the effects of genetic variation associated with alcohol consumption on lipid profiles using data from two Korean population studies. We performed a genotype association study using the HEXA (n = 51,349) and KNHANES (n = 9158) data. Genotype analyses of the two sets of Korean population data showed associations of increased total cholesterol and high-density lipoprotein (HDL)-cholesterol with CETP rs708272. The HEXA and KNHANES populations revealed differences in HDL cholesterol according to the presence of CETP rs708272, independent of ALDH2 rs671 and alcohol consumption. In contrast, total cholesterol levels were associated with alcohol consumption and ALDH2 rs671 in men with CETP rs708272 (CT and TT genotypes). Furthermore, in drinkers with ALDH2 rs671 (GA and AA genotypes), higher total cholesterol was associated with the CETP rs708272 TT minor homozygous genotype based on both HEXA and KNHANES data. Our findings demonstrated that alcohol consumption and genetic variation in either CETP or ALDH2 may be associated with cholesterol levels. We hope these findings will provide a better understanding of the relationship between alcohol consumption and cholesterol according to each individual’s genetic background.

Evaluation of clinical and genetic factors in the population pharmacokinetics of carbamazepine

Aims

Carbamazepine can cause hypersensitivity reactions in ~10% of patients. An immunogenic effect can be produced by the electrophilic 10,11‐epoxide metabolite but not by carbamazepine. Hypothetically, certain single nucleotide polymorphisms might increase the formation of immunogenic metabolites, leading ultimately to hypersensitivity reactions. This study explores the role of clinical and genetic factors in the pharmacokinetics (PK) of carbamazepine and 3 metabolites known to be chemically reactive or formed through reactive intermediates.

Methods

A combination of rich and sparse PK samples were collected from healthy volunteers and epilepsy patients. All subjects were genotyped for 20 single nucleotide polymorphisms in 11 genes known to be involved in the metabolism or transport of carbamazepine and carbamazepine 10,11‐epoxide. Nonlinear mixed effects modelling was used to build a population‐PK model.

Results

In total, 248 observations were collected from 80 subjects. A 1‐compartment PK model with first‐order absorption and elimination best described the parent carbamazepine data, with a total clearance of 1.96 L/h, central distribution volume of 164 L and absorption rate constant of 0.45 h⁻¹. Total daily dose and coadministration of phenytoin were significant covariates for total clearance of carbamazepine. EPHX1‐416G/G genotype was a significant covariate for the clearance of carbamazepine 10,11‐epoxide.

Conclusion

Our data indicate that carbamazepine clearance was affected by total dose and phenytoin coadministration, but not by genetic factors, while carbamazepine 10,11‐epoxide clearance was affected by a variant in the microsomal epoxide hydrolase gene. A much larger sample size would be required to fully evaluate the role of genetic variation in carbamazepine pharmacokinetics, and thereby predisposition to carbamazepine hypersensitivity.

Population Pharmacokinetic, Pharmacogenetic, and Pharmacodynamic Analysis of Cyclophosphamide in Ethiopian Breast Cancer Patients

Cyclophosphamide (CPA) containing chemotherapy regimen is the standard of care for breast cancer treatment in sub-Saharan Africa. Wide inter-individual variations in pharmacokinetics (PK) of cyclophosphamide (CPA) influence the efficacy and toxicity of CPA containing chemotherapy. Data on the pharmacokinetics (PK) profile of CPA and its covariates among black African patients is lacking. We investigated population pharmacokinetic/pharmacogenetic/pharmacodynamic (PK-PG-PD) of CPA in Ethiopian breast cancer patients. During the first cycle of CPA-based chemotherapy, the population PK parameters for CPA were determined in 267 breast cancer patients. Absolute neutrophil count was recorded at baseline and day 20 post-CPA administration. A population PK and covariate model analysis was performed using non-linear mixed effects modeling. Semi-mechanistic and empiric drug response models were explored to describe the relationship between the area under concentration-time curve (AUC), and neutrophil toxicity. One compartment model better described CPA PK with population clearance and apparent volume of distribution (V_D) of 5.41 L/h and 46.5 L, respectively. Inter-patient variability in CPA clearance was 54.5%. Patients carrying CYP3A5*3 or *6 alleles had lower elimination rate constant and longer half-life compared to wild type carriers. CYP2C9 *2 or *3 carriers were associated with increased clearance of CPA. Patients who received 500 mg/m² based CPA regimen were associated with a 32.3% lower than average clearance and 37.1% lower than average V_D compared to patients who received 600 mg/m². A 0.1 m² unit increase in body surface area (BSA) was associated with a 5.6% increment in V_D. The mean V_D (33.5 L) in underweight group (BMI < 18.5 kg/m²) was significantly lower compared to those of overweight (48.1 L) or obese patients (51.9 L) (p < 0.001). AUC of CPA was positively correlated with neutropenic toxicity. In conclusion, we report large between-patient variability in clearance of CPA. CYP3A5 and CYP2C9 genotypes, BSA, BMI, and CPA dosage regimen influence PK of CPA. Plasma CPA exposure positively predicts chemotherapy-associated neutropenic toxicity.

CYP2J2∗7 Genotype Predicts Risk of Chemotherapy-Induced Hematologic Toxicity and Reduced Relative Dose Intensity in Ethiopian Breast Cancer Patients

Chemotherapy-induced hematologic toxicity is the primary reasons of dose reductions and/or delays, low relative dose intensity (RDI), and predicts anticancer response. We investigated the incidence and predictors of chemotherapy-induced hematologic toxicities and reduced RDI in Ethiopian breast cancer patients, and implication of pharmacogenetics variations. Breast cancer patients (n = 249) were enrolled prospectively to receive cyclophosphamide based chemotherapy. Hematological toxicity (neutropenia, anemia, and thrombocytopenia) were monitored throughout chemotherapy cycle. The primary and secondary outcomes were incidence of grade 3 or 4 toxicity and reduced RDI, respectively. CYP2B6^∗6, CYP3A5^∗3, CYP2C9 (^∗2,^∗3), CYP2C19 (^∗2,^∗3), CYP2J2^∗7, POR^∗28, and ABCB1 (rs3842) genotyping were done. Cox proportional hazard and logistic regression were used to estimate risk predictors of toxicity and reduced RDI, respectively. Majority (73.5%) of the patients were < 45 years of age. The incidence of grade 3 or 4 hematological toxicity was 51.0% (95% CI = 44.54–57.46%). Multivariate Cox proportional hazard regression indicated CYP2J2^∗7 genotype [Hazard ratio (HR) = 1.82; 95% CI = 1.14–2.90], pretreatment grade 1 leukopenia (HR = 2.75; 95% CI = 1.47–5.15) or grade 1 or 2 neutropenia (HR = 2.75; 95% CI = 1.73–4.35) as significant predictors of hematologic toxicities. The odds of having hematologic toxicities was lower in CYP2C9^∗2 or ^∗3 carriers (p = 0.024). The prevalence of reduced RDI was 56.6% (95% CI = 50.3–62.9%). Higher risk of reduced RDI was associated with CYP2J2^∗7 allele [Adjusted odds ratio (AOR) = 2.79; 95% CI = 1.21–6.46], BMI ≤ 18.4 kg/m² (AOR = 5.98; 95% CI = 1.36–26.23), baseline grade 1 leukopenia (AOR = 6.09; 95% CI = 1.24–29.98), and baseline neutropenia (AOR = 3.37; 95% CI = 1.41–8.05). The odds of receiving reduced RDI was lower in patients with CYP2B6 ^∗6/^∗6 genotype (AOR = 0.19; 95% CI = 0.06–0.77). We report high incidence of chemotherapy-induced hematological toxicities causing larger proportion of patients to receive reduced RDI in Ethiopian breast cancer patients. Patients carrying CYP2J2^∗7 allele and low baseline blood counts are at a higher risk for chemotherapy-induced hematologic toxicities and receiving reduced RDI, and may require prior support and close follow up during chemotherapy.

Vitamin D Status and Association of VDR Genetic Polymorphism to Risk of Breast Cancer in Ethiopia

Emerging evidence associates vitamin D deficiency and vitamin D receptor (VDR) genetic variations with risk for breast cancer. This study investigated the prevalence of vitamin D deficiency and its association with tumor characteristics and the implications of VDR genetic variations for risk of breast cancer in Ethiopia. This unmatched case–control study involved 392 female breast cancer patients and 193 controls. The plasma 25-hydroxyvitamin D (25(OH)D₃) level was quantified in chemotherapy-naïve (N = 112) and tamoxifen-treated patients (N = 89). Genotyping for the VDR common variant alleles rs7975232 (ApaI), rs2228570 (FokI), and rs731236 (TaqI) was done. Eighty-six percent of the patients were vitamin D deficient (<50 nmol/L). Chemotherapy-naïve breast cancer patients had a higher prevalence of vitamin D deficiency (91.9% vs. 78.3%) compared to the tamoxifen-treated group (p < 0.001). The prevalence of severe vitamin D deficiency (<25 nmol/L) was significantly higher in chemotherapy-naïve (41.1%) than tamoxifen-treated (11.2%) patients. Vitamin D deficiency was not significantly associated with tumor characteristics or VDR genotype. The rs2228570 GG genotype was associated with increased risk of breast cancer (OR = 1.44, 95% confidence interval = 1.01−2.06). Our result indicates that rs2228570 might be a moderate risk factor for breast cancer development in the Ethiopian population. The high prevalence of severe vitamin D deficiency in treatment-naïve breast cancer patients indicates the need for nutritional supplementation of vitamin D at the time of chemotherapy initiation.

Effects of Khat (Catha edulis) use on catalytic activities of major drug-metabolizing cytochrome P450 enzymes and implication of pharmacogenetic variations

In a one-way cross-over study, we investigated the effect of Khat, a natural amphetamine-like psychostimulant plant, on catalytic activities of five major drug-metabolizing cytochrome P450 (CYP) enzymes. After a one-week Khat abstinence, 63 Ethiopian male volunteers were phenotyped using cocktail probe drugs (caffeine, losartan, dextromethorphan, omeprazole). Phenotyping was repeated after a one-week daily use of 400 g fresh Khat leaves. Genotyping for CYP1A2, CYP2C9, CYP2C19, CYP2D6, CYP3A5 were done. Urinary cathinone and phenylpropanolamine, and plasma probe drugs and metabolites concentrations were quantified using LC-MS/MS. Effect of Khat on enzyme activities was evaluated by comparing caffeine/paraxanthine (CYP1A2), losartan/losartan carboxylic acid (CYP2C9), omeprazole/5-hydroxyomeprazole (CYP2C19), dextromethorphan/dextrorphan (CYP2D6) and dextromethorphan/3-methoxymorphinan (CYP3A4) metabolic ratios (MR) before and after Khat use. Wilcoxon-matched-pair-test indicated a significant increase in median CYP2D6 MR (41%, p < 0.0001), and a marginal increase in CYP3A4 and CYP2C19 MR by Khat. Repeated measure ANOVA indicated the impact of CYP1A2 and CYP2C19 genotype on Khat-CYP enzyme interactions. The median MR increased by 35% in CYP1A2*1/*1 (p = 0.07) and by 40% in carriers of defective CYP2C19 alleles (p = 0.03). Urinary log cathinone/phenylpropanolamine ratios significantly correlated with CYP2D6 genotype (p = 0.004) and CYP2D6 MR (P = 0.025). Khat significantly inhibits CYP2D6, marginally inhibits CYP3A4, and genotype-dependently inhibit CYP2C19 and CYP1A2 enzyme activities.

Precision medicine: does ethnicity information complement genotype-based prescribing decisions?

Inter-ethnic differences in drug response are all too well known. These are underpinned by a number of factors, including pharmacogenetic differences across various ethnic populations. Precision medicine relies on genotype-based prescribing decisions with the aim of maximizing efficacy and mitigating the risks. When there is no access to genotyping tests, ethnicity is frequently regarded as a proxy of the patient's probable genotype on the basis of overall population-based frequency of genetic variations in the ethnic group the patient belongs to, with some variations being ethnicity-specific. However, ever-increasing transcontinental migration of populations and the resulting admixing of populations have undermined the utility of self-identified ethnicity in predicting the genetic ancestry, and therefore the genotype, of the patient. An example of the relevance of genetic ancestry of a patient is the inadequate performance of European-derived pharmacogenetic dosing algorithms of warfarin in African Americans, Brazilians and Caribbean Hispanics. Consequently, genotyping a patient potentially requires testing for all known clinically actionable variants that the patient may harbour, and new variants that are likely to be identified using state-of the art next-generation sequencing-based methods. Furthermore, self-identified ethnicity is associated with a number of ethnicity-related attributes and non-genetic factors that potentially influence the risk of phenoconversion (genotype-phenotype discordance), which may adversely impact the success of genotype-based prescribing decisions. Therefore, while genotype-based prescribing decisions are important in implementing precision medicine, ethnicity should not be disregarded.