Nada Božina

Genetic Polymorphism of Metabolic Enzymes P450 (CYP) as a Susceptibility Factor for Drug Response, Toxicity, and Cancer Risk

Genetic Polymorphism of Metabolic Enzymes P450 (CYP) as a Susceptibility Factor for Drug Response, Toxicity, and Cancer Risk The polymorphic P450 (CYP) enzyme superfamily is the most important system involved in the biotransformation of many endogenous and exogenous substances including drugs, toxins, and carcinogens. Genotyping for CYP polymorphisms provides important genetic information that help to understand the effects of xenobiotics on human body. For drug metabolism, the most important polymorphisms are those of the genes coding for CYP2C9, CYP2C19, CYP2D6, and CYP3A4/5, which can result in therapeutic failure or severe adverse reactions. Genes coding for CYP1A1, CYP1A2, CYP1B1, and CYP2E1 are among the most responsible for the biotransformation of chemicals, especially for the metabolic activation of pre-carcinogens. There is evidence of association between gene polymorphism and cancer susceptibility. Pathways of carcinogen metabolism are complex, and are mediated by activities of multiple genes, while single genes have a limited impact on cancer risk. Multigenic approach in addition to environmental determinants in large sample studies is crucial for a reliable evaluation of any moderate gene effect. This article brings a review of current knowledge on the relations between the polymorphisms of some CYPs and drug activity/toxicity and cancer risk. Uloga genskog polimorfizma metaboličkih enzima P450(CYP) kao čimbenika osjetljivosti na učinkovitost i toksičnost lijeka te nastanak karcinoma

Association between lamotrigine concentrations and ABCB1 polymorphisms in patients with epilepsy.

Background: Epilepsy is treated with a variety of anticonvulsants that are often used concomitantly. Therefore, therapeutic drug monitoring is often necessary. Along with clinical and environmental factors, genetic predisposition has been recognized to be relevant for interindividual variability in drug response. Polymorphic transporter proteins such as P-glycoprotein significantly influence pharmacokinetics and bioavailability of many structurally unrelated drugs. The aim of the study was to evaluate the impact of polymorphisms in the P-glycoprotein–encoding gene ABCB1 (C1236T, G2677T/A, C3435T) on antiepileptic drug disposition. Methods: We recruited 222 patients with epilepsy who were prescribed lamotrigine in monotherapy or polytherapy. Lamotrigine plasma concentrations were analyzed and compared with ABCB1 gene variants. The ABCB1 genotyping was performed by real-time polymerase chain reaction methods. The therapeutic drug monitoring was performed by high-performance liquid chromatography–diode array detector (DAD) and immunoassay. Results: A significant correlation was confirmed between lamotrigine concentration and additional drugs (P < 0.001). In the whole group, statistical analysis showed correlations between lamotrigine concentrations and ABCB1 C1236T variants: 10.1 and 6.5 &mgr;mol/L for CC versus CT + TT, respectively (P = 0.021), and for dose corrected lamotrigine 0.068 and 0.053 &mgr;mol·L−1·mg−1, for CC versus CT + TT, respectively (P = 0.017). Analysis of a specific haplotype showed that 1236C–2677G–3435C carriers had higher lamotrigine concentrations than 1236T–2677G–3435T carriers (P < 0.001), followed by 1236T–2677T–3435C carriers (P < 0.001). Conclusions: ABCB1 C1236T, G2677T/A, C3435T polymorphisms have an influence on lamotrigine serum concentrations.

Suicide ideators and attempters with schizophrenia – The role of 5-HTTLPR, rs25531, and 5-HTT VNTR Intron 2 variants

AIM To examine the role of 5-HTTLPR, rs25531 and 5-HTT VNTR Intron 2 variants in subjects with psychotic disorders manifesting suicide ideation and behaviour. METHODS The study included 519 subsequently hospitalized subjects who were genotyped for 5-HTTLPR, rs25531 and 5-HTT VNTR In2 variants. Clinical assessments included structured psychiatric interview, sociodemographic characteristics, suicide ideation and behaviour (SIBQ), severity of psychopathology (PANSS) and depression (CDSS). RESULTS Three subgroups were identified: suicide attempters (N = 161), suicide ideators (N = 174) and subjects who never reported suicide ideation or behaviour (comparative group, N = 184). MAJOR FINDINGS 1) Suicide attempters scored highest on the CDSS, while no differences between the three clinical subgroups were detected in the PANSS scores; 2) Suicide attempters were more frequently the carriers of L(A) allele, while subjects in the comparative group were more frequently the carriers of low expression 5-HTTLPR/5-HTT rs25531 haplotype SL(G); 3) No difference was found between the three clinical groups in the 5-HTT VNTR In2 variants; 4) Subjects with 5-HTTLPR/5-HTT rs25531 intermediate expression haplotype (L(A)L(G,)SL(A)) scored higher on the PANSS general psychopathology subscale; 5) There was no association between suicide attempt or ideation and 5-HTTLPR/In2 or 5-HTTLPR/rs25531/In2 haplotype distribution. CONCLUSION The suicide ideators, attempters and controls did not differ significantly in 5-HTTLPR or 5-HTT VNTR In 2 variants, but 5-HTTLPR/5-HTT rs25531 haplotype might be a useful genetic marker in distinguishing these three clinical groups.

Adverse drug reactions caused by drug-drug interactions reported to Croatian Agency for Medicinal Products and Medical Devices: a retrospective observational study

Aim To analyze potential and actual drug-drug interactions reported to the Spontaneous Reporting Database of the Croatian Agency for Medicinal Products and Medical Devices (HALMED) and determine their incidence. Methods In this retrospective observational study performed from March 2005 to December 2008, we detected potential and actual drug-drug interactions using interaction programs and analyzed them. Results HALMED received 1209 reports involving at least two drugs. There were 468 (38.7%) reports on potential drug-drug interactions, 94 of which (7.8% of total reports) were actual drug-drug interactions. Among actual drug-drug interaction reports, the proportion of serious adverse drug reactions (53 out of 94) and the number of drugs (n = 4) was significantly higher (P < 0.001) than among the remaining reports (580 out of 1982; n = 2, respectively). Actual drug-drug interactions most frequently involved nervous system agents (34.0%), and interactions caused by antiplatelet, anticoagulant, and non-steroidal anti-inflammatory drugs were in most cases serious. In only 12 out of 94 reports, actual drug-drug interactions were recognized by the reporter. Conclusion The study confirmed that the Spontaneous Reporting Database was a valuable resource for detecting actual drug-drug interactions. Also, it identified drugs leading to serious adverse drug reactions and deaths, thus indicating the areas which should be in the focus of health care education.

CYP2C9 and ABCG2 polymorphisms as risk factors for developing adverse drug reactions in renal transplant patients taking fluvastatin: a case–control study

AIM To investigate whether an association exists between fluvastatin-induced adverse drug reactions (ADRs) and polymorphisms in genes encoding the metabolizing enzyme CYP2C9 and the drug transporter ABCG2 in renal transplant recipients (RTRs). MATERIALS & METHODS Fifty-two RTRs that experienced fluvastatin ADRs and 52 controls matched for age, gender, dose of fluvastatin and immunosuppressive use were enrolled in the study. Genotyping for CYP2C9*2, *3 and ABCG2 421C>A variants was performed by real-time PCR. RESULTS CYP2C9 homozygous and heterozygous mutant allele (*2 or *3) carriers had 2.5-times greater odds of developing adverse effects (χ² = 4.370; degrees of freedom = 1; p = 0.037; φ = 0.21, odds ratio [OR]: 2.44; 95% CI: 1.05-5.71). Patients who were the carriers of at least one mutant CYP2C9 allele (*2 or *3) and who were receiving CYP2C9 inhibitors, had more than six-times greater odds of having adverse effects than those without the inhibitor included in their therapy (p = 0.027; OR: 6.59; 95% CI: 1.24-35.08). Patients with ABCG2 421CA or AA (taken together) had almost four-times greater odds of developing adverse effects than those with ABCG2 421CC genotype (χ² = 6.190; degrees of freedom = 1; p = 0.013; φ = 0.24, OR: 3.81; 95% CI: 1.27-11.45). Patients with A allele had 2.75-times (95% CI: 1.02-7.40) greater odds of developing adverse effects than those with C allele. CONCLUSION Our preliminary data demonstrate an association between fluvastatin-induced ADRs in RTRs and genetic variants in the CYP2C9 and ABCG2 genes.

ABCG2 gene polymorphisms as risk factors for atorvastatin adverse reactions: a case–control study

AIM To explore the association between dose-related adverse drug reactions (ADRs) of atorvastatin and polymorphisms of ABCG2, taking into account the influence of CYP3A4 and SLCO1B1 genes. MATERIALS & METHODS Sixty patients who experienced atorvastatin dose-related ADRs and 90 matched patients without ADRs were enrolled in the study. Genotyping for ABCG2 421C > A, CYP3A4*22, SLCO1B1 388A > G, SLCO1B1 521T > C variants was performed by real-time PCR. RESULTS Patients with ABCG2 421CA or AA genotypes had 2.9 times greater odds of developing atorvastatin dose-dependent ADRs (OR: 2.91; 95% CI: 1.22-6.95; p = 0.016) than those with ABCG2 421CC genotype. After adjustments for clinical and genetic risk factors, ABCG2 remained a statistically significant predictor of adverse drug reactions (OR: 2.75; 95% CI: 1.1-6.87; p = 0.03;). Also, carriers of SLCO1B1 521 TC or CC genotypes had 2.3 greater odds (OR: 1.03-4.98; 95% CI: 1.03-4.98; p = 0.043) of experiencing ADRs caused by atorvastatin in comparison with carriers of SLCO1B1 521 TT genotype. CONCLUSION Our study demonstrated an association between atorvastatin-induced ADRs and genetic variants in the ABCG2 gene.

Clinical significance of a CYP2D6 poor metabolizer--a patient with schizophrenia on risperidone treatment.

A case of a 46-year-old woman with schizophrenia who was treated with risperidone and followed up for 1 year is reported. She was genotyped as a CYP2D6 poor metabolizer (PM): CYP2D6-4*/*6, which was confirmed by a dextromethorphan (DM) test (metabolic ratio = 5.8). Genotypes of ABCB1 (MDR1) were 2677TT and 3435TT. Because risperidone is CYP2D6 and P-glycoprotein substrate, the patient might have been expected to accumulate risperidone and suffer from significant side effects. However, the patient tolerated the drug extremely well. Plasma concentration of risperidone was 73.2 nmol/L and of 9-OH-risperidone was below the limit of quantitation (6.1 nmol/L). Target range of risperidone plus 9-hydroxyrisperidone is 50-150 nmol/L. During the follow-up, patient was continuously taking 3 mg/day of risperidone. Plasma levels of risperidone and 9-OH-risperidone were 70.2 and 18.1 nmol/L, respectively. We repeated a DM test, metabolic ratio was 3.6, thus confirming that the patient remained a PM. Psychopathology was assessed with Positive and Negative Syndrome Scale, and stable remission of illness was achieved over the stated period. No adverse effects were observed or reported by the patient. We conclude that PM phenotype for CYP2D6 does not necessarily have clinical significance in regard to risperidone treatment. DM and risperidone are both CYP2D6 and P-glycoprotein substrates and significant interactions might occur with both drugs, in parallel with the possible impact of ABCB1 and CYP2D6 polymorphic gene variants.

How polymorphisms of the cytochrome P450 genes affect ibuprofen and diclofenac metabolism and toxicity.

Abstract Interindividual variability in drug metabolism is an important cause of adverse drug reactions and variability in drug efficiency. Polymorphisms of cytochrome P450 (CYPs) genes have a significant effect on drug metabolism and toxicity. This review brings an update about how genetic polymorphisms of CYP2C8 and CYP2C9 enzymes affect the disposition and clinical outcomes of ibuprofen and diclofenac, two of the most common pain relievers. The most common side effects associated with the influence of CYP2C8*3 and CYP2C9*2*3 variants on ibuprofen and diclofenac pharmacokinetics are hepatotoxicity and gastrointestinal bleeding. CYP genotyping may therefore identify patients at increased risk of these adverse reactions, and these patients could have their doses adjusted or start receiving another NSAID that does not share the same metabolic pathways with ibuprofen or diclofenac. However, before genotyping is introduced into regular clinical practice, more research is needed to evaluate the effectiveness of this strategy in improving treatment with ibuprofen and diclofenac.

CYP2D6 *6/*6 genotype and drug interactions as cause of haloperidol-induced extrapyramidal symptoms

A 66-year-old male Caucasian, received 1 mg of haloperidol orally and rapidly developed severe iatrogenic extrapyramidal symptoms. Treatment was immediately discontinued, and the side effects resolved. Haloperidol is mainly metabolized by Phase I CYP2D6 and to the lesser extent by CYP3A4 and by Phase II UGT2B7 enzymes. Genotyping was performed revealing CYP2D6*6/*6, CYP3A4*1/*1, and UGT2B7 -161 C/T genotypes, implicating poor, extensive and intermediate metabolism, respectively. Of the CYPs, haloperidol is metabolized by CYP2D6 and CYP3A4 primarily. It was the introduction of ciprofloxacin which was a trigger for the development of adverse drug reaction due to inhibition of CYP3A4, which was in presented patient main metabolic pathway for haloperidol since he was CYP2D6 poor metabolizer. Presented case report highlights the importance of genotyping. Pharmacogenetics testing should be considered when drug toxicity is suspected, polymorphic metabolic pathways used and drugs concomitantly applied.

Erlotinib-related rhabdomyolysis: the role of pharmacogenetics and drug–drug interaction

but is an uncommon complication of antineoplastic treatment [5–8]. However, cases of rhabdomyolysis have been described in patients treated with imatinib and, up to now, only one case in patient treated with erlotinib alone [9, 10]. Erlotinib is mainly metabolized by cytochrome P450 (CYP) 3A4 isoenzyme and is transported across different barriers by P-glycoprotein (MDR1/ABCB1) and ABCG2 drug transporters; the potential for CYPand transportermediated drug–drug interactions (DDIs) is high, especially with CYP3A4, P-glycoprotein (P-gp), and ABCG2 inhibitors. According to in vitro and in vivo studies, erlotinib is not only the substrate but also a P-gp/ABCG2 inhibitor [11, 12]. Interindividual pharmacokinetic variability of erlotinib is affected not only by the genetic heterogeneity of drug targets, but also by patient’s pharmacogenetic background. Published data show higher erlotinib through concentrations at steady state in patients with the ABCB1 1236TT-2677TT-3435TT genotypes compared with other groups. Patients carrying these genotypes had a higher risk of developing high grade 2 toxicity (moderate to severe skin rash and diarrhea) [13].