Possible role of CYP2B6 genetic polymorphisms in ifosfamide‐induced encephalopathy: report of three cases

Ifosfamide (IFA) is a potent alkylating antitumoral agent, but its use is limited by neurological side effects. IFA is a racemic mixture of two enantiomeric forms, R‐IFA and S‐IFA with a stereoselective metabolism by CYP3A4 and CYP2B6, leading either to bioactive or to toxic pathways. In three consecutive cases of pediatric patients who exhibited IFA‐induced encephalopathy (IIE), genotyping of clinically relevant single‐nucleotide polymorphisms associated with decreased CYP3A4 and CYP2B6 activities was performed. Genetic investigations revealed the presence of CYP2B6 rs4803419 (C>T) in one patient while the two others carried the CYP2B6*6 allelic variant. All patients carried CYP3A4 wild‐type genotype (CYP3A4*1/*1). Because CYP2B6‐deficient alleles may be responsible for an increased conversion of S‐IFA into neurotoxic metabolites, screening for CYP2B6 polymorphisms may help to avoid IIE and improve clinical outcomes.     

Bromuconazole-induced hepatotoxicity is accompanied by upregulation of PXR/CYP3A1 and downregulation of CAR/CYP2B1 gene expression

Despite widespread use of bromuconazole as a pesticide for food crops and fruits, limited studies have been done to evaluate its toxic effects. Here, we evaluated the hepatotoxic effect of bromuconazole using classical toxicological (biochemical analysis and histopathological examination) and gene-based molecular methods. Male rats were treated either orally or topically with bromuconazole at doses equal to no observed adverse effect level (NOAEL) and 1/10 LD50 for 90?d. Bromuconazole increased activities of liver enzymes (ALT, AST, ALP, and ACP), and levels of bilirubin. It also induced hepatic oxidative stress as evidenced by significant decrease in the activities of superoxide dismutase (SOD), and significant increase in levels of malondialdehyde (MDA) in liver. In addition, bromuconazole caused an increase in liver weights and necrobiotic changes (vacuolation and hepatocellular hypertrophy). It also strongly induced the expression of PXR and its downstream target CYP3A1 gene as well as the activity of CYP3A1. However, it inhibited the expression of CAR and its downstream target CYP2B1 gene without significant changing in CYP2B1 activity. Overall, the oral route showed higher hepatotoxic effect and molecular changes than the dermal route and all changes were dose dependent. This is the first investigation to report that bromuconazole-induced liver oxidative damage is accompanied by upregulation of PXR/CYP3A1 and downregulation of CAR/CYP2B1.     

State-of-the-art Tools for Computational Site of Metabolism Predictions: Comparative Analysis,Mechanistical Insights,and Future Applications

In drug design, it is crucial to have reliable information on how a chemical entity behaves in the presence of metabolizing enzymes. This requires substantial experimental efforts. Consequently, being able to predict the likely site/s of metabolism in any compound, synthesized or virtual, would be highly beneficial and time efficient.

In this work, six different methodologies for predictions of the site of metabolism (SOM) have been compared and validated using structurally diverse data sets of drug-like molecules with well-established metabolic pattern in CYP3A4, CYP2C9, or both. Three of the methods predict the SOM based on the ligand's chemical structure, two additional methods use structural information of the enzymes, and the sixth method combines structure and ligand similarity and reactivity. The SOM is correctly predicted in 50 to 90% of the cases, depending on method and enzyme, which is an encouraging rate. We also discuss the underlying mechanisms of cytochrome P450 metabolism in the light of the results from this comparison.     

Voriconazole and the liver

Voriconazole is an azole useful for the prophylaxis and the treatment of aspergillosis and other fungal infections in immunosuppressed subjects, as those found in aplasia after aggressive polychemotherapy treatments, after hematopoietic stem cell, liver or lung transplantation. Its administration in therapeutic doses lead to extremely varied serum levels from patient to patient and even to the same patient. The explanations are varied: nonlinearpharmacokinetics, certain patient-related factors, including genetic polymorphisms in the cytochrome P450 2C19 gene, the kidney and liver function, simultaneous administration with other drugs metabolised by the same cytochrome. It is recommended to maintain the serum concentrations of voriconazole between 1.5 and 4 μg/m L. At lower values its efficacy decreases and at higher values the risk of neurological toxicity increases. Even at these concentrations it is not excluded the possible appearance of a variety of toxic effects, including on the liver, manifested by cholestasis, hepatocytolisis, or their combination. It is recommended to monitor the clinical and laboratory evolution of all patients treated with voriconazole, and of the serum levels of the drug of those who belong to risk groups, even if there is still no consensus on this issue, given the lack of correlation between the serum level and the occurrence of adverse effects in many patients.     

CYP2F1 genetic polymorphism: Identification of interethnic variations

Since human cytochrome P450 2F1 (CYP2F1) is predominantly expressed in lung tissue and is involved in the metabolism of various pneumotoxicants with potential carcinogenic effects, variations in the nucleotidic sequence of its gene may contribute to interindividual and interethnic differences in the susceptibility to lung tumorigenesis. The aim of the current study was to compare the frequency of a previously reported frameshift mutation, namely c.14_15insC, responsible for the synthesis of a severely truncated protein, between several populations of different ethnic origins. The frequencies of this polymorphism were 26.1, 51.6, 42.7 and 22.9% in French, Gabonese, Senegalese, and Tunisian population samples, respectively, thereby representing a substantial inter ethnic variation in the CYP2F1 gene. These findings provide data for further studies that investigate the potential association of CYP2F1 haplotypes with an incidence of lung cancer genesis in respect of ethnicity.     

Serotonin (5-hydroxytryptamine) glucuronidation in vitro : assay development,human liver microsome activities and species differences

1. The main purpose was to develop a high-performance liquid chromatography (HPLC)-based method to assay serotonin glucuronidation activity using liver microsomal fractions. Application of this method was then demonstrated by determining serotonin UDP-glucuronosyltransferase (UGT) enzyme kinetics using human liver microsomes and recombinant human UGT1A6. Interspecies differences were also evaluated using liver microsomes from 10 different mammalian species. 2. Incubation of liver microsomes with serotonin, UDP-glucuronic acid and magnesium resulted in the formation of a single product peak using HPLC with fluorescence and ultraviolet absorbance detection. This peak was confirmed as serotonin glucuronide based on sensitivity to β-glucuronidase and by obtaining the expected mass of 352 with positive-ion mass spectrometry. 3. Following a preparative HPLC isolation, the structure of this metabolite was established as serotonin-5- O -glucuronide by 1 H-NMR spectroscopy. 4. Enzyme kinetic studies showed apparent K m and V max of 8.8 ±0.3 mM and 43.4 ±0.4 nmoles min <1 mg <1 protein, respectively, for human liver microsomes, and 5.9 ±0.2 mM and 15.8 ±0.2 nmoles min <1 mg <1, respectively, for recombinant UGT1A6. 5. The order of serotonin-UGT activities in animal liver microsomes was rat > mouse > human > cow > pig > horse > dog > rabbit > monkey > ferret. Cat livers showed no serotonin-UGT activity. Heterozygous and homozygous mutant Gunn rat livers had 40 and 13%, respectively, of the activity of the normal Wistar rat, indicating a significant contribution by a rat UGT1A isoform to serotonin glucuronidation. 6. This assay provides a novel sensitive and specific technique for the measurement of serotonin-UGT activity in vitro.