Contribution of cytochrome P450 3A pathway to bromocriptine metabolism and effects of ferrous iron and hypoxia-re-oxygenation on its elimination in the perfused rat liver

Advances in understanding genomic markers and pharmacogenetics of Parkinson's disease

INTRODUCTION

The inheritance pattern of Parkinson's disease (PD) is likely multifactorial (owing to the interplay of genetic predisposition and environmental factors). Many pharmacogenetic studies have tried to establish a possible role of candidate genes in PD risk. Several studies have focused on the influence of genes in the response to antiparkinsonian drugs and in the risk of developing side-effects of these drugs.

AREAS COVERED

This review presents an overview of current knowledge, with particular emphasis on the most recent advances, both in case-control association studies on the role of candidate genes in the risk for PD as well as pharmacogenetic studies on the role of genes in the development of side effects of antiparkinsonian drugs. The most reliable results should be derived from meta-analyses of case-control association studies on candidate genes involving large series of PD patients and controls, and from genome-wide association studies (GWAS).

EXPERT OPINION

Prospective studies of large samples involving several genes with a detailed history of exposure to environmental factors in the same cohort of subjects, should be useful to clarify the role of genes in the risk for PD. The results of studies on the role of genes in the development of side-effects of antiparkinsonian drugs should, at this stage, only be considered preliminary.

Distinguishing between the permeability relationships with absorption and metabolism to improve BCS and BDDCS predictions in early drug discovery

The biopharmaceutics classification system (BCS) and biopharmaceutics drug distribution classification system (BDDCS) are complementary classification systems that can improve, simplify, and accelerate drug discovery, development, and regulatory processes. Drug permeability has been widely accepted as a screening tool for determining intestinal absorption via the BCS during the drug development and regulatory approval processes. Currently, predicting clinically significant drug interactions during drug development is a known challenge for industry and regulatory agencies. The BDDCS, a modification of BCS that utilizes drug metabolism instead of intestinal permeability, predicts drug disposition and potential drug–drug interactions in the intestine, the liver, and most recently the brain. Although correlations between BCS and BDDCS have been observed with drug permeability rates, discrepancies have been noted in drug classifications between the two systems utilizing different permeability models, which are accepted as surrogate models for demonstrating human intestinal permeability by the FDA. Here, we recommend the most applicable permeability models for improving the prediction of BCS and BDDCS classifications. We demonstrate that the passive transcellular permeability rate, characterized by means of permeability models that are deficient in transporter expression and paracellular junctions (e.g., PAMPA and Caco-2), will most accurately predict BDDCS metabolism. These systems will inaccurately predict BCS classifications for drugs that particularly are substrates of highly expressed intestinal transporters. Moreover, in this latter case, a system more representative of complete human intestinal permeability is needed to accurately predict BCS absorption.

Anti-Parkinson's disease drugs and pharmacogenetic considerations

INTRODUCTION

The development of pharmacogenetic-based clinical practice guidelines for the use of anti-Parkinson's disease drugs requires, as a pre-requisite, the identification and validation of genetic biomarkers. These biomarkers are then used as surrogate endpoints. This review analyzes potential genetic biomarkers which can be used to improve anti-Parkinson's disease therapy.

AREAS COVERED

The authors present an overview of current knowledge of pharmacogenetic implications of anti-Parkinson's disease drugs, including genes coding for the corresponding drug-metabolizing enzymes and drug targets. The gene/drug pairings with the strongest potential for pharmacogenetic recommendations include: CYP2C19/benztropine, COMT/levodopa and entacapone, CYP2B6/selegiline, UGT1A/entacapone, DRD2/ropinirole, pramipexole and cabergoline, and DRD3/ropinirole and pramipexole. Evidence supporting the effect of substrates, inhibitor or inducers for drug specific metabolizing enzymes in anti-Parkinson's disease drug response includes CYP1A2 in the response to ropinirole and rasagiline, and CYP3A4 in the response to bromocriptine, lisuride, pergolide and cabergoline. The authors present and discuss the current information on gene variations according to the 1000 genomes catalog and other databases with regards to anti-Parkinson's disease drugs. They also review and discuss the clinical implications of these variations.

EXPERT OPINION

The goal of pharmacogenomic testing for anti-Parkinson's disease drugs should be conservative and aimed at selecting determined drugs for determined patients. However, much additional research is still needed to obtain reliable pre-prescription tests.

Effect of hypoxia alone or combined with inflammation and 3-methylcholanthrene on hepatic cytochrome P450 in conscious rabbits

1 To investigate the effect of moderate hypoxia alone or combined with an inflammatory reaction or after 3-methylcholanthrene (3MC) pre-treatment on cytochrome P450 (P450), conscious rabbits were exposed for 24 h to a fractional concentration of inspired O2 of 10% (mean PaO2 of 34 mmHg). Hypoxia decreased theophylline metabolic clearance (ClM) from 1.73+/-0.43 to 1.48+/-0.13 ml min-1 kg-1 (P<0. 05), and reduced (P<0.05) the formation clearance of theophylline metabolites, 3-methylxanthine (3MX), 1-methyluric acid (1MU) and 1,3-dimethyluric acid (1,3DMU). Hypoxia reduced the amount of CYP1A1 and 1A2 but increased CYP3A6 proteins. 2 Turpentine-induced inflammatory reaction reduced (P<0.05) the formation clearance of 3MX, 1MU, and 1,3DMU, and diminished the amount of CYP1A1, 1A2 and 3A6 proteins. However, when combined with hypoxia, inflammation partially prevented the decrease in ClM, especially by impeding the reduction of 1,3DMU. The amount of CYP1A1 and 1A2 remained reduced but the amount of CYP3A6 protein returned to normal values. 3 Pre-treatment with 3MC augmented the ClM by 114% (P<0.05) due to the increase in the formation clearance of 3MX, 1MU and 1,3DMU. 3MC treatment increased the amount of CYP1A1 and 1A2 proteins. Pre-treatment with 3MC prevented the hypoxia-induced decrease in amount and activity of the P450. 4 It is concluded that acute moderate hypoxia and an inflammatory reaction individually reduce the amount and activity of selected apoproteins of the P450. However, the combination of hypoxia and the inflammatory reaction restores P450 activity to near normal values. On the other hand, pre-treatment with 3MC prevents the hypoxia-induced depression of the P450.