Marie-Anne Loriot

Optimization of Initial Tacrolimus Dose Using Pharmacogenetic Testing

Retrospective studies have demonstrated that patients who are expressors of cytochrome P4503A5 (CYP3A5) require a higher tacrolimus dose to achieve a therapeutic trough concentration (C0). The aim of this study was to evaluate this effect prospectively by pretransplantation adaptation. We randomly assigned 280 renal transplant recipients to receive tacrolimus either according to CYP3A5 genotype or according to the standard daily regimen. The primary end point was the proportion of patients within the targeted C0. Secondary end points included the number of dose modifications and the delay in achieving the targeted C0. In the group receiving the adapted dose, a higher proportion of patients had values within the targeted C0 at day 3 after initiation of tacrolimus (43.2% vs. 29.1% P = 0.03); they required fewer dose modifications, and the targeted C0 was achieved by 75% of these patients more rapidly. The clinical end points were similar in the two groups. Pharmacogenetic adaptation of the daily dose of tacrolimus is associated with improved achievement of the target C0. Whether this improvement will affect clinical outcomes requires further evaluation.

Analgesic effect of acetaminophen in humans: First evidence of a central serotonergic mechanism

Preclinical studies have suggested that the mechanism of the analgesic action of acetaminophen (INN, paracetamol) is linked to the serotonergic system and that it is inhibited by tropisetron, a 5‐hydroxytryptamine type 3 antagonist. The aim of this study was to confirm these findings in humans.

Thymidylate Synthase Gene Polymorphism Predicts Toxicity in Colorectal Cancer Patients Receiving 5-Fluorouracil-based Chemotherapy

Purpose: The target enzyme for 5-fluorouracil (5-FU) is thymidylate synthase (TS). The TYMS gene encoding this enzyme is polymorphic, having either double (2R) or tri-tandem (3R) repeats of a 28-bp sequence in the promoter region and a 6-bp variation in the 3′-untranslated region (3′-UTR). TS expression predicts response to 5-FU-based chemotherapy, and the expression seems to be determined by the TYMS gene promoter. The aim of this study was to investigate the utility of determining these two TYMS gene polymorphisms to predict the toxicity and efficacy of 5-FU treatment in patients with colorectal cancer. Experimental Design: The determination of TYMS genotypes was performed in tumor and normal tissues by PCR amplification from 90 patients with colorectal cancer who were treated with adjuvant or palliative 5-FU-based chemotherapy. Associations between polymorphisms in the TYMS promoter and in the 3′-UTR gene and clinical outcome of these 90 patients treated with 5-FU based chemotherapy were evaluated individually. The linkage between TYMS promoter and TYMS 3′-UTR region polymorphisms was evaluated and a haplotype analysis was performed. Results: Individuals who were homozygous for the double repeat in the TYMS promoter region had more severe side effects to 5-FU. Patients with a 2R/2R, a 2R/3R, or a 3R/3R genotype had a grade 3 or 4 toxicity rate of 43, 18, and 3% respectively (P < 0.01). The TYMS promoter and TYMS 3′-UTR polymorphisms were in linkage disequilibrium, and the haplotype 2R/ins 6-bp was significantly associated with a high risk of severe side effects to 5-FU. The TYMS promoter and TYMS 3′-UTR polymorphisms were not associated with a response to 5-FU and survival of patients who received palliative 5-FU-based chemotherapy. Conclusions: This study demonstrated that TYMS genotyping could be of help in predicting toxicity to 5-FU-based chemotherapy. TYMS genotyping might make it possible to individualize treatment for patients with colorectal cancer.

Glutathione S-Transferase P1 Polymorphism (Ile105Val) Predicts Cumulative Neuropathy in Patients Receiving Oxaliplatin-Based Chemotherapy

Purpose: Glutathione S-transferases (GST) are xenobiotic metabolizing enzymes involved in the detoxification of a variety of chemotherapeutic drugs, including platinum derivatives. Genetic polymorphisms of GSTs have been associated with enzyme activity variations. Thus, a study was done to investigate the relationship between GST polymorphisms and oxaliplatin-related cumulative neuropathy in gastrointestinal cancer patients treated with oxaliplatin-based chemotherapy. Experimental Design: Ninety patients were included. Clinical neurologic evaluation was done at baseline and before each cycle of treatment. We determined genetic variants for GSTP1 exon 5 (Ile105Val), GSTP1 exon 6 (Ala114Val), GSTM1 (homozygous deletion), and GSTT1 (homozygous deletion). We conducted analyses in a subgroup of 64 patients receiving a minimal cumulative dose of 500 mg/m2 of oxaliplatin to examine whether the GST polymorphisms are associated with oxaliplatin-related cumulative neuropathy. Results: Among patients receiving a minimal cumulative dose of 500 mg/m2 of oxaliplatin, 15 patients showed clinically evident oxaliplatin-related cumulative neuropathy scored grade 3 according to an oxaliplatin-specific scale. The oxaliplatin-related cumulative neuropathy scored grade 3 was significantly more frequent in patients homozygous for the GSTP1 105Ile allele than in patients homozygous or heterozygous for the GSTP1 105Val allele (odds ratio, 5.75; 95% confidence interval, 1.08-30.74; P = 0.02). No association was found with respect to any of the GSTM1, GSTT1, or GSTP1 exon 6 genotypes. Conclusions: The results of the current study suggest that the 105Val allele variant of the GSTP1 gene at exon 5 confers a significantly decreased risk of developing severe oxaliplatin-related cumulative neuropathy.

Genome-wide association study confirms BST1 and suggests a locus on 12q24 as the risk loci for Parkinson's disease in the European population

We performed a three-stage genome-wide association study (GWAS) to identify common Parkinsons disease (PD) risk variants in the European population. The initial genome-wide scan was conducted in a French sample of 1039 cases and 1984 controls, using almost 500 000 single nucleotide polymorphisms (SNPs). Two SNPs at SNCA were found to be associated with PD at the genome-wide significance level (P < 3 × 10(-8)). An additional set of promising and new association signals was identified and submitted for immediate replication in two independent case-control studies of subjects of European descent. We first carried out an in silico replication study using GWAS data from the WTCCC2 PD study sample (1705 cases, 5200 WTCCC controls). Nominally replicated SNPs were further genotyped in a third sample of 1527 cases and 1864 controls from France and Australia. We found converging evidence of association with PD on 12q24 (rs4964469, combined P = 2.4 × 10(-7)) and confirmed the association on 4p15/BST1 (rs4698412, combined P = 1.8 × 10(-6)), previously reported in Japanese data. The 12q24 locus includes RFX4, an isoform of which, named RFX4_v3, encodes brain-specific transcription factors that regulate many genes involved in brain morphogenesis and intracellular calcium homeostasis.

Xenobiotic-metabolizing enzymes and transporters in the normal human brain: regional and cellular mapping as a basis for putative roles in cerebral function.

Cytochrome P450 (P450) enzymes and ATP-binding cassette (ABC) transporters modulate the transport and metabolism of both endogenous and exogenous substrates and could play crucial roles in the human brain. In this study, we report the transcript expression profile of seven ABC transporters (ABCB1, ABCC1–C5, and ABCG2), 24 P450s (CYP1, CYP2, and CYP3 families and CYP46A1), and 14 related transcription factors [aryl hydrocarbon receptor, nuclear receptor (NR)1I2/pregnane X receptor, NR1I3/constitutive androstane receptor and NR1C/peroxisome proliferator-activated receptor, NR1H/liver X receptor, NR2B/retinoid X receptor, and NR3A/estrogen receptor subfamilies] in the whole brain, the dura mater, and 17 different encephalic areas. In addition, Western blotting and immunohistochemistry analysis were used to characterize the distribution of the P450s at the cellular and subcellular levels in some brain regions. Our results show the presence of a large variety of xenobiotic transporters and metabolizing enzymes in human brain and show for the first time their apparent selective distribution in different cerebral regions. The most abundant transporters were ABCC5 and ABCG2, which, interestingly, had a higher mRNA expression in the brain compared with that found in the liver. CYP46A1, CYP2J2, CYP2U1, CYP1B1, CYP2E1, and CYP2D6 represented more than 90% of the total P450 and showed selective distribution in different brain regions. Their presence in both microsomal and mitochondrial fractions was shown both in neuronal and glial cells in several brain areas. Thus, our study shows key enzymes of cholesterol and fatty acid metabolism to be present in the human brain and provides novel information of importance for elucidation of enzymes responsible for normal and pathological processes in the human brain.

Genetic Factors (VKORC1, CYP2C9, EPHX1, and CYP4F2) Are Predictor Variables for Warfarin Response in Very Elderly, Frail Inpatients

Determining the optimal dose of warfarin for frail elderly patients is a challenging task because of the low dose requirements in such patients, the wide interindividual variability of response, and the associated risk of bleeding. The objective of this study was to address the influence of 13 common variations in eight genes on the maintenance dose of warfarin in a cohort of frail elderly inpatients. For our study, we enrolled 300 Caucasian subjects who were hospital inpatients, with a mean age of 86.7 ± 6 years. In addition to age, genetic variants of VKORC1, CYP2C9, CYP4F2, and EPHX1 were found to be significant predictor variables for the maintenance dose of warfarin, explaining 26.6% of dose variability. Among 132 patients in whom warfarin therapy was initiated with the same low‐dose regimen, we studied the relative influences of genetic and nongenetic factors. The time to first international normalized ratio (INR) ≥2 was influenced by VKORC1 and CYP2C9 genotypes (P = 0.0003 and P = 0.0016, respectively); individuals with multiple variant alleles were at highest risk for overanticoagulation (INR >4) (odds ratio, 12.8; 95% confidence interval, 2.73–60.0). In this special population of frail elderly patients with multiple comorbidities and polypharmacy, we demonstrated the main impact of genetic factors on warfarin response.

Review article: the benefits of pharmacogenetics for improving thiopurine therapy in inflammatory bowel disease.

Aliment Pharmacol Ther 2012; 35: 15–36

Acetaminophen Reinforces Descending Inhibitory Pain Pathways

The mechanism of the analgesic action of acetaminophen involves the serotonergic system. This study explores how acetaminophen interferes with serotonergic descending pain pathways. Eighteen rapid metabolizers of tropisetron were included in this double‐blind cross‐over study. After ethical approval, the healthy volunteers took 1 g oral acetaminophen (A) or placebo (p) combined with either the 5‐HT3 antagonist tropisetron (T) (5 mg) or saline, intravenously, at weekly intervals. Mechanical pain thresholds, determined before and after a cold pressor test (CPT), were repeated seven times during the three post‐dosing hours, and area under the concentration–time curves (AUCs) of the three treatments were compared. After CPT, AUC (%*min) of Ap (1,561±429) was larger than before CPT (393±382, P<0.05); these effects were totally inhibited by tropisetron. Acetaminophen reinforces descending inhibitory pain pathways; it suggests a supraspinal target for acetaminophens antinociceptive action. This study also confirmed that there is a central serotonergic mechanism of action for acetaminophen that is not stimulus‐dependent.

Persistence of hepatitis B virus DNA in serum and liver from patients with chronic hepatitis B after loss of HBsAg

BACKGROUND/AIMS The persistence of serum and liver hepatitis B virus (HBV) sequences in patients with chronic hepatitis B after loss of HBsAg has already been described. We have attempted to elucidate the significance of these HBV sequences after loss of HBsAg. METHODS Fifteen patients were studied. We looked for serum and liver HBV DNA, using polymerase chain reaction (PCR) with different sets of primers and in situ hybridization. The sedimentation velocity of serum HBV DNA was measured on a gradient of sucrose in two patients. RESULTS Serum HBV DNA was detected by PCR in four of the 14 patients tested at 0 months after loss of HBsAg, two patients remained HBV DNA positive until 12 months, and none was positive at 24 months. The sedimentation velocity of serum HBV DNA in sucrose was relatively similar to that of a chronic HBV carrier with active viral replication. Liver HBV DNA was demonstrated by PCR in all 15 patients and by in situ hybridization in six patients. CONCLUSIONS Our results show that: 1) HBV DNA may persist in the serum in a minority of patients and may be associated with circulating viral particles; 2) HBV DNA persists in the liver in all patients and its extrachromosomal localization was shown by in situ hybridization technique in some cases. These results suggest the persistence of low-level HBV replication after loss of HBsAg.