Cytochrome P450 1A2 activity and incidence of thyroid disease and cancer after chronic or acute exposure to dioxins.

BACKGROUND: Dioxin (2,3,7,8-tetrachlorodibenzo-p-dioxin; TCDD) is the most toxic congener of a family of structurally and mechanistically related persistent organic pollutants whose effects are mediated through the aryl hydrocarbon receptor (AhR). Induction of CYP1A1/2 by TCDD through the AhR depends on the magnitude and the duration of exposure. We aimed to assess CYP1A2 activity after acute and chronic exposure to TCDD. The Maincy cohort is a sample population from Melun in the Val-de-Seine region in France that lived for at least 5 years close to a waste incinerator emitting polluted vapours (1974-2002) with high concentrations of dioxins (up to 2000 times the maximal recommended values). Acute exposure to TCDD (Viktor Yushchenko) has been described elsewhere by Sorg et al (Toxicol. Sci. 2012; 125:310-317). Both are rare cases of well-identified source of chronic and acute exposure to TCDD. METHODS: All subjects underwent a full medical history and physical examination and had a cutaneous examination, and a retro-auricular skin biopsy was taken. A questionnaire was designed and used regarding demographic, personal, environmental and occupational characteristics. CYP1A2 activity was assessed 2 hours after the ingestion of a drink containing caffeine through measurement of the metabolic ratio of paraxanthine (17X) over caffeine (137X) by LC-MS/MS or LC-UV. CYP1A1 expression in skin biopsies was determined by immunohistochemical analysis. RESULTS: Forty-seven exposed subjects (age 11-78) and 31 controls were included in the study. Eleven exposed subjects had a history of thyroid disease (23.4%), and 7 (14.8%) had a cancer vs none and 1, respectively, in controls. Nodular skin lesions were found in 13 exposed subjects (27.7%) vs none in controls. Mean CYP1A2 activity of the exposed population was modestly elevated as compared to controls (17X/137X metabolic ratio of 0.475 vs 0.374, P = .051). CYP1A2 was, however, induced (17X/137X, metabolic ratio >0.5) in 27.6% of the exposed cases vs 6.4% of the controls. In contrast, acute dioxin exposure was associated with a strong induction (mean 17X/137X, metabolic ratio of 1.9) still present 29 months after the acute exposure. CYP1A1 was expressed in 59.6% of the skin biopsies (highly expressed in 31.9%) of the Maincy cohort. No correlation between CYP1A2 activity, CYP1A1 expression and clinical manifestations (thyroid disease, cancer, skin lesions) could be demonstrated. CONCLUSION: Higher frequencies of dysthyroidism and cancer were detected in the population exposed chronically to dioxins from a waste incinerator. CYP1A2 was induced in 27.6% of the exposed population, while the magnitude of induction was fourfold higher after acute exposure in the case of Yushchenko.

Therapeutic Drug Monitoring of Busulfan for the Management of Pediatric Patients: Cross-Validation of Methods and Long-Term Performance.

BACKGROUND: Busulfan (Bu) is an alkylating agent used as part of the conditioning regimen in pediatric patients before hematopoietic stem cell transplantation. Despite intravenous (IV) administration and dosing recommendations based on age and weight, reports have revealed interindividual variability in Bu pharmacokinetics and the outcomes of hematopoietic stem cell transplantation. In this context, adjusting doses to Bu's narrow therapeutic window is advised. We aimed to assess the utility of therapeutic drug monitoring (TDM) of Bu in children, the reliability of Bu quantification methods, and its stability in plasma when stored for up to 5 years. METHODS: Eighteen patients from our TDM center (252 samples) were included. All of them received a 2-hour Bu IV infusion 4 times daily for a total of 16 doses. The first dose of Bu was age/weight-based, and the subsequent doses were adjusted from third or fifth dose onward based on the estimated first dose pharmacokinetic parameters to target steady-state concentrations (Css) of 600-900 ng/mL. The performance of our unit's high-performance liquid chromatography with tandem mass spectrometry method was assessed using a quality control (QC, 35 series) chart. International, multicenter, cross-validation test (n = 21) was conducted to validate different analytical methods. To assess Bu stability, regression analyses and Bland-Altman plots were performed on measurements at repeated time points on samples stored at -80°C for up to 5 years. RESULTS: We observed a 4.2-fold interindividual variability in Bu Css after the first dose, with only 28% of children having a Css within the target range. During the 4 days of conditioning, 83% of children had their doses modified according to TDM recommendations. This achieved a Css within the target range in 75% of the children. Routine QC measurements were generally within the ±15% range around theoretical values, showing the optimal robustness of our center's analytical method. Two of the 21 Bu TDM centers returned inadequate results during cross-validation testing; both used a UV detection method. Storage at -80°C led to a fall in Bu content of 14.9% ± 13.4% at 2-4 years and of 20% ± 5% by 5 years (roverall = 0.92). CONCLUSIONS: We conclude that TDM is an effective method of achieving targeted Bu levels in children. QC programs are crucial to monitoring and maintaining the quality of an analytical method.

The Association of Combined GSTM1 and CYP2C9 Genotype Status with the Occurrence of Hemorrhagic Cystitis in Pediatric Patients Receiving Myeloablative Conditioning Regimen Prior to Allogeneic Hematopoietic Stem Cell Transplantation.

Hemorrhagic cystitis (HC) is one of the complications of busulfan-cyclophosphamide (BU-CY) conditioning regimen during allogeneic hematopoietic stem cell transplantation (HSCT) in children. Identifying children at high risk of developing HC in a HSCT setting could facilitate the evaluation and implementation of effective prophylactic measures. In this retrospective analysis genotyping of selected candidate gene variants was performed in 72 children and plasma Sulfolane (Su, water soluble metabolite of BU) levels were measured in 39 children following treatment with BU-CY regimen. The cytotoxic effects of Su and acrolein (Ac, water soluble metabolite of CY) were tested on human urothelial cells (HUCs). The effect of Su was also tested on cytochrome P 450 (CYP) function in HepaRG hepatic cells. Cumulative incidences of HC before day 30 post HSCT were estimated using Kaplan-Meier curves and log-rank test was used to compare the difference between groups in a univariate analysis. Multivariate Cox regression was used to estimate hazard ratios with 95% confidence intervals (CIs). Multivariate analysis included co-variables that were significantly associated with HC in a univariate analysis. Cumulative incidence of HC was 15.3%. In the univariate analysis, HC incidence was significantly (p < 0.05) higher in children older than 10 years (28.6 vs. 6.8%) or in children with higher Su levels (>40 vs. <11%) or in carriers of both functional GSTM1 and CYP2C9 (33.3 vs. 6.3%) compared to the other group. In a multivariate analysis, combined GSTM1 and CYP2C9 genotype status was associated with HC occurrence with a hazards ratio of 4.8 (95% CI: 1.3-18.4; p = 0.02). Ac was found to be toxic to HUC cells at lower concentrations (33 µM), Su was not toxic to HUC cells at concentrations below 1 mM and did not affect CYP function in HepaRG cells. Our observations suggest that pre-emptive genotyping of CYP2C9 and GSTM1 may aid in selection of more effective prophylaxis to reduce HC development in pediatric patients undergoing allogeneic HSCT. Article summary: (1) Children carrying functional alleles in GSTM1 and CYP2C9 are at high risk for developing hemorrhagic cystitis following treatment with busulfan and cyclophosphamide based conditioning regimen. (2) Identification of children at high risk for developing hemorrhagic cystitis in an allogeneic HSCT setting will enable us to evaluate and implement optimal strategies for its prevention. Trial registration: This study is a part of the trail "clinicaltrials.gov identifier: NCT01257854."

Intestinal permeability and P-glycoprotein-mediated efflux transport of ticagrelor in Caco-2 monolayer cells.

Ticagrelor is the unique reversible oral antiplatelet drug commercialized today. During this study, the intestinal permeability of ticagrelor and its potential P-glycoprotein (P-gp)-mediated active transport were assessed. To this end, bidirectional transport of ticagrelor was performed across Caco-2 (human epithelial colorectal adenocarcinoma) monolayer model in the presence and absence of potent P-gp inhibitor valspodar. Ticagrelor presented an apical-basolateral apparent permeability coefficient (Papp ) of 6.0 × 10-6 cm/s. On the other hand, mean efflux ratio (ER) of 2.71 was observed for ticagrelor describing a higher efflux permeability compared to the influx component. Valspodar showed a significant inhibitory effect on the efflux of ticagrelor suggesting involvement of P-gp in its oral disposition. Co-incubation of the P-gp inhibitor decreased the efflux Papp of ticagrelor from 1.60 × 10-5 to 1.13 × 10-5 cm/s and decreased its ER by 70%. Results suggest a modest active transport of ticagrelor by P-gp across the Caco-2 cell monolayer. The co-administration of ticagrelor with a P-gp inhibitor seems altogether unlikely to have an extended impact on pharmacokinetics of ticagrelor and cause bleeding events in patients.