Fiora Bartoli

Glutathione‐S‐transferase genotypes and the adverse effects of azathioprine in young patients with inflammatory bowel disease

Background: Adverse drug reactions to azathioprine, the prodrug of 6‐mercaptopurine, occur in 15%–38% of patients and the majority are not explained by thiopurine‐S‐methyltransferase (TPMT) deficiency. Azathioprine is known to induce glutathione depletion and consumption of glutathione is greater in cells with high glutathione‐S‐transferase (GST) activity compared with those with low activity; moreover, some reports indicate that GST might play a direct role in the reaction of glutathione with azathioprine. The association between polymorphisms of GST‐M1, GST‐P1, GST‐T1, and TPMT genes and the adverse effects of azathioprine was therefore investigated. Methods: Seventy patients with inflammatory bowel disease (IBD), treated with azathioprine, were enrolled and clinical data were retrospectively determined. TPMT and GST genotyping were performed by polymerase chain reaction (PCR) assays on DNA extracted from blood samples. Results: Fifteen patients developed adverse effects (21.4%); there was a significant underrepresentation of the GST‐M1 null genotype among patients developing adverse drug reactions to azathioprine (odds ratio [OR] = 0.18, 95% confidence interval [CI] = 0.037–0.72, P = 0.0072) compared with patients who did not develop adverse effects. Patients heterozygous for TPMT mutations presented a marginally significant increased probability of developing adverse effects (OR = 6.38, 95% CI = 0.66–84.1, P = 0.062). Moreover, among the 55 patients who did not develop adverse effects, there was a significant underrepresentation of the GST‐M1 null genotype among patients who displayed lymphopenia as compared with those that did not display this effect of azathioprine (OR = 0.15, 95% CI = 0.013–1.08, P = 0.032). Conclusion: Patients with IBD with a wildtype GST‐M1 genotype present increased probability of developing adverse effects and increased incidence of lymphopenia during azathioprine treatment.

Association of BclI polymorphism of the glucocorticoid receptor gene locus with response to glucocorticoids in inflammatory bowel disease

Glucocorticoids (GCs) are immunosuppressive drugs used for the acute treatment of patients with moderate to severe inflammatory bowel disease (IBD),1 but interindividual variability in the response to these agents is frequently observed.2 GCs diffuse freely into cells and bind to an intracellular receptor (hGR/NR3C1), so the sensitivity to these drugs may depend on the receptor number and affinity or on their availability to the receptors, and transport proteins (including P-glycoprotein (Pgp) encoded by the MDR1/ABCB1 gene) can modify their intracellular concentration.3,4 Polymorphisms in the hGR and MDR1 genes have been described in different populations and may contribute to the variability in sensitivity to GCs observed in the clinical setting.3,4 A study was conducted to estimate the impact of genetic variations in hGR and MDR1 genes on the efficacy and individual response to GCs in young patients with IBD. Polymorphisms of the hGR gene ( Bcl I and N363S which are related to GC hypersensitivity and ER22/23EK which is associated with relative resistance to GCs5) and the MDR1 gene (C3435T and G2677T which are associated with changes in Pgp expression and activity6) were studied in 119 young patients …

Physiological regulation of P‐glycoprotein, MRP1, MRP2 and cytochrome P450 3A2 during rat ontogeny

P‐glycoprotein and the multidrug resistance‐related proteins MRP1 and MRP2 belong to the ATP binding cassette family of proteins and transport a wide range of substrates. These proteins are also involved in metabolic and excretory processes of xenobiotics. The rat genes mdr1a and mdr1b code for P‐glycoproteins, while mrp1 and mrp2 genes code for MRP1 and MRP2 proteins, respectively. In this study, the physiological modulation of the level of transcript for these genes during rat ontogeny in the liver, kidney, lung, brain and heart was analyzed by reverse transcription–polymerase chain reaction. An increasing level of transcript during ontogeny was demonstrated for mdr1a and mdr1b in all tissues considered, as well as for mrp2, which was detected only in the liver and kidney. In contrast, mrp1 transcript, present in all tissues, did not show any modulation. The maximum level of expression was reached in adult animals and a significant decrease was demonstrated in aging rats. Western blot analysis with C219 and M2III‐6 monoclonal antibodies confirmed this different pattern of expression during ontogeny in the liver. The physiological regulation of cytochrome P450 3A2 was also considered: in the rat liver, an increase in the level of transcript during ontogeny, with a maximum in 60‐day‐old rats and a decrease in 8‐month‐old rats, was evident.

Genetic predictors of glucocorticoid response in pediatric patients with inflammatory bowel diseases

Background Glucocorticoids (GCs) are used in moderate-to-severe inflammatory bowel diseases (IBD) but their effect is often unpredictable. Aim To determine the influence of 4 polymorphisms in the GC receptor [nuclear receptor subfamily 3, group C, member 1 (NR3C1)], interleukin-1&bgr; (IL-1&bgr;), and NACHT leucine-rich-repeat protein 1 (NALP1) genes, on the clinical response to steroids in pediatric patients with IBD. Methods One hundred fifty-four young IBD patients treated with GCs for at least 30 days and with a minimum follow-up of 1 year were genotyped. The polymorphisms considered are the BclI in the NR3C1 gene, C-511T in IL-1&bgr; gene, and Leu155His and rs2670660/C in NALP1 gene. Patients were grouped as responder, dependant, and resistant to GCs. The relation between GC response and the genetic polymorphisms considered was examined using univariate, multivariate, and Classification and Regression Tree (CART) analysis. Results Univariate analysis showed that BclI polymorphism was more frequent in responders compared with dependant patients (P=0.03) and with the combined dependant and resistant groups (P=0.02). Moreover, the NALP1 Leu155His polymorphism was less frequent in the GC responsive group compared with resistant (P=0.0059) and nonresponder (P=0.02) groups. Multivariate analysis comparing responders and nonresponders confirmed an association between BclI mutated genotype and steroid response (P=0.030), and between NALP1 Leu155His mutant variant and nonresponders (P=0.033). An association between steroid response and male sex was also observed (P=0.034). In addition, Leu155His mutated genotype was associated with steroid resistance (P=0.034). Two CART analyses supported these findings by showing that BclI and Leu155His polymorphisms had the greatest effect on steroid response (permutation P value=0.046). The second CART analysis also identified age of disease onset and male sex as important variables affecting response. Conclusions These results confirm that genetic and demographic factors may affect the response to GCs in young patients with IBD and strengthen the importance of studying high-order interactions for predicting response.

Toxicologic and pharmacokinetic study of low doses of verapamil combined with doxorubicin.

The effect of a chronic treatment with low oral doses of verapamil, a calcium channel blocker commonly employed in cardiovascular therapy, on doxorubicin toxicity, was evaluated in CD1 mice. Verapamil, administered at a dosage corresponding to a typical cardiovascular posology in humans, significantly increased doxorubicin toxicity. In particular the mortality was significantly higher and earlier and histological analysis revealed an increase in the severity of lesions in the liver, kidney and small bowel of verapamil pretreated animals. The pharmacokinetic profiles revealed that verapamil treated group had higher doxorubicin peak plasma and tissue levels and AUCs. This study shows that verapamil, administered at low doses, dramatically increases doxorubicin toxicity, probably through an interaction between the two drugs, both P-glycoprotein substrates, on the protein expressed in normal tissues, and suggests caution in the use of the calcium channel blocker for cardiovascular pathologies in patients who have to be treated with antineoplastic agents, substrates of P-glycoprotein.

Response to glucocorticoids and toxicity in childhood acute lymphoblastic leukemia: role of polymorphisms of genes involved in glucocorticoid response.

Glucocorticoids (GCs) play a fundamental role in the treatment of pediatric acute lymphoblastic leukemia (ALL), but therapy with these agents often results in a number of severe side effects. The aim of our study was to evaluate the association between polymorphisms of genes encoding for proteins involved in the pharmacokinetics/pharmacodynamics of these drugs and the occurrence of side effects, in particular infections, in a small population of ALL children.

Association between BclI polymorphism in the NR3C1 gene and in vitro individual variations in lymphocyte responses to methylprednisolone

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT In vitro lymphocyte steroid sensitivity has been suggested as a useful tool to predict in vivo response to glucocorticoid treatment in different inflammatory chronic diseases. A correlation between genetic polymorphisms and clinical response to glucocorticoids has been demonstrated in these patients. WHAT THIS STUDY ADDS The BclI polymorphism in the glucocorticoid receptor (NR3C1) gene is associated with higher methylprednisolone potency in vitro. The combined evaluation of the in vitro sensitivity to methylprednisolone and BclI polymorphism could represent an aid for physicians to adjust therapy a priori. AIM To evaluate the association between the in vitro sensitivity of peripheral blood mononuclear cells (PBMCs) to methylprednisolone (MP) and the presence of genetic polymorphisms involved in glucocorticoid (GC) response. METHODS In vitro MP inhibition of the proliferation of lymphocytes stimulated with concanavalin A was determined. Non linear regression of dose-response data was performed computing the MP concentration required to reduce proliferation to 50% (IC(50) ). The maximum inhibition achievable at the highest MP concentration (I(max) ) was also calculated. Moreover, the Taqman technique was used to analyze the BclI polymorphism in the NR3C1 gene and the Leu155His polymorphism in the NALP1 gene. RESULTS A significant association between the BclI mutated genotype and an increased in vitro sensitivity to GCs was observed. CONCLUSIONS The a priori evaluation of the BclI polymorphism, associated with a lymphocyte proliferation assay, could represent a useful diagnostic tool for the optimization of steroid treatment.

Deletion of glutathione-s-transferase m1 reduces azathioprine metabolite concentrations in young patients with inflammatory bowel disease.

Goals: To investigate, in young patients with inflammatory bowel disease (IBD) treated with azathioprine, the association between genetic polymorphisms of thiopurine-S-methyl-transferase (TPMT), inosine-triphosphate-pyrophosphatase (ITPA), and glutathione-S-transferases (GST), involved in azathioprine metabolism, the concentration of the main metabolites of azathioprine, thioguanine nucleotides (TGNs) and the methylated nucleotides (MMPN), and the dose of the medication. Background: Azathioprine is widely used in IBD as an immunosuppressive agent, particularly to maintain remission in patients with steroid refractory disease. Azathioprine is a prodrug and requires conversion to its active form mercaptopurine, which has no intrinsic activity, and is activated by the enzymes of the purine salvage pathway to TGNs. Polymorphisms in genes of enzymes involved in azathioprine metabolism influence the efficacy and toxicity of treatment. Study: Seventy-five young patients with IBD treated with azathioprine at least for 3 months were enrolled and genotyped for the selected genes; for these patients, TGN and MMPN metabolites were measured by high performance liquid chromatography in erythrocytes. Results: GST-M1 deletion was associated with lower TGN/dose ratio (P=0.0030), higher azathioprine dose requirement (P=0.022), and reduced response to therapy (P=0.0022). TPMT variant genotype was associated with lower MMPN concentration (P=0.0064) and increased TGN/dose ratio (P=0.0035). ITPA C94A polymorphism resulted in an increased MMPN concentration (P=0.037). Conclusions: This study describes the effect of candidate genetic polymorphisms in TPMT, ITPA, and GST-M1 on azathioprine pharmacokinetics in IBD patients, showing, for the first time, relevant effects of GST-M1 genotype on azathioprine metabolites concentration.

Prevalence of methylenetetrahydrofolate reductase polymorphisms in young patients with inflammatory bowel disease.

Inflammatory bowel disease (IBD) has been related to mutations of methylenetetrahydrofolate reductase (MTHFR), a critical enzyme in the metabolism of folate and methionine, both of which are important factors in DNA methylation and synthesis. A mutated MTHFR genotype was associated with increased toxicity of methotrexate treatment. The objective of this study was to verify, in a population of young patients with IBD, the presence of an association among mutations in the MTHFR gene, the incidence of IBD, and the risk of adverse events during the treatment with thiopurines azathioprine (AZA) or 6-mercaptopurine (6MP). Ninety-two patients with IBD were enrolled; 63 were treated with thiopurines; patients and 130 controls were genotyped for MTHFR mutations by PCR-based methods. The incidence of mutations in the MTHFR gene was not different between patients with IBD and control subjects; the mutated genotype was not associated with an increased risk of toxicity during thiopurine treatment.

Usefulness of the measurement of azathioprine metabolites in the assessment of non-adherence

Azathioprine is a thiopurine immunosuppressive antimetabolite used to chronically treat inflammatory bowel disease and autoimmune hepatitis. Azathioprine treatment is a long-term therapy and therefore it is at risk for non-adherence, which is considered an important determinant of treatment inefficacy. Measurement of 6-thioguanine and 6-methylmercaptopurine nucleotides has been recently suggested as a screener for non-adherence detection. We describe four young patients in which non-adherence to azathioprine therapy was detected only through the measurement of drug metabolite concentrations, and the criterion for non-adherence was undetectable metabolite levels. After the identification of non-adherence, patients and their families were approached and the importance of a correct drug administration was thoroughly enlightened and discussed; this allowed obtaining a full remission in all subjects. Our observations support the use of undetectable metabolite levels as indicators of non-adherence to therapy in azathioprine treated patients. The additional level of medical supervision given by this assay allows getting a better adherence to medical treatment, which results in an improvement in the response to therapy; these benefits may justify the costs associated with the assay.