Association Of HGPRT And IMPDH Activity And Gene Polymorphism With Adverse Reactions Caused By Azathioprine In Kidney Transplant Recipients

BackgroundAnti-metabolite azathioprine (AZA) is a thiopurine prodrug commonly used in the chemotherapy of acute lymphoblastic leukemia (ALL), autoimmune diseases, chronic inflammatory bowel disease and organ transplantation as an immunosuppressive agent. However, its use has been complicated by narrow therapeutic window and a high incidence of serious adverse drug reactions such as hepatotoxicity, hematotoxicity, and gastrointestinal disturbance. It is reported that the thiopurine S-methyltransferase (TPMT) and inosine triphosphate pyrophosphatase(ITPA) activity and genetic polymorphisms are associated with azathioprine-related adverse drug reactions in renal transplant,but TPMT and ITPA can only explain part of the AZA-induced adverse reactions. Hypoxanthine guanine phosphoribosyl transferase (HGPRT) and hypoxanthine-phosphate dehydrogenase (IMPDH) are also important metabolic enzyme in the metabolism of AZA. However, whether HGPRT and IMPDH activity and gene polymorphism are associated with azathioprine-related adverse drug reactions in renal transplant still remains unknown and needs further extensive investigation.ObjectiveThe purpose of this study is to investigate the associations between HGPRT, IMPDH activities and genetic polymorphisms and AZA-related adverse reactions in renal transplant recipients so as to provide enough theoretic and experiment evidence for rational use of AZA.MethodsIn the present study,86cases of renal transplant recipients who are taking or took AZA before were recruited in this retrospective study. Firstly, the incidence and risk factors of AZA-related adverse reactions were evaluated. Erythrocyte HGPRT and IMPDH activity were measured in86cases of renal transplant recipients by a modified high-performance liquid chromatography (HPLC) procedure. Genotype was determined for the HGPRT IVS6-12C> A, IMPDH I rs2278293, IMPDH II rs11706052mutation by direct sequencing method and for IMPDH I rs2278294by PCR-restriction fragment length polymorphism (PCR-RFLP) method. According to these results, the occurrence and type of adverse reactions to AZA, the relationships between IMPDH, HGPRT activity and genetic polymorphisms and AZA-induced adverse reactions were systematically analyzed.ResultsIn86cases of renal transplant recipients, AZA-related adverse reactions were found in36cases. These AZA-related adverse reactions included14patients with hematotoxicity,11patients with hepatotoxicity,9patients with gastrointestinal disturbance and3patients with flu-like symptoms. All36patients with AZA-related adverse reactions could be recovered after reducing the dosage of AZA or stopping use of AZA. The total rate of AZA-related adverse reactions was41.8%. A logistic regression model showed that male was a risk factor of post-transplant liver injury in patients taking AZA. The risk of hepatotoxicity in male patients was9.67fold-higher than that in female patients (p<0.05). Other factors such as non-genetic factors and combination of drug use couldn’t increase the risk of AZA-related adverse reactions.In this study, HGPRT activity in86cases of renal transplant recipients ranged from44.59U to262.16U and the average activity was I00.17±33.50U. HGPRT activity in healthy subjects ranged from28.43to153.65U and the average activity was99.30±17.21U. Both of them showed normal distribution. HGPRT activity between the renal transplant recipients and the healthy subjects was found no significant differences(P>0.05). But significant differences in the distribution rate of high activity, low activity and normal activity of HGPRT were found between renal transplant recipients and healthy subjects(p<0.05).The rate of low HGPRT activity in the renal transplant recipients was significantly higher than that in the healthy subjects (p<0.05). The rate of normal HGPRT activity in the renal transplant recipients was significantly lower than that in the healthy subjects (p<0.05)In the renal transplant recipients,2cases of HGPRT-IVS6-12C>A mutation was found and the mutation frequency was2.30%. No IVS6-12C> A mutation was found in the health subjects. No association was observed between HGPRT activity and genetic polymorphisms (P>0.05)The average HGPRT activity in patients with flu-like symptoms was significantly higher than that in the renal transplant recipients who had no AZA-related adverse reactions (147.47±101.24U vs100.46±29.31U, p<0.05). The average HGPRT activities in patients with hematotoxicity, hepatotoxicity and gastrointestinal disturbance were found no significant differences compared with the patients who had no AZA-related adverse reactions (P>0.05). No association was observed between HGPRT genetic polymorphisms and AZA-related adverse reactions (P>0.05)The mutation frequency for IMPDH rs2278293, rs2278294and rs11706052mutation in the renal transplant recipients was9.2%,68.97and6.9%, respectively. The mutation frequency for IMPDH rs2278293, rs2278294, rs11706052mutation in the healthy subjects was14.14%,77.96%, and9.87%, respectively. There was significant difference about the distribution rate of rs2278294between the healthy subjects and the renal transplant recipients (P<0.001). The distribution rate of rs2278294GA in the renal transplant recipients was higher than that in the healthy subjects (P<0.01), the distribution rate of rs2278294AA in the renal transplant recipients was lower than that in the healthy subjects (P<0.01).This study showed that significant association was found between rs2278294mutation and hematotoxicity in the renal transplant recipients (P<0.05).No association was observed between rs2278293and rs11706052mutation and AZA-related adverse reactions (P>0.05).ConclusionsIn conclusion, before commencing AZA treatment, it is important to measure HPGRT activity in renal transplant recipients in order to prevent AZA-related flu-like symptoms. Pre-therapeutic screening of patients for rs2278294mutation should be useful to avoid AZA-related hematotoxicity. In addition, liver function should be frequently determined especially in male patients so as to avoid hepatotoxicity.