New-Onset Diabetes Mellitus Associated with Sirolimus Use in Renal Transplant Recipients

New-onset diabetes after transplantation and impaired glucose tolerance are very common in renal transplant patients. New-onset diabetes after transplantation (NODAT) is associated with increased cardiovascular morbidity and mortality, reduced graft and patient survival. Several risk factors for NODAT have been identified: age, obesity, family history of diabetes mellitus and HCV infection. In addition, steroid and calcineurin inhibitors also contribute to the development of NODAT. Sirolimus causes immunosuppressive effects by inhibiting mammalian target of rapamycin (mTOR), and has well known side effects. The effects of sirolimus on glucose metabolism and contribution to NODAT development are not clearly known. In this report, we presented five RTX patients who developed NODAT under the treatment of sirolimus.


Introduction
New-onset diabetes after transplantation (NODAT) and impaired glucose tolerance are very common among RTX patients.It has been reported in different studies that NODAT rates have ranged between 20% and 50% [1].NODAT is associated with increased cardiovascular morbidity and mortality, reduced graft and patient survival.With regard to cardiovascular risk factors, NODAT is a more serious risk factor compared to hypertension and hyperlipidaemia [2].
Several risk factors for NODAT have been identified: family history, cytomegalovirus infection, hepatitis C virus infection, age and weight [3].In addition, steroid and calcineurin inhibitors also contribute to the development of NODAT.In the early period of transplantation, it has been reported that tacrolimus is more diabetogenic than cyclosporine, although it has been shown that both cause similar rate of NODAT development in long term follow up [4].In the pathogenetic process of NODAT, calcineurin inhibitors inhibit insulin secretion by causing beta cell damage [5].

Cases 2-3-4-5
We also observed NODAT development in four renal transplant patients receiving sirolimus (3 mg/day , target blood level: 8-10 mg/mL), mycophenolate mofetil (1.5 gr/day ) and prednisolone (doses were same amount of firs patients) treatment.General characteristic features are presented in Table 1.All renal transplantation types were living-related.There is only family history of DM in second case.However, acute rejection attacks were not observed in any case.In our patients, at the first three months of post-transplant period, FBG started to rise.All our patients were diagnosed as diabetes mellitus according to the criteria of ADA between 5 th and 6 th months.Adequate blood glucose level was achieved by diet at the 2 nd case, by nateglinide treatment for the 3 rd and 4 th cases and glyburide treatment for the 5 th case.When DM was diagnosed, LDL, triglyceride and total cholesterol levels also increased to approximately 2-2.5 folds of preoperative values.The serum levels of fasting blood glucose, postprandial blood glucose and hemoglobine-A1C are presented in Table 2.
Informed consent was obtained from all patients for this study.

Discussion
In this study, we presented five renal transplant patients who developed NODAT under the treatment of sirolimus.
NODAT has multifactorial aetiology.Drugs (steroids, calcineurin inhibitors, proliferation signal inhibitors), obesity, family history, male sex, positive test results for hepatitis-c virus, transplantation from deceased-donor are identified risk factors associated with NODAT.Evidence suggests that obesity and immunosuppressive drugs are major risk factors for the development of NODAT.Among the immunosuppressive drugs, cyclosporine and tacrolimus are well known drugs associated with NODAT [1].
Sirolimus causes immunosuppressive effects by acting on mammalian target of rapamycin (mTOR).mTOR inhibits interleukin-2 mediated signal transduction, resulting in cell cycle arrest in the G1-S phase.By this mechanism, sirolimus blocks the response of T-and B-cell activation by cytokines, which prevents cell-cycle progression and proliferation [6].It is well known that sirolimus may show adverse effects on gastrointestinal, hematologic and pulmonary system.One of the discussed subjects for sirolimus is that whether it has beneficial or adverse effect on glucose metabolism.In our cases, although we cannot exclude genetic susceptibility, family history (in one case) and prednisolone use for the NODAT risk factors, we can say that common risk factors in all cases for NODAT was the use of sirolimus.Therefore, our cases led us to think that sirolimus use in our patients might cause NODAT by clearly unknown mechanism.
New-onset diabetes after transplantation is especially associated with the uses of tacrolimus, cyclosporine and high dose prednisolone due to acute rejection attack in early post-transplant period and the risk of development of NODAT much more raised in the presence of other diabetogenic factors.We almost excluded all other secondary diabetogenic factors for example obesity, the history of family and hepatitis C virus infection except for the using of the immunosuppressive drugs.Acute rejection attacks were not observed in any patients.As well as, NODAT developed in other four patients except for first case at the late post-transplant period.Due to all these causes, we think that using of sirolimus is the most important factor for the developed of NODAT in our cases.
Indeed, the effects of sirolimus on glucose metabolism are not very clear.Insulin receptor substrate-1 (IRS-1) and mTOR play a role in insulin signalling.Early in-vitro studies suggest that it increases insulin responses in chronic insulin stimulation by inhibiting IRS-1 degradation [7].Contrary to this finding, more recent in-vitro studies showed that longterm mTOR inhibition impairs activation of IRS-1 and AKT and augments insulin resistance and β-cell dysfunction [8,9].Other possible mechanisms, by which sirolimus may cause NODAT, include impaired insulin-mediated suppression of hepatic glucose production, insulin resistance from ectopic triglyceride deposition or direct β-cell toxicity.Recently, Johnston et al. [10] analysed the data of USRDS and reported that sirolimus may be independently associated with NODAT.Nevertheless, our cases may support this in-vitro and clinic study reporting that sirolimus may play a role in the development of NODAT and the need for further studies, which contain more patients.
In conclusion, our study has suggested that sirolimus is associated with NODAT, but this is not well established and our findings should be confirmed in prospective studies or in meta-analyses of existing trials that involved sirolimus.