Incidence and Risk Factors of Clinical Characteristics, Tacrolimus Pharmacokinetics, and Related Genomic Polymorphisms for Posttransplant Diabetes Mellitus in the Early Stage of Renal Transplant Recipients

Significant Association between Toll-Like Receptor Gene Polymorphisms and Posttransplantation Diabetes Mellitus

<b><i>Background:</i></b> Posttransplantation diabetes mellitus (PTDM) is an important metabolic complication after renal transplantation. Activation of the innate immune system via toll-like receptors (TLRs) is implicated in the pathogenesis of insulin resistance and deficiency. Although links between diabetes, dysregulated innate immune responses, and the TLR signaling pathway have been reported, no study so far has investigated their associations with PTDM. In this study, we ascertained whether single nucleotide polymorphisms (SNPs) in TLRs are associated with PTDM in the Korea population. <b><i>Methods:</i></b> A total of 305 patients who received renal transplants without previously diagnosed diabetes were included. We analyzed the association between PTDM development and 6 SNPs within 2 genes of <i>TLR2</i>, 1 gene of <i>TLR4</i>, and 3 genes of <i>TRL6</i>. <b><i>Results:</i></b> Of 305 patients, PTDM developed in 51 patients (16.6%). Patients in the PTDM group were older than those in the non-PTDM group (45.56 ± 1.28 vs. 38.28 ± 0.71 years). Patients with PTDM had significantly higher allele frequency compared to those without PTDM for the <i>TLR</i>4 rs1927914*T, <i>TLR6 </i>rs3775073*A, <i>TLR6</i> rs3821985*C, and <i>TLR6</i> rs1039559*C alleles. Of the 6 SNPs, rs1927914 in the <i>TLR4</i> gene and rs1039559 in the <i>TLR6</i> gene were significantly associated with the development of PTDM after adjustment for age, gender, and tacrolimus usage. <b><i>Conclusions:</i></b> Our study demonstrates a significant association between SNPs<i> rs1927914</i> in <i>TLR4</i> and rs1039559 in <i>TLR6</i> and PTDM in the renal transplantation recipient group. These data suggest that the activation of the innate immune system and inflammation via TLR activation might have an essential role in the pathogenesis of PTDM in renal transplantation.

The incidence of posttransplantation diabetes mellitus during follow-up in kidney transplant recipients and relationship to Fok1 vitamin D receptor polymorphism

BACKGROUND

Posttransplantation diabetes mellitus (PTDM) is a common, serious complication of kidney transplantation. The purpose of this study was to investigate the incidence of and risk factors for PTDM in relationship to Fok1 vitamin D receptor (VDR) polymorphisms.

METHODS

One hundred five kidney transplant recipients with normal glucose values before transplantation were recruited for this study. All patients underwent fasting plasma glucose (FPG) determinations followed by oral glucose tolerance tests (OGTTs) among normal FPG recipients. Every recipient underwent Fok1 VDR polymorphism analysis using polymerase chain reaction (PCR)-restriction fragment length polymorphism (RFLP).

RESULTS

Among 105 recipients, 16 (15.24%) developed new-onset PTDM within 6 months after kidney transplantation. Compared with 89 non-PTDM recipients, the mean age was significantly higher among recipients with PTDM: 47.81 ± 15.54 vs 36.62 ± 11.43 years (P = .001). Patients treated with tacrolimus were more susceptible to PTDM (56.25% vs 28.09%; P = .027). The distribution frequencies of Fok1 genotypes in this cohort followed the Hardy-Weinberg equilibrium. The frequencies of 3 genotypes (FF/Ff/ff; P = .040) and 2 alleles (F/f; P = .009) differed between the 2 groups. Multivariate analysis by logistic regression showed age older than 40 years (odds ratio, 7.774; P = .005), VDR Fok1 f allele (odds ratio, 11.765; P = .012), and tacrolimus therapy (odds ratio, 7.499; P = .007) to be related to the development of PTDM.

CONCLUSIONS

The incidence of newly diagnosed PTDM in this study was 15.24%. Fok1 VDR polymorphism was a genetic marker predicting PTDM risk. Age older than 40 years and tacrolimus were independent risk factors for PTDM.

Cellular and physiological mechanisms of new-onset diabetes mellitus after solid organ transplantation

New-onset diabetes after transplantation is recognized as one of the metabolic consequences which may increase the risk of morbidity and mortality after solid organ transplantation. The pathophysiology of new-onset diabetes after transplantation has not been clearly defined and may resemble that of Type 2 diabetes, characterized by predominantly insulin resistance or defective insulin secretion, or both. This review aims to summarize the current state of knowledge regarding the prevalence, consequences, pathogenesis, and management of new-onset diabetes after transplantation, with a major focus on the possible mechanisms involved in the pathogenesis of the disorder. The aetiology of new-onset diabetes after transplantation is multifactorial, with diabetogenic immunosuppressive drugs playing a major role. Multiple cellular and physiologic mechanisms are involved in the process. Selection of an appropriate maintenance immunosuppressive regimen should involve balancing the risk of patient and graft survival vs. the potential for new-onset diabetes after transplantation.

Risk factors for medication-induced diabetes and type 2 diabetes

OBJECTIVE

To compare the prevalence of risk factors in children aged <18 years diagnosed with medication-induced diabetes mellitus versus those diagnosed with type 2 diabetes.

STUDY DESIGN

This retrospective observational study used data from a Canadian prospective surveillance study in which clinical features of new cases of type 2 diabetes (n = 225) and medication-induced diabetes (n = 58) were reported over a 2-year period. The presence of risk factors for type 2 diabetes (eg, obesity, family history of type 2 diabetes, ethnicity, acanthosis nigricans, hypertension, polycystic ovarian syndrome) was compared in the 2 groups using descriptive statistics and logistic regression.

RESULTS

Compared with the children with type 2 diabetes, the children with medication-induced diabetes were more likely to be Caucasian (P < .0001) and less likely to be obese (P < .0001), to have a positive family history of type 2 diabetes (P = .0001), to have acanthosis nigricans (P < .0001) on clinical examination, and to have an obesity-related comorbidity, such as polycystic ovarian syndrome (P = .04), dyslipidemia (P = .02), hypertension (P = .04), or an elevated alanine aminotransferase level (P = .05).

CONCLUSIONS

Evaluating for the typical risk factors for type 2 diabetes is not sufficient to identify all children at risk for developing medication-induced diabetes. Further studies are needed to help inform guidelines on screening for and prevention of medication-induced diabetes in children.

Effect of CYP3A and ABCB1 single nucleotide polymorphisms on the pharmacokinetics and pharmacodynamics of calcineurin inhibitors: Part II

The calcineurin inhibitors ciclosporin (cyclosporine) and tacrolimus are immunosuppressant drugs used for the prevention of organ rejection following transplantation. Both agents are metabolic substrates for cytochrome P450 (CYP) 3A enzymes - in particular, CYP3A4 and CYP3A5 - and are transported out of cells via P-glycoprotein (ABCB1). Several single nucleotide polymorphisms (SNPs) have been identified in the genes encoding for CYP3A4, CYP3A5 and P-glycoprotein, including CYP3A4 -392A>G (rs2740574), CYP3A5 6986A>G (rs776746), ABCB1 3435C>T (rs1045642), ABCB1 1236C>T (rs1128503) and ABCB1 2677G>T/A (rs2032582). The aim of this review is to provide the clinician with an extensive overview of the recent literature on the known effects of these SNPs on the pharmacodynamics of ciclosporin and tacrolimus in solid-organ transplant recipients. Literature searches were performed and all relevant primary research articles were critiqued and summarized. There is no evidence that the CYP3A4 -392A>G SNP has an effect on the pharmacodynamics of either ciclosporin or tacrolimus; however, studies have been limited. For patients prescribed ciclosporin, the CYP3A5 6986A>G SNP may influence long-term survival, possibly because of a different metabolite pattern over time. This SNP has no clear association with acute rejection during ciclosporin therapy. Despite a strong association between the CYP3A5 6986A>G SNP and tacrolimus pharmacokinetics, there is no consistent evidence of organ rejection as a result of genotype-related under-immunosuppression. This is likely to be explained by the practice of performing tacrolimus dose adjustments in the early phase after transplantation. The effect of the CYP3A5 6986A>G SNP on ciclosporin- and tacrolimus-related nephrotoxicity and development of hypertension is unclear. Similarly, the ABCB1 SNPs exert no clear influence on either ciclosporin or tacrolimus pharmacodynamics, with studies showing conflicting results in regard to the main parameters of acute rejection and nephrotoxicity. In kidney transplant patients, consideration of the donor kidney genotype rather than the recipient genotype may be more important when assessing development of nephrotoxicity. Studies with low patient numbers may account for many inconsistent results to date. The majority of studies have only evaluated the effects of individual SNPs; however, multiple polymorphisms may interact to produce a combined effect. Further haplotype analyses are likely to be useful, particularly ones that consider both donor and recipient genotype. The effects of polymorphisms associated with the pregnane X receptor, organic anion transporting polypeptides, calcineurin inhibitor target sites and immune response pathways need to be further investigated. A large standardized clinical trial is now required to evaluate the relationship between the pharmacokinetics and pharmacodynamics of CYP3A5-mediated tacrolimus metabolism, particularly in regard to the outcomes of acute rejection and nephrotoxicity. It is not yet clear whether pharmacogenetic profiling of calcineurin inhibitors will be a useful clinical tool for personalizing immunosuppressant therapy.

Vitamin D receptor polymorphisms and diseases

The vitamin D endocrine system is central to the control of bone and calcium homeostasis. Thus, alterations in the vitamin D pathway lead to disturbances in mineral metabolism. Furthermore, a role for vitamin D has been suggested in other diseases, like cancer, diabetes and cardiovascular disease. Expression and nuclear activation of the vitamin D receptor (VDR) are necessary for the effects of vitamin D. Several genetic variations have been identified in the VDR. DNA sequence variations, which occur frequently in the population, are referred to as "polymorphisms" and can have biological effects. To test whether there is a linkage between VDR polymorphisms and diseases, epidemiological studies are performed. In these studies, the presence of a variation of the gene is studied in a population of patients, and then compared to a control group. Thus, association studies are performed, and a link among gene polymorphisms and diseases can be established. Since the discovery of VDR polymorphisms a number of papers have been published studying its role in bone biology, renal diseases, diabetes, etc. The purpose of this review is to summarize the vast amount of information regarding vitamin D receptor polymorphisms and human diseases, and discuss its possible role as diagnostic tools.