Mitochondrial DNA haplogroups and risk of new-onset diabetes among tacrolimus-treated renal transplanted patients

Genetic and Epigenetic Associations with Post-Transplant Diabetes Mellitus

Post-transplant diabetes mellitus (PTDM) is a common complication of solid organ transplantation. PTDM prevalence varies due to different diabetes definitions. Consensus guidelines for the diagnosis of PTDM have been published based on random blood glucose levels, glycated hemoglobin (HbA1c), and oral glucose tolerance test (OGTT). The task of diagnosing PTDM continues to pose challenges, given the potential for diabetes to manifest at different time points after transplantation, thus demanding constant clinical vigilance and repeated testing. Interpreting HbA1c levels can be challenging after renal transplantation. Pre-transplant risk factors for PTDM include obesity, sedentary lifestyle, family history of diabetes, ethnicity (e.g., African-Caribbean or South Asian ancestry), and genetic risk factors. Risk factors for PTDM include immunosuppressive drugs, weight gain, hepatitis C, and cytomegalovirus infection. There is also emerging evidence that genetic and epigenetic variation in the organ transplant recipient may influence the risk of developing PTDM. This review outlines many known risk factors for PTDM and details some of the pathways, genetic variants, and epigenetic features associated with PTDM. Improved understanding of established and emerging risk factors may help identify people at risk of developing PTDM and may reduce the risk of developing PTDM or improve the management of this complication of organ transplantation.

Association Study of Mitochondrial DNA Haplogroup D and C5178A Polymorphisms with Chronic Kidney Disease

Objective: To explore the associations of common mitochondrial DNA polymorphisms with chronic kidney disease (CKD). Methods: Data from 286 longevous individuals aged 95 years or older from the longevity arm from the Rugao Longevity and Ageing Study (RuLAS) were used. Twenty-eight common haplogroups defined by 33 single nucleotide polymorphisms were genotyped using SNaPshot minisequencing reaction assays. The creatinine-based estimated glomerular filtration rate (eGFR) was calculated using the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation. Results: The prevalence of CKD was 23.6% among the longevous participants aged 95 years and older. The D haplogroup (67.37 ± 14.72 vs. 70.65 ± 11.07, p = 0.045), the D5 haplogroup (60.86 ± 18.36 vs. 70.34 ± 11.53, p = 0.002), and the 5178A allele (67.23 ± 14.48 vs. 70.75 ± 11.10, p = 0.029) were associated with lower eGFR levels compared with noncarriers. The D5 haplogroup (13.8% vs. 3.6%, p = 0.005) was significantly higher, while D haplogroup (35.4% vs. 24%, p = 0.067) and the 5178A allele (36.9% vs. 24.9%, p = 0.056) were borderline significantly higher in CKD individuals than those without CKD. Further, after adjusting for multiple covariates, the D haplogroup, the D5 haplogroup, and the 5178A allele were associated with increased odds of CKD with odds ratios of 1.93 (95% confidence interval [CI]: 1.00-3.72, p = 0.050), 4.76 (95% CI: 1.49-15.22, p = 0.009) and 2.04 (95% CI: 1.05-3.96, p = 0.035), respectively. Conclusions: The D and D5 haplogroups, as well as the 5178A allele are associated with decreased eGFR levels and an increased risk of CKD in a longevous population.

The Role of Mitonuclear Incompatibility in Bipolar Disorder Susceptibility and Resilience Against Environmental Stressors

It has been postulated that mitochondrial dysfunction has a significant role in the underlying pathophysiology of bipolar disorder (BD). Mitochondrial functioning plays an important role in regulating synaptic transmission, brain function, and cognition. Neuronal activity is energy dependent and neurons are particularly sensitive to changes in bioenergetic fluctuations, suggesting that mitochondria regulate fundamental aspects of brain function. Vigorous evidence supports the role of mitochondrial dysfunction in the etiology of BD, including dysregulated oxidative phosphorylation, general decrease of energy, altered brain bioenergetics, co-morbidity with mitochondrial disorders, and association with genetic variants in mitochondrial DNA (mtDNA) or nuclear-encoded mitochondrial genes. Despite these advances, the underlying etiology of mitochondrial dysfunction in BD is unclear. A plausible evolutionary explanation is that mitochondrial-nuclear (mitonuclear) incompatibility leads to a desynchronization of machinery required for efficient electron transport and cellular energy production. Approximately 1,200 genes, encoded from both nuclear and mitochondrial genomes, are essential for mitochondrial function. Studies suggest that mitochondrial and nuclear genomes co-evolve, and the coordinated expression of these interacting gene products are essential for optimal organism function. Incompatibilities between mtDNA and nuclear-encoded mitochondrial genes results in inefficiency in electron flow down the respiratory chain, differential oxidative phosphorylation efficiency, increased release of free radicals, altered intracellular Ca²⁺ signaling, and reduction of catalytic sites and ATP production. This review explores the role of mitonuclear incompatibility in BD susceptibility and resilience against environmental stressors.

Hypomagnesemia is associated with new-onset diabetes mellitus following heart transplantation

BACKGROUND

Diabetes mellitus (DM) is a major cause of morbidity and mortality following heart transplantation (HT), with 21% and 35% of survivors being affected within 1 and 5 years following HT, respectively. Magnesium deficiency is common among HT patients treated with calcineurin inhibitors and is a known risk factor for DM in non-HT patients. We therefore investigated the association between serum Mg (s-Mg) levels and new-onset diabetes after transplantation (NODAT).

METHODS

Between 2002 and 2017, 102 non-DM HT patients were assessed. In accordance with the mean value of all s-Mg levels recorded during the first year post-HT, patients were divided into high s-Mg (≥ 1.8 mg/dL) and low s-Mg (< 1.8 mg/dL) groups. The endpoint was NODAT, defined according to the diagnostic criteria of the American Diabetes Association.

RESULTS

Baseline clinical and demographic characteristics for the high (n = 45) and low s-Mg (n = 57) groups were similar. Kaplan-Meier survival analysis showed that 15-year freedom from NODAT was significantly higher among patients with high vs low s-Mg (85% vs 46% log-rank test, p < 0.001). Consistently, multivariate analysis adjusted for age, gender, immunosuppression therapies, BMI and mean creatinine values in the first year post-HT, showed that low s-Mg was independently associated with a significant > 8-fold increased risk for NODAT (95% CI 2.15-32.63, p = 0.003). Stroke rate was significantly higher in patients with low s-Mg levels vs high s-Mg (14% vs 0, p = 0.025), as well as long term mortality (HR 2.6, 95% CI 1.02-6.77, p = 0.05).

CONCLUSIONS

Low s-Mg level post-HT is an independent risk factor for NODAT in HT patients. The implications of interventions, focusing on preventing or correcting low s-Mg, for the risk of NODAT and for clinical outcomes should be evaluated.

Mitochondrial Haplogroup and the Risk of Acute Kidney Injury Following Cardiac Bypass Surgery

Although mitochondrial dysfunction plays a key role in the pathophysiology of acute kidney injury (AKI), the influence of mitochondrial genetic variability in this process remains unclear. We explored the association between the risk of post-cardiac bypass AKI and mitochondrial haplotype - inherited mitochondrial genomic variations of potentially functional significance. Our single-centre study recruited consecutive patients prior to surgery. Exclusions included stage 5 CKD, non-Caucasian race and subsequent off-pump surgery. Haplogroup analysis allowed characterisation of the study population using the common mutations and by phylogenetic supergroup (WXI and HV). Chi-square tests for association allowed the identification of potential predictors of AKI for use in logistic regression analysis. AKI occurred in 12.8% of the study population (n = 881; male 69.6%, non-diabetic 78.5%, median (interquartile range) age 68.0 (61.0-75.0) years). The haplogroup profile comprised H (42.7%), J (12.1%), T (10.9%), U (14.4%) and K (7.6%). Although the regression model was statistically significant (χ² = 95.483, p < 0.0005), neither the phylogenetic supergroups nor any individual haplogroup was a significant contributor. We found no significant association between common European haplogroups and the risk of post-cardiac bypass AKI. However, given the major role of mitochondrial dysfunction in AKI, there is a need to replicate our findings in other cohorts and with other aetiologies of AKI.

[Post-transplantation diabetes mellitus in kidney recipients]

Post-transplantation diabetes mellitus is defined as diabetes that is diagnosed in grafted patients. It affects 20 to 30 % of kidney transplant recipients, with a high incidence in the first year. The increasing age at transplantation and the rising incidence of obesity may increase its prevalence in the next years. Post-transplantation diabetes mellitus is associated with poor outcomes, such as mortality, cardiovascular events or graft dysfunction. Its occurrence is mainly related to immunosuppressive agents, affecting both insulin secretion and sensibility. Immunosuppressants may be iatrogenic, and as such, induce an early and transient diabetes. They may also precociously determine a permanent diabetes, acting here as a promoting factor in patients proned to the development of type 2 diabetes. Lastly, they may behave, far from transplantation, as an additional risk factor for type 2 diabetes. The screening, management and prognosis of these different subtypes of post-transplantation diabetes mellitus will be different.

Transplant genetics and genomics

Ever since the discovery of the major histocompatibility complex, scientific and clinical understanding in the field of transplantation has been advanced through genetic and genomic studies. Candidate-gene approaches and recent genome-wide association studies (GWAS) have enabled a deeper understanding of the complex interplay of the donor-recipient interactions that lead to transplant tolerance or rejection. Genetic analysis in transplantation, when linked to demographic and clinical outcomes, has the potential to drive personalized medicine by enabling individualized risk stratification and immunosuppression through the identification of variants associated with immune-mediated complications, post-transplant disease or alterations in drug-metabolizing genes.

Hypomagnesemia and increased risk of new-onset diabetes mellitus after transplantation in pediatric renal transplant recipients

BACKGROUND

New-onset diabetes after transplantation (NODAT) is a significant co-morbidity following kidney transplantation. Lower post-transplant serum magnesium levels have been found to be an independent risk factor for NODAT in adult kidney transplant recipients.

METHODS

We undertook a retrospective analysis of risk factors for NODAT in pediatric renal transplant recipients at our institution with the aim of determining if hypomagnesemia confers a significant risk of developing NODAT in this patient population.

RESULTS

A total of 173 children with a median age at transplantation of 7.0 (range 1.3-17.5) years were included. Hypomagnesemia was found to be a significant independent risk factor for NODAT (p = 0.01). High trough tacrolimus levels were also independently associated with NODAT (p < 0.001). There was no significant association between NODAT and body mass index at the time of transplantation, monthly cumulative steroid dose or post-transplant cytomegalovirus viremia (p = 0.9, 0.6 and 0.7, respectively).

CONCLUSIONS

This study identifies hypomagnesemia as a significant independent risk factor for the development of NODAT in pediatric renal transplant recipients. Given the clear association between hypomagnesemia and NODAT in both adults and children following renal transplantation, further studies are merited to clarify the etiology of this association and to examine the effect of magnesium supplementation on NODAT.

Importance of glucokinase -258G/A polymorphism in Asian Indians with post-transplant and type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) and post-transplant diabetes mellitus (PTDM) are non-synonymous forms of diabetes. Glucokinase (GCK) plays a key role in glucose metabolism. The relationship between the GCK promoter and specific types of diabetes, such as PTDM and T2DM, in the Asian Indian population is unknown. We examined the occurrence of a specific GCK promoter variant (-258G/A) in patients with T2DM and PTDM. The case-control study enrolled 640 Asian Indian subjects, including controls (n = 250) and T2DM (n = 250), PTDM (n = 42), and non-post-transplant diabetes mellitus (non-PTDM) (n = 98) patients. Purified Deoxyribonucleic acid (DNA) was genotyped with the polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP) analysis. The digested PCR products were analyzed on 12% polyacrylamide gels. The anthropometric, biochemical, and clinical details of each group were documented. GCK -258G/A alleles and genotypes were not associated with T2DM. However, among PTDM subjects, we detected a higher frequency of heterozygotes (52.4%) and a positive association with alleles/genotypes. The results suggest that the promoter region (-258G/A) of GCK plays an important role in PTDM in Asian Indians.

Role of pharmacogenomics in dialysis and transplantation

PURPOSE OF REVIEW

Pharmacogenomics is the study of differences in drug response on the basis of individual genetic background. With rapidly advancing genomic technologies and decreased costs of genotyping, the field of pharmacogenomics continues to develop. Application to patients with kidney disease provides growing opportunities for improving drug therapy.

RECENT FINDINGS

Pharmacogenomics studies are lacking in patients with chronic kidney disease and dialysis, but are abundant in the kidney transplant field. A potentially clinically actionable genetic variant exists in the CYP3A5 gene, with the initial tacrolimus dose selection being optimized based on CYP3A5 genotype. Although many pharmacogenomics studies have focused on transplant immunosuppression pharmacokinetics, an expanding literature on pharmacodynamic outcomes, such as calcineurin inhibitor toxicity and new onset diabetes, is providing new information on patients at risk.

SUMMARY

Appropriately powered pharmacogenomics studies with well-defined phenotypes are needed to validate existing studies and unearth new findings in patients with kidney disease, especially the chronic kidney disease and dialysis population.

Validation of the association of TCF7L2 and SLC30A8 gene polymorphisms with post-transplant diabetes mellitus in Asian Indian population

The rs7903146 and rs13266634 polymorphisms in the TCF7L2 and SLC30A8 genes, respectively, have been reported to be associated with type 2 diabetes. However, little is known about the association of these polymorphisms with post-transplant diabetes mellitus (PTDM). To study this linkage, we determined a distribution of allele and genotype frequencies in Asian Indians. 42 PTDM and 98 non-PTDM subjects were recruited. Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis was performed to detect for rs7903146 and rs13266634 polymorphisms. The clinical details and statistical analysis for PTDM and non-PTDM subjects were recorded. Our results observed higher frequencies of the minor alleles in rs7903146 and rs13266634 polymorphisms in the PTDM group compared to the non-PTDM subjects. The allele frequencies also found to be significantly associated with PTDM (rs7903146: T vs C: OR-2.6; (95%CI: 1.2-5.6); p = 0.01; rs13266634: T vs C: OR-2.0; (95%CI: 1.1-3.4); p = 0.01). These findings suggest that rs7903146 and rs13266634 polymorphisms are associated with PTDM in the Asian Indian population despite a relatively small study group.

New-onset diabetes mellitus after kidney transplantation: Current status and future directions

A diagnosis of new-onset diabetes after transplantation (NODAT) carries with it a threat to the renal allograft, as well as the same short- and long-term implications of type 2 diabetes seen in the general population. NODAT usually occurs early after transplantation, and is usually diagnosed according to general population guidelines. Non-modifiable risk factors for NODAT include advancing age, African American, Hispanic, or South Asian ethnicity, genetic background, a positive family history for diabetes mellitus, polycystic kidney disease, and previously diagnosed glucose intolerance. Modifiable risk factors for NODAT include obesity and the metabolic syndrome, hepatitis C virus and cytomegalovirus infection, corticosteroids, calcineurin inhibitor drugs (especially tacrolimus), and sirolimus. NODAT affects graft and patient survival, and increases the incidence of post-transplant cardiovascular disease. The incidence and impact of NODAT can be minimized through pre- and post-transplant screening to identify patients at higher risk, including by oral glucose tolerance tests, as well as multi-disciplinary care, lifestyle modification, and the use of modified immunosuppressive regimens coupled with glucose-lowering therapies including oral hypoglycemic agents and insulin. Since NODAT is a major cause of post-transplant morbidity and mortality, measures to reduce its incidence and impact have the potential to greatly improve overall transplant success.

Relationship between European mitochondrial haplogroups and chronic renal allograft rejection in patients with kidney transplant

Mitochondrial DNA variants may contribute to differences in mitochondrial function, leading to an altered immune system. The aim of this study was to analyze the relationship between mtDNA haplogroups and the development of chronic allograft dysfunction in patients with kidney transplant. A retrospective observational study was carried out on 261 patients who received kidney transplant (114 had stable transplant and 147 patients developed chronic allograft dysfunction). DNA samples were genotyped for 14 mtDNA polymorphisms by using Sequenom's MassARRAY platform (San Diego, CA, USA). Only European white patients within the N macro-cluster were included. Patients with haplogroups V (odds ratio (OR)=0.32; p=0.037) and J (OR=0.36; p=0.038) showed lower odds for developing CRAD than patients with haplogroup H. After adjusting for the most significant variables, haplogroups V and J tended to statistical significance (p=0.091 and p=0.067 respectively). This is a preliminary study in which mtDNA haplogroups seem to be implicated in susceptibility or protection for developing chronic allograft dysfunction.