Association of hypertension genotypes and decline in renal function after kidney transplantation

The impact of donor and recipient common clinical and genetic variation on estimated glomerular filtration rate in a European renal transplant population

Genetic variation across the human leukocyte antigen loci is known to influence renal-transplant outcome. However, the impact of genetic variation beyond the human leukocyte antigen loci is less clear. We tested the association of common genetic variation and clinical characteristics, from both the donor and recipient, with posttransplant eGFR at different time-points, out to 5 years posttransplantation. We conducted GWAS meta-analyses across 10 844 donors and recipients from five European ancestry cohorts. We also analyzed the impact of polygenic risk scores (PRS), calculated using genetic variants associated with nontransplant eGFR, on posttransplant eGFR. PRS calculated using the recipient genotype alone, as well as combined donor and recipient genotypes were significantly associated with eGFR at 1-year posttransplant. Thirty-two percent of the variability in eGFR at 1-year posttransplant was explained by our model containing clinical covariates (including weights for death/graft-failure), principal components and combined donor-recipient PRS, with 0.3% contributed by the PRS. No individual genetic variant was significantly associated with eGFR posttransplant in the GWAS. This is the first study to examine PRS, composed of variants that impact kidney function in the general population, in a posttransplant context. Despite PRS being a significant predictor of eGFR posttransplant, the effect size of common genetic factors is limited compared to clinical variables.

Change in Mycophenolate and Tacrolimus Exposure by Transplant Vintage and Race

OBJECTIVES

Although both tacrolimus and mycophenolate have improved outcomes after kidney transplant, studies regarding effects of exposure on outcomes, specifically related to racial disparities, are sparse.

MATERIALS AND METHODS

In this 8-year longitudinal cohort study of adult kidney transplant recipients, mycophenolate and tacrolimus levels were compared across transplant vintage stratified by non-African Americans versus African Americans. Data were analyzed with standard univariate tests and multivariable regression models.

RESULTS

Our study included 1217 patients (transplanted from 2005-2013) who had tacrolimus and myco-phenolate exposure data, with follow-up through 2015 (53.7% were African Americans). Mean mycophenolate dose was 1672 ± 463 mg/day during the first 3 years posttransplant. Although transplant vintage did not appreciably impact mycophenolate dosing in non-African Americans (0.7 mg/day/y; P = .903), doses significantly decreased in African Americans across transplant vintage (-20.5 mg/day/y; P < .001). Rate of mycophenolate being held or discontinued based on transplant vintage significantly increased in African Americans but did not change in non-African Americans. At the beginning of the study, mean tacrolimus levels were lower in African Americans; however, levels then slightly decreased in non-African Americans (-0.03 ng/mL/y; P = .279) and slightly increased in African Americans (+0.03 ng/mL/y; P = .247), with similar levels by 2013. Higher tacrolimus levels were protective against rejection in African Americans only but were protective against death-censored graft loss in both race/ethnicity groups. Mycophenolate dosing had no appreciable impact on outcomes in African Americans, but higher mycophenolate dosing was a significant risk factor for death-censored graft loss in non-African Americans.

CONCLUSIONS

Tacrolimus and mycophenolate exposure levels have significantly changed over time and differed by race/ethnicity. In non-African Americans, those transplanted more recently tended to have lower tacrolimus but similar mycophenolate exposure. Although mycophenolate exposure in African Americans has recently decreased, tacrolimus has increased. Differences in outcomes likely reflect improved understanding of immunosuppressant tolerability by recipient race/ethnicity.

Using omics to explore complications of kidney transplantation

The importance of genetic and biochemical variation in renal transplant outcomes has been clear since the discovery of the HLA in the 1950s. Since that time, there have been huge advancements in both transplantation and omics. In recent years, there has seen an increased number of genome-, proteome- and transcriptome-wide studies in the field of transplantation moving away from the earlier candidate gene/protein approaches. These areas have the potential to lead to the development of personalized treatment depending on individual molecular risk profiles. Here, we discuss recent progress and the current literature surrounding omics and renal transplant complications.

Risk given by AGT polymorphisms in inducing susceptibility to essential hypertension among isolated populations from a remote region of China: A case-control study among the isolated populations

INTRODUCTION

Hypertension is a serious risk factor affecting up to 30% of the world's population with a heritability of more than 30-50%. The aim of this study was to investigate the contribution of the polymorphisms localized in the angiotensinogen (AGT) gene, a main component of the renin-angiotensin-aldosterone system, in inducing the susceptibility to essential hypertension (EH) among isolated populations (Yi and Hani minorities) with low prevalence rate from the remote region of Yunnan in China.

METHODS

A case-control association study was performed, and all subjects were genotyped for the seven single nucleotide polymorphisms localized in the AGT region by polymerase chain reaction-restriction fragment length polymorphism analysis.

RESULTS

Three polymorphisms, i.e. rs5046, rs5049, and rs2478544, were significantly associated with EH among the Hani minority. The associations, found in the Yi minority, did not reach a conclusive level of statistical significance. The polymorphisms of rs2478544 and rs5046 caused the transformations of exonic splicing enhancer sites and transcription factor binding sites, respectively, in the bioinformatic analyses. The haplotype-rs5046T, rs5049A, rs11568020G, rs3789679C, rs2478544C was susceptible for EH among the Hani minority.

CONCLUSION

Our findings suggested that the AGT polymorphisms have played a vital role in determining an individual's susceptibility to EH among the isolated population, which would be helpful for EH management in the remote mountainous region of Yunnan in China.

Long-term outcomes in African American kidney transplant recipients under contemporary immunosuppression: a four-yr analysis of the Mycophenolic acid Observational REnal transplant (MORE) study

Mycophenolic acid Observational REnal transplant (MORE) was a prospective, observational study of de novo kidney transplant patients receiving mycophenolic acid (MPA). Four-yr data on 904 patients receiving tacrolimus and enteric-coated mycophenolate sodium (EC-MPS) or mycophenolate mofetil (MMF) were analyzed to evaluate immunosuppression and graft outcomes in African American (AA, n = 218) vs. non-AA (n = 686) patients. Mean tacrolimus dose was higher in AA vs. non-AA patients but mean tacrolimus trough concentration was similar. Use of the recommended MPA dose in AA patients decreased from 78.9% at baseline to 33.1% at year 3. More AA patients received the recommended MPA dose with EC-MPS than MMF at month 6 (56.2% vs. 35.7%, p = 0.016) and month 36 (46.6% vs. 16.7%, p = 0.029), with no safety penalty. Significantly, more AA patients received corticosteroids than non-AA patients. Biopsy-proven acute rejection was higher in AA vs. non-AA patients (18.9% vs. 10.7%, p = 0.003), as was graft loss (10.9% vs. 4.4%, p = 0.003); differences were confirmed by Cox regression analysis. Patient survival was similar. Estimated GFR was comparable in AA vs. non-AA patients. Kidney allograft survival remains lower for AA vs. non-AA recipients even under the current standard of care.

The contribution of donor quality to differential graft survival in African American and Caucasian renal transplant recipients

Although a number of factors contributing to the disparity in graft survival between African American (AA) and Caucasian kidney transplant recipients have been described, the role of donor quality is less well understood. This study was undertaken to determine the impact of donor quality differences on this disparity, based on review of UNOS (United Network for Organ Sharing) data on deceased donor renal transplantation from 2000 to 2010. Donor quality was determined by the kidney donor risk index (DRI), and was compared between AA and Caucasian recipients. There were 33,405 Caucasians and 22,577 African Americans in the study, with mean DRI of 1.17 versus 1.27 (p < 0.001), respectively. In analysis 2,446 recipients of each race matched by propensity scoring (based on medical, socioeconomic and immunologic covariates), mean DRI was 1.25 for Caucasians and 1.28 (p = 0.02) for AA. The hazard ratio (HR) for graft failure associated with AA race was 1.8 (p < 0.001) on unadjusted analysis, and decreased to 1.6 (p < 0.001) after matching for DRI. These results indicate a significant disparity in quality of kidneys received by African Americans, which propensity analysis indicates is partially explained by differences in medical, immunologic and socioeconomic factors. Furthermore, this difference in donor quality partially accounts for poorer graft survival in African Americans.

Association of angiotensin II type 1-receptor gene polymorphisms with the risk of developing hypertension in Mexican individuals

INTRODUCTION

Hypertension is a complex disease in which a significant interaction between genetic and environmental factors takes place. The renin-angiotensin system plays an important role regulating blood pressure to maintain homeostasis and vascular tone. In the present work, the role of angiotensin II type 1-receptor (AGTR1) gene polymorphisms as susceptibility markers for hypertension was evaluated.

MATERIALS AND METHODS

Five polymorphisms in the AGTR1 gene were genotyped by 5' exonuclease TaqMan genotyping assays in 239 hypertensive and 371 non-hypertensive individuals.

RESULTS

A similar distribution of rs275651, rs275652, rs275653, and rs5183 polymorphisms was observed in both studied groups. Different distribution of rs5182 genotypes was observed between the studied groups (p = 0.016). According to the co-dominant model, individuals with rs5182 CC genotype have a 1.83-fold increased risk of developing hypertension (p = 0.009). Polymorphisms were distributed in two blocks: block 1 included the rs275651, rs275652, and rs275653 polymorphisms, whereas block 2 included the rs5183 and rs5182 polymorphisms. Individuals with hypertension showed increased frequency of 'CA' haplotype of block 2 when compared to non-hypertensive individuals (p = 0.015, odds ratio = 1.33).

CONCLUSION

The results suggest that the rs5182 gene polymorphism could be involved in the risk of developing hypertension in Mexican individuals.

Insertion/Deletion polymorphism of Angiotensin-converting enzyme as a risk factor for chronic allograft nephropathy

Angiotensin-converting enzyme (ACE) inhibitor therapy is widely used to treat chronic allograft nephropathy (CAN), which suggests a possible role of the renin-angiotensin system in the pathologic mechanism of the disease. The objective of this study was to investigate the possible link between CAN and ACE. The ACE insertion/deletion polymorphism and the amount and activity of ACE were determined in cadaver kidney recipients with CAN (n = 38) or normal renal function (n = 34). The DD genotype was observed significantly more frequently in the CAN group compared with the group with normal renal function. Moreover, the DD genotype was associated with a higher serum ACE concentration and greater serum ACE activity, compared with II genotype homozygotes. The insertion/deletion polymorphism of ACE affects ACE expression and activity in serum, and, therefore, may have an important role in the pathogenesis of CAN. These findings suggest that determination of the ACE genotype may be useful in identifying patients at high risk. In particular, the DD genotype may be considered an indication for ACE inhibitor therapy.

Access and outcomes among minority transplant patients, 1999-2008, with a focus on determinants of kidney graft survival

Coincident with an increasing national interest in equitable health care, a number of studies have described disparities in access to solid organ transplantation for minority patients. In contrast, relatively little is known about differences in posttransplant outcomes between patients of specific racial and ethnic populations. In this paper, we review trends in access to solid organ transplantation and posttransplant outcomes by organ type, race and ethnicity. In addition, we present an analysis of categories of factors that contribute to the racial/ethnic variation seen in kidney transplant outcomes. Disparities in minority access to transplantation among wait-listed candidates are improving, but persist for those awaiting kidney, simultaneous kidney and pancreas and intestine transplantation. In general, graft and patient survival among recipients of solid organ transplants is highest for Asians and Hispanic/Latinos, intermediate for whites and lowest for African Americans. Although much of the difference in outcomes between racial/ethnic groups can be accounted for by adjusting for patient characteristics, important observed differences remain. Age and duration of pretransplant dialysis exposure emerge as the most important determinants of survival in an investigation of the relative impact of center-related versus patient-related variables on kidney graft outcomes.

Rationale and criteria of eligibility for calcineurin inhibitor interruption following kidney transplantation

PURPOSE OF REVIEW

To summarize predictive low-risk parameters of renal allograft recipients for purposes of improving the initiation of calcineurin inhibitor withdrawal protocols.

RECENT FINDINGS

Clinical trials have demonstrated the potential global benefit of calcineurin inhibitor interruption protocols on graft survival despite being associated with an increased rate of acute rejection episodes, thus underlying a number of risk factors. Recent identification or confirmation of variables updating the list of parameters and molecular markers that can be used to predict graft outcome are described.

SUMMARY

The effect of calcineurin inhibitor withdrawal on long-term graft and recipient survival patterns is assessed in relation to the large number of calcineurin inhibitor-related side-effects. However, current protocols are based on empirical observations and there is a clear requirement for reliable parameters to define patient eligibility for calcineurin inhibitor weaning procedures. Here, we review biological, clinical and genetic parameters that can be used as predictive markers of long-term graft outcome and could serve as criteria for patient selection in calcineurin inhibitor weaning protocols.