Polymorphism of the renin-angiotensin-aldosterone system in patients with chronic allograft dysfunction

Validation of systems biology derived molecular markers of renal donor organ status associated with long term allograft function

Donor organ quality affects long term outcome after renal transplantation. A variety of prognostic molecular markers is available, yet their validity often remains undetermined. A network-based molecular model reflecting donor kidney status based on transcriptomics data and molecular features reported in scientific literature to be associated with chronic allograft nephropathy was created. Significantly enriched biological processes were identified and representative markers were selected. An independent kidney pre-implantation transcriptomics dataset of 76 organs was used to predict estimated glomerular filtration rate (eGFR) values twelve months after transplantation using available clinical data and marker expression values. The best-performing regression model solely based on the clinical parameters donor age, donor gender, and recipient gender explained 17% of variance in post-transplant eGFR values. The five molecular markers EGF, CD2BP2, RALBP1, SF3B1, and DDX19B representing key molecular processes of the constructed renal donor organ status molecular model in addition to the clinical parameters significantly improved model performance (p-value = 0.0007) explaining around 33% of the variability of eGFR values twelve months after transplantation. Collectively, molecular markers reflecting donor organ status significantly add to prediction of post-transplant renal function when added to the clinical parameters donor age and gender.

Assessment of the relationship between ACE I/D gene polymorphism and renal allograft survival

BACKGROUND AND OBJECTIVE

The relationship between the angiotensin-converting enzyme (ACE) insertion/deletion (I/D) gene polymorphism and renal allograft survival after renal transplantation from the published reports are still debatable. This study was performed to evaluate the relationship between the ACE I/D gene polymorphism and renal allograft survival after renal transplantation using meta-analysis.

METHOD

Eligible studies were identified from PubMed and Cochrane Library on 1 November 2014, and eligible studies were recruited and synthesized using a meta-analysis methodology.

RESULTS

Twelve investigations were included in this meta-analysis for the assessment of the relationship between the ACE I/D gene polymorphism and renal allograft survival. In this meta-analysis, the ACE I/D gene polymorphism was not associated with renal allograft survival after renal transplantation for overall populations, Caucasians, Brazilians and Africans. Interestingly, the ACE D allele and DD genotype were associated with renal allograft survival after renal transplantation in the Asian population.

CONCLUSIONS

ACE D allele and DD genotype were associated with renal allograft survival after renal transplantation in the Asian population. However, more studies should be performed to confirm this association.

The role of genetic polymorphisms of the Renin-Angiotensin System in renal diseases: A meta-analysis

Renal failure has a complex phenotype resulting from an underlying kidney disease as well as environmental and genetic factors. In the present study we performed a systematic review and meta-analyses to evaluate the association of the A1166C polymorphism of Angiotensin II type 1 Receptor gene (AGTR1) with Chronic Kidney Disease (CKD), End Stage Renal Disease (ESRD), IgA Nephropathy (IgAN) and Vesicoureteral Reflux (VUR) as well as the association of A1332G polymorphism of Angiotensin II type 2 Receptor (AGTR2) gene with Vesicoureteral Reflux (VUR). We found that neither AGTR1 Α1166C, nor AGTR2 A1332G polymorphisms were significantly associated with any of the aforementioned renal diseases, suggesting that they cannot be used as predictive markers in either general or subgroup ethnic populations.

Association of angiotensin II type-1 receptor A1166C gene polymorphism with the susceptibility of end-stage renal disease

Association between angiotensin II type-1 receptor (AT1R) A1166C gene polymorphism and end-stage renal disease (ESRD) risk is still controversial. This meta-analysis was performed to evaluate the association of AT1R A1166C gene polymorphism with ESRD susceptibility. The search was performed in the databases of PubMed, Embase and Cochrane Library as of 1 May 2012, and the eligible investigations were recruited for this meta-analysis. Nineteen literatures were identified for the analysis of association between AT1R A1166C gene polymorphism and ESRD susceptibility. There was no association between AT1R A1166C gene polymorphism and ESRD susceptibility for overall populations, Caucasians, Asians and Turkish population. Interestingly, CC genotype was associated with a higher risk of ESRD in Africans (OR = 3.36, 95% CI: 1.42-7.99, p = 0.006). However, C allele and AA genotype were not associated with the ESRD risk in African population. In conclusion, CC genotype might be a risk factor for the ESRD susceptibility in African population. However, more case-control association investigations on larger, stratified populations are required in the future.

Association of angiotensinogen M235T gene polymorphism with end-stage renal disease risk: a meta-analysis

Association between angiotensinogen (AGT) M235T gene polymorphism and end-stage renal disease (ESRD) risk is still controversial. This meta-analysis was performed to evaluate the association of AGT M235T gene polymorphism with ESRD susceptibility. A predefined literature search and selection of eligible relevant studies were performed to collect data from electronic databases of PubMed, Embase and Cochrane Library. Sixteen literatures were identified for the analysis of association of AGT M235T gene polymorphism with ESRD risk. T allele and TT genotype were associated with ESRD susceptibility in Caucasians (T: OR = 1.13, 95 % CI: 1.02-1.25, P = 0.02; TT: OR = 1.22, 95 % CI: 1.03-1.45, P = 0.02). However, MM genotype might not play a protective role against ESRD risk in Caucasians. Furthermore, there was no a markedly positive association between AGT M235T gene polymorphism and ESRD susceptibility in overall populations, Asians and Africans. In conclusion, T allele or TT homozygote is associated with the onset of ESRD in Caucasians. However, more studies should be performed in the future.

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.

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.

The renin-angiotensin system: an old, newly discovered player in immunoregulation

Clinical and experimental studies that discuss the different immune functions of the renin-angiotensin system (RAS) in kidney diseases were reviewed, with emphasis on studies of kidney transplantation. The RAS has been shown to affect both the innate and adaptive immune responses and has a well-established role in fibrinogenesis. Of special clinical interest is the ability of the RAS to activate the transforming growth factor beta(1) and the Smad pathways leading to fibrinogenesis. In addition to the RAS enhancing effect on the activity of T cells, several components of the RAS have also been shown to be chemotactic to macrophages, T cells, and natural killer cells. Experimental studies have found that RAS blockade decreases the histologic lesions of chronic allograft nephropathy but can enhance acute graft vasculopathy. Although the blockade of RAS has been commonly practiced to reduce posttransplantation hypertension, proteinuria, and erythrocytosis, however, its role in prolonging graft survival is not well established.

Genetic prediction of renal transplant outcome

PURPOSE OF REVIEW

In the present study, we reviewed recent publications regarding potential genetic predictors of transplant outcome, including acute rejection, metabolism of immunosuppressive medications, long-term transplant outcome, and posttransplant complications.

RECENT FINDINGS

Recent studies are based on the candidate gene analysis; specifically, cytokine genes and innate immune response molecules present popular targets for studies of acute rejection and long-term outcome. Pharmacogenomic studies are mostly focused on the genes of drug targets or the corresponding enzymes metabolizing the drug. Posttransplant complications (i.e. infections, diabetes, and malignancies) are associated with a variety of genes of different pathways. Most of the studies are based on just recipient, but not donor, genotype analysis. Positive results are balanced by reports of no association when evaluating the same genetic polymorphisms. Some of the reports might be affected by insufficient study design, including small sample size, lack of adjustment for potential confounders, and multiple comparisons.

SUMMARY

The field remains controversial because of differences in populations, study design, and statistical methods. Studies are based on candidate gene analysis; however, genome-wide association studies are lacking. Future research should be directed at better designed studies, larger sample size, evaluating both recipients and donors, and implementation of genome-wide association studies.

Angiotensinogen, angiotensine converting enzyme and plasminogen activator inhibitor-1 gene polymorphism in chronic allograft dysfunction

Despite dramatic improvements in first-year patient and graft survival rates, chronic allograft dysfunction (CAD) remains the leading cause of late renal allograft loss, while current immunologic strategies have little effect on this condition. The renin-angiotensin system (RAS) plays an important role in progression of chronic renal disease. It was shown that plasminogen activator inhibitor-1 (PAI-1) functions in the RAS. This study investigates the possible links between angiotensinogen (AGT M235T), angiotensin-converting enzyme (ACE) and PAI-1 genotypes with CAD. Assessments of polymorphism were performed in 127 renal allograft recipients (77 with CAD and 50 with normal renal function). Fifty healthy subjects were also considered for comparison. Genotypes were determined using polymerase chain reaction (PCR) sequence-specific primers and PCR followed by restriction fragment length polymorphism analysis. Kidney recipients with CAD had significantly higher frequencies of the TT than the recipients without CAD (P < 0.05). The transplant recipients with CAD also had significantly higher frequencies of the DD genotype than those without CAD (P < 0.05). No significant differences were observed between the allelic and genotypic distributions of PAI-1 polymorphisms. Therefore, determination of AGT M235T and ACE genotypes prior to transplantation may be useful to identify patients who are at risk for chronic renal transplant dysfunction.

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

BACKGROUND

Polymorphisms of genes such as angiotensin-converting enzyme (ACE), angiotensinogen (AGT), and angiotensin receptor type I (AGTR1) have been associated with hypertension. Hypertension, in turn, has been associated with decreased renal allograft survival. Therefore, this study investigated whether single nucleotide polymorphisms (SNPs) in these genes are associated with decline in renal function posttransplantation.

METHODS

We enrolled patients from a prospective cohort of renal transplant recipients of deceased donor kidneys being conducted at 9 centers in the Delaware Valley Region. Medical records were assessed every 6 months and estimated glomerular filtration rate (eGFR) was calculated using the Modification of Diet in Renal Disease equation. Genotypes of 10, 2, and 5 SNPs in the AGTR1, AGT, and ACE gene were analyzed, respectively.

RESULTS

The G and the T alleles of the respective AGTR1 SNPs rs275704 and rs5182 were both associated with 50% decline in eGFR (HR for rs275704: CG=1.22, 95% confidence interval [CI] 0.67-2.25 and GG=2.55, 95% CI 1.22-5.32, overall P=0.03; HR for rs5182: CT=1.26, 95% CI 0.72-2.19 and TT=3.09, 95% CI 1.50-6.37, overall P=0.007) in the adjusted analysis. Similarly, haplotype analysis showed that AGTR1 SNPs were associated with 50% decline in eGFR (global P=0.010). The GG genotype of SNP rs275704 occurred more frequently in African Americans than in non-African Americans (44% vs. 7%, chi2=36.03, P<0.0001). In contrast, the TT genotype of SNP rs5182 occurred more frequently in non-African Americans than in African-Americans (24% vs. 2%, chi2=21.40, P<0.0001). Polymorphisms in the ACE and AGT genes were not associated with renal allograft outcomes.

CONCLUSIONS

SNPs in AGTR1 gene are associated with decline in renal function posttransplantation.