Association of Single Nucleotide Polymorphisms on Chromosome 9p21.3 With Cardiovascular Death in Kidney Transplant Recipients

Genome-wide association study for time to failure of kidney transplants from African American deceased donors

Two renal-risk variants in the apolipoprotein L1 gene (APOL1) in African American (AA) deceased donors (DD) are associated with shorter renal allograft survival after transplantation. To identify additional genes contributing to allograft survival, a genome-wide association study was performed in 532 AA DDs. Phenotypic data were obtained from the Scientific Registry of Transplant Recipients. Association and single-nucleotide polymorphism (SNP)-by-APOL1 interaction tests were conducted using death-censored renal allograft survival accounting for relevant covariates. Replication and inverse-variance-weighted meta-analysis were performed using data from 250 AA DD in the Genomics of Transplantation study. Accounting for APOL1, multiple SNPs near the Nudix Hydrolase 7 gene (NUDT7) showed strong independent effects (P = 1.6 × 10^-8 -2.2 × 10^-8 ). Several SNPs in the Translocation protein SEC63 homolog (SEC63; P = 2 × 10^-9 -3.7 × 10^-8 ) and plasmacytoma variant translocation 1 (PVT1) genes (P = 4.0 × 10^-8 -7 × 10^-8 ) modified the effect of APOL1 on allograft survival. SEC63 is expressed in human renal tubule cells and glomeruli, and PVT1 is associated with diabetic kidney disease. Overall, associations were detected for 41 SNPs (P = 2 × 10^-9 -5 × 10^-8 ) contributing independently or interacting with APOL1 to impact renal allograft survival after transplantation from AA DD. Given the small sample size of the discovery and replication sets, independent validations and functional genomic efforts are needed to validate these results.

Genetic markers associated with long-term cardiovascular outcome in kidney transplant recipients

There is a clear genetic contribution to the risk of cardiovascular diseases, and a composite genetic risk score (GRS) based on 27 single nucleotide polymorphisms (SNPs) was reported to predict risk of cardiovascular events in the general population. We aimed to evaluate this risk score in renal transplant recipients, a population with heightened cardiovascular risk, with a yet unknown genetic contribution. A total of 1640 participants from the ALERT trial (Assessment of Lescol in Renal Transplantation), a study comparing fluvastatin with placebo in stable renal transplant recipients, were genotyped for all SNPs making up the GRS. Risk alleles were weighted by the log of odds ratios reported in genome wide association studies and summed. Associations between GRS and time from study inclusion to first major cardiovascular event (MACE) were analyzed by Cox regression. In analyses adjusted for cardiovascular risk factors, GRS was significantly associated with MACE (hazard ratio [HR] 1.81, P = .006) when comparing genetic high-risk patients (quartile 4) with genetic low-risk participants (quartile 1). A 27-SNP GRS, which predicted cardiovascular events in the nontransplant population, appears to have predictive value also in kidney allograft recipients. Refining the score to better fit the transplant population seems feasible.

ANRIL as a genetic marker for cardiovascular events in renal transplant patients - an observational follow-up cohort study

Cardiovascular disease is the leading cause of morbidity and mortality in kidney transplant recipients. Several single-nucleotide polymorphisms (SNPs) in the ANRIL gene pathway have been associated with cardiovascular events (CE). The main objective was to ascertain whether ANRIL (rs10757278) and CARD8 (rs2043211) SNPs could mediate susceptibility to CE. This was an observational follow-up cohort study of renal transplant recipients at Bellvitge University Hospital (Barcelona) from 2000 to 2014. A total of 505 recipients were followed up until achievement of a CE. Patients who did not achieve the endpoint were followed up until graft loss, lost to follow-up or death. Survival analysis was used to ascertain association between genetic markers, clinical data, and outcome. Fifty-three patients suffered a CE after renal transplantation. Results showed a significant association between ANRIL SNP and CE. Homozygous GG for the risk allele showed higher risk for CE than A carriers for the protective allele [HR = 2.93(1.69-5.11), P < 0.0001]. This effect was maintained when it was analyzed in combination with CARD8, suggesting that CARD8 SNP could play a role in the ANRIL mechanism. However, our study does not clarify the molecular mechanism for the CARD8 SNP regulation by ANRIL. ANRIL SNP may predispose to the development of CE after successful kidney transplantation.

Cardiovascular disease after transplantation: an emerging role of the immune system

Cardiovascular disease (CVD) after transplantation remains a major concern. Little is known about what drives the increased cardiovascular risk in transplant recipients apart from traditional risk factors. The immune system is involved in the pathogenesis of hypertension, atherosclerosis, and coronary artery disease in the general population. Recently, inhibition of interleukin 1 - β by canakinumab versus placebo decreased the incidence of cardiovascular events. Emerging evidence points to a role of adaptive cellular immunity in the development of CVD. Especially, expansion of pro-inflammatory and antiapoptotic cytotoxic CD4⁺ CD28^null T cells is closely associated with incident CVD in various study populations including transplant recipients. The association of cytomegalovirus exposure with increased cardiovascular mortality might be explained by its capacity to upregulate these cytotoxic cells. Also, humoral immunity seems to be relevant for cardiovascular outcome in transplant recipients. Panel-reactive antibodies at baseline and donor-specific antibodies are independently associated with poor cardiovascular outcome after kidney transplantation. Cardiovascular effects of immunosuppressive drugs and statins do not only imply indirect positive or negative effects on traditional cardiovascular risk factors but also intrinsic immunological effects. How immunosuppressive drugs modify atherosclerosis largely remains elusive.

Polymorphisms in genes involved in vasoactive eicosanoid synthesis affect cardiovascular risk in renal transplant recipients

OBJECTIVE

Arachidonic acid metabolism by cytochrome P450 (CYP) epoxygenases leads to epoxyeicosatrienoic acids (EETs), which are eicosanoids with vasodilator and anti-inflammatory properties. We aim to determine whether genetic variability in these routes may contribute to cardiovascular (CV) risk in renal transplant recipients.

METHODS

In a cohort of 355 patients, we determined the presence of two polymorphisms, CYP2C8*3 and CYP2J2*7, known to affect eicosanoid levels. Associations with CV mortality, CV event-free long-term survival and graft survival were retrospectively investigated by logistic regression models.

RESULTS

CYP2J2*7 showed a statistical trend towards higher CV mortality (p = .06) and lower cardiac or cerebral event-free long-term survival (p = .05), whilst CYP2C8*3 displayed a significant inverse association with the risk of CV event (hazard ratio [HR] = 0.34 [0.15-0.78], p = .01). The association of CYP2J2*7 with CV mortality became significant when the analysis was restrained to 316 patients without a history of CV events prior to transplantation (HR = 15.72 [2.83-91.94], p = .005). In this subgroup of patients both single nucleotide polymorphisms (SNPs) were significantly associated with event-free survival. HR values were 5.44 (1.60-18.51), p = .007 and 0.26 (0.09-0.75), p = .012 for CYP2J2*7 and CYP2C8*3, respectively.

CONCLUSIONS

Our results show, for the first time to our knowledge, that two SNPs in CYP2C8 and CYP2J2, which synthesize EETs, may modify CV outcomes in renal transplant recipients, a population that is already at a high risk of suffering these events.