Jennifer McCaughan

Recipient obesity and outcomes after kidney transplantation: a systematic review and meta-analysis

BACKGROUND The prevalence of obesity is increasing globally and is associated with chronic kidney disease and premature mortality. However, the impact of recipient obesity on kidney transplant outcomes remains unclear. This study aimed to investigate the association between recipient obesity and mortality, death-censored graft loss and delayed graft function (DGF) following kidney transplantation. METHODS A systematic review and meta-analysis was conducted using Medline, Embase and the Cochrane Library. Observational studies or randomized controlled trials investigating the association between recipient obesity at transplantation and mortality, death-censored graft loss and DGF were included. Obesity was defined as a body mass index (BMI) of ≥30 kg/m(2). Obese recipients were compared with those with a normal BMI (18.5-24.9 kg/m(2)). Pooled estimates of hazard ratios (HRs) for patient mortality or death-censored graft loss and odds ratios (ORs) for DGF were calculated. RESULTS Seventeen studies including 138 081 patients were analysed. After adjustment, there was no significant difference in mortality risk in obese recipients [HR = 1.24, 95% confidence interval (CI) = 0.90-1.70, studies = 5, n = 83 416]. However, obesity was associated with an increased risk of death-censored graft loss (HR = 1.06, 95% CI = 1.01-1.12, studies = 5, n = 83 416) and an increased likelihood of DGF (OR = 1.68, 95% CI = 1.39-2.03, studies = 4, n = 28 847). CONCLUSIONS Despite having a much higher likelihood of DGF, obese transplant recipients have only a slightly increased risk of graft loss and experience similar survival to recipients with normal BMI.

Genetics of New-Onset Diabetes after Transplantation

New-onset diabetes after transplantation is a common complication that reduces recipient survival. Research in renal transplant recipients has suggested that pancreatic β-cell dysfunction, as opposed to insulin resistance, may be the key pathologic process. In this study, clinical and genetic factors associated with new-onset diabetes after transplantation were identified in a white population. A joint analysis approach, with an initial genome-wide association study in a subset of cases followed by de novo genotyping in the complete case cohort, was implemented to identify single-nucleotide polymorphisms (SNPs) associated with the development of new-onset diabetes after transplantation. Clinical variables associated with the development of diabetes after renal transplantation included older recipient age, female sex, and percentage weight gain within 12 months of transplantation. The genome-wide association study identified 26 SNPs associated with new-onset diabetes after transplantation; this association was validated for eight SNPs (rs10484821, rs7533125, rs2861484, rs11580170, rs2020902, rs1836882, rs198372, and rs4394754) by de novo genotyping. These associations remained significant after multivariate adjustment for clinical variables. Seven of these SNPs are associated with genes implicated in β-cell apoptosis. These results corroborate recent clinical evidence implicating β-cell dysfunction in the pathophysiology of new-onset diabetes after transplantation and support the pursuit of therapeutic strategies to protect β cells in the post-transplant period.

Epigenetics: Time to translate into transplantation

Substantial progress has been made in identifying genetic loci associated with multifactorial disorders, including variants that seem to impact outcomes following solid organ transplantation. Despite these advances, much of the heritability and susceptibility to chronic disease processes remains unexplained. Epigenetic modifications may exert their effect independently or complementary to genetic variants. Epigenetic modifications can change gene expression without altering the DNA sequence. These modifications are dynamic, potentially heritable, and can be induced by environmental stimuli or drugs. The impact of epigenetic phenomena on the outcomes of organ transplantation is currently poorly understood. Epigenetic modifications can occur during periods of illness; these may persist and potentially influence allograft outcomes. Epigenetic mechanisms influence the activation, proliferation, and differentiation of the immune cells involved in allograft rejection. The donor’s epigenome may also impact transplant survival, and initial research has demonstrated that peritransplant conditions induce rapid epigenetic modification within the allograft. Further research will help to define the importance of epigenetic modifications in transplantation. This will potentially lead to the identification of useful biomarkers and the development of novel pharmacotherapies. This review explores the nature of epigenetic modification in disease and the emerging evidence for epigenetic influences on allograft survival.

The complement cascade in kidney disease: from sideline to center stage.

Activation of the complement pathway is implicated in the pathogenesis of many kidney diseases. The pathologic and clinical features of these diseases are determined in part by the mechanism and location of complement activation within the kidney parenchyma. This review describes the physiology, action, and control of the complement cascade and explains the role of complement overactivation and dysregulation in kidney disease. There have been recent advances in the understanding of the effects of upregulation of the complement cascade after kidney transplantation. Complement plays an important role in initiating and propagating damage to transplanted kidneys in ischemia-reperfusion injury, antibody-mediated rejection, and cell-mediated rejection. Complement-targeting therapies presently are in development, and the first direct complement medication for kidney disease was licensed in 2011. The potential therapeutic targets for anticomplement drugs in kidney disease are described. Clinical and experimental studies are ongoing to identify further roles for complement-targeting therapy.

Surveillance of nonmelanoma skin cancer incidence rates in kidney transplant recipients in Ireland.

Background The incidence of nonmelanomatous skin cancer (NMSC) is substantially higher among renal transplant recipients (RTRs) than in the general population. With a growing RTR population, a robust method for monitoring skin cancer rates in this population is required. Methods A modeling approach was used to estimate the trends in NMSC rates that adjusted for changes in the RTR population (sex and age), calendar time, the duration of posttransplant follow-up, and background population NMSC incidence rates. RTR databases in both Northern Ireland (NI) and the Republic of Ireland (ROI) were linked to their respective cancer registries for diagnosis of NMSC, mainly squamous cell carcinoma (SCC) and basal cell carcinoma (BCC). Results RTRs in the ROI had three times the incidence (P<0.001) of NMSC compared with NI. There was a decline (P<0.001) in NMSC 10-year cumulative incidence rate in RTRs over the period 1994–2009, which was driven by reductions in both SCC and BCC incidence rates. Nevertheless, there was an increase in the incidence of NMSC with time since transplantation. The observed graft survival was higher in ROI than NI (P<0.05) from 1994–2004. The overall patient survival of RTRs was similar in NI and ROI. Conclusion Appropriate modeling of incidence trends in NMSC among RTRs is a valuable surveillance exercise for assessing the impact of change in clinical practices over time on the incidence rates of skin cancer in RTRs. It can form the basis of further research into unexplained regional variations in NMSC incidence.

β Cell Glucotoxic-Associated Single Nucleotide Polymorphisms in Impaired Glucose Tolerance and New-Onset Diabetes After Transplantation

Emerging paradigms of new-onset diabetes after transplantation (NODAT) have focused on pathways and risk factors (e.g., posttransplant hyperglycemia and immunosuppressive agents) to its pathogenesis with the aim of identifying those at risk and developing preventative strategies (1). Identification of potential NODATassociated single nucleotide polymorphisms (SNPs) has increased our knowledge base of these pathways (2, 3). In particular, a recent genome-wide association study of 26 NODAT patients (and 230 controls), with subsequent de novo SNP genotyping in 57 NODAT patients (and 383 controls), discovered eight SNPs associated with pancreatic A-cell apoptosis (4). This Belfast cohort was limited to white, nondiabetic adult recipients who had received a cadaveric renal transplant between 1986 and 2005. New-onset diabetes after transplantation was defined as a new requirement for oral hypoglycemics or insulin after transplantation until August 2012. However, evidence is now emerging to identify abnormal glucose metabolism post transplantation by means of biochemical analyses including the oral glucose tolerance test (OGTT) (5, 6). We sought to examine the association of the identified eight SNPs in an independent cohort using biochemical diagnoses of impairedglucosetolerance(IGT)andNODAT. From 2009 to 2012, 112 patients were prospectively followed up over a 12-month period in a single-center adult tertiary center. To exclude preexisting diabetes, patients underwent glucose testing (minimum 8 hr fasting) immediately before transplantation and excluded if 6.1 mmol/L or higher or HbA1c of 6.5% or higher. In addition, live donor recipients underwent OGTTs within a week of transplantation. Oral glucose tolerance tests were then performed at 7 days, and then 3 months and 12 months for all renal transplants if fasting glucose was less than 7.0 mmol/L, to confirm the presence or persistence of posttransplant hyperglycemia. Impaired glucose tolerance was diagnosed if 2-hr OGTT glucose was 7.8 to 11 mmol/L. New-onset diabetes after transplantation was diagnosed if fasting glucose was 7 mmol/L or higher or 2-hr OGTT was 11.1 mmol/L or higher from day 7 onward, or HbA1c was 6.5% or higher from 3 months onward. Exclusion criteria of pretransplant diabetes and non-white ethnicity resulted in 68 patients being tested for the eight candidate SNPs (rs10484821, rs11580170, rs1836882, rs198372, rs2020902, rs2861484, rs4394754, rs7533125); genotyping was performed using Sequenom iPLEX and Taqman technologies. Event analyses using binary logistic regression was used adjusting for age, sex, baseline body mass index (BMI), and change in BMI over 12 months from transplantation. All patients had a homogenous immunosuppression regimen over the 12 months consisting of CD25 monoclonal antibody induction and maintenance tacrolimus, mycophenolic acid, and prednisolone. The cohort was aged 45 years (T15), 2.81 (T1.41) human leukocyte antigen mismatch, were 59% men, and 73% live donor recipients. Either IGT or NODAT occurred in over half the study population, with median time of onset 7 days and 18 days, respectively, after transplantation (IGT, 18/68 patients; NODAT, 18/68 patients). Significant differences were seen in the BMI change over 12 months for those who developed IGT (P=0.007) and NODAT (P=0.002) compared to those who did not. The NODAT group were also significantly older compared to those without NODAT (54 vs. 41 years; P=0.002). One candidate SNP that was found to be associated with posttransplant hyperglycemia in both cohorts was rs198372 for gene NPPA. Rs198372 genotype GG (vs. non-GG) was protective for IGT-onset on univariate (P=0.015) and multivariate analysis (OR, 0.21 [0.05Y 0.88]; P=0.033) in the adjusted model. No other SNPs demonstrated statistical significance for association with NODAT or IGT, although the power to detect an effect size of 1.5 was on average 10.2% across the tested SNPs and therefore (as expected) the possibility of a type II error certainly exists. NPPA encodes natriuretic peptides that inhibit cytokine and leptin production that are associated with inflammation and insulin resistance in human adipose tissue. Indeed, the Birmingham cohort who developed IGT exhibited an average increase in BMI of 2.3 kg/m at 1 year after transplantation, consistent with leptin level or weight gain known association (7). Elevated leptin levels increase interleukin-1A promoting Acell apoptosis in pancreatic islets and free fatty acids inducing apoptosis by caspase activation (4). McCaughan et al. (4) reported a 9.6% NODAT incidence over 12 years follow-up (57 patients with a median onset of 100 months), whereas in Birmingham at only 12 months, over 25% (18 patients) developed IGT and the same number had NODAT. This may reflect differences between the cohorts (for instance, all patients in Birmingham received maintenance CNI therapy compared with 75% in Belfast). However, it also highlights the importance of the use of detailed OGTT data in unmasking posttransplant glucose abnormalities. Also, this in turn may influence the genotype-phenotype relationship. This study supports further replication of the initial Belfast findings in regard to rs198372 as a candidate SNP for identifying patients at risk for developing posttransplant hyperglycemia and a potential biochemical pathway for manipulation.

Posttransplant Lymphoproliferative Disorders in Irish Renal Transplant Recipients: Insights From a National Observational Study

Background Posttransplant lymphoproliferative disorders (PTLD) are a common malignancy after renal transplantation with a high incidence of PTLD described in the first posttransplant year. We sought to determine incidence and risk determinants of PTLD in Irish kidney transplant recipients. Methods Retrospective observational study of 1996 adult first kidney transplant recipients between 1991 and 2010 in the Republic of Ireland. Recipients were cross-referenced with the National Cancer Registry to determine incidence of PTLD. Kaplan-Meier analysis was performed for PTLD-free survival, allograft survival, and patient survival after PTLD. Cox proportional hazards models were used to identify independent risk factors for PTLD in our population. Results We identified 31 cases of PTLD during the study period. Histological subgroups included: early lesions (n = 1); polymorphic PTLD (n = 1); monomorphic PTLD (n = 27), Hodgkin disease (n = 2). Median time to PTLD diagnosis was 8.3 (range, 1.2-13.9) years. Cumulative incidence (95% CI) of PTLD at 1, 2, 3, 5, 10, and 15 years was 0%, 0.16% (0.05-0.5%), 0.21% (0.08-0.57%), 0.21% (0.08-0.57%), 1.76% (1.15-2.69%), and 3.07% (2.1-4.43%), respectively. Allograft survival after PTLD diagnosis was 94.4% (66.6-99.2%) at 5 years. Patient survival after PTLD diagnosis was 64% at 1 year, 53% at 2 years, 48% at 5 years, and 37% at 10 years. No risk factors for PTLD were identified. Conclusions We found a paucity of early onset PTLD in our cohort with no cases in the first posttransplant year. Potential contributing factors included a high prevalence of previous Epstein-Barr virus exposure and a relatively low immunological risk profile in our recipient cohort compared with prior studies. Further studies are required to reevaluate the epidemiology of PTLD in the modern era of transplant immunosuppression.

Electrostatic Potential Change in a Paired Epitope: A Novel Explanation for Bw4 Antibodies in Patients With B13 (Bw4) Antigens.

It is established that HLA antibodies are specific for epitopes as opposed to antigens. An epitope may be present on a small number of HLAmolecules, with shared epitopes now established as the basis for cross-reacting groups, or be widely expressed. The Bw4/6 epitopes are mutually exclusive “public epitopes” present on all HLA-B antigens with Bw4 also existing on a number of HLA-A molecules. The characterization of epitopes as 3 Å regions of polymorphic residues and in relation to their electrostatic potential (EP) has led to an improved definition of antibody reactivity. In addition, HLA antibodies have been described that require 2 sites for stable binding; these are thought to consist of a self-epitope and non–self-epitope on the antigen surface. In this model, it is possible that the non–self-epitope determines antibody specificity and that the self-epitope confers stability to the antigenantibody complex. We report 2 cases of individuals awaiting kidney transplantation who have HLA-B13 as their only Bw4 antigen and have developed HLA antibodies to all other Bw4 antigens present within the Luminex single antigen bead panel (Figure 1). The first patient is a 38-year-old man with HLA class I type A2, B13, B62, Bw4, Bw6, Cw6, Cw9 who received a kidney transplant mismatched at B27. After allograft failure, the patient demonstrated HLA antibodies to all Bw4 antigens with the exception of B13. The second patient, a 33-year-old woman, with HLA class I type A2, A11, B13, B62, Bw4, Bw6, Cw1, Cw6, was exposed to

Comprehensive Investigation of the Caveolin 2 Gene: Resequencing and Association for Kidney Transplant Outcomes

Caveolae are plasma membrane structures formed from a complex of the proteins caveolin-1 and caveolin-2. Caveolae interact with pro-inflammatory cytokines and are dysregulated in fibrotic disease. Although caveolae are present infrequently in healthy kidneys, they are abundant during kidney injury. An association has been identified between a CAV1 gene variant and long term kidney transplant survival. Chronic, gradual decline in transplant function is a persistent problem in kidney transplantation. The aetiology of this is diverse but fibrosis within the transplanted organ is the common end point. This study is the first to investigate the association of CAV2 gene variants with kidney transplant outcomes. Genomic DNA from donors and recipients of 575 kidney transplants performed in Belfast was investigated for common variation in CAV2 using a tag SNP approach. The CAV2 SNP rs13221869 was nominally significant for kidney transplant failure. Validation was sought in an independent group of kidney transplant donors and recipients from Dublin, Ireland using a second genotyping technology. Due to the unexpected absence of rs13221869 from this cohort, the CAV2 gene was resequenced. One novel SNP and a novel insertion/deletion in CAV2 were identified; rs13221869 is located in a repetitive region and was not a true variant in resequenced populations. CAV2 is a plausible candidate gene for association with kidney transplant outcomes given its proximity to CAV1 and its role in attenuating fibrosis. This study does not support an association between CAV2 variation and kidney transplant survival. Further analysis of CAV2 should be undertaken with an awareness of the sequence complexities and genetic variants highlighted by this study.

Estimated Glomerular Filtration Rate Decline as a Predictor of Dialysis in Kidney Transplant Recipients

Background: It is now common for individuals to require dialysis following the failure of a kidney transplant. Management of complications and preparation for dialysis are suboptimal in this group. To aid planning, it is desirable to estimate the time to dialysis requirement. The rate of decline in the estimated glomerular filtration rate (eGFR) may be used to this end. Methods: This study compared the rate of eGFR decline prior to dialysis commencement between individuals with failing transplants and transplant-naïve patients. The rate of eGFR decline was also compared between transplant recipients with and without graft failure. eGFR was calculated using the four-variable MDRD equation with rate of decline calculated by least squares linear regression. Results: The annual rate of eGFR decline in incident dialysis patients with graft failure exceeded that of the transplant-naïve incident dialysis patients. In the transplant cohort, the mean annual rate of eGFR decline prior to graft failure was 7.3 ml/min/1.73 m2 compared to 4.8 ml/min/1.73 m2 in the transplant-naïve group (p < 0.001) and 0.35 ml/min/1.73 m2 in recipients without graft failure (p < 0.001). Factors associated with eGFR decline were recipient age, decade of transplantation, HLA mismatch and histological evidence of chronic immunological injury. Conclusions: Individuals with graft failure have a rapid decline in eGFR prior to dialysis commencement. To improve outcomes, dialysis planning and management of chronic kidney disease complications should be initiated earlier than in the transplant-naïve population.