Mitochondrial DNA copy number is associated with mortality and infections in a large cohort of patients with chronic kidney disease

Damage of mitochondrial DNA (mtDNA) with reduction in copy number has been proposed as a biomarker for mitochondrial dysfunction and oxidative stress. Chronic kidney disease (CKD) is associated with increased mortality and risk of cardiovascular disease, but the underlying mechanisms remain incompletely understood. Here we investigated the prognostic role of mtDNA copy number for cause-specific mortality in 4812 patients from the German Chronic Kidney Disease study, an ongoing prospective observational national cohort study of patients with CKD stage G3 and A1-3 or G1-2 with overt proteinuria (A3) at enrollment. MtDNA was quantified in whole blood using a plasmid-normalized PCR-based assay. At baseline, 1235 patients had prevalent cardiovascular disease. These patients had a significantly lower mtDNA copy number than patients without cardiovascular disease (fully-adjusted model: odds ratio 1.03, 95% confidence interval [CI] 1.01-1.05 per 10 mtDNA copies decrease). After four years of follow-up, we observed a significant inverse association between mtDNA copy number and all-cause mortality, adjusted for kidney function and cardiovascular disease risk factors (hazard ratio 1.37, 95% CI 1.09-1.73 for quartile 1 compared to quartiles 2-4). When grouped by causes of death, estimates pointed in the same direction for all causes but in a fully-adjusted model decreased copy numbers were significantly lower only in infection-related death (hazard ratio 1.82, 95% CI 1.08-3.08). A similar association was observed for hospitalizations due to infections in 644 patients (hazard ratio 1.19, 95% CI 1.00-1.42 in the fully-adjusted model). Thus, our data support a role of mitochondrial dysfunction in increased cardiovascular disease and mortality risks as well as susceptibility to infections in patients with CKD

Association of relative telomere length with cardiovascular disease in a large chronic kidney disease cohort: the GCKD study

Background Chronic kidney disease (CKD) affects 10–15% of the general population and affected individuals are at an increased risk for cardiovascular disease (CVD). Since telomere length is considered to be involved in biological aging, we tested whether relative telomere length (RTL) might be a marker for these two diseases. Methods The German Chronic Kidney Disease (GCKD) study is an ongoing prospective cohort study including patients with CKD of moderate severity. RTL was measured by qPCR in 4955 out of 5217 GCKD patients at baseline. Results RTL was distributed in the cohort with a mean ± SD of 0.95 ± 0.19. CVD was present in 1266 patients. Each decrease of RTL by 0.1 unit was associated with a higher probability for prevalent CVD: OR = 1.06, 95% CI 1.02–1.11, p = 0.007 (adjusted for age, sex, eGFR, BMI, ln-CRP, smoking, hypertension, diabetes, and lipids). Similar findings were observed for history of specific CVD entities, such as coronary artery disease (OR = 1.05, p = 0.025), myocardial infarction (OR = 1.08, p = 0.013) and percutaneous transluminal coronary angioplasty (OR = 1.06, p = 0.032). The strongest associations were found for interventions at the carotid arteries (OR = 1.25, p = 0.001) as well as aortic aneurysms (OR = 1.22, p = 0.001). Conclusions In the presence of CKD there is a significant association between shorter RTL and CVD manifestations. RTL appears to be a marker reflecting changes in homeostasis associated with CKD that may contribute to the excess CVD risk

Do telomeres have a higher plasticity than thought? Results from the German Chronic Kidney Disease (GCKD) study as a high-risk population

Telomere length is considered as a biological marker for aging. It is expected that telomeres shorten with age and with conditions associated with oxidative stress and inflammation. Both are present in patients with chronic kidney disease (CKD) who have a very high cardiovascular risk. We investigated whether CKD duration is associated with relative telomere length (RTL) in 4802 patients from the German Chronic Kidney Disease (GCKD) study. We measured RTL in each sample in quadruplicates using a quantitative polymerase chain reaction (qPCR). We observed a U-shaped association of RTL with CKD duration: the longest RTL was found in those 339 patients who reported the shortest disease duration (< 6 months) and shorter RTL in 2108 patients with duration between 6 months and less than 5 years. Most importantly, those 2331 patients who reported a CKD duration of 5 years and more had significantly longer RTL compared to those with intermediate CKD duration (6 months to less than 5 years): mean 0.954, 95%CI 0.946–0.961 versus 0.937, 95%CI 0.929–0.944, p = 0.002). Due to the cross-sectional nature of the study these surprising results have to be considered with caution and as hypothesis-generating. Whether the longer RTL in patients with long-lasting disease is caused by an activation of telomerase to counteract the shortening of RTL due to oxidative stress and inflammation or whether they are caused by a survival bias needs to be investigated in longitudinal studies. Our data are in support of a higher plasticity of shortening and elongations of RTL as until recently anticipated

Frequent LPA KIV-2 Variants Lower Lipoprotein(a) Concentrations and Protect Against Coronary Artery Disease

Background: Lipoprotein(a) (Lp(a)) concentrations are a major independent risk factor for coronary artery disease (CAD) and are mainly determined by variation in LPA. Up to 70% of the LPA coding sequence is located in the hypervariable kringle IV type 2 (KIV-2) region. It is hardly accessible by conventional technologies, but may contain functional variants. Objectives: This study sought to investigate the new, very frequent splicing variant KIV-2 4733G>A on Lp(a) and CAD. Methods: We genotyped 4733G>A in the GCKD (German Chronic Kidney Disease) study (n = 4,673) by allele-specific polymerase chain reaction, performed minigene assays, identified proxy single nucleotide polymorphisms and used them to characterize its effect on CAD by survival analysis in UK Biobank (n = 440,234). Frequencies in ethnic groups were assessed in the 1000 Genomes Project. Results: The 4733G>A variant (38.2% carrier frequency) was found in most isoform sizes. It reduces allelic expression without abolishing protein production, lowers Lp(a) by 13.6 mg/dL (95% CI: 12.5-14.7; P A and 4925G>A, another KIV-2 splicing mutation, reduces Lp(a) by 31.8 mg/dL and most importantly narrows the interquartile range by 9-fold (from 42.1 to 4.6 mg/dL) when compared to the wild type. In UK Biobank 4733G>A alone and compound heterozygosity with 4925G>A reduced HR for CAD by 9% (95% CI: 7%-11%) and 12% (95% CI: 7%-16%) (both P < 0.001). Frequencies in ethnicities differ notably. Conclusions: Functional variants in the previously inaccessible LPA KIV-2 region cooperate in determining Lp(a) variance and CAD risk. Even a moderate but lifelong genetic Lp(a) reduction translates to a noticeable CAD risk reduction

Genetic determinants of the ankle-brachial index:a meta-analysis of a cardiovascular candidate gene 50K SNP panel in the candidate gene association resource (CARe) consortium

Background: Candidate gene association studies for peripheral artery disease (PAD), including subclinical disease assessed with the ankle-brachial index (ABI), have been limited by the modest number of genes examined. We conducted a two stage meta-analysis of similar to 50,000 SNPs across similar to 2100 candidate genes to identify genetic variants for ABI. Methods and results: We studied subjects of European ancestry from 8 studies (n = 21,547, 55% women, mean age 44-73 years) and African American ancestry from 5 studies (n = 7267, 60% women, mean age 41-73 years) involved in the candidate gene association resource (CARe) consortium. In each ethnic group, additive genetic models were used (with each additional copy of the minor allele corresponding to the given beta) to test each SNP for association with continuous ABI (excluding ABI > 1.40) and PAD (defined as ABI <0.90) using linear or logistic regression with adjustment for known PAD risk factors and population stratification. We then conducted a fixed-effects inverse-variance weighted meta-analyses considering a p <2 x 10(-6) to denote statistical significance. Results: In the European ancestry discovery meta-analyses, rs2171209 in SYTL3 (beta = -0.007, p = 6.02 x 10(-7)) and rs290481 in TCF7L2 (beta = -0.008, p = 7.01 x 10(-7)) were significantly associated with ABI. None of the SNP associations for PAD were significant, though a SNP in CYP2B6 (p = 4.99 x 10(-5)) was among the strongest associations. These 3 genes are linked to key PAD risk factors (lipoprotein(a), type 2 diabetes, and smoking behavior, respectively). We sought replication in 6 population-based and 3 clinical samples (n = 15,440) for rs290481 and rs2171209. However, in the replication stage (rs2171209, p = 0.75; rs290481, p = 0.19) and in the combined discovery and replication analysis the SNP-ABI associations were no longer significant (rs2171209, p = 1.14 x 10(-3); rs290481, p = 8.88 x 10(-5)). In African Americans, none of the SNP associations for ABI or PAD achieved an experiment-wide level of significance. Conclusions: Genetic determinants of ABI and PAD remain elusive. Follow-up of these preliminary findings may uncover important biology given the known gene-risk factor associations. New and more powerful approaches to PAD gene discovery are warranted. (C) 2012 Elsevier Ireland Ltd. All rights reserved