Abstract 271: Mitochondrial DNA Copy Number in Peripheral Blood Cells is Associated With All -Cause Mortality in Older Cardiovascular Patients

Abstract

Background: Mitochondrial DNA copy number (Mt CN) is a surrogate marker of mitochondrial function. Variations in Mt CN have been associated with several age-related diseases. Lower Mt CN may indicate impaired cellular energy production whereas higher Mt CN may compensate for energy disbalance but also may lead to cellular damage through oxidative stress. This study evaluated the association of Mt CN and all-cause mortality in older cardiovascular patients (Pt). Methods: The study was approved by the Intermountain Healthcare Institutional Review Board. Consenting subjects (n=2,253) were participants in the INSPIRE registry undergoing cardiac catheterization at the Intermountain Heart Institute. Total DNA was extracted from EDTA stabilized blood with either Puregene (Qiagen) or Reliaprep (Promega) reagents. Relative Mt CN measurements were performed with multiplexed real-time polymerase chain reaction coamplifying a stable site of Mt D- Loop and a region of a single copy nuclear β-2-microglobulin gene(β2M) and calculated as a ratio of Mt to β2M DNA. Cox regression was used to evaluate the association of Mt CN with all-cause mortality, with adjustment considering 32 covariables. Further adjustment entered the Intermountain Risk Score (IMRS), a validated mortality risk predictor. Results: Mean Pt age was age 62.3±13.8 yrs.; 65.2% were male; 1,122 (50%) died during 25.4 years of follow-up. Mt CN was lower for males (539±449 vs 654 ± 1053 for females; p=0.004). Mt CN was 616±917 in decedents and 542±438 in survivors (p=0.014). In univariable Cox regression, Quartile 1 versus Quartile 4 of Mt CN was associated with the highest mortality risk (hazard ratio [HR]=1.45, CI=1.22, 1.71, p<0.001). This association remained significant after multivariable adjustment (HR=1.30, CI=1.10, 1.54, p=0.003). There was minimal correlation between IMRS and Mt CN continuous values (r= -0.09 for males, r= -0.13 for females). In Cox regression, adjustment for IMRS and covariables showed Mt CN remained associated with mortality (HR=1.30, CI=1.08, 1.57, p=0.006). Conclusions: Low Mt CN is independently associated with higher risk of all-cause mortality. Further studies validating this finding and examining potential underlying physiologic protective mechanisms may prove to be of therapeutic and prognostic value.