Altered profiles of extracellular mitochondrial DNA in immunoparalyzed pediatric patients after thermal injury

Abstract

Abstract Background Thermal injury is a major cause of morbidity and mortality in the pediatric population world-wide with secondary infection being the most common acute complication. Suppression of innate and adaptive immune function is predictive of infection in pediatric burn patients, but little is known about the mechanisms causing these effects. Circulating mtDNA which induces a proinflammatory signal, has been described in multiple disease states, but has not been studied in pediatric burn injuries. This study examined the quantity of circulating mtDNA and mtDNA mutations in immunocompetent (IC) and immunoparalyzed (IP) pediatric burn patients. Methods Circulating DNA was isolated from plasma of pediatric burn patients treated at Nationwide Children’s Hospital Burn Center at early (1-3 days) and late (4-7 days) time points post-injury. These patients were categorized as IP or IC based on previously established immune function testing and secondary infection. Three mitochondrial genes, D loop, ND1, and ND4, were quantified by multiplexed qPCR to assess both mtDNA quantity and mutation load. Results At the early timepoint, there were no differences in plasma mtDNA quantity, however IC patients had a progressive increase in mtDNA over time when compared to IP patients (change in ND1 copy number over time 3880 vs 87 copies/day, p = 0.0004). Conversely, the IP group had an increase in mtDNA mutation burden over time. Conclusions IC patients experienced a significant increase in circulating mtDNA quantity over time, demonstrating an association between increased mtDNA release, and proinflammatory phenotype in the burn patients. IP patients had significant increases in mtDNA mutation load likely representative of degree of oxidative damage. Together, these data provide further insight into the inflammatory and immunological mechanisms following pediatric thermal injury.