9 The Potential for Mitochondrial Respiration and Circulating mtDNA Levels for Early Diagnosis of Sepsis in Burn Patients
Abstract Introduction Sepsis is a common consequence of burns associated with greater morbidity. While early treatment of sepsis in burn patients improves outcomes identifying sensitive biomarkers has proven difficult. In burns, sepsis often occurs in the absence of positive blood cultures, and associated inflammation precludes the use of inflammatory markers. We hypothesized that lymphocyte mitochondrial bioenergetics and/or circulating mtDNA (a Damage-Associated Molecular Pattern) may serve as novel sepsis biomarkers in burn patients. Methods Whole blood was obtained from adult patients (19–73 years of age) with 34–75% total body surface area burns admitted to the Burn Intensive Care Unit or healthy volunteers. Samples were categorized into one of three groups: 1) Healthy control, 2) Non-septic, or 3) Septic. The amount of mtDNA (NADH dehydrogenase 3 gene) was assessed by real-time PCR. Lymphocyte mitochondrial respiration was measured in a closed-chamber high-resolution respirometry Oxygraph-2k (Oroboros Instruments) with the addition of substrates to measure routine, leak, and maximum oxidative flux (MOF). Results Routine respiration was not different between non-septic and septic (27.0±30.0 and 27.2±10.8 pmol O2/mg/s) samples however, both were greater than healthy (13.1±5.00 pmol O2/mg/s; P≤0.05). Leak respiration was not different amongst groups. MOF (maximum capacity of the electron transport chain when not limited by ATP synthase/uncoupling) was different (P≤0.05) between populations with healthy (12.0±2.6 pmol O2/mg/s) having the lowest values, followed by septic (26.3±13.9 pmol O2/mg/s) and non-septic patients (34.7±23.1 pmol O2/mg/s). mtDNA levels were elevated in septic patients (70,061±65,975 copies/µL) when compared with non-septic and healthy patients (3,738±1,701 and 6,848±5,893 copies/µL, respectively; P=0.017). Levels of bacterial 16S DNA were not detected. Conclusions Taken together, increases in lymphocyte mitochondrial respiration may represent a compensatory response. Moreover, these data support the notion that mtDNA may trigger the onset of sepsis in burn patients in the absence of bacterial DNA. Investigating mitochondrial function/circulating DNA levels as they correlate with the onset/progression of sepsis in burn patients may beget useful biomarkers for early sepsis diagnosis. Applicability of Research to Practice Markers of mitochondrial function and damage in the burn patient may reveal powerful diagnostic targets to allow for interventions to stop sepsis before it occurs.