Plasma Bacterial and Mitochondrial DNA Distinguish Bacterial Sepsis From Sterile Systemic Inflammatory Response Syndrome and Quantify Inflammatory Tissue Injury in Nonhuman Primates

Abstract

Systemic inflammatory response syndrome (SIRS) is a fundamental host response common to bacterial infection and sterile tissue injury. SIRS can cause organ dysfunction and death but its mechanisms are incompletely understood. Moreover, SIRS can progress to organ failure or death despite being sterile or after control of the inciting infection. Biomarkers discriminating between sepsis, sterile SIRS and post-infective SIRS would therefore help direct care. Circulating mitochondrial DNA (mtDNA) is a damage-associated molecular pattern (DAMP) reflecting cellular injury. Circulating bacterial 16S-DNA (bDNA) is a pathogen-associated pattern (PAMP) reflecting ongoing infection. We developed qPCR assays to quantify these markers and predicted their plasma levels might help distinguish sterile injury from infection. To study these events in primates we assayed banked serum from papio baboons that had undergone a brief challenge of intravenous Bacillus anthracis deltaSterne (modified to remove toxins) followed by antibiotics (anthrax) that causes organ failure and death. To investigate the progression of sepsis to “severe” sepsis and death we studied animals where anthrax was pretreated with drotrecogin alfa (aPC), which attenuates sepsis in baboons. We also contrasted lethal anthrax bacteremia against non-lethal E.coli bacteremia and against sterile tissue injury from Shiga-like toxin-1 (Stx1). bDNA and mtDNA levels in timed samples were correlated with blood culture results and assays of organ function. Sterile injury by Stx1 increased mtDNA but bDNA was undetectable: consistent with the absence of infection. The bacterial challenges caused parallel early bDNA and mtDNA increases, but bDNA detected pathogens even after bacteria were undetectable by culture. Sub-lethal E.coli challenge only caused transient rises in mtDNA consistent with a self-limited injury. In lethal anthrax challenge (n=4) bDNA increased transiently but mtDNA levels remained elevated until death, consistent with persistent septic tissue damage after bacterial clearance. Critically, aPC pre-treatment (n=4) allowed mtDNA levels to decay after bacterial clearance with sparing of organ function and survival. In summary, host tissue injury correlates with mtDNA whether infective or sterile. mtDNA and bDNA PCRs can quantify tissue injury incurred by septic or sterile mechanisms and suggest the source of SIRS of unknown origin.

Impact of Intravenous Ascorbic Acid Infusion on Novel Biomarkers in Patients with Severe Sepsis

“…These mediators activate neutrophils in circulation promoting non-specific organ attack and suppressing chemotactic responses to infective stimuli [29]. Recent evidence further suggests that in response to stimuli such as trauma [32] and microbial infection [33] cellular mtDNA levels decrease while circulating cell-free mtDNA levels are increased [34]. To that effect, Nakahira et al showed that mtDNA could serve as a viable plasma biomarker in medical ICU patients and that increased circulating mtDNA was associated with mortality [35].…”

The Roles of Mitochondrial Damage-Associated Molecular Patterns in Diseases

“…For example, while the elevation of ATP in BALF is observed in patients with IPF (129) or asthma (65), the elevated levels of ATP are also observed in BALF from the experimental mice models of fibrosis (129) or bronchial hypersensitivity (65). Similarly, the levels of circulating cell-free mtDNA are elevated in patients with trauma (167,179) or sepsis (82,167) and also observed in animal models of trauma/hemorrhagic shock (178) or bacterial sepsis (155). In addition, the exogenous administration of mitochondrial DAMPs is able to develop the similar pathological conditions with human diseases in animals.…”

“…DAMPs, damage-associated molecular patterns; FPR, formyl peptide receptor; TLR, toll-like receptor. To see this illustration in color, the reader is referred to the web version of this article at www.liebertpub.com/ars (155). Serum: Acetaminophen-induced acute liver injury in mice (97).…”

“…Intra-articular injection of mtDNA induces arthritis in mice (25). Activated protein C treatment reduces plasma level of mtDNA and lethality in response to Bacillus anthracis-induced sepsis in baboons (155).…”

Trial of Short-Course Antimicrobial Therapy for Intraabdominal Infection

“…More recent experimental data, however, suggest that a prolonged SIRS may be more a reflection of host immune activity than an indication of the presence of viable microorganisms. [13][14][15] As such, efforts have begun to shorten the duration of antimicrobial therapy in the presence of traditional markers of sepsis. These efforts have already been successful in other severe infections such as ventilator-associated pneumonia.…”