Endotracheal intubation results in acute tracheal damage induced by mtDNA/TLR9/NF-κB activity

Abstract

Tracheitis secondary to placement of an endotracheal tube (ETT) is characterized by neutrophil accumulation in the tracheal lumen, which is generally associated with epithelial damage. Mitochondrial DNA (mtDNA), has been implicated in systemic inflammation and organ dysfunction following trauma; however, less is known about the effects of a foreign body on local trauma and tissue damage. We hypothesized that tracheal damage secondary to the ETT will result in local release of mtDNA at sufficient levels to induce TLR9 and NF‐κB activation. In a swine model we compared the differences between uncoated, and chloroquine (CQ) and N‐acetylcysteine (NAC) coated ETTs as measured by tracheal lavage fluids (TLF) over a period of 6 h. The swine model allowed us to recreate human conditions. ETT presence was characterized by neutrophil activation, necrosis, and release of proinflammatory cytokines mediated by TLR9/NF‐κB induction. Amelioration of the tracheal damage was observed in the CQ and NAC coated ETT group as shown in tracheal tissue specimens and TLF. The role of TLR9/NF‐κB dependent activity was confirmed by HEK‐Blue hTLR9 reporter cell line analysis after coincubation with TLF specimens with predetermined concentrations of NAC or CQ alone or TLR9 inhibitory oligodeoxynucleotide (iODN). These findings indicate that therapeutic interventions aimed at preventing mtDNA/TLR9/NF‐κB activity may have benefits in prevention of acute tracheal damage.

The role of extracellular DNA in COVID-19: Clues from inflamm-aging

“…Its activity is mainly due to the lack of methylation at CpG sites, which triggers the activation of Toll-Like-Receptor-9 (TLR-9) receptors, mimicking bacterial DNA (Riley et al, 2020). MtDNA also engages cytoplasmic DNA detectors, such as Absent in Melanoma-2 (AIM2) and cGAS ( Bruno et al, 2020 ; Barnes et al, 2020 ; Dalpke et al, 2006 ; Bae et al, 2019 ; Itagaki et al, 2015 ; Puyo et al, 2019 ). Mitochondrial damage in the anti-viral response have been reported in a number of viral infections: such as Herpes simplex, hepatitis B, HIV, severe fever with thrombocytopenia syndrome, Dengue virus (a single-strand positive RNA virus) ( Lai et al, 2018 ; Saffran et al, 2007 ; Cao et al, 2020 ; Pinti et al, 2012 ; Li et al, 2020 ).…”

“…These latter are likely to preserve mtDNA stability and facilitate its systemic pro-inflammatory activity. Current data indicate that mtDNA levels increase and correlate with the extent of tissue damage, clinical evolution and the onset of multi-organ failure in patients affected by multiple systemic damage, sepsis and Acute Respiratory Distress Syndrome ( Itagaki et al, 2015 ; Puyo et al, 2019 ; Simmons et al, 2013 ; Nakahira et al, 2013 ). Notably, increased levels of circulating mtDNA have been found in elderly people even in absence of any overt systemic inflammation (Dalpke, A., et al, 2006; Pinti et al, 2014 ).…”

Myeloid cells in sensing of tissue damage

“…During tissue injury, mitochondrial DNA (mtDNA) is also released extracellularly as a pro-inflammatory DAMP [ 16 ] that is primarily recognized by the endosomal Toll-Like Receptor 9 (TLR9) upon phagocytosis by myeloid cells [ 17 ]. The relevance of extracellular mtDNA recognition by myeloid cells through TLR9 has been shown in pathologic conditions as diverse as Inflammatory Bowel Disease (IBD) [ 18 ], Systemic Inflammatory Response Syndrome (SIRS) [ 17 ] or tissue injury due to endotracheal intubation [ 19 ]. In addition, upon access of mtDNA to the cytosol, intracellular receptors such as STING [ 20 ] or the NLRP3 inflammasome [ 21 ] can also sense mtDNA.…”

<strong>How studies on inflamm-aging may help to understand and combat COVID-19 pandemic.</strong>

“…In this regard, the data indicate that the free telomeric DNA fragment can favorably switch off the mtDNA/TLR-9/NF-kappaB axis following ssRNA virus infection 19 . In addition, free telomeric DNA dampens the mtDNA/TLR-9/NF-kappaB axis in the respiratory system where the massive release of mtDNA following endotracheal intubation has been described 37 . Following these findings, the progressive loss of the telomeric anti-inflammatory reserve with aging is likely to be associated with the phenomenon of inflamm-aging 10, 12 .…”