Melatonin attenuated brain death tissue extract-induced cardiac damage by suppressing DAMP signaling

We tested the hypothesis that melatonin prevents brain death (BD) tissue extract (BDEX)-induced cardiac damage by suppressing inflammatory damage-associated molecular pattern (DAMP) signaling in rats. Six hours after BD induction, levels of a DAMP component (HMGB1) and inflammatory markers (TLR-2, TLR-4, MYD88, IκB, NF-κB, IL-1β, IFN-γ, TNF-α and IL-6) were higher in brain tissue from BD animals than controls. Levels of HMGB1 and inflammatory markers were higher in BDEX-treated H9C2 cardiac myoblasts than in cells treated with healthy brain tissue extract. These increases were attenuated by melatonin but re-induced with luzindole (all P < 0.001). Additional male rats (n = 30) were divided into groups 1 (negative control), 2 (healthy brain tissue extract implanted in the left ventricular myocardium [LVM]), 3 (BDEX-LVM), 4 (BDEX-LVM + melatonin), and 5 (BDEX-LVM + melatonin + luzindole). Collagen deposition/fibrosis and LVM levels of MTR2, HMGB1, inflammatory markers, oxidative stress, apoptosis, mitochondrial damage and DNA damage were highest in group 3, lowest in groups 1 and 2, and higher in group 5 than in group 4. Heart function and LVM levels of MTR1 and anti-inflammatory, mitochondrial-integrity and anti-oxidative markers exhibited a pattern opposite that of the inflammatory markers in the five groups (all P < 0.0001). These results indicate melatonin inhibits BDEX-induced cardiac damage by suppressing the DAMP inflammatory axis.