Capsaicin attenuates sepsis‑associated encephalopathy by inhibiting neuroinflammation and apoptosis whilst activating mitophagy through the BNIP3/NIX pathway.

Abstract

Sepsis‑induced abnormalities in brain function or sepsis‑associated encephalopathy (SAE) can manifest as cognitive dysfunction and other neuropsychiatric symptoms; however, the underlying mechanisms remain unclear. The aim of the present study was to elucidate the possible effects and mechanism of capsaicin, a transient receptor potential vanilloid 1 (TRPV1) agonist, on the pathological features of SAE. A model of SAE in C57BL/6 mice was generated using cecal ligation and puncture (CLP). Capsaicin (1 mg/kg) was injected subcutaneously before surgery. Cognitive function in mice was evaluated using the novel object recognition test (NORT) and Morris water maze (MWM). Immunofluorescence staining, ELISA, western blotting and transmission electron microscopy were performed to detect the degree of microglial activation (ionized calcium‑binding adapter molecule 1), proinflammatory cytokine levels (TNF‑α), autophagy and apoptosis‑related protein expression, and autophagosomes. Autophagic flux was monitored using the LC3‑GFP‑mCherry fluorescent reporter. Compared with that in the sham group mice, the expression levels of TRPV1 were significantly reduced in the hippocampal tissue of mice with sepsis. Mice with sepsis also exhibited cognitive dysfunction. Notably, a single administration of capsaicin reduced the mortality rate, but did not improve cognitive function in mice with sepsis. Furthermore, repeated administration of capsaicin was revealed to enhance the recognition index of novel objects among mice with sepsis, to reduce the latency to locate the platform and to augment the duration of mouse platform quadrant movements, according to the NORT and MWM tasks. Increased microglial activation, release of proinflammatory cytokines and expression levels of apoptosis‑related proteins were all observed in mice with CLP‑induced sepsis, as was brain tissue destruction in the hippocampal regions. By contrast, capsaicin treatment ameliorated CLP‑induced microglial activation, inflammation, neuronal apoptosis (cleaved caspase 3 expression increased) and brain tissue destruction. Furthermore, application of capsaicin increased the expression levels of LC3, reduced the expression of p62 and elevated autophagic flux compared with those in the CLP group. Finally, treatment with capsaicin effectively enhanced the levels of Bcl‑2‑interacting protein 3 (BNIP3) and BNIP3‑like (NIX) expression. These findings suggested that capsaicin may be considered a potential drug for the treatment of SAE, and BNIP3/NIX‑mediated mitophagy may be involved in this process.