Abstract: This study aimed to explore the protective effect of aplysin on ethanol-induced liver injury in rats and to explore the possible underlying mechanism from the perspective of the Toll-like receptor 4 (TLR4) signaling pathway. Male Wistar rats were randomly assigned into three groups: normal control, model control and aplysin-treated groups. The rats in the model control and aplysin-treated groups were given ethanol orally at 8 g/(kg·d) for two weeks, and then at 12 g/(kg·d) for another six weeks. The rats in the aplysin-treated group were administered with aplysin at 150 mg/(kg·d) via gavage one hour before ethanol for 8 weeks. After the last administration, all the animals were fasted with free access to water for 12 h and subsequently sacrificed; liver tissues were collected for histological and biochemical assessments; the levels of serum biomarkers for liver damage and endotoxin levels were detected with biochemical assay kits; primary rat Kupffer cells were cultured for assessment of their phagocytic activity with ink phagocytosis test. The mRNA expression levels of CD14, TLR4 and nuclear factor-kappa B (NF-κB) in Kupffer cells were assessed via reversed transcription polymerase chain reaction; the protein expression levels of TLR4, MyD88, NF-κB p65 and tumor necrosis factor-α (TNF-α) in Kupffer cells were assessed via western blotting; the levels of TNF-α and interleukin-1β (IL-1β) in Kupffer cells were measured by enzyme-linked immunosorbent assay. Aplysin relieved alcohol-induced hepatic histopathological changes, decreased plasma endotoxin levels and suppressed the elevation of liver damage biomarkers. Aplysin treatment effectively restored the phagocytic activity of Kupffer cells. Moreover, aplysin significantly decreased the expression levels of CD14, TLR4, MyD88, NF-κB p65 and TNF-α and the concentrations of TNF-α and IL-1β. These findings showed that aplysin exerted a potent hepatoprotective effect, which might be associated with the inhibition of the TLR4 signaling pathway.

Key words: aplysin, alcoholic liver disease, endotoxin, Toll-like receptor 4 signaling pathway, Kupffer cells