Sophocarpine attenuates toll-like receptor 4 in steatotic hepatocytes to suppress pro-inflammatory cytokines synthesis.

Sophocarpine, a tetracyclic quinolizidine alkaloid derived from Sophora alopecuroides L., has been documented that it can suppress pro-inflammatory cytokines synthesis in alleviating nonalcoholic steatohepatitis (NASH) in vivo. Toll-like receptor 4 (TLR4) is a pattern recognition receptor whose activation results in the production of several pro-inflammatory cytokines. It has been reported that TLR4 is upregulated in nonalcoholic fatty liver disease and plays an important role in the pathogenesis of NASH. This study aimed to examine the changes of TLR4 and its signaling pathways in sophocarpine's anti-inflammatory process on experimental NASH in vitro. Primary hepatocytes were isolated, and oleic acid-induced steatosis model was established. Cell Counting Kit-8 assay was used to detect the number of metabolically active mitochondria and viable cells. Immunocytochemistry analysis was applied to evaluating pro-inflammatory cytokines synthesis. Total RNA and protein were extracted for real-time polymerase chain reaction and Western blot detection. Enhanced expression of TLR4 was observed in oleic acid-induced steatotic hepatocytes. Sophocarpine suppressed pro-inflammatory cytokines synthesis and reduced the expression of TLR4 in steatotic hepatocytes. Expression of TLR4 and pro-inflammatory cytokines recovered after sophocarpine was removed. Moreover, sophocarpine restrained the activation of nuclear factor-kappaB (NF-κB), c-Jun-N-terminal kinase (JNK), and Extracellular regulated protein kinases (ERK) signaling pathways in the anti-inflammatory process. Sophocarpine could decrease the expression of TLR4 in steatotic hepatocytes and suppress pro-inflammatory cytokines synthesis. NF-κB, JNK, and ERK signaling pathways were important workable downstream pathways.