Chaihu-shugan san inhibits inflammatory response to improve insulin signaling in liver and prefrontal cortex of CUMS rats with glucose intolerance

Depression is a mental illness comorbid risk factor for glucose intolerance worldwide. Chaihu-shugan san, a 'ShuGan' formula in traditional Chinese medicine, is clinically used in the treatment of depression. The aim of this study was to investigate whether Chaihu-shugan san improved glucose tolerance with its antidepressant activity in rat model of depression and explore the mechanisms underlying its action on liver-brain inflammation axis. After 6 weeks of chronic unpredictable mild stress (CUMS) procedure, male Wistar rats were given Chaihushugan san water extract (925 and 1850 mg/kg) by gavage for the next 6 consecutive weeks. Sucrose consumption test was used to assess animal depressive-like behaviors. Oral glucose tolerance test (OGTT) was employed to define the status of glucose tolerance in rats. Serum alanine aminotransferase (ALT) and interleukin-1 beta (IL-1 beta) were measured by commercial kits, respectively. Western blot was used to detect the expression of key proteins in inflammatory signaling cascades including toll-like receptor 4 (TLR4), myeloid differentiation protein 88 (MyD88), nuclear factor-kappa B (NF-kappa B), Nod-like receptor family pyrin domain containing 3 (NLRP3), apoptosis-associated speck-like protein containing CARD (ASC), cysteinyl aspartate specific proteinase-1 (Caspase-1) and IL-1 beta, as well as insulin signaling in liver and prefrontal cortex of rats. Immunohistochemical staining or immunofluorescence staining of NF-kappa B, and nuclear/cytoplasmic ratio of NF-kappa B by Western blot were used to describe its nuclear entry in liver and prefrontal cortex of rats. RT-qPCR and Western blot analysis, as well as microRNA-155 (miR-155) mimic or inhibitor transfection were used to explore possible association of MyD88 and miR-155. In this study, Chaihu-shugan san increased sucrose consumption and reduced serum glucose levels in CUMS rats, showing its antidepressant activity with glucose tolerance improvement. Chaihu-shugan san reduced serum levels of ALT and IL-1 beta in this animal model. Furthermore, this formula inhibited hepatic and prefrontal cortical inflammatory response by suppressing TLR4/MyD88/NF-kappa B pathway and NLRP3 inflammasome activation, and improved insulin signaling in CUMS rats. More importantly, Chaihu-shugan san up-regulated miR-155 expression in liver and prefrontal cortex of CUMS rats. These results provide direct evidence that Chaihushugan San can ameliorate depressive-like behaviors by inhibiting liverbrain inflammation axis.