Rhinacanthin-C, A Fat-Soluble Extract from Rhinacanthus nasutus, Modulates High-Mobility Group Box 1-Related Neuro-Inflammation and Subarachnoid Hemorrhage-Induced Brain Apoptosis in a Rat Model

Abstract

High-mobility group box 1 (HMGB1) was shown to be a major extracellular mediator involved in relayed neuro-inflammation in animals after subarachnoid hemorrhage (SAH). It is of interest to examine the effect of rhinacanthin-C (RCT-C, C25H30O5) on pro-inflammatory cytokines/HMGB1 in an SAH-related early brain injury model. A rodent double SAH model was used. RCT-C was administered orally at 100, 200, and 400 μmol/kg/day. Cerebral spinal fluid samples were obtained to assess interleukin (IL)-1β, IL-6, IL-8, and tumor necrosis factor α using a real-time polymerase chain reaction. Basilar arteries were harvested and cerebral cortex was examined for HMGB1 mRNA and protein expression (western blot) and caspases (real-time polymerase chain reaction). An intrathecal injection of 1 ng of HMGB-1 recombinant protein was given in the 400 μmol/kg/day RCT-C plus SAH groups. The levels of IL-1β, IL-6, and tumor necrosis factor α mRNA were significantly increased in animals subject to SAH, compared with the healthy controls, but were absent in the RCT-C groups. Cleaved caspase-9a as well as HMGB-1 mRNA and protein were significantly reduced in the 400 μmol/kg/day RCT-C treatment groups. Similarly, administration of RCT-C reduced HMGB-1 mRNA and protein expression (P <0.01). RCT-C exerts a neuroprotective effect by reducing cleaved caspase-3- and caspase-9a-related apoptosis. Decreased HMGB-1 mRNA and protein expression in the RCT-C groups corresponds to its anti-inflammatory effect. HMGB-1 recombinant protein administration impaired the neuroprotective and immunosuppressive effect of RCT-C. This finding lends credence that RCT-C modulates the HMGB-1-related pathway and attenuates brain apoptosis in the pathogenesis of SAH.