Mechanism of moxibustion in treating chronic inflammatory visceral pain: regulation of the p38 MAPK/ELK1 signaling pathway in the spinal cord

Objective: To investigate the central mechanism of moxibustion in treating chronic inflammatory visceral pain (CIVP) and its analgesic effect from the perspective of the p38 mitogen-activated protein kinase (MAPK)/Ets-like transcription factor 1 (ELK1) signaling pathway in the spinal cord. Methods: Clean-grade male Sprague-Dawley rats were randomly divided into a normal group, a model group, a herb-partitioned moxibustion (HPM) group, a sham-HPM group, a p38 MAPK inhibitor group, and a dimethyl sulfoxide (DMSO) group. CIVP rat models were prepared using an enema mixture of 2,4,6-trinitrobenzene sulfonic acid solution and 50% ethanol. The HPM group was treated with HPM; the sham-HPM group was treated the same as the HPM group, but the moxa cones were not ignited; rats in the p38 MAPK inhibitor group received L-5-L-6 intrathecal injection of p38 MAPK inhibitor (SB203580); rats in the DMSO group received L-5-L-6 intrathecal injection of 2% DMSO. Abdominal withdrawal reflex (AWR), mechanical withdrawal threshold (MWT), and thermal withdrawal latency (TWL) were used to observe pain-related behaviors in each group. Hematoxylin-eosin staining was used to observe the morphological changes in rat colon tissue. Western blotting and real-time quantitative reverse-transcription polymerase chain reaction were used to detect the phosphorylated protein and mRNA expression of apoptosis signal-regulating kinase 1 (ASK1), MAPK kinase (MKK) 3/6, p38 MAPK, ELK1, and mitogen and stress-activated protein kinase 1 (MSK1) in the spinal cord. ResultsCompared with the normal group, CIVP rats had severe colonic inflammatory injuries, and the pathological injury scores increased significantly, along with increased AWR scores under different colorectal distension (CRD) stimulation pressures and decreased MWT and TWL; the mRNA and phosphorylated protein expression of p38 MAPK, ELK1, MSK1, ASK1, MKK3, and MKK6 all increased in the spinal cord (P<0.01). After HPM treatment, the colon injuries were repaired, and the pathological injury scores decreased; under different CRD stimulation pressures, the AWR scores decreased, and the MWT and TWL increased; the mRNA and phosphorylated protein expression of p38 MAPK, ELK1, ASK1, and MKK3 in the spinal cord also decreased, with statistically significant differences compared with the model group and the sham-HPM group (P<0.01). There were no significant differences in the above indicators between the HPM group and the p38 MAPK inhibitor group (P>0.05), and the same was true regarding the comparisons between the model group and the DMSO group. ConclusionHPM exerted analgesic effects via downregulating the mRNA and phosphorylated protein expression of ASK1, MKK3, p38 MAPK, and ELK1 in the spinal cord of CIVP rats. The inhibition of spinal p38 MAPK/ELK1 signaling pathway activation may be one of the mechanisms by which HPM relieves pain in CIVP.