[Regulatory effect of curcumin on splenic inflammation in overtraining rats and its mechanism]

Objective: To study the alleviating effects of curcumin on splenic inflammation in overtraining rats by regulating toll-like receptor 4 (TLR4)-p38 mitogen-activated protein kinase (p38 MAPK)/nuclear factor-kappa B (NF-κB) signaling pathway. Methods: Male Wistar rats of 7-week old were divided into control group (C group, 12), overtraining model group (OM group, 11), curcumin + overtraining model group (COM group, 14). C Group did not undergo any exercise intervention. OM and COM group underwent 8-week incremental load swimming training. During the training, rats in the COM group were treated with 200 mg/ (kg·d) curcumin in the volume as 5 ml/kg, and the other groups were treated with an equal volume of 0.5 % sodium carboxymethylcellulose. 24 hours after the last training, the spleen index was calculated by weighing, the pathological changes of the spleen were observed by light microscopy, and the biochemical indicators of blood and spleen were detected. Results: After 8-week incremental load swimming training, the splenic structure in C group was normal under light microscope; the spleen index of OM group was significantly lower than that of C group (P＜0.01) and pathological changes of inflammation were obvious; the spleen index of COM group was significantly higher than that of OM group (P＜0.05) and pathological changes of inflammation were alleviated. Compared with C group, in OM group, the serum levels of corticosterone (Cor), NF-κB, tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6) and TLR4 expression rate on splenic monocytes surface, splenic TNF-α, IL-6 were increased (P＜0.05 or P＜0.01), the expressions of p38 MAPK, phosphorylated p38 mitogen-activated protein kinase (p-p38 MAPK) and NF-κB in spleen were increased (P＜0.05 or P＜ 0.01); serum testosterone (T), serum and splenic interleukin-10 (IL-10) were decreased (P＜0.01). Compared with OM group, in COM group, serum levels of Cor, NF-κB, TNF-α, IL-6 and TLR4 expression rate on splenic monocytes surface, splenic TNF-α, IL-6 were decreased (P＜0.05 or P＜0.01), the expressions of p38 MAPK, p-p38 MAPK and NF-κB in spleen were decreased (P＜ 0.05); serum T, serum and splenic IL-10 were increased (P＜0.05). The trend of T/Cor ratio between groups was consistent with testosterone change. Conclusion: The 8-week incremental load swimming training aggravated inflammation of spleen in rats, led to pathological inflammatory changes. Curcumin supplementation during training can down-regulate expressions of TLR4-p38 MAPK/NF-κB signaling pathway-related proteins, thereby maintaining a dynamic equilibrium between pro-inflammatory/anti-inflammatory cytokines, protecting the spleen.