Excessive exposure to
manganese (Mn) may lead to neurotoxicity, referred to as manganism. In several studies,
sodium para-aminosalicylic acid (PAS-Na) has shown efficacy against Mn-induced neurodegeneration by attenuating the neuroinflammatory response. The present study investigated the effect of Mn on
inflammation and apoptosis in the rat thalamus, as well as the underlying mechanism of the PAS-Na protective effect. The study consisted of sub-acute (Mn treatment for 4 weeks) and sub-chronic (Mn and PAS-Na treatment for 8 weeks) experiments. In the sub-chronic experiments, pro-inflammatory
cytokines, namely
tumor necrosis factor α (TNF-α),
interleukin 1β (IL-1β), and
cyclooxygenase 2 (COX-2) were significantly increased in the Mn-exposed group compared to the control II. PAS-Na treatment led to a significant reduction in the Mn-induced
neuroinflammation by inhibiting IL-1β and COX-2
mRNA expression and reducing IL-1β secretion and JNK/
p38 MAPK pathway activity. Furthermore, immunohistochemical analysis showed that the expression of
caspase-3 was significantly increased in both the sub-acute and sub-chronic experimental paradigms concomitant with a significant decrease in
B-cell lymphoma 2 (Bcl-2) in the thalamus of Mn-treated rats. PAS-Na also decreased the expression levels of several apoptotic markers downstream of the MAPK pathway, including Bcl-2/Bax and
caspase-3, while up-regulating anti-apoptotic Bcl-2
proteins. In conclusion, Mn exposure led to
inflammation in the rat thalamus concomitant with apoptosis, which was mediated via the MAPK signaling pathway. PAS-Na treatment antagonized effectively Mn-induced neurotoxicity by inhibiting the MAPK activity in the same brain region.