摘要：

SUMMARYKetamine has been reported to reduce lipopolysaccharide (LPS)-induced tumour necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6) production in an equine macrophage cell line (e-CAS cells) by directly inhibiting nuclear factor-kappa B (NF-κB) expression.1 NF-κB is a key regulatory transcription factor associated with the expression of various pro-inflammatory mediators, including cytokines and inducible enzymes like cyclooxygenase-2 (COX-2). Prostaglandin E2 (PGE2), the main product of COX-2, significantly contributes to the clinical symptoms of inflammation. Hence, COX-2 inhibitors such as the non-steroidal anti- inflammatory drugs (NSAIDs) are commonly used to reduce PGE2 production. Considering the effect of ketamine on LPS-induced NF-κB expression, it was hypothesised that ketamine might have also an effect on LPS-induced COX-2 expression.To this end, we studied the effect of ketamine (0-1000 μM) on LPS-induced (1 μg/ml) COX-2 expression and PGE2 production in e-CAS cells. Furthermore, the intracellular signalling molecules, c-Jun N-terminal kinase (JNK), mitogen- activated protein kinase p38 (p38), extracellular signal-regulated kinase (ERK), and NF-κB were selectively inhibited, to elucidate the molecular mechanism underlying LPS-induced COX-2 expression and subsequent PGE2 production in e- CAS cells. For comparison RAW 264.7 cells were used.In LPS-treated e-CAS cells, ketamine did not affect COX-2 expression at any of the concentrations tested. Ketamine significantly reduced LPS-induced PGE2 production only at the highest ketamine concentration (1000 μM) investigated. The inhibition experiments suggest that COX-2 expression and the subsequent PGE2 production are mainly regulated at the level of JNK, p38 and ERK in the e-CAS cell model and that activated NF-κB does not significantly contribute to COX-2 induction in e-CAS cells. In previous experiments with e-CAS cells, ketamine was found to inhibit the LPS-induced signalling pathways only at the level of NF-κB,1 which is in line with the finding that ketamine does not inhibit COX-2 expression in LPS-treated e-CAS cells. Hence, despite its potency to reduce LPS-induced TNF- α and IL-6 production, the role of ketamine in COX-2 and PGE2 associated equine inflammatory disorders might be limited.

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