Differential effects of flunixin meglumine and meloxicam on TNF- α production in LPS-stimulated equine neutrophils in vitro

Systemic inflammatory response syndrome (SIRS) induced by endotoxemia is usually secondary to colitis and is a major cause of high morbidity and mortality in horses. Non-steroidal anti-inflammatory drugs (NSAIDs), such as flunixin meglumine (FM) and meloxicam (MX), are used to improve clinical outcomes in SIRS/endotoxemia. These NSAIDs suppress tumor necrosis factor-alpha (TNF-α) levels; however, the underlying mechanisms remain unclear. The aim of this study was to investigate the inhibitory effects of FM and MX on TNF-α in lipopolysaccharide (LPS)-stimulated peripheral blood mononuclear cells (PBMCs) and neutrophils <i>in vitro</i>. Blood samples were collected from three healthy thoroughbred horses, and PBMCs and neutrophils were isolated using density gradient centrifugation. Cells were cultured with LPS (0.3 ng/mL) and FM or MX (5, 10, or 50 μM). TNF-α gene expression was analyzed using quantitative real-time PCR, and protein levels were measured using ELISA. No significant inhibitory effects of FM or MX on TNF-α gene or protein expression were observed in LPS-stimulated PBMCs. However, FM significantly inhibited the increase in TNF-α protein levels in LPS-stimulated neutrophils in a concentration-dependent manner (<i>p</i> < 0.05). MX showed a similar tendency in LPS-stimulated neutrophils, but the differences were not significant. The regulation of neutrophil-derived TNF-α by FM administration could be a promising therapeutic strategy for equine SIRS/endotoxemia, providing mechanistic insight for optimizing anti-inflammatory therapy.