Selenomethionine attenuates heat stress-associated inflammatory responses and apoptosis in porcine alveolar macrophages.

Heat stress disrupts immune homeostasis, but how thermal exposure alters macrophage inflammatory responsiveness remains unclear. Here, we investigated whether thermal exposure enhances LPS-associated inflammatory responses in porcine alveolar macrophages and whether selenomethionine (SeMet) confers protection. Porcine alveolar macrophage 3D4/21 cells were exposed to 41 °C for 24 h before lipopolysaccharide (LPS) stimulation, or to 41 °C for 36 h without LPS. Thermal exposure markedly enhanced LPS-induced IL-1β, IL-6, and IL-8 transcription, and NF-κB p65 nuclear translocation during LPS stimulation. Cellular redox homeostasis was disrupted, as shown by reduced total antioxidant capacity, superoxide dismutase, and glutathione peroxidase activities, together with increased malondialdehyde and reactive oxygen species (ROS). Prolonged heat exposure independently induced apoptosis-associated changes, including increased Annexin V positivity, a reduced Bcl-2/Bax ratio, and caspase-3 activation. Pharmacological ROS scavenging with N-acetyl-L-cysteine (NAC) suppressed heat-enhanced cytokine transcription and apoptosis, whereas exogenous H₂O₂ exacerbated both responses, supporting a functional contribution of cellular redox imbalance to both phenotypes. SeMet improved redox indices, reduced p65 nuclear accumulation during LPS stimulation, and attenuated inflammatory transcription and apoptosis-associated changes. Furthermore, pharmacological inhibition of IKK/NF-κB signaling with BMS-345,541 significantly reduced LPS-induced IL-1β, IL-6, and IL-8 expression under both normothermic and heat conditions, further supporting the involvement of NF-κB signaling in heat stress-associated inflammatory responses. These findings indicate that heat-associated macrophage dysfunction is accompanied by redox imbalance, enhanced NF-κB activation during LPS stimulation, and apoptosis under prolonged thermal exposure. The relative contribution of NF-κB compared with other redox-sensitive pathways remains to be further defined.