Anti-Inflammatory Mechanisms of <i>Pleurotus citrinopileatus</i>: Inhibition of MAPK and NF-κB Signaling Pathways, and Activation of ROS/PI3K/Nrf2/HO-1 Signaling Pathway in LPS-Stimulated RAW264.7 Cells

This study explores the anti-inflammatory potential of <i>Pleurotus citrinopileatus</i> by examining its impact on inflammation-related signaling pathways in lipopolysaccharide (LPS)-stimulated RAW264.7 macrophages. Fractions obtained using hexane (HE), dichloromethane (DCM), and ethyl acetate (EA) were found to suppress LPS-induced nitric oxide (NO) production and the expression of inducible nitric oxide synthase (iNOS). Additionally, these fractions inhibited the phosphorylation of key mitogen-activated protein kinases (MAPKs), including extracellular signal-regulated kinases 1/2 (ERK1/2), p38, and c-Jun N-terminal kinase (JNK), as well as the nuclear factor kappa B (NF-κB) subunit p65. The HE, DCM, and EA fractions also promoted the nuclear accumulation of nuclear factor erythroid 2-related factor 2 (Nrf2) and increased the expression of heme oxygenase-1 (HO-1). Notably, the suppression of HO-1 activity using zinc (II) protoporphyrin IX (ZnPP) reversed the NO-inhibitory effects of these fractions. Furthermore, treatment with the HE, DCM, and EA fractions enhanced phosphoinositide 3-kinase (PI3K) activation, whereas PI3K inhibition by LY294002 attenuated HO-1 expression and nuclear Nrf2 translocation. Reactive oxygen species (ROS) scavenging by N-acetyl-L-cysteine (NAC) similarly reduced PI3K activation and the upregulation of HO-1 and nuclear Nrf2. Collectively, these findings indicate that the HE, DCM, and EA fractions mitigate NO production by downregulating iNOS expression through the suppression of MAPK and NF-κB signaling, while also engaging the ROS/PI3K/Nrf2/HO-1 pathway to exert anti-inflammatory effects.