The Anti-Inflammatory Activity of Palmitoylethanolamide Ameliorates Osteoarthritis Induced by Monosodium Iodoacetate in Sprague Dawley Rats

Abstract Novel treatment strategies are urgently required for osteoarthritis (OA), a degenerative joint disease. Palmitoylethanolamide (PEA) is a naturally occurring fatty acid amide with analgesic and anti-inflammatory effects. We aimed to examine its effect on OA and molecular mechanism of actions in monosodium iodoacetate (MIA)-induced OA Sprague Dawley rats. The experimental animals were divided into five groups: normal control group (injected with saline + treated with phosphate-buffered saline (PBS), NOR), control group (injected with MIA + treated with PBS, CON), 50 or 100 mg/kg body weight (BW)/day PEA-treated group (injected with MIA + treated with 50 or 100 mg of PEA/kg BW/day, PEA50 or PEA 100), and positive control group (injected with MIA + treated with 6 mg of diclofenac/kg BW/day, DiC). Changes in blood and body parameters, gene expression of inflammatory mediators and cytokines, knee thickness, and joint tissue were observed. We found no adverse effects of oral administration of PEA on BW, liver, or kidneys. PEA reduced knee joint swelling and cartilage degradation in MIA-induced OA rats. The serum levels of leukotriene B4, nitric oxide, tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and prostaglandin E2 considerably reduced in the PEA100 group compared to those in the CON group. In the synovia of knee joints, mRNA expression of iNOS, 5-Lox, Cox-2, Il-1β, Tnf-α, Mmp-2, -3, -9, and − 13 noticeably reduced with MIA administration. Meanwhile, Timp-1 mRNA expression noticeably decreased in the CON group but increased to the normal level with PEA treatment. Thus, we demonstrated that PEA can be used as an effective therapeutic agent for OA.