Anti-inflammatory effect of the monoterpene myrtenol is dependent on the direct modulation of neutrophil migration and oxidative stress

Myrtenol is a bicyclic monoterpene with anti-inflammatory properties. However, the mechanisms involved are partially unknown. Here, we investigated the effect of myrtenol during experimental chronic arthritis and the possible modulating activity of oxidative stress and neutrophil migration. Complete Freund's Adjuvant (CFA)-sensitized rats were treated with vehicle (1 mL/kg, po), myrtenol (12.5, 25 or 50 mg/kg, po), indomethacin (10 mg/kg, po) or dexamethasone (0.4 mg/kg) followed by intra-articular injection of CFA (0.5 mg/mL, 50 μL per joint). Then, paw edema and articular incapacitation (paw elevation time) were evaluated for 14 days. On the last day, a blood concentration superoxide dismutase (SOD) and nitrite was determined. In another experimental setting, human neutrophils were incubated with vehicle (sterile saline, 1 mL) or myrtenol (10-100 ng/mL) and the in vitro chemotaxis to N-formylmethionine-leucyl-phenylalanine (fMLP) (10−7 M/well) was evaluated. In addition, antiinflammatory effect of myrtenol was investigated in carrageenan-induced peritonitis. We found that CFA induced a prominent paw swelling and incapacitation of the joint, which were significantly prevented by myrtenol (P < 0.05). In addition, blood accumulation nitrite was attenuated by myrtenol when compared with vehicle-treated CFA group (P < 0.05). Furthermore, plasma levels of SOD were significantly increased by myrtenol versus vehicle-treated CFA group (P < 0.05). Moreover, fMLP-triggered neutrophil chemotaxis and carrageenan-induced peritonitis were markedly prevented by myrtenol (P < 0.05). Therefore, myrtenol showed anti-inflammatory and antinociceptive effects on experimental chronic arthritis, which seems to be related to the direct modulation of neutrophil migration and antioxidant activity.