Gastroprotective and ulcer healing effects of (-)-Myrtenol

(-)-Myrtenol is a bicyclic monoterpene alcohol structurally related to a-pinene found in diverse plant, such as herb Myrtus communis L. (Myrtaceae) used traditionally for the treatment of gastrointestinal disorders. This study was aimed to assess the potential gastroprotective and ulcer healing effects of (-)-myrtenol and the possible mechanisms involved, in vivo experimental models of gastric lesion and in vitro scratch assay. The results showed that (-)-myrtenol at the dose of 2000 mg/kg did not promote acute toxicity during the 14 days observation period in mice. Pretreatment with (-)-myrtenol (50 and 100 mg/kg, p.o.) significantly reduced (p<0.05) the area of gastric lesions induced by ethanol (83 and 83%, respectively) by indomethacin (89 and 87%, respectively), and by retention cold stress (79 and 73%, respectively), as compared to the respective vehicle groups. The mechanistic evaluation of (-)-myrtenol (50 mg/kg, p.o.) in ethanol-induced gastric ulcer involved antioxidant and anti-inflammatory activity, with increase in the activity of glutathione peroxidase, superoxide dismutase and catalase, a decrease in the activity of myeloperoxidase and malondialdehyde in gastric tissue and with increase in levels of nitrite/nitrate, gastric mucus and non-protein sulfhydryls. Pretreatment with GABA-A receptor antagonist flumazenil, the cyclooxygenase inhibitor indomethacin, and nitric oxid synthase inhibitor L-NAME significantly (p<0.05) blocked the (-)-myrtenol gastroprotection. The (-)-myrtenol (50 and 100 mg/kg) administered for seven days was also able to significantly reduced (p<0.05) acetic acid-induced gastric ulcer, increasing the rate of wound healing (47 and 32%, respectively) as compared to the vehicle group. Treatment with (-)-myrtenol (25, 50 and 100 mg/kg, v.o.) in acetic acid-induced gastric ulcer model did not changes significantly the body weight, absolute organ weight and biochemical parameters. The (-)-myrtenol also stimulated re-epithelialization in the ulcer area, reduced activity of N-acetylglicosaminidase and metalloproteinases (2 and 9) and proinflammatory cytokines expression (IL-1β and TNF-α), increased cyclooxygenase-2 expression, gastric mucus content and percentage of collagen fibers, as compared to the respective vehicle groups. In vitro scratch assay with AGS cells, (-)-myrtenol (0.1, 1, 10 and 100 nM) did not alter cell viability, stimulated cell migration in the presence and absence of hydroxyurea, with 6 and 24 hours of incubation, compared to the control group. In summary, these results provide, for the first time, evidence that (-)-myrtenol exert gastroprotective effect mainly due to inhibition of oxidative stress and peripheral GABA-A receptor modulation, regulating blood flow in the mucosa, probably by stimulate the production of nitric oxide and prostaglandins. The (-)-myrtenol shows a healing-promoting effect on acetic acid-induced gastric ulcers to modulate the proinflammatory cytokines expression (IL-1β and TNF-α) and COX-2 expression and to increase the mucus content of the stomach, reepithelialization and gastric cell matrix remodeling.O (-)-mirtenol é um monoterpeno álcool bicíclico, com estrutura semelhante ao α-pineno, presente em algumas espécies vegetais, como a Myrtus communis L. (Myrtaceae) utilizada tradicionalmente para tratar problemas gastrintestinais. No presente estudo avaliou-se a atividade gastroprotetora e cicatrizante do (-)-mirtenol, e os possíveis mecanismos envolvidos nesse efeito, em modelos experimentais de lesão gástrica in vivo e de ferida in vitro. A administração oral e única do (-)-mirtenol na dose de 2000 mg/kg, não promoveu toxicidade aguda, durante 14 dias de observação, em camundongos. O pré-tratamento com (-)-mirtenol (50 e 100 mg, v.o) reduziu significativamente (p<0,05) a área de lesões gástricas induzidas por etanol (83 e 83%, respectivamente), por indometacina (89 e 87%, respectivamente), e por estresse de retenção e frio (79 e 73%, respectivamente), quando comparados aos respectivos grupos veículo. A avaliação mecanística do (-)-mirtenol (50 mg/kg, v.o.) em modelo de lesões gástricas induzida por etanol, em camundongos, envolveu ação antioxidante e anti-inflamatória, com aumento da atividade das enzimas catalase, superóxido dismutase e glutationa peroxidase, aumento dos grupamentos sulfidrilas não proteicos, dos níveis de nitrato/nitrito e do conteúdo de muco gástrico aderido, redução dos níveis de malondialdeido e da atividade de mieloperoxidase. O pré-tratamento com antagonista dos recepetores GABA-A (flumazenil), com inibidor das ciclo-oxigenases (indometacina) e da sintase de óxido nítrico (L-NAME), inibiu estatisticamente (p<0,05) o efeito gastroprotetor do (-)-mirtenol em modelo de lesão induzida por etanol. O (-)-mirtenol (50 e 100 mg/kg), administrado durante sete dias, também foi capaz de reduzir significativamente (p