Background: Melissa officinalis (MO) has potent antioxidant activity. Recent research has demonstrated the anti-ulcer properties of some medicinal plants through their antioxidant properties.
Objectives: The aim of this study was to evaluate the effects of methanolic extracts of MO on experimental gastric ulcers in rats.
Materials and methods: Male Wistar rats (200 - 250 g) were starved for 24 hours prior to the induction of gastric ulceration by either indomethacin (48 mg/kg/oral) or water immersion restraint (WIR) stress. Experimental rats received either ranitidine (25 mg/kg) or MO extract (150, 300 and 450mg/kg) orally 2 hours prior to WIR stress or indomethacin treatment, for the evaluation of their gastroprotective effects. The control group received the same volume of saline. Gastric lesions were scored according to the surface of lesions on the ulcer index. Superoxide dismutase (SOD) and glutathione peroxidase (GPX) were determined as measures of antioxidant defense, and malondialdehyde (MDA) was determined to measure tissue oxidation.
Results: MO extract (150 and 300 mg/kg) significantly decreased the ulcer index in both the indomethacin (1.3 ± 0.09 and 1.5 ± 0.19, respectively) and WIR stress groups (1.5 ± 0.17 and 1.5 ± 0.22, respectively), as compared to the control rats (2.5 ± 0.28) (P < 0.01). MO extract (450 mg/kg) significantly reduced ulcer index readings in WIR stress rats (1.8 ± 0.31 vs. 2.4 ± 0.15 in the WIR group), however, MO extract at a dose of 450 mg/kg did not prevent indomethacin-induced gastric ulceration (2.4 ± 0.26). There was no significant difference in the ulcer index for MO extract- (150 and 300 mg/kg) and ranitidine-treated rats (P > 0.05). Also, MO extract (150 and 300 mg/kg) significantly reduced MDA serum levels (0.69 ± 0.6 µmol/L and 0.85 ± 0.24 µmol/L, respectively, vs. 4.5 ± 1.9 µmol/L in the saline group) and significantly increased antioxidants' SOD activities (296.3 ± 146.4 U/mL and 561.4 ± 120 U/mL, respectively, vs. 190.2 ± 63.8U/mL in the control group) and GPX levels (8273 ± 3049 U/mL and 14574 ± 5012 U/mL, respectively), compared to the control (3236 ± 1699 U/mL).
Conclusions: Our results showed that MO extract may have a gastroprotective effect against experimental gastric ulcers in rats. The exact mechanism has not yet been determined, but it may be due to enhancing enzymatic antioxidant defenses and inhibiting lipid peroxidation.
Keywords: Anti-ulcer; Antioxidant; Gastroprotective; Indomethacin; Melissa officinalis; Ulcer index; Water Immersion Restraint Stress.