摘要：Aim: To identify the chemical components of the major bioactive fraction from a propolis extract and investigate the gastric cytoprotective effects of the said fraction. Place and Duration of Study: Department of Animal Biology & Physiology (Animal Physiology Laboratory), Department organic chemistry (Laboratory of medicinal chemistry), Faculty of Science, University of Yaoundé I in collaboration with the IOCCP, Bulgarian academy of sciences between August 2014 and April 2017. Methodology: The propolis extract previously shown to possess gastric cytoprotective activity was subjected to column chromatography to obtain fractions, the major one of which was used in this study. About 5 mg of this fraction was silylated using BSTFA and subjected to GC–MS analysis on a Hewlett–Packard gas chromatograph. Identification of individual compounds was performed based on mass-spectral fragmentation and by comparison with some literature data and authentic samples. Gastric cytoprotective activity and antioxidant properties of the fraction were then evaluated using experimentally-induced gastric ulcers in rat models including HCl/ethanol, HCl/ethanol pretreated with indomethacin, absolute ethanol and stress-induced gastric ulcers. In each experimental model percentage of ulcerated surfaces, ulcer indices, mucus production as well as the percentage inhibition of ulceration were evaluated. The effects of this fraction on the anti-oxidative parameters in stomach tissues of rats subjected to cold/restraint stress were equally evaluated. Results: The GC-MS profile of the major fraction under investigation revealed that it was a mixture of pentacyclic triterpenes; lanosterol, α-amyrine, 28-norolean-12-en-3-ol, Cycloartenol, 3-epi-α-amyrine, lupeol and 24-methylenecycloartenol. In the HCl/ethanol-induced gastric lesions model the fraction significantly (p < 0.01) reduced ulcer index at dose 50 mg/kg with a percentage inhibition of 47.25%, a significant increase in mucus production from 70.60 mg (p < 0.5) to 88.00 mg (p < 0.001) for the 25 and 50 mg/kg doses, respectively, compared with 53.40 mg for the negative controls. HCl/ethanol-induced gastric lesions in rats pre-treated with indomethacin showed that ulcer index decreased significantly (p < 0.001) from 1.93 to 1.50 for the 25 and 50 mg/kg doses, respectively, compared with 5.77 for the control. This corresponded with 66.55 and 74 percentage inhibition for the same doses of triterpenes, and the quantity of mucus increased to 104.20, 116.20 and 139.40 mg for the 25, 50 and 100 mg/kg doses. With absolute ethanol the fraction significantly reduced ulcer indices to 3.63 and 2.28 for the 25 and 50 mg/kg doses, respectively, compared with 4.87 for controls. The highest dose (50 mg/kg) of the fraction provided 53.18% inhibition of ulceration and the increase in mucus production was significant (p < 0.001) at the two doses. In the cold/restraint stress model, the fraction showed significant reduction in ulcer index, and the highest dose (50 mg/kg) prevented lesion formation by 52.51% inhibition while mucus production increased significantly. Cold/restraint stress significantly increased tissue concentrations of NO and MDA but the positive control (Omeprazole) and the fraction (50 mg/kg) reduced these parameters back to normal levels. The fraction (50 mg/kg) also reverted the increased concentrations of SOD and GSH (but not of catalase) back to normal values. Conclusion: Cameroonian propolis likewise tropical and subtropical propolis samples are rich in triterpenes. The triterpene fraction dose-dependently acts by different and complementary mechanisms to improve the mucosal defensive factors. The mode of its gastroprotective activity may be attributed to reduction in gastric mucosal lipid peroxidation (MDA), elevation of glutathione (GSH), superoxide dismutase (SOD) and nitric oxide (NO).
