| Nowaday, diabetes mellitus is becoming one of the diseases with highest incidence and mortality, and very difficult to treat. The complications of diabetes also seriously threatened the health and safety of the patient. Oroxylum indicum seed extracts (OISE) and acarbose, could synergetic inhibit the elevation of postprandial blood glucose (PBG). Adding OISE could lower the effective dose of acarbose, but the mechanism is still not clear. The aim of this paper is to explore the mechanism of synergetic effect of OISE and acarbose on reducing blood suger. The optimized method for drug administration in vivo was also studied.Firstly, the synergetic inhibition of OISE and acarbose on elevation of mice PBG didn’t show significant difference when the OISE and acarbose was administrated with food simultaneously or1hr earlier than food administration. This data suggested that the synergetic effect occured before OISE entered the blood. The combined effect of OISE and acarbose on rat intestinal a-glycosidase was investigated. The two inhibitors showed synergetic inhibition at all tested dosages. When starch was used as the substrate, the inhibitory rate for40μg/mL OISE alone,0.02μg/mL acarbose alone and combination of40μg/mL OISE and0.02μg/mL acarbose against rat intestinal a-glycosidase were43%,38%and70%, respectively. When the maltose was used as the substrate, the inhibitory rate for40μg/mL OISE alone,0.04μug/mL acarbose alone and combination of40μg/mL OISE and0.04μg/mL acarbose against rat intestinal a-glycosidase were31%,50%and74%, respectively. This enhanced the efficacy of acabose more than200times.When OISE is at higher concentration(40μg/mL), CI is around0.3, which presented as strong synergy. The fact of no obvious difference when the substrates were maltose and starch, indicated that the synergetic effect of OISE and acarbose is targeted to the a-glucosidases in intestine.Secondly, the combined effect of OISE and acarbose on yeast a-glucosidase and porcine pancreatin a-amylase was investigated. To yeast a-glucosidase, the IC50S of OISE and acarbose alone were312μM and1.23mM, respectively. The two inhibitors showed additive effect at low dose and antagonism effect at high dose. In the experiment of porcine pancreatin a-amylase assay, OISE worked as an agonist., acarbose displayed strong inhibition, with IC50at7μg/mL. The combination of OISE and acarbose did not showed synergetic effect. The effect of OISE on glucose transportation was invesgated by everted gut sacs experiment, gOISE could increase the glucose transportation in mouse interstine.finally, the condition of drug administration for acarbose and OISE extraction were optimized, and the inhibitory activites on elevation of PBG OISE from different producing areas were also assayed. The optimized conditions were:starch was administrated at the dose of2g/kg as starch paste and the the herb was extracted by75%ethanol, the OISE extracted by100%,90%,50%ethanol were also showed relative strong activeties (significant difference (p<0.05) in30and60min blood glucose, compared with acarbose alone). Compared with acarbose alone, the OISE from Guang xi, Gui zhou, and Yun nan showed combined inhibition with acarbose on elevation of PBG (significant difference (p<0.05) on PBG at30min and60min). However, the OISE from Qing hai did not.This study proved that the OISE and acarbose synergetic inhibited the elevation of PBG through their combined inhibition against intestinal a-glucosidase, the synergetic effect was specific on mammal. This work lays the foundation in understanding the mechanism of synergetic inhibiton of evelation of PBG by OISE and acarbose, and also provides an alternative method for new anti-diabetes drugs discovery. |
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