Interestingly, our results demonstrated that MA restores
the vascular response of diabetic rats to both vasodilator and
vasoconstrictor. This effect of MA is probably due to its
hypoglycemic and also antioxidant activities. Because we
found that MA-treated diabetic rats had a significant lower
MDA concentration in various tissues than that of nontreated
diabetic rats especially in the aortic tissue (Table 2), the
significant increased MDA concentrations in various tissues
in chronic diabetic rats point to ROS-mediated cellular
damage, denoting the presence of oxidative stress in chronic
diabetes[22]. Mulberry leaf extract components, especially
flavonoids (ie, quercetin, rutin, and isoquercitrin), possess
the free radical scavenging effect, showing the possibility of
antioxidant activity [23]. The antioxidant compounds in
mulberry leaf ethanol extract are able to pass from the small
intestine into the blood circulation with their intact
antioxidant activity in the rat [14]. For quercetin, its
metabolites produced by microbial in the gut are absorbed
and still retain systemic antioxidant activity[24]. Anthocyanin is another antioxidant found in wild mulberry fruit and is
absorbed from gastrointestinal tract, even at the small
amount, giving antioxidant activity in plasma[25]. It has
also been demonstrated that synthetic quercetin administration to diabetic rats restored the vascular function [26,27].
Moreover, the clinical effectiveness of a flavonoid-rich
dietary supplement in alleviating the vascular complication
in diabetic patients has been reported