BackgroundThe present investigation was aimed at evaluating the hypoglycemic and hypolipidemic properties of the aqueous and methanolic extracts from Bersama engleriana leaves in streptozotocin/nicotinamide (STZ-NA)-induced type 2 diabetic rats.MethodsAnimals were orally treated for 4 consecutive weeks with Bersama engleriana extracts at doses of 300 or 600 mg/kg. The anti-diabetic effect was examined by measuring blood glucose (BG) at 0, 1, 14 and 28 days after STZ-NA treatment and, total cholesterol (TC), high density lipoprotein cholesterol (HDL-C), low density lipoprotein cholesterol (LDL-C) and triglycerides (TG) levels at sacrifice (day 29). Glibenclamide (0.25 mg/kg) was used for comparison.ResultsSTZ-NA-induced diabetic rats showed moderate to significant increases in the levels of BG, TG, TC, LDL-C while body weight, HDL-C levels and relative weights of liver and pancreas were decreased compared to controls (non diabetic rats). Administration of the plant extracts to STZ-NA diabetic rats resulted in a significant decrease in BG, TG, TC and LDL-C and the dose 600 mg/kg of the methanolic extract was the most effective; HDL-C level was markedly increased after four weeks compared to untreated diabetic rats. A dose-dependent increase in the relative weights of the diabetogenic organs was observed in the Bersama engleriana groups. It can be also noticed that the methanolic extract, especially the dose 600 mg/kg (p<0.001), produced more effects than glibenclamide and aqueous extract. Rats treated with glibenclamide (0.25 mg/kg) generally gave lower results compared to groups treated with plant extracts.ConclusionResults of the present study showed that Bersama engleriana extracts and especially its methanolic extract possess antidiabetogenic properties and beneficial effects on diabetic hyperlipidemia. All these effects could be due to the bioactive components revealed in the Bersama engleriana extracts such as triterpenes and phenols and which could justify its ethnomedical use.

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Present findings suggest the involvement of dopaminergic system in the activity of B. engleriana and further support its aphrodisiac potentials due to sterols and saponins revealed in this plant.

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Endothelial cells (ECs) line the lumen of all blood vessels and regulate functions, including contractility. Physiological stimuli, such as acetylcholine (ACh) and intravascular flow, activate transient receptor potential vanilloid 4 (TRPV4) channels, which stimulate small (SK3)- and intermediate (IK)-conductance Ca 2+ -activated potassium channels in ECs to produce vasodilation. Whether physiological vasodilators also modulate the surface abundance of these ion channels in ECs to elicit functional responses is unclear. Here, we show that ACh and intravascular flow stimulate rapid anterograde trafficking of an intracellular pool of SK3 channels in ECs of resistance-size arteries, which increases surface SK3 protein more than two-fold. In contrast, ACh and flow do not alter the surface abundance of IK or TRPV4 channels. ACh triggers SK3 channel trafficking by activating TRPV4-mediated Ca 2+ influx, which stimulates Rab11A, a Rab GTPase associated with recycling endosomes. Superresolution microscopy data demonstrate that SK3 trafficking specifically increases the size of surface SK3 clusters which overlap with TRPV4 clusters. We also show that Rab11A-dependent trafficking of SK3 channels is an essential contributor to vasodilator-induced SK current activation in ECs and vasorelaxation. In summary, our data demonstrate that vasodilators activate Rab11A, which rapidly delivers an intracellular pool of SK3 channels to the vicinity of surface TRPV4 channels in ECs. This trafficking mechanism increases surface SK3 cluster size, elevates SK3 current density, and produces vasodilation. These data also demonstrate that SK3 and IK channels are differentially regulated by trafficking-dependent and -independent signaling mechanisms in endothelial cells.

Endothelial cells (ECs) line the lumen of blood vessels and regulate functions, including contractility. Physiological stimuli, such as acetylcholine (ACh) and intraluminal flow, activate small conductance calcium‐activated potassium (SK3) channels in ECs, leading to hyperpolarization and vasodilation. Whether these stimuli modulate SK3 surface abundance in ECs to elicit vasodilation is unclear. Here, we investigated physiological regulation of SK3 channel surface trafficking in mesenteric artery (MA) ECs. Biotinylation experiments demonstrated that ACh or intravascular flow rapidly (2 min) increased surface SK3 protein ~ 2.0‐ and 2.1‐fold, respectively in MAs, with similar results obtained in primary‐cultured ECs. Brefeldin A, an anterograde trafficking inhibitor, removal of extracellular Ca2+, GSK2193874, a selective TRPV4 channel blocker or TRPV4 knockdown using siRNA, each inhibited the ACh‐induced increase in surface SK3 channels in MAs. Super resolution microscopy (SMLM) experiments demonstrated that ACh increased the size of surface SK3 clusters in ECs. ACh activated whole‐cell SK currents and this effect was inhibited by brefeldin A. Brefeldin A also reduced vasodilation induced by ACh and intravascular flow to between ~48 and 57 % of those in control. Brefeldin A blocked the SK channel component of ACh‐ and flow‐mediated vasodilations. In summary, our data indicate that ACh and flow stimulate anterograde trafficking of SK3 channels in ECs via a TRPV4‐dependent Ca2+ signaling mechanism to elicit vasodilation.