The effects of moringa oleifera lam leaf extract and its compounds on the intracellular calcium release in human aortic smooth muscle cells

Abstract

Nowadays, more people are using herbal therapies to treat and control cardiovascular diseases (CVDs). Hypertension is one of the risk factors of CVDs. Moringa oleifera is a herb that has drawn commercial interest in lowering blood pressure. The antihypertensive effect of M. oleifera has been scientifically shown and supported the traditional use of this plant in the treatment of hypertension. However, studies on the pharmacological effects of M. oleifera are very limited and the mechanism of action on how the blood lowering effect is achieved has not been fully explored. This study aimed to investigate the calcium channel blocking activity of M. oleifera leaf extracts (MOL) and its compounds in vitro, and the possible effects of MOL and its compounds when used in combination with amlodipine. The cell viability of human aortic smooth muscle cells (HAoSMCs) treated with MOL, amlodipine and five marker compounds (gallic acid, quercetin, chlorogenic acid, kaempferol and vicenin-2) was determined by the 3- (4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay. Treatment of MOL at the concentration range from 10 μg/mL to 200 μg/mL for 24 hours maintained HAoSMCs viability above 85%, therefore concentration of 80 μg/mL was selected for the subsequent experiments. HAoSMCs were treated with different concentrations of amlodipine (5 to 160 μg/mL) for 24 h and 5 μg/mL was selected as an optimal concentration of amlodipine for subsequent bioassays. HAoSMCs were also incubated with marker compounds at different concentrations and these concentrations were chosen for the study; chlorogenic acid (35.5 μg/mL), gallic acid (8.50 μg/mL), kaempferol (3.20 μg/mL), quercetin (30 μg/mL) and vicenin-2 (30 μg/mL). The results showed that all the concentrations significantly (p <0.001) inhibited the influx of extracellular Ca2+ into cytosol of HAoSMCs through Ca2+ channels. The compounds also significantly (p <0.001) decreased the concentration of cytosolic free Ca2+ in the absence of extracellular Ca2+. The compounds in addition significantly (p <0.001) affected the intracellular Ca2+ metabolism, regulated by the caffeine-sensitive storage site in HAoSMCs. Finally, MOL and its compounds significantly (p <0.001) reduced the cytosolic Ca2+ increased by K+-depolarization. When MOL and its compounds were used in combination with amlodipine, they failed to demonstrate any additive effect in decreasing cytosolic Ca2+ level. Results from this study demonstrated that MOL and the compounds may act as Ca2+ channel blockers (CCBs) to block the release of Ca2+. Also, there is a possibility of drug-herb interaction between MOL as well as other individual compound with amlodipine, manifested by significant comparison between experimental groups involved. Thus, this finding implicates that M. oleifera leaf extract may serve as a potential adjuvant to anti-hypertensive agents.