Antihypertensive effect of Mali-Nil surin rice bran hydrolysate and its mechanisms related to the EDHF-mediated vasorelaxation and L-type Ca2+ channel-mediated vasoconstriction in L-NAME hypertensive rats

Mali-Nil Surin rice bran hydrolysate (MRH) contains highly nutritional proteins and beneficial phenolic compounds. This study investigated an antihypertensive effect of MRH and evaluated the mechanisms mediating this action in N^ω-nitro-L-arginine-methyl ester (L-NAME)-induced hypertensive rats. Antihypertensive activity was determined in male rats orally administered with MRH (100 or 300 mg/kg) or enalapril (15 mg/kg) daily together with L-NAME (50 mg/kg/day) in drinking water, for 21 days. Concurrent oral treatment with MRH lowered the high blood pressure in the L-NAME-induced hypertensive rats. MRH treatment improved endothelial function and increased the endothelium-derived hyperpolarizing factor-mediated vasorelaxation in L-NAME hypertensive rats. L-NAME rats treated with MRH had reduced adrenergic hypercontractility, which was associated with a decrease in L-type calcium channel-mediated vasoconstriction. In addition, MRH exhibited antioxidant activity in hypertensive rats, as indicated by suppression of vascular superoxide anion production and reduction of malondialdehyde levels, as well as magnification of superoxide dismutase and catalase activities in serum. This study demonstrated the nutraceutical potential of MRH to prevent oxidative stress-related vascular dysfunction in hypertension.

Hydrogen sulfide as a mediator of endothelium-dependent relaxation evoked by Moringa oleifera leaf extract in mesenteric arterial beds isolated from L-NAME hypertensive rats

OBJECTIVES

Aqueous extract of Moringa oleifera leaves (MOE) is a potent inducer of endothelium-dependent relaxation of mesenteric resistance arteries of rats induced to be hypertensive using N^ω-nitro-L-arginine methyl ester (L-NAME). Hydrogen sulfide (H₂S) has been shown to participate in endothelium-dependent relaxation of small resistance arteries. Therefore, this study aimed to investigate whether endothelial H₂S-dependent signaling plays a role in the vasorelaxation in response to MOE.

METHODS

Mesenteric arterial beds isolated from L-NAME hypertensive rats were set up in an ex vivo perfusion system for measurement of vasoreactivity. All experiments were performed in the presence of the nitric oxide synthase inhibitor, L-NAME (100 µM) and the cyclooxygenase inhibitor, indomethacin (10 µM) to prevent the formation of nitric oxide and prostanoids, respectively.

RESULTS

In the presence of the nitric oxide synthase inhibitor, L-NAME and the cyclooxygenase inhibitor, indomethacin, the endothelium-dependent vasorelaxation induced by MOE (0.001-3 mg) was completely inhibited by DL-propargylglycine (100 µM), which inhibits the H₂Sgenerating enzyme, cystathionine γ-lyase. This H₂Sdependent response was reduced by the K_ATP channel blocker; glibenclamide (10 µM), the K_Ca channel blocker; tetraethylammonium (1 µM), and the myo-endothelial gap-junctional uncoupler; 18α-glycyrrhetinic acid (10 µM). In contrast, the muscarinic receptor antagonist, atropine (100 µM), did not affect the response to MOE.

CONCLUSIONS

The results may suggest that H₂S is the likely mediator of endothelium-dependent relaxation in response to MOE in mesenteric arterial beds of L-NAME-induced hypertensive rats. MOE-induced H₂S-dependent vasorelaxation involves activation of K_ATP and K_Ca channels and requires myo-endothelial gap-junctional communication.

Moringa oleifera leaf extract induces vasorelaxation via endothelium-dependent hyperpolarization and calcium channel blockade in mesenteric arterial beds isolated from L-NAME hypertensive rats

BACKGROUND

An aqueous extract of Moringa oleifera leaves (MOE) is known to cause relaxation of mesenteric resistance arteries of rats in which hypertension has been induced by the administration of L-NAME, but the mechanism(s) of action of MOE remains unclear. The purpose of this study was to investigate these mechanisms in mesenteric arterial beds isolated from L-NAME induced hypertensive rats. Methods: An investigation of vascular reactivity was conducted on isolated mesenteric arterial beds by measuring the changes in perfusion pressure using an in vitro system.

RESULTS

MOE (0.001-3 mg in 0.1 ml injection volume) caused a dose-dependent relaxation in methoxamine (5 µM) pre-contracted arterial beds, which was partially abolished by endothelium removal. The endothelium-dependent component of vasorelaxation was insensitive to both L-NAME (100 µM) and indomethacin (10 µM), while completely inhibited in high KCl (45 mM)-induced contraction. MOE (1 and 3 mg/ml) showed a dose-dependent inhibitory effect on CaCl₂-induced contractions of denuded preparations in Ca²⁺-free medium containing a high KCl (60 mM) or methoxamine (10 µM). In Ca²⁺-free medium, MOE (3 mg/ml) also inhibited phenylephrine-induced contractions of denuded preparations. Conclusion: These findings suggest that MOE relaxes mesenteric arterial beds of L-NAME hypertensive rats via both endothelium-dependent and endothelium-independent mechanisms. The endothelium-dependent action occurred via endothelium-derived hyperpolarizing factor-mediated hyperpolarization. The endothelium-independent action was related to blocking the entry of extracellular Ca²⁺ via voltage-operated and receptor-operated Ca²⁺ channels, and inhibiting mobilization of sarcolemmal Ca²⁺ via inositol trisphosphate receptor Ca²⁺ channels. MOE may be potentially useful as a natural vasodilator against hypertension.

Moringa oleifera leaf extract lowers high blood pressure by alleviating vascular dysfunction and decreasing oxidative stress in L-NAME hypertensive rats

BACKGROUND

Enhancing relaxation of resistance arteries and decreasing oxidative stress by using natural products are potential strategies for prevention and treatment of hypertension.

PURPOSE

This study investigated whether aqueous extract of Moringa oleifera leaves (MOE) could alleviate N^ω-nitro-L-arginine-methyl ester (L-NAME)-induced high blood pressure via modulation of vascular function and antioxidant properties.

METHODS

An experimental hypertensive model was established by administration of L-NAME (50 mg/kg/day) in drinking water to male Wistar rats for 3 weeks. Arterial pressure was measured indirectly by tail-cuff plethysmography and directly via femoral artery catheterization. Vasoreactivity of isolated rat mesenteric arterial bed was determined by the changes in perfusion pressure detected by a pressure transducer. Vascular superoxide anion (O₂^•-) production was determined by lucigenin-enhanced chemiluminescence. Other biochemical measurements including malondialdehyde (MDA) level, superoxide dismutase (SOD), and catalase (CAT) activities were measured by colorimetric assay.

RESULTS

L-NAME-treated rats developed significantly increased blood pressure and heart rate. Concurrent oral treatment with MOE (30 and 60 mg/kg/day) could decrease the high blood pressure and tachycardia in a dose-dependent manner. MOE reduced the impairment of acetylcholine-induced relaxation and decreased the hyperreactivity of adrenergic-mediated contraction in response to periarterial nerve stimulation and phenylephrine in isolated mesenteric arterial beds. In addition, MOE exhibited antioxidant effects in the hypertensive rats, as indicated by suppression of vascular O₂^•- production, decrease of plasma and thoracic aorta MDA levels, and increase of antioxidant activities of SOD and CAT. Moreover, MOE (0.001-0.3 mg) produced a dose-dependent relaxation in methoxamine pre-contracted arterial beds isolated from L-NAME hypertensive rats, which was abolished by endothelium denudation.

CONCLUSION

These findings suggest that the antihypertensive effect of MOE in L-NAME-hypertensive rats may be mediated by alleviating vascular dysfunction and oxidative stress and promoting endothelium-dependent vasorelaxation. MOE may be potentially useful as a natural product against hypertension.

Increase in L-type amino acid transporter 1 expression during cholangiocarcinogenesis caused by liver fluke infection and its prognostic significance

L-type amino acid transporter 1 (LAT1) is highly expressed in various human cancers, including cholangiocarcinoma (CCA), the most common cancer in Northeast Thailand. Chronic inflammation and oxidative stress induced by liver fluke, Opisthorchis viverrini, infection has been recognized as the major cause of CCA in this area. We show here that an increased expression of LAT1 and its co-functional protein CD98 are found during carcinogenesis induced by Ov in hamster CCA tissues. We also demonstrate that oxidative stress induced by H₂O₂ is time-dependent and dramatically activates LAT1 and CD98 expression in immortal cholangiocytes (MMNK1). In addition, H₂O₂ treatment increased LAT1 and CD98 expression, as well as an activated form of AKT and mTOR in MMNK1 and CCA cell lines (KKU-M055 and KKU-M213). We also show that suppression of PI3K/AKT pathway activity with a dual PI3K/mTOR inhibitor, BEZ235, causes a reduction in LAT1 and CD98 expression in KKU-M055 and KKU-M213 in parallel with a reduction of activated AKT and mTOR. Interestingly, high expression of LAT1 in human CCA tissues is a significant prognostic factor for shorter survival. Taken together, our data show that LAT1 expression is significantly associated with CCA progression and cholangiocarcinogenesis induced by oxidative stress. Moreover, the expression of LAT1 and CD98 in CCA is possibly regulated by the PI3K/AKT signaling pathway.

Protons modulate perivascular axo-axonal neurotransmission in the rat mesenteric artery

BACKGROUND AND PURPOSE

Previous studies have demonstrated that nicotine releases protons from adrenergic nerves via stimulation of nicotinic ACh receptors and activates transient receptor potential vanilloid-1 (TRPV1) receptors located on calcitonin gene-related peptide (CGRP)-containing (CGRPergic) vasodilator nerves, resulting in vasodilatation. The present study investigated whether perivascular nerves release protons, which modulate axon-axonal neurotransmission.

EXPERIMENT APPROACH

Perfusion pressure and pH levels of perfusate in rat-perfused mesenteric vascular beds without endothelium were measured with a pressure transducer and a pH meter respectively.

KEY RESULTS

Periarterial nerve stimulation (PNS) initially induced vasoconstriction, which was followed by long-lasting vasodilatation and decreased pH levels in the perfusate. Cold-storage denervation of the preparation abolished the decreased pH and vascular responses to PNS. The adrenergic neuron blocker guanethidine inhibited PNS-induced vasoconstriction and effects on pH, but not PNS-induced vasodilatation. Capsaicin (CGRP depletor), capsazepine and ruthenium red (TRPV1 inhibitors) attenuated the PNS-induced decrease in pH and vasodilatation. In denuded preparations, ACh caused long-lasting vasodilatation and lowered pH; these effects were inhibited by capsaicin pretreatment and atropine, but not by guanethidine or mecamylamine. Capsaicin injection induced vasodilatation and a reduction in pH, which were abolished by ruthenium red. The use of a fluorescent pH indicator demonstrated that application of nicotine, ACh and capsaicin outside small mesenteric arteries reduced perivascular pH levels and these effects were abolished in a Ca(2+) -free medium.

CONCLUSION AND IMPLICATION

These results suggest that protons are released from perivascular adrenergic and CGRPergic nerves upon PNS and these protons modulate transmission in CGRPergic nerves.

Adrenergic stimulation-released histamine taken-up in adrenergic nerves induces endothelium-dependent vasodilation in rat mesenteric resistance arteries

The present study investigated whether histamine was taken up by perivascular adrenergic nerves and released by periarterial nerve stimulation (PNS) to induce vascular responses. In rat mesenteric vascular beds treated with capsaicin to eliminate calcitonin gene-related peptide (CGRP)ergic vasodilation and with active tone, PNS (1 - 4 Hz) induced only adrenergic nerve-mediated vasoconstriction. Histamine treatment for 20 min induced PNS-induced vasoconstriction followed by vasodilation without affecting CGRP-induced vasodilation. Chlorpheniramine, guanethidine, combination of histamine and desipramine, and endothelium-removal abolished PNS-induced vasodilation in histamine-treated preparations. These results suggest that histamine taken up by and released from adrenergic nerves by PNS causes endothelium-dependent vasodilation in rat mesenteric arteries.

Adrenergic stimulation-released 5-HT stored in adrenergic nerves inhibits CGRPergic nerve-mediated vasodilatation in rat mesenteric resistance arteries

BACKGROUND AND PURPOSE

5-HT is taken up by and stored in adrenergic nerves and periarterial nerve stimulation (PNS) releases 5-HT to cause vasoconstriction in rat mesenteric arteries. The present study investigated whether PNS-released 5-HT stored in adrenergic nerves affects the function of perivascular calcitonin gene-related peptide-containing (CGRPergic) nerves.

EXPERIMENTAL APPROACH

Rat mesenteric vascular beds without endothelium and with active tone were perfused with Krebs solution. Changes in perfusion pressure in response to PNS and CGRP injection were measured before (control) and after perfusion of Krebs solution containing 5-HT (10 µM) for 20 min. Distributions of 5-HT- and TH-immunopositive fibres in mesenteric arteries were studied using immunohistochemical methods.

KEY RESULTS

PNS (1-4 Hz) frequency dependently caused adrenergic nerve-mediated vasoconstriction followed by CGRPergic nerve-mediated vasodilatation. 5-HT treatment inhibited PNS-induced vasodilatation without affecting exogenous CGRP-induced vasodilatation, while it augmented PNS-induced vasoconstriction. Guanethidine (adrenergic neuron blocker), methysergide (non-selective 5-HT receptor antagonist) and BRL15572 (selective 5-HT1D receptor antagonist) abolished inhibition of PNS-induced vasodilatation in 5-HT-treated preparations. Combined treatment with 5-HT and desipramine (catecholamine transporter inhibitor), but not fluoxetine (selective 5-HT reuptake inhibitor), did not inhibit PNS-induced vasodilatation. Exogenous 5-HT inhibited PNS-induced vasodilatation, which was antagonized by methysergide. In immunohistochemical experiments, 5-HT-immunopositive nerves, colocalized with adrenergic TH-immunopositive nerves, were observed only in 5-HT-treated mesenteric arteries, but not in control preparations or arteries co-treated with desipramine.

CONCLUSIONS AND IMPLICATIONS

These results suggest that 5-HT can be taken up by and released from adrenergic nerves in vitro by PNS to inhibit CGRPergic nerve transmission in rat mesenteric arteries.

Do cholinergic nerves innervating rat mesenteric arteries regulate vascular tone?

Vascular blood vessels have various types of cholinergic acetylcholine receptors (AChR), but the source of ACh has not been confirmed. Perivascular adrenergic nerves and nonadrenergic calcitonin gene-related peptide (CGRP)-containing (CGRPergic) nerves innervate rat mesenteric arteries and regulate vascular tone. However, function of cholinergic innervation remains unknown. The present study investigated cholinergic innervation by examining effects of cholinesterase inhibitor (neostigmine), a muscarinic AChR antagonist (atropine), and a nicotinic AChR antagonist (hexamethonium) on adrenergic nerve-mediated vasoconstriction and CGRPergic nerve-mediated vasodilation in rat mesenteric vascular beds without endothelium. In preparations treated with capsaicin (CGRP depletor) or in the presence of N(ω)-nitro-l-arginine methyl ester (nonselective nitric oxide synthase inhibitor), perivascular nerve stimulation (PNS; 2-12 Hz) evoked a frequency-dependent vasoconstriction. In the same preparations, exogenous norepinephrine induced a concentration-dependent vasoconstriction. Atropine, hexamethonium, and neostigmine had no effect on vasoconstrictor responses to PNS and norepinephrine injections. In denuded preparations, these cholinergic agents did not affect the PNS (12 Hz)-evoked release of norepinephrine in perfusate. In preconstricted preparations without endothelium in the presence of guanethidine (adrenergic neuron blocker), PNS (1-4 Hz) induced a frequency-dependent vasodilation, which was not affected by atropine, hexamethonium, and neostigmine. In denuded preparations treated with capsaicin and guanethidine, PNS did not induce vascular responses, and atropine, neostigmine, and physostigmine had no effect on PNS. Immunohistochemistry study showed choline acetyltransferase-immunopositive fibers, which were resistant to capsaicin and 6-hydroxydopamine (adrenergic toxin). These results suggest that rat mesenteric arteries have cholinergic innervation, which is different from adrenergic and capsaicin-sensitive nerves and not associated with vascular tone regulation.

Neurogenic vascular responses in male mouse mesenteric vascular beds

Rat mesenteric arteries were maintained by both adrenergic vasoconstrictor nerves and calcitonin gene-related peptide (CGRP) vasodilator nerves. However, functions of these nerves in a pathophysiological state have not fully been analyzed. The use of disease models developed genetically in mice is expected to clarify neural function of perivascular nerves. Thus, we investigated basic mouse vascular responses. Mesenteric vascular beds isolated from male C57BL/6 mouse were perfused with Krebs solution and perfusion pressure was measured. Periarterial nerve stimulation (PNS, 8 - 24 Hz) induced frequency-dependent vasoconstriction, which increased flow rate-dependently. PNS-induced vasoconstriction was abolished by tetrodotoxin (neurotoxin) and guanethidine (adrenergic neuron blocker) and blunted by prazosin (α(1)-adrenoceptor antagonist). Injection of norepinephrine caused vasoconstriction, which was abolished by prazosin. In preparations with active tone, PNS (1 - 8 Hz) induced frequency-dependent vasodilation, which was inhibited by tetrodotoxin, capsaicin (CGRP depletor), and CGRP8-37 (CGRP-receptor antagonist). Injections of CGRP, acetylcholine, and sodium nitroprusside induced vasodilations. Vasodilator response to CGRP was inhibited by CGRP8-37. Immunohistochemical study showed innervation of tyrosine hydroxylase- and CGRP-immunopositive fibers in mesenteric arteries and veins. These results suggest that male mouse mesenteric vascular beds are useful for studying neural regulation of mesenteric arteries, which are innervated by adrenergic and CGRPergic nerves regulating vascular tone.

Paracrine control of mesenteric perivascular axo-axonal interaction

Immunohistochemical study of rat mesenteric arteries showed dense innervation of adrenergic nerves, calcitonin gene-related peptide (CGRP)-containing nerves (CGRPergic nerves), nitric oxide-containing nerves (nitrergic nerves). Double-immunostaining revealed that most CGRPergic or nitrergic nerves were in close contact with adrenergic nerves. CGRPergic and transient receptor potential vanilloid-1 (TRPV1)-immunopositive nerves appeared in the same neurone. In rat perfused mesenteric vascular beds without endothelium and with active tone, perfusion of nicotine, or bolus injection of capsaicin and acetylcholine and periarterial nerve stimulation (PNS) lowered pH levels of out flowed perfusate concomitant with vasodilation. Cold-storage denervation of preparations abolished pH lowering induced by nicotine and PNS. Guanethidine inhibited PNS- and nicotine-, but not acetylcholine- and capsaicin-, induced pH lowering. Pharmacological analysis showed that protons were released not only from adrenergic nerves but also from CGRPergic nerves. A study using a fluorescent pH indicator demonstrated that nicotine, acetylcholine and capsaicin applied outside small mesenteric artery lowered perivascular pH levels, which were not observed in Ca(2+) free medium. Exogenously injected hydrochloric acid in denuded preparations induced pH lowering and vasodilation, which was inhibited by denervation, TRPV1 antagonists and capsaicin without affecting pH lowering. These results suggest that excitement of adrenergic nerves releases protons to activate TRPV1 in CGRPergic nerves and thereby induce vasodilation. It is also suggested that CGRPergic nerves release protons with exocytosis to facilitate neurotransmission via a positive feedback mechanism.