Selective inhibition of NADPH-oxidase isoforms as a therapeutic strategy in hypertension

Endothelium-independent and calcium channel-dependent relaxation of the porcine cerebral artery by different species and strains of turmeric

Objective

To clarify the underlying mechanism of turmeric, which is traditionally used as a medicinal plant for the treatment of cardiovascular disorders, such as hypertension, and palpitations.

Methods

Methanol extracts of different turmeric were used. A tissue-organ-bath system was used to investigate the vasoactive effects of methanol extracts from 5 kinds of turmeric on isolated porcine basilar arteries. The arterial rings were suspended in physiological solution that was maintained at 37 °C temperature with a continuous supply of 95% O₂ and 5% CO₂.

Results

All turmeric extracts (20–800 μg/mL) induced concentration-dependent relaxation of the isolated porcine basilar artery pre-contracted with U46619 (1-5 × 10⁻⁹ M) in arterial rings with or without endothelium. There were no significant differences in the relaxation induced by different turmeric or between the endothelium-intact and denuded arteries. In depolarized, Ca²⁺-free medium, the turmeric extracts inhibited CaCl₂-induced contractions and caused a concentration-dependent rightward shift of the response curves. In addition, propranolol (a non-specific β-adrenoceptor antagonist) slightly inhibited the relaxation induced by turmeric. In contrast, Nω-nitro-l-arginine, indomethacin, tetraethylammonium, glibenclamide and 4-aminopyridine did not affect turmeric-induced relaxation.

Conclusion

These results demonstrated that turmeric induced endothelium-independent relaxation of the porcine basilar artery, which may be due to the inhibition of extracellular and intracellular Ca²⁺ receptors and the partial inhibition of β-adrenergic receptors in vascular smooth muscle cells.

Synthesis of sulfonyl curcumin mimics exerting a vasodilatation effect on the basilar artery of rabbits

In order to discover novel small vasodilatory molecules for potential use in the treatment of vascular disease, we tested the vasodilatation effect of two types of synthetic curcumin mimics, amide type (3) and sulfonyl amide type (4), upon the basilar artery of rabbits. In general, the sulfonyl amide type mimic (4) is more potent than the amide type (3). Curcumin (1) and compounds 12 and 20 effectively dilated the basilar artery of white rabbits.

Vasodilatation effect of farnesylacetones, active constituents of Sargassum siliquastrum, on the basilar and carotid arteries of rabbits

Two farnesylacetones, 311 and 312, major active constituents of Sargassum siliquastrum collected from the coast of the East Sea in Korea, showed a moderate vasodilatation effect on the basilar arteries of rabbits. Therefore, treatment with farnesylacetones 311 and 312 may selectively accelerate cerebral blood flow through dilatation of the basilar artery.

Selective vasodilatation effect of sargahydroquinoic acid, an active constituent of Sargassum micracanthum, on the basilar arteries of rabbits

Sargahydroquinoic acid (2), a major active constituent of Sargassum micracanthum collected from the coast of the East Sea in Korea, showed a selective vasodilatation effect on the basilar arteries of rabbits. Therefore, treatment with sargahydroquinoic acid may selectively accelerate cerebral blood flow through dilatation of the basilar artery without lowering systemic blood pressure.

Novel isoforms of NADPH-oxidase in cerebral vascular control

Reactive oxygen species (ROS) are thought to play an important role in the initiation and progression of a variety of vascular diseases. Furthermore, accumulating evidence indicates that ROS may also serve as important cell signalling molecules for the regulation of normal vascular function. Recently, a novel family of proteins (Nox1, 2 and 4) that act as the catalytic subunit of the superoxide (O2-) producing enzyme NADPH-oxidase has been discovered in vascular cells. There is now preliminary evidence suggesting that NADPH-oxidase-derived ROS may serve as a physiological vasodilator mechanism in the cerebral circulation. Moreover, the activity of NADPH-oxidase is profoundly greater in cerebral versus systemic arteries. Studies have shown that Nox1, Nox2 (also known as gp91phox) and Nox4 are all expressed in cerebral arteries, suggesting that multiple isoforms of NADPH-oxidase may be important for ROS production by cerebral arteries. Enhanced NADPH-oxidase activity is associated with several vascular-related diseases, including hypertension, stroke, subarachnoid haemorrhage and Alzheimer's dementia; however, the consequences of this for cerebral vascular function are controversial. For example, there is some evidence suggesting that NADPH-oxidase-derived O2- may play a role in endothelial dysfunction of cerebral arteries and a subsequent rise in cerebral vascular tone, associated with hypertension. However, activation of NADPH-oxidase elicits cerebral vasodilatation in vivo, and this mechanism is enhanced in chronic hypertension. While further supportive evidence is needed, it is an intriguing possibility that NADPH-oxidase-derived ROS may play a protective role in regulating cerebral vascular tone during disease.

Reactive oxygen species in the cerebral circulation: are they all bad?

Reactive oxygen species (ROS) are a diverse family of molecules generated by all cells. ROS may serve as important cell-signalling molecules in the cerebral circulation. Indeed, in contrast to systemic arteries, major products of superoxide metabolism, including hydrogen peroxide, are powerful cerebral vasodilators, raising the possibility that ROS represent important molecules for increasing local cerebral blood flow. Two major determinants of the overall effects of ROS on cerebrovascular tone are the rate of production of the parent molecule, superoxide, and its rate of metabolism by superoxide dismutases. Although the major enzymatic source of ROS in cerebral arteries has not been clarified, nicotinamide adenine dinucleotide phosphate, reduced form (NADPH)-oxidases, along with cyclooxygenases and lipoxygenases, are probably the primary sources. In cerebral arteries, activation of NADPH-oxidase elicits both an increase in superoxide production and vasodilatation. The identity of the ROS molecule responsible for the vasodilator effects may be hydrogen peroxide, generated from the dismutation of superoxide. NADPH-oxidase activity and function appears to be profoundly greater in cerebral versus systemic arteries. Furthermore, NADPH-oxidase-derived ROS partly contribute to flow-dependent dilatation and may offset angiotensin II-induced constriction of cerebral arteries, consistent with the hypothesis that NADPH-oxidase-derived ROS may play a physiologic role in the control of cerebrovascular tone.