Ageing and endothelium‐mediated vascular dysfunction: the role of the NADPH oxidases

Abstract

The present study aimed to determine the isoform‐specific role of the NADPH oxidases (NOX) in the endothelium‐mediated vascular dysfunction associated with ageing. Endothelium‐dependent [intraluminal flow‐ and acetylcholine (ACh)‐induced] vasodilatation in human skeletal muscle feed arteries (SMFAs) of young (24 ± 1 years, n = 16), middle aged (45 ± 1 years, n = 18) and old (76 ± 2 years, n = 21) subjects was assessed in vitro with and without the inhibition of NOX1 (ML090), NOX2 (gp91) and NOX4 (plumbagin). To identify the role of nitric oxide (NO) bioavailability in these responses, NO synthase blockade (l‐NG‐monomethyl arginine citrate) was utilized. SMFA NOX1, NOX2 and NOX4 protein expression was determined by western blotting. Age related endothelium‐dependent vasodilatory dysfunction was evident in response to flow (young: 69 ± 3; middle aged: 51 ± 3; old: 27 ± 3%, P < 0.05) and ACh (young: 89 ± 2; middle aged: 72 ± 3; old: 45 ± 4%, P < 0.05). NOX1 inhibition had no effect on SMFA vasodilatation, whereas NOX2 inhibition restored flow‐ and ACh‐induced vasodilatation in the middle aged and the old SMFAs (middle aged + gp91: 69 ± 3; 86 ± 3, old + gp91: 65 ± 5; 83 ± 2%, P < 0.05) and NOX4 inhibition tended to restore these vasodilatory responses in these two groups, but neither achieved statistical significance (P ≈ 0.06). l‐NG‐monomethyl arginine citrate negated the restorative effects of NOX2 and NOX4 blockade. Only NOX2 and NOX4 protein expression was significantly greater in the two older groups and inversely related to vascular function (r = 0.48 to 0.93, P < 0.05). NOX2 and, to a lesser extent, NOX4 appear to play an important, probably NO‐mediated, role in age‐related endothelial dysfunction. Key points The present study aimed to determine the isoform‐specific role of the NADPH oxidases (NOX) in the endothelium‐mediated vascular dysfunction associated with ageing. Age related endothelium‐dependent vasodilatory dysfunction was evident in skeletal muscle feed arteries in response to both flow and acetylcholine. NOX2 inhibition (gp91) restored endothelium‐dependent vasodilatation in the middle aged and the old skeletal muscle feed arteries, and NOX4 inhibition (plumbagin) tended to restore these vasodilatory responses in these two groups. Nitric oxide synthase inhibition negated the restorative effects of NOX2 and NOX4 blockade. NOX2 and NOX4 protein expression was significantly greater in the two older groups and inversely related to vascular function. NOX2 and, to a lesser extent, NOX4 appear to play an important, probably nitric oxide‐mediated, role in age‐related endothelial dysfunction and could be important therapeutic targets to maintain vascular health with ageing.

School of ‘hard NOX’ for the ageing artery

“…In closing, the work of Kwon et al. (2023) demonstrates elegantly that NOX2 and potentially NOX4 mediate the age‐related impairment of endothelial function. It builds upon the past work of this group that implicated mitochondrial ROS as a contributor to impaired NO bioavailability in human SMFAs (Park et al., 2018).…”

“…It is within this framework that the work of Kwon et al. (2023) should be contextualized and valued. Using SMFAs from human axillary or superficial inguinal subcutaneous regions, these investigators used pressure myography to define which NOX isoforms might be responsible for elevated ROS production and blunted NO‐dependent dilatation.…”

“…Kwon et al. (2023) build on this foundation by using selective NOX isoform inhibitors to block NOX1 (ML090), NOX2 (GP91) and NOX4 (Plumbagin) to assess in SMFAs the endothelial function in young (<35 years; n = 16), middle‐aged (>40 and <60 years; n = 18) and older (>65 years; n = 21) humans. The overarching hypothesis was that each inhibitor would improve age‐related endothelial dysfunction by enhancing NO bioavailability.…”

“…Although a useful clinical measure of endothelial health, the experimental utility of this measure is limited because mechanisms are difficult to target, and the brachial artery itself is more conduit than resistive. It is within this framework that the work of Kwon et al (2023) should be contextualized and valued. Using SMFAs from human axillary or superficial inguinal subcutaneous regions, these investigators used pressure myography to define which NOX isoforms might be responsible for elevated ROS production and blunted NO-dependent dilatation.…”

“…Trott and colleagues (2011) were the first to demonstrate that ROS production by NOX impaired endothelial function in SMFAs from aged rodents and that pan-blockade of all NOX isoforms reversed this effect. Kwon et al (2023) build on this foundation by using selective NOX isoform inhibitors to block NOX1 (ML090), NOX2 (GP91) and NOX4 (Plumbagin) to assess in SMFAs the endothelial function in young (<35 years; n = 16), middle-aged (>40 and <60 years; n = 18) and older (>65 years; n = 21) humans. The overarching hypothesis was that each inhibitor would improve age-related endothelial dysfunction by enhancing NO bioavailability.…”