Can aerobic exercise alleviate the compound detrimental effects of age and Western diet on vascular function?

Ageing is a well-established risk factor for cardiovascular disease (CVD) which remains the leading cause of morbidity and mortality worldwide. Two factors contributing to the age-related increase in CVD risk include endothelial dysfunction and arterial stiffness. Endothelial dysfunction is a condition manifested by a shift of the endothelium towards a vasoconstrictive, proinflammatory and prothrombotic state (Seals et al. 2011). Arterial stiffness results from structural changes mediated by increased elastin degradation and collagen deposition as well as functional changes mediated by increased vascular smooth muscle tone (Rossman et al. 2020). The Baltimore Longitudinal Study of Aging was one of the early reports examining the effect of ageing on arterial stiffness and demonstrated that aortic pulse wave velocity (aPWV), a recognized marker of arterial stiffness, is predominantly associated with advanced age and systolic blood pressure (AlGhatrif et al. 2013). Physical activity and dietary patterns are major factors affecting vascular health. A Western diet (WD) that is high in saturated fat and sugar, but low in fibre content, is associated with adverse vascular effects (Rossman et al. 2020). Numerous studies have repeatedly demonstrated that WD diminishes endothelial function and increases arterial stiffness (Lesniewski et al. 2013; Rossman et al. 2020). Moreover, mechanistic ex vivo data, using carotid arteries, has demonstrated that younger mice fed a WD exhibit reduced endothelial dependent dilatation, comparable to that of old mice. This effect was mediated by higher oxidative stress that ultimately compromised nitric oxide (NO) bioavailability (Lesniewski et al. 2013). In addition to reduced NO bioavailability as a result of WD, primary mechanisms that underly vascular complications associated with ageing include heightened inflammation and superoxide production (scavenges NO) without a compensatory increase in antioxidant activity (Seals et al. 2011; Rossman et al. 2020). Interestingly, aerobic exercise ameliorates endothelial dysfunction associated with short-term consumption of WD in young and old mice (Lesniewski et al. 2013). The interactive effect of lifestyle factors (diet and physical activity) and age across the lifespan is a research area of high importance and remains to be fully elucidated. In a recent article published in The Journal of Physiology, investigators (Gioscia-Ryan et al. 2021) set out to examine the interplay between diet and exercise across the lifespan by monitoring key markers of endothelial function and arterial stiffness in mice. Cohorts of 3-month old C57BL/6 male mice were randomized into one of four treatment groups: (1) normal chow sedentary (NC-SED), (2) Western diet sedentary (WD-SED), (3) normal chow voluntary wheel running (NC-VWR), and (4) Western diet voluntary wheel running (WD-VWR). All mice were provided a 2-week acclimation period prior to the study and were given ad libitum access to food and a running wheel. Longitudinal measures of aortic stiffness were conducted every 3–6 months by assessing aPWV using Doppler ultrasound. Subgroups of mice were killed at the ages of 6, 13, 19 and 27 months for terminal measures. Carotid arteries were harvested to assess endothelial function, while aortas were harvested to assess intrinsic arterial stiffness as well as markers of oxidative stress and inflammation. To control for the effect of recent exercise, running wheels were removed 24 h prior to performing terminal measures. Endothelium dependent and independent dilatation were assessed by pressure myography and MitoQ was used to evaluate the influence of mitochondrial oxidative stress on endothelial function. Intrinsic aortic stiffness was determined in thoracic segments by wire myography. Further, superoxide bioactivity was quantified by electron paramagnetic resonance spectroscopy and inflammatory cytokines were determined using a commercially available multiplex ELISA kit. The primary findings of the investigation suggest that WD accelerates vascular ageing, specifically leading to endothelial dysfunction and heightened arterial stiffness. However, incorporating aerobic exercise across the lifespan preserved vascular function by attenuating increased pro-inflammatory cytokine (IL-1β , IL-6, IFN-γ , TNF-α, IL-2) production in thoracic aorta segments as well as whole-cell and mitochondria-derived superoxide production, resulting in sustained NO-mediated dilatation. Moreover, age-related endothelial dysfunction and increased arterial stiffness in the NC-SED group, occurred at various late-life time points. This was demonstrated by a 26% decline in endothelium dependent dilatation (EDD) which was largely mediated by a reduction in NO bioavailability at 27 months (vs. 6 months NC-SED). The incorporation of MitoQ for ex vivo vasodilator experiments revealed that higher mitochondrial superoxide production with ageing was associated with suppressed endothelial function. Additionally, at 27months, a 4-fold increase in pro-inflammatory cytokine production and a 2-fold increase in whole-cell and mitochondria-derived oxidative stress was observed (vs. 6 months NC-SED). As for aortic stiffness, increases in aPWV were apparent as early as 18 months with a 40% final increase at 24 months compared to baseline. Across the lifespan, WD-SED mice were 30–60% heavier in body weight compared to all other treatment groups. Notably, the increase in body weight suggests that at least some of the negative effects associated with the WD could be due to a positive energy balance. The onset of endothelial dysfunction and arterial stiffness appeared earlier in the lifespan of WD-SED mice. Endothelial dysfunction was accelerated and present at 6 months with a 36% decline in EDD compared to age-matched NC-SED mice. On par with the decline