Chronic calorie restriction (CR) improves cardiovascular function and several other physiological markers of healthspan. However, CR is impractical in non-obese older humans due to potential loss of lean mass and bone density, poor adherence, and risk of malnutrition. Time-restricted feeding (TRF), which limits the daily feeding period without requiring a reduction in calorie intake, may be a promising alternative healthspan-extending strategy for midlife and older adults; however, there is limited evidence for its feasibility and efficacy in humans. We conducted a randomized, controlled pilot study to assess the safety, tolerability, and overall feasibility of short-term TRF (eating <8 h day −1 for 6 weeks) without weight loss in healthy non-obese midlife and older adults, while gaining initial insight into potential efficacy for improving cardiovascular function and other indicators of healthspan. TRF was safe and well-tolerated, associated with excellent adherence and reduced hunger, and did not influence lean mass, bone density, or nutrient intake. Cardiovascular function was not enhanced by short-term TRF in this healthy cohort, but functional (endurance) capacity and glucose tolerance were modestly improved. These results provide a foundation for conducting larger clinical studies of TRF in midlife and older adults, including trials with a longer treatment duration.

Age-related vascular endothelial dysfunction is a major antecedent to cardiovascular diseases. We investigated whether increased circulating levels of the gut microbiome-generated metabolite trimethylamine-N-oxide induces endothelial dysfunction with aging. In healthy humans, plasma trimethylamine-N-oxide was higher in middle-aged/older (64±7 years) versus young (22±2 years) adults (6.5±0.7 versus 1.6±0.2 µmol/L) and inversely related to brachial artery flow-mediated dilation ( r 2 =0.29, P <0.00001). In young mice, 6 months of dietary supplementation with trimethylamine-N-oxide induced an aging-like impairment in carotid artery endothelium-dependent dilation to acetylcholine versus control feeding (peak dilation: 79±3% versus 95±3%, P <0.01). This impairment was accompanied by increased vascular nitrotyrosine, a marker of oxidative stress, and reversed by the superoxide dismutase mimetic 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl. Trimethylamine-N-oxide supplementation also reduced activation of endothelial nitric oxide synthase and impaired nitric oxide-mediated dilation, as assessed with the nitric oxide synthase inhibitor L-NAME (N G -nitro-L-arginine methyl ester). Acute incubation of carotid arteries with trimethylamine-N-oxide recapitulated these events. Next, treatment with 3,3-dimethyl-1-butanol for 8 to 10 weeks to suppress trimethylamine-N-oxide selectively improved endothelium-dependent dilation in old mice to young levels (peak: 90±2%) by normalizing vascular superoxide production, restoring nitric oxide-mediated dilation, and ameliorating superoxide-related suppression of endothelium-dependent dilation. Lastly, among healthy middle-aged/older adults, higher plasma trimethylamine-N-oxide was associated with greater nitrotyrosine abundance in biopsied endothelial cells, and infusion of the antioxidant ascorbic acid restored flow-mediated dilation to young levels, indicating tonic oxidative stress-related suppression of endothelial function with higher circulating trimethylamine-N-oxide. Using multiple experimental approaches in mice and humans, we demonstrate a clear role of trimethylamine-N-oxide in promoting age-related endothelial dysfunction via oxidative stress, which may have implications for prevention of cardiovascular diseases.

Key pointsr Age-related arterial dysfunction, characterized by oxidative stress-and inflammation-mediated endothelial dysfunction and arterial stiffening, is the primary risk factor for cardiovascular diseases.Vienna E. Brunt received her PhD in Human Physiology from the University of Oregon in 2016. She is currently a postdoctoral fellow in Dr D. R. Seals' Integrative Physiology of Aging Laboratory at the University of Colorado Boulder. The studies described in the present study represent work carried out as part of an NIH T32 fellowship through the Division of Cardiology at the University of Colorado Denver. Her long-term research goals are to investigate the efficacy of novel interventions for preserving vascular function with ageing, thereby preventing and/or delaying the progression of cardiovascular diseases. Rachel A. Gioscia-Ryan completed her PhD in the Integrative Physiology of Aging Laboratory at the University of Colorado Boulder in 2016 and is currently in medical school at the University of Michigan. She is pursuing a career as a clinician-scientist conducting integrative physiological studies with the aim of improving human health and patient care. * These authors contributed equally to this work.Abstract Oxidative stress-mediated arterial dysfunction (e.g. endothelial dysfunction and large elastic artery stiffening) is the primary mechanism driving age-related cardiovascular diseases. Accumulating evidence suggests the gut microbiome modulates host physiology because dysregulation ('gut dysbiosis') has systemic consequences, including promotion of oxidative stress. The present study aimed to determine whether the gut microbiome modulates arterial function with ageing. We measured arterial function in young and older mice after 3-4 weeks of treatment with broad-spectrum, poorly-absorbed antibiotics to suppress the gut microbiome. To identify potential mechanistic links between the gut microbiome and age-related arterial dysfunction, we sequenced microbiota from young and older mice and measured plasma levels of the adverse gut-derived metabolite trimethylamine N-oxide (TMAO). In old mice, antibiotics reversed endothelial dysfunction [area-under-the-curve carotid artery dilatation to acetylcholine in young: 345 ± 16 AU vs. old control (OC): 220 ± 34 AU, P < 0.01; vs. old antibiotic-treated (OA): 334 ± 15 AU; P < 0.01 vs. OC] and arterial stiffening (aortic pulse wave velocity in young: 3.62 ± 0.15 m s −1 vs. OC: 4.43 ± 0.38 m s −1 ; vs. OA: 3.52 ± 0.35 m s −1 ; P = 0.03). These improvements were accompanied by lower oxidative stress and greater antioxidant enzyme expression. Ageing altered the abundance of gut microbial taxa associated with gut dysbiosis. Lastly, plasma TMAO was higher with ageing (young: 2.6 ± 0.4 μmol L −1 vs. OC: 7.2 ± 2.0 μmol L −1 ; P < 0.0001) and suppressed by antibiotic treatment (OA: 1.2 ± 0.2 μmol L −1 ; P < 0.0001 vs. OC). The results of the present study provide the first evidence for the gut microbiome being an important mediator of age-related arterial dysfunction and ...

Key points The results of the present study establish the temporal pattern of age‐related vascular dysfunction across the adult lifespan in sedentary mice consuming a non‐Western diet, and the underlying mechanisms The results demonstrate that consuming a Western diet accelerates and exacerbates vascular ageing across the lifespan in sedentary mice They also show that lifelong voluntary aerobic exercise has remarkable protective effects on vascular function throughout the lifespan, in the setting of ageing alone, as well as ageing compounded by Western diet consumption Overall, the results indicate that amelioration of mitochondrial oxidative stress and inflammation are key mechanisms underlying the voluntary aerobic exercise‐associated preservation of vascular function across the lifespan in both the presence and absence of a Western dietary pattern Abstract Advancing age is the major risk factor for cardiovascular diseases, driven largely by vascular endothelial dysfunction (impaired endothelium‐dependent dilatation, EDD) and aortic stiffening (increased aortic pulse wave velocity, aPWV). In humans, vascular ageing occurs in the presence of differences in diet and physical activity, but the interactive effects of these factors are unknown. We assessed carotid artery EDD and aPWV across the lifespan in mice consuming standard (normal) low‐fat chow (NC) or a high‐fat/high‐sucrose Western diet (WD) in the absence (sedentary, SED) or presence (voluntary wheel running, VWR) of aerobic exercise. Ageing impaired nitric oxide‐mediated EDD (peak EDD 88 ± 12% 6 months P = 0.003 vs. 59 ± 9% 27 months NC‐SED), which was accelerated by WD (60 ± 18% 6 months WD‐SED). In NC mice, aPWV increased 32% with age (423 ± 13 cm/s at 24 months P < 0.001 vs. 321 ± 12 cm/s at 6 months) and absolute values were an additional ∼10% higher at any age in WD mice (P = 0.042 vs. NC‐SED). Increases in aPWV with age in NC and WD mice were associated with 30–65% increases in aortic intrinsic wall stiffness (6 vs. 19–27 months, P = 0.007). Lifelong aerobic exercise prevented age‐ and WD‐related vascular dysfunction across the lifespan, and this protection appeared to be mediated by mitigation of vascular mitochondrial oxidative stress and inflammation. Our results depict the temporal impairment of vascular function over the lifespan in mice, acceleration and exacerbation of that dysfunction with WD consumption, the remarkable protective effects of voluntary aerobic exercise, and the underlying mechanisms.

Aging is associated with stiffening of the large elastic arteries and consequent increases in systolic blood pressure (SBP), which together increase cardiovascular disease risk; however, the upstream mechanisms are incompletely understood. Using complementary translational approaches in mice and humans, we investigated the role of the gut microbiome-derived metabolite trimethylamine N-oxide (TMAO) in age-related aortic stiffening and increased SBP. Aortic stiffness was measured using carotid-femoral or aortic pulse wave velocity (PWV) in humans and mice, respectively. Study 1: Plasma TMAO concentrations were elevated ( P <0.001) in healthy middle-aged to older (6.3±5.8 µmol/L) versus young (1.8±1.4 µmol/L) humans and positively related to carotid-femoral PWV ( r 2 =0.15, P <0.0001) and SBP ( r 2 =0.09, P <0.001), independent of traditional cardiovascular risk factors. Study 2: Dietary supplementation with TMAO increased aPWV in young mice and exacerbated the already elevated aPWV of old mice, accompanied by increases in SBP of ≈10 mm Hg in both groups. TMAO-supplemented versus control-fed mice also had higher intrinsic mechanical stiffness of the aorta (stress-strain testing) associated with higher aortic abundance of advanced glycation end-products, which form crosslinks between structural proteins to promote aortic stiffening. Study 3: Ex vivo incubation of aortic rings with TMAO increased intrinsic stiffness, which was attenuated by the advanced glycation end-products crosslink breaker alagebrium and prevented by inhibition of superoxide signaling. TMAO induces aortic stiffening and increases SBP via formation of advanced glycation end-products and superoxide-stimulated oxidative stress, which together increase intrinsic wall stiffness. Increases in circulating TMAO with aging represent a novel therapeutic target for reducing risk of aortic stiffening-related clinical disorders.