Body mass-normalized moderate dose of dietary nitrate intake improves endothelial function and walking capacity in patients with peripheral artery disease

Influence of acute dietary nitrate supplementation timing on nitrate metabolism, central and peripheral blood pressure and exercise tolerance in young men

PURPOSE

Dietary nitrate (NO3-) supplementation can lower systolic blood pressure (SBP) and improve exercise performance. Salivary flow rate (SFR) and pH are key determinants of oral NO3- reduction and purported to peak in the afternoon. We tested the hypotheses that NO3--rich beetroot juice (BR) would increase plasma [nitrite] ([NO2-]), lower SBP and improve exercise performance to a greater extent in the afternoon (AFT) compared to the morning (MORN) and evening (EVE).

METHOD

Twelve males completed six experimental visits in a repeated-measures, crossover design. NO3--depleted beetroot juice (PL) or BR (~ 13 mmol NO3-) were ingested in the MORN, AFT and EVE. SFR and pH, salivary and plasma [NO3-] and [NO2-], brachial SBP and central SBP were measured pre and post supplementation. A severe-intensity exercise tolerance test was completed to determine cycling time to exhaustion (TTE).

RESULTS

There were no between-condition differences in mean SFR or salivary pH. The elevation in plasma [NO2-] after BR ingestion was not different between BR-MORN, BR-AFT and BR-EVE. Brachial SBP was unchanged following BR supplementation in all conditions. Central SBP was reduced in BR-MORN (- 3 ± 4 mmHg), BR-AFT (- 4 ± 3 mmHg), and BR-EVE (- 2 ± 3 mmHg), with no differences between timepoints. TTE was not different between BR and PL at any timepoint.

CONCLUSION

Acute BR supplementation was ineffective at improving TTE and brachial SBP and similarly effective at increasing plasma [NO2-] and lowering central SBP across the day, which may have implications for informing NO3- supplementation strategies.

Limited Effects of Inorganic Nitrate Supplementation on Exercise Training Responses: A Systematic Review and Meta-analysis

BACKGROUND

Inorganic nitrate (NO3-) supplementation is purported to benefit short-term exercise performance, but it is unclear whether NO3- improves longer-term exercise training responses (such as improvements in VO2peak or time to exhaustion (TTE)) versus exercise training alone. The purpose of this systematic review and meta-analysis was to determine the effects of NO3- supplementation combined with exercise training on VO2peak and TTE, and to identify potential factors that may impact outcomes.

METHODS

Electronic databases (PubMed, Medscape, and Web of Science) were searched for articles published through June 2022 with article inclusion determined a priori as: (1) randomized placebo-controlled trials, (2) exercise training lasted at least three weeks, (3) treatment groups received identical exercise training, (4) treatment groups had matched VO2peak at baseline. Study quality was assessed using the Cochrane Risk-of-Bias 2 tool. Standardized mean difference (SMD) with 95% confidence intervals (CI) were calculated using restricted maximum likelihood estimation between pre- and post-training differences in outcomes. Moderator subgroup and meta-regression analyses were completed to determine whether the overall effect was influenced by age, sex, NO3- dosage, baseline VO2peak, health status, NO3- administration route, and training conditions.

RESULTS

Nine studies consisting of eleven trials were included: n = 228 (72 females); age = 37.7 ± 21 years; VO2peak: 40 ± 18 ml/kg/min. NO3- supplementation did not enhance exercise training with respect to VO2peak (SMD: 0.18; 95% CI: -0.09, 0.44; p = 0.19) or TTE (SMD: 0.08; 95% CI: - 0.21, 0.37; p = 0.58). No significant moderators were revealed on either outcome. Subset analysis on healthy participants who consumed beetroot juice (BRJ) revealed stronger trends for NO3- improving VO2peak (p = 0.08) compared with TTE (p = 0.19), with no significant moderators. Sunset funnel plot revealed low statistical power in all trials.

CONCLUSIONS

NO3- supplementation combined with exercise training may not enhance exercise outcomes such as VO2peak or TTE. A trend for greater improvement in VO2peak in healthy participants supplemented with BRJ may exist (p = 0.08). Overall, future studies in this area need increased sample sizes, more unified methodologies, longer training interventions, and examination of sex as a biological variable to strengthen conclusions.

Effect of Dietary Supplements Which Upregulate Nitric Oxide on Walking and Quality of Life in Patients with Peripheral Artery Disease: A Meta-Analysis

This systematic review pooled evidence from randomised controlled trials (RCTs) on the effectiveness of dietary upregulators of nitric oxide (NO) in improving the walking and quality of life of patients with peripheral artery disease (PAD). RCTs examining the effect of dietary upregulators of NO in patients with PAD were included. The primary outcome was the maximum walking distance. Secondary outcomes were the initial claudication distance, the six-minute walking distance, quality of life, the ankle-brachial pressure index (ABI), adverse events and risk of mortality, revascularisation or amputation. Meta-analyses were performed using random effects models. The risk of bias was assessed using Cochrane's ROB-2 tool. Leave-one-out and subgroup analyses were conducted to assess the effect of individual studies, the risk of bias and intervention type on pooled estimates. Thirty-four RCTs involving 3472 participants were included. Seven trials tested NO donors, nineteen tested antioxidants, three tested NO synthase inducers and five tested enhancers of NO availability. Overall, the dietary supplements significantly improved the initial claudication (SMD 0.34; 95%CI 0.04, 0.64; p = 0.03) but not maximum walking (SMD 0.13; 95%CI -0.17, 0.43; p = 0.39) distances. Antioxidant supplements significantly increased both the maximum walking (SMD 0.36; 95%CI 0.14, 0.59; p = 0.001) and initial claudication (SMD 0.58; 95%CI 0.26, 0.90; p < 0.001) distances. The dietary interventions did not improve the physical function domain of the Short Form-36 (SMD -0.16; 95%CI -0.32, 0.00; p = 0.38), ABI or risk of adverse events, mortality, revascularisation or amputation. Dietary NO upregulators, especially antioxidants, appear to improve the initial claudication distance in patients with PAD. Larger high-quality RCTs are needed to fully examine the benefits and risks of these treatments. PROSPERO Registration: CRD42022256653.

Nutraceuticals in the Prevention and Therapeutic Treatment of Cardiovascular and Cerebrovascular Disease

PURPOSE

This review overviews and highlights arterial stiffening as a key physiological process and target for the prevention and/or lowering of cardio- and cerebrovascular disease (collectively CVD) risk.

METHODS

We identified nutraceutical approaches from randomized controlled trials and discussed the associated mechanisms by which these compounds lower age-related arterial stiffness. Age-related CVD are the leading cause of mortality in modernized societies. Arterial dysfunction, specifically stiffening of the large elastic arteries during midlife, is a key physiological process resulting in increased CVD risk. Current pharmaceutical approaches for lowering age-related arterial stiffness have limited efficacy, thus highlighting the need to identify novel approaches for lowering arterial stiffness and thereby CVD risk. Lifestyle interventions are a historical first-line approach to prevent and/or lower the adverse arterial stiffening effects observed with aging. Nutraceutical interventions, defined as a food or part of a food providing health benefits, are a nonpharmacological, novel lifestyle approach to lower age-associated arterial stiffness. Therefore, identifying nutraceutical approaches to lower CVD risk is clinically significant.

SUMMARY

This review provides a basic, yet essential, understanding for emerging nutraceutical strategies for the prevention and therapeutic treatment of CVD.

Moderate dose of dietary nitrate improves skeletal muscle microvascular function in patients with peripheral artery disease

Peripheral artery disease (PAD) is an atherosclerotic disease characterized by compromised lower-extremity blood flow that impairs walking ability. We showed that a moderate dose of dietary nitrate in the form of beetroot juice (BRJ, 0.11 mmol/kg) can improve macrovascular function and maximal walking distance in patients with PAD. However, its impacts on the microcirculation and autonomic nervous system have not been examined. Therefore, we investigated the impacts of this dose of dietary nitrate on skeletal muscle microvascular function and autonomic nervous system function and further related these measurements to 6-min walking distance, pain-free walking distance, and exercise recovery in patients with PAD. Patients with PAD (n = 10) ingested either BRJ or placebo in a randomized crossover design. Heart rate variability, skeletal muscle microvascular function, and 6-min walking distance were performed pre- and post-BRJ and placebo. There were significant group × time interactions (P < 0.05) for skeletal muscle microvascular function, 6-min walking distance, and exercise recovery, but no changes (P > 0.05) in heart rate variability or pain-free walking distance were noted. The BRJ group demonstrated improved skeletal muscle microvascular function (∆ 22.1 ± 7.5 %·min-1), longer 6-min walking distance (Δ 37.5 ± 9.1 m), and faster recovery post-exercise (Δ -15.3 ± 4.2 s). Furthermore, changes in skeletal muscle microvascular function were positively associated with changes in 6-min walking distance (r = 0.5) and pain-free walking distance (r = 0.6). These results suggest that a moderate dose of dietary nitrate may support microvascular function, which is related to improvements in walking distance and claudication in patients with PAD.

Agreement between multiparametric MRI (PIVOT), Doppler ultrasound, and near-infrared spectroscopy-based assessments of skeletal muscle oxygenation and perfusion

Skeletal muscle perfusion and oxygenation are commonly evaluated using Doppler ultrasound and near-infrared spectroscopy (NIRS) techniques. However, a recently developed magnetic resonance imaging (MRI) sequence, termed PIVOT, permits the simultaneous collection of skeletal muscle perfusion and T2* (an index of skeletal muscle oxygenation).

PURPOSE

To determine the level of agreement between PIVOT, Doppler ultrasound, and NIRS-based assessments of skeletal muscle perfusion and oxygenation.

METHODS

Twelve healthy volunteers (8 females, 25 ± 3 years, 170 ± 11 cm, 71.5 ± 8.0 kg) performed six total reactive hyperemia protocols. During three of these reactive hyperemia protocols, Tissue Saturation Index (TSI) and oxygenated hemoglobin (O2Hb) were recorded from the medial gastrocnemius (MG) and tibialis anterior (TA), and blood flow velocity was recorded from the popliteal artery (BFvpop) via Doppler Ultrasound. The other three trials were performed inside the bore of a 3 T MRI scanner, and the PIVOT sequence was used to assess perfusion (PIVOTperf) and oxygenation (T2*) of the medial gastrocnemius and tibialis anterior muscles. Positive incremental areas under the curve (iAUC) and times to peak (TTP) were calculated for each variable, and the level of agreement between collection methods was evaluated via Bland-Altman analyses and Spearman's Rho correlation analyses.

RESULTS

The only significant bivariate relationships observed were between the T2* vs. TSI iAUC and PIVOTperf vs. BFvpop values recorded from the MG. Significant mean differences were observed for all comparisons (all P ≤ 0.038), and significant proportional biases were observed for the PIVOTperf vs. tHb TTP (R2 = 0.848, P < 0.001) and T2* vs. TSI TTP comparisons in the TA (R2 = 0.488, P = 0.011), and the PIVOTperf vs. BFvpop iAUC (R2 = 0.477, P = 0.013) and time to peak (R2 = 0.851, P < 0.001) comparisons in the MG.

CONCLUSIONS

Our findings suggest that the PIVOT technique has, at best, a moderate level of agreement with Doppler ultrasound and NIRS assessment methods and is subject to significant proportional bias. These findings do not challenge the accuracy of either measurement technique but instead reflect differences in the vascular compartments, sampling volumes, and parameters being evaluated.

Agri-Food Waste from Apple, Pear, and Sugar Beet as a Source of Protective Bioactive Molecules for Endothelial Dysfunction and Its Major Complications

Endothelial damage is recognized as the initial step that precedes several cardiovascular diseases (CVD), such as atherosclerosis, hypertension, and coronary artery disease. It has been demonstrated that the best treatment for CVD is prevention, and, in the frame of a healthy lifestyle, the consumption of vegetables, rich in bioactive molecules, appears effective at reducing the risk of CVD. In this context, the large amount of agri-food industry waste, considered a global problem due to its environmental and economic impact, represents an unexplored source of bioactive compounds. This review provides a summary regarding the possible exploitation of waste or by-products derived by the processing of three traditional Italian crops-apple, pear, and sugar beet-as a source of bioactive molecules to protect endothelial function. Particular attention has been given to the bioactive chemical profile of these pomaces and their efficacy in various pathological conditions related to endothelial dysfunction. The waste matrices of apple, pear, and sugar beet crops can represent promising starting material for producing "upcycled" products with functional applications, such as the prevention of endothelial dysfunction linked to cardiovascular diseases.

Acute dietary nitrate supplementation does not change venous volume and compliance in healthy young adults

In this randomized single-blind, placebo-controlled, crossover study, we investigated the influence of inorganic nitrate (NO₃^-) supplementation on venous volume and compliance in the resting forearm and calf. Twenty healthy young adults were assigned to receive an NO₃^--rich beverage (beetroot juice [BRJ]: 140 mL; ~8 mmol NO₃^-) or an NO₃^¯-depleted control beverage (prune juice [CON]: 166 mL; < 0.01 mmol NO₃^-). Two hours after consuming the allocated beverage, each participant rested in the supine position for 20 min. Cuffs were then placed around the right upper arm and right thigh, inflated to 60 mmHg for 8 min, and then decreased to 0 mmHg at a rate of 1 mmHg/s. During inflation and deflation of cuff pressure, changes in venous volume in the forearm and calf were measured by venous occlusion plethysmography. Venous compliance was calculated as the numerical derivative of the cuff pressure‒venous volume curve in the limbs. The plasma NO₃^- concentration was elevated by intake of BRJ (before, 15.5 ± 5.8 µM; after, 572.0 ± 116.1 µM, P < 0.05) but not by CON (before, 14.8 ± 7.2 µM; after, 15.3 ± 7.4 µM, P > 0.05). On the other hand, there was no significant difference in venous volume or compliance in the forearm or calf between BRJ and CON. These findings suggest that although acute inorganic NO₃^- supplementation may enhance the activity of nitric oxide (NO) via NO₃^- → nitrite → NO pathway, it does not influence venous volume or compliance in the limbs in healthy young adults.

Plant-Based Foods and Vascular Function: A Systematic Review of Dietary Intervention Trials in Older Subjects and Hypothesized Mechanisms of Action

Cardiovascular diseases, still the leading cause of mortality in the world, are closely related to vascular function. Older subjects are more susceptible to endothelial dysfunction and therefore it is important to define possible preventive or support strategies, such as consumption of foods with health-promoting effects. This systematic review aims to summarize the currently available evidence on acute or chronic trials testing the effect of selected plant-based foods on vascular function parameters in older subjects, and consider plausible mechanisms that may support the main findings. A total of 15 trials were included and analyzed, testing the effects of beetroot, plum, blueberry, and vegetable oils. We found some interesting results regarding markers of vascular reactivity, in particular for beetroot, while no effects were found for markers of arterial stiffness. The amelioration of vascular function seems to be more related to the restoration of a condition of nitric oxide impairment, exacerbated by diseases or hypoxic condition, rather than the enhancement of a physiological situation, as indicated by the limited effects on healthy older subjects or in control groups with young subjects. However, the overall set of selected studies is, in any case, rather limited and heterogeneous in terms of characteristics of the studies, indicating the need for additional high-quality intervention trials to better clarify the role of vegetable foods in restoring and/or improving vascular function in order to better elucidate the mechanisms through which these foods may exert their vascular health benefits in older subjects.

Impaired microcirculatory function, mitochondrial respiration, and oxygen utilization in skeletal muscle of claudicating patients with peripheral artery disease

Peripheral artery disease (PAD) is an atherosclerotic disease that impairs blood flow and muscle function in the lower limbs. A skeletal muscle myopathy characterized by mitochondrial dysfunction and oxidative damage is present in PAD; however, the underlying mechanisms are not well established. We investigated the impact of chronic ischemia on skeletal muscle microcirculatory function and its association with leg skeletal muscle mitochondrial function and oxygen delivery and utilization capacity in PAD. Gastrocnemius samples and arterioles were harvested from patients with PAD (n = 10) and age-matched controls (Con, n = 11). Endothelium-dependent and independent vasodilation was assessed in response to flow (30 μL·min-1), acetylcholine, and sodium nitroprusside (SNP). Skeletal muscle mitochondrial respiration was quantified by high-resolution respirometry, microvascular oxygen delivery, and utilization capacity (tissue oxygenation index, TOI) were assessed by near-infrared spectroscopy. Vasodilation was attenuated in PAD (P < 0.05) in response to acetylcholine (Con: 71.1 ± 11.1%, PAD: 45.7 ± 18.1%) and flow (Con: 46.6 ± 20.1%, PAD: 29.3 ± 10.5%) but not SNP (P = 0.30). Complex I + II state 3 respiration (P < 0.01) and TOI recovery rate were impaired in PAD (P < 0.05). Both flow and acetylcholine-mediated vasodilation were positively associated with complex I + II state 3 respiration (r = 0.5 and r = 0.5, respectively, P < 0.05). Flow-mediated vasodilation and complex I + II state 3 respiration were positively associated with TOI recovery rate (r = 0.8 and r = 0.7, respectively, P < 0.05). These findings suggest that chronic ischemia attenuates skeletal muscle arteriole endothelial function, which may be a key mediator for mitochondrial and microcirculatory dysfunction in the PAD leg skeletal muscle. Targeting microvascular dysfunction may be an effective strategy to prevent and/or reverse disease progression in PAD.NEW & NOTEWORTHY Ex vivo skeletal muscle arteriole endothelial function is impaired in claudicating patients with PAD, and this is associated with attenuated skeletal muscle mitochondrial respiration. In vivo skeletal muscle oxygen delivery and utilization capacity is compromised in PAD, and this may be due to microcirculatory and mitochondrial dysfunction. These results suggest that targeting skeletal muscle arteriole function may lead to improvements in skeletal muscle mitochondrial respiration and oxygen delivery and utilization capacity in claudicating patients with PAD.