Nitrate-rich beetroot juice supplementation in midlife and older adults with renal dysfunction increases vascular endothelial function and changes the circulating milieu to improve endothelial cell nitric oxide production and oxidative stress

Abstract

BACKGROUND: Midlife and older (ML/O) adults with mild-to-moderate renal dysfunction (MRD) are at increased risk for cardiovascular disease (CVD). A key antecedent to CVD in ML/O adults with MRD is vascular endothelial dysfunction, mediated by declines in nitric oxide (NO) bioavailability due to excess reactive oxygen species (ROS)-related oxidative stress. We have shown that targeting the nitrate-nitrite-NO pathway with sodium nitrite in heathy ML/O adults improves endothelial function and changes the circulating milieu to lower endothelial cell (EC) ROS bioactivity. However, if nitrate-rich beetroot juice (N-BRJ) is effective for improving endothelial function in ML/O men and women with MRD is unknown. HYPOTHESES: We tested the hypotheses that chronic N-BRJ in ML/O men and women with MRD would: 1) improve endothelial function and 2) induce changes to the circulating milieu to increase EC NO production and lower EC ROS bioactivity. We also assessed possible sex differences in the effcacy of N-BRJ for improving endothelial function. METHODS: Twenty-six ML/O men and women with MRD (estimated glomerular filtration rate [eGFR; CKD-EPI]: 40-89 mL/min/1.73m2) underwent three months of supplementation with N-BRJ (70 mL with 6.45 mmol nitrate/day) (n=13, 7 women; age: 65±2 years; eGFR: 69.2±3.3 mL/min/1.73m2) or nitrate-depleted BRJ (placebo, PBO) (n=13, 7 women; age: 68±2 years; eGFR: 79.8±3.1 mL/min/1.73m2) in a randomized, placebo-controlled, parallel-group design clinical trial. Endothelial function was assessed by brachial artery flow-mediated dilation (FMDBA). Smooth muscle sensitivity to NO was assessed by brachial artery dilation to sublingual nitroglycerin. Human aortic ECs (HAECs) in culture were exposed to 10% subject serum (n=10[6-7 women]/group) collected before and after N-BRJ and PBO supplementation. Acetylcholine-stimulated NO production (DAR-4M-AM) and whole-cell ROS bioactivity (CellROX) were assessed in HAECs using immunofluorescence. Results: N-BRJ supplementation increased FMDBA by 28% (pre: 4.6±0.7%, post: 5.9±0.8%; p=0.03). FMDBA did not change with PBO (pre: 4.6±0.9%, post: 4.7±0.8%; p>0.05). Traditional CVD risk factors (i.e., blood pressure, cholesterol) and smooth muscle sensitivity to NO were unchanged in both groups (p>0.05). Preliminary assessments suggest greater improvements in endothelial function with N-BRJ in women (Δ=post-pre intervention; ΔFMDBA=1.6±0.4) compared to men (ΔFMDBA=0.9±1.0). Compared to pre-intervention, NO production was (trending) 7% higher (p=0.05) and ROS bioactivity was 25% lower (p=0.02) in HAECs exposed to serum collected post N-BRJ. Serum from PBO had no effects (p>0.05). CONCLUSION: N-BRJ supplementation in ML/O adults with MRD holds promise for improving endothelial function, in part by inducing changes to the circulating milieu that increase NO production and decrease oxidative stress in ECs. The effects on endothelial function may be greater in women compared to men. Targeting the nitrate-nitrite-NO pathway with N-BRJ may be an effective strategy for improving endothelial function in ML/O adults with renal dysfunction to possibly reduce CVD risk. K01DK115524 (MJR); R01AG013038 (DRS); F32HL167552 (KOM); NIH/NCATS CTSA UL1TR002535. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.