Inorganic Nitrate as a Treatment for ANOCA: NO-ANOCA

Females with heart disease often present unique phenotypes but are underrepresented in clinical trials. In females with angina, 40-65% have non-obstructive coronary artery disease (ANOCA), often due to coronary microvascular dysfunction (CMD), which represents ~52% of ANOCA cases. CMD impairs myocardial perfusion (endothelial and/or non-endothelial dysfunction), often detected as reduced coronary flow reserve (CFR). CMD is underdiagnosed despite an elevated risk for major cardiac events and current treatments for it (e.g., beta-blockers, long-acting nitrates) may confer only marginal benefits.

A critical contributor to CMD is impaired nitric oxide (NO) production, essential for vascular function. Oral inorganic nitrate (NO3-) supplementation offers a promising strategy to enhance NO bioavailability through its conversion to nitrite (NO2-) by bacteria in the mouth. NO2- acts as a precursor to NO, releasing it under hypoxic or acidic conditions commonly seen in CMD. This non-enzymatic pathway bypasses the limitations of traditional nitrate therapies, such as systemic hypotension and nitrate tolerance. Moreover, despite established benefits of physical activity ~60% of ANOCA patients experience exercise-induced angina, reduced exercise tolerance, and diminished quality of life (QoL). Recent evidence suggests, however, that exercise can increase endothelial function, endogenous NO production, LVEF, and VO2peak in ANOCA patients. Thus, increased plasma NO2- via inorganic nitrate supplementation may enhance NO delivery, promote physical activity, improve fitness and QoL in this population, which in turn may increase vascular endothelial health.

In the WISE study, >50% of women with angina had minimal or no obstructive CAD (ANOCA), yet experience worse outcomes than asymptomatic women. ANOCA involves diverse mechanisms, including coronary microvascular dysfunction (CMD), endothelial dysfunction, and vasospasm. These heterogeneities hinder responses to traditional treatments, with CMD being the most common and often linked to endothelial dysfunction.

Nitric oxide (NO) is crucial for coronary microvascular function, regulating vasodilation. In CMD, reduced NO bioavailability and endothelial nitric oxide synthase (eNOS) uncoupling impairs vasodilation and increases oxidative stress. Inflammation in CMD further exacerbates microvascular dysfunction.

Our group and others have utilized inorganic nitrate (NO3-) supplementation to increase NO bioavailability in conditions with vascular dysfunction. NO3- decreases blood pressure, arterial stiffness, oxidative stress and inflammation, while improving vascular and cardiac function. NO3- is reduced to NO under slight hypoxic or acidic conditions, common in CMD, bypassing the limitations of long-acting nitrates. ANOCA patients, a population with the high levels of initial dysfunction, may gain the most benefit from exogenous NO3-.

Dr. Allen's lab has shown that acute NO3- supplementation increases NO metabolites and augments post-exercise vascular function. Our preliminary data in postmenopausal females (PMF) also suggest a link between NO3- supplementation and reduced ET-1 and IL-6 levels compared to PL. Supplementation with NO3- may increase the "delivery pool" of NO and improve ET-1 and Il-6 dysregulation, thus augmenting vascular function, leading to improved physical function and quality of life in females with CMD.

Approach:

This will be a single-site, double-blind, randomized crossover pilot study to investigate the effects of twice daily 70 mL of beetroot juice (BTR) (~13 mmol total NO3-/day) versus PL (NO3- -depleted) in eight females. Participants with clinically stable CMD (diagnosis <2 by CMR) will be enrolled. Participants will have angina or equivalent symptoms, and no evidence of obstructive epicardial CAD (stenosis <50%) by invasive catheterization or coronary computer tomography angiography (CCTA) or FFR/CT-FFR > 0.8 within the previous 2 years.

STUDY PROCEDURES:

Participants will undergo eligibility screening and informed consent by the study coordinators. Following baseline testing, subjects will be randomized to receive consume either ∼13 mmol of NO3- (BTR) or NO3- depleted placebo (PL) daily via two (morning and night) 70-mL bottles of juice (Beet It, James White Drinks Ltd., Ipswich, UK) for 14 days. Following a 7 day washout period, participants will consume the alternate treatment (BTR or PL) for an additional 14 days.

Baseline and testing at the end of each treatment allocation will include resting vitals, fasting venous blood draw (for plasma NO3-, NO2-, ET-1, IL-6), vascular function (brachial artery flow-mediated dilation, pulse wave velocity and reflection), exercise economy testing at 2 submaximal cycle workloads, QofL questionnaires (EQ-5D-3L, Duke Activity Status Inventory, Modified Morisky Medicine Scale, Rose Dyspnea Score, and Seattle Angina Q), and stress cardiac MRI (to evaluate myocardial perfusion using dynamic first-pass imaging).

Inclusion criteria

• Age ≥18 years.
• Female sex.
• Willing and able to provide written informed consent.
• Signs and symptoms of suspected ischemia prompted referral for further evaluation by cardiac catheterization or CCTA within two years of consent.
• No evidence of obstructive epicardial CAD (stenosis >50%) of a major epicardial vessel or an FFR ≤0.80 by invasive catheterization or CCTA. Patients who have not undergone cardiac catheterization of CT angiogram within the last 2 years for chest pain can be scheduled for a screening CT angiogram of the coronary arteries to confirm eligibility.
• Impaired coronary flow reserve (cut-off values depending on methodology use between ≤2.0 and ≤2.5 by stress testing PET/CMR or Invasive assessment) or Abnormal index of coronary microcirculatory resistance (e.g., IMR > 25)
• SGLT2i Naïve

Exclusion criteria

• History of non-ischemic cardiomyopathy LVEF <40% or hypertrophic cardiomyopathy.
• History of congestive heart failure, severe pulmonary disease, liver disease
• History of acute coronary syndrome (ACS) within previous 30 days
• Stroke within the last 180 days or intracranial hemorrhage at any time.
• Severe valvular disease
• Life expectancy <3 years, due to non-cardiovascular comorbidity.
• Pregnancy or women who are breast-feeding
• Type 1 diabetes mellitus
• Symptomatic hypotension or systolic BP<95 mmHg on 2 consecutive measurements
• Active malignancy requiring treatment at the time of visit
• Severe (eGFR <30 mL/min/1.73 m2 by CKD-EPI), unstable, or rapidly progressing renal disease at the time of randomization
• History of recurrent UTI/bladder/kidney infections
• Asthma with ongoing wheezing
• Known or suspected bronchoconstrictive or bronchospastic lung disease (ARDS, emphysema)
• Greater than first degree heart block
• Implanted cardiac device
• Profound sinus bradycardia (heart rates<40 beats per minute)
• Atrial fibrillation or supraventricular arrhythmias at time of imaging
• Known intolerance of nitrates (other than hypotension)
• History of reaction to iodinated contrast agents
• Any orthopedic, neurological, or other condition that prevents participant from exercising
• Individuals currently taking nitroglycerine (or inorganic nitrates), PDE-5 inhibitors (ex: Cialis, Viagra), and xanthine oxidase inhibitors (ex: Allopurinol)
• Smokers within the last 5 years
• Prisoners
• Cognitively impaired individuals
• Non-English Speaking