Effect of Dietary Nitrate Ingestion in Heart Failure

This study evaluates the addition of inorganic dietary nitrate to the optimal treatment of patients diagnosed with heart failure with reduced ejection fraction. Some vegetables contain large amounts of inorganic nitrate, and research suggests that this nitrate has beneficial effects on the heart and blood vessels. We have shown in lab experiments that nitrate has positive effects on the heart. We wish to test whether dietary nitrate might be useful in halting deterioration and/or improving heart function in patients with heart failure, with a specific focus on a marker of poor outcome in heart failure: high uric acid levels. Half of the patients will receive nitrate-rich beetroot juice, and the other half a nitrate-deplete placebo beetroot juice.

Background: Heart failure (HF) affects 1-2% of those under 70 years, and 10-20% of those over 70 years in developed countries; approximately 900,000 people in the UK suffer with HF. Despite several promising pre-clinical targets, clinical translation has been disappointing, with very few successful phase 3 studies of new HF therapeutics. Dysfunction of the classical pathways that underlie endothelial nitric oxide (NO) production, with deficient cardiac constitutive NO supply, are thought to play a major role in the pathogenesis of HF. It has been mooted that novel strategies that replace/restore this diminished NO have therapeutic potential.

The organic nitrates, as a method of NO delivery, provide an efficacious treatment in the acute HF setting. However, the development of tolerance, tachyphylaxis, and endothelial dysfunction with long-term use severely limits their utility in chronic heart disease. Alternative methods for sustained NO delivery without tolerance are therefore of interest.

Recent clinical research demonstrates that inorganic nitrate offers this possibility through sequential chemical reduction, first via the enterosalivary circuit to nitrite, and subsequently from nitrite to NO. In particular, pre-clinical research suggests that delivery of NO via this pathway imparts benefit in HF models. Dietary inorganic nitrate is known to provide a safe and non-invasive method to elevate NO in humans, and a once daily dose (5-6mmol), in the form of a beetroot juice, can improve vascular function and reduce blood pressure in hypertensives.

Inorganic nitrate as a HF treatment is particularly exciting since a key pathway involved in the generation of NO from nitrate is xanthine oxidoreductase (XOR); an enzyme upregulated in HF. Conventionally, XOR is considered detrimental as it generates superoxide and uric acid; both exert negative effects on cardiac function, and are associated with worse outcomes in HF. However, XOR also plays an important role in the second step of nitrate bioactivation: conversion of nitrite to NO in the heart. Importantly, we have hypothesised that in an environment of elevated XOR activity, such as HF, delivery of inorganic nitrate to the body would result in reductions in superoxide/uric acid with concomitant elevations in NO. This might prove more efficacious than simply inhibiting the enzyme using classical inhibitors. Importantly, a recent study (EXACT-HF) has shown a trend for reduced HF re-hospitalisations in those with XOR inhibition via allopurinol; it has been suggested that greater benefits might be seen if these effects are coupled with NO delivery.

Research Hypothesis and Aims: We aim to investigate whether dietary inorganic nitrate provides benefit in patients with HF. We will determine whether inorganic nitrate delivery by elevating nitrite, delivers substrate to XOR resulting in a two-fold benefit: increasing NO production, whilst concomitantly reducing superoxide and uric acid levels.

Plan of Investigation: a randomised double-blind placebo-controlled parallel two-limb study in New York Heart Association (NHYA) class II-III HF patients. Patients with left ventricular ejection fraction (LVEF) \<50% and elevated NT-proBNP/ BNP levels will be enrolled and stratified by degree of hyperuricaemia. 92-patients will receive a once daily dose of nitrate-rich beetroot juice (versus nitrate-deplete beetroot juice) for 12-weeks. The study is powered for significant reductions in hyperuricaemia. Powered secondary outcomes include circulating nitrite/nitrate levels, nitrite reductase activity, and a difference in LVEF from baseline by contrast echocardiography. A number of mechanistic exploratory outcomes will also be reported, including assessments of oxidative stress, erythrocytic XOR activity, 6-minute walk test, quality of life questionnaire and levels of NT-proBNP/BNP as surrogate measures of cardiac dysfunction.

Benefits: This trial if positive will identify a new, safe and easy-to-deliver therapeutic option for HF patients. The NHS would benefit by providing a new inexpensive pharmacotherapy for a disease with significant unmet need and increasing burden to the health service.

Eligibility Criteria:
Inclusion Criteria:

1. Age ≥18 years
2. Diagnosed with heart failure with reduced ejection fraction on the basis of:

   1. LVEF ≤50% as assessed by Echocardiography (or cardiac MRI)
   2. raised BNP and/or NT-proBNP levels placing patients in the "high risk" category, to ensure heart failure is the cause of symptoms:

      * stable heart failure: NT-proBNP \>600pg/mL and BNP \>150pg/mL
      * hospitalisation within 12 months: NT-proBNP \>400pg/mL and BNP \>100pg/mL
3. NYHA Class II-III symptoms
4. On optimally-tolerated, stable (\>12 weeks) prognostic medical therapy (beta-blocker, ACE-inhibitor or ARB, mineralocorticoid therapy if deemed necessary)
5. No heart failure-related hospitalisation for \>12 weeks
6. Clinic systolic blood pressure ≥95mmHg
7. Able and willing to give written informed consent

The intervention with dietary nitrate is intentionally designed to be in addition to the patient's own lifestyle. There will be no restrictions placed on diet, anti-oxidant supplements or prescription medications, other than those listed in the exclusion criteria below.

Exclusion Criteria:

1. Use of anti-bacterial mouthwash or tongue scrapes (current or unwillingness to cease such mouthcare for at least one month prior to entering the study, and for the duration of the trial) as this interrupts the enterosalivary circuit and thus prevents the bioactivity of nitrate
2. History of recurrent symptomatic gout or current treatment with xanthine oxidase inhibitors for hyperuricaemia
3. Concomitant use of long acting organic nitrates or phosphodiesterase inhibitors (not including on an as required basis)
4. Angina at CCS Class III/IV, requiring regular use of sublingual GTN (considered \>twice/week), or awaiting revascularisation
5. If LVEF in the range 40-50%, impaires systolic function secondary to uncorrected valve disease, primary pulmonary hypertension, active myocarditis, constrictive pericarditis, restrictive cardiomyopathy or hypertrophic cardiomyopathy
6. Renal failure with eGFR\<30 at screening
7. History of symptomatic renal stone disease
8. Current life-threatening condition that might prevent a patient-subject completing the study
9. Allergy to SonoVue Echo contrast
10. Pregnancy, breast feeding or planned pregnancy
11. Anaemia, defined as Haemaglobin \<80g/L
12. Subjects with any acute infection, or recent systemic antibiotics (oral or intravenous) within 3 months of screening, or significant trauma (burns, fractures)
13. The subject has a three-month prior history of regular alcohol consumption exceeding an average weekly intake of \> 28 units (or an average daily intake of greater than 3 units) for males, or an average weekly intake of \> 21 units (or an average daily intake of greater than 2 units) for females. 1 unit is equivalent to a half-pint (284mL) of beer/lager; 25mL measure of spirits or 125mL of wine
14. Mobility thought to be restricted significantly by other illnesses apart from heart failure
15. Any other subject whom the Investigator deems unsuitable for the study (e.g. due to other medical reasons, laboratory abnormalities, expected study medication noncompliance, or subject's unwillingness to comply with all study-related study procedures)