Nitrites, Skeletal Muscle Mitochondrial Bioenergetics, and Physical Activity in Old Age

This 2-site randomized double blinded controlled trial is to confirm and more definitively clarify the impact of a 12-week course of nitrite versus placebo on mitochondrial bioenergetics in older sedentary adults. This investigator will take an integrative physiology approach to determine the effect of nitrite therapy on a comprehensive assessment of mitochondrial energetics, skeletal muscle vascular function, and whole body physical function (cardiorespiratory function, exercise endurance, strength, balance, and physical activity) and fatigability.

Old age is associated with declining skeletal muscle mitochondrial bioenergetics with related decrements in cardiorespiratory fitness (CRF) and physical function that predispose to frailty, disability, and diminished quality of life. While exercise training may moderate and possibly even reverse declines in mitochondrial bioenergetics, potential for such benefit is typically confounded by exercise intolerance with early fatigability that results from the same age-related mitochondrial declines. Consequently, sedentariness is endemic and insidious among the growing population of older adults. This trial is to study the utility of inorganic nitrite salts as a novel means to modify this detrimental pattern. Classic studies demonstrate that nitrite facilitates hypoxic vasodilation in muscle. This investigator's preliminary data suggests that nitrite treatment also augments skeletal muscle mitochondrial bioenergetics in older adults. This investigator proposes improving mitochondrial function will also be reflected in clinical parameters, including CRF as well as broader functional attributes (endurance, strength, and balance) that enable physical activity (PA) and opportunity to mitigate frailty and disability. As such, this application is in line with the National Institute on Aging's mission to develop targeted interventions to prevent and treat age-associated conditions. This multi-disciplinary team has published seminal work indicating that mitochondrial bioenergetics and CRF are significant determinants of physical function in older adults. In parallel efforts, this investigative team showed efficacy of chronic nitrite therapy to improve mitochondrial bioenergetics in older sedentary adults. Only one month of nitrite therapy significantly improved ex vivo assessments of mitochondrial energetics in skeletal muscle biopsies, concomitant with increased skeletal muscle sirtuin-3 expression, a nicotinamide adenine dinucleotide (NAD) dependent lysine deacetylase and key regulator of mitochondrial metabolism. These key data reinforce the premise that nitrite enhances vital mitochondrial metabolism in older adults. Moreover, improvement in muscle energetics in nitrite-treated older adults was linked with increased exercise efficiency as evidenced by reduced oxygen consumption (VO2) during submaximal steady-state walking. This data supports the hypothesis that nitrite will make physical function easier such that physical activity will increase.

Eligibility Criteria:
Inclusion Criteria:

* Age ≥70 years
* Sedentary (\<1 hour/week of volitional exercise activity)
* Clinically stable (euvolemic; baseline HR \<100 bpm) and without hospitalization or invasive cardiac procedure for 6 weeks

Exclusion Criteria:

* Blood pressure \<110 or \>160/95 mmHg
* Orthopedic or other chronic condition which limits physical activity or exercise testing assessments
* If valve replacement has been performed, patient may not be enrolled for 12 months after this procedure
* Severe peripheral or pulmonary artery disease
* Anemia: Hgb \<11.0 (♂),10.0 (♀) gm/dl
* Participants with diabetes whose HgbA1c \>10.0%
* Chronic alcohol (\>14 drinks ETOH a week) or drug (any cocaine, methamphetamine, and cannabis ≥4 x week) dependency
* Allergy to lidocaine and red dye
* Chronic use of oral corticosteroids or other medications that affect muscle function
* Current use of organic nitrates or phosphodiesterase type 5 (PDE5) inhibitors
* Unable to hold warfarin, direct-acting oral anticoagulants (DOACs), non-steroidal anti-inflammatory medications (NSAIDs) or aspirin for 3 days prior to muscle biopsy, or to hold thienopyridine medications for 5 days prior to muscle biopsy. Participants unable or unwilling to hold will follow the modified ASA hold plan
* Any bleeding disorder that would contraindicate biopsy such as history of clinically significant bleeding diathesis (e.g., Hemophilia A or B, Von Willebrand's Disease or congenital Factor VII deficiency)
* Unstable psychiatric diagnosis that would affect adherence and ability to complete the protocol
* Dementia or inability to give informed consent or follow study protocol
* End-stage disease
* Other chronic unstable disease such as active neoplasm, end stage chronic kidney, liver or other organ disease