Inspiratory Muscle Strength Training Improves Vascular Endothelial Function in Older Adults by Altering Circulating Factors that Suppress Superoxide and Enhance Nitric Oxide
Authors: Craighead Daniel H. , Ziemba Brian P. , Freeberg Kaitlin A. , Rossman Matthew J. , Brown Benjamin C. , Nemkov Travis , Reisz Julie A. , D’Alessandro Angelo , Chonchol Michel , Bailey E. Fiona , Seals Douglas R. 
Published: April 2020

BackgroundVascular endothelial dysfunction associated with decreased nitric oxide (NO)‐bioavailability secondary to excessive superoxide‐associated oxidative stress is a key antecedent of age‐associated cardiovascular diseases. High‐resistance inspiratory muscle strength training (IMST) is a promising form of time‐efficient physical training for promoting cardiovascular health with aging. However, the efficacy and mechanisms of IMST for improving endothelial function in older adults have not been established. We hypothesized IMST may induce changes in the molecular composition of the circulating blood that improve endothelial function via superoxide suppression‐related increases in NO bioavailability.PurposeTo determine the efficacy of IMST for improving vascular endothelial function in vivo, the influence of IMST‐induced changes in circulating factors on endothelial superoxide and NO production ex vivo, and IMST‐induced changes in the molecular composition of the circulation.MethodsTwenty older adults underwent 6 weeks of IMST (30 breaths/day; 6 days/week; 75% maximum inspiratory pressure [PIMAX]) (n=10, 5M/5F, age: 68±2 years) or low‐resistance sham (15% PIMAX) training (n=10, 6M/4F, age 70±2 years) in a randomized, double‐blind study. Vascular endothelial function was assessed via brachial artery flow‐mediated dilation [FMDBA]. HUVECs were cultured with serum collected at baseline and post‐intervention (n=12; 5 IMST, 7 sham). NO production stimulated with acetylcholine and basal superoxide production from HUVECs were measured using fluorescent microscopy. Plasma metabolite levels were assessed via targeted metabolomics (n=14; 7 IMST, 7 sham) at baseline and post‐intervention with ultra‐high‐performance liquid chromatography‐mass spectrometry.ResultsFMDBA increased 45% after 6 weeks of IMST (pre: 4.7±0.8 Δ%, post: 6.8±0.7 Δ%; p=0.01) but not after sham training (pre: 3.7±0.6 Δ%, post: 3.8±0.6 Δ%; p=0.99), such that FMDBA was 79% higher in the IMST group compared to sham training post‐intervention (p=0.01). HUVEC production of NO was 66% higher (p=0.04) while superoxide production was 38% lower post‐intervention in the IMST group vs. sham, though the latter was not statistically significant (p=0.17). Plasma metabolomics revealed greater levels of arginine (p=0.02) and ornithine (p=0.06) in the IMST group vs. sham post‐intervention, consistent with increased NO production. A greater level of dehydroascorbate (p=0.04) and changes in markers of glutathione synthesis (decreased alanine p=0.02; increased cystine p=0.06) were observed in the IMST group vs. sham post‐intervention, suggesting greater antioxidant defense status with IMST.ConclusionThese findings suggest IMST is a promising intervention for improving vascular endothelial function in older adults, in part by inducing changes in the molecular composition of the blood that increases NO bioavailability by suppressing superoxide.Support or Funding InformationAHA 18POST33990034, R21 AG061677