The Use of L-arginine to Mitigate the Cardiovascular Effects of Exposure to Traffic-related Air Pollution
Condition: Blood Pressure; Cardiac Ischemia
MeSH terms: Coronary Artery Disease; Myocardial Ischemia; Ischemia
Study type: Interventional

Summary: 
      The present study is aimed to investigate whether oral L-arginine supplementation reduces the
      adverse cardiovascular effects of exposure to traffic-related air pollution among a group of
      non-smoking adults with elevated blood pressure.
    

Detailed description: 
      The present study is designed as a randomized, double-blind, placebo-controlled trial of
      L-arginine (L-Arg, a precursor of nitric oxide in human body) supplement to counteract the
      acute cardiovascular effects of exposure to traffic-related air pollution among a group of
      non-smoking adults with elevated blood pressure. A large number of epidemiological studies
      have provided compelling evidence that exposure to traffic-related air pollution contributes
      to the increases in cardiovascular morbidity and mortality, and the mechanism of action
      includes vasoconstriction and cardiac ischemia. It is well known that nutritional factors are
      very important determinants of cardiovascular health. However, few studies have explored the
      joint effects of air pollution and nutritional factors on cardiovascular health. Existing
      data from many laboratory studies and small clinical trials suggest that L-Arg has beneficial
      effects on the cardiovascular system by lowering blood pressure and protecting myocardiocytes
      against external stimuli. The study will explore whether L-Arg supplement improves blood
      pressure levels and prevents potential cardiac ischemia upon acute exposure to
      traffic-related air pollution among high-risk individuals.

      Dietary intakes, lifestyle habits, use of medication/dietary supplements, blood pressure,
      resting electrocardiogram and plasma parameters were assessed for potential eligible
      participants at screening visits. Over 500 participants completed the screening visits, and
      118 of them were eligible after a 5-day L-Arg-free run-in period and willing to participate
      in the following intervention. Eligible participants were assigned to either the
      interventional group or control group using a computerized method with a randomized block
      design. They received 2 weeks (may float back and forth for 1-3 days due to scheduling
      issues) daily doses of either L-Arg (9g/day in 3 times) or placebo and undergo a 2-h exposure
      scenario (0900-1100 hours) of walking along a traffic road on the 14th day. Participants were
      counseled to maintain an isocaloric diet and to abstain from other L-Arg rich foods during
      the study. Concentrations of major traffic-related air pollutants, including particulate
      matter with an aerodynamic diameter ≤ 2.5 μm (PM2.5), black carbon, and nitrogen dioxide,
      were measured from the beginning of the 2-h exposure scenario to 22h after exposure or during
      the 2-h exposure scenario, and primary and secondary outcome measures including blood
      pressure, ST-segment depression and plasma parameters were assessed repeatedly at various
      time points (depending on the parameters) around the 2-h exposure scenario. Other
      environmental factors, including noise, temperature and relative humidity, were also recorded
      during the 2-h exposure scenario and up to 22h after exposure.
    

Intervention name(s): L-Arg supplement; Placebo
Intervention type(s): Dietary Supplement; Dietary Supplement
Intervention description(s): L-Arg supplement will be prepared as pills, administered 9g each day in 3 times for 2 weeks.; Placebo will be prepared as pills (the same size, color and shape as of L-Arg), administered 3 times daily for 2 weeks.
Allocation: Randomized
Intervention model: Parallel Assignment
Masking: Quadruple (Participant, Care Provider, Investigator, Outcomes Assessor)
Primary purpose: Prevention
Keywords: air pollution; blood pressure; cardiac ischemia; L-arginine; nitric oxide