Bioactive Compounds in Watermelon Modulating Oxidative Stress and Inflammation in Elders

Purpose and Objectives:

Vascular endothelial dysfunction is an early independent predictor of cardiovascular diseases (CVD), the leading cause of death for women ages 60 and older in the United States1. It is well-known that age-related decreases in vascular endothelial function are partially due to increases in oxidative stress and inflammation.In attempts to combat CVD, previous intervention studies have investigated provision of isolated bioactive food compounds (BFC) in supplemental form. For example, purified lycopene has been shown to decrease oxidative stress, and our previous work supports the supplemental use of glutamine and arginine in improving vascular endothelial function of older adults. Arginine is a precursor for the vasodilatory molecule nitric oxide (NO), and both glutamine and arginine have been shown to attenuate inflammation. Thus, if supplemented together, these compounds would be expected to exert synergist mechanistic effects that improve vascular function.

Watermelon is one of the richest sources of lycopene, and it is among the greatest plant sources of arginine and glutamine. Watermelon also provides high amounts of citrulline (a precursor of arginine) along with the antioxidant ascorbic acid, which enhances the antioxidant and anti-inflammatory effects of carotenoids such as lycopene in biological samples. To date, clinical studies evaluating the potential synergy of these compounds provided by the whole food are lacking on mechanistic and clinical outcomes of CVD. The effects of watermelon supplementation on robust measures of vascular function, inflammation, and oxidative stress in women ages 60 and older are unknown. This study will evaluate the possible impact of multiple bioactive compounds in the natural food matrix of watermelon in order to fully characterize their potential synergy and their influence on CVD risk. Specifically, our proposed study seeks to evaluate the influence of bioactive compounds in 100% watermelon juice, a convenient serving alternative to fresh fruit, using a randomized, double-blind placebo-controlled trial with a crossover design.

Specific Aims:

1. Mechanistic: To determine whether community-dwelling, non-obese women ages 55-69 consuming two 12-ounce servings of 100% watermelon juice per day versus placebo for four weeks will demonstrate:

   1. increases in circulating levels of serum lycopene, citrulline, and arginine using ultra high performance liquid chromatography with photodiode array detector (UPLC-PDA).
   2. improvement in antioxidant status as assessed by the oxygen radical absorbance capacity assay (ORAC) of whole and deproteinated serum
   3. decreases in circulating biomarkers of inflammation Hypotheses: Four-week dietary supplementation with 100% watermelon juice will result in increased antioxidant capacity and decreased inflammation, related to increased serum lycopene, citrulline, and arginine

2. Clinical: To determine whether community-dwelling, women ages 55-69 consuming two 12-ounce servings of 100% watermelon juice per day versus placebo for four weeks will exhibit:

   1. improved vascular endothelial function as assessed by flow-mediated dilation (FMD) and decreased arterial stiffness as assessed by pulse wave analysis (PWA)
   2. decreased low density lipoprotein (LDL) oxidation as assessed by enzyme immunoassay Hypotheses: Four-week dietary supplementation with 100% watermelon juice will result in improved vascular endothelial function, decreased arterial stiffness, and decreased LDL oxidation.