Topical Area: Dietary Bioactive Components
Endothelial dysfunction is one of the early predictors of cardiovascular disease and proper functioning of the endothelium is dependent upon nitric oxide (NO) bioavailability. Watermelon is a rich source of bioactive components such as L-citrulline and arginine which can increase NO bioavailability directly and indirectly. The objective of this pilot study was to assess the effects of watermelon intake on endothelial function using Flow Mediated Dilation (FMD) and to assess the relationship of FMD overtime with circulating watermelon metabolites, such as L-citrulline and arginine in humans.
Middle-age overweight/obese adults (n= 6; age 32.4 ± 8.0 y and BMI 29.0 ± 1.7 kg/m2) participated in a 4-arm, randomized, cross-over energy-controlled clinical trial. Subjects consumed one of four 100 kcal salads containing watermelon flesh (WF) or rind (WR) or seed (WS) or no watermelon components (Control) on four separate occasions. Blood samples were collected at baseline (t= 0h) and then 0.5h, 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 24h post meal. The FMD was assessed at baseline 0h, 1h, 3h, 5h and 7h. L-Citrulline and arginine were extracted from plasma at each time point and quantified using an ultra-high-performance liquid chromatography coupled with triple quadrupole mass spectrometer.
Maximum concentration (Cmax) and peak time (Tmax) for L-citrulline after WF intake was 153.1±38.8 µmol/L with Tmax of 1h while after WR intake Cmax was 153.9±38.5 µmol/L with tmax of 0.5h. Cmax of L-citrulline was 76.1±20.9 µmol/L at time 1h after WS consumption. Arginine peaked at 1h after WF, WR, WS intake with Cmax of 242.5±35.8 µmol/L, 249.9±38.7 µmol/L, and 249.5±43.3 µmol/L respectively. An increase in %FMD was observed at 1h after WF and WR compared to control, which coincided with the Cmax and Tmax of arginine and citrulline. However, the data was statistically not significant.
The data from this pilot study is the first to show a possible association between %FMD increase and circulating L-citrulline and arginine concentrations providing support for future research on watermelon with a larger sample size in order to determine the potential clinical impact of watermelon intake on improvement of endothelial function.
Funding Sources : National Watermelon Promotion Board