Effects of Freeze-Dried Grape Powder on High-Density Lipoprotein Function in Adults with Metabolic Syndrome: A Randomized Controlled Pilot Study.

BACKGROUND: High-density lipoprotein (HDL) particles are protective against atherosclerosis. However, HDL function is impaired in metabolic syndrome (MetS) due to low-grade inflammation and dyslipidemia. Foods containing polyphenols, such as grapes, may prevent HDL dysfunction via antioxidant or anti-inflammatory effects. We evaluated the effects of grape powder ingestion on measures of HDL function in adults with MetS. METHODS: Twenty adults (age: 32-70 years; body mass index: 25.3-45.4 kg/m2) consumed either 60 grams/day of freeze-dried grape powder (GRAPE) or a placebo for 4 weeks, separated by a 3-week washout period, in a randomized, double-blind crossover study. The primary outcome was serum paraoxonase-1 (PON1) arylesterase activity, a measure of HDL antioxidant function. Secondary outcomes included PON1 lactonase activity, plasma lipids, metabolic markers, cholesterol efflux capacity, and other HDL functional markers. RESULTS: After 4 weeks, GRAPE did not alter the serum PON1 activity or other markers of HDL function compared with placebo. Measures of HDL function were positively correlated with each other and inversely with measures of insulin resistance and inflammation. GRAPE intake led to a significant reduction in fasting plasma triglycerides compared with placebo (P = 0.032). No other significant effects of GRAPE were observed for other plasma lipids, anthropometrics, or metabolic measures. CONCLUSIONS: Grape powder consumption did not impact HDL function in this cohort of adults with MetS. However, it was shown to improve fasting triglycerides, a risk factor for cardiovascular disease.

Effects of Dietary Flavonoids on Reverse Cholesterol Transport, HDL Metabolism, and HDL Function.

Strong experimental evidence confirms that HDL directly alleviates atherosclerosis. HDL particles display diverse atheroprotective functions in reverse cholesterol transport (RCT), antioxidant, anti-inflammatory, and antiapoptotic processes. In certain inflammatory disease states, however, HDL particles may become dysfunctional and proatherogenic. Flavonoids show the potential to improve HDL function through their well-documented effects on cellular antioxidant status and inflammation. The aim of this review is to summarize the basic science and clinical research examining the effects of dietary flavonoids on RCT and HDL function. Based on preclinical studies that used cell culture and rodent models, it appears that many flavonoids (e.g., anthocyanidins, flavonols, and flavone subclasses) influence RCT and HDL function beyond simple HDL cholesterol concentration by regulating cellular cholesterol efflux from macrophages and hepatic paraoxonase 1 expression and activity. In clinical studies, dietary anthocyanin intake is associated with beneficial changes in serum biomarkers related to HDL function in a variety of human populations (e.g., in those who are hyperlipidemic, hypertensive, or diabetic), including increased HDL cholesterol concentration, as well as HDL antioxidant and cholesterol efflux capacities. However, clinical research on HDL functionality is lacking for some flavonoid subclasses (e.g., flavanols, flavones, flavanones, and isoflavones). Although there has been a tremendous effort to develop HDL-targeted drug therapies, more research is warranted on how the intake of foods or specific nutrients affects HDL function.