Hiroko Jokura

Chlorogenic acid attenuates hypertension and improves endothelial function in spontaneously hypertensive rats.

Background and objectives Epidemiologic studies indicate that ingestion of vegetables and fruit inhibits the development of cardiovascular disease. Chlorogenic acids are abundant phenolic compounds contained in vegetables and fruits, but the impact of dietary chlorogenic acids on vascular function in hypertension is not known. We therefore examined the effects of 5-caffeoylquinic acid (CQA), a representative chlorogenic acid, on blood pressure and vascular function in age-matched normotensive Wistar–Kyoto rats and spontaneously hypertensive rats. Methods and results A single ingestion of CQA (30–600 mg/kg) reduced blood pressure in spontaneously hypertensive rats, an effect that was blocked by administration of a nitric oxide synthase inhibitor, N(G)-nitro-L-arginine methyl ester. When spontaneously hypertensive rats were fed diets containing 0.5% CQA for 8 weeks (approximately 300 mg/kg per day), the development of hypertension was inhibited compared with the control diet group. CQA ingestion increased urinary excretion of nitric oxide metabolites and decreased urinary excretion of hydrogen peroxide; decreased NADPH-dependent superoxide anion production in the aorta, suggesting that dietary CQA inhibited vascular NADPH oxidase activity; significantly improved acetylcholine-induced endothelium-dependent vasodilation in the aorta; and markedly reduced the degree of immunohistochemical staining for nitrotyrosine and media hypertrophy in aorta sections. In contrast, CQA had no effects in Wistar–Kyoto rats. Conclusions Dietary CQA reduces oxidative stress and improves nitric oxide bioavailability by inhibiting excessive production of reactive oxygen species in the vasculature, and leads to the attenuation of endothelial dysfunction, vascular hypertrophy, and hypertension in spontaneously hypertensive rats.

Coffee polyphenol consumption improves postprandial hyperglycemia associated with impaired vascular endothelial function in healthy male adults

Epidemiological studies indicate that habitual coffee consumption lowers the risk of diabetes and cardiovascular diseases. Postprandial hyperglycemia is a direct and independent risk factor for cardiovascular diseases. We previously demonstrated that coffee polyphenol ingestion increased secretion of Glucagon-like peptide 1 (GLP-1), which has been shown to exhibit anti-diabetic and cardiovascular effects. We hypothesized coffee polyphenol consumption may improve postprandial hyperglycemia and vascular endothelial function by increasing GLP-1 release and/or reducing oxidative stress. To examine this hypothesis, we conducted a randomized, acute, crossover, intervention study in healthy male adults, measuring blood parameters and flow-mediated dilation (FMD) after ingestion of a meal with or without coffee polyphenol extract (CPE). Nineteen subjects consumed a test meal with either a placebo- or CPE-containing beverage. Blood biomarkers and FMD were measured at fasting and up to 180 minutes postprandially. The CPE beverage led to a significantly lower peak postprandial increase in blood glucose and diacron-reactive oxygen metabolite, and significantly higher postprandial FMD than the placebo beverage. Postprandial blood GLP-1 increase tended to be higher after ingestion of the CPE beverage, compared with placebo. Subclass analysis revealed that the CPE beverage significantly improved postprandial blood GLP-1 response and reduced blood glucose increase in the subjects with a lower insulinogenic index. Correlation analysis showed postprandial FMD was negatively associated with blood glucose increase after ingestion of the CPE beverage. In conclusion, these results suggest that coffee polyphenol consumption improves postprandial hyperglycemia and vascular endothelial function, which is associated with increased GLP-1 secretion and decreased oxidative stress in healthy humans.

Rice bran triterpenoids improve postprandial hyperglycemia in healthy male adults: a randomized, double-blind, placebo-controlled study

Background Compared to white rice, brown rice induces a lower glycemic response in healthy and diabetic humans. This effect is partly attributed to the higher amounts of water- or oil-soluble bran components and dietary fiber in brown rice. We hypothesized that dietary supplementation with oil-soluble rice bran triterpenoids (RBTs; triterpene alcohol and sterol prepared from rice bran) might reduce the incidence of postprandial hyperglycemia in healthy humans. Objective We examined the acute effects of a single RBT-supplemented meal on the postprandial blood glucose responses of healthy male adults in a double-blind, randomized, placebo-controlled, crossover trial. Design Nineteen subjects consumed a test meal containing either placebo- or RBT-supplemented olive oil. Blood biomarkers were evaluated in a fasting state and up to 240 min postprandially. Results Compared to the placebo-supplemented meal, the RBT-supplemented meal significantly suppressed the increase in postprandial blood glucose level. A subclass analysis revealed that RBT-supplemented oil significantly reduced blood glucose increases in subjects with higher postprandial blood glucose elevations. Postprandial increases in blood insulin, glucose-dependent insulinotropic peptide (GIP), and glucagon-like peptide-1 (GLP-1) levels did not differ between the groups. Conclusion These results suggest that RBT consumption improves postprandial hyperglycemia in healthy humans, especially those with higher postprandial glucose increases.

The Divergent Effect of Coffee Polyphenol and Hydroxyhydroquinone Ingestion on Postprandial Hyperglycemia and Vascular Function in Healthy Men

Epidemiological studies indicate that coffee consumption reduces the risk of diabetes and cardiovascular diseases. However, interventional studies have failed to clarify the beneficial effects of coffee consumption on blood glucose and the cardiovascular system. We previously demonstrated that 1) coffee polyphenol (CPP) consumption improved postprandial hyperglycemia and vascular endothelial function in humans, and 2) improvement in vascular endothelial function due to CPP was impaired by hydroxyhydroquinone (HHQ) in rats. This study aimed to elucidate the impact of concomitant consumption of HHQ, a prooxidant in coffee, on the beneficial effects of CPP consumption on postprandial blood glucose and vascular function in humans. We conducted a single-blind, randomized, placebo-controlled, crossover intervention study in healthy male adults, measuring blood and urine parameters and flow-mediated dilation after ingestion of a meal with CPP with or without HHQ up to 180 min postprandially. Ten healthy male adults consumed a test meal with either a placebo, control (CPP with HHQ), or active (CPP without HHQ) beverage. The CPP-including active (without HHQ) beverage significantly blunted the postprandial increase in blood glucose and decline in flow-mediated dilation but not the control (with HHQ) beverage, compared with the placebo beverage. The active beverage reduced blood oxidative stress biomarker response compared with the control beverage. In conclusion, these results demonstrate that concomitant ingestion of HHQ, which increases oxidative stress, interferes with the improvement of postprandial blood glucose and vascular endothelial function after CPP consumption in healthy humans.