The Effects of Wild Blueberry Consumption on Plasma Markers and Gene Expression Related to Glucose Metabolism in the Obese Zucker Rat

Abstract

Impaired fasting blood glucose is one of the landmark signs of metabolic syndrome, together with hyperinsulinemia, dyslipidemia, hypertension, and a chronic proinflammatory, pro-oxidative, and prothrombotic environment. This study investigates the effect of wild blueberry (WB) consumption on blood glucose levels and other parameters involved in glucose metabolism in the obese Zucker rat (OZR), an experimental model of metabolic syndrome. Sixteen OZRs and 16 lean littermate controls (lean Zucker rat [LZR]) were fed an 8% enriched WB diet or a control (C) diet for 8 weeks. Plasma concentrations of glucose, insulin, glycated hemoglobin GHbA1c, resistin, and retinol-binding protein 4 (RBP4) were measured. Expression of the resistin, RBP4, and glucose transporter GLUT4 genes was also determined both in the liver and the abdominal adipose tissue (AAT). Plasma glycated hemoglobin HbA1c, RBP4, and resistin concentrations were significantly lower in OZRs following the WB diet (-20%, -22%, and -27%, respectively, compared to C diet, P<.05). Following WB consumption, resistin expression was significantly downregulated in the liver of both OZRs and LZRs (-28% and -61%, respectively, P<.05), while RBP4 expression was significantly downregulated in the AAT of both OZRs and LZRs (-87% and -43%, respectively, P<.05). All other markers were not significantly affected following WB consumption. In conclusion, WB consumption normalizes some markers related to glucose metabolism in the OZR model of metabolic syndrome, but has no effect on fasting blood glucose or insulin concentrations.

Antiobesity Effects of Anthocyanins in Preclinical and Clinical Studies

“…Following the above mentioned studies, Vendrame et al [43] reported that supplementation with 8% (wt/wt) wild blueberry powder (WBP) after 8 weeks of feeding significantly increased blood adiponectin levels as well as reduced the levels of inflammatory markers in WAT [43] and improved dyslipidemia [6]. However, WBP did not obtain reduced fasting blood glucose (FBG) and insulin levels in obese Zucker rats in this study [44]. …”

Blueberries’ Impact on Insulin Resistance and Glucose Intolerance

“…In opposition to the previous positive anti-diabetic blueberry studies, other researchers documented no influence of blueberries on insulin resistance and/or glucose tolerance in obese mice and rats [15,27,28,29]. Although Vendrame and Colleagues [29] did not observe any significant changes on HOMA-IR with blueberry supplementation, they did find significant biological changes in the glucose metabolism related plasma markers (hemoglobin A1c, retinol-binding protein 4, and resistin concentrations).…”

“…Although Vendrame and Colleagues [29] did not observe any significant changes on HOMA-IR with blueberry supplementation, they did find significant biological changes in the glucose metabolism related plasma markers (hemoglobin A1c, retinol-binding protein 4, and resistin concentrations). These markers were lower in the obese Zucker rats that consumed a 8% blueberry diet for 8 weeks when compared to the rats that did not consume blueberries.…”

“…These markers were lower in the obese Zucker rats that consumed a 8% blueberry diet for 8 weeks when compared to the rats that did not consume blueberries. Also, the gene expression related to glucose metabolism (resistin in liver and retinol-binding protein 4 in adipose tissue) was downregulated in the obese Zucker rats following blueberry intake [29]. …”

A Review of Biologically Active Natural Products from Mediterranean Wild Edible Plants: Benefits in the Treatment of Obesity and Its Related Disorders

“…The effects of wild blueberry on blood glucose levels and other parameters involved in glucose metabolism were investigated in obese Zucker rats [30]. Wild blueberries are one of the richest fruit sources of anthocyanins, a class of phenolic bioactive compounds that have been shown to have insulin-sensitizing effects and to improve glucose utilization.…”