Antilipemic and Hypoglycemic Effects

Because bilberry has traditionally been used to treat diabetes, which is associated with alteration of lipid metabolism, the effects of a bilberry leaf extract on plasma glucose and triglycerides were studied in various rat models (1). The study preparation was made by percolation of bilberry leaf powder with ethanol 40% (Indena, Milano, Italy). All statistical comparisons were done using unpaired i-tests.

In Sprague-Dawley rats made diabetic with streptozocin, plasma glucose levels were 26% lower (p < 0.05) 4 days after streptozocin administration, and 26.6% lower (p < 0.01, unpaired i-test) 3 weeks after streptozocin administration in rats treated with bilberry extract at a dose of 3 g/kg twice daily for five doses compared with untreated diabetic rats. Triglycerides were also 38.8% (p < 0.05) lower in the treated rats. The extract did not affect glucose levels in control animals, and did not affect weight (1).

In rats with diet-induced hyperlipidemia, triglycerides were lower in rats treated with the extract at doses of 1.2 g/kg (p < 0.05) and 3 g/kg (p < 0.01) than in untreated rats. Weight was not affected. In genetically hyperlipidemic Yoshida rats, and in rats with alcohol-induced hypertriglyceridemia, triglycerides were 31.8% (p < 0.05) and 61.5% (p < 0.01) lower, respectively, in bilberry-treated rats than in untreated rats (1).

The antilipemic effect of bilberry may be caused by improved breakdown of triglyceride-rich lipoproteins, as evidenced by findings of a third part of this study (1). Rats were administrered Triton WR-1339 to induce hypertriglyceridemia. This agent has an acute effect of blocking lipoprotein clearance, and a secondary effect of stimulation of liver lipoprotein synthesis. Bilberrry was able to attenuate only the acute effect of Triton on triglycerides, suggesting that bilberry improves lipoprotein clearance, but does not affect lipoprotein production.

Although bilberry's effect on triglycerides is similar to that of the fibric acid derivatives (e.g., gemfibrozil, fenofibrate) used therapeutically to treat hypertriglyceridemia, bilberry did not affect thrombus size or composition, suggesting that it does not possess antithrombotic activity, as has been demonstrated with some fibric acid derivatives (1).

Oxidized low-density liporpotein (LDL) is known for its ability to stimulate inflammatory processes involved in the formation of atherosclerotic plaques. For this reason, there has been interest in the use of antioxidants such as bilberry to protect against LDL oxidation.

In an in vitro study (9), the ability of a bilberry extract (Leurquin-Mediolanum Laboratories, Neuilly sur Marne, France) containing 74.2 ± 4.9 mg/g polyphenols with 17.3 ± 3.3% catechin (mean ± standard deviation [SD] of 10 preparations) to attenuate copper-mediated LDL oxidation was studied. LDL was taken from six volunteers with normal lipid levels, and markers of oxidation were measured in the presence of bilberry extract at concentrations of 0, 5, 10, 15, 20, and 30 ^g/mL. All comparisons were made using the Mann-Whitney test. Compared with control, bilberry was able to prolong the time to conjugated diene formation at concentrations of 20 and 30 ^g/mL (p < 0.01), decrease production of lipoperoxides and malondialdehyde at concentrations of 10 ^g/mL or higher for at least 1 hour and 0.5 hour (p < 0.05), respectively, and attenuate change in the net negative charge of LDL at concentrations of at least 15 ^g/mL (p < 0.01).

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