Chronic feeding with 3% dried raw blueberries (V. corymbosum) reduces apomorphine-induced rotations and striatal dopaminergic loss in hemiparkinsonian rats

Abstract

Blueberries (BB) are rich in antioxidant polyphenols, and their intake could prevent Parkinson's disease (PD). Here we assessed whether rats chronically fed dried raw BB develop resistance to dopaminergic denervation and motor disorders caused by unilateral intrastriatal injection of 6-hydroxydopamine (6-OHDA), a dopaminergic neurotoxin acting mainly by inducing oxidative stress. Male rats were fed either with LabDiet® alone or supplemented with 3% lyophilized raw BB for 2 weeks before and 3 weeks after injecting 6-OHDA (day 0) or vehicle (mock lesion) into the right striatum. The cylinder test was performed on days -14, -7, -1, +7, +14, and +21; the percentage of ipsilateral forepaw (IF) use asymmetry was determined by counting the wall contacts made with either forepaw or with both. Apomorphine (0.25 mg/kg, s.c.)-induced rotation was performed on days -1, +7, +14, and +21. Full contralateral rotations were counted in 3-min periods, every 15 min, up to 90 min. Striatal slices were immunostained for tyrosine hydroxylase (TH) and the ionized calcium-binding protein-1 adapter (Iba1) [immunoreactive area or microglia count in right striatum expressed as % of the left striatum]. Antioxidants in BB methanolic extracts neutralized the free radical 2,2-diphenyl-1-picrylhydrazyl in a concentration-dependent manner. Anthocyanins have been reported as the most abundant polyphenols in BB. Using the pH differential method, the total anthocyanin content (malvidin-3-glucoside equivalents) in raw BB averaged 21.04 mg/g dry weight. The range of anthocyanin intake by rats throughout the study varied from 37.7 to 72.2 mg/kg body weight. The time and food type factors, as well as their interaction were significant according to two-way RM-ANOVA in both the apomorphine-induced rotations and the cylinder test. Compared with LabDiet® alone, chronic supplementation with 3% dried raw BB decreased apomorphine-induced rotations on days +14 and +21 (p < 0.001) and produced a 46% reduction in total rotations post-surgery (p < 0.05), but only caused a partial, non-significant, decrease of IF asymmetry. BB supplementation reduced TH loss in the striatum (p < 0.05) but did not attenuate the increase of Iba1⁺ microglia. The consumption of 3% dried raw blueberries attenuates dopaminergic denervation and partially reverses motor disorders in the 6-OHDA-induced PD model in rats. The phytochemicals of raw blueberries that contribute to the observed neuroprotective effect are yet to be identified.

Keywords: Anthocyanins; Antioxidant; Forepaw asymmetry; Microglia; Oxidative stress; Parkinson’s disease; Rotation behavior; Tyrosine hydroxylase.