Polyphenol-rich extract from grape and blueberry attenuates cognitive decline and improves neuronal function in aged mice

Abstract

Ageing is characterised by memory deficits, associated with brain plasticity impairment. Polyphenols from berries, such as flavan-3-ols, anthocyanins, and resveratrol, have been suggested to modulate synaptic plasticity and cognitive processes. In the present study we assessed the preventive effect of a polyphenol-rich extract from grape and blueberry (PEGB), with high concentrations of flavonoids, on age-related cognitive decline in mice. Adult and aged (6 weeks and 16 months) mice were fed a PEGB-enriched diet for 14 weeks. Learning and memory were assessed using the novel object recognition and Morris water maze tasks. Brain polyphenol content was evaluated with ultra-high-performance LC-MS/MS. Hippocampal neurotrophin expression was measured using quantitative real-time PCR. Finally, the effect of PEGB on adult hippocampal neurogenesis was assessed by immunochemistry, counting the number of cells expressing doublecortin and the proportion of cells with dendritic prolongations. The combination of grape and blueberry polyphenols prevented age-induced learning and memory deficits. Moreover, it increased hippocampal nerve growth factor (Ngf) mRNA expression. Aged supplemented mice displayed a greater proportion of newly generated neurons with prolongations than control age-matched mice. Some of the polyphenols included in the extract were detected in the brain in the native form or as metabolites. Aged supplemented mice also displayed a better survival rate. These data suggest that PEGB may prevent age-induced cognitive decline. Possible mechanisms of action include a modulation of brain plasticity. Post-treatment detection of phenolic compounds in the brain suggests that polyphenols may act directly at the central level, while they can make an impact on mouse survival through a potential systemic effect.

Keywords: Ageing; Bdnf, brain-derived neurotrophic factor; Berries; Cognitive decline; DCX, doublecortin; DG, dentate gyrus; Hippocampus; IR, immunoreactive; MWM, Morris water maze; NOR, novel object recognition; Neurogenesis; Ngf, nerve growth factor; PEGB, polyphenol-rich extract from grape and blueberry; Polyphenols.

Fig. 1.

Survival curve of aged mice from the beginning until the end of the 14-week supplementation diet. An absence of mortality in aged mice supplemented with polyphenol-rich extract from grape and blueberry (PEGB; ) during this observation period contrasted with almost 20 % mortality of aged mice on the control diet () (χ² analysis on Kaplan–Meir survival curves: P < 0·05; n 27 per group).

Fig. 2.

Novel object recognition memory. Percentage time spent exploring the novel object compared with percentage time spent exploring the familiar object for each group. Values are means, with their standard errors represented by vertical bars (n 9–10 per group). Adult mice on the control diet () or the polyphenol-rich extract from grape and blueberry (PEGB)-enriched diet () spent preferentially more time exploring the novel object than the familiar object. Aged mice on the control diet did not present a preference for the novel object. Aged mice fed the PEGB-enriched diet spent more time exploring the novel object than the familiar one, similarly to the control adult mice. ** P < 0·01, *** P < 0·001.

Fig. 3.

Spatial learning and memory. (a) Distance to reach the platform in adult control mice (–○–), adult mice fed the polyphenol-rich extract from grape and blueberry (PEGB)-enriched diet (), aged control mice (–□–) and aged PEGB-enriched diet-fed mice (). Values are means, with their standard errors represented by vertical bars (n 14–20 per group). Performance differed significantly on days 4 and 5 of the learning phase (* P < 0·05, ** P < 0·01 v. adult control). (b) Percentage of time spent by control mice () and PEGB-enriched diet-fed mice () in the target quadrant during the probe test. The dotted line corresponds to chance level (25 %). Values are means, with their standard errors represented by vertical bars (n 14–20 per group). All groups remembered the platform location, as they spent more time in the target quadrant (* P < 0·05, ** P < 0·01, *** P < 0·001 v. chance level).

Fig. 4.

mRNA expression of hippocampal plasticity-related genes in control mice () and polyphenol-rich extract from grape and blueberry (PEGB)-enriched diet-fed mice (). Values are means, with their standard errors represented by vertical bars (n 10 per group). (a) PEGB supplementation significantly increased hippocampal nerve growth factor (NGF) mRNA expression in both adult and aged mice (* P < 0·05, diet effect). (b) Hippocampal brain-derived neurotrophic factor (BDNF) mRNA expression was not modified by age or polyphenol supplementation. GAPDH, glyceraldehyde-3-phosphate dehydrogenase.

Fig. 5.

Hippocampal adult neurogenesis in control mice () and polyphenol-rich extract from grape and blueberry (PEGB)-enriched diet-fed mice (). Values are means, with their standard errors represented by vertical bars (n 9–10 per group). (a) Analysis of the number of doublecortin-immunoreactive (DCX-IR) cells in the hippocampus. The number of newly generated immature neurons in the hippocampus decreased significantly with age (*** P < 0·0001, age effect). (b) Aged mice on the PEGB-enriched diet had a greater proportion of newly generated immature neurons with prolongations than the other groups (*** P < 0·0001 v. adult control; †† P < 0·01 v. adult PEGB; ‡‡‡ P < 0·001 v. aged control).