Researchers from the Taipei Medical University said polyphenols from grape powder produced antioxidative and blood sugar-lowering properties that reduced the damage caused by a high-fat-high-fructose (HFHF) diet.
“Fruit and vegetable consumption has been found to prevent or diminish cognitive impairment, while diets high in fructose and fat have been shown to be metabolically stressful,” they wrote in the Journal of Nutritional Biochemistry.
“Here, we have presented results showing that grape consumption exerted beneficial effects on the expression of neurodegeneration-related proteins in aged rats on a long-term HFHF diet.”
Previous work had identified refined sugars and fats as some of the candidate dietary components that cause cognitive impairment, the study noted.
“Therefore, in an effort to further elucidate the underlying relationship between diet and cognitive disorders, we used the HFHF diet in this study to induce a type 2 diabetes-like metabolic disorder in rats and then examined brain proteins that are known to be altered in neurodegenerative diseases such as Alzheimer’s disease (AD),” the researchers wrote.
For the rat study, 60 rats were randomly assigned to two groups and maintained on the HFHF diet from the age of eight weeks to 66 weeks.
Grape powder intervention
In the intervention period (66–78 weeks old), the rats were then separated into four groups: control (HFHF), low and high grape powder with HFHF (LGP and HGP), and metformin with HFHF (MT) groups. The LGP and HGP group diets contained 3% and 6% grape powder in the HFHF diet.
Findings revealed that 6% grape powder group had reduced RAGE, or receptor for advanced glycation end products in the brain tissue.
“Inclusion of up to 6% grape powder in the diet markedly reduced RAGE expression and tau hyperphosphorylation, but upregulated the expression of Nrf2 and BDNF, as well as the phosphorylation of PI3K and ERK, in the brain tissues of aged rats fed the HFHF diet,” the researchers reported.
The upregulated or increase of both BDNF and Nrf2 were crucial, as BDNF plays a critical role in learning and memory by maintaining neuronal synaptic plasticity, while Nrf2, a leucine zipper protein, regulates the expression of antioxidant proteins that protect against oxidative damage triggered by injury and inflammation.
Thus, while long-term diet high in fructose and fat levels can cause hyperglycemia-related cognitive dysfunction in aged rats, grape powder supplementation can help ease the damaging changes in the brain protein related to neurodegeneration.
“Consumption of the HFHF diet containing grape powder ameliorated hyperphosphorylation, normalised the levels of other signalling cascades and lowered the amounts of over-glycation products in the cortex and hippocampus of aged rats,” researchers said.
“These findings will facilitate further studies on treatments for AD-like neurodegenerative diseases.”
Source: Journal of Nutritional Biochemistry
DOI: 10.1016/j.jnutbio.2017.02.013
“Grape powder consumption affects the expression of neurodegeneration-related brain proteins in rats chronically fed a high-fructose–high-fat diet”
Authors: Hsiang Liao, Liang-Mao Chou et al.