Potential neuroprotective effects of blueberry and lingonberry fruits and leaves

Kalidindi, Swetha (2014) Potential neuroprotective effects of blueberry and lingonberry fruits and leaves. Masters thesis, Memorial University of Newfoundland.

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Abstract

Production of reactive oxygen species (ROS) and reactive nitrogen species (RNS) are natural processes occurring in the brain. However, overproduction of ROS and RNS may occur during aging and contribute to neurodegenerative diseases and disorders such as stroke. Phenolic compounds constitute a large class of phytochemicals that are widespread in the plant kingdom and known to have antioxidant capacities. This study aimed to determine the radical scavenging capacity and reducing power, as well as the polyphenolic content in fruits and leaves of blueberries and lingonberries growing in Newfoundland. We determined the potential neuroprotective effect of extracts against glutamate-mediated excitotoxicity, which is believed to contribute to disorders such as stroke and neurodegenerative diseases. We found that extracts of fruits and leaves of blueberry and lingonberry plants have high levels of total soluble phenolics, anthocyanins, tannins, and flavonoids. Overall, the levels of these compounds were significantly higher in the leaves of these plants versus the fruits. Total antioxidant capacity, in terms of radical scavenging activity and reducing power, were much higher in the leaves of both plants as compared to their fruits. We then tested the effects of the extracts against glutamate-mediated excitotoxicity, a pathological process partially involving overproduction of ROS and RNS. Brain-derived cortical cell cultures from neonatal rat pups were prepared and grown for 9-16 days in vitro. Cells were exposed to glutamate (100 μM) for 24 hours. Glutamate-exposed cells displayed morphological alterations such as disrupted cell bodies, and increased dark punctae, which is often indicative of condensed nuclei and delayed cell death. Glutamate caused a ~23% cell loss after 24 hours as determined by the amount of DAPI-positive nuclei. A specific NMDA receptor blocker (AP5) was used to determine the contribution of this receptor type to cell damage. While lingonberry fruit extract did not provide protection from glutamate toxicity, blueberry fruit extracts were protective. Cultures treated with leaf extracts of lingonberry and blueberry showed no cell loss in the presence of glutamate, indicating a strong protective effect of both the leaf extracts. The overall greater protective effect of leaf extracts was in correlation with the levels of phenolics and antioxidant capacity. Treatment with AP5 (NMDA receptor blocker) gave us positive results and the cell death caused by 100 μM glutamate was suppressed, but the trend was not clear enough to make any conclusion. Recent studies have analyzed antibody staining against alpha-synuclein, a protein involved with Parkinson’s disease, after glutamate exposure. These studies helped us raise a set of questions on the various factors leading to increased expression of alpha-synuclein and allowed us to get some preliminary data. I have measured levels of lactate in the culture media from different conditions which may be indicative of altered cell health. Overall, these findings suggest that berries or their components may provide protection to the brain from various pathologies such as stroke, trauma and neurodegenerative diseases. This protective effect of berry extracts may be due to a decrease in oxidative stress, nitrosative stress, or other damaging mechanisms caused by exposure to glutamate.

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