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While the number of patients diagnosed with neurodegenerative disorders like Alzheimer's disease, amyotrophic lateral sclerosis, and Parkinson's disease is increasing, there are currently no effective treatments that significantly limit the neuronal cell death underlying these diseases. Chlorogenic acid (CGA), a polyphenolic compound found in high concentration in coffee, is known to possess antioxidant and free radical scavenging activity. In this study, we investigated the neuroprotective effects of CGA and its major metabolites in primary cultures of rat cerebellar granule neurons. We show that CGA and caffeic acid displayed a dramatic protective effect against the nitric oxide donor, sodium nitroprusside. In marked contrast, ferulic acid and quinic acid had no protective effect against this nitrosative stress. While CGA and quinic acid had no protective effect against glutamate-induced cell death, caffeic acid and ferulic acid significantly protected neurons from excitotoxicity. Finally, caffeic acid was the only compound to display significant protective activity against hydrogen peroxide, proteasome inhibition, caspase-dependent intrinsic apoptosis, and endoplasmic reticulum stress. These results indicate that caffeic acid displays a much broader profile of neuroprotection against a diverse range of stressors than its parent polyphenol, CGA, or the other major metabolites, ferulic acid and quinic acid. We conclude that caffeic acid is a promising candidate for testing in pre-clinical models of neurodegeneration.

Neurodegenerative disorders such as amyotrophic lateral sclerosis (ALS), Alzheimer&rsquo, s disease, and Parkinson&rsquo, s disease, are characterized by the progressive loss of neurons in specific regions of the brain and/or spinal cord. Neuronal cell loss typically occurs by either apoptotic or necrotic mechanisms. Oxidative stress and nitrosative stress, along with excitotoxicity and caspase activation, have all been implicated as major underlying causes of neuronal cell death. Diverse nutraceuticals (bioactive compounds found in common foods) have been shown to have neuroprotective effects in a variety of in vitro and in vivo disease models. In the current study, we compared the neuroprotective effects of two polyphenolic compounds, rosmarinic acid and carnosic acid, which are both found at substantial concentrations in the herb rosemary. The capacity of these compounds to rescue primary cultures of rat cerebellar granule neurons (CGNs) from a variety of stressors was investigated. Both polyphenols significantly reduced CGN death induced by the nitric oxide donor, sodium nitroprusside (nitrosative stress). Rosmarinic acid uniquely protected CGNs from glutamate-induced excitotoxicity, while only carnosic acid rescued CGNs from caspase-dependent apoptosis induced by removal of depolarizing extracellular potassium (5K apoptotic condition). Finally, we found that carnosic acid protects CGNs from 5K-induced apoptosis by activating a phosphatidylinositol 3-kinase (PI3K) pro-survival pathway. The shared and unique neuroprotective effects of these two compounds against diverse modes of neuronal cell death suggest that future preclinical studies should explore the potential complementary effects of these rosemary polyphenols on neurodegenerative disease progression.