Differential molecular mechanism of the neuroprotective activity of mulberries ( <i>Morus Alba &amp; Morus Nigra</i> ) against glutamate induced-excitotoxicity on cortical neurons

Abstract

Neurotoxicity induced by glutamate is used herein in his study for testing the neuroprotective effects of Tunisian mulberries fruits extracts from two different varieties, white and black mulberries ( Morus alba and Morus nigra ).The polyphenols content and composition between the two samples was determined using HPLC- LCMS mass spectrometry. Caffeoylquinic acid and chlorogenic acid isomers are the most abundant cinnamic acids in our extracts, while rutin, quercetin, and kaempferol are the predominant flavonols. Pre-incubation of cell with Morus alba extract (MAE) or Morus nigra extract (MNE) (2.5; 5 and 10 μg/mL) protect neurons against oxidative stress triggered by glutamate in both concentration and time-dependent manner. Remarquably, M.nigra, exhibititing the higher antioxidant activity and polyphenols contents, enhanced more efficiently neurons survival rate after glutamate insult. However, pretreatment with Chelerytrine, a PKC –inhibitor pathway, abolished the protective effect of both MAE and MNE on cell viability suggesting the involvement of PKC signaling pathway is in the neuro-protective activities of mulberries against Glutamate excitotoxicity. Protective effect of extracts may be due to both the inhibition of caspase-1, −8, and −9 activities via intrinsic mitochondrial pathways, as well as a decrease in reactive oxygen species (ROS) production. Moreover, glutamate treatment resulted in the induction of calpain inhibitors (PD150606 and calpeptin) protected neurons against the glutamate-induced neurons alteration in the brain and notably reduced the observed neuro-protective effects of MAE against Glutamate excitotoxicity. Our data suggest that mulberries protect against neuronal damage by inhibiting apoptosis and oxidative stress. The MAP kinase pathways play a crucial role in these neuroprotective effects.