Neuroprotective Potential of Laurus nobilis Antioxidant Polyphenol-Enriched Leaf Extracts

Oxidative stress has been proposed to be an important factor in the pathogenesis of Alzheimer's disease (AD), playing a central role in amyloid beta-protein (A beta) generation and neuronal apoptosis. Oxidative damage directly correlates with the presence of A beta deposits. A beta and oxidative stress jointly induce neuronal death, A beta deposits, gliosis, and memory impairment in AD. In order to counteract AD neurodegeneration, the inhibition of the vicious cycle of A beta generation and oxidation is an attractive therapeutic strategy, and antiamyloidogenic and antioxidant herbal drugs could represent an alternative and valid approach. In this context, an alcoholic extract from Laurus nobilis leaves (LnM) and seven fractions obtained therefrom were of interest. All extracts prepared through extractive and chromatographic techniques were phytochemically studied by chromatographic techniques including gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-tandem mass spectrometry (LC-MSn). The potential antioxidant efficacy of the obtained fractions was screened by DPPH center dot and ABTS(center dot+) assays, as well as specific assay media characterized from the presence of highly reactive ROS and RNS species (ROO center dot, OH center dot, O-2(center dot-), and NO). In order to evaluate the preparation of safe and nontoxic extracts, MTT, SRB, and LDH assays toward SH-SYSY and SK-N-BE(2)-C human neuronal cell lines, as well as on C6 mouse glial cell line, were performed. The apoptosis-inducing properties by spectroscopic evaluation of the extracts' ability to activate caspase-3 and by a DNA fragmentation assay were also investigated. Data thus obtained allowed us to state the absence of toxic effects induced by phenolic-rich fractions (LnM, LnM-1, LnM-1a, LnM-1b, and LnM-2c), which at the same time exerted significant cytoprotective and antioxidant responses in hydrogen peroxide and A beta 3(25-35)-fragment-oxidized cell systems. The potential antiamyloidogenic efficacy of Laurus nobilis leaf polar extracts in the A beta(25-35) fragment oxidized cell systems was further analyzed by Congo red staining.