Acai Berry (Euterpe sp.) Extracts Are Neuroprotective against L-Glutamate-Induced Toxicity by Limiting Mitochondrial Dysfunction and Cellular Redox Stress

Abstract

Aberrant accumulation of the neurotransmitter L-glutamate (L-Glu) has been implicated as a mechanism of neurodegeneration, and the release of L-Glu after stroke onset leads to a toxicity cascade that results in neuronal death. The acai berry (Euterpe oleracea) is a potential dietary nutraceutical. The aim of this research was to investigate the neuroprotective effects of acai berry aqueous and ethanolic extracts to reduce the neurotoxicity to neuronal cells triggered by L-Glu application. L-Glu and acai berry effects on cell viability were quantified using 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and lactate dehydrogenase (LDH) assays, and effects on cellular bioenergetics were assessed via quantitation of the levels of cellular ATP, mitochondrial membrane potential (MMP), and production of reactive oxygen species (ROS) in neuroblastoma cells. Cell viability was also evaluated in human cortical neuronal progenitor cell culture after L-Glu or/and acai berry application. In isolated cells, activated currents using patch-clamping were employed to determine whether L-Glu neurotoxicity was mediated by ionotropic L-Glu-receptors (iGluRs). L-Glu caused a significant reduction in cell viability, ATP, and MMP levels and increased ROS production. The co-application of both acai berry extracts with L-Glu provided neuroprotection against L-Glu with sustained cell viability, decreased LDH production, restored ATP and MMP levels, and reduced ROS levels. Whole-cell patch-clamp recordings showed that L-Glu toxicity is not mediated by the activation of iGluRs in neuroblastoma cells. Fractionation and analysis of acai berry extracts with liquid chromatography-mass spectrometry identified several phytochemical antioxidants that may have provided neuroprotective effects. In summary, the acai berry contains nutraceuticals with antioxidant activity that may be a beneficial dietary component to limit pathological deficits triggered by excessive L-Glu accumulations.

An In Silico and In Vitro Assessment of the Neurotoxicity of Mefloquine

“…ATP levels are also used as a surrogate for cell viability since lethal cell damage and a loss of membrane integrity results in an inability to synthesize ATP and a corresponding reduction in cellular ATP levels [ 43 , 44 ]. A decline in ATP levels can match the IC 50 values generated by MTT and/or LDH assays in undifferentiated and differentiated SH-SY5Y cells in response to different neurotoxicants [ 27 , 32 ]. However, in our study, the sensitivity to MQ indicated notable potency for limiting mitochondrial function and blunting the generation of intracellular ATP ( Figure 4 ), with a 24-h IC 50 value of approximately 6 µM, lower than that estimated by MTT or LDH assays.…”

“…The final product was measured spectrophotometrically at 490 nm and 680 nm using a Varioskan™ LUX multimode microplate reader (ThermoFisher Scientific, Waltham, MA, USA). The reading taken at 680 nm absorbance value was subtracted from the 490 nm absorbance value to calculate LDH activity as previously described [ 27 ]. The OD values for each of the treatments were normalised to the mean of the negative control, and the percentage of LDH production was determined.…”

“…Each experiment was conducted in triplicate, with blank values subtracted from the average. For each treatment, corrected luminometric readings were normalised to the control mean so that ATP levels could be expressed as a percentage of that value [ 27 ].…”

“…The mitochondrial membrane potential (MMP) was investigated using a MitoTracker Green FM probe (M-7514, ThermoFisher Scientific, Waltham, MA, USA) that can passively diffuse across the plasma membrane to label active mitochondria. SH-SY5Y cells (3 × 10 3 cells/well) were treated with MQ at concentrations of 0.1, 0.4, 1.1, 3.3, and 10 µM in a 96-well plate for 6, 24, and 48 h. After the incubation period with MQ, 50 nM MitoTracker Green FM dye was added to each well and incubated for 30 min at 37 °C, and then the plates were resuspended in PBS [ 27 ]. Carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone (FCCP) (300 µM for 24 h) was used as a positive control for mitochondrial membrane uncoupling.…”

Differential Effects of Paraquat, Rotenone, and MPTP on Cellular Bioenergetics of Undifferentiated and Differentiated Human Neuroblastoma Cells

“…Instead, PQ accumulates in mitochondria and acts as a potent redox cycler that converts free radicals interacting with molecular oxygen to form superoxide and other ROS [12,13]. In addition, PQ can elevate ROS generation through glutamate excitotoxicity by Ca 2+ efflux, depolarization of N-methyl-D-aspartate (NMDA) receptor channels, and activation of non-NMDA receptor channels, although activation of NMDA receptors may be limited in SH-SY5Y cells [56]. Therefore, our research study outcomes are consistent with previous studies suggesting that PQ can induce oxidative stress through mechanisms that in part involve ROS generation and inhibition of mitochondrial complex I, but this may be augmented by additional mechanisms that were not studied further.…”