Protective Effects of Coixol Against Nε-Carboxymethyllysine-Induced Injury in IMR-32 Neuronal Cells: Modulation of Endoplasmic Reticulum Stress and Amyloidogenic Pathways.

Abstract

Background/objectives: The accumulation of Nε-carboxymethyllysine (CML), a major advanced glycation end product (AGE), has been implicated in neuronal dysfunction by promoting oxidative stress, endoplasmic reticulum (ER) stress, and dysregulation of amyloid-β (Aβ) metabolism. This study evaluated the neuroprotective properties of coixol, a naturally occurring polyphenolic compound derived from the outer layers of Coix lacryma-jobi L. var. ma-yuen, in a CML-induced injury model using IMR-32 human neuronal-like cells.

Methods: Cells were pretreated with coixol (1 μmol/L), N-acetyl-L-cysteine (NALC, 1 mmol/L), or 4-phenylbutyric acid (4-PBA, 200 μmol/L) for 1 h prior to CML (100 μmol/L) exposure for 24 h. Cell viability was determined by colorimetric analysis of 3-(4,5-dimethyl-2-yl)-2,5-diphenyltetrazolium bromide, while intracellular reactive oxygen species (ROS) generation was quantified using a fluorescence-based oxidative stress probe. Activities of key antioxidant enzymes and caspase-3 were determined using commercial assay kits. The expression of Aβ isoforms, amyloidogenic enzymes, ER stress markers, and apoptosis-related signaling proteins was quantified through validated immunoassays.

Results: Coixol pretreatment significantly enhanced cell viability by attenuating ROS accumulation and restoring antioxidant enzyme activities. Concurrently, coixol suppressed ER stress signaling via downregulation of the protein kinase R-like ER kinase/C/EBP homologous protein axis and modulated apoptosis by increasing B-cell lymphoma (Bcl)-2, reducing Bcl-2-associated X protein expression, and inhibiting caspase-3 activation and DNA fragmentation. Furthermore, coixol regulated Aβ metabolism by inhibiting the expression of β-site amyloid precursor protein-cleaving enzyme 1 and presenilin 1, while restoring insulin-degrading enzyme and neprilysin levels, leading to reduced accumulation of Aβ40 and Aβ42.

Conclusions: Compared to NALC and 4-PBA, coixol demonstrated comparable or superior modulation across multiple pathological pathways. These findings highlight coixol's potential as a neuroprotective candidate in AGE-associated neurodegenerative conditions.