Modulatory Effect of Natural Antioxidants on Tissue Transglutaminase Levels in Olfactory Ensheathing Cells Exposed to Amyloid-β: Integrated Biochemical and Computational Analysis

Herein, we adopted a dual approach combining molecular modeling and biological studies, in order to assess the interaction between four selected natural antioxidants (NAs; berberine, curcumin, astaxanthin, indicaxanthin) and tissue transglutaminase (TG2) levels both in the absence and in the presence of full native peptide of amyloid-beta (A beta). Docking studies were performed to ascertain the binding affinity of NAs against the TG2 closed, Ca2+-bound closed, and open forms. In the biological investigation, the effect of berberine and curcumin treatment on TG2 in Olfactory Ensheathing Cells (OECs) exposed to A beta(1-42) or to A beta(25-35), a A beta toxic fragment, or to reverse-sequence fragment A beta(35-25), an A beta not toxic fragment, was tested. In addition, their effect on the percentage of cell viability and cytoskeleton marker (GFAP, vimentin and nestin) levels were evaluated. The role of berberine and curcumin on both endocellular levels of reactive oxygen species (ROS) and apoptotic pathway activation were also assessed. Our findings demonstrate that pretreatment of OECs with these NAs counteracted the A beta-induced upregulation of TG2, restoring its expression to control levels and preserving its predominant cytosolic localization. Furthermore, antioxidant pretreatment reinstated cell viability, normalized the expression of GFAP, vimentin, and nestin, reduced intracellular ROS accumulation, and prevented activation of the apoptotic cascade. Our findings demonstrate that integrating computational and biological approaches, enhances the identification of potent therapeutic agents and also highlights berberine and curcumin as promising candidates for the development of novel neuroprotective drugs against neurodegenerative disorders, including Alzheimer's disease.