Targeting novel synthetic antioxidants towards reducing free radical-induced cell damage.

摘要

The main objective of the thesis was to develop novel synthetic compounds with antioxidant activity superior to Vitamin E aimed at reducing free radical-induced cell damage. The bond dissociation enthalpy (BDE) for the most active (weakest) OH bond in each molecule was used as predictor of antioxidant activity. After synthesis and testing in chemical solvent, the novel synthetic compounds were tested for cytotoxicity and then for protective effects against oxidative stress in biological systems such as: (a) HL-60 cells used as a model for testing the antioxidant capacity of the novel compounds; (b) an adherent clone of rat pheochromocytoma cells (PC12-AC). Oxidative stress was induced by the aqueous-phase peroxyl radical generator AAPH. Four members of the naphthalenediol family were tested, along with the reference compound epigallocatechin gallate (EGCG). The observed cytotoxicity and cytoprotection was explained based on the different electronic structures of the compounds, characterized by the first and second bond dissociation enthalpies and the pKa's for the parent (diol) and semiquinone. The data were combined to create a measure of cytoprotective efficacy for each compound, defined by the CPA (cytoprotective area). The mechanism of cytotoxicity of catechols in PC12-AC cells was also studied. The three catechols tested strongly upregulated glutathione (GSH) synthesis in the first 24 h due to the production of hydrogen peroxide; (c) primary cortical neurons. The study was extended in order to examine the effect of naphthalenediols on primary cortical neurons exposed to glutamate or peroxyl-radical oxidative stress. In cytotoxicity studies, cells were exposed to compounds for 24 h, leading to observed toxicity in the order 1,4-ND > 1,2 ND 2,3-ND ≈ EGCG > 1,8-ND. This order was explained on the basis of the tendency of each compound to form their corresponding quinone, a factor which depends upon the loss of aromaticity in the quinone product. Excellent protection, superior to EGCG, was provided by 2,3- and 1,8-NDs. Additional studies using glutamate as a stressor showed that 1,8-ND prevented neurotoxicity in a concentration-dependent manner, with a significant protective effect observed at concentrations as low as 500 nM.