Abstract
Oxidative stress is an imbalance between the production of free radicals and antioxidant defense mechanisms, potentially leading to tissue damage. Oxidative stress has a key role in the development of cerebrovascular and/or neurodegenerative diseases. This phenomenon is mainly mediated by an enhanced superoxide production by the vascular endothelium with its consequent dysfunction. Thioctic, also known as alpha-lipoic acid (1,2-dithiolane-3-pentanoic acid), is a naturally occurring antioxidant that neutralizes free radicals in the fatty and watery regions of cells. Both the reduced and oxidized forms of the compound possess antioxidant ability. Thioctic acid has two optical isomers designated as (+)- and (−)-thioctic acid. Naturally occurring thioctic acid is the (+)-thioctic acid form, but the synthetic compound largely used in the market for stability reasons is a mixture of (+)- and (−)-thioctic acid. The present study was designed to compare the antioxidant activity of the two enantiomers versus the racemic form of thioctic acid on hydrogen peroxide-induced apoptosis in a rat pheochromocytoma PC12 cell line. Cell viability was evaluated by MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay and free oxygen radical species (ROS) production was assessed by flow cytometry. Antioxidant activity of the two enantiomers and the racemic form of thioctic acid was also evaluated in spontaneously hypertensive rats (SHR) used as an in vivo model of increased oxidative stress. A 3-h exposure of PC12 cells to hydrogen peroxide (H2O2) significantly decreased cell viability and increased levels of intracellular ROS production. Pre-treatment with racemic thioctic acid or (+)-enantiomer significantly inhibited H2O2-induced decrease in cell viability from the concentration of 50 μmol/L and 20 μmol/L, respectively. Racemic thioctic acid and (+)-salt decreased levels of intracellular ROS, which were unaffected by (−)-thioctic acid. In the brain of SHR, the occurrence of astrogliosis and neuronal damage, with a decreased expression of neurofilament 200 kDa were observed. Treatment of SHR for 30 days with (+)-thioctic acid reduced the size of astrocytes and increased the neurofilament immunoreaction. The above findings could contribute to clarify the role played by thioctic acid in central nervous system injury related to oxidative stress. The more pronounced effect of (+)-thioctic acid observed in this study may have practical therapeutic implications worthy of being investigated in further preclinical and clinical studies.
Highlights
Free radical (e.g., *OH) generation following stroke and traumatic brain injury has been documented [1,2,3]
The occurrence of lipid peroxidation was shown in animal models of both global and focal ischemia [4], in which an increase of conjugated dienes and aldehydes derived from oxidized lipids have been reported [5,6]
The ability of thioctic acid to reduce Reactive oxygen species (ROS) was measured in PC12 cells treated with 200 μmol/L H2O2 using DCFDA and flow cytometric analysis
Summary
Free radical (e.g., *OH) generation following stroke and traumatic brain injury has been documented [1,2,3]. The occurrence of lipid peroxidation was shown in animal models of both global and focal ischemia [4], in which an increase of conjugated dienes and aldehydes derived from oxidized lipids have been reported [5,6]. Free radical involvement in neurodegeneration following stroke is facilitated by antioxidant defenses breakdown. Both ischemic [8] and traumatic [9] central nervous system (CNS) injuries result in the loss of α-tocopherol. Decreases in both ascorbic acid and glutathione have been described in animal models of CNS injury. Antioxidants of natural and/or synthetic origin were proposed as neuroprotective agents in CNS [10,11,12]
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