R-lipoic acid is the natural form, and S-lipoic acid is the synthetic form (Figure 1) (Carrier and Rideout 2013;Hofmann et al. 1995). Alpha lipoic acid was named (R)-5-(1,2-dithiolan-3-yl) pentatonic acid.Alpha lipoic acid has different names, including thioctic acid, 6,8-thioctic acid, 6,8-dithioctane acid, 1,2-dithiol-3-valeric acid, lipoate, and alpha-lipoic acid (Rentier et al 2015). Alpha lipoic acid propertiesThe Alpha lipoic acid has antioxidants properties discovered in 1988; it has the same ability as vitamin C, vitamin E, and coenzyme Q 10 (Naji et al 2018; Shindyapina et al 2017). In addition to its ability to neutralize free radicals in intracellular and extracellular environments, ALA differs from antioxidants. It neutralizes free radicals within the aqueous and lipid regions of the cell (Naji 2017). The characteristics of ALA allow it to pass through cell membranes to neutralize free radicals. Vitamin C protects the watery portion of the cell from free radicals, while vitamin E can protect the fatty membrane, while AlA protects the watery and fatty portions (Naji and Zenad 2016;Park et al 2014).ALA can also neutralize a diverse range of free radicals, including singlet oxygen, peroxyl, superoxide, and hydroxyl radicals, peroxynitrite and hypochlorite, and other antioxidants that neutralize a single type of free radical. Therefore ALA is called a "universal antioxidant" (Naji and Zenad 2016).

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