α -lipoic acid – antioxidant of antioxidants : properties and determination metods

Attention has been paid to healthy lifestyle in recent years. This is possible through increased physical activity and proper nutrition. This involves a significant increase in the interest in natural ingredients in a human daily diet. They come from both vegetable and animal products. This group of substances includes, for example, ascorbic acid (vitamin C), tocopherol (vitamin E), vitamin D, coenzyme Q10 and others. The important role of many compounds provided with food is their antioxidant action, which protects the body against the harmful effects of reactive oxygen species. They also exhibit therapeutic effects in diseases caused by oxidative stress. α-Lipoic acid (LA) also fits well into this group of substances and even gains the title of an “universal antioxidant” and an “antioxidant of antioxidants”. LA is produced in the human body in small amounts, and its biosynthesis occurs in the mitochondria. It is a compound with a very broad spectrum of therapeutic and biological activity. The amounts produced in the body are not sufficient and should therefore be supplied to the body from external sources. Food is the second, except de novo synthesis, the source of this compound. LA is a great antioxidant that can counteract the effects of aging. It is used mainly in the treatment of diabetic neuropathy and cardiovascular diseases, multiple sclerosis and Alzheimer’s disease. Such a wide action and occurrence causes the development of determination methods. Literature data indicate that free LA is primarily determined by liquid and gas chromatography, capillary electrophoresis, spectrophotometric and electrochemical techniques. In plant and animal cells it is mainly in the form of lipoyllysine. Determination of such a bound LA requires the proper preparation of the sample. This is usually acid, alkaline or enzymatic hydrolysis. This review summarizes the basic physicochemical and biochemical properties of α-lipoic acid and the methods of its determination