Métodos químicos para medir la actividad antioxidante de extractos brutos, fracciones cromatográficas y enriquecidas y polifenoles puros obtenidos a partir de liquenes

Abstract

Chronic diseases such as cancer, diabetes, neurodegenerative and cardiovascular diseases are characterized by an enhanced state of oxidative stress, which results from both the overproduction of reactive oxygen and nitrogen species and a decrease in antioxidant defenses. The search for new chemical entities with an antioxidant profile is therefore a field of great interest. At present, it is suspected that many of the widely used synthetic antioxidants have toxic and carcinogenic effects. Consequently, there is a growing interest in finding new antioxidants, devoid of undesirable effects and from natural resources. The present book covers all currently available knowledge regarding the antioxidant properties of lichens, in both in vitro as well as in vivo studies. Lichen species normally have a profile that’s typical of secondary metabolites. Some of the most abundant sources of these lichen compounds are the Hypogymnia Tavaresii (D. Hawksw. & P. James), the Lethariella Canariensis ((Ach.) H. Krog), and the Evernia Prunastri ((L.) (Ach.)), all of which originate in the Canary Islands. Dense populations of these species grow frequently as epiphytes on tree branches or on rocks. Previous studies have demonstrated that lichen substances have more than one phenolic hydroxyl group attached to one or more benzene rings, thus qualifying them as polyphenols. These polyphenols have been restudied with intention to find compounds that protect living beings against oxidative stress and from free radical-induced damage. Purified polyphenol-enriched fractions are able to decrease the absorbance of MDA-TBA adduct in lipid peroxidation assays, and do so in a concentration-dependent manner. The strong relationship between the total polyphenol content and the antioxidant activity in tested fractions suggest that these compounds play an important role in antioxidant activity. The free-radical inhibiting activity was tested using the free stable radical 2,2-diphenyl-1-picrylhydrazyl (DPPH•) model. Pure polyphenols obtained from H. Tavaresii, L. Canariensis and E. Prunastri exhibited free-radical destruction capacities expressed with the values IC50 from the DPPH• model. Those were 180-8261 times inferior to the antioxidant reference compound, α-(+)-tocopherol. A bibliographical survey was performed, by using databases such as Scifinder, PubMed, Google Scholar, Scopus, Science Direct, LILACS and Web of Science, as well as literature on lichens published until February 2016. The search terms on the Internet were “lichen” and “antioxidant”. The present study demonstrates that the tested lichen species exhibit moderate antioxidant activity and can be considered as good sources of natural antioxidants. On the basis of these results, lichens appear to be good and safe natural source of antioxidants and could be helpful in increasing the nutritional/ cosmetic/ pharmaceutical value of different products. Thus, further study is necessary in order to determine the antioxidant capacities of the individual chemical components that constitute the extracts of other lichen species. These compounds are potential candidates for the management of oxidative stress and may be useful in the treatment of many chronic diseases.