Antioxidant and antitumoral potential of amazonian plants with medicinal use

Resumen

There is an increasing interest in finding natural antioxidants in order to replace synthetic ones, which often possess side effects. Medicinal plants are considered sources of antioxidant compounds. The aim of this thesis was to study a) the antioxidant potential of different plants of Colombian Amazonia, which are traditionally used in folk medicine, and b) assess their cytotoxicity in various hepatoma cell lines. For this purpose, 21 Amazonian plants were collected and extracts of different parts of the plants (leaf, stem, bark, fruit, and root) were prepared from infusions. The antioxidant activities were evaluated by Trolox equivalent antioxidant capacity (TEAC) and oxygen radical absorbance capacity (ORAC) assays. All the extracts showed different degrees of antioxidant activity. TEAC and ORAC values correlated with the total phenol and flavonoid content. The aqueous extracts of V. baccifera, S. grandiflorum, P. putumayoense, P. glandulosissimum, and P. krukoffii leaves and stem, and B. rosademonte bark showed elevated antioxidant activities. These plants were selected to study lipid peroxidation inhibitory activity, using rat liver microsomes and liver- and brain mitochondria as the lipid sources. Their effects on mitochondrial function were also studied. All the extracts exerted antioxidant effects against iron-induced microsomal lipid peroxidation, except P. glandulosissimum stem, which showed no effect. Respecting cytotoxicity, P. krukoffii and P. putumayoense extracts were particularly interesting, since they induced cytotoxicity in human cell lines (such as HTB-52) and rat McA-RH7777, while being innocuous (P. krukoffii) or increasing the cell viability (P. putumayoense) in non transformed hepatocytes. In a similar way, V. baccifera leaf (< 100 micrograms/ml) induced toxicity in human HepG2 and rat McARH7777 cell lines, not affecting hepatocyte viability. In order to establish the possible mechanisms of cell toxicity, cell cycle by flow cytometry, ROS generation, several antioxidant enzyme activities, and caspase-3 activity were determined. Results show that in tumor cell lines, the extracts induce cytotoxicity probably by a mechanism that involves the generation of ROS (in particular H2O2).