RESUMEN
ß-Sitosterol (ßSito) is the most abundant phytosterol found in vegetable oils, grains such as wheat, beans, and corn, and in many phytosterol-enriched foods. It is prone to oxidation by reactive oxygen species, such as ozone, leading to the formation of oxyphytosterols. A better understanding regarding the biological effects and mechanism of action of oxyphytosterols is required since the beneficial and adverse side effects of these compounds on human health remain highly controversial. In this work, we investigated the biological effects of ß-Secosterol (ßSec), a new oxyphytosterol generated by the reaction of ßSito with ozone. Treatment of HepG2 cells with ßSito or ßSec (0.1-100 µM) for 24, 48, and 72 h induced a dose-dependent reduction of cell viability in the MTT assay, with ßSec showing higher efficacy than ßSito. However, ßSec presented a lower potency than ßSito, showing IC50 = 37.32 µM, higher than ßSito (IC50 = 0.23 µM) at 48 h. Cell cycle analyses by flow cytometry showed a slight decrease of G0/G1 phase with ßSito 0.5 µM, but a significant cell cycle arrest at the G0/G1 phase in the treatment for 48 h with ßSec 20 µM (62.69 ± 2.15%, p < 0.05) and ßSec 40 µM (66.96 ± 5.39%, p < 0.0001) when compared to control (56.97 ± 2.60%). No suggestion of apoptosis was indicated by flow cytometry data. Also, ßSec (20 and 40 µM) reduced the mitotic index. In the laser scanning confocal microscopy analysis no alterations in cell morphology were observed with ßSito (0.5 µM). Nevertheless, round-shaped cells, abnormal nuclear morphology with shrinkage, and formation of microtubules clusters were observed in the treatment with ßSec, indicating a disruption in the microtubules network organization. N-acetyl-l-cysteine was not able to inhibit any of these cellular effects, indicating a lack of involvement of oxidative stress in the mechanism of action of ßSec. Although not further investigated in this study, it was discussed the hypothesis that covalent adduct formation with lysine residues of proteins, could play an important role in the biological effects elicited by ßSec. Elucidation of the primary cellular processes induced by ßSec provides the essential knowledge to be aware of its potential adverse side effects or therapeutic use of this oxyphytosterol.