masterThesis
Avaliação do caráter oxidante da violaceína
Fecha
2011-09-28Registro en:
LEAL, Angélica Maria de Sousa. Avaliação do caráter oxidante da violaceína. 2011. 81 f. Dissertação (Mestrado em Bioquímica; Biologia Molecular) - Universidade Federal do Rio Grande do Norte, Natal, 2011.
Autor
Leal, Angélica Maria de Sousa
Resumen
Violacein is a violet pigment isolated from many gram-negative bacteria,
especially from Chromobacterium violaceum, a betaproteobacterium found in
the Amazon River in Brazil. It has potential medical applications as an
antibacterial, fungicide, anti-tryptanocidal, anti-ulcerogenic and anti-cancer
drug, among others. Furthermore, its pro-oxidant activity has been suggested,
but only in two specific tumor lineages. Thus, in the present study, the prooxidant
effects of violacein were investigated in both normal and tumor cells,
seeking to evaluate the cell responses. The evaluation of violacein cytotoxicity
using the Trypan blue dye exclusion method indicated that CHO-K1 cells were
more resistant than tumor HeLa cells. The oxidative stress induced by violacein
was manifested as an increase in intracellular SOD activity in CHO-K1 and
MRC-5 cells at a specific concentration range. Nevertheless, a decrease was
detected specifically at 6-12 μM in HeLa and MRC-5 cells. Interestingly, the
increase in SOD activity was not followed by a concomitant increase in catalase
activity. Regarding to oxidative stress biomarkers, increased protein
carbonylation and lipid hydroperoxides levels were detected respectively in
CHO-K1 and MRC-5 cells treated with violacein at 1.5-3 μM and 3 μM, which
may be an evidence that this compound causes oxidative stress specifically in
these conditions. Additionally, it is believed that the decline in cell viability
observed in MRC-5 cells and HeLa treated with violacein at 6-12 M is due to
mechanisms not related to oxidative stress. Moreover, the results suggested
that violacein might cause oxidative stress by increasing endogenous levels of
O2
-, since the occurrence of an expressive change in SOD activity. In addition,
in order to evaluate the antioxidant activity of violacein in the absence of a
biological system, the total antioxidant and iron chelating activity were
evaluated, so that antioxidant activities were detected at 30 and 60 μM of
violacein. Altogether, the results indicate that although oxidative stress is
triggered by incubation with violacein, it did not seem to be high enough to
cause serious damage to cell biomolecules in HeLa cells and only at specific
concentrations in CHOK-1 and MRC-5 cells. Comparing the results obtained in
cell culture and the in vitro antioxidant activity evaluation, the results confirmed
that violacein presents opposing oxidant features when in presence or absence
of a biological system and the antioxidant character only occurs at high
concentrations of the pigment.