b-carotene at physiologically attainable concentration induces apoptosis and down-regulates cell survival and antioxidant markers in human breast cancer (MCF-7) cells

Although b-carotene is known for its anti-carcinogenic
and antioxidant properties, a few recent epidemiological
and experimental evidence show that at
higher concentration it acts as pro-oxidant and induces
cancer. Since the global burden of breast cancer exceeds all
other types of cancer, and its incidence rates is also in
increasing trend, the present study attempted to evaluate
the anti-cancer molecular mechanism of b-carotene (at
1 lM concentration) isolated from Spinacia oleracea in
human breast cancer (MCF-7) cells. The carotenoid was
purified by open column chromatography and identified by
LC–MS. The anti-proliferative effect of b-carotene at different
concentrations was evaluated by WST-1 assay and
the changes in cell morphology were examined by microscopic
observation. The induction of apoptosis by b-carotene
was observed by DAPI staining and colorimetric
caspase-3 assay. The expression of cell survival, apoptotic,
and antioxidant marker proteins was measured by western
blot analysis. Purified b-carotene inhibited the viability of
MCF-7 cells in a dose-dependent manner, which was well
correlated with changes in cell morphology. Increased
apoptotic cells were observed in b-carotene (1 lM)-treated
cells. This apoptosis induction was associated with
increased caspase-3 activity. The protein expression studies
showed that b-carotene at 1 lM concentration effectively
decreases the expression of the anti-apoptotic protein, Bcl-
2 and PARP, and survival protein, NF-kB. It also inhibited
the activation of intracellular growth signaling proteins,
Akt and ERK1/2. The inhibition of Akt activation by bcarotene
results in decreased phosphorylation of Bad.
Further, it down-regulated antioxidant enzyme, SOD-2,
and its transactivation factor (Nrf-2), and endoplasmic
reticulum (ER) stress marker, XBP-1, at protein levels.
These findings exhibit the key role of b-carotene even at a
low physiological concentration in MCF-7 cells which
further explains its predominant anti-cancer activity.