Antioxidants May Protect Cancer Cells from Apoptosis Signals and Enhance Cell Viability

Reactive oxygen species (ROS) are highly reactive molecules generated predominantly during cellular respiration and normal metabolism. These side products can damage many biological molecules; they can change protein functions, damage DNA material and cause lipid peroxidation of cell membranes (Kulbacka et al., 2009). In general, the reducing environment inside cells helps to prevent free radical mediated damage. This reducing environment is maintained by the action of antioxidant enzymes and substances, such as superoxide dismutase (SOD), catalase, glutathione peroxidase, glutathione, vitamins C and E (Bayir, 2005; Schafer et al., 2001). Oxidative stress can be result of dysbalance between the production of free radicals and antioxidant system which plays a role in the pathogenesis of fatal diseases such as cancer and cardiovascular diseases (Kopani et al., 2006). Excessive production of ROS may lead to programmed cell death and may accelerate the process of aging (Chamond et al., 1999). For a long time, reactive oxygen species (ROS) have been considered harmful mediators of inflammation owing to their highly reactive nature. However, there are an increasing number of findings suggesting that ROS can play role in anti-inflammatory and prevent autoimmune responses (Hultqvist et al., 2009).


Introduction
Reactive oxygen species (ROS) are highly reactive molecules generated predominantly during cellular respiration and normal metabolism.These side products can damage many biological molecules; they can change protein functions, damage DNA material and cause lipid peroxidation of cell membranes (Kulbacka et al., 2009).In general, the reducing environment inside cells helps to prevent free radical mediated damage.This reducing environment is maintained by the action of antioxidant enzymes and substances, such as superoxide dismutase (SOD), catalase, glutathione peroxidase, glutathione, vitamins C and E (Bayir, 2005;Schafer et al., 2001).
Oxidative stress can be result of dysbalance between the production of free radicals and antioxidant system which plays a role in the pathogenesis of fatal diseases such as cancer and cardiovascular diseases (Kopani et al., 2006).Excessive production of ROS may lead to programmed cell death and may accelerate the process of aging (Chamond et al., 1999).
For a long time, reactive oxygen species (ROS) have been considered harmful mediators of inflammation owing to their highly reactive nature.However, there are an increasing number of findings suggesting that ROS can play role in anti-inflammatory and prevent autoimmune responses (Hultqvist et al., 2009).

Antioxidants May Protect Cancer Cells from Apoptosis Signals and Enhance Cell Viability
Zafer Akan 1 *, Ayse Inhan Garip 2 Neutralization of free radical is important to prevent the damage of cells, tissues and organs.Control of free radical neutralizations are under the control of internal antioxidant enzymes such as SOD, NADH, NADPH (Kopani et al., 2006).Destruction of balance between the oxidant and antioxidants depends on age, environmental conditions and some mutations.Uses of herbal sourced ingredients to improve balance of antioxidant system are common way, between the public.
Flavonoids are polyphenolic compounds that occur ubiquitously in foods of plant origin (Formica and Regelson, 1995).Surface OH groups of flavonoids such as Quercetin, tends to get relationship with reactive or free oxygen species.It has been reported that some flavonoids such as rutin (quercetin-3-rutinoside) and quercetin shows antioxidant activity via this way (Ueno et al., 1984).
Quercetin is one of the most abundant dietary flavonoids.It can be found in apples, black, green and buckwheat tea, onions, raspberries, red grapes, cherries, citrus fruits as well as in some well known medical plants (ginkgo biloba, cranberries and St John's wort) (Hertog and Hollman, 1996;Terao, 2009).
In previous in vitro studies has shown that quercetin acts as an antioxidant and anti-inflammatory agent and that it has potent anticarcinogenic properties as apoptosis inductor.
In the normal conditions, herbal sourced antioxidants intake could be beneficial for cancer prevention (Gerhauser, 2008;Murakami et al., 2008), coronary artery disease prevention (Siu, 2010) and moderation of aging process.But what will happen if cancer patient takes artificial herbal sourced antioxidants such as quercetin which is abundantly present in many herbs, fruits and grains.Will it facilitate anticancer therapy or not?To examine that, K562 erythroleukemia cell line was induced to apoptosis by hydrogen peroxide and effect of quercetin over the apoptosis and viability of K562 cells was observed with flow cytometer.

FITC-Annexin V staining assay
After induction with H 2 O 2 and Quercetin, K562 cells were washed twice with PBS and suspended in 1x binding buffer (10 mM HEPES, 140 mM NaCl, and 5 mM CaCl 2 at pH 7.4) at a concentration of approx 1510 5 cells/ml.Five μl of FITC-Annexin V and 10 μl of propidium iodide (Sigma, A2214, 1;100) was added to both control and induced cell suspension from the 50 μg/ml stock.After incubation at room temperature for 10 minutes at dark, the fluorescence of the cells was determined immediately with a flow cytometer (FACS Calibur, Becton-Dickinson, San Jose, CA, USA).

Statistical analysis
Measurements were repeated more than 3 times and student t-test was used for statistical analysis.Descriptive statistics for studied variables (characteristics) were presented as mean, standard deviation, minimum and maximum values.Two ways Factorial ANOVA was used to compare Groups.Duncan multiple comparison test was used to determine different groups.Statistical significance levels were considered as 1% (p<0.01).The SPSS (ver.13) statistical program was used for all statistical computations.
In third probe, hydrogen peroxide (H 2 O 2 ) was applied in dose 150, 300 and 600 µM for 24h.Kind of ROS, hydrogen peroxide (H 2 O 2 ) induced apoptosis of K562 cells had been shown previously and similar results was obtained in our study (p<0.01)(Figure 3, Table 1).

Discussion
In previous studies quercetin was implied as an apoptotic activator and antioxidant as well as protective agent against various types of cancer (Jung et al., 2010).It was shown that quercetin can inhibit proliferation of tumor cells and reduce the number of aberrant crypt foci in colon tumors (Van Erk et al., 2005) that it can facilitate programmed cell death in lung carcinoma (Nguyen et al., 2004) and colonorectal tumor cells (Richter et al., 1999).Other researchers had showed that quercetin acts as a free radical scavenger and protects cells from oxidizier molecules (Orsolic et al., 2007;Benkovic et al., 2009).As known, oxidative stress and free radicals are important activators for apoptosis (Rinaldi et al., 2009).
On the other hand, studies conducted in last ten years showed that quercetin can act as an antiapoptotic agent as well (Ishikawa and Kitamura, 2000).In a few studies it has been shown that quercetin can partially prevent H 2 O 2 -induced apoptosis (Chow et al., 2005) and it was suggested that protective effects of quercetin against oxidative injuries of some cells may be achieved via modulation of mitochondrial dysfunction and inhibition of caspase activity (Park et al., 2003).
In this study, our results showed that higher dose of quercetin than 200 μM reduce K562 cell viability (which considered as toxic doses by Cao et al. (2007) but low doses of quercetin (<200 µM) can increase cell viability and considered as therapeutic dose.As it known, hydrogen peroxide is an important apoptotic mediator over mitochondrial dependent apoptotic mechanism; we also showed protective effect of quercetin over the K562 cells which induced to apoptosis with H 2 O 2 .
Free radical generation and inactivation's are under the strict control of oxidoreductive reactions.Excessive superoxide production can accelerate cell death, DNA damage and can lead to cancer, also excessive inactivation of superoxides can disturb apoptosis signals.Inactivation of radiation and environmental sourced superoxides by the herb sourced flavonoid free radical scavengers seems beneficial for cancer prevention (Murakami et al., 2008) but if cancer is already present, as known as free radicals are important for apoptosis signals.For this reason, uncontrolled consumption of flavonoid free radical scavengers such as quercetin during chemothrapy may weaken the effect of chemotherapeutics and radiotherapy rather then help it.
It has been theorized that cancer risk reduction may be achieved by greater consumption of phytochemicalrich fruits and vegetables (Davis et al., 2009;Rinaldi et al., 2009).However, results of our research suggest that antioxidants can interfere and attenuate success of anticancer therapy so antioxidant intakes should be strictly controlled in the cancer diagnosed patients.

Figure 1 .
Figure 1.Effect of Quercetin Over the Viability of K562 Cells for 3 Hours.Non-apoptotic cell rate (% viable cells) was assessed by FITC-Annexin V/PI flow cytometer assay.*p<0.05

Table 1 . Descriptive Statistics and Comparison Results for Groups
*Different lower case represent differences among HP level (p<0.01);**Different upper case represent differences among groups (p<0.01)