In order to demonstrate whether the known biological effects of Aloe vera (L.) Burm. fil. could correlate with the antioxidant activity of the plant, the antioxidant activity of the aqueous leaf extract was investigated. The present study demonstrated that the aqueous extract from A. vera leaves contained naturally occuring antioxidant components, including total phenols, flavonoids, ascorbic acid, β-carotene and α-tocopherol. The extract exhibited inhibitory capacity against Fe3+/ascorbic acid induced phosphatidylcholine liposome oxidation, scavenged stable DPPH•, ABTS•+ and superoxide anion radicals, and acted as reductant. In contrast, the leaf inner gel did not show any antioxidant activity. It was concluded that the known beneficial effects of Aloe vera could be attributed to its antioxidant activity and could be related to the presence of phenolic compounds and antioxidant vitamins.

Background:Flavonoids are natural compounds with antioxidant, anticarcinogenic, and anti-inflammatory effects.Aims:To determine the cytotoxic effects of flavonoids and drug resistance related to P-gp on K562 human chronic myeloid leukemia cells. We also aimed to evaluate the therapeutic potential of imatinib and flavonoid combinations.Study Design:Cell culture study.Methods:In this study, K562 cells were treated with apigenin, luteolin, 5-desmethyl sinensetin and the anticancer drug imatinib mesylate. The effect of flavonoids on K562 cell proliferation was detected using the 3-(4,5-dimethylthiazolyl)2,5‑diphenyl‑tetrazolium bromide assay. Concentrations of apigenin, luteolin, and 5-desmethyl sinensetin ranging from 25 to 200 μM and of imatinib from 5 to 50 μM administered for 72 h were studied. Apoptosis/necrosis and P-gp activity were measured using flow cytometry. The combined effects of different concentrations of flavonoids with imatinib were evaluated according to combination index values calculated using CompuSyn software.Results:In our study, the IC50 values for apigenin, luteolin, and 5-desmethyl sinensetin were found to be 140 μM, 100 μM, and >200 μM, respectively. Luteolin (100 μM) had the highest cytotoxic activity of these flavonoids. These results were statistically significant (p<0.05). Among the flavonoids studied, the combination of luteolin and imatinib was the most effective and is therefore recommended for its cytotoxic activity in the K562 cell line. After 72 h of incubation at their respective IC50 concentrations, all flavonoids were associated with an apoptosis rate of approximately 50%. P-glycoprotein activity was increased in all groups. Combination treatment may provide better outcomes in terms of cytotoxicity and thus reduce the dosages of imatinib used.Conclusion:The combination of some flavonoids and imatinib mesylate may increase the cytotoxic effect; However, the antagonistic effect should be considered in combined use on k562 cells.

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Known for centuries as a "wonder" plant, Aloe vera (L.) Burm. f. has many biological and pharmacological activities. These effects are due to the variety of the chemical compounds including anthraquinones, glycoproteins, polysaccharides, vitamins and enzymes contained (Choi and Chung 2003; Du Plessis and Hamman 2014; Akev et al. 2015; Shrestha et al. 2015). Many of the medicinal effects have also been attributed to the immunomodulatory properties of the inner gel (Im et al. 2010), but it is also believed that synergistic action of the compounds contained in the whole leaf extracts is responsible for the multiple and diverse beneficial properties of the plant (Eshun and He 2004).The mucilageneous gel part of A. vera is used commercially as a softener in various cosmetic preparations, soaps and shampoos due to its glycoprotein content. The first known effects of A. vera after its cathartic activity, is the wound and burn healing effect of the leaves gel portion, widely supported in scientific literature (Capasso et al. 1998; Chithra et al. 1998; Heggers et al. 1995). Because of this effect, the gel is also added to many preparations used for skin treatment.Antitumor and cytotoxic potential of A. vera extracts continues to be the interest of scientific research from 1980's (Winters et al. 1981; Tsuda et al. 1993; Corsi et al. 1998) until recent years (Naveena Bharath and Selvasubramanian 2011; Du Plessis and Hamman 2014). In a research undertaken in our laboratory, A. vera leaf skin aqueous extract was proved to be effective as prophylactic against Ehrlich ascites tumours in vivo (Akev et al. 2007). The Food and Drug Administration of the USA has approved the developmental study of A. vera for the treatment of cancer and AIDS (Nandal and Bhardwaj 2012).Antitumor effect of aloe emodin (AE), the major anthraquinone derivative of A. vera, was reported in recent years (Cárdenas et al. 2006; Lee et al. 2006; Lin et al. 2006) and attention has been given recently to the possibility of utilizing AE as a chemothera-

Background: Flavonoids are natural compounds with antioxidant, anticarcinogenic, and anti-inflammatory effects. Aims: To determine the cytotoxic effects of flavonoids and drug resistance related to P-gp on K562 human chronic myeloid leukemia cells. We also aimed to evaluate the therapeutic potential of imatinib and flavonoid combinations. Study Design: Cell culture study. Methods: In this study, K562 cells were treated with apigenin, luteolin, 5-desmethyl sinensetin and the anticancer drug imatinib mesylate. The effect of flavonoids on K562 cell proliferation was detected using the 3-(4,5-dimethylthiazolyl)2,5-diphenyl-tetrazolium bromide assay. Concentrations of apigenin, luteolin, and 5-desmethyl sinensetin ranging from 25 to 200 μM and of imatinib from 5 to 50 μM administered for 72 h were studied. Apoptosis/necrosis and P-gp activity were measured using flow cytometry. The combined effects of different concentrations of flavonoids with imatinib were evaluated according to combination index values calculated using CompuSyn software. Results: In our study, the IC 50 values for apigenin, luteolin, and 5-desmethyl sinensetin were found to be 140 μM, 100 μM, and >200 μM, respectively. Luteolin (100 μM) had the highest cytotoxic activity of these flavonoids. These results were statistically significant (p<0.05). Among the flavonoids studied, the combination of luteolin and imatinib was the most effective and is therefore recommended for its cytotoxic activity in the K562 cell line. After 72 h of incubation at their respective IC 50 concentrations, all flavonoids were associated with an apoptosis rate of approximately 50%. P-glycoprotein activity was increased in all groups. Combination treatment may provide better outcomes in terms of cytotoxicity and thus reduce the dosages of imatinib used. Conclusion: The combination of some flavonoids and imatinib mesylate may increase the cytotoxic effect; However, the antagonistic effect should be considered in combined use on k562 cells.