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Background The multidrug resistance (MDR) of cancer cells is a major obstacle to cancer treatment. Glutathione S-transferase Pi (GSTP1-1) catalyzes the conjugation of glutathione with anticancer drugs and therefore reduces their efficacy. Phenolic compounds have the potential to inhibit GST P1-1 activity, which is a promising goal to overcome MDR and increase the efficacy of chemotherapy. Results Three fractions (dichloromethane, ethyl acetate, and n-butanol) were prepared from Tamarindus indica seeds to determine their phenolic and flavonoid properties as well as their antioxidant/pro-oxidant properties. The n-butanol fraction displayed the highest levels of phenol ( 378 ± 11.7 mg gallic acid equivalent/g DW) and flavonoids (83 ± 6.0 mg rutin equivalent/g DW). Inhibiting effects on purified GSTP1-1 activity in human erythrocytes (eGST), placenta (pGST), and hGSTP1-1 have been studied. The n-butanol fraction was the most effective in inhibiting eGST, hGSTP1-1, and pGST with IC50 values of 3.0 ± 0.7, 4.85 ± 0.35, and 6.6 ± 1.2 μg/ml, respectively. Cellular toxicity was investigated for the T. indica n-butanol fraction on various human cancerous cell lines. The only ones affected were MCF-7 cell lines (72%) and HePG2 (52%) indicated cytotoxicity. The value of IC50 is 68.5 μg/ml of T. indica n-butanol fraction was observed compared to 1.7 μg/ml tamoxifen in MCF-7 cell lines. The combination of treatment of T. indica extract with the medicinally approved drug tamoxifen had unexpected effects; complete elimination of the cytotoxic inhibition effect of tamoxifen and the plant extract was observed. Conclusions However T. indica extract has a cytotoxic effect on the MCF-7 cell line; in certain situations, plant products can have an opposite effect to the intended drug, which decreases the impact of the drug.

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Glutathione (GSH) concentration, the activity of its metabolizing enzymes, glutathione transferase (GST), glutathione peroxidase (GPx), glutathione reductase (GR), and the antioxidant enzyme catalase (CAT) in O. niloticus ovary and testis were examined. GSH concentration of O. niloticus testis exhibited high concentration (129 ± 21 nmol/g tissue) compared with GSH concentration (49.2 ± 8.3 nmol/g tissue) in the ovary. GST, GPx, GR, and CAT activities of O. niloticus testis exhibited high values compared with their corresponding values in ovary homogenates. However, protein concentration in ovary homogenates exhibited higher values (175 ± 40.6 mg) compared with testis homogenates (27.1 ± 3.7 mg). O. niloticus ovary was less effective in excretion of xenobiotices compared with the testis, where its function is mainly in increasing the protein content of the eggs; however, in O. niloticus testis, the glutathione cycle operated in accelerated way in the direction of reduced GSH production in order to protect the maturation stages in a save way. A simple reproducible procedure for the purification of GST from O. niloticus ovary was established. The enzymes proved to be homogenous as judged by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and its molecular weight was calculated to be 25.1 kDa. GST of O. niloticus ovary exhibited maximum activity at pH 7.5. The Michaelis-Menten constant (K(m)) of the purified ovary GST for GSH and CDNB was 0.076 mM and 1.0 mM, respectively. Cibacron blue was the most potent inhibitor of ovary GST activity (IC50 value, concentration of inhibitor that will give 50% inhibition, equal 0.002 μM). The specific activity of GST toward different electrophilic substrates was determined. GST activity toward benzyl isothiocyanate was the highest compared with phenethyl isothiocyanate and allyl isothiocyanate.