Influence of combinations of digitonin with selected phenolics, terpenoids, and alkaloids on the expression and activity of P-glycoprotein in leukaemia and colon cancer cells.

P-glycoprotein (P-gp or MDR1) is an ATP-binding cassette (ABC) transporter. It is involved in the efflux of several anticancer drugs, which leads to chemotherapy failure and multidrug resistance (MDR) in cancer cells. Representative secondary metabolites (SM) including phenolics (EGCG and thymol), terpenoids (menthol, aromadendrene, ß-sitosterol-O-glucoside, and ß-carotene), and alkaloids (glaucine, harmine, and sanguinarine) were evaluated as potential P-gp inhibitors (transporter activity and expression level) in P-gp expressing Caco-2 and CEM/ADR5000 cancer cell lines. Selected SM increased the accumulation of the rhodamine 123 (Rho123) and calcein-AM (CAM) in a dose dependent manner in Caco-2 cells, indicating that they act as competitive inhibitors of P-gp. Non-toxic concentrations of ß-carotene (40µM) and sanguinarine (1µM) significantly inhibited Rho123 and CAM efflux in CEM/ADR5000 cells by 222.42% and 259.25% and by 244.02% and 290.16%, respectively relative to verapamil (100%). Combination of the saponin digitonin (5µM), which also inhibits P-gp, with SM significantly enhanced the inhibition of P-gp activity. The results were correlated with the data obtained from a quantitative analysis of MDR1 expression. Both compounds significantly decreased mRNA levels of the MDR1 gene to 48% (p<0.01) and 46% (p<0.01) in Caco-2, and to 61% (p<0.05) and 1% (p<0.001) in CEM/ADR5000 cells, respectively as compared to the untreated control (100%). Combinations of digitonin with SM resulted in a significant down-regulation of MDR1. Our findings provide evidence that the selected SM interfere directly and/or indirectly with P-gp function. Combinations of different P-gp substrates, such as digitonin alone and together with the set of SM, can mediate MDR reversal in cancer cells.

Synergism of three-drug combinations of sanguinarine and other plant secondary metabolites with digitonin and doxorubicin in multi-drug resistant cancer cells.

We determined the ability of some phytochemicals, including alkaloids (glaucine, harmine, and sanguinarine), phenolics (EGCG and thymol), and terpenoids (menthol, aromadendrene, ß-sitosterol-O-glucoside, and ß-carotene), alone or in combination with the saponin digitonin to reverse the relative multi-drug resistance of Caco-2 and CEM/ADR5000 cells to the chemotherapeutical agent doxorubicin. The IC(50) of doxorubicin in Caco-2 and CEM/ADR5000 was 4.22 and 44.08µM, respectively. Combination of non-toxic concentrations of individual secondary metabolite with doxorubicin synergistically sensitized Caco-2 and CEM/ADR5000 cells, and significantly enhanced the cytotoxicity of doxorubicin. Furthermore, three-drug combinations (secondary metabolite+digitonin+doxorubicin) were even more powerful. The best synergist was the benzophenanthridine alkaloid sanguinarine. It reduced the IC(50) value of doxorubicin 17.58-fold in two-drug combinations (sanguinarine+doxorubicin) and even 35.17-fold in three-drug combinations (sanguinarine+digitonin+doxorubicin) in Caco-2 cells. Thus synergistic drug combinations offer the possibility to enhance doxorubicin efficacy in chemotherapy.

Digitonin synergistically enhances the cytotoxicity of plant secondary metabolites in cancer cells.

In phytotherapy, extracts from medicinal plants are employed which contain mixtures of secondary metabolites. Their modes of action are complex because the secondary metabolites can react with single or multiple targets. The components in a mixture can exert additive or even synergistic activities. In this study, the cytotoxicity of some phytochemicals, including phenolics (EGCG and thymol), terpenoids (menthol, aromadendrene, ß-sitosterol-O-glucoside, and ß-carotene) and alkaloids (glaucine, harmine, and sanguinarine) were investigated alone or in combination with the cytotoxic monodesmosidic steroidal saponin digitonin in Caco-2, MCF-7, CEM/ADR5000, and CCRF-CEM cells. Digitonin was combined in non-toxic concentrations (5µM in each cell line; except in MCF-7 the concentration was 2µM), together with a selection of phenolics, terpenoids, and alkaloids to evaluate potential synergistic or additive effects. An enhanced cytotoxicity was observed in most combinations. Even multi-drug resistant (MDR) cells (such as CEM/ADR5000 cells), with a high expression of P-glycoprotein, were responsive to combinations. Sanguinarine was the most cytotoxic alkaloid against CEM/ADR5000, MCF-7, and CCRF-CEM cells alone and in combination with digitonin. As compared to sanguinarine alone, the combination was 44.53-, 15.38-, and 6.65-fold more toxic in each cell line, respectively. Most combinations synergistically increased the cytotoxicity, stressing the importance of synergy when using multi-target drugs and mixtures in phytotherapy.

Effects of digitonin on hyperglycaemia and dyslipidemia induced by high-sucrose intake.

This study examined whether high-sucrose intake effects on lipid profile and oral glucose tolerance may be inhibited by a single administration of digitonin, a saponin from the seeds of Digitalis purpurea Male Wistar 24 rats were initially divided into two groups (n=12): (C) was given standard chow and water; (S) received standard chow and 30% sucrose in its drinking water. After 30 days of treatments, C rats were divided into two groups (n=6): (CC) given an intra-gastric dose 0.5 mL saline; (CD) given a single intra-gastric dose of 15 mg/kg digitonin. S rats were also divided into two groups (n=6): (SC) given intra-gastric saline and (SD) given digitonin. Rats were sacrificed after the oral glucose tolerance test (OGTT) at 2 h after the digitonin administration. S rats had higher total energy intake and final body weight than C. SC rats had fasting hyperglycaemia and impaired OGTT. Digitonin in SD group improved the glucose tolerance. Triacylglycerol (TG), very-low-density lipoprotein (VLDL-C) and free fatty acid (FFA) serum concentrations were increased in SD rats from CC. Digitonin in SD rats decreased FFA and led TG and VLDL-C concentrations at the levels observed in the CC group. Despite the enhanced cholesterol in CD group from CC, the high-density lipoprotein (HDL-C) was increased in these animals. HDL-C/TG ratio was higher in CD and SD than in CC and SC, respectively. No significant differences were observed in lipid hydroperoxide(LH) between the groups. VLDL-C/LH ratio and gamma-glutamyl transferase (GGT) activity were increased in SC group and were decreased in SD rats from the SC. In conclusion digitonin enhanced glucose tolerance and had beneficial effects on serum lipids by improve antioxidant activity.

[The hypolipidemic action of water-soluble enterosorbents of cholesterol and bile acids in an experiment]. / Gipolipidemicheskoe deistvie vodorastvorimykh énterosorbentov kholesterina i zhelchnykh kislot v éksperimente.

Experiments on rats, guinea pigs and rabbits with experimental dyslipoproteinemia have revealed that the new water-soluble high-molecular weight polymers containing digitonin (ED) or a quaternary nitrogen atom (EA) have a more marked hypolipidemic action than cholestyramine and normalize lipoprotein metabolism. The digitonin-containing enterosorbent has been shown to decrease the absorption of 4-14C-cholesterol, while the nitrogen-containing enterosorbent diminishes the absorption of 3H-cholic acid.

Prevention of hypercholesterolemia in monkeys (Macaca fascicularis) by digitonin.

Digitonin mixed in the diet was well tolerated by rats and cynomolgus monkeys (Macaca fascicularis), and prevented the expected rise in plasma cholesterol in monkeys fed a diet containing butter and cholesterol. Both digitonin and mildly hydrolyzed digitonin precipitated cholesterol dispersed in micellar suspensions and decreased intestinal absorption of cholesterol in rats, but only digitonin bound cholesterol in vitro. The hypocholesterolemic effect of digitonin may be secondary to decreased intestinal absorption of cholesterol associated with a disturbance in the micellar suspension of cholesterol in the intestinal content. Modification of other mechanisms that may be involved in membrane transport of cholesterol through the intestinal epithelium is not ruled out by the present findings.