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ORIGINAL RESEARCH ARTICLE

Saponins from Tribulus terrestris L. Are Less Toxic for Normal Human Fibroblasts than for Many Cancer Lines: Influence on Apoptosis and Proliferation

V. K. Neychev^*,1, E. Nikolova^*, N. Zhelev and V. I. Mitev^*

^* Department of Chemistry and Biochemistry, Medical University, Sofia 1431, Bulgaria; and University of Abertay Dundee, Dundee DD1 1HG, Scotland

To whom requests for reprints should be addressed at ¹ Department of Chemistry and Biochemistry, Medical University, 2 Zdrave Street, Sofia 1431, Bulgaria. E-mail: neychev{at}dir.bg

The objective of the study was to explore the influence of saponins derived from Tribulus terrestris L. (TT) on normal human skin fibroblasts and to compare it with their anticancer properties. In this study, [³H]thymidine incorporation and MTT to assess cell proliferation and viability, respectively, and immunoblotting and HPLC analysis to explore intracellular signal transduction pathways have been used. We found that TT caused a dose-dependent decrease in [³H]thymidine incorporation into the DNA of treated fibroblast compared to the untreated controls. Viability of treated cells remained within the control levels with treatment of up to 5 µg TT/ml medium. It was significantly depressed with incubation in 6 µg TT/ml medium with an IC50 of 12.6 µg TT/ml of cultivating media. ERK1/2 was significantly dephosphorylated at 5 mins of incubation with TT until the 48th hour, when phosphorylation slightly recovered, but was still below the control levels. In contrast, p38 and JNK phosphorylation was positively influenced, with peaks at 1 hr and 24 hrs of incubation respectively. Phosphorylation/dephosphorylation events of SAPK/MAPK clearly correlated with Mkp-1 induction. Procaspase 3 was activated after 5 mins of incubation and coincided with a rapid actin cleavage. There was a significant decrease of putrescine concentration and a concomitant increase of spermidine and spermine at 2 mins of treatment. According to our results, TT is less toxic for normal human skin fibroblasts in comparison to many cancer lines investigated in previous studies. The molecular mechanism of this cytotoxicity involves up- and downregulation of polyamines’ homeostasis, suppression of proliferation, and induction of apoptosis. Further research in this field using animal models would help to explore and interpret the potential properties of TT as an anticancer supplement.

Key Words: Tribulus terrestris L. • fibroblast • cytotoxicity • saponins