Question: 

Extracts of various plants growing in restricted regions of the Mongolian People's Republic are widely used for a variety of disorders including liver diseases and Diabetes mellitus. We tested different concentrations of aqueous and MeOH/H₂O as well as MeOH/BuOH extracts from five defined plants, i.e. Saussurea amara (SA), Lilium pumilum (LP), Dianthus versicolor (DI), Gentiana barbata (GB) and Leonurus sibiricus (LS) on their effects on insulin secretion from clonal rat insulinoma (INS-1E) cells and cell proliferation.

Methods and Results: 

All plant extracts displayed a dose- and time-dependent (24, 48 and 72h) decrease in the number of INS-1E cells attached to culture dishes. Detached cells were however viable as determined by a cell viability assay. Aqueous extracts of LP, DI and SA (500mg/l) led to a time-dependent inhibition of cell proliferation. In contrast, dose-dependent increase in cell number was measured in cells treated with DI (250mg/l) after 48 and 72h, LP (250mg/l) after 24, 48 and 72h and GB (250 and 500mg/l) after 48h, as well as LS (500mg/l aqueous extract, 500mg/l MeOH/H₂O extract and 500mg/l MeOH/BuOH extract; respectively) after 24, 48 and 72h. Interestingly the contrary effects of SA and LS on cell proliferation are in both cases paralleled by an enhanced insulin secretion after 24h as determined by ELISA. This increase in insulin secretion could activate, in an autocrine manner, the insulin-receptor signaling cascade, promoting cell survival via phosphorylation of protein kinase AKT. Therefore the phosphorylation status of AKT in INS-1E cells was assessed by Western Blotting. Cells treated with 500mg/l aqueous extract of SA displayed a decreased, whereas cells treated with 500mg/l aqueous extract of LS showed an increased Phospho-AKT/AKT-ratio. Whole-cell patch-clamp experiments revealed a strong, transient activation of the inward component of a swelling-dependent chloride current (IClswell) by SA in three experiments, thereby changing the current rectification from outward to inward. Cell-cycle analysis (DAPI-staining), assessment of apoptosis (annexin-V and 7-AAD staining; cell volume, side scatter) and necrosis (7-AAD staining; cell debris assessment) by flow cytometry did not reveal significant alterations in any of the extract-treated cells compared to control cells.

Conclusion: 

In conclusion extracts from the Mongolian medicinal plants SA, LP, DI, GB and LS, used in Traditional Mongolian Medicine for treatment of liver diseases and Diabetes mellitus, exert prominent effects on cell proliferation and cell adhesion. In addition SA and LS enhance insulin secretion and SA further elicits inward chloride currents in INS-1E cells.