The higher concentrations of extract should not be less toxic or become non-toxic compared to the lower concentrations. If you exceed the solubility of your extract components in a medium, still you should have some components dissolved. I think, it could be an interference with the method you use for establishing cell viability. Do you use MTT assay? Another question: did you check the maximum possible concentration of your methanolic extract in a medium before adding it to the cells, ath which you still do not have any precipitation? I should not use the concentrations when extract components are aggregating, as you will not know the real concentrations you have in a medium. Also, as you use methanolic extracts, I would also test the highest concentration of methanol which is not too much toxic too cells.

Hello Sioud,

I am very much suspected to the method you used for preparing the required extract concentration. You use higher methanol/DMSO for preparing lower titre of the extract. You should prepare a stock solution (with very high concentration) of your extract and dissolve it with sterile culture medium to make required concentration. This reduces the amount of cytotoxic solvents to the minimum.

Good Luck

Hii...i am also suspected to the method that you used for preparing your sample:

(1). You can prepare a stock solution in DMSO (10mg/mL for extract), then make a serial dilution using DMEM (for example from 60;30;15;7.5;3.75; 1;875 µg/mL).

(2). Don't use methanol solvent on preparing your sample (it could be effect on cytotoxicity result).

If you don't have any problem with those two reasons, another reason may be come from the interaction between chemical constituents in your sample. At low concentration, chemical constituent that might have contribution in cytotoxicity activity could give low effect, thus it will shown non cytotoxic effect. While, in higher concentration they will be given the contrary effect (cytotoxicity effect).