Can the plant extracts of influence the outcome of the MTT test especially at higher concentrations which may result to one registering a false positive result from his/her research?
As Suleiman has said, at high concentrations the extracts will show some activity. The best conclusions can only be made when the samples are tested at low concentrations. Its also good to know some extracts may show a low activity but upon isolation of compounds, some of these compounds may register interesting results.
If the extract has color, it may interfere with the result. to avoid that you must run color control and extract its reading form the obtained result. another source of false positive results is that mitochondrial dehydrogenase can work and produce MTT crystals after cell death. I suggest that you examine your cells before staining to make sure that the blue color is coming from viable cells not extract color.
Plant extracts can easily interfere with the redox-process of formazan formation if compounds are present which get oxidize and reduce the MTT reagent. This is often the case if polyphenols are present or other compounds with redox activity. There are some ways to overcome this problem: first make a control without cells, but including all reagents. If this is positive the respective value can be subtracted from cell tests groups.
If this will not work the assay can be done this way that the cells are incubated with the extract for a defined time, than the extract compounds are washed out extensively and then the MTT reagent is added and the formazan reduction can take place without contact with the extract compounds.
As discussed below using fractions of a extract is mostly not the solution of the problem, as it must be ensure that the fractions or even the pure compounds have no redox potential.
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