I have carried out the MTS test several times. The same dilution factor and sample. The results show that the absorbance of sample are higher than the control. When I plotted the graph percentage of inhibition vs concentration the value sometimes negative. Is it shows that the "negative value e.g. -10%" is growth of cell? Attached herewith an example of the graph I get.
There is a concept called hormetic response, an example of biphasic response. In this view, a given chemical can stimulate at lower concentrations but inhibit at higher concentrations. This is a true response. This is more of a norm than exception.
That can mean few things. One of them is that your extract is acting as cell division stimulant or it is possible that the -10% is just a SD of number of cells, in other words your extract is not doing nothing at those concentrations its just a SD that you cant recognize at first glance.
Also it is possible that something is not well dissolved in plate, some wells contain insoluble particles that interfere with the absorbance measurnents.
It means that you have proliferation in your samples instead inhibition.
The MTT assay is a colorimetric assay for assessing cell metabolic activity and reflect the number of viable cells present.
I recommend to plot proliferation to have more coherent graph.
If the absorbance of the sample is higher than the control, that means your samples promoted the cell growth thus increased the cell viability. Since there is no inhibition in cell viability, you can't get positive value in inhibiton. Here is an example:
Abs. non treated = 0.600 ; Abs sample = 0.450 ==> Cell viability in treated cells is 75%
Percentage of inhibiton = 25%
Abs. non treated = 0.600 ; Abs sample = 0.900 ==> Cell viability in treated cells is 150%
Percentage of inhibiton = -50%
So, in short, yes when you see -10% inhibtion it means 10% growth. I would not recommend using inhibiton plot when there is growth.
thank you for all the answer.. i'll try to look back at my method, the graph and any related issue regarding this problem. probably i should look back at my data and try to get any other graph rather than inhibition graph. it's difficult to explain because the negative value.
Strictly in terms of the calculation perspective, a negative PI means the samples have higher values than the negative controls. This could also mean a negative control isnt working well.
There is a concept called hormetic response, an example of biphasic response. In this view, a given chemical can stimulate at lower concentrations but inhibit at higher concentrations. This is a true response. This is more of a norm than exception.
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