MTT assay

MTT assay is a laboratory test and a standard colorimetric assay (an assay which measures changes in color) for measuring the activity of enzymes that reduce MTT to formazan, giving a purple color. This mostly happens in mitochondria, and as such it is in large a measure of mitochondrial activity. It can also be used to determine cytotoxicity of potential medicinal agents and other toxic materials.

Yellow MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, a tetrazole) is reduced to purple formazan in the mitochondria of living cells. A solubilization solution (usually either dimethyl sulfoxide, an acidified ethanol solution, or a solution of the detergent sodium dodecyl sulfate in diluted hydrochloric acid) is added to dissolve the insoluble purple formazan product into a colored solution. The absorbance of this colored solution can be quantified by measuring at a certain wavelength (usually between 500 and 600 nm) by a spectrophotometer. The absorption maximum is dependent on the solvent employed.

This reduction takes place only when mitochondrial reductase enzymes are active, and therefore conversion is often used as a measure of viable (living) cells. However, it is important to keep in mind that other viability tests sometimes give completely different results, as many different conditions can increase or decrease metabolic activity. Changes in metabolic activity can give large changes in MTT results while the number of viable cells is constant. When the amount of purple formazan produced by cells treated with an agent is compared with the amount of formazan produced by untreated control cells, the effectiveness of the agent in causing death, or changing metabolism of cells, can be deduced through the production of a dose-response curve.

References

* Mosmann, T., Rapid Colorimetric Assay for Cellular Growth and Survival: Application to Proliferation and Cytotoxicity Assays. J. Immunol. Meth. 1983, 65, 55-63.
* Wilson, A. P., "Cytotoxicity and Viability Assays" in Animal Cell Culture: A Practical Approach, 3rd ed. (ed. Masters, J. R. W.) Oxford University Press: oXford 2000, Vol. 1,

See also

*Tetrazolium chloride
*Formazan