Cellular metabolism

Rather than looking at DNA synthesis, it is possible to assay cell proliferation by measuring the metabolic activity of your cells in culture via tetrazolium salts. These salts form a dye when present in a metabolically active environment. The resulting color change of the media can be quantified in a spectrophotometer, giving an indication of the extent of proliferation.

Although sensitive, some of these salts are insoluble in normal culture medium, and the dye crystals often need to be dissolved in a solvent like DMSO or isopropanol. However, others are soluble in culture medium and nontoxic.

• Accurate to varying degrees
• High- and low-throughput options
• Protocol is simple
• Some dyes require toxic solvents
• Metabolic assays may not accurately represent changes in cell growth

MTT

• 2-(4,5-Dimethyl-2-thiazolyl)-3,5-diphenyl-2H-tetrazolium bromide (MTT)
• MTT is soluble in water
• Respiring cells convert MTT to a purple formazan dye
• Resulting dye is insoluble in water
• Primarily an endpoint measurement due to needing to dissolve the dye crystals in a solvent

MTT molecular structure

XTT

• 2,3-Bis-(2-Methoxy-4-Nitro-5-Sulfophenyl)-2H-Tetrazolium-5-Carboxanilide (XTT)
• XTT is soluble in water
• Respiring cells convert the XTT to an orange colored formazan dye
• Resulting dye is soluble in water
• No solubilization required prior to quantification
• Sensitivity equal to or better than that of MTT

XTT molecular structure

WST-1

• Water-soluble tetrazolium salt-1 (WST-1)
• Respiring cells convert WST-1 to a dye that is measured at OD420–450
• Resulting dye is soluble in water
• More sensitive than MTT, XTT or MTX
• Assay can be performed in the sample microtiter plate
• No additional steps like washing harvesting or solubilization

WST-1 molecular structure