Hello Dewi Murda,

LC50 refers to the concentration of a substance that is lethal to 50% of a population. LC50 is typically used to assess the toxicity of a substance to organisms or populations. 

In MTT assay, you should use IC50 value to determine the inhibitory effect of a compound on cell viability. IC50 focuses on the inhibition of a specific process (cell viability), while LC50 focuses on the lethality of a substance. LC50 is typically used in larger animal models to determine the dose that kills 50% of the test population. So, in MTT assay, LC50 is not used.

The MTT assay measures the metabolic activity of cells by detecting the conversion of a yellow tetrazolium salt to a purple formazan crystal by metabolically active cells. The amount of formazan produced is proportional to the number of viable cells. 

The data from MTT assay is used to create a dose-response curve, plotting the percentage of cell viability against the substance's concentration.

To calculate percentage cell viability use the formula: 

Percentage Viability = [(Mean Absorbance of Treated Cells - Background) / (Mean Absorbance of Control Cells - Background)] x 100%. 

You need to run a well containing all the necessary reagent (except cells) to measure the background absorbance.

You will have to plot a graph where in the percentage of cell viability is typically plotted on the y-axis, while the concentration of the compound being tested is plotted on the x-axis. The x-axis represents the concentration of the compound, which is often expressed in units like µg/mL or µM. The y-axis, representing cell viability, is usually expressed as a percentage, where 100% indicates that the compound has no effect on cell viability, and lower percentages indicate a reduction in cell viability. This type of plot will allow you to determine the half maximal inhibitory concentration (IC50), which is the concentration of the compound that results in 50% inhibition of cell growth or viability. The IC50 value is a key parameter for evaluating the potency of a compound. 

So, by using the above method, you will be able to calculate the IC50 value with the help of the absorbance readings.

Best,

Dear Murda,

The viability and toxicity of the test compound to the cells mean the same thing, except that you are looking at opposite sides of the same coin. We talk of the viability of the cells measured by MTT assay or LC50 (toxicity of the test compound) measured by the same. When doing in vivo work, we talk of LD50, and not LC50. Otherwise, the response by Malcolm is adequate.