Brief Note on Cell Viability and Cytotoxicity and its Effects

About the Study

The quality of being toxic to cells is known as cytotoxic. An immune cell or some types of venom, such as that generated by the puff adder (Bitis arietans) or the brown recluse spider, are examples of harmful agents. Cytotoxic activity tests are commonly used in the pharma companies to screen chemical libraries for toxicity. If they wish to produce a therapy that targets rapidly dividing cancer cells, for example, researchers can explore for cytotoxic compounds, or they can screen "hits" from initial high-throughput drug screens for unwanted cytotoxic effects before investing in their development as a medication.

One of the most common methods used to determine cell viability and cytotoxic effects is to evaluate cell membrane integrity. The integrity of cell membranes is frequently compromised by cytotoxic compounds. Vital dyes like the game can be played blue and took place in the early iodide are generally kept out of healthy cells' innards; however, if the cell membrane is damaged, they can freely penetrate it and stain internal components. Alternatively, the flow of substances ordinarily sequestered inside cells to the outside can be used to assess membrane integrity.

Lactate dehydrogenase (LDH) is a chemical that is commonly tested using the LDH assay. When LDH interacts with a specific probe, it converts NAD to NADH, which causes a color shift. Researchers have found protease indicators that allow them to count the amount of live and dead cells in a given cell population. The live-cell enzyme is only active in cells with a normal cell membrane; if the cell is compromised and the enzyme is exposed to the outside world, it loses its action. The dead-cell trypsin is unable to cross the cell membrane and can only be identified in culture conditions after the cell membrane has been breached.

The 3-(4,5-Dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) or 2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxamide (XTT), which provides a water-soluble product, or the MTS assay can also be used to evaluate toxicity. Using a colorimetric reaction, this assay determines the cell's reducing potential. The MTS reagent will be reduced to a colorful formazan with viable cells. A redox-based assay using the fluorescent dye to perform specific functions has also been developed. Researchers developed assays that employ ATP concentration as a viability marker, in addition to using dyes to signal the oxidation state of cells to monitor their viability. Luminescent assays in which ATP is the limiting reagent for the reporter reaction are examples of ATP-based assays.

The sulforhodamine B (SRB) assay, the WST assay, and the clonogenic assay can all be used to evaluate cytotoxicity. To reduce assay-specific false positive or false negative results, suitable assays might be integrated and repeated sequentially on the same cells. LDH-XTT-NR (Neutral red assay)-SRB is a possible combination that is also accessible as a kit.

Electric impedance measurements when the cells are maintained on gold-film electrodes provide a label-free system for monitoring the cytotoxic response of adherent animal cells instantaneously. Electric Cell-Substrate (ECIS) impedance sensing is the name given to this technology. Unlike so many colorimetric endpoint tests, label-free real-time techniques reveal the kinetics of the cytotoxic response rather than just a snapshot.

Once cells are exposed to the toxic compound, they can develop a range of cell fates. Necrosis is a situation in which cells lose their membrane integrity and die quickly as a result of cell lysis. The cells can either stop actively growing and dividing (a drop in cell viability) or activate a technology which allows of controlled cell death (a decrease in cell viability).

Necrosis causes cells to enlarge quickly, lose their membrane structure, shut down respiration, and spill their contents into to the environment. Rapid necrosis in vitro leaves cells with little time or inclination to activate apoptotic machinery, hence they do not express apoptotic markers. Apoptosis is defined by the change in the cell's refractive index, cytoplasmic shrinkage, nuclear condensation, and DNA cleavage into regularly sized fragments, among other cytological and molecular events. Cellular senescence cells in culture fall victim to secondary necrosis. They'll stop producing energy; lose membrane integrity, and lyzed.