XTT Cytotoxicity is a Ready to use assay for the biological evaluation and screening of chemical, pharmaceutical, cosmetic compounds or of a medical device using in vitro mammalian or animal cell cultures. The XTT assay is preferred as an early, simple, fast and sensitive assay. Moreover, the assays are fully in line with 3R’s - Replace, Refine, Reduce and avoids animal testing. The kit includes a detailed instruction for use.
Chemical compounds, pharmaceuticals, cosmetic products, natural plant extracts or materials used for implants can have a toxic effect on mammalian cells. There are different mechanisms of toxicity, i.e. loss of membrane integrity, lysosomal toxicity, inhibition of protein synthesis or interference in metabolism. Not only for the development of pharmaceuticals, cosmetics, plant extracts or chemicals and implants, but also for the environment it is important to discriminate between no toxicity, negligible and strong toxicity. For example, compounds with promising biological activity and negligible cytotoxicity should not be ruled out, because “The dose makes the poison", i.e. all things are poison, and nothing is without poison, the dosage alone makes it so a thing is not a poison (Paracelsus, 1493–1541).
Several different eukaryotic and prokaryotic cell lines are used to assess cytotoxicity. Cytotoxicity assays detect cellular or metabolic changes associated with viable or nonviable cells. Different assays can detect different mechanisms in cells, such as biochemical activities in the electron transport chain, protein synthesis, lysosomal activity, or loss of membrane integrity, which are indicative signs of living cells. XTT or other redox dies are a valuable tool to assess quantitatively viable cells, since dyes are only reduced by metabolic active cells.
The XTT assay is based on the cleavage of the yellow tetrazolium salt XTT to form an orange formazan dye. The formazan dye formed from XTT is soluble in aqueous solutions and can be monitored quantitatively by a microplate spectrophotometer. The quantity of formazan product is directly proportional to the number of living and respiring cells. Most assays can be automated allowing high throughput processing. Implants or chemicals used in implants have to be tested for cytotoxicity according to ISO 10993. A usual XTT cell viability assay is shortly described here: Cells are grown in 96 well tissue culture plates and are incubated with one of the above mentioned stain solution and test compound during 4–24 h. After this incubation period, formazan solution is formed, which is spectrophotometrically quantified. An increase in number of living cells results in an increase in the OD.
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