Viability measurements in mammalian cell systems

The term “cellular viability” and the diverse assays used to determine viability can strongly influence the interpretation of experimental results. With such one-component systems as purified enzymes, an effect usually can be assigned unambiguously to the modification of a specific enzymatic property. With a highly integrated and multicomponent system such as a cell, however, the assessment of a chemical effect may depend heavily on the specific assay used. Terms such as cell survival, cell killing, cytotoxicity, integrity, and toxicity are often arbitrarily applied, but in an effort to quantify and characterize the term “viability” a number of assays that correlate with either reproductive or functional capabilities have been developed. Not surprisingly, different disciplines have a tendency to favor a specific assay method to the exclusion of others. It is the purpose of this review to examine the merits of the major groups of currently available viability assays (Table 1) as they apply to mammalian cell systems. In addition, it is our intention to show that while some assays may be clearly superior in measuring a final endpoint, technical and practical considerations may limit their usefulness.