ABSTRACT
An accurate assessment of the efficacy of a biopreservation solution and protocol ultimately resides on the quality and reliability of the viability and functional assays used to assess the preservation process. The field of biopreservation viability assessment is continuing to evolve. Early in the history of the discipline red blood cell preservation was monitored using simple spectrophotometers that measured hemoglobin leakage from these cells; whereas sperm preservation was often scored based on motility. Now, however, there are a variety of assessment assays that can track a multitude of changes in cell physiology and function that either reflect cell death or herald the initiation of a key death cascade precipitated by poor preservation procedures. Yet with dozens of assays now available, a quandary is now presented on which assay(s) to choose to assess preservation efficacy. This article reviews the current slate of viability assays that have been organized into four assay tiers. The current state of the art indicates that multiple endpoint fluorescence assays hold the strongest position as a battery of viability assessment tools. Nearly all of these viability assays can be broadly applied for most cell types, whereas functional assays typically need to be tailor-matched to the particular cell type being evaluated. A review of the literature indicates that (1) no single assay should be used to assess viability or function of cells undergoing a preservation process, (2) the unique behavior of a particular viability probe must be considered in the context of each cell
type (e.g., primary hepatocytes will detoxify many fluorescent probes leading to erroneous conclusions), (3) new noninvasive assays should be developed to adequately determine the preservation efficacy of thick tissues or whole organs, (4) the future of biopreservation viability assays will be driven by a mechanism approach that may ultimately lead to the use of proteomic and genomic profiling of preserved tissues, and (5) a recommendation is posited arguing that the best method of comprehensively assessing preservation efficacy is to choose at least one assay from Tiers 1, 2, and 3 as defined herein. Thus, the portfolio of assays that is emerging is more reliable and constitutes an array of assays that should be used as a multiple endpoint approach. Furthermore, these assays are now yielding more information about the stress and cell death pathways in cells that are being activated as a consequence of biopreservation. This information, in turn, will yield improved preservation solutions and protocols in the future to support the cell therapy, gamete preservation, and tissue and organ preservation arenas.
