A statistical design for estimating functional survival

Permeabilization of cells of hemopoietic origin by extracellular ATP4-: elimination of osteoclasts, macrophages, and their precursors from isolated bone cell populations and fetal bone rudiments

Skeletal tissues contain, apart from cells of the osteogenic and chondrogenic lineage, cells of hemopoietic origin, e.g., macrophages, osteoclasts, and their precursors. In the present study we examined the sensitivity for extracellular ATP4- of the above-mentioned cell types in freshly isolated, bone-derived cell populations and in explanted fetal metatarsal bones. Cells of hemopoietic origin reacted to the presence of ATP4- with an increased permeability for impermeant cytotoxic molecules, e.g., ethidium bromide (EB), thiocyanate (KSCN), and an increased non-ion selective membrane conductance. As a consequence, these cells could be killed by a short treatment with adenosine-5' triphosphate (ATP)+KSCN. On the other hand, cells of nonhemopoietic origin (e.g., osteoblasts, chondrocytes) were found to be insensitive to ATP4- in this respect. These cells survived the treatment without apparent damage to their alkaline phosphatase activities, osteogenic potentials, and osteoclast induction capacities. The elimination of the endogenous cells of hemopoietic origin from bone tissue or cell populations derived therefrom offers the possibility to study the properties and functions of osteogenic or chondrogenic cells without interference by the presence of cells of hemopoietic origin. It also allows the study of interactions between osteogenic cells and selected cell populations of hemopoietic origin in coculture experiments.

Parameters for evaluation of viability assays: accuracy, precision, specificity, sensitivity, and standardization

The selection of appropriate viability assays is critical in evaluating the efficacy of any cryopreservation procedure. The appropriateness of a given assay depends on the specific tissue and the function which is being optimized. Although a broad range of "viability" assays have been used, these assays can be classified in seven principle groups: (i) Morphological procedures, including routine histology, surface antigen localization, and transmission electron or scanning microscopy; (ii) proliferation studies; (iii) metabolic assays; (iv) implantation; (v) mechanical assays; (vi) motility; and (vii) DNA or RNA synthetic assays. Regardless of the class of assay, each assay may be further characterized as qualitative, quantitative, or quantal and each type may vary in the degree of subjectivity. In selecting a specific viability assay, biological variability, assay bias, and the statistical probability of both Type I and Type II errors should be considered crucial. Here we discuss a number of critical factors involved in validating viability assays, including accuracy, precision, standardization, specificity, sensitivity, selection of statistical methodology, and range of the assay.

Basic principles of cryobiology

The ultimate aim of most cryopreservation procedures is the retention of the structural and functional integrity of the frozen cells or tissue. Designing strategies for achieving high "viability" of the frozen tissue requires an appreciation of the complex physical-chemical events which occur during freezing and thawing, as well as the importance of other processing steps including tissue procurement and post-thaw processing of the tissue, all of which can adversely affect the tissue. Here we have provided a general overview of cryobiology with special emphasis on techniques for organ preservation.