ON THE PHYSICOCHEMICAL REGULATION OF THE GROWTH OF TISSUES : THE EFFECTS OF THE DILUTION OF THE MEDIUM ON THE GROWTH OF THE SPLEEN

Historical foundations of wound healing and its potential for acceleration: dose-response considerations

This paper provides a detailed historical assessment of the origin and developmental progress of the concept of wound healing and its attempted acceleration from its start in the beginning of the 20th century to approximately 1960. Emphasis is placed on the development of cell culture in the assessment of wound healing and in attempts to validate experimental findings via clinical research. Of particular interest were the observations that wound healing could be accelerated in the 30-50% range with the dose response displaying biphasic characteristics consistent with the hormesis dose-response model. Such findings set the stage for the hormetic dose-response revolution that is occurring within the biological and biomedical sciences, including wound healing, whereby considerable research now supports the capacity for endogenous and exogenous agents to accelerate the process of wound healing and its functional performance.

THE EFFECT OF VARIOUS TISSUE EXTRACTS UPON THE GROWTH OF ADULT MAMMALIAN CELLS IN VITRO

The cultivation of cells in vitro affords a valuable means of estimating the effects of tissue extracts. Tissue extracts have a definite effect upon the growth of adult mammalian cells in vitro. The majority of tissue extracts stimulate the growth of connective tissue, but liver extract inhibits it. The extracts are to a certain extent specific in their action upon the growth of parenchymatous cells. Some cells are stimulated by one extract and inhibited by another, and those extracts which inhibit one type of parenchymatous cell may stimulate another type. Homogenous and autogenous extracts are equally efficacious in their action upon the growth of cells. The extracts may be preserved for a short period of time without suffering any change in their power of affecting the growth of cells.

THE EFFECT OF DILUTION OF PLASMA MEDIUM ON THE GROWTH AND FAT ACCUMULATION OF CELLS IN TISSUE CULTURES

1. Dilution of plasma with isotonic solutions causes a more extensive migration in cultures of cells of the actively migratory type, such as those of spleen and bone marrow. Dilution with a limited quantity of distilled water produces the same effect. Less actively motile cells are influenced little or not at all by dilution. The effect on cells of the first type is probably due to the reduction in the quantity of fibrin in the clot producing lessened resistance to cell locomotion. 2. Dilution of plasma with either isotonic solutions or distilled water is without effect on cell multiplication, as is shown by records of the number of mitoses in living culture preparations. 3. Dilution of plasma with suitable quantities of Ringer's solution causes a marked diminution in the quantity of fat accumulated by the cells. This reduction is to be attributed to the decrease in the quantity of fat in the medium. The accumulation of fat by cells in cultures is therefore not to be regarded as the result of a cell degeneration, but as an accumulation, the source of the fat being the medium in which the cells are growing.

THE EFFECT OF THE VARIATION IN THE OSMOTIC TENSION AND OF THE DILUTION OF CULTURE MEDIA ON THE CELL PROLIFERATION OF CONNECTIVE TISSUE

For the first few days of cultivation of connective tissue in hypertonic, hypotonic, and diluted medium, cell proliferation was stimulated. The first outgrowths of new cells in the modified media did not occur sooner than in normal medium. In hypertonic medium the density of the area of cell proliferation appeared to be greater than the control, but in hypotonic or diluted medium there seemed to be no increase in actual mass over the control. These observations confirm the conclusions of Carrel and Burrows, as well as those of Lambert. Subsequent to the first few days of cultivation in hypertonic medium the area of cell proliferation decreased and in a short time conditions developed which were unfavorable to growth, and finally resulted in death of the culture, unless it revived before this stage. Hypotonic medium after about ten days no longer caused more extensive areas of proliferating cells; but instead, the extent of new growth gradually decreased, and the culture merely remained alive unless revived. In diluted medium the extent of the area of cell proliferation remained greater with no actual increase in mass. The area of cell proliferation which is observed during the first few days in a culture of fresh tissue recently extirpated does not indicate the actual influence of modified media. It was only after continued cultivation of strains of connective tissue in these modified media that their influence on cell proliferation was determined.

Molecular markers of senescence in fibroblast-like cultures

The loss of replicative capacity in vitro of normal human diploid fibroblasts is a model for studying molecular changes that accompany both regulated growth control and cellular senescence. We describe the molecular phenotype of senescent fibroblasts in terms of markers that are altered with proliferative decline. We describe these markers by analyzing pathways and associated mechanisms related to the responsiveness of proliferatively competent and senescent cells to growth signals including changes in the extracellular environment, growth factors, growth factor receptors, secondary messengers, cell-cycle progression, transcription factors, and the fidelity of DNA synthesis. There is an abundance of molecular markers for senescence in culture at every level of information transfer. Although it seems clear that some alterations in gene expression with senescence are the result of specific changes in upstream events, more global dysregulation of coordinated growth control point to as yet undefined mechanisms.

Molecular biology of aging

Aging is an extremely complex biologic phenomenon of immense importance. Currently we have only a poor and incomplete understanding of the fundamental molecular mechanisms involved. Despite numerous observations and diverse theories, no unifying or proven hypotheses have emerged. It is reasonable to conclude, however, that aging is a multifactorial process composed of both genetic and environmental components. Each physiologic system within an organism, each tissue within a system, and each cell type with a tissue appears to have its own trajectory of aging. Thus, aging must be studied as parts of a whole and understood as the sum of its parts. Cellular "clocks" exist and operate in the absence of higher-order "clocks". However, higher-order clocks are certainly in place in vivo, but their relationship to cellular clocks is not well understood. All aging changes have a cellular basis, and aging is perhaps best studied, fundamentally, at the cellular level under defined and controlled environmental conditions. Aging changes at the cellular level must be viewed, however, as components of a hierarchical, dynamic, and interacting network whose functional integrity progressively deteriorates with time. The powerful tools of molecular biology are now being applied by scientists to evaluate the leading hypotheses. The results of these studies should serve to advance our understanding of aging and to focus future research efforts. This work should provide the scientific foundation to enhance the quality of life for people suffering the failings of age.

The ultrastructure of mouse neuroblastoma cells in tissue culture

Neuroblastoma cells grown in suspension culture are round and have no distinctive structural characteristics. However, cells transferred to substrates flatten, develop long neurites, and assume the morphology of normal neurons. The resemblance of monolayered neuroblastoma cells to normal neurons is amplified by treatment with hypertonic medium; under these conditions, cell division is inhibited and the neurites become long and differentiated. The treated cells contain clusters of clear vesicles, 400-600 A in diameter, which are morphologically indistinguishable from the synaptic vesicles of normal neurons. Specialized cell contacts are observed between the treated cells as well as between confluent cells grown in normal medium.