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THEORY
Cell culture studies are significantly reducing the need for animal research. Cell cultures contain living cells that grow in laboratory dishes and that scientists call in-vitro (in glass) cells. These cultures grow in nutrients (growth factors) collectively referred to as medium. There are tens of thousands of cell types. They come from human volunteers, animals, bacteria and plants.
Toxicologists often use cell cultures to study the effects of natural and artificial substances on the genes of plants and animals, including genetic mutations. If a compound "passes" mutagenicity studies, it graduates to carcinogenecity studies, which are required by the FDA. In • they are supplied with a liquid solution containing the nutrients necessary for cell growth. This is called growth medium (GM) and contains the correct balance of salts, an energy source, vitamins, aminoacids and animal serum.
• they are provided with a suitable surface which allows them to attach and spread.
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• they are maintained at an appropriate temperature, normally 7 0C.
Animal cells are generally isolated from embryos and the cultures set up directly from the tissues of an organisms are termed primary cultures. If cells in primary cultures are removed from the culture vessels, they can then be used to set up large numbers of secondary cultures. Cells from these secondary cultures can, in turn, be used to set up further cultures and so on. This is termed variously as passaging, sub-culturing or cell plating ( the cultures are still called secondary cultures). Primary and secondary cultures are useful for example for studying the biochemistry, physiology and behaviour of cells in defined conditions, though one should be cautious in relating these results and to the behaviour of cells in the animal i.e. in vivo.
Secondary cultures can not be maintained for longer than a few months. Most cultured animal cells die after a finite number of cell divisions (50-100 generations in the case of human skin fibroblasts). However variant cells sometimes appear in cultures which will divide indefinitely. These immortal cell cultures are called established cell lines. The nature of the inheritable change which leads to "immortalisation" is unknown. It is not exactly the same as the malignant transformation which gives rise to cancer cells, though cell lines seem to be one step nearer cancer cells.
Very large stocks of cells can be produced by the growth of established cell lines and secondary cultures and stores of cells can be kept in a deep freeze ( -70 0C ) for indefinite periods. Cell cultures especially, cell lines are widely used in scientific and medical research and have industrial usages, e.g. in vaccine production.
this phase, scientists test whether the compound causes cancer in animals, usually rodents.
Before going on the market, a new drug compound must be tested for safety and efficacy in cell cultures, whole animals, and humans. Only when a compound is found to be safe in cell cultures and animals, will it be tested on volunteers in human clinical trials. A drug becomes available after it is found safe and effective through rigorous testing.
The techniques of cell culture or tissue culture allow cells to be maintained outside the body. An enormous variety of plant and animal cells can be maintained in vitro and given appropriate conditions, cells will not only survive, but multiply, grow, providing
• they can be kept sterile i.e. by keeping out contaminants e.g. bacteria, yeasts, or viruses.
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