PHAR Test 2.Queens University PHAR 380
Two Types of Experimental Models
- There are two overarching groupings of models that are used experimentally to conduct toxicological experiments: in vitro models and
in vivo models
In vitro
Refer to experiments that occur outside of a body, such as within a petri dish
In vivo
Refer to experiments that occur within the
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PHAR Test 2.Queens University PHAR 380
Two Types of Experimental Models
- There are two overarching groupings of models that are used experimentally to conduct toxicological experiments: in vitro models and
in vivo models
| In vitro |
Refer to experiments that occur outside of a body, such as within a petri dish |
| In vivo |
Refer to experiments that occur within the body, such as experiments conducted with animals |
In Vitro Cell Models
- In vitro experiments in toxicology usually involve cells or tissues maintained or grown in controlled laboratory conditions to examine the
toxic properties of various compounds and mixtures
- Allows isolation of the fundamental mechanisms of xenobiotic toxicity without interaction with an organisms entire physiological system
Cell Culture
- In the lab, mammalian (or other) cells can be maintained and propagated under specific conditions outside of the organism from which
they were derives
| Vessel |
A vessel in which to contain and nourish the cells (i.e., a culture dish or flask) |
| Nutrient media |
A nutrient media to 'feed' the cells |
| Incubator |
An incubator to house the cells at an ideal temperature, humidity level, and oxygen and/or carbon dioxide levels |
Terminology
Primary cell
culture |
- A primary cell culture refers to cells that have been extracted directly from a tissue or organism
- These cells are transferred to a culture vessel, where they are maintained and proliferated under appropriate
conditions outside of their original environment |
| Cell line |
- Cell lines are subcultures of cells from the primary cell culture
- Primary cells, grown under appropriate conditions, will multiply to the point in which they occupy all the space in the
cell culture dish (termed confluency)
- At this point, they continue proliferating, cells are transferred to a new dish where they can continue to grow and
proliferate; these subcultures are the cell lines |
Cell Lines
| Finite |
- Finite cell lines are derived from primary cell culture
- Unless modified, finite cells have a limited number of cell divisions they are capable of before they senesce, losing their
ability to proliferate
- Although finite cell lines can be more indicative of in vivo cellular and tissue characteristics than continuous cell lines,
they can be short-lived in culture, and suffer from rapid dedifferentiation within hours to days |
| Continuous |
- Continuous cell lines are originally derived from primary cell culture, but are modified in a way to prevent senescence,
allowing cells to maintain their replicative ability
- Theoretically, immortalized cell lines could be maintained and propagated in culture indefinitely
- Immortalized cell lines became transformed, meaning they are either spontaneously or purposefully altered by viruses
or chemicals, resulting in their expression of traits that prevents senescence
- Uncoincidentally, many immortal cell lines are cancerous in nature, since cells possess characteristics that maintain the
cell's replicative ability |
Choosing a Cell Line
- Both finite and continuous cell lines can be useful in toxicology research; deciding which to use is an important step in the development
of a research proposal
- There are numerous factors to consider when choosing a cell line to use as an experimental model
| Species |
- Given your research question, which species of animal makes the most sense to use?
- Some cell types (non-human and non-primate cell lines) may be easier to gain access to, but ultimately
the purpose of your experiment(s) should dictate whether to use species-specific cultures or not
- For example, if researching whether a chemical is toxic to human breast cancer cells as possible
treatment for that cancer, it would make sense to use human breast cancer cells, rather than a mouse or
rate mammary tumour cell line |
Experimental
purpose |
- What is the purpose of your experiment?
- Are you interested in examining the mechanism of toxicity of a chemical that is known liver toxicant?
• In this case, you may want to consider using liver cells
- Are your interested in the development toxicity of a xenobiotic?
• In this case, you may want to consider use of a cell line derived from embryonic or fetal tissue
- Are you interested in studying a signalling pathway that is specific to humans?
• In this case, you may want to consider using a human cell line |
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