DESCRIPTION OF EX VIVO

Ex vivo (Latin: out of the living) means that which takes place outside an organism . In science, ex vivo refers to experimentation or measurements done in or on tissue in an artificial environment outside the organism with the minimum alteration of natural conditions. Ex vivo conditions allow experimentation under more controlled conditions than possible in the intact organism, at the expense of altering the "natural" environment.

A primary advantage of using ex vivo tissues is the ability to perform tests or measurements that would otherwise not be possible or ethical in living subjects. Tissues may be removed in many ways, including in part, as whole organs , or as larger organ systems.

Examples of ex vivo specimen use include:

• assays;
• measurements of physical , thermal , electrical , mechanical , optical and other tissue properties, especially in various environments that may not be life-sustaining (for example, at extreme pressures or temperatures );
• realistic models for surgical procedure development;
• investigations into the interaction of different energy types with tissues;
• or as phantoms in imaging technique development.

The term ex vivo is often differentiated from the term in vitro in that the tissue or cells need not be in culture; these two terms are not necessarily synonymous.

In cell biology , ex vivo procedures often involve living cells or tissues taken from an organism and cultured in a laboratory apparatus, usually under sterile conditions with no alterations for up to 24 hours. Experiments lasting longer than this using living cells or tissue are typically considered to be in vitro . One widely performed ex vivo study is the chick chorioallantoic membrane (CAM) assay. In this assay, angiogenesis is promoted on the CAM membrane of a chicken embryo outside the organism (chicken).

DESCRIPTION OF IN VITRO

A procedure performed in vitro ( Latin : within the glass ) is performed not in a living organism but in a controlled environment, such as in a test tube or Petri dish . Many experiments in cellular biology are conducted outside of organisms or cells; because the test conditions may not correspond to the conditions inside of the organism, this may lead to results that do not correspond to the situation that arises in a living organism. Consequently, such experimental results are often annotated with in vitro , in contradistinction with in vivo .

This type of research aims at describing the effects of an experimental variable on a subset of an organism's constituent parts. It tends to focus on organs , tissues , cells , cellular components, proteins , and/or biomolecules . In vitro research is better suited than in vivo research for deducing biological mechanisms of action. With fewer variables and perceptually amplified reactions to subtle causes, results are generally more discernible.

The massive adoption of low-cost in vitro molecular biology techniques has caused a shift away from in vivo research which is more idiosyncratic and expensive in comparison to its molecular counterpart. Currently, in vitro research is vital and highly productive.

However, the controlled conditions present in the in vitro system differ significantly from those in vivo , and may give misleading results. Therefore, in vitro studies are usually followed by in vivo studies. Examples include:

• In biochemistry, non-physiological stoichiometric concentration may result in enzymatic active in a reverse direction, for example several enzymes in the Krebs cycle may appear to have incorrect nomenclature.
• DNA may adopt other configurations, such as A-DNA .
• Protein folding may differ as in a cell there is a high density of other protein and there are systems to aid in the folding, while in vitro, conditions are less clustered and not aided.

It should be pointed out that the term is historical, as currently most lab ware is disposable and made out of polypropylene (sterilizable by autoclaving, ex: microcentrifuge tubes) or clear polystyrene (ex: serological pipettes) rather than glass to ease labwork, ensure sterility, and minimize the possibility of cuts from broken glass.

DESCRIPTION OF IN VIVO

In vivo ( Latin for "within the living") is experimentation using a whole, living organism as opposed to a partial or dead organism, or an in vitro controlled environment. Animal testing and clinical trials are two forms of in vivo research. In vivo testing is often employed over in vitro because it is better suited for observing the overall effects of an experiment on a living subject. This is often described by the maxim in vivo veritas.

In molecular biology in vivo is often used to refer to experimentation done in live isolated cells rather than in a whole organism, for example, cultured cells derived from biopsies. In this situation, the more specific term is ex vivo . Once cells are disrupted and individual parts are tested or analyzed, this is known as in vitro . in vivo experiment is in living; in vitro study is in test tube.

According to Christopher Lipinski and Andrew Hopkins, "Whether the aim is to discover drugs or to gain knowledge of biological systems, the nature and properties of a chemical tool cannot be considered independently of the system it is to be tested in. Compounds that bind to isolated recombinant proteins are one thing; chemical tools that can perturb cell function another; and pharmacological agents that can be tolerated by a live organism and perturb its systems are yet another. If it were simple to ascertain the properties required to develop a lead discovered in vitro to one that is active in vivo , drug discovery would be as reliable as drug manufacturing."

In the past, the guinea pig was such a commonly used in vivo experimental subject that they became part of idiomatic English: to be a guinea pig. However, they have largely been replaced by their smaller, cheaper, and faster-breeding cousins, rats and mice .

In vivo imaging provides a noninvasive method for imaging biological processes in live animals in order to understand metabolic processes, effects of drugs and disease progression. Near-infrared (NIR) fluorescent detection has proven useful for in vivo imaging in small animals. Low tissue autofluorescence at 800 nm makes it possible to use probes with NIR labels to image tumors and organs. In vivo imaging is an important tool for any research that uses animal models to study diseases, such as Alzheimer's disease.