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A biomarker, or biological marker, generally refers to a measurable indicator of some biological state or condition. The term is also occasionally used to refer to a substance whose presence indicates the existence of a living organism. Further, life forms are known to shed unique chemicals, including DNA, into the environment as evidence of their presence in a particular location.
Biomarkers are often measured and evaluated to examine normal biological processes, pathogenic processes, or pharmacologic responses to a therapeutic intervention. Biomarkers are used in many scientific fields.
The use of the term "biomarker" has been dated back to as early as 1980. In 1998, the National Institutes of Health Biomarkers Definitions Working Group defined a biomarker as “a characteristic that is objectively measured and evaluated as an indicator of normal biological processes, pathogenic processes, or pharmacologic responses to a therapeutic intervention.”
In medicine, a biomarker can be a traceable substance that is introduced into an organism as a means to examine organ function or other aspects of health. For example, rubidium chloride is used as a radioactive isotope to evaluate perfusion of heart muscle. It can also be a substance whose detection indicates a particular disease state, for example, the presence of an antibody may indicate an infection. More specifically, a biomarker indicates a change in expression or state of a protein that correlates with the risk or progression of a disease, or with the susceptibility of the disease to a given treatment.
Biochemical biomarkers are often used in clinical trials, where they are derived from bodily fluids that are easily available to the early phase researchers. A useful way of finding genetic causes of diseases such as schizophrenia has been the use of a special kind of biomarker called an endophenotype.
Other biomarkers can be based on measures of the electrical activity of the brain (using Electroencephalography or Magnetoencephalography), or volumetric measures of certain brain regions (using Magnetic resonance imaging) or saliva testing of natural metabolites, such as saliva nitrite, a surrogate marker for nitric oxide.
One example of a commonly used biomarker in medicine is prostate-specific antigen (PSA). This marker can be measured as a proxy of prostate size with rapid changes potentially indicating cancer.
Biomarker regulatory validation
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Proof of concept
Previously to identify the specific characteristics of the biomarker, this step is essential for doing an in situ validation of these benefits. A large number of candidates must be testing for selected the most relevant.
This step allows to develop the most adapted protocol for use routinely the biomarker. Simultaneously, it possible to confirm the relevance of the protocol with various methods (histology, PCR, ELISA, ...) and define strata based on results.
Analytical performances validation
One of the most important step, serves to identify specific characteristic of the candidate biomarker before to develop a routine test. Several parameters are considered :
- sensitivity - specificity - robustness - accuracy - repeatability ...
Optimization on the validated protocol for use routinely. Analysis of the critical points by scanning the entire procedure for identify and control the potential risks.
In cell biology, a biomarker is a molecule that allows the detection and isolation of a particular cell type (for example, the protein Oct-4 is used as a biomarker to identify embryonic stem cells).
In genetics, a biomarker (identified as genetic marker) is a DNA sequence that causes disease or is associated with susceptibility to disease. They can be used to create genetic maps of whatever organism is being studied.
Geology and astrobiology
A biomarker can be any kind of molecule indicating the existence, past or present, of living organisms. In the fields of geology and astrobiology, biomarkers, versus geomarkers, are also known as biosignatures. The term biomarker is also used to describe biological involvement in the generation of petroleum.
Biomarkers are used to indicate an exposure to or the effect of xenobiotics which are present in the environment and in organisms. The biomarker may be an external substance itself (e.g. asbestos particles or NNK from tobacco), or a variant of the external substance processed by the body (a metabolite) that usually can be quantified. (See also: Bioindicator.)
- Zimmer, Carl (January 22, 2015). "Even Elusive Animals Leave DNA, and Clues, Behind". New York Times. Retrieved January 23, 2015.
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- Biomarkers for Psychiatric Disorders. Publisher: Springer U.S. doi:10.1007/978-0-387-79251-4 Copyright: 2009 ISBN 978-0-387-79250-7 (Print) 978-0-387-79251-4 (Online)
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