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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.

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.

Regulatory Validation for Clinical Use:
The Early Detection Research Network (EDNR) compiled a list of seven criteria by which biomarkers can be assessed in order to streamline clinical validation.

Proof of concept
The biologic rationale of a study must be assessed on a small scale before any large studies can occur.

Analytical performances validation:
This step serves to identify specific characteristics of the candidate biomarker before developing a routine test. Several parameters are considered including:


 * sensitivity
 * specificity
 * robustness
 * accuracy
 * reproducibility
 * practicality
 * ethicality

Applications in Chemistry, Geology and Astrobiology:
Biomarkers were used in the Geo-chemical Investigation of an Oil Spill in the San Francisco Bay, California in 1988. On April 22-23 around 400,000 gallons of crude oil was accidentally released into the San Joaquin Valley by a refinery and manufacturing complex of the Shell Oil Company. The oil affected many surrounding areas. Samples of the crude oil were collected in the various regions where it had spread and compared to samples that were unreleased in an attempt to distinguish between the spilled oil and the petrogenic background present in the spill area. Mass Spectra was performed to identify biomarkers and cyclic aliphatic hydrocarbons within the samples. Variations in the concentration of constituents of the crude oil samples and sediments were found.

Ethical Issues:
In 1997 the National Institute of Health suggested a need for guidelines and legislation development that would regulate the ethical dimensions of biomarker studies. Similar to the way that the Human Genome Project collaborated with the U.S. Office of Technology Assessment, biomarker susceptibility studies should collaborate to create ethical guidelines that can be implemented into the groundwork and proposal requirements of the studies.

Ensuring that all of the participants that are included each step of the project (i.e. planning, implementation, and the compilation of the results) are provided with the protection of ethical principles that are put in place prior to beginning the project. These ethical protections should not only protect the participants in the study, but also the non participants, researchers, sponsors, regulators, and all other persons or groups involved in the study. Some ethical protections could include but are not limited to :


 * Informed consent of the participant
 * Access to participation opportunities independent of race, socio-economic status, gender, sexuality, etc. (within the range allowed by the experimental protocol)
 * Scientific integrity
 * Confidentiality of data (anonymity)
 * Acknowledgement of conflict of interest in terms of funding and sponsorship by given sponsors
 * Transparency and recognition of health and legal risks involved in participation

'''***I have added to the history section, the ecotoxicology section, and have proposed the need for a new section within the history header that discusses the definition of biomarkers through history. I have suggested an addition of a section called active biomonitoring. All additions are bold.***'''

History
'''The manner in which the environment was monitored and studied near the end of the 1980’s was still mainly reliant on the study of chemical substances that were considered dangerous or toxic when found in moderate concentrations in water, sediments, and aquatic organisms. The methods used to identify these chemical compounds were chromatography, spectrophotometry, electrochemistry, and radiochemistry. Although these methods were successful in elucidating the chemical makeup and concentrations present in the environment of the contaminants and the compounds in question, the tests did not provide data that was informative on the impact of a certain pollutant or chemical on a living organism or ecosystem. It was proposed that characterizing biomarkers could create a warning system to check in on the well being of a population or an ecosystem before a pollutant or compound could wreak havoc on the system. Now, due to the development of biomarker studies, biomarkers can be used and applied in the fields of human medicine and in the detection of diseases .'''

A Timeline of the Definition of a Biomarker
The term "biological marker" was introduced in 1950s.

'''In 1987, biological markers were defined as “indicators signaling events in biological systems or samples” that could be classified into three categories: exposure, effect and susceptibility markers. '''

'''In 1990, McCarthy and Shugart defined biomarkers as, “measurements at the molecular, biochemical, or cellular level in either wild populations from contaminated habitats or in organisms experimentally exposed to pollutants that indicate that the organism has been exposed to toxic chemicals, and the magnitude of the organism's response”. '''

In 1994, Depledge defined a biomarker as, “a biochemical, cellular, physiological or behavioral change which can be measured in body tissues or fluids or at the level of the whole organism that reveals the exposure at/or the effects of one or more chemical pollutants.”

'''In 1996, Van Gestel and Van Brummelen attempted to  redefine biomarkers to unambiguously differentiate a biomarker from a bioindicator. According to Van Gestel and Van Brummelen, a biomarker by definition should be used only to describe sublethal biochemical changes resulting from individual exposure to xenobiotics.'''

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 2000, De Lafontaine defined the term biomarker as a “biochemical and/or physiological change(s) in organisms exposed to contaminants, and thus represent initial responses to environmental perturbation and contamination".

Active Biomonitoring
'''De Kock and Kramer developed the concept of active biomonitoring in 1994. Active biomonitoring is a comparison of the chemical/biological properties of a sample that has been relocated to a new environment that contains different conditions than its original environment.'''

Ecotoxicology
Rachel Carson, the author of Silent Spring, raised the issue of using organochlorine pesticides and discussed the possible negative effects that said pesticides have on living organisms '''. Her book raised ethical issues against chemical corporations that were controlling the general reception of the effect of pesticides on the environment, which pioneered the need for ecotoxicological studies. Ecotoxicologial studies could be considered the precursors to biomarker studies .''' 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.