Overview of the Molecular Biomarker Service
at Dartmouth

Advances in molecular biology have put a powerful new tool in the hands of scientists who study gene-environment interactions and their role in human disease. The research tool, called molecular biomarkers, is a bridge between the molecular-scale science of genes and the large-scale sciences of epidemiology and ecology. The Molecular Biomarkers Service at Dartmouth is a central resource to scientists at the Center for Environmental Health Sciences and other research programs at Dartmouth.


Molecular biomarkers are an early sign of change in an organism's physiological state - such as adaptation, stress or injury - due to environmental factors or disease. For example, it is possible to tell that animals have been exposed to the toxic metal cadmium by measuring their levels of a specific molecule that binds to cadmium - the protein called metallothionein. Increased levels of metallothionein, as well as increased expression of the gene that leads to elevated protein levels, are called molecular biomarkers of exposure. Changes in molecules such as these are sensitive and specific, making them useful sentinels of an organism's exposure to a specific environmental agent.


Other molecular changes indicate progression of a disease process. For example, hemoglobin is the protein that carries oxygen in red blood cells. A form of hemoglobin called hemoglobin 1AC is a biomarker of diabetes. As blood glucose levels increase in people with adult-onset diabetes, the levels of this form of hemoglobin in their blood increase accordingly, providing a diagnostic marker of the progression of disease. Measurements of Hemoglobin 1Ac are considered a molecular biomarker of effect.

A link between disciplines

The development of molecular biomarkers provides a link between ecologists or epidemiologists who study health effects in populations and molecular biologists who study the underlying mechanisms of these health effects. Investigators in Dartmouth's Toxic Metals Research Program are collaborating to develop and test molecular biomarkers of toxic metal exposure and molecular biomarkers of toxic metal effects. The goal of this work is to identify genes and proteins whose expression is modified either by exposure to specific environmental agents or as part of a particular disease process and to use this information to develop sensitive and specific biomarkers. The Toxic Metals group is using these biomarkers in the laboratory for mechanistic studies, and in the field for ecology and epidemiology studies.

For example, contamination of lake fish by mercury and other metals has been recognized as a serious concern for the health of ecosystems and humans. Dartmouth researchers have found that when the plankton population in a lake is exposed to stressful levels of metals, two genes are turned on: the gene that produces metallothionein and a stress or "heat shock" gene. The planktonic animal species Daphnia appears to be a sentinel species for this effect and may provide ecologists and resource managers with an early warning sign that a lake's ecosystem is being threatened by metal contamination. Measuring this effect in a species at the lower levels of the food web can also provide predictions of how toxic metals might be transferred up the food web to fish and ultimately to humans.

In another project in the Toxic Metals program, epidemiologists are using Hemoglobin A1C levels to determine how environmental agents such as arsenic affect the development of adult-onset diabetes. One goal of this work is to develop a biomarker that can predict an individualÕs risk of developing diabetes in the future. Another goals is to determine whether arsenic exposure increases an individual's risk for developing diabetes apart from other risk factors such as diet and genetics.

Tools and techniques

Developing and using molecular biomarkers employs techniques of modern molecular biology that investigate the three basic pathways of gene expression: the gene itself, the messenger RNA that it produces, and the protein that is coded for by the messenger RNA. For example, studies of genetic mutations that result in altered biological behavior, such as the mutations involved in the development of a cancer cell from a normal cell, focus on the coding sequence of the gene itself. Studies of alterations in expression of a gene focus on the messenger RNA for that gene, or the protein it produces.

Genes suspected of harboring mutations important in a disease process or adverse response are cloned (copied) and sequenced. Once a mutation has been identified, simple screening techniques can be developed to look for this mutation in different individuals. Changes in messenger RNA expression can be assessed using techniques such as RNA differential display, RNase Protection Assay (RPA) and various Polymerase Chain Reaction (PCR)-based methods including Real-Time PCR. More global assessments of changes in patterns of gene expression can be assessed using recently developed DNA "microarray" technology, which assesses large numbers of individual genes simultaneously. Protein expression can be assessed by Western blotting, Enzyme-Linked Immunosorbent Assay (ELISA) and antibody based methods.


The Molecular Biomarkers service has developed each of these tools for use in the Center investigators' individual research projects, and can assist in method selection, method development, biomarker identification and development, and assay validation. The investigator is then given these tools and provided with expert advice in how to apply these to a given research objective.