Superfund Research Program
Arsenic as an Endocrine Disrupter
Aims: The goal of the Arsenic as an Endocrine Disruptor project is to understand the molecular basis for the ability of arsenic to act as a potent endocrine disruptor (Aims 1 and 2), and to determine the pathophysiological consequences of such endocrine disruption (Aim 3).
Studies and results: In previous studies Dr. Hamilton and his research team demonstrated that arsenic disrupts the ability of nuclear hormone receptors to regulate gene expression. To elucidate the mechanism, the team of researcher's focused on the glucocorticoid receptor (GR) and the effects of arsenic to increase hormone-activated transcription at extremely low doses while suppressing transcription at higher, non-cytotoxic doses. The researchers constructed a GR molecule with a green fluorescent protein (GFP) tag and stably expressed this construct in a cell line that is hormone-responsive. Using confocal microscopy and digital quantitation, the researchers demonstrated that arsenic decreases the amount and rate of GR entry into the nucleus following sub-saturating hormone stimulation, correlating directly with decreased transcriptional activation and mRNA expression by target genes. These observations were confirmed by Western blot and other biochemical approaches. The team is currently revising the manuscript that summarizes this work. Another paper in revision demonstrates that the monomethylated form of arsenic disrupts GR binding to its DNA recognition element, whereas inorganic arsenic does not, suggesting a role for arsenic metabolism and speciation in nuclear hormone receptor alterations.
Dr. Hamilton and his team have also completed studies to understand the effects of arsenic on PPAR receptors and the role of such effects in arsenic-mediated dysregulation of lipid metabolism. The team has shown that arsenic has adverse effects on the ability of undifferentiated cells to differentiate into mature adipocytes and to accumulate lipid droplets, as well as changes in other measures of lipid metabolism in response to normal hormone signaling, suggesting that one consequence of arsenic exposure and endocrine disruption at the hormone receptor level. This correlates with recent studies demonstrating that arsenic has adverse effects on growth and development in mice. The researchers have revised a manuscript describing these studies.
Significance: The team's research is significant because it demonstrates that very low levels of arsenic, relevant to the US population, cause significant endocrine disruption in cell culture systems and animal models, resulting in significant pathophysiological responses that are directly related to endocrine disruption of specific hormone-mediated pathways. Furthermore, the team's studies of pregnant mice who were exposed to arsenic at the current US drinking water standard that is considered "safe" indicate that arsenic may cause profound effects on in utero and early childhood development, which may result in later in life health effects in both the mothers and their offspring.
Plans: This project was not included in the competitive renewal of the SRP application, and the team is planning on submitting an R01 to continue this research.