Exposure to environmental chemicals is a major concern for human health as natural and man-made substances can adversely affect physiological processes which may contribute to the incidence of obesity, metabolic syndrome, and type 2 diabetes. In adults, type 2 diabetes accounts for about 90% of diagnosed diabetes cases and is a major risk factor for heart disease, stroke, kidney failure, non-traumatic lower-limb amputations and blindness. The goal of this proposal is to identify endocrine disruptors affecting the circadian hormone melatonin and its ability to signal "time-of-day" messages to target peripheral tissues. The release of melatonin from the pineal gland is regulated by biological clocks in the suprachiasmatic nucleus (SCN) of the hypothalamus which in turn regulates peripheral target tissues through activation of MT1 and MT2 melatonin receptors. In pancreatic ?-cells, disruption of melatonin receptor signaling may alter homeostatic rhythmic balance of glucose metabolism and insulin release leading to diabetes and metabolic disorders. Our overarching hypothesis is that, certain classes of environmental chemicals act as circadian disruptors by persistent and irregular activation and/or blockade of melatonin receptors in the SCN and in target peripheral tissues (eg. pancreatic islets).
Specific aims designed to accomplish our goals are: 1) to use an integrated pharmacoinformatics approach to identify environmental circadian disruptors from a knowledgebase of environmental agents using in silico 2D/3D melatonergic pharmacophore fingerprinting;2a) to iteratively assess ligand affinity, selectivity and efficacy of environmental disruptors in competition for 2[125I]- iodomelatonin binding to hMT1 and hMT2 melatonin receptors expressed in mammalian CHO cells both in the absence and presence of GTP, and 2b) to modulate forskolin-mediated CRE-luciferase reporter gene expression and insulin secretion via functional activation of rat melatonin receptors expressed in rat INS1 ?-cells;3) To determine the potential of selected environmental chemicals to alter the rhythmic homeostatic balance of diabetes markers through changes of melatonin receptor sensitivity and signaling in rat INS-1 pancreatic ?-cells (MT1) altering MT1-mediated sensitization and in SCN 2.2 cells by attenuating melatoin- mediated inhibition of cAMP formation (MT1, MT2) and Protein Kinase C stimulation (MT2) using in vitro bioassays. Furthermore, cell proliferation, and lipid peroxidation in pancreatic b-cells will be measured to assess the potential of these disruptors to increase the risk of diabetes associated metabolic disorders. Our integrated Chem2Risk strategy will provide the essential impetus to pursue further testing in animal models and be useful in future assessment of risk factors associated with environmental disruptors carrying similar chemical-structural features and to establish exposure regulatory guidelines.
The experiments proposed in this application are aimed to screen environmental toxicants that may increase the risk of developing obesity, metabolic syndrome and type-2 diabetes in humans. Accomplishment of these specific aims will lead to the discovery and identification of environmental toxicants, which will allow the EPA to establish guidelines to reduce exposure in places where such toxicant is generated.