Research Project
9377975
Project Summary/Abstract Cadmium (Cd) is a ubiquitous environmental and industrial pollutant that currently ranks seventh on the US EPA/ATSDR Priority List of Hazardous Substances and is a known human carcinogen that causes kidney, liver and bone damage. Cd is associated with diabetes mellitus (DM) and prediabetes in epidemiological and experimental studies. In a study of the US population, 25% of individuals that were diabetic or prediabetic had elevated urinary Cd levels. It is unknown how Cd disrupts blood glucose levels. However, Cd exposure is associated with low serum insulin levels in individuals with occupational exposure and Cd has been shown to impair glucose-stimulated insulin secretion in animal studies. For a large subsection of patients with DM impaired glucose-stimulated insulin, secretion occurs in the progression of type II DM. The overall aim of the proposed project is to determine the mechanism by which Cd causes impaired glucose-stimulated insulin release. Normal insulin secretion and pancreatic ?-cell function are dependent upon cell-cell adhesion; especially important is the role of the calcium-dependent cell adhesion molecule, E-cadherin. Cd has been shown to disrupt E-cadherin mediated cell-cell adhesion in the kidney. Initial studies will establish a range of doses and duration of exposure of Cd that result in necrotic and/or apoptotic cell death in isolated islets and the pancreatic ?-cell line, MIN6. Subsequent studies will be determined if impaired glucose-stimulated insulin release is a response to a generalized Cd-induced oxidative stress response or altered energy status (ADP/ATP) at doses and durations of exposure below those that cause cell death. Live cell imaging studies will be utilized with sensitive fluorophores to detect changes in the production of mediators of oxidative stress. Studies outlined in Aim two will determine the ability of Cd to cause loss of E-cadherin mediated cell-cell adhesion in relation to glucose- stimulated insulin release in isolated islets and the MIN6 cell line. Additional studies will examine the effects of E-cadherin antibodies that bind to the extracellular domain and siRNA of E-cadherin to experimentally disrupt cell-cell adhesion to determine if there are synergistic effects of Cd on inhibiting glucose-stimulated insulin release. Aim three will determine if Cd causes voltage-gated calcium channel blockade resulting in subsequent impaired glucose-stimulated insulin release in isolated islets and MIN6 cells. Additional studies will determine if there are synergistic effects of Cd to impair glucose-stimulated insulin release in the presence or absence of the L-type voltage-gated calcium channel blockers. Also, live cell imaging will be utilized with fluorophores that selectively detect changes of intracellular Cd, zinc or calcium. In Aims two and three, in vivo studies using a well-characterized model of long term Cd poisoning will be used to verify the in vitro findings. Overall, these studies will identify the mechanism of the diabetogenic effects of Cd, a widespread environmental contaminant that is associated with DM and prediabetes.
