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Aldosteron, Intracellular Leukocyte Magnesium and Inflammation in Diabetes

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Aldosterone and mineralocorticoid receptor (MR) activation play key roles in mediating inflammation and vascular injury leading to damage of hearts and kidneys in humans and rodents. The mechanisms by which this occurs are unclear. Two candidates for aldosterone-mediated inflammation are monocyte chemoattractant protein-1 (MCP-1) and 12-lipoxygenase (12-LO), the enzyme responsible for generation of 12- (S)Hydroxyeicosatetraenoate (12-HETE). Individuals with type 2 diabetes and diabetic animals have increased MCP-1 and 12-HETE levels and decreased circulating Mg2+ levels. In humans, low circulating Mg2+ levels are associated with increased inflammation, obesity, diabetes mellitus and increased urinary 12-HETE, suggesting an association between Mg2+ and inflammation. Our preliminary data demonstrate that intracellular Mg2+ is reduced in blood cells from diabetic subjects as compared with nondiabetic subjects. Blood cells (both red blood cells and polymorphonuclear leukocytes [PMN] cells) from human subjects express MR and stimulation of these cells with aldosterone increases Na+/Mg2+ exchanger activity and decreases intracellular Mg2+ levels. Our studies demonstrate that cellular Mg2+ levels are reduced in blood cells from obese, diabetic db/db mice as compared to levels in cells from lean db/+ mice and that treatment with a MR antagonist significantly increases intracellular Mg2+ levels in cells of diabetic mice. Our preliminary studies demonstrate that treatment of diabetic db/db mice with a MR antagonist significantly reduces this inflammation, including decreasing circulating MCP- 1 levels, decreasing 12-LO and MCP-1 mRNA levels, and reducing inflammation in kidney and adipose tissue. Aldosterone appears to directly promote inflammation as we showed that aldosterone increases mRNA levels of MCP-1 in human cells. Infiltration of PMN cells from the circulation into tissue is a key component of aldosterone-induced inflammatory response. We hypothesize that a major mechanism mediating aldosterone's inflammatory effects in diabetes is aldosterone-induced stimulation of Na+/Mg2+ exchanger activity leading to decreases in intracellular Mg2+ resulting in elevated pro-inflammatory factors. We propose a translational research approach involving ex vivo cellular studies in leukocytes isolated from patients with type 2 diabetes that are randomized into a double-blinded trial with spironolactone therapy. We will test our hypothesis through the following Aims: (1) To test the hypothesis that aldosterone stimulates Na+/Mg2+ exchange activity in isolated human leukocytes leading to a decrease in intracellular magnesium and an increase in expression of pro-inflammatory factors. (2) To test the hypothesis that in humans with type 2 diabetes treatment with a MR antagonist will improve measures of cellular Mg2+ homeostasis and inflammation. Understanding the mechanisms by which aldosterone regulates cellular Mg2+, MCP-1, and 12-LO will allow us to develop new strategies to treat inflammation and its consequences in diabetes.

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