calcimycin and Hyperglycemia

Clinical manifestations of diabetic nephropathy are an expression of diabetic microangiopathy. This review revisits the previously proposed Steno hypothesis and advances our hypothesis that development of endothelial cell dysfunction represents a common pathophysiological pathway of diabetic complications. Specifically, the ability of glucose to scavenge nitric oxide is proposed as the initiation phase of endothelial dysfunction. Gradual accumulation of advanced glycated end products and induction of plasminogen activator inhibitor-1, resulting in the decreased expression of endothelial nitric oxide synthase and reduced generation of nitric oxide, are proposed to be pathophysiologically critical for the maintenance phase of endothelial dysfunction. The proposed conceptual shift toward the role of endothelial dysfunction in diabetic complications may provide new strategies for their prevention.

Topics: Albuminuria; Animals; Bradykinin; Calcimycin; Cells, Cultured; Diabetes Mellitus, Type 2; Diabetic Angiopathies; Diabetic Nephropathies; Down-Regulation; Endothelium, Vascular; Glucose; Glycation End Products, Advanced; Humans; Hyperglycemia; Nitric Oxide; Nitric Oxide Synthase; Nitric Oxide Synthase Type III; Plasminogen Activator Inhibitor 1

Evidence suggests that capillary degeneration in early diabetic retinopathy results from chronic inflammation, and leukotrienes have been implicated in this process. The authors investigated the cellular sources of leukotriene biosynthesis in diabetic retinas and the effects of hyperglycemia on leukotriene production.. Retinas and bone marrow cells were collected from diabetic and nondiabetic mice. Mouse retinal glial cells and retinal endothelial cells (mRECs) were cultured under nondiabetic and diabetic conditions. Production of leukotriene metabolites was assessed by mass spectrometry, and Western blot analysis was used to quantitate the expression of enzymes and receptors involved in leukotriene synthesis and signaling.. Bone marrow cells from nondiabetic mice expressed 5-lipoxygenase, the enzyme required for the initiation of leukotriene synthesis, and produced leukotriene B(4) (LTB(4)) when stimulated with the calcium ionophore A23187. Notably, LTB(4) synthesis was increased threefold over normal (P < 0.03) in bone marrow cells from diabetic mice. In contrast, retinas from nondiabetic or diabetic mice produced neither leukotrienes nor 5-lipoxygenase mRNA. Despite an inability to initiate leukotriene biosynthesis, the addition of exogenous leukotriene A(4) (LTA(4); the precursor of LTB(4)) to retinas resulted in robust production of LTB(4). Similarly, retinal glial cells synthesized LTB(4) from LTA(4), whereas mRECs produced both LTB(4) and the cysteinyl leukotrienes. Culturing the retinal cells in high-glucose concentrations enhanced leukotriene synthesis and selectively increased expression of the LTB(4) receptor BLT1. Antagonism of the BLT1 receptor inhibited LTB(4)-induced mREC cell death.. Transcellular delivery of LTA(4) from marrow-derived cells to retinal cells results in the generation of LTB(4) and the death of endothelial cells and, thus, might contribute to chronic inflammation and retinopathy in diabetes.

Topics: Animals; Apoptosis; Arachidonate 5-Lipoxygenase; Blotting, Western; Bone Marrow Cells; Calcimycin; Cells, Cultured; Chromatography, High Pressure Liquid; Diabetes Mellitus, Experimental; Diabetic Retinopathy; Endothelium, Vascular; Glucose; Hyperglycemia; Leukotriene A4; Leukotriene B4; Mass Spectrometry; Mice; Mice, Inbred C57BL; Neuroglia; Receptors, Leukotriene B4; Retina; Retinal Vessels; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger

An increased glucose utilization by aldose reductase (ALR-2) has been implicated in the pathogenesis of diabetic vascular complications. In this process, several mechanisms are involved, including the depletion of cofactors required for the action of antioxidant enzymes or endothelial NO synthase. In this study, the effect of a novel ALR-2 inhibitor JMC-2004 on hyperglycemia-induced endothelial dysfunction was studied.. Bovine aortic endothelial cells (BAEC) were treated with glucose (30 mM), JMC-2004 (0.01mM), or glucose and JMC-2004 for 24 h. The cells were then stimulated with calcium ionophore A23187 after which NO production was measured electrochemically using a porphyrine-coated carbon NO electrode. Nitrite concentrations were determined in the cell supernatants. The peroxyl and hydroxyl radical-scavenging activity of JMC-2004 was measured with luminol-enhanced chemiluminescence. The expression of eNOS was determined by Western blotting. JMC-2004 IC50 for ALR-2 was determined colorimetrically with D-glyceraldehyde as a substrate.. Incubating the cells with 30 mM glucose strongly diminished A23187- induced NO production. Treatment with JMC-2004 restored NO production by 40% without affecting eNOS expression. This effect was probably antioxidantindependent, since JMC-2004 did not have any antioxidant capacity. JMC-2004 exerted high selectivity towards ALR-2.. ALR-2 inhibition with JMC-2004 was able to abolish hyperglycemia- induced endothelial dysfunction in bovine aortic endothelial cells.

Topics: Aldehyde Reductase; Animals; Blotting, Western; Calcimycin; Cattle; Cell Line; Electrochemistry; Endothelial Cells; Endothelium, Vascular; Enzyme Inhibitors; Glucose; Glyceraldehyde; Hydroxyl Radical; Hyperglycemia; Luminescence; Nitric Oxide; Nitric Oxide Synthase Type III; Peroxides; Phenols; Pyrroles

Inexplicable controversies with regard to possible functional defects of neutrophilic polymorphonuclear leukocytes (PMNs) in diabetes persist. The purpose of the present study was to elucidate the relative effectiveness of several PMN agonists in stimulating lysosomal-enzyme secretion and leukotriene (LT) B(4) production by PMNs isolated from diabetic subjects. Formyl-methionyl-leucyl-phenylalanine (fMLP) and platelet-activating factor (PAF) induced significantly less lysosomal-enzyme secretion and LTB(4) production in diabetic-subject PMNs than in normal-subject PMNs. It is surprising that PMNs from these same diabetic subjects responded normally after stimulation with A23187, serum-opsonized zymosan, or phorbol myristate acetate. The in vitro responsiveness of PMNs stimulated with fMLP or PAF was inversely correlated with indices of in vivo glycemic control (fasting plasma glucose and glycated-hemoglobin levels). In combination, these results indicate that hyperglycemia is associated with sustained decreases in PMN function but only in response to agonists that initiate stimulus-response coupling via G-protein-coupled receptors. This agonist-selective reduction in PMN responsiveness may contribute to the compromised host defense associated with sustained hyperglycemia in diabetes.

Topics: Adult; Blood Glucose; Calcimycin; Cells, Cultured; Cross-Sectional Studies; Diabetes Mellitus; Female; Humans; Hyperglycemia; Leukotriene B4; Lysosomes; Male; Middle Aged; N-Formylmethionine Leucyl-Phenylalanine; Neutrophil Activation; Neutrophils; Platelet Activating Factor; Tetradecanoylphorbol Acetate; Zymosan

Insulinopenic diabetes is known to produce endothelial dysfunction. This dysfunction could arise from either hyperglycemia or inadequate insulin. It is not known whether endothelial dysfunction occurs when hyperglycemia is present with elevated insulin levels. In this study, we utilized an experimental model of hyperglycemia with hyperinsulinemia to investigate latent endothelial dysfunction. Rats were continuously infused with glucose or saline for 72 h to achieve peak plasma glucose concentrations of approximately 25 mM. Plasma insulin rose by 12-fold in glucose-infused rats. No significant differences in serum electrolyte concentration were noted between control and glucose-infused rats after 72 h. Blood pressure was not altered by this intervention. Aortic rings taken from control rats relaxed to the endothelium-dependent vasodilators, acetylcholine and A-23187, and to the endothelium-independent vasodilator, nitroglycerin. Relaxation to acetylcholine but not to A-23187 or nitroglycerin was impaired in glucose-infused rat aortic rings. Incubation in vitro with either indomethacin or superoxide dismutase did not restore the impaired relaxation to acetylcholine in rings taken from glucose-infused rats. Thus hyperglycemia with hyperinsulinemia selectively impairs receptor-dependent, endothelium-dependent relaxation. These studies suggest that elevated glucose may be a common pathway leading to endothelial dysfunction in insulin-dependent diabetes mellitus and hyperglycemia-induced insulin resistance.

Topics: Acetylcholine; Animals; Aorta; Calcimycin; Endothelium, Vascular; Hyperglycemia; Hyperinsulinism; Male; Nitroglycerin; Rats; Rats, Sprague-Dawley; Vasodilation; Vasodilator Agents