arachidonic-acid-omega-9-hydroperoxide and Diabetes-Mellitus--Type-2

12-Hydroperoxy-eicosatetraenoic acid (12-HpETE), the main hydroperoxide formed in platelets from arachidonic acid (AA) by 12-lipoxygenase, has been shown to increase the sensitivity of platelets to agonists resulting in increased aggregation. The aim of the present study was to determine the direct effect of low concentrations of 12-HpETE on the signaling pathways leading to AA release from membrane phospholipids and thromboxane A2 (TxA2) formation. Exogenous 12-HpETE activated platelet p38 mitogen-activated protein kinase (p38 MAPK), as assessed by its phosphorylation, at a concentration as low as 100 nM and was much more potent than hydrogen peroxide. Moreover, the incubation of platelets with 100 nM 12-HpETE for 2 min led to the phosphorylation of cytosolic phospholipase A2 (cPLA2). It was associated with a significant decrease in the concentration of AA esterified in phospholipids and an increased concentration of thromboxane B2, the stable catabolite of TxA2. Additionally, decreasing glutathione peroxidase activity pharmacologically favored endogenous 12-HpETE formation and led to an increase in phosphorylated p38 MAPK, while a thiol-reducing agent such as N-acetyl-cysteine fully prevented it. Finally, significant activation of p38 MAPK was also observed in platelets from type 2 diabetic patients with mild hyperglycemia. In conclusion, our data provide a new insight into the mechanism of 12-HpETE-induced platelet priming, suggesting that hydroperoxide-induced p38 MAPK activation could play a relevant role in the exacerbated platelet activation associated with oxidative stress as found in diabetes.

Topics: Acetylcysteine; Arachidonic Acid; Blood Platelets; Cytosol; Diabetes Mellitus, Type 2; Enzyme Activation; Glutathione Peroxidase; Humans; Hydrogen Peroxide; Leukotrienes; Mitogen-Activated Protein Kinases; Oxidative Stress; Oxygen; p38 Mitogen-Activated Protein Kinases; Phospholipases A; Phospholipases A2; Phospholipids

In 33 insulin-dependent, I and II type diabetic patients the authors evaluated the intraplatelet concentration of 12-hydroperoxyeicozatetraenoic acid (12-HPETE) and malonylodialdehyde (MDA) which are the products of lipoxygenase (LO) and cyclooxygenase (CO) metabolism of arachidonic acid (AA) in blood platelets. Moreover, in all patients, determinations of cholesterol total lipids, phospholipids, triacylglycerols were performed as well as serum lipoproteinogram. The studies were done in diabetic ketoacidosis and 2 weeks after compensation of diabetes was attained. Sixty healthy persons, with no changes in the coagulation system, constituted the control group. In patients with diabetic ketoacidosis a higher intraplatelet concentration of 12-HPETE (7.2 +/- 4.0 nmol/10(9) platelets) was found as compared with the values observed in the control group (4.7 +/- 2.1 nmol MDA/10(9) platelets); p less than 0.01. Intraplatelet MDA concentration did not, however, show a statistically significant difference. When compensation of diabetes was obtained the mean intraplatelet 12-HPETE concentration fell to values close the normal ones (5.5 +/- 3.4 nmol MDA/10(9) platelets). Nevertheless, the results of comparative determinations of mean values of both 12-HPETE and MDA concentrations in ketoacidosis as well as in compensated diabetes did not show statistically significant difference. High intraplatelet 12-HPETE concentration in diabetic ketoacidosis may be a cause of the formation or intensification of atherosclerotic changes, typical of this group of patients. The studies did not prove any correlation between the intraplatelet concentration of AA metabolism products and blood glucose concentration and lipid metabolism products. Neither was there any correlation between 12-HPETE and MDA concentration and the duration of clinically symptomatic diabetes.

Topics: Adult; Aged; Blood Platelets; Diabetes Mellitus, Type 1; Diabetes Mellitus, Type 2; Diabetic Ketoacidosis; Humans; Leukotrienes; Malondialdehyde; Middle Aged; Platelet Aggregation Inhibitors