Tyrosine kinase-mediated activation of NADPH oxidase enhances proliferative capacity of diabetic vascular smooth muscle cells

Reactive oxygen and nitrogen species in pathogenesis of vascular complications of diabetes

Macrovascular and microvascular diseases are currently the principal causes of morbidity and mortality in subjects with diabetes. Disorders of the physiological signaling functions of reactive oxygen species (superoxide and hydrogen peroxide) and reactive nitrogen species (nitric oxide and peroxynitrite) are important features of diabetes. In the absence of an appropriate compensation by the endogenous antioxidant defense network, increased oxidative stress leads to the activation of stress-sensitive intracellular signaling pathways and the formation of gene products that cause cellular damage and contribute to the vascular complications of diabetes. It has recently been suggested that diabetic subjects with vascular complications may have a defective cellular antioxidant response against the oxidative stress generated by hyperglycemia. This raises the concept that antioxidant therapy may be of great benefit to these subjects. Although our understanding of how hyperglycemia-induced oxidative stress ultimately leads to tissue damage has advanced considerably in recent years, effective therapeutic strategies to prevent or delay the development of this damage remain limited. Thus, further investigation of therapeutic interventions to prevent or delay the progression of diabetic vascular complications is needed.

Tyrosine kinase inhibitor, genistein, reduces renal inflammation and injury in streptozotocin-induced diabetic mice

Tyrosine kinase inhibition is known to reduce diabetes-induced end-organ damage but the mechanisms remain elusive. We hypothesized that inhibition of tyrosine kinase reduces renal inflammation and injury in streptozotocin-induced diabetes. Male C57BL/6 mice were given daily injections of streptozotocin (45 mg/kg/day, i.p. for 5 days); control animals received the vehicle (citrate buffer). Thereafter, streptozotocin-treated mice were treated with genistein (10 mg/kg, i.p three times a week for 10 weeks, n=8-10/group) or the vehicle (5% DMSO). The streptozotocin-treated mice displayed significant elevation in blood glucose level and decrease in plasma insulin level compared to their vehicle-treated controls. Treatment with genistein reduced blood glucose level (~15%; p<0.05) without a significant effect on plasma insulin level; however, blood glucose remained significantly higher than the control group. The development of diabetes was associated with significant increases in total protein, albumin, nephrin and collagen excretions compared to their controls. In addition, the diabetic mice displayed increased urinary MCP-1 excretion in association with increased renal ICAM-1 expression and apoptotic cells. Furthermore, renal gp91 expression levels and urinary Thio-Barbituric Acid Reactive Substances (TBARs) excretion, indices of oxidative stress, were also elevated in diabetic mice. These changes were associated with increased renal phospho-tyrosine expression and renal phospho-ERK/ERK ratio. Importantly, treatment with genistein reduced all these parameters towards control values. Collectively, the results suggest that the reno-protective effect of genistein likely relates to reduced renal inflammation, oxidative stress and apoptosis in diabetic mice.

Signaling of reactive oxygen and nitrogen species in Diabetes mellitus

Disorder of physiological signaling functions of reactive oxygen species (ROS) superoxide and hydrogen peroxide and reactive nitrogen species (RNS) nitric oxide and peroxynitrite is an important feature of diabetes mellitus type 1 and type 2. It is now known that hyperglycemic conditions of cells are associated with the enhanced levels of ROS mainly generated by mitochondria and NADPH oxidase. It has been established that ROS stimulate many enzymatic cascades under normal physiological conditions, but hyperglycemia causes ROS overproduction and the deregulation of ROS signaling pathways initiating the development of diabetes mellitus. On the other hand the deregulation of RNS signaling leads basically to a decrease in NO formation with subsequent damaging disorders. In the present work we will consider the pathological changes of ROS and RNS signaling in enzyme/gene regulated processes catalyzed by protein kinases C and B (Akt/B), phosphatidylinositol 3'-kinase (PI3-kinase), extracellular signal-regulated kinase 1/2 (ERK1/2), and some others. Furthermore we will discuss a particularly important role of several ROS-regulated genes and adapter proteins such as the p66shc, FOXO3a, and Sirt2. The effects of low and high ROS levels in diabetes will be also considered. Thus the regulation of damaging ROS levels in diabetes by antioxidants and free radical scavengers must be one of promising treatment of this disease, however, because of the inability of traditional antioxidative vitamin E and C to interact with superoxide and hydrogen peroxide, new free radical scavengers such as flavonoids, quinones and synthetic mimetics of superoxide dismutase (SOD) should be intensively studied.

Protein tyrosine phosphatase PTPepsilonM negatively regulates PDGF beta-receptor signaling induced by high glucose and PDGF in vascular smooth muscle cells

Vascular smooth muscle cell (VSMC) proliferation and migration and vascular endothelial cell (VEC) dysfunction are closely associated with the development of atherosclerosis. We previously demonstrated that protein tyrosine phosphatase ε M (PTPεM) promotes VEC survival and migration. The present study investigates the biological functions of PTPεM in VSMCs and determines whether PTPεM is implicated in diabetes-accelerated atherosclerosis. We overexpressed wild-type and inactive PTPεM and an small interfering RNA (siRNA) of PTPεM by using an adenovirus vector to investigate the effects of PTPεM upon platelet-derived growth factor (PDGF)- and high glucose (HG)-induced responses of rat VSMCs in vitro. We found that PTPεM decreased PDGF-induced DNA synthesis and migration by reducing the phosphorylation level of the PDGF β-receptor (PDGFRβ) with subsequently suppressed H(2)O(2) generation. The HG content in the medium generated H(2)O(2), upregulated PDGFRβ expression and its tyrosine-phosphorylation, and elevated NADPH oxidase 1 (Nox1) expression even without exogenous PDGF, all of which were downregulated by PTPεM. The PDGFR inhibitor AG1296 also blocked HG-induced Nox1 expression and H(2)O(2) production. Moreover, HG suppressed PTPεM expression itself, which was blocked by the antioxidant N-acetyl-l-cysteine. The effects of PTPεM siRNA were the opposite of those of wild-type PTPεM. Therefore, PTPεM negatively regulates PDGFRβ-mediated signaling pathways that are crucial for the pathogenesis of atherosclerosis, and PTPεM may be involved in diabetes-accelerated atherosclerosis.

Inhibition of the cellular uptake of anandamide by genistein and its analogue daidzein in cells with different levels of fatty acid amide hydrolase-driven uptake

BACKGROUND AND PURPOSE

Genistein, a tyrosine kinase inhibitor used to block caveolae dependent endocytosis, reduces the cellular uptake of anandamide in RBL2H3 basophilic leukaemia cells. However, genistein is also a competitive inhibitor of fatty acid amide hydrolase, the enzyme responsible for anandamide hydrolysis. Here we have investigated whether inhibition of fatty acid amide hydrolase rather than inhibition of endocytosis is the primary determinant of genistein actions upon anandamide uptake.

EXPERIMENTAL APPROACH

Cellular uptake of anandamide, labelled in the arachidonoyl part of the molecule was assessed in four different cell lines using a standard method. Fatty acid amide hydrolase activity in homogenates and intact cells was measured using anandamide labelled in the ethanolamine part of the molecule.

KEY RESULTS

The fatty acid amide hydrolase inhibitor URB597 inhibited anandamide uptake into RBL2H3 cells and R3327 AT-1 prostate cancer cells, but not into 3T3-L1 preadipocytes or PC-3 prostate cancer cells. An identical pattern was seen with genistein. The related compound daidzein inhibited anandamide hydrolysis in homogenates and intact cells, and reduced its uptake into RBL2H3 and R3327 AT-1, but not PC-3 cells. Anandamide hydrolysis by cell homogenates was in the order RBL2H3 > R3327 AT-1 > PC-3 approximately 3T3-L1.

CONCLUSIONS AND IMPLICATIONS

The ability of genistein to inhibit anandamide uptake is mimicked by daidzein (which does not affect tyrosine kinase), and is only seen in cells that show sensitivity to URB597. This indicates that blockade of fatty acid amide hydrolase is the primary determinant of the effects of genistein on cellular anandamide uptake.

Calorie restriction improves cardiovascular risk factors via reduction of mitochondrial reactive oxygen species in type II diabetic rats

Uncoupling protein 2 (UCP2) is an important regulator of intracellular reactive oxygen species (ROS) production. We determined the effects of calorie restriction (CR) on the dynamic aspects of mitochondrial ROS production, UCP2, and the nitric oxide (NO)-cGMP pathway in the cardiovascular tissues of type II diabetic Otsuka Long-Evans Tokushima Fatty (OLETF) rats. Some rats were on restricted diets (30% reduction from free intake) from age 29 to 42 weeks. Blood glucose, hemoglobin A1c, plasma levels of free fatty acid, triacylglycerol, and plasminogen activator inhibitor-1 in OLETF rats were significantly higher than those in nondiabetic control [Long-Evans Tokushima Otsuka (LETO)] rats at 29 weeks. Mitochondrial ROS production and UCP2 expression significantly increased in the heart and aorta of OLETF rats compared with those in LETO rats. A fibrogenic growth factor, transforming growth factor (TGF)-beta1 in the coronary vessels, endothelial nitric-oxide synthase, and aortic nitrotyrosine were increased in OLETF rats at 42 weeks. In contrast, an index of the NO-cGMP pathway, phosphorylated vasodilator-stimulated phosphoprotein, and superoxide dismutase activity in the aorta were significantly diminished. The relationship between UCP2 and ROS production in the cardiovascular function of diabetic rats being fed a calorie-restricted diet is unknown. These abnormalities in OLETF rats were reversed to normal levels by CR. CR significantly improved the NO-cGMP pathway via normalizing ROS generation in OLETF rats. A decrease in UCP2 expression by CR may be a compensatory mechanism to counteract decreased intracellular oxidative stress. The data suggest that CR may prevent cardiovascular tissues from oxidative stress provoked by diabetes mellitus.