Elevated vascular level of ortho-tyrosine contributes to the impairment of insulin-induced arterial relaxation.

Previous studies have shown that in diabetes mellitus, insulin-induced relaxation of arteries is impaired and the level of ortho-tyrosine (o-Tyr), an oxidized amino acid is increased. Thus, we hypothesized that elevated vascular level of o-Tyr contributes to the impairment of insulin-induced vascular relaxation. Rats were fed with o-Tyr for 4 weeks. Insulin-induced vasomotor responses of isolated femoral artery were studied using wire myography. Vascular o-Tyr content was measured by HPLC, whereas immunoblot analyses were preformed to detect eNOS phosphorylation. Sustained oral supplementation of rats with o-Tyr increased the content of o-Tyr in the arterial wall and significantly reduced the relaxations to insulin. Sustained supplementation of cultured endothelial cells with o-Tyr increased the incorporation of o-Tyr and mitigated eNOS Ser (1 177) phosphorylation to insulin. Increasing arterial wall o-Tyr level attenuates insulin-induced relaxation - at least in part - by decreasing eNOS activation. Elevated level of o-Tyr could be an underlying mechanism for vasomotor dysfunction in diabetes mellitus.

Increase in insulin-induced relaxation of consecutive arterial segments toward the periphery: Role of vascular oxidative state.

RATIONALE: The oxidative state has been implicated in the signaling of various vasomotor functions, yet its role regarding the vasomotor action of insulin is less known. OBJECTIVE: To investigate the insulin-evoked relaxations of consecutive arterial segments of different oxidative state and the role of extracellular signal-regulated kinase (ERK) pathway. METHODS AND RESULTS: The oxidative state, as assessed by the level of ortho-tyrosine, was higher in the thoracic aorta of rats than in the abdominal aorta, and was the lowest in the femoral artery. The vasomotor function of vessels of same origin was studied using a small-vessel myograph. Insulin-induced relaxations increased toward the periphery (i.e., thoracic < abdominal < femoral). Aortic banding and hydrogen peroxide/aminotriazole increased the oxidative state of the thoracic aorta that was accompanied by ERK activation and decreased relaxation to insulin, and vice versa, acutely lowered oxidative state by superoxide dismutase/catalase improved relaxation. In contrast, insulin-induced relaxation of the femoral artery could be enhanced with a higher oxidative state, and reduced with a lower state. CONCLUSIONS: Oxidative state of vessels modulates the magnitude of vasomotor responses to insulin, which appears to be mediated via the ERK signaling pathway.

Effects of erythropoietin on glucose metabolism.

We purposed to determine the impact of erythropoietin on altering glucose metabolism in the settings of in vitro and in vivo experiments. The acute effect of erythropoietin on lowering blood glucose levels was studied in animal experiments. In [³H]-deoxy-D-glucose isotope studies we measured glucose uptake with insulin and erythropoietin using 3T3-L1 cells cultured under normal or high glucose conditions. Altered activation of Akt and ERK pathways was evaluated in immunoblot analyses. Immunocytochemistry was conducted to determine the glucose transporter 4 translocation to the plasma membrane. Addition of erythropoietin significantly lowered blood glucose levels in vivo in rats. The glucose uptake was markedly increased by erythropoietin treatment (at concentrations 0.15, 0.3, and 0.625 ng/ml) in adipocytes grown in high glucose medium (p<0.05), but it remained unaltered in cells under normal glucose conditions. Significant increase of phosphorylation of ERK and Akt was detected due to erythropoietin (p<0.05). Co-administration of erythropoietin and insulin resulted in higher phosphorylation of Akt and [³H]-deoxy-D-glucose uptake in adipocytes than insulin treatment alone. We found that erythropoietin induced the trafficking of glucose transporter 4 to the plasma membrane. Our data showed that erythropoietin significantly decreased blood glucose levels both in vivo and in vitro, in part, by increasing glucose uptake via the activation of Akt pathway. Preliminary data revealed that adipocytes most likely exhibit a specific receptor for erythropoietin.

Cigarette smoke-induced alterations in endothelial nitric oxide synthase phosphorylation: role of protein kinase C.

Endothelial nitric oxide synthase (eNOS) is regulated by phosphorylation of Ser(1177) and Thr(495), which affects NO bioavailability. Cigarette smoke disturbs the eNOS-cGMP-NO pathway and causes decreased NO production. Here the authors investigated the acute effects of cigarette smoke on eNOS phosphorylation, focusing on protein kinases (PKs). Endothelial cell culture was concentration- and time-dependently treated first with cigarette smoke buffer (CSB), then with reduced glutathione (GSH) or various PK inhibitors (H-89, LY-294002, Ro-318425, and ruboxistaurin). eNOS, phospho-Ser(1177)-eNOS, phospho-Thr(495)-eNOS, Akt(PKB), and phospho-Akt protein levels were determined by Western blot. CSB increased the phosphorylation of eNOS at Ser(1177) and more at Thr(495) in a concentration- and time-dependent manner (p < .01, p < .05 versus control, respectively) and resulted in the dissociation of the active dimeric form of eNOS (p < .05). GSH decreased the phosphorylation of eNOS at both sites (p < .05 versus CSB without GSH) and prevented the decrease of dimer eNOS level. CSB treatment also decreased the level of phospho-Ser(473)-Akt (p < .05 versus control). Inhibition of PKA by H-89 did not affect CSB-induced phosphorylation, whereas the PKB inhibitor LY-294002 enhanced it at Ser(1117). The PKC blockers Ro-318425 and ruboxistaurin augmented the CSB-induced phosphorylation at Ser(1177) but decreased phosphorylation at Thr(495) (p < .05 versus CSB). Cigarette smoke causes a disruption of the enzymatically active eNOS dimers and shifts the eNOS phosphorylation to an inhibitory state. Both effects might lead to reduced NO bioavailability. The shift of the eNOS phosphorylation pattern to an inhibitory state seems to be independent of the PKA and phosphoinositol 3-kinase (PI3-K)/Akt pathways, whereas PKC appears to play a key role.

Single dose of acetylsalicylic acid in patients with Type 2 diabetes mellitus and/or chronic renal failure ameliorates anaemia by decreasing the rate of neocytolysis.

BACKGROUND: Anaemia in diabetes mellitus (DM) and/or chronic renal failure (CRF) may be caused by a decreased production of erythropoietin (EPO), EPO resistance, and by the lysis of the young circulating red blood cells (neocytolysis) induced by subclinical inflammation and low EPO level. Aims of this study were to detect EPO resistance in patients with DM and/or CRF and to prove, that acetylsalicylic acid (ASA) is able to improve the haemopoietic status by decreasing neocytolysis. METHODS: In a cross-sectional study, three groups of selected patients (patients with DM; patients with DM+CRF; patients with CRF without DM, n=15 each) and a group of controls (non-diabetic, nonazotemic subjects, n = 10) were compared. In the intervention part of the study, the effect of a single dose of 1 gram ASA on neocytolysis was investigated in a subgroup of these patients. RESULTS: Despite the similar EPO level (p = 1.000), all three patient groups had lower haemoglobin and haematocrit than control persons (p < 0.05 in all cases). Patients with DM+CRF had lower haemoglobin than patients with DM or CRF alone (p < 0.05). Single dose of ASA induced a fast increase in serum EPO level, a concomitant rise of the Rtc number and rate, red blood cell count, haematocrit and haemoglobin p < 0.01 for each). These changes were accompanied by a marked decrease in serum lactate dehydrogenase activity (p < 0.01). CONCLUSIONS: DM and CRF may induce erythropoietin resistance. In these patients, ASA treatment increases serum EPO level. The higher EPO level and the anti-inflammatory effect of ASA may decrease neocytolysis.