High-glucose incubation of human umbilical-vein endothelial cells does not alter expression and function either of G-protein alpha-subunits or of endothelial NO synthase

The effect of glucose tolerance test on fetoplacental circulation

OBJECTIVE

Acute hyperglycemia affects the fetoplacental circulation. This study aims to investigate the possible effect of acute hyperglycemia induced by 50 g oral glucose tolerance test (OGTT) on fetoplacental circulation in women between 24 and 28 weeks of gestation.

MATERIALS AND METHODS

Between January 2019 and April 2019, a total of 29 women who were between 24 and 28 weeks of gestation with a singleton gestation and were in low-risk group were included in this prospective study. All patients underwent fetal biometric measurements using ultrasonography (USG) and were administered 50 g OGTT. Before and 1 h after the test, Doppler USG was used to measure uterine artery, umbilical artery (UA), middle cerebral artery (MCA), pulsatility index (PI), resistance index (RI), and systolic/diastolic (S/D) ratio. The cerebroplacental ratio (CPR) was calculated as the ratio of the MCA-PI/UA-PI.

RESULTS

There was a decline in the MCA-RI (p = 0.008) and UA-PI (p = 0.021) at 1 h after the administration of 50 g OGTT. Z-scores of the mean UA-PI, MCA-PI, and CPR were calculated and a statistically significant increase in the Z-scores of the mean UA-PI was observed (p = 0.028).

CONCLUSION

Our study results show that acute hyperglycemia induced by OGTT significantly increases the Z-scores of the UA-PI, affecting the fetoplacental circulation.

Evaluation of ameliorative effect of sodium nitrate in experimental model of streptozotocin-induced diabetic neuropathy in male rats

OBJECTIVE

Diabetes induces sensory symptoms of neuropathy as positive (hyperalgesia), negative (hypoalgesia), or both.

METHODS

In the present study, fifty male Wistar rats were allocated to five groups: control, control+nitrate, diabetes, diabetes+insulin, and diabetes+nitrate. Thirty days after diabetes confirmation, insulin (2-4 U/day) was injected subcutaneously in diabetes+insulin group and nitrate (100 mg/l) was added into drinking water of the control+nitrate and diabetes+nitrate groups for a period of 2 months. In order to assess the mechanical and thermal algesia, tail immersion, hot plate, and von Frey tests were performed. The serum insulin levels were determined with insulin ELISA Kit. Serum level of NOx was determined by the Griess method.

RESULTS

Both thermal and mechanical nociceptive thresholds showed a significant decrease (p<0.05) which was followed by a significant increase (p<0.01) in the thermal nociceptive threshold in the diabetes group. Chronic nitrate or insulin treatment led to a significant decrease (p<0.01) in blood glucose levels, as well as a significant (p<0.05) increase in the body weight and serum NOx. Moreover, nitrate treatment significantly increased serum insulin levels (p<0.001) compared to the other groups.

CONCLUSION

Chronic nitrate treatment modified the thermal and mechanical sensitivities in diabetic animals.

L-arginine and Alzheimer's disease

Alzheimer's disease (AD), the most common form of dementia, is characterized by progressive neurodegeneration and loss of cognitive and memory functions. Although the exact causes of AD are still unclear, evidence suggests that atherosclerosis, redox stress, inflammation, neurotransmitter dysregulation, and impaired brain energy metabolism may all be associated with AD pathogenesis. Herein, we explore a possible role for L-arginine (L-arg) in AD, taking into consideration known functions for L-arg in atherosclerosis, redox stress and the inflammatory process, regulation of synaptic plasticity and neurogenesis, and modulation of glucose metabolism and insulin activity. L-arg, a precursor of nitric oxide and polyamine, exhibits multiple functions in human health and may play a prominent role in age-related degenerative diseases such as AD.

Dysregulation of the endothelial nitric oxide synthase–soluble guanylate cyclase pathway is normalized by insulin in the aorta of diabetic rat

Antiatherogenic effects of nitric oxide (NO) are mediated by activation of soluble guanylate cyclase (sGC) and are impaired by diabetes in animals and humans. We investigated whether uncontrolled diabetes and insulin therapy effect expression and function of the main enzymes of the endothelial nitric oxide (eNOS)-sGC signaling pathway in vivo. Expression and function of eNOS, sGC and protein kinase G (PKG) were studied by Western blot analysis and vasorelaxation to NO-donor in thoracic aortas from control (CON) and streptozotocin (SZT)-induced diabetic rats during uncontrolled diabetes (DM) and insulin treatment (INS) for 8 weeks. Protein level of eNOS was increased (+300%, P < 0.05), while sGC (-50%) and PKG (-65%) proteins were reduced (P < 0.03) in aortas of DM. Insulin treatment normalized these defects resulting in eNOS, sGC and PKG aortic protein content comparable to control. In aortic rings, diethylamine NONOate (DEA-NONOate)-induced vasorelaxation was attenuated (P< or =0.05) in DM compared to control and returned to normal in INS. Thus, experimental diabetes decreases sGC and PKG expression and their NO-dependent activation in aorta despite overexpression of eNOS. These abnormalities are normalized by insulin treatment and improved metabolic control.

Left ventricular mitogen activated protein kinase signaling following polymicrobial sepsis during streptozotocin-induced hyperglycemia

We hypothesized that sepsis during hyperglycemia would activate left ventricular (LV) mitogen activated protein kinase (MAPK) signaling mechanisms and modulate generation of endothelin-1 (ET-1) and nitric oxide (NO) that can contribute to the progression of LV dysfunction. A single injection of streptozotocin (STZ, 60 mg/kg, via tail vein) was used to produce type 2 diabetes in male SD rats. Polymicrobial sepsis and sham-sepsis were induced using single i.p. injection of cecal inoculum and sterile 5% dextrose water, respectively, on the 13th and 27th day following STZ injection. Both 2-week (2-wk) and 4-wk diabetes groups were associated with hyperglycemia and weight loss. LV end diastolic pressure (LVEDP) was significantly increased in 4-wk diabetes but not in 2-wk diabetes group. Plasma concentration of tumor necrosis factor-alpha (TNF-alpha) was significantly increased in 4-wk diabetes+sepsis group as compared to sham, 2-wk diabetes+sepsis and sepsis groups. Elevated plasma and LV ET-1 and NO byproducts (NOx) along with LV preproET-1 and inducible nitric oxide synthase (iNOS) protein expression were observed in 4-wk but not in 2-wk diabetes group. Sepsis further elevated LV iNOS and preproET-1 in 4-wk diabetes group. Up-regulated phosphorylation of LV p38-MAPK, extracellular signal-regulated kinase 1/2 (ERK1/2) and heat shock protein-27 (Hsp27) was observed in 4-wk diabetes group. Sepsis caused a factorial increase in LV p38-MAPK and Hsp27 phosphorylation and iNOS up-regulation but not ERK1/2 following progression from 2-wk to 4-wk diabetes. The study provides evidence that sepsis up-regulated LV iNOS, p38-MAPK phosphorylation and elevated LVEDP during 4-wk diabetes. We concluded that sepsis contributes in the development of LVEDP dysfunction and alteration in signaling mechanisms depending upon the progression from 2-wk to 4-wk diabetes in the rat.

Effect of a beta 2-adrenoceptor stimulation on hyperglycemia-induced endothelial dysfunction

To investigate whether beta(2)-adrenoceptors exist on endothelial cells and whether a beta(2)-adrenoceptor stimulation might prevent the development of hyperglycemia-induced endothelial dysfunction, porcine aortic endothelial cells (PAECs) were cultured and chronically exposed to either 5 mM D-glucose ("normoglycemia") or 20 mM D-glucose ("hyperglycemia"), with or without 100 nM salbutamol in absence or presence of beta(2)-adrenoceptor antagonist ICI 118,551 [1-[2,3-(dihydro-7-methyl-1H-inden-4-yl)oxyl]-3-[(1-methylethyl)-amino]-2-butanol] or beta(1)-antagonist metoprolol. For osmotic control, PAECs were exposed to 15 mM L-glucose. We measured nitric oxide release using the met-hemoglobin assay and assessed beta-adrenoceptor density and subtypes by radioligand binding. Furthermore, we determined intracellular NADH and NADPH using high-performance liquid chromatography. High D-glucose concentrations but not L-glucose led to significantly reduced basal and stimulated nitric oxide release. Chronic salbutamol treatment significantly antagonized the impairment of the nitric oxide response, which was inhibited by ICI 118,551 but not by metoprolol. The number of giant cells was significantly increased in hyperglycemia, which could be prevented by salbutamol. Binding of the radioligand (-)-[(125)I]iodocyanopindolol revealed a total beta-adrenoceptor density of 29.8 +/- 3.7 (normoglycemic) and 30.3 +/- 3.6 (hyperglycemic) fmol/mg protein. Displacement by ICI 118,551 revealed beta-adrenoceptor subtype distribution with 30.3 +/- 4.4 (normoglycemic) and 29.1 +/- 3.8% beta(2)-adrenoceptors. NADH production increased in hyperglycemia, which was completely prevented by salbutamol. We conclude that hyperglycemia in PAEC induces endothelial dysfunction with impaired nitric oxide release and that this can be prevented by beta(2)-adrenoceptor stimulation.

Decreased activity and impaired induction of nitric oxide synthase by lipopolysaccharides in streptozotocin-induced diabetic rats

The effect of diabetes was determined on nitric oxide synthase (NOS) activity in rat heart and liver. The diabetes was induced by streptozotocin (STZ) and NOS activity was determined after 1 or 12 weeks post-STZ injection. In both tissues, the majority of NOS activity was associated with endothelial constitutive calcium-sensitive NOS (ecNOS) isoform and found in the particulate (100,000xg pellet) fraction in young rats. The diabetes as well as age reduced this activity significantly in heart, whereas only the age caused a decrease in ecNOS activity in liver tissue. Lipopolysaccharides (LPS) induced calcium-insensitive iNOS activity in both young and old rats. The induction was significantly higher (up to 10-fold) in liver as compared to heart. Although the maximum induction of iNOS in young rats was almost similar in diabetic tissues as compared to control animals, there was a lag period for induction of iNOS in diabetic tissues. In old diabetic rats, the induction by LPS was almost completely abolished. These results suggest that diabetes causes either no change or a decrease in ecNOS activity and impairment in the induction of iNOS by LPS in rat heart and liver.

Gq signaling is required for allergen-induced pulmonary eosinophilia

The complexity and magnitude of interactions leading to the selective infiltration of eosinophils in response to inhaled allergens are formidable obstacles to a larger understanding of the pulmonary pathology associated with allergic asthma. This study uses knockout mice to demonstrate a novel function for the heterotrimeric G protein, G(q), in the regulation of pulmonary eosinophil recruitment. In the absence of G(q) signaling, eosinophils failed to accumulate in the lungs following allergen challenge. These studies demonstrate that the inhibition of eosinophil accumulation in the airways is attributed to the failure of hemopoietically derived cells to elaborate GM-CSF in the airways. The data suggest that activation of a G(q)-coupled receptor(s) on resident leukocytes in the lung elicits expression of GM-CSF, which, in turn, is required for allergen-induced pulmonary eosinophilia, identifying a novel pathway of eosinophil-associated effector functions leading to pulmonary pathology in diseases such as asthma.

Influence of diabetes on cardiac nitric oxide synthase expression and activity

There is some evidence that the endothelium dependent vasodilatation of coronary arteries is impaired in both types of diabetes. The underlying mechanisms are not yet clear, in particular whether this defect is caused by a direct effect of diabetes on the activity and the expression of nitric oxide synthases (NOS) or indirectly by an enhanced inactivation of nitric oxide.

METHODS

To study this question we determined the activity (conversion of L-arginine to citrulline) and the mRNAs encoding the isoforms of NOS (using polymerase chain reaction after reverse transcription of the mRNAs into cDNAs by reverse transcriptase) in hearts of streptozotocin diabetic rats and in rat heart endothelial cells (RHEC). The formation of reactive oxygen intermediates (ROI) was measured by the dichloro-dihydro-fluorescein method.

RESULTS

The activity of total NOS and the amounts of mRNAs encoding ecNOS and iNOS were dependent on the duration of diabetes. After a diabetes duration of 4 to 6 weeks both the total activity as well as the mRNAs encoding ecNOS and iNOS were elevated. A reduction of NOS activity and the amounts of mRNAs of ecNOS and iNOS was only seen after a diabetes duration longer than 20 weeks, a time at which a loss of endothelium has been described. In RHEC, high glucose (22 mM) and H(2)O(2) (100 microM) were able to increase the mRNA encoding ecNOS, but not iNOS. This increase in ecNOS mRNA was inhibited by lipoic acid (1 microM). In addition, high glucose (22 and 30 mM) led to an enhanced formation of ROI and to activation of the transcription NF kappa B.

CONCLUSION

These observations suggest that diabetes causes a temporary increase in NOS activity and ecNOS mRNA in the rat heart which is presumably the consequence of an enhanced oxidative stress exerted by hyperglycaemia. Together with previously published observations, our data suggest that the impairment of endothelium dependent vasodilatation in rat heart is not the consequence of a reduced activity and expression of NOS, but is caused by an enhanced inactivation of nitric oxide by ROI.

Impaired nitric oxide production in coronary endothelial cells of the spontaneously diabetic BB rat is due to tetrahydrobiopterin deficiency

Endothelial cells (EC) from diabetic BioBreeding (BB) rats have an impaired ability to produce NO. This deficiency is not due to a defect in the constitutive isoform of NO synthase in EC (ecNOS) or alterations in intracellular calcium, calmodulin, NADPH or arginine levels. Instead, ecNOS cannot produce sufficient NO because of a deficiency in tetrahydrobiopterin (BH(4)), a cofactor necessary for enzyme activity. EC from diabetic rats exhibited only 12% of the BH(4) levels found in EC from normal animals or diabetes-prone animals which did not develop disease. As a result, NO synthesis by EC of diabetic rats was only 18% of that for normal animals. Increasing BH(4) levels with sepiapterin increased NO production, suggesting that BH(4) deficiency is a metabolic basis for impaired endothelial NO synthesis in diabetic BB rats. This deficiency is due to decreased activity of GTP-cyclohydrolase I, the first and rate-limiting enzyme in the de novo biosynthesis of BH(4). GTP-cyclohydrolase activity was low because of a decreased expression of the protein in the diabetic cells.

Role of nitric oxide in the pathogenesis of diabetic nephropathy in streptozotocin-induced diabetic rats

OBJECTIVES

Several reports suggest that enhanced generation or actions of nitric oxide (NO) have been implicated in the pathogenesis of glomerular hyperfiltration and hyperperfusion that occurs in early diabetes. However, the precise role of altered NO generation in the pathogenesis of diabetic nephropathy is unclear. The present study was aimed at investigating the role of nitric oxide in the pathogenesis of glomerular hyperfiltration and hyperperfusion in streptozotocin-induced diabetic rats.

METHODS

To evaluate the role of NO in diabetic hyperfiltration, we measured plasma and urine concentrations of NO2-/NO3-, stable metabolic products of NO and protein expressions of three isoforms of nitric oxide synthase (NOS) in streptozotocin-induced diabetic rats. We also investigated renal hemodynamic changes, such as glomerular filtration rate (GFR) and renal plasma flow (RPF), in responses to acute and chronic administration of NO synthesis inhibitor, nitro-L-arginine methyl ester (L-NAME), in diabetic and control rats.

RESULTS

Diabetic rats exhibited significantly elevated plasma and urinary NO2-/NO3- levels at 28 days after streptozotocin injection, and total excretion of NO2-/NO3- was approximately five-fold higher in diabetic rats than controls. Insulin and L-NAME treatment prevented the increases in plasma and urinary NO2-/NO3- concentrations in diabetic rats, respectively. The three isoforms of NOS (bNOS, iNOS, and ecNOS) were all increased in the renal cortex, whereas they remained unaltered in the renal medulla at day 28. GFR and RPF were significantly elevated in diabetic rats, and acute and chronic inhibition of NO synthesis by L-NAME attenuated the renal hemodynamic changes (increases in GFR and RPF) in diabetic rats, respectively.

CONCLUSIONS

NO synthesis was increased due to enhanced NOS expression in diabetic rats, and chronic NO blockade attenuated renal hyperfiltration and hyperperfusion in diabetic rats. In addition, diabetic rats exhibited enhanced renal hemodynamic responses to acute NO inhibition and excreted increased urinary NO2-/NO3-. These results suggest that excessive NO production may contribute to renal hyperfiltration and hyperperfusion in early diabetes.

Expression of G-protein subtypes in cultured cerebral endothelial cells

This paper describes Western-blotting evidence for the presence of various guanine nucleotide binding proteins, G-proteins in cultured rat cerebral endothelial cells (CECs) and two immortalized cerebral endothelial cell lines, RBE4 and GP8. By using specific antibodies raised against known sequences of appropriate G-protein types that were previously characterized, we demonstrated the presence of Gsalpha, Gi2alpha, Gi3alpha, Gq/11alpha, Goalpha and Gbeta in cell lysates of primary cultures of CECs, and plasma membranes of RBE4 and GP8 cells. The appearance of Goalpha proteins in CECs might be of special importance, since they were not detected in peripheral endothelial cells in previous studies. Isoproterenol and bradykinin displayed significant, dose-dependent stimulation of [35S]GTPgammaS binding above basal values. This assay, reflecting the GDP-GTP exchange reaction on Galpha-subunits by receptor agonists, suggested that there were functional, G-protein coupled beta-adrenergic and bradykinin receptors in these systems. No significant stimulation of [35S]GTP7gammaS binding was noted with serotonin under our experimental conditions. Since stimulation of [35S]GTPgammaS binding by isoproterenol and bradykinin was additive, it was concluded that different Galpha proteins were activated by these two ligands. In analogy to other systems, activation of Gs is most likely by isoproterenol, while Gi and/or Gq/11 proteins might be activated by bradykinin receptors. The possible significance of the receptors and G-proteins detected is being discussed in the functioning of cerebral endothelium, and thus the blood-brain barrier.

Ca2+ mobilization in the aortic endothelium in streptozotocin-induced diabetic and cholesterol-fed mice

1. Experiments were performed to compare Ca2+ mobilization in the aortic endothelium in streptozotocin (STZ)-induced diabetic and cholesterol-fed mice with that in age-matched controls. 2. The intracellular free Ca2+ ([Ca2+]i) in the fura PE-3 loaded endothelium of aortic rings was dose-dependently increased by cumulative administration of acetylcholine (ACh). ACh caused a transient rise in [Ca2+]i in Ca2+-free medium. The ACh-induced increase in [Ca2+]i in normal or Ca2+-free medium was significantly weaker in both STZ-induced diabetic and cholesterol-fed mice. 3. The weaker [Ca2+]i response in Ca2+-containing medium in STZ-induced diabetic and cholesterol-fed mice was normalized by chronic administration of cholestyramine. 4. The increased low density lipoprotein (LDL) levels seen in both STZ-induced diabetic and cholesterol-fed mice were normalized by the same chronic administration of cholestyramine (300 mg kg(-1), p.o. daily for 10 weeks). Chronic administration of cholestyramine had no effect on the plasma glucose level. 5. Lysophosphatidylcholine (LPC) decreased the [Ca2+]i responses to ACh in the aortic endothelium from normal mice. 6. These results suggest that ACh increases both Ca2+ influx and Ca2+ release from storage in the aortic endothelium. The weaker [Ca2+]i influx seen in the endothelium of aortae from both STZ-induced diabetic and cholesterol-fed mice was improved by the chronic administration of cholestyramine, and we suggest that this improvement is due, at least in part, to a lowering of the plasma LDL level. It is further suggested that LPC may have an important influence over Ca2+ mobilization in the endothelium.

Regulation of the cerebral circulation: role of endothelium and potassium channels

Several new concepts have emerged in relation to mechanisms that contribute to regulation of the cerebral circulation. This review focuses on some physiological mechanisms of cerebral vasodilatation and alteration of these mechanisms by disease states. One mechanism involves release of vasoactive factors by the endothelium that affect underlying vascular muscle. These factors include endothelium-derived relaxing factor (nitric oxide), prostacyclin, and endothelium-derived hyperpolarizing factor(s). The normal vasodilator influence of endothelium is impaired by some disease states. Under pathophysiological conditions, endothelium may produce potent contracting factors such as endothelin. Another major mechanism of regulation of cerebral vascular tone relates to potassium channels. Activation of potassium channels appears to mediate relaxation of cerebral vessels to diverse stimuli including receptor-mediated agonists, intracellular second messenger, and hypoxia. Endothelial- and potassium channel-based mechanisms are related because several endothelium-derived factors produce relaxation by activation of potassium channels. The influence of potassium channels may be altered by disease states including chronic hypertension, subarachnoid hemorrhage, and diabetes.

The cyclin-dependent kinase inhibitor p21cip1 mediates the growth inhibitory effect of phorbol esters in human venous endothelial cells

Long-term application of the phorbol ester phorbol 12,13-dibutyrate (PDBu) inhibits the proliferation of human venous endothelial cells. The cyclin-dependent kinase inhibitor p21cip1 is a potential candidate mediating the PDBu-induced delayed entry of the cells into S-phase (by approximately 10 h when compared with cells stimulated with basic fibroblast growth factor (bFGF)). Levels of p21cip1 (protein and mRNA) rapidly rise (within approximately 2 h) in endothelial cells treated with the active isomer beta-PDBu, but not with alpha-PDBu; this effect is blocked by the mitogen-activated protein kinase kinase-1 (Mek1) inhibitor PD098059 and by the protein kinase C (PKC) antagonists GF109203X and rottlerin (selective for PKC-delta), but not Gö 6976 (selective for Ca2+-dependent PKC isoforms). Rapamycin blocks the PDBu-induced accumulation of p21cip1 (but not of the cognate mRNA), indicating an action of PKC on p21(cip1) mRNA translation. If endothelial cells are recruited into the cell cycle by bFGF, p21cip1 mRNA and protein levels rise initially (within 2 h) and decline subsequently such that p21cip1 drops to a minimum prior to the initiation of DNA synthesis (i.e. after approximately 12 h). In bFGF-stimulated cells, changes in p21cip1 mRNA and protein are strictly linked. In contrast, the levels of p21cip1 mRNA decline substantially (>10 h) before the protein decreases in PDBu-stimulated cells. Thus, PKC (presumably PKC-delta) regulates the amounts of p21cip1 in endothelial cells at the level of mRNA accumulation and translation, leading to a rapid and robust induction; following persistent PKC activation, p21(cip1) remains elevated despite reduced mRNA levels, indicating an enhanced stability of the protein. The bFGF-mediated increase in p21cip1 is blocked by the Mek1 inhibitor, but not by GF109203X; hence, in endothelial cells, induction of p21cip1 by PKC- and growth factor-dependent signaling is achieved by distinct pathways that converge and require activation of the mitogen-activated protein kinase cascade. The beta-PDBu-induced delayed S-phase entry and drop in p21cip1 are reversed if GF109203X is added 4 h after beta-PDBu to prevent persistent PKC activation. These observations indicate a cause and effect relation between sustained p21cip1 elevations and the delay in S-phase entry induced by beta-PDBu.