Vascular endothelial growth factor up-regulates ICAM-1 expression via the phosphatidylinositol 3 OH-kinase/AKT/Nitric oxide pathway and modulates migration of brain microvascular endothelial cells

Endothelium of the cerebral blood microvessels, which constitutes the major component of the blood-brain barrier, controls leukocyte and metastatic cancer cell adhesion and trafficking into the brain parenchyma. In this study, using rat primary brain microvascular endothelial cells (BMEC), we demonstrate that the vascular endothelial growth factor (VEGF), a potent promoter of angiogenesis, up-regulates the expression of the intracellular adhesion molecule-1 (ICAM-1) through a novel pathway that includes phosphatidylinositol 3 OH-kinase (PI3K), AKT, and nitric oxide (NO), resulting in the migration of BMEC. Upon VEGF treatment, AKT is phosphorylated in a PI3K-dependent manner. AKT activation leads to NO production and release and activation-deficient AKT attenuates NO production stimulated by VEGF. Transfection of the constitutive myr-AKT construct significantly increased basal NO release in BMEC. In these cells, VEGF and the endothelium-derived NO synergistically up-regulated the expression of ICAM-1, which was mediated by the PI3K pathway. This activity was blocked by the PI3K-specific inhibitor, wortmannin. Furthermore, VEGF and NO significantly increased BMEC migration, which was mediated by the up-regulation of ICAM-1 expression and was dependent on the integrity of the PI3K/AKT/NO pathway. This effect was abolished by wortmannin, by the specific ICAM-1 antibody, by the specific inhibitor of NO synthase, N(G)-l-monomethyl-arginine (l-NMMA) or by a combination of wortmannin, ICAM-1 antibody, and l-NMMA. These findings demonstrate that the angiogenic factor VEGF up-regulates ICAM-1 expression and signals to ICAM-1 as an effector molecule through the PI3K/AKT/NO pathway, which leads to brain microvessel endothelial cell migration. These observations may contribute to a better understanding of BMEC angiogenesis and the physiological as well as pathophysiological function of the blood-brain barrier, whose integrity is crucial for normal brain function.

Monoclonal endothelial cells in appetite suppressant-associated pulmonary hypertension

Anorexigens such as aminorex fumarate and dexfenfluramine are associated with the development of severe pulmonary hypertension (PH), which clinically and histopathologically is considered indistinguishable from idiopathic or primary pulmonary hypertension (PPH). For the current study, we asked whether anorexigen-associated PH is characterized by monoclonal pulmonary endothelial cell proliferation (such as in PPH) or, alternatively, is associated with a polyclonal endothelial cell proliferation as found in secondary PH. Analysis of clonality by the human androgen receptor assay was performed in microdissected endothelial cells of plexiform lesions of two patients with anorexigen-associated PH. The four plexiform lesions of Patient 1 and the six of Patient 2 with anorexigen-associated PH exhibited a monoclonal expansion of pulmonary endothelial cells, with a mean clonality ratio of 0.03 +/- 0.01 SE. Our results indicate that appetite suppressant-associated PH is identical to PPH not only in clinical and histopathologic features but also, at a molecular level, in terms of the monoclonal nature of the endothelial cell proliferation. The anorexigens may accelerate the growth of pulmonary endothelial cells in patients with predisposition to develop PPH.

Xanthine oxidase decreases production of gut wall nitric oxide

Multiorgan failure is often the lethal outcome of intratracheal aspiration of acidic gastric juice. The pathogenesis of multiorgan failure may involve a systemic imbalance between pro-inflammatory and anti-inflammatory factors. In an anesthetized rat model, intratracheal instillation of HCl elicited intestinal inflammation which was exaggerated by xanthine oxidase (XO) and attenuated by nitric oxide (NO). We hypothesized that XO may mediate injury in part by suppression of NO formation. Therefore, we measured intestinal tissue concentrations of the stable NO oxidative metabolites (NO2- and NO3-) following intratracheal (IT) instillation of NaCl or HCl alone or in combination with interventions aimed at increasing or decreasing XO activity. Compared with IT NaCl (control treatment) jejunal tissue NO2- and NO2- + NO3- concentrations were increased by allopurinol pretreatment, which inhibits XO, and were decreased by systemically administered XO, as well as by IT HCl. The decreased NO2- and NO2- + NO3- concentrations found following IT HCl were completely reversed by either allopurinol or by systemically administered L-arginine (the precursor of NO). We conclude that manipulation of the pro-inflammatory XO system has a reciprocal effect on the intestinal anti-inflammatory NO system in either the undamaged or the endobronchially acidified lung model.

Nitric oxide attenuates and xanthine oxidase exaggerates lung damage-induced gut injury

Aspirated gastric contents can evoke multiorgan failure. We hypothesized that secondary intestinal epithelial dysfunction after lung damage would be mediated by xanthine oxidase (XO) and antagonized by endogenous gut nitric oxide (NO). Isosmotic saline or HCl solutions were instilled intratracheally in anesthetized rats, and intestinal injury was assessed 190 min later by measuring the blood-to-lumen clearance of 51Cr-labeled EDTA (51Cr-EDTA clearance) and gut wall neutrophil population density. Intratracheal HCl increased 51Cr-EDTA clearance, and this transepithelial leak was attenuated by either systemic L-arginine or intraluminal NO and by chronic dietary pretreatment with allopurinol or sodium tungstate. Conversely, lung damage-induced gut leak was exaggerated by NO synthase inhibition or intravenous XO administration. Intratracheal HCl also increased intestinal wall neutrophil density and myeloperoxide activity. We conclude that two enzymatic systems involved in remote gut barrier dysfunction after endobronchial acidification are XO as mediator and NO synthase as antagonist.

Burn-induced nitric oxide release in humans

Nitric oxide (NO) generation in a series of 20 burn patients was studied with a novel anion exchange high-performance liquid chromatographic method for the simultaneous determination of nitrite (NO2-) and nitrate (NO3-), the stable metabolic endproducts of NO. The NO values within our survivor group (n = 17) were significantly altered at days 1, 6, and 12 postburn in contrast to controls (n = 23) (p < or = 0.03). NO2- values were significantly depressed in both plasma and urine, whereas NO3- values were significantly elevated in contrast to control values (p < or = 0.03). The ratio of NO2-:NO3- was significantly lower for burn patients versus controls in both plasma and urine (p < 0.01). The NO generation seemed in part to be dependent on the percentage of total body surface area burn, most dramatically elevated in patients with burns of 10 to 40% total body surface area. In subjects who did not survive beyond 36 hours postinjury because of irreversible shock (n = 3), the production of NO was significantly depressed in contrast to survivors and controls (p < 0.0001). However, the NO2-:NO3- ratio (0.001) was relatively unchanged, with reflection of a global depression in NO formation with no change in the individual component release. Burn injury resulted in an increased release/production of NO that in the first postburn week is maximally elevated immediately postinjury. NO release, although decreased at day 6 relative to the day 1 values, remained elevated into the second week postinjury when there was evidence for a further increase in NO production. The enhanced NO3- formation may well result from NO reacting with oxygen-free radicals counteracting superoxide anion-induced destruction of tissue, thereby potentially functioning as a protectant molecule.

Hypertension-induced dysfunction of circulation in hemorrhagic shock

Arterial blood pressure and plasma concentration of Na+, K+, glucose, and urea were studied in patients with essential hypertension during hemorrhagic shock. All 15 patients had established essential hypertension, and all had massive hemorrhage and shock. The control group included 37 normotensive patients in hemorrhagic shock. There were no differences in blood volume loss and age between the hypertensive and normotensive groups. A significant reduction (P < .001) of systolic and diastolic blood pressure as well as plasma concentration of Na+ and K+ were observed in hypertensive patients with hemorrhagic shock as compared with normotensive patients in hemorrhagic shock. Hypertensive patients in shock were found to have significantly elevated (P < .001) plasma glucose, urea, and heart rate compared with normotensive patients in shock. The hypertensive group mortality was significantly (P < .001) higher (80%) than the normotensive group in shock (24.3%). These data suggest that essential hypertension induces alterations in regulation and modulation of peripheral resistance, Na+/K+ membrane exchange, and the metabolism of glucose and urea during hemorrhagic shock. This heterogeneity of dysfunction induced by essential hypertension during hemorrhagic shock is probably caused by a change in the mechanism (diminish) of oxygen consumption at the cellular level, which results in an increase in nitric oxide production (which is O2 dependent), and may play an important role in hypertension and hemorrhagic shock.

Norepinephrine modulates excitatory amino acid-induced responses in developing human and adult rat cerebral cortex

These experiments were designed to assess the ability of norepinephrine and its beta-receptor agonist, isoproterenol, to modulate responses induced by activation of excitatory amino acid receptors in brain slices obtained from developing human cortex or adult rat cortex. Human cortical slices were obtained from children undergoing surgery for intractable epilepsy (9 months to 10 yr of age). For comparison, slices were also obtained from rats (2-3 months of age). Iontophoretic application of glutamate, N-methyl-D-aspartate or alpha-amino-3-hydroxy-5-methyl-4- isoxazolepropionic acid (AMPA) produced excitatory responses consisting of membrane depolarizations accompanied by action potentials. Iontophoretic or bath application of norepinephrine or isoproterenol enhanced responses evoked by glutamate or N-methyl-D-aspartate. Depolarizations occurred with shorter latencies and their amplitudes increased. Action potential frequency was also increased and responses were of longer duration. In contrast, norepinephrine or isoproterenol had no effect on responses induced by AMPA. The enhancement of responses induced by N-methyl-D-aspartate or glutamate was antagonized by the beta-adrenergic receptor antagonist propranolol. Similar findings were obtained from neurons in humans or rats. These results suggest that norepinephrine, possibly via beta-receptors, potentiates responses mediated by glutamate and N-methyl-D-aspartate receptors without affecting those mediated by AMPA receptors. These effects were observed at all ages studied, indicating that the ability of norepinephrine to modulate excitatory neuronal transmission is well developed in human cortex by 9 months of age.

Evidence for enhanced synaptic excitation in transplanted neostriatal neurons

Fetal neostriatal tissue was transplanted into either the neostriatum or substantia nigra of adult rats. One to 6 months after transplantation, coronal brain slices were taken through the rostrocaudal extent of the transplants and neurons were characterized electrophysiologically using an in vitro slice preparation. When compared to control neurons taken from intact adult neostriata, transplanted neostriatal neurons (TSNs) had higher input resistances and longer time constants. All other passive and active membrane properties assessed were comparable between transplanted and control neostriatal neurons. Regardless of the transplantation site, local extracellular stimulation outside the graft elicited high-amplitude, long-duration depolarizing synaptic potentials that typically triggered bursts of action potentials. These synaptic potentials contrast with lower amplitude, shorter duration synaptic potentials consistently elicited in control neostriatal neurons. The depolarizing synaptic potentials evoked in the TSNs appeared to be mediated by a combined activation of N-methyl-D-aspartate (NMDA) and non-NMDA excitatory amino acid receptors. Both the broad-spectrum excitatory amino acid antagonist kynurenic acid and the specific non-NMDA receptor antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione significantly reduced postsynaptic potentials elicited in TSNs. The specific NMDA antagonist 2-amino-5-phosphonovalerate had less effect on the amplitude but markedly reduced the duration of the synaptic potentials. The duration and amplitude of the bursts were augmented by the gamma-aminobutyric acid (GABA)A receptor antagonist bicuculline methiodide, indicating that inhibition occurred in TSNs. TSNs were also more sensitive than control neurons to direct application of glutamate or NMDA. These findings demonstrate that TSNs express altered electrophysiological properties. The pharmacological analysis indicates that depolarizing postsynaptic potentials were mediated by activation of excitatory amino acid receptors, suggesting either innervation of the graft by host fibers which contain excitatory amino acids or development of novel local excitatory interactions intrinsic to the graft. Furthermore, the occurrence of high-amplitude, long-duration depolarizing synaptic potentials in TSNs, regardless of the site of transplantation, suggests that grafted neostriatal neurons become hyperexcitable to synaptic input.

Age-induced changes in electrophysiological responses of neostriatal neurons recorded in vitro

The present studies were undertaken to determine whether the major electrophysiological characteristics of neostriatal neurons are altered during aging. The passive and active membrane properties of 130 neostriatal neurons obtained from young (three to five months, N = 65) and aged (24-26 months, N = 65) Fischer 344 rats were compared using an in vitro slice preparation. The results indicated that in a population of aged neostriatal neurons the majority of the electrophysiological changes that occurred resulted in decreases in cellular excitability. These changes included increased threshold to induce action potentials by intracellular current injection and decreased negativity of membrane potentials at which such action potentials were induced. In addition, there were increases in the amplitude of the action potential afterhyperpolarization and increases in the frequency of occurrence of accommodation when trains of action potentials were induced. These two latter effects can limit the frequency of action potential generation. The thresholds to elicit synaptically evoked depolarizing responses and action potentials were increased. The results also indicated that a number of basic electrophysiological parameters were unchanged by the aging process. These included action potential amplitude, rise time and duration, resting membrane potential, input resistance and time constant. Although thresholds for the induction of synaptic and action potentials by extracellular stimulation were increased, the latency, amplitude and duration of the evoked depolarization remained unchanged. These findings suggest that the ability of neostriatal neurons to integrate spatiotemporal inputs must be severely compromised in this population of aged cells. Furthermore, the present findings, when compared with age-induced electrophysiological alterations in neurons in other brain areas, indicate that age may differentially alter electrophysiological properties of neurons in separate nuclei. Profiles of age-related changes in neurophysiological properties of neurons provide important information that can be related to the contributions of individual neural areas to the behavioral effects of aging.

Differential modulation by dopamine of responses evoked by excitatory amino acids in human cortex

The responses of human neocortical neurons to iontophoretic application of excitatory amino acids and their modulation by dopamine (DA) were studied in vitro. Brain slices were obtained from children undergoing surgery for intractable epilepsy. Application of N-methyl-D-aspartate (NMDA) to the slices induced slow depolarizations accompanied by decreased input conductances and sustained action potentials in cortical neurons. Glutamate produced rapid depolarizations and firing with few changes in input conductances. Quisqualate also induced depolarization and firing, but input conductances increased during the rising phase of the membrane depolarization. Iontophoretic application of DA alone produced no change in membrane potential or input conductance. However, when DA was applied in conjunction with the excitatory amino acids, it produced contrasting effects. With either bath application of DA or when iontophoresis of DA preceded application of NMDA, the amplitude of the membrane depolarizations and the number of action potentials were increased, whereas the latency of these responses decreased. In contrast, DA decreased the amplitude of the depolarizations and the number of action potentials evoked by glutamate or quisqualate. The fact that DA affects responses to NMDA and glutamate or quisqualate in opposite directions is of considerable importance to the understanding of cellular mechanisms of neuromodulation and the role of DA in cognitive processing and in epilepsy.

Arterial oxygen consumption after hemorrhagic shock: the effect of beta-adrenergic agonist

Oxygen consumption of the rabbit femoral artery after hemorrhagic shock was studied. Hemorrhagic shock was initiated and maintained at 60 mm Hg of systolic blood pressure for 2 hours. A significant reduction in femoral artery oxygen consumption was observed after hemorrhagic shock (1.64 +/- 0.14 microliter/g/hr) when compared to oxygen consumption in the normal condition (2.52 +/- 0.22 microliter/g/hr). Application of the beta-agonist isoproterenol significantly increased oxygen consumption in the isolated femoral artery after hemorrhagic shock (2.66 +/- 0.20 microliter/g/hr), but did not exceed the normal values recorded without stimulation. Also, isoproterenol significantly increased oxygen consumption in the femoral artery of nonhemorrhagic condition (4.84 +/- 0.42 microliter/g/hr). The increase in oxygen consumption conditioned by isoproterenol was significantly lower after hemorrhagic shock compared with values in the nonhemorrhagic state. The data suggest that oxygen consumption is regulated by beta-adrenergic receptors, and the phenomenon of diminished oxygen consumption after hemorrhagic shock probably occurs because of changes in beta-adrenergic receptors, causing the appearance of change in the mechanism of oxygen consumption.