Hemoglobin augmentation of interleukin-1 beta-induced production of nitric oxide in smooth-muscle cells

Inducible nitric oxide synthase (NOS-2) in subarachnoid hemorrhage: Regulatory mechanisms and therapeutic implications

Aneurysmal subarachnoid hemorrhage (SAH) typically carries a poor prognosis. Growing evidence indicates that overabundant production of nitric oxide (NO) may be responsible for a large part of the secondary injury that follows SAH. Although SAH modulates the activity of all three isoforms of nitric oxide synthase (NOS), the inducible isoform, NOS-2, accounts for a majority of NO-mediated secondary injuries after SAH. Here, we review the indispensable physiological roles of NO that must be preserved, even while attempting to downmodulate the pathophysiologic effects of NO that are induced by SAH. We examine the effects of SAH on the function of the various NOS isoforms, with a particular focus on the pathological effects of NOS-2 and on the mechanisms responsible for its transcriptional upregulation. Finally, we review interventions to block NOS-2 upregulation or to counteract its effects, with an emphasis on the potential therapeutic strategies to improve outcomes in patients afflicted with SAH. There is still much to be learned regarding the apparently maladaptive response of NOS-2 and its harmful product NO in SAH. However, the available evidence points to crucial effects that, on balance, are adverse, making the NOS-2/NO/peroxynitrite axis an attractive therapeutic target in SAH.

Age-related changes in adrenomedullin expression and hypoxia-inducible factor-1 activity in the rat lung and their responses to hypoxia

Male rats aged 3 months, 12 months and 20 months were subjected to breathing 8% oxygen for 6 hours. Lung preproadrenomedullin (AM) messenger RNA (mRNA) levels were measured by solution hybridization-RNase protection assay while AM was measured by radioimmunoassay. The binding of hypoxia-inducible factor-1alpha (HIF-1alpha) to DNA was determined by electrophoretic mobility shift. There was an age-related increase in basal levels of preproAM mRNA and AM and of the binding of hypoxia-inducible factor (HIF) to DNA. Upon hypoxic stimulation, HIF binding to DNA increased in the young and middle-aged rats, but not in the old rats. AM gene expression increased in response to hypoxia in rats of all ages, but the increase was much less in the old rats. AM peptide levels in the lung decreased with age in hypoxia. In a separate experiment, male rats aged 3 months and 20 months were subjected to hypoxia as described above. PreproAM, calcitonin receptor-like receptor (CRLR), receptor activity modifying protein (RAMP) mRNA, HIF-1 and peptidyl-glycine-amidating monooxygenase (PAM) mRNA levels were measured by reverse transcription-polymerase chain reaction. All except PAM showed a decrease in basal levels and a diminished response to hypoxia in the old rats. Polysome profiling demonstrated decreases in the percentages of translatable preproAM mRNA in response to hypoxia, with a greater decrease in the old than the young rats. It is concluded that an age-dependent decrease in the hypoxic response of the AM system in the lung was associated with high basal levels of HIF activity and AM expression in the old rats, and a lower proportion of translatable preproAM mRNA in the old rats in response to hypoxia. Thus, the HIF-AM pathway may be impaired in the aged lung, and other mechanisms may be present to maintain an AM response to hypoxia.

Mathematical models of the acute inflammatory response

PURPOSE OF REVIEW

Trauma and infection elicit an acute inflammatory response. In certain circumstances the degree of the acute inflammatory response may result in pathologic manifestations, namely, sepsis and multiple organ failure. Despite an extensive series of clinical trials designed to modulate inflammation in sepsis, only one compound, activated protein C, has emerged from more than 250 failed trials. There is a growing recognition that the complexity of the acute inflammatory response precludes the efficient development of therapies for sepsis and multiple organ failure until systems approaches are brought to bear on this problem.

RECENT FINDINGS

Work carried out by the authors' groups suggests that mathematical modeling can provide a means by which in vitro and in vivo data can be synthesized into system-level analytic models of the acute inflammatory response. The authors have focused on agent-based modeling and modeling with ordinary differential equations. Some of the advantages and disadvantages of these modeling approaches are presented, and methods for calibration and validation of these models are discussed. Finally, the usefulness of mathematical models to evaluate the prospective therapeutic strategies in clinical trials of sepsis and trauma is examined.

SUMMARY

Simulations using various methods can shed insight into the pathophysiology of the acute inflammatory response and may lead to better design of clinical trials in sepsis and trauma.

Cerebrovascular inflammation following subarachnoid hemorrhage

Aneurysmal subarachnoid hemorrhage frequently results in complications including intracranial hypertension, rebleeding and vasospasm. The extravasated blood is responsible for a cascade of reactions involving release of various vasoactive and pro-inflammatory factors (several of which are purported to induce vasospasm) from blood and vascular components in the subarachnoid space. The authors review the available evidence linking these factors to the development of inflammatory lesions of the cerebral vasculature, emphasizing: 1) neurogenic inflammation due to massive release of sensory nerve neuropeptides; 2) hemoglobin from lysed erythrocytes, which creates functional lesions of endothelial and smooth muscle cells; 3) activity, expression and metabolites of lipoxygenases cyclooxygenases and nitric oxide synthases; 4) the possible role of endothelin-1 as a pro-inflammatory agent; 5) serotonin, histamine and bradykinin which are especially involved in blood-brain barrier disruption; 6) the prothrombotic and pro-inflammatory action of complement and thrombin towards endothelium; 7) the multiple actions of activated platelets, including platelet-derived growth factor production; 8) the presence of perivascular and intramural macrophages and granulocytes and their interaction with adhesion molecules; 9) the evolution, origins, and effects of pro-inflammatory cytokines, especially IL-1, TNF-alpha and IL-6. Human and animal studies on the use of anti-inflammatory agents in subarachnoid hemorrhage include superoxide and other radical scavengers, lipid peroxidation inhibitors, iron chelators, NSAIDs, glucocorticoids, and serine protease inhibitors. Many animal studies claim reduced vasospasm, but these effects are not always confirmed in human trials, where symptomatic vasospasm and outcome are the major endpoints. Despite recent work on penetrating vessel constriction, there is a paucity of studies on inflammatory markers in the microcirculation.

Expression of endothelial nitric oxide synthase after exposure to perivascular blood

OBJECTIVE

Although nitric oxide (NO) has been implicated in the development of vasospasm after subarachnoid hemorrhage, little is known regarding the time course of NO synthesis in vessel wall after exposure to perivascular blood. This study measures temporal characteristics of changes in vessel wall NO synthesis.

METHODS

Rat femoral arteries exposed to perivascular blood for 3, 5, or 7 days were assayed for the endothelial isoform of NO synthase (eNOS) by Western blot testing. Additionally, rat femoral arteries exposed to perivascular blood for intervals from 3 to 14 days were analyzed by means of immunohistochemistry for eNOS.

RESULTS

Semiquantitative densitometry of femoral artery Western blots demonstrated a biphasic pattern of eNOS expression after exposure to perivascular blood. Compared with control arteries, eNOS expression increased at 3 days (53 +/- 36%), normalized at 5 days (-6 +/- 7%), and decreased by 7 days (-39 +/- 15%). Immunohistochemistry confirmed the changes in expression of immunoreactive eNOS in femoral endothelium during the first week after chronic perivascular blood exposure and apparent reduced eNOS immunostaining, which persisted up to 14 days after application of blood.

CONCLUSION

The expression of endothelial-derived NO in rat femoral artery exposed to perivascular whole blood does not directly correlate with changes in vessel caliber during this interval. The biphasic expression of eNOS observed in these experiments highlights the complexity of processes occurring in the vicinity of the vessel wall during vasospasm and may be related to several mechanisms that modulate vessel tone and response to injury.

Inhibition of poly(ADP-ribose) polymerase attenuates cerebral vasospasm after subarachnoid hemorrhage in rabbits

BACKGROUND AND PURPOSE

Poly(ADP-ribose) polymerase (PARP) is important in modulating inflammation, which has been implicated in cerebral vasospasm after subarachnoid hemorrhage (SAH). We investigated the role of PARP in vasospasm using 3-aminobenzamide (3-AB), a PARP inhibitor, in a rabbit model.

METHODS

Twenty-four New Zealand White rabbits were divided into 4 groups: (1) no treatment (control group, n=6); (2) blood injection without pretreatment (SAH-only group, n=6); (3) blood injection with pretreatment by vehicle (SAH+vehicle group, n=6); and (4) blood injection with pretreatment by 3-AB (SAH+3-AB group, n=6). We used the single-hemorrhage model of SAH, injecting autologous arterial blood into the cisterna magna. Angiography was performed before (baseline) and after (day 2) SAH, and the diameter of the basilar artery (BA) was measured. Animals were euthanatized after the second angiogram. After perfusion and fixation, the brains were cut into sections for hematoxylin and eosin and immunohistochemical staining for poly(ADP-ribosyl)ation.

RESULTS

In the control group, there were no differences in the BA lumen caliber between baseline and day 2 (96.8+/-10.4%). Cerebral vasospasm in the SAH+3-AB group (88.2+/-6. 2%) was remarkably attenuated in comparison with that in the SAH-only group (64.9+/-8.0%) and the SAH+vehicle group (65.6+/-10. 8%). The BA in the SAH+3-AB group showed less corrugation of the tunica elastica interna than that in the SAH-only and SAH+vehicle groups. Staining for poly(ADP-ribosyl)ation was markedly inhibited in smooth muscle and adventitial cells of the BA in the SAH+3-AB group compared with other groups.

CONCLUSIONS

Inhibiting ADP-ribosylation attenuates cerebral vasospasm after SAH in rabbits, and PARP activation may play an important role in the development of cerebral vasospasm.

Inducible nitric oxide synthase: a possible key factor in the pathogenesis of chronic vasospasm after experimental subarachnoid hemorrhage

OBJECT

The role of nitric oxide (NO) in the pathogenesis of cerebral vasospasm after subarachnoid hemorrhage (SAH) is not well understood. Nitric oxide is a well-established vasodilatory substance; however, in SAH, NO may become a major source for the production of injurious free-radical species, leading to chronic cerebral vasospasm. Reactive overproduction of NO to counteract vascular narrowing might potentiate the detrimental effects of NO. The focus of the present study is to determine the extent of reactive induction of inducible nitric oxide synthase (iNOS) after experimental SAH.

METHODS

Chronic vasospasm was induced in male Wistar rats by an injection of autologous blood (100 microl) into the cisterna magna followed by a second injection 24 hours later. A control group of 10 animals was treated with injections of 0.9% sodium chloride solution. Vasospasm was verified by pressure-controlled angiography after retrograde cannulation of the external carotid artery 7 days later. In 11 of 15 animals radiographic evidence of cerebral vasospasm was seen. The animals were perfusion fixed and their brains were removed for immunohistochemical assessment. With the aid of a microscope, staining for iNOS was quantified in 40-microm floating coronal sections. Immunohistochemical staining for iNOS was markedly more intense in animals with significant angiographic evidence of vasospasm. Virtually no staining was observed in control animals. Seven days after the second experimental SAH, labeling of iNOS was found in endothelial cells, in vascular smooth-muscle cells, and, above all, in adventitial cells. Some immunohistochemical staining of iNOS was observed in rod cells (activated microglia), in glial networks, and in neurons.

CONCLUSIONS

The present study demonstrates induction of iNOS after experimental SAH.

Intracranial aneurysms and subarachnoid hemorrhage management of the poor grade patient

Between 20 and 30% of patients who suffer cerebral aneurysm rupture are in poor clinical grade when first evaluated. Management of these patients is controversial and challenging but can be successful with an aggressive proactive approach that begins with in the field resuscitation and continues through rehabilitation. In this article we review the epidemiology, pathology and pathophysiology, clinical features, evaluation, surgical and endovascular management, critical care, cost, and outcome prediction of patients in poor clinical grade after subarachnoid hemorrhage.

Subarachnoid hemorrhage in rats: effect of singular or sustained hemodilution with alpha-alpha diaspirin crosslinked hemoglobin on cerebral hypoperfusion

OBJECTIVE

To evaluate the effect of singular or sustained hemodilution, with alpha-alpha diaspirin crosslinked hemoglobin (DCLHb), on the area of hypoperfusion after subarachnoid hemorrhage.

DESIGN

Prospective animal study.

SETTING

Animal research laboratory.

SUBJECTS

Isoflurane anesthetized, mechanically ventilated rats.

INTERVENTIONS

Subarachnoid hemorrhage was induced by injecting 0.3 mL of blood into the cisterna magna. The animals were randomly assigned to one of the following groups (n = 16 in each hemodilution group; eight animals received a single treatment of hemodilution after subarachnoid hemorrhage; and, for eight animals, treatment was sustained for 48 hrs): control group (n = 8), no hematocrit (45%) manipulation; DCLHb group (n = 16), hematocrit decreased to 30% with DCLHb; or Alb group (n = 16), hematocrit decreased to 30% with human serum albumin. After 48 hrs, the area of hypoperfusion (cerebral blood flow < 40 ml/100g/min) was determined with 14C-iodoantipyrine in five coronal brain sections.

MEASUREMENTS AND MAIN RESULTS

For both singular and sustained treatment, the area of hypoperfusion was less in both hemodilution groups than in the control group (p<.05). For four of the five coronal brain sections, no differences were found between the DCLHb and Alb groups within a given hemodilution protocol. In addition, in four of the five coronal brain sections for the DCLHb hemodilution groups and in all five sections for the albumin hemodilution groups, the area of hypoperfusion was less for rats that received sustained hemodilution compared with their respective groups in the singular treatment protocol (p<.05).

CONCLUSIONS

These data support the hypothesis that hemodilution with molecular hemoglobin decreases hypoperfusion after subarachnoid hemorrhage and that sustained hemodilution is more effective than singular treatment. The data do not support the notion that intravascular DCLHb has an adverse effect on cerebral ischemia after subarachnoid hemorrhage.

Cerebrospinal fluid interleukin-1 receptor antagonist and tumor necrosis factor-alpha following subarachnoid hemorrhage

Subarachnoid hemorrhage (SAH) causes an inflammatory reaction and may lead to ischemic brain damage. Experimental ischemia has been shown to be connected with the alarm-reaction cytokines interleukin-1 receptor antagonist (IL-1Ra) and tumor necrosis factor-alpha (TNF alpha). Increased levels of these cytokines, however, have not been detected thus far in patients following an SAH event. For this reason daily cerebrospinal fluid (CSF) samples were collected from 22 consecutively enrolled patients with SAH and from 10 non-SAH patients (controls). The CSF samples were studied using immunoassays for IL-1Ra and TNF alpha to investigate whether an SAH caused increased cytokine levels. The mean IL-1Ra levels were significantly higher in patients with SAH who were in poor clinical condition on admission than in those who were in good condition (318 pg/ml vs. 82 pg/ml, p < 0.02). The IL-1Ra levels increased during delayed ischemic episodes and after surgery in patients who were in poor clinical condition. Significant increases in IL-1Ra and TNF alpha were detected during Days 4 through 10 in patients suffering from SAH who eventually had a poor outcome (p < 0.05). Patients with good outcomes and control patients had low levels of these cytokines. The levels of IL-1Ra increased after surgery in patients with Hunt and Hess Grades III through V, but not in those with Grade I or II. This finding indicates that patients in poor clinical condition have a labile biochemical state in the brain that is reflected in increased cytokine levels following the surgical trauma. Both IL-1Ra and TNF alpha are known to induce fever, malaise, leukocytosis, and nitric oxide synthesis and to mediate ischemic and traumatic brain injuries. The present study shows that levels of these cytokines increase after SAH occurs and that high cytokine levels correlate with brain damage. It is therefore likely that fever, leukocytosis, and nitric oxide synthesis are also mediated by IL-1 in patients suffering from SAH and it is probable that the inflammatory mediators contribute to brain damage.

Impairment of the modulatory role of nitric oxide on the endothelin-1-elicited contraction of cerebral arteries: a pathogenetic factor in cerebral vasospasm after subarachnoid hemorrhage?

OBJECTIVE

Nitric oxide (NO) and endothelin-1 (ET-1) are two endothelium-derived factors probably involved in the pathogenesis of cerebral vasospasm after subarachnoid hemorrhage (SAH). Our aim was twofold, i.e., to ascertain whether endothelial and nonendothelial NO modulates the contractile response of cerebral arteries to ET-1 and to analyze whether this relationship might be impaired after experimental SAH.

METHODS

Rings of middle cerebral artery from goats in the control group and from goats with SAH were set up for isometric tension recordings. SAH was induced 3 days before the experiments by infusion of 10 ml of autologous arterial blood through a catheter previously inserted into the subarachnoid space (basal cistern). In goats in the control group, the response to ET-1 was obtained as follows: 1) in control arteries (unrubbed and nonincubated arteries); 2) in rubbed arteries (arteries in which the endothelium was mechanically removed); 3) during incubation with NG-nitro-L-arginine (L-NOArg) alone or plus L- or D-arginine; and 4) in rubbed arteries plus incubation with L-NOArg. In goats with SAH, that response was obtained in control arteries, rubbed arteries, and during incubation with L-NOArg. Specimens of middle cerebral artery were processed for transmission electron microscopy study.

RESULTS

In goats in the control group, ET-1 elicited concentration-dependent contraction of the middle cerebral artery that was significantly potentiated after endothelium denudation or during incubation with L-NOArg. The latter effect was reversed by L-arginine but not by D-arginine. Combined endothelium denudation and incubation with L-NOArg produced a contractile response to ET-1 significantly higher than that induced by each treatment separately. Hyperreactivity to ET-1 was observed in goats with SAH. Endothelium denudation did not alter the enhanced response to ET-1, but it was further significantly increased after incubation with L-NOArg.

CONCLUSION

These results demonstrate that an ET-1-NO interaction exists in control cerebral arteries in such a way that endothelial and nonendothelial NO partially counteract the contractile response to ET-1 and that although SAH did not modify the effect of nonendothelial NO, the absence of endothelial NO after SAH may contribute to the hyperreactivity of cerebral arteries to ET-1 and, thereby, to the development of cerebral vasospasm.

Effect of subarachnoid administration of alpha-alpha diaspirin crosslinked hemoglobin on cerebral blood flow in rats

As extravasated red blood cells have been implicated in the pathogenesis of perfusion deficits after subarachnoid hemorrhage, alpha-alpha diaspirin crosslinked hemoglobin (DCLHb) might have a detrimental effect on cerebral perfusion after subarachnoid hemorrhage. We evaluated the effect of subarachnoid administration of DCLHb on cerebral blood flow (CBF). Rats were randomized to receive one of the following solutions into the cisterna magna: Control-0.3 ml of mock cerebrospinal fluid; Blood-0.3 ml of autologous blood; DCLHb-0.3 ml of 10% DCLHb. After 20-min, the area of cerebral hypoperfusion was determined (CBF < 40 ml.100g-1.min-1). The area of hypoperfusion (% area of a coronal brain section, mean +/- SD) was greater in the Blood group (58 +/- 16) than the DCLHb (16 +/- 7) and Control (5 +/- 5) groups (p < 0.05), and was greater in the DCLHb group than the Control group (p < 0.05). These data support a hypothesis that extravasation of blood from the intravascular to the subarachnoid space induces cerebral hypoperfusion. Moreover, the data support the hypothesis that although extravasated molecular hemoglobin decreases CBF, the adverse effect is not as severe as a similar volume of blood.

Hypertensive, hypervolemic, hemodilutional therapy for aneurysmal subarachnoid hemorrhage. Is it efficacious? No

Many neurosurgeons routinely use hypertensive, hypervolemic, hemodilutional, or hyperdynamic therapy (HT) in some form to prevent or to treat vasospasm. Despite the widespread use of this therapy during the past 20 years, however, there are no randomized, prospective, controlled clinical studies demonstrating that HT improves the short- or long-term neurologic outcome or survival after subarachnoid hemorrhage. Guidelines need to be developed to standardize the clinical application of HT, and well-controlled, prospective, randomized clinical trials must be conducted before HT can become an accepted treatment for vasospasm.

Hemin activation of an inducible isoform of nitric oxide synthase in vascular smooth-muscle cells

Hemin is a prominent breakdown product of hemoglobin, and high levels of hemin are found in the cerebrospinal fluid during subarachnoid hemorrhage-induced vasospasm. The possible role of hemin in modifying vascular function was examined in the present study by testing its effects on nitric oxide synthase (NOS) activity in cultured rat aortic smooth-muscle cells. Nitric oxide synthase activity was estimated from the amounts of accumulated nitrite and nitrate, which are oxidative products of nitric oxide (NO). Hemin (1-100 microM) increased the levels of nitrite and nitrate in culture medium in a dose- and time-dependent manner. The hemin-induced elevation of nitrite and nitrate was inhibited significantly by the NOS inhibitor, N omega-nitro-L-arginine (300 microM), and by the protein synthesis inhibitor, cycloheximide (5 micrograms/ml). These results indicate that hemin is capable of stimulating the expression of an inducible isoform of NOS (iNOS) in vascular smooth muscle. Transcriptional expression of iNOS is known to cause injurious effects on the maintenance of cellular homeostasis by generating extremely high levels of NO. The generation of hemin from methemoglobin during hemolysis of a subarachnoid blood clot could therefore stimulate an excessive production of NO in vascular smooth-muscle cells. It is postulated that this series of events contributes to the development of vascular injury associated with cerebral vasospasm after aneurysmal subarachnoid hemorrhage.