Increased S-nitrosothiols and S-nitrosoalbumin in cerebrospinal fluid after severe traumatic brain injury in infants and children: indirect association with intracranial pressure

Protecting the injured central nervous system: Do anesthesia or hypothermia ameliorate secondary injury?

Traumatic injury to the central nervous system (CNS) and stroke initiate a cascade of processes that expand the area of tissue loss. The current review considers recent studies demonstrating that the induction of an anesthetic state or cooling the affected tissue (hypothermia) soon after injury can have a therapeutic effect. We first provide an overview of the neurobiological processes that fuel tissue loss after traumatic brain injury (TBI), spinal cord injury (SCI) and stroke. We then examine the rehabilitative effectiveness of therapeutic anesthesia across a variety of drug categories through a systematic review of papers in the PubMed database. We also review the therapeutic benefits hypothermia, another treatment that quells neural activity. We conclude by considering factors related to the safety, efficacy and timing of treatment, as well as the mechanisms of action. Clinical implications are also discussed.

Stability of S-nitrosothiols and S-nitrosylated proteins: A struggle for cellular existence!

Nitric oxide is a well-known gasotransmitter molecule that covalently docks to sulfhydryl groups of proteins resulting in S-nitrosylation of proteins and nonprotein thiols that serve a variety of cellular processes including cGMP signaling, vasodilatation, neurotransmission, ion-channel modulation, and cardiac signaling. S-nitrosylation is an indispensable modification like phosphorylation that directly regulates the functionality of numerous proteins. However, recently there has been a controversy over the stability of S-nitrosylated proteins (PSNOs) within the cell. It has been argued that PSNOs formed within the cell is a transient intermediate step to more stable disulfide formation and disulfides are the predominant end effector modifications in NO-mediated signaling. The present article accumulates state-of-the-art evidence from numerous research that strongly supports the very existence of PSNOs within the cell and attempts to put an end to the controversy. This review illustrates critical points including comparative bond dissociation energies of S-NO bond, the half-life of S-nitrosothiols and PSNOs, cellular concentrations of PSNOs, X ray crystallographic studies on PSNOs, and stability of PSNOs at physiological concentration of antioxidants. These logical evidence cumulatively support the endogenous stability and inevitable existence of PSNOs/RSNOs within the cell that directly regulate the functionality of proteins and provide valuable insight into understanding stable S-nitrosylation mediated cell signaling.

Enzyme Mimics for the Catalytic Generation of Nitric Oxide from Endogenous Prodrugs

The highly diverse biological roles of nitric oxide (NO) in both physiological and pathophysiological processes have prompted great interest in the use of NO as a therapeutic agent in various biomedical applications. NO can exert either protective or deleterious effects depending on its concentration and the location where it is delivered or generated. This double-edged attribute, together with the short half-life of NO in biological systems, poses a major challenge to the realization of the full therapeutic potential of this molecule. Controlled release strategies show an admirable degree of precision with regard to the spatiotemporal dosing of NO but are disadvantaged by the finite NO deliverable payload. In turn, enzyme-prodrug therapy techniques afford enhanced deliverable payload but are troubled by the inherent low stability of natural enzymes, as well as the requirement to control pharmacokinetics for the exogenous prodrugs. The past decade has seen the advent of a new paradigm in controlled delivery of NO, namely localized bioconversion of the endogenous prodrugs of NO, specifically by enzyme mimics. These early developments are presented, successes of this strategy are highlighted, and possible future work on this avenue of research is critically discussed.

Regulation of nerve growth and patterning by cell surface protein disulphide isomerase

Contact repulsion of growing axons is an essential mechanism for spinal nerve patterning. In birds and mammals the embryonic somites generate a linear series of impenetrable barriers, forcing axon growth cones to traverse one half of each somite as they extend towards their body targets. This study shows that protein disulphide isomerase provides a key component of these barriers, mediating contact repulsion at the cell surface in chick half-somites. Repulsion is reduced both in vivo and in vitro by a range of methods that inhibit enzyme activity. The activity is critical in initiating a nitric oxide/S-nitrosylation-dependent signal transduction pathway that regulates the growth cone cytoskeleton. Rat forebrain grey matter extracts contain a similar activity, and the enzyme is expressed at the surface of cultured human astrocytic cells and rat cortical astrocytes. We suggest this system is co-opted in the brain to counteract and regulate aberrant nerve terminal growth.

Cytoprotective effects of albumin, nitrosated or reduced, in cultured rat pulmonary vascular cells

S-nitrosoalbumin (SNO-Alb) has been shown to be an efficacious cytoprotective molecule in acute lung injury, as well as ischemia-reperfusion injury in heart and skeletal muscle. Nonetheless, limited information is available on the cellular mechanism of such protection. Accordingly, we investigated the protective effects of SNO-Alb [ and its denitrosated congener, reduced albumin (SH-Alb) ] on tert-butyl hydroperoxide (tBH)-mediated cytotoxicity in cultured rat pulmonary microvascular endothelial cells (RPMEC), as well as hydrogen sulfide (H(2)S)-mediated cytotoxicity in rat pulmonary artery smooth muscle cells (RPASMC). We noted that tBH caused a concentration-dependent necrosis in RPMEC, and pretreatment of RPMEC with SNO-Alb dose-dependently decreased the sensitivity of these cells to tBH. A component of SNO-Alb cytoprotection was sensitive to N(G)-nitro-L-arginine methyl ester and was associated with activation of endothelial nitric oxide synthase (eNOS), phenomena that could be reproduced with pretreatment with SH-Alb. Exogenous H(2)S caused concentration-dependent apoptosis in RPASMC due to activation of ERK1/2 and p38, as well as downregulation of Bcl-2. Pretreatment with SNO-Alb reduced H(2)S-mediated apoptosis in a concentration-dependent manner that was associated with SNO-Alb-mediated inhibition of activation of ERK1/2 and p38. Pretreatment with SNO-Alb reduced toxicity of 1 mM sodium hydrosulfide in an N(G)-nitro-L-arginine methyl ester-sensitive fashion in RPASMC that expressed gp60 and neuronal NOS and was capable of transporting fluorescently labeled SH-Alb. Therefore, SNO-Alb is cytoprotective against models of oxidant-induced necrosis (tBH) and inhibitors of cellular respiration and apoptosis (H(2)S) in both pulmonary endothelium and smooth muscle, respectively, and a component of such protection can be attributed to a SH-Alb-mediated activation of constitutive NOS.

Detectable levels of cytochrome C and activated caspase-9 in cerebrospinal fluid after human traumatic brain injury

BACKGROUND

The intrinsic pathway of apoptosis has been proposed as one mechanism of cell death after traumatic brain injury (TBI). This study tested the hypothesis that cytochrome c and activated caspase-9 are released into the cerebrospinal fluid (CSF) after severe TBI and that their presence correlates with mitochondrial injury and severity of neurologic outcome.

METHODS

Nine adult patients with severe TBI (GCS < or = 8) underwent placement of intraventricular catheters for monitoring and management of intracranial pressure. CSF was sampled at catheter insertion (2-26 h after injury) and at intervals of 24, 48, and 72 h thereafter. Control samples were obtained from patients undergoing spinal anesthesia (ASA1). CSF levels of cytochrome c and activated caspase-9 were measured using ELISA.

RESULTS

Cytochrome c was detected in 18 (51.4%) samples, in the range of 0.08-5 ng/ml; mean value for cytochrome c was 0.44 ng/ml (SD +/- 0.632). Activated caspase-9 was detected in 10 samples (28.6%); mean value was 0.28 ng/ml (SD +/- 0.39). R (s) between cytochrome c and Glasgow outcome score (GOS) was -0.25 (P = 0.14), and between GOS and activated caspase-9 was -0.35 (P = 0.04). R calculated based on linear regression of activated caspase-9 and cytochrome c concentrations was 0.18. Control CSF samples had no detectable levels of either marker (detection level for cytochrome c was 0.08 ng/ml and 0.20 for activated caspase-9).

CONCLUSIONS

We concluded that activated caspase-9 and cytochrome c are present in the CSF of patients with severe TBI. Activated caspase-9 shows weak correlation with poor neurologic outcome.

Drug targets for traumatic brain injury from poly(ADP-ribose)polymerase pathway modulation

The deleterious pathophysiological cascade induced after traumatic brain injury (TBI) is initiated by an excitotoxic process triggered by excessive glutamate release. Activation of the glutamatergic N-methyl-D-aspartate receptor, by increasing calcium influx, activates nitric oxide (NO) synthases leading to a toxic production of NO. Moreover, after TBI, free radicals are highly produced and participate to a deleterious oxidative stress. Evidence has showed that the major toxic effect of NO comes from its combination with superoxide anion leading to peroxynitrite formation, a highly reactive and oxidant compound. Indeed, peroxynitrite mediates nitrosative stress and is a potent inducer of cell death through its reaction with lipids, proteins and DNA. Particularly DNA damage, caused by both oxidative and nitrosative stresses, results in activation of poly(ADP-ribose) polymerase (PARP), a nuclear enzyme implicated in DNA repair. In response to excessive DNA damage, massive PARP activation leads to energetic depletion and finally to cell death. Since 10 years, accumulating data have showed that inactivation of PARP, either pharmacologically or using PARP null mice, induces neuroprotection in experimental models of TBI. Thus TBI generating NO, oxidative and nitrosative stresses promotes PARP activation contributing in post-traumatic motor, cognitive and histological sequelae. The mechanisms by which PARP inhibitors provide protection might not entirely be related to the preservation of cellular energy stores, but might also include other PARP-mediated mechanisms that needed to be explored in a TBI context. Ten years of experimental research provided rational basis for the development of PARP inhibitors as treatment for TBI.

Selective early cardiolipin peroxidation after traumatic brain injury: an oxidative lipidomics analysis

OBJECTIVE

Enhanced lipid peroxidation is well established in traumatic brain injury. However, its molecular targets, identity of peroxidized phospholipid species, and their signaling role have not been deciphered.

METHODS

Using controlled cortical impact as a model of traumatic brain injury, we employed a newly developed oxidative lipidomics approach to qualitatively and quantitatively characterize the lipid peroxidation response.

RESULTS

Electrospray ionization and matrix-assisted laser desorption/ionization mass spectrometry analysis of rat cortical mitochondrial/synaptosomal fractions demonstrated the presence of highly oxidizable molecular species containing C(22:6) fatty acid residues in all major classes of phospholipids. However, the pattern of phospholipid oxidation at 3 hours after injury displayed a nonrandom character independent of abundance of oxidizable species and included only one mitochondria-specific phospholipid, cardiolipin (CL). This selective CL peroxidation was followed at 24 hours by peroxidation of other phospholipids, most prominently phosphatidylserine, but also phosphatidylcholine and phosphatidylethanolamine. CL oxidation preceded appearance of biomarkers of apoptosis (caspase-3 activation, terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling-positivity) and oxidative stress (loss of glutathione and ascorbate).

INTERPRETATION

The temporal sequence combined with the recently demonstrated role of CL hydroperoxides (CL-OOH) in in vitro models of apoptosis suggest that CL-OOH may be both a key in vivo trigger of apoptotic cell death and a therapeutic target in experimental traumatic brain injury.

Nitrotyrosine as an Oxidative Stress Marker: Evidence for Involvement in Neurologic Outcome in Human Traumatic Brain Injury

BACKGROUND

Oxidative stress has been indicated as a mechanism of secondary neuronal injury in traumatic brain injury (TBI). Nitrotyrosine in the cerebrospinal fluid (CSF) may be an in vivo marker of oxidative nitric oxide damage. We tested the hypothesis that increased levels of nitrotyrosine correlate with poor neurologic outcomes in patients with TBI and attempted to identify the source of increased CSF nitrotyrosine.

METHODS

This institutional-review-board-approved study included 10 adults with severe closed TBI (Glasgow Coma Scale score <8) and no documented hypoxic brain injury. These patients underwent routine evaluation and, when indicated, placement of an intraventricular catheter. CSF samples (n = 27) were collected 2 to 72 hours after TBI and were also obtained from four healthy individuals. Nitrotyrosine levels were measured, and immunohistochemistry was performed. Neurologic follow-up extended to 1 month after injury.

RESULTS

Nitrotyrosine was not detected in the control samples but was detected in 13 CSF samples from 7 TBI patients (range, 22.4-97.6 nM/mL). Seven patients had poor outcomes, and, in each, nitrotyrosine was detected. Nitrotyrosine immunoreactivity was detected in neurons and glia and confirmed in brain homogenate.

CONCLUSION

Oxidative stress contributes to secondary brain injury in patients with TBI. Poor neurologic outcome is associated with increased levels of nitrotyrosine in the CSF. Identifying patients or the stage at which oxidative stress is more active using CSF markers of oxidative injury may help in the development of more targeted treatments.

Physiological and pathological changes in the redox state of human serum albumin critically influence its binding properties

Binding and transport of a number of endogenous and exogenous compounds is an important function of the main plasma protein, albumin. In vivo and in vitro, albumin may be oxidatively modified in different ways with different agents at different sites. These modifications have various consequences on the physiological functions of albumin. Diabetes mellitus, liver diseases and nephropathy are just a few examples of disorders in which oxidative stress is involved and altered albumin functions have been described. This review is focussed on the consequences of oxidative modification on the binding properties of albumin. These range from no effect to decreased or increased binding affinities depending on the ligand under investigation and the type of modification. Indicators for modification include glycosylation, disulphide formation or the content of carbonyl groups. The redox state of albumin can affect the binding properties in several ways, including altered conformation and consequently altered affinities at binding sites and altered binding when the binding reaction itself is redox sensitive. The physiological or pathophysiological concentrations of different oxidatively modified albumin molecules vary over a wide range and are crucial in assessing the clinical relevance of altered ligand binding properties of a particularly modified albumin species in various disease conditions.

Nitrosative stress inhibits the aminophospholipid translocase resulting in phosphatidylserine externalization and macrophage engulfment: implications for the resolution of inflammation

Macrophage recognition of apoptotic cells depends on externalization of phosphatidylserine (PS), which is normally maintained within the cytosolic leaflet of the plasma membrane by aminophospholipid translocase (APLT). APLT is sensitive to redox modifications of its -SH groups. Because activated macrophages produce reactive oxygen and nitrogen species, we hypothesized that macrophages can directly participate in apoptotic cell clearance by S-nitrosylation/oxidation and inhibition of APLT causing PS externalization. Here we report that exposure of target HL-60 cells to nitrosative stress inhibited APLT, induced PS externalization, and enhanced recognition and elimination of "nitrosatively" modified cells by RAW 264.7 macrophages. Using S-nitroso-L-cysteine-ethyl ester (SNCEE) and S-nitrosoglutathione (GSNO) that cause intracellular and extracellular trans-nitrosylation of proteins, respectively, we found that SNCEE (but not GSNO) caused significant S-nitrosylation/oxidation of thiols in HL-60 cells. SNCEE also strongly inhibited APLT, activated scramblase, and caused PS externalization. However, SNCEE did not induce caspase activation or nuclear condensation/fragmentation suggesting that PS externalization was dissociated from the common apoptotic pathway. Dithiothreitol reversed SNCEE-induced S-nitrosylation, APLT inhibition, and PS externalization. SNCEE but not GSNO stimulated phagocytosis of HL-60 cells. Moreover, phagocytosis of target cells by lipopolysaccharide-stimulated macrophages was significantly suppressed by an NO. scavenger, DAF-2. Thus, macrophage-induced nitrosylation/oxidation plays an important role in cell clearance, and hence in the resolution of inflammation.

Heterogeneity and oxidation status of commercial human albumin preparations in clinical use

OBJECTIVE

Human serum albumin is indicated for the treatment of shock, acute restoration of blood volume, and in hypoalbuminemia. Conflicting reports are found in the literature for the clinical safety and efficacy of human serum albumin administration to critically ill patients. We sought to analyze various commercially available albumin preparations for common, posttranslational modifications.

DESIGN

Analysis of six commercially available albumin preparations for clinical use.

SETTING

Trauma research laboratory.

SUBJECTS

Commercially available human serum albumin preparations and healthy volunteers.

INTERVENTIONS

Six commercially available human serum albumin preparations were analyzed by high-performance liquid chromatography. The presence of various posttranslational modifications was identified by positive electrospray ionization, time-of-flight mass spectrometry. Three different lots from three preparations were also analyzed to assess variability within lots from the same manufacturer. Also, for the purpose of comparison, human serum albumin was analyzed in the plasma of healthy volunteers.

MEASUREMENTS AND MAIN RESULTS

The six human serum albumin preparations analyzed contained a high percentage (57.2 +/- 3.3%) of bound Cys34 (oxidation of cysteine in position 34 on the human serum albumin molecule) in comparison to the plasma human serum albumin from healthy volunteers (22.9 +/- 4.8%). Lot-to-lot variability in native human serum albumin ranged between 4.8% and 11.2% in three separate commercial albumins. Significant differences existed among the various commercial preparations in other posttranslational modifications of albumin.

CONCLUSIONS

Human serum albumin species with a bound Cys34 account for a large percentage of the composition of human serum albumin preparations used for the treatment of critically ill patients. Also, the variability within lots from the same manufacturer is significant. Consequences of the administration of these oxidized forms of human serum albumin to critically ill patients warrants further investigation.

Enhanced oxidative stress in iNOS-deficient mice after traumatic brain injury: support for a neuroprotective role of iNOS

Studies in experimental traumatic brain injury (TBI) suggest both deleterious and protective effects of inducible nitric oxide synthase (iNOS). Early after injury, iNOS may be detrimental via formation of peroxynitrite and iNOS inhibitors are protective. In contrast, we reported impaired long-term functional outcome after TBI in iNOS knockout (ko) versus wild-type (wt) mice. To elucidate potential neuroprotective and neurotoxic mechanisms for iNOS, we studied nitric oxide formation by electron paramagnetic resonance (EPR) spectroscopy using diethyldithiocarbamate-iron (DETC-Fe) as a spin trap and markers of nitrosative (S-nitrosothiol (RSNO, Fluorescent assay); nitrotyrosine (3NT, ELISA)) and oxidative stress (ascorbate, HPLC) at 72 h after controlled cortical impact (CCI) in iNOS ko and wt and in uninjured iNOS ko and wt mice. 3NT immunostaining with macrophage and myeloperoxidase (MPO) dual labeling was also assessed in brain sections. Brain DETC-Fe-NO low-temperature EPR signal intensity was approximately 2-fold greater in wt versus iNOS ko at 72 h after CCI. Ascorbate levels decreased in injured hemisphere in wt and iNOS ko versus uninjured -this decrease was more pronounced in iNOS ko. In wt mice, RSNO and 3NT levels were increased after CCI versus uninjured (50% and 400%, respectively, P < 0.05). RSNO levels were not increased in iNOS ko after CCI. Nitrotyrosine levels increased after CCI in wt and ko versus respective uninjured -this increase was more pronounced in wt (2.34 +/- 0.95 versus 1.27 +/- 0.49 pmol/mg protein, P < 0.05). Increased 3NT immunoreactivity was detected in wt versus iNOS ko at 72 h after CCI, and colocalized with macrophage marker and MPO. Our data support a role for iNOS-derived NO as an endogenous antioxidant after CCI. iNOS also contributes protein nitrosylation and nitration. Colocalization of 3NT with macrophages and MPO suggests generation of nitrating agents by macrophages and/or phagocytosis of nitrated proteins.

ET-1 induces cortical spreading depression via activation of the ETA receptor/phospholipase C pathway in vivo

Recently, it has been shown that brain topical superfusion of endothelin (ET)-1 at concentrations around 100 nM induces repetitive cortical spreading depressions (CSDs) in vivo. It has remained unclear whether this effect of ET-1 is related to a primary neuronal/astroglial effect, such as an increase in neuronal excitability or induction of interastroglial calcium waves, or a penumbra-like condition after vasoconstriction. In vitro, ET-1 regulates interastroglial communication via combined activation of ET(A) and ET(B) receptors, whereas it induces vasoconstriction via single activation of ET(A) receptors. We have determined the ET receptor profile and intracellular signaling pathway of ET-1-induced CSDs in vivo. In contrast to the ET(B) receptor antagonist BQ-788 and concentration dependently, the ET(A) receptor antagonist BQ-123 completely blocked the occurrence of ET-1-induced CSDs. The ET(B) receptor antagonist did not increase the efficacy of the ET(A) receptor antagonist. Direct stimulation of ET(B) receptors with the selective ET(B) agonist BQ-3020 did not trigger CSDs. The phospholipase C (PLC) antagonist U-73122 inhibited CSD occurrence in contrast to the protein kinase C inhibitor Gö-6983. Our findings indicate that ET-1 induces CSDs through ET(A) receptor and PLC activation. We conclude that the induction of interastroglial calcium waves is unlikely the primary cause of ET-1-induced CSDs. On the basis of the receptor profile, likely primary targets of ET-1 mediating CSD are either neurons or vascular smooth muscle cells.