Impact of early transcranial Doppler screening and intensive therapy on cerebral vasculopathy outcome in a newborn sickle cell anemia cohort.

Transcranial Doppler (TCD) is used to detect children with sickle cell anemia (SCA) who are at risk for stroke, and transfusion programs significantly reduce stroke risk in patients with abnormal TCD. We describe the predictive factors and outcomes of cerebral vasculopathy in the Créteil newborn SCA cohort (n = 217 SS/Sß(0)), who were early and yearly screened with TCD since 1992. Magnetic resonance imaging/magnetic resonance angiography was performed every 2 years after age 5 (or earlier in case of abnormal TCD). A transfusion program was recommended to patients with abnormal TCD and/or stenoses, hydroxyurea to symptomatic patients in absence of macrovasculopathy, and stem cell transplantation to those with human leukocyte antigen-genoidentical donor. Mean follow-up was 7.7 years (1609 patient-years). The cumulative risks by age 18 years were 1.9% (95% confidence interval [95% CI] 0.6%-5.9%) for overt stroke, 29.6% (95% CI 22.8%-38%) for abnormal TCD, which reached a plateau at age 9, whereas they were 22.6% (95% CI 15.0%-33.2%) for stenosis and 37.1% (95% CI 26.3%-50.7%) for silent stroke by age 14. Cumulating all events (stroke, abnormal TCD, stenoses, silent strokes), the cerebral risk by age 14 was 49.9% (95% CI 40.5%-59.3%); the independent predictive factors for cerebral risk were baseline reticulocytes count (hazard ratio 1.003/L × 10(9)/L increase, 95% CI 1.000-1.006; P = .04) and lactate dehydrogenase level (hazard ratio 2.78/1 IU/mL increase, 95% CI1.33-5.81; P = .007). Thus, early TCD screening and intensification therapy allowed the reduction of stroke-risk by age 18 from the previously reported 11% to 1.9%. In contrast, the 50% cumulative cerebral risk suggests the need for more preventive intervention.

G6PD deficiency, absence of alpha-thalassemia, and hemolytic rate at baseline are significant independent risk factors for abnormally high cerebral velocities in patients with sickle cell anemia.

Stroke is predicted by abnormally high cerebral velocities by transcranial doppler (TCD). This study aimed at defining predictive factors for abnormally high velocities (>/= 2 m/sec) based on the Créteil pediatric sickle cell anemia (SCA) cohort composed of 373 stroke-free SCA children. alpha genes and beta-globin haplotypes were determined. Biologic parameters were obtained at baseline. alpha-thalassemia was present in 155 of 325 and G6PD deficiency in 36 of 325 evaluated patients. TCD was abnormal in 62 of 373 patients. Multivariate logistic regression analysis showed that G6PD deficiency (odds ratio [OR] = 3.36, 95% confidence interval [CI] 1.10-10.33; P = .034), absence of alpha-thalassemia (OR = 6.45, 95% CI 2.21-18.87; P = .001), hemoglobin (OR per g/dL = 0.63, 95% CI 0.41-0.97; P = .038), and lactate dehydrogenase (LDH) levels (OR per IU/L = 1.001, 95% CI 1.000-1.002; P = .047) were independent risk factors for abnormally high velocities. This study confirms the protective effect of alpha-thalassemia and shows for the first time that G6PD deficiency and hemolysis independently increase the risk of cerebral vasculopathy.

Mitogen-activated protein kinase assays.

Polymorphonuclear neutrophils (PMN) play an essential role in host defense against bacteria and fungi through coordinated responses such as adhesion, migration, phagocytosis, secretion, and activation of the NADPH oxidase. The mitogen-activated protein kinases (MAPKs) and their activation kinase cascades, which transduce signals from the plasma membrane to the cytosol and nucleus, are an integral part of signaling pathways involved in many cellular responses. PMN express several members of the MAPK family that have been shown, mainly through the use of pharmacological inhibitors, to mediate the cellular activities triggered by a variety of extracellular agonists. Methods to determine MAPK activation have been greatly simplified with the availability of antibodies raised to active MAPKs. The recent development of novel inhibitors for the MAPK pathways may further our understanding of their role in neutrophil function.

Stimulation of the alveolar macrophage respiratory burst by ADP causes selective glutathionylation of protein tyrosine phosphatase 1B.

H(2)O(2) produced by stimulation of the macrophage NADPH oxidase is involved both in bacterial killing and as a second messenger in these cells. Protein tyrosine phosphatases (PTPs) are targets for H(2)O(2) signaling through oxidation of their catalytic cysteine, resulting in inhibition of their activity. Here, we show that, in the rat alveolar macrophage NR8383 cell line, H(2)O(2) produced through the ADP-stimulated respiratory burst induces the formation of a disulfide bond between PTP1B and GSH that was detectable with an antibody to glutathione-protein complexes and was reversed by DTT addition. PTP1B glutathionylation was dependent on H(2)O(2) as the presence of catalase at the time of ADP stimulation inhibited the formation of the conjugate. Interestingly, other PTPs, i.e., SHP-1 and SHP-2, did not undergo glutathionylation in response to ADP stimulation of the respiratory burst, although glutathionylation of these proteins could be shown by reaction with 25 mM glutathione disulfide in vitro. While previous studies have suggested the reversible oxidation of PTP1B during signaling or showed PTP1B glutathionylation in vitro, the present study directly demonstrates that physiological stimulation of H(2)O(2) production results in PTP1B glutathionylation in intact cells, which may affect downstream signaling.

The ADP-stimulated NADPH oxidase activates the ASK-1/MKK4/JNK pathway in alveolar macrophages.

The role of H2O2 as a second messenger in signal transduction pathways is well established. We show here that the NADPH oxidase-dependent production of O2*(-) and H2O2 or respiratory burst in alveolar macrophages (AM) (NR8383 cells) is required for ADP-stimulated c-Jun phosphorylation and the activation of JNK1/2, MKK4 (but not MKK7) and apoptosis signal-regulating kinase-1 (ASK1). ASK1 binds only to the reduced form of thioredoxin (Trx). ADP induced the dissociation of ASK1/Trx complex and thus resulted in ASK1 activation, as assessed by phosphorylation at Thr845, which was enhanced after treatment with aurothioglucose (ATG), an inhibitor of Trx reductase. While dissociation of the complex implies Trx oxidation, protein electrophoretic mobility shift assay detected oxidation of Trx only after bolus H2O2 but not after ADP stimulation. These results demonstrate that the ADP-stimulated respiratory burst activated the ASK1-MKK4-JNK1/c-Jun signaling pathway in AM and suggest that transient and localized oxidation of Trx by the NADPH oxidase-mediated generation of H2O2 may play a critical role in ASK1 activation and the inflammatory response.

Glutathione, stress responses, and redox signaling in lung inflammation.

Changes in the ratio of intracellular reduced and disulfide forms of glutathione (GSH/GSSG) can affect signaling pathways that participate in various physiological responses from cell proliferation to gene expression and apoptosis. It is also now known that many proteins have a highly conserved cysteine (sulfhydryl) sequence in their active/regulatory sites, which are primary targets of oxidative modifications and thus important components of redox signaling. However, the mechanism by which oxidants and GSH/protein-cysteine-thiols actually participate in redox signaling still remains to be elucidated. Initial studies involving the role of cysteine in various proteins have revealed that cysteine-SH may mediate redox signaling via reversible or irreversible oxidative modification to Cys-sulfenate or Cys-sulfinate and Cys-sulfonate species, respectively. Oxidative stress possibly via the modification of cysteine residues activates multiple stress kinase pathways and transcription factors nuclear factor-kappaB and activator protein-1, which differentially regulate the genes for proinflammatory cytokines as well as the protective antioxidant genes. Understanding the redox signaling mechanisms for differential gene regulation may allow for the development of novel pharmacological approaches that preferentially up-regulate key antioxidants genes, which, in turn, reduce or resolve inflammation and injury. This forum article features the current knowledge on the role of GSH in redox signaling, particularly the regulation of transcription factors and downstream signaling in lung inflammation.

Mitogen-activated protein kinase pathways in redox signaling.

It has been known for quite some time that proper cellular function requires tight control of the cellular redox state. In recent years, a growing body of literature has provided evidence of a role for reactive oxygen species (ROS) as important mediators of proliferation, acting as second messengers to modulate the activation of various signaling molecules and pathways. In contrast to high levels of ROS that may induce modifications that inhibit the activity of cellular components or result in damage, repair and cell death, the hypothesis that low levels of ROS, produced enzymatically and in a regulated fashion, are required participants of signaling pathways controlling essential cellular function is gaining grounds. The concept that ROS specifically target components of these pathways is only beginning to be examined. The mitogen-activated protein kinases (MAPK) are a large family of proline-directed, serine/threonine kinases that require tyrosine and threonine phosphorylation of a ThrXTyr motif in the activation loop for activation. Receptor-ligand interaction leads to activation of a phosphorylation cascade where the minimal module is formed by MAPK, MAPK kinase and MAPK kinase kinase. Four separate MAPK and activating cascades have been identified, based on the TXY motif and the dual-specificity kinases that strictly phosphorylate their particular TXY sequence. They are the extracellular signal regulated kinases (ERK), c-jun N-terminal kinases (JNK), p38MAPK and ERK5. This review will summarize recent findings regarding the activation of the MAPK and the role played by ROS in their activation.

Redox signaling and the MAP kinase pathways.

The mitogen-activated protein (MAP) kinases are a large family of proline-directed, serine/threonine kinases that require tyrosine and threonine phosphorylation of a TxY motif in the activation loop for activation through a phosphorylation cascade involving a MAPKKK, MAPKK and MAPK, often referred to as the MAP kinase module. Three separate such modules have been identified, based on the TxY motif of the MAP kinase and the dual-specificity kinases that strictly phosphorylate their specific TxY sequence. They are the extracellular signal regulated kinases (ERKs), c-jun N-terminal kinases (JNKs) and p38 MAPKs. The ERKs are mainly associated with proliferation and differentiation while the JNKs and p38MAP kinases regulate responses to cellular stresses. Redox homeostasis is critical for proper cellular function. While reactive oxygen species (ROS) and oxidative stress have been implicated in injury, a rapidly growing literature suggests that a transient increase in ROS levels is an important mediator of proliferation and results in activation of various signaling molecules and pathways, among which the MAP kinases. This review will summarize the role of ROS in MAP kinase activation in various systems, including in macrophages, cells of myeloid origin that play an essential role in inflammation and express a multi-component NADPH oxidase that catalyzes the receptor-regulated production of ROS.

Reactive oxygen species and cell signaling: respiratory burst in macrophage signaling.

Phagocytes such as neutrophils and macrophages produce reactive oxygen species (ROS) during phagocytosis or stimulation with a wide variety of agents through activation of nicotinamide adenine dinucleotide phosphate reduced (NADPH) oxidase that is assembled at the plasma membrane from resident plasma membrane and cytosolic protein components. One of the subunits of the phagocyte NADPH oxidase is now recognized as a member of a family of NADPH oxidases, or NOX, present in cells other than phagocytes. Physiologic generation of ROS has been implicated in a variety of physiologic responses from transcriptional activation to cell proliferation and apoptosis. The increase in superoxide and hydrogen peroxide (H2O2) that results from stimulation of the NADPH oxidase is transient, in part due to the presence of the antioxidant enzymes, which return their concentrations to the prestimulation steady state level. Thus, the antioxidant enzymes may function in the "turn-off" phase of signal transduction by ROS. During its transient elevation, H2O2 may act as a modifier of key signaling enzymes through reversible oxidation of critical thiols. The rapid reaction of thiols with H2O2 when in their unprotonated state would provide a potential mechanism for the specificity that is necessary for physiologic cell signaling.

Redox signaling: thiol chemistry defines which reactive oxygen and nitrogen species can act as second messengers.

Except for the role of NO in the activation of guanylate cyclase, which is well established, the involvement of reactive oxygen species (ROS) and reactive nitrogen species (RNS) in signal transduction remains controversial, despite a large body of evidence suggestive of their participation in a variety of signaling pathways. Several problems have limited their acceptance as signaling molecules, with the major one being the difficulty in identifying the specific targets for each pathway and the chemical reactions supporting reversible oxidation of these signaling components, consistent with a second messenger role for ROS and RNS. Nevertheless, it has become clear that cysteine residues in the thiolate (i.e., ionized) form that are found in some proteins can be specific targets for reaction with H(2)O(2) and RNS. This review focuses on the chemistry of the reversible oxidation of those thiolates, with a particular emphasis on the critical thiolate found in protein tyrosine phosphatases as an example.

Redox signaling.

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) have recently been shown to be involved in a multiplicity of physiological responses through modulation of signaling pathways. Some of the specific signaling components altered by reactive oxygen and nitrogen species (RONS) have begun to be identified. We will discuss RONS signaling by detailing the chemistry of signaling, the roles of antioxidant enzymes as signaling components, thiol chemistry in the specificity of RONS signaling, .NO-heme interactions, and some do's and don'ts of redox signal research. The principal points raised are that: (1) as with classic signaling pathways, signaling by RONS is regulated; (2) antioxidant enzymes are essential 'turn-off components in signaling; (3) spatial relationships are probably more important in RONS signaling than the overall 'redox state' of the cell; (4) deprotonation of cysteines to form the thiolate, which can react with RONS, occurs in specific protein sites providing specificity in signaling; (5) although multiple chemical mechanisms exist for producing nitrosothiols, their formation in vivo remains unclear; and (6) caution should be taken in the use of 'antioxidants' in signal transduction.

Bio-effectiveness of Tat-catalase conjugate: a potential tool for the identification of H2O2-dependent cellular signal transduction pathways.

Reactive oxygen species such as hydrogen peroxide (H(2)O(2)) have taken center stage as bona fide second messengers in various signaling pathways. Here, we report the synthesis, metabolic fate, and effectiveness in modulating such pathways of a Tat-catalase conjugate. Incubation of L2 cells with Tat-catalase greatly increased cell-associated enzymatic activity, reaching close to a plateau by 30 min. The cell-associated catalase activity and antibody-detectable Tat-derivatives declined over time after changing medium, although still remaining at significantly higher levels than baseline even at 4h. While most cell-associated Tat-catalase was apparently tightly attached to the cell surface, a small fraction entered the cells as the proteasome inhibitor MG-132 slightly prevented the disappearance of the enzyme. Tat-catalase, either membrane-bound or intracellular, but not native catalase, inhibited serum-induced Elk phosphorylation and anisomycin- and/or MG-132-induced ERK phosphorylation, suggesting the involvement of H(2)O(2). Thus, Tat-catalase should be a useful tool to dissect H(2)O(2)-dependent events in signaling pathways.