Molecular Mechanisms for Regulation of Neutrophil Apoptosis under Normal and Pathological Conditions.

Neutrophils are one of the main cells of innate immunity that perform a key effector and regulatory function in the development of the human inflammatory response. Apoptotic forms of neutrophils are important for regulating the intensity of inflammation and restoring tissue homeostasis. This review summarizes current data on the molecular mechanisms of modulation of neutrophil apoptosis by the main regulatory factors of the inflammatory response-cytokines, integrins, and structural components of bacteria. Disturbances in neutrophil apoptosis under stress are also considered, molecular markers of changes in neutrophil lifespan associated with various diseases and pathological conditions are presented, and data on pharmacological agents for modulating apoptosis as potential therapeutics are also discussed.

[JUN N-TERMINAL KINASES AND THEIR PHARMACOLOGICAL MODULATION OF ISCHE-MIC AND REPERFUSION INJURY OF THE BRAIN].

The article reviews the literature regarding the role of c-Jun-N-terminal kinases (JNK) and its inhibitors in brain damage in the settings of ischemia and reperfusion injury. The implication of JNK in signaling mechanisms involved in ischemia-reperfusion-induced cerebral injury are discussed. Described effects associated with JNK inhibition using synthetic and natural substances in experimental models of ischemic and reperfusion injury of the brain. Results of experimental studies demonstrated that JNK represent promising therapeutic targets for brain protection against ischemic stroke. However, multiple physiologic functions of various JNK family members do not allow for the systemic use of non-specific JNK inhibitors for therapeutic purposes. The authors conclude that the continuous search for selective inhibitors of JNK3 remains an important task.

In vivo quantification of transvascular water exchange during the acute phase of permanent stroke.

Mechanisms that underlie early ischemic damages to the blood-brain-barrier (BBB) are not well understood. This study presents a novel magnetic resonance imaging (MRI) technique using a widely available pulse sequence and a long-circulating intravascular contrast agent to quantify water movements across the BBB at early stages of stroke progression. We characterized the integrity of the BBB by measuring the flip angle dependence of the water exchange-affected MRI signal intensity, to generate an efficient quantitative index of vascular permeability (WEI, or water exchange index). We performed in vivo MRI experiments to measure the transvascular WEI immediately after the permanent filament occlusion of the middle cerebral artery of mice (n = 5), in which we monitored changes in blood volume (V(b)), apparent diffusion coefficient (ADC), and intra-/extravascular WEI for 4 hours. Statistically significant elevations (P < 0.05) of WEI in the ischemic tissue were observed as early as 1 hour after ischemic onset. Initial reduction of the apparent blood volume (V(app)) in the infarct cortex was followed by a continuous increase of V(app) over time. Although the measured ADC in the ipsilesional cortex continuously decreased, the abnormally high intra-/extravascular WEI remained constant at a significantly elevated level, indicating apparent BBB injury at this early stage of stroke.

Mouse model of microembolic stroke and reperfusion.

BACKGROUND AND PURPOSE: To test the role of fibrinolysis in stroke, we used a mouse model in which preformed 2.5- to 3-microm-diameter fibrin microemboli are injected into the cerebral circulation. The microemboli lodge in the downstream precapillary vasculature and are susceptible to fibrinolysis. METHODS: We injected various doses of microemboli into the internal carotid artery in mice and characterized their distribution, effects on cerebral blood flow, neurological deficit, infarct area, and spontaneous dissolution. By comparing wild-type and tissue plasminogen activator (tPA) knockout (tPA-/-) mice, we analyzed the role of endogenous tPA in acute thrombotic stroke. RESULTS: Microemboli cause dose-dependent brain injury. Although moderate doses of microemboli are followed by spontaneous reperfusion, they result in reproducible injury. Gene knockout of tPA markedly delays dissolution of cerebral emboli and restoration of blood flow and aggravates ischemic thrombotic infarction in the brain. CONCLUSIONS: We describe a microembolic model of stroke, in which degree of injury can be controlled by the dose of microemboli injected. Unlike vessel occlusion models, this model can be modulated to allow spontaneous fibrinolysis. Application to tPA-/- mice supports a key role of endogenous tPA in restoring cerebral blood flow and limiting infarct size after thrombosis.

Contributions of endothelial and neuronal nitric oxide synthases to cerebrovascular responses to hyperoxia.

Hyperoxia causes a transient decrease in CBF, followed by a later rise. The mediators of these effects are not known. We used mice lacking endothelial or neuronal nitric oxide synthase (NOS) isoforms (eNOS-/- and nNOS-/- mice) to study the roles of the NOS isoforms in mediating changes in cerebral vascular tone in response to hyperoxia. Resting regional cerebral blood flow (rCBF) did not differ between wild type (WT), eNOS-/- mice, and nNOS-/- mice. eNOS-/- mice showed decreased cerebrovascular reactivities to NG-nitro-L-arginine methyl ester (L-NAME), PAPA NONOate, acetylcholine (Ach), and SOD1. In response to hyperbaric oxygen (HBO2) at 5 ATA, WT and nNOS-/- mice showed decreases in rCBF over 30 minutes, but eNOS-/- mice did not. After 60 minutes HBO2, rCBF increased more in WT mice than in eNOS-/- or nNOS-/- mice. Brain NO-metabolites (NOx) decreased in WT and eNOS-/- mice within 30 minutes of HBO2, but after 45 minutes, NOx rose above control levels, whereas they did not change in nNOS-/- mice. Brain 3NT increased during HBO2 in WT and eNOS-/- but did not change in nNOS-/- mice. These results suggest that modulation of eNOS-derived NO by HBO2 is responsible for the early vasoconstriction responses, whereas late HBO2-induced vasodilation depends upon both eNOS and nNOS.

[Hyperbaric oxygen inhibits neutrophil infiltration and reduces postischemic brain injury in rats]. / Giperbaricheskii kislorod ingibiruet infil'tratsiiu neitrofilov i oslabliaet postishemicheskoe porazhenie mozga u krys.

Reversible occlusion of the middle cerebral artery (MCA) was used to test hypothesis that hyperbaric oxygen inhibits the neutrophile infiltration into the ischemic brain thus reducing the brain injury. Treatment with hyperbaric oxygen prior to ischemia or during MCA occlusion significantly reduced neutrophile infiltration, motor disorders, and cerebral infarction volume.

[Involvement of nitrogen oxide in the cerebral vasoconstriction during respiration with high pressure oxygen]. / Rol' oksida azota v tserebral'noi vazokonstriktsii u krys pri dykhanii kislorodom pod davleniiem.

High pressure oxygen evokes a cerebral vasoconstriction and diminishes cerebral blood flow with the aid of mechanisms which are not yet sufficiently studied. We were checking a hypothesis that the hyperbaric oxygen (HBO2) inactivates cerebral nitrogen oxide (NO), interrupts its basal relaxing effect, and evokes a vasoconstriction. In our experiments, HBO2 decreased cerebral blood flow depending on the pressure. Inhibiting the NO-synthase weakened basal vasorelaxation in breathing with atmosphere air and eliminated the vasoconstriction in exposure to the HBO2. Inactivation of O2 prevented the HBO2-induced vasoconstriction. The data obtained reveal that diminishing of cerebral blood flow in HBO is related to the NO inactivation and weakening of its basal vasorelaxing effect. Possible mechanisms of the NO inactivation may involve its reaction with oxygen and superoxide anion which lead to diminishing of the tissue NO concentration and weakening of its vasorelaxing effect.

Neutrophil sequestration and the effect of hyperbaric oxygen in a rat model of temporary middle cerebral artery occlusion.

A rat model of reversible occlusion of the middle cerebral artery was developed to assess the role of neutrophils and prophylactic hyperbaric oxygen (HBO2) on cerebral injury. Blood flow to the ipsilateral caudate putamen nucleus was reduced by approximately 50% during 2 h of arterial occlusion, but unaffected on the contralateral side. Neutrophil accumulation in brain was documented as myeloperoxidase concentration, which was elevated in both ipsilateral and contralateral cerebral hemispheres at 1 and 46 h after occlusion/reperfusion. HBO2 administered before ischemia at 2.8 atm abs for 45 min, as well as antibody-induced neutropenia, reduced neutrophil accumulation, functional neurologic deficits, and cerebral infarct volume. These data demonstrate that one mechanism for benefit of HBO2 is related to its ability to ameliorate post-ischemic injury by inhibiting neutrophil sequestration. This mechanism should be taken into consideration when choosing partial pressures of oxygen for investigational clinical protocols.

[Monitoring brain PO2 as a means of predicting brain PN2 changes under hyperbaric oxygenation simulating free-floating conditions]. / Monitoring PO2 mozga kak sposob prognozirovaniia izmenenii PN2 mozga pri giperbaricheskom vozdeistvii, imitiruiushchem usloviia svobodnogo vsplytiia.

In rabbits, rats and mice, the delays of maximum of the brain oxygenation curves in respect to the maximum pressure curves were found to be 47.4 +/- 5.5 s; 32.6 +/- 2.9 s; and 26.4 +/- 2.0 s, resp. The data obtained shows the brain oxygenation monitoring to help to predict the nitrogen tension dynamics in the "fast" tissues during simulation of free surfacing.

[Cerebral blood flow dynamics in monkeys breathing a helium-oxygen mixture under high pressure]. / Dinamika mozgovogo krovotoka u obez'ian pri dykhanii geliokislorodnoi smes'iu pod vysokim davleniem.

Breathing with normoxic helium-oxygen mixture under high pressure successively induced tremor, myoclonia, seizures. Blood flow and the pO2 during the motor disorders increased, depending in the pressure, in the cortex, caudate nucleus, black substance and reticular formation.

[The local blood supply of the brain in guinea pigs during the development of the high-pressure nervous syndrome]. / Lokal'noe krovosnabzhenie golovnogo mozga morskikh svinok pri razvitii nervnogo sindroma vysokogo davleniia.

Under continuous compression with normoxic helium-oxygen mixture up to 100 Ata with the velocity 1 Ata/min, guinea pigs developed successively tremor, myoclonias, seizures of clonic and tonic types. Blood supply of cerebral structures (cortex, black substance, caudate nucleus) during motor disorders increased depending on the stage of development of the high pressure neural syndrome. The role of cerebral circulation in the latter's pathogenesis is discussed.

[The oxygenation status of the brain in guinea pigs breathing high-density gaseous mixtures]. / Sostoianie oksigenatsii golovnogo mozga morskikh svinok pri dykhanii gazovymi smesiami vysokoi plotnosti.

Compression of helium-oxygen mixture (HOM) and neon-oxygen one (NOM) led to changes in the guinea pig black substance, caudate nucleus and occipital cortex concerning the pO2. The pO2 level increased along with the increase in the HOM density to 15.56 milligrams and NOM to 76.61 milligrams. The pO2 changes were unequal in the cortex and deep structures of the brain. The increase in oxygenation of the brain under these conditions seems to occur because of compensatory responses of the cardiorespiratory system and redistribution of cerebral blood flow.