Protein tyrosine kinase inhibitors suppress the production of nitric oxide in mixed glia, microglia-enriched or astrocyte-enriched cultures

Batroxobin inhibits astrocyte activation following nigrostriatal pathway injury

Batroxobin is a thrombin-like serine protease from the venom of the Bothrops atrox and Bothrops moojeni snake species. Sirtuin 1 (Sirt1) has been shown to play an important role in neuroprotection after traumatic brain injury. However, its underlying mechanism of action remains poorly understood. The purpose of this study was to investigate whether the mechanism by which batroxobin participates in the activation of astrocytes is associated with Sirt1. Mouse models of nigrostriatal pathway injury were established. Immediately after modeling, mice were intraperitoneally administered 39 U/kg batroxobin. Batroxobin significantly reduced the expression of cleaved caspase-3 in both the substantia nigra and striatum, inhibited neuronal apoptosis, and promoted the recovery of rat locomotor function. These changes coincided with a remarkable reduction in astrocyte activation. Batroxobin also reduced Sirt1 expression and extracellular signal-regulated kinase activation in brain tissue. Intraperitoneal administration of the Sirt1-specific inhibitor EX527 (5 mg/kg) 30 minutes prior to injury could inhibit the abovementioned effects. In mouse astrocyte cultures, 1 ng/mL batroxobin attenuated interleukin-1β-induced activation of astrocytes and extracellular signal-regulated kinase. EX527 could also inhibit the effects of batroxobin. These findings suggest that batroxobin inhibits astrocyte activation after nigrostriatal pathway injury through the Sirt1 pathway. This study was approved by the Animal Ethics Committee of China Medical University, China (approval No. CMU2020037) on July 19, 2015.

Interactions between Sirt1 and MAPKs regulate astrocyte activation induced by brain injury in vitro and in vivo

Background

Astrocyte activation is a hallmark of traumatic brain injury resulting in neurological dysfunction or death for an overproduction of inflammatory cytokines and glial scar formation. Both the silent mating type information (Sirt1) expression and mitogen-activated protein kinase (MAPK) signal pathway activation represent a promising therapeutic target for several models of neurodegenerative diseases. We investigated the potential effects of Sirt1 upregulation and MAPK pathway pharmacological inhibition on astrocyte activation in vitro and in vivo. Moreover, we attempted to confirm the underlying interactions between Sirt1 and MAPK pathways in astrocyte activation after brain injury.

Methods

The present study employs an interleukin-1β (IL-1β) stimulated primary cortical astrocyte model in vitro and a nigrostriatal pathway injury model in vivo to mimic the astrocyte activation induced by traumatic brain injury. The activation of GFAP, Sirt1, and MAPK pathways were detected by Western blot; astrocyte morphological hypertrophy was assessed using immunofluorescence staining; in order to explore the neuroprotective effect of regulation Sirt1 expression and MAPK pathway activation, the motor and neurological function tests were assessed after injury.

Results

GFAP level and morphological hypertrophy of astrocytes are elevated after injury in vitro or in vivo. Furthermore, the expressions of phosphorylated extracellular regulated protein kinases (p-ERK), phosphorylated c-Jun N-terminal kinase (p-JNK), and phosphorylated p38 activation (p-p38) are upregulated, but the Sirt1 expression is downregulated. Overexpression of Sirt1 significantly increases the p-ERK expression and reduces the p-JNK and p-p38 expressions. Inhibition of ERK, JNK, or p38 activation respectively with their inhibitors significantly elevated the Sirt1 expression and attenuated the astrocyte activation. Both the overproduction of Sirt1 and inhibition of ERK, JNK, or p38 activation can alleviate the astrocyte activation, thereby improving the neurobehavioral function according to the modified neurological severity scores (mNSS) and balance latency test.

Conclusions

Thus, Sirt1 plays a protective role against astrocyte activation, which may be associated with the regulation of the MAPK pathway activation induced by brain injury in vitro and in vivo.

Berberine protects against neuronal damage via suppression of glia-mediated inflammation in traumatic brain injury

Traumatic brain injury (TBI) triggers a series of neuroinflammatory processes that contribute to evolution of neuronal injury. The present study investigated the neuroprotective effects and anti-inflammatory actions of berberine, an isoquinoline alkaloid, in both in vitro and in vivo TBI models. Mice subjected to controlled cortical impact injury were injected with berberine (10 mg·kg⁻¹) or vehicle 10 min after injury. In addition to behavioral studies and histology analysis, blood-brain barrier (BBB) permeability and brain water content were determined. Expression of PI3K/Akt and Erk signaling and inflammatory mediators were also analyzed. The protective effect of berberine was also investigated in cultured neurons either subjected to stretch injury or exposed to conditioned media with activated microglia. Berberine significantly attenuated functional deficits and brain damage associated with TBI up to day 28 post-injury. Berberine also reduced neuronal death, apoptosis, BBB permeability, and brain edema at day 1 post-injury. These changes coincided with a marked reduction in leukocyte infiltration, microglial activation, matrix metalloproteinase-9 activity, and expression of inflammatory mediators. Berberine had no effect on Akt or Erk 1/2 phosphorylation. In mixed glial cultures, berberine reduced TLR4/MyD88/NF-κB signaling. Berberine also attenuated neuronal death induced by microglial conditioned media; however, it did not directly protect cultured neurons subjected to stretch injury. Moreover, administration of berberine at 3 h post-injury also reduced TBI-induced neuronal damage, apoptosis and inflammation in vivo. Berberine reduces TBI-induced brain damage by limiting the production of inflammatory mediators by glial cells, rather than by a direct neuroprotective effect.

Regional difference in inflammatory response to LPS-injection in the brain: role of microglia cell density

To elucidate whether density of cells could contribute to the extent of microglial activation, we performed in vitro assays using three different densities of N13 microglia stimulated with LPS. Our results showed that induction of pro-inflammatory factors as TNF-α and iNOS was directly related to cell density, meanwhile the induction of the anti-inflammatory IL-10 was inversely related to cell density. Accordingly, in vivo assays showed that after LPS-injection, iNOS expression was more intense in substantia nigra, a brain area showing specific susceptibility to neurodegeneration after microglia activation, whereas IL-10 expression was more sustained in striatum, an area resistant to damage. These results support that microglia density is pivotal to control the balance between pro- and anti-inflammatory factors release.

Involvement of nitric oxide in maneb- and paraquat-induced Parkinson's disease phenotype in mouse: is there any link with lipid peroxidation?

The study aimed to investigate the involvement of nitric oxide (NO) in maneb (MB)- and paraquat (PQ)-induced Parkinson's disease (PD) phenotype in mouse and its subsequent contribution to lipid peroxidation. Animals were treated intraperitoneally with or without MB and PQ, twice a week for 3, 6 and 9 weeks. In some sets of experiments (9 weeks treated groups), the animals were treated intraperitoneally with or without inducible nitric oxide synthase (iNOS) inhibitor-aminoguanidine, tyrosine kinase inhibitor-genistein, nuclear factor-kappa B (NF-kB) inhibitor-pyrrolidine dithiocarbamate (PDTC) or p38 mitogen activated protein kinase (MAPK) inhibitor-SB202190. Nitrite content and lipid peroxidation were measured in all treated groups along with respective controls. RNA was isolated from the striatum of control and treated mice and reverse transcribed into cDNA. RT-PCR was performed to amplify iNOS mRNA and western blot analysis was done to check its protein level. MB- and PQ-treatment induced nitrite content, expressions of iNOS mRNA and protein and lipid peroxidation as compared with respective controls. Aminoguanidine resulted in a significant attenuation of iNOS mRNA expression, nitrite content and lipid peroxidation demonstrating the involvement of nitric oxide in MB- and PQ-induced lipid peroxidation. Genistein, SB202190 and PDTC reduced the expression of iNOS mRNA, nitrite content and lipid peroxidation in MB- and PQ-treated mouse striatum. The results obtained demonstrate that nitric oxide contributes to an increase of MB- and PQ-induced lipid peroxidation in mouse striatum and tyrosine kinase, p38 MAPK and NF-kB regulate iNOS expression.

Attenuation of lipopolysaccharide-induced acute lung injury by treatment with IL-10

BACKGROUND AND OBJECTIVE

The aim of this study was to characterize the changes in neutrophils and cytokines in BAL fluid following acute lung injury (ALI), and to determine the protective effect of post-injury treatment with IL-10.

METHODS

A rat model of ALI was established by evenly spraying LPS (16 mg/kg) into the lungs followed by observation for 48 h. Histological changes and the kinetics of neutrophil infiltration were evaluated in the injured lungs. The cytokines (TNF-alpha, IL-6, IL-10 and interferon-gamma) and macrophage-inflammatory protein (MIP-2) were measured in BAL fluid by ELISA. The activation of BAL fluid neutrophils was investigated after treatment with IL-10 in vitro. The protective effect on histology and MIP-2 levels of intra-tracheal instillation of IL-10 12 and 16 h after LPS treatment was studied in vivo.

RESULTS

Intra-tracheal instillation of LPS caused significant lung injury and the activation of neutrophils. The levels of TNF-alpha and IL-6 in BAL fluid peaked at 8 and 16 h after LPS instillation respectively. IL-10 levels reached a maximum at 16-24 h, at the beginning of resolution of tissue injury. IL-10 inhibited the activation of neutrophils in vitro and MIP-2 induction in vivo. IL-10 had a protective effect if it was administered 12 but not 16 h after LPS.

CONCLUSIONS

Neutrophils appeared to play an important role in ALI. Time-dependent treatment with IL-10 after intra-tracheal instillation of LPS was effective in protecting rats from ALI, probably by suppressing pulmonary infiltration with activated neutrophils.

Japanese encephalitis virus infection stimulates Src tyrosine kinase in neuron/glia

Japanese encephalitis virus (JEV) is a neurotropic virus. The clinically manifestation of JEV-induced encephalitis is characterized by the brain inflammation and neuronal dysfunction and/or destruction. Currently, the cellular signaling molecules that underlie JEV-induced cerebral inflammation and cellular alterations are not well understood. Protein tyrosine phosphorylation events are key regulators of cellular signaling processes, including inflammation. We investigated whether Src protein tyrosine kinase (PTK) function in JEV-induced cellular changes in neuron/glia cultures. JEV infection modulated tyrosine phosphorylation events. Src PTK was hyperphosphorylated at the early stage of infection. Biochemical studies demonstrated that both inhibitors of the Src family PTK and Ras attenuated JEV-induced extracellular signal-regulated kinase (ERK) activation. Our results further revealed that PTK, Ras, and ERK inhibitors effectively suppressed JEV-induced pro-inflammatory cytokine expression and neurotoxicity. Pharmacological studies suggested that microglia secreted pro-inflammatory cytokine via Src/Ras/ERK pathway in responding to JEV infection. Another interesting observation was that nonstructural protein 3 (NS3) was able to interact with Src and showed tyrosine phosphorylation. However, the biological consequences of their interaction and exact control of NS3 tyrosine phosphorylation required further investigation. Our results suggest that the Src/Ras/ERK signaling cascade is involved in JEV-induced pro-inflammatory cytokine expression and neurotoxicity.

Protective effect of radicicol against LPS/IFN-gamma-induced neuronal cell death in rat cortical neuron-glia cultures

We investigated the protective activity of radicicol, an antifungal antibiotic, against inflammation-induced neurotoxicity in neuron-glia cultures. Radicicol potently prevented the loss of neuronal cell bodies and neurites from LPS/IFN-gamma-induced neurotoxicity in rat cortical neuron-glia cultures with an EC(50) value of 0.09 microM. Radicicol inhibited the LPS/IFN-gamma-induced expression of inducible nitric oxide synthase (iNOS) and production of nitric oxide (NO) in microglia. Additionally, radicicol decreased the LPS/IFN-gamma-induced release of tumor necrosis factor-alpha (TNF-alpha) in the cultures. The inhibitory potency of radicicol against the production of NO and TNF-alpha was well correlated with the protection of neurons. These results suggest that the protective effect of radicicol against LPS/IFN-gamma-induced neuronal cell death in neuron-glia cultures is mediated via the inhibition of TNF-alpha release, as well as the suppression of iNOS expression in microglia.

TGF-beta1 potentiates astrocytic nitric oxide production by expanding the population of astrocytes that express NOS-2

Both transforming growth factor-beta1 (TGF-beta1) and nitric oxide synthase-2 (NOS-2) are upregulated under various neuropathological states. Evidence suggests that TGF-beta1 can either attenuate or augment NOS-2 expression, with the prevailing effect dependent on the experimental paradigm employed and the cell-type under study. The purpose of the present study was to determine the effect of TGF-beta1 on astrocytic NOS-2 expression. In purified astrocyte cultures, TGF-beta1 alone did not induce NOS-2 or NO production. However, NO production induced by lipopolysaccharide (LPS) plus IFNgamma was enhanced by TGF-beta1 in a concentration-dependent manner between 10 and 1,000 pg/mL. The presence of IFNgamma was not necessary for this effect to occur, as TGF-beta1 enhanced NO production induced by LPS in a similar fashion. In cultures stimulated with LPS plus IFNgamma, the enhancement of NO production by TGF-beta1 was associated with a corresponding increase in NOS-2 mRNA and protein expression. Interestingly, immunocytochemical assessment of NOS-2 protein expression demonstrated that TGF-beta1 augmented astrocytic NO production, specifically by increasing the pool of astrocytes capable of expressing NOS-2 induced by either LPS (approximately threefold) or LPS plus IFNgamma (approximately sevenfold). In a broader sense, our results suggest that TGF-beta1 recruits a latent population of astrocytes to respond to stimulation by pro-inflammatory mediators.

Ferritin levels in microglia depend upon activation: Modulation by reactive oxygen species

Iron is one of the trace elements playing a key role in the normal cellular metabolism. Since an excess of free iron is catalyzing the Fenton reaction, most of the intracellular iron is sequestered in the iron storage protein ferritin. The binding of iron into ferritin is well described for physiological conditions, however, under certain pathophysiological situations, the efficiency of this process is unknown. In the brain, microglial cells are among others the cell population most importantly responsible for the maintenance of the extracellular environment. These cells might undergo activation, and little is known about the expression of ferritin during activation of microglial cells. Therefore, we tested the microglial model cell line RAW264.7 for the expression of ferritin after LPS activation. A significant decrease in the levels of the ferritin H-chain during activation and a significant increase in the early recovery phase were found. We were able to demonstrate that reactive oxygen species are responsible for a suppression of the H-chain of ferritin, whereas iNOS expression and NO synthesis are counteracting the reactive oxygen species effect. The balance of reactive oxygen species and NO production are, therefore, determining expression levels of the ferritin H-chain during activation of microglial cells.

Polyamine and aminoguanidine treatments to promote structural and functional recovery in the adult mammalian brain after injury: a brief literature review and preliminary data about their combined administration

The regeneration potential of the adult mammalian central nervous system (CNS) is very modest, due to, among other factors, the presence of either a glial scar, or myelin-associated regeneration inhibitors such as Nogo-A, MAG and OMgp, which all interact with the same receptor (NgR). After a brief review of the key proteins (Rho and PKC) implicated in NgR-mediated signalling cascades, we will tackle the implications of cAMP and Arginase I in overcoming myelin growth-inhibitory influence, and then will focus on the effects of polyamines and aminoguanidine to propose (and to briefly support this proposal by our own preliminary data) that their association might be a potent way to enable functionally-relevant regeneration in the adult mammalian CNS.

Role of p38 and inducible nitric oxide synthase in the in vivo dopaminergic cells' degeneration induced by inflammatory processes after lipopolysaccharide injection

Accumulating evidences suggest that neuroinflammation is involved in the progressive death of dopaminergic neurons in Parkinson's disease. Several studies have shown that intranigral injection of lipopolysaccharide induces inflammation in the substantia nigra leading to death of tyrosine hydroxylase-positive cells. To better understand how the inflammatory response gives rise to neurotoxicity we induced inflammation in substantia nigra by injecting lipopolysaccharide. The damage of substantia nigra dopaminergic neurons was evaluated by immunohistochemistry, reverse transcription-PCR and Western blot analysis of tyrosine hydroxylase. In parallel, activation of microglial cells, a hallmark of inflammation in CNS, was revealed by immunohistochemistry. Similarly the expression of molecules involved in the inflammatory response and apoptotic pathway was also tested, such as cytokines (tumor necrosis factor-alpha, interleukin-1beta, interleukin-6), inducible nitric oxide synthase and caspase-11. Tyrosine hydroxylase expression (both mRNA and protein) started to decrease around 3 days post-injection. At the mRNA level, our results showed that the cytokines expression peaked shortly (3-6 h) after lipopolysaccharide injection, followed by the induction of inducible nitric oxide synthase and caspase-11 (14 h). However, inducible nitric oxide synthase protein peaked at 24 h and lasted for 14 days. The lipopolysaccharide-induced loss of substantia nigra dopaminergic neurons was partially inhibited by co-injection of lipopolysaccharide with S-methylisothiourea, an inducible nitric oxide synthase inhibitor. Co-injections of lipopolysaccharide with SB203580, a p38 MAP kinase inhibitor, reduced inducible nitric oxide synthase and caspase-11 mRNA expression, and also rescued dopaminergic neurons in substantia nigra. In summary, this is the first report to describe in vivo the temporal profile of the expression of these inflammatory mediators and proteins involved in dopaminergic neuronal death after intranigral injection of lipopolysaccharide. Moreover data strongly support that lipopolysaccharide-induced dopaminergic cellular death in substantia nigra could be mediated, at least in part, by the p38 signal pathway leading to activation of inducible nitric oxide synthase and caspase-11.

Regulation of inducible nitric oxide synthase gene in glial cells

Elevated levels of NO produced within the central nervous system (CNS) are associated with the pathogenesis of neuroinflammatory and neurodegenerative human diseases such as multiple sclerosis, HIV dementia, brain ischemia, trauma, Parkinson's disease, and Alzheimer's disease. Resident glial cells in the CNS (astroglia and microglia) express inducible nitric oxide synthase (iNOS) and produce high levels of NO in response to a wide variety of proinflammatory and degenerative stimuli. Although pathways resulting in the expression of iNOS may vary in two different glial cells of different species, the intracellular signaling events required for the expression of iNOS in these cells are slowly becoming clear. Various signaling cascades converge to activate several transcription factors that control the transcription of iNOS in glial cells. The present review summarizes different results and discusses current understandings about signaling mechanisms for the induction of iNOS expression in activated glial cells. A complete understanding of the regulation of iNOS expression in glial cells is expected to identify novel targets for therapeutic intervention in NO-mediated neurological disorders.

Inhibition of microglial inflammation by the MLK inhibitor CEP-1347

CEP-1347 is a potent inhibitor of the mixed lineage kinases (MLKs), a distinct family of mitogen-activated protein kinase kinase kinases (MAPKKK). It blocks the activation of the c-Jun/JNK apoptotic pathway in neurons exposed to various stressors and attenuates neurodegeneration in animal models of Parkinson's disease (PD). Microglial activation may involve kinase pathways controlled by MLKs and might contribute to the pathology of neurodegenerative diseases. Therefore, the possibility that CEP-1347 modulates the microglial inflammatory response [tumour necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6), and monocyte chemotactic protein-1 (MCP-1)] was explored. Indeed, the MLK inhibitor CEP-1347 reduced cytokine production in primary cultures of human and murine microglia, and in monocyte/macrophage-derived cell lines, stimulated with various endotoxins or the plaque forming peptide Abeta1-40. Moreover, CEP-1347 inhibited brain TNF production induced by intracerebroventricular injection of lipopolysaccharide in mice. As expected from a MLK inhibitor, CEP-1347 acted upstream of p38 and c-Jun activation in microglia by dampening the activity of both pathways. These data imply MLKs as important, yet unrecognized, modulators of microglial inflammation, and demonstrate a novel anti-inflammatory potential of CEP-1347.

The conditioned enhancement of neutrophil activity is catecholamine dependent

Neutrophil activity was elevated in the conditioned mice for the first time through an established conditioned training process. Catecholamines were proved to be important in the regulation of this conditioned innate immunity. In the study, the camphor odor (as the conditioned stimulus, CS) and poly I: C (as the unconditioned stimulus, US) was used to conditionally elevate the activity of the splenic neutrophils. The mechanism(s) responsible for the conditioned enhancement of neutrophil activity was further investigated using the neurochemical blocking assay and immunohistochemical analysis. Results showed that the neutrophil activity was significantly enhanced through the conditioned training process; both reserpine and 6-hydroxydopamine (6-OHDA) significantly blocked this conditioned innate immunity at the conditioned recall stage. Dexamethasone (Dex), however, showed no effect on the conditioned neutrophil response. Tyrosine hydroxylase (TH)-positive cells significantly increased in the locus coeruleus (LC), hypothalamus, and cortex but not in the spleen of the conditioned animals. These results indicate that during the conditioned recall stage, the brain signals the splenic neutrophils via the sympathetic nervous system (SNS) by releasing the peripheral catecholamines in spleen. The activation of the SNS, on the other hand, is also under the influence of catecholamines released in the LC. The hypothalamic pituitary (HP) axis, on the other hand, plays no role in the regulation of the conditioned neutrophil response.

Modulation of cerebral vascular tone by activated glia: involvement of nitric oxide

The ability of activated glia to affect cerebral vascular tone has been evaluated using an in vitro experimental system in which basilar arteries were incubated with glial cultures activated by treatment with lipopolysaccharide (LPS). Vascular tone was measured with an isometric myograph. Contraction in response to high KCl and serotonin was reduced in arteries co-incubated for 24 h with LPS-activated glia, whereas the response to acetylcholine was not modified. The reduced contraction was prevented when the nitric oxide synthase (NOS) inhibitor L-N-nitro-arginine (L-NNA) was added throughout the whole incubation time (activation of glial cells with LPS + co-incubation of glial cells with cerebral arteries). Under these conditions, nitrite levels were drastically reduced. A reduced contraction to KCl was also observed after treatment of the cerebral vessel with sodium nitroprusside. In contrast, L-NNA added to the vessel did not modify the response to contracting stimuli and the expression of endothelial NOS was not modified in cerebral arteries pre-incubated with activated glia. These results suggest that activated glia, which finds an in vivo correlate in several neuropathological conditions, can contribute to changes of vascular tone by modifying the levels of nitric oxide (NO) to which the vessel is exposed.

Tyrosine kinase inhibitors attenuate Japanese encephalitis virus-induced neurotoxicity

The cellular signaling molecules that underlie Japanese encephalitis virus (JEV)-induced inflammation and neurotoxicity are not well understood. We examined whether protein tyrosine kinase (PTK) inhibitors play roles in JEV replication and cytopathic effect in neuron/glia cultures. JEV infection caused significant neuronal injury. PTK inhibitors, genistein, herbimycin A, and PP2, attenuated JEV-induced neurotoxicity but failed to affect JEV replication. Infection of neuron/glia cultures with JEV produced elevated levels of tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta). PTK inhibitors suppressed JEV-induced TNF-alpha and IL-1beta production at the transcriptional level. Neutralizing antibodies against TNF-alpha and IL-1beta partially suppressed JEV-induced neurotoxicity. JEV infection modulated tyrosine phosphorylation events within the course of infection. Currently, the nature of the affected phosphorylated proteins was not characterized. Our results suggest that PTKs, especially Src-related PTK, play roles in the production of TNF-alpha and IL-1beta during JEV infection and in the induction of neuronal death in neuron/glia cultures.

Genistein protects dopaminergic neurons by inhibiting microglial activation

Inflammation participates in the pathogenesis and progression of Parkinson's disease, in which microglia play a key role. Inhibition of microglia activation has been shown to attenuate inflammation-mediated dopaminergic neurodegeneration. In this study, we found that genistein, the primary soybean isoflavone, concentration-dependently attenuated the lipopolysaccharide-induced decrease in dopamine uptake and loss of tyrosine hydroxylase-immunoreactive neurons in rat mesencephalic neuron-glia cultures. Genistein also inhibited lipopolysaccharide-induced microglia activation and production of tumor necrosis factor-alpha, nitric oxide and superoxide in mesencephalic neuron-glia cultures and microglia-enriched cultures. Our results indicate that genistein may protect dopaminergic neurons from lipopolysaccharide-induced injury and its effective inhibition of microglia activation may be one of the mechanisms.

Critical role of the automodification of poly(ADP-ribose) polymerase-1 in nuclear factor-kappaB-dependent gene expression in primary cultured mouse glial cells

Synthesis of ADP-ribose polymers catalyzed by poly-(ADP-ribose) polymerase-1 (PARP-1) has been implicated in transcriptional regulation. Recent studies with PARP-1 null mice and PARP-1 inhibitors have also demonstrated that PARP-1 has an essential role in nuclear factor-kappaB (NF-kappaB)-dependent gene expression induced by various inflammatory stimuli. In this study, we used primary cultured mouse glial cells to investigate the role of poly(ADP-ribosyl)ation by PARP-1 in NF-kappaB-dependent gene expression. PARP-1 inhibitors and the antisense RNA for PARP-1 mRNA suppressed lipopolysaccharide (LPS)-induced expression of tumor necrosis factor-alpha and inducible nitric-oxide synthase, suggesting that PARP-1 activity has a critical role in synthesis. Western blotting with anti-poly(ADP-ribose) antibody revealed that PARP-1 itself was mainly poly(ADP-ribosyl)ated in glial cells, i.e. automodified PARP-1 (AM-PARP). The amounts of AM-PARP were not affected by LPS treatment, but were decreased by PARP-1 inhibitors. Electrophoretic mobility shift assay revealed that PARP-1 inhibitors and the antisense RNA for PARP-1 mRNA reduced the LPS-induced DNA binding of NF-kappaB. Non-modified PARP-1 also reduced the DNA binding of NF-kappaB via its physical association with NF-kappaB, whereas AM-PARP had no effect. On the other hand, enhancement of the automodification of PARP-1 by the addition of NAD+, its substrate, promoted the DNA binding of NF-kappaB. Furthermore, in in vitro transcription assay, the addition of AM-PARP or NAD+ to nuclear extracts promoted NF-kappaB p50-dependent transcription. These results indicate that automodification of PARP-1 positively up-regulates formation of the NF-kappaB.DNA complex and enhances transcriptional activation. Therefore, AM-PARP may be critical for the NF-kappaB-dependent gene expression of some inflammatory mediators in glial cells.

The role of inflammatory processes in the pathophysiology and treatment of brain and spinal cord trauma

Traumatic injury to the brain and spinal cord results in an early inflammatory response that is initiated by the release of proinflammatory cytokines followed by the infiltration and accumulation of polymorphonuclear leukocytes (PMNLs). The role of the inflammatory cascade on traumatic outcome remains controversial. Pleiotropic cytokines appear to function both protectively and destructively. The induction of cytokines can lead to the expression of the inducible form of nitric oxide synthase (iNOS), which in turn provokes the release of excessive amounts of nitric oxide (NO) that may participate in the pathogenesis of tissue injury. Hypothermia has been reported by various groups to be neuroprotective in brain and spinal cord trauma. We studied the effect of therapeutic hypothermia on cerebral IL-1beta concentrations, PMNL accumulation and iNOS activity after traumatic brain injury (TBI) and spinal cord injury (SCI). Based on current data therapeutic hypothermia may protect in models of traumatic injury by modulating deleterious inflammatory processes.

Transforming growth factor beta1 prevents IL-1beta-induced microglial activation, whereas TNFalpha- and IL-6-stimulated activation are not antagonized

Microglia rapidly respond to CNS injury, yet the mechanisms leading to their activation and inactivation remain poorly defined. In particular, few studies have established how interactions between inflammatory mediators affect the innate immune response of microglia. To begin to establish how microglia integrate signals from multiple inflammatory mediators, we examined the effects of interleukin 1beta (IL-1beta), interleukin 6 (IL-6), tumor necrosis factor alpha (TNFalpha), interferon gamma (IFN-gamma), and transforming growth factor beta1 (TGFbeta1) on both newborn and bulk-isolated adult microglia. To assess the functional state of the cells, we assayed the expression of cyclooxygenase 2 (Cox-2), interleukin 6, and tumor necrosis factor alpha, and two protein tyrosine kinases that have been implicated in microglial responses to activational stimuli, HCK and FAK. These studies demonstrated that IL-1beta, TNFalpha, IL-6, but not IFN-gamma increase the expression of Cox-2, whereas they all increase the expression of HCK and FAK. In these studies, TGFbeta1 either had no effect, or it decreased basal levels of these proteins. TGFbeta1 blocked activation by IL-1beta when given prior to, or simultaneously with, IL-1beta. TGFbeta1 blocked the induction of the tyrosine kinases, Cox-2, and the induction of IL-6 and TNFalpha mRNAs. However, TGFbeta1 was ineffective in antagonizing the induction of Cox-2 by either IL-6 or TNFalpha. We conclude that the TGFbeta receptor signaling cascades intersect with IL-1, but they may not interact with IL-6 or TNFalpha signaling pathways that lead to activation.

Differential expression of protein tyrosine kinase genes during microglial activation

Protein tyrosine kinase (PTK) activity is abundant in microglia, but the PTKs that participate in their activation have not been identified. For these studies, we used three paradigms to characterize PTK expression during microglial activation: resting and activated microglia were bulk fractionated from the adult brain, cultured newborn microglia were treated with lipopolysaccharide (LPS) to model the transition from activated toward phagocytic microglia, and PTK expression was examined in activated microglia in situ after facial nerve axotomy. Two PCR-based strategies were used to show that 21 different PTK genes are expressed by rat brain microglia: 5 receptor PTKs, 10 nonreceptor PTKs, and 6 members of the src family. Seven of the 21 PTKs were examined in greater detail. Five PTK mRNAs (fgr, hck, fak, jak-2, and flk-1) increased expression across all three models of activation. We conclude that they represent key components in the cascades that participate in microglial activation. In contrast, expression of fes and fms correlated with stimuli that affect microglial proliferation. Four of the PTKs (hck, fgr, fes, and fms) are believed to be myeloid cell specific and were not expressed by cultured astrocytes. HCK and FAK protein were also not expressed in lysates of immature astrocytes and oligodendrocytes. Because of their putative specificity, these kinases represent potential targets for inhibitors of microglial activation. Because reactive microglia can exacerbate the severity of neurological diseases, the identification of specific kinases that participate in microglial activation represents an important advance toward the development of new therapeutics.

Astrocytes enhance lipopolysaccharide-induced nitric oxide production by microglial cells

Several stimuli result in glial activation and induce nitric oxide (NO) production in microglial and astroglial cells. The bacterial endotoxin lipopolysaccharide (LPS) has been widely used to achieve glial activation in vitro, and several studies show that both microglial and, to a lesser extent, astroglial cell cultures produce NO after LPS treatment. However, NO production in endotoxin-treated astrocyte cultures is controversial. We characterized NO production in microglial, astroglial and mixed glial cell cultures treated with lipopolysaccharide, measured as nitrite accumulation in the culture media. We also identified the NO-producing cells by immunocytochemistry, using specific markers for the inducible NO synthase (iNOS) isoform, microglial and astroglial cells. Only microglial cells showed iNOS immunoreactivity. Thus, contaminating microglial cells were responsible for NO production in the secondary astrocyte cultures. We then analysed the effect of astrocytes on NO production by microglial cells using microglial-astroglial cocultures, and we observed that this production was clearly enhanced in the presence of astroglial cells. Soluble factors released by astrocytes did not appear to be directly responsible for such an effect, whereas nonsoluble factors present in the cell membrane of LPS-treated astrocytes could account, at least in part, for this enhancement.

Down-regulation of complement receptor 3 and major histocompatibility complex I and II antigen-like immunoreactivity accompanies ramification in isolated rat microglia

Isolated primary microglia are highly activated in conventional culture systems. This has restricted studies to the use of late stage measures of activation rather than highly sensitive immunophenotypic and morphological criteria that mark even very early stages of microglial activation in vivo. In the present study, serum-free, serine- and glycine-free medium and poly-L-lysine coated surfaces have been used to demonstrate for the first time isolated rat microglia which (i) downregulate their immunoreactivity for antibodies recognizing complement receptor 3 and major histocompatibility complex antigens while differentiating into ramified cells, and (ii) respond to a subset of modulators with upregulation of complement receptor 3-like immunoreactivity. During 2 weeks of culturing under basal conditions, ramification was accompanied by strong downregulation of OX-42, OX-18 and OX-6 immunoreactivity (antibodies recognizing complement receptor 3 and major histocompatibility complex class I and II antigens, respectively). Ramified cells had lower level immunoreactivity for all three markers than non-ramified cells. High OX-42 immunoreactivity was also associated with morphological signs of activation previously described in vivo. Enhanced OX-42 immunoreactivity was induced by applying either serine and glycine or lipopolysaccharide (LPS) while granulocyte macrophage-colony stimulating factor increased cell number without affecting OX-42 immunoreactivity. LPS induced alterations were apparent within 24 h, were transient, and did not include changes in OX-18 or OX-6 immunoreactivity, cell number or proportion of ramified cells. The results attest to the special efficacy of this culture method for the investigation of the early microglial reaction by use of highly sensitive immunophenotypic criteria.

Gö6976 protects mesencephalic neurons from lipopolysaccharide-elicited death by inhibiting p38 MAP kinase phosphorylation

Glial activation is associated with inflammation-related neuron degeneration in the brain. A variety of protein kinases are assumed to contribute to the expression of inflammation-related products, such as nitric oxide (NO) and proinflammatory cytokines, however, the mechanisms of glial activation and glia-mediated neurotoxicity remain unclear. We found that the indolocarbazole, Gö6976, originally known as a selective protein kinase C (PKC) inhibitor, protects neurons from glia-mediated damage and suppresses lipopolysaccharide (LPS)-induced microglial production of inflammatory factors. The purpose of the study we report here was to determine the mechanism underlying the neuroprotective effect of Gö6976 in mesencephalic neuron/glia cultures. Gö6976 suppressed LPS-induced neurotoxicity in mesencephalic neuron/glia cultures and the protective effect of Gö6976 paralleled the suppression of p38 mitogen activated protein kinase (MAPK) activation and inhibition of NO production. Gö6976 did not directly inhibit the activity of p38 MAPK; rather, the inhibitor suppressed the phosphorylation of p38 MAPK, suggesting that the target of Gö6976 is a signaling event upstream of p38 MAPK. Although Gö6976 was originally known to be a selective PKC inhibitor, the neuroprotection was not mediated through its reputed effects on PKC activity. This paper demonstrates that the neuroprotective effect of Gö6976 against LPS-induced damage is mediated through the inhibition of proinflammatory factors, such as NO from microglia, by inhibiting the phosphorylation of p38 MAPK.

p38 MAP kinase is involved in lipopolysaccharide-induced dopaminergic neuronal cell death in rat mesencephalic neuron-glia cultures

Immune stimulants, such as the bacterial endotoxin, lipopolysaccharide (LPS), the human immunodeficiency virus-1 coat protein gp120, or beta-amyloid peptides, lead to glial activation and production of various immune mediators, such as nitric oxide (NO) and proinflammatory cytokines in the brain. These mediators appear to contribute to neuronal cell death in neurodegenerative diseases. However, the signaling pathways, which mediate the neurotoxic effect by the endotoxin, are not understood. The purpose of this study was to determine the role of mitogen-activated protein kinase (MAPK) in LPS-induced neurodegeneration using mesencephalic dopaminergic neuron/glia cultures. We have found that the p38 MAPK is important in LPS-induced death of mesencephalic neurons in rat neuron-glia mixed cultures. Upon treatment with 10 ng/ml LPS, the number of dopaminergic neurons decreased by 80% within 48 h, preceded by a significant production of NO by glia. Neuroprotection by selective inhibition of p38 MAPK activity paralleled a decrease in LPS-induced inducible nitric oxide synthase (iNOS) expression. These events were significantly reduced by the selective p38 MAPK inhibitor, SB202190, but not by the inactive analogue SB202474. Inhibition of iNOS activity and NO production by treatment with GW274150 was also neuroprotective. Although the p38 MAPK inhibitor afforded significant neuroprotection from LPS toxicity in the neuron-glia mixed culture, it failed to protect dopaminergic neurons from 6-hydroxy-dopamine-induced toxicity, which acts directly on dopaminergic neurons by inducing hydroxyl radical formation from the mitochondria. The results suggest that p38 MAPK in glia plays a significant role in the LPS-induced death of mesencephalic neurons through induction of nitric oxide synthase and resulting NO production.

Stromelysin-1 and gelatinase A are upregulated before TNF-alpha in LPS-stimulated neuroinflammation

Neuroinflammation induces a complex molecular cascade that leads to the proteolysis of cells. Matrix metalloproteinases (MMPs) attack all components of the extracellular matrix in a number of neuroinflammatory diseases and cause a delayed opening of the blood-brain barrier (BBB). Earlier, we showed that lipopolysaccharide (LPS) disrupted the BBB through the action of gelatinase B (MMP-9). In a study of cerebral ischemia, gelatinase A (MMP-2) was seen in astrocytic end-feet and stromelysin-1 (MMP-3) in microglia. Since other MMPs may be important in LPS-induced injury, we studied the gene transcription and cellular localization of several MMPs and an inflammatory mediator, tumor necrosis factor (TNF-alpha), using competitive polymerase chain reaction (PCR) and immunohistochemical methods. Significantly elevated levels of MMP-2 and -3 mRNA were observed in LPS-injected brains by 2 h after injection as compared to non-injected brain tissue (P<0.05). By 8 h post-LPS injection, gene expression of MMP-2 and -3 had declined in both saline- and LPS-injected tissue, while TNF-alpha mRNA levels rose significantly. Immunohistochemistry of control brains confirmed the earlier observation of MMP-2 immunoreactivity in processes abutting cerebral blood vessels, which increased after LPS injection. The expression of MMP-9 and MMP-3 was localized mainly to the cerebrovasculature in LPS-stimulated brain tissue, predominantly in the perivascular cells of the basal lamina near the site of injection. Both of these proteinases were present at the site of LPS injection at 8 h, but MMP-2 was absent. Our results show that MMP genes are up-regulated prior to the induction of cytokines such as TNF-alpha, and that MMP proteins are prominent around blood vessels in LPS-induced neuroinflammation.

Differential regulation of microglial NO production by protein kinase C inhibitors

Nitric oxide (NO) produced by microglia has been implicated in the pathogenesis of various central nervous system diseases; however, the intracellular signal pathways for the production of NO are not well known. Protein kinase C (PKC) plays a key role in a variety of signal transduction processes. To elucidate how PKC regulates microglial NO production, we examined the effects of PKC inhibitors on lipopolysaccharide (LPS)-stimulated NO production by primary cultured rat microglia. Staurosporine, a non-selective PKC inhibitor, increased LPS-induced production of NO at 0.1-10 nM range of concentration. Protein kinase A (PKA) inhibitor, H89, did not affect LPS-induced NO production, suggesting that staurosporine effect is not mediated by inhibition of PKA. However, other two PKC inhibitors, whose specificities for PKC isoforms were different, Gö6976 and Ro-32-0432, exhibited different effects on NO production from staurosporine; the former inhibited and the latter showed no effect. Interestingly, an activator of PKC, phorbol 12-myristate 13-acetate (PMA) also increased LPS-induced production of NO at 1-10 nM range of concentration, suggesting that prolonged incubation with PMA caused down-regulation of PKC. These results indicate that the inhibition or down-regulation of some PKC isoforms causes the enhancement of NO production. The different effects of PKC inhibitors on the NO production suggest that the different PKC isoforms play different roles in regulation of NO production in microglia.

Time dependency of the action of nitric oxide in lipopolysaccharide-interferon-gamma-induced neuronal cell death in murine primary neuron-glia co-cultures

We investigated the time-dependency of the action of nitric oxide (NO) on glia-mediated neuronal cell death. Cortical neuron-glia co-cultures were treated with lipopolysaccharide and interferon gamma (LPS/IFNgamma). The production of NO was first detectable 9 h after the exposure to LPS/IFNgamma and increased for up to 48 h. A significant neuronal cell death was observed 36-48 h after treatment with LPS/IFNgamma. The NO generated at the initial stage of NO synthesis (about 12 h) following exposure to LPS/IFNgamma was found to be critical for LPS/IFNgamma-induced neurotoxicity. Furthermore, the rate of NO production at the initial stage of NO synthesis was correlated linearly with the extent of neuronal cell death. These findings suggest that the maximal rate of NO synthesis, instead of the accumulated NO(2)(-) level, is a sensitive index for predicting endotoxin-induced cytotoxicity.

Reduction by naloxone of lipopolysaccharide-induced neurotoxicity in mouse cortical neuron-glia co-cultures

An inflammatory response in the CNS mediated by activation of microglia is a key event in the early stages of the development of neurodegenerative diseases. Using mouse cortical mixed glia cultures, we have previously demonstrated that the bacterial endotoxin lipopolysaccharide induces the activation of microglia and the production of proinflammatory factors. Naloxone, an opioid receptor antagonist, inhibits the lipopolysaccharide-induced activation of microglia and the production of proinflammatory factors. Using neuron-glia co-cultures, we extended our study to determine if naloxone has a neuroprotective effect against lipopolysaccharide-induced neuronal damage and analysed the underlying mechanism of action for its potential neuroprotective effect. Pretreatment of cultures with naloxone (1 microM) followed by treatment with lipopolysaccharide significantly inhibited the lipopolysaccharide-induced production of nitric oxide and the release of tumor necrosis factor-alpha, and significantly reduced the lipopolysaccharide-induced damage to neurons. More importantly, both naloxone and its opioid-receptor ineffective enantiomer (+)-naloxone were equally effective in inhibiting the lipopolysaccharide-induced generation of proinflammatory factors and the activation of microglia, as well as in the protection of neurons. These results indicate that the neuroprotective effect of naloxone is mediated by its inhibition of microglial activity and may be unrelated to its binding to the classical opioid receptors.

Agmatine suppresses nitric oxide production in microglia

We investigated the effect of agmatine, an arginine metabolite synthesized in the brain, in cultured microglia obtained from neonatal rat cerebral cortex. Agmatine (1-300 microM) did not affect viability of cultured microglia. Activation of microglia by lipopolysaccharide (LPS, 1 microg/ml) caused the expression of inducible nitric oxide synthase (iNOS) and the production of nitric oxide (NO) assessed as the accumulation of nitrite in the culture supernatants. Agmatine had no effect on the expression of iNOS, but significantly suppressed the LPS-induced NO production in a concentration-dependent manner. Agmatine was also effective in suppressing the production of NO induced by a combination of interferon-gamma (500 U/ml) and amyloid beta protein (10 microM). In co-cultures of rat cortical neurons and microglia, LPS caused significant loss of neuron viability. The LPS neurotoxicity was not observed in the absence of microglia, and was completely blocked by the NOS inhibitor diphenyleneiodoium chloride. The neuronal death induced by microglia-derived NO was significantly attenuated by the presence of agmatine. These results suggest that agmatine works to protect neurons by inhibiting the production of NO in microglia.

Post-transcriptional inhibition of lipopolysaccharide-induced expression of inducible nitric oxide synthase by Gö6976 in murine microglia

Glia in the brain respond to various toxins with an increased expression of inducible nitric oxide synthase (iNOS) and an increased production of nitric oxide (NO). Here, we report that lipopolysaccharide (LPS)-induced expression of iNOS was down-regulated post-transcriptionally through the destabilization of iNOS mRNA by the indolocarbazole compound, Gö6976, in murine microglia. This Gö6976 effect is specific for iNOS since tumor necrosis factor alpha was unaffected by the compound. Interestingly, the post-transcriptional effects ascribed to Gö6976 were not observed with other inhibitors of protein kinase A, C (PKC), G, or protein tyrosine kinases. Instead, these kinases appear to affect the iNOS/NO system at the transcriptional level. In the past, Gö6976 has been reported to be a rather specific inhibitor of PKC in vitro. Results from our experiments, through prolonged treatment with phorbol esters and with the various PKC inhibitors including phorbol ester-insensitive PKC isotype inhibitor, suggest that the Gö6976-mediated post-transcriptional regulation of iNOS gene expression and NO production in microglia is not mediated through its reputed effects on PKC activity. Since the effects of various neurotoxins and certain neurodegenerative diseases may be manifested through alterations in the iNOS/NO system, post-transcriptional control of this system may represent a novel strategy for therapeutic intervention.

The indolocarbazole Gö6976 protects neurons from lipopolysaccharide/interferon-gamma-induced cytotoxicity in murine neuron/glia co-cultures

The expression of inducible nitric oxide synthase (iNOS) and the production of nitric oxide (NO) after exposure to endotoxins has been implicated in immune-mediated neurotoxicity. The indolocarbazole compound Gö6976, which has been described as a selective protein kinase C (PKC) inhibitor in vitro, rescued neurons from lipopolysaccharide/interferon-gamma (LPS/IFNgamma)- or interleukin-1alpha/tumor necrosis alpha/IFNgamma (IL-1alpha/TNFalpha/IFNgamma)-induced cytotoxicity in murine primary neuron-glia co-cultures. Other compounds known to inhibit PKC, Ro31-8220, GF109203X, Gö7874, H7, staurosporine and H89, failed to rescue neurons from the LPS/IFNgamma-induced cytotoxicity. These results suggest that the neuroprotection by Gö6976 from the LPS/IFNgamma-induced neuronal cell death is not mediated through its reputed effects on PKC activity. The neuroprotection paralleled the inhibition of iNOS gene expression and NO production. However, further analyses correlating NO production with the extent of neurotoxicity suggested that additional mechanism(s) besides the inhibition of the iNOS/NO system may be responsible for the neuroprotective effects of Gö6976. An understanding of the mechanism underlying the neuroprotective effect of Gö6976 may provide key insights into potential interventions for immune-mediated neurodegenerative diseases.

A novel effect of an opioid receptor antagonist, naloxone, on the production of reactive oxygen species by microglia: a study by electron paramagnetic resonance spectroscopy

Microglia as the first line of defensive cells in the brain produce free radicals including superoxide and nitric oxide (NO), contributing to neurodegeneration. An opioid receptor antagonist, naloxone, has been considered pharmacologically beneficial to endotoxin shock, experimental cerebral ischemia, and spinal cord injury. However, the mechanisms underlying these beneficial effects of naloxone are still not clear. This study explores the effects of naloxone on the production of superoxide and NO by the murine microglial cell line, BV2, stimulated with lipopolysaccharide (LPS) as measured by electron paramagnetic resonance (EPR). The production of superoxide triggered by phobol-12-myristate-13-acetate (PMA) resulted in superoxide dismutase (SOD)-inhibitable, catalase-uninhibitable 5,5-dimethyl-1-pyrroline N-oxide (DMPO) hydroxyl radical adduct formation. LPS enhanced the production of superoxide and triggered the formation of non-heme iron-nitrosyl complex. Cells pre-treated with naloxone showed significant reduction of superoxide production by 35%. However, it could not significantly reduce the formation of non-heme iron-nitrosyl complex and nitrite. Taken together, the results expand our understanding of the neuroprotective effects of naloxone as it decreases superoxide production by microglia.

Influence of neurons on lipopolysaccharide-stimulated production of nitric oxide and tumor necrosis factor-alpha by cultured glia

Cerebral inflammation often originates in a region where neuronal death occurs and thereafter slowly spreads outward. This study aimed to elucidate the roles of neurons in modulating the production of inflammatory factors stimulated by the bacterial endotoxin lipopolysaccharide (LPS). Culturing neurons with mixed glia reduced nitrite and tumor necrosis factor-alpha (TNF-alpha) production compared to cultures with only mixed glia, and shifted the dose-response curve to the right. The decreased nitrite and TNF-alpha production were not due to the cytotoxicity of LPS. Immunocytochemical analysis of glia-neuron co-cultures revealed the morphological changes in the activated microglia. Culturing PC12 cells with rat mixed-glia also reduced nitrite production. The influence of neurons on glial inflammation was partly due to the cell-cell contacts between neurons and glia via neural cell adhesion molecules (NCAM) because NCAM significantly reduced LPS-stimulated nitrite production. These results demonstrate that neurons reduce the production of inflammatory factors by glia. Since cerebral inflammation is important in many neurological disorders, this study might provide insight about the role of glia-neuron interactions in inflammatory responses in the brain.

In vivo evidence that activation of tyrosine kinase is a trigger for lipopolysaccharide-induced fever in rats

We measured the rectal temperature of free-moving, conscious rats after intracerebroventricular (i.c.v.) injections of lipopolysaccharide (LPS) and interleukin-1beta (IL-1beta) with or without various antagonists to investigate the mechanisms involved in LPS-induced fever. LPS (3 microg) elicited significant increases in rectal temperature, which lasted from 0.5 h to more than 8 h after administration. This febrile response was inhibited by pretreatment with L-nitro-arginine (LNA), indomethacin (IND), genistein (GEN), tyrphostin 46 and anti-rat IL-1beta antibody (anti-IL-1beta Ab), but was not inhibited by pretreatment with daidzein or chelerythrine (CHE) into the ventricle. LPS (0.3 microg) following orthovanadate (i.c.v.) produced fever, although the small amount of LPS (0.3 microg) or orthovanadate alone showed no effect on rectal temperature. I.c.v. injections of IL-1beta also induced fever of approximately 4-h duration. This effect was inhibited by pretreatment with IND and anti-IL-1beta Ab, but was not inhibited by pretreatment with LNA, GEN or CHE into the ventricle. These findings demonstrate that in the central nervous system, LPS increases IL-1beta production after activation of tyrosine kinase and NO synthase, and IL-1beta promotes prostaglandin production resulting in increased rectal temperature. Activation of tyrosine kinase in the central nervous system is probably a trigger for the febrile response induced by LPS.

Screening in a cell-based assay for inhibitors of microglial nitric oxide production reveals calmodulin-regulated protein kinases as potential drug discovery targets

A high-throughput screening (HTS) assay for inhibitors of nitric oxide (NO) production by activated microglia was developed and used to compare the relative activities of various anti-inflammatory compounds and cell-permeable protein kinase inhibitors. BV-2 cells, an immortalized line that retains phenotypic features of microglia and produces NO in response to lipopolysaccharide (LPS), were used in the activation paradigm for the HTS assay. A characteristic feature of the compounds that were the most potent dose-dependent inhibitors of NO production is their ability to modulate serine/threonine protein kinases. The anti-inflammatory compound K252a, an inhibitor of calmodulin (CaM)-regulated protein kinases, had one of the highest potencies in the assay. Other classes of kinase inhibitors, including the protein kinase A inhibitor H-89, the mitogen activated protein kinase inhibitors PD98059 and SB203580, and the tyrosine kinase inhibitor genistein, were less potent and efficacious than K252a or the general serine/threonine/tyrosine kinase inhibitor staurosporine. K252a suppresses production of the inducible nitric-oxide synthase (iNOS). The inhibitory effect of K252a is not due to cell toxicity and does not correlate with inhibition of NFkappaB nuclear translocation. The mechanism of action appears to involve inhibition of phosphorylation of the transcription factor CREB, a protein whose activity is modulated by phosphorylation by CaM-dependent protein kinases. These data suggest that signal transduction pathways mediated by CaM-dependent protein kinases warrant future study as potential drug discovery targets.

Reduction of lipopolysaccharide-induced neurotoxicity in mixed cortical neuron/glia cultures by femtomolar concentrations of pituitary adenylate cyclase-activating polypeptide

Stimulation of murine primary mixed cortical neuron/glia cultures with lipopolysaccharide, an endotoxin, was used as a model for inflammatory disorders of the central nervous system. Lipopolysaccharide (20 microg/ml) increased the secretion of lactate dehydrogenase, a marker for cell injury, and nitric oxide into the culture medium. The lipopolysaccharide-induced release of lactate dehydrogenase into the culture medium was reduced by pituitary adenylate cyclase-activating polypeptide (PACAP) at 10(-14)-10(-12) M. The 27- and 38-amino-acid forms of PACAP were equipotent and their dose-response curves were U-shaped. PACAP6-38, a specific type I PACAP receptor antagonist, blocked the reduction by PACAP38 of the lipopolysaccharide-induced release of lactate dehydrogenase. The lipopolysaccharide-induced secretion of nitric oxide into the culture medium was reduced by PACAP at 10(-14)-10(-12) M and 10(-8)-10(-6) M. The 27- and 38-amino-acid forms of PACAP were equipotent. PACAP6-38 blocked the reduction of the lipopolysaccharide-induced secretion of nitric oxide by PACAP38 at 10(-12) M, but not at 10(-8) M. Vasoactive intestinal polypeptide reduced the lipopolysaccharide-induced release of lactate dehydrogenase into the culture medium at 10(-14)-10(-12) M, but these concentrations of vasoactive intestinal polypeptide had no effect on the lipopolysaccharide-induced secretion of nitric oxide. PACAP6-38 did not effect the reduction of the lipopolysaccharide-induced release of lactate dehydrogenase into the culture medium by 10(-12) M vasoactive intestinal polypeptide. These results indicate that stimulation of type I PACAP receptors by femtomolar concentrations of PACAP can prevent neuron death in a model for inflammatory disorders of the CNS. These results suggest that PACAP is also an extraordinarily potent inhibitor of some microglial functions.

Rapid inactivation of NOS-I by lipopolysaccharide plus interferon-gamma-induced tyrosine phosphorylation

Human astrocytoma T67 cells constitutively express a neuronal NO synthase (NOS-I) and, following administration of lipopolysaccharide (LPS) plus interferon-gamma (IFNgamma), an inducible NOS isoform (NOS-II). Previous results indicated that a treatment of T67 cells with the combination of LPS plus IFNgamma, by affecting NOS-I activity, also inhibited NO production in a very short time. Here, we report that under basal conditions, a NOS-I protein of about 150 kDa was weakly and partially tyrosine-phosphorylated, as verified by immunoprecipitation and Western blotting. Furthermore, LPS plus IFNgamma increased the tyrosine phosphorylation of NOS-I, with a concomitant inhibition of its enzyme activity. The same effect was observed in the presence of vanadate, an inhibitor of phosphotyrosine-specific phosphatases. On the contrary, genistein, an inhibitor of protein-tyrosine kinases, reduced tyrosine phosphorylation of NOS-I, enhancing its enzyme activity. Finally, using reverse transcriptase-polymerase chain reaction, we have observed that a suboptimal induction of NOS-II mRNA expression in T67 cells was enhanced by vanadate (or L-NAME) and inhibited by genistein. Because exogenous NO has been found to suppress NOS-II expression, the decrease of NO production that we have obtained from the inactivation of NOS-I by LPS/IFNgamma-induced tyrosine phosphorylation provides the best conditions for NOS-II expression in human astrocytoma T67 cells.

Inducible nitric oxide synthase expression after traumatic brain injury and neuroprotection with aminoguanidine treatment in rats

OBJECTIVE

We investigated the time course of inducible nitric oxide synthase (iNOS) enzymatic activity and immunocytochemical localization of iNOS expression after traumatic brain injury (TBI), as well as the possible role of iNOS in the pathogenesis of TBI.

METHODS

Male Sprague-Dawley rats were anesthetized and underwent moderate parasagittal fluid-percussion brain injury. Rats were decapitated 5 minutes, 6 hours, 1 day, 3 days, 7 days, or 14 days later, and iNOS enzymatic activities were measured (n = 6-8). To determine whether nitric oxide produced by iNOS contributed to the histopathological consequences of TBI, inhibition of iNOS activity using aminoguanidine (intraperitoneal injections of 100 mg/kg aminoguanidine [n = 9] or vehicle [n = 8], twice each day) was conducted for 3 days.

RESULTS

Significantly elevated iNOS activity was detected at 3 days (276.8+/-72.3% of contralateral value, means +/- standard errors; P < 0.05), and the most robust increase occurred 7 days after TBI (608.0+/-127.0%, P < 0.01) in the injured parietal cerebral cortex. Immunostaining for iNOS and glial fibrillary acidic protein, at 3 and 7 days after TBI, revealed that the major cellular sources of iNOS expression were cortical Layer 1 astrocytes and macrophages within the subarachnoid space. Administration of aminoguanidine did not reduce contusion volume significantly; however, treatment reduced total cortical necrotic neuron counts (1367.6+/-210.3; P < 0.01, compared with vehicle, 2808.5+/-325.1).

CONCLUSION

These data indicate that iNOS is expressed after moderate parasagittal fluid-percussion brain injury, in a time-dependent manner, and that inhibition of iNOS synthesis improves histopathological outcomes. Thus, inhibition of iNOS activation may represent a potential therapeutic strategy for the treatment of TBI.

Ethanol modulates induction of nitric oxide synthase in glial cells by endotoxin

Although ethanol has long been recognized as an immunosuppressant, the effects of ethanol on immune functions in the central nervous system (CNS) have not been well characterized. Glial cells function as immune effector cells within the CNS. Nitric oxide (NO), generated by inducible NO synthase (iNOS) of activated glial cells, appears to participate in the immune defense and the pathogenesis of brain injury and several neurologic diseases. The goal of the present study was to examine the effects of ethanol on NO production and mRNA expression of iNOS following its induction by bacterial endotoxin lipopolysaccharide (LPS) in cultured glial cells. After incubation of mixed glia with LPS for 24 hr, the levels of nitrite in the culture medium were assayed by Griess reaction. We found that LPS (10-500 ng/ml) induced a concentration-dependent increase in the production of NO which was abolished by the selective iNOS inhibitor aminoguanidine. While ethanol treatment (25 to 400 mM, 24 hr exposure) had no direct effect on basal NO production, it significantly suppressed the LPS-induced increase of nitrite levels in a concentration-dependent manner. Using a semiquantitative reverse transcriptase polymerase chain reaction, we found that while ethanol by itself was unable to induce iNOS mRNA, it nevertheless suppressed LPS-induced iNOS mRNA expression. Our results that ethanol had no direct effect on NO production but inhibited LPS-induced NO, indicated an immunomodulatory role by ethanol. These findings suggest that ethanol may ameliorate the consequences of overwhelming NO generation through iNOS induction in glial cells following infection, inflammation or CNS injuries.

Role of PKC and tyrosine kinase in ethanol-mediated inhibition of LPS-inducible nitric oxide synthase

Ethanol increases human and animal susceptibility to opportunistic lung infections in part by suppression of endotoxin (LPS) and bacteria-mediated upregulation of inducible nitric oxide synthase (iNOS) in alveolar macrophages (AM). LPS and cytokine-induced NOS mRNA are dependent on NF-kappaB/Rel (NFkappaB) and Activator Protein-1 (AP-1), which are regulated in turn by protein kinase C and tyrosine kinase-dependent phosphorylation. ETOH does not directly inhibit NFkappaB or AP-1, in vivo, but rather inhibits LPS-induced activation of the MEKK/MAP kinase system and inhibition of inhibitory protein IkappaBalpha required for formation of AP-1 and NFkappaB, respectively. in AM. Both transcription factors are involved iNOS mRNA transcription. LPS-induced upregulation of MEKK/MAP tyrosine kinase upregulates NADPH oxidase activity and oxygen free radical formation required for activation of NFkappaB and AP-1 and phosphorylation of IkappaBalpha. LPS downregulates endogenous calcium-sensitive PKC isozymes (PKCdelta), which repress iNOS mRNA expression. ETOH inhibits LPS-induced upregulation of iNOS mRNA by preventing its ability to decrease PKCdelta and upregulate tyrosine kinase-mediated phosphorylation. This effect of ETOH is prevented by inhibitors of PKC and tyrosine kinase. The data support the hypothesis that ETOH inhibits LPS-induced upregulation of iNOS mRNA by interfering with the phosphorylation processes involved in activation of the nuclear transcription factors NFkappaB and AP-1.

Protein kinase C eta mediates lipopolysaccharide-induced nitric-oxide synthase expression in primary astrocytes

The signaling pathway involved in protein kinase C (PKC) activation and role of PKC isoforms in lipopolysaccharide (LPS)-induced nitric oxide (NO) release were studied in primary cerebellar astrocytes. LPS caused a dose- and time-dependent increase in NO release and inducible NO synthase (iNOS) expression. The tyrosine kinase inhibitor, genestein, the phosphatidylcholine-phospholipase C inhibitor, D609, and the phosphatidate phosphodrolase inhibitor, propranolol, attenuated the LPS effects, whereas the PI-PLC inhibitor, U73122, had no effect. The PKC inhibitors (staurosporine, Ro 31-8220, Go 6976, and calphostin C) also inhibited LPS-induced NO release and iNOS expression. However, long term (24 h) pretreatment of cells with 12-O-tetradecanoyl phorbol-13-acetate (TPA) did not affect the LPS response. Previous results have shown that TPA-induced translocation, but not down-regulation, of PKCeta occurs in astrocytes (Chen, C. C., and Chen, W. C. (1996) Glia 17, 63-71), suggesting possible involvement of PKCeta in LPS-mediated effects. Treatment with antisense oligonucleotides for PKCeta or delta, another isoform abundantly expressed in astrocytes, demonstrated the involvement of PKCeta, but not delta, in LPS-mediated effects. Stimulation of cells for 1 h with LPS caused activation of nuclear factor (NF)-kB in the nuclei as detected by the formation of a NF-kB-specific DNA-protein complex; this effect was inhibited by genestein, D609, propranolol, or Ro 31-8220 or by PKCeta antisense oligonucleotides, but not by long term TPA treatment. These data suggest that in astrocytes, LPS might activate phosphatidylcholine-phospholipase C and phosphatidylcholine-phospholipase D through an upstream protein tyrosine kinase to induce PKC activation. Of the PKC isoforms present in these cells, only activation of PKCeta by LPS resulted in the stimulation of NF-kB-specific DNA-protein binding and then initiated the iNOS expression and NO release. This is further evidence demonstrating that different members of the PKC family within a single cell are involved in specific physiological responses.

Monophosphoryl lipid A attenuates myocardial stunning in dogs: role of ATP-sensitive potassium channels

Results of previous studies indicate that monophosphoryl lipid A (MLA) reduces myocardial infarct size when administered 24 but not 1 h before a prolonged period of regional ischemia in dogs and rabbits. This cardioprotective effect of MLA could be reversed by the administration of the adenosine triphosphate (ATP)-sensitive potassium channel (K(ATP)) blockers, glibenclamide, or 5-hydroxydecanoate. MLA also was shown to attenuate myocardial stunning in dogs; however, its mechanism in this model remains unknown. Therefore the major aim of our study was to determine the dose-related effect of MLA to enhance contractile function in stunned myocardium and to determine the role of the K(ATP) channel in mediating its cardioprotective effect. To produce myocardial stunning, barbital-anesthetized dogs were subjected to five cycles of 5 min of left anterior descending (LAD) coronary artery occlusion interspersed with 10 min of reperfusion and finally followed by 2 h of reperfusion. Regional segment shortening (%SS) was determined by sonomicrometers implanted in the subendocardium of the ischemic region. Single intravenous doses of MLA in the range of 10-35 microg/kg given 24 h before ischemia resulted in an improvement in %SS over a 2-h reperfusion period. Similar to results obtained in the canine and rabbit infarct models, cardioprotection against stunning with MLA appears to require activation of K(ATP) channels during ischemia, because glibenclamide (50 microg/kg, 15 min before ischemia) completely blocked the effect of MLA to improve regional %SS during reperfusion. Cardioprotective doses of MLA were without effect on systemic hemodynamics, blood gases, and pH throughout the experiment. No treatment-related effects on regional myocardial blood flow were observed during ischemia or reperfusion. These results suggest that MLA improves %SS at doses of 10-35 microg/kg by an ATP-sensitive potassium channel-dependent process, and that MLA may mimic the antistunning effects observed during the second window of ischemic preconditioning.

Synergistic neurotoxic effects of combined treatments with cytokines in murine primary mixed neuron/glia cultures

Activation of brain glial cells with the bacterial endotoxin lipopolysaccharide (LPS), the HIV-1 coat protein gp120, or beta-amyloid-derived peptides, stimulates the expression of several cytokines, including tumor necrosis factor-alpha (TNFalpha), interleukin-1 (IL-1) and IL-6. and nitric oxide (NO) which have been proposed as causes of neurodegeneration in the brain. In the present study, the neurotoxic effects of several cytokines, alone or in various combinations, and the correlations of the release of lactate dehydrogenase, the loss of neurons, and the secretion of NO in brain neuronal cell injury were investigated in murine primary mixed neuronal/glial cell cultures. A specific combination of cytokines, i.e., IL-1 (1 ng/ml)+ TNFalpha (10 ng/ml)/interferon-gamma (IFNgamma) (200 u/ml), induced a dramatic neuronal cell injury in the neuron/glia cultures, and its cytotoxic profile was very similar to that seen with the LPS/IFNgamma-induced neuron injury. This indicates that among the many toxic immune mediators secreted in response to LPS, IL-1 and TNFalpha can mimic LPS as the triggering signals and primary mediators for glia-mediated neuron injury in the presence of IFNgamma. This study provides new insights about the cytotoxic mechanism(s) for cytokine-mediated neuron injury.

Involvement of protein kinases in the induction of NO synthase II in human DLD-1 cells

1. Protein phosphorylation is involved in the induction of nitric oxide synthase II (NOS II, iNOS) in several types of animal cells. Here we have investigated the possible involvement of major protein kinases in the induction of NOS II expression in human DLD-1 cells. 2. In DLD-1 cells, interferon--gamma alone induced a submaximal NOS II expression; a cytokine mixture consisting of interferon-gamma, tumour necrosis factor-alpha and interleukin-1beta produced maximal NOS II induction. 3. Activators of protein kinase A (forskolin, 8-dibutyryl-cyclic AMP), of protein kinase C (tetradecanoylphorbol-13-acetate), and of protein kinase G (8-bromo cyclic GMP) did not induce NOS II mRNA by themselves, nor did they alter NOS II mRNA induction in response to cytokines. 4. Inhibitors of protein kinase A (compound H89), of protein kinase C (bisindolylmaleimide, chelerythrine or staurosporine), of phosphatidylinositol 3-kinase (wortmannin), of p38 mitogen-activated protein kinase (compound SB 203580) and of extracellular signal-regulated kinase (compound PD 98059) also had no influence on basal or cytokine-induced NOS II mRNA expression. 5. Immunoprecipitation kinase assays showed no activation of extracellular signal-regulated kinase or p38 mitogen-activated protein kinase in cytokine-incubated DLD-1 cells. The c-Jun NH2-terminal kinase was activated by cytokines, but the most efficacious cytokine was tumour necrosis factor-alpha which did not induce NOS II by itself. 6. In contrast, the protein tyrosine kinase inhibitor tyrphostin B42 (a specific inhibitor of interferon-gamma-activated janus kinase 2) and the protein tyrosine kinase inhibitor tyrphostin A25 both reduced CM-induced NOS II mRNA expression in a concentration-dependent manner. 7. These results suggest that activation of NOS II expression in DLD-1 cells is independent of the activities of protein kinases A, C and G, phosphatidylinositol 3-kinase, extracellular signal regulated kinase and p38 mitogen-activated protein kinase, but seems to require protein tyrosine kinase activity, especially the interferon-gamma-activated janus kinase 2.

Suppression of nitric oxide formation by tyrosine kinase inhibitors in murine N9 microglia

1. Microglial cells represent the first line of defence in the brain against infection and damage. However, under conditions of chronic inflammation and neurodegeneration, excessive activation of microglia can contribute to the neurodegenerative process by releasing a cornucopia of potentially cytotoxic substances including the cytotoxic free radical nitric oxide (NO). Although the cell signalling events implicated in NO formation in peripheral macrophages are well defined, events occurring in the phenotypically homologous cerebral microglial cell are not yet fully characterized. 2. In the present study, a cloned murine microglial cell line (N9), stimulated with combined lipopolysaccharide/interferon-gamma (LPS/IFN) incubation, was shown to produce a significant increase in NO formation, as measured by medium nitrite levels, during 8-72 h exposure. 3. LPS/IFN-stimulated NO production was partially inhibited with the nitric oxide synthase (NOS) competitive antagonists; N(omega)-nitro-L-arginine methyl ester and N(omega)-nitro-L-arginine. The ability of the selective inducible (iNOS) inhibitor, aminoguanidine, but not the selective 'neuronal-type' constitutive (cNOS) inhibitor 7-nitroindazole, to inhibit NO production suggested a primary role of iNOS in this response and was confirmed by immunolabelling of activated cells with a specific iNOS antibody. 4. A series of tyrosine kinase inhibitors, herbimycin A, genestein, tyrphostins, AG-126, AG-556 and the tyrosine phosphatase inhibitors, sodium orthovanadate and phenylarsine oxide, significantly attenuated LPS/IFN-mediated NO production. The serine/threonine kinase inhibitors, staursporine (protein kinase C), H-9 (cyclic GMP/cyclic AMP-dependent kinase) or serine/threonine phosphatase inhibitors, cyclosporin A (phosphatase 2B) and okadaic acid (phosphatase 1/2A), reduced NO formation by an apparent cytostatic mechanism, as determined by cellular reduction of 3-(4,5-dimethylthiazol-2-yi)-2,5-diphenyl-tetrazolium bromide (MTT). 5. The present results suggest that the co-ordinated activation of protein tyrosine kinases/phosphatases, and proximal signalling events implicating the interplay between serine-threonine kinases/phosphatases, is intricately linked with inflammatory mediated mechanisms of iNOS activation in microglial cells by regulating the activation of the transcription factor NFkappaB.

Activation of Stat1 and subsequent transcription of inducible nitric oxide synthase gene in C6 glioma cells is independent of interferon-gamma-induced MAPK activation that is mediated by p21ras

Rat C6 glioma cells have been used to characterize molecular events involved in the regulation of inducible nitric oxide synthase (iNOS) gene expression stimulated by interferon-gamma (IFN-gamma) plus lipopolysaccharide (LPS). IFNs induce a signaling event which involves activation of Stat1 transcription factor. Previous studies have shown that IFNs also induce extracellular signal-regulated kinase/mitogen-activated protein kinase (ERK/MAPK) activation. However, the mechanisms by which IFNs stimulate MAPK activation remain elusive. Here we show that in C6 glioma cells, transiently expressing the dominant-negative form of c-Ha-Ras (Asn-17) abrogated IFN-gamma-induced ERK1 and ERK2 activation. Furthermore, PD98059, a specific MEK1 inhibitor, also blocked this activation. These results indicate that p21ras and MEK1 are required for IFN-gamma-induced ERK1 and ERK2 activation. Recent studies have reported that MAPK is responsible for serine phosphorylation of Stat1 which is required for Stat1's DNA binding and maximal transcriptional activity. Thus, we examined the role of the Ras-MAPK pathway in Stat1 activation and subsequent iNOS induction in C6 glioma cells. Further experiments showed that neither Asn-17 Ras expression nor concentrations of PD98059, which completely abrogated IFN-gamma-induced ERK1 and ERK2 activation, affected Stat1 DNA binding activity or iNOS induction, indicating that the Ras-MAPK pathway does not appear to be involved in the activation of Stat1 and subsequent iNOS induction in C6 glioma cells.