A3 adenosine receptor activation decreases mortality and renal and hepatic injury in murine septic peritonitis

The role of A3 adenosine receptors (ARs) in sepsis and inflammation is controversial. In this study, we determined the effects of A3AR modulation on mortality and hepatic and renal dysfunction in a murine model of sepsis. To induce sepsis, congenic A3AR knockout mice (A3AR KO) and wild-type control (A3AR WT) mice were subjected to cecal ligation and double puncture (CLP). A3AR KO mice had significantly worse 7-day survival compared with A3AR WT mice. A3AR KO mice also demonstrated significantly higher elevations in plasma creatinine, alanine aminotransferase, aspartate aminotransferase, keratinocyte-derived chemokine, and TNF-alpha 24 h after induction of sepsis compared with A3AR WT mice. Renal cortices from septic A3AR KO mice exhibited increased mRNA encoding proinflammatory cytokines and enhanced nuclear translocation of NF-kB compared with samples from A3AR WT mice. A3AR WT mice treated with N6-(3-iodobenzyl)ADO-5'N-methyluronamide (IB-MECA; a selective A3AR agonist) or 3-ethyl-5-benzyl-2-methyl-4-phenylethynyl-6-phenyl-1,4-(+/-)-dihydropyridine-3,5-dicarboxylate (MRS-1191; a selective A3AR antagonist) had improved or worsened 7-day survival after induction of sepsis, respectively. Moreover, A3AR WT mice treated with IB-MECA or MRS-1191 showed acutely improved or worsened, respectively, renal and hepatic function following CLP. IB-MECA significantly reduced mortality in mice lacking the A1AR or A2aAR but not the A3AR, demonstrating specificity of IB-MECA in activating A3ARs and mediating protection against sepsis-induced mortality. We conclude that endogenous or exogenous A3AR activation confers significant protection from murine septic peritonitis primarily by attenuating the hyperacute inflammatory response in sepsis.

Transient neuronal but persistent astroglial activation of ERK/MAP kinase after focal brain injury in mice

Astrogliosis is a nearly ubiquitous response to a variety of insults to the central nervous system (CNS). This reaction is triggered rapidly, but can persist for years after the initial trauma. Little is known about the signaling mechanisms responsible for this activation and its chronic maintenance. Extracellular signal-regulated kinase/mitogen-activated protein kinase (ERK/MAPK) activation is implicated in several functions important to the reactive glial phenotype such as cellular proliferation and motility. Here we utilize immunohistochemistry with a phosphorylation state-specific antibody (pERK) to characterize the temporal and spatial pattern of ERK/MAPK activation in neurons and glia following a forebrain stab lesion (FSL) in mice. Early activation (1 h) was primarily in perilesional neuronal elements, particularly of the hippocampus. Occasional perilesional glia were also positive for pERK. Additionally, ependymal cells bilaterally stained prominently for pERK. These patterns of pERK immunoreactivity at 1 h were abolished by pretreatment with the selective MEK inhibitor, SL327. ERK/MAPK activation at later time points between 1 day (d) and 30 d was primarily restricted to perilesional astrocytes with maximum labeling at 3 d. However, pERK-positive astrocytes represented only a subset of total GFAP-positive cells and were found more proximal to the lesion suggesting specific functional activation of these cells. Finally, immunostaining for the phosphorylated form of cAMP response element-binding (CREB) protein, a downstream target of the ERK/MAPK cascade, was increased in perilesional glia 7 d after FSL. Sustained activation of the ERK/MAPK signaling pathway in perilesional reactive glia suggests a critical role for this cascade in astrogliosis.

Enhanced glial activation and expression of specific CNS inflammation-related molecules in aged versus young rats following cortical stab injury

Aging is associated with increased glial responsiveness that may enhance the brain's susceptibility to injury and disease. To determine whether unique age-related molecular responses occur in brain injury, we assessed mRNA levels of representative central nervous system (CNS) inflammation-related molecules in young (3 months) and aged (36 months) Fisher 344/Brown Norwegian F1 hybrid rats following cortical stab. Enhanced glial activation in older animals was accompanied by increased expression of a subset of inflammation-related mRNAs, including IL-1beta, TNFalpha, IL-6, ICAM-1, inducible nitric oxide synthase (iNOS), metalloproteinase-9 (MMP-9), and complement 3alpha-chain 1 (C3alpha1). Recognition of these age-specific differences may guide development of novel treatment regimes for older individuals.

Traumatic brain injury induces prolonged accumulation of cyclooxygenase-1 expressing microglia/brain macrophages in rats

Inflammatory cellular responses to brain injury are promoted by proinflammatory messengers. Cyclooxygenases (prostaglandin endoperoxide H synthases [PGH]) are key enzymes in the conversion of arachidonic acid into prostanoids, which mediate immunomodulation, mitogenesis, apoptosis, blood flow, secondary injury (lipid peroxygenation), and inflammation. Here, we report COX-1 expression following brain injury. In control brains, COX-1 expression was localized rarely to brain microglia/macrophages. One to 5 days after injury, we observed a highly significant (p < 0.0001) increase in COX-1+ microglia/macrophages at perilesional areas and in the developing core with a delayed culmination of cell accumulation at day 7, correlating with phagocytic activity. There, cell numbers remained persistently elevated up to 21 days following injury. Further, COX-1+ cells were located in perivascular Virchow-Robin spaces also reaching maximal numbers at day 7. Lesion-confined COX-1+ vessels increased in numbers from day 1, reaching the maximum at days 5-7. Double-labeling experiments confirmed coexpression of COX-1 by ED-1+ and OX-42+ microglia/ macrophages. Transiently after injury, most COX-1+ microglia/macrophages coexpress the activation antigen OX-6 (MHC class II). However, the prolonged accumulation of COX-1+, ED-1+ microglia/macrophages in lesional areas enduring the acute postinjury inflammatory response points to a role of COX-1 in the pathophysiology of secondary injury. We have identified localized, accumulated COX-1 expression as a potential pharmacological target in the treatment of brain injury. Our results suggest that therapeutic approaches based on long-term blocking including COX-1, might be superior to selective COX-2 blocking to suppress the local synthesis of prostanoids.

Cytokines regulate expression of the type 1 interleukin-1 receptor in rat hippocampal neurons and glia

Interleukin-1 beta is a key mediator of inflammation and stress in the central nervous system (CNS). This cytokine induces CNS glial cells to produce numerous additional cytokines and growth factors under inflammatory conditions. We have investigated regulation of the signal transducing type 1 interleukin-1 receptor (IL-1R1) in the CNS. In vivo, IL-1R1 was not detected in glial cells under basal conditions but was strongly induced after a stab lesion. Cultured astrocytes were used to identify specific signals that regulate expression of the receptor. IL-1R1 mRNA and protein were induced by inflammatory stimuli including tumor necrosis factor (TNF alpha) and IL-1 beta itself. Although expression of the receptor was not detected in glia under basal conditions in vivo, pyramidal neurons in the hippocampus expressed the IL-1 receptor in the normal, unlesioned brain. Cultured embryonic hippocampal neurons were used to investigate specific stimuli that regulate IL-1R1 in neurons. As in astrocytes, IL-1 and TNF alpha induced expression of IL-1R1. The expression of IL-1R1 in hippocampal neurons suggests a possible role for IL-1 in regulating neuronal function, and indicates that these neurons may be directly influenced by cytokines.

Transient in vivo activation of rat brain macrophages/microglial cells and astrocytes by immunostimulatory multiple CpG oligonucleotides

Certain DNA sequences containing motifs of unmethylated CpG nucleotides are immunostimulatory and might contribute to the development of inflammatory lesions after infections. CpG motifs might further contribute to side effects of oligonucleotide-based therapeutic approaches. Here we have analyzed the effects of intracranial injections of synthetic CpG oligonucleotides. We observed that oligonucleotides with several unmethylated CpG motifs, but not methylated or inverted GpC motifs, stimulated microglial cells and astrocytes of the rat brain. This transient, self-limiting response is maximal at day 3 after injection and subsides until day 5. Activated microglial cells could be identified to produce two novel monocytic peptides, the allograft inflammatory factor-1 (AIF-1) and endothelial monocyte activating polypeptide II (EMAP II). Astrocytes were similarly activated as shown by expression of the enzyme heme-oxygenase-1 (HO-1). Glial cell proliferation (expression of PCNA) or aptosis was not observed. Thus immunostimulatory DNA activates the local innate immune defense system of the brain, and might contribute transiently to infectious, inflammatory and degenerative responses of the central nervous system.

Regulation of the heparan sulfate proteoglycan, perlecan, by injury and interleukin-1alpha

Perlecan is a specific proteoglycan that binds to amyloid precursor protein and beta-amyloid peptide, is present within amyloid deposits, and has been implicated in plaque formation. Because plaque formation is associated with local inflammation, we hypothesized that the mechanisms involved in brain inflammatory responses could influence perlecan biosynthesis. To test this hypothesis, we first studied perlecan regulation in mice after inflammation induced by a brain stab wound. Perlecan mRNA and immunoreactivity were both increased 3 days after injury. Interleukin-1alpha (IL-1alpha) is a cytokine induced after injury and plays an important role in inflammation. As such, IL-1alpha may be one of the factors participating in regulating perlecan synthesis. We thus studied perlecan regulation by IL-1alpha, in vivo. Regulation of perlecan mRNA by this cytokine was area-specific, showing up-regulation in hippocampus, whereas in striatum, perlecan mRNA was unchanged. To support this differential regulation of perlecan mRNA by IL-1alpha, basic fibroblast growth factor (bFGF), a growth factor also present in plaques, was studied in parallel. bFGF mRNA did not show any regional difference, being up-regulated in both hippocampus and striatum in vivo. In vitro, both astrocyte and microglia were immunoreactive for perlecan. Moreover, perlecan mRNA was increased in hippocampal glial cultures after IL-1alpha but not in striatal glia. These results show an increase in perlecan biosynthesis after injury and suggest a specific regulation of perlecan mRNA by IL-1alpha, which depends on brain area. Such regulation may have important implications in the understanding of regional brain variations in amyloid plaque formation.

Patterns of injury and white cell response in critically ill trauma patients who present with leucopenia

The outcome of critically ill trauma patients who presented to the intensive care unit with leucopenia (total peripheral white cell count < 4 x 10(9)/1) was studied prospectively with respect to the total white cell and neutrophil response. A total of 105 patients, of whom 30 were leucopenic, were admitted to the ICU during a 4-month period. The prevalence of leucopenia was significantly higher in patients with gunshot wounds (P < 0.05) and hollow visceral intra-abdominal injury (P < 0.001). Eight (27%) of the leucopenic patients died. No significant difference was found in initial mean total white cell or neutrophil count, or in the differential percentages, between survivors and non-survivors. The total peripheral white cell count increased significantly in survivors compared with non-survivors (P < 0.001), and significant differences were found in absolute neutrophil counts and differential percentages by days 5 and 10 (counts P = 0.01, P < 0.02; differentials P < 0.01, P < 0.01). These results suggest that granulocyte colony-stimulating factor may have a role in the treatment of trauma patients with persistent neutropenia following intra-abdominal hollow visceral injury.

Astrogliosis in the neonatal and adult murine brain post-trauma: elevation of inflammatory cytokines and the lack of requirement for endogenous interferon-gamma

The relevance of astrogliosis remains controversial, especially with respect to the beneficial or detrimental influence of reactive astrocytes on CNS recovery. This dichotomy can be resolved if the mediators of astrogliosis are identified. We have measured the levels of transcripts encoding inflammatory cytokines in injury systems in which the presence or absence of astrogliosis could be produced selectively. A stab injury to the adult mouse brain using a piece of nitrocellulose (NC) membrane elicited a prompt and marked increase in levels of transcripts for interleukin (IL)-1alpha, IL-1beta, and tumor necrosis factor (TNF)-alpha, which are considered to be microglia/macrophage cytokines. The elevations preceded, or occurred concomitantly with, the rise in glial fibrillary acidic protein mRNA, an early manifestation of astrogliosis. In neonatal mice, IL-1 and TNF-alpha mRNA were elevated to a greater extent by an NC-implant injury, which produced astrogliosis, than after an NC-stab, with minimal astrogliosis. We determined whether endogenous interferon (IFN)-gamma could be responsible for the observed increases in IL-1 and TNF-alpha, because IFN-gamma is a potent microglia/macrophage activator, and because its exogenous administration to rodents enhanced astrogliosis after adult or neonatal insults. A lack of requirement for endogenous IFN-gamma was demonstrated by three lines of evidence. First, no increase in IFN-gamma transcripts could be found at injury. Second, the administration of a neutralizing antibody to IFN-gamma did not attenuate astrogliosis. Third, in IFN-gamma knockout adult mice, astrogliosis and increases in levels of IL-1alpha and TNF-alpha were induced rapidly by injury. The marked elevation of inflammatory cytokines is discussed in the context of astrogliosis and general CNS recovery.

Early events of the inflammatory reaction induced in rat brain by lipopolysaccharide intracerebral injection: relative contribution of peripheral monocytes and activated microglia

We have previously demonstrated that lipopolysaccharide (LPS) intracerebral injection induced only minimal inflammatory reaction in rat brain, apart from an increased number of 'brain macrophages' observed 24 h after LPS administration [Montero-Menei et al., Brain Res., 653 (1994) 101-111]. However, the nature of these 'brain macrophages' in the inflammatory response is still unclear. The present study focused on the early time-points (from 5 h to 24 h) after LPS injection or stab-lesion, and was aimed at the identification of the peripheral (monocytes) or parenchymal (microglia) origin of these 'brain macrophages'. OX42- and ED1-labeling did not clearly discriminate between monocytes/macrophages and reactive microglia, both cell types being immunoreactive. In other experiments, rats were made aplasic by irradiation prior to lesioning. These experiments clearly demonstrated that LPS induces an intense monocyte recruitment and, to a lesser extent, microglial activation since about 80% of the cells present 24 h after LPS injection consisted of recruited monocytes not observed in aplasic rats. Interestingly, our data show that LPS exerts a sequential dual action by first inhibiting the monocyte recruitment observed 5 h after stab lesion and then enhancing it at 15 h and 24 h after injection. A possible involvement of cytokines, chemokines and adhesion molecules in the mechanisms occurring in the early events of brain inflammatory reaction is discussed.

Increased blood-brain barrier dysfunction around cerebral stab wounds in rats immunized to brain antigens. A quantitative study on endogenous albumin and globulin

The extravasation of serum albumin and immunoglobulin G (IgG) was assayed by electroimmunoassay in cerebral cortex homogenates of rats subjected to stab wound injury either 2 weeks after immunisation to brain antigens or without prior immunisation. The amount of IgG in the brain was significantly higher in immunised than in non-immunised rats 3 and 24 h after injury. A significantly enhanced extravasation of albumin in immunised rats was found only after 24 h. It is concluded that immunisation to brain antigens enhances the vulnerability of the blood-brain barrier in rats subjected to stab wound injury.