Tyrosine kinase inhibition reduces inflammation in the acute stage of experimental pneumococcal meningitis

Tyrphostin AG126 exerts neuroprotection in CNS inflammation by a dual mechanism

The putative protein tyrosine kinase (PTK) inhibitor tyrphostin AG126 has proven beneficial in various models of inflammatory disease. Yet molecular targets and cellular mechanisms remained enigmatic. We demonstrate here that AG126 treatment has beneficial effects in experimental autoimmune encephalomyelitis (EAE), a model for multiple sclerosis. AG126 alleviates the clinical symptoms, diminishes encephalitogenic Th17 differentiation, reduces inflammatory CNS infiltration as well as microglia activation and attenuates myelin damage. We show that AG126 directly inhibits Bruton's tyrosine kinase (BTK), a PTK associated with B cell receptor and Toll-like receptor (TLR) signaling. However, BTK inhibition cannot account for the entire activity spectrum. Effects on TLR-induced proinflammatory cytokine expression in microglia involve AG126 hydrolysis and conversion of its dinitrile side chain to malononitrile (MN). Notably, while liberated MN can subsequently mediate critical AG126 features, full protection in EAE still requires delivery of intact AG126. Its anti-inflammatory potential and especially interference with TLR signaling thus rely on a dual mechanism encompassing BTK and a novel MN-sensitive target. Both principles bear great potential for the therapeutic management of disturbed innate and adaptive immune functions.

Treatment and prevention strategies to combat pediatric pneumococcal meningitis

Pneumococcal meningitis is a severe, life-threatening infection of the nervous system affecting infants, children and adults alike. The incidence of pneumococcal meningitis in infants and children less than 2 years of age in Europe is approximately 10 out of 100,000 per year, rising to approximately 148 out of 100,000 per year in Gambian infants. The use of highly sensitive tests such as PCR may increase the likelihood of detecting the infection by 20% or more. Epidemics of serotype 1 pneumococcal meningitis in northern Ghana, have had many of the characteristics of meningococcal meningitis epidemics. Neurologic sequelae may occur in 28-63% of cases, and serotype 3 is associated with a 2.54 relative risk of death. The pathogenic process can be divided into invasion, inflammatory pathways, bacterial toxicity and damage; pneumolysin being particularly associated with apoptosis. In the future, neuroprotection may be achieved, targeting this process at all these levels. Therapeutic guidelines have been published by the Infectious Diseases Society of America. Standard empiric therapy, in those aged greater than or equal to 1 month, is a third-generation cephalosporin plus vancomycin. There is insufficient evidence relating to the use or otherwise of corticosteroids in pneumococcal meningitis to make a firm recommendation. The advent of a pneumococcal conjugate vaccine is the most powerful tool available for the prevention of pneumococcal meningitis in all parts of the world.

Src kinase is a direct target of apigenin against UVB-induced skin inflammation

Apigenin, a flavonoid abundant in various vegetables and fruits, including parsley and onions, has been reported to possess anticarcinogenic effects. However, the direct molecular target of apigenin and its chemopreventive effect on ultraviolet (UV)-induced skin inflammation are not understood fully. Herein, we examined the anti-inflammatory effect of apigenin and its associated mechanisms in JB6 P+ cell line and SKH-1 hairless mouse model. Apigenin inhibited UVB-induced cyclooxygenase-2 (COX-2) expression, which is a well-known key mediator of inflammation and cancer, and restored the upstream stimulatory factor level in JB6 P+ cells. Immunoblot and kinase assay data demonstrate that Src activity was attenuated by apigenin, and this led to subsequent inhibition of UVB-induced phosphorylation of epidermal growth factor receptor, mitogen-activated protein kinases and Akt signaling. Inhibitory effects of apigenin on UVB-induced signaling were also confirmed in HaCaT human keratinocytes. In addition, in vitro pull-down assays revealed that apigenin binds Src in an adenosine triphosphate-competitive manner. Results using in vivo skin model indicate apigenin significantly inhibits UVB-induced ear edema development, COX-2 expression and Src kinase activity in SKH-1 hairless mice. Collectively, these findings suggest that apigenin exerts potent chemopreventive activity against UVB-induced skin inflammation primarily by targeting Src.

Comparison of MEK/ERK pathway inhibitors on the upregulation of vascular G-protein coupled receptors in rat cerebral arteries

Organ culture is an in vitro method for investigating cellular mechanisms involved in upregulation of vasocontractile G-protein coupled receptors. We hypothesize that mitogen-activated-protein kinase (MEK) and/or extracellular-signal-regulated kinase (ERK) specific inhibitors will attenuate the G-protein coupled receptor expression following organ culture. Rat cerebral arteries were incubated 48h in the presence of MEK/ERK specific inhibitors U0126, PD98059, SL327, or AG126 for different time periods. Contractile responses by activation of endothelin receptor type A and type B, serotonin receptor 5-HT(1B), prostanoid TP receptor, and angiotensin II receptor type 1 and type 2 were investigated. Results were verified by measurement of mRNA with real time PCR and by protein immunohistochemistry. Organ culture induced transcriptional upregulation of endothelin ET(B) receptor and of serotonin 5-HT(1B) receptor on translational level and increased respective contractions. The prostanoid TP receptor mediated contraction curve was left-wards shifted by organ culture. Organ culture was associated with elevated pERK1/2 in the vascular smooth muscle cells: the MEK1/2 inhibitor U0126 attenuated the endothelin ET(B) receptor mediated contraction at post-translational level or by changing the receptor affinities. The serotonin 5-HT(1B) receptor and prostanoid TP receptor mediated contractions were abolished by U0126. Administration of U0126 6h after start of incubation blocked the receptor upregulation. In conclusion, MEK specific inhibitor U0126 is a potent inhibitor of G-protein coupled receptor alteration seen during organ culture. Given the ability to inhibit G-protein coupled receptor alteration at the clinically relevant time-point 6h post incubation makes it an attractive therapeutic agent for in vivo studies.

Headache attributed to infections nosography and differential diagnosis

Headache is a very frequent symptom of infection. It has many possible underlying mechanisms, of which two or more can coexist in a single patient. It can be caused by direct stimulation of intracranial pain-producing structures, as in the case of brain abscesses, by irritation of the pachy- and leptomeninges, as in cases of bacterial or viral meningitis, or by a state of intracranial hypertension, as seen in obstructive hydrocephalus. There is no doubt that headache is often the first or the predominant symptom of serious, sometimes life-threatening, infectious diseases; certainly, it is a condition frequently encountered in all epidemiological studies. Indeed, it is estimated that over 60% of people have, at some point in their lives, experienced headache during an infection. This evidence leads to the need for a systematic approach to headache secondary to infection. This chapter provides some elements on pain mechanisms in systemic and intracranial infections and on the possible role of antimicrobial agents in the genesis of headache. The first section provides a detailed "etiology-based" description of the International Classification of Headache Disorders, 2nd edition (ICHD-II: Headache Classification Subcommittee of the International Headache Society, 2004), while the second section presents a "symptom-based" algorithm applicable in the first diagnostic assessment, according to the headache features and to the most frequently associated clinical manifestations during infections of the central nervous system (CNS).

Inhibition of tyrosine kinase-mediated cellular signalling by Tyrphostins AG126 and AG556 modulates secondary damage in experimental spinal cord trauma

Protein tyrosine kinases help to regulate the expression of many genes, which play an important role in the pathophysiology of a number of diseases. Here we investigate the effects of the tyrosine kinase inhibitors, AG126 and AG556 on the degree of experimental spinal cord trauma induced by the application of vascular clips to the dura via a four-level T4-T8 laminectomy. Spinal cord injury in mice resulted in severe trauma characterized by oedema, neutrophil infiltration, production of a range of inflammatory mediators, tissue damage, and apoptosis. Treatment of the mice with AG126 and AG556 significantly reduced the degree of (1) spinal cord inflammation and tissue injury (histological score), (2) neutrophil infiltration (myeloperoxidase activity), (3) iNOS, nitrotyrosine, and PARP expression and (4) apoptosis (TUNEL staining and Bax and Bcl-2 expression). In a separate set of experiments, AG126 and AG556 significantly ameliorated the recovery of limb function (evaluated by motor recovery score). This study provides an experimental evidence that (1) prevention of the activation of protein tyrosine kinases reduces the development of inflammation and tissue injury associated with spinal cord trauma, and (2) inhibition of the activity of certain tyrosine kinases may represent a novel approach for the therapy of spinal cord trauma.

Differential regulation of blood–brain barrier permeability in brain trauma and pneumococcal meningitis—role of Src kinases

Increased vascular permeability causing vasogenic brain edema is characteristic for many acute neurological diseases such as stroke, brain trauma, and meningitis. Src family kinases, especially c-Src, play an important role in regulating blood-brain barrier permeability in response to VEGF, but also mediate leukocyte function and cytokine signalling. Here we demonstrate that pharmacological inhibition of Src or c-Src deficiency does not influence cerebrospinal fluid (CSF) pleocytosis, brain edema formation, and bacterial outgrowth during experimental pneumococcal meningitis despite the increased cerebral expression of inflammatory chemokines, such as IL-6, CCL-9, CXCL-1, CXCL-2 and G-CSF as determined by protein array analysis. In contrast, inhibition of Src significantly reduced brain edema formation, lesion volume, and clinical worsening in cold-induced brain injury without decreasing cytokine/chemokine expression. While brain trauma was associated with increased cerebral VEGF formation, VEGF levels significantly declined during pneumococcal meningitis. Therefore, we conclude that in brain trauma blood-brain barrier tightness is regulated by the VEGF/Src pathway whereas c-Src does not influence brain edema formation and leukocyte function during bacterial meningitis.

Drug Insight: adjunctive therapies in adults with bacterial meningitis

Despite the availability of effective antibiotics, mortality and morbidity rates associated with bacterial meningitis are high. Studies in animals have shown that bacterial lysis, induced by treatment with antibiotics, leads to inflammation in the subarachnoid space, which might contribute to an unfavorable outcome. The management of adults with bacterial meningitis can be complex, and common complications include meningoencephalitis, systemic compromise, stroke and raised intracranial pressure. Various adjunctive therapies have been described to improve outcome in such patients, including anti-inflammatory agents, anticoagulant therapies, and strategies to reduce intracranial pressure. Although a recent randomized trial provided evidence in favor of dexamethasone treatment, few randomized clinical studies are available for other adjunctive therapies in adults with bacterial meningitis. This review briefly summarizes the pathogenesis and pathophysiology of bacterial meningitis, and focuses on the evidence for and against use of the available adjunctive therapies in clinical practice.

Gene expression in cortex and hippocampus during acute pneumococcal meningitis

Background

Pneumococcal meningitis is associated with high mortality (~30%) and morbidity. Up to 50% of survivors are affected by neurological sequelae due to a wide spectrum of brain injury mainly affecting the cortex and hippocampus. Despite this significant disease burden, the genetic program that regulates the host response leading to brain damage as a consequence of bacterial meningitis is largely unknown.

We used an infant rat model of pneumococcal meningitis to assess gene expression profiles in cortex and hippocampus at 22 and 44 hours after infection and in controls at 22 h after mock-infection with saline. To analyze the biological significance of the data generated by Affymetrix DNA microarrays, a bioinformatics pipeline was used combining (i) a literature-profiling algorithm to cluster genes based on the vocabulary of abstracts indexed in MEDLINE (NCBI) and (ii) the self-organizing map (SOM), a clustering technique based on covariance in gene expression kinetics.

Results

Among 598 genes differentially regulated (change factor ≥ 1.5; p ≤ 0.05), 77% were automatically assigned to one of 11 functional groups with 94% accuracy. SOM disclosed six patterns of expression kinetics. Genes associated with growth control/neuroplasticity, signal transduction, cell death/survival, cytoskeleton, and immunity were generally upregulated. In contrast, genes related to neurotransmission and lipid metabolism were transiently downregulated on the whole. The majority of the genes associated with ionic homeostasis, neurotransmission, signal transduction and lipid metabolism were differentially regulated specifically in the hippocampus. Of the cell death/survival genes found to be continuously upregulated only in hippocampus, the majority are pro-apoptotic, while those continuously upregulated only in cortex are anti-apoptotic.

Conclusion

Temporal and spatial analysis of gene expression in experimental pneumococcal meningitis identified potential targets for therapy.

Strategies to prevent neuronal damage in paediatric bacterial meningitis

PURPOSE OF REVIEW

The mortality of bacterial meningitis can reach 30%, and up to 50% of survivors suffer from persisting neurological deficits as a consequence of the disease. The incidence of neurological sequelae of bacterial meningitis has not improved over the last decade. Adjunctive therapeutic options are limited, and ongoing research into the pathophysiology of brain damage in bacterial meningitis aims at providing the scientific basis for future development of more efficient adjunctive options.

RECENT FINDINGS

In a population with good access to health care, dexamethasone given before or at the time of initiation of antibiotic therapy acts beneficially in paediatric pneumococcal meningitis, but not in meningococcal meningitis. In experimental animal models, brain-derived neurotrophic factor protected against brain injury and improved hearing while melatonin, which has antioxidant properties among other effects, reduced neuronal death. Transgene technology can be used to provide new insights into the pathophysiology of the disease and to identify potential therapeutic targets.

SUMMARY

Although dexamethasone improves outcome of bacterial meningitis under defined circumstances, the morbidity of bacterial meningitis still remains unacceptably high. Experimental models may help to identify new therapeutic strategies to further improve the neurological outcome in young children suffering from bacterial meningitis.

Inhibition of tyrosine-kinase-mediated cellular signaling by tyrphostins AG 126 and AG556 modulates murine experimental acute pancreatitis

BACKGROUND

The effects of the tyrosine kinase inhibitors, tyrphostin AG126 and AG556 in a murine model of acute pancreatitis are investigated.

METHODS

Intraperitoneal injection of cerulein in mice resulted in a severe, acute pancreatitis, which was characterized by edema, neutrophil infiltration, tissue hemorrhage, and cell necrosis as well as elevation in the serum activities of amylase or lipase.

RESULTS

Infiltration of the pancreatic tissue of these animals with neutrophils (measured as increase in myeloperoxidase activity) was associated with signs of enhanced lipid peroxidation (increased tissue levels of malondialdehyde). Immunohistochemical examination showed a marked increase in immunoreactivity for nitrotyrosine and poly (ADP-ribose) polymerase (PARP) in the pancreas of cerulein-treated mice. Pretreatment or posttreatment with tyrphostin AG126 and AG556, 2 different tyrosine kinase inhibitors, significantly reduced the degree of pancreatic inflammation and tissue injury (histologic score). In particular, the treatment with the 2 tyrosine kinase inhibitors reduced the cerulein-induced nitrotyrosine formation and PARP activation in the pancreas as well as the systemic release of tumor necrosis factor alpha.

CONCLUSIONS

This study provides the first evidence that (1) prevention of the activation of protein tyrosine kinases reduces the development of acute pancreatitis, and (2) inhibition of the activity of certain tyrosine kinases may represent a novel approach for the therapy of acute pancreatitis.