Ischemic stroke and traumatic brain injury: the role of the kallikrein-kinin system

Tissue Kallikrein Alleviates Cerebral Ischemia-Reperfusion Injury by Activating the B2R-ERK1/2-CREB-Bcl-2 Signaling Pathway in Diabetic Rats

Diabetes mellitus (DM) substantially increases the risk of ischemic stroke and reduces the tolerance to ischemic insults. Tissue kallikrein (TK) has been demonstrated to protect neurons from ischemia/reperfusion (I/R) injury in orthoglycemic model by activating the bradykinin B2 receptor (B2R). Considering the differential effects of B2R or bradykinin B1 receptor (B1R) on cardioprotection and neuroprotection in I/R with or without diabetes, this study was designed to investigate the role of TK during cerebral I/R injury in streptozotocin-induced diabetic rats. Intravenous injection of TK inhibited apoptosis in neurons, alleviated edema and inflammatory reactions after focal cerebral I/R, significantly reduced the infarct volume, and improved functional recovery. These beneficial effects were accompanied by activation of the extracellular signal-regulated kinase 1/2 (ERK1/2), cAMP response element-binding (CREB), and Bcl-2 signal proteins. Inhibition of the B2R or ERK1/2 pathway abated the effects of TK, whereas an antagonist of B1R enhanced the effects. These findings reveal that the neuroprotective effect of TK against cerebral I/R injury in streptozotocin-induced diabetic rats mainly involves the enhancement of B2R and ERK1/2-CREB-Bcl-2 signaling pathway activity.

Long-Term Estrogen Receptor Beta Agonist Treatment Modifies the Hippocampal Transcriptome in Middle-Aged Ovariectomized Rats

Estradiol (E2) robustly activates transcription of a broad array of genes in the hippocampal formation of middle-aged ovariectomized rats via estrogen receptors (ERα, ERβ, and G protein-coupled ER). Selective ERβ agonists also influence hippocampal functions, although their downstream molecular targets and mechanisms are not known. In this study, we explored the effects of long-term treatment with ERβ agonist diarylpropionitrile (DPN, 0.05 mg/kg/day, sc.) on the hippocampal transcriptome in ovariectomized, middle-aged (13 month) rats. Isolated hippocampal formations were analyzed by Affymetrix oligonucleotide microarray and quantitative real-time PCR. Four hundred ninety-seven genes fulfilled the absolute fold change higher than 2 (FC > 2) selection criterion. Among them 370 genes were activated. Pathway analysis identified terms including glutamatergic and cholinergic synapse, RNA transport, endocytosis, thyroid hormone signaling, RNA degradation, retrograde endocannabinoid signaling, and mRNA surveillance. PCR studies showed transcriptional regulation of 58 genes encoding growth factors (Igf2, Igfb2, Igf1r, Fgf1, Mdk, Ntf3, Bdnf), transcription factors (Otx2, Msx1), potassium channels (Kcne2), neuropeptides (Cck, Pdyn), peptide receptors (Crhr2, Oprm1, Gnrhr, Galr2, Sstr1, Sstr3), neurotransmitter receptors (Htr1a, Htr2c, Htr2a, Gria2, Gria3, Grm5, Gabra1, Chrm5, Adrb1), and vesicular neurotransmitter transporters (Slc32a1, Slc17a7). Protein-protein interaction analysis revealed networking of clusters associated with the regulation of growth/troph factor signaling, transcription, translation, neurotransmitter and neurohormone signaling mechanisms and potassium channels. Collectively, the results reveal the contribution of ERβ-mediated processes to the regulation of transcription, translation, neurogenesis, neuromodulation, and neuroprotection in the hippocampal formation of ovariectomized, middle-aged rats and elucidate regulatory channels responsible for DPN-altered functional patterns. These findings support the notion that selective activation of ERβ may be a viable approach for treating the neural symptoms of E2 deficiency in menopause.

Blood coagulation factor XII drives adaptive immunity during neuroinflammation via CD87-mediated modulation of dendritic cells

Aberrant immune responses represent the underlying cause of central nervous system (CNS) autoimmunity, including multiple sclerosis (MS). Recent evidence implicated the crosstalk between coagulation and immunity in CNS autoimmunity. Here we identify coagulation factor XII (FXII), the initiator of the intrinsic coagulation cascade and the kallikrein-kinin system, as a specific immune cell modulator. High levels of FXII activity are present in the plasma of MS patients during relapse. Deficiency or pharmacologic blockade of FXII renders mice less susceptible to experimental autoimmune encephalomyelitis (a model of MS) and is accompanied by reduced numbers of interleukin-17A-producing T cells. Immune activation by FXII is mediated by dendritic cells in a CD87-dependent manner and involves alterations in intracellular cyclic AMP formation. Our study demonstrates that a member of the plasmatic coagulation cascade is a key mediator of autoimmunity. FXII inhibition may provide a strategy to combat MS and other immune-related disorders.

Rodent Hypoxia-Ischemia Models for Cerebral Palsy Research: A Systematic Review

Cerebral palsy (CP) is a complex multifactorial disorder, affecting approximately 2.5-3/1000 live term births, and up to 22/1000 prematurely born babies. CP results from injury to the developing brain incurred before, during, or after birth. The most common form of this condition, spastic CP, is primarily associated with injury to the cerebral cortex and subcortical white matter as well as the deep gray matter. The major etiological factors of spastic CP are hypoxia/ischemia (HI), occurring during the last third of pregnancy and around birth age. In addition, inflammation has been found to be an important factor contributing to brain injury, especially in term infants. Other factors, including genetics, are gaining importance. The classic Rice-Vannucci HI model (in which 7-day-old rat pups undergo unilateral ligation of the common carotid artery followed by exposure to 8% oxygen hypoxic air) is a model of neonatal stroke that has greatly contributed to CP research. In this model, brain damage resembles that observed in severe CP cases. This model, and its numerous adaptations, allows one to finely tune the injury parameters to mimic, and therefore study, many of the pathophysiological processes and conditions observed in human patients. Investigators can recreate the HI and inflammation, which cause brain damage and subsequent motor and cognitive deficits. This model further enables the examination of potential approaches to achieve neural repair and regeneration. In the present review, we compare and discuss the advantages, limitations, and the translational value for CP research of HI models of perinatal brain injury.

Tissue Kallikrein Prevents Restenosis After Stenting of Severe Atherosclerotic Stenosis of the Middle Cerebral Artery: A Randomized Controlled Trial

In-stent restenosis (ISR) following intracranial artery stenting affects long-term clinical outcome. This randomized controlled trial sought to identify the long-term efficacy of exogenous tissue kallikrein (TK) for preventing ISR after intracranial stenting of symptomatic middle cerebral artery (MCA) atherosclerotic stenosis.Sixty-one patients successfully treated with intracranial stenting for symptomatic MCA M1 segment stenosis (>70%) were enrolled and randomized into 2 groups: control group and TK group. Patients in the TK group received human urinary kallidinogenase for 7 days, followed by maintenance therapy of pancreatic kallikrein for 6 months. The primary end point was angiographically verified ISR at 6 months, and secondary end points included vascular events and death within 12 months. Endogenous TK plasma concentrations of patients were measured before stenting and at the 6-month follow-up time-point.Patients in the TK group had lower occurrence rates of ISR and vascular events than patients in the control group. There was no difference in endogenous TK levels in plasma at 6 months postoperatively between the TK and control groups. Further subgroup analysis revealed that patients without ISR had higher endogenous TK levels at baseline and lower concentrations at 6 months postoperatively compared with patients who underwent ISR.Exogenous TK is effective for the prevention of ISR after intracranial stenting.

Ischemic, traumatic and neurodegenerative brain inflammatory changes

This review serves to link the role of the immune system in the neuropathology of acute ischemic stroke, traumatic brain injury and neurodegenerative disease. The blood–brain barrier delineates the CNS from the peripheral immune system. However, the blood–cerebrospinal fluid barrier acts as a gate between the periphery and the brain, permitting immune activity crosstalk and modulation. In acute ischemic stroke, traumatic brain injury and other neurodegenerative diseases, the blood–brain barrier is compromised and an influx of inflammatory cells and plasma proteins occurs, resulting in edema, demyelination, cell dysfunction and death, and neurobehavioral changes. The role of the complement system, key cytokines, microglia and other neuroglia in brain degenerative pathology will be discussed.

The Coagulation Factor XIIa Inhibitor rHA-Infestin-4 Improves Outcome after Cerebral Ischemia/Reperfusion Injury in Rats

Background and Purpose

Ischemic stroke provokes severe brain damage and remains a predominant disease in industrialized countries. The coagulation factor XII (FXII)-driven contact activation system plays a central, but not yet fully defined pathogenic role in stroke development. Here, we investigated the efficacy of the FXIIa inhibitor rHA-Infestin-4 in a rat model of ischemic stroke using both a prophylactic and a therapeutic approach.

Methods

For prophylactic treatment, animals were treated intravenously with 100 mg/kg rHA-Infestin-4 or an equal volume of saline 15 min prior to transient middle cerebral artery occlusion (tMCAO) of 90 min. For therapeutic treatment, 100 mg/kg rHA-Infestin-4, or an equal volume of saline, was administered directly after the start of reperfusion. At 24 h after tMCAO, rats were tested for neurological deficits and blood was drawn for coagulation assays. Finally, brains were removed and analyzed for infarct area and edema formation.

Results

Within prophylactic rHA-Infestin-4 treatment, infarct areas and brain edema formation were reduced accompanied by better neurological scores and survival compared to controls. Following therapeutic treatment, neurological outcome and survival were still improved although overall effects were less pronounced compared to prophylaxis.

Conclusions

With regard to the central role of the FXII-driven contact activation system in ischemic stroke, inhibition of FXIIa may represent a new and promising treatment approach to prevent cerebral ischemia/reperfusion injury.

Neuroprotective Effect of Scutellarin on Ischemic Cerebral Injury by Down-Regulating the Expression of Angiotensin-Converting Enzyme and AT1 Receptor

Background and Purpose

Previous studies have demonstrated that angiotensin-converting enzyme (ACE) is involved in brain ischemic injury. In the present study, we investigated whether Scutellarin (Scu) exerts neuroprotective effects by down-regulating the Expression of Angiotensin-Converting Enzyme and AT1 receptor in a rat model of permanent focal cerebral ischemia.

Methods

Adult Sprague–Dawley rats were administrated with different dosages of Scu by oral gavage for 7 days and underwent permanent middle cerebral artery occlusion (pMCAO). Blood pressure was measured 7 days after Scu administration and 24 h after pMCAO surgery by using a noninvasive tail cuff method. Cerebral blood flow (CBF) was determined by Laser Doppler perfusion monitor and the neuronal dysfunction was evaluated by analysis of neurological deficits before being sacrificed at 24 h after pMCAO. Histopathological change, cell apoptosis and infarct area were respectively determined by hematoxylin–eosin staining, terminal deoxynucleotidyl transfer-mediated dUTP nick end labeling (TUNEL) analysis and 2,3,5-triphenyltetrazolium chloride staining. Tissue angiotensin II (Ang II) and ACE activity were detected by enzyme-linked immunosorbent assays. The expression levels of ACE, Ang II type 1 receptor (AT1R), tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and interleukin-1β (IL-1β) were measured by Western blot and real-time PCR. ACE inhibitory activity of Scu in vitro was detected by the photometric determination.

Results

Scu treatment dose-dependently decreased neurological deficit score, infarct area, cell apoptosis and morphological changes induced by pMCAO, which were associated with reductions of ACE and AT1R expression and the levels of Ang II, TNF-α, IL-6, and IL-1β in ischemic brains. Scu has a potent ACE inhibiting activity.

Conclusion

Scu protects brain from acute ischemic injury probably through its inhibitory effect on the ACE/Ang II/AT1 axis, CBF preservation and proinflammation inhibition.

Urinary kallidinogenase for the treatment of cerebral arterial stenosis

Aim

Urinary kallidinogenase (UK) has shown promise in improving cerebral perfusion. This study aimed to examine how UK affects cognitive status and serum levels of amyloid betas (Aβs) 1-40 and 1-42 in patients with cerebral arterial stenosis.

Methods

Ninety patients with cerebral arterial stenosis were enrolled, of whom 45 patients received UK + conventional treatment (UK group), and 45 patients received conventional treatment alone as control group. Cognitive status and Aβ1-40 and Aβ1-42 serum levels were determined before treatment and at 4 weeks and 8 weeks after treatment.

Results

At 4 weeks after treatment, cognitive status in patients treated with UK clearly improved accompanied by Aβ1-40 serum levels decreasing while there was no change of Aβ1-42. Cognitive status in patients receiving UK continued to improve, Aβ1-40 serum levels declined further as well as Aβ1-42 serum levels began to decrease dramatically at 8 weeks after treatment.

Conclusion

UK could improve cognitive status and decrease both Aβ1-40 and Aβ1-42 serum levels to prevent ischemic cerebral injury, which represents a good option for patients with cerebral arterial stenosis.

The cough reflex is upregulated by lisinopril microinjected into the caudal nucleus tractus solitarii of the rabbit

We have previously shown that cough potentiation induced by intravenous administration of the AT1 receptor antagonist losartan is lower than that induced by the ACE inhibitor lisinopril in anesthetized and awake rabbits. Since losartan and lisinopril cross the blood-brain barrier, their central action on the cough reflex can be hypothesized. Mechanical stimulation of the tracheobronchial tree and citric acid inhalation were used to induce cough reflex responses in pentobarbital sodium-anesthetized, spontaneously breathing rabbits. Bilateral microinjections (30-50 nl) of losartan (5mM), lisinopril (1mM), bradykinin (0.05 mM), HOE-140 (0.2mM, a bradykinin B2 receptor antagonist) and CP-99,994 (1mM, an NK1 receptor antagonist) were performed into the caudal nucleus tractus solitarii, the predominant site of termination of cough-related afferents. Lisinopril, but not losartan increased the cough number. This effect was reverted by HOE-140 or CP-99,994. Cough potentiation was also induced by bradykinin. The results support for the first time a central protussive action of lisinopril mediated by an accumulation of bradykinin and substance P.

Human Urinary Kallidinogenase Promotes Angiogenesis and Cerebral Perfusion in Experimental Stroke

Angiogenesisis a key restorative mechanism in response to ischemia, and pro-angiogenic therapy could be beneficial in stroke. Accumulating experimental and clinical evidence suggest that human urinary kallidinogenase (HUK) improves stroke outcome, but the underlying mechanisms are not clear. The aim of current study was to verify roles of HUK in post-ischemic angiogenesis and identify relevant mediators. In rat middle cerebral artery occlusion (MCAO) model, we confirmed that HUK treatment could improve stroke outcome, indicated by reduced infarct size and improved neurological function. Notably, the ¹⁸F-FDG micro-PET scan indicated that HUK enhanced cerebral perfusion in rats after MCAO treatment. In addition, HUK promotespost-ischemic angiogenesis, with increased vessel density as well as up-regulated VEGF andapelin/APJ expression in HUK-treated MCAO mice. In endothelial cell cultures, induction of VEGF and apelin/APJ expression, and ERK1/2 phosphorylation by HUK was further confirmed. These changes were abrogated by U0126, a selective ERK1/2 inhibitor. Moreover, F13A, a competitive antagonist of APJ receptor, significantly suppressed HUK-induced VEGF expression. Furthermore, angiogenic functions of HUK were inhibited in the presence of selective bradykinin B1 or B2 receptor antagonist both in vitro and in vivo. Our findings indicate that HUK treatment promotes post-ischemic angiogenesis and cerebral perfusion via activation of bradykinin B1 and B2 receptors, which is potentially due to enhancement expression of VEGF and apelin/APJ in ERK1/2 dependent way.

Characterization of the Kallikrein-Kinin System Post Chemical Neuronal Injury: An In Vitro Biochemical and Neuroproteomics Assessment

Traumatic Brain Injury (TBI) is the result of a mechanical impact on the brain provoking mild, moderate or severe symptoms. It is acknowledged that TBI leads to apoptotic and necrotic cell death; however, the exact mechanism by which brain trauma leads to neural injury is not fully elucidated. Some studies have highlighted the pivotal role of the Kallikrein-Kinin System (KKS) in brain trauma but the results are still controversial and inconclusive. In this study, we investigated both the expression and the role of Bradykinin 1 and 2 receptors (B1R and B2R), in mediating neuronal injury under chemical neurotoxicity paradigm in PC12 cell lines. The neuronal cell line PC12 was treated with the apoptotic drug Staurosporine (STS) to induce cell death. Intracellular calcium release was evaluated by Fluo 4-AM staining and showed that inhibition of the B2R prevented calcium release following STS treatment. Differential analyses utilizing immunofluorescence, Western blot and Real-time Polymerase Chain Reaction revealed an upregulation of both bradykinin receptors occurring at 3h and 12h post-STS treatment, but with a higher induction of B2R compared to B1R. This implies that STS-mediated apoptosis in PC12 cells is mainly conducted through B2R and partly via B1R. Finally, a neuroproteomics approach was conducted to find relevant proteins associated to STS and KKS in PC12 cells. Neuroproteomics results confirmed the presence of an inflammatory response leading to cell death during apoptosis-mediated STS treatment; however, a “survival” capacity was shown following inhibition of B2R coupled with STS treatment. Our data suggest that B2R is a key player in the inflammatory pathway following STS-mediated apoptosis in PC12 cells and its inhibition may represent a potential therapeutic tool in TBI.

Blocking of plasma kallikrein ameliorates stroke by reducing thromboinflammation

OBJECTIVE

Recent evidence suggests that ischemic stroke is a thromboinflammatory disease. Plasma kallikrein (PK) cleaves high-molecular-weight kininogen to release bradykinin (BK) and is a key constituent of the proinflammatory contact-kinin system. In addition, PK can activate coagulation factor XII, the origin of the intrinsic coagulation cascade. Thus, PK triggers 2 important pathological pathways of stroke formation, thrombosis and inflammation.

METHODS

We investigated the consequences of PK inhibition in transient and permanent models of ischemic stroke.

RESULTS

PK-deficient mice of either sex challenged with transient middle cerebral artery occlusion developed significantly smaller brain infarctions and less severe neurological deficits compared with controls without an increase in infarct-associated hemorrhage. This protective effect was preserved at later stages of infarctions as well as after permanent stroke. Reduced intracerebral thrombosis and improved cerebral blood flow could be identified as underlying mechanisms. Moreover, blood-brain barrier function was maintained in mice lacking PK, and the local inflammatory response was reduced. PK-deficient mice reconstituted with PK or BK again developed brain infarctions similar to wild-type mice. Important from a translational perspective, inhibition of PK in wild-type mice using a PK-specific antibody was likewise effective even when performed in a therapeutic setting up to 3 hours poststroke.

INTERPRETATION

PK drives thrombus formation and inflammation via activation of the intrinsic coagulation cascade and the release of BK but appears to be dispensable for hemostasis. Hence, PK inhibition may offer a safe strategy to combat thromboembolic disorders including ischemic stroke.

C1-Inhibitor protects from focal brain trauma in a cortical cryolesion mice model by reducing thrombo-inflammation

Traumatic brain injury (TBI) induces a strong inflammatory response which includes blood-brain barrier damage, edema formation and infiltration of different immune cell subsets. More recently, microvascular thrombosis has been identified as another pathophysiological feature of TBI. The contact-kinin system represents an interface between inflammatory and thrombotic circuits and is activated in different neurological diseases. C1-Inhibitor counteracts activation of the contact-kinin system at multiple levels. We investigated the therapeutic potential of C1-Inhibitor in a model of TBI. Male and female C57BL/6 mice were subjected to cortical cryolesion and treated with C1-Inhibitor after 1 h. Lesion volumes were assessed between day 1 and day 5 and blood-brain barrier damage, thrombus formation as well as the local inflammatory response were determined post TBI. Treatment of male mice with 15.0 IU C1-Inhibitor, but not 7.5 IU, 1 h after cryolesion reduced lesion volumes by ~75% on day 1. This protective effect was preserved in female mice and at later stages of trauma. Mechanistically, C1-Inhibitor stabilized the blood-brain barrier and decreased the invasion of immune cells into the brain parenchyma. Moreover, C1-Inhibitor had strong antithrombotic effects. C1-Inhibitor represents a multifaceted anti-inflammatory and antithrombotic compound that prevents traumatic neurodegeneration in clinically meaningful settings.

What have we learned about the kallikrein-kinin and renin-angiotensin systems in neurological disorders?

The kallikrein-kinin system (KKS) is an intricate endogenous pathway involved in several physiological and pathological cascades in the brain. Due to the pathological effects of kinins in blood vessels and tissues, their formation and degradation are tightly controlled. Their components have been related to several central nervous system diseases such as stroke, Alzheimer’s disease, Parkinson’s disease, multiple sclerosis, epilepsy and others. Bradykinin and its receptors (B1R and B2R) may have a role in the pathophysiology of certain central nervous system diseases. It has been suggested that kinin B1R is up-regulated in pathological conditions and has a neurodegenerative pattern, while kinin B2R is constitutive and can act as a neuroprotective factor in many neurological conditions. The renin angiotensin system (RAS) is an important blood pressure regulator and controls both sodium and water intake. AngII is a potent vasoconstrictor molecule and angiotensin converting enzyme is the major enzyme responsible for its release. AngII acts mainly on the AT1 receptor, with involvement in several systemic and neurological disorders. Brain RAS has been associated with physiological pathways, but is also associated with brain disorders. This review describes topics relating to the involvement of both systems in several forms of brain dysfunction and indicates components of the KKS and RAS that have been used as targets in several pharmacological approaches.

Oligodendrocyte pathophysiology and treatment strategies in cerebral ischemia

Oligodendrocytes (OLs), the myelin-forming cells of the central nervous system, form a functional unit with axons and play a crucial role in axonal integrity. An episode of hypoxia-ischemia causes rapid and severe damage to these particularly vulnerable cells via multiple pathways such as overactivation of glutamate and ATP receptors, oxidative stress, and disruption of mitochondrial function. The cardinal effect of OL pathology is demyelination and dysmyelination, and this has profound effects on axonal function, transport, structure, metabolism, and survival. The OL is a primary target of ischemia in adult-onset stroke and especially in periventricular leukomalacia and should be considered as a primary therapeutic target in these conditions. More emphasis is needed on therapeutic strategies that target OLs, myelin, and their receptors, as these have the potential to significantly attenuate white matter injury and to establish functional recovery of white matter after stroke. In this review, we will summarize recent progress on the role of OLs in white matter ischemic injury and the current and emerging principles that form the basis for protective strategies against OL death.

Non-pharmaceutical therapies for stroke: mechanisms and clinical implications

Stroke is deemed a worldwide leading cause of neurological disability and death, however, there is currently no promising pharmacotherapy for acute ischemic stroke aside from intravenous or intra-arterial thrombolysis. Yet because of the narrow therapeutic time window involved, thrombolytic application is very restricted in clinical settings. Accumulating data suggest that non-pharmaceutical therapies for stroke might provide new opportunities for stroke treatment. Here we review recent research progress in the mechanisms and clinical implications of non-pharmaceutical therapies, mainly including neuroprotective approaches such as hypothermia, ischemic/hypoxic conditioning, acupuncture, medical gases and transcranial laser therapy. In addition, we briefly summarize mechanical endovascular recanalization devices and recovery devices for the treatment of the chronic phase of stroke and discuss the relative merits of these devices.

Proton-sensitive cation channels and ion exchangers in ischemic brain injury: new therapeutic targets for stroke?

Ischemic brain injury results from complicated cellular mechanisms. The present therapy for acute ischemic stroke is limited to thrombolysis with the recombinant tissue plasminogen activator (rtPA) and mechanical recanalization. Therefore, a better understanding of ischemic brain injury is needed for the development of more effective therapies. Disruption of ionic homeostasis plays an important role in cell death following cerebral ischemia. Glutamate receptor-mediated ionic imbalance and neurotoxicity have been well established in cerebral ischemia after stroke. However, non-NMDA receptor-dependent mechanisms, involving acid-sensing ion channel 1a (ASIC1a), transient receptor potential melastatin 7 (TRPM7), and Na(+)/H(+) exchanger isoform 1 (NHE1), have recently emerged as important players in the dysregulation of ionic homeostasis in the CNS under ischemic conditions. These H(+)-sensitive channels and/or exchangers are expressed in the majority of cell types of the neurovascular unit. Sustained activation of these proteins causes excessive influx of cations, such as Ca(2+), Na(+), and Zn(2+), and leads to ischemic reperfusion brain injury. In this review, we summarize recent pre-clinical experimental research findings on how these channels/exchangers are regulated in both in vitro and in vivo models of cerebral ischemia. The blockade or transgenic knockdown of these proteins was shown to be neuroprotective in these ischemia models. Taken together, these non-NMDA receptor-dependent mechanisms may serve as novel therapeutic targets for stroke intervention.

Functional up-regulation of endopeptidase neurolysin during post-acute and early recovery phases of experimental stroke in mouse brain

In this study, we provide evidence for the first time that membrane-bound endopeptidase neurolysin is up-regulated in different parts of mouse brain affected by focal ischemia-reperfusion in a middle cerebral artery occlusion model of stroke. Radioligand binding, enzymatic and immunoblotting experiments in membrane preparations of frontoparietal cortex, striatum, and hippocampus isolated from the ischemic hemisphere of mouse brain 24 h after reperfusion revealed statistically significant increase (≥ twofold) in quantity and activity of neurolysin compared with sham-operated controls. Cerebellar membranes isolated from the ischemic hemisphere served as negative control supporting the observations that up-regulation of neurolysin occurs in post-ischemic brain regions. This study also documents sustained functional up-regulation of neurolysin in frontoparietal cortical membranes for at least 7 days after stroke, which appears not to be transcriptionally or translationally regulated, but rather depends on translocation of cytosolic neurolysin to the membranes and mitochondria. Considering diversity of endogenous neurolysin substrates (neurotensin, bradykinin, angiotensins I/II, substance P, hemopressin, dynorphin A(1-8), metorphamide, somatostatin) and the well-documented role of these peptidergic systems in pathogenesis of stroke, resistance to ischemic injury and/or post-stroke brain recovery, our findings suggest that neurolysin may play a role in processes modulating the brain's response to stroke and its recovery after stroke.

Kinin-B2 receptor exerted neuroprotection after diisopropylfluorophosphate-induced neuronal damage

The kinin-B2 receptor (B2BKR) activated by its endogenous ligand bradykinin participates in various metabolic processes including the control of arterial pressure and inflammation. Recently, functions for this receptor in brain development and protection against glutamate-provoked excitotoxicity have been proposed. Here, we report neuroprotective properties for bradykinin against organophosphate poisoning using acute hippocampal slices as an in vitro model. Following slice perfusion for 10min with diisopropylfluorophosphate (DFP) to initiate the noxious stimulus, responses of pyramidal neurons upon an electric impulse were reduced to less than 30% of control amplitudes. Effects on synaptic-elicited population spikes were reverted when preparations had been exposed to bradykinin 30min after challenging with DFP. Accordingly, bradykinin-induced population spike recovery was abolished by HOE-140, a B2BKR antagonist. However, the kinin-B1 receptor (B1BKR) agonist Lys-des-Arg(9)-bradykinin, inducing the phosphorylation of mitogen-activated protein kinase (MEK/MAPK) and cell death, abolished bradykinin-mediated neuroprotection, an effect, which was reverted by the ERK inhibitor PD98059. In agreement with pivotal B1BKR functions in this process, antagonism of endogenous B1BKR activity alone was enough for restoring population spike activity. On the other hand pralidoxime, an oxime, reactivating acetylcholinesterase (AChE) after organophosphate poisoning, induced population spike recovery after DFP exposure in the presence of bradykinin and Lys-des-Arg(9)-bradykinin. Lys-des-Arg(9)-bradykinin did not revert protection exerted by pralidoxime, however when instead bradykinin and Ly-des-Arg(9)-bradykinin were superfused together, recovery of population spikes diminished. These findings again confirm the neuroprotective feature of bradykinin, which is, diminished by its endogenous metabolites, stimulating the B1BKR, providing a novel understanding of the physiological roles of these receptors.