uPA modulates the age-dependent effect of brain injury on cerebral hemodynamics through LRP and ERK MAPK

Role of statins in regulating molecular pathways following traumatic brain injury: A system pharmacology study

Traumatic brain injury (TBI) is a serious disorder with debilitating physical and psychological complications. Previous studies have indicated that genetic factors have a critical role in modulating the secondary phase of injury in TBI. Statins have interesting pleiotropic properties such as antiapoptotic, antioxidative, and anti-inflammatory effects, which make them a suitable class of drugs for repurposing in TBI. In this study, we aimed to explore how statins modulate proteins and pathways involved in TBI using system pharmacology. We first explored the target associations with statins in two databases to discover critical clustering groups, candidate hub and critical hub genes in the network of TBI, and the possible connections of statins with TBI-related genes. Our results showed 1763 genes associated with TBI. Subsequently, the analysis of centralities in the PPI network displayed 55 candidate hub genes and 15 hub genes. Besides, MCODE analysis based on threshold score:10 determined four modular clusters. Intersection analysis of genes related to TBI and statins demonstrated 204 shared proteins, which suggested that statins influence 31 candidate hub and 9 hub genes. Moreover, statins had the highest interaction with MCODE1. The biological processes of the 31 shared proteins are related to gene expression, inflammation, antioxidant activity, and cell proliferation. Biological enriched pathways showed Programmed Cell Death proteins, AGE-RAGE signaling pathway, C-type lectin receptor signalling pathway, and MAPK signaling pathway as top clusters. In conclusion, statins could target several critical post-TBI genes mainly involved in inflammation and apoptosis, supporting the previous research results as a potential therapeutic agent.

Large animal models of traumatic brain injury

Purpose/Aim: Animal models of traumatic brain injury (TBI) provide powerful tools to study TBI in a controlled, rigorous and cost-efficient manner. The mostly used animals in TBI studies so far are rodents. However, compared with rodents, large animals (e.g. swine, rabbit, sheep, ferret, etc.) show great advantages in modeling TBI due to the similarity of their brains to human brain. The aim of our review was to summarize the development and progress of common large animal TBI models in past 30 years.

MATERIALS AND METHODS

Mixed published articles and books associated with large animal models of TBI were researched and summarized.

RESULTS

We majorly sumed up current common large animal models of TBI, including discussion on the available research methodologies in previous studies, several potential therapies in large animal trials of TBI as well as advantages and disadvantages of these models.

CONCLUSIONS

Large animal models of TBI play crucial role in determining the underlying mechanisms and screening putative therapeutic targets of TBI.

A chimeric platelet-targeted urokinase prodrug selectively blocks new thrombus formation

The use of fibrinolytic agents to prevent new thrombus formation is limited by an increased risk of bleeding due to lysis of hemostatic clots that prevent hemorrhage in damaged blood vessels. We sought to develop an agent that provides thromboprophylaxis without carrying a significant risk of causing systemic fibrinolysis or disrupting hemostatic clots. We previously showed that platelet (PLT) α granule-delivered urokinase plasminogen activator (uPA) is highly effective in preventing thrombosis, while being associated with little systemic fibrinolysis or bleeding. Here, we generated a chimeric prodrug composed of a single-chain version of the variable region of an anti-αIIbβ3 mAb fused to a thrombin-activatable, low-molecular-weight pro-uPA (PLT/uPA-T). PLT/uPA-T recognizes human αIIbβ3 on both quiescent and activated platelets and is enzymatically activated specifically by thrombin. We found that this prodrug binds tightly to human platelets even after gel filtration, has a prolonged half-life in mice transgenic for human αIIb compared with that of uPA-T, and prevents clot formation in a microfluidic system. Importantly, in two murine injury models, PLT/uPA-T did not lyse preexisting clots, even when administration was delayed by as little as 10 minutes, while it concurrently prevented the development of nascent thrombi. Thus, PLT/uPA-T represents the prototype of a platelet-targeted thromboprophylactic agent that selectively targets nascent over preexisting thrombi.

RBC-coupled tPA Prevents Whereas tPA Aggravates JNK MAPK-Mediated Impairment of ATP- and Ca-Sensitive K Channel-Mediated Cerebrovasodilation After Cerebral Photothrombosis

The sole Food and Drug Administration-approved treatment for acute stroke is tissue-type plasminogen activator (tPA), but tPA aggravates impairment of cerebrovasodilation during hypotension in a newborn pig photothrombotic model of stroke. Coupling to carrier red blood cells (RBC) enhances thrombolytic effects of tPA, while reducing its side effects. ATP- and Ca-sensitive K channels (Katp and Kca) are important regulators of cerebrovascular tone and mediate cerebrovasodilation during hypotension. Mitogen-activated protein kinase, a family of at least three kinases, ERK, p38, and c-Jun-N-terminal kinase (JNK), is upregulated after photothrombosis. This study examined the effect of photothrombosis on Katp- and Kca-induced cerebrovasodilation and the roles of tPA and JNK during/after injury. Photothrombosis blunted vasodilation induced by the Katp agonists cromakalim, calcitonin gene-related peptide, and the Kca agonist NS 1619, which was aggravated by injection of tPA. In contrast, both pre- or post-injury thrombosis injection of RBC-tPA and JNK antagonist SP 600125 prevented impairment of Katp- and Kca-induced vasodilation. Therefore, JNK activation in thrombosis impairs K channel-mediated cerebrovasodilation. Standard thrombolytic therapy of central nervous system ischemic disorders using free tPA poses the danger of further dysregulation of cerebrohemodynamics by impairing cation-mediated control of cerebrovascular tone, whereas RBC-coupled tPA both restores reperfusion and normalizes cerebral hemodynamics.

tPA-S(481)A prevents impairment of cerebrovascular autoregulation by endogenous tPA after traumatic brain injury by upregulating p38 MAPK and inhibiting ET-1

Traumatic brain injury (TBI) is associated with loss of cerebrovascular autoregulation, which leads to cerebral hypoperfusion. Mitogen activated protein kinase (MAPK) isoforms ERK, p38, and JNK and endothelin-1 (ET-1) are mediators of impaired cerebral hemodynamics after TBI. Excessive tissue plasminogen activator (tPA) released after TBI may cause loss of cerebrovascular autoregulation either by over-activating N-methyl-D-aspartate receptors (NMDA-Rs) or by predisposing to intracranial hemorrhage. Our recent work shows that a catalytically inactive tPA variant (tPA-S(481)A) that competes with endogenous wild type (wt) tPA for binding to NMDA-R through its receptor docking site but that cannot activate it, prevents activation of ERK by wt tPA and impairment of autoregulation when administered 30 min after fluid percussion injury (FPI). We investigated the ability of variants that lack proteolytic activity but bind/block activation of NMDA-Rs by wt tPA (tPA-S(481)A), do not bind/block activation of NMDA-Rs but are proteolytic (tPA-A(296-299)), or neither bind/block NMDA-Rs nor are proteolytic (tPA-A(296-299)S(481)A) to prevent impairment of autoregulation after TBI and the role of MAPK and ET-1 in such effects. Results show that tPA-S(481)A given 3 h post-TBI, but not tPA-A(296-299) or tPA-A(296-299)S(481)A prevents impaired autoregulation by upregulating p38 and inhibiting ET-1, suggesting that tPA-S(481)A has a realistic therapeutic window and focuses intervention on NMDA-Rs to improve outcome.

Influence of Sex and ERK MAPK on the Pressure Reactivity Index in Newborn Piglets After Fluid Percussion Injury

Greater impairment in autoregulation is seen in male versus female piglets following fluid percussion injury (FPI). This is partially mediated by a greater upregulation of extracellular signal-related kinase mitogen-activated protein kinase (ERK MAPK). We hypothesized that these trends would be reflected by the pressure reactivity index (PRx), a clinical measure of autoregulation. We further hypothesized that PRx values would correlate well with pial artery dilatory responses to hypotension. Male and female piglets were subjected to FPI and treated with a vehicle or ERK MAPK antagonist U 0126 (1 mg/kg IV) 30 min post-injury. FPI led to upregulation of CSF ERK MAPK in untreated piglets of both sexes, however significantly higher PRx values were seen in male versus female piglets. Following administration of U 0126, elevation of ERK MAPK levels was blocked in both sexes and PRx values were significantly improved in the male. A strong correlation was seen between the PRx and pial artery vasomotor activity. These data support previous observations that male piglets demonstrate reversible ERK MAPK-mediated impairment in autoregulation following FPI, which is reflected by the PRx. The strong correlation between the PRx and pial artery vasomotor activity supports the practice of continuously monitoring cerebrovascular autoregulation in patients using this index.

Dopamine prevents impairment of autoregulation after traumatic brain injury in the newborn pig through inhibition of Up-regulation of endothelin-1 and extracellular signal-regulated kinase mitogen-activated protein kinase

OBJECTIVE

Traumatic brain injury contributes to morbidity in children and boys are disproportionately represented. Autoregulation is impaired more in male compared with female piglets after traumatic brain injury through sex-dependent up-regulation of the spasmogen endothelin-1 and extracellular signal-regulated kinase (ERK) mitogen-activated protein kinase (MAPK), a family of three kinases: ERK, p38, and JNK). Elevation of mean arterial pressure leading to increased cerebral perfusion pressure via phenylephrine improves impairment of autoregulation after traumatic brain injury in female but not male piglets through modulation of endothelin-1 and ERK MAPK up-regulation, blocked in females, but aggravated in males. We hypothesized that pressor choice to elevate cerebral perfusion pressure is important in improving cerebral hemodynamics after traumatic brain injury and that dopamine will prevent impairment of autoregulation in both male and female piglets through blockade of endothelin-1 and ERK MAPK.

DESIGN

Prospective, randomized animal study.

SETTING

University laboratory.

SUBJECTS

Newborn (1-5 days old) pigs.

INTERVENTIONS

Cerebral perfusion pressure and pial artery diameter were determined before and after lateral fluid percussion brain injury was produced in piglets equipped with a closed cranial window. Dopamine (15 µg/kg/min IV) was administered 30 mins post fluid percussion injury. Cerebrospinal fluid ERK MAPK was determined by enzyme-linked immunosorbent assay.

MEASUREMENTS AND MAIN RESULTS

Dopamine increased cerebral perfusion pressure equivalently in both sexes and prevented sex-dependent reductions in pial artery diameter after fluid percussion injury. Loss of pial artery dilation during hypotension was greater in male than in female piglets after fluid percussion injury, but dopamine prevented such impairment equivalently in both sexes post injury. endothelin-1 and ERK MAPK release was greater in male compared to female piglets after fluid percussion injury, but dopamine also blocked their up-regulation equivalently in male and female piglets after fluid percussion injury.

CONCLUSIONS

These data indicate that dopamine is protective of autoregulation after fluid percussion injury in both sexes. These observations advocate for the consideration of development of sex based therapies for treatment of hemodynamic sequalae of pediatric traumatic brain injury.

Influence of Sex and ERK MAPK on the Pressure Reactivity Index in Newborn Piglets After Fluid Percussion Injury

Greater impairment in autoregulation is seen in male versus female piglets following fluid percussion injury (FPI). This is partially mediated by a greater upregulation of extracellular signal-related kinase mitogen-activated protein kinase (ERK MAPK). We hypothesized that these trends would be reflected by the pressure reactivity index (PRx), a clinical measure of autoregulation. We further hypothesized that PRx values would correlate well with pial artery dilatory responses to hypotension. Male and female piglets were subjected to FPI and treated with a vehicle or ERK MAPK antagonist U 0126 (1 mg/kg IV) 30 min post-injury. FPI led to upregulation of CSF ERK MAPK in untreated piglets of both sexes, however significantly higher PRx values were seen in male versus female piglets. Following administration of U 0126, elevation of ERK MAPK levels was blocked in both sexes and PRx values were significantly improved in the male. A strong correlation was seen between the PRx and pial artery vasomotor activity. These data support previous observations that male piglets demonstrate reversible ERK MAPK-mediated impairment in autoregulation following FPI, which is reflected by the PRx. The strong correlation between the PRx and pial artery vasomotor activity supports the practice of continuously monitoring cerebrovascular autoregulation in patients using this index.

tPA-S481A prevents neurotoxicity of endogenous tPA in traumatic brain injury

Traumatic brain injury (TBI) is associated with loss of autoregulation due to impaired responsiveness to cerebrovascular dilator stimuli, which leads to cerebral hypoperfusion and neuronal impairment or death. Upregulation of tissue plasminogen activator (tPA) post-TBI exacerbates loss of cerebral autoregulation and NMDA-receptor-mediated impairment of cerebral hemodynamics, and enhances excitotoxic neuronal death. However, the relationship between NMDA-receptor activation, loss of autoregulation, and neurological dysfunction is unclear. Here, we evaluated the potential therapeutic efficacy of a catalytically inactive tPA variant, tPA S481A, that acts by competing with wild-type tPA for binding, cleavage, and activation of NMDA receptors. Lateral fluid percussion brain injury was produced in anesthetized piglets. Pial artery reactivity was measured via a closed cranial window, and cerebrospinal fluid (CSF) extracellular signal-regulated kinase (ERK) mitogen-activated protein kinase (MAPK) was quantified by enzyme-linked immunosorbent assay (ELISA). tPA-S481A prevented impairment of cerebral autoregulation and reduced histopathologic changes after TBI by inhibiting upregulation of the ERK isoform of MAPK. Treatment with this tPA variant provides a novel approach for limiting neuronal toxicity caused by untoward NMDA-receptor activation mediated by increased tPA and glutamate following TBI.

Combination therapy with glucagon and a novel plasminogen activator inhibitor-1-derived peptide enhances protection against impaired cerebrovasodilation during hypotension after traumatic brain injury through inhibition of ERK and JNK MAPK

OBJECTIVE

Outcome of traumatic brain injury (TBI) is impaired by hypotension and glutamate, and TBI-associated release of endogenous tissue plasminogen activator (tPA) impairs cerebral autoregulation. Glucagon decreases central nervous system glutamate, lessens neuronal cell injury, and improves neurological score in mice after TBI. Glucagon partially protects against impaired cerebrovasodilation during hypotension after TBI in piglets by upregulating cAMP which decreases release of tPA. Pial artery dilation during hypotension is due to release of cAMP-dependent dilator prostaglandins (PG), such as PGE2 and PGI2. TBI impairs PGE2 and PGI2-mediated pial artery dilation, which contributes to disturbed cerebral autoregulation post-insult, by upregulating mitogen-activated protein kinase (MAPK). This study was designed to investigate relationships between tPA, prostaglandins, and MAPK as a mechanism to improve the efficacy of glucagon-mediated preservation of cerebrovasodilation during hypotension after TBI.

METHODS

Lateral fluid percussion brain injury (FPI) was induced in piglets equipped with a closed cranial window. ERK and JNK MAPK concentrations in cerebrospinal fluid were quantified by enzyme-linked immunosorbent assay.

RESULTS

Cerebrospinal fluid JNK MAPK was increased by FPI, but blunted by glucagon and the novel plasminogen activator inhibitor-1-derived peptide (PAI-1DP), Ac-RMAPEEIIMDRPFLYVVR-amide. FPI modestly increased, while glucagon and PAI-1DP decreased ERK MAPK. PGE2, PGI2, N-methyl-D-aspartate, and hypotension-induced pial artery dilation was blunted after FPI, partially protected by glucagon, and fully protected by glucagon+PAI-1DP, glucagon+JNK antagonist SP600125 or glucagon+ERK inhibitor U 0126.

DISCUSSION

Glucagon+PAI-1DP act in concert to protect against impairment of cerebrovasodilation during hypotension after TBI via inhibition of ERK and JNK MAPK.

Endothelin and the neurovascular unit in pediatric traumatic brain injury

OBJECTIVE

This study characterized the association between endothelin-1, cerebral hemodynamics, and histopathology after fluid percussion brain injury in the newborn pig.

METHODS

Lateral fluid percussion injury was induced in newborn pigs equipped with a closed cranial window. Cerebral blood flow was determined with radiolabeled microspheres and cerebrospinal fluid endothelin-1 was measured by radioimmunoassay.

RESULTS

Cerebrospinal fluid endothelin-1 was increased from 26±4 to 296±37 pg/ml (∼10(-10) M) at 8 hours following fluid percussion injury. Post-injury treatment (30 minutes) with the endothelin-1 antagonist BQ-123 (1 mg/kg, intravenous) blocked pial artery vasoconstriction to topical endothelin-1 (∼10(-10) M) and blunted fluid percussion injury-induced reductions in cerebral blood flow at 8 hours post-insult (56±6 and 26±4 ml/minute versus 57±6 and 40± ml/minute; 100 g for cerebral blood flow before injury and 8 hours post-fluid percussion injury in vehicle and BQ-123 post-treated animals, respectively). Fluid percussion injury resulted in neuronal cell loss and decreased microtubule associated protein 2 immunoreactivity in the parietal cortex, which were blunted by BQ-123.

DISCUSSION

These data indicate that fluid percussion injury-induced changes in cerebral hemodynamics are associated with neuronal damage and that endothelin-1 contributes to fluid percussion injury-induced histopathologic changes.

TBI sex dependently upregulates ET-1 to impair autoregulation, which is aggravated by phenylephrine in males but is abrogated in females

Traumatic brain injury (TBI) contributes to morbidity in children, and boys are disproportionately represented. Endothelin-1 (ET-1) contributes to impaired autoregulation via oxygen (O₂⁻) after TBI in piglets, but its relative role in males compared with females has not been previously investigated. Increased cerebral perfusion pressure (CPP) via phenylephrine (Phe) sex dependently improves impairment of autoregulation after TBI through modulation of extracellular signal-related kinase (ERK) mitogen-activated protein kinase (MAPK) upregulation, aggravated in males, but blocked in females. Activation of adenosine-5'-triphosphate (ATP) and Ca sensitive K channels produce vasodilation, contributing to autoregulation. We hypothesized that ET-1 upregulation is greater in males after TBI and that disturbed autoregulation will be prevented by Phe in a sex-dependent manner through modulation of ET-1, O₂⁻, and ERK. Results show that ET-1 release was greater in males after fluid percussion injury (FPI), blunted by Phe in females, but aggravated in males. K channel vasodilation was impaired more in males than in females after TBI. Phe prevented reductions in K channel vasodilation in females, but further reduced dilation in males after TBI. Co-administration of BQ-123, U0126, or PEG-SOD (ET-1, ERK antagonist, and O₂⁻ scavenger) with Phe restored dilation to K agonists and hypotension in males after TBI. ERK upregulation was blocked by BQ-123 and PEG-SOD. These data indicate that TBI upregulates ET-1 more in males than in females. Elevation of CPP with Phe sex dependently prevents impairment of cerebral autoregulation after TBI through modulation of ET-1, O₂⁻, and ERK mediated impairment of K channel vasodilation. These observations advocate for the consideration of development of sex-based therapies for the treatment of hemodynamic sequelae of pediatric TBI.

tPA contributes to impaired NMDA cerebrovasodilation after traumatic brain injury through activation of JNK MAPK

OBJECTIVE

N-methyl-D-aspartate (NMDA)-induced pial artery dilation (PAD) is reversed to vasoconstriction after fluid percussion brain injury (FPI). Tissue type plasminogen activator (tPA) is up-regulated and the tPA antagonist, EEIIMD, prevents impaired NMDA PAD after FPI. Mitogen-activated protein kinase (MAPK), a family of at least three kinases, ERK, p38, and JNK, is also up-regulated after traumatic brain injury (TBI). We hypothesize that tPA impairs NMDA-induced cerebrovasodilation after FPI in a MAPK isoform-dependent mechanism.

METHODS

Lateral FPI was induced in newborn pigs. The closed cranial window technique was used to measure pial artery diameter and to collect cerebrospinal fluid (CSF). ERK, p38, and JNK MAPK concentrations in CSF were quantified by ELISA.

RESULTS

CSF JNK MAPK was increased by FPI, increased further by tPA, but blocked by JNK antagonists SP600125 and D-JNKI1. FPI modestly increased p38 and ERK isoforms of MAPK. NMDA-induced PAD was reversed to vasoconstriction after FPI, whereas dilator responses to papaverine were unchanged. tPA, in post-FPI CSF concentration, potentiated NMDA-induced vasoconstriction while papaverine dilation was unchanged. SP 600125 and D-JNKI1, blocked NMDA-induced vasoconstriction and fully restored PAD. The ERK antagonist U 0126 partially restored NMDA-induced PAD, while the p38 inhibitor SB203580 aggravated NMDA-induced vasoconstriction observed in the presence of tPA after FPI.

DISCUSSION

These data indicate that tPA contributes to impairment of NMDA-mediated cerebrovasodilation after FPI through JNK, while p38 may be protective. These data suggest that inhibition of the endogenous plasminogen activator system and JNK may improve cerebral hemodynamic outcome post-TBI.

Phenylephrine infusion prevents impairment of ATP- and calcium-sensitive potassium channel-mediated cerebrovasodilation after brain injury in female, but aggravates impairment in male, piglets through modulation of ERK MAPK upregulation

Traumatic brain injury (TBI) contributes to morbidity in children and boys, and hypotension worsens outcome. Extracellular signal-related kinase (ERK) mitogen-activated protein kinase (MAPK) is upregulated more in males and reduces cerebral blood flow (CBF) after fluid percussion injury (FPI). Increased cerebral perfusion pressure (CPP) via phenylephrine (Phe) sex-dependently improves impairment of the cerebral autoregulation seen after FPI through modulation of ERK MAPK upregulation, which is aggravated in males, but is blocked in females. Activation of ATP- and calcium-sensitive (Katp and Kca) channels produces cerebrovasodilation and contributes to autoregulation, both of which are impaired after FPI. Using piglets equipped with a closed cranial window, we hypothesized that potassium channel functional impairment after FPI is prevented by Phe in a sex-dependent manner through modulation of ERK MAPK upregulation. The Katp and Kca agonists cromakalim and NS 1619 produced vasodilation that was impaired after FPI more in males than in females. Phe prevented reductions in cerebrovasodilation after cromakalim and NS 1619 in females, but reduced dilation after these potassium channel agonists were given to males after FPI. Co-administration of U 0126, an ERK antagonist, and Phe fully restored dilation to cromakalim, calcitonin gene-related peptide (CGRP), and NS 1619, in males after FPI. These data indicate that Phe sex-dependently prevents impairment of Katp and Kca channel-mediated cerebrovasodilation after FPI in females, but aggravates impairment in males, through modulation of ERK MAPK upregulation. Since autoregulation of CBF is dependent on intact functioning of potassium channels, these data suggest a role for sex-dependent mechanisms in the treatment of cerebral autoregulation impairment after pediatric TBI.

Glucagon protects against impaired NMDA-mediated cerebrovasodilation and cerebral autoregulation during hypotension after brain injury by activating cAMP protein kinase A and inhibiting upregulation of tPA

Outcome of traumatic brain injury (TBI) is impaired by hyperglycemia, hypotension, and glutamate, and improved by insulin. Insulin reduces glutamate concentration, making it uncertain whether its beneficial effect accrues from euglycemia. Glucagon decreases CNS glutamate, lessens neuronal cell injury, and improves neurological scores in mice after TBI. In vitro, glucagon limits NMDA-mediated excitotoxicity by increasing cAMP and protein kinase A (PKA). NMDA receptor activation couples cerebral blood flow (CBF) to metabolism. Dilation induced by NMDA is impaired after fluid percussion brain injury (FPI) due to upregulation of endogenous tPA, which further disturbs cerebral autoregulation during hypotension after fluid percussion injury (FPI). We hypothesized that glucagon prevents impaired NMDA receptor-mediated dilation after FPI by upregulating cAMP, which decreases release of tPA. NMDA-induced pial artery dilation (PAD) was reversed to vasoconstriction after FPI. Glucagon 30 min before or 30 min after FPI blocked NMDA-mediated vasoconstriction and restored the response to vasodilation. PAD during hypotension was blunted after FPI, but protected by glucagon. Glucagon prevented FPI-induced reductions in CSF cAMP, yielding a net increase in cAMP, and blocked FPI-induced elevation of CSF tPA. Co-administration of the PKA antagonist Rp 8Br cAMPs prevented glucagon-mediated preservation of NMDA-mediated dilation after FPI. The pKA agonist Sp 8Br cAMPs prevented impairment of NMDA-induced dilation. These data indicate that glucagon protects against impaired cerebrovasodilation by upregulating cAMP, which decreases release of tPA, suggesting that it may provide neuroprotection when given after TBI, or prior to certain neurosurgical or cardiac interventions in which the incidence of perioperative ischemia is high.

Impaired cerebral blood flow autoregulation during posttraumatic arterial hypotension after fluid percussion brain injury is prevented by phenylephrine in female but exacerbated in male piglets by extracellular signal-related kinase mitogen-activated protein kinase upregulation

OBJECTIVE

Traumatic brain injury contributes to morbidity and mortality in children and boys are disproportionately represented. Hypotension is common and worsens outcome after traumatic brain injury. Extracellular signal-related kinase mitogen-activated protein kinase is upregulated and reduces cerebral blood flow after fluid percussion brain injury in piglets. We hypothesized that increased cerebral perfusion pressure through phenylephrine sex dependently reduces impairment of cerebral autoregulation during hypotension after fluid percussion brain injury through modulation of extracellular signal-related kinase mitogen-activated protein kinase.

DESIGN

Prospective, randomized animal study.

SETTING

University laboratory.

SUBJECTS

Newborn (1- to 5-day-old) pigs.

INTERVENTIONS

Cerebral blood flow, pial artery diameter, intracranial pressure, and autoregulatory index were determined before and after fluid percussion brain injury in untreated, preinjury, and postinjury phenylephrine (1 microg/kg/min intravenously) treated male and female pigs during normotension and hemorrhagic hypotension. Cerebrospinal fluid extracellular signal-related kinase mitogen-activated protein kinase was determined by enzyme-linked immunosorbent assay.

MEASUREMENTS AND MAIN RESULTS

Reductions in pial artery diameter, cerebral blood flow, cerebral perfusion pressure, and elevated intracranial pressure after fluid percussion brain injury were greater in males, which were blunted by phenylephrine pre- or postfluid percussion brain injury. During hypotension and fluid percussion brain injury, pial artery dilation was impaired more in males. Phenylephrine decreased impairment of hypotensive pial artery dilation after fluid percussion brain injury in females, but paradoxically caused vasoconstriction after fluid percussion brain injury in males. Papaverine-induced pial artery vasodilation was unchanged by fluid percussion brain injury and phenylephrine. Cerebral blood flow, cerebral perfusion pressure, and autoregulatory index decreased markedly during hypotension and fluid percussion brain injury in males but less in females. Phenylephrine prevented reductions in cerebral blood flow, cerebral perfusion pressure, and autoregulatory index during hypotension in females but increased reductions in males. Cerebrospinal fluid extracellular signal-related kinase mitogen-activated protein kinase was increased more in males than females after fluid percussion brain injury. Phenylephrine blunted extracellular signal-related kinase mitogen-activated protein kinase upregulation in females but increased extracellular signal-related kinase mitogen-activated protein kinase upregulation in males after fluid percussion brain injury.

CONCLUSIONS

These data indicate that elevation of cerebral perfusion pressure with phenylephrine sex dependently prevents impairment of cerebral autoregulation during hypotension after fluid percussion brain injury through modulation of extracellular signal-related kinase mitogen-activated protein kinase. These data suggest the potential role for sex-dependent mechanisms in cerebral autoregulation after pediatric traumatic brain injury.

Adrenomedullin prevents sex-dependent impairment of autoregulation during hypotension after piglet brain injury through inhibition of ERK MAPK upregulation

Cerebrospinal fluid (CSF) adrenomedullin (ADM) levels are increased in female, but remain unchanged in male, piglets after fluid percussion injury (FPI) of the brain. Subthreshold vascular concentrations of ADM restore impaired hypotensive pial artery dilation after FPI more in males than females. Extracellular signal-related kinase (ERK) mitogen-activated protein kinase (MAPK) is upregulated and contributes to reductions in cerebral blood flow (CBF) after FPI. We hypothesized that ADM prevents sex-dependent impairment of autoregulation during hypotension after FPI through inhibition of ERK MAPK upregulation. FPI increased ERK MAPK more in males than in females. CBF was unchanged during hypotension in sham animals, was reduced more in males than in females after FPI during normotension, and was further reduced in males than in females during hypotension and after FPI. ADM and the ERK MAPK antagonist U 0126 prevented reductions in CBF during hypotension and FPI more in males than in females. Transcranial Doppler (TCD) blood flow velocity was unchanged during hypotension in sham animals, was decreased during hypotension and FPI in male but not in female pigs, and was ameliorated by ADM. Intracranial pressure (ICP) was increased after FPI more in male than in female animals. ADM blunted elevated ICP during FPI and hypotension in males, but not in females. ADM prevented reductions in cerebral perfusion pressure (CPP) during FPI and hypotension in males but not in females. The calculated autoregulatory index was unchanged during hypotension in sham animals, but was reduced more in males than females during hypotension and FPI. ADM prevented reductions in autoregulation during hypotension and FPI more in males than females. These data indicate that ADM prevented loss of cerebral autoregulation after FPI in a sex-dependent and ERK MAPK-dependent manner.

Signaling, delivery and age as emerging issues in the benefit/risk ratio outcome of tPA For treatment of CNS ischemic disorders

Stroke is a leading cause of morbidity and mortality. While tissue-type plasminogen activator (tPA) remains the only FDA-approved treatment for ischemic stroke, clinical use of tPA has been constrained to roughly 3% of eligible patients because of the danger of intracranial hemorrhage and a narrow 3 h time window for safe administration. Basic science studies indicate that tPA enhances excitotoxic neuronal cell death. In this review, the beneficial and deleterious effects of tPA in ischemic brain are discussed along with emphasis on development of new approaches toward treatment of patients with acute ischemic stroke. In particular, roles of tPA-induced signaling and a novel delivery system for tPA administration based on tPA coupling to carrier red blood cells will be considered as therapeutic modalities for increasing tPA benefit/risk ratio. The concept of the neurovascular unit will be discussed in the context of dynamic relationships between tPA-induced changes in cerebral hemodynamics and histopathologic outcome of CNS ischemia. Additionally, the role of age will be considered since thrombolytic therapy is being increasingly used in the pediatric population, but there are few basic science studies of CNS injury in pediatric animals.

SNP improves cerebral hemodynamics during normotension but fails to prevent sex dependent impaired cerebral autoregulation during hypotension after brain injury

Traumatic brain injury (TBI) is a leading cause of morbidity in children and boys are disproportionately represented. Hypotension is common and worsens outcome after TBI. Previous studies show that adrenomedullin, a cerebrovasodilator, prevented sex dependent impairment of autoregulation during hypotension after piglet fluid percussion brain injury (FPI). We hypothesized that this concept was generalizable and that administration of another vasodilator, sodium nitroprusside (SNP), may equally improve CBF and cerebral autoregulation in a sex dependent manner after FPI. SNP produced equivalent percent cerebrovasodilation in male and female piglets. Reductions in pial artery diameter, cortical CBF, and cerebral perfusion pressure (CPP) concomitant with elevated intracranial pressure (ICP) after FPI were greater in male compared to female piglets during normotension which was blunted by SNP. During hypotension, pial artery dilation (PAD) was impaired more in the male than the female after FPI. However, SNP did not improve hypotensive PAD after FPI in females and paradoxically caused vasoconstriction in males. SNP did not prevent reductions in CBF, CPP or autoregulatory index during combined hypotension and FPI in either sex. SNP aggravated ERK MAPK upregulation after FPI. These data indicate that despite prevention of reductions in CBF after FPI, SNP does not prevent impairment of autoregulation during hypotension after FPI. These data suggest that therapies directed at a purely hemodynamic increase in CPP will fail to improve outcome during combined TBI and hypotension.