Peripheral thermal injury causes blood–brain barrier dysfunction and matrix metalloproteinase (MMP) expression in rat

The impact of burn injury on the central nervous system

Burn injuries can be devastating, with life-long impacts including an increased risk of hospitalization for a wide range of secondary morbidities. One area that remains not fully understood is the impact of burn trauma on the central nervous system (CNS). This review will outline the current findings on the physiological impact that burns have on the CNS and how this may contribute to the development of neural comorbidities including mental health conditions. This review highlights the damaging effects caused by burn injuries on the CNS, characterized by changes to metabolism, molecular damage to cells and their organelles, and disturbance to sensory, motor and cognitive functions in the CNS. This damage is likely initiated by the inflammatory response that accompanies burn injury, and it is often long-lasting. Treatments used to relieve the symptoms of damage to the CNS due to burn injury often target inflammatory pathways. However, there are non-invasive treatments for burn patients that target the functional and cognitive damage caused by the burn, including transcranial magnetic stimulation and virtual reality. Future research should focus on understanding the mechanisms that underpin the impact of a burn injury on the CNS, burn severity thresholds required to inflict damage to the CNS, and acute and long-term therapies to ameliorate deleterious CNS changes after a burn.

Pathological changes in the brain after peripheral burns

Brain injuries are common complications in patients with thermal burns and are associated with unpleasant outcomes. In clinical settings, it was once believed that brain injuries were not major pathological processes after burn, at least in part due to the unavailability of specific clinical manifestations. Burn-related brain injuries have been studied for more than a century, but the underlying pathophysiology has not been completely clarified. This article reviews the pathological changes in the brain following peripheral burns at the anatomical, histological, cytological, molecular and cognitive levels. Therapeutic indications based on brain injury as well as future directions for research have been summarized and proposed.

Researches on cognitive sequelae of burn injury: Current status and advances

Burn injury is a devastating disease with high incidence of disability and mortality. The cognitive dysfunctions, such as memory defect, are the main neurological sequelae influencing the life quality of burn-injured patients. The post-burn cognitive dysfunctions are related to the primary peripheral factors and the secondary cerebral inflammation, resulting in the destruction of blood-brain barrier (BBB), as is shown on Computed Tomography (CT) and magnetic resonance imaging examinations. As part of the neurovascular unit, BBB is vital to the nutrition and homeostasis of the central nervous system (CNS) and undergoes myriad alterations after burn injury, causing post-burn cognitive defects. The diagnosis and treatment of cognitive dysfunctions as burn injury sequelae are of great importance. In this review, we address the major manifestations and interventions of post-burn cognitive defects, as well as the mechanisms involved in memory defect, including neuroinflammation, destruction of BBB, and hormone imbalance.

Glia and extracellular matrix molecules: What are their importance for the electrographic and MRI changes in the epileptogenic zone?

Glial cells and extracellular matrix (ECM) molecules are crucial for the maintenance of brain homeostasis. Especially because of their actions regarding neurotransmitter and ionic control, and synaptic function, these cells can potentially contribute to the hyperexcitability seen in the epileptogenic, while ECM changes are linked to synaptic reorganization. The present review will explore glial and ECM homeostatic roles and their potential contribution to tissue plasticity. Finally, we will address how glial, and ECM changes in the epileptogenic zone can be seen in magnetic resonance imaging (MRI), pointing out their importance as markers for the extension of the epileptogenic area. This article is part of the Special Issue "NEWroscience 2018".

Treatment and protective effects of metalloproteinase inhibitors alone and in combination with N-Acetyl cysteine plus vitamin E in rats exposed to aflatoxin B1

This study was conducted to investigate the effects of matrix metalloproteinase (MMP) inhibitors dexamethasone and minocycline administrations -both single and in combination with N-acetylcysteine (NAC) and vitamin E-on the tissue distribution and lethal dose (LD)₅₀ of aflatoxin (AF)B₁ in rats. We performed this study on male Wistar rats (8-10 weeks) in two phases. In the first phase, rats were administered dexamethasone (5 and 20 mg/kg) and minocycline (45 and 90 mg/kg), both as single treatments and in combination with NAC (200 mg/kg) and vitamin E (600 mg/kg); these treatments followed AFB₁ administration (2 mg/kg). In the second phase, the therapeutic effect value (TEV) was calculated to determine the treatment effect on the LD₅₀ level of AFB₁. The tissue affinity of AFB1 from high to low was liver, kidney, intestine, brain, heart, spleen, lung, testis, and vitreous humor, respectively. Dexamethasone at the 20 mg/kg dose significantly reduced AFB₁ concentrations in the plasma and the other tissues, except for the vitreous humor. The effects of minocycline on the plasma and tissue concentrations of AFB₁ varied by dose and tissue. The combinations of dexamethasone or minocycline with NAC and vitamin E increased the AFB₁ concentrations in the plasma and all tissues, except for vitreous humor and liver. In male rats, the LD₅₀ value of AFB₁ was 11.86 mg/kg. The TEV of dexamethasone (20 mg/kg) was calculated to be 1.5. Dexamethasone can be administered in repeated doses at ≥20 mg/kg to increase survival in AFB₁ poisoning.

Pseudomonal Meningoencephalitis With Ventriculitis Secondary to Bacteremia in a Burn Patient: A Novel Case

Burn patients with large burn surface area involvement are at increased risk of infection due to the presence of large wounds, multiple surgeries, prolonged intensive care unit admission, and immunosuppression. Pseudomonas aeruginosa is the most commonly isolated organism in this population. Even with frequent infections in the burn population, meningitis and encephalitis are rare, and ventriculitis is exceptional. We report the case of a 66-year-old woman who developed P. aeruginosa bacteremia during her hospital course, causing secondary meningoencephalitis with ventriculitis. She was admitted for partial- and full-thickness burns affecting the neck, chest, abdomen, upper medial arms, and bilateral anteromedial thighs for an estimated 20% total body surface area burn. She met sepsis criteria and broad-spectrum antimicrobial coverage was initiated. Magnetic resonance imaging of the brain, performed for altered mental status, revealed meningitis and ventriculitis. Cerebrospinal fluid analysis demonstrated findings consistent with bacterial meningitis, with cultures positive for P. aeruginosa. Serial neuroimaging with computerized tomography revealed new areas of ischemia concerning for septic emboli. In the presence of altered mental status and fever of unknown origin, workup should remain broad. Even in the presence of another source, it is important to keep an open mind for the rarer intracerebral infection as it requires different management, including urgent evaluation of antibiotic selection and dosing to ensure central nervous system penetration, and neurosurgical evaluation.

Mortality following combined burn and traumatic brain injuries: An analysis of the national trauma data bank of the American College of Surgeons

BACKGROUND

Severe burn and traumatic brain injuries (TBI) lead to significant mortality, and combined burn-TBI injuries may predispose towards even worse outcomes. The purpose of this study was to investigate the mortality of patients with burn, burn with non-TBI trauma, and combined burn/TBI to determine if combined injury portends a worse outcome.

METHODS

We obtained the National Trauma Data Bank from 2007 to 2012, identifying 32,334 patients with burn related injuries, dividing this cohort into three injury types: BURN ONLY, BURN with TRAUMA/NO TBI, and BURN with TBI. For each patient, demographic data was obtained, including age, gender, presence of trauma, TBI, or inhalation injury, burn total body surface area (TBSA), Glasgow Coma Scale, Injury Severity Score, and mortality. Multivariable logistic regression was performed.

RESULTS

Age, gender, and TBSA were similar across the three injury groups, but the incidence of inhalation injury was doubled in the BURN with TRAUMA/NO TBI (15.4 %) and BURN with TBI (15.3 %) groups when compared to the BURN ONLY (7.2 %) group. Mortality differed across injury categories after adjusting for age, TBSA, and inhalation injury. Increased mortality was seen in BURN with TRAUMA/NO TBI versus BURN ONLY (OR = 1.27 [1.06, 1.53]) and was higher when comparing BURN with TBI versus BURN ONLY (OR = 4.22 [2.85, 6.18]). BURN with TBI also had higher mortality when compared to BURN with TRAUMA/NO TBI (OR = 3.33 [2.30, 4.82]). The logs odds of mortality also increased with increasing age, TBSA and presence of inhalation injury.

DISCUSSION

This analysis of the NTDB suggests that mortality following burn-related injuries may be higher when burn injury is combined with TBI when compared to burns with other trauma, even after correcting for age, TBSA, and inhalation injury. Further clinical and laboratory research is needed to validate these findings and better understand how to optimize combined TBI and burn injury treatment.

Exploring blood-brain barrier hyperpermeability and potential biomarkers in traumatic brain injury

Blood-brain barrier breakdown and associated vascular hyperpermeability leads to vasogenic edema in traumatic brain injury (TBI). Tight junctions maintain blood-brain barrier integrity; their disruption in TBI holds significant promise for diagnosis and treatment. A controlled cortical impactor was used for TBI in mouse studies. Blood was collected 1 h after injury and sent for antibody microarray analysis. Twenty human subjects with radiographic evidence of TBI were enrolled and blood collected within 48 h of admission. Control subjects were individuals with nontrauma diagnoses. The subjects were matched by age and gender. Enzyme-linked immunosorbent assays were performed on each TBI and control sample for tight junction-associated proteins (TJPs), inflammatory markers, and S100β. Plasma was used to conduct in vitro monolayer permeability studies with human brain endothelial cells. S100β and the TJP occludin were significantly elevated in TBI plasma in both the murine and human studies. Monolayer permeability studies showed increased hyperpermeability in TBI groups. Plasma from TBI subjects increases microvascular hyperpermeability in vitro. TJPs in the blood may be a potential biomarker for TBI.

T2 relaxation time measurements in the brains of scalded rats

This study aimed to evaluate the T2 relaxation time of the brain in severely scalded rats using a magnetic resonance (MR) T2 mapping sequence, and to investigate the correlation between T2 relaxation time and plasma glucose level. Twenty-eight Wistar rats were randomly divided into the scalded group (n=21) and control group (n=7). Magnetic resonance scans were performed with T1WI, T2WI, and T2-mapping sequences in the scalded group; the scans were performed 1 day prior to scalding and 1, 3, 5, and 7 days post-scalding; in addition, identical MR scans were performed in the control group at the same time points. T2-maps were generated and T2 relaxation times were acquired from the following brain regions: the hippocampus, thalamus, caudate-putamen, and cerebrum. Pathological changes of the hippocampus were observed. The plasma glucose level of each rat was measured before each MR scan, and a correlation analysis was performed between T2 relaxation time and plasma glucose level. We found that conventional T1WI and T2WI did not reveal any abnormal signals or morphological changes in the hippocampus, thalamus, caudate-putamen, or cerebrum post-scalding. Both the T2 relaxation times of the selected brain regions and plasma glucose levels increased 1, 3, and 5 days post-scalding, and returned to normal levels 7 days post-scalding. The most marked increase of T2 relaxation time was found in the hippocampus; similar changes were also revealed in the thalamus, caudate-putamen, and cerebrum. No correlation was found between T2 relaxation time and plasma glucose level in scalded rats. Pathological observation of the hippocampus showed edema 1, 3, and 5 days post-scalding, with recovery to normal findings at 7 days post-scalding. Thus, we concluded that T2 mapping is a sensitive method for detecting and monitoring scald injury in the rat brain. As the hippocampus is the main region for modulating a stress reaction, it showed significantly increased water content along with an increased plasma glucose level post-scalding.

Thermal injury lowers the threshold for radiation-induced neuroinflammation and cognitive dysfunction

The consequences of radiation exposure alone are relatively well understood, but in the wake of events such as the World War II nuclear detonations and accidents such as Chernobyl, other critical factors have emerged that can substantially affect patient outcome. For example, ~70% of radiation victims from Hiroshima and Nagasaki received some sort of additional traumatic injury, the most common being thermal burn. Animal data has shown that the addition of thermal insult to radiation results in increased morbidity and mortality. To explore possible synergism between thermal injury and radiation on brain, C57BL/6J female mice were exposed to either 0 or 5 Gy whole-body gamma irradiation. Irradiation was immediately followed by a 10% total-body surface area full thickness thermal burn. Mice were sacrificed 6 h, 1 week or 6 month post-injury and brains and plasma were harvested for histology, mRNA analysis and cytokine ELISA. Plasma analysis revealed that combined injury synergistically upregulates IL-6 at acute time points. Additionally, at 6 h, combined injury resulted in a greater upregulation of the vascular marker, ICAM-1 and TNF-α mRNA. Enhanced activation of glial cells was also observed by CD68 and Iba1 immunohistochemistry at all time points. Additionally, doublecortin staining at 6 months showed reduced neurogenesis in all injury conditions. Finally, using a novel object recognition test, we observed that only mice with combined injury had significant learning and memory deficits. These results demonstrate that thermal injury lowers the threshold for radiation-induced neuroinflammation and long-term cognitive dysfunction.

Elevated serum ubiquitin carboxy-terminal hydrolase L1 is associated with abnormal blood-brain barrier function after traumatic brain injury

Serum S100B elevations accurately reflect blood-brain barrier (BBB) damage. Because S100B is also present in peripheral tissues, release of this protein may not be specific to central nervous system (CNS) injury. Ubiquitin C-terminal hydrolase 1 (UCHL1), and phosphorylated neurofilament heavy chain (pNF-H) are found exclusively in neurons, but their relationship to BBB dysfunction has not been determined. The objective of this study was to determine the accuracy of serum UCHL1 and pNF-H as measures of BBB integrity after traumatic brain injury (TBI), to and compare them to S100B. We performed a prospective study of 16 patients with moderate to severe TBI (Glasgow Coma Scale [GCS] score ≤12) and 6 patients with non-traumatic headache who had cerebrospinal fluid (CSF) collected by ventriculostomy or lumbar puncture (LP). Serum and CSF were collected at the time of LP for headache patients and at 12, 24, and 48 h after injury for TBI patients. BBB function was determined by calculating albumin quotients (Q(A)), where Q(A)=[albumin(CSF)]/[albumin(serum)]. S100B, UCHL1, and pNF-H were measured by enzyme-linked immunosorbent assay (ELISA). Pearson's correlation coefficient and area under the receiver operator characteristic (ROC) curve were used to determine relationships between serum markers and Q(A). At 12 hours after TBI, a significant relationship was found between Q(A) and serum UCHL1 concentrations (AUC=0.76; 95% CI 0.55,1.00), and between Q(A) and serum S100B concentrations (AUC=0.794; 95% CI 0.57,1.02). There was no significant relationship found between these markers and Q(A) at other time points, or between pNF-H and Q(A) at any time point. We conclude that serum concentrations of UCHL1 are associated with abnormal BBB status 12 h after moderate to severe TBI. This relationship is similar to that observed between serum S100B and Q(A,) despite the fact that S100B may be released from peripheral tissues after multi-trauma. We conclude that peripheral release of S100B after multi-trauma is probably negligible and that UCHL1 may have some utility to monitor BBB disruption following TBI.

Cerebral metabolism after forced or voluntary physical exercise

The pathophysiology of stroke, a leading cause of morbidity and mortality, is still in the process of being understood. Pre-ischemic exercise has been known to be beneficial in reducing the severity of stroke-induced brain injury in animal models. Forced exercise with a stressful component, rather than voluntary exercise, was better able to induce neuroprotection. This study further determined the changes in cerebral metabolism resulting from the two methods of exercise (forced versus voluntary). Adult male Sprague-Dawley rats were randomly assigned to 3 groups: the control group (no exercise), the forced treadmill exercise group, and the voluntary running wheel exercise group. In order to measure the extent of cerebral metabolism in animals with different exercise regimens, mRNA levels and protein expression of glucose transporter 1 and glucose transporter 3 (GLUT-1 and GLUT-3), phosphofructokinase (PFK), lactate dehydrogenase (LDH), and adenosine monophosphate kinase (AMPK) were measured utilizing real-time reverse transcription polymerase chain reaction (PCR) analysis as well as Western blot analysis. Phosphorylated AMPK activity was also measured using an ELISA activity kit, and hypoxic inducible factor (HIF)-1α was measured at transcription and translation levels. The data show that the forced exercise group had a significant (p < 0.05) increase in cerebral glycolysis, including expressions of GLUT-1, GLUT-3, PFK, LDH, phosphorylated AMPK activity and HIF-1α, when compared to the voluntary exercise and the control groups. Our results suggest that the effects of different exercise on HIF-1α expression and cerebral glycolysis may provide a possible reason for the discrepancy in neuroprotection, with forced exercise faring better than voluntary exercise through increased cerebral metabolism.

Matrix metalloproteinase levels in the drained dialysate reflect the peritoneal solute transport rate: a multicentre study in Japan

BACKGROUND

Long-term peritoneal dialysis (PD) leads to peritoneal injury with high solute transport of the peritoneal membrane. At worst, peritoneal injury leads to encapsulating peritoneal sclerosis with an extremely high mortality rate. To perform PD safely and adequately, it is necessary to monitor peritoneal injury. The aim of this study was to investigate the potential of matrix metalloproteinases (MMPs) as new indicators of peritoneal injury.

METHODS

The subjects included 215 PD patients with end-stage renal disease at 20 centres in Japan. MMPs or tissue inhibitors of MMP (TIMPs) in the drained dialysate were quantified with enzyme-linked immunosorbent assay. The peritoneal solute transport rate was assessed to estimate peritoneal injury and PD efficiency by the peritoneal equilibration test (PET).

RESULTS

MMP-2, MMP-3 and TIMP-1 levels in the drained dialysate obtained by the PET were correlated with the D/P Cr ratios (ρ = 0.69, ρ = 0.52, ρ = 0.55, respectively) and the D/D0 glucose ratios (ρ = -0.60, ρ = -0.47, ρ = -0.48, respectively). The measured D/S ratios of MMP-2 and TIMP-1 were significantly higher than the expected D/S ratios when MMP-2 and TIMP-1 would have been transported from only the circulation. The measured D/S ratios of MMP-3 nearly corresponded to the expected ratios. MMP-1 and TIMP-2 in the drainage were undetected in most patients.

CONCLUSIONS

From these results, most MMP-2 in the drained dialysate may be produced from the peritoneum, and MMP-2 is expected to be a useful marker of peritoneal injury or change in peritoneal solute transport.

Matrix metalloproteinase-9 (MMP-9) expression and extracellular signal-regulated kinase 1 and 2 (ERK1/2) activation in exercise-reduced neuronal apoptosis after stroke

Exercise preconditioning has been shown to reduce neuronal damage in ischemic/reperfusion (I/R) injury. ERK1/2 signaling in injury has been thought to modulate neuroprotection. In this study, we investigated the effects of ERK1/2 activation on the expression and activity of MMP-9 and downstream neuronal apoptosis. Adult male Sprague-Dawley rats were subjected to 30min of exercise on a treadmill for 3 weeks. Stroke was induced by a 2-h middle cerebral artery (MCA) occlusion using an intraluminal filament. Apoptotic protein caspase-3 and neuronal apoptosis in cortex and striatum was determined by Western blot at 24h reperfusion and TUNEL staining at 48h reperfusion in 5 I/R injury groups: no treatment, MMP-9 inhibitor (doxycycline), pre-ischemic exercise, exercised animals undergone ERK1/2 inhibition (U0126), and dual inhibition of ERK1/2 and MMP-9 in exercised ischemic rats. Cerebral MMP-9 expression in ischemic rats with different treatment was determined at 6, 12 and 24h reperfusion by real-time PCR for mRNA, Western blot for protein and zymography for enzyme activity. Exercise preconditioning significantly (p<0.05) reduced apoptosis determined by caspase-3 and TUNEL. In non-exercised rats, doxycycline treatment had significant (p<0.05) reductions in apoptosis after I/R injury. The dual ERK1/2-MMP-9 inhibited exercised animals had significantly (p<0.05) reduced neuronal apoptosis that was similar to that seen in exercised ischemic rats. MMP-9 expression in I/R injury was significantly (p<0.05) reduced in the exercised animals as compared to non-exercised controls. When ERK1/2 was inhibited, the reduced MMP-9 expression was reversed to the level seen in the non-exercised controls. This study has suggested that exercise-induced neuroprotection in I/R injury may be mediated by MMP-9 and ERK1/2 expression, leading to a reduction in neuronal apoptosis.

Estrogen treatment following severe burn injury reduces brain inflammation and apoptotic signaling

Background

Patients with severe burn injury experience a rapid elevation in multiple circulating pro-inflammatory cytokines, with the levels correlating with both injury severity and outcome. Accumulations of these cytokines in animal models have been observed in remote organs, however data are lacking regarding early brain cytokine levels following burn injury, and the effects of estradiol on these levels. Using an experimental animal model, we studied the acute effects of a full-thickness third degree burn on brain levels of TNF-α, IL-1β, and IL-6 and the protective effects of acute estrogen treatment on these levels. Additionally, the acute administration of estrogen on regulation of inflammatory and apoptotic events in the brain following severe burn injury were studied through measuring the levels of phospho-ERK, phospho-Akt, active caspase-3, and PARP cleavage in the placebo and estrogen treated groups.

Methods

In this study, 149 adult Sprague-Dawley male rats received 3rd degree 40% total body surface area (TBSA) burns. Fifteen minutes following burn injury, the animals received a subcutaneous injection of either placebo (n = 72) or 17 beta-estradiol (n = 72). Brains were harvested at 0.5, 1, 2, 4, 6, 8, 12, 18, and 24 hours after injury from the control (n = 5), placebo (n = 8/time point), and estrogen treated animals (n = 8/time point). The brain cytokine levels were measured using the ELISA method. In addition, we assessed the levels of phosphorylated-ERK, phosphorylated-Akt, active caspase-3, and the levels of cleaved PARP at the 24 hour time-point using Western blot analysis.

Results

In burned rats, 17 beta-estradiol significantly decreased the levels of brain tissue TNF-α (~25%), IL-1β (~60%), and IL-6 (~90%) when compared to the placebo group. In addition, we determined that in the estrogen-treated rats there was an increase in the levels of phospho-ERK (p < 0.01) and Akt (p < 0.05) at the 24 hour time-point, and that 17 beta-estradiol blocked the activation of caspase-3 (p < 0.01) and subsequent cleavage of PARP (p < 0.05).

Conclusion

Following severe burn injury, estrogens decrease both brain inflammation and the activation of apoptosis, represented by an increase in the levels of phospho-Akt and inhibition of caspase-3 activation and PARP cleavage. Results from these studies will help further our understanding of how estrogens protect the brain following burn injury, and may provide a novel, safe, and effective clinical treatment to combat remote secondary burn injury in the brain and to preserve cognition.

Early protection from burn-induced acute lung injury by deletion of preprotachykinin-A gene

RATIONALE

Burn-induced acute lung injury (ALI) is a common clinical disorder associated with high mortality even in the absence of inhalational injury. Identification of endogenous triggers that mediate the early onset of remote ALI after burn represents an important goal but remains poorly defined.

OBJECTIVES

We investigated the role of proinflammatory neuropeptide, substance P (SP), in instigating remote ALI and its effects on respiratory function early after severe local burn injury.

METHODS

A 30% total body surface area full-thickness burn was induced in wild-type (WT) mice, preprotachykinin-A (PPT-A) gene deficient mice, which encodes for SP, and PPT-A(-/-) mice challenged with exogenous SP, followed by ALI and lung function analysis.

MEASUREMENTS AND MAIN RESULTS

Endogenous SP production was heightened in burn-injured WT mice, which induced significant elevation of proinflammatory cytokines, chemokines, and endothelial adhesion molecules concurrent with disruption of pulmonary permeability barrier, excessive neutrophil infiltration, and severe ALI. Additionally, decreased neutral endopeptidase and elevated matrix metalloproteinase-9 were evident. Notably, disruption of respiratory function demonstrates a critical role of SP in lungs after burn. These effects were significantly attenuated in PPT-A(-/-) mice, whereas the exogenous administration of SP to PPT-A(-/-) mice restored the inflammatory response and ALI. Furthermore, analysis of neurokinin-1-receptor (NK1R), to which SP binds preferentially, revealed that SP in conjunction with burn injury regulates NK1R expression.

CONCLUSIONS

We show that the absence of a single endogenous factor, SP, significantly provides early protection against burn-induced ALI in mice with marked improvement in respiratory function. Thereby, the blockade of SP may be beneficial in preventing early inflammation and ALI in patients with critical burn injuries.

Onset of symptomatic hydrocephalus requiring emergency cerebrospinal fluid diversion following high-voltage electrical burn injury

High-voltage electrical injuries have been reported to cause a plethora of neurological complications including cognitive, motor, and sensory deficits in an immediate or delayed fashion. In this setting, new-onset symptomatic hydrocephalus requiring CSF shunt placement has not been described. The authors present the case of an 18-year-old man who sustained a high-voltage electrical injury with a calvarial contact point that required emergency CSF diversion within hours of injury and subsequently required placement of a lumboperitoneal shunt. Management of the open calvarial wound, which required rotational flap reconstruction, and the need for ongoing CSF diversion required care and a team approach.

Exercise pre-conditioning reduces brain inflammation in stroke via tumor necrosis factor-alpha, extracellular signal-regulated kinase 1/2 and matrix metalloproteinase-9 activity

OBJECTIVE

We sought to determine whether cerebral inflammation in ischemic rats was reduced by a neuroprotective action of pre-ischemic tumor necrosis factor-alpha up-regulation, which down-regulated matrix metalloproteinase-9 activity via extracellular signal-regulated kinase 1/2 phosphorylation.

MATERIAL AND METHODS

Adult male Sprague-Dawley rats were subjected to 30 minutes of exercise on a treadmill for 3 weeks. Stroke was induced by a 2 hour middle cerebral artery occlusion using an intraluminal filament. The exercised animals were treated with tumor necrosis factor-alpha antibody, UO126 (extracellular signal-regulated kinase 1/2 inhibitor), or both UO126 and doxycycline (matrix metalloproteinase-9 inhibitor). Brain infarct volume was assessed using Nissl staining. Leukocyte infiltration was evaluated using myeloperoxidase immunostaining. Intercellular adhesion molecule-1 and matrix metalloproteinase protein levels were determined by Western blot, and enzyme activity was evaluated using zymography.

RESULTS

There was a significant decrease in neurological deficits, brain infarct volume and leukocyte infiltration, in association with reduction in matrix metalloproteinase-9 and intercellular adhesion molecule-1 expression in exercised animals. Exercised animals treated with either tumor necrosis factor-alpha antibody or with UO126 showed a reversal of neurological outcome, infarct volume and leukocyte infiltration. Matrix metalloproteinase-9 activity was reversed, at least partially, but the intercellular adhesion molecule-1 expression was not. Neuroprotection remained when the exercised ischemic rats were treated with both UO126 and doxycycline.

CONCLUSION

These results suggest that exercise-induced up-regulation of tumor necrosis factor-alpha before stroke and extracellular signal-regulated kinase 1/2 phosphorylation play a role in decreasing brain inflammation by regulating matrix metalloproteinase-9 activity.

Role of tumor necrosis factor-alpha and matrix metalloproteinase-9 in blood-brain barrier disruption after peripheral thermal injury in rats

OBJECT

A relationship has been found between peripheral thermal injury and cerebral complications leading to injury and death. In the present study, the authors examined whether tumor necrosis factor-alpha (TNF-alpha) and matrix metalloproteinase-9 (MMP-9) play a causative role in blood-brain barrier (BBB) disruption after peripheral thermal injury.

METHODS

Thirty-two male Sprague-Dawley rats were subjected to thermal injury. One hour later, 8 rats were injected with TNF-alpha neutralizing antibody, and 8 were injected with doxycycline, an inhibitor of the MMP family proteins; 16 rats did not receive any treatment. Brain tissue samples obtained 7 hours after injury in the treated animals were examined for BBB function by using fluorescein isothiocyanate-dextran and by assessing parenchymal water content. Protein expression of basement membrane components (collagen IV, laminin, and fibronectin) was quantified on Western blot analysis, and MMP-9 protein expression and enzyme activity were determined using Western blot and gelatin zymography. Thermally injured rats that did not receive treatment were killed at 3, 7, or 24 hours after injury and tested for BBB functioning at each time point. Histological analysis for basement membrane proteins was also conducted in untreated rats killed at 7 hours after injury. Results of testing in injured rats were compared with those obtained in a control group of rats that did not undergo thermal injury.

RESULTS

At 7 hours after thermal injury, a significant increase in the fluorescein isothiocyanate-dextran and water content of the brain was found (p < 0.05), but BBB dysfunction was significantly decreased in the rats that received TNF-alpha antibody or doxycycline (p < 0.05). In addition, the components of the basal lamina were significantly decreased at 7 hours after thermal injury (p < 0.01), and there were significant increases in MMP-9 protein expression and enzyme activity (p < 0.05). The basal lamina damage was reversed by inhibition of TNF-alpha and MMP-9, and the increase in MMP-9 protein was reduced in the presence of doxycycline (p < 0.05). The authors found that MMP-9 enzyme activity was significantly increased after thermal injury (p < 0.01) but decreased in the presence of either TNF-alpha antibody or doxycycline (p < 0.01).

CONCLUSIONS

The dual, inhibitory activity of both TNF-alpha and MMP-9 in brain injury suggests that a TNF-alpha and MMP-9 cascade may play a key role in BBB disruption. These results offer a better understanding of the pathophysiology of burn injuries, which may open new avenues for burn treatment beyond the level of current therapies.

Bench-to-bedside review: Burn-induced cerebral inflammation--a neglected entity?

Severe burn injury remains a major burden on patients and healthcare systems. Following severe burns, the injured tissues mount a local inflammatory response aiming to restore homeostasis. With excessive burn load, the immune response becomes disproportionate and patients may develop an overshooting systemic inflammatory response, compromising multiple physiological barriers in the lung, kidney, liver, and brain. If the blood–brain barrier is breached, systemic inflammatory molecules and phagocytes readily enter the brain and activate sessile cells of the central nervous system. Copious amounts of reactive oxygen species, reactive nitrogen species, proteases, cytokines/chemokines, and complement proteins are being released by these inflammatory cells, resulting in additional neuronal damage and life-threatening cerebral edema. Despite the correlation between cerebral complications in severe burn victims with mortality, burn-induced neuroinflammation continues to fly under the radar as an underestimated entity in the critically ill burn patient. In this paper, we illustrate the molecular events leading to blood–brain barrier breakdown, with a focus on the subsequent neuroinflammatory changes leading to cerebral edema in patients with severe burns.

Effects of novel semiselective matrix metalloproteinase inhibitors on ex vivo cardiac structure-function

The purpose of this study was to evaluate the ability of novel semiselective matrix metalloproteinase inhibitors (MMPI) to protect myocardial structure-function in the setting of ischemia-reperfusion injury. For this purpose, an isolated rat model of myocardial stunning and infarction was used. Isolated hearts were subjected to 20-30 minutes of global no-flow ischemia and 30-minute reperfusion. Myocardial performance was assessed as the product of the heart rate and left ventricular developed pressure (rate-pressure product, RPP). Coronary flow rates, ventricular weights, indicators of muscle (troponin I), and fibrillar collagen damage (collagen opalation) were measured. Four MMPI were tested: 2 non-hydroxamate, semiselective inhibitors (PY-2 and 1,2-HOPO-2) and 2 broad-spectrum inhibitors (PD166793 and CGS27023A). The non-hydroxamate, semiselective inhibitors were shown to be nontoxic in cocultures of cardiac cells. Results indicate that semiselective inhibitors (in particular 1,2-HOPO-2) yield improved cardiac performance (approximately 23% higher RPP vs. controls) and coronary flow rates (approximately 22%), reducing muscle (approximately 25%) and fibrillar collagen damage (approximately 60%). Evidence suggests the involvement of matrix metalloproteinase-2 in these actions. Interestingly, broad-spectrum inhibitors only show modest improvement (approximately 8% higher RPP vs. controls) without affecting the other measured parameters. In conclusion, semiselective MMPI can act as cardioprotectors in isolated perfused rat hearts. Protection is observed in all structural components of the myocardium translating into improved contractile function. Based on these findings, non-hydroxamate, semiselective MMPI warrant further studies as to their ability to protect ischemic myocardium in the in vivo setting.

Synapse loss regulated by matrix metalloproteinases in traumatic brain injury is associated with hypoxia inducible factor-1alpha expression

The present study assessed the role of matrix metalloproteinase-2 (MMP-2) and -9 in synapse loss after traumatic brain injury (TBI) and the role of hypoxia inducible factor-1alpha (HIF-1alpha), a transcription factor up-regulated during hypoxia, in the regulation of MMP-2 and -9 expression post-TBI. Adult male Sprague-Dawley rats (n=6 per group, 400 g-425 g) were injured using Marmarou's closed-head acceleration impact model and allowed to survive for 1, 4, 24 and 48 h. In another set of experiments, 30 min after TBI, animals were treated with Minocycline (inhibitor of MMPs), or 2-Methoxyestradiol (2ME2, inhibitor of HIF-1alpha) and sacrificed at 4 h after injury. Relative amounts of synaptophysin, a presynaptic vesicular protein, HIF-1alpha, as well as MMP-2 and -9 were assessed by real-time PCR and Western blotting. Activity levels of MMP-2 and -9 were determined by zymography. Synaptophysin expression was significantly (p<0.05) decreased at 1 h through 48 h after TBI. A significant increase in gene and protein expressions of HIF-1alpha, MMP-2 and -9, as well as enzyme activity of MMP-2 and -9 at the same time points was also detected. Inhibition of either MMPs or HIF-1alpha significantly reversed the TBI-induced decrease in synaptophysin. Inhibition of HIF-1alpha reduced expression of MMP-2 and -9. This study showed an early detection of a correlation between synaptic loss and MMP expression after TBI. The data also supports a role for HIF-1alpha in the MMP regulatory cascade in synapse loss after TBI, suggesting potential targets for reducing loss of synaptic terminals.

Preischemic induction of TNF-alpha by physical exercise reduces blood-brain barrier dysfunction in stroke

This study explores the neuroprotective action of tumor necrosis factor-alpha (TNF-alpha) induced during physical exercise, which, consequently, reduces matrix metalloproteinase-9 (MMP-9) activity and ameliorates blood-brain barrier (BBB) dysfunction in association with extracellular signal-regulated kinase 1 and 2 (ERK1/2) phosphorylation. Adult male Sprague-Dawley rats were subjected to exercise on a treadmill for 3 weeks. A 2-h middle cerebral artery occlusion and reperfusion was administered to exercised and nonexercised animals to induce stroke. Exercised ischemic rats were subjected to TNF-alpha inhibition and ERK1/2 by TNF-alpha antibody or UO126. Nissl staining of coronal sections revealed the infarct volume. Evans blue extravasation and water content evaluated BBB function. Western blot was performed to analyze protein expression of TNF-alpha, ERK1/2, phosphorylated ERK1/2, the basal laminar protein collagen IV, and MMP-9. The activity of MMP-9 was determined by gelatin zymography. Tumor necrosis factor-alpha expression and ERK1/2 phosphorylation were upregulated during exercise. Infarct volume, brain edema, and Evans blue extravasation all significantly decreased in exercised ischemic rats. Collagen IV production increased in exercised rats and remained high after stroke, whereas MMP-9 protein level and activity decreased. These results were negated and returned toward nonexercised values once TNF-alpha or ERK1/2 was blocked. We concluded that preischemic, exercise-induced TNF-alpha markedly decreases BBB dysfunction by using the ERK1/2 pathway.

Forced, not voluntary, exercise effectively induces neuroprotection in stroke

Previous treadmill exercise studies showing neuroprotective effects have raised questions as to whether exercise or the stress related to it may be key etiologic factors. In this study, we examined different exercise regimens (forced and voluntary exercise) and compared them with the effect of stress-only on stroke protection. Adult male Sprague-Dawley rats (n = 65) were randomly assigned to treatment groups for 3 weeks. These groups included control, treadmill exercise, voluntary running wheel exercise, restraint, and electric shock. Levels of the stress hormone, corticosterone, were measured in the different groups using ELISA. Animals from each group were then subjected to stroke induced by a 2-h middle cerebral artery (MCA) occlusion followed by 48-h reperfusion. Infarct volume was determined in each group, while changes in gene expression of stress-induced heat shock proteins (Hsp) 27 and 70 were compared using real-time PCR between voluntary and treadmill exercise groups. The level of corticosterone was significantly higher in both stress (P < 0.05) and treadmill exercise (P < 0.05) groups, but not in the voluntary exercise group. Infarct volume was significantly reduced (P < 0.01) following stroke in rats exercised on a treadmill. However, the amelioration of damage was not duplicated in voluntary exercise, even though running distance in the voluntary exercise group was significantly (P < 0.01) longer than that of the forced exercise group (4,828 vs. 900 m). Furthermore, rats in the electric shock group displayed a significantly increased (P < 0.01) infarct volume. Expression of both Hsp 27 and Hsp 70 mRNA was significantly increased (P < 0.01) in the treadmill exercise group as compared with that in the voluntary exercise group. These results suggest that exercise with a stressful component, rather than either voluntary exercise or stress alone, is better able to reduce infarct volume. This exercise-induced neuroprotection may be attributable to up-regulation of stress-induced heat shock proteins 27 and 70.

Pre-ischemic exercise reduces matrix metalloproteinase-9 expression and ameliorates blood-brain barrier dysfunction in stroke

Exercise reduces ischemia and reperfusion (I/R) injury in the rat stroke model. We investigated whether pre-ischemic exercise ameliorates blood-brain barrier (BBB) dysfunction in stroke by reducing matrix metalloproteinase (MMP)-9 expression and strengthening basal lamina. Adult male Sprague-Dawley rats were subjected to a 30 min exercise program on a treadmill 5 days a week for 3 weeks. Stroke was induced by a 2-h middle cerebral artery (MCA) occlusion using an intraluminal filament in the exercised and non-exercised groups. Brain infarction was measured and neurological deficits were scored. BBB dysfunction was determined by examining brain edema and Evans Blue extravasation. Expression of collagen IV, the major component of basal lamina essential for maintenance of the endothelial permeability barrier, was quantitatively detected by Western blot and immunocytochemistry. Ex vivo techniques were used to compare collagen IV-labeled vessels in response to ischemic insult. Temporal relationship of expression of MMP-9 and its endogenous inhibitor, the tissue inhibitors of metalloproteinase-1 (TIMP-1), was determined by real-time PCR for mRNA and Western blot for protein during reperfusion. Brain edema and Evans Blue leakage were both significantly (P<0.01) reduced after stroke in the exercised group, in association with reduced brain infarct volume and neurological deficits. Western blot analysis indicated that exercise enhanced collagen IV expression and reduced the collagen loss after stroke. Immunocytochemistry demonstrated that collagen IV-labeled vessels were significantly (P<0.01) increased in exercised rats. In the ex vivo study, after exercised brains were incubated with ischemic brain tissue, a significantly (P<0.01) higher level of collagen IV-labeled vessels was observed as compared with non-exercised brains following the same treatment. The ex vivo study also revealed a key role of MMP-9 in exercise-strengthened collagen IV expression against I/R injury. TIMP-1 protein levels were significantly (P<0.01) increased by exercise. Our results indicate that pre-ischemic exercise reduces brain injury by improving BBB function and enhancing basal lamina integrity in stroke. This study suggests that the neuroprotective effect of physical exercise is associated with an imbalance of MMP-9 and TIMP-1 expression.