Magnesium restores altered aquaporin-4 immunoreactivity following traumatic brain injury to a pre-injury state

Magnesium and the Brain: A Focus on Neuroinflammation and Neurodegeneration

Magnesium (Mg) is involved in the regulation of metabolism and in the maintenance of the homeostasis of all the tissues, including the brain, where it harmonizes nerve signal transmission and preserves the integrity of the blood-brain barrier. Mg deficiency contributes to systemic low-grade inflammation, the common denominator of most diseases. In particular, neuroinflammation is the hallmark of neurodegenerative disorders. Starting from a rapid overview on the role of magnesium in the brain, this narrative review provides evidences linking the derangement of magnesium balance with multiple sclerosis, Alzheimer's, and Parkinson's diseases.

Neuro-Inflammation Modulation and Post-Traumatic Brain Injury Lesions: From Bench to Bed-Side

Head trauma is the most common cause of disability in young adults. Known as a silent epidemic, it can cause a mosaic of symptoms, whether neurological (sensory-motor deficits), psychiatric (depressive and anxiety symptoms), or somatic (vertigo, tinnitus, phosphenes). Furthermore, cranial trauma (CT) in children presents several particularities in terms of epidemiology, mechanism, and physiopathology-notably linked to the attack of an immature organ. As in adults, head trauma in children can have lifelong repercussions and can cause social and family isolation, difficulties at school, and, later, socio-professional adversity. Improving management of the pre-hospital and rehabilitation course of these patients reduces secondary morbidity and mortality, but often not without long-term disability. One hypothesized contributor to this process is chronic neuroinflammation, which could accompany primary lesions and facilitate their development into tertiary lesions. Neuroinflammation is a complex process involving different actors such as glial cells (astrocytes, microglia, oligodendrocytes), the permeability of the blood-brain barrier, excitotoxicity, production of oxygen derivatives, cytokine release, tissue damage, and neuronal death. Several studies have investigated the effect of various treatments on the neuroinflammatory response in traumatic brain injury in vitro and in animal and human models. The aim of this review is to examine the various anti-inflammatory therapies that have been implemented.

Aquaporin 4 in Traumatic Brain Injury: From Molecular Pathways to Therapeutic Target

Traumatic brain injury (TBI) is known as an acute degenerative pathology of the central nervous system, and has been shown to increase brain aquaporin 4 (AQP4) expression. Various molecular mechanisms affect AQP4 expression, including neuronal high mobility group box 1, forkhead box O3a, vascular endothelial growth factor, hypoxia-inducible factor-1 α (HIF-1 α) sirtuin 2, NF-κB, Malat1, nerve growth factor and Angiotensin II receptor type 1. In addition, inhibition of AQP4 with FK-506, MK-801 (indirectly by targeting N-methyl-D-aspartate receptor), inactivation of adenosine A2A receptor, levetiracetam, adjudin, progesterone, estrogen, V1aR inhibitor, hypertonic saline, erythropoietin, poloxamer 188, brilliant blue G, HIF-1alpha inhibitor, normobaric oxygen therapy, astaxanthin, epigallocatechin-3-gallate, sesamin, thaliporphine, magnesium, prebiotic fiber, resveratrol and omega-3, as well as AQP4 gene silencing lead to reduced edema upon TBI. This review summarizes current knowledge and evidence on the relationship between AQP4 and TBI, and the potential mechanisms involved.

Heparanase overexpression impedes perivascular clearance of amyloid-β from murine brain: relevance to Alzheimer's disease

Defective amyloid-β (Aβ) clearance from the brain is a major contributing factor to the pathophysiology of Alzheimer's disease (AD). Aβ clearance is mediated by macrophages, enzymatic degradation, perivascular drainage along the vascular basement membrane (VBM) and transcytosis across the blood-brain barrier (BBB). AD pathology is typically associated with cerebral amyloid angiopathy due to perivascular accumulation of Aβ. Heparan sulfate (HS) is an important component of the VBM, thought to fulfill multiple roles in AD pathology. We previously showed that macrophage-mediated clearance of intracortically injected Aβ was impaired in the brains of transgenic mice overexpressing heparanase (Hpa-tg). This study revealed that perivascular drainage was impeded in the Hpa-tg brain, evidenced by perivascular accumulation of the injected Aβ in the thalamus of Hpa-tg mice. Furthermore, endogenous Aβ accumulated at the perivasculature of Hpa-tg thalamus, but not in control thalamus. This perivascular clearance defect was confirmed following intracortical injection of dextran that was largely retained in the perivasculature of Hpa-tg brains, compared to control brains. Hpa-tg brains presented with thicker VBMs and swollen perivascular astrocyte endfeet, as well as elevated expression of the BBB-associated water-pump protein aquaporin 4 (AQP4). Elevated levels of both heparanase and AQP4 were also detected in human AD brain. These findings indicate that elevated heparanase levels alter the organization and composition of the BBB, likely through increased fragmentation of BBB-associated HS, resulting in defective perivascular drainage. This defect contributes to perivascular accumulation of Aβ in the Hpa-tg brain, highlighting a potential role for heparanase in the pathogenesis of AD.

Posterior reversible encephalopathy syndrome in an oncological normotensive patient: evidence for a pathogenic role of concomitant low magnesium serum levels and chemotherapy treatment

Background:

Posterior reversible encephalopathy (PRES) is a rare syndrome characterized by headache, confusion, seizures, visual changes and white matter edema at radiological imaging. Its pathophysiology is not clarified and different causes, including uncontrolled hypertension, eclampsia, chemotherapy and hypomagnesemia have been suggested.

Case report:

A woman affected by stage IV breast cancer with lower extremity deep vein thrombosis treated with low-molecular-weight-heparin, currently in therapy with Palbociclib/Fulvestrant (antiCDK4 and 6/estrogen receptor antagonist) but previously treated with several other chemotherapy lines (including VEGF inhibitor bevacizumab), was admitted to our Internal Medicine department because of ascites and abdominal pain. She was treated with diuretics (and paracentesis). Recently (six-month earlier) a pan-encephalic radiotherapy was done because of brain and skull metastasis. Among blood tests, low serum levels of hypomagnesemia were observed. She developed PRES that rapidly progressed to lethargy, unresponsiveness till coma without changes in blood pressure. Magnetic Resonance Imaging study showed bilateral parieto-occipital edema and a thrombosis of left transverse and sigmoid sinuses. Anti-edema therapy, intravenous supplementation of magnesium and decoagulation were started, with complete and rapid recovery (within 18 hours) of clinical and radiologic changes.

Conclusions:

PRES diagnosis was based on the rapid clinical recovery after antiedema treatment and magnesium supplementation. Low magnesium level related to both diuretic and Fulvestrant/Palbociclib therapies and recent radiotherapy can represent potential mechanisms favouring PRES development. The previous bevacizumab treatment may also be involved as a PRES predisposing factor. The concomitant occurrence of cerebral thrombosis can have precipitated the clinical situation. (www.actabiomedica.it)

Magnesium sulfate protects blood-brain barrier integrity and reduces brain edema after acute ischemic stroke in rats

Brain edema is a fatal complication of acute ischemic stroke and associated with worse outcomes in patients. This study was designed to evaluate the effects of magnesium sulfate on vasogenic brain edema formation and blood-brain barrier (BBB) disruption caused by ischemia-reperfusion (IR) in a rat model of ischemic stroke. A total of 72 male Sprague-Dawley rats were categorized into the following three primary groups: sham, control ischemic, magnesium-sulfate-treated (300 mg/kg loading dose, followed by an additional 100 mg/kg) ischemic (n = 24 in each group). Transient focal cerebral ischemia was induced by 60-min-long occlusion of the left middle cerebral artery, followed by 24-h-long reperfusion. Sensorimotor deficits, infarct volume, and brain edema were evaluated at the end of the reperfusion period. The BBB permeability was assessed by Evans Blue extravasation technique. Lipid peroxidation levels were assessed by measuring the malondialdehyde content in the brain tissue homogenate, and the activities of the antioxidant enzymes superoxide dismutase, catalase, and glutathione peroxidase were detected according to the technical manual of the assay kits. Induction of cerebral ischemia in the control group produced considerable BBB damage in conjunction with severe brain edema formation. Treatment with magnesium sulfate significantly attenuated brain edema and protected BBB integrity in the ischemic lesioned hemisphere. In addition, magnesium sulfate reduced lipid peroxidation and increased antioxidant protection of brain tissue by upregulating the activities of antioxidant enzymes. Treatment with magnesium sulfate protected BBB integrity against IR-induced damage and reduced vasogenic edema formation partly via antioxidant mechanisms in a rat model of acute ischemic stroke.

Vitamins and nutrients as primary treatments in experimental brain injury: Clinical implications for nutraceutical therapies

With the numerous failures of pharmaceuticals to treat traumatic brain injury in humans, more researchers have become interested in combination therapies. This is largely due to the multimodal nature of damage from injury, which causes excitotoxicity, oxidative stress, edema, neuroinflammation and cell death. Polydrug treatments have the potential to target multiple aspects of the secondary injury cascade, while many previous therapies focused on one particular aspect. Of specific note are vitamins, minerals and nutrients that can be utilized to supplement other therapies. Many of these have low toxicity, are already FDA approved and have minimal interactions with other drugs, making them attractive targets for therapeutics. Over the past 20 years, interest in supplementation and supraphysiologic dosing of nutrients for brain injury has increased and indeed many vitamins and nutrients now have a considerable body of the literature backing their use. Here, we review several of the prominent therapies in the category of nutraceutical treatment for brain injury in experimental models, including vitamins (B2, B3, B6, B9, C, D, E), herbs and traditional medicines (ginseng, Gingko biloba), flavonoids, and other nutrients (magnesium, zinc, carnitine, omega-3 fatty acids). While there is still much work to be done, several of these have strong potential for clinical therapies, particularly with regard to polydrug regimens. This article is part of a Special Issue entitled SI:Brain injury and recovery.

Silencing TRPM7 in mouse cortical astrocytes impairs cell proliferation and migration via ERK and JNK signaling pathways

Transient receptor potential melastatin 7 (TRPM7), a non-selective cation channel, is highly expressed expressed in the brain and plays a critical role in ischemic neuronal death. Astrocyte, the most abundant cell type in central nervous system (CNS), exerts many essential functions in the physiological and pathological conditions. Here we investigated the expression and functions of the TRPM7 channel in mouse cortical astrocytes. Using reverse transcription (RT)-PCR, immunostaining, western blot and patch clamp recording, we showed that functional TRPM7 channel is expressed in cultured mouse cortical astrocytes. Knocking down TRPM7 with specific siRNA impairs the proliferation and migration of astrocytes by 40.2% ± 3.9% and 40.1% ± 11.5%, respectively. Consistently, inhibition of TRPM7 with 2-aminoethoxydiphenyl borate (2-APB) also decreases astrocyte proliferation and migration by 46.1% ± 2.5% and 64.2% ± 2.4%. MAPKs and Akt signaling pathways have been shown to be implicated in TRPM7-mediated responses including cell proliferation and migration. Our data show that suppression of TRPM7 in astrocytes reduces the phosphorylation of extracellular signal-regulated kinases (ERK) and c-Jun N-terminal kinases (JNK), but not p38 mitogen-activated protein kinase and Akt. In addition, TRPM7, as a cation channel, has been involved in the Ca²⁺ and Mg²⁺ homeostasis in several types of cells. In our study, we found that silencing TRPM7 decreases the intracellular basal Mg²⁺ concentration without affecting Ca²⁺ concentration in astrocytes. However, an addition of Mg²⁺ to the growth medium could not rescue the impaired proliferation of astrocytes. Together, our data suggest that TRPM7 channel may play a critical role in the proliferation and migration of astrocytes via the ERK and JNK pathways.

Electron microscopy of astrocyte changes and subtypes in traumatic human edematous cerebral cortex: a review

The astrocyte subtypes in moderate and severe human brain trauma complicated with subdural hematoma or hygroma are described. Clear and dense edematous and hypertrophic reactive astrocytes are distinguished in severe vasogenic brain edema. Swollen perineuronal astrocytes appear compressing and indenting dark, degenerated pyramidal and nonpyramidal nerve cells. Glycogen-depleted and glycogen-rich astrocytes also are seen. Reactive hypertrophic astrocytes exhibit increased amounts of dilated smooth and rough endoplasmic reticulum, microtubules, and gliofilaments. Perisynaptic astrocyte ensheathments of neuropil synaptic contacts are lost, and the perivascular astrocyte end-feet appear dissociated from the capillary basement membrane. The interastrocytary gap junctions appear fragmented.

Postconcussion syndrome: a review of pathophysiology and potential nonpharmacological approaches to treatment

The incidence of all-cause concussions in the United States is estimated to range from 1.6 to 3.8 million annually, with the reported number of sport- or recreation-related concussions increasing dramatically, especially in youth sports.(1,2) Additionally, the use of roadside bombs in Iraq and Afghanistan has propelled the incidence of concussion and other traumatic brain injuries to the highest levels ever encountered by the US military. As a result, there has also been a marked increase in postconcussion syndrome (PCS) and the associated cognitive, emotional, and memory disabilities associated with the condition. Unfortunately, however, there have been no significant advancements in the understanding or treatment of PCS for decades. The current management of PCS mainly consists of rest, reduction of sensory inputs, and treating symptoms as needed. Recently, researchers investigating the underlying mechanisms of PCS have proposed that activation of the immune inflammatory response may be an underlying pathophysiology that occurs in those who experience prolonged symptoms after a concussion. This article reviews the literature and summarizes the immune inflammatory response known as immunoexcitotoxicity. This article also discusses the use of nonpharmacological agents for the management of PCS that directly address this underlying mechanism.

Natural plant products and extracts that reduce immunoexcitotoxicity-associated neurodegeneration and promote repair within the central nervous system

Our understanding of the pathophysiological and biochemical basis of a number of neurological disorders has increased enormously over the last three decades. Parallel with this growth of knowledge has been a clearer understanding of the mechanism by which a number of naturally occurring plant extracts, as well as whole plants, can affect these mechanisms so as to offer protection against injury and promote healing of neurological tissues. Curcumin, quercetin, green tea catechins, balcalein, and luteolin have been extensively studied, and they demonstrate important effects on cell signaling that go far beyond their antioxidant effects. Of particular interest is the effect of these compounds on immunoexcitotoxicity, which, the authors suggest, is a common mechanism in a number of neurological disorders. By suppressing or affecting microglial activation states as well as the excitotoxic cascade and inflammatory mediators, these compounds dramatically affect the pathophysiology of central nervous system disorders and promote the release and generation of neurotrophic factors essential for central nervous system healing. We discuss the various aspects of these processes and suggest future directions for study.

Minocycline and magnesium in combination may be a good therapeutic intervention for cerebral ischemia

A neuroprotective strategy through a combination therapy is always being superior to any other singular therapeutic interventions, as these acts through a multifauceted approach within the brain during cerebral ischemia. Therefore, the development of a potential new combination of drug is necessitated which can bring about desirable improved neuroprotection targeting different pathways against ischemic stroke. Numerous past studies have enumerated the neuroprotective roles of minocycline and magnesium administered in single against cerebral ischemia in animal model hence we hypothesized that by using magnesium with minocycline in combination would provide additive neuroprotection than either of the agents used alone. In this article, we discuss our hypothesis regarding the possibility of minocycline and magnesium as a potent combination which may have a positive therapeutic role in treatment of cerebral ischemia through its anti-inflammatory, anti-apoptotic and anti-oxidative characteristics with magnesium contributing as a regulator of increased calcium influx.

Aquaporin-4 expression in cultured astrocytes after fluid percussion injury

The development of cytotoxic brain edema resulting in increased intracranial pressure is a major cause of death occurring in the early phase of traumatic brain injury (TBI). Such edema predominantly develops as a consequence of astrocyte swelling. We recently documented that fluid percussion injury (FPI) to cultured astrocytes causes cell swelling. Since aquaporin-4 (AQP4) has been strongly implicated in the development of brain edema/astrocyte swelling in various neurological conditions, this study examined the effect of in vitro trauma on AQP4 protein expression in cultured astrocytes. Exposure of astrocytes to FPI resulted in a significant upregulation of AQP4 protein in the plasma membrane due to neosynthesis, as cycloheximide blocked the trauma-induced AQP4 upregulation. Silencing the aqp4 gene by siRNA resulted in a significant reduction in trauma-induced astrocyte swelling, indicating a critical role of AQP4 in this process. We recently documented that oxidative/nitrative stress (ONS), the mitochondrial permeability transition (mPT), and activation of mitogen-activated protein kinases (MAPKs), contribute to trauma-induced astrocyte swelling in culture. We now show that inhibition of these factors reduces the upregulation of AQP4 following trauma. Since TBI has been shown to activate nuclear factor-kappa B (NF-κB), as well as the Na(+),K(+),Cl(-) co-transporter (NKCC), both of which are implicated in brain edema/astrocyte swelling in other conditions, we also examined the effect of BAY 11-7082 and bumetanide, inhibitors of NF-κB and NKCC, respectively, and found that these agents also significantly inhibited the trauma-induced AQP4 upregulation. Our findings show that in vitro trauma upregulates AQP4, and that ONS, MAPKs, mPT, NF-κB, and NKCC are involved in its upregulation.

Hypermagnesemia does not prevent intracranial hypertension and aggravates cerebral hyperperfusion in a rat model of acute hyperammonemia

Intravenous infusion of magnesium sulfate prevents seizures in patients with eclampsia and brain edema after traumatic brain injury. Neuroprotection is achieved by controlling cerebral blood flow (CBF), intracranial pressure, neuronal glutamate release, and aquaporin-4 (Aqp4) expression. These factors are also thought to be involved in the development of brain edema in acute liver failure. We wanted to study whether hypermagnesemia prevented development of intracranial hypertension and hyperperfusion in a rat model of portacaval anastomosis (PCA) and acute hyperammonemia. We also studied whether hypermagnesemia had an influence on brain content of glutamate, glutamine, and aquaporin-4 expression. The study consisted of three experiments: The first was a dose-finding study of four different dosing regimens of magnesium sulfate (MgSO4) in healthy rats. The second involved four groups of PCA rats receiving ammonia infusion/vehicle and MgSO4) /saline. The effect of MgSO(4) on mean arterial pressure (MAP), intracranial pressure (ICP), CBF, cerebral glutamate and glutamine, and aquaporin-4 expression was studied. Finally, the effect of MgSO4 on MAP, ICP, and CBF was studied, using two supplementary dosing regimens. In the second experiment, we found that hypermagnesemia and hyperammonemia were associated with a significantly higher CBF (P < 0.05, two-way analysis of variance [ANOVA]). Hypermagnesemia did not lead to a reduction in ICP and did not affect the brain content of glutamate, glutamine, or Aqp-4 expression. In the third experiment, we achieved higher P-Mg but this did not lead to a significant reduction in ICP or CBF.

CONCLUSION

Our results demonstrate that hypermagnesemia does not prevent intracranial hypertension and aggravates cerebral hyperperfusion in rats with PCA and hyperammonemia.

Mechanisms of cerebral edema in traumatic brain injury: therapeutic developments

PURPOSE OF REVIEW

Although a number of factors contribute to the high mortality and morbidity associated with traumatic brain injury (TBI), the development of cerebral edema with brain swelling remains the most significant predictor of outcome. The present review summarizes the most recent advances in the understanding of mechanisms associated with development of posttraumatic cerebral edema, and highlights areas of therapeutic promise.

RECENT FINDINGS

Despite the predominance of cytotoxic (or cellular) edema in the first week after traumatic brain injury, brain swelling can only occur with addition of water to the cranial vault from the vasculature. As such, regulation of blood-brain barrier permeability has become a focus of recent research seeking to manage brain edema. Aquaporins, matrix metalloproteinases and vasoactive inflammatory agents have emerged as potential mediators of cerebral edema following traumatic brain injury. In particular, kinins (bradykinins) and tachykinins (substance P) seem to play an active physiological role in modulating blood-brain barrier permeability after trauma. Substance P neurokinin-1 receptor antagonists show particular promise as novel therapeutic agents.

SUMMARY

Attenuating blood-brain barrier permeability has become a promising approach to managing brain edema and associated swelling given that increases in cranial water content can only be derived from the vasculature. Inflammation, both classical and neurogenic, offers a number of attractive targets.

Use of magnesium in traumatic brain injury

Depletion of magnesium is observed in animal brain and in human blood after brain injury. Treatment with magnesium attenuates the pathological and behavioral changes in rats with brain injury; however, the therapeutic effect of magnesium has not been consistently observed in humans with traumatic brain injury (TBI). Secondary brain insults are observed in patients with brain injury, which adversely affect clinical outcome. Systemic administration studies in rats have shown that magnesium enters the brain; however, inducing hypermagnesemia in humans did not concomitantly increase magnesium levels in the CSF. We hypothesize that the neuroprotective effects of magnesium in TBI patients could be observed by increasing its brain bioavailability with mannitol. Here, we review the role of magnesium in brain injury, preclinical studies in brain injury, clinical safety and efficacy studies in TBI patients, brain bioavailability studies in rat, and pharmacokinetic studies in humans with brain injury. Neurodegeneration after brain injury involves multiple biochemical pathways. Treatment with a single agent has often resulted in poor efficacy at a safe dose or toxicity at a therapeutic dose. A successful neuroprotective therapy needs to be aimed at homeostatic control of these pathways with multiple agents. Other pharmacological agents, such as dexanabinol and progesterone, and physiological interventions, with hypothermia and hyperoxia, have been studied for the treatment of brain injury. Treatment with magnesium and hypothermia has shown favorable outcome in rats with cerebral ischemia. We conclude that coadministration of magnesium and mannitol with pharmacological and physiological agents could be an effective neuroprotective regimen for the treatment of TBI.

Magnesium sulfate for the treatment of eclampsia: a brief review

BACKGROUND AND PURPOSE

Magnesium sulfate is used extensively for prevention of eclamptic seizures. Empirical and clinical evidence supports the effectiveness of magnesium sulfate; however, questions remain as to its safety and mechanism. This review summarizes current evidence supporting the possible mechanisms of action and several controversies for magnesium sulfate treatment.

SUMMARY OF REVIEW

Several mechanisms are presented, including the effects of magnesium sulfate on peripheral and cerebral vasodilation, blood-brain barrier protection, and as an anticonvulsant.

CONCLUSIONS

Though the specific mechanisms of action remain unclear, the effect of magnesium sulfate in the prevention of eclampsia is likely multi-factorial. Magnesium sulfate may act as a vasodilator, with actions in the peripheral vasculature or the cerebrovasculature, to decrease peripheral vascular resistance or relieve vasoconstriction. Additionally, magnesium sulfate may also protect the blood-brain barrier and limit cerebral edema formation, or it may act through a central anticonvulsant action.

Glial cell aquaporin-4 overexpression in transgenic mice accelerates cytotoxic brain swelling

Aquaporin-4 (AQP4) is a water transport protein expressed in glial cell plasma membranes, including glial cell foot processes lining the blood-brain barrier. AQP4 deletion in mice reduces cytotoxic brain edema produced by different pathologies. To determine whether AQP4 is rate-limiting for brain water accumulation and whether altered AQP4 expression, as occurs in various pathologies, could have functional importance, we generated mice that overexpressed AQP4 in brain glial cells by a transgenic approach using the glial fibrillary acid protein promoter. Overexpression of AQP4 protein in brain by approximately 2.3-fold did not affect mouse survival, appearance, or behavior, nor did it affect brain anatomy or intracranial pressure (ICP). However, following acute water intoxication produced by intraperitoneal water injection, AQP4-overexpressing mice had an accelerated progression of cytotoxic brain swelling, with ICP elevation of 20 +/- 2 mmHg at 10 min, often producing brain herniation and death. In contrast, ICP elevation was 14 +/- 2 mmHg at 10 min in control mice and 9.8 +/- 2 mmHg in AQP4 knock-out mice. The deduced increase in brain water content correlated linearly with brain AQP4 protein expression. We conclude that AQP4 expression is rate-limiting for brain water accumulation, and thus, that altered AQP4 expression can be functionally significant.

Magnesium sulphate treatment decreases blood-brain barrier permeability during acute hypertension in pregnant rats

Eclampsia is associated with increased blood-brain barrier (BBB) permeability and formation of cerebral oedema. Magnesium sulphate is used to treat eclampsia despite an unclear mechanism of action. This study was to determine the effect of magnesium sulphate on in vivo BBB permeability and formation of cerebral oedema during acute hypertension and on brain aquaporin-4 (AQP4) protein expression. An in vivo model of hypertensive encephalopathy was used in late-pregnant (LP) rats following magnesium sulphate treatment, 270 mg kg(-1) i.p. injection every 4 h for 24 h. Permeability of the BBB was determined by in situ brain perfusion of Evan's Blue (EB) and sodium fluorescein (NaFl), and dye clearance determined by fluorescence spectrophotometry. Cerebral oedema was determined following acute hypertension by measuring brain water content. The effect of magnesium treatment on AQP4 expression was determined by Western blot analysis. Acute hypertension with autoregulatory breakthrough increased BBB permeability to EB in both brain regions studied (P < 0.05). Magnesium attenuated BBB permeability to EB during acute hypertension by 41% in the posterior cerebrum (P < 0.05) but had no effect in the anterior cerebrum (P > 0.05). Treatment with magnesium did not change NaFl permeability, cerebral oedema formation or AQP4 expression. In summary, BBB permeability to Evan's Blue was increased by acute hypertension in LP rats, and this was attenuated by treatment with magnesium sulphate. The greatest effect on BBB permeability to EB was in the posterior cerebrum, an area particularly susceptible to oedema formation during eclampsia.

Serum and Cerebrospinal Fluid Magnesium in Severe Traumatic Brain Injury Outcome

Serum magnesium concentration has a neuroprotective effect in experimental models of traumatic brain injury (TBI). This study was designed to assess the relationship between initial serum magnesium, cerebrospinal fluid (CSF) magnesium, neurological outcome and the efficacy of magnesium replacement therapy (MgSO4). A retrospective analysis was performed on a prospectively collected dataset from 216 patients admitted during 1996-2006 to the University of Pittsburgh Medical Center with severe TBI. Admission serum and CSF magnesium were dichotomized into low and normal magnesium concentration groups for serum and normal and high concentration groups for CSF. A logistic-regression analysis was performed with 6-month Glasgow Outcome Scale (GOS) scores as outcome variable. The outcome of a subset of 31 patients who presented with low serum magnesium and who were rapidly corrected within 24 h of admission was also analyzed. Low initial serum magnesium was measured in 56.67% of all patients. Patients with an initial serum magnesium of <1.3 mEq/L were 2.37 times more likely to have a poor outcome (CI: 1.18-4.78, p = 0.016). The prognostic significance of depressed serum magnesium remained, even in patients whose serum magnesium levels were corrected within 24 h (OR = 11.03, CI: 1.87-68.14, p = 0.008). Patients with an initial high CSF magnesium were 7.63 more likely to have a poor outcome (p = 0.05). Elevated CSF magnesium correlated with depressed serum magnesium only in patients with poor outcome (p = 0.013). Patients with low serum magnesium and high CSF magnesium are most likely to have poor outcome after severe TBI. Rapid correction of serum magnesium levels does not reverse the prognostic value of these markers.

Effects of polyethylene glycol and magnesium sulfate administration on clinically relevant neurological outcomes after spinal cord injury in the rat

The purpose of this study was to determine the long-term effects of polyethylene glycol (PEG) and magnesium sulfate (MgSO(4)) on clinically relevant motor, sensory, and autonomic outcomes after spinal cord injury (SCI). Rats were injured by clip compression (50 g; T4) and treated 15 min and 6 hr postinjury intravenously (tail vein) with PEG (1 g/kg, 30% w/w in saline; n = 11), MgSO(4) (300 mg/kg; n = 5), PEG + MgSO(4) (n = 6), or saline (n = 10). Behavioral testing lasted for 6 weeks, followed by histological analysis of the spinal cord. Both PEG and MgSO(4) resulted in enhanced locomotor recovery and lower susceptibility to neuropathic pain (mechanical allodynia) compared with saline. At 6 weeks, BBB scores were 7.3 +/- 0.2, 7.7 +/- 0.4, and 6.4 +/- 0.6 in PEG-treated, MgSO(4)-treated, and saline-treated control groups, respectively. Likewise, at 6 weeks PEG-, MgSO(4)-, and saline-treated control animals showed 3.5 +/- 0.4, 2.8 +/- 0.9, and 5.0 +/- 0.5 avoidance responses to at-level touch, respectively. PEG + MgSO(4) improved locomotor recovery and reduced pain but did not provide additional benefit compared with either treatment alone. Neither treatment, nor their combination, attenuated mean arterial pressure (MAP) increases during autonomic dysreflexia. However, saline-treated controls had significantly lower resting MAP than PEG-treated rats and tended to have lower resting MAP than MgSO(4)-treated rats 6 weeks postinjury. MgSO(4) treatment and PEG + MgSO(4) treatment resulted in significant increases in dorsal myelin sparing, and the latter resulted in significant reductions in lesion volume, compared with saline-treated controls. Furthermore, mean lesion volumes correlated negatively with the corresponding mean BBB scores and positively with the corresponding mean pain scores. In conclusion, both PEG and MgSO(4) enhanced long-term clinical outcomes after SCI.