Anish Bhardwaj

An α-syntrophin-dependent pool of AQP4 in astroglial end-feet confers bidirectional water flow between blood and brain

The water channel AQP4 is concentrated in perivascular and subpial membrane domains of brain astrocytes. These membranes form the interface between the neuropil and extracerebral liquid spaces. AQP4 is anchored at these membranes by its carboxyl terminus to α-syntrophin, an adapter protein associated with dystrophin. To test functions of the perivascular AQP4 pool, we studied mice homozygous for targeted disruption of the gene encoding α-syntrophin (α-Syn−/−). These animals show a marked loss of AQP4 from perivascular and subpial membranes but no decrease in other membrane domains, as judged by quantitative immunogold electron microscopy. In the basal state, perivascular and subpial astroglial end-feet were swollen in brains of α-Syn−/− mice compared to WT mice, suggesting reduced clearance of water generated by brain metabolism. When stressed by transient cerebral ischemia, brain edema was attenuated in α-Syn−/− mice, indicative of reduced water influx. Surprisingly, AQP4 was strongly reduced but α-syntrophin was retained in perivascular astroglial end-feet in WT mice examined 23 h after transient cerebral ischemia. Thus α-syntrophin-dependent anchoring of AQP4 is sensitive to ischemia, and loss of AQP4 from this site may retard the dissipation of postischemic brain edema. These studies identify a specific, syntrophin-dependent AQP4 pool that is expressed at distinct membrane domains and which mediates bidirectional transport of water across the brain–blood interface. The anchoring of AQP4 to α-syntrophin may be a target for treatment of brain edema, but therapeutic manipulations of AQP4 must consider the bidirectional water flux through this molecule.

Selective inhibition of NAALADase, which converts NAAG to glutamate, reduces ischemic brain injury

We describe here a new strategy for the treatment of stroke, through the inhibition of NAALADase (N-acetylated-α-linked-acidic dipeptidase), an enzyme responsible for the hydrolysis of the neuropeptide NAAG (N-acetyl-aspartyl-glutamate) to N-acetyl-aspartate and glutamate. We demonstrate that the newly described NAALADase inhibitor 2-PMPA (2-(phosphonomethyl)pentanedioic acid) robustly protects against ischemic injury in a neuronal culture model of stroke and in rats after transient middle cerebral artery occlusion. Consistent with inhibition of NAALADase, we show that 2-PMPA increases NAAG and attenuates the ischemia-induced rise in glutamate. Both effects could contribute to neuroprotection. These data indicate that NAALADase inhibition may have use in neurological disorders in which excessive excitatory amino acid transmission is pathogenic.

Treatment of refractory intracranial hypertension with 23.4% saline.

ObjectiveTo evaluate the effect of intravenous bolus administration of 23.4% saline (8008 mOsm/L) on refractory intracranial hypertension (RIH) in patients with diverse intracranial diseases.DesignRetrospective chart review.SettingA neurosciences intensive care unit in a university hospital.Patients

Alpha-syntrophin deletion removes the perivascular but not endothelial pool of aquaporin-4 at the blood–brain barrier and delays the development of brain edema in an experimental model of acute hyponatremia

The formation of brain edema, commonly occurring as a potentially lethal complication of acute hyponatremia, is delayed following knockout of the water channel aquaporin‐4 (AQP4). Here we show by high‐resolution immunogold analysis of the blood–brain‐barrier that AQP4 is expressed in brain endothelial cells as well as in the perivascular membranes of astrocyte endfeet. A selective removal of perivascular AQP4 by α‐syntrophin deletion delays the buildup of brain edema (assessed by Diffusion‐weighted MRI) following water intoxication, despite the presence of a normal complement of endothelial AQP4. This indicates that the perivascular membrane domain, which is peripheral to the endothelial blood–brain barrier, may control the rate of osmotically driven water entry. This study is also the first to demonstrate that the time course of edema development differs among brain regions, probably reflecting differences in aquaporin‐4 distribution. The resolution of the molecular basis and subcellular site of osmotically driven brain water uptake should help design new therapies for acute brain edema.

Use of hypertonic (3%) saline/acetate infusion in the treatment of cerebral edema : Effect on intracranial pressure and lateral displacement of the brain

OBJECTIVE To determine the effect of continuous hypertonic (3%) saline/acetate infusion on intracranial pressure (ICP) and lateral displacement of the brain in patients with cerebral edema. DESIGN Retrospective chart review. SETTINGS Neurocritical care unit of a university hospital. PATIENTS Twenty-seven consecutive patients with cerebral edema (30 episodes), including patients with head trauma (n = 8), postoperative edema (n = 5), nontraumatic intracranial hemorrhage (n = 8), and cerebral infarction (n = 6). INTERVENTION Intravenous infusion of 3% saline/acetate to increase serum sodium concentrations to 145 to 155 mmol/L. MEASUREMENTS AND MAIN RESULTS A reduction in mean ICP within the first 12 hrs correlating with an increase in the serum sodium concentration was observed in patients with head trauma (r2 = .91, p = .03), and postoperative edema (r2 = .82, p = .06), but not in patients with nontraumatic intracranial hemorrhage or cerebral infarction. In patients with head trauma, the beneficial effect of hypertonic saline on ICP was short-lasting, and after 72 hrs of infusion, four patients required intravenous pentobarbital due to poor ICP control. Among the 21 patients who had a repeat computed tomographic scan within 72 hrs of initiating hypertonic saline, lateral displacement of the brain was reduced in patients with head trauma (2.8 +/- 1.4 to 1.1 +/- 0.9 [SEM]) and in patients with postoperative edema (3.1 +/- 1.6 to 1.1 +/- 0.7). This effect was not observed in patients with nontraumatic intracranial bleeding or cerebral infarction. The treatment was terminated in three patients due to the development of pulmonary edema, and was terminated in another three patients due to development of diabetes insipidus. CONCLUSIONS Hypertonic saline administration as a 3% infusion appears to be a promising therapy for cerebral edema in patients with head trauma or postoperative edema. Further studies are required to determine the optimal duration of benefit and the specific patient population that is most likely to benefit from this treatment.

Treatment of Intraventricular Hemorrhage With Urokinase Effects on 30-Day Survival

BACKGROUND AND PURPOSE Intraventricular hemorrhage (IVH) remains associated with high morbidity and mortality. Therapy with external ventricular drainage alone has not modified outcome in these patients. METHODS Twelve pilot IVH patients who required external ventricular drainage were prospectively treated with intraventricular urokinase followed by the randomized, double-blinded allocation of 8 patients to either treatment or placebo. Observed 30-day mortality was compared with predicted 30-day mortality obtained by use of a previously validated method. RESULTS Twenty patients were enrolled; admission Glasgow Coma Scale score in 11 patients was </=8; 10 patients had pulse pressure <85 mm Hg. Mean+/-SD ICH volume in 16 patients was 6.21+/-7.53 cm(3) (range 0 to 23.88 cm(3)), and mean+/-SD intraventricular hematoma volume was 44.26+/-31.65 cm(3) (range 1.31 to 100.36 cm(3)). Four patients (20%) died within 30 days. Predicted mortality for these 20 patients was 68.42% (range 3% to 100%). Probability of observing </=4 deaths among 20 patients under a 68.42% expected mortality is 0.000012. CONCLUSIONS Intraventricular urokinase may significantly improve 30-day survival in IVH patients. On the basis of current evidence, a double-blinded, placebo-controlled, multicenter study that uses thrombolysis to treat IVH has received funding and began January 1, 2000.

Temporary loss of perivascular aquaporin-4 in neocortex after transient middle cerebral artery occlusion in mice

The aquaporin-4 (AQP4) pool in the perivascular astrocyte membranes has been shown to be critically involved in the formation and dissolution of brain edema. Cerebral edema is a major cause of morbidity and mortality in stroke. It is therefore essential to know whether the perivascular pool of AQP4 is up- or down-regulated after an ischemic insult, because such changes would determine the time course of edema formation. Here we demonstrate by quantitative immunogold cytochemistry that the ischemic striatum and neocortex show distinct patterns of AQP4 expression in the reperfusion phase after 90 min of middle cerebral artery occlusion. The striatal core displays a loss of perivascular AQP4 at 24 hr of reperfusion with no sign of subsequent recovery. The most affected part of the cortex also exhibits loss of perivascular AQP4. This loss is of magnitude similar to that of the striatal core, but it shows a partial recovery toward 72 hr of reperfusion. By freeze fracture we show that the loss of perivascular AQP4 is associated with the disappearance of the square lattices of particles that normally are distinct features of the perivascular astrocyte membrane. The cortical border zone differs from the central part of the ischemic lesion by showing no loss of perivascular AQP4 at 24 hr of reperfusion but rather a slight increase. These data indicate that the size of the AQP4 pool that controls the exchange of fluid between brain and blood during edema formation and dissolution is subject to large and region-specific changes in the reperfusion phase.

Risk factors for multiple intracranial aneurysms

OBJECTIVE Risk factors that predispose to the formation of multiple intracranial aneurysms, which are present in up to 34% of patients with intracranial aneurysms, are not well defined. In this study, we examined the association between known risk factors for cerebrovascular disease and presence of multiple intracranial aneurysms. METHODS We reviewed the medical records and results of conventional angiography in all patients with a diagnosis of intracranial aneurysms admitted to the Johns Hopkins University hospital between January 1990 and June 1997. We determined the independent association between various cerebrovascular risk factors and the presence of multiple aneurysms using logistic regression analysis. RESULTS Of 419 patients admitted with intracranial aneurysms (298 ruptured and 121 unruptured), 127 (30%) had multiple intracranial aneurysms. In univariate analysis, female gender (odds ratio [OR] = 1.9; 95% confidence interval [CI], 1.1-3.3) and cigarette smoking at any time (OR = 1.8; 95% CI, 1.1-3.0) were significantly associated with presence of multiple aneurysms. In the multivariate analysis, cigarette smoking at any time (OR = 1.7; 95% CI, 1.1-2.8) and female gender (OR = 2.1; 95% CI 1.2-3.5) remained significantly associated with multiple aneurysms. Hypertension, diabetes mellitus, and alcohol and illicit drug use were not significantly associated with presence of multiple aneurysms. CONCLUSION Cigarette smoking and female gender seem to increase the risk for multiple aneurysms in patients predisposed to intracranial aneurysm formation. Further studies are required to investigate the mechanism underlying the association between cigarette smoking and intracranial aneurysm formation.

Glucocorticoid therapy in neurologic critical care

Background:The pivotal role of inflammation and edema across the spectrum of central nervous system injury has driven extensive investigation into the therapeutic potential of glucocorticoids. Objective:To review the experimental and clinical data relating to the efficacy and adverse effects of glucocorticoids in conditions encountered in critical neurologic and neurosurgical illness. Data Source:Search of MEDLINE and Cochrane databases, manual review of article bibliographies. Data Synthesis and Conclusions:The efficacy of glucocorticoids is well established in ameliorating edema associated with brain tumors and in improving outcome in subsets of patients with bacterial meningitis. Despite frequently encouraging experimental results, clinical trials of glucocorticoids in ischemic stroke, intracerebral hemorrhage, aneurysmal subarachnoid hemorrhage, and traumatic brain injury have not shown a definite therapeutic effect. The evidence supporting glucocorticoid therapy for spinal cord injury is controversial; however methylprednisolone continues to be widely employed in this setting.

Hypertonic saline solutions in brain injury.

Purpose of review Hypertonic saline solutions have received renewed attention as effective agents for the treatment of cerebral edema and in brain resuscitation in a variety of brain injury paradigms. Although evidence of the beneficial action of hypertonic saline solutions in traumatic brain injury is robust, data supporting use in other conditions are only now mounting. Recent findings Osmotic properties of hypertonic saline solutions have been well studied in laboratory-based studies in animal models and in patients with acute brain injury. There are, in addition, emerging data on the extraosmotic actions on brain pathophysiology. This review cites baseline literature and provides new evidence of actions of hypertonic saline solutions: (a) in augmenting cerebral blood flow after subarachnoid hemorrhage, (b) as an antiinflammatory adjunct, and (c) utility in chemonucleolysis for intervertebral disc disease and treatment of seizures associated with severe hyponatremia. Summary Brain injury from diverse etiologies including trauma, ischemic stroke, global cerebral ischemia from cardiac arrest, intraparenchymal or subarachnoid hemorrhage, infection, or toxic-metabolic derangements are commonly encountered in the clinical setting. Many of these conditions are associated with cerebral edema with or without elevated intracranial pressure. Osmotherapy constitutes the cornerstone of medical therapy for such patients. Hypertonic saline solutions have received renewed attention in clinical practice as osmotic agents for cerebral resuscitation. This article reviews experimental and clinical evidence of the efficacy of hypertonic saline solutions and elaborates on their use in patients with acute neurologic injury. Important areas for current and future research are highlighted before the use of hypertonic saline solutions can be accepted for widespread use.