Role In Brain Edema Formation Research Articles

Aquaporin 4 Blockade Attenuates Acute Lung Injury Through Inhibition of Th17 Cell Proliferation in Mice

Acute lung injury (ALI) is a syndrome characterized by damage to the alveolar-capillary wall, pulmonary edema and recruitment of inflammatory cells. Previous studies have indicated that aquaporin 4 (AQP4) plays a key role in brain edema formation and resolution. However, the role of AQP4 in the development and progression of ALI is not clear and needs to be resolved. In our current study, mouse ALI was induced by intratracheal instillation of lipopolysaccharide (LPS) at a concentration of 30mg/kg. For the inhibition of AQP4, 200mg/kg of TGN-020 (Sigma, USA) was administered intraperitoneally every 6h starting at 30min before intratracheal instillation of LPS. The results of the present work indicate, for the first time, that mice treated with the AQP4 inhibitor TGN-020 had attenuated LPS-induced lung injury, reduced proinflammatory cytokine release (including IL-1α, IL-1β, IL-6, TNF-α, IL-23, and IL-17A), and an improved survival rate. Additionally, we found that the attenuated lung injury scores, increased survival rate, and decreased BALF total protein concentration in TGN-020-treated mice were all abrogated by rIL-17A administration. Furthermore, TGN-020 treatment downregulated the phosphorylation of PI3K and Akt, increased the expression of SOCS3, and decreased the expression of p-STAT3 and RORγt. In conclusion, inhibition of AQP4 by TGN-020 has a detectable protective effect against lung tissue injury induced by LPS, and this effect is associated with inhibition of IL-17A through the downregulation of the PI3K/Akt signaling pathway and upregulation of SOCS3 protein.

Potential Contribution of Hypoxia-Inducible Factor-1α, Aquaporin-4, and Matrix Metalloproteinase-9 to Blood–Brain Barrier Disruption and Brain Edema After Experimental Subarachnoid Hemorrhage

The current research aimed to investigate the role of hypoxia-inducible factor-1α (HIF-1α), aquaporin-4 (AQP-4), and matrix metalloproteinase-9 (MMP-9) in blood-brain barrier (BBB) dysfunction and cerebral edema formation in a rat subarachnoid hemorrhage (SAH) model. The SAH model was induced by injection of 0.3 ml fresh arterial, non-heparinized blood into the prechiasmatic cistern in 20 s. Anti-AQP-4 antibody, minocycline (an inhibitor of MMP-9), or 2-methoxyestradiol (an inhibitor of HIF-1α), was administered intravenously at 2 and 24 h after SAH. Brain samples were extracted at 48 h after SAH and examined for protein expressions, BBB impairment, and brain edema. Following SAH, remarkable edema and BBB extravasations were observed. Compared with the control group, the SAH animals have significantly upregulated expressions of HIF-1α, AQP-4, and MMP-9, in addition to decreased amounts of laminin and tight junction proteins. Brain edema was repressed after inhibition of AQP-4, MMP-9, or HIF-1α. Although BBB permeability was also ameliorated after inhibition of either HIF-1α or MMP-9, it was not modulated after inhibition of AQP-4. Inhibition of MMP-9 reversed the loss of laminin. Finally, inhibition of HIF-1α significantly suppressed the level of AQP-4 and MMP-9, which could induce the expression of laminin and tight junction proteins. Our results suggest that HIF-1α plays a role in brain edema formation and BBB disruption via a molecular signaling pathway involving AQP-4 and MMP-9. Pharmacological intervention of this pathway in patients with SAH may provide a novel therapeutic strategy for early brain injury.

Pentoxifylline attenuates TNF-α protein levels and brain edema following temporary focal cerebral ischemia in rats

Cerebral edema is the most common cause of neurological deterioration and mortality during acute ischemic stroke. Despite the clinical importance of cerebral ischemia, the underlying mechanisms remain poorly understood. Recent studies suggest a role for TNF-α in the brain edema formation. To further investigate whether TNF-α would play a role in brain edema formation, we examined the effects of pentoxifylline (PTX, an inhibitor of TNF-α synthesis) on the brain edema and TNF-α levels in a model of transient focal cerebral ischemia. The right middle cerebral artery (MCA) of rats was occluded for 60 min using the intraluminal filament method. The animals received PTX (60 mg/kg) immediately, 1, 3, or 6 h post-ischemic induction. Twenty-four hours after induction of ischemic injury, permeability of the blood–brain barrier (BBB) and brain edema were determined by in situ brain perfusion of Evans Blue (EB) and wet-to-dry weight ratio, respectively. TNF-α protein levels in ischemic cortex were also measured at 1, 4, and 24 h after the beginning of an ischemic stroke by using an enzyme-linked immunosorbent assay method. The administration of PTX up to 6 h after occlusion of the MCA significantly reduced the brain edema. Moreover, PTX significantly reduced the concentration of TNF-α in ischemic brain cortex up to 4 h post-transient focal stroke ( P < 0.002). Finally, treatment by PTX led to a significant decrease in EB extravasations ( P < 0.001). Our data demonstrate that PTX administration up to 6 h after ischemia can reduce brain edema in a model of transient focal cerebral ischemia. The beneficial effects of PTX may be mediated, at least in part, through a decline in TNF-α production and BBB breakdown.

The role of hypoxia-inducible factor-1α, aquaporin-4, and matrix metalloproteinase-9 in blood-brain barrier disruption and brain edema after traumatic brain injury

The present study investigated the role of hypoxia-inducible factor-1α (HIF-1α), aquaporin-4 (AQP-4), and matrix metalloproteinase-9 (MMP-9) in blood-brain barrier (BBB) permeability alterations and brain edema formation in a rodent traumatic brain injury (TBI) model. The brains of adult male Sprague-Dawley rats (400-425 g) were injured using the Marmarou closed-head force impact model. Anti-AQP-4 antibody, minocycline (an inhibitor of MMP-9), or 2-methoxyestradiol (2ME2, an inhibitor of HIF-1α), was administered intravenously 30 minutes after injury. The rats were killed 24 hours after injury and their brains were examined for protein expression, BBB permeability, and brain edema. Expression of HIF-1α, AQP-4, and MMP-9 as well as expression of the vascular basal lamina protein (laminin) and tight junction proteins (zona occludens-1 and occludin) was determined by Western blotting. Blood-brain barrier disruption was assessed by FITC-dextran extravasation, and brain edema was measured by the brain water content. Significant (p < 0.05) edema and BBB extravasations were observed following TBI induction. Compared with sham-operated controls, the injured animals were found to have significantly (p < 0.05) enhanced expression of HIF-1α, AQP-4, and MMP-9, in addition to reduced amounts (p < 0.05) of laminin and tight junction proteins. Edema was significantly (p < 0.01) decreased after inhibition of AQP-4, MMP-9, or HIF-1α. While BBB permeability was significantly (p < 0.01) ameliorated after inhibition of either HIF-1α or MMP-9, it was not affected following inhibition of AQP-4. Inhibition of MMP reversed the loss of laminin (p < 0.01). Finally, while inhibition of HIF-1α significantly (p < 0.05) suppressed the expression of AQP-4 and MMP-9, such inhibition significantly (p < 0.05) increased the expression of laminin and tight junction proteins. The data support the notion that HIF-1α plays a role in brain edema formation and BBB disruption via a molecular pathway cascade involving AQP-4 and MMP-9. Pharmacological blockade of this pathway in patients with TBI may provide a novel therapeutic strategy.

Effects of hypothermia on thrombin-induced brain edema formation

Recent studies have shown that thrombin plays an important role in brain edema formation after intracerebral hemorrhage (ICH). The possible mechanisms of thrombin-induced brain edema formation include blood–brain barrier (BBB) disruption and inflammatory response involving polymorphonuclear (PMN) leukocyte. Animal experiments have revealed that moderate therapeutic hypothermia improves pathological and functional outcome in various models of brain injury. In this study, we examined the effect of hypothermia on thrombin-induced brain edema formation. Effects of hypothermia on BBB permeability and the accumulation of PMN leukocytes were also determined to clarify the protective mechanism of hypothermia in this model. Anesthetized adult rats received an injection of 10 Units of thrombin into the basal ganglia. Animals were separated into the normothermic and hypothermic groups, which were housed in a room maintained at 25°C and in a cold room maintained at 5°C, respectively, for 24 h after the thrombin injection. The brain temperature in rats housed in a cold room reduced temporarily to approximately 30°C and then gradually recovered to 35°C by the end of the observation. Brain water content in the basal ganglia was significantly reduced in rats treated with hypothermia compared to the normothermic rats (84.3±0.2 vs. 82.4±0.1%; P<0.01). The decrease of brain water content was accompanied with a significant reduction in BBB permeability to Evan’s blue dye and in accumulation of PMN leukocytes. This study indicates that hypothermic treatment significantly reduces thrombin-induced brain edema formation in the rat. Inhibition of thrombin-induced BBB breakdown and inflammatory response by hypothermia appear to contribute to brain protection in this model. Hypothermic treatment may provide an approach to potentially reduce ongoing edema after ICH.

Seizures induced by intracerebral injection of thrombin: a model of intracerebral hemorrhage.

The coagulation cascade plays an important role in brain edema formation caused by intracerebral blood. In particular, thrombin produces brain injury via direct brain cell toxicity. Seizures and increased cerebral electrical activity are commonly associated with intracerebral blood and are possible effects of thrombin leading to cell injury in the brain. In this study, artificial clots containing concentrations of thrombin found in hematomas were infused intracerebrally in rats. The animals were observed clinically for seizure activity, behavior, and neurological deficits. Several animals underwent video electroencephalographic (EEG) monitoring during intracerebral infusion and for 30 minutes postinfusion. All animals were killed 24 hours after injection, and brain water and ion contents were measured to determine the amount of brain edema. Clinically, thrombin produced focal motor seizures in all animals. None of the control animals or those receiving N[alpha]-(2-Naphthalenesulfonyl-glycyl)-4-amidino-DL-phenylalanine -piperidide (alpha-NAPAP), a thrombin inhibitor added to the thrombin, showed clinical evidence of seizures. Of the rats undergoing EEG monitoring, all animals receiving thrombin showed electrical evidence of seizure activity, whereas none of the control animals exhibited seizure activity. There was no evidence of seizure activity on EEG monitoring when alpha-NAPAP was injected along with the thrombin. In addition, the artificial clots containing thrombin produced agitation and a circling tendency in the rats, along with brain edema. These results indicate that the coagulation cascade is involved in seizure production and increased brain electrical activity, which contribute to the neurological deficits and brain edema formation that are seen with intracerebral hemorrhage.

The role of the coagulation cascade in brain edema formation after intracerebral hemorrhage.

The coagulation cascade has a potential role in brain edema formation due to intracerebral hemorrhage. In this study blood and other solutions were injected stereotactically into the right basal ganglia in rats. Twenty-four hours following injection, brain water and ion contents were measured to determine the amount of brain edema. Intracerebral blood resulted in an increase in brain water content. The amount of brain edema surrounding the intracerebral hematoma was reduced by a thrombin inhibitor N alpha-(2-Naphthalenesulfonylglycyl)-4-amidino-DL-phenylalaninep iperidide, (alpha-NAPAP) infused into the hematoma after the clot had been allowed to solidify. The inhibitor did not alter the actual size of the clot mass. An artificial clot composed of fibrinogen, thrombin, and styrene microspheres also produced brain edema. A fibrin clot led to edema formation even in the absence of mass effect provided by the microspheres. The single component responsible for production of brain edema in all these models was thrombin. The edema was formed in response to a fibrinogen-independent pathway. These results indicate that the coagulation cascade is involved in brain edema that develops adjacent to an intracerebral hematoma.

5-hydroxytryptamine injected intraventricularly fails to influence the brain water content.

Measurement of the content of brain water and electrolytes after the intraventricular administration of 5-hydroxytryptamine in rats, with and without exposure to osmotic stress, failed to show water accumulation in the brain parenchyma. It is suggested that elevation of serotonin in the cerebrospinal fluid--resembling pathological situations such as subarachnoid hemorrhage--does not play a primary role in brain edema formation.