Arginine vasopressin receptor antagonists for treatment of vasogenic brain edema: an experimental study

Therapeutic potential of vasopressin in the treatment of neurological disorders

Vasopressin (VP) is a nonapeptide made of nine amino acids synthesized by the hypothalamus and released by the pituitary gland. VP acts as a neurohormone, neuropeptide and neuromodulator and plays an important role in the regulation of water balance, osmolarity, blood pressure, body temperature, stress response, emotional challenges, etc. Traditionally VP is known to regulate the osmolarity and tonicity. VP and its receptors are widely expressed in the various region of the brain including cortex, hippocampus, basal forebrain, amygdala, etc. VP has been shown to modulate the behavior, stress response, circadian rhythm, cerebral blood flow, learning and memory, etc. The potential role of VP in the regulation of these neurological functions have suggested the therapeutic importance of VP and its analogues in the management of neurological disorders. Further, different VP analogues have been developed across the world with different pharmacotherapeutic potential. In the present work authors highlighted the therapeutic potential of VP and its analogues in the treatment and management of various neurological disorders.

The Role of Consecutive Plasma Copeptin Levels in the Screening of Delayed Cerebral Ischemia in Poor-Grade Subarachnoid Hemorrhage

The prognostic value of copeptin in subarachnoid hemorrhage (SAH) has been reported, but the prognosis was largely affected by the initial clinical severity. Thus, the previous studies are not very useful in predicting delayed cerebral ischemia (DCI) in poor-grade SAH patients. Here, we first investigated the feasibility of predicting DCI in poor-grade SAH based on consecutive measurements of plasma copeptin. We measured copeptin levels of 86 patients on days 1, 3, 5, 7, 9, 11, and 13 using ELISA. The primary outcome was the association between consecutive copeptin levels and DCI development. The secondary outcomes were comparison of copeptin with C-reactive protein (CRP) in predicting DCI. Additionally, we compared the prognostic value of transcranial Doppler ultrasonography (TCD) with copeptin using TCD alone to predict DCI. Increased copeptin (OR = 1.022, 95% CI: 1.008–1.037) and modified Fisher scale IV (OR = 2.841; 95% CI: 0.998–8.084) were closely related to DCI. Consecutive plasma copeptin measurements showed significant differences between DCI and non-DCI groups (p < 0.001). Higher CRP and DCI appeared to show a correlation, but it was not statistically significant. Analysis of copeptin changes with TCD appeared to predict DCI better than TCD alone with AUCROC differences of 0.072. Consecutive measurements of plasma copeptin levels facilitate the screening of DCI in poor-grade SAH patients.

Treating head injury using a novel vasopressin 1a receptor antagonist

Arginine vasopressin (AVP) is a chemical signal in the brain that influences cerebral vascular resistance and brain water permeability. Increases in AVP contribute to the pathophysiology of brain edema following traumatic brain injury (TBI). These effects are mediated through AVP V1a receptors that are expressed in cortical and subcortical brain areas. This exploratory study characterizes the effects of a novel, V1a receptor antagonist, AVN576, on behavioral and magnetic resonance imaging (MRI) measures after severe TBI. Male Sprague Dawley rats were impacted twice producing contusions in the forebrain, putative cerebral edema, and cognitive deficits. Rats were treated with AVN576 after initial impact for 5 days and then tested for changes in cognition. MRI was used to assess brain injury, enlargement of the ventricles, and resting state functional connectivity. Vehicle treated rats had significant deficits in learning and memory, enlarged ventricular volumes, and hypoconnectivity in hippocampal circuitry. AVN576 treatment eliminated the enlargement of the lateral ventricles and deficits in cognitive function while increasing connectivity in hippocampal circuitry. These data corroborate the extensive literature that drugs selectively targeting the AVP V1a receptor could be used to treat TBI in the clinic.

The Effects of Clinically Relevant Hypertonic Saline and Conivaptan Administration on Ischemic Stroke

Cerebral edema after stroke is associated with poor neurological outcomes. Current therapies are limited to osmotic agents, such as hypertonic saline (HS), which reduce intracranial pressure. Although studies have demonstrated edema reductions following HS, tissue survival has not been thoroughly examined. Additionally, the efficacy of promising pharmacological agents has not been evaluated for synergy with osmotic agents. Conivaptan is an FDA-approved vasopressin receptor antagonist that may exert both osmotic and anti-inflammatory effects. In this study, rats were subjected to middle cerebral artery occlusion prior to treatment with 5 % HS bolus +5 % HS maintenance (HS), conivaptan alone (Con), conivaptan +5 % HS maintenance (Con + HS), or conivaptan +5 % HS bolus +5 % maintenance (Con + HSb). Treatments were initiated at six (Early) or 24 h (Late) following stroke and rats were euthanized at 48 h to evaluate infarct volume, brain edema, and microglia/macrophage activation. Infarct volume and brain edema in the Early HS, Early Con, and Late HS groups were significantly reduced compared with controls. Interestingly, only the Early Con group demonstrated reduced microglia/macrophage activation. These data suggest an anti-inflammatory mechanism for conivaptan and provide support for a multipronged approach combining osmotic agents with compounds that inhibit the neuroinflammatory response to stroke.

Selective vasopressin-1a receptor antagonist prevents brain edema, reduces astrocytic cell swelling and GFAP, V1aR and AQP4 expression after focal traumatic brain injury

A secondary and often lethal consequence of traumatic brain injury is cellular edema that we posit is due to astrocytic swelling caused by transmembrane water fluxes augmented by vasopressin-regulated aquaporin-4 (AQP4). We therefore tested whether vasopressin 1a receptor (V1aR) inhibition would suppress astrocyte AQP4, reduce astrocytic edema, and thereby diminish TBI-induced edematous changes. V1aR inhibition by SR49059 significantly reduced brain edema after cortical contusion injury (CCI) in rat 5h post-injury. Injured-hemisphere brain water content (n=6 animals/group) and astrocytic area (n=3/group) were significantly higher in CCI-vehicle (80.5±0.3%; 18.0±1.4 µm(2)) versus sham groups (78.3±0.1%; 9.5±0.9 µm(2)), and SR49059 blunted CCI-induced increases in brain edema (79.0±0.2%; 9.4±0.8µm(2)). CCI significantly up-regulated GFAP, V1aR and AQP4 protein levels and SR49059 suppressed injury induced up regulation (n=6/group). In CCI-vehicle, sham and CCI-SR49059 groups, GFAP was 1.58±0.04, 0.47±0.02, and 0.81±0.03, respectively; V1aR was 1.00±0.06, 0.45±0.05, and 0.46±0.09; and AQP4 was 2.03±0.34, 0.49±0.04, and 0.92±0.22. Confocal immunohistochemistry gave analogous results. In CCI-vehicle, sham and CCI-SR49059 groups, fluorescence intensity of GFAP was 349±38, 56±5, and 244±30, respectively, V1aR was 601±71, 117.8±14, and 390±76, and AQP4 was 818±117, 158±5, and 458±55 (n=3/group). The results support that edema was predominantly cellular following CCI and documented that V1aR inhibition with SR49059 suppressed injury-induced up regulation of GFAP, V1A and AQP4, blunting edematous changes. Our findings suggest V1aR inhibitors may be potential therapeutic tools to prevent cellular swelling and provide treatment for post-traumatic brain edema.

Real-time monitoring of changes in brain extracellular sodium and potassium concentrations and intracranial pressure after selective vasopressin-1a receptor inhibition following focal traumatic brain injury in rats

Brain swelling and increased intracranial pressure (ICP) following traumatic brain injury (TBI) contribute to poor outcome. Vasopressin-1a receptors (V1aR) and aquaporin-4 (AQP4) regulate water transport and brain edema formation, perhaps in part by modulating cation fluxes. After focal TBI, V1aR inhibitors diminish V1aR and AQP4, reduce astrocytic swelling and brain edema. We determined whether V1aR inhibition with SR49059 after lateral controlled-cortical-impact (CCI) injury affects extracellular Na(+) and K(+) concentrations ([Na(+)]e; [K(+)]e). Ion-selective Na(+) and K(+) electrodes (ISE) and an ICP probe were implanted in rat parietal cortex, and [Na(+)]e, [K(+)]e, and physiological parameters were monitored for 5 h post-CCI. Sham-vehicle-ISE, CCI-vehicle-ISE and CCI-SR49059-ISE groups were studied, and SR49059 was administered 5 min to 5 h post-injury. We found a significant injury-induced decrease in [Na(+)]e to 80.1 ± 15 and 87.9 ± 7.9 mM and increase in [K(+)]e to 20.9 ± 3.8 and 13.4 ± 3.4 mM at 5 min post-CCI in CCI-vehicle-ISE and CCI-SR49059-ISE groups, respectively (p<0.001 vs. baseline; ns between groups). Importantly, [Na(+)]e in CCI-SR49059-ISE was reduced 5-20 min post-injury and increased to baseline at 25 min, whereas recovery in CCI-vehicle-ISE required more than 1 hr, suggesting SR49059 accelerated [Na(+)]e recovery. In contrast, [K(+)]e recovery took 45 min in both groups. Further, ICP was lower in the CCI-SR49059-ISE group. Thus, selective V1aR inhibition allowed faster [Na(+)]e recovery and reduced ICP. By augmenting the [Na(+)]e recovery rate, SR49059 may reduce trauma-induced ionic imbalance, blunting cellular water influx and edema after TBI. These findings suggest SR49059 and V1aR inhibitors are potential tools for treating cellular edema post-TBI.

Role of vasopressin V(1a) and V2 receptors for the development of secondary brain damage after traumatic brain injury in mice

Brain edema is still one of the most deleterious sequels of traumatic brain injury (TBI), and its pathophysiology is not sufficiently understood. The goal of the current study was to investigate the role of arginine vasopressin (AVP), also known as antidiuretic hormone (ADH), an important regulator of tissue water homeostasis, for the formation of post-traumatic brain edema, intracranial pressure (ICP), brain damage, and functional deficits following brain trauma. C57/B16 mice (n=112) were subjected to controlled cortical impact (CCI; 8m/s, 1 mm). At 3 min after trauma, animals received 500 ng of the AVP V(1a)-receptor antogonist (deamino-Pen(1), O-Me-Tyr(2), Arg(8)]-Vasopressin) or 500 ng of the AVP V2-receptor antagonist (adamantaneacetyl(1), O-Et-D-Tyr(2),Val(4), Abu(6),Arg(8,9)]-Vasopressin) by intracerebroventricular injection. After trauma, cerebral water content (24 h), ICP (24 h), contusion volume (24 h and 7 days), and functional outcome (1-7 days) were assessed (n=8 per experimental group). Post-traumatic inhibition of AVP V(1A) receptors reduced ICP by 29% (p < 0.05), brain water content by 45% (p < 0.05), and secondary contusion expansion by 37% (p < 0.05), and it significantly improved motor function 6 and 7 days after trauma (p < 0.05). Inhibition of AVP V2 receptors had no significant effect. The current results demonstrate that vasopressin V(1A) receptors are involved in the pathogenesis of brain edema formation and the subsequent development of secondary brain damage after traumatic brain injury. Accordingly, our study suggests that vasopressin V(1A) receptors may represent a novel therapeutic target for the treatment of post-traumatic brain edema and secondary brain damage.

Arginine vasopressin increases glutamate release and intracellular Ca2+ concentration in hippocampal and cortical astrocytes through two distinct receptors

Arginine vasopressin (AVP), released from the CNS, plays an important role in regulating several aspects of CNS functions including aggression, anxiety, and cognition. In this study, we report a novel finding that AVP induces glutamate release from astrocytes isolated from the cerebral cortex and hippocampus. We also investigated the types of AVP receptors involved in the AVP-induced increase in glutamate release from astrocytes isolated from the hippocampus and cortex of neonatal rats. We showed that the AVP (0.1-1000 nmol/L) induced increase in glutamate release and [Ca(2+)](i) is brought about by two distinct subtypes of V(1) receptors (V(1a) and V(1b)). Our results suggested that V(1b) receptors are predominantly expressed in astrocytes isolated from the hippocampus and V(1a) receptors are solely expressed in astrocytes isolated from the cerebral cortex of neonatal rats. The results of the western blot analyses confirmed these pharmacological data. In addition, the AVP-induced increase in glutamate did not contribute to an increase in [Ca(2+)](i), as blockade of metabotropic glutamate receptors did not alter the AVP-induced increase in [Ca(2+)](i). In addition, the administration of a phospholipase A(2) inhibitor failed to alter AVP-induced [Ca(2+)](i) increase suggesting the lack of involvement of this enzyme.

Arginine vasopressin as a supplementary vasopressor in refractory hypertensive, hypervolemic, hemodilutional therapy in subarachnoid hemorrhage

INTRODUCTION

Hypertensive, hypervolemic, and hemodilutional (HHH) therapy for vasospasm in subarachnoid hemorrhage (SAH) refractory to phenylephrine requires high doses of catecholamines, leading to adverse adrenergic effects. Arginine vasopressin (AVP) has been shown to stabilize advanced shock states while facilitating reduction of catecholamine doses, but its use has never been reported in SAH. In this retrospective study, we investigated the hemodynamic effects and feasibility of supplementary AVP in refractory HHH therapy in SAH.

METHODS

Hemodynamic response (mean arterial pressure [MAP], heart rate, central venous pressure, cardiac index, systemic vascular resistance index, and end diastolic volume index) to a supplementary AVP infusion (0.01-0.04 IU/minute) was recorded within the first 24 hours in 22 patients. Secondary endpoints (serum sodium concentration, incidence of vasospasm, and intracranial pressure [ICP]) were compared to controls on HHH therapy with phenylephrine alone.

RESULTS

After initiation of AVP, MAP increased significantly compared to baseline. Phenylephrine doses decreased significantly, whereas other hemodynamic parameters remained stable. Serum sodium concentrations decreased similarly in both groups (-5 +/- 7 mmol/L versus -6 +/- 4 mmol/L; p = 0.25). No detrimental effects on vasospasm incidence or ICP and cerebral perfusion pressure were noted.

CONCLUSION

AVP may be considered as an alternative supplementary vasopressor in refractory HHH therapy with phenylephrine in SAH. Although we did not observe any deleterious effect of AVP on cerebral circulation, close observation for development of cerebral vasospasm should be undertaken, until it is clearly demonstrated that AVP has no adverse effects on regional cerebral blood flow and symptomatic cerebral vasospasm. Our limited data suggest that low-dose AVP does not cause brain edema, but further study is merited.

S100B is not a reliable prognostic index in paediatric TBI

BACKGROUND

As far as paediatric traumatic brain injury is concerned, it is difficult to quantify the extent of the primary insult, to monitor secondary changes and to predict neurological outcomes by means of the currently used diagnostic tools: physical examination, Glasgow Coma Scale (GCS) score and computed tomography. For this reason, several papers focused on the use of biochemical markers (S100B, neuron-specific enolase) to detect and define the severity of brain damage and predict outcome after traumatic head injury or cardiac arrest.

OBJECTIVE

The aim of this paper is measuring the range of S100B serum concentrations in children affected by traumatic brain injury and describing the possible roles of this protein in the reaction to trauma.

METHODS

Fifteen children aged 1-15 years were included in the study. Traumatic brain injury severity was defined by paediatric GCS score as mild (9 patients), moderate (2 patients) or severe (4 patients). Blood samples for S100B serum measurement were taken at emergency department admission and after 48 h.

RESULTS

The serum S100B concentration was higher in the group of severe trauma patients, who scored the lowest on the GCS at admission, and among them, the highest values were reported by the children with concomitant peripheral lesions.

CONCLUSIONS

The role of S100B in paediatric traumatic brain injury has not been clarified yet, and the interpretation of its increase when the head trauma is associated with other injuries needs the understanding of the physiopathological mechanisms that rule its release in the systemic circulation. The levels of S100B in serum after a brain injury could be related to the mechanical discharge from a destroyed blood-brain barrier, or they could be due to the active expression by the brain, as a part of its involvement in the systemic inflammatory reaction. Early increase of this protein is not a reliable prognostic index of neurological outcome after pediatric traumatic brain injury, since even very elevated values are compatible with a complete neurological recovery.

Increased Expression of Vasopressin V1aReceptors after Traumatic Brain Injury

Experimental evidence obtained in various animal models of brain injury indicates that vasopressin promotes the formation of cerebral edema. However, the molecular and cellular mechanisms underlying this vasopressin action are not fully understood. In the present study, we analyzed the temporal changes in expression of vasopressin V1a receptors after traumatic brain injury (TBI) in rats. In the intact brain, the V1a receptor was expressed in neurons located in all layers of the frontoparietal cortex. The V1a receptor-immunoreactive product was predominantly localized to neuronal nuclei and had both a diffused and punctate staining pattern. The V1a receptors were also expressed in astrocytes, especially in layer 1 of the frontoparietal cortex. In these cells, two distinctive patterns of immunopositive staining for V1a receptors were observed: a diffused cytosolic staining of cell bodies and processes and a clearly punctate staining pattern that was predominantly localized to the astrocytic cell bodies. The real-time reverse-transcriptase polymerase chain reaction analysis of changes in mRNA for the V1a receptor demonstrated that after TBI, there is an early (4 h post-TBI) increase in the number of transcripts in the ipsilateral frontoparietal cortex, when compared to the contralateral hemisphere or the sham-injured rats. This increase in the message was followed by the up-regulation of expression of the V1a receptors at the protein level. This was most evident in cortical astrocytes in the areas surrounding the lesion. The number of the V1a receptor-immunopositive astrocytes in the traumatized parenchyma gradually increased, starting at 8 h and peaking at 4-6 days after TBI. Furthermore, a redistribution of V1a receptors from the astrocytic cell bodies to the astrocytic processes was observed. In addition to astrocytes, an increased expression of V1a receptors was found in the endothelium of both blood microvessels and the large-diameter blood vessels in the frontoparietal cortex ipsilateral to injury. This increase in the V1a receptor expression was apparent between 2 and 4 days after TBI. As early as 1-2 h following the impact, there was also a striking increase in the number of the V1a receptor-immunopositive beaded axonal processes, with greatly enlarged varicosities, that were localized to various areas of the injured parenchyma. It is suggested that the increased expression of V1a receptors plays an important role in the vasopressin-mediated formation of edema in the injured brain.

The hypothalamo-pituitary-adrenal axis response to experimental traumatic brain injury

Alterations in the hypothalamo-pituitary-adrenal (HPA) axis following traumatic brain injury have not been documented in detail. We used fluid percussion injury (FPI) to evaluate the early changes in components of the HPA axis following experimental traumatic brain injury. Wistar rats were sacrificed at 2 or 4 h following sham or FPI surgery. In situ hybridization histochemistry was used to determine the expression of mRNAs of corticotrophin releasing hormone (CRH) and arginine vasopressin (AVP) in the hypothalamus and pro-opiomelanocortin (POMC) in the pituitary. A group of animals undergoing no surgery were used as control. Repeated blood sampling from an indwelling catheter demonstrated that plasma corticosterone (CORT) levels peaked 30 min following surgery in sham and FPI animals but there was no significant difference in CORT concentration between these groups at any time. Pituitary POMC expression was increased following sham and FPI surgery (compared with control non-operated animals) but with no significant difference between the two groups undergoing surgery. Hypothalamic CRH mRNA expression was significantly higher in animals undergoing FPI compared with sham surgery. Hypothalamic AVP mRNA expression was not significantly increased when compared with control nonoperated animals. These data indicate that the anaesthesia and/or surgery associated with FPI or sham surgery induces a generalised activation of the HPA axis. The selective increase in CRH mRNA in animals undergoing FPI may be due to specific effects of traumatic brain injury rather than a general stress response and may suggest an additional neurotransmitter role for CRH following head injury. The absence of an AVP response suggests that the effects of FPI may be mediated through the CRH-alone-containing subpopulation of neurons.

Salt-loading increases vasopressin and vasopressin 1b receptor mRNA in the hypothalamus and choroid plexus

The choroid plexus plays a pivotal role in the production of cerebrospinal fluid (CSF). Messenger RNA (mRNA) transcripts encoding arginine vasopressin (AVP) and the vasopressin 1b receptor (V(1b)R) are found in various structures of the central nervous system, including the choroid plexus. The present study measured AVP and V(1b)R mRNA production in response to plasma hyperosmolality. Compared to rats maintained on water, 2% salt-drinking rats had increased levels of AVP and V(1b)R mRNAs in the supraoptic (SON) and paraventricular (PVN) nuclei of the hypothalamus and in the choroid plexus. The increase in V(1b)R mRNA in the SON and PVN as a result of plasma hyperosmolality may reflect changes in receptor production that, in turn, have a role in AVP autoregulation of hypothalamic magnocellular neurons. The increase of AVP and V(1b)R mRNAs in the choroid plexus further shows the involvement of AVP in the regulation of brain water content and cerebral edema.

Treatment of brain edema with a nonpeptide arginine vasopressin V1 receptor antagonist OPC-21268 in rats

OBJECTIVE

Recent experimental evidence suggests that centrally released arginine vasopressin plays a significant role in brain capillary water permeability as well as in pathogenesis of vasogenic brain edema. The purpose of this study was to examine the effects of orally administered OPC-21268, a nonpeptide arginine vasopressin V1 receptor antagonist, on cold-induced brain edema in rats.

METHODS

Cold brain injury was induced for 1 minute in 140 rats. Treatment with OPC-21268, at dosages of 100 mg (n = 20), 200 mg (n = 20), and 300 mg/kg (n = 15), or with saline (n = 17) was started 1 hour after the induction of cold injury and was continued every 8 hours for 24 hours. Two percent Evans blue in saline (1 ml/kg) was administered intravenously before cold injury in another group of rats, 15 of which were saline-treated and 55 of which were OPC-21268-treated at the above dosages. After 24 hours, brain tissue water and electrolytes, brain tissue swelling, blood-brain barrier permeability to Evans blue, and plasma electrolytes and osmolality were determined.

RESULTS

Compared with the saline-treated group, OPC-21268 treatment at the dosages of 200 and 300 mg/kg significantly reduced brain water content in both hemispheres (P<0.01). Swelling of the traumatized hemispheres was also significantly reduced at 200 and 300 mg/kg dosages (P<0.05). Brain tissue sodium content was significantly reduced at the dosage of 300 mg/kg (P<0.05). Blood-brain barrier permeability to Evans blue was significantly decreased in a dose-dependent manner compared with the saline-treated group (P<0.01). No significant changes were observed in other parameters.

CONCLUSION

Our results indicate that OPC-21268 predominantly exerts a protective effect in areas where the maximum amount of blood-brain barrier breakdown occurs, and it is effective in the treatment of cold-induced vasogenic brain edema.

OPC-21268, an orally effective, nonpeptide arginine vasopressin V1 receptor antagonist reduces vasogenic brain edema

We examined the effect of orally administered OPC-21268, a nonpeptide Arginine Vasopressin V1 receptor antagonist, on cold induced vasogenic brain edema in rat. Cold brain injury was induced by applying a copper rode cooled with liquid nitrogen for one minute. To mimic clinical use, one hour after induction of the cold lesion, rats were treated with orally administered OPC-21268 at doses of 100 mg, 200 mg, and 300 mg/kg every 8 hr for 24 hours. Two percent Evans blue in saline, in a volume of 1 ml/kg was given intravenously prior to cold injury. Twenty four hours after induction the cold lesion, brain water, brain tissue electrolytes, and plasma osmolality and electrolytes were measured. Quantitative evaluation of BBB permeability was performed using the Evans blue fluorescence method. The injury resulted in significant increases in the brain water and brain tissue sodium, and Evans blue concentration in both the lesioned and contralateral hemispheres (p < 0.01). OPC-21268 at doses of 200 mg and 300 mg/kg significantly decreased brain water and Evans blue concentrations in both the lesioned and contralateral hemispheres (p < 0.01). Brain tissue sodium content was significantly reduced at a dose of 300 mg/kg in the lesioned side (p < 0.05). There were no significant changes in other parameters throughout the experiments. Our results indicate that OPC-21268 exerts a protective effect in areas where the maximal amount of BBB breakdown occurs.