Endothelin B receptor agonist, IRL-1620, enhances angiogenesis and neurogenesis following cerebral ischemia in rats

To evaluate the effect of endothelin receptor agonist IRL-1620 alone and in combination with donepezil in modulating neurodegeneration elicited by amyloid-β in rats

BACKGROUND

The development of efficient therapies for Alzheimer''s disease is essential since it is a serious public health problem. This investigation sought to ascertain any potential synergistic benefits of treating Alzheimer's disease with IRL-1620 monotherapy in addition to Donepezil. Additionally, the effect of IRL-1620 was evaluated using different doses (5 μg/kg,7 μg/kg, and 9 μg/kg). The study further assessed neurobehavioral, biochemical, molecular, and histopathological parameters to evaluate the efficacy of both IRL1620 by its own and in association with Donepezil. Fifty-eight adult male Wistar rats were allocated to eight experimental groups. A dose-ranging study of IRL-1620 was conducted using different doses administered via intravenous injection. Alzheimer's disease was induced by Aβ administration, and treatment arms included disease Control (Sham), Donepezil monotherapy, and combination treatment with IRL-1620 5 μg/kg (Dose selected from the dose-ranging study). The treatment using IRL-1620 (9 μg/kg) intravenously and Donepezil (1 mg/kg orally) both on its own and in addition substantially enhanced memory in comparison with the control group (p < 0.05). Dose of IRL-1620 (9 μg/kg) intravenously, escape latency decreased and the time spent in the target quadrant was considerably increased, and they further benefited from combination therapy. Moreover, IRL-1620 (9 μg/kg) intravenously and combination treatment reduced lipid peroxidation and acetylcholinesterase levels while increasing antioxidant enzyme levels. Immunohistochemistry and molecular analysis revealed enhanced expression of neurotrophic factors with combination treatment. The combination of IRL-1620 and Donepezil showed significant improvements in memory and neurobehavioral parameters (p < 0.05). Alzheimer's disease in male Wistar rats. These results indicate to the probable therapeutic advantages of IRL-1620 and Donepezil in the management of Alzheimer's disease. The combination treatment exhibited enhanced effects compared to monotherapy, highlighting its potential promising therapeutic approach. Additional research is required to understand the mechanisms behind these synergistic benefits and to establish the ideal dosage and duration of therapy for therapeutic applications.

Sovateltide (ILR-1620) Improves Motor Function and Reduces Hyperalgesia in a Rat Model of Spinal Cord Injury

BACKGROUND

Spinal cord injury (SCI) presents a major global health challenge, with rising incidence rates and substantial disability. Although progress has been made in understanding SCI's pathophysiology and early management, there is still a lack of effective treatments to mitigate long-term consequences. This study investigates the potential of sovateltide, a selective endothelin B receptor agonist, in improving clinical outcomes in an acute SCI rat model.

METHODS

Thirty male Sprague-Dawley rats underwent sham surgery (group A) or SCI and treated with vehicle (group B) or sovateltide (group C). Clinical tests, including Basso, Beattie, and Bresnahan scoring, inclined plane, and allodynia testing with von Frey hair, were performed at various time points. Statistical analyses assessed treatment effects.

RESULTS

Sovateltide administration significantly improved motor function, reducing neurological deficits and enhancing locomotor recovery compared with vehicle-treated rats, starting from day 7 post injury. Additionally, the allodynic threshold improved, suggesting antinociceptive properties. Notably, the sovateltide group demonstrated sustained recovery, and even reached preinjury performance levels, whereas the vehicle group plateaued.

CONCLUSIONS

This study suggests that sovateltide may offer neuroprotective effects, enhancing neurogenesis and angiogenesis. Furthermore, it may possess anti-inflammatory and antinociceptive properties. Future clinical trials are needed to validate these findings, but sovateltide shows promise as a potential therapeutic strategy to improve functional outcomes in SCI. Sovateltide, an endothelin B receptor agonist, exhibits neuroprotective properties, enhancing motor recovery and ameliorating hyperalgesia in a rat SCI model. These findings could pave the way for innovative pharmacological interventions for SCI in clinical settings.

Advances in Therapies to Treat Neonatal Hypoxic-Ischemic Encephalopathy

Neonatal hypoxic-ischemic encephalopathy (HIE) is a condition that results in brain damage in newborns due to insufficient blood and oxygen supply during or after birth. HIE is a major cause of neurological disability and mortality in newborns, with over one million neonatal deaths occurring annually worldwide. The severity of brain injury and the outcome of HIE depend on several factors, including the cause of oxygen deprivation, brain maturity, regional blood flow, and maternal health conditions. HIE is classified into mild, moderate, and severe categories based on the extent of brain damage and resulting neurological issues. The pathophysiology of HIE involves different phases, including the primary phase, latent phase, secondary phase, and tertiary phase. The primary and secondary phases are characterized by episodes of energy and cell metabolism failures, increased cytotoxicity and apoptosis, and activated microglia and inflammation in the brain. A tertiary phase occurs if the brain injury persists, characterized by reduced neural plasticity and neuronal loss. Understanding the cellular and molecular aspects of the different phases of HIE is crucial for developing new interventions and therapeutics. This review aims to discuss the pathophysiology of HIE, therapeutic hypothermia (TH), the only approved therapy for HIE, ongoing developments of adjuvants for TH, and potential future drugs for HIE.

Sovateltide: First Approval

Sovateltide (Tycamzzi™), a highly selective endothelin-B receptor agonist and synthetic analog of endothelin-1, is being developed by Pharmazz, Inc. as a neural progenitor cell therapeutic agent for the treatment of acute cerebral ischemic stroke (ACIS), hypoxic-ischemic encephalopathy (HIE), spinal cord injuries and Alzheimer's disease. In May 2023, sovateltide was approved in India for the treatment of cerebral ischemic stroke within 24 h of stroke onset. This article summarizes the milestones in the development of sovateltide leading to this first approval for use in patients with ACIS.

Angiogenesis after ischemic stroke

Owing to its high disability and mortality rates, stroke has been the second leading cause of death worldwide. Since the pathological mechanisms of stroke are not fully understood, there are few clinical treatment strategies available with an exception of tissue plasminogen activator (tPA), the only FDA-approved drug for the treatment of ischemic stroke. Angiogenesis is an important protective mechanism that promotes neural regeneration and functional recovery during the pathophysiological process of stroke. Thus, inducing angiogenesis in the peri-infarct area could effectively improve hemodynamics, and promote vascular remodeling and recovery of neurovascular function after ischemic stroke. In this review, we summarize the cellular and molecular mechanisms affecting angiogenesis after cerebral ischemia registered in PubMed, and provide pro-angiogenic strategies for exploring the treatment of ischemic stroke, including endothelial progenitor cells, mesenchymal stem cells, growth factors, cytokines, non-coding RNAs, etc.

Oxidative stress: A target to treat Alzheimer's disease and stroke

Oxidative stress has been established as a well-known pathological condition in several neurovascular diseases. It starts with increased production of highly oxidizing free-radicals (e.g. reactive oxygen species; ROS and reactive nitrogen species; RNS) and becomes too high for the endogenous antioxidant system to neutralize them, which results in a significantly disturbed balance between free-radicals and antioxidants levels and causes cellular damage. A number of studies have evidently shown that oxidative stress plays a critical role in activating multiple cell signaling pathways implicated in both progression as well as initiation of neurological diseases. Therefore, oxidative stress continues to remain a key therapeutic target for neurological diseases. This review discusses the mechanisms involved in reactive oxygen species (ROS) generation in the brain, oxidative stress, and pathogenesis of neurological disorders such as stroke and Alzheimer's disease (AD) and the scope of antioxidant therapies for these disorders.

Roles of Astrocytic Endothelin ETB Receptor in Traumatic Brain Injury

Traumatic brain injury (TBI) is an intracranial injury caused by accidents, falls, or sports. The production of endothelins (ETs) is increased in the injured brain. ET receptors are classified into distinct types, including ET_A receptor (ET_A-R) and ET_B receptor (ET_B-R). ET_B-R is highly expressed in reactive astrocytes and upregulated by TBI. Activation of astrocytic ET_B-R promotes conversion to reactive astrocytes and the production of astrocyte-derived bioactive factors, including vascular permeability regulators and cytokines, which cause blood-brain barrier (BBB) disruption, brain edema, and neuroinflammation in the acute phase of TBI. ET_B-R antagonists alleviate BBB disruption and brain edema in animal models of TBI. The activation of astrocytic ET_B receptors also enhances the production of various neurotrophic factors. These astrocyte-derived neurotrophic factors promote the repair of the damaged nervous system in the recovery phase of patients with TBI. Thus, astrocytic ET_B-R is expected to be a promising drug target for TBI in both the acute and recovery phases. This article reviews recent observations on the role of astrocytic ET_B receptors in TBI.

Clinical Trials Targeting Secondary Damage after Traumatic Spinal Cord Injury

Spinal cord injury (SCI) often causes loss of sensory and motor function resulting in a significant reduction in quality of life for patients. Currently, no therapies are available that can repair spinal cord tissue. After the primary SCI, an acute inflammatory response induces further tissue damage in a process known as secondary injury. Targeting secondary injury to prevent additional tissue damage during the acute and subacute phases of SCI represents a promising strategy to improve patient outcomes. Here, we review clinical trials of neuroprotective therapeutics expected to mitigate secondary injury, focusing primarily on those in the last decade. The strategies discussed are broadly categorized as acute-phase procedural/surgical interventions, systemically delivered pharmacological agents, and cell-based therapies. In addition, we summarize the potential for combinatorial therapies and considerations.

Molecular mediators of angiogenesis and neurogenesis after ischemic stroke

The mechanisms governing neurological and functional recovery after ischemic stroke are incompletely understood. Recent advances in knowledge of intrinsic repair processes of the CNS have so far translated into minimal improvement in outcomes for stroke victims. Better understanding of the processes underlying neurological recovery after stroke is necessary for development of novel therapeutic approaches. Angiogenesis and neurogenesis have emerged as central mechanisms of post-stroke recovery and potential targets for therapeutics. Frameworks have been developed for conceptualizing cerebral angiogenesis and neurogenesis at the tissue and cellular levels. These models highlight that angiogenesis and neurogenesis are linked to each other and to functional recovery. However, knowledge of the molecular framework linking angiogenesis and neurogenesis after stroke is limited. Studies of potential therapeutics typically focus on one mediator or pathway with minimal discussion of its role within these multifaceted biochemical processes. In this article, we briefly review the current understanding of the coupled processes of angiogenesis and neurogenesis after stroke. We then identify the molecular mediators and signaling pathways found in pre-clinical studies to upregulate both processes after stroke and contextualizes them within the current framework. This report thus contributes to a more-unified understanding of the molecular mediators governing angiogenesis and neurogenesis after stroke, which we hope will help guide the development of novel therapeutic approaches for stroke survivors.

Sovateltide Mediated Endothelin B Receptors Agonism and Curbing Neurological Disorders

Neurological/neurovascular disorders constitute the leading cause of disability and the second leading cause of death globally. Major neurological/neurovascular disorders or diseases include cerebral stroke, Alzheimer’s disease, spinal cord injury, neonatal hypoxic-ischemic encephalopathy, and others. Their pathophysiology is considered highly complex and is the main obstacle in developing any drugs for these diseases. In this review, we have described the endothelin system, its involvement in neurovascular disorders, the importance of endothelin B receptors (ETBRs) as a novel potential drug target, and its agonism by IRL-1620 (INN—sovateltide), which we are developing as a drug candidate for treating the above-mentioned neurological disorders/diseases. In addition, we have highlighted the results of our preclinical and clinical studies related to these diseases. The phase I safety and tolerability study of sovateltide has shown it as a safe and tolerable compound at therapeutic dosages. Furthermore, preclinical and clinical phase II studies have demonstrated the efficacy of sovateltide in treating acute ischemic stroke. It is under development as a first-in-class drug. In addition, efficacy studies in Alzheimer’s disease (AD), acute spinal cord injury, and neonatal hypoxic-ischemic encephalopathy (HIE) are ongoing. Successful completion of these studies will validate that ETBRs signaling can be an important target in developing drugs to treat neurological/neurovascular diseases.

Structural and Functional Diversity of Animal Toxins Interacting With GPCRs

Peptide toxins from venoms have undergone a long evolutionary process allowing host defense or prey capture and making them highly selective and potent for their target. This has resulted in the emergence of a large panel of toxins from a wide diversity of species, with varied structures and multiple associated biological functions. In this way, animal toxins constitute an inexhaustible reservoir of druggable molecules due to their interesting pharmacological properties. One of the most interesting classes of therapeutic targets is the G-protein coupled receptors (GPCRs). GPCRs represent the largest family of membrane receptors in mammals with approximately 800 different members. They are involved in almost all biological functions and are the target of almost 30% of drugs currently on the market. Given the interest of GPCRs in the therapeutic field, the study of toxins that can interact with and modulate their activity with the purpose of drug development is of particular importance. The present review focuses on toxins targeting GPCRs, including peptide-interacting receptors or aminergic receptors, with a particular focus on structural aspects and, when relevant, on potential medical applications. The toxins described here exhibit a great diversity in size, from 10 to 80 amino acids long, in disulfide bridges, from none to five, and belong to a large panel of structural scaffolds. Particular toxin structures developed here include inhibitory cystine knot (ICK), three-finger fold, and Kunitz-type toxins. We summarize current knowledge on the structural and functional diversity of toxins interacting with GPCRs, concerning first the agonist-mimicking toxins that act as endogenous agonists targeting the corresponding receptor, and second the toxins that differ structurally from natural agonists and which display agonist, antagonist, or allosteric properties.

Neuroprotective Effect of Sovateltide (IRL 1620, PMZ 1620) in a Neonatal Rat Model of Hypoxic-Ischemic Encephalopathy

Therapeutic hypothermia with modest results is the only treatment currently available for neonatal hypoxic ischemic encephalopathy (HIE). Endothelin B (ETB) receptors in the brain are shown to have neural restorative capacity. ETB receptors agonist sovateltide alone or as an adjuvant therapy may enhance neurovascular remodeling in HIE. Sprague-Dawley rat pups were grouped based on treatments into (1) Control; (2) HIE + Vehicle; (3) HIE + Hypothermia; (4) HIE + sovateltide; and (5) HIE + sovateltide + hypothermia. HIE was induced on postnatal day (PND) 7, followed by sovateltide (5 µg/kg) intracerebroventricular injection and/or hypothermia. On PND 10, brains were analyzed for the expression of vascular endothelial growth factor (VEGF), nerve growth factor (NGF), ETB receptors, oxidative stress and cellular damage markers. Vehicle-treated animals had high oxidative stress level as indicated by an increase in lipid peroxidation factor, malondialdehyde, and decreased antioxidants, reduced glutathione and superoxide dismutase, compared to control. These effects were reversed in sovateltide alone (p < 0.001) or in combination with the therapeutic hypothermia (p < 0.001), indicating that ETB receptor activation reduces oxidative stress injury following HIE. Animals receiving sovateltide demonstrated a significant (p < 0.0001) upregulation of ETB receptor, VEGF, and NGF expression in the brain compared to vehicle-treated animals. Additionally, sovateltide alone or in combination with therapeutic hypothermia significantly (p < 0.001) reduced cell death when compared to vehicle or therapeutic hypothermia alone, demonstrating that sovateltide is neuroprotective and attenuates neural damage following HIE. These findings are important and merit additional studies for development of new interventions for improving neurodevelopmental outcomes after HIE.

Crosstalk Among NLRP3 Inflammasome, ETBR Signaling, and miRNAs in Stress-Induced Depression-Like Behavior: a Modulatory Role for SGLT2 Inhibitors

Depression is an overwhelming health concern, and many patients fail to optimally respond to available standard therapies. Neuroplasticity and blood-brain barrier (BBB) integrity are the cornerstones of a well-functioning central nervous system, but they are vulnerable to an overly active NLRP3 inflammasome pathway that can also indirectly trigger the release of ET-1 and contribute to the ET system disturbance, which further damages stress resilience mechanisms. Here, the promising yet unexplored antidepressant potential of dapagliflozin (Dapa), a sodium-glucose co-transporter-2 inhibitor, was investigated by assessing its role in the modulation of the NLRP3 inflammasome pathway and ETBR signal transduction, and their impact on neuroplasticity and BBB integrity in an animal model of depression. Dapa (1 mg/kg/day; p.o.) with and without BQ-788 (1 mg/kg/day; i.p.), a specific ETBR blocker, were administered to adolescent male Wistar rats exposed to a 5-week chronic unpredictable stress protocol. The depressive animals demonstrated marked activation of the NLRP3 inflammasome pathway (NF-κB/NLRP3/caspase-1/IL/TNF-α), which was associated with both peripheral and central inflammatory responses. The ET system was disrupted, with noticeable reduction in miR-125a-5p and ETBR gene expression. Cortical ZO-1 expression was downregulated under the influence of NLRP3/TNF-α/miR-501-3p signaling, along with a prominent reduction in hippocampal BDNF and synapsin-1. With ETBR up-regulation being a cornerstone outcome, Dapa administration efficiently created an overall state of resilience, improved histopathological and behavioral variables, and preserved BBB function. These observations were further verified by the results obtained with BQ-788 co-administration. Thus, Dapa may exert its antidepressant action by reinforcing BBB integrity and promoting neuroplasticity through manipulation of the NLRP3/ET-1/ETBR/BDNF/ZO-1 axis, with a significant role for ETBR signaling. Graphical illustration for the proposed mechanisms of the anti-depressant potential of Dapa. Dapa suppressed NLRP3 inflammasome activation and assembly with subsequent inhibition of pro-inflammatory ILs. This results in attenuation of neuro-inflammation, BBB disruption, glial cell activation, TNF-α and ET-1 release, and the enhanced production of neurotrophins. The role of ETBR signaling was emphasized; Dapa possibly augmented ETBR expression, which is thought to boost neurotrophins production. The ETBR blocker, BQ-788, suppressed most of the positive outcomes of Dapa. Finally, miR-125a-5p and miR-501-3p that played major roles in these pathological pathways were modulated by Dapa. It is not yet clear whether Dapa has a direct or rather indirect effect on their expression. BBB, blood-brain barrier; Dapa, dapagliflozin; ET-1, endothelin-1; ETBR, endothelin B receptor; IL, interleukin; NF-κB, nuclear factor kappa B; NLRP3, nucleotide-binding oligomerization domain, leucine-rich repeat and pyrin domain-containing protein 3; TNF-α, tumor necrosis factor-α. Created with BioRender.com.

Brain size reductions associated with endothelin B receptor mutation, a cause of Hirschsprung's disease

Background

ET_B has been reported to regulate neurogenesis and vasoregulation in foetal development. Its dysfunction was known to cause HSCR, an aganglionic colonic disorder with syndromic forms reported to associate with both small heads and developmental delay. We therefore asked, "is CNS maldevelopment a more general feature of ET_B mutation?" To investigate, we reviewed the micro-CT scans of an ET_B^−/− model animal, sl/sl rat, and quantitatively evaluated the structural changes of its brain constituents.

Methods

Eleven neonatal rats generated from ET_B^+/− cross breeding were sacrificed. Micro-CT scans were completed following 1.5% iodine-staining protocols. All scans were reviewed for morphological changes. Selected organs were segmented semi-automatically post-NLM filtering: TBr, T-CC, T-CP, OB, Med, Cer, Pit, and S&I Col. Volumetric measurements were made using Drishti rendering software. Rat genotyping was completed following analysis. Statistical comparisons on organ volume, organ growth rate, and organ volume/bodyweight ratios were made between sl/sl and the control groups based on autosomal recessive inheritance. One-way ANOVA was also performed to evaluate potential dose-dependent effect.

Results

sl/sl rat has 16.32% lower body weight with 3.53% lower growth rate than the control group. Gross intracranial morphology was preserved in sl/sl rats. However, significant volumetric reduction of 20.33% was detected in TBr; similar reductions were extended to the measurements of T-CC, T-CP, OB, Med, and Pit. Consistently, lower brain and selected constituent growth rates were detected in sl/sl rat, ranging from 6.21% to 11.51% reduction. Lower organ volume/bodyweight ratio was detected in sl/sl rats, reflecting disproportional neural changes with respect to body size. No consistent linear relationships exist between ET_B copies and intracranial organ size or growth rates.

Conclusion

Although ET_B^−/− mutant has a normal CNS morphology, significant size reductions in brain and constituents were detected. These structural changes likely arise from a combination of factors secondary to dysfunctional ET-1/ET-3/ET_B signalling, including global growth impairment from HSCR-induced malnutrition and dysregulations in the neurogenesis, angiogenesis, and cerebral vascular control. These changes have important clinical implications, such as autonomic dysfunction or intellectual delay. Although further human study is warranted, our study suggested comprehensive managements are required for HSCR patients, at least in ET_B^−/− subtype.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12868-021-00646-z.

Endothelin ETB Receptor-Mediated Astrocytic Activation: Pathological Roles in Brain Disorders

In brain disorders, reactive astrocytes, which are characterized by hypertrophy of the cell body and proliferative properties, are commonly observed. As reactive astrocytes are involved in the pathogenesis of several brain disorders, the control of astrocytic function has been proposed as a therapeutic strategy, and target molecules to effectively control astrocytic functions have been investigated. The production of brain endothelin-1 (ET-1), which increases in brain disorders, is involved in the pathophysiological response of the nervous system. Endothelin B (ET_B) receptors are highly expressed in reactive astrocytes and are upregulated by brain injury. Activation of astrocyte ET_B receptors promotes the induction of reactive astrocytes. In addition, the production of various astrocyte-derived factors, including neurotrophic factors and vascular permeability regulators, is regulated by ET_B receptors. In animal models of Alzheimer’s disease, brain ischemia, neuropathic pain, and traumatic brain injury, ET_B-receptor-mediated regulation of astrocytic activation has been reported to improve brain disorders. Therefore, the astrocytic ET_B receptor is expected to be a promising drug target to improve several brain disorders. This article reviews the roles of ET_B receptors in astrocytic activation and discusses its possible applications in the treatment of brain disorders.

Endothelin-1 decreases the expression of Ephrin-A and B subtypes in cultured rat astrocytes through ETB receptors

Ephrin family proteins are cell surface molecules that regulate several cellular functions through cell-cell interactions. During nervous tissue repair after injury, the expression of ephrin subtypes in astrocytes is altered, affecting the axonal elongation and migration of neuronal precursors. However, the mechanism regulating the expression of ephrin subtypes in astrocytes has not been investigated. Herein, we studied the effects of endothelin-1 (ET-1) on the expression of ephrin subtypes in cultured rat astrocytes. Our results showed that ET-1 (100 nM) treatment for 1-24 h reduced the expression of ephrin-A2, -A4, -B2, and -B3 mRNA and protein in astrocytes, whereas the expression of ephrin-A1, -A3, -A5, and -B1 mRNA were not affected. Sarafotoxin S6c, a selective ETB receptor agonist, decreased the expression of ephrin-A2, -A4, -B2, and -B3 in cultured astrocytes. The decrease in ephrin-A2, -A4, -B2, and -B3 expression by ET-1 treatment was reduced in the presence of BQ788, an ETB receptor antagonist, while FR139317, an ETA receptor antagonist, had no effects. These results suggest that ET-1 is a signaling molecule that downregulates ephrin-A2, -A4, -B2, and -B3 expression in astrocytes.

Safety and Efficacy of Sovateltide (IRL-1620) in a Multicenter Randomized Controlled Clinical Trial in Patients with Acute Cerebral Ischemic Stroke

BACKGROUND

Sovateltide (IRL-1620, PMZ-1620), an endothelin-B receptor agonist, has been previously shown to increase cerebral blood flow, have anti-apoptotic activity and produce neurovascular remodeling when administered intravenously following acute cerebral ischemic stroke in rats. Its safety and tolerability were confirmed in healthy human volunteers (CTRI/2016/11/007509).

OBJECTIVE

Our objective was to determine the safety, tolerability and efficacy of sovateltide as an addition to standard of care (SOC) in patients with acute cerebral ischemic stroke.

METHODS

A prospective, multicentric, randomized, double-blind, placebo-controlled study was conducted to compare the safety (primary objective) and efficacy (secondary objective) of sovateltide in patients with acute cerebral ischemic stroke. Adult males or females aged 18-70 years who had experienced a radiologically confirmed ischemic stroke within the last 24 h were included in the study. Patients with intracranial hemorrhage and those receiving endovascular therapy were excluded. Patients randomized to the sovateltide group received three doses of sovateltide (each dose 0.3 µg/kg) administered as an intravenous bolus over 1 min at an interval of 3 ± 1 h on day 1, day 3 and day 6 (total dose of 0.9 µg/kg/day). Patients randomized to the placebo group received an equal volume of saline. Every patient in both groups received SOC for stroke. Efficacy was evaluated using neurological outcomes based on National Institute of Health Stroke Scale (NIHSS), modified Rankin Scale (mRS) and Barthel Index (BI) scores from day 1 through day 90. Quality of life was measured using the EuroQoL-5 Dimensions (EQ-5D) and Stroke-Specific Quality of Life (SSQoL) at 60 and 90 days of follow-up.

RESULTS

A total of 40 patients with acute cerebral ischemic stroke were enrolled in this study, of whom 36 completed the 90-day follow-up. Patients received saline (n = 18; 11 male and 7 female) or sovateltide (n = 18; 15 male and 3 female) within 24 h of onset of stroke. The number of patients receiving investigational drug within 20 h of onset of stroke was 14/18 in the saline group and 10/18 in the sovateltide group. The baseline characteristics and SOC in both cohorts was similar. Sovateltide was well-tolerated, and all patients received complete treatment with no incidence of drug-related adverse events. Hemodynamic, biochemical or hematological parameters were not affected by sovateltide. Sovateltide treatment resulted in improved mRS and BI scores on day 6 compared with day 1 (p < 0.0001), an effect not seen in the saline group. Sovateltide increased the frequency of favorable outcomes at 3 months. An improvement of ≥ 2 points on the mRS was observed in 60 and 40% of patients in the sovateltide and saline groups, respectively (p = 0.0519; odds ratio [OR] 5.25). An improvement on the BI of ≥ 40 points was seen in 64 and 36% of the sovateltide and saline groups, respectively (p = 0.0112; OR 12.44). An improvement of ≥6 points on the NIHSS was seen in 56% of patients in the sovateltide group versus 43% in the saline group (p = 0.2714; OR 2.275). The number of patients with complete recovery (defined as an NIHSS score of 0 and a BI of 100) was significantly greater (p < 0.05) in the sovateltide group than in the saline group. An assessment of complete recovery using an mRS score of 0 did not show a statistically significant difference between the treatment groups. Sovateltide treatment resulted in improved quality of life as measured by the EQ-5D and SSQoL on day 90.

CONCLUSION

Sovateltide was safe and well-tolerated and resulted in improved neurological outcomes in patients with acute cerebral ischemic stroke 90 days post-treatment.

TRIAL REGISTRATION

The study is registered at CTRI/2017/11/010654 and NCT04046484.

Sovateltide (IRL-1620) activates neuronal differentiation and prevents mitochondrial dysfunction in adult mammalian brains following stroke

The development of effective drugs for stroke is urgently required as it is the 2nd largest killer in the world and its incidence is likely to increase in the future. We have demonstrated cerebral endothelin B receptors (ETBR) as a potential target to treat acute cerebral ischemic stroke. However, the mechanism of ETBR mediated neural regeneration and repair remains elusive. In this study, a permanent middle cerebral artery occluded (MCAO) rat model was used. Sovateltide (an ETBR agonist) injected intravenously showed better survival and neurological and motor function improvement than control. Higher neuronal progenitor cells (NPCs) differentiation along with better mitochondrial morphology and biogenesis in the brain of sovateltide rats were noted. Exposure of cultured NPCs to hypoxia and sovateltide also showed higher NPC differentiation and maturation. This study shows a novel role of ETBR in NPCs and mitochondrial fate determination in cerebral ischemia, and in improving neurological deficit after stroke.

Sovateltide (IRL-1620) affects neuronal progenitors and prevents cerebral tissue damage after ischemic stroke

Stimulation of endothelin B receptors by its agonist IRL-1620 (INN, sovateltide) provides neuroprotection and neurological and motor function improvement following cerebral ischemia. We investigated the effect of sovateltide on stem and progenitor cells mediated neural regeneration and its effect on the cerebral tissue repair and restoration of neurological and motor function. Sovateltide (5 μg/kg) was injected intravenously in permanent middle cerebral artery occluded (MCAO) rats at 4, 6, and 8 h at days 0, 3, and 6. Neurological and motor function tests were carried out pre-MCAO and at day 7 post-MCAO. At day 7, significantly reduced expression of neuronal differentiation markers HuC/HuD and NeuroD1 was seen in MCAO + vehicle than sham rats. Sovateltide treatment upregulated HuC/HuD and NeuroD1 compared to MCAO + vehicle and their expression was similar to sham. Expression of stem cell markers Oct 4 and Sox 2 was similar in rats of all of the groups. Significantly reduced infarct volume and DNA damage with recovery of neurological and motor function was observed in sovateltide-treated MCAO rats. These results indicate that sovateltide initiates a regenerative response by promoting differentiation of neuronal progenitors and maintaining stem cells in an equilibrium following cerebral ischemic stroke.

Endothelin: 30 Years From Discovery to Therapy

Discovered in 1987 as a potent endothelial cell-derived vasoconstrictor peptide, endothelin-1 (ET-1), the predominant member of the endothelin peptide family, is now recognized as a multifunctional peptide with cytokine-like activity contributing to almost all aspects of physiology and cell function. More than 30 000 scientific articles on endothelin were published over the past 3 decades, leading to the development and subsequent regulatory approval of a new class of therapeutics-the endothelin receptor antagonists (ERAs). This article reviews the history of the discovery of endothelin and its role in genetics, physiology, and disease. Here, we summarize the main clinical trials using ERAs and discuss the role of endothelin in cardiovascular diseases such as arterial hypertension, preecclampsia, coronary atherosclerosis, myocardial infarction in the absence of obstructive coronary artery disease (MINOCA) caused by spontaneous coronary artery dissection (SCAD), Takotsubo syndrome, and heart failure. We also discuss how endothelins contributes to diabetic kidney disease and focal segmental glomerulosclerosis, pulmonary arterial hypertension, as well as cancer, immune disorders, and allograft rejection (which all involve ET_A autoantibodies), and neurological diseases. The application of ERAs, dual endothelin receptor/angiotensin receptor antagonists (DARAs), selective ET_B agonists, novel biologics such as receptor-targeting antibodies, or immunization against ET_A receptors holds the potential to slow the progression or even reverse chronic noncommunicable diseases. Future clinical studies will show whether targeting endothelin receptors can prevent or reduce disability from disease and improve clinical outcome, quality of life, and survival in patients.

Anti-apoptotic activity of ETB receptor agonist, IRL-1620, protects neural cells in rats with cerebral ischemia

Endothelin-B receptor agonist, IRL-1620, provides significant neuroprotection following cerebral ischemia in rats. Whether this neuroprotection is due to inhibition of apoptosis is unknown. IRL-1620-treated rats following permanent middle cerebral artery occlusion (MCAO) showed significant improvement in neurological and motor functions along with a decrease in infarct volume at 24 h (-81.3%) and day 7 (-73.0%) compared to vehicle group. Cerebral blood flow (CBF) significantly improved in IRL-1620-treated animals compared to vehicle by day 7 post MCAO. IRL-1620-treated rats showed an increase in phospho-Akt and decrease in Bad level 7 h post-occlusion compared to vehicle, while Akt and Bad expression was similar in cerebral hemispheres at 24 h post-MCAO. The phospho-Bad level was lower in vehicle- but not in IRL-1620-treated rats at 24 h. Anti-apoptotic Bcl-2 expression decreased, while pro-apoptotic Bax expression increased in vehicle-treated MCAO rats, these changes were attenuated (P < 0.01) by IRL-1620. Mitochondrial membrane-bound Bax intensity significantly decreased in IRL-1620 compared to vehicle-treated MCAO rats. IRL-1620 treatment reduced (P < 0.001) the number of TUNEL-positive cells compared to vehicle at 24 h and day 7 post MCAO. The results demonstrate that IRL-1620 is neuroprotective and attenuates neural damage following cerebral ischemia in rats by increasing CBF and reducing apoptosis.

A novel neuroregenerative approach using ET(B) receptor agonist, IRL-1620, to treat CNS disorders

Endothelin B (ET(B)) receptors present in abundance the central nervous system (CNS) have been shown to have significant implications in its development and neurogenesis. We have targeted ET(B) receptors stimulation using a highly specific agonist, IRL-1620, to treat CNS disorders. In a rat model of cerebral ischemia intravenous administration IRL-1620 significantly reduced infarct volume and improved neurological and motor functions compared to control. This improvement, in part, is due to an increase in neuroregeneration. We also investigated the role of IRL-1620 in animal models of Alzheimer's disease (AD). IRL-1620 improved learning and memory, reduced oxidative stress and increased VEGF and NGF in Abeta treated rats. IRL-1620 also improved learning and memory in an aged APP/PS1 transgenic mouse model of AD. These promising findings prompted us to initiate human studies. Successful chemistry, manufacturing and control along with mice, rat and dog toxicological studies led to completion of a human Phase I study in healthy volunteers. We found that a dose of 0.6 microg/kg of IRL-1620 can be safely administered, three times every four hours, without any adverse effect. A Phase II clinical study with IRL-1620 has been initiated in patients with cerebral ischemia and mild to moderate AD.

New drugs and emerging therapeutic targets in the endothelin signaling pathway and prospects for personalized precision medicine

During the last thirty years since the discovery of endothelin-1, the therapeutic strategy that has evolved in the clinic, mainly in the treatment of pulmonary arterial hypertension, is to block the action of the peptide either at the ET(A) subtype or both receptors using orally active small molecule antagonists. Recently, there has been a rapid expansion in research targeting ET receptors using chemical entities other than small molecules, particularly monoclonal antibody antagonists and selective peptide agonists and antagonists. While usually sacrificing oral bio-availability, these compounds have other therapeutic advantages with the potential to considerably expand drug targets in the endothelin pathway and extend treatment to other pathophysiological conditions. Where the small molecule approach has been retained, a novel strategy to combine two vasoconstrictor targets, the angiotensin AT(1) receptor as well as the ET(A) receptor in the dual antagonist sparsentan has been developed. A second emerging strategy is to combine drugs that have two different targets, the ET(A) antagonist ambrisentan with the phosphodiesterase inhibitor tadalafil, to improve the treatment of pulmonary arterial hypertension. The solving of the crystal structure of the ET(B) receptor has the potential to identify allosteric binding sites for novel ligands. A further key advance is the experimental validation of a single nucleotide polymorphism that has genome wide significance in five vascular diseases and that significantly increases the amount of big endothelin-1 precursor in the plasma. This observation provides a rationale for testing this single nucleotide polymorphism to stratify patients for allocation to treatment with endothelin agents and highlights the potential to use personalized precision medicine in the endothelin field.

Alterations in endothelin receptors following hemorrhage and resuscitation by centhaquin

Endothelin-1 (ET-1) acts on ET(A) and ET(B) receptors and has been implicated in hemorrhagic shock (shock). We determined effect of shock and resuscitation by hypertonic saline (saline) or centhaquin on ET(A) and ET(B) receptor expression. Rats were anesthetized, a pressure catheter was placed in the left femoral artery; blood was withdrawn from the right femoral artery to bring mean arterial pressure (MAP) to 35 mm Hg for 30 min, resuscitation was performed and 90 min later sacrificed to collect samples for biochemical estimations. Resuscitation with centhaquin decreased blood lactate and increased MAP. Protein levels of ET(A) or ET(B) receptor were unaltered in the brain, heart, lung and liver following shock or resuscitation. In the abdominal aorta, shock produced an increase (140 %) in ET(A) expression which was attenuated by saline and centhaquin; ET(B) expression was unaltered following shock but was increased (79 %) by centhaquin. In renal medulla, ET(A) expression was unaltered following shock, but was decreased (-61 %) by centhaquin; shock produced a decrease (-34 %) in ET(B) expression which was completely attenuated by centhaquin and not saline. Shock induced changes in ET(A) and ET(B) receptors in the aorta and renal medulla are reversed by centhaquin and may be contributing to its efficacy.

Neuroprotective Effect of IRL-1620, an Endothelin B Receptor Agonist, on a Pediatric Rat Model of Middle Cerebral Artery Occlusion

Objective: The purpose of this study was to determine the potential neuroprotective effect of endothelin B (ET_B) receptor agonist IRL-1620 treatment in a pediatric model of ischemic stroke. Design: A prospective, animal model study. Setting: An experimental laboratory. Subjects: Three-month-old male Wistar Han rats. Interventions: The rats underwent permanent middle cerebral artery occlusion (MCAO). At 2, 4, and 6 h post MCAO, they were treated with saline, IRL-1620 (5 μg/kg, IV), and/or ET_B antagonist BQ788 (1 mg/kg, IV). Measurements and Main Results: The rats were evaluated over the course of 7 days for neurological and motor deficit, cerebral blood flow (CBF), and infarct volume. Young rats treated with IRL-1620 following MCAO improved significantly in neurological and motor assessments as compared to the vehicle-treated group, as measured by neurological score (P = 0.00188), grip test (P < 0.0001), and foot-fault error (P = 0.0075). CBF in the infarcted hemisphere decreased by 45-50% in all groups immediately following MCAO. After 7 days, CBF in the infarcted hemisphere of the IRL-1620 group increased significantly (P = 0.0007) when compared to the vehicle-treated group (+2.3 ± 23.3 vs. -45.4 ± 10.2%). Additionally, infarct volume was significantly reduced in IRL-1620-treated rats as compared to vehicle-treated rats (P = 0.0035, 41.4 ± 35.4 vs. 115.4 ± 40.9 mm³). Treatment with BQ788 blocked the effects of IRL-1620. Conclusions: IRL-1620 significantly reduced neurological and motor deficit as well as infarct volume while increasing CBF in a pediatric rat model of cerebral ischemia. These results indicate that selective ET_B receptor stimulation may provide a novel therapeutic strategy in the treatment of pediatric ischemic stroke as has been demonstrated in adult ischemic stroke.

Attenuation of opioid tolerance by ETB receptor agonist, IRL-1620, is independent of an accompanied decrease in nerve growth factor in mice

AIM

ET_A receptor antagonists reverse opioid tolerance but the involvement of ET_B receptors is unknown. In morphine or oxycodone tolerant mice we investigated (1) the effect of ET_B receptor agonist, IRL-1620, on analgesic tolerance; (2) changes in expression of the brain ET_A and ET_B receptors; and (3) alterations in the brain VEGF, NGF, PI3K and notch-1 expression.

MAIN METHODS

Body weight, body temperature, and tail-flick latency were assessed before and after a challenge dose of morphine or oxycodone in vehicle or IRL-1620 treated mice. Expression studies were carried out using Western blots.

KEY FINDINGS

Tail flick latency to a challenge dose of opioid was significantly increased by IRL-1620 from 39% to 100% in morphine tolerant and from 8% to 83% in oxycodone tolerant mice. Morphine or oxycodone did not alter ET_A or ET_B receptor expression. IRL-1620 had no effect on ET_A however it increased (61%) expression of ET_B receptors. IRL-1620-induced increase in ET_B receptor expression was attenuated by morphine (39.8%) and oxycodone (51.8%). VEGF expression was not affected by morphine or oxycodone and was unaltered by IRL-1620. However, NGF and PI3K expression was decreased (P < 0.001) by morphine and oxycodone and was unaffected by IRL-1620. Notch-1 expression was not altered by morphine, oxycodone or IRL-1620.

SIGNIFICANCE

ET_B receptor agonist, IRL-1620, restored analgesic tolerance to morphine and oxycodone, but it did not affect morphine and oxycodone induced decrease in NGF/PI3K expression. It is concluded that IRL-1620 attenuates opioid tolerance without the involvement of NGF/PI3K pathway.

Endothelin Confers Protection against High Glucose-Induced Neurotoxicity via Alleviation of Oxidative Stress

Recent findings linked the inhibition in the neuromodulator peptide endothelin-1 (ET-1) level to the high glucose-evoked neurotoxicity. However, definitive neuroprotective role for ET-1 and the major neuronal ET (ET-3) against high glucose-evoked toxicity and the implicated neurochemical responses triggered by their ET-A and ET-B receptors remain unknown. Here, we tested the hypothesis that ET-B activation alleviates high glucose-evoked oxidative stress and cell death. High glucose (100 mM for 48 hours)-evoked cell death was associated with elevation in reactive oxygen species, inhibition of catalase activity, and a paradoxical upregulation of hemeoxygenase-1 expression along with ET-A and ET-B receptors were downregulated and upregulated, respectively. ET-1 or ET-3, in concentrations that had no effect on PC12 cell viability in normal glucose medium, alleviated all high glucose-evoked neurochemical responses, except for the reduction in ET-A receptor expression. Prior (4 hours) incubation with a selective ET-A (BQ123) or ET-B (BQ788) receptor blocker abrogated the neuroprotection conferred by ET-1 or ET-3. However, the ET-B receptor played a greater role because BQ788 abrogated the favorable ET-1- or ET-3-mediated reversal of the ERK1/2 phosphorylation and the inhibition in catalase activity caused by high glucose. These findings suggest that endothelin exerts ET-B receptor-dependent favorable redox and neuroprotective effects against high glucose-evoked oxidative damage and neurotoxicity.

Endothelin Receptors, Mitochondria and Neurogenesis in Cerebral Ischemia

Background: Neurogenesis is most active during pre-natal development, however, it persists throughout the human lifespan. The putative role of mitochondria in neurogenesis and angiogenesis is gaining importance. Since, ET_B receptor mediated neurogenesis and angiogenesis has been identified, the role of these receptors with relevance to mitochondrial functions is of interest.

Methods: In addition to work from our laboratory, we undertook an extensive search of bibliographic databases for peer-reviewed research literature. Specific technical terms such as endothelin, mitochondria and neurogenesis were used to seek out and critically evaluate literature that was relevant.

Results: The ET family consists of three isopeptides (ET-1, ET-2 and ET-3) that produce biological actions by acting on two types of receptors (ET_A and ET_B). In the central nervous system (CNS) ET_A receptors are potent constrictors of the cerebral vasculature and appear to contribute in the causation of cerebral ischemia. ET_A receptor antagonists have been found to be effective in animal model of cerebral ischemia; however, clinical studies have shown no efficacy. Mitochondrial functions are critically important for several neural development processes such as neurogenesis, axonal and dendritic growth, and synaptic formation. ET appears to impair mitochondrial functions through activation of ET_A receptors. On the other hand, blocking ET_B receptors has been shown to trigger apoptotic processes by activating intrinsic mitochondrial pathway. Mitochondria are important for their role in molecular regulation of neurogenesis and angiogenesis. Stimulation of ET_B receptors in the adult ischemic brain has been found to promote angiogenesis and neurogenesis mediated through vascular endothelial growth factor and nerve growth factor. It will be interesting to investigate the effect of ET_B receptor stimulation on mitochondrial functions in the CNS following cerebral ischemia.

Conclusion: The findings of this review implicate brain ET_B receptors in angiogenesis and neurogenesis following cerebral ischemia, it is possible that the positive effect of stimulating ET_B receptors in cerebral ischemia may be mediated through mitochondrial functions.

Centhaquin attenuates hyperalgesia and non-evoked guarding in a rat model of postoperative pain primarily through α2B-adrenoceptors

Centhaquin has been shown to produce antinociception in the mouse hot plate and tail flick assays through the opioid, the α2A and α2B adrenoceptors. Present study was conducted to determine the effects of centhaquin in a rat model of postoperative pain. Involvement of opioid, and adrenergic receptors was assessed by pretreating rats with antagonists at the opioid (naloxone), α2-(atipamezole) or α2B-(imiloxan) adrenergic receptors. Postoperative pain was induced by hind paw plantar incision in male Sprague Dawley rats. Antihyperalgesic effects were determined by measurement of paw withdrawal latencies and withdrawal force, using dynamic von Frey filaments; attenuation of non-evoked guarding was measured by assigning pain scores to spontaneous behaviors. Rotarod test was used to determine motor impairment. Animals received saline, centhaquin or antagonist plus centhaquin. Centhaquin produced dose-dependent antihyperalgesic effect and attenuation of non-evoked guarding behavior, versus saline treated rats (P<0.05). Naloxone partially blocked while atipamezole and imiloxan significantly reversed centhaquin's antihyperalgesic effects (P<0.05). Attenuation of non-evoked guarding behavior was also blocked, but was not statistically significant. Imiloxan produced a greater block compared to atipamezole while naloxone had no significant effect. Rotarod testing indicated that centhaquin did not cause motor impairment. This is the first report demonstrating centhaquin antinociception in the rat postoperative pain model. Opioid, α2 adrenergic, and particularly α2B adrenergic receptors are involved in mediating antihyperalgesia while attenuation of nonevoked guarding is mediated by α2B/α2 adrenergic receptors. Centhaquin could be an effective non-sedating alternative in treating postoperative pain in ambulatory surgeries.

Endothelin

The endothelins comprise three structurally similar 21-amino acid peptides. Endothelin-1 and -2 activate two G-protein coupled receptors, ETA and ETB, with equal affinity, whereas endothelin-3 has a lower affinity for the ETA subtype. Genes encoding the peptides are present only among vertebrates. The ligand-receptor signaling pathway is a vertebrate innovation and may reflect the evolution of endothelin-1 as the most potent vasoconstrictor in the human cardiovascular system with remarkably long lasting action. Highly selective peptide ETA and ETB antagonists and ETB agonists together with radiolabeled analogs have accurately delineated endothelin pharmacology in humans and animal models, although surprisingly no ETA agonist has been discovered. ET antagonists (bosentan, ambrisentan) have revolutionized the treatment of pulmonary arterial hypertension, with the next generation of antagonists exhibiting improved efficacy (macitentan). Clinical trials continue to explore new applications, particularly in renal failure and for reducing proteinuria in diabetic nephropathy. Translational studies suggest a potential benefit of ETB agonists in chemotherapy and neuroprotection. However, demonstrating clinical efficacy of combined inhibitors of the endothelin converting enzyme and neutral endopeptidase has proved elusive. Over 28 genetic modifications have been made to the ET system in mice through global or cell-specific knockouts, knock ins, or alterations in gene expression of endothelin ligands or their target receptors. These studies have identified key roles for the endothelin isoforms and new therapeutic targets in development, fluid-electrolyte homeostasis, and cardiovascular and neuronal function. For the future, novel pharmacological strategies are emerging via small molecule epigenetic modulators, biologicals such as ETB monoclonal antibodies and the potential of signaling pathway biased agonists and antagonists.

Vascular endothelial growth factor: an attractive target in the treatment of hypoxic/ischemic brain injury

Cerebral hypoxia or ischemia results in cell death and cerebral edema, as well as other cellular reactions such as angiogenesis and the reestablishment of functional microvasculature to promote recovery from brain injury. Vascular endothelial growth factor is expressed in the central nervous system after hypoxic/ischemic brain injury, and is involved in the process of brain repair via the regulation of angiogenesis, neurogenesis, neurite outgrowth, and cerebral edema, which all require vascular endothelial growth factor signaling. In this review, we focus on the role of the vascular endothelial growth factor signaling pathway in the response to hypoxic/ischemic brain injury, and discuss potential therapeutic interventions.

Evidence for biased agonists and antagonists at the endothelin receptors

Biased ligands represent a new strategy for the development of more effective and better tolerated drugs. To date there has been a paucity of research exploring the potential of ligands that exhibit either G protein or β-arrestin pathway selectivity at the endothelin receptors. Re-analysis of data may allow researchers to determine whether there is existing evidence that the endogenous ET peptides or currently available agonists and antagonists exhibit pathway bias in a particular physiological or disease setting and this is explored in the review. An alternative to molecules that bind at the orthosteric site of the ET receptors are cell penetrating peptides that interact with a segment of an intracellular loop of the receptor to modify signalling behaviour. One such peptide IC2B has been shown to have efficacy in a model of pulmonary arterial hypertension. Finally, understanding the molecular pathways that contribute to disease is critical to determining whether biased ligands will provide clinical benefit. The role of ET_A signalling in ovarian cancer has been delineated in some detail and this has led to the suggestion that the development of ET_A G protein biased agonists or β-arrestin biased antagonists should be explored.

Stimulation of endothelin B receptors by IRL-1620 decreases the progression of Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by severe cognitive impairment that ultimately leads to death. Endothelin (ET) and its receptors have been considered as therapeutic targets for AD. Recent studies in our lab have shown that stimulation of ETB receptors provide significant neuroprotection following Aβ1-40 administration. It is possible that IRL-1620 may be neuroprotective due to angiogenesis. However, the effect of IRL-1620 on neurovascular remodeling following Aβ1-40 administration has not been established. The purpose of this study was to determine the effect of stimulation of ETB receptors by IRL-1620 on vascular and neuronal growth factors after Aβ1-40 administration. Rats were treated with Aβ1-40 (day 1, 7 and 14) in the lateral cerebral ventricles using stereotaxically implanted cannula and received three intravenous injections of IRL-1620 (an ETB agonist), and/or BQ788 (an ETB antagonist) at 2-h interval on day 8; experiments were performed on day 15. Rats were sacrificed for estimation of brain ETB receptors, vascular endothelial growth factor (VEGF) and nerve growth factor (NGF) expression using immunofluorescence and Western blot. In the Morris swim task, amyloid-β (Aβ)-treated rats showed a significant (p<0.0001) impairment in spatial memory. Rats treated with IRL-1620 significantly (p<0.001) reduced the cognitive impairment induced by Aβ. BQ788 treatment completely blocked IRL-1620-induced improvement in cognitive impairment. IRL-1620 treatment enhanced the number of blood vessels labeled with VEGF compared to vehicle treatment. Additionally, cells showed increased (p<0.001) positive staining for NGF in IRL-1620-treated animals. ETB, VEGF and NGF protein expression significantly (p<0.001) increased in the brain of IRL-1620-treated rats as compared to vehicle. Pretreatment with BQ788 blocked the effects of IRL-1620, thus confirming the role of ETB receptors in the neurovascular remodeling actions of IRL-1620. Results of the present study demonstrate that IRL-1620 improves both acquisition (learning) and retention (memory) on the water maze task and enhances angiogenic and neurogenic remodeling. These findings indicate that the ETB receptor may be a novel therapeutic target for AD and other neurovascular degenerative disorders.

Endothelin ETA receptor antagonist reverses naloxone-precipitated opioid withdrawal in mice

Long-term use of opioids for pain management results in rapid development of tolerance and dependence leading to severe withdrawal symptoms. We have previously demonstrated that endothelin-A (ETA) receptor antagonists potentiate opioid analgesia and eliminate analgesic tolerance. This study was designed to investigate the involvement of central ET mechanisms in opioid withdrawal. The effect of intracerebroventricular administration of ETA receptor antagonist BQ123 on morphine and oxycodone withdrawal was determined in male Swiss Webster mice. Opioid tolerance was induced and withdrawal was precipitated by the opioid antagonist naloxone. Expression of ETA and ETB receptors, nerve growth factor (NGF), and vascular endothelial growth factor was determined in the brain using Western blotting. BQ123 pretreatment reversed hypothermia and weight loss during withdrawal. BQ123 also reduced wet shakes, rearing behavior, and jumping behavior. No changes in expression of vascular endothelial growth factor, ETA receptors, and ETB receptors were observed during withdrawal. NGF expression was unaffected in morphine withdrawal but significantly decreased during oxycodone withdrawal. A decrease in NGF expression in oxycodone- but not in morphine-treated mice could be due to mechanistic differences in oxycodone and morphine. It is concluded that ETA receptor antagonists attenuate opioid-induced withdrawal symptoms.

Ontogeny of endothelin receptors in the brain, heart, and kidneys of neonatal rats

BACKGROUND

Endothelin (ET) plays an important role in many physiological functions. It has been demonstrated that endogenous ET-1 concentration in the central nervous system (CNS) changes with age; however the ontogeny of ETA and ETB receptors in the brain, heart, and kidneys during postnatal development has not been studied.

METHODS

Brains, hearts and kidneys of rats at postnatal days 1, 7, 14 and 28 were evaluated for the expression of ETA and ETB receptors via Western blot. ETB receptors within the developing brain were further accessed via immunofluorescence.

RESULTS

The mean organ and body weights increased proportionally with advancing age demonstrating normal growth. The expression of ETA receptors in the brain, heart, and kidneys and ETB receptor expression in the heart and kidneys was similar in these rats at postnatal ages 1, 7, 14 and 28days. However, brain ETB receptor expression significantly (P<0.001) decreased by 72% on day 28 compared to the levels on postnatal day 1. Upon immunofluorescent analysis, the intensity of ETB staining in the cerebral cortex and subventricular zones of the developing rat brain decreased significantly from day 1 to day 7 (P<0.001) and from day 7 to day 14 (P<0.0001). There was no further decrease in ETB intensity noted in the cerebral cortex and subventricular zones between day 14 and day 28 of postnatal age. The intensity of ETB receptor staining within the cerebrovasculature, on the other hand, increased significantly (P<0.05) from days 1 and 7 to day 14.

CONCLUSIONS

These results demonstrate that expression of ETA receptors does not change with postnatal development. On the other hand ETB receptors in the cerebral cortex and subventricular zones of the brain decrease with age, while ETB receptors in the cerebrovasculature increase with age, implicating ETB receptor involvement in the structural maturity and development of the CNS.

Endothelin@25 - new agonists, antagonists, inhibitors and emerging research frontiers: IUPHAR Review 12

Since the discovery of endothelin (ET)-1 in 1988, the main components of the signalling pathway have become established, comprising three structurally similar endogenous 21-amino acid peptides, ET-1, ET-2 and ET-3, that activate two GPCRs, ETA and ETB . Our aim in this review is to highlight the recent progress in ET research. The ET-like domain peptide, corresponding to prepro-ET-193-166 , has been proposed to be co-synthesized and released with ET-1, to modulate the actions of the peptide. ET-1 remains the most potent vasoconstrictor in the human cardiovascular system with a particularly long-lasting action. To date, the major therapeutic strategy to block the unwanted actions of ET in disease, principally in pulmonary arterial hypertension, has been to use antagonists that are selective for the ETA receptor (ambrisentan) or that block both receptor subtypes (bosentan). Macitentan represents the next generation of antagonists, being more potent than bosentan, with longer receptor occupancy and it is converted to an active metabolite; properties contributing to greater pharmacodynamic and pharmacokinetic efficacy. A second strategy is now being more widely tested in clinical trials and uses combined inhibitors of ET-converting enzyme and neutral endopeptidase such as SLV306 (daglutril). A third strategy based on activating the ETB receptor, has led to the renaissance of the modified peptide agonist IRL1620 as a clinical candidate in delivering anti-tumour drugs and as a pharmacological tool to investigate experimental pathophysiological conditions. Finally, we discuss biased signalling, epigenetic regulation and targeting with monoclonal antibodies as prospective new areas for ET research.

Bosentan protects the spinal cord from ischemia reperfusion injury in rats through vascular endothelial growth factor receptors

STUDY DESIGN

Experimental study.

OBJECTIVES

To investigate whether Bosentan, an endothelin-A/-B dual receptor antagonist, could protect neurons after spinal cord ischemia reperfusion (SCIR) injury in rats and its underlying signaling pathway.

SETTING

Department of Neurosurgery, the Second Affiliated Hospital, Xi'an Jiaotong University School of Medicine, Xi'an, Shaanxi Province, China.

METHODS

Sprague-Dawley rats were randomly divided into two groups, saline group (IRS, n=48) and Bosentan group (IRB, 5 mg kg(-1), n=48). After ischemia for 1 h with occlusion of the infrarenal aorta, spinal cord were reperfused for 6h, 12h, 24h, 3d, 5d, and 7d separately. Enzyme-linked immunosorbent assay was used to detect vascular endothelial growth factor (VEGF) in serum. Immunohistochemistry was performed to detect protein expression of VEGF, VEGF receptor 1 (FLT-1) and VEGF receptor 2 (FLK-1). Gene expressions of VEGF and its receptors were evaluated using the quantitative reverse transcription polymerase chain reaction.

RESULTS

Compared with the IRS group, gene and protein expressions of VEGF, FLT-1 and FLK-1 were significantly increased (P<0.05), so was the concentration of VEGF in plasma (P<0.05). FLK-1 was expressed on spinal cord neurons.