In vitro blood-brain barrier permeability and cerebral endothelial cell uptake of the neuroprotective nitrone compound NXY-059 in normoxic, hypoxic and ischemic conditions

α-Phenyl-N-tert-Butylnitrone and Analogous α-Aryl-N-alkylnitrones as Neuroprotective Antioxidant Agents for Stroke

The recent advances in research on the use of the antioxidant and neuroprotective agent α-phenyl-N-tert-butylnitrone (PBN) for the therapy of stroke have been reviewed. The protective effect of PBN in the transient occlusion of the middle cerebral artery (MCAO) has been demonstrated, although there have been significant differences in the neuronal salvaging effect between PBN-treated and untreated animals, each set of data having quite large inter-experimental variation. In the transient forebrain ischemia model of gerbil, PBN reduces the mortality after ischemia and the neuronal damage in the hippocampal cornu ammonis 1 (CA1) area of the hippocumpus caused by ischemia. However, PBN fails to prevent postischemic CA1 damage in the rat. As for focal cerebral ischemia, PBN significantly reduces cerebral infarction and decreases neurological deficit after ischemia using a rat model of persistent MCAO in rats. Similarly, the antioxidant and neuroprotective capacity of a number of PBN-derived nitrones prepared in the author's laboratory have also been summarized here, showing their high potential therapeutic power to treat stroke.

Hearing loss drug discovery and medicinal chemistry: Current status, challenges, and opportunities

Hearing loss is a severe high unmet need condition affecting more than 1.5 billion people globally. There are no licensed medicines for the prevention, treatment or restoration of hearing. Prosthetic devices, such as hearing aids and cochlear implants, do not restore natural hearing and users struggle with speech in the presence of background noise. Hearing loss drug discovery is immature, and small molecule approaches include repurposing existing drugs, combination therapeutics, late-stage discovery optimisation of known chemotypes for identified molecular targets of interest, phenotypic tissue screening and high-throughput cell-based screening. Hearing loss drug discovery requires the integration of specialist therapeutic area biology and otology clinical expertise. Small molecule drug discovery projects in the global clinical portfolio for hearing loss are here collated and reviewed. An overview is provided of human hearing, inner ear anatomy, inner ear delivery, types of hearing loss and hearing measurement. Small molecule experimental drugs in clinical development for hearing loss are reviewed, including their underpinning biology, discovery strategy and activities, medicinal chemistry, calculated physicochemical properties, pharmacokinetics and clinical trial status. SwissADME BOILED-Egg permeability modelling is applied to the molecules reviewed, and these results are considered. Non-small molecule hearing loss assets in clinical development are briefly noted in this review. Future opportunities in hearing loss drug discovery for human genomics and targeted protein degradation are highlighted.

Preclinical Characterization of Antioxidant Quinolyl Nitrone QN23 as a New Candidate for the Treatment of Ischemic Stroke

Nitrones are encouraging drug candidates for the treatment of oxidative stress-driven diseases such as acute ischemic stroke (AIS). In a previous study, we found a promising quinolylnitrone, QN23, which exerted a neuroprotective effect in neuronal cell cultures subjected to oxygen–glucose deprivation and in experimental models of cerebral ischemia. In this paper, we update the biological and pharmacological characterization of QN23. We describe the suitability of intravenous administration of QN23 to induce neuroprotection in transitory four-vessel occlusion (4VO) and middle cerebral artery occlusion (tMCAO) experimental models of brain ischemia by assessing neuronal death, apoptosis induction, and infarct area, as well as neurofunctional outcomes. QN23 significantly decreased the neuronal death and apoptosis induced by the ischemic episode in a dose-dependent manner and showed a therapeutic effect when administered up to 3 h after post-ischemic reperfusion onset, effects that remained 11 weeks after the ischemic episode. In addition, QN23 significantly reduced infarct volume, thus recovering the motor function in a tMCAO model. Remarkably, we assessed the antioxidant activity of QN23 in vivo using dihydroethidium as a molecular probe for radical species. Finally, we describe QN23 pharmacokinetic parameters. All these results pointing to QN23 as an interesting and promising preclinical candidate for the treatment of AIS.

PBN protects NP cells from AAPH-induced degenerative changes by inhibiting the ERK1/2 pathway

Aim: Intervertebral disc (IVD) degeneration (IDD) is one of the main causes for spinal degenerative diseases, such as disk herniation, spinal canal stenosis, and spinal deformities. Growing evidence has highlighted the contribution of oxidative stress in pathogenesis of IDD, and antioxidant treatment is thus considered to be a promising therapeutic strategy for IDD. The aim of this study was to investigate whether N-tert-butyl-α-phenylnitrone (PBN), a free radical scavenger, could attenuate the pathological changes of IDD by alleviating oxidative stress.Materials and Methods: Nucleus pulposus (NP) cells were isolated from rabbit lumbar disks. MTT assay, real-time PCR and western blotting were employed to evaluate the effects of PBN on oxidative damages induced by 2,2'-azobis (2-amidinopropane) dihydrochloride (AAPH) in NP cells.Results: AAPH induced oxidative stress and the subsequent degenerative changes in NP cells via the ERK/MAPK pathway. On the contrary, the oxidative stress induced by AAPH was significantly ameliorated by PBN. Moreover, PBN also attenuated AAPH-induced expression of matrix degradation proteases and apoptosis. PBN suppresses AAPH-induced activation of ERK/MAPK pathway, which may be the underlying mechanism for the protective effects of PBN.Conclusions: Our study for the first time identified a novel role and mechanism for PBN in protecting the IVD against oxidative stress, matrix catabolism and apoptosis, which may have implications for its further application in combating IVD degenerative diseases.Abbreviations: AAPH: 2,2'-azobis(2-methylpropanimidamidine) dihydrochloride; ADAMTS: a disintegrin and metalloproteinase with thrombospondin motifs; AF: annulus fibrosus; CEP: cartilage endplate; DCF: 2'7'-dichlorofluorescein; IDD: intervertebral disc degeneration; IVD: intervertebral disc; LPS: lipopolysaccharide; MMP: matrix metalloproteinase; MTT: methyl-thiazolyl-tetrazolium; NP: nucleus pulposus; PBN: N-tert-butyl-alfa-phenylnitrone; PGs: proteoglycans; ROS: reactive oxygen species; SDS: sodium dodecyl sulfate.

Cytoprotective effects of antioxidant supplementation on mesenchymal stem cell therapy

Mesenchymal stem cells (MSCs) are earmarked as perfect candidates for cell therapy and tissue engineering due to their capacity to differentiate into different cell types. However, their potential for application in regenerative medicine declines when the levels of the reactive oxygen and nitrogen species (RONS) increase from the physiological levels, a phenomenon which is at least inevitable in ex vivo cultures and air-exposed damaged tissues. Increased levels of RONS can alter the patterns of osteogenic and adipogenic differentiation and inhibit proliferation, as well. Besides, oxidative stress enhances senescence and cell death, thus lowering the success rates of the MSC engraftment. Hence, in this review, we have selected some representatives of antioxidants and newly emerged nano antioxidants in three main categories, including chemical compounds, biometabolites, and protein precursors/proteins, which are proved to be effective in the treatment of MSCs. We will focus on how antioxidants can be applied to optimize the clinical usage of the MSCs and their associated signaling pathways. We have also reviewed several paralleled properties of some antioxidants and nano antioxidants which can be simultaneously used in real-time imaging, scaffolding techniques, and other applications in addition to their primary antioxidative function.

NXY-059, a Failed Stroke Neuroprotectant, Offers No Protection to Stem Cell-Derived Human Neurons

BACKGROUND

Developing new medicines is a complex process where understanding the reasons for both failure and success takes us forward. One gap in our understanding of most candidate stroke drugs before clinical trial is whether they have a protective effect on human tissues. NXY-059 is a spin-trap reagent hypothesized to have activity against the damaging oxidative biology which accompanies ischemic stroke. Re-examination of the preclinical in vivo dataset for this agent in the wake of the failed SAINT-II RCT highlighted the presence of a range of biases leading to overestimation of the magnitude of NXY-059's effects in laboratory animals. Therefore, NXY-059 seemed an ideal candidate to evaluate in human neural tissues to determine whether human tissue testing might improve screening efficiency.

MATERIALS AND METHODS

The aim of this randomized and blinded study was to assess the effects of NXY-059 on human stem cell-derived neurons in the presence of ischemia-like injury induced by oxygen glucose deprivation or oxidative stress induced by hydrogen peroxide or sodium nitroprusside.

RESULTS

In MTT assays of cell survival, lactate dehydrogenase assays of total cell death and terminal deoxynucleotidyl transferase dUTP nick end labeling staining of apoptotic-like cell death, NXY-059 at concentrations ranging from 1 µm to 1 mm was completely without activity. Conversely an antioxidant cocktail comprising 100 µm each of ascorbate, reduced glutathione, and dithiothreitol used as a positive control provided marked neuronal protection in these assays.

CONCLUSION

These findings support our hypothesis that stroke drug screening in human neural tissues will be of value and provides an explanation for the failure of NXY-059 as a human stroke drug.

How is edaravone effective against acute ischemic stroke and amyotrophic lateral sclerosis?

Edaravone is a low-molecular-weight antioxidant drug targeting peroxyl radicals among many types of reactive oxygen species. Because of its amphiphilicity, it scavenges both lipid- and water-soluble peroxyl radicals by donating an electron to the radical. Thus, it inhibits the oxidation of lipids by scavenging chain-initiating water-soluble peroxyl radicals and chain-carrying lipid peroxyl radicals. In 2001, it was approved in Japan as a drug to treat acute-phase cerebral infarction, and then in 2015 it was approved for amyotrophic lateral sclerosis (ALS). In 2017, the U.S. Food and Drug Administration also approved edaravone for treatment of patients with ALS. Its mechanism of action was inferred to be scavenging of peroxynitrite. In this review, we focus on the radical-scavenging characteristics of edaravone in comparison with some other antioxidants that have been studied in clinical trials, and we summarize its pharmacological action and clinical efficacy in patients with acute cerebral infarction and ALS.

NXY-059: Review of Neuroprotective Potential for Acute Stroke

Objective:

To review available literature on the pharmacology, pharmacokinetics, efficacy, and tolerability of NXY-059, an Investigational agent with a potential role in the treatment of acute stroke.

Data Sources:

Information was obtained from a MEDLINE search (1966–February 2006) of English-language literature utilizing the following search terms: NXY-059, cerovive, nitrones, neuroprotection, free radical trapper, and secondary neurologic injury.

Study Selection and Data Extraction:

Data from animal and human trials were evaluated to summarize the mechanism of action, efficacy, and safety of NXY-059. All published and unpublished trials and abstracts citing NXY-059 were selected.

Data Synthesis:

NXY-059 is an intravenous, nitrone-based, free radical trapping agent in Phase III trials for treatment of acute stroke. In various animal models, NXY-059 has shown reductions in infarct volume and neurologic deficits. Pharmacokinetic studies indicate that NXY-059 displays a predictable pharmacokinetic profile and primarily undergoes renal elimination. Results from 2 Phase II clinical trials showed favorable results for the safety and tolerability of the drug. A recent analysis of one of the Phase III trials showed a statistically significant reduction in the primary outcome of disability after acute stroke in patients who received NXY-059 compared with placebo.

Conclusions:

NXY-059 is a novel agent undergoing worldwide Phase III trials. Initial safety and efficacy data have not revealed any serious adverse events requiring special monitoring and/or precautions, with the exception of drug accumulation in patients with renal insufficiency. The potential benefit of this agent can change the current management algorithm for acute stroke and may represent significant advancement for the care of these patients.

Melatonin and Nitrones As Potential Therapeutic Agents for Stroke

Stroke is a disease of aging affecting millions of people worldwide, and recombinant tissue-type plasminogen activator (r-tPA) is the only treatment approved. However, r-tPA has a low therapeutic window and secondary effects which limit its beneficial outcome, urging thus the search for new more efficient therapies. Among them, neuroprotection based on melatonin or nitrones, as free radical traps, have arisen as drug candidates due to their strong antioxidant power. In this Perspective article, an update on the specific results of the melatonin and several new nitrones are presented.

Expanding the concept of neuroprotection for acute ischemic stroke: The pivotal roles of reperfusion and the collateral circulation

This review surveys the efforts taken to achieve clinically efficacious protection of the ischemic brain and underscores the necessity of expanding our purview to include the essential role of cerebral perfusion and the collateral circulation. We consider the development of quantitative strategies to measure cerebral perfusion at the regional and local levels and the application of these methods to elucidate flow-related thresholds of ischemic viability and to characterize the ischemic penumbra. We stress that the modern concept of neuroprotection must consider perfusion, the necessary substrate upon which ischemic brain survival depends. We survey the major mechanistic approaches to neuroprotection and review clinical neuroprotection trials, focusing on those phase 3 multicenter clinical trials for acute ischemic stroke that have been completed or terminated. We review the evolution of thrombolytic therapies; consider the lessons learned from the initial, negative multicenter trials of endovascular therapy; and emphasize the highly successful positive trials that have finally established a clinical role for endovascular clot removal. As these studies point to the brain's collateral circulation as key to successful reperfusion, we next review the anatomy and pathophysiology of collateral perfusion as it relates to ischemic infarction, as well as the molecular and genetic influences on collateral development. We discuss the current MR and CT-based diagnostic methods for assessing the collateral circulation and the prognostic significance of collaterals in ischemic stroke, and we consider past and possible future therapeutic directions.

ST6GALNAC5 Expression Decreases the Interactions between Breast Cancer Cells and the Human Blood-Brain Barrier

The ST6GALNAC5 gene that encodes an α2,6-sialyltransferase involved in the biosynthesis of α-series gangliosides, was previously identified as one of the genes that mediate breast cancer metastasis to the brain. We have shown that the expression of ST6GALNAC5 in MDA-MB-231 breast cancer cells resulted in the expression of G_D1α ganglioside at the cell surface. By using a human blood-brain barrier in vitro model recently developed, consisting in CD34⁺ derived endothelial cells co-cultivated with pericytes, we show that ST6GALNAC5 expression decreased the interactions between the breast cancer cells and the human blood-brain barrier.

Metalloporphyrins as therapeutic catalytic oxidoreductants in central nervous system disorders

SIGNIFICANCE

Metalloporphyrins, characterized by a redox-active transitional metal (Mn or Fe) coordinated to a cyclic porphyrin core ligand, mitigate oxidative/nitrosative stress in biological systems. Side-chain substitutions tune redox properties of metalloporphyrins to act as potent superoxide dismutase mimics, peroxynitrite decomposition catalysts, and redox regulators of transcription factor function. With oxidative/nitrosative stress central to pathogenesis of CNS injury, metalloporphyrins offer unique pharmacologic activity to improve the course of disease.

RECENT ADVANCES

Metalloporphyrins are efficacious in models of amyotrophic lateral sclerosis, Alzheimer's disease, epilepsy, neuropathic pain, opioid tolerance, Parkinson's disease, spinal cord injury, and stroke and have proved to be useful tools in defining roles of superoxide, nitric oxide, and peroxynitrite in disease progression. The most substantive recent advance has been the synthesis of lipophilic metalloporphyrins offering improved blood-brain barrier penetration to allow intravenous, subcutaneous, or oral treatment.

CRITICAL ISSUES

Insufficient preclinical data have accumulated to enable clinical development of metalloporphyrins for any single indication. An improved definition of mechanisms of action will facilitate preclinical modeling to define and validate optimal dosing strategies to enable appropriate clinical trial design. Due to previous failures of "antioxidants" in clinical trials, with most having markedly less biologic activity and bioavailability than current-generation metalloporphyrins, a stigma against antioxidants has discouraged the development of metalloporphyrins as CNS therapeutics, despite the consistent definition of efficacy in a wide array of CNS disorders.

FUTURE DIRECTIONS

Further definition of the metalloporphyrin mechanism of action, side-by-side comparison with "failed" antioxidants, and intense effort to optimize therapeutic dosing strategies are required to inform and encourage clinical trial design.

Current preclinical studies on neuroinflammation and changes in blood-brain barrier integrity by MDMA and methamphetamine

The blood-brain barrier (BBB) is essential in the maintenance of brain homeostasis both by preserving normal brain functioning and also by protecting the brain from exposure to a range of potentially harmful substances. This review presents some of the evidence of BBB disruption following exposure to the substituted amphetamines 3,4-methylenedioxymethamphetamine (MDMA, 'ecstasy') and methamphetamine (METH), two drugs of abuse which are widely consumed recreationally by younger sectors of the population. Both MDMA and METH have been shown to produce disruption of the BBB as reflected by IgG extravasation and Evans Blue leakage. In particular, METH decreases the expression of basal lamina proteins associated with an increase in matrix metalloproteinase activity. These changes in BBB integrity appear to be related to MDMA-induced activation of the mitogen-activated protein kinase (MAPK) JNK1/2. The consequences of the disruption in the BBB by these two drugs remain to be established, but there is evidence in the literature that, at least in the case of METH, increased matrix metalloproteinase (MMP) activity may be related to increased behavioural sensitization and reward perhaps because of the modification of the passage of the drug into the CNS. In addition, the high incidence of AIDS-related neurologic disease in METH users may also be related to increased entry into the brain of virally derived neurotoxic products. This article is part of the Special Issue entitled 'CNS Stimulants'.

Steps to translate preconditioning from basic research to the clinic

Efforts to treat cardiovascular and cerebrovascular diseases often focus on the mitigation of ischemia-reperfusion (I/R) injury. Many treatments or "preconditioners" are known to provide substantial protection against the I/R injury when administered prior to the event. Brief periods of ischemia itself have been validated as a means to achieve neuroprotection in many experimental disease settings, in multiple organ systems, and in multiple species suggesting a common pathway leading to tolerance. In addition, pharmacological agents that act as potent preconditioners have been described. Experimental induction of neuroprotection using these various preconditioning paradigms has provided a unique window into the brain's endogenous protective mechanisms. Moreover, preconditioning agents themselves hold significant promise as clinical-stage therapies for prevention of I/R injury. The aim of this article is to explore several key steps involved in the preclinical validation of preconditioning agents prior to the conduct of clinical studies in humans. Drug development is difficult, expensive and relies on multi-factorial analysis of data from diverse disciplines. Importantly, there is no single path for the preclinical development of a novel therapeutic and no proven strategy to ensure success in clinical translation. Rather, the conduct of a diverse array of robust preclinical studies reduces the risk of clinical failure by varying degrees depending upon the relevance of preclinical models and drug pharmacology to humans. A strong sense of urgency and high tolerance of failure are often required to achieve success in the development of novel treatment paradigms for complex human conditions.

Inhibition of ROS-induced apoptosis in endothelial cells by nitrone spin traps via induction of phase II enzymes and suppression of mitochondria-dependent pro-apoptotic signaling

Oxidative stress is the main etiological factor behind the pathogenesis of various diseases including inflammation, cancer, cardiovascular and neurodegenerative disorders. Due to the spin trapping abilities and various pharmacological properties of nitrones, their application as therapeutic agent has been gaining attention. Though the antioxidant properties of the nitrones are well known, the mechanism by which they modulate the cellular defense machinery against oxidative stress is not well investigated and requires further elucidation. Here, we have investigated the mechanisms of cytoprotection of the nitrone spin traps against oxidative stress in bovine aortic endothelial cells (BAEC). Cytoprotective properties of both the cyclic nitrone 5,5-dimethyl-pyrroline N-oxide (DMPO) and linear nitrone α-phenyl N-tert-butyl nitrone (PBN) against H₂O₂-induced cytotoxicity were investigated. Preincubation of BAEC with PBN or DMPO resulted in the inhibition of H₂O₂-mediated cytotoxicity and apoptosis. Nitrone-treatment resulted in the induction and restoration of phase II antioxidant enzymes via nuclear translocation of NF-E2-related factor 2 (Nrf-2) in oxidatively-challenged cells. Furthermore, the nitrones were found to inhibit the mitochondrial depolarization and subsequent activation of caspase-3 induced by H₂O₂. Significant down-regulation of the pro-apoptotic proteins p53 and Bax, and up-regulation of the anti-apoptotic proteins Bcl-2 and p-Bad were observed when the cells were preincubated with the nitrones prior to H₂O₂-treatment. It was also observed that Nrf-2 silencing completely abolished the protective effects of nitrones. Hence, these findings suggest that nitrones confer protection to the endothelial cells against oxidative stress by modulating phase II antioxidant enzymes and subsequently inhibiting mitochondria-dependent apoptotic cascade.

Anti-cancer activity of nitrones and observations on mechanism of action

The nitrone compound PBN, α-phenyl-tert-butylnitrone, and closely related nitrones have anti-cancer activity in several experimental cancer models. The three experimental models most extensively studied include A) the rat choline deficiency liver cancer model, B) the rat C6 glioma model and C) the mouse APC(Min/+) colon cancer model. The two PBN-nitrones mostly studied are PBN and a PBN derivative 2,4-disulfophenyl-tert-butylnitrone, referred as OKN-007. OKN-007 is a proprietary compound that has had extensive commercial development (designated as NXY-059) for another indication, acute ischemic stroke, and after extensive clinical studies was shown to lack efficacy for this indication but was shown to be very safe for human use. This compound administered orally in the rat glioma model has potent activity in treating fully formed gliomas. In this report observations made on the PBN-nitrones in experimental cancer models will be summarized. In addition the experimental results will be discussed in the general framework of the properties of the compounds with a view to try to understand the mechanistic basis of how the PBN-nitrones act as anti-cancer agents. Possible mechanisms related to the suppression of NO production, S-nitrosylation of critical proteins and inhibition of NF-κB activation are discussed.

Experimental models for assaying microvascular endothelial cell pathophysiology in stroke

It is important to understand the molecular mechanisms underlying neuron death following stroke in order to develop effective neuroprotective strategies. Since studies on human stroke are extremely limited due to the difficulty in collecting post-mortem tissue at different time points after the onset of stroke, brain ischaemia research focuses on information derived from in-vitro models of neuronal death through ischaemic injury [1]. This review aims to provide an update on the different in-vitro stroke models with brain microvascular endothelial cells that are currently being used. These models provide a physiologically relevant tool to screen potential neuroprotective drugs in stroke and to study the molecular mechanisms involved in brain ischaemia.

Cerebral effects of hyperglycemia in experimental cardiac arrest

OBJECTIVE

To investigate the effects of cardiac arrest on cerebral perfusion and oxidative stress during hyperglycemia and normoglycemia.

DESIGN

Experimental animal model.

SETTING

University laboratory.

SUBJECTS

Triple-breed pigs (weight, 22-27 kg).

INTERVENTIONS

Thirty-three pigs were randomized and clamped at blood glucose levels of 8.5-10 mM (high) or 4-5.5 mM (normal) and thereafter subjected to alternating current-induced 12-min cardiac arrest followed by 8 mins of cardiopulmonary resuscitation and direct-current shock to restore spontaneous circulation.

MEASUREMENTS AND MAIN RESULTS

Hemodynamics, regional near-infrared light spectroscopy, regional venous Hbo2, and biochemical markers (Protein S100beta, troponin I, F2-isoprostanes reflecting oxidative stress and inflammation) were monitored and/or sampled throughout an observation period of 4 hrs. No significant differences were seen in hemodynamics or biochemical profile. The cerebral oxygenation by means of regional near-infrared light spectroscopy was higher in the hyperglycemic (H) than in the normal (N) group after restoration of spontaneous circulation (p < .05). However, tendencies toward increased protein S100beta and 15-keto-dihydro-prostaglandin F2alpha were observed in the H group but were not statistically significant.

CONCLUSIONS

The responses to 12-min cardiac arrest and cardiopulmonary resuscitation share large similarities during hyperglycemia and normoglycemia. The higher cerebral tissue oxygenation observed in the hyperglycemia needs to be confirmed and the phenomenon needs to be addressed in future studies.

Nitrones as therapeutics

Nitrones have the general chemical formula X-CH=NO-Y. They were first used to trap free radicals in chemical systems and then subsequently in biochemical systems. More recently several nitrones, including alpha-phenyl-tert-butylnitrone (PBN), have been shown to have potent biological activity in many experimental animal models. Many diseases of aging, including stroke, cancer development, Parkinson disease, and Alzheimer disease, are known to have enhanced levels of free radicals and oxidative stress. Some derivatives of PBN are significantly more potent than PBN and have undergone extensive commercial development for stroke. Recent research has shown that PBN-related nitrones also have anti-cancer activity in several experimental cancer models and have potential as therapeutics in some cancers. Also, in recent observations nitrones have been shown to act synergistically in combination with antioxidants in the prevention of acute acoustic-noise-induced hearing loss. The mechanistic basis of the potent biological activity of PBN-related nitrones is not known. Even though PBN-related nitrones do decrease oxidative stress and oxidative damage, their potent biological anti-inflammatory activity and their ability to alter cellular signaling processes cannot readily be explained by conventional notions of free radical trapping biochemistry. This review is focused on our studies and others in which the use of selected nitrones as novel therapeutics has been evaluated in experimental models in the context of free radical biochemical and cellular processes considered important in pathologic conditions and age-related diseases.

Neonatal rat hypoxia-ischemia: Effect of the anti-oxidant mitoquinol, and S-PBN

BACKGROUND

The production of oxygen free radicals after perinatal hypoxia-ischemia is thought to play a critical role in the pathogenesis of the brain injury. Administration of anti-oxidants may thus be neuroprotective. The aim of the present study was to investigate the effect of a mitochondria-targeted anti-oxidant mitoquinol (mitoQ) administered in the form of the prodrug mitoquinone, and an extracellular anti-oxidant N-tert-butyl-(2-sulfophenyl)-nitrone (S-PBN; Aldrich, St Louis, MO, USA), on neuronal survival in the rat striatum after acute perinatal hypoxia-ischemia.

METHODS

Mitoquinone at 17 micromol/L (n = 6) or 51 micromol/L (n = 6), or its diluent (n = 12), was continuously infused over 3 days into the right striatum of Sprague-Dawley rats. Infusion was via an Alzet micro-osmotic pump (Alza, Los Angeles, CA, USA), stereotaxically implanted on postnatal day (PN) 7 under anesthesia. In another experiment, S-PBN (100 mg/kg) (n = 8) or its diluent (n = 8) was administered in six s.c. injections every 12 h from the evening of PN7. Hypoxia-ischemia was induced on PN8 by right common carotid artery ligation under anesthesia, followed 2.5 h later by exposure to 8% oxygen for 1.5 h. On PN14 the pups were euthanased and 40 microm serial sections were cut through the entire striatum. The total number of medium-spiny neurons within the right striatum was stereologically determined using the optical disector/Cavalieri method.

RESULTS

No significant difference was seen in the total number of striatal medium-spiny neurons between the 17 micromol/L or 51 micromol/L mitoQ-treated pups and their respective diluent-treated controls. No significant difference was seen in the total number of striatal medium-spiny neurons between the S-PBN-treated and diluent-treated pups.

CONCLUSION

Solely targeting mitochondrial oxidants with mitoQ, or extracellular oxidants with S-PBN, is not protective for striatal medium-spiny neurons after perinatal hypoxia-ischemia.

Development and efficacy of NXY-059 for the treatment of acute ischemic stroke

NXY-059 is a neuroprotective compound that prevents ischemic damage by trapping free radicals. Preclinical animal stroke models demonstrated that the agent is able to reduce histological damage and improve behavioral outcome. Phase II studies showed that NXY-059 administration does not cause any serious adverse events and it is well tolerated by both healthy volunteers and stroke patients. The first Phase III trial indicated that NXY-059 treatment results in a small, but significant improvement of the primary neurological outcome, as measured by the modified Rankin scale. However, NXY-059 did not improve coprimary outcomes assessed by the NIH Stroke Scale (NIHSS) and the Barthel index. For patients receiving thrombolysis together with NXY-059, there was an associated reduction of symptomatic intracerebral hemorrhage. Although NXY-059 showed positive results in this Phase III study, a larger scale Phase III study revealed that the efficacy of NXY-059 is not better than placebo in treating acute stroke patients. Hence, NXY-059 failed to materialize as an effective acute stroke treatment. This article summarizes the path of the drug from bench to bedside and points out what possibly went wrong. How such an outcome can be prevented in future trials for neuroprotective agents will also be discussed.

Clinical pharmacological issues in the development of acute stroke therapies

The demonstration of the ischaemic penumbra in animal models and the effectiveness of reperfusion therapy in humans led to considerable optimism for neuroprotection in acute stroke. Initial experience with failure of phase II and III trials led to the STAIR recommendations for pre-clinical and clinical studies. Review of pre-clinical studies suggests that selection of agents for clinical development may not have been optimal. The neuroprotective agent NXY-059 fulfilled pre-clinical and many clinical STAIR criteria but a second large phase III study failed to demonstrate any benefit. Many of the STAIR criteria have not been fulfilled in the development of recent neuroprotective agents. Other issues not addressed include the use of animal models more reflective of older stroke patients with physiological derangement, demonstration of drug distribution to the proposed site of action in humans, selection of patients with salvageable tissue, achieving very early treatment, refinement of measurement of neurological impairment and disability, and physiological optimization in proof of concept human studies. Increasing the number and quality of clinical centres undertaking acute stroke research, use of surrogate imaging markers and adaptive dose designs in phase II trials could improve the likelihood of identifying an effective neuroprotective. Neuroprotection in acute stroke remains a significant challenge but has not been clearly shown to be ineffective. Given the profound burden of stroke and limited applicability of reperfusion to currently at best 10% patients, further proof of concept studies of neuroprotection remain indicated with careful review of pre-clinical data and more rigorous phase II trial design.

Neonatal rat hypoxia-ischemia: long-term rescue of striatal neurons and motor skills by combined antioxidant-hypothermia treatment

Perinatal hypoxia-ischemia can cause long-term neurological and behavioral disability. Recent multicenter clinical trials suggest that moderate hypothermia, within 6 h of birth, offers significant yet incomplete protection. We investigated the effect of combined treatment with the antioxidant N-tert-butyl-(2-sulfophenyl)-nitrone (S-PBN) and moderate hypothermia on long-term neuronal injury and behavioral disability. S-PBN or its diluent was administered 12-hourly to rats from postnatal day (PN) 7 to 10. On PN8, hypoxia-ischemia was induced. Immediately post-hypoxia, additional S-PBN and 6 h of moderate hypothermia or additional diluent and 6 h of normothermia were administered. At 1 week, and at 11 weeks, after hypoxia-ischemia, the absolute number of surviving medium-spiny neurons was measured in the coded right striatum. In a separate experiment, skilled forepaw ability was investigated in coded 9- to 11-week-old rats. Normal, uninjured animals were also tested for motor skills at 9- to 11-weeks-of-age. The combination of S-PBN and moderate hypothermia provided statistically significant short- and long-term protection of the striatal medium-spiny neurons to normal control levels. This combinatorial treatment also preserved fine motor skills to normal control levels. The impressive histological and functional preservation suggests that S-PBN and moderate hypothermia is a safe and attractive combination therapy for perinatal hypoxia-ischemia.

Neuroprotection for ischemic stroke: past, present and future

Neuroprotection for ischemic stroke refers to strategies, applied singly or in combination, that antagonize the injurious biochemical and molecular events that eventuate in irreversible ischemic injury. There has been a recent explosion of interest in this field, with over 1000 experimental papers and over 400 clinical articles appearing within the past 6 years. These studies, in turn, are the outgrowth of three decades of investigative work to define the multiple mechanisms and mediators of ischemic brain injury, which constitute potential targets of neuroprotection. Rigorously conducted experimental studies in animal models of brain ischemia provide incontrovertible proof-of-principle that high-grade protection of the ischemic brain is an achievable goal. Nonetheless, many agents have been brought to clinical trial without a sufficiently compelling evidence-based pre-clinical foundation. At this writing, around 160 clinical trials of neuroprotection for ischemic stroke have been initiated. Of the approximately 120 completed trials, two-thirds were smaller early-phase safety-feasibility studies. The remaining one-third were typically larger (>200 subjects) phase II or III trials, but, disappointingly, only fewer than one-half of these administered neuroprotective therapy within the 4-6h therapeutic window within which efficacious neuroprotection is considered to be achievable. This fact alone helps to account for the abundance of "failed" trials. This review presents a close survey of the most extensively evaluated neuroprotective agents and classes and considers both the strengths and weakness of the pre-clinical evidence as well as the results and shortcomings of the clinical trials themselves. Among the agent-classes considered are calcium channel blockers; glutamate antagonists; GABA agonists; antioxidants/radical scavengers; phospholipid precursor; nitric oxide signal-transduction down-regulator; leukocyte inhibitors; hemodilution; and a miscellany of other agents. Among promising ongoing efforts, therapeutic hypothermia, high-dose human albumin therapy, and hyperacute magnesium therapy are considered in detail. The potential of combination therapies is highlighted. Issues of clinical-trial funding, the need for improved translational strategies and clinical-trial design, and "thinking outside the box" are emphasized.

Pharmacological approaches to acute ischaemic stroke: reperfusion certainly, neuroprotection possibly

Stroke is a major cause of both death and disability. However, there are no pharmacological treatments used in most countries other than recombinant tissue plasminogen activator, a thrombolytic, and this is only used in about 4% of patients presenting after an acute ischaemic stroke. One novel thrombolytic (desmoteplase) has just been reported to have failed in a Phase IIb/III trial, but other thrombolytics and reperfusion agents remain in development. The picture with neuroprotectant agents, that is compounds that act to preserve neurones following an acute cerebral ischaemic insult, is even more bleak. Despite the development of over 1,000 compounds, many proving effective in animal models of stroke, none has demonstrated efficacy in patients in the over 100 clinical trials conducted. This includes NXY-059, which was developed in accordance with the guidelines proposed by an academic-industry roundtable group (STAIR). This review examines the available data on compounds currently in development. It also proposes that the failure of translation between efficacy in preclinical models and patients is likely to terminate most current neuroprotective drug development. It is suggested that animal models must be made more representative of the patient condition (with other co-morbid conditions) and suggests that since stroke is primarily a cardiovascular disease with a neurological outcome, more research on the neurovascular unit would be valuable. New approaches on neuroinflammation, neurorestoration and neurorepair are also likely to gain prominence in the search for new drugs to treat this major clinical problem.

The nitrone disodium 2,4-sulphophenyl-N-tert-butylnitrone is without cytoprotective effect on sodium nitroprusside-induced cell death in N1E-115 neuroblastoma cells in vitro

Disodium 2,4-sulphophenyl-N-tert-butylnitrone (NXY-059) is a novel free radical-trapping compound that is neuroprotective in both rodent and primate models of acute ischaemic stroke. Neuroprotection in vitro by NXY-059 has not been reported previously, and we have now investigated whether such an effect can be detected using a simple cell culture model of neurotoxicity. Neuron-like cells of the neuroblastoma-derived clonal cell line N1E-115 were exposed to the free radical-generating agent sodium nitroprusside (SNP), which produced a concentration-dependent reduction in mitochondrial complex II activity 24 h later (EC(50) approximately 100 micromolar). Cell death induced by SNP (100 micromolar), assessed either by an increased proportion of apoptotic nuclear morphology or by mitochondrial complex II activity, was inhibited by a cocktail of known antioxidants (ascorbate, reduced glutathione, and dithiothreitol, all at 100 micromolar) but not by NXY-059 at a concentration known to be neuroprotective in vivo (300 micromolar). Disodium 2,4-sulphophenyl-N-tert-butylnitrone was also without effect on H(2)O(2)-mediated cytotoxicity. These results support recent data suggesting that in vivo NXY-059 probably acts at the neurovascular unit rather than at an intracellular site as a neuroprotective agent.

Prevention of in vitro and in vivo acute ischemic neuronal damage by (2S)-1-(4-amino-2,3,5-trimethylphenoxy)-3-{4-[4-(4-fluorobenzyl) phenyl]-1-piperazinyl}-2-propanol dimethanesulfonate (SUN N8075), a novel neuroprotective agent with antioxidant properties

(2S)-1-(4-Amino-2,3,5-trimethylphenoxy)-3-{4-[4-(4-fluorobenzyl) phenyl]-1-piperazinyl}-2-propanol dimethanesulfonate (SUN N8075) is a novel antioxidant with neuroprotective properties. We examined whether SUN N8075 inhibited the neuronal damage resulting from permanent focal cerebral ischemia, and examined its neuroprotective properties in vivo and in vitro mechanism. Focal cerebral ischemia was induced by permanent middle cerebral artery occlusion in mice, and the resulting infarction, brain swelling, and neurological deficits were evaluated after 24 h or 72 h. Brain damage was assessed histochemically using terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) staining and antibody recognizing 4-hydroxynonenal histidine adduct (4-HNE). In the in vitro study, we examined the effects of SUN N8075 on 1) lipid peroxidation in mouse brain homogenates and 2) cell viability and caspase-3 protease activity under a hypoxic insult or FeSO(4) in rat cultured cerebrocortical neurons. SUN N8075 administered either 10 min before or at 1 h after the occlusion reduced both infarction size and neurological deficits. SUN N8075 reduced brain swelling when administered 10 min before, 1 h, or 3 h after occlusion. Furthermore, only pretreatment (administered 10 min before) decreased infarct volume and brain swelling at 72 h after middle cerebral artery occlusion. SUN N8075 reduced the number of TUNEL-positive cells and decreased the level of oxidative damage, as assessed by immunopositive staining to 4-HNE. SUN N8075 inhibited lipid peroxidation, leakage of lactate dehydrogenase, caspase-3 activation induced by in vitro hypoxia, and the neuronal damage induced by in vitro FeSO(4) exposure. These findings indicate that SUN N8075 has neuroprotective effects against acute ischemic neuronal damage in mice and may prove promising as a therapeutic drug for stroke.

The role of permeability in drug ADME/PK, interactions and toxicity--presentation of a permeability-based classification system (PCS) for prediction of ADME/PK in humans

PURPOSE

The objective was to establish in vitro passive permeability (Pe) vs in vivo fraction absorbed (fa)-relationships for each passage through the human intestine, liver, renal tubuli and brain, and develop a Pe-based ADME/PK classification system (PCS).

MATERIALS AND METHODS

Pe- and intestinal fa-data were taken from an available data set. Hepatic fa was calculated based on extraction ratios of the unbound fraction of drugs (with support from animal in vivo uptake data). Renal fa (reabsorption) was estimated using renal pharmacokinetic data, and brain fa was predicted using animal in vitro and in vivo brain Pe-data. Hepatic and intestinal fa-data were used to predict bile excretion potential.

RESULTS

Relationships were established, including predicted curves for bile excretion potential and minimum oral bioavailability, and a 4-Class PCS was developed: I (very high Pe; elimination mainly by metabolism); II (high Pe) and III (intermediate Pe and incomplete fa); IV (low Pe and fa). The system enables assessment of potential drug-drug transport interactions, and drug and metabolite organ trapping.

CONCLUSIONS

The PCS and high quality Pe-data (with and without active transport) are believed to be useful for predictions and understanding of ADME/PK, elimination routes, and potential interactions and organ trapping/toxicity in humans.

Life After Cerovive

The SAINT II Trial, a large randomized multicenter clinical trial of the putative neuroprotectant, NXY-059, failed to demonstrate a treatment benefit in acute ischemic stroke. The further development of this agent was suspended. The implications of this outcome are considered from several perspectives, including: (1) the marginally positive antecedent trial, SAINT I, and the critical commentary stimulated by it, which called attention to its interpretively challenging primary outcome measure—a shift in the full-scale modified Rankin scale score—and to other statistical shortcomings; (2) the cogency of the STAIR recommendations, to which the development of NXY-059 closely adhered; and (3) the inherent physiochemical shortcomings of NXY-059 as a neuroprotective agent—its polar, nonlipophilic nature, poor blood–brain barrier penetrability, nonphysiological oxidation potential, and low potency. Caution is urged, however, regarding the unwarranted adoption of a nihilistic view toward neuroprotection on the part of the stroke community in view of the abundant preclinical evidence demonstrating proof-of-principle of the feasibility of neuroprotection, as well as the multiplicity of biochemical and molecular neuroprotective targets. The author offers the personal example of a translational journey in which a promising neuroprotectant agent targeting multiple injury mechanisms, high-dose albumin therapy, has proceeded successfully from preclinical studies that established efficacy through a pilot clinical trial that demonstrated safety and offered strong suggestions of clinical efficacy, leading to a large multicenter clinical trial currently in progress.

Emerging therapies for acute ischemic stroke

Stroke is a major public health problem in the United States and the development of novel therapeutic strategies is an important research priority. Advances in this field are proceeding on several fronts, including the use of next-generation plasminogen activators and glycoprotein IIb/ IIIa inhibitors, refined patient selection with advanced magnetic resonance imaging sequences, endovascular approaches to thrombolysis and thrombectomy, and adjuvant use of ultrasound. There remains no proven therapy for intracerebral hemorrhage, but early results with recombinant activated factor VII look very promising. It is hoped that in the near future, physicians managing patients with acute neurological events will have a robust armamentarium of therapies to bring to bear on both ischemic and hemorrhagic vascular disease.

Advances in ischemic stroke treatment: neuroprotective and combination therapies

Thrombolysis with intravenous alteplase (recombinant tissue-type plasminogen activator) continues to be the sole recourse for acute ischemic stroke therapy, provided that patients seek treatment preferably within 3 h of stroke onset. The narrow window of efficacy, coupled with the significant risk of hemorrhage and the high mortality rate, preclude the use of alteplase beyond this time frame. Moreover, in part because of safety concerns, only a small percentage (6-15%) of eligible patients is treated with alteplase. Clearly, safer and more effective treatments that focus on improving the shortcomings of the present thrombolysis for stroke need to be identified. Therefore, newer thrombolytics are being developed with the goal of minimizing side effects, while also shortening the time of cerebral reperfusion and extending the therapeutic window of efficacy. Besides thrombolytics, new and potentially useful drugs and devices are also being studied either as monotherapeutic agents or for use in conjunction with alteplase. In animal models of stroke, neuroprotective agents that affect various components of the ischemic injury cascade that results in neurodegeneration have shown promise for the latter. Examples of such agents include spin traps that block oxidative stress, metalloprotease inhibitors that prevent vascular damage, anti-inflammatory drugs that suppress inflammation and transcranial infrared laser irradiation, which promotes recovery of function. Ideally, a successful combination of neuroprotectant (drug or device) and thrombolytic therapy for stroke would minimize the side effects of thrombolysis followed by supplementary neuroprotection thereafter.

Translational vehicles for neuroprotection

This review will analyse particular criteria in the analysis of stroke diagnosis and treatment, which are pivotal for the successful translation of experimental data from the laboratory to humans.

NXY-059 for acute ischemic stroke

BACKGROUND

NXY-059 is a free-radical-trapping agent that is neuroprotective in animal models of stroke. We tested whether it would reduce disability in humans after acute ischemic stroke.

METHODS

We conducted a randomized, double-blind, placebo-controlled trial involving 1722 patients with acute ischemic stroke who were randomly assigned to receive a 72-hour infusion of placebo or intravenous NXY-059 within 6 hours after the onset of the stroke. The primary outcome was disability at 90 days, as measured according to scores on the modified Rankin scale for disability (range, 0 to 5, with 0 indicating no residual symptoms and 5 indicating bedbound, requiring constant care).

RESULTS

Among the 1699 subjects included in the efficacy analysis, NXY-059 significantly improved the overall distribution of scores on the modified Rankin scale, as compared with placebo (P=0.038 by the Cochran-Mantel-Haenszel test). The common odds ratio for improvement across all categories of the scale was 1.20 (95 percent confidence interval, 1.01 to 1.42). Mortality and rates of serious and nonserious adverse events were each similar in the two groups. NXY-059 did not improve neurologic functioning as measured according to the National Institutes of Health Stroke Scale (NIHSS): the difference between the two groups in the change from baseline scores was 0.1 point (95 percent confidence interval, -1.4 to 1.1; P=0.86). Likewise, no improvement was observed according to the Barthel index (P=0.14). In a post hoc analysis of patients who also received alteplase, NXY-059 was associated with a lower incidence of any hemorrhagic transformation (P=0.001) and symptomatic intracranial hemorrhage (P=0.036).

CONCLUSIONS

The administration of NXY-059 within six hours after the onset of acute ischemic stroke significantly improved the primary outcome (reduced disability at 90 days), but it did not significantly improve other outcome measures, including neurologic functioning as measured by the NIHSS score. Additional research is needed to confirm whether NXY-059 is beneficial in ischemic stroke. (ClinicalTrials.gov number, NCT00119626.).

Brain penetration of the novel free radical trapping neuroprotectant NXY-059 in rats subjected to permanent focal ischemia

The penetration of the free radical trapping neuroprotectant NXY-059 into the brain has been examined in rats subjected to permanent middle cerebral artery occlusion (pMCAO). NXY-059 (125 mg/kg bolus followed by 125 mg/kg/h) was infused for 4 h 45 min starting 15 min after right pMCAO or sham operation. At 5 h, there was a similar plasma total NXY-059 concentration (micromol/L) in both groups [sham: 623 +/- 44 (6); pMCAO: 605 +/- 43 (5)] and a similar drug concentration (nmol/g) in the right cortex [sham: 6.92 +/- 1.05 (6); pMCAO: 6.14 +/- 2.18 (6)]. A subsequent experiment in normal rats, infusing NXY-059 at both a similar and higher concentration (252 mg/kg bolus and 252 mg/kg/h), demonstrated that the concentration of NXY-059 in cortex increased linearly with respect to the plasma concentration. These data demonstrate that NXY-059 does penetrate brain tissue in control animals and ischemic tissue of animals subjected to pMCAO.

In vivo neuroprotective effects of the novel imidazolyl nitrone free-radical scavenger (Z)-alpha-[2-thiazol-2-yl)imidazol-4-yl]-N-tert-butylnitrone (S34176)

Herein, we report an extensive investigation of the neuroprotective effects of the compound (Z)-alpha-[2-thiazol-2-yl)imidazol-4-yl]-N-tert-butylnitrone (S34176) and the prototypic nitrone alpha-phenyl-N-tert-butylnitrone (PBN), in different in vivo paradigms of neuronal degeneration. Administration of S34176 (75 mg/kg i.p.) 30 min before transient (10 min) global ischaemia in Wistar rats significantly prevented delayed neuronal cell death in the hippocampal CA1 area 7 days post-ischaemia (24% vs. 73% in ischaemia control; P<0.05) whereas PBN was inactive under similar conditions. Furthermore, oral administration of S34176 (30 mg/kg) 60 min before and during (1 x 30 mg/kg p.o.) 6 days post-ischaemia, in combination with an acute post-ischaemia sub-protective dose (3 x 10 mg/kg i.p.) of the glutamate receptor antagonist, 1,2,3,4-tetrahydro-6-nitro-2,3-dioxo-benzo[f]quinoxaline-7-sulfonamide (NBQX), resulted in an increased neuroprotective action (29% cell loss in drug-treated vs. 84% in ischaemia control P<0.001) compared to either compound alone. S34176 (20 mg/kg i.p.) also partially prevented kainic acid-induced neuronal cell death at 7 days post-exposure in the CA1 (41% in drug-treated vs. 74% for kainate-treated controls; P<0.01) and CA3 hippocampal region (22% vs. 53%; P<0.01). Under similar conditions, S34176 administered orally (40 mg/kg) produced a more marked protection against kainate-induced neuronal cell loss in the CA1 (13% in drug-treated vs. 82%; P<0.001) and CA3 areas (10% vs. 52%; P<0.001). Sub-chronic oral administration of S34176 (10 mg/kg) also partially reduced kainate-induced hippocampal cell death in the CA1 (53% vs. 77%; P<0.01) and CA3 (23% vs. 53%; P<0.01) areas. Dopamine depletion in the striatum of C57BL/6 mice induced by systemic D-methamphetamine injection was significantly reduced by S34176 (40+/-5% vs. 11.5+/-8%; P<0.001) (150 mg/kg i.p.) whereas PBN was inactive under similar conditions. S34176 represents a new centrally acting nitrone-based radical scavenger with neuroprotective properties in in vivo models of delayed neuronal cell death, and supports the therapeutic potential of this class of compound for the treatment of cerebral pathologies implicating chronic neurodegeneration.

Permeability studies on in vitro blood-brain barrier models: physiology, pathology, and pharmacology

(1) The specifically regulated restrictive permeability barrier to cells and molecules is the most important feature of the blood-brain barrier (BBB). The aim of this review was to summarize permeability data obtained on in vitro BBB models by measurement of transendothelial electrical resistance and by calculation of permeability coefficients for paracellular or transendothelial tracers. (2) Results from primary cultures of cerebral microvascular endothelial cells or immortalized cell lines from bovine, human, porcine, and rodent origin are presented. Effects of coculture with astroglia, neurons, mesenchymal cells, blood cells, and conditioned media, as well as physiological influence of serum components, hormones, growth factors, lipids, and lipoproteins on the barrier function are discussed. (3) BBB permeability results gained on in vitro models of pathological conditions including hypoxia and reoxygenation, neurodegenerative diseases, or bacterial and viral infections have been reviewed. Effects of cytokines, vasoactive mediators, and other pathogenic factors on barrier integrity are also detailed. (4) Pharmacological treatments modulating intracellular cyclic nucleotide or calcium levels, and activity of protein kinases, protein tyrosine phosphatases, phospholipases, cyclooxygenases, or lipoxygenases able to change BBB integrity are outlined. Barrier regulation by drugs involved in the metabolism of nitric oxide and reactive oxygen species, as well as influence of miscellaneous treatments are also listed and evaluated. (5) Though recent advances resulted in development of improved in vitro BBB model systems to investigate disease modeling, drug screening, and testing vectors targeting the brain, there is a need for checking validity of permeability models and cautious interpretation of data.

Stilbazulenyl nitrone, a second-generation azulenyl nitrone antioxidant, confers enduring neuroprotection in experimental focal cerebral ischemia in the rat: neurobehavior, histopathology, and pharmacokinetics

Stilbazulenyl nitrone (STAZN) is a potent lipophilic second-generation azulenyl nitrone antioxidant, which is highly neuroprotective in rodent models of cerebral ischemia and trauma. This study was conducted to establish whether the neuroprotection induced by STAZN persists with chronic survival and to characterize STAZN's pharmacokinetics. Physiologically regulated rats received a 2-h middle cerebral artery occlusion by intraluminal suture and were treated with either STAZN [four 0.6 mg/kg doses i.p. administered at 2 (i.e., onset of recirculation), 4, 24, and 48 h; n = 16] or dimethyl sulfoxide vehicle (n = 11). They received sequential neurobehavioral examinations followed by quantitative neuropathology at 30 days. STAZN improved neurological deficits compared with vehicle controls, beginning within <2 h of the first dose and persisting throughout a 30-day survival. Large cystic necrotic infarcts were common in vehicle-treated rats but infrequent in STAZN-treated rats, and noninfarcted forebrain tissue was increased on average by 15%. In normal rats administered 5 mg/kg STAZN i.v. in Solutol HS 15/ethanol/saline vehicle, STAZN blood levels exhibited a biexponential decline, with an initial half-life of 28 min and a subsequent slow decay with half-life of approximately 7 h. STAZN tissue levels at 2 to 3 h were, on average, 2.5% of blood levels in forebrain, 56% in myocardium, and 41% in kidney. STAZN was concentrated in liver with initial concentrations averaging 5.2-fold above blood levels and a subsequent linear decline of 40% between 24 and 72 h. These results establish that STAZN confers enduring ischemic neuroprotection, has a long circulating half-life, and penetrates well into brain and other organs-characteristics favoring its potential therapeutic utility.

Nitrone-related therapeutics: potential of NXY-059 for the treatment of acute ischaemic stroke

At present, none of the neurodegenerative diseases such as Parkinson's disease, Alzheimer's disease and stroke are treatable with compounds that slow or halt neuronal cell death. However, the prototype nitrone radical trap alpha-phenyl-tert-butylnitrone (PBN) has been shown to be an effective neuroprotective agent in various models of neurodegeneration. Some of these data are briefly reviewed as an introduction to an examination of the effect of the novel nitrone radical trapping agent disodium 2,4-disulfophenyl-N-tert-butylnitrone (NXY-059) in various animal models of stroke. NXY-059 has been shown to be an effective neuroprotective agent in both transient (reperfusion) and permanent focal ischaemia models in rats. In both types of model, NXY-059 has a large window of opportunity, providing effective neuroprotection when given up to 5 hours after the start of the occlusion in transient ischaemia and 4 hours after the start of permanent ischaemia. The compound is also effective in a marmoset permanent ischaemia model when administered up to 4 hours after the start of the occlusion. In this model it has been found to attenuate the problem of spatial neglect and maintain function to the paretic arm. NXY-059 administration also improves motor function in a rat haemorrhagic stroke model and has a neuroprotective effect in a rabbit thromboembolic stroke model. The compound is also well tolerated in stroke patients at plasma levels shown to provide a maximum neuroprotective effect in animal models of stroke.NXY-059, like PBN, is a nitrone with free radical trapping properties and this may be the basis of its neuroprotective action. However, experiments with PBN and NXY-059 suggest the possibility of other mechanisms being involved and these are also reviewed. Further experiments are required to fully elucidate the mechanism of action of these very effective neuroprotective agents.

Prediction of blood-brain barrier permeation in drug discovery from in vivo, in vitro and in silico models

The properties of the blood-brain barrier (BBB) are important considerations when designing drugs to target or avoid the brain. In vivo models provide some of the most reliable measurements of BBB drug permeability, whereas several new cell-based in vitro technologies give valuable mechanistic insights. Higher throughout methods (cell- and non-cell-based; in silico modelling) can help in prediction of permeation, but a combination of techniques is still required to cover the range of BBB drug entry and efflux mechanisms.:

Development of the nitrone-based spin trap agent NXY-059 to treat acute ischemic stroke

The only current FDA-approved treatment for acute ischemic stroke is thrombolysis with tissue plasminogen activator (tPA). However, there are numerous shortcomings to tPA treatment including an increased incidence of intracerebral hemorrhage (ICH) and a short therapeutic window (3-6 h). In recent years, studies have attempted to identify new therapeutics that might be neuroprotective following ischemic strokes. Free radical scavenging spin trap agents have been proposed as potential candidates for stroke therapy because of the hypothesized role of free radicals in the progression of stroke and ischemia-induced neurodegeneration. Novel spin trap agents like (disodium-[(tert-butylimino) methyl] benzene-1,3-disulfonate N-oxide (NXY-059) are of particular interest, not only because they are broad-spectrum nitrone-based free radical scavengers, but also because of their safety profile in humans. Moreover, the rationale for developing NXY-059 for the treatment of acute ischemic stroke is further supported by the drug's reported neuroprotective effects. In addition, NXY-059 may represent a useful adjunct stroke therapy to tPA, since preclinical studies have demonstrated that NXY-059 increases the therapeutic window for tPA and lowers the occurrence of tPA-induced ICH.

Nitrones as neuroprotective agents in cerebral ischemia, with particular reference to NXY-059

Stroke is a major clinical problem, and acute pharmacological intervention with neuroprotective agents has so far been unsuccessful. Recently, there has been considerable interest in the potential therapeutic benefit of nitrone-derived free radical trapping agents as neuroprotective agents. Nitrone compounds have been shown to be beneficial in animal models of various diseases, and the prototypic compound alpha-phenyl-N-tert-butylnitrone (PBN) has been extensively demonstrated to be neuroprotective in rat models of transient and permanent focal ischemia. The nitrone radical trapping agent disodium 2,4-disulfophenyl-N-tert-butylnitrone (NXY-059) has also been shown to be neuroprotective in these models. Furthermore, it has recently been shown to improve neurological function and reduce infarct volume in a primate model of permanent focal ischemia even when given 4 hr postocclusion. While radical trapping activity is demonstrable with NXY-059 and other nitrone compounds such as PBN, this activity is weak. Arguments for and against ascribing radical trapping as the therapeutic mechanism of action are discussed. This compound is well tolerated in human stroke patients and can be administered to produce plasma concentrations exceeding those effective in animal models; crucially, at the same time, it has also been shown to be effective in animal models. NXY-059 may thus be the first compound to be examined in stroke patients using drug exposure and time to treatment that have been shown to be effective in animal models of stroke.

Functional and histological evidence for the protective effect of NXY-059 in a primate model of stroke when given 4 hours after occlusion

BACKGROUND AND PURPOSE

NXY-059 has substantial protective effects when administered immediately after the onset of ischemia in a primate model of stroke. This study examined the efficacy of this drug when administered 4 hours after onset, a more clinically relevant time point.

METHODS

Before surgery, marmosets were trained and tested on a number of neurological tests, which assessed general neurological function, motor ability, and spatial awareness. Four hours after permanent middle cerebral artery occlusion (pMCAO), marmosets received a bolus of saline (n=13) or NXY-059 (n=13), and osmotic minipumps were implanted, providing 48-hour saline or drug (85 micromol/kg per hour) infusion. The monkeys were retested 3 and 10 weeks after surgery. Finally, infarct size was evaluated with histological analysis.

RESULTS

The unbound plasma NXY-059 concentration was 200+/-9 micromol/L after 24-hour infusion, a concentration well tolerated in stroke patients. Drug treatment ameliorated the long-term motor impairment produced by pMCAO; the marmosets were better at using their contralesional, stroke-affected arm than controls at both 3 and 10 weeks. Saline-treated animals had a debilitating spatial neglect at 3 weeks with residual signs evident at 10 weeks. NXY-059 treatment substantially attenuated neglect at 3 weeks, with no deficit being seen at 10 weeks. NXY-059 reduced the overall infarct size by 28% (saline, 324+/-46 mm3; NXY-059, 234+/-30 mm3) with protection to the cortex, white matter, and subcortical structures.

CONCLUSIONS

NXY-059 is an effective neuroprotective agent when administered 4 hours after pMCAO in a primate species, attenuating both motor and spatial neglect. The compound also substantially lessened the volume of cerebral damage.

Neuroprotective effects of nitrone radical scavenger S-PBN on reperfusion nerve injury in rats

The nitrone-based free radical scavengers have potent neuroprotective activities in models of stroke in which oxidative stress plays a key role in its development. We examined the effects of S-PBN (sodium 4-[(tert-butylimino) methyl]benzene-3-sulfonate N-oxide), a spin trap nitrone, on reperfusion injury in rat peripheral nerves. Immediately after the onset of 4-h ischaemia in rat right hindlimb, S-PBN was administered via mini-osmotic pumps, containing 2 ml of S-PBN (1.2 M), inserted subcutaneously. S-PBN, in addition, was given by a single injection (50 mg/kg BW, i.p.). Mean plasma concentrations of S-PBN were significantly greater in S-PBN-treated rats than in controls after 24, 48 and 72 h of reperfusion. Pump and dosing solution analysis indicated that the rats received between 82 and 99% of the target S-PBN concentration. Morphology in sciatic, tibial and peroneal nerves was assessed after 4 h of ischaemia followed by 72 h and 7 days of reperfusion. After 72 h of reperfusion, saline-treated control rats showed endoneurial oedema at the thigh level and diffuse axonal degeneration of myelinated nerve fibres distally. S-PBN-treated nerves were normal or revealed less severe abnormalities in myelinated fibres after 72 h and 7 days of reperfusion, when compared with those in saline-treated control nerves. Morphometrically, the frequency of abnormal myelinated fibres at calf levels was significantly less in S-PBN-treated nerves than in controls. In conclusion, post-ischaemic administration of S-PBN exhibits substantial neuroprotective properties in ischemia/reperfusion nerve injury.