Dexanabinol; a novel neuroprotective drug in experimental focal cerebral ischemia

Molecular Pharmacology of Synthetic Cannabinoids: Delineating CB1 Receptor-Mediated Cell Signaling

Synthetic cannabinoids (SCs) are a class of new psychoactive substances (NPSs) that exhibit high affinity binding to the cannabinoid CB1 and CB2 receptors and display a pharmacological profile similar to the phytocannabinoid (-)-trans-Δ9-tetrahydrocannabinol (THC). SCs are marketed under brand names such as K2 and Spice and are popular drugs of abuse among male teenagers and young adults. Since their introduction in the early 2000s, SCs have grown in number and evolved in structural diversity to evade forensic detection and drug scheduling. In addition to their desirable euphoric and antinociceptive effects, SCs can cause severe toxicity including seizures, respiratory depression, cardiac arrhythmias, stroke and psychosis. Binding of SCs to the CB1 receptor, expressed in the central and peripheral nervous systems, stimulates pertussis toxin-sensitive G proteins (Gi/Go) resulting in the inhibition of adenylyl cyclase, a decreased opening of N-type Ca2+ channels and the activation of G protein-gated inward rectifier (GIRK) channels. This combination of signaling effects dampens neuronal activity in both CNS excitatory and inhibitory pathways by decreasing action potential formation and neurotransmitter release. Despite this knowledge, the relationship between the chemical structure of the SCs and their CB1 receptor-mediated molecular actions is not well understood. In addition, the potency and efficacy of newer SC structural groups has not been determined. To address these limitations, various cell-based assay technologies are being utilized to develop structure versus activity relationships (SAR) for the SCs and to explore the effects of these compounds on noncannabinoid receptor targets. This review focuses on describing and evaluating these assays and summarizes our current knowledge of SC molecular pharmacology.

Cannabinoids in experimental stroke: a systematic review and meta-analysis

Cannabinoids (CBs) show promise as neuroprotectants with some agents already licensed in humans for other conditions. We systematically reviewed CBs in preclinical stroke to guide further experimental protocols. We selected controlled studies assessing acute administration of CBs for experimental stroke, identified through systematic searches. Data were extracted on lesion volume, outcome and quality, and analyzed using random effect models. Results are expressed as standardized mean difference (SMD) with 95% confidence intervals (CIs). In all, 144 experiments (34 publications) assessed CBs on infarct volume in 1,473 animals. Cannabinoids reduced infarct volume in transient (SMD -1.41 (95% CI -1.71), -1.11) P<0.00001) and permanent (-1.67 (-2.08, -1.27), P<0.00001) ischemia and in all subclasses: endocannabinoids (-1.72 (-2.62, -0.82), P=0.0002), CB1/CB2 ligands (-1.75 (-2.19, -1.31), P<0.00001), CB2 ligands (-1.65 (-2.09, -1.22), P<0.00001), cannabidiol (-1.20 (-1.63, -0.77), P<0.00001), Δ(9)-tetrahydrocannabinol (-1.43 (-2.01, -0.86), P<0.00001), and HU-211 (-2.90 (-4.24, -1.56), P<0.0001). Early and late neuroscores significantly improved with CB use (-1.27 (-1.58, -0.95), P<0.00001; -1.63 (-2.64, -0.62), P<0.002 respectively) and there was no effect on survival. Statistical heterogeneity and publication bias was present, median study quality was 4 (range 1 to 6/8). Overall, CBs significantly reduced infarct volume and improve functional outcome in experimental stroke. Further studies in aged, female and larger animals, with other co-morbidities are required.

The role of tumor necrosis factor-α and TNF-α receptors in cerebral arteries following cerebral ischemia in rat

Background

Tumour necrosis factor-α (TNF-α) is a pleiotropic pro-inflammatory cytokine, which is rapidly upregulated in the brain after injury. TNF-α acts by binding to its receptors, TNF-R1 (p55) and TNF-R2 (p75), on the cell surface. The aim of this study was first to investigate if there is altered expression of TNF-α and TNF-α receptors in cerebral artery walls following global or focal ischemia, and after organ culture. Secondly, we asked if the expression was regulated via activation of the MEK-ERK1/2 pathway.

Methods

The hypothesis was tested in vivo after subarachnoid hemorrhage (SAH) and middle cerebral artery occlusion (MCAO), and in vitro by organ culture of isolated cerebral arteries. The localization and amount of TNF-α, TNF-α receptor 1 and 2 proteins were analysed by immunohistochemistry and western blot after 24 and 48 h of organ culture and at 48 h following SAH or MCAO. In addition, cerebral arteries were incubated for 24 or 48 h in the absence or presence of a B-Raf inhibitor (SB386023-b), a MEK- inhibitor (U0126) or an NF-κB inhibitor (IMD-0354), and protein expression evaluated.

Results

Immunohistochemistry revealed enhanced expression of TNF-α, TNF-R1 and TNF-R2 in the walls of cerebral arteries at 48 h after MCAO and SAH compared with control. Co-localization studies showed that TNF-α, TNF-R1 and TNF-R2 were primarily localized to the cell membrane and the cytoplasm of the smooth muscle cells (SMC). There was, in addition, some expression of TNF-R2 in the endothelial cells. Immunohistochemistry and western blot analysis showed that these proteins were upregulated after 24 and 48 h in culture, and this upregulation reached an apparent maximum at 48 h of organ culture. Treatment with U0126 significantly reduced the enhanced SMC expression of TNF-α, TNF-R1 and TNF-R2 immunoreactivities after 24 and 48 h of organ culture. The Raf and NF-κB inhibitors significantly reduced organ culture induced TNF-α expression while they had minor effects on the TNF-α receptors.

Conclusion

The present study shows that cerebral ischemia and organ culture induce expression of TNF-α and its receptors in the walls of cerebral arteries and that upregulation is transcriptionally regulated via the MEK/ERK pathway.

Cannabinoid/agonist WIN 55,212-2 reduces cardiac ischaemia–reperfusion injury in Zucker diabetic fatty rats: role of CB2 receptors and iNOS/eNOS

BACKGROUND

Diabetes increases cardiac damage after myocardial ischaemia. Cannabinoids can protect against myocardial ischaemia/reperfusion injury. The aim of this study was to examine the cardioprotective effect of the cannabinoid agonist WIN 55,212-2 (WIN) against ischaemia/reperfusion injury in an experimental model of type 2 diabetes. We performed these experiments in the Zucker diabetic fatty rat, and focused on the role of cannabinoid receptors in modulation of cardiac inducible nitric oxide synthase (iNOS)/endothelial-type nitric oxide synthase (eNOS) expression.

METHODS

Male 20-week-old Zucker diabetic fatty rats were treated with vehicle, WIN, the selective CB1 or CB2 receptor antagonists AM251 and AM630, respectively, AM251 + WIN or AM630 + WIN. Hearts were isolated from these rats, and the cardiac functional response to ischaemia/reperfusion injury was evaluated. In addition, cardiac iNOS and eNOS expression were determined by western blot.

RESULTS

WIN significantly improved cardiac recovery after ischaemia/ reperfusion in the hearts from Zucker diabetic fatty rats by restoring coronary perfusion pressure and heart rate to preischaemic levels. Additionally, WIN decreased cardiac iNOS expression and increased eNOS expression after ischaemia/reperfusion in diabetic hearts. WIN-induced cardiac functional recovery was completely blocked by the CB2 antagonist AM630. However, changes in NOS isoenzyme expression were not affected by the CB antagonists.

CONCLUSIONS

This study shows a cardioprotective effect of a cannabinoid agonist on ischaemia/reperfusion injury in an experimental model of a metabolic disorder. The activation mainly of CB2 receptors and the restoration of iNOS/eNOS cardiac equilibrium are mechanisms involved in this protective effect. These initial studies have provided the basis for future research in this field.

Bone marrow-derived nonreactive astrocytes in the mouse brain after permanent middle cerebral artery occlusion

We studied the effect of permanent unilateral middle cerebral artery occlusion (PMCAO) on the generation of bone marrow (BM)-derived astrocytes in female mice previously transplanted with enhanced green fluorescent protein-expressing BM from male donors. In addition to an untreated PMCAO group, one group of mice also received intracerebral infusion of transforming growth factor-alpha, resulting in a decrease in the size of the infarct. Two months after PMCAO, we found a specific type of astrocyte of BM origin in the side of the injury, near the lesion. These astrocytes did not express glial fibrillary acidic protein (GFAP) by conventional fluorescence immunostaining; however, GFAP was easily detectable by tyramide signal amplification. These cells also expressed S100β, confirming their astrocytic character. Unlike the endogenous reactive astrocytes, these BM-derived astrocytes did not proliferate during the first week of ischemia and did not contribute to the glial scar formation. Transforming growth factor-alpha infusion increased the number of BM-derived astrocytes, without affecting their distribution. Interestingly, exclusively by tyramide signal amplification staining, we found that endogenous astrocytes displaying an identical morphology were also present in control mouse and human brains. Our data demonstrate that a subpopulation of nonreactive astrocytes expressing low levels of GFAP can originate from transplanted BM in the ischemic brain. We believe that these cells represent a subpopulation of astrocytes earlier considered to be GFAP negative. The high number of astrocytes with identical morphology and chemical character in control brains suggest that these type of astrocytes may have important functional role in the central nervous system that calls for further studies.

Cannabinoid receptors in acute and chronic complications of atherosclerosis

Atherosclerosis is a chronic inflammatory disease that is the primary cause of myocardial infarction and stroke, which occur after sudden thrombotic occlusion of an artery. A growing body of evidence suggests that cannabinoid signalling plays a fundamental role in atherosclerosis development and its clinical manifestations. Thus, CB2 receptors are protective in myocardial ischaemia/reperfusion and implicated in the modulation of chemotaxis, which is crucial for the recruitment of leukocytes during inflammation. Delta-9-Tetrahydrocannabinol (THC)-mediated activation has been shown to inhibit atherosclerotic plaque progression in a CB2 dependent manner. Although CB1 and CB2 expression has been reported on platelets, their involvement in thrombus formation is still controversial. While several reports suggest that CB1 receptors may have a relevant role in neuroprotection after ischaemic stroke, recent studies show the protective effects in various forms of neuroprotection are not related to CB1 stimulation, and a protective role of CB1 blockade has also been reported. In addition, vascular and myocardial CB1 receptors contribute to the modulation of blood pressure and heart rate. It is tempting to suggest that pharmacological modulation of the endocannabinoid system is a potential novel therapeutic strategy in the treatment of atherosclerosis. For these purposes, it is important to better understand the complex mechanisms of endocannabinoid signalling and potential consequences of its pharmacological modulation, as it may have both pro- and anti-atherosclerotic effects.

Tumor necrosis factor-α is involved in thrombolytic-induced hemorrhage following embolic strokes in rabbits

The present study assessed whether tumor necrosis factor-alpha (TNFalpha) is involved in hemorrhage following large clot embolism-induced ischemia in New Zealand white rabbits by intracisternally administering either TNFalpha or a goat-anti-rabbit-TNFalpha antibody following a stroke. The first aim of the study showed that TNFalpha administration increased stroke-induced hemorrhage incidence to 53.3% from 18.5% (an increase of 188%) in the control group and also increased hemorrhage volume by 87% (p<0.05). The second aim showed that administration of tissue plasminogen activator (tPA) using a standard dose of 3.3 mg/kg increased hemorrhage incidence in rabbits to 76.5% from 18.5% (an increase of 314%) and this effect was reversed by administration of an anti-TNFalpha antibody. In the tPA-anti-TNFalpha antibody group, the absolute hemorrhage rate was 38.8% and the hemorrhage volume was 98% of control. In conclusion, following an embolic stroke, TNFalpha administration increased the incidence and volume of hemorrhage and an anti-TNFalpha antibody counteracted tPA-induced hemorrhage. The results suggest that TNFalpha may either be directly or indirectly involved in vascular damage following an embolic stroke. Moreover, TNFalpha may mediate some of the detrimental effects of tPA on the vascular compartment. Based upon our studies, TNFalpha receptor antagonists or TNFalpha processing inhibitors should be further pursued as targets for the treatment of hemorrhagic stroke as adjuvant treatment for stroke patients receiving thrombolytic treatment.

The endocannabinoid system as an emerging target of pharmacotherapy

The recent identification of cannabinoid receptors and their endogenous lipid ligands has triggered an exponential growth of studies exploring the endocannabinoid system and its regulatory functions in health and disease. Such studies have been greatly facilitated by the introduction of selective cannabinoid receptor antagonists and inhibitors of endocannabinoid metabolism and transport, as well as mice deficient in cannabinoid receptors or the endocannabinoid-degrading enzyme fatty acid amidohydrolase. In the past decade, the endocannabinoid system has been implicated in a growing number of physiological functions, both in the central and peripheral nervous systems and in peripheral organs. More importantly, modulating the activity of the endocannabinoid system turned out to hold therapeutic promise in a wide range of disparate diseases and pathological conditions, ranging from mood and anxiety disorders, movement disorders such as Parkinson's and Huntington's disease, neuropathic pain, multiple sclerosis and spinal cord injury, to cancer, atherosclerosis, myocardial infarction, stroke, hypertension, glaucoma, obesity/metabolic syndrome, and osteoporosis, to name just a few. An impediment to the development of cannabinoid medications has been the socially unacceptable psychoactive properties of plant-derived or synthetic agonists, mediated by CB(1) receptors. However, this problem does not arise when the therapeutic aim is achieved by treatment with a CB(1) receptor antagonist, such as in obesity, and may also be absent when the action of endocannabinoids is enhanced indirectly through blocking their metabolism or transport. The use of selective CB(2) receptor agonists, which lack psychoactive properties, could represent another promising avenue for certain conditions. The abuse potential of plant-derived cannabinoids may also be limited through the use of preparations with controlled composition and the careful selection of dose and route of administration. The growing number of preclinical studies and clinical trials with compounds that modulate the endocannabinoid system will probably result in novel therapeutic approaches in a number of diseases for which current treatments do not fully address the patients' need. Here, we provide a comprehensive overview on the current state of knowledge of the endocannabinoid system as a target of pharmacotherapy.

Targeting the endocannabinoid system in treating brain disorders

Recent cannabinoid research has a primary focus on developing therapeutics against human diseases. Many studies on cannabinoids indicate important progress for protection against several neurodegenerative disorders. Agonists of cannabinoid receptors activate signalling pathways in the brain that are linked to neuronal repair and cell maintenance, and endogenous ligands can also activate neuroprotective responses. These endocannabinoids are bioactive fatty acid amides and esters that are synthesised in the brain and include arachidonoyl ethanolamide (anandamide) and 2-arachidonoyl glycerol. Endocannabinoids are released in response to pathogenic events, thus representing a potential compensatory repair mechanism. Enhancing this on-demand action of endocannabinoids is a strategy with which to promote endogenous repair signalling. For such enhancement, considerable work has gone into modulating the availability of endocannabinoids by blocking the processes of their deactivation. The targets include the anandamide-hydrolysing enzyme fatty acid amide hydrolase, the carrier-mediated anandamide transport system and 2-arachidonoyl glycerol-deactivating enzyme monoacylglycerol lipase. The activity of endocannabinoids is terminated through transport and degradation and, accordingly, selective inhibitors of these processes effectively exploit the protective nature of cannabinergic responses. This review highlights recent studies implicating the endocannabinoid system in neuroprotection against different disorders of the CNS.

Cannabis and tobacco smoke are not equally carcinogenic

More people are using the cannabis plant as modern basic and clinical science reaffirms and extends its medicinal uses. Concomitantly, concern and opposition to smoked medicine has occurred, in part due to the known carcinogenic consequences of smoking tobacco. Are these reactions justified? While chemically very similar, there are fundamental differences in the pharmacological properties between cannabis and tobacco smoke. Cannabis smoke contains cannabinoids whereas tobacco smoke contains nicotine. Available scientific data, that examines the carcinogenic properties of inhaling smoke and its biological consequences, suggests reasons why tobacco smoke, but not cannabis smoke, may result in lung cancer.

Tumor necrosis factor-α mediates the proliferation of rat C6 glioma cells via β-adrenergic receptors

In the present study, we observed that isoproterenol, a beta-adrenergic receptor (beta-AR) agonist, stimulated rat C6 glioma cell proliferation, while propranolol, a beta-AR blocker, greatly reduced the proliferative effect of TNF-alpha on C6 cells. The gene and protein expressions of both beta1- and beta2-ARs were enhanced in C6 cells after TNF-alpha treatment, and the increase in beta-AR was due to an increased number of binding sites and not due to increase in receptor affinity. We further showed that protein kinase C (PKC) was involved in the TNF-alpha-induced beta-AR expression. Collectively, our results indicate that TNF-alpha-induced proliferation in C6 glioma cells might be via the induction and activation of beta-ARs.

Angiogenesis and stem cell transplantation as potential treatments of cerebral ischemic stroke

Ischemic stroke is a leading cause of human death and disability. Although stroke survivors may gain spontaneous partial functional recovery, they often suffer from sensory-motor dysfunctions, behavioral/neurological alterations, and various degrees of paralysis. Currently, limited clinical intervention is available to prevent ischemic damage and restore lost function in stroke victims. In addition to the extensive research on protective maneuvers against ischemia-induced cell death, increasing attention has been focused on potential strategies of promoting tissue repair and functional recovery in the damaged post-ischemic brain. Angiogenesis, or the growth of new blood vessels, may contribute to cell survival and functional recovery of the area of insult. The study of angiogenesis will increase the understanding of the mechanism underlying post-ischemia neurovascular plasticity and regeneration. Additionally, stem cell transplantation has emerged in the last few years as a potential therapy for ischemic stroke, because of their capability to differentiate into multiple cell types and the possibility that they may provide trophic support for cell survival, tissue repair, and functional recovery.

Neurocognitive performance of methamphetamine users discordant for history of marijuana exposure

Abuse of the stimulant drug methamphetamine is associated with neural injury and neuropsychological (NP) deficits, while the residual effects of marijuana use remain uncertain. We sought to determine if methamphetamine dependent persons who also met criteria for marijuana abuse or dependence evidenced different NP performance than those with dependence for methamphetamine alone. We examined three groups that did not differ significantly on important demographic factors: (1) subjects with a history of methamphetamine dependence and history of marijuana abuse/dependence (METH+/MJ+, n=27); (2) methamphetamine dependent subjects without history of marijuana abuse/dependence (METH+/MJ-, n=26); (3) a control group with minimal or no drug use (n=41). A comprehensive NP battery was administered and performance was quantified for five cognitive ability areas. The METH+/MJ- group generally demonstrated the greatest NP impairment, with statistically significant differences observed between the METH+/MJ- and control group in learning, retention/retrieval, and a summary score of global NP performance. The METH+/MJ+ group did not differ significantly from the control or METH+/MJ- group on any NP ability. However, there was a significant linear trend in the global NP score suggesting that the METH+/MJ+ performed intermediate to the control and METH+/MJ- groups. Based on these findings, we cannot conclude that there is a protective effect of marijuana use in methamphetamine users; however, marijuana use clearly did not appear to exacerbate methamphetamine neurotoxicity. Further investigations are needed to determine if the emerging literature, suggesting that certain cannabinoids might have neuroprotective actions, is generalizable to community-dwelling substance abusers.

Cannabinoids prevent the acute hyperthermia and partially protect against the 5-HT depleting effects of MDMA (“Ecstasy”) in rats

Cannabinoid-MDMA interactions were examined in male Wistar rats. MDMA (4 x 5 mg/kg or 2 x 10 mg/kg over 4 h on each of 2 days) was administered with or without Delta 9-tetrahydrocannabinol (THC) (4 x 2.5 mg/kg), the synthetic cannabinoid receptor agonist CP 55,940 (2 x 0.1 or 0.2 mg/kg) or the cannabinoid receptor antagonist SR 141716 (2 x 5 mg/kg). Co-administered Delta 9-THC and CP 55,940 but not SR 141716 prevented MDMA-induced hyperthermia, causing a powerful hypothermia. Co-administered Delta 9-THC, CP 55,940 and SR 141716 all tended to decrease MDMA-induced hyperactivity. Co-administered Delta 9-THC provided protection against the long-term increases in anxiety seen in the emergence test, but not the social interaction test, 6 weeks after MDMA treatment. Co-administered Delta 9-THC and CP 55,940, but not SR 141716, partly prevented the long-term 5-HT and 5-HIAA depletion caused by MDMA in various brain regions. SR 141716 administered with CP 55,940 and MDMA prevented the hypothermic response to the CP 55,940/MDMA combination but did not alter the CP 55,940 attenuation of MDMA-induced 5-HT depletion. These results suggest a partial protective effect of co-administered cannabinoid receptor agonists on MDMA-induced 5-HT depletion and long-term anxiety. This action appears to operate independently of cannabinoid CB1 receptors.

BAY 38-7271: a novel highly selective and highly potent cannabinoid receptor agonist for the treatment of traumatic brain injury

Traumatic brain injury (TBI) is the most common cause of mortality and morbidity in adults under 40 years of age in industrialized countries. Worldwide the incidence is increasing, about 9.5 million people are hospitalized per year due to TBI, and the death rate is estimated to be more than one million people per year. Recently BAY 38-7271 has been characterized as a structurally novel, selective and highly potent cannabinoid CB1/CB2 receptor agonist in vitro and in vivo with pronounced neuroprotective efficacy in a rat traumatic brain injury model, showing a therapeutic window of at least 5 h. Furthermore, neuroprotective efficacy was also found in models of transient and permanent occlusion of the middle cerebral artery and brain edema models as well. In this article we review the in vitro and in vivo pharmacology of BAY 38-7271, the results from acute and subacute toxicity studies, pharmacokinetics and drug metabolism in animals and healthy male volunteers. In phase I studies BAY 38-7271 was safe and well tolerated when administered by i.v. infusion for either 1 or 24 h. As the doses of BAY 38-7271 in animals needed for maximal neuroprotective efficacy were significantly lower than those inducing typical cannabinoid-like side effects, it is to be expected that the compound will offer a novel therapeutic approach with a favorable therapeutic window for the treatment of TBI or cerebral ischemia.

[Therapeutic use of cannabinoids in neurology]

This review gives insight into the potential therapeutical role of cannabinoids in neurology. Preclinical data are presented which could give a rationale for the clinical use of cannabinoids in the fields of multiple sclerosis, spasticity, epilepsy, movement disorders, and neuroprotection after traumatic head injury or ischemic stroke. Besides, clinical data (case reports, open-label and randomised controlled studies) dealing with the therapeutical use of cannabinoids in these fields are reported and discussed. At present, clinical data are insufficient to recommend the use of cannabinoids in any neurological disease as standard therapy. Several questions still have to be answered (which cannabinoid? which way of administration? stimulation of endogenous cannabinoids? separation between desired and undesired effects?), and controlled studies are still needed to clarify the potential therapeutical role of cannabinoids in neurology.

Combination of dexanabinol and tempol in focal cerebral ischemia: is there a ceiling effect?

Because ischemic neuronal death is triggered by several parallel mechanisms, a combination of drugs active against individual death-promoting mechanisms may have synergistic effects. Dexanabinol is a noncompetitive NMDA antagonist with anti-inflammatory effects and tempol is a nitroxide antioxidant. Therefore, we explored whether their combined use results in smaller infarct volumes as compared with their individual administration. Rats underwent permanent middle cerebral artery occlusion (PMCAO) and were given vehicle, dexanabinol alone, tempol alone, or a combination of dexanabinol and tempol (n = 13 per group) 1 h later. Five animals in each group were evaluated with a motor rating scale 24 h after PMCAO and the infarct volumes were then measured. The remaining animals were examined with motor and behavioral scales up to 30 days after PMCAO and their infarct volumes were then determined. Motor disability and water maze latencies at all time points examined and infarct volumes at days 1 and 30 were significantly reduced in all active treatment groups when compared with vehicle. However, no significant differences were observed between the active treatment groups. In conclusions, combination therapy with dexanabinol and tempol does not appear to have additional neuroprotective effects compared to those conferred by each agent alone even when administered at optimal timing and dosing. Therefore, a ceiling neuroprotective effect that is impossible to overcome may exist.

Detrimental and beneficial effects of injury-induced inflammation and cytokine expression in the nervous system

Lesions in the nervous system induce rapid activation of glial cells and under certain conditions additional recruitment of granulocytes, T-cells and monocytes/macrophages from the blood stream triggered by upregulation of cell adhesion molecules, chemokines and cytokines. Hematogenous cell infiltration is not restricted to infectious or autoimmune disorders of the nervous system, but also occurs in response to cerebral ischemia and traumatic lesions. Neuroinflammation can cause neuronal damage, but also confers neuroprotection. Granulocytes occlude vessels during reperfusion after transient focal ischemia, while the functional role of T-cells and macrophages in stroke development awaits further clarification. After focal cerebral ischemia neurotoxic mediators released by microglia such as the inducible nitric oxide synthase (leading to NO synthesis) and the cytokines interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha) are upregulated prior to cellular inflammation in the evolving lesion and functionally contribute to secondary infarct growth as revealed by numerous pharmacological experiments and by use of transgenic animals. On the other hand, cytokine induction remote from ischemic lesions involves NMDA-mediated signalling pathways and confers neuroprotection. After nerve injury T cells can rescue CNS neurons. In the peripheral nervous system neuroinflammation is a prerequisite for successful regeneration that is impeded in the CNS. In conclusion, there is increasing evidence that neuroinflammation represents a double edged sword. The opposing neurotoxic and neuroprotective properties of neuroinflammation during CNS injury provide arich and currently unexplored set of research problems.

Inhibition of apoptosis by hyperbaric oxygen in a rat focal cerebral ischemic model

The hypothesis was tested that hyperbaric oxygen therapy (HBO) reduced brain infarction by preventing apoptotic death in ischemic cortex in a rat model of focal cerebral ischemia. Male Sprague-Dawley rats were subjected to middle cerebral artery occlusion/reperfusion (MCAO/R) and subsequently were exposed to HBO (2.5 atmospheres absolute) for 2 h, at 6 h after reperfusion. Rats were killed and brain samples were collected at 24, 48, 72 h, and 7 days after reperfusion. Neurologic deficits, infarction area, and apoptotic changes were evaluated by clinical scores, 2,3,7-triphenyltetrazolium chloride staining, caspase-3 expression, DNA fragmentation assay, and terminal deoxynucleotidyl transferase-mediated 2'-deoxyuridine 5'-triphosphate-biotin nick end labeling (TUNEL)-hematoxylin and eosin (H&E) costaining. In MCAO/R without HBO treatment animals, DNA fragmentation was observed in injured cortex at 24, 48, and 72 h but not in samples at 7 days after reperfusion. Double labeling of brain slides with NeuN and caspase-3 demonstrated neurons in the injured cortex labeled with caspase-3. TUNEL+H&E costaining revealed morphologic apoptotic changes at 24, 48, and 72 h after reperfusion. Hyperbaric oxygen therapy abolished DNA fragmentation and reduced the number of TUNEL-positive cells. Hyperbaric oxygen therapy reduced infarct area and improved neurologic scores at 7 days after reperfusion. One of the molecular mechanisms of HBO-induced brain protection is to prevent apoptosis, and this effect of HBO might preserve more brain tissues and promote neurologic functional recovery.

Therapeutic potential of cannabinoids in CNS disease

The major psychoactive constituent of Cannabis sativa, delta(9)-tetrahydrocannabinol (delta(9)-THC), and endogenous cannabinoid ligands, such as anandamide, signal through G-protein-coupled cannabinoid receptors localised to regions of the brain associated with important neurological processes. Signalling is mostly inhibitory and suggests a role for cannabinoids as therapeutic agents in CNS disease where inhibition of neurotransmitter release would be beneficial. Anecdotal evidence suggests that patients with disorders such as multiple sclerosis smoke cannabis to relieve disease-related symptoms. Cannabinoids can alleviate tremor and spasticity in animal models of multiple sclerosis, and clinical trials of the use of these compounds for these symptoms are in progress. The cannabinoid nabilone is currently licensed for use as an antiemetic agent in chemotherapy-induced emesis. Evidence suggests that cannabinoids may prove useful in Parkinson's disease by inhibiting the excitotoxic neurotransmitter glutamate and counteracting oxidative damage to dopaminergic neurons. The inhibitory effect of cannabinoids on reactive oxygen species, glutamate and tumour necrosis factor suggests that they may be potent neuroprotective agents. Dexanabinol (HU-211), a synthetic cannabinoid, is currently being assessed in clinical trials for traumatic brain injury and stroke. Animal models of mechanical, thermal and noxious pain suggest that cannabinoids may be effective analgesics. Indeed, in clinical trials of postoperative and cancer pain and pain associated with spinal cord injury, cannabinoids have proven more effective than placebo but may be less effective than existing therapies. Dronabinol, a commercially available form of delta(9)-THC, has been used successfully for increasing appetite in patients with HIV wasting disease, and cannabinoid receptor antagonists may reduce obesity. Acute adverse effects following cannabis usage include sedation and anxiety. These effects are usually transient and may be less severe than those that occur with existing therapeutic agents. The use of nonpsychoactive cannabinoids such as cannabidiol and dexanabinol may allow the dissociation of unwanted psychoactive effects from potential therapeutic benefits. The existence of other cannabinoid receptors may provide novel therapeutic targets that are independent of CB(1) receptors (at which most currently available cannabinoids act) and the development of compounds that are not associated with CB(1) receptor-mediated adverse effects. Further understanding of the most appropriate route of delivery and the pharmacokinetics of agents that act via the endocannabinoid system may also reduce adverse effects and increase the efficacy of cannabinoid treatment. This review highlights recent advances in understanding of the endocannabinoid system and indicates CNS disorders that may benefit from the therapeutic effects of cannabinoid treatment. Where applicable, reference is made to ongoing clinical trials of cannabinoids to alleviate symptoms of these disorders.

Experimental models in focal cerebral ischemia: are we there yet?

Therapeutic options available for acute stroke management are sparse and inadequate. Therefore, new insights into stroke pathophysiology leading to new therapeutic targets are needed. In order to attain these goals, adequate animal models for cerebral ischemia are needed. In the following paper the authors will review the various animal models for stroke and emphasize their potential strengths and weaknesses.

Cannabinoids ablate release of TNFalpha in rat microglial cells stimulated with lypopolysaccharide

Upon activation, brain microglial cells release proinflammatory mediators, such as TNFalpha, which may play an important role in eliciting neuroinflammatory processes causing brain damage. As cannabinoids have been reported to exert anti-inflammatory and neuroprotective actions in the brain, we here examined the effect of both synthetic and endogenous cannabinoids on TNFalpha release elicited by bacterial endotoxin lypopolysaccharide (LPS) in cultured microglia. Exposure of primary cultures of rat cortical microglial cells to LPS significantly stimulated TNFalpha mRNA expression and release. The endogenous cannabinoids anandamide and 2-arachidonylglycerol (2-AG), as well as the synthetic cannabinoids (+)WIN 55,212-2, CP 55,940, and HU210, inhibited in a concentration-dependent manner (1-10 microM) the LPS-induced TNFalpha release. Unlike the high-affinity cannabinoid receptor agonist (+)WIN 55,212-2, the low-affinity stereoisomer (-)WIN 55,212-2 did not exert any significant inhibition on TNFalpha release. Given this stereoselectivity, the ability of (+)WIN 55,212-2 to inhibit LPS-induced TNFalpha release from microglia is most likely receptor-mediated. By RT-PCR we found that the two G(i/o) protein-coupled cannabinoid receptors (type 1 and 2) are both expressed in microglial cultures. However, selective antagonists of type 1 (SR141716A and AM251) and type 2 (SR144528) cannabinoid receptors did not affect the effect of (+)WIN 55,212-2. Consistent with this finding is the observation that the ablative effect of (+)WIN 55,212-2 on LPS-evoked release of TNFalpha was not sensitive to the G(i/o) protein inactivator pertussis toxin. In addition, the cAMP elevating agents dibutyryl cAMP and forskolin both abolished LPS-induced TNFalpha release, thus rendering unlikely the possibility that (+)WIN 55,212-2 could ablate TNFalpha release through the inhibition of adenylate cyclase via the G(i)-coupled cannabinoid receptors type 1 and 2. In summary, our data indicate that both synthetic and endogenous cannabinoids inhibit LPS-induced release of TNFalpha from microglial cells. By showing that such effect does not appear to be mediated by either CB receptor type 1 or 2, we provide evidence suggestive of the existence of yet unidentified cannabinoid receptor(s) in brain microglia.

Cannabinoids in the treatment of glaucoma

The leading cause of irreversible blindness is glaucoma, a disease normally characterized by the development of ocular hypertension and consequent damage to the optic nerve at its point of retinal attachment. This results in a narrowing of the visual field, and eventually results in blindness. A number of drugs are available to lower intraocular pressure (IOP), but, occasionally, they are ineffective or have intolerable side-effects for some patients and can lose efficacy with chronic administration. The smoking of marijuana has decreased IOP in glaucoma patients. Cannabinoid drugs, therefore, are thought to have significant potential for pharmaceutical development. However, as the mechanism surrounding their effect on IOP initially was thought to involve the CNS, issues of psychoactivity hindered progress. The discovery of ocular cannabinoid receptors implied an explanation for the induction of hypotension by topical cannabinoid applications, and has stimulated a new phase of ophthalmic cannabinoid research. Featured within these investigations is the possibility that at least some cannabinoids may ameliorate optic neuronal damage through suppression of N-methyl-D-aspartate receptor hyperexcitability, stimulation of neural microcirculation, and the suppression of both apoptosis and damaging free radical reactions, among other mechanisms. Separation of therapeutic actions from side-effects now seems possible through a diverse array of novel chemical, pharmacological, and formulation strategies.

The nitroxide antioxidant tempol is cerebroprotective against focal cerebral ischemia in spontaneously hypertensive rats

Free radicals appear to participate in the final common pathway of neuronal death in ischemia and may therefore be an adequate target for therapy. Tempol is a nitroxide antioxidant with proven protective efficacy in several animal models, including myocardial ischemia, that has not been previously tested in models of permanent cerebral ischemia. Spontaneously hypertensive rats underwent permanent middle cerebral artery occlusion (PMCAO). Following dose-response and time-window-finding experiments rats were given vehicle or tempol (50 mg/kg) subcutaneously 1 h after PMCAO (n = 10/group). Five animals in each group were evaluated with a motor scale 24 h after the infarct and were then sacrificed and the injury volume was measured. The remaining animals were examined daily with the motor scale and also with a Morris water maze test on days 26-30 after PMCAO and sacrificed on day 30. Motor scores at all time points examined were significantly better in the tempol-treated animals (P < 0.05 for all). Significantly better performance in the water maze test for performance on days 26-30 was noted in the tempol group compared with the vehicle-treated group (P < 0.05). Injury volumes at days 1 and 30 were significantly reduced in the tempol group (9.83 +/- 1.05 vs 19.94 +/- 1.43% hemispheric volume, P = 0.0009, and 13.2 +/- 2.97 vs 24.4 +/- 2.38% hemispheric volume, P = 0.02, respectively). In conclusion, treatment with tempol led to significant motor and behavioral improvement and reduced injured tissue volumes both in the short and in the long term after stroke.

Cerebral ischemia and trauma-different etiologies yet similar mechanisms: neuroprotective opportunities

Cerebral ischemia leads to brain damage caused by pathogenetic mechanisms that are also activated by neurotrauma. These mechanisms include among others excitotoxicity, over production of free radicals, inflammation and apoptosis. Furthermore, cerebral ischemia and trauma both trigger similar auto-protective mechanisms including the production of heat shock proteins, anti-inflammatory cytokines and endogenous antioxidants. Neuroprotective therapy aims at minimizing the activation of toxic pathways and at enhancing the activity of endogenous neuroprotective mechanisms. The similarities in the damage-producing and endogenous auto-protective mechanisms may imply that neuroprotective compounds found to be active against one of these conditions may indeed be also protective in the other. This review summarizes the pathogenetic events of ischemic and traumatic brain injury and reviews the neuroprotective strategies employed thus far in each of these conditions with a special emphasize on their clinical relevance and on future directions in the field of neuronal protection.

NAP, a femtomolar-acting peptide, protects the brain against ischemic injury by reducing apoptotic death

BACKGROUND AND PURPOSE

We sought to determine the cerebroprotective potential of NAP, a synthetic octapeptide related to vasoactive intestinal peptide. Activity-dependent neuroprotective protein mediates some of the protective effects of vasoactive intestinal peptide. The neuroprotective NAP sequence is derived from activity-dependent neuroprotective protein.

METHODS

Spontaneously hypertensive rats underwent permanent middle cerebral artery occlusion by craniotomy and electrocoagulation. After dose-response and time-course experiments, the animals were injected with NAP (3 microg/kg) or vehicle intravenously 1 hour after stroke onset. Another group of rats was injected with the D-amino acid isomer of NAP (D-NAP) and served as a negative control. Rats were examined for motor and behavioral deficits 24 hours to 30 days later, and infarct volumes were determined. The effect of NAP administration on apoptotic death was determined by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) and caspase-3 stainings.

RESULTS

NAP significantly reduced motor disability and infarct volumes compared with vehicle or D-NAP when tested at 24 hours after stroke onset (9.67+/-1.4% versus 17.04+/-1.18% and 19.19+/-1.9% of hemispheric volume, respectively; P<0.05). NAP given 4 but not 6 hours after permanent middle cerebral artery occlusion still conferred significant neuroprotection (infarct volume 10.9+/-3.9% of hemispheric volume; P<0.05 versus vehicle). Long-term studies demonstrated that infarct volumes and disability scores remained significantly lower after 30 days in NAP-treated animals. NAP significantly reduced the number of apoptotic cells.

CONCLUSIONS

Our results indicate that the durable cerebroprotection by NAP involves antiapoptotic mechanisms.

Delta9 -tetrahydrocannabinol increases brain temperature and inverts circadian rhythms

Delta9-tetrahydrocannabinol (THC) has been shown to protect against focal and global ischemia. Hypothermia is thought to be one mechanism for this protection. These observations are important since brain hyperthermia is known to increase ischemic damage while hypothermia is protective. To establish the effect of THC on brain and body core temperature, brain and body temperature probes were inserted for chronic temperature monitoring (n = 20). THC treated groups were administered THC at either low (0.1 mg/kg) or high (10 mg/kg) dose for 1 week. Brain temperature was recorded during this period and for 1 week following the discontinuation of THC. Chronic administration of THC at either dose increased brain temperature (p < 0.0001) but did not significantly change body core temperature (p = 0.4767) in the freely moving rat.

Early TNF-alpha levels correlate with ischaemic stroke severity

OBJECTIVES

The study aimed to evaluate the levels of an important proinflammatory cytokine tumour necrosis factor-alpha (TNF-alpha) in cerebrospinal fluid (CSF) and serum in acute stroke and to study the relation between those and the neurological stroke severity and functional disability.

MATERIAL AND METHODS

The investigations comprised 23 ischaemic stroke patients. CSF and blood samples were obtained 24 h after the onset of stroke, and stored until analysis. Patients were examined according to Scandinavian Stroke Scale (SSS) and to Barthel Index (BI).

RESULTS

The patients displayed statistically significant high levels of TNF-alpha in CSF and sera within the first 24 h of stroke. These correlated significantly with SSS and BI scores calculated within the same interval, and 1 and 2 weeks later.

CONCLUSION

Our results suggest the involvement of TNF-alpha in mechanisms of early stroke-induced inflammation and a predictive value of the initial TNF-alpha levels for the outcome of stroke.

Long term cerebroprotective effects of dexanabinol in a model of focal cerebral ischemia

In order to test the long-term cerebroprotective effects of dexanabinol, a synthetic non-competitive NMDA antagonist that also has anti-TNFalpha effects, spontaneously hypertensive rats underwent permanent middle cerebral artery occlusion (PMCAO). Rats were given vehicle or dexanabinol (4.5 mg/kg) 1, 3 or 6 h after PMCAO. The research consisted of 2 stages. In the short-term set of experiments animals (n=5/group), were tested with a motor disability scale 24 h post PMCAO, then sacrificed and the infarct volume was measured using 2,3,5-Triphenyltetrazolium chloride (TTC) staining. In the long-term set of experiments the rats (n=7/group) were examined daily with a motor disability scale up to 30 days after PMCAO and then sacrificed and infarct volumes were determined using TTC staining. Motor scores were significantly improved in the dexanabinol treated rats (P<0.05 for all groups) at all the time points examined. Infarct volumes were significantly reduced 24 h after PMCAO in the groups treated 1 or 3 h, but not 6 h after PMCAO compared with vehicle (Mean+/-S.D., 11.5+/-2.02, 12+/-3.2 and 14.4+/-2.4% vs. 20.8+/-1.3% hemispheric volume respectively). The lesions remained significantly smaller in the dexanabinol groups 30 days after PMCAO (Mean+/-S.D., 24.49+/-1.9% vs. 8.1+/-0.6, 11.1+/-2.3 and 13.8+/-2.5% hemispheric volume in animals treated with vehicle vs. dexanabinol 1, 3 or 6 h after PMCAO respectively; P<0.05 for all). In conclusion, the extended therapeutic window and the multi-mechanistic durable neuroprotective effects of dexanabinol make it a promising candidate for future stroke therapy.

TNF-alpha stimulates caspase-3 activation and apoptotic cell death in primary septo-hippocampal cultures

Primary septo-hippocampal cell cultures were incubated in varying concentrations of tumor necrosis factor (TNF-alpha; 0.3-500 ng/ml) to examine proteolysis of the cytoskeletal protein alpha-spectrin (240 kDa) to a signature 145 kDa fragment by calpain and to the apoptotic-linked 120-kDa fragment by caspase-3. The effects of TNF-alpha incubation on morphology and cell viability were assayed by fluorescein diacetate-propidium iodide (FDA-PI) staining, assays of lactate dehydrogenase (LDH) release, nuclear chromatin alterations (Hoechst 33258), and internucleosomal DNA fragmentation. Incubation with varying concentrations of TNF-alpha produced rapid increases in LDH release and nuclear PI uptake that were sustained over 48 hr. Incubation with 30 ng/ml TNF-alpha yielded maximal, 3-fold, increase in LDH release and was associated with caspase-specific 120-kDa fragment but not calpain-specific 145-kDa fragment as early as 3.5 hr after injury. Incubation with the pan-caspase inhibitor, carbobenzosy- Asp-CH(2)-OC (O)-2-6-dichlorobenzene (Z-D-DCB, 50-140 microM) significantly reduced LDH release produced by TNF-alpha. Apoptotic-associated oligonucleosomal-sized DNA fragmentation on agarose gels was detected from 6 to 72 hr after exposure to TNF-alpha. Histochemical changes included chromatin condensation, nuclear fragmentation, and formation of apoptotic bodies. Results of this study suggest TNF-alpha may induce caspase-3 activation but not calpain activation in septo-hippocampal cultures and that this activation of caspase-3 at least partially contributes to TNF-alpha-induced apoptosis.

Neuroprotection: is it already applicable to glaucoma therapy?

Many categories of both natural and synthetic compounds have been reported to have neuroprotective activity. These include not only antioxidants, N-methyl-D-aspartate receptor antagonists, inhibitors of glutamate release, calcium channel blockers, polyamine antagonists, and nitric oxide synthase inhibitors, but cannabinoids, aspirin, melatonin, and vitamin B-12. The lack of availability of specific neuroprotectant compounds in the United States and the lack of clinical trials examining the benefits of neuroprotective agents for glaucoma currently limit the use of these agents. This article provides a short overview of the concept of neuroprotection as it applies to glaucoma and suggests the possibility of neuroprotective activity that might be provided by compounds that are presently easily available.