Pharmacology of caffeinol in embolized rabbits: clinical rating scores and intracerebral hemorrhage incidence

Extra-endothelial TRPV1 channels participate in alcohol and caffeine actions on cerebral artery diameter

Alcohol (ethyl alcohol; ethanol) and caffeine are the two most widely used psychoactive substances in the world. Caffeine and ethanol have both been reported to constrict cerebral arteries in several species, including humans. We have recently shown that application of 10-μM caffeine mixed with 50 mM ethanol to in vitro pressurized cerebral arteries of rats reduced ethanol-induced constriction. This effect was dependent on the presence of nitric oxide (NO^•) and could be observed in de-endothelialized arteries supplied with the NO donor sodium nitroprusside (SNP). The molecular target(s) of ethanol-caffeine interaction in cerebral arteries has remained unknown. In the present work, we used rat and mouse middle cerebral arteries (MCA) to identify the extra-endothelial effectors of NO-mediated, caffeine-induced protection against ethanol-evoked arterial constriction. Constriction of intact MCA of rat by either 50 mM ethanol or 10 μM caffeine was ablated in the presence of a selective TRPV1 pharmacological blocker. TRPV1 pharmacological block, but not block of TRPA1, PKG, or BK channels, removed caffeine-induced protection against ethanol-evoked rat MCA constriction, whether evaluated in arteries with intact endothelium or in SNP-supplemented, de-endothelialized arteries. In mouse arteries, caffeine-induced protection against ethanol-induced MCA constriction was significantly amplified, resulting in actual vasodilation, upon pharmacological block of TRPV1, and in TRPV1 knock-out arteries. Despite some species-specific differences, our study unequivocally demonstrates the presence of functional, extra-endothelial TRPV1 that participates in both endothelium-independent MCA constriction by separate exposure to ethanol or caffeine and caffeine-induced protection against ethanol-evoked MCA constriction.

Phase I and Phase II Therapies for Acute Ischemic Stroke: An Update on Currently Studied Drugs in Clinical Research

Acute ischemic stroke is a devastating cause of death and disability, consequences of which depend on the time from ischemia onset to treatment, the affected brain region, and its size. The main targets of ischemic stroke therapy aim to restore tissue perfusion in the ischemic penumbra in order to decrease the total infarct area by maintaining blood flow. Advances in research of pathological process and pathways during acute ischemia have resulted in improvement of new treatment strategies apart from restoring perfusion. Additionally, limiting the injury severity by manipulating the molecular mechanisms during ischemia has become a promising approach, especially in animal research. The purpose of this article is to review completed and ongoing phases I and II trials for the treatment of acute ischemic stroke, reviewing studies on antithrombotic, thrombolytic, neuroprotective, and antineuroinflammatory drugs that may translate into more effective treatments.

A novel method to promote behavioral improvement and enhance mitochondrial function following an embolic stroke

Tissue plasminogen activator (tPA) is the only FDA-approved treatment for stroke; tPA increases cerebral reperfusion, blood flow and improved behavior. Novel transcranial laser therapy (TLT) also enhances cerebral blood flow and activates mitochondrial function. Using the rabbit small clot embolic stroke model (RSCEM), we studied the effects of continuous wave TLT (7.5mW/cm(2)) alone or in combination with standardized intravenous (IV) tPA (3.3mg/kg) applied 1h post-embolization on 3 endpoints: 1) behavioral function measured 2 days [effective stroke dose (P50 in mg) producing neurological deficits in 50% of embolized rabbits], 2) intracerebral hemorrhage (ICH) rate, and 3) cortical adenosine-5'-triphosphate (ATP) content was measured 6h following embolization. TLT and tPA significantly (p<0.05) increased P50 values by 95% and 56% (p<0.05), respectively over control. TLT-tPA increased P50 by 136% over control (p<0.05). Embolization reduced cortical ATP content by 39%; decreases that were attenuated by either TLT or tPA treatment (p<0.05). TLT-tPA further enhanced cortical ATP levels 22% above that measured in naïve control. TLT and tPA both effectively and safely, without affecting ICH rate, improved behavioral outcome in embolized rabbits; and there was a trend (p>0.05) for the TLT-tPA combination to further increase P50. TLT and tPA both attenuated stroke-induced ATP deficits, and the combination of tPA and TLT produced an additive effect on ATP levels. This study demonstrates that the combination of TLT-tPA enhances ATP production, and suggests that tPA-induced reperfusion in combination with TLT neuroprotection therapy may optimally protect viable cells in the cortex measured using ATP levels as a marker.

A blinded, randomized study of L-arginine in small clot embolized rabbits

OBJECTIVE

Tissue plasminogen activator (tPA) is administered to acute ischemic stroke victims in a vehicle formulation containing high concentrations of L-arginine (3.5g/100mg vial), a well-known nitric oxide synthase (NOS) substrate and precursor to nitric oxide (NO), as well as an enhancer of cerebral blood flow.

METHODS

We studied the effects of tPA vehicle compared to tPA (3.3mg/kg) formulated in the same vehicle containing L-arginine, normal saline or normal saline containing L-arginine, on behavioral function following small clot embolic strokes in rabbits using clinical rating scores and quantal analysis curves as the primary end point. Treatments were administered intravenously (1ml/kg; 20% bolus/80% infused over 30min) starting 1h following the injection of small-sized blood clots into the brain vasculature and terminal behavior was measured 2days following embolization. Behavioral rating scores were used to calculate the effective stroke dose (P50 in mg) that produces neurological deficits in 50% of the rabbits.

RESULTS

In this study, tPA significantly (p=0.001) improved behavior compared to all other treatments including tPA vehicle, saline and saline-L-arginine, increasing the P50 by 141% over tPA vehicle. Saline-L-arginine was not significantly different from either saline or tPA vehicle (p>0.05).

CONCLUSION

This study demonstrates that the L-arginine component of the tPA vehicle does not contribute to the reproducible clinical improvement observed following tPA administration in rabbits. Moreover, the administration of L-arginine was not an effective method to promote behavioral recovery following embolic strokes in the stringent rabbit small clot stroke model, nor did L-arginine exacerbate behavioral deficits or intracerebral hemorrhage in embolized rabbits.

Vascular protection to increase the safety of tissue plasminogen activator for stroke

Thrombolytic therapy with tissue plasminogen activator (tPA) remains the most effective treatment for acute ischemic stroke, but can cause vascular damage leading to edema formation and hemorrhagic transformation (HT). In this review, we discuss how tPA contributes to the pathogenesis of vascular damage and highlight evidence to support combination therapy of tPA with pharmacological agents that are vascular protective. There is an unmet need to develop therapeutic interventions which target the underlying mechanisms of vascular damage after acute ischemic stroke in order to prevent HT and improve the safety and impact of tPA.

Impacts of methylxanthines and adenosine receptors on neurodegeneration: human and experimental studies

Neurodegenerative disorders are some of the most feared illnesses in modern society, with no effective treatments to slow or halt this neurodegeneration. Several decades after the earliest attempt to treat Parkinson's disease using caffeine, tremendous amounts of information regarding the potential beneficial effect of caffeine as well as adenosine drugs on major neurodegenerative disorders have accumulated. In the first part of this review, we provide general background on the adenosine receptor signaling systems by which caffeine and methylxanthine modulate brain activity and their role in relationship to the development and treatment of neurodegenerative disorders. The demonstration of close interaction between adenosine receptor and other G protein coupled receptors and accessory proteins might offer distinct pharmacological properties from adenosine receptor monomers. This is followed by an outline of the major mechanism underlying neuroprotection against neurodegeneration offered by caffeine and adenosine receptor agents. In the second part, we discuss the current understanding of caffeine/methylxantheine and its major target adenosine receptors in development of individual neurodegenerative disorders, including stroke, traumatic brain injury Alzheimer's disease, Parkinson's disease, Huntington's disease and multiple sclerosis. The exciting findings to date include the specific in vivo functions of adenosine receptors revealed by genetic mouse models, the demonstration of a broad spectrum of neuroprotection by chronic treatment of caffeine and adenosine receptor ligands in animal models of neurodegenerative disorders, the encouraging development of several A(2A) receptor selective antagonists which are now in advanced clinical phase III trials for Parkinson's disease. Importantly, increasing body of the human and experimental studies reveals encouraging evidence that regular human consumption of caffeine in fact may have several beneficial effects on neurodegenerative disorders, from motor stimulation to cognitive enhancement to potential neuroprotection. Thus, with regard to neurodegenerative disorders, these potential benefits of methylxanthines, caffeine in particular, strongly argue against the common practice by clinicians to discourage regular human consumption of caffeine in aging populations.

Effect of internal carotid artery reperfusion in combination with Tenecteplase on clinical scores and hemorrhage in a rabbit embolic stroke model

In the present study, we used a modification of the rabbit small clot embolic stroke model (RSCEM), a multiple infarct ischemia model to achieve reperfusion (REP) through the internal carotid artery (ICA) following small clot embolization. We determined if increasing regional cortical blood flow (RCBF) following an embolic stroke is beneficial to neurological outcome. We compared this to cerebral reperfusion induced by the administration of the thrombolytic Tenecteplase (TNK, 1.5 mg/kg, IV bolus) in the presence or absence of REP. In this study, we also measured the incidence of ICH following REP and thrombolytic treatment. Following embolization, RCBF was reduced to 48-55% of baseline. When REP was induced by removal of a CCA ligature, RCBF initially increased to 185% of baseline. REP (P(50)=1.18+/-0.43 mg) had no effect on embolization-induced behavior measured 24 h following embolization compared to control (P(50)=1.01+/-0.48 mg). However, TNK treatment (2-hours post-embolization) in the absence or presence of REP (initiated 2 h following embolization) significantly (p<0.05) increased the group P(50) to 2.92+/-0.55 mg and 2.42+/-0.40 mg, respectively. In addition, ICH was increased in the REP (42%, p<0.05) and REP-TNK (35%, p>0.05) group compared to either the control group (5.5%) or TNK group (10%). This study show that reperfusion of ICA can increase RCBF following embolization, but this is not associated with improved neurological outcome measured using quantal analysis. However, TNK administration significantly increased behavioral outcome when given 2 h following embolization; an increase that is not affected by combining TNK with REP.

Combined neuroprotective modalities coupled with thrombolysis in acute ischemic stroke: a pilot study of caffeinol and mild hypothermia

BACKGROUND

Both caffeinol and hypothermia are neuroprotective in preclinical models of transient middle cerebral artery occlusion. We tested whether combining caffeinol and hypothermia with tissue plasminogen activator (t-PA) in patients with acute stroke is safe and feasible.

METHODS

Twenty patients with acute ischemic stroke were treated with caffeinol (caffeine 8-9 mg/kg + ethanol 0.4 g/kg intravenously [IV] x 2 hours, started by 4 hours after symptom onset) and hypothermia (started by 5 hours and continued for 24 hours [target temperature 33-35 degrees C] followed by 12 hours of rewarming). IV t-PA was given to eligible patients. Meperidine and buspirone were used to suppress shivering.

RESULTS

All patients received caffeinol, and most reached target blood levels. Cooling was attempted in 18 patients via endovascular (n = 8) or surface (n = 10) approaches. Two patients were not cooled due to catheter or machine failure. Thirteen patients reached target temperature; average time from symptom onset was 9 hours and 43 minutes. The last 5 hypothermia patients received surface cooling with iced saline induction and larger doses of meperidine; all patients reached target temperature, on average within 2 hours and 30 minutes from induction and 6 hours and 21 minutes from symptom onset. Three patients died: one from symptomatic hemorrhage, one from malignant cerebral edema, and one from unrelated medical complications. No adverse events were attributed to caffeinol. One patient had reduced respiratory drive due to meperidine, requiring BiPAP.

DISCUSSION

Combining caffeinol with hypothermia in patients with acute stroke given IV t-PA is feasible. A prospective placebo-controlled randomized study is needed to further assess safety and to test the efficacy of caffeinol, hypothermia, or both.

Methodological quality of animal studies of neuroprotective agents currently in phase II/III acute ischemic stroke trials

BACKGROUND AND PURPOSE

Numerous neuroprotective agents have proven effective in animal stroke studies, but every drug has failed to achieve its primary outcome when brought forward to clinical trials. We analyzed the quality and adequacy of animal studies supporting the efficacy of NXY-059 and other neuroprotective agents that are currently being investigated in phase II/III trials.

METHODS

We conducted a systematic search of all neuroprotective drugs in Phase II or III trials and collected data from animal studies of focal cerebral ischemia testing agents systemically administered within 24 hours of occlusion. The methodological rigor of each individual study was evaluated using 5 criteria derived from the STAIR guidelines. The adequacy of the preclinical "package" for each drug was then evaluated by combining the results of all studies for each drug to determine which of a further 5 STAIR criteria were met before moving forward from animal to human studies.

RESULTS

Our search yielded 13 agents of which 10 had published data in peer-reviewed journals. There is substantial within-drug variability in the quality of preclinical studies as well as substantial variation in the completeness of the collective preclinical literature for different drugs. There has been little or no improvement in the quality of animal studies since NXY-059, and current agents have not been subjected to a more complete preclinical evaluation.

CONCLUSIONS

There is significant heterogeneity in the quality of animal testing for neuroprotective agents in stroke. Drugs in the post-SAINT era have not been subjected to more thorough preclinical evaluation.

Neuroprotection in cerebral ischemia: emphasis on the SAINT trial

Acute ischemic stroke (AIS) is a significant cause of death and disability in the United States. It has been 10 years since tissue plasminogen activator became the first medication approved by the US Food and Drug Administration for treatment for AIS. However, this treatment simply reopens arteries. The identification of deleterious cellular reactions that occur secondary to cerebral ischemia has led investigators to search for neuroprotection strategies to complement reperfusion. More than 100 human trials, including a handful of phase III trials, had failed to produce an efficacious neuroprotective agent. In 2006, the first positive trial of neuroprotection was published: the SAINT I (Stroke-Acute Ischemic NXY Treatment) study. In February 2008, the SAINT II study was published, indicating that NXY-059 was not effective for AIS treatment.

Therapeutic potential of adenosine A2A receptor antagonists in Parkinson's disease

In the pursuit of improved treatments for Parkinson's disease (PD), the adenosine A(2A) receptor has emerged as an attractive nondopaminergic target. Based on the compelling behavioral pharmacology and selective basal ganglia expression of this G-protein-coupled receptor, its antagonists are now crossing the threshold of clinical development as adjunctive symptomatic treatment for relatively advanced PD. The antiparkinsonian potential of A(2A) antagonism has been boosted further by recent preclinical evidence that A(2A) antagonists might favorably alter the course as well as the symptoms of the disease. Convergent epidemiological and laboratory data have suggested that A(2A) blockade may confer neuroprotection against the underlying dopaminergic neuron degeneration. In addition, rodent and nonhuman primate studies have raised the possibility that A(2A) receptor activation contributes to the pathophysiology of dyskinesias-problematic motor complications of standard PD therapy--and that A(2A) antagonism might help prevent them. Realistically, despite being targeted to basal ganglia pathophysiology, A(2A) antagonists may be expected to have other beneficial and adverse effects elsewhere in the central nervous system (e.g., on mood and sleep) and in the periphery (e.g., on immune and inflammatory processes). The thoughtful design of new clinical trials of A(2A) antagonists should take into consideration these counterbalancing hopes and concerns and may do well to shift toward a broader set of disease-modifying as well as symptomatic indications in early PD.

Lost in translation: taking neuroprotection from animal models to clinical trials

Caffeinol has been proposed as a neuroprotectant for human trials. This review covers a variety of animal models used and various attempts to take animal protocols to human trials. The accompanying paper discusses the rabbit model that was used to identify the efficacy of tissue plasminogen activator (tPA) treatment. To date, this is the only model that was able to achieve laboratory to clinical translational success. Use of caffeinol as a cytoprotective agent in rat models yielded exciting results, which led to clinical trials. However, caffeinol given with tPA in rabbits leads to increased hemorrhage. Caffeinol alone does not prove to be neuroprotective, as vasodilation by itself is not efficacious. However, vasodilation combined with thrombolysis (caffeinol with tPA) poses an increased risk of hemorrhage. For a more translational approach to study neuroprotection and neuroprotective agents in human trials, it is necessary to demonstrate the efficacy of the procedure and purported agents in several animal models.