Cerebro-protective effects of ENA713, a novel acetylcholinesterase inhibitor, in closed head injury in the rat

The effect of donepezil on the cognitive ability early in the course of recovery from traumatic brain injury

OBJECTIVE

To investigate the effect of donepezil on cognitive ability in patients who have sustained a traumatic brain injury (TBI). We hypothesized that donepezil, an acetylcholinesterase inhibitor, would enhance cognitive recovery beyond that of usual care in an acute rehabilitation facility.

METHODS

This retrospective, longitudinal analysis included 55 patients who were non-randomly prescribed donepezil during acute care and compared them to 74 patients who received usual rehabilitation treatment. All 129 patients completed neuropsychological assessment at two time points. Donepezil was increased from 5 to 10 mg 7-10 days after initiation and maintained until follow-up cognitive assessment.

MAIN OUTCOMES

Primary cognitive abilities of interest included processing speed, attention and memory. Cognitive and functional abilities were assessed by a standard neuropsychological battery for TBI.

RESULTS

Propensity scores were used to adjust for differences between groups. Mixed effect model analysis showed no significant differences between treatment and control groups on all neuropsychological subtests over time.

CONCLUSIONS

Acute administration of donepezil did not significantly improve measures of cognitive or functional ability beyond that of treatment as usual in patients with moderate-to-severe TBI.

Weight Drop Models in Traumatic Brain Injury

Weight drop models in rodents have been used for several decades to advance our understanding of the pathophysiology of traumatic brain injury. Weight drop models have been used to replicate focal cerebral contusion as well as diffuse brain injury characterized by axonal damage. More recently, closed head injury models with free head rotation have been developed to model sports concussions, which feature functional disturbances in the absence of overt brain damage assessed by conventional imaging techniques. Here, we describe the history of development of closed head injury models in the first part of the chapter. In the second part, we describe the development of our own weight drop closed head injury model that features impact plus rapid downward head rotation, no structural brain injury, and long-term cognitive deficits in the case of multiple injuries. This rodent model was developed to reproduce key aspects of sports concussion so that a mechanistic understanding of how long-term cognitive deficits might develop will eventually follow. Such knowledge is hoped to impact athletes and war fighters and others who suffer concussive head injuries by leading to targeted therapies aimed at preventing cognitive and other neurological sequelae in these high-risk groups.

Alterations in Cholinergic Pathways and Therapeutic Strategies Targeting Cholinergic System after Traumatic Brain Injury

Traumatic brain injury (TBI) results in varying degrees of disability in a significant number of persons annually. The mechanisms of cognitive dysfunction after TBI have been explored in both animal models and human clinical studies for decades. Dopaminergic, serotonergic, and noradrenergic dysfunction has been described in many previous reports. In addition, cholinergic dysfunction has also been a familiar topic among TBI researchers for many years. Although pharmacological agents that modulate cholinergic neurotransmission have been used with varying degrees of success in previous studies, improving their function and maximizing cognitive recovery is an ongoing process. In this article, we review the previous findings on the biological mechanism of cholinergic dysfunction after TBI. In addition, we describe studies that use both older agents and newly developed agents as candidates for targeting cholinergic neurotransmission in future studies.

Pharmacotherapy of traumatic brain injury: state of the science and the road forward: report of the Department of Defense Neurotrauma Pharmacology Workgroup

Despite substantial investments by government, philanthropic, and commercial sources over the past several decades, traumatic brain injury (TBI) remains an unmet medical need and a major source of disability and mortality in both developed and developing societies. The U.S. Department of Defense neurotrauma research portfolio contains more than 500 research projects funded at more than $700 million and is aimed at developing interventions that mitigate the effects of trauma to the nervous system and lead to improved quality of life outcomes. A key area of this portfolio focuses on the need for effective pharmacological approaches for treating patients with TBI and its associated symptoms. The Neurotrauma Pharmacology Workgroup was established by the U.S. Army Medical Research and Materiel Command (USAMRMC) with the overarching goal of providing a strategic research plan for developing pharmacological treatments that improve clinical outcomes after TBI. To inform this plan, the Workgroup (a) assessed the current state of the science and ongoing research and (b) identified research gaps to inform future development of research priorities for the neurotrauma research portfolio. The Workgroup identified the six most critical research priority areas in the field of pharmacological treatment for persons with TBI. The priority areas represent parallel efforts needed to advance clinical care; each requires independent effort and sufficient investment. These priority areas will help the USAMRMC and other funding agencies strategically guide their research portfolios to ensure the development of effective pharmacological approaches for treating patients with TBI.

Effects of treadmill training on limb motor function and acetylcholinesterase activity in rats with stroke

[Purpose] In the present study, we investigated the effects of treadmill training on limb motor function and acetylcholinesterase activity following focal cerebral ischemia injury. [Methods] Focal cerebral ischemia was examined in adult male Sprague-Dawley rats by using a middle cerebral artery occlusion model. Rats were randomly divided into 3 groups. Group I included untreated normal rats (n=12), Group II included untreated rats with focal cerebral ischemia (n=12), and Group III included rats that performed treadmill exercise (20 m/min) training after focal cerebral ischemia (n=12). We determined the limb placement test score for each rat on days 1,7, 14, and 21; acetylcholinesterase activity in the hippocampus was examined at the end of the experiment. [Results] We observed that the motor behavior index improved in the treadmill group, and hippocampal acetylcholinesterase activity was decreased. [Conclusion] These results indicated that treadmill training after focal cerebral ischemia exerts a neuroprotective effects against ischemic brain injury by improving motor performance and decreasing the levels of acetylcholinesterase activity. Furthermore, these results suggest that treadmill training at an appropriate intensity is critical for post-stroke rehabilitation.

Impact of pharmacological treatments on outcome in adult rodents after traumatic brain injury: a meta-analysis

Pharmacological treatments have been widely investigated in pre-clinical animal trials to evaluate their usefulness in reducing cognitive, behavioural and motor problems after traumatic brain injury (TBI). However, the relative efficacy of these agents has yet to be evaluated, making it difficult to assess the strength of evidence for their use in a clinical population. A meta-analytic review of research (1980-2009) was therefore conducted to examine the impact of pharmacological treatments administered to adult male rodents after experimental TBI on cognitive, behavioural, and motor outcome. The PubMed and PsycInfo databases were searched using 35 terms. Weighted Cohen's d effect sizes, percent overlap, Fail-Safe N statistics and confidence intervals were calculated for each treatment. In total, 91 treatments were evaluated in 223 pre-clinical trials, comprising 5988 rodents. Treatments that were investigated by multiple studies and showed large and significant treatment effects were of greatest interest. Of the 16 treatments that were efficacious, six improved cognition, 10 improved motor function and no treatment improved behaviour (depression/anxiety, aggression, zoosocial behaviour). Treatment benefits were found across a range of TBI models. Drug dosage and treatment interval impacted on treatment effects.

Cholinergic deficiency involved in vascular dementia: possible mechanism and strategy of treatment

Vascular dementia (VaD) is a progressive neurodegenerative disease with a high prevalence. Several studies have recently reported that VaD patients present cholinergic deficits in the brain and cerebrospinal fluid (CSF) that may be closely related to the pathophysiology of cognitive impairment. Moreover, cholinergic therapies have shown promising effects on cognitive improvement in VaD patients. The precise mechanisms of these cholinergic agents are currently not fully understood; however, accumulating evidence indicates that these drugs may act through the cholinergic anti-inflammatory pathway, in which the efferent vagus nerve signals suppress pro-inflammatory cytokine release and inhibit inflammation, although regulation of oxidative stress and energy metabolism, alleviation of apoptosis may also be involved. In this paper, we provide a brief overview of the cholinergic treatment strategy for VaD and its relevant mechanisms of anti-inflammation.Acta Pharmacologica Sinica (2009) 30: 879-888; doi: 10.1038/aps.2009.82.

The effects of rivastigmine plus selegiline on brain acetylcholinesterase, (Na, K)-, Mg-ATPase activities, antioxidant status, and learning performance of aged rats

We investigated the effects of rivastigmine (a cholinesterase inhibitor) and selegiline ((-)deprenyl, an irreversible inhibitor of monoamineoxidase-B), alone and in combination, on brain acetylcholinesterase (AChE), (Na(+), K(+))-, Mg(2+)-ATPase activities, total antioxidant status (TAS), and learning performance, after long-term drug administration in aged male rats. The possible relationship between the biochemical and behavioral parameters was evaluated.

METHODS

Aged rats were treated (for 36 days) with rivastigmine (0.3 mg/kg rat/day ip), selegiline (0.25 mg/kg rat/day im), rivastigmine plus selegiline in the same doses and way of administration as separately. Aged and adult control groups received NaCl 0.9% 0.5 ml ip.

RESULTS

TAS was lower in aged than in adult rats, rivastigmine alone does not affect TAS, decreases AChE activity, increases (Na(+), K(+))-ATPase and Mg(2+)-ATPase activity of aged rat brain and improves cognitive performance. Selegiline alone decreases free radical production and increases AChE activity and (Na(+), K(+))-ATPase activity, improving cognitive performance as well. In the combination: rivastigmine seems to cancel selegiline action on TAS and AChE activity, while it has additive effect on (Na(+), K(+))-ATPase activity. In the case of Mg(2+)-ATPase selegiline appears to attenuate rivastigmine activity. No statistically significant difference was observed in the cognitive performance.

CONCLUSION

Reduced TAS, AChE activity and learning performance was observed in old rats. Both rivastigmine and selesiline alone improved performance, although they influenced the biochemical parameters in a different way. The combination of the two drugs did not affect learning performance.

Alterations of acetylcholinesterase activity after traumatic brain injury in rats

OBJECTIVE

The cholinergic system is highly vulnerable to traumatic brain injury (TBI). However, limited information is available to what extent the degrading enzyme acetylcholinesterase (AChE) is involved. The present study addresses this question.

METHOD

Thirty-six anaesthetized Sprague-Dawley rats were subjected to sham operation or to TBI using controlled cortical impact (CCI). The AChE activity was histochemically determined in frozen brain slices at 2, 24 and 72 hours after TBI.

RESULTS

High enzyme activity was observed in regions rich in cholinergic innervation such as the olfactory tubercle, basal forebrain, putamen and superior colliculi. Low activity was found in the cortex, cerebellum and particularly in the white matter. A decrease of AchE activity (20-35%) was found in the hippocampus and hypothalamus already at 2 hours after TBI. An increase of approximately 30% was found in the basal forebrain at 2 and 24 hours. No changes occurred at 72 hours.

CONCLUSION

The findings are consistent with impairment of the cholinergic neurotransmission after TBI and suggest the involvement of the AChE in short-term regulatory mechanisms.

Effect of 3-[1-(phenylmethyl)-4-piperidinyl]-1-(2,3,4,5-tetrahydro-1H-1-benzazepin-8-yl)-1-propanone fumarate, a novel acetylcholinesterase inhibitor, on spatial cognitive impairment induced by chronic cerebral hypoperfusion in rats

It is of interest whether the acetylcholinesterase inhibitor, 3-[1-(phenylmethyl)-4-piperidinyl]-1-(2,3,4,5-tetrahydro-1H-1-benzazepin-8-yl)-1-propanone fumarate (TAK-147), can improve cognitive impairment caused by chronic cerebral ischemia in rats. Two weeks after four-vessel occlusion, apparent impairments of spatial retrieval memory were observed in the Morris water maze. Both TAK-147 at doses of 0.1, 0.3 and 1.0 mg/kg and donepezil at doses of 0.3 and 1.0 mg/kg significantly ameliorated ischemia-induced memory deficits dose-dependently, but tacrine had no appreciable effect. Furthermore, we demonstrate that the intensity of staining by 2,3,5-triphenyltetrazolium in the hippocampal and cortical slices was significantly decreased by ischemia (10 min anoxia/aglycemia), and that it was also significantly restored by treatment with TAK-147 and donepezil.

Rivastigmine, a new-generation cholinesterase inhibitor for the treatment of Alzheimer's disease

Rivastigmine is a cholinesterase inhibitor (ChEI) with a structural formula different from that of currently available ChEIs. Tacrine and donepezil are classified as short-acting or reversible agents since binding to acetylcholinesterase enzyme (AChE) is hydrolyzed within minutes. Rivastigmine is classified as an intermediate-acting or pseudo-irreversible agent due to its long inhibition on AChE of up to 10 hours. Preclinical biochemical studies indicated that rivastigmine has central nervous system selectivity over peripheral inhibition. It ameliorated memory impairment in rats with forebrain lesions. The drug is rapidly absorbed orally, with a bioavailability of 0.355 and low protein binding (40%). Its elimination half-life is less than 2 hours, and it is converted to an inactive metabolite at the site of action, bypassing hepatic metabolic pathways. Its disposition essentially is unaltered in patients with renal or hepatic impairment. It also has dose-dependent effects on AChE inhibition. In the two large multicenter clinical trials (total 1324 patients) that used a forced-dosage titration scheme, rivastigmine 6-12 mg/day was superior to placebo on three cognitive and functioning scales (p<0.001). Gastrointestinal symptoms are the most frequently reported adverse events. They occurred mostly during the dosage titration phase and decreased during the maintenance phase. Rivastigmine offers clinicians another therapeutic agent to treat Alzheimer's disease.

Rivastigmine, a brain-region selective acetylcholinesterase inhibitor for treating Alzheimer's disease: review and current status

Alzheimer's disease is, in part, characterised by the loss of neurones in the basal forebrain cholinergic cells that project to the cerebral cortex and hippocampus. These impairments have correlated with the memory loss noted in dementia of the Alzheimer's type. This 'cholinergic hypothesis' has led to the rational design of drugs to enhance or stimulate acetylcholine-mediated neurotransmission. Early acetylcholinesterase inhibitors, such as tacrine and physostigmine, are poorly tolerated and have a short duration of action. Rivastigmine is a centrally-selective acetylcholinesterase inhibitor with a relatively long duration of action and is a 'pseudo-irreversible' cholinesterase inhibitor due to slow dissociation of a carbamoyl derivative from the esteratic site of acetylcholinesterase. Preclinical studies confirmed the central selectivity of the drug and its distribution into the cerebrospinal fluid (CSF). Early studies demonstrated that rivastigmine improved cognition and was relatively well-tolerated at moderate doses. Clinical investigations of rivastigmine administered at doses of 6 - 12 mg/day significantly improved cognition, as measured by the ADAS-Cog score, and activities of daily living, as measured by the Progressive Deterioration Scale. Significant global improvements were also noted as measured by the Clinician's Interview Based Impression of Change that required the use of caregiver information. The most frequent adverse effects noted in clinical trials were consistent with peripheral cholinergic stimulation and included nausea, vomiting, abdominal pain, dizziness and diarrhoea. These effects were dose-related and minimised by slow dose-escalation upon initiation of therapy. Rivastigmine undergoes minimal metabolism by the cytochrome P450 system. As a result, it has few drug interactions. The drug is currently marketed widely in over 60 countries worldwide. In the United States, the drug received 'approvable' status subsequent to the NDA filing, and should be available later this year.

Rivastigmine. A review of its use in Alzheimer's disease

Rivastigmine (SDZ ENA 713) is a carbamylating, long-acting reversible and noncompetitive carbamate acetylcholinesterase inhibitor that is indicated as an oral treatment for patients with mild to moderately severe Alzheimer's disease. The drug has been evaluated for this use in 3 well designed, adequately powered, phase II/III, 26-week clinical trials that included a total of 1479 rivastigmine and 647 placebo recipients. Most of these patients had concomitant disorders that were being treated with numerous other drugs. Individual and pooled results of these trials indicate that rivastigmine 6 to 12 mg/day usually produces cognitive, global and functional changes that indicate significantly less deterioration than was observed with placebo in patients with mild to moderately severe Alzheimer's disease. Individual results of the 2 pivotal trials and pooled analysis also show that, compared with placebo recipients, significantly more rivastigmine 6 to 12 mg/day recipients respond to therapy. Indeed, after 26 weeks of therapy in the 2 pivotal trials, significantly more rivastigmine 6 to 12 mg/day than placebo recipients achieved clinically meaningful improvements as defined by 3 separate response criteria. The lower dosage range of 1 to 4 mg/day was not as effective as 6 to 12 mg/day, as measured using these criteria and other efficacy parameters. Rivastigmine causes adverse events that are generally those expected from an acetylcholinesterase inhibitor. They are usually mild to moderate, of short duration and responsive to dosage reduction. Unpublished data from 3989 patients indicate that rivastigmine and placebo were associated with similar incidences of serious adverse events and changes in laboratory parameters, ECG and cardiorespiratory vital signs. The most common events were gastrointestinal, central and peripheral nervous system and whole body adverse events. However, compared with placebo, rivastigmine more commonly caused adverse events resulting in treatment withdrawal. These events were most frequently gastrointestinal and were more common in women.

CONCLUSION

Rivastigmine is a useful option for the treatment of patients with mild to moderately severe Alzheimer's disease. Although only short term (6- month) comparisons with placebo are available, given the lack of established treatment options it should be considered for first-line use in this population.