The norepinephrine precursor L-threo-3,4-dihydroxyphenylserine facilitates motor recovery in chronic stroke patients

Pharmacotherapy in stroke rehabilitation

BACKGROUND

Pharmacotherapy is commonly given to patients recovering from a stroke to prevent further complications (e.g. recurrent stroke, seizures) or enhance recovery. However, some drugs may have a negative impact on neuroplasticity.

OBJECTIVES

This review examines currently used drugs that are believed to promote recovery from motor and cognitive disturbances associated with stroke.

METHODS

Literature regarding the properties, efficacy, safety, and dosing of drugs used to promote recovery after stroke was reviewed.

RESULTS

The data on pharmacotherapy are insufficient to support a claim of significantly improved rehabilitation outcomes. Moreover, a growing body of evidence indicates that some agents can impair functional reorganization and slow the recovery process. However, a few chemicals are reported to be beneficial for stroke rehabilitation. The most promising are noradrenergic and dopaminergic agents, as well as several growth factors; these should be the future focus of extensive randomized clinical trials.

CONCLUSIONS

Currently there is no drug with proven efficacy in enhancing poststroke recovery.

Large scale analysis of genes contributing to the herbal preparation dependent hippocampal plasticity in postischemic rehabilitation

Herbal preparations can affect the expression of many genes involved in the ischemic process. These genes have been providing insights into the molecular basis of brain plasticity in stroke rehabilitation. However, the extent of plasticity has not been investigated using a chemogenomic approach. A herbal preparation (270 mg/kg) used to treat ischemic mice for 45 days after global ischemia resulted in a significant decrease in infarct volume and neurological score compared with that of vehicle. This effect was characterized by investigating chemical genomic profiles of the mouse hippocampus with a cDNA microarray containing 1176 known genes. Treatment with the herbal preparation reversed the expression of 46 genes out of 100 genes altered in untreated ischemic mouse hippocampus. These data indicated that more genes were upregulated (60.78%) than downregulated (30.61%), and only 46 genes (46%) appear to be prime targets for therapeutic intervention in ischemia. The altered genes can be classified into seven groups, including signal transduction (12 genes, 27%), oncogene (8 genes, 17%), and transcriptional regulation (7 genes, 15%). Such multiple plasticity of expression could be considered as the beneficial role of this herbal preparation in stroke rehabilitation. Changes in gene expression of nuclear factor of activated T cells, 14-3-3 eta, and beta-arrestin suggest a potential role for the immune system in this plasticity. Brain plasticity originates from a balance of up and downregulated genes (Yin and Yang), and reversal of gene expression in multiple pathways indicates that a complex signaling network may be constructed and investigated further.

Midodrine Hydrochloride and l-threo-3,4-dihydroxy-Phenylserine Preserve Cerebral Blood Flow in Hemodialysis Patients With Orthostatic Hypotension

Orthostatic hypotension (OH) after hemodialysis (HD) is a serious complication, as it causes various neurological symptoms and even ischemic brain damage. The aim of the present study was to evaluate the effects of antihypotensive agents, midodrine hydrochloride (MID) and L-threo-3,4-dihydroxyphenylserine (L-DOPS), on OH after HD. We measured systolic blood pressure (SBP) and cerebral blood flow velocity in the middle cerebral artery (MCVm, by transcranial Doppler sonography), in patients with OH during a 5-min 60-degree head-up tilt test at both before and after 4-week treatment with MID at 4 mg/day (N = 6) or L-DOPS at 400 mg/day (N = 7). Both MID and L-DOPS did not significantly protect against falls in systolic BP (SBP) after passive head-up tilt. However, a significant improvement was achieved in MCVm-decrement in the MID group at 3 min and the L-DOPS group at 0, 1 and 3 min during head-up tilt. Although MID and L-DOPS did not prevent OH after HD in HD patients, both agents preserved cerebral blood flow during orthostasis in HD patients with OH.

L-Dihydroxyphenylserine (L-DOPS): A Norepinephrine Prodrug

L-threo-3,4-dihydroxyphenylserine (L-DOPS, droxydopa) is a synthetic catecholamino acid. When taken orally, L-DOPS is converted to the sympathetic neurotransmitter, norepinephrine (NE), via decarboxylation catalyzed by L-aromatic-amino-acid decarboxylase (LAAAD). Plasma L-DOPS levels peak at about 3 h, followed by a monoexponential decline with a half-time of 2 to 3 h. Plasma levels of NE and of its main neuronal metabolite, dihydroxyphenylglycol (DHPG) peak approximately concurrently but at much lower concentrations. The relatively long half-time for disappearance of L-DOPS from plasma, compared to that of NE, explains their very different attained plasma concentrations. In patients with neurogenic orthostatic hypotension, L-DOPS increases blood pressure and ameliorates orthostatic intolerance. Inhibition of LAAAD, such as by treatment with carbidopa, which does not penetrate the blood-brain barrier, prevents the blood pressure effects of the drug, indicating that L-DOPS increases blood pressure by augmenting NE production outside the brain. Patients with pure autonomic failure (which usually entails loss of sympathetic noradrenergic nerves), and patients with multiple system atrophy (in which noradrenergic innervation remains intact) have similar plasma NE responses to L-DOPS. This suggests mainly non-neuronal production of NE from L-DOPS. L-DOPS is very effective in treatment of deficiency of dopamine-beta-hydroxylase (DBH), the enzyme required for conversion of dopamine to NE in sympathetic nerves. L-DOPS holds promise for treating other much more common conditions involving decreased DBH activity or NE deficiency, such as a variety of syndromes associated with neurogenic orthostatic hypotension.

No effects of enhanced central norepinephrine on finger-sequence learning and attention

RATIONALE

When paired with training, substances that increase monoaminergic transmission in the brain support motor and language learning in healthy subjects and in rehabilitation after brain lesions.

OBJECTIVES

To test the hypotheses that enhancement of central norepinephrine by the selective norepinephrine reuptake inhibitor reboxetine (1) improves skilled motor performance, (2) promotes skilled motor learning, and (3) does not exert these effects by modulation of attention.

METHODS

In a double blind, placebo-controlled, crossover study in healthy, adult subjects (n=16), finger-sequence performance and learning was measured after the stimulation of the central noradrenergic system with a single dose (8 mg) of reboxetine and placebo. Effects on attention were assessed by the standardized continuous performance test "CPT-M".

RESULTS

No differential effects of reboxetine or placebo on finger-sequence performance, learning and parameters of attention were found.

CONCLUSION

Selective stimulation of the central noradrenergic system did not promote skilled motor learning or performance as assessed by finger-sequences. The plasticity-enhancing effect of reboxetine, documented in other studies, appears to be dependent on specific neurophysiological and neuropsychological characteristics of the task, and cannot be generalized to other behavioral paradigms.

Veterans Affairs/Department of Defense Clinical Practice Guideline for the Management of Adult Stroke Rehabilitation Care: executive summary

BACKGROUND

A panel of experts developed stroke rehabilitation guidelines for the Veterans Health Administration and Department of Defense Medical Systems.

METHODS

Starting from previously established guidelines, the panel evaluated published literature through 2002, using criteria developed by the US Preventive Services Task Force. Recommendations were based on evidence from randomized clinical trials, uncontrolled studies, or consensus expert opinion if definitive data were lacking.

RESULTS

Recommendations with Level I evidence include the delivery of poststroke care in a multidisciplinary rehabilitation setting or stroke unit, early patient assessment via the NIH Stroke Scale, early initiation of rehabilitation therapies, swallow screening testing for dysphagia, an active secondary stroke prevention program, and proactive prevention of venous thrombi. Standardized assessment tools should be used to develop a comprehensive treatment plan appropriate to each patient's deficits and needs. Medical therapy for depression or emotional lability is strongly recommended. A speech and language pathologist should evaluate communication and related cognitive disorders and provide treatment when indicated. The patient, caregiver, and family are essential members of the rehabilitation team and should be involved in all phases of the rehabilitation process. These recommendations are available in their entirety at http://stroke.ahajournals.org/cgi/content/full/36/9/e100. Evidence tables for each of the recommendations are also in the full document.

CONCLUSIONS

These recommendations should be equally applicable to stroke patients receiving rehabilitation in all medical system settings and are not based on clinical problems or resources unique to the Federal Medical System.

Drugs for Stroke Recovery

Clinical trials of pharmacological agents in stroke have mainly focused on events that need to be modified in the very acute stage, such as restoration of blood flow with thrombolytic therapy or reducing the effects of ischaemia with neuroprotective therapy. Thrombolytic therapy is, however, only effective within the first few hours of stroke onset and so far, no neuroprotective therapy has proven to be efficacious in humans. Thus, there is a great need for new pharmacological strategies to improve outcome after stroke. Accumulating evidence supports the assumption that the brain is plastic and improvements can be expected after permanent injuries. Acute and chronic alterations in neurotransmitter regulation after injury affects plasticity and may thus provide a basis for new pharmacological targets for stroke recovery. The search for pharmacological therapies that affect the recovery process after a permanent injury has been intensified during the last decade. Amphetamines, in combination with training, are currently one of the most promising pharmacological strategies studied for recovery after stroke. Several non-mutually exclusive hypotheses, more or less supported by experimental studies, have tried to explain the mechanisms underlying the facilitation of recovery of function with amphetamine treatment. Amphetamines are believed to hasten the processes in the brain, such as plasticity mechanisms and resolution of diaschisis. The combination of amphetamine and task-specific training seems to be of importance to the outcome. Results from animal studies are consistent between different models and species, and mainly show an increased rate of recovery but there are a few exceptions, with some studies reporting no effect or even a decreased recovery rate. In humans the number of randomised controlled studies of amphetamines is growing rapidly. Results from a Cochrane systematic review indicate a faster motor and language recovery rate with treatment, but the number of studies is too few and studies are too small to draw definite conclusions about the effect on recovery of stroke. Data in the systematic review also indicate that the mortality rate is higher in amphetamine-treated patients compared with placebo-treated patients. However, this is most likely because of baseline imbalances between the treatment groups with patients with more severe strokes being allocated to amphetamine treatment. Further clinical trials are justified, but at present amphetamines should not be used in clinical practice.

Toward wisdom from failure: lessons from neuroprotective stroke trials and new therapeutic directions

BACKGROUND

Neuroprotective drugs for acute stroke have appeared to work in animals, only to fail when tested in humans. With the failure of so many clinical trials, the future of neuroprotective drug development is in jeopardy. Current hypotheses and methodologies must continue to be reevaluated, and new strategies need to be explored. Summary of Review- In part 1, we review key challenges and complexities in translational stroke research by focusing on the "disconnect" in the way that neuroprotective agents have traditionally been assessed in clinical trials compared with animal models. In preclinical studies, determination of neuroprotection has relied heavily on assessment of infarct volume measurements (instead of functional outcomes), short-term (instead of long-term) end points, transient (instead of permanent) ischemia models, short (instead of extended) time windows for drug administration, and protection of cerebral gray matter (instead of both gray and white matter). Clinical trials have often been limited by inappropriately long time windows, insufficient statistical power, insensitive outcome measures, inclusion of protocol violators, failure to target specific stroke subtypes, and failure to target the ischemic penumbra. In part 2, we explore new concepts in ischemic pathophysiology that should encourage us also to think beyond the hyperacute phase of ischemia and consider the design of trials that use multiagent therapy and exploit the capacity of the brain for neuroplasticity and repair.

CONCLUSIONS

By recognizing the strengths and limitations of animal models of stroke and the shortcomings of previous clinical trials, we hope to move translational research forward for the development of new therapies for the acute and subacute stages after stroke.