Herbal therapy: a new pathway for the treatment of Alzheimer's disease
It has been a clinical challenge to treat Alzheimer's disease (AD). In the present commentary we discuss whether herbal therapy could be a novel treatment method for AD on the basis of results from clinical trials, and discuss the implications for potential therapy for AD pathophysiology. There is evidence to suggest that single herbs or herbal formulations may offer certain complementary cognitive benefits to the approved drugs. The current evidence supporting their use alone, however, is inconclusive or inadequate owing to many methodological limitations. Herbal mixtures may have advantages with multiple target regulation compared with the single-target antagonist in the view of traditional Chinese medicine. Several clinical trials using herbal mixtures are being conducted in China and will hopefully show promising results for treating AD in the near future.
KeywordsMild Cognitive Impairment Memantine Clinical Dementia Rate Aniracetam Ginkgo Biloba Extract
Alzheimer Disease Assessment Scale.
The ultimate aim of Alzheimer's disease (AD) therapy is to stop or slow down the disease progression. Cholinesterase inhibitors have a modest clinical effect on the symptoms, however, and memantine - the currently available N-methyl-D-aspartate receptor antagonist - does not prevent the deterioration of dementia [1, 2]. Finding an effective method to treat AD still poses a significant clinical challenge.
Different herbs and formulations effective in the treatment of Alzheimer's disease
An extract from Lycopodium
A 12-week randomized, double-blind, placebo-controlled trial
ADAS-cog, MMSE, CIBIC-plus, ADL of patients with mild to moderate AD
Zhang and colleagues 
A 24-week randomized, placebo- controlled, double-blind study
MMSE and CGI in patients with mild to moderate AD
Mazza and colleagues 
A 12-week open-label, randomized double-blind, placebo-controlled study
ADAS and MMSE scores of AD patients
Lee and colleagues 
Leaf extract containing monoterpene, flavonoids, polyphenol
A 4-month, parallel-group, placebo- controlled trial
ADAS-cog and CDR in patients with mild to moderate AD
Akhondzadeh and colleagues 
Ba Wei Di Hunag Wan
Powder of Rehmannia with another seven plants mixed with honey
An 8-week randomized, double-blind, placebo-controlled trial
MMSE and Barthel Index scores in patients with mild to severe dementia
Iwasaki and colleagues 
Yi-Gan San formula
A mixture of seven different rootstock and branches, lyophilized dry extract
A 4-week randomized, observer-blind, controlled trial
NPI and ADL in patients with mild to severe dementia
Iwasaki and colleagues 
Single herbs or extracts from herbs
Ginkgo biloba extract is among the most widely used complementary therapies. A Cochrane review included 36 trials of gingko biloba, but most trials were small and of duration <3 months . Nine trials were of 6 months duration and of adequate size, and were conducted to a reasonable standard. Of the four most recent trials to report results, three studies found no difference between Ginkgo biloba, at different doses, and placebo , and one study found very large treatment effects in favor of Ginkgo biloba, but the trial sample size was very small . Another recent trial reported negative results in reducing cognitive decline in older adults with normal cognition or with mild cognitive impairment . The current overall evidence that Ginkgo has a predictable and clinically significant benefit for people with dementia or cognitive impairment therefore seems inconsistent and unreliable.
Huperzine A extracted from the serrate clubmoss herb is a potent, reversible and selective inhibitor of acetyl-cholinesterase. Considering the available evidence from six trials, Huperzine A seems to have some beneficial effects on improvement of general cognitive function, global clinical status, behavioral disturbance and functional performance, with no obvious serious adverse events for patients with AD . Only one study was of adequate quality and size, but the period during this study that found very large treatment effects was only 12 weeks . Overall the current evidence supporting clinical use of Huperzine A is presently inconclusive or inadequate.
Panaxi ginseng's main active ingredient is panaxsaponin, which can enhance psychomotor and cognitive performance, and can benefit AD by improving brain cholinergic function, reducing the level of Aβ and repairing damaged neuronal networks . The high-dose ginseng group showed statistically significant improvement on the Alzheimer Disease Assessment Scale (ADAS) and Clinical Dementia Rating (but not on the Mini-Mental State Examination) at the end of the study, when compared with the control group. This study was poorly designed, with an insufficient description of randomization and without blinding. Furthermore, the sample size was small (n = 15 for each group), and there was also a confounding effect due to concurrently administered western medications . The evidence for ginseng as a treatment of AD is thus scarce and inconclusive. Further rigorous trials seem warranted .
Salvia officinalis has been used in herbal medicine for many centuries. After 4 months of treatment, salvia officinalis extract produced a significantly better outcome on cognitive functions than placebo - as seen on the ADAS cognitive subscale and the Clinical Dementia Rating Sum of Boxes scale in patients with mild to moderate AD aged between 65 and 80 years . There were no significant differences between salvia officinalis and placebo in terms of the observed side effects. In addition, salvia officinalis may reduce agitation in patients. More high-quality large-scale randomized controlled trials are needed, however, for further determination of the herb's efficacy .
Herbal formulations or mixtures of herbal ingredients
Herbal formulations or mixtures of herbal ingredients may have advantages with multiple target regulation compared with the single target antagonist in the view of traditional Chinese medicine, although there have been few clinical trials examining the efficacy and safety of herbal formulations in AD patients.
Shenwu capsule, a mixture of six herbs that is thought to reduce amyloid cytotoxicity, increased the memory score from baseline (n = 83) - but without significant difference from aniracetam (n = 83) - in a 12-week phase II trial for patients with mild cognitive impairment . A phase III trial is now underway. Stilbene glycoside, an extract of Shenwu capsule, has been evaluated in a phase I trial for AD. Further results for both of these formulations will be available in the next few years.
Furthermore, the herbal preparations Ba Wei Di Huang Wan and Yi-Gan San are individually reported to significantly improve cognition or behavior and function on the Mini-Mental State Examination, the Neuropsychiatric Inventory and the Barthel Index in the patients with AD [15, 16].
Single herbs or formulations may be able to complement approved drugs for AD. No serious adverse events have been reported. The current evidence to support their use alone, however, is inconclusive or inadequate. This uncertainty is mainly caused by methodological limitations such as poor study design, relatively small sample sizes without a power calculation, inappropriate outcome measures and primary and secondary end-point selection, and invalid statistical analysis. In addition, the herbs' potential value for prevention and treatment of AD only results from symptomatic changes and short treatment periods (< 6 months). Several studies currently underway or in early-stage development in China to evaluate herb mixtures will hopefully show promising results in the near future.
The present work was supported by the 111 Project (No. B08006), the Beijing Cooperative Study Project of the Capital Foundation of Medical Developments (No. 2005-SF-1-007), New Century Excellent Talents in University (No. NCET-07-0117) and the Innovative Research Team of Alzheimer's Disease and Other Neurodegenerative Diseases of the Ministry of Education of China (No. IRT-08-010).
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