Huperzine a as potential treatment of Alzheimer's disease: an assessment on chemistry, pharmacology, and clinical studies.

Alzheimer's disease (AD) is the fourth leading cause of death in adults, characterized by hallmark neuritic plaques and neurofibrillary tangles. Current treatments focus only on symptom relief. As a possible new treatment option for AD, huperzine A's chemistry, pharmacology, and clinical effectiveness are assessed. The chemical synthesis of huperzine A has been optimized, while an in vitro technique has provided a renewable plant source. Pharmacological studies showed that the drug inhibits the enzyme acetylcholinesterase reversibly and selectively. Huperzine A also displayed good pharmacokinetics with a rapid absorption and a wide distribution in the body at a low to moderate rate of elimination. Presently, inadequate toxicity data in human have been reported, yet animal studies demonstrated mild to moderate cholinergic side effects at therapeutic doses. Previous clinical trials have shown improvement in memory function using MMSE, MQ, ADAS-COG, and ADL tests. In an unpublished phase II clinical trial, the ADAS-COG and MMSE tests indicated cognitive enhancement at a dose of 0.4 mg, yet no improvement was observed at a dose of 0.2 mg. The MMSE scores indicated cognitive enhancement at 0.4 mg. Promising data suggested that huperzine A is well tolerated at doses up to 0.4 mg for 24 weeks. Therefore, huperzine A seems to be a potential treatment option for AD.