X-ray structures of Torpedo californica acetylcholinesterase complexed with (+)-huperzine A and (-)-huperzine B: structural evidence for an active site rearrangement.

Kinetic and structural data are presented on the interaction with Torpedo californica acetylcholinesterase (TcAChE) of (+)-huperzine A, a synthetic enantiomer of the anti-Alzheimer drug, (-)-huperzine A, and of its natural homologue (-)-huperzine B. (+)-Huperzine A and (-)-huperzine B bind to the enzyme with dissociation constants of 4.30 and 0.33 microM, respectively, compared to 0.18 microM for (-)-huperzine A. The X-ray structures of the complexes of (+)-huperzine A and (-)-huperzine B with TcAChE were determined to 2.1 and 2.35 A resolution, respectively, and compared to the previously determined structure of the (-)-huperzine A complex. All three interact with the "anionic" subsite of the active site, primarily through pi-pi stacking and through van der Waals or C-H.pi interactions with Trp84 and Phe330. Since their alpha-pyridone moieties are responsible for their key interactions with the active site via hydrogen bonding, and possibly via C-H.pi interactions, all three maintain similar positions and orientations with respect to it. The carbonyl oxygens of all three appear to repel the carbonyl oxygen of Gly117, thus causing the peptide bond between Gly117 and Gly118 to undergo a peptide flip. As a consequence, the position of the main chain nitrogen of Gly118 in the "oxyanion" hole in the native enzyme becomes occupied by the carbonyl of Gly117. Furthermore, the flipped conformation is stabilized by hydrogen bonding of Gly117O to Gly119N and Ala201N, the other two functional elements of the three-pronged "oxyanion hole" characteristic of cholinesterases. All three inhibitors thus would be expected to abolish hydrolysis of all ester substrates, whether charged or neutral.

Huperzine A attenuates cognitive deficits and hippocampal neuronal damage after transient global ischemia in gerbils.

The protective effects of huperzine A on transient global ischemia in gerbils were investigated. Five min of global ischemia in gerbils results in working memory impairments shown by increased escape latency in a water maze and reduced time spent in the target quadrant. These signs of dysfunction are accompanied by delayed degeneration of pyramidal hippocampal CA1 neurons and by decrease in acetylcholinesterase activity in the hippocampus. Subchronic oral administration of huperzine A (0.1 mg/kg, twice per day for 14 days) after ischemia significantly reduced the memory impairment, reduced neuronal degeneration in the CA1 region, and partially restored hippocampal choline acetyltransferase activity. The ability of huperzine A to attenuate memory deficits and neuronal damage after ischemia might be beneficial in cerebrovascular type dementia.

Huperzine B, a novel acetylcholinesterase inhibitor, attenuates hydrogen peroxide induced injury in PC12 cells.

A number of studies indicate that free radicals are involved in the neurodegeneration in Alzheimer's disease (AD). The present study was mainly conducted to examine the effect of Huperzine B on H(2)O(2) induced toxicity in rat pheochromocytoma line PC12 by measuring cell lesion, level of lipid peroxidation and antioxidant enzyme activities. Following a 30 min exposure of the cells to H(2)O(2) (150 microM), a marked decrease in cell survival, activities of glutathione peroxidase and catalase as well as increased production of malondialdehyde (MDA) were found. Pretreatment of the cells with huperzine B (10-100 microM) prior to H(2)O(2) exposure significantly elevated the cell survival, antioxidant enzyme activities and decreased the level of MDA. The above-mentioned neuroprotective effects are also observed with tacrine (1 microM), donepezil (10 microM) and galanthamine (10 microM), suggesting that the neuroprotective effects of cholinesterase inhibitor might partly contribute to the clinical efficacy in AD treatment.

Huperzine A, a potential therapeutic agent for treatment of Alzheimer's disease.

HupA is a potent, reversible and selective inhibitor of AChE with a rapid absorption and penetration into the brain in animal tests. It exhibits memory-enhancing activities in animal and clinical trials. Compared to tacrine and donepezil, HupA possesses a longer duration of action and higher therapeutic index, and the peripheral cholinergic side effects are minimal at therapeutic doses. This review article deals with a comprehensive survey of the progress in chemical and pharmacological studies of HupA including the isolation and structure elucidation, pharmacological actions, total synthesis, SAR studies and the future development of HupA. Recently, it has been reported that HupA could reduce neuronal cell death caused by glutamate. The dual bio-activities of HupA would further enhance its value and potentiality as the therapeutic agent for Alzheimer s disease.

Inhibitory effects of huperzine B on cholinesterase activity in mice.

AIM: To determine the anticholinesterase properties of huperzine B (Hup B) and compare with tacrine in vitro and in vivo. METHODS: Spectrophotometry was used to determine ChE activity. RESULTS: Hup B showed much more selective inhibition to acetylcholinesterase (AChE) than tacrine. The IC50 ratios of Hup B and tacrine for butyrylcholinesterase (BuChE): AChE were 65.8 and 0.54, respectively. Hup B ig exhibited higher efficacy on the inhibition of brain AChE than that of tacrine. Tacrine was more effective in the inhibition of serum BuChE in mice with severe concomitant peripheral adverse effects than Hup B. A single ig dose of Hup B produced steady state of AChE inhibition in 4 h. CONCLUSION: Hup B exhibits higher selectivity and efficacy in the inhibition of AChE, and lower toxicity in mice than tacrine.

Reversal of scopolamine-induced deficits in radial maze performance by (-)-huperzine A: comparison with E2020 and tacrine.

The effects of (-)-huperzine A ((5R,9R,11E)-5-amino-11-ethylidene-5,6,9,10-tetrahydro-7-methyl-5, 9-methanocycloocta[b]pyridin-2(1H)-one), and of the hydrochloride salt of E2020 ((R,S)-1-benzyl-4-[(5,6-dimethoxy-1-indanon)-2-yl]-methyl piperidine) and tacrine (9-amino-1,2,3,4-tetrahydroacridine), on the scopolamine-induced memory deficits in rats were compared in a radial maze, using a 4-out-of-8 baiting procedure. Scopolamine (0.15 mg/kg, i.p.) caused significant impairment in the rats' ability to fulfil the radial maze task. (-)-Huperzine A (0.2-0.4 mg/kg, p.o.; 0.1-0.4 mg/kg, i.p.) had greater efficacy than E2020 (0.6-0.9 mg/kg, p.o.; 0.3-0.6 mg/kg, i.p.) and tacrine (1.5-2.5 mg/kg, p.o.; 0.3-0.6 mg/kg, i.p.) on the improvement of scopolamine-induced working and reference memory errors, respectively. There appeared to be an inverse bell-shape dose-dependent effect for all three compounds tested. The compared data demonstrate that (-)-huperzine A is the most potent and orally active acetylcholinesterase inhibitor of the three, and fits more closely the established criterions for an ideal acetylcholinesterase inhibitor to be used in clinical studies.

Comparison of the effects of natural and synthetic huperzine-A on rat brain cholinergic function in vitro and in vivo.

(-)-Huperzine-A has been shown to be a promising agent for the treatment of dementia of the Alzheimer type. This substance is rare in nature. We have been able to prepare a racemic mixture of (+/-)-huperzine-A in quantity. In the absence of a chiral synthetic procedure for (-)-huperzine-A, this study sought to determine whether the racemic mixture would yield an in vitro and in vivo pharmacological profile of activity similar to that of the natural compound. The synthetic racemic mixture (+/-)-huperzine-A was 3 times less potent than (-)-huperzine-A in vitro (IC50s of 3 x 10(-7) M and 10(-7) M, respectively) because the former consisted of a racemic mixture of the compound in which the (+)-huperzine component was considerably less potent (IC50 = 7 x 10(-6) M). A comparable magnitude of effect was also observed in studies conducted in vivo, in which, over a range of 0.1-2.0 mg/kg administered intraperitoneally (i.p.), both (-)-huperzine-A and (+/-)-huperzine-A exerted significant inhibition of acetylcholinesterase activity, in all brain regions tested (hippocampus, striatum, hypothalamus and frontal cortex). This inhibition of acetylcholinesterase activity was inversely related to levels of acetylcholine measured in the hippocampus and followed the same time course of effect. (-)-Huperzine-A and (+/-)-huperzine-A were shown to be more potent than physostigmine as inhibitors of acetylcholinesterase in vitro (IC50 = 6 x 10(-7) M).

[Drug evaluation of huperzine A in the treatment of senile memory disorders].

Huperzine A is an alkaloid which was first isolated from Huperzia serrata (Thumb) Trev by Zhejiang Academy of Medical Sciences and Shanghai Institute of Materia Medica, Chinese Academy of Sciences. It exhibits a significant anticholinesterase activity and has been used on myasthenia gravis patients. The therapeutic effects were studied by random, match and double-blind method on 56 patients of multi-infarct dementia or senile dementia and 104 patients of senile and presenile simple memory disorders. The curative effects were evaluated by Wechsler memory scale. The im dose for multi-infarct dementia was 0.05 mg bid for 4 wk, whereas that for senile and presenile simple memory disorders was 0.03 mg bid for 2 wk. Saline was used on control group. The result showed that the curative effect of huperzine A was significant. Only a few patients felt slight dizziness and this did not affect the therapeutic effects.