This article is a U.S. Government work and is in the public domain in the U.S.A.
The NMDA receptor ion channel: a site for binding of huperzine A†
Version of Record online: 18 FEB 2002
Copyright © 2001 John Wiley & Sons, Ltd.
Journal of Applied Toxicology
Supplement: Medical Countermeasures for Nerve Agents
Volume 21, Issue Supplement 1, pages S47–S51, December 2001
How to Cite
Gordon, R. K., Nigam, S. V., Weitz, J. A., Dave, J. R., Doctor, B. P. and Ved, H. S. (2001), The NMDA receptor ion channel: a site for binding of huperzine A. J. Appl. Toxicol., 21: S47–S51. doi: 10.1002/jat.805
- Issue online: 18 FEB 2002
- Version of Record online: 18 FEB 2002
- Manuscript Revised: 10 JUN 1999
- Manuscript Accepted: 10 JUN 1999
- Manuscript Received: 16 FEB 1999
- huperzine A;
- ion channel;
Huperzine A (HUP-A), first isolated from the Chinese club moss Huperzia serrata, is a potent, reversible and selective inhibitor of acetylcholinesterase (AChE) over butyrylcholinesterase (BChE) (Life Sci. 54: 991–997). Because HUP-A has been shown to penetrate the blood–brain barrier, is more stable than the carbamates used as pretreatments for organophosphate poisoning (OP) and the HUP-A:AChE complex has a longer half-life than other prophylactic sequestering agents, HUP-A has been proposed as a pretreatment drug for nerve agent toxicity by protecting AChE from irreversible OP-induced phosphonylation. More recently (NeuroReport8: 963–968), pretreatment of embryonic neuronal cultures with HUP-A reduced glutamate-induced cell death and also decreased glutamate-induced calcium mobilization. These results suggest that HUP-A might interfere with and be beneficial for excitatory amino acid overstimulation, such as seen in ischemia, where persistent elevation of internal calcium levels by activation of the N-methyl-D-aspartate (NMDA) glutamate subtype receptor is found. We have now investigated the interaction of HUP-A with glutamate receptors. Freshly frozen cortex or synaptic plasma membranes were used, providing 60–90% specific radioligand binding. Huperzine A (≤100 µM) had no effect on the binding of [3H]glutamate (low- and high-affinity glutamate sites), [3H]MDL 105,519 (NMDA glycine regulatory site), [3H]ifenprodil (NMDA polyamine site) or [3H]CGS 19755 (NMDA antagonist). In contrast with these results, HUP-A non-competitively (Hill slope < 1) inhibited [3H]MK-801 and [3H]TCP binding (co-located NMDA ion channel PCP site) with pseudo Ki ∼ 6 µM. Furthermore, when neuronal cultures were pretreated with HUP-A for 45 min prior to NMDA exposure, HUP-A dose-dependently inhibited the NMDA-induced toxicity. Although HUP-A has been implicated to interact with cholinergic receptors, it was without effect at 100 µM on muscarinic (measured by inhibition of [3H]QNB or [3H]NMS binding) or nicotinic [3H]epibatidine binding) receptors; also, HUP-A did not perturb adenosine receptor binding [3H]PIA or [3H]NECA). Therefore, HUP-A most likely attenuates excitatory amino acid toxicity by blocking the NMDA ion channel and subsequent Ca2+ mobilization at or near the PCP and MK-801 ligand sites. Thus, on the one hand, HUP-A could be used as a pretreatment against OPs and it might also be a valuable therapeutic intervention in a variety of acute and chronic disorders by protecting against overstimulation of the excitatory amino acid pathway. By blocking NMDA ion channels without psychotomimetic side-effects, HUP-A may protect against diverse neurodegenerative states observed during ischemia or Alzheimer's disease. Copyright © 2001 John Wiley & Sons, Ltd.