Huperzine A is the sesquiterpene alkaloid that is isolated from the Chinese club moss (Huperzia serrata) — it is one of the most potent natural inhibitors of the acetylcholinesterase (the enzyme that breaks down the acetylcholine in the synaptic cleft), and it is one of the most studied and most effective nootropics for the memory support and for the treatment of the Alzheimer’s disease. The acetylcholinesterase (AChE) is the enzyme that hydrolyses the acetylcholine in the synaptic cleft — it is the primary mechanism by which the acetylcholine signalling is terminated, and it is the target of the most widely used drugs for the Alzheimer’s disease (donepezil, rivastigmine, galantamine). The inhibition of the AChE by the huperzine A prevents the breakdown of the acetylcholine in the synaptic cleft, thereby prolonging and enhancing the acetylcholine signalling and improving the cholinergic neurotransmission. The huperzine A is unique among the AChE inhibitors because it is a reversible and selective inhibitor of the AChE (it does not significantly inhibit the butyrylcholinesterase, which is the other cholinesterase enzyme in the brain), it has a high oral bioavailability (compared to the other AChE inhibitors, which have poor oral absorption), and it has a long duration of action (with a half-life of 10-14 hours, which allows for the once-daily or twice-daily dosing). Without adequate huperzine A and acetylcholine, the cholinergic neurotransmission is impaired, the memory formation is disrupted, and the cognitive decline accelerates — the hallmark of the huperzine A deficiency and of the cholinergic hypofunction that is associated with the Alzheimer’s disease and with the normal ageing. The typical huperzine A supplement dose is 50-200mcg daily — making it one of the most potent and most evidence-based nootropics for the memory support and for the cognitive protection.
Huperzine A and the Acetylcholine Protection
Huperzine A inhibits the acetylcholinesterase through the reversible binding to the active site of the enzyme — it forms a hydrogen bond with the active site serine residue (Ser203) and an electrostatic interaction with the catalytic histidine residue (His447), thereby preventing the acetylcholine from binding to the active site and being hydrolysed. This inhibition is reversible (the huperzine A dissociates from the enzyme over time, which allows the enzyme activity to recover), and it is selective (the huperzine A does not significantly inhibit the butyrylcholinesterase, which is the other cholinesterase enzyme in the brain and which is increasingly active in the Alzheimer’s disease). By inhibiting the AChE, the huperzine A prevents the breakdown of the acetylcholine in the synaptic cleft, thereby increasing the concentration and the duration of the acetylcholine in the synaptic cleft and enhancing the cholinergic neurotransmission. This enhanced cholinergic neurotransmission is the primary mechanism of the huperzine A’s beneficial effects on the memory and on the cognitive function — it improves the memory formation, the attention, the learning, and the executive function by increasing the acetylcholine levels in the hippocampus, the cortex, and the other cholinergic pathways that are involved in these cognitive processes.
The clinical importance of the huperzine A for the cognitive function is underscored by the observation that the huperzine A supplementation improves the memory and the cognitive function in people with the mild cognitive impairment, the Alzheimer’s disease, and the healthy older adults. A meta-analysis of 8 RCTs in over 500 participants with the Alzheimer’s disease found that the huperzine A supplementation at 100-300mcg daily significantly improved the cognitive function (by 10-15% on the MMSE and the ADAS-Cog), improved the activities of daily living (by 10-15%), and reduced the decline in the global function (by 10-15%) — demonstrating the potent and disease-modifying effect of the huperzine A in the Alzheimer’s disease.
Practical Application
For general huperzine A supplementation for the memory support and for the cognitive protection, the evidence-based approach is to supplement with 50-200mcg of huperzine A daily (as the pure huperzine A powder or capsule, taken in the morning and in the early afternoon in divided doses). The huperzine A should be cycled (taken for 2-4 weeks followed by a 1-2 week break) to prevent the downregulation of the acetylcholine receptors and to minimise the side effects. It should not be combined with the other acetylcholinesterase inhibitors (donepezil, rivastigmine, galantamine) or with the anticholinergic drugs, because the combined effect would be excessive acetylcholine stimulation. The huperzine A is generally well-tolerated with no significant adverse effects at doses up to 400mcg daily, though it may cause the nausea, the diarrhoea, the muscle cramps, the excessive salivation, and the insomnia (if taken late in the day) at the high doses. For comprehensive cognitive and cholinergic support, huperzine A pairs well with the alpha-GPC (which provides the choline precursor for the acetylcholine synthesis and which works synergistically with the huperzine A for the cholinergic enhancement), with the acetyl-L-carnitine (which supports the mitochondrial function and which works synergistically with the huperzine A for the neuronal energy metabolism and the cognitive function), with the phosphatidylserine (which supports the neuronal membrane integrity and which works synergistically with the huperzine A for the membrane function and the cognitive support), and with the bacopa monnieri (which is an Ayurvedic nootropic that supports the memory and the cognitive function through a complementary mechanism involving the bacosides, the neuroprotection, and the synaptic plasticity).
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