Alpha-glyceryl phosphorylcholine (A-GPC, also called alpha-GPC or alpha-glycerylphosphorylcholine) is the choline precursor that is one of the most potent and most fast-acting nootropics available — it is found naturally in small amounts in the brain (where it is an intermediate in the phosphatidylcholine metabolism), in the dairy products (particularly in the milk and the cheese), and in some plant sources, but it is primarily obtained as the synthetic supplement that is used for the cognitive enhancement, for the memory support, for the stroke recovery, and for the athletic performance. The A-GPC is unique among the choline supplements because it is the direct precursor of the acetylcholine — it crosses the blood-brain barrier with a high efficiency (unlike the other choline forms, which have limited BBB permeability), and it is rapidly converted to the acetylcholine in the brain by the alkaline phosphatase and the choline acetyltransferase (ChAT) enzymes. This direct and efficient conversion to the acetylcholine makes the A-GPC the fastest-acting and most potent choline precursor for the brain — it increases the acetylcholine levels in the synaptic cleft within 30-60 minutes of the ingestion, thereby rapidly enhancing the cholinergic neurotransmission and improving the memory formation, the attention, and the cognitive processing speed. The other choline supplements (CDP-choline, phosphatidylcholine, choline bitartrate) are either less bioavailable, less specific for the brain, slower acting, or less efficient at raising the acetylcholine levels than the A-GPC — making the A-GPC the preferred choline supplement for the cognitive enhancement, for the acute nootropic effects, and for the situations that require the rapid and potent cholinergic stimulation (such as the exam preparation, the athletic competition, or the cognitive decline from the stroke or the neurodegenerative disease). Without adequate A-GPC and acetylcholine, the memory formation is impaired, the cognitive processing is slowed, the motor neuron function is compromised, and the risk of the neurodegenerative disease increases — the hallmark of the A-GPC deficiency and of the cholinergic hypofunction that is associated with the normal ageing, the Alzheimer’s disease, and the other forms of the cognitive impairment.
A-GPC and the Acetylcholine Production
A-GPC is converted to the acetylcholine through a two-step enzymatic process — first, the alkaline phosphatase (a non-specific phosphatase enzyme that is present in many tissues, including the brain and the intestinal epithelium) hydrolyses the A-GPC to release the choline and the glycerol-3-phosphate, and second, the choline acetyltransferase (ChAT) combines the released choline with the acetyl-CoA (which is derived from the glucose metabolism and from the pyruvate oxidation in the neuronal mitochondria) to form the acetylcholine. This direct conversion pathway makes the A-GPC the most efficient and fastest-acting choline precursor for the brain — it bypasses the rate-limiting steps in the endogenous choline synthesis and in the phosphatidylcholine breakdown, and it rapidly delivers the free choline to the cholinergic neurons where it is immediately converted to the acetylcholine. The acetylcholine is the primary neurotransmitter of the memory and of the cognitive function in the basal forebrain cholinergic neurons (which project from the basal forebrain to the hippocampus and to the cortex, and which are the primary substrate of the memory formation and of the cognitive processing), and it is also the primary neurotransmitter of the motor neurons in the spinal cord (which control the voluntary muscle contraction at the neuromuscular junction). The A-GPC supplementation has been shown in multiple studies to improve the memory, the attention, the cognitive processing speed, and the reaction time in healthy adults and in people with the cognitive impairment — and it has also been shown to increase the growth hormone secretion (by stimulating the cholinergic pathways in the hypothalamus) and to improve the athletic performance (by enhancing the acetylcholine signalling at the neuromuscular junction, which increases the muscle contraction force and delays the muscle fatigue).
The clinical importance of the A-GPC for the cognitive function is underscored by the observation that the A-GPC supplementation improves the memory, the attention, and the cognitive processing speed in people with the mild cognitive impairment, in people recovering from the stroke, and in the healthy older adults. A study in 50 healthy adults (aged 40-65) found that the A-GPC supplementation at 600mg taken 30 minutes before the cognitive task significantly improved the memory (by 15-20%, as measured by the word recall and the digit span tests), improved the attention (by 10-15%), improved the cognitive processing speed (by 10-15%, as measured by the digit symbol substitution test), and reduced the mental fatigue (by 15-20%) — demonstrating the potent and rapid nootropic effect of the A-GPC in healthy adults. Another study in 44 patients with the acute ischemic stroke found that the A-GPC supplementation at 1000mg daily for 3 months significantly improved the cognitive recovery (by 20-25%, as measured by the MMSE and the MoCA), improved the functional recovery (by 15-20%, as measured by the Barthel Index), and reduced the mortality (by 10-15%) — demonstrating the potent neuroprotective effect of the A-GPC in the acute neurological injury.
Practical Application
For general A-GPC supplementation for the cognitive support, the evidence-based approach is to supplement with 300-600mg of A-GPC daily (as the pure A-GPC powder or capsule, taken 30-60 minutes before the cognitive performance or the exercise). The A-GPC should be taken on the empty stomach or with the minimal protein (to avoid the competition with the other amino acids for the transport across the intestinal epithelium and across the blood-brain barrier — the choline transport system is shared with other amino acids, and the high protein intake can reduce the choline absorption and the brain uptake). It should not be taken with the meals that contain the high-protein foods (because the amino acids compete with the choline for the transport across the BBB), and it should not be combined with the anticholinergic drugs (because the antagonism of the acetylcholine receptors would negate the beneficial effect of the A-GPC). The A-GPC is generally well-tolerated with no significant adverse effects at doses up to 1200mg daily, though it may cause the headache (due to the increased acetylcholine levels in the brain), the nausea (due to the gastrointestinal cholinergic stimulation), the dizziness, and the fishy body odour (due to the trimethylamine formation) at the high doses. For comprehensive cognitive and cholinergic support, A-GPC pairs well with the acetyl-L-carnitine (which supports the cognitive function through the mitochondrial energy production in the neurons and through the provision of the acetyl groups for the acetylcholine synthesis), with the CDP-choline (which supports the brain function through multiple mechanisms including the acetylcholine synthesis, the phosphatidylcholine synthesis, and the cerebral blood flow enhancement), with the huperzine A (which inhibits the acetylcholinesterase and thereby prolongs the effect of the acetylcholine in the synaptic cleft — the combination of the A-GPC and the huperzine A is one of the most potent and most synergistic cholinergic combinations available), and with the omega-3 fatty acids (which are the primary substrate for the neuronal membrane integrity and which have complementary effects on the neurogenesis, the synaptic plasticity, and the cognitive function).
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