to the stimulation of the production of nitric oxide in the vascular endothelium. It is hypothesized that meldonium may increase the formation of the gamma-butyrobetaine esters, which are potent parasympathomimetics, and may activate the endothelial NOS (eNOS) enzyme, which causes nitric oxide production via stimulation of the M3 muscarinic acetylcholine receptor or specific gamma-butyrobetaine ester receptors. Meldonium is believed to continually train the heart pharmacologically, even without physical activity, inducing preparation of cellular metabolism and membrane structures (specifically in myocardial mitochondria) to survive ischemic stress conditions. This is done by adapting myocardial cells to lower fatty acid inflow and by activating glycolysis; the heart eventually begins using glycolysis instead of beta oxidation during real life ischaemic conditions. This reduces oxidative stress on cells, formation of cytotoxic products of fatty acid oxidation and subsequent cellular damage. This has made meldonium a possible pharmacological agent for ischemic preconditioning. The mechanisms underlying the central nervous system effects of meldonium are unclear. In a study in a transgenic mouse model of Alzheimer's disease, meldonium increased cognition and mental performance by reducing amyloid beta deposition in the hippocampus. Pharmacology The mechanism of action of meldonium is to act as a fatty acid oxidation inhibitor, presumably by inhibiting enzymes in the carnitine biosynthesis pathway such as γ-butyrobetaine hydroxylase. Although initial reports suggested meldonium is a non-competitive and non-hydroxylatable analogue of gamma-butyrobetaine; further studies have identified that meldonium is a substrate for gamma-butyrobetaine dioxygenase. X-ray crystallographic and in vitro biochemical studies suggest that meldonium binds to the substrate pocket of γ-butyrobetaine hydroxylase and acts as an alternative substrate, and therefore a competitive inhibitor. Normally, this enzyme's action on its substrates γ-butyrobetaine and 2-oxoglutarate gives, in the presence of the further substrate oxygen, the products L-carnitine, succinate, and carbon dioxide; in the presence of this alternate substrate, the reaction yields malonic acid semialdehyde, formaldehyde (akin to the action of histone demethylases), dimethylamine, and (1-methylimidazolidin-4-yl)acetic acid, "an unexpected product with an additional carbon-carbon bond resulting from N-demethylation coupled to oxidative rearrangement, likely via an unusual radical mechanism." The unusual mechanism is thought likely to involve a Steven's type rearrangement. Meldonium's inhibition of γ-butyrobetaine hydroxylase gives a half maximal inhibitory concentration (IC50) value of 62 micromolar, which other study authors have described as "potent." Meldonium is an example of an inhibitor that acts as a non-peptidyl substrate mimic. Meldonium has also been shown by NMR to bind to carnitine acetyltransferase.