N-arachidonoylphenolamine alleviates ischaemia/reperfusion-induced cardiomyocyte necroptosis by restoring proteasomal activity

Necroptosis and apoptosis contribute to the pathogenesis of myocardial ischaemia/reperfusion (I/R) injury and subsequent heart failure. N-arachidonoylphenolamine (AM404) is a paracetamol lipid metabolite that has pleiotropic activity to modulate the endocannabinoid system. However, the protective role of AM404 in modulating I/R-mediated myocardial damage and the underlying mechanism remain largely unknown. A murine I/R model was generated by occlusion of the left anterior descending artery. AM404 (20 mg/kg) was injected intraperitoneally into mice at 2 and 24 h before the I/R operation. Our data revealed that AM404 administration to mice greatly ameliorated I/R-triggered impairment of myocardial performance and reduced infarct area, myocyte apoptosis, oxidative stress and inflammatory response accompanied by the reduction of receptor interacting protein kinase (RIPK)1/3- mixed lineage kinase domain-like (MLKL)-mediated necroptosis and upregulation of the immunosubunits (β2i and β5i). In contrast, administration of epoxomicin (a proteasome inhibitor) dramatically abolished AM404-dependent protection against myocardial I/R damage. Mechanistically, AM404 treatment increases β5i expression, which interacts with Pellino-1 (Peli1), an E3 ligase, to form a complex with RIPK1/3, thereby promoting their degradation, which leads to inhibition of cardiomyocyte necroptosis in the I/R heart. In conclusion, these findings demonstrate that AM404 could prevent cardiac I/R damage and may be a promising drug for the treatment of ischaemic heart disease.

First evidence of the conversion of paracetamol to AM404 in human cerebrospinal fluid

Paracetamol is arguably the most commonly used analgesic and antipyretic drug worldwide, however its mechanism of action is still not fully established. It has been shown to exert effects through multiple pathways, some actions suggested to be mediated via N-arachidonoylphenolamine (AM404). AM404, formed through conjugation of paracetamol-derived p-aminophenol with arachidonic acid in the brain, is an activator of the capsaicin receptor, TRPV1, and inhibits the reuptake of the endocannabinoid, anandamide, into postsynaptic neurons, as well as inhibiting synthesis of PGE₂ by COX-2. However, the presence of AM404 in the central nervous system following administration of paracetamol has not yet been demonstrated in humans. Cerebrospinal fluid (CSF) and blood were collected from 26 adult male patients between 10 and 211 minutes following intravenous administration of 1 g of paracetamol. Paracetamol was measured by high-performance liquid chromatography with UV detection. AM404 was measured by liquid chromatography-tandem mass spectrometry. AM404 was detected in 17 of the 26 evaluable CSF samples at 5–40 nmol⋅L⁻¹. Paracetamol was measurable in CSF within 10 minutes, with a maximum measured concentration of 60 μmol⋅L⁻¹ at 206 minutes. This study is the first to report on the presence of AM404 in human CSF following paracetamol administration. This may represent an important finding in our understanding of paracetamol’s mechanism of action, although measured concentrations were far below the previously documented IC50 for this metabolite.