Is NAPQI part of paracetamol efficacy? Insights from ion channel modulation
Abstract
Paracetamol (acetaminophen, APAP) remains one of the most widely used analgesic and antipyretic drugs, yet its mechanism of action is not fully resolved. A recurring observation in APAP pharmacology is that structural analogues designed to limit formation of the reactive metabolite N-acetyl-p-benzoquinone imine (NAPQI) often show reduced analgesic efficacy, raising the possibility that NAPQI could contribute to certain aspects of the therapeutic effects in addition to its established role in hepatotoxicity. Recent studies indicate that, at concentrations compatible with therapeutic exposure, NAPQI can covalently modify redox-sensitive cysteine residues on specific ion channels. In particular, NAPQI potentiates neuronal Kv7 (KCNQ) channels by altering PIP 2 and Ca 2+ sensitivity, thereby enhancing the M-current and reducing neuronal excitability. NAPQI has also been shown to modulate TRP channels, including TRPA1 and TRPV1, through redox-dependent mechanisms. For TRPV1, this includes channel activation with potential subsequent desensitization under certain conditions. These findings support the view that limited and spatially restricted NAPQI formation is theoretically capable of influencing nociceptive and thermoregulatory pathways. At higher concentrations, however, NAPQI overwhelms detoxification systems, leading to oxidative stress, mitochondrial dysfunction, and tissue injury. A concentration-dependent perspective may therefore help contextualize aspects of…
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