Nav1.8 mediates peripheral-to-central nociceptive transmission independently of central presynaptic mechanisms in human DRG-spinal cord circuits

Abstract Suzetrigine, a selective Nav1.8 blocker, despite its significant role as a non-opioid analgesic, exhibits modest efficacy. The potential enhancement of Nav1.8 blocker efficacy through engagement of Nav1.8 at central terminals remains uncertain. We established a donor-derived human organotypic nociceptive circuit to determine where and how clinically relevant analgesics suppress pain signaling. Using ELISA and immunohistochemistry, we quantified calcitonin gene-related peptide (CGRP) release from acute explants of adult human spinal cord, dorsal root ganglia (DRG), and an intact DRG-spinal cord preparation preserving primary afferent anatomy and directional signaling. In isolated spinal cords, capsaicin evoked concentration-dependent spinal CGRP release without compromising viability, and clinically used analgesics inhibited it, validating the assay. In the intact circuit, the application of capsaicin to the DRG cell bodies triggered CGRP release exclusively in the spinal cord, consistent with compartmentalized neuropeptide release at central terminals. Selective Nav1.8 inhibition with suzetrigine reduced spinal CGRP release only when applied to the DRG or nerve root, not the spinal cord, indicating that Nav1.8 regulates peripheral action potential propagation rather than presynaptic transmitter release. These findings establish the first intact human pain circuit-based assay to study analgesics and demonstrate that the analgesic efficacy of Nav1.8 inhibitors is unlikely to increase with improved CNS penetration. Competing Interest Statement Conflict of Interest Statement: T.J.P. is a co-founder of and holds equity in 4E Therapeutics, NuvoNuro, PARMedics, and Nerveli. T.J.P. has received research grants from AbbVie, Eli Lilly, Grunenthal, Evommune, Hoba Therapeutics, and The National Institutes of Health. The authors declare no conflicts of interest related to this work. Footnotes Declaration of Interests: Conflict of Interest Statement: T.J.P. is a co-founder of and holds equity in 4E Therapeutics, NuvoNuro, PARMedics, and Nerveli. T.J.P. has received research grants from AbbVie, Eli Lilly, Grunenthal, Evommune, Hoba Therapeutics, and The National Institutes of Health. The authors declare no conflicts of interest related to this work. We updated the abstract to remove "peripherally restricted" and updated a spelling error for the corresponding author last name.