TRPV1-Mediated Delivery of Chloroprocaine, a Local Anesthetic with High pKa, Produces Pain-Selective Anesthesia Without Neurotoxicity
BackgroundConventional local anesthetics (LAs) provide pain relief but also block motor and non-nociceptive fibers, causing undesirable side effects. Approaches using permanently charged derivatives, such as QX-314, delivered via TRPV1 channels, selectively target nociceptors but are limited by neurotoxicity. We hypothesized that clinically approved LAs with high pKa and low toxicity, such as 2-chloroprocaine (chloroprocaine), which is predominantly protonated and membrane-impermeant at physiological pH, would preferentially enter TRPV1-expressing nociceptors when co-administered with a TRPV1 agonist, thereby producing prolonged pain-selective anesthesia without neurotoxicity. MethodsWhole-cell voltage-clamp recordings from rat dorsal root ganglion (DRG) neurons assessed sodium current inhibition. Behavioral experiments in male Sprague-Dawley rats (N=6 -12/group) evaluated sensitivity to noxious thermal and mechanical stimuli and motor function following intraplantar and perisciatic injections of 0.5% or 2% chloroprocaine combined with capsaicin or cannabidiol (CBD). TRPV1 activation was examined by calcium imaging in hTRPV1-expressing HEK293 cells and in capsaicin- and AITC-sensitive DRG neurons. Neurotoxicity was assessed using propidium iodide uptake, long-term behavioral monitoring (35 days), and immunohistochemistry for TRPV1, ATF-3, and GFAP. ResultsCo-application of chloroprocaine with capsaicin enhanced sodium current blockade (76{+/-}15%) compared to either drug alone (p<0.05). Perisciatic injection produced thermal analgesia that persisted for 4 hours, whereas motor block resolved within 30 minutes. Unlike other LAs, chloroprocaine did not activate TRPV1 (98% non-responders) and showed no cytotoxicity. Long-term evaluation revealed no hypersensitivity, neuronal loss, or ATF-3 upregulation. Replacing capsaicin with CBD preserved prolonged ([~] 3.5 h) pain-selective anesthesia without motor impairment. ConclusionsTRPV1-mediated delivery of high-pKa LA chloroprocaine produces prolonged, nociceptor-selective anesthesia without neurotoxicity. Combining a clinically approved high-pKa LAs with low intrinsic toxicity and TRPV1 agonists such as CBD offers a potentially safe strategy for pain-selective regional anesthesia, with implications for perioperative and chronic pain management.