Coapplication of lidocaine and the permanently charged sodium channel blocker QX-314 produces a long-lasting nociceptive blockade in rodents

Abstract

Background: Nociceptive-selective local anesthesia is produced by entry of the permanently charged lidocaine-derivative QX-314 into nociceptors when coadministered with capsaicin, a transient receptor potential vanilloid 1 (TRPV1) channel agonist. However, the pain evoked by capsaicin before establishment of the QX-314-mediated block would limit clinical utility. Because TRPV1 channels are also activated by lidocaine, the authors tested whether lidocaine can substitute for capsaicin to introduce QX-314 into nociceptors through TRPV1 channels and produce selective analgesia.

Methods: Lidocaine (0.5% [17.5 mM], 1% [35 mM], and 2% [70 mM]) alone, QX-314 (0.2% [5.8 mM]) alone, and a combination of the two were injected subcutaneously and adjacent to the sciatic nerve in rats and mice. Mechanical and thermal responsiveness were measured, as was motor block.

Results: Coapplication of 0.2% QX-314 with lidocaine prolonged the nociceptive block relative to lidocaine alone, an effect attenuated in TRPV1 knockout mice. The 0.2% QX-314 alone had no effect when injected intraplantary or perineurally, and it produced only weak short-lasting inhibition of the cutaneous trunci muscle reflex. Perisciatic nerve injection of lidocaine with QX-314 produced a differential nociceptive block much longer than the transient motor block, lasting 2 h (for 1% lidocaine) to 9 h (2% lidocaine). Triple application of lidocaine, QX-314, and capsaicin further increased the duration of the differential block.

Conclusions: Coapplication of lidocaine and its quaternary derivative QX-314 produces a long-lasting, predominantly nociceptor-selective block, likely by facilitating QX-314 entry through TRPV1 channels. Delivery of QX-314 into nociceptors by using lidocaine instead of capsaicin produces sustained regional analgesia without nocifensive behavior.

Fig. 1. The duration of the elevation in thermal (radiant heat) response latency (A) and mechanical threshold (von Frey) (B) produced by intraplantar injection of a combination of QX-314 together with lidocaine (0.2% QX-314, 1% lidocaine, 10 μl) exceeds that produced by lidocaine alone (1%, 10 μl). QX-314 alone did not alter mechanical or thermal responsiveness (0.2%, 10 μl). Arrows indicate the cutoffs, and the dotted line indicates baseline level (mean ± SEM; * P < 0.05, ANOVA followed by Dunnett's test; n = 6 for each group)

Fig. 2. Inhibition of the pinprick-evoked cutaneous trunci muscle reflex (CTMR) produced by intracutaneous injection of a combination of 1% lidocaine and 0.2% QX-314, lidocaine alone (1%), and QX-314 alone (0.2%) (100% = no response to the pinprick) expressed as percentage of maximal block (* P < 0.05, analysis of variance [ANOVA] followed by Dunnett's test, n = 8 for each group)

Fig. 3. Blockade of the pinch-induced withdrawal response after perisciatic nerve injection of a combination of lidocaine (0.5%, 1%, and 2%) and 0.2% QX-314; lidocaine alone (0.5%, 1%, and 2%) and QX-314 (0.2%) alone. Note that application of QX-314 alone (0.2%) did not produce detectable changes in the response to the pinch. Grading was as follows: 3 = complete block, no withdrawal, no vocalization; 2 = partial block, vocalization accompanied with slow withdrawal and flexion of the leg; 1 = minimal block, rapid flexion of the leg, or other escape response with loud vocalization; 0 = baseline. n = 8 for each group

Fig. 4. Injection of lidocaine and QX-314 close to the sciatic nerve produces a short complete sensory and motor block followed by a prolonged nociceptive-selective block. (A) Coinjection of lidocaine (0.5%, 1%, and 2%) and QX-314 (0.2%) produced a differential block since the block to a noxious pinch exceeds the short-duration motor deficit. (B) Lidocaine (0.5%, 1%, and 2%) injected alone produces a short-duration nonselective local anesthesia where nociceptive (closed squares) and motor (open squares) block have exactly the same duration. Grading for the nociceptive block is as in Fig. 3. Grading for motor block: 0 = baseline (115.8 g ± 2, n = 24), 1 = minimal block (50–100% of baseline); 2 = moderate block (less than 50% of baseline to 20 g); 3 = complete block, force less than 20 g (see Materials and Methods). (C) Summary of differential block produced after sciatic injection of 1% lidocaine alone and lidocaine coinjected with 0.2% QX-314

Fig. 5. Application of capsaicin (0.05%) after injection of either (A) 1% or (B) 2% of lidocaine + QX-314 (0.2%) significantly increased the nociceptive blockade produced by lidocaine coinjected only with QX-314 (0.2%). (C) Comparison of the duration of nociceptive (closed diamonds) and motor (open diamonds) blockade produced by triple application of 1% lidocaine/capsaicin/QX-314 (black diamonds) or 2% lidocaine/capsaicin/QX-314 (gray diamonds). Grading for the nociceptive block is as in Fig. 3. Grading for the motor block is as in Fig. 4. (D) Differential block produced after sciatic nerve injection of lidocaine, QX-314, and capsaicin

Fig. 6. Number of flinches during the first 5 min after intraplantar application of capsaicin alone (0.05%), capsaicin (0.05%) + QX-314 (0.2%), lidocaine (1%) + QX-314 (0.2%), and capsaicin (0.05%) + lidocaine (1%) + QX-314 (0.2%). # P > 0.05 analysis of variance (ANOVA), n = 6

Fig. 7. The prolonged analgesic effect of the lidocaine–QX-314 combination depends largely, but not exclusively, on activation of transient receptor potential vanilloid1 (TRPV1) channels. (A) In TRPV1 knockout (KO) mice, the duration of the elevation of mechanical threshold assessed using von Frey hairs after combined injection of lidocaine and QX-314 (0.2% QX-314, 5% lidocaine, 10 μl, n = 6) is significantly shorter than in wild type (WT) animals (P < 0.0001, analysis of variance [ANOVA], n = 4), but it exceeds that produced by lidocaine alone (5%, 10 μl; P < 0.05, ANOVA, n = 4). Lidocaine alone (5%, 10 μl) produced similar effects in TRPV1 KO and WT animals (P = 0.4, n = 4, two-way ANOVA). Injection of QX-314 alone (0.2%, 10 μl) did not change mechanical threshold both in TRPV1 KO and WT mice (n = 4). * P < 0.05. (B) Representative traces from two cells (black and gray) recorded simultaneously during consecutive application of lidocaine (20 s, 30 mm) and capsaicin (20 s, 1 μm). Lidocaine induces an increase in intracellular calcium concentration (increase in fluorescent ratio [ΔF340/380]) through both TRPV1-dependent (capsaicin-sensitive) and TRPV1-independent mechanisms