Involvement of voltage-gated sodium channels blockade in the analgesic effects of orphenadrine

Abstract

Orphenadrine is a drug acting on multiple targets, including muscarinic, histaminic, and NMDA receptors. It is used in the treatment of Parkinson's disease and in musculoskeletal disorders. It is also used as an analgesic, although its mechanism of action is still unknown. Both physiological and pharmacological results have demonstrated a critical role for voltage-gated sodium channels in many types of chronic pain syndromes. We tested the hypothesis that orphenadrine may block voltage-gated sodium channels. By using patch-clamp experiments, we evaluated the effects of the drug on whole-cell sodium currents in HEK293 cells expressing the skeletal muscle (Nav1.4), cardiac (Nav1.5) and neuronal (Nav1.1 and Nav1.7) subtypes of human sodium channels, as well as on whole-cell tetrodotoxin (TTX)-resistant sodium currents likely conducted by Nav1.8 and Nav1.9 channel subtypes in primary culture of rat DRG sensory neurons. The results indicate that orphenadrine inhibits sodium channels in a concentration-, voltage- and frequency-dependent manner. By using site-directed mutagenesis, we further show that orphenadrine binds to the same receptor as the local anesthetics. Orphenadrine affinities for resting and inactivated sodium channels were higher compared to those of known sodium channels blockers, such as mexiletine and flecainide. Low, clinically relevant orphenadrine concentration produces a significant block of Nav1.7, Nav1.8, and Nav1.9 channels, which are critical for experiencing pain sensations, indicating a role for sodium channel blockade in the clinical efficacy of orphenadrine as analgesic compound. On the other hand, block of Nav1.1 and Nav1.5 may contribute to the proconvulsive and proarrhythmic adverse reactions, especially observed during overdose.

Molecular Dissection of Lubeluzole Use–Dependent Block of Voltage-Gated Sodium Channels Discloses New Therapeutic Potentials

“…The halfmaximum inhibitory concentrations (IC 50 ) were about 35 mM at 0.1 Hz and 1.8 mM at 10 Hz. Lubeluzole appears among the more efficient and use-dependent sodium channel blockers tested so far in these experimental conditions (Desaphy et al, 2003(Desaphy et al, , 2004(Desaphy et al, , 2009(Desaphy et al, , 2010. Since no stereoselective activity was discerned, the next experiments were performed using the racemic R,S-lubeluzole only.…”

“…We previously showed that the F1586C mutation completely prevented block of inactivated channels by mexiletine and other use-dependent sodium channel blockers (Desaphy et al, 2009(Desaphy et al, , 2010. Figure 5A illustrates F1586C sodium current traces in the presence of 10 mM lubeluzole to be compared with the wild-type (WT) current traces shown in Fig.…”

“…The generation of permanent HEK293 (human embryonic kidney 293) cell lines expressing the human skeletal muscle subtype of voltage-gated sodium channels (hNav1.4), and its F1586C or Y1583C mutants, has been previously reported (Desaphy et al, 2009(Desaphy et al, , 2010.…”

“…The drugs were also tested on sodium channels mutated at Phe1586 [F1586C mutant (FC)] and Tyr1593 (Y1593C), which are thought to be part of the local anesthetic receptor within the channel ion pore (Ragsdale et al, 1994). These mutations usually impair the high-affinity, use-dependent binding of local anesthetics (Ragsdale et al, 1994;Desaphy et al, 2009Desaphy et al, , 2010. The results define the molecular interaction of lubeluzole with sodium channels, and underscore its potential in the treatment of membrane excitability disorders.…”

Validated Stability-Indicating Reversed-Phase-HPLC Method for Simultaneous Determination of Orphenadrine Citrate, Caffeine and Aspirin

“…6) It may be possible for its antihistaminergic properties and NMDA-receptor inhibition activity, however, the hypothesis of inhibiting the voltage-gated sodium channels has become recently solidified as a strong contributor to the analgesic action of orphenadrine. 7) A thorough literature survey revealed ORPH, CAF and ASP were reported by pharmacopeial and non-pharmacopeial methods. Both CAF and ASP were assayed alone or in combination in both the British Pharmacopeia (BP 2007) and the United States Pharmacopeia (USP 30-NF 25).…”