Evaluation of Rhodojaponin III from Rhododendron molle G. Don on oral antinociceptive activity, mechanism of action, and subacute toxicity in rodents.

ETHNOPHARMACOLOGICAL RELEVANCE: In Chinese traditional medicine, Rhododendron molle G. Don is a recognized herb to ease pain. Rhodojaponin III (RJ-III) has been identified as the main pharmacological activity and toxic component of the herb; however, oral antinociception and mechanism of RJ-III have not yet been investigated. AIM OF THE STUDY: The significance of this study is to evaluate the effects of RJ-III on nociceptive and neuropathic pain, and to preliminarily explore the underlying mechanisms and subacute toxicity. MATERIALS AND METHODS: The antinociception of RJ-III was evaluated by hot plate, tail-immersion, acetic acid writhing, formalin test and chronic constriction injury (CCI) model in rodents. An experimental validation was conducted using whole-cell patch clamp technique based on the most likely mechanisms of action after screening and prediction by molecular docking study. In addition, the oral subacute toxicity of RJ-III was assessed. RESULTS: Behavioral experiments showed that RJ-III (0.20 mg/kg) reduced the latency of the nociceptive response in the hot plate and tail-immersion tests. Acetic acid and formalin-induced pain were significantly inhibited by RJ-III (0.10 and 0.05 mg/kg, respectively). Furthermore, 0.30 mg/kg of RJ-III improved hyperalgesia in the CCI-induced rats. Based on molecular docking results, electrophysiological experiments were used to demonstrate mild inhibition of voltage-gated sodium channel-related subtypes. Additionally, oral subacute toxicity that may cause leukopenia and abnormal liver function requires further attention in subsequent studies. CONCLUSION: RJ-III mildly blocks voltage-gated sodium channel to inhibit nociceptive pain and peripheral neuralgia, but 0.375 mg/kg and above may cause side effect after long-term oral administration.

Rhodojaponin III-Loaded Chitosan Derivatives-Modified Solid Lipid Nanoparticles for Multimodal Antinociceptive Effects in vivo.

Background: Rhodojaponin III (RJ-III) is a bioactive diterpenoid, which is mainly found in Rhododendron molle G. Don (Ericaceae), a potent analgesia in traditional Chinese medicine with several years of clinical applications in the country. However, its clinical use is limited by its acute toxicity and poor pharmacokinetic profiles. To reduce such limitations, the current study incorporated RJ-III into the colloidal drug delivery system of hydroxypropyl trimethyl ammonium chloride chitosan (HACC)-modified solid lipid nanoparticles (SLNs) to improve its sustained release and antinociceptive effects in vivo for oral delivery. Results: The optimized RJ-III@HACC-SLNs were close to spherical, approximately 134 nm in size, and with a positive zeta potential. In vitro experiments showed that RJ-III@HACC-SLNs were stable in the simulated gastric fluid and had a prolonged release in PBS (pH = 6.8). Pharmacokinetic results showed that after intragastric administration in mice, the relative bioavailability of RJ-III@HACC-SLNs was 87.9%. Further, it was evident that the peak time, half-time, and mean retention time of RJ-III@HACC-SLNs were improved than RJ-III after the administration. In addition, pharmacodynamic studies revealed that RJ-III@HACC-SLNs markedly reduced the acetic acid, hot, and formalin-induced nociceptive responses in mice (P < 0.001), and notably increased the analgesic time (P < 0.01). Moreover, RJ-III@HACC-SLNs not only showed good biocompatibility with Caco-2 cells in vitro but its LD50 value was also increased by 1.8-fold as compared with that of RJ-III in vivo. Conclusion: These results demonstrated that RJ-III@HACC-SLNs improved the pharmacokinetic characteristics of the RJ-III, thereby exhibiting toxicity-attenuating potential and antinociceptive enhancing properties. Consequently, HACC-SLNs loaded with RJ-III could become a promising oral formulation for pain management that deserves further investigation in the future.