Magnolol inhibits sodium currents in freshly isolated mouse dorsal root ganglion neurons

Plant-derived natural products targeting ion channels for pain

Chronic pain affects approximately one-fifth of people worldwide and reduces quality of life and in some cases, working ability. Ion channels expressed along nociceptive pathways affect neuronal excitability and as a result modulate pain experience. Several ion channels have been identified and investigated as potential targets for new medicines for the treatment of a variety of human diseases, including chronic pain. Voltage-gated channels Na⁺ and Ca²⁺ channels, K⁺ channels, transient receptor potential channels (TRP), purinergic (P2X) channels and acid-sensing ion channels (ASICs) are some examples of ion channels exhibiting altered function or expression in different chronic pain states. Pharmacological approaches are being developed to mitigate dysregulation of these channels as potential treatment options. Since natural compounds of plant origin exert promising biological and pharmacological properties and are believed to possess less adverse effects compared to synthetic drugs, they have been widely studied as treatments for chronic pain for their ability to alter the functional activity of ion channels. A literature review was conducted using Medline, Google Scholar and PubMed, resulted in listing 79 natural compounds/extracts that are reported to interact with ion channels as part of their analgesic mechanism of action. Most in vitro studies utilized electrophysiological techniques to study the effect of natural compounds on ion channels using primary cultures of dorsal root ganglia (DRG) neurons. In vivo studies concentrated on different pain models and were conducted mainly in mice and rats. Proceeding into clinical trials will require further study to develop new, potent and specific ion channel modulators of plant origin.

Plant and fungi derived analgesic natural products targeting voltage-gated sodium and calcium channels

Voltage-gated sodium and calcium channels (VGSCs and VGCCs) play an important role in the modulation of physiologically relevant processes in excitable cells that range from action potential generation to neurotransmission. Once their expression and/or function is altered in disease, specific pharmacological approaches become necessary to mitigate the negative consequences of such dysregulation. Several classes of small molecules have been developed with demonstrated effectiveness on VGSCs and VGCCs; however, off-target effects have also been described, limiting their use and spurring efforts to find more specific and safer molecules to target these channels. There are a great number of plants and herbal preparations that have been empirically used for the treatment of diseases in which VGSCs and VGCCs are involved. Some of these natural products have progressed to clinical trials, while others are under investigation for their action mechanisms on signaling pathways, including channels. In this review, we synthesize information from ~30 compounds derived from natural sources like plants and fungi and delineate their effects on VGSCs and VGCCs in human disease, particularly pain. [Figure: see text].

Antinociceptive Effect of Magnolol in a Neuropathic Pain Model of Mouse

BACKGROUND AND OBJECTIVE

Neuropathic pain remains a clinical challenge with limited effective treatments. Previous studies have found that magnolol (Mag), an ingredient existing in some herbs, showed neuroprotective effect. However, it remains unclear whether Mag can alleviate neuropathic pain.

METHODS

Chronic constriction injury (CCI) is used as the neuropathic pain model. Mice were randomly divided into 5 groups: Sham, CCI, CCI + 5, 10, 30 mg/kg Mag groups. Thermal and mechanical paw withdrawal threshold were performed at baseline and on the 3rd, 5th, 7th, 14th days post-surgery. Lumbar spinal cord and blood samples were collected on the 14th day. Blood lipid profile, kidney and liver functions, as well as the activation of microglia were evaluated, along with the related signal pathway examined using multiple methods including immunohistochemistry, RT-PCR and Western blot.

RESULTS

Mag alleviated thermal and mechanical hypersensitivity in CCI mice. CCI activated microglia and upregulated the expression of P2Y12, while Mag inhibited microglial activation, and downregulated the expression of P2Y12. Mag also blocked the activation of p38 mitogen-activated protein kinase (MAPK) and other pain-related cytokines such as IL-6, TNF-α and IL-1β.

CONCLUSION

The findings indicate that Mag has antinociceptive effect on neuropathic pain, probably mediated through P2Y12 receptors and p38 MAPK mediated pathways. With its relatively safe profile, Mag may be a potential therapeutic agent for neuropathic pain.

Magnolol attenuates inflammatory pain by inhibiting sodium currents in mouse dorsal root ganglion neurons

Voltage-gated sodium channels are currently recognized as one of the targets of analgesics. Magnolol (Mag), an active component isolated from Magnolia officinalis, has been reported to exhibit analgesic effects. The objective of this study was to investigate whether the analgesic effect of Mag was associated with blocking Na⁺ channels. Inflammatory pain was induced by the injection of carrageenan into the hind paw of mice. Mag was administered orally. Mechanical hyperanalgesia was evaluated by using von Frey filaments. Na⁺ currents and neuronal excitability in acutely isolated mouse dorsal root ganglion (DRG) neurons were recorded with the whole-cell patch clamp technique. Results showed that Mag (10 ~ 40 mg/kg) dose-dependently inhibited the paw edema and reduced mechanical pain in the inflammatory animal model. Injection of carrageenan significantly increased the amplitudes of TTX-sensitive and TTX-resistant Na⁺ currents. Compared with the carrageenan group, Mag inhibited the upregulation of two types of Na⁺ currents induced by carrageenan in a dose-dependent manner. Mag 40 mg/kg shifted the inactivation curves of two types of Na⁺ currents to hyperpolarization and returned to normal animal level without changing their activation curves. Mag 40 mg/kg significantly reduced the percentage of cells firing multiple spikes and inhibited the neuronal hyperexcitability induced by carrageenan. Our data suggest that the analgesic effect of Mag may be associated with a decreased neuronal excitability by blocking Na⁺ current.