Effects of protopanaxatriol-ginsenoside metabolites on rat N-methyl-d-aspartic Acid receptor-mediated ion currents

Emerging signals modulating potential of ginseng and its active compounds focusing on neurodegenerative diseases

Common features of neurodegenerative diseases (NDDs) include progressive dysfunctions and neuronal injuries leading to deterioration in normal brain functions. At present, ginseng is one of the most frequently used natural products. Its use has a long history as a cure for various diseases because its extracts and active compounds exhibit several pharmacological properties against several disorders. However, the pathophysiology of NDDs is not fully clear, but researchers have found that various ion channels and specific signaling pathways might have contributed to the disease pathogenesis. Apart from the different pharmacological potentials, ginseng and its active compounds modulate various ion channels and specific molecular signaling pathways related to the nervous system. Here, we discuss the signal modulating potential of ginseng and its active compounds mainly focusing on those relevant to NDDs.

Effect of intraperitoneal administered ginseng total saponins on hyperalgesia induced by repeated intramuscular injection of acidic saline in rats

The aim of this study was to assess the antinociceptive activity of ginseng total saponins (GTS) on hyperalgesia induced by repeated intramuscular injections of acidic saline in rats and to examine the mechanisms involved. Rats were injected intraperitoneally with a 0.9% saline vehicle or various doses of GTS after the development of hyperalgesia. Rats were then injected with N-methyl-D-aspartate (NMDA) or naloxone 10 min before GTS injection. The mechanical withdrawal threshold (MWT) was assessed with von Frey filaments. The MWT was significantly increased after intraperitoneal injection of 100 mg/kg and 200 mg/kg of GTS when compared with the MWT after the development of hyperalgesia. Injection of GTS with NMDA showed a significant decrease in the MWT when compared with GTS injection. GTS showed an antinociceptive activity against chronic muscle-induced pain, and the effect of GTS may be mediated by NMDA.

Ginseng ginsenoside pharmacology in the nervous system: involvement in the regulation of ion channels and receptors

Ginseng, the root of Panax ginseng C.A. Meyer, is one of the oldest traditional medicines and is thought to be a tonic. It has been claimed that ginseng may improve vitality and health. Recent studies have advanced ginseng pharmacology and shown that ginseng has various pharmacological effects in the nervous system. Ginsenosides, steroid glycosides extracted from ginseng, were one of the first class of biologically active plant glycosides identified. The diverse pharmacological effects of ginsenosides have been investigated through the regulation of various types of ion channels and receptors in neuronal cells and heterologous expression systems. Ginsenoside Rg3 regulates voltage-gated ion channels such as Ca(2+), K(+), and Na(+) channels, and ligand-gated ion channels such as GABAA, 5-HT3, nicotinic acetylcholine, and N-methyl-D-aspartate (NMDA) receptors through interactions with various sites including channel blocker binding sites, toxin-binding sites, channel gating regions, and allosteric channel regulator binding sites when the respective ion channels or receptors are stimulated with depolarization or ligand treatment. Treatment with ginsenoside Rg3 has been found to stabilize excitable cells by blocking influxes of cations such as Ca(2+) and Na(+), or by enhancing Cl(-) influx. The aim of this review is to present recent findings on the pharmacological functions of the ginsenosides through the interactions with ion channels and receptors. This review will detail the pharmacological applications of ginsenosides as neuroprotective drugs that target ion channels and ligand-gated ion channels.

Differential effects of ginsenoside metabolites on slowly activating delayed rectifier K(+) and KCNQ1 K(+) channel currents

Channels formed by the co-assembly of the KCNQ1 subunit and the mink (KCNE1) subunit underline the slowly activating delayed rectifier K⁺ channels (I_Ks) in the heart. This K⁺ channel is one of the main pharmacological targets for the development of drugs against cardiovascular disease. Panax ginseng has been shown to exhibit beneficial cardiovascular effects. In a previous study, we showed that ginsenoside Rg3 activates human KCNQ1 K⁺ channel currents through interactions with the K318 and V319 residues. However, little is known about the effects of ginsenoside metabolites on KCNQ1 K⁺ alone or the KCNQ1 + KCNE1 K⁺ (I_Ks) channels. In the present study, we examined the effect of protopanaxatriol (PPT) and compound K (CK) on KCNQ1 K⁺ and I_Ks channel activity expressed in Xenopus oocytes. PPT more strongly inhibited the I_Ks channel currents than the currents of KCNQ1 K⁺ alone in concentration- and voltage-dependent manners. The IC₅₀ values on I_Ks and KCNQ1 alone currents for PPT were 5.18±0.13 and 10.04±0.17 μM, respectively. PPT caused a leftward shift in the activation curve of I_Ks channel activity, but minimally affected KCNQ1 alone. CK exhibited slight inhibition on I_Ks and KCNQ1 alone K⁺ channel currents. These results indicate that ginsenoside metabolites show limited effects on I_Ks channel activity, depending on the structure of the ginsenoside metabolites.

Antihyperalgesic effects of ginseng total saponins in a rat model of incisional pain

BACKGROUND

The aim of this study was to assess whether intraperitoneal administration of ginseng total saponins (GTS) has antihyperalgesic effects in a rat model of incisional pain. The proinflammatory responses and reversal of the antihyperalgesic effect of GTS by N-methyl-d-aspartate (NMDA) or naloxone were also evaluated.

MATERIALS AND METHODS

Rats were injected intraperitoneally with 0.9% saline vehicle or various doses of GTS before or after a plantar incision. Paw withdrawal in response to application of the von Frey filament with the lowest bending force marked the mechanical withdrawal threshold (MWT). Blood samples were collected for the assessment of serum interleukin (IL)-1β and IL-6 levels. The IL levels were measured using an enzyme-linked immunosorbent assay kit. Rats were injected intraperitoneally with NMDA or naloxone before the GTS injection to assess the reversal of the antihyperalgesic effect of GTS.

RESULTS

The MWT measured 2 h after the plantar incision increased significantly after the postincision administration of 50, 100, or 200 mg/kg of GTS compared with the MWT at 2 h after plantar incision. The MWT also increased significantly after the preincision injection of 100 or 200 mg/kg of GTS compared with the MWT of the vehicle control. Administration of GTS suppressed the postincision rise in serum IL-1β levels and NMDA inhibited the increase in the MWT compared with GTS alone.

CONCLUSIONS

Intraperitoneal administration of GTS before or after surgery induces antihyperalgesic effects in a rat model of incisional pain. The effects on mechanical hyperalgesia may be associated with anti-inflammatory cytokines and NMDA signaling.

Inhibitory Effects of Ginsenoside Metabolites, Compound K and Protopanaxatriol, on GABAC Receptor-Mediated Ion Currents

Ginsenosides, one of the active ingredients of Panax ginseng, show various pharmacological and physiological effects, and they are converted into compound K (CK) or protopanaxatriol (M4) by intestinal microorganisms. CK is a metabolite derived from protopanaxadiol (PD) ginsenosides, whereas M4 is a metabolite derived from protopanaxatriol (PT) ginsenosides. The γ-aminobutyric acid receptor_C (GABA_C) is primarily expressed in retinal bipolar cells and several regions of the brain. However, little is known of the effects of ginsenoside metabolites on GABA_C receptor channel activity. In the present study, we examined the effects of CK and M4 on the activity of human recombinant GABA_C receptor (ρ1) channels expressed in Xenopus oocytes by using a 2-electrode voltage clamp technique. In oocytes expressing GABA_C receptor cRNA, we found that CK or M4 alone had no effect in oocytes. However, co-application of either CK or M4 with GABA inhibited the GABA-induced inward peak current (I_GABA). Interestingly, pre-application of M4 inhibited I_GABA more potently than CK in a dose-dependent and reversible manner. The half-inhibitory concentration (IC₅₀) values of CK and M4 were 52.1±2.3 and 45.7±3.9 µM, respectively. Inhibition of I_GABA by CK and M4 was voltage-independent and non-competitive. This study implies that ginsenoside metabolites may regulate GABA_C receptor channel activity in the brain, including in the eyes.