Ginsenoside Rg1 inhibits the brain cAMP phosphodiesterase activity in young and aged rats

Inhibition of phosphodiesterase: A novel therapeutic target for the treatment of mild cognitive impairment and Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia and is ranked as the 6th leading cause of death in the US. The prevalence of AD and dementia is steadily increasing and expected cases in USA is 14.8 million by 2050. Neuroinflammation and gradual neurodegeneration occurs in Alzheimer's disease. However, existing medications has limitation to completely abolish, delay, or prevent disease progression. Phosphodiesterases (PDEs) are large family of enzymes to hydrolyze the 3'-phosphodiester links in cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) in signal-transduction pathways for generation of 5'-cyclic nucleotides. It plays vital role to orchestrate several pharmacological activities for proper cell functioning and regulating the levels of cAMP and cGMP. Several evidence has suggested that abnormal cAMP signaling is linked to cognitive problems in neurodegenerative disorders like AD. Therefore, the PDE family has become a widely accepted and multipotential therapeutic target for neurodegenerative diseases. Notably, modulation of cAMP/cGMP by phytonutrients has a huge potential for the management of AD. Natural compounds have been known to inhibit phosphodiesterase by targeting key enzymes of cGMP synthesis pathway, however, the mechanism of action and their therapeutic efficacy has not been explored extensively. Currently, few PDE inhibitors such as Vinpocetine and Nicergoline have been used for treatment of central nervous system (CNS) disorders. Considering the role of flavonoids to inhibit PDE, this review discussed the therapeutic potential of natural compounds with PDE inhibitory activity for the treatment of AD and related dementia.

Natural Molecules as Talented Inhibitors of Nucleotide Pyrophosphatases/Phosphodiesterases (PDEs)

BACKGROUND

Phosphodiesterases (PDEs) are a wide group of enzymes with multiple therapeutic actions, including vasorelaxation, cardiotonic, antidepressant, anti-inflammatory, antithrombotic, anti-spasmolytic, memory-enhancing, and anti-asthmatic. PDEs with eleven subtypes from PDE-1 to PDE-11 typically catalyze the cleavage of the phosphodiester bond and, hence, degrades either cyclic adenosine monophosphate (cAMP) or cyclic guanosine monophosphate (cGMP).

OBJECTIVE

Several selective or non-selective inhibitors of the PDE subtypes are used clinically, i.e. sildenafil, rolipram, cysteine, etc. Recently, interest in plant-based pharmacologically bioactive compounds having potent PDEs inhibitory potential has increased. Purposely, extensive research has been carried out on natural products to explore new inhibitors of various PDEs. Therefore, this review summarizes the published data on natural PDEs inhibitors and their potential therapeutic applications.

METHODS

For this purpose, natural compounds with PDE inhibitory potential have been surveyed through several databases, including PubMed, Web of Sciences (WoS), Scopus, and Google Scholar.

RESULTS

According to a detailed literature survey, the most promising class of herbal compounds with PDE-inhibiting property has been found to belong to phenolics, including flavonoids (luteolin, kaempferol, icariin, etc.). Many other encouraging inhibitors from plants have also been identified, such as coumarins (23, 24) (licoarylcoumarin and glycocoumarin,), saponins ( agapanthussaponins), lignans (31, 33) [(±)-schizandrin and kobusin], terpenes (28, 29, 31) (perianradulcin A, quinovic acid, and ursolic acid), anthraquinones (18, 19) (emodin and chrysophanol), and alkaloids (Sanjoinine-D) (36).

CONCLUSION

In this review, studies have revealed the PDE-inhibitory potential of natural plant extracts and their bioactive constituents in treating various diseases; however, further clinical studies comprising synergistic use of different therapies (synthetic & natural) to acquire multi-targeted results might also be a promising option.

Nonsaponin fractions of Korean Red Ginseng extracts prime activation of NLRP3 inflammasome

Background

Korean Red Ginseng extracts (RGE) have been suggested as effective immune modulators, and we reported that ginsenosides possess anti-inflammasome properties. However, the properties of nonsaponin components of RGE have not been well studied.

Methods

To assess the roles of nonsaponin fractions (NS) in NLRP3 inflammasome activation, we treated murine macrophages with or without first or second inflammasome activation signals with RGE, NS, or saponin fractions (SF). The first signal was nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB)-mediated transcription of pro-interleukin (IL)-1β and NLRP3 while the second signal triggered assembly of inflammasome components, leading to IL-1β maturation. In addition, we examined the role of NS in IL-6 production and IL-1β maturation in mice.

Results

NS induced IL-1β and NLRP3 transcription via toll-like receptor 4 signaling, whereas SF blocked expression. During the second signal, SF attenuated NLRP3 inflammasome activation while NS did not. Further, NS-injected mice presented increased IL-1β maturation and IL-6 production.

Conclusion

SF and NS of RGE play differential roles in the NLRP3 inflammasome activation. Hence, RGE can be suggested as an NLRP3 inflammasome modulator.

Ginsenosides Rg1 and Rb1 enhance glutamate release through activation of protein kinase A in rat cerebrocortical nerve terminals (synaptosomes)

We examined the effect of ginsenoside Rg1 or Rb1, the active ingredients of ginseng, on the release of endogenous glutamate from glutamatergic nerve terminals purified from rat cerebral cortex. Result showed that the Ca(2+)-dependent release of glutamate evoked by 4-aminopyridine was facilitated by ginsenoside Rg1 or Rb1 in a concentration-dependent manner. Sequential experiments reveal that ginsenoside Rg1 or Rb1-mediated facilitation of glutamate release (i) results from an enhancement of vesicular exocytosis; (ii) is not due to an alternation of synaptosomal excitability; (iii) is associated with an increase in Ca(2+) influx through presynaptic N- and P/Q-type voltage-dependent Ca(2+) channels; (iv) appears to involve a protein kinase A pathway. These results conclude that ginsenoside Rg1 or Rb1 exerts their presynaptic facilitatory effect, likely through the activation of protein kinase A, which subsequently enhances Ca(2+) entry to cause an increase in evoked glutamate release from rat cortical synaptosomes. This finding might provide important information regarding the action of ginseng in the central nervous system.

Relaxation of canine corporal smooth muscle relaxation by ginsenoside saponin Rg3 is independent from eNOS activation

It has been reported that nitric oxide (NO) is involved in the relaxation mechanism of ginsenoside saponin in various smooth muscle in experimental animals. Although ginsenoside Rg(3) showed both endothelium-dependent and -independent component relaxation in vascular smooth muscle, the action mechanism of the relaxation of corporal muscle is not clear. We, thus, investigated the relaxation mechanism of ginsenoside Rg(3) using isolated canine corpus cavernosum. Ginsenoside Rg(3) concentration-dependently relaxed the canine corpus cavernosum that had been contracted by phenylephrine (PE), in which IC(50) was 1.68 x 10(-5) g/ml. Ginsenoside Rg(3) significantly (P < 0.05) potentiated acetylcholine (ACh)-induced relaxation in endothelium intact corpus cavernosum. Methylene blue (MB) but not N(omega)-nitro-L-arginine methylester (L-NAME) or ODQ (1H-[1,2,4]oxadiazol-[4,3-]quinoxsalin-1-one) modified the dose-response curve of ginsenoside Rg(3). Ginsenoside Rg(3) also significantly potentiated relaxation response to UV light in the presence of streptozotocin (STZ), which was almost completely (P < 0.01) blocked by ODQ. Ginsenoside Rg(3) concentration-dependently inhibited corporal phosphodiesterases (PDE), which resulted in increase of cyclic adenosine monophosphate (cAMP) as well as cyclic guanosine monophosphate (cGMP) contents in corporal smooth muscles. MB inhibited the accumulation of cGMP but not cAMP by ginsenoside Rg(3). These results indicate that mechanism responsible for the relaxation by ginsenoside Rg(3) is not by stimulating endothelial nitric oxide synthase (eNOS) of the canine corporal smooth muscle but by increasing cyclic nucleotide levels through PDE inhibition.

Changes of [3H]MK-801, [3H]muscimol and [3H]flunitrazepam Binding in Rat Brain by the Prolonged Ventricular Infusion of Transformed Ginsenosides

Ameliorating effects of ginseng were observed on neuronal cell death associated with ischemia or glutamate toxicity. Ginseng saponins are transformed by intestinal microflora and the transformants would be absorbed from intestine. In the present study, we have investigated the effects of transformed ginsenoside Rg3, Rh2 and compound K on the modulation of NMDA receptor and GABAA receptor binding in rat brain. The NMDA receptor binding was analyzed by quantitative autoradiography using [3H]MK-801 binding, and GABAA receptor bindings were analyzed by using [3H]muscimol and [3H]flunitrazepam binding in rat brain slices. Ginsenoside Rg3, Rh2 and compound K were infused (10 microg/10 microl/h) into rat brain lateral ventricle for 7 days, through pre-implanted cannula by osmotic minipumps (Alzet, model 2ML). The levels of [3H]MK-801 binding were highly decreased in almost all regions of frontal cortex and hippocampus by ginsenoside Rh2 and compound K. The levels of [3H]muscimol binding were elevated in part of frontal cortex and granule layer of cerebellum by the treatment of ginsenoside Rh2 and compound K. However, the [3H]flunitrazepam binding was not modulated by any tested ginsenosides. Ginsenoside Rh2 and compound K induced the downregulation of the [3H]MK-801 binding as well as upregulation of the and [3H]muscimol binding in a region-specific manner after prolonged infusion into lateral ventricle. However, ginsenoside Rg3 did not show the significant changes of ligand bindings. In addition, ginsenoside Rh2 decreased the expression of nNOS in the hippocampus although Rg3 decreased the expression in the cortex. These results suggest that biotransformed ginsenoside Rh2 and compound K could play an important role in the biological activities in the central nervous systems and neurodegenerative disease.

Interactions between herbal medicines and prescribed drugs: a systematic review

Despite the widespread use of herbal medicines, documented herb-drug interactions are sparse. We have reviewed the literature to determine the possible interactions between the seven top-selling herbal medicines (ginkgo, St John's wort, ginseng, garlic, echinacea, saw palmetto and kava) and prescribed drugs. Literature searches were performed using the following databases: Medline (via Pubmed), Cochrane Library, Embase and phytobase (all from their inception to July 2000). All data relating to herb-drug interactions were included regardless of whether they were based on case reports, case series, clinical trials or other types of investigation in humans. In vitro experiments were excluded. Data were extracted by the first author and validated by the second author. 41 case reports or case series and 17 clinical trials were identified. The results indicate that St John's wort (Hypericum perforatum) lowers blood concentrations of cyclosporin, amitriptyline, digoxin, indinavir, warfarin, phenprocoumon and theophylline; furthermore it causes intermenstrual bleeding, delirium or mild serotonin syndrome, respectively, when used concomitantly with oral contraceptives (ethinylestradiol/desogestrel), loperamide or selective serotonin-reuptake inhibitors (sertaline, paroxetine, nefazodone). Ginkgo (Ginkgo biloba) interactions include bleeding when combined with warfarin, raised blood pressure when combined with a thiazide diuretic and coma when combined with trazodone. Ginseng (Panax ginseng) lowers blood concentrations of alcohol and warfarin, and induces mania if used concomitantly with phenelzine. Garlic (Allium sativum) changes pharmacokinetic variables of paracetamol, decreases blood concentrations of warfarin and produces hypoglycaemia when taken with chlorpropamide. Kava (Piper methysticum) increases 'off' periods in Parkinson patients taking levodopa and can cause a semicomatose state when given concomitantly with alprazolam. No interactions were found for echinacea (Echinacea angustifolia, E. purpurea, E. pallida) and saw palmetto (Serenoa repens). In conclusion, interactions between herbal medicines and synthetic drugs exist and can have serious clinical consequences. Healthcare professionals should ask their patients about the use of herbal products and consider the possibility of herb-drug interactions.

Panax ginseng and Eleutherococcus senticosus may exaggerate an already existing biphasic response to stress via inhibition of enzymes which limit the binding of stress hormones to their receptors

A mechanism of action for Panax ginseng (PG) and Eleutherococcus senticosus (ES) is proposed which explains how they could produce the paradoxical effect of sometimes increasing and sometimes decreasing the stress response. The mechanism suggests that this biphasic effect results from increased occupancy of positive and negative feedback stress hormone receptors by their natural ligands due to inhibition of specific enzymes which function to limit receptor occupancy. Specifically, it is suggested that PG inhibits 11-beta hydroxysteroid dehydrogenase one and ES inhibits catechol- O -methyl transferase, both of which reside in close proximity to stress hormone receptors and catalyse the degradation of stress hormones into inactive compounds. In addition, it is suggested that the increased energy said to result from PG and ES may be a consequence of their increasing the occupancy of stress hormone receptors which function to redistribute the body's energy reserves from regeneration to activity.

Ginsenoside Rc and Rg1 differentially modulate NMDA receptor subunit mRNA levels after intracerebroventricular infusion in rats

We investigated the influence of centrally administered ginsenoside on the regulation of mRNA levels of the family of NMDA receptor subtypes (NR1, NR2A, NR2B, NR2C) by in situ hybridization histochemistry in the rat brain. The ginsenosides Rc and Rg1, the major components of ginseng saponin, differentially modulate NMDA receptor subunit mRNA levels in rat brain following prolonged i.c.v.-infusion. Ginsenosides Rc or Rg1 (10 microg/10 microl/hr for 7 days) was infused through preimplanted cannulae connected to osmotic mini-pumps. The level of NR1 mRNA is significantly increased in temporal cortex, caudate putamen, hippocampus, and granule layer of cerebellum in Rg1-infused rats as compared to control group. The level of NR2A mRNA is elevated in the frontal cortex. In contrast, it was decreased in CAI area of hippocampus in Rg1-infused rats. However, there was no significant change of NR1 and NR2A mRNA levels in Rc-infused rats. The level of NR2B mRNA is elevated in cortex, caudate putamen, and thalamus in both Rc- and Rg-infused rats. In contrast, NR2B level is decreased in CA3 in Rg1-infused rats. The level of NR2C mRNA is increased in the granule layer of cerebellum in only Rg1 but not Rc infused rats. These results show that structure difference of ginsenoside may diversely affect the modulation of expression of NMDA receptor subunit mRNA after infusion into cerebroventricle in rats.