Inhibitory effects of Coptidis Rhizoma on the intestinal absorption and metabolism of Scutellariae Radix

ETHNOPHARMACOLOGICAL RELEVANCE

The Scutellariae Radix (SR) and Coptidis Rhizoma (CR) herb couple is widely used in traditional Chinese medicine prescriptions for the treatment of diabetes mellitus due to its interaction and synergistic effect compared to either herb alone, but the underlying mechanism of interaction between these herbs is unclear. This study aimed to investigate the effects of CR on the metabolism and absorption of SR.

MATERIALS AND METHODS

After rats were treated with normal saline (NS group) or the CR extract (CR-treated group) for seven consecutive days, the intestinal flora was extracted from rat faeces for a co-incubation with the SR extract to investigate the metabolism of SR flavonoids, and a non-everted gut sac was prepared in vitro to evaluate the intestinal absorption of the SR extract. The components of the SR extract, the metabolites of the SR extract that was co-incubated with intestinal flora, and the dialysate acquired from non-everted gut sacs were identified and determined by an HPLC-MS/MS method. The absorption rate constant (Ka) and the apparent permeability (Papp) of each compound were calculated, and the effects of CR on the metabolism and absorption of flavonoids in SR were evaluated, by comparison the Ka and Papp between two groups using Student's t-test.

RESULTS

Twenty-nine flavonoids were detected and identified in the SR extract, including 16 glycosides and 13 aglycones. In the co-incubation with the intestinal flora, differences in metabolite classes were not observed between the NS group and CR-treated group; however, the metabolic rates of 17 flavonoids in the CR-treated group were significantly higher than the NS group. The Papp of 11 compounds (4 glycosides and 7 aglycones) across the gut sac were greater than 2 × 10-5 cm/s in both groups, while the Papp values of 7 compounds including wogonoside (WG) and other aglycones were significantly decreased in the CR-treated group.

CONCLUSION

Based on these results, CR decreased the metabolism and absorption of SR flavonoids, and exerted much greater inhibitory effects on aglycones than glycosides, which may be one of the potential mechanisms underlying the therapeutic effects of the combination of SR and CR on diabetes mellitus.

Peltatoside Isolated from Annona crassiflora Induces Peripheral Antinociception by Activation of the Cannabinoid System

Peltatoside is a natural compound isolated from leaves of Annona crassiflora Mart., a plant widely used in folk medicine. This substance is an analogue of quercetin, a flavonoid extensively studied because of its diverse biological activities, including analgesic effects. Besides, a previous study suggested, by computer structure analyses, a possible quercetin-CB₁ cannabinoid receptor interaction. Thus, the aim of this work was to assess the antinociceptive effect of peltatoside and analyze the cannabinoid system involvement in this action. The mouse paw pressure test was used and hyperalgesia was induced by intraplantar injection of carrageenan (200 µg/paw). All used drugs were administered by intraplantar administration in Swiss male mice (n = 6). Peltatoside (100 µg/paw) elicited a local inhibition of hyperalgesia. The peripheral antinociceptive action of peltatoside was antagonized by the CB₁ cannabinoid antagonist AM251 (160 µg/paw), but not by CB₂ cannabinoid antagonist AM630 (100 µg/paw). In order to assess the role of endocannabinoids in this peripheral antinociceptive effect, we used (i) [5Z,8Z,11Z,14Z]-5,8,11,14-eicosatetraenyl-methyl ester phosphonofluoridic acid, an inhibitor of anandamide amidase; (ii) JZL184, an inhibitor for monoacylglycerol lipase, the primary enzyme responsible for degrading the endocannabinoid 2-arachidonoylglycerol; and (iii) VDM11, an endocannabinoid reuptake inhibitor. MAFP, JZL184, and VDM11 did not induce antinociception, respectively, at the doses 0.5, 3.8, and 2.5 µg/paw, however, these three drugs were able to potentiate the peripheral antinociceptive effect of peltatoside at an intermediary dose (50 µg/paw). Our results suggest that this natural substance is capable of inducing analgesia through the activation of peripheral CB₁ receptors, involving endocannabinoids in this process.

Secoisolariciresinol diglycoside, a flaxseed lignan, exerts analgesic effects in a mouse model of type 1 diabetes: Engagement of antioxidant mechanism

Peripheral painful neuropathy is one of the most common complications in diabetes and necessitates improved treatment. Secoisolariciresinol diglycoside (SDG), a predominant lignan in flaxseed, has been shown in our previous studies to exert antidepressant-like effect. As antidepressant drugs are clinically used to treat chronic neuropathic pain, this work aimed to investigate the potential analgesic efficacy of SDG against diabetic neuropathic pain in a mouse model of type 1 diabetes. We subjected mice to diabetes by a single intraperitoneal (i.p.) injection of streptozotocin (STZ, 200 mg/kg), and Hargreaves test or von Frey test was used to assess thermal hyperalgesia or mechanical allodynia, respectively. Chronic instead of acute SDG treatment (3, 10 or 30 mg/kg, p.o., twice per day for three weeks) ameliorated thermal hyperalgesia and mechanical allodynia in diabetic mice, and these analgesic actions persisted about three days when SDG treatment was terminated. Although chronic treatment of SDG to diabetic mice did not impact on the symptom of hyperglycemia, it greatly attenuated excessive oxidative stress in sciatic nerve and spinal cord tissues, and partially counteracted the condition of weight decrease. Furthermore, the analgesic actions of SDG were abolished by co-treatment with the reactive oxygen species donor tert-butyl hydroperoxide (t-BOOH), but potentiated by the reactive oxygen species scavenger phenyl-N-tert-butylnitrone (PBN). These findings indicate that chronic SDG treatment can correct neuropathic hyperalgesia and allodynia in mice with type 1 diabetes. Mechanistically, the analgesic actions of SDG in diabetic mice may be associated with its antioxidant activity.

GPR18 Inhibiting Amauromine and the Novel Triterpene Glycoside Auxarthonoside from the Sponge-Derived Fungus Auxarthron reticulatum

The marine sponge-derived fungus Auxarthron reticulatum produces the cannabinoid receptor antagonist amauromine (1). Recultivation of the fungus to obtain further amounts for more detailed pharmacological evaluation of 1 additionally yielded the novel triterpene glycoside auxarthonoside (2), bearing, in nature, a rather rare sugar moiety, i.e., N-acetyl-6-methoxy-glucosamine. Amauromine (1), which inhibited cannabinoid CB1 receptors (Ki 0.178 µM) also showed antagonistic activity at the cannabinoid-like orphan receptor GPR18 (IC50 3.74 µM). The diketopiperazine 1 may thus serve as a lead structure for the development of more potent and selective GPR18 antagonists, which are required to study the orphan receptor's potential as a new drug target. Despite the execution of many biological assays, to date, no bioactivity could be found for auxarthonoside (2).

Pseudopterosin A inhibits phagocytosis and alters intracellular calcium turnover in a pertussis toxin sensitive site in Tetrahymena thermophila

The free living ciliate Tetrahymena thermophila was chosen as a cellular model in order to investigate the mode of action of the anti-inflammatory marine natural product Pseudopterosin A (PsA). In this paper we present evidence that PsA inhibits phagosome formation (KD=10.5 microM) and triggers a discrete intracellular calcium release (depletion) from a site in T. thermophila cells (KD=6.4 microM). Pre-treatment with the Gi/o protein inhibitor, pertussis toxin (PTX), inhibits PsA activity of both responses providing pharmacological evidence that the site of action for PsA is at a PTX sensitive G protein or a G protein coupled receptor (GPCR). Addition of extracellular calcium induced a concentration dependent increase in the incidence of phagosome formation (KD=30.3 microM) and was blocked by PsA pre-treatment. This particular effect of PsA on extracellular calcium was not blocked by PTX pre-treatment.

Phenylarsine oxide inhibits the fusicoccin-induced activation of plasma membrane H(+)-ATPase

To investigate the mechanism by which fusicoccin (FC) induces the activation of the plasma membrane (PM) H(+)-ATPase, we used phenylarsine oxide (PAO), a known inhibitor of protein tyrosine-phosphatases. PAO was supplied in vivo in the absence or presence of FC to radish (Raphanus sativus L.) seedlings and cultured Arabidopsis cells prior to PM extraction. Treatment with PAO alone caused a slight decrease of PM H(+)-ATPase activity and, in radish, a decrease of PM-associated 14-3-3 proteins. When supplied prior to FC, PAO drastically inhibited FC-induced activation of PM H(+)-ATPase, FC binding to the PM, and the FC-induced increase of the amount of 14-3-3 associated with the PM. On the contrary, PAO was completely ineffective on all of the above-mentioned parameters when supplied after FC. The H(+)-ATPase isolated from PAO-treated Arabidopsis cells maintained the ability to respond to FC if supplied with exogenous, nonphosphorylated 14-3-3 proteins. Altogether, these results are consistent with a model in which the dephosphorylated state of tyrosine residues of a protein(s), such as 14-3-3 protein, is required to permit FC-induced association between the 14-3-3 protein and the PM H(+)-ATPase.

Solasodine glycosides. In vitro preferential cytotoxicity for human cancer cells

Solamargine [(22R,25R)-spiro-5-en-3 beta-yl-alpha-L-rhamnopyranosyl- (1----2glu)-O-alpha-L-rhamnopyranozyl (1----4glu)-beta-D-glucopyranoze], a glycoside of solasodine preferentially inhibits the uptake of tritiated thymidine by cancer cells. In contrast, solamargine at equivalent concentration, and the mono- and diglycosides of solasodine have a limited effect on the uptake of tritiated thymidine for other cell types, including unstimulated lymphocytes and lymphocytes stimulated with Con A. In contrast the solasodine glycosides do not inhibit the uptake of tritiated thymidine by lymphocytes stimulated with PHA or PWM. The inhibition of tritiated thymidine uptake by solamargine and the mono- and di-glycosides of solasodine are dependent upon their cellular uptake by endogenous endocytic lectins (EELs). The mode of action of the solasodine glycosides, in particular solamargine, appears to be the induction of cell lysis, as determined by morphological examination.

Stevioside, the sweet glycoside of Stevia rebaudiana, inhibits the action of atractyloside in the isolated perfused rat liver

Stevioside inhibits the action of atractyloside on energy metabolism in the isolated perfused rat liver. The effects of atractyloside on glycolysis, glycogenolysis, gluconeogenesis and oxygen uptake are decreased by stevioside. The concentration for half-maximal action is 0.5 mM. The site of the action is located on the outside of the cell. Possibly, stevioside affects the transport of atractyloside across the cell membrane.

Mechanism of action of 1- -D-ribofuranosyl-1,2,4-triazole-3-carboxamide (Virazole), a new broad-spectrum antiviral agent

The antiviral activity of the synthetic nucleoside, Virazole (1-beta-D-ribofuranosyl-1,2,4-triazole-3-carboxamide), against measles virus in Vero cell cultures was substantially reversed by xanthosine, guanosine, and to a slightly lesser extent by inosine. Virazole 5'-phosphate was subsequently found to be a potent competitive inhibitor of inosine 5'-phosphate dehydrogenase (IMP:NAD(+) oxidoreductase, EC 1.2.1.14) isolated from Escherichia coli (K(m) = 1.8 x 10(-5) M) with a K(i) of 2.7 x 10(-7) M. Guanosine 5'-phosphate (GMP) was a competitive inhibitor of this enzyme with a K(i) of 7.7 x 10(-5) M. Virazole 5'-phosphate was similarly active against IMP dehydrogenase isolated from Ehrlich ascites tumor cells, with a K(i) of 2.5 x 10(-7) M. The K(m) for this enzyme was 1.8 x 10(-5) M, and the K(i) for GMP was 2.2 x 10(-4) M. These results suggest that the antiviral activity of Virazole might be due to the inhibition of GMP biosynthesis in the infected cell at the step involving the conversion of IMP to xanthosine 5'-phosphate. This inhibition would consequently result in inhibition of the synthesis of vital viral nucleic acid.

Interaction of concanavalin A with an arabinogalactan from the cell wall of Mycobacterium bovis

The arabinogalactan isolated from the cell wall of Mycobacterium bovis reacts to form a precipitate with concanavalin A, the phytohemagglutinin of the jack bean. A typical precipitin-like curve is obtained when increasing amounts of the polysaccharide are added to a constant quantity of concanavalin A. Inhibitor studies suggest that concanavalin A reacts with the arabinogalactan by interacting with the C-2, C-3, and C-5 hydroxyl groups of the alpha-d-arabinofuranosyl residues situated at the chain ends of this polysaccharide.

Aminoglycoside antibiotics: inactivation by phosphorylation in Escherichia coli carrying R factors

R-factor strains which are streptomycin-resistant and spectinomycin-sensitive have been found to inactivate streptomycin by a new mechanism. The 3'-OH group of the 2-deoxy-2-methylamino-l-glucopyranosyl moiety is phosphorylated.