Resibufogenin

Xenobiotica. 2013 May;43(5):479-85.

Isolation and identification of phase I metabolites of resibufogenin in rats.[Pubmed: 23153055]

1. Resibufogenin (1), a major bufadienolide of Chinese medicine Chan Su, had a wide range of pharmacological activities. In present work, the metabolism of 1 in male Sprague-Dawley rats was investigated by identifying the metabolites of Resibufogenin excreted in rat bile.
METHODS AND RESULTS:
2. Following an oral dose of 60 mg/kg resibufagenin, nine metabolites were isolated from bile of rats, and their structures were identified as 3-keto- Resibufogenin (2), 3-epi-Resibufogenin (3), 5β-hydroxy-3-epi-Resibufogenin (4), 1α, 5β-dihydroxy-3-epi-Resibufogenin (5), 3α, 5β, 14α, 15β-tetrahydroxyl-bufa- 20, 22-dienolide (6), 3α, 14α, 15β-trihydroxy-bufa-20, 22-dienolide (7), 3-epi- 5β-hydroxy-bufalin (8), 12α, 16β-dihydroxy-3-epi-Resibufogenin (9), and 5β, 16β-dihydroxy-3-epi-Resibufogenin (10), respectively, on the basis of widely spectroscopic methods including 2D-NMR technology. It is first time to describe the metabolites of 1 in vivo, and metabolites 5-7 and 9-10 are novel.
CONCLUSIONS:
3. On the basis of these identified metabolites, a possible metabolism pathway for 1 in rats has been proposed. This is the first systematic study on the phase I metabolites of Resibufogenin.

Hypertens Pregnancy. 2010 Jan;29(1):1-9.

Resibufogenin prevents the manifestations of preeclampsia in an animal model of the syndrome.[Pubmed: 19277924 ]

We have developed a rat model of preeclampsia which is based upon excessive volume expansion and includes hypertension, proteinuria and intrauterine growth restriction. In this model, the urinary excretion of the circulating steroid inhibitor of Na +/ K+ ATPase, marinobufagenin, is increased prior to the development of hypertension and proteinuria. An analogue of marinobufagenin, Resibufogenin, successfully treats the hypertension and proteinuria.
METHODS AND RESULTS:
We administered Resibufogenin early in pregnancy in this model, prior to the development of the syndrome. We found that Resibufogenin not only prevented the advent of hypertension and proteinuria, but also the development of intrauterine growth restriction.
CONCLUSIONS:
These results may have relevance to the human condition.

PLoS One . 2015 Jun 29;10(6):e0129851.

Resibufogenin Induces G1-Phase Arrest through the Proteasomal Degradation of Cyclin D1 in Human Malignant Tumor Cells[Pubmed: 26121043]

Abstract Huachansu, a traditional Chinese medicine prepared from the dried toad skin, has been used in clinical studies for various cancers in China. Resibufogenin is a component of huachansu and classified as bufadienolides. Resibufogenin has been shown to exhibit the anti-proliferative effect against cancer cells. However, the molecular mechanism of Resibufogenin remains unknown. Here we report that Resibufogenin induces G1-phase arrest with hypophosphorylation of retinoblastoma (RB) protein and down-regulation of cyclin D1 expression in human colon cancer HT-29 cells. Since the down-regulation of cyclin D1 was completely blocked by a proteasome inhibitor MG132, the suppression of cyclin D1 expression by Resibufogenin was considered to be in a proteasome-dependent manner. It is known that glycogen synthase kinase-3β (GSK-3β) induces the proteasomal degradation of cyclin D1. The addition of GSK-3β inhibitor SB216763 inhibited the reduction of cyclin D1 caused by Resibufogenin. These effects on cyclin D1 by Resibufogenin were also observed in human lung cancer A549 cells. These findings suggest that the anti-proliferative effect of Resibufogenin may be attributed to the degradation of cyclin D1 caused by the activation of GSK-3β.

Drug Metab Dispos. 2015 Mar;43(3):299-308.

Characterization of phase I metabolism of resibufogenin and evaluation of the metabolic effects on its antitumor activity and toxicity.[Pubmed: 25504504]

Resibufogenin (RB), one of the major active compounds of the traditional Chinese medicine Chansu, has displayed great potential as a chemotherapeutic agent in oncology. However, it is a digoxin-like compound that also exhibits extremely cardiotoxic effects. The present study aimed to characterize the metabolic behaviors of RB in humans as well as to evaluate the metabolic effects on its bioactivity and toxicity. The phase I metabolic profile in human liver microsomes was characterized systemically, and the major metabolite was identified as marinobufagenin (5β-hydroxylResibufogenin, 5-HRB) by liquid chromatography-mass spectrometry and nuclear magnetic imaging techniques.
METHODS AND RESULTS:
Both cytochrome P450 (P450) reaction phenotyping and inhibition assays using P450-selective chemical inhibitors demonstrated that CYP3A4 was mainly involved in RB 5β-hydroxylation with much higher selectivity than CYP3A5. Kinetic characterization demonstrated that RB 5β-hydroxylation in both human liver microsomes and human recombinant CYP3A4 obeyed biphasic kinetics and displayed similar apparent kinetic parameters. Furthermore, 5-HRB could significantly induce cell growth inhibition and apoptosis in A549 and H1299 by facilitating apoptosome assembly and caspase activation. Meanwhile, 5-HRB displayed very weak cytotoxicity of human embryonic lung fibroblasts, and in mice there was a greater tolerance to acute toxicity.
CONCLUSIONS:
In summary, CYP3A4 dominantly mediated 5β-hydroxylation and was found to be a major metabolic pathway of RB in the human liver, whereas its major metabolite (5-HRB) displayed better druglikeness than its parent compound RB. Our findings lay a solid foundation for RB metabolism studies in humans and encourage further research on the bioactive metabolite of RB.

Toxicol In Vitro. 2011 Dec;25(8):1644-53.

Effects of Resibufogenin and Cinobufagin on voltage-gated potassium channels in primary cultures of rat hippocampal neurons.[Pubmed: 21798339]

Outward delayed rectifier potassium channel and outward transient potassium channel have multiple important roles in maintaining the excitability of hippocampal neurons. The present study investigated the effects of two bufadienolides, Resibufogenin (RBG) and Cinobufagin (CBG), on the outward delayed rectifier potassium current (IK) and outward transient potassium current (IA) in rat hippocampal neurons.
METHODS AND RESULTS:
RBG and CBG have similar structures and both were isolated from the venom gland of toad skin. RBG inhibited both IK and IA, whereas CBG inhibited IK without noticeable effect on IA. Moreover, at 1 μM concentration both RBG and CBG could alter some channel kinetics and gating properties of IK, such as steady-state activation and inactivation curves, open probability and time constants.
CONCLUSIONS:
These findings suggested that IK is probably a target of bufadienolides, which may explain the mechanisms of bufadienolides' pathological effects on central nervous system.

Exp Biol Med (Maywood). 2006 Feb;231(2):215-20.

Resibufogenin corrects hypertension in a rat model of human preeclampsia.[Pubmed: 16446498]

The study of the pathogenesis of preeclampsia has been hampered by a relative dearth of animal models.
METHODS AND RESULTS:
We developed a rat model of preeclampsia in which the excretion of a circulating inhibitor of Na/K ATPase, marinobufagenin (MBG), is elevated. These animals develop hypertension, proteinuria, and intrauterine growth restriction. The administration of a congener of MBG, Resibufogenin (RBG), reduces blood pressure to normal in these animals, as is the case when given to pregnant animals rendered hypertensive by the administration of MBG. Studies of Na/K ATPase inhibition by MBG and RBG reveal that these agents are equally effective as inhibitors of the enzyme.