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The inhibition of Na(+)/K(+) -ATPase by versatile steroid-like compounds contributes to the putative therapeutic effects of many Chinese medicinal cardiac products via the same molecular mechanism triggered by cardiac glycosides. Five major steroid-like compounds, antcin A, B, C, H, and K were isolated from Niuchangchih (Antrodia camphorata), a unique Taiwan mushroom, and all inhibited Na(+)/K(+) -ATPase. Antcin A exhibited significantly higher inhibitory potency than the other four antcins, though weaker than ginsenoside Rh2 . In contrast, cortisone (an analogous steroid with anti-inflammatory effects stronger than antcin A) showed no detectable inhibitory potency. Molecular modeling has shown that antcins bind to Na(+)/K(+) -ATPase with the steroidal skeleton structurally upside-down in comparison with ginsenoside Rh2 . The inhibitory potency of antcin A is attributed to steroidal hydrophobic interaction within the binding pocket and the formation of three hydrogen bonds between its carboxyl group and two cationic residues around the cavity entrance of Na(+)/K(+) -ATPase. The presence of an additional carbonyl or hydroxyl group at C7 of the other four antcins leads to severe repulsion in the hydrophobic pocket, and thus significantly reduces inhibitory potency. It is proposed that antcin A is a bi-functional compound that exerts anti-inflammatory effects and that enhances blood circulation via two different molecular mechanisms.

Aim: To determine the active ingredient of Niuchangchih (Antrodia camphorata) responsible for its anti-inflammatory effects and the relevant molecular mechanisms., Methods: Five major antcins (A, B, C, H, and K) were isolated from fruiting bodies of Niuchangchih. Structural similarity between the antcins and 2 glucocorticoids (cortisone and dexamethasone) was compared. After incubation with each compound, the cytosolic glucocorticoid receptor (GR) was examined for its migration into the nucleus. Mo lecular docking was performed to model the tertiary structure of GR associated with antcins., Results: Incubation with cortisone, dexamethasone or antcin A (but not antcins B, C, H, and K) led to the migration of glucocorticoid receptor into the nucleus. The minimal concentration of antcin A, cortisone and dexamethasone to induce nuclear migration of glucocorticoid receptor was 10, 1, and 0.1 mol/L, respectively. The results are in agreement with the simulated binding affinity scores of these three ligands docking to the glucocorticoid receptor. Molecular modeling indicates that C-7 of antcin A or glucocorticoids is exposed to a hydrophobic region in the binding cavity of the glucocorticoid receptor, and the attachment of a hydrophilic group to C-7 of the other four antcins presumably results in their being expelled when docking to the cavity., Conclusion: The anti-inflammatory effect of Niuchangchih is, at least, partly attributed to antcin A that mimics glucocorticoids and triggers translocation of glucocorticoid receptor into nucleus to initiate the suppressing inflammation.

Aim: To examine if steroid-like compounds found in many Chinese medicinal products conventionally used for the promotion of blood circulation may act as active components via the same molecular mechanism triggered by cardiac glycosides, such as ouabain., Methods: The inhibitory potency of ouabain and the identified steroid-like compounds on Na(+)/K(+)-ATPase activity was examined and compared. Molecular modeling was exhibited for the docking of these compounds to Na(+)/K(+)-ATPase., Results: All the examined steroid-like compounds displayed more or less inhibition on Na(+)/K(+)-ATPase, with bufalin (structurally almost equivalent to ouabain) exhibiting significantly higher inhibitory potency than the others. In the pentacyclic triterpenoids examined, ursolic acid and oleanolic acid were moderate inhibitors of Na(+)/K(+)-ATPase, and their inhibitory potency was comparable to that of ginsenoside Rh2. The relatively high inhibitory potency of ursolic acid or oleanolic acid was due to the formation of a hydrogen bond between its carboxyl group and the Ile322 residue in the deep cavity close to two K(+) binding sites of Na(+)/K(+)-ATPase. Moreover, the drastic difference observed in the inhibitory potency of ouabain, bufalin, ginsenoside Rh2, and pentacyclic triterpenoids is ascribed mainly to the number of hydrogen bonds and partially to the strength of hydrophobic interaction between the compounds and residues around the deep cavity of Na(+)/K(+)-ATPase., Conclusion: Steroid-like compounds seem to contribute to therapeutic effects of many cardioactive Chinese medicinal products. Chinese herbs, such as Prunella vulgaris L, rich in ursolic acid, oleanolic acid and their glycoside derivatives may be adequate sources for cardiac therapy via effective inhibition on Na(+)/K(+)-ATPase.

The positive inotropic effect of cardiac glycosides lies in their reversible inhibition on the membrane-bound Na+/K+-ATPase in human myocardium. Steroid-like compounds containing a core structure similar to cardiac glycosides are found in many Chinese medicines conventionally used for promoting blood circulation. Some of them are demonstrated to be Na+/K+-ATPase inhibitors and thus putatively responsible for their therapeutic effects via the same molecular mechanism as cardiac glycosides. On the other hand, magnesium lithospermate B of danshen is also proposed to exert its cardiac therapeutic effect by effectively inhibiting Na+/K+-ATPase. Theoretical modeling suggests that the number of hydrogen bonds and the strength of hydrophobic interaction between the effective ingredients of various medicines and residues around the binding pocket of Na+/K+-ATPase are crucial for the inhibitory potency of these active ingredients. Ginsenosides, the active ingredients in ginseng and sanqi, substantially inhibit Na+/K+-ATPase when sugar moieties are attached only to the C-3 position of their steroid-like structure, equivalent to the sugar position in cardiac glycosides. Their inhibitory potency is abolished, however, when sugar moieties are linked to C-6 or C-20 position of the steroid nucleus; presumably, these sugar attachments lead to steric hindrance for the entrance of ginsenosides into the binding pocket of Na+/K+-ATPase. Neuroprotective effects of cardiac glycosides, several steroid-like compounds, and magnesium lithospermate B against ischemic stroke have been accordingly observed in a cortical brain slice-based assay model, and cumulative data support that effective inhibitors of Na+/K+-ATPase in the brain could be potential drugs for the treatment of ischemic stroke. [ABSTRACT FROM AUTHOR]