Cardenolide glycosides from root of Streptocaulon juventas

Bioassay-Guided Fractionation and Biological Activity of Cardenolides from Streptocaulon juventas

The discovery that Na/K-ATPase acts as a signal transducer led us to investigate the structural diversity of cardiotonic steroids and study their ligand effects. By applying Na/K-ATPase activity assay-guided fractionation, we isolated a total of 20 cardiotonic steroids from Streptocaulon juventas, including an undescribed juventasoside B (10: ) and 19 known cardiotonic steroids. Their structures have been elucidated. Using our platform of purified Na/K-ATPase and an LLC-PK1 cell model, we found that 10: , at a concentration that induces less than 10% Na/K-ATPase inhibition, can stimulate the Na/K-ATPase/Src receptor complex and selectively activate downstream pathways, ultimately altering prostate cancer cell growth. By assessing the ligand effect of the isolated cardiotonic steroids, we found that the regulation of cell viability by the isolated cardiotonic steroids was not associated with their inhibitory potencies against Na/K-ATPase activity but reflected their ligand-binding affinity to the Na/K-ATPase receptor. Based on this discovery, we identified a unique active cardiotonic steroid, digitoxigenin (1: ), and verified that it can protect LLC-PK1 cells from hypoxic injury, implicating its potential use in ischemia/reperfusion injury and inducing collagen synthesis in primary human dermal fibroblast cells, and implicating that compound 2: is the molecular basis of the wound healing activity of S. juventas.

Cardenolide and pregnatriene compounds from the roots of Nerium oleander

Cardenolide and pregnatriene compounds were isolated from the chloroform fraction of the 95% aqueous ethanolic extract of dried roots of Nerium oleander. The stereochemical structure of the cardenolide and pregnatriene compounds was determined to be 3β-O-(D-diginosyl)-14β-hydroxy card-20(22)-enolide and 12β-hydroxy pregna-4,6,16-triene-3,20-dione using spectroscopic methods including IR, HRMS and NMR spectroscopy.

A new cardenolide glycoside from the roots of Streptocaulon juventas (lour.) merr. (Asclepiadaceae)

From remaining aqueous fraction of the roots of Streptocaulon juventas, one new cardiac glycoside named periplogenin 3-O-β-gentiobioside (1) together with six known ones (2-7) were isolated. Their relative structures were elucidated based on NMR spectroscopic analysis. Compound 1 showed moderate cytotoxicity against non-small cell lung carcinoma NCI-H460 and ovarian cancer HeLa cells. Moreover, compounds 2 and 3 exhibited remarkable cytotoxicity against NCI-H460 cell with the IC₅₀ values of 0.34 and 0.068 μM, respectively.

Caspase-Dependent Apoptosis in Prostate Cancer Cells and Zebrafish by Corchorusoside C from Streptocaulon juventas

Corchorusoside C (1), isolated from Streptocaulon juventas collected in Vietnam, was found to be nontoxic in a zebrafish ( Danio rerio) model and to induce cytotoxicity in several cancer cell lines with notable selective activity against prostate DU-145 cancer cells (IC50 0.08 μM). Moreover, corchorusoside C induced DU-145 cell shrinkage and cell detachment. In CCD-112CoN colon normal cells, 1 showed significantly reduced cytotoxic activity (IC50 2.3 μM). A preliminary mechanistic study indicated that 1 inhibits activity and protein expression of NF-κB (p50 and p65), IKK (α and β), and ICAM-1 in DU-145 cells. ROS concentrations increased at 5 h post-treatment, and MTP decreased in a dose-dependent manner. Moreover, decreased protein expression of Bcl-2 and increased expression of PARP-1 was observed. Furthermore, corchorusoside C increased both the activity and protein levels of caspases 3 and 7. Additionally, 1 induced sub-G1 population increase of DU-145 cells and modulated caspases in zebrafish with nondifferential morphological effects. Therefore, corchorusoside C (1) induces apoptosis in DU-145 cells and targets the same pathways both in vitro and in vivo in zebrafish. Thus, the use of zebrafish assays seems worthy of wider application than is currently employed for the evaluation of potential anticancer agents of natural origin.

Cardenolides: Insights from chemical structure and pharmacological utility

Cardiac glycosides (CGs) are a class of naturally occurring steroid-like compounds, and members of this class have been in clinical use for more than 1500 years. They have been used in folk medicine as arrow poisons, abortifacients, heart tonics, emetics, and diuretics as well as in other applications. The major use of CGs today is based on their ability to inhibit the membrane-bound Na⁺/K⁺-ATPase enzyme, and they are regarded as an effective treatment for congestive heart failure (CHF), cardiac arrhythmia and atrial fibrillation. Furthermore, increasing evidence has indicated the potential cytotoxic effects of CGs against various types of cancer. In this review, we highlight some of the structural features of this class of natural products that are crucial for their efficacy, some methods of isolating these compounds from natural resources, and the structural elucidation tools that have been used. We also describe their physicochemical properties and several modern biotechnological approaches for preparing CGs that do not require plant sources.

C21 steroids from Streptocaulon juventas (Lour) Merr. induce apoptosis in HepG2

Three new C₂₁ steroids, i.e., (3β,17α,20S)-pregn-5(6)-ene-3, 17, 20-triol-3-O-β-d-digitalopyranosyl-(1 → 4)-β-d-digitalopyranoside (4), (3β,17α,20S)-pregn-5(6)-ene-3, 17, 20-triol-20-O-β-d-glucopyranosyl-(1 → 6)-β-d-glucopyranosyl-(1 → 2)-β-d-digital-opyranoside (8), (3β, 20R)-pregn-14(15)-ene-3, 20, 21-triol-3-O-β-d-glucopy-ranoside (10), along with ten known C₂₁ steroids were isolated from Streptocaulon juventas. Their structures were elucidated on the basis of 1D and 2D NMR spectroscopic techniques, mass spectrometry as well as comparison with the literature. All the isolated compounds were screened for their in vitro cytotoxicity against human liver cancer cells (HepG2) and the structure-activity relationships were also analyzed. Moreover, compounds 1-3, 5, 10-12, which displayed cytotoxic activities in HepG2 cells, were tested for the selective index (SI) by the ratio of cytotoxic effect on human hepatocytes (LO2) to that on HepG2. As a result, new compound 10 exhibited a good inhibitory activity against HepG2 with IC₅₀ value 11.7 μM as well as high SI value 3.5. Furthermore, compound 10 could induce HepG2 cells apoptosis by flow cytometry.

Octreotide-periplocymarin conjugate prodrug for improving targetability and anti-tumor efficiency: synthesis, in vitro and in vivo evaluation

Cardiac glycosides could increase intracellular Ca²⁺ ion by inhibiting the Na⁺/K⁺ATPase to induce apoptosis in many tumor cells. However, narrow therapeutic index, poor tumor selectivity and severe cardiovascular toxicity hinder their applications in cancer treatment. To improve the safety profile and tumor targetablility of cardiac glycosides, we designed octreotide conjugated periplocymarin, a cardiac glycoside isolated from Cortex periplocae. The conjugate showed higher cytotoxicity on MCF-7 cells and HepG2 tumor cells (SSTRs overexpression) but much less toxicity in L-02 normal cells. Tissue distribution studies of the conjugate using H₂₂ tumor model in mice showed higher accumulation in tumor and lower distribution in heart and liver than periplocymarin. Furthermore, in vivo anticancer effects of the conjugate on mice bearing H₂₂ cancer xenografts confirmed enhanced anti-tumor efficacy and decreased systemic toxicity. Altogether, octreotide-conjugated periplocymarin demonstrated tumor selectivity and may be useful as a targeting agent to improve the safety profile of cardiac glycosides for cancer therapy.

Apoptotic activities of cardenolide glycosides from Asclepias subulata

ETHNOPHARMACOLOGICAL RELEVANCE

Asclepias subulata Decne. (Apocynaceae) is a shrub occurring in Sonora-Arizona desert. The ethnic groups of Sonora, Mexico, Seris and Pimas, use this plant for the treatment of sore eyes, gastrointestinal disorders and cancer.

AIM OF THE STUDY

To determine the cell death pathways that the cardenolide glycosides with antiproliferative activity found in the methanol extract of A. subulata are able to activate.

MATERIALS AND METHODS

The effect of cardenolide glycosides isolated of A. subulata on induction of apoptosis in cancer cells was evaluated through the measuring of several key events of apoptosis. A549 cells were treated for 12h with doses of 3.0, 0.2, 3.0 and 1.0µM of 12, 16-dihydroxicalotropin, calotropin, corotoxigenin 3-O-glucopyranoside and desglucouzarin, respectively. Apoptotic and necrotic cell levels were measured by double staining with annexin V-FITC/PI. Mitochondrial membrane depolarization was examined through JC-1 staining. Apoptosis cell death and the apoptosis pathways activated by cardenolide glycosides isolated of A. subulata were further characterized by the measurement of caspase-3, caspase-8 and caspase-9 activity.

RESULTS

Apoptotic assays showed that the four cardenolide glycosides isolated of A. subulata induced apoptosis in A549 cells, which was evidencing by phosphatidylserine externalization in 18.2%, 17.0%, 23.9% and 22.0% for 12, 16-dihydroxicalotropin, calotropin, corotoxigenin 3-O-glucopyranoside and desglucouzarin, respectively, compared with 4.6% of control cells. Cell death was also associated with a decrease in mitochondrial membrane potential, which was more than 75% in the treated cultures respect to control. The activation of caspase-3 was observed in all cardenolide glycosides-treated cancer cells indicating the caspase-dependent apoptosis of A549 cells. Extrinsic and intrinsic apoptosis pathways were activated by cardenolide glycosides treatment at the doses tested.

CONCLUSION

In this study was found that cardenolide glycosides, 12, 16-dihydroxicalotropin, calotropin, corotoxigenin 3-O-glucopyranoside and desglucouzarin, isolated from A. subulata induced the cell death trough caspase-dependent apoptosis, which was activated, preferably, by extrinsic pathway.

Antiproliferative activity of cardenolide glycosides from Asclepias subulata

ETHNOPHARMACOLOGICAL RELEVANCE

Asclepias subulata Decne. is a shrub occurring in Sonora-Arizona desert (Mexico-USA). The ethnic groups, Seris and Pimas, use this plant for the treatment of sore eyes, gastrointestinal disorders and cancer.

AIM OF THE STUDY

To isolate the compounds responsible for antiproliferative activity of the methanol extract of A. subulata.

MATERIALS AND METHODS

A bioguided fractionation of methanol extract of A. subulata was performed using MTT assay to measure the antiproliferative activity of different compounds on three human cancer cell lines (A549, LS 180 and PC-3), one murine cancer cell line (RAW 264.7) and one human normal cell line (ARPE-19). The methanol extract was partitioned with hexane, ethyl acetate and ethanol. The active fractions, ethanol and residual, were fractioned by silica-column chromatography and active sub-fractions were separated using HPLC. The chemical structures of isolated compounds were elucidated with different chemical and spectroscopic methods.

RESULTS

A new cardenolide glycoside, 12, 16-dihydroxycalotropin, and three known, calotropin, corotoxigenin 3-O-glucopyranoside and desglucouzarin, were isolated of active sub-fractions. All isolated compounds showed a strong antiproliferative activity in human cancer cells. Calotropin was the more active with IC50 values of 0.0013, 0.06 and 0.41 µM on A549, LS 180 and PC-3 cell lines, respectively; while 12, 16-dihydroxycalotropin reached values of 2.48, 5.62 and 11.70 µM, on the same cells; corotoxigenin 3-O-glucopyranoside had IC50 of 2.64, 3.15 and 6.62 µM and desglucouzarin showed values of 0.90, 6.57 and 6.62, µM. Doxorubicin, positive control, showed IC50 values of 1.78, 6.99 and 3.18 µM, respectively. The isolated compounds had a weak effect on murine cancer cells and human normal cells, exhibiting selectivity to human cancer cells.

CONCLUSION

In this study, we found that 12, 16-dihydroxicalotropin, calotropin, corotoxigenin 3-O-glucopyranoside and desglucouzarin are responsible of antiproliferative properties of A. subulata, and that these compounds are highly selective to human cancer cells. Further studies are needed in order to establish the action mechanisms of the isolated compounds.

Chemical characterization and assessment of antioxidant potentiality of Streptocaulon sylvestre Wight, an endangered plant of sub-Himalayan plains of West Bengal and Sikkim

Background

S. sylvestre Wright is an extremely rare plant, found only in the sub-Himalayan Terai region of West Bengal and neighboring Sikkim foot-hills. The plant has never been evaluated for any pharmaceutical properties. The phytochemical status of the plant is still unknown. Therefore, the aim of the study was to explore the antioxidant and free radical scavenging activities and analysis of bioactive compounds present in S. sylvestre.

Methods

S. sylvestre methanolic extract (SSME) was evaluated for different free radical scavenging activities such as hydroxyl radical, nitric oxide, singlet oxygen, hypochlorous acid, peroxynitrite, superoxide radical and hydrogen peroxide scavenging etc. Iron chelating capacity and inhibition of lipid peroxidation were studied in addition to the assessment of haemolytic activity and erythrocyte membrane stabilizing activity (EMSA). Chemical characterization of SSME were performed by high performance liquid chromatography (HPLC) and gas chromatography–mass spectrometry (GC-MS).

Results

The results indicate that SSME possess potent antioxidant activity with IC₅₀ value of 113.06 ± 5.67 μg/ml, 63.93 ± 4.16 μg/ml and 142.14 ± 6.13 μg/ml for hydroxyl radical, superoxide radical and hypochlorous acid, respectively. HPLC analysis revealed presence of different phenolic secondary metabolites such as gallic acid, ferulic acid, p-coumaric acid, syringic acid, myricetin, quercetin etc. GC-MS analysis displayed the predominance of γ-sitosterol, vitamin E and squalene in SSME.

Conclusion

The present study provides a convincing evidence that S. sylvestre not only possess potent antioxidant activity but also can be used as a source of natural bioactive phytochemicals in the future.

Electronic supplementary material

The online version of this article (doi:10.1186/s12906-015-0629-0) contains supplementary material, which is available to authorized users.

TXA9, a cardiac glycoside from Streptocaulon juventas, exerts a potent anti-tumor activity against human non-small cell lung cancer cells in vitro and in vivo

Non-small cell lung cancer is the most common type of lung cancer and the most common cause of cancer-related death in humans. TXA9, which is a natural product separated from an anti-tumor-active fraction of the roots of Streptocaulon juventas, may possess potent anti-proliferative activity according to the present study. In this study, the anti-tumor effects and toxicity of TXA9 were tested against human non-small cell lung cancer cell lines (A549, NCI-H1299, Ltep-α2, PC-9, and Lu99) and a normal human lung embryonic fibroblast cell (HE-lung) in vitro, and then toward A549 cells in vivo in a murine xenograft model. The results show that TXA9 exhibits potent cytotoxic activities against non-small lung cancer cells and has no toxic effect on the normal human lung embryonic fibroblast cells. The mechanistic studies demonstrate that TXA9 can induce the apoptosis of A549 cells through the extrinsic pathway. The in vivo study results reveal that the intravenous administration of TXA9 at high-dose (15 mg kg(-1)) induces significant tumor growth inhibition of non-small cell lung cancer xenografts with tumor inhibition rate up to 64.2%, compared with mice in the control group. The inhibitory effect was similar to that of taxol (62.5%). In particular, no significantly adverse effects were exerted by TXA9, which suggests that it is well tolerated. This promising natural product may be useful as a potential novel anti-tumor candidate.

Minor cytotoxic cardenolide glycosides from the root of Streptocaulon juventas

In order to determine new minor natural cardenolide glycosides as cytotoxic candidates, we isolated six new cardenolide glycosides together with four known ones, which had never previously been reported in the genus, by bioassay-guided separation from the 75% ethanol extract of Streptocaulon juventas (Asclepiadaceae). Their structures were elucidated on the basis of spectroscopic analysis, including homo- and heteronuclear correlation NMR experiments (COSY, HSQC and HMBC). The cytotoxic activities of these compounds were evaluated against A549 and NCI-H460 cell lines by MTT assay and compound 7 exhibited inhibitory activity against the two cell lines, while other compounds displayed a range of inhibitory activity against NCI-H460 and A549 cells. Their structure-activity relationships were also discussed.

The cytotoxic activities of cardiac glycosides from Streptocaulon juventas and the structure-activity relationships

A series of cardiac glycosides were isolated and identified from the anti-tumor fraction of the root of Streptocaulon juventas in previous studies. In the present research, the cytotoxic activities of the 43 cardiac glycosides on three cell lines, human lung A549 adenocarcinoma cell, large cell lung cancer NCI-H460 cell and normal human fetal lung fibroblast MRC-5 cell, were evaluated in vitro. Most of the tested compounds showed potent inhibitory activities toward the three cell lines. Then, the structure-activity relationships were discussed in detail. It was indicated that hydroxyl and acetyl groups at C-16 increased the activity, whereas hydroxyl group at C-1 and C-5 can both increase and decrease the activity. Two glucosyl groups which were connected by C1'→C6' showed better inhibitory activity against cancer cell lines, while the C1'→C4' connection showed stronger inhibitory activity against the normal cell line. Also, this is the first report that the activities of these compounds exhibited different variation trends between A549 and NCI-H460 cell lines, which indicated that these compounds could selectively inhibit the cell growth. The results would lay a foundation for further research on new anti-tumor drug development.