Mixtures of Milkweed Cardenolides Protect Monarch Butterflies against Parasites

Plants have evolved a diverse arsenal of defensive secondary metabolites in their evolutionary arms race with insect herbivores. In addition to the bottom-up forces created by plant chemicals, herbivores face top-down pressure from natural enemies, such as predators, parasitoids and parasites. This has led to the evolution of specialist herbivores that do not only tolerate plant secondary metabolites but even use them to fight natural enemies. Monarch butterflies (Danaus plexippus) are known for their use of milkweed chemicals (cardenolides) as protection against vertebrate predators. Recent studies have shown that milkweeds with high cardenolide concentrations can also provide protection against a virulent protozoan parasite. However, whether cardenolides are directly responsible for these effects, and whether individual cardenolides or mixtures of these chemicals are needed to reduce infection, remains unknown. We fed monarch larvae the four most abundant cardenolides found in the anti-parasitic-milkweed Asclepias curassavica at varying concentrations and compositions to determine which provided the highest resistance to parasite infection. Measuring infection rates and infection intensities, we found that resistance is dependent on both concentration and composition of cardenolides, with mixtures of cardenolides performing significantly better than individual compounds, even when mixtures included lower concentrations of individual compounds. These results suggest that cardenolides function synergistically to provide resistance against parasite infection and help explain why only milkweed species that produce diverse cardenolide compounds provide measurable parasite resistance. More broadly, our results suggest that herbivores can benefit from consuming plants with diverse defensive chemical compounds through release from parasitism.

Progesterone Metabolism In Digitalis And Other Plants - 60 Years Research And Recent Results

5β-Cardenolides are pharmaceutically important metabolites of the specialized metabolism of Digitalis lanata. They were used over decades to treat cardiac insufficiency and supraventricular tachycardia. Since the 1960s, plant scientists have known that progesterone is an essential precursor of cardenolide formation. Therefore, plant progesterone biosynthesis was mainly analyzed in species of the cardenolide-containing genus Digitalis during the following decades. Today, Digitalis enzymes catalyzing the main steps of progesterone biosynthesis are known. Most of them were found in a broad range of organisms. This review will summarize the findings of 60 years of research on plant progesterone metabolism with a particular focus on the recent results in Digitalis lanata and other plants.

Toxic profile of marinobufagin from poisonous Amazon toads and antitumoral effects on human colorectal carcinomas

ETHNOPHARMACOLOGICAL RELEVANCE

South Americans natives have extensively used the toad "kururu" to reduce/treat skin infections, cutaneous lesions and sores. They release secretions rich in bufadienolides, polyhydroxy steroids with well-documented cardiotonic and antiproliferative actions, but in vivo antitumoral evaluations in mammals are rare, and toxicological safety has been left in second place.

AIMS OF THE STUDY

This investigation used in silico, in vitro and in vivo tools to evaluate acute and subacute toxic effects of marinobufagin and the anticancer action in tumor-bearing mice models.

MATERIALS AND METHODS

Initially, in silico toxic predictions were performed, followed by in vitro assays using human and murine normal and tumor lines. Next, acute and subacute studies on mice investigated the behavior, hematological and intestinal transit profile and antitumoral activity of marinobufagin in sarcoma 180- and HCT-116 colorectal carcinoma-transplanted mice for 7 and 15 days, respectively. Ex vivo and in vivo cytogenetic assays in Sarcoma 180 and bone marrow cells and histopathological examinations were also executed.

RESULTS

In silico studies revealed ecotoxicological effects on crustaceans (Daphnia sp.), fishes (Pimephales promelas and Oryzias latipes), and algae. A 24-h marinobufagin-induced acute toxicity included signals of central activity, mainly (vocal frenzy, absence of body tonus, increased ventilation, ataxia, and equilibrium loss), and convulsions and death at 10 mg/kg. The bufadienolide presented effective in vitro cytotoxic action on human lines of colorectal carcinomas in a similar way to ouabain and tumor reduction in marinobufagin-treated SCID-bearing HCT-116 heterotopic xenografts. Animals under subacute nonlethal doses exhibited a decrease in creatinine clearance with normal levels of blood urea, probably as a result of a marinobufagin-induced renal perfusion fall. Nevertheless, only minor morphological side effects were identified in kidneys, livers, hearts and lungs.

CONCLUSIONS

Marinobufagin has in vitro and in vivo anticancer action on colorectal carcinoma and mild and reversible alterations in key metabolic organs without direct chemotherapy-induced gastrointestinal effects at subacute exposure, but it causes acute ataxia, equilibrium loss, convulsions and death at higher acute exposure.

No physiological costs of dual sequestration of chemically different plant toxins in the milkweed bug Spilostethus saxatilis (Heteroptera: Lygaeidae)

Many herbivorous insects not only cope with plant toxins but also sequester them as a defense against predators and parasitoids. Sequestration is a product of the evolutionary arms race between plants and herbivorous insects and has been hypothesized to incur physiological costs due to specific adaptations required. Contradictory evidence about these costs exists for insects sequestering only one class of toxin, but very little is known about the physiological implications for species sequestering structurally different classes of compounds. Spilostethus saxatilis is a milkweed bug belonging to the cardenolide-sequestering heteropteran subfamily Lygaeinae (Heteroptera: Lygaeidae) that has shifted to the colchicine-containing plant Colchicum autumnale, a resource of chemically unrelated alkaloids. Using feeding-assays on artificial diet and chemical analysis, we assessed whether S. saxatilis is still able to sequester cardenolides apart from colchicine and related metabolites (colchicoids), and tested the effect of (1) either a natural cardenolide concentration (using ouabain as a model compound) or a natural colchicine concentration, (2) an increased concentration of both toxins, and (3) seeds of either Asclepias syriaca (cardenolides) or C. autumnale (colchicoids) on a set of life-history traits. For comparison, we assessed the same life-history traits in the milkweed bug Oncopeltus fasciatus exposed to cardenolides only. Although cardenolides and colchicoids have different physiological targets (Na⁺/K⁺-ATPase vs tubulin) and thus require different resistance traits, chronic exposure and sequestration of both isolated toxins caused no physiological costs such as reduced growth, increased mortality, lower fertility, or shorter adult life span in S. saxatilis. Indeed, an increased performance was observed in O. fasciatus and an according trend was found in S. saxatilis when feeding on isolated ouabain and isolated colchicine, respectively. Positive effects were even more pronounced when insects were provided with natural toxic seeds (i.e. C. autumnale for S. saxatilis and A. syriaca for O. fasciatus), especially in O. fasciatus. Our findings suggest, that S. saxatilis can sequester two chemically unrelated classes of plant compounds at a cost-free level, and that colchicoids may even play a beneficial role in terms of fertility.

Spatial metabolomics reveal divergent cardenolide processing in the monarch (Danaus plexippus) and the common crow butterfly (Euploea core)

Although being famous for sequestering milkweed cardenolides, the mechanism of sequestration and where cardenolides are localized in caterpillars of the monarch butterfly (Danaus plexippus, Lepidoptera: Danaini) is still unknown. While monarchs tolerate cardenolides by a resistant Na⁺ /K⁺ -ATPase, it is unclear how closely related species such as the non-sequestering common crow butterfly (Euploea core, Lepidoptera: Danaini) cope with these toxins. Using novel atmospheric-pressure scanning microprobe matrix-assisted laser/desorption ionization mass spectrometry imaging, we compared the distribution of cardenolides in caterpillars of D. plexippus and E. core. Specifically, we tested at which physiological scale quantitative differences between both species are mediated and how cardenolides distribute across body tissues. Whereas D. plexippus sequestered most cardenolides from milkweed (Asclepias curassavica), no cardenolides were found in the tissues of E. core. Remarkably, quantitative differences already manifest in the gut lumen: while monarchs retain and accumulate cardenolides above plant concentrations, the toxins are degraded in the gut lumen of crows. We visualized cardenolide transport over the monarch midgut epithelium and identified integument cells as the final site of storage where defenses might be perceived by predators. Our study provides molecular insight into cardenolide sequestration and highlights the great potential of mass spectrometry imaging for understanding the kinetics of multiple compounds including endogenous metabolites, plant toxins, or insecticides in insects.

Calotropis procera (Aiton) Dryand (Apocynaceae): State of the art of its uses and Applications

Calotropis procera (Aiton) Dryand (Apocynaceae), popularly known as milkweed, has been traditionally used to treat diseases particularly associated with gastric disorders, skin disease and inflammatory processes. The present study aimed to review the current scientific evidence regarding the pharmacological effects of C. procera extracted phytochemicals and possible research opportunities as complementary and alternative medicine. Scientific publications were searched in various electronic databases (PubMed, Scopus, Web of Science, Google Scholar, Springer, Wiley, and Mendeley) using the following search terms: Calotropis procera, medicinal plants, toxicity, phytochemical characterization, and biological effects. Collected data showed that cardenolides, steroid glycoside and flavonoids are the main classes of phytochemicals identified in C. procera latex and leaves. In addition, lignans, terpenes, coumarins, and phenolic acids have been reported. These metabolites have been correlated with their biological activities, including mainly antioxidant, anti-inflammatory, antitumoral, hypoglycemic, gastric protective, anti-microbial, insecticide, anti-fungal, anti-parasitic, among others. However, some of the studies were carried out with only a single dose or with a high dose not achievable under physiological conditions. Therefore, the validity of C. procera biological activity may be questionable. Not less important to highlight are the risks associated with its use and the possibility of accumulation of heavy metals that can be toxic. Furthermore, there are no clinical trials with C. procera to date. In conclusion, the need of bioassayguided isolation of bioactive compounds, bioavailability and efficacy, as well as pharmacological and toxicity studies, are needed using in vivo models and clinical trials in order to support the traditionally claimed health benefits.

LC-MS-based metabolite profiling of aqueous extract of Pergularia tomentosa L. and its anti-hyperglycemic effect

Objectives

In this study, to find scientific evidence for the traditional use of Pergularia tomentosa as an anti-diabetic remedy, the effects of its aqueous extract on streptozotocin-induced diabetes mellitus in rats were evaluated.

Materials and Methods

Wistar rats were fasted overnight and diabetes mellitus was induced using streptozotocin (50 mg/kg body weight). The rats were randomly and equally divided into four groups (n=5): group I (normoglycaemic control), group II (diabetic rats), group III (diabetic rats treated with 200 mg/kg BW of an aqueous extract of P. tomentosa), group IV (normoglycemic rats treated with 200 mg/kg BW of an aqueous extract of P. tomentosa). Chemical profiling of the aqueous extract was carried out using liquid chromatography coupled with electrospray ionization and multiple-stage linear ion-trap and orbitrap high-resolution mass spectrometry (LC-ESI/LTQOrbitrap/MS/MS). In addition, the quantitative determination of the main cardenolides in the extract was carried out by an analytical approach based on LC coupled to tandem mass spectrometry with ESI source and hybrid triple quadrupole-linear ion trap mass analyzer (LC-ESI/QTrap/MS/MS).

Results

Aqueous extract of P. tomentosa showed a reasonable reduction in blood glucose level. Probably, the P. tomentosa effect on hyperglycemic and hyperlipidemic diabetic animals was associated with antioxidant properties, triglyceride levels, as well as liver enzymes. Meanwhile, LC-ESI/LTQOrbitrap/MS/MS analysis led to identification of double-linked cardenolides along with cardenolides and flavone glycosides as the main bioactive compounds.

Conclusion

The extract decreased the glucose level and induced a beneficial effect on the lipid profile, probably due to the presence of cardenolide glycosides.

Antitumor effects of oleandrin in different types of cancers: Systematic review

Oleandrin, a cardiac glycoside isolated from the leaves of Nerium oleander, has known effects on the heart. Evidence from recent studies have highlighted its potential for anticancer properties. Therefore, we aimed to investigate the effects of oleandrin on cancer cell proliferation, viability and apoptosis in vitro and in vivo. We performed a systematic search in six electronic databases up to Jan 2022. We extracted information about the effects of oleandrin on cell proliferation, cell viability, apoptosis and/or cell cycle arrest in in vitro studies, and the effects on tumor size and volume in animal experimental models. We have retrieved 775 scientific studies. 14 studies met the inclusion criteria. They investigated the effects of oleandrin on breast, lung, pancreatic, colon, prostate, colorectal, oral, ovarian, glioma, melanoma, glioblastoma, osteosarcoma, and histiocytic lymphoma cancers. Overall, in vitro studies demonstrated that oleandrin was able to inhibit cell proliferation, decrease cell viability, and induce apoptosis and/or cell cycle arrest. In addition, oleandrin had an effect on reducing mean tumor size and volume in animal studies. Oleandrin, as a cytotoxic agent, demonstrated antitumor effects in different types of cancers, however important clinical limitations remain a concern. These results encourage future studies to verify the applicability of oleandrin in antineoplastic therapeutic protocols human and veterinary medicine, the investigation of antimetastatic properties, as well as the potential increase in patient survival and the decrease of tumor markers.

Calotropin and corotoxigenin 3-O-glucopyranoside from the desert milkweed Asclepias subulata inhibit the Na+/K+-ATPase activity

Na⁺/K⁺-ATPase is an essential transmembrane enzyme found in all mammalian cells with critical functions for cell ion homeostasis. The inhibition of this enzyme by several cardiotonic steroids (CTS) has been associated with the cytotoxic effect on cancer cell lines of phytochemicals such as ouabain and digitoxin. This study evaluated the inhibitory capacity of cardenolides calotropin and corotoxigenin 3-O-glucopyranoside (C3OG) from Asclepias subulata over the Na⁺/K⁺-ATPase activity in vitro and silico. The inhibitory assays showed that calotropin and C3OG decreased the Na⁺/K⁺-ATPase activity with IC₅₀ values of 0.27 and 0.87 μM, respectively. Furthermore, the molecules presented an uncompetitive inhibition on Na⁺/K⁺-ATPase activity, with K_i values of 0.2 μM to calotropin and 0.5 μM to C3OG. Furthermore, the molecular modeling indicated that calotropin and C3OG might interact with the Thr⁷⁹⁷ and Gln¹¹¹ residues, considered essential to the interaction with the Na⁺/K⁺-ATPase. Besides, these cardenolides can interact with amino acid residues such as Phe⁷⁸³, Leu¹²⁵, and Ala³²³, to establish hydrophobic interactions on the binding site. Considering the results, these provide novel evidence about the mechanism of action of cardenolides from A. subulata, proposing that C3OG is a novel cardenolide that deserves further consideration for in vitro cellular antiproliferative assays and in vivo studies as an anticancer molecule.

Comparative Therapeutic Potential of Cardioactive Glycosides in Doxorubicin Model of Heart Failure

In the present study, we investigated the cardioactive glycosides oleandrin and ouabain, and compared them to digoxin in a model of cardiotoxicity induced by doxorubicin. Adult rats were distributed into four experimental groups. Each group was challenged with a single intraperitoneal application of doxorubicin at a dose of 12 mg/kg. Then, they were treated with saline solution and the glycosides oleandrin, ouabain, and digoxin at a dose of 50 µg/kg, for 7 days. They underwent echocardiography, electrocardiography, hematologic, biochemical tests, and microscopic evaluation of the heart. All animals presented congestive heart failure, which was verified by a reduction in the ejection fraction. Oleandrin and digoxin were able to significantly reduce (p < 0.05) the eccentric remodeling caused by doxorubicin. Oleandrin and digoxin were significantly lower (p < 0.05) than the control group in maintaining systolic volume and left ventricular volume in diastole. Other parameters evaluated did not show significant statistical differences. All animals showed an increase in erythrocyte count, and an increase in the duration of the QRS complex on the ECG and myocardial necrosis at the histopathological analysis. It is concluded that the glycosides oleandrin, ouabain, and digoxin in the used dosage do not present therapeutic potential for the treatment of congestive heart failure caused by doxorubicin.

Cytotoxic cardenolides from Calotropis gigantea

Sixteen cardiac glycosides, including five previously undescribed compounds, were extracted and purified from whole plants of Calotropis gigantea (L.). Spectroscopic data and electronic circular dichroism (ECD) analyses were used to determine their structures. Calogiganin C is the first naturally occurring example of a cardenolide containing a 7-membered lactone in ring A. The cytotoxic activities of these compounds against A172, U251, AGS, PANC-1, HepG2, HCT116 and NCI-H226 cell lines were evaluated. Four of them exhibited the most potent growth inhibitory activity against a panel of human cancer cell lines, including A172, U251, AGS, PANC-1 and HCT116. Notably, uscharidin and calotropin showed pronounced cytotoxicities at low nanomolar concentrations against A172 and U251 cells, and possible cell death mechanism studies manifested that these two compounds induced G2/M cell cycle arrest, which demonstrated promising anticancer potential.

21-Hydroxypregnane 21-O-malonylation, a crucial step in cardenolide biosynthesis, can be achieved by substrate-promiscuous BAHD-type phenolic glucoside malonyltransferases from Arabidopsis thaliana and homolog proteins from Digitalis lanata

Three putative 21-hydroxypregnane 21-O-malonyltransferases (21MaT) from Digitalis lanata were partially purified. Two of them were supposed to be BAHD-type enzymes. We were unable to purify them in quantities necessary for reliable sequencing. We identified two genes in A. thaliana coding for substrate-promiscuous BAHD-type phenolic glucoside malonyltransferases (AtPMaT1, AtPMaT2) and docked various 21-hydroxypregnanes into the substrate-binding site of a homology model built on the BAHD template 2XR7 (NtMaT1 from N. tabacum). Recombinant forms of Atpmat1 and Atpmat2 were expressed in E. coli and the recombinant enzymes characterized with regard to their substrate preferences. They were shown to malonylate various 21-hydroxypregnanes. The Atpmat1 sequence was used to identify candidate genes in Digitalis lanata (Dlmat1 to Dlmat4). Dlmat1 and Dlmat2 were also expressed in E. coli and shown to possess 21-hydroxypregnane 21-O-malonyltransferase activity.

Liposomes co-encapsulating doxorubicin and glucoevatromonoside derivative induce synergic cytotoxic response against breast cancer cell lines

Cancer is one of the main causes of death in the world and thus a global public health problem. Among the treatments available for cancer are surgery, radiotherapy, and chemotherapy. Currently, there is increased interest in the combination of two or more antitumor agents to achieve a synergistic effect in cancer therapy. Doxorubicin (DOX), a chemotherapeutic which has a potent antineoplastic action, has been used in the treatment of various tumors. However, the use of DOX is limited, mainly due to the cardiotoxicity. Therefore, nanostructured systems, such as liposomes, have been developed to carry this drug and target the tumor region, since tumor tissues present enhanced permeability and retention for nanosystems. Cardiac glycosides, such as digitoxin, have recently shown great antitumor potential despite the low therapeutic index which may limit their use. Furthermore, some compounds of this class have low water solubility, which makes their in vivo administration difficult. In this context, liposomes represent a valid strategy to carry simultaneously antitumor drugs allowing their intravenous administration. In this study, liposomes loaded with glucoevatromonoside containing peracetylated glucose hydroxyl groups (GEVPG) and DOX at molar ratio of 1:1 (SpHL-GEVPG:DOX 1:1) were developed, and their chemical and physicochemical properties were evaluated. This formulation presented a combination index (CI) lower than 1 at inhibitory concentration of 90 % growth (IC₉₀) for three human breast tumor lines evaluated (0.52 ± 0.39 for MDA-MB-231, 0.19 ± 0.13 for MCF-7, and 0.99 ± 0.09 for SKBR-3). These results indicate a synergistic cytotoxic effect of the GEVPG and DOX combination encapsulated in liposomes. In addition, SpHL-GEVPG:DOX 1:1 presented selectivity towards these cancer cells. Long-term in vitro cytotoxicity studies demonstrated that MDA-MB-231 surviving cells after treatment with SpHL-GEVPG:DOX 1:1 did not recover proliferation capacity after 21 d. From the studies of cell cycle and death pathway evaluation, it was observed that SpHL-GEVPG:DOX 1:1 arrested the cell cycle in the G2/M phase and similarly induced apoptosis and necrosis. However, SpHL-GEVPG:DOX at molar ratio of 1:1 showed lower induction of both apoptotic and necrotic pathways compared to free DOX and SpHL-DOX, suggesting that the mechanism of death involved may not be related to necrosis or apoptosis. Lastly, SpHL-GEVPG:DOX 1:1 showed a good storage stability for 90 d at 4 °C. Therefore, the results of the present work indicate the potential use of SpHL-GEVPG:DOX 1:1 as a new anticancer formulation.

Antimutagenic effect of an Asclepias subulata extract against heterocyclic aromatic amines commonly found in cooked meat and its heat stability

The antimutagenicity of an extract from the medicinal plant Asclepias subulata (ASE) against heterocyclic aromatic amines (HAAs) commonly found in cooked meat, as well as its stability to heat treatment (HT), was evaluated. HT (180 °C/3 min) had no effect on the content in ASE of the bioactive compound corotoxigenin-3-O-glucopyranoside; conversely, calotropin significantly decreased by 72%. ASE exerted antimutagenicity against PhIP, MelQ, and MelQx in TA98 and TA100 Salmonella strains, and this activity was not affected by heat, with the exception of MelQ (p < 0.05). Since HAAs can induce colorectal cancer, the thermal stability of ASE's antiproliferative effect against colorectal cancer cells was also evaluated. HT decreased (p < 0.05) the antiproliferative activity of ASE; however, the remaining activity was still strong with an IC₅₀ of 16.8 ± 2.03 µg/mL. Therefore, ASE can be used as a food ingredient to reduce the carcinogenic potential of thermally induced HAAs.

Antiproliferative activity of cardenolides on cell line A549: structure-activity relationship analysis

Since the beginning, natural products have represented an important source of bioactive molecules for cancer treatment. Among them, cardenolides attract the attention of different research groups due to their cardiotonic and antitumor activity. The observed biological activity is closely related to their Na⁺/K⁺-ATPase inhibition potency. Currently, the discovery of new compounds against cancer is an urgent need in modern pharmaceutical research. Thus, the aim of this work is to determine the physicochemical properties and substituent effects that module the antiproliferative activity of cardenolides on the human lung cancer cell line A549. We build and curate a library with results obtained from literature; molecular descriptors were calculated in PaDEL software, and SAR/QSAR analysis was performed. The SAR results showed that cardenolides were sensitive to modifications in C and D steroidal ring and required substituent groups with the function of hydrogen bond acceptor at the C3 position. QSAR models to doubly linked-type cardenolides indicated that properties as lipoaffinity and atoms with the capacity to be hydrogen bond acceptors are involved in the increment of antiproliferative activity on A549 cell line. In contrast, the presence and position of very electro-negative atoms on the molecule decreased the antiproliferative effect on A549 cells. These results suggest that the antiproliferative capacity of cardenolides on the cell line A549 is strongly related to substituent groups on the C3 position, which must not be carbohydrate. Additionally, the steroidal rings C and D must remain without modifications.

Synthesis and evaluation of Na+/K+-ATP-ase inhibiting and cytotoxic in vitro activities of oleandrigenin and its selected 17β-(butenolidyl)- and 17β-(3-furyl)- analogues

Natural cardiac-active principles built upon the 14,16β-dihydroxy-5β,14β-androstane core and bearing a heterocyclic substituent at 17β, in particular, a cardenolide - oleandrin and a bufadienolide - bufotalin, are receiving a great deal of attention as potential anticancer drugs. The densely substituted and sterically shielded ring D is the particular structural feature of these compounds. The first synthesis of oleandrigenin from easily available steroid starting material is reported here. Furthermore, selected 17β-(4-butenolidyl)- and 17β-(3-furyl)-14,16β-dihydroxy-androstane derivatives were en route synthesized and examined for their Na⁺/K⁺-ATP-ase inhibitory properties as well as cytotoxic activities in normal and cancer cell lines. It was found that the furyl-analogue of oleandrigenin/bufatalin (7) and some related 17-(3-furyl)- derivatives (19, 21) show remarkably high Na⁺/K⁺-ATP-ase inhibitory activity as well as significant cytotoxicity in vitro. In addition, oleandrigenin 2 compared to derivatives 21 and 25 induced strong apoptosis in human cervical carcinoma HeLa cells after 24 h of treatment.

Comparative Cardiotoxicity of Low Doses of Digoxin, Ouabain, and Oleandrin

The aim of this study was to evaluate the comparative effects of CGs on heart physiology. Twenty-eight Wistar rats were distributed into four groups (n = 7), control group received NaCl 0.9% every 24 h for 21 days; treated groups received respectively 50 μg/kg of digoxin (DIG), ouabain (OUA) and oleandrin (OLE) every 24 h for 21 days. Serial ECGs were performed, as well as serum levels of creatinine kinase (CK), its MB fraction, troponin I (cTnI), calcium (Ca²⁺) and lactic dehydrogenase (LDH). Heart tissue was processed for histology, scanning electron microscopy and Western blot analysis for cTnI, brain natriuretic peptide (BNP), sodium potassium pump alpha-1 and alpha-2. Ventricle samples were also analyzed for thiobarbituric acid reactive substances and antioxidant enzymes (SOD, GPX, and CAT). ECGs showed decrease in QT and progressive shortening of QRS. No arrhythmias were observed. No significant differences were associated with CGs treatment and serum levels of CK, CK-MB, and cTnI. Only oleandrin increased LDH levels. Histological analysis showed degenerative changes and only oleandrin promoted moderate focal necrosis of cardiomyocytes. Scanning microscopy also confirmed the greatest effect of oleandrin, with rupture and shortening of cardiac fibers. The expression of troponin I and alpha-1 isoform were not altered, however, the protein levels of BNP and alpha-2 were higher in the groups that received oleandrin and ouabain in relation to the digoxin group. All GCs affected the production of ROS, without causing lipid peroxidation, through the activation of different antioxidant pathways. It is concluded that the administration of digoxin, ouabain, and oleandrin at 50 µg/kg for 21 days caused cardiovascular damage that represent an important limitation into its future use in heart failure and antineoplastic therapy.

Drug Repurposing for Retinoblastoma: Recent Advances

Retinoblastoma is the intraocular malignancy that occurs during early childhood. The current standard of care includes chemotherapy followed by focal consolidative therapies, and enucleation. Unfortunately, these are associated with many side and late effects. New drugs and/or drug combinations need to be developed for safe and effective treatment. This compelling need stimulated efforts to explore drug repurposing for retinoblastoma. While conventional drug development is a lengthy and expensive process, drug repurposing is a faster, alternate approach, where an existing drug, not meant for treating cancer, can be repurposed to treat retinoblastoma. The present article reviews various attempts to test drugs approved for different purposes such as calcium channels blockers, non-steroidal antiinflammatory drugs, cardenolides, antidiabetic, antibiotics and antimalarial for treating retinoblastoma. It also discusses other promising candidates that could be explored for repurposing for retinoblastoma.

Cardenolides from the leaves of Nerium oleander

Six new cardenolides (1-6), including three 14-hydroxylated cardenolides and three 14-carbonylated cardenolides were isolated from the dried aerial parts of Nerium oleander Linn in addition to twenty-seven known compounds (7-33). Their structures were elucidated on the basis of extensive spectroscopic evidences and single-crystal X-ray diffraction analysis. Compounds 1, 4, 7-10 and 13 exhibited significant cytotoxicity against four colon cancer cell lines (HCT116, HT29, SW620, RKO), one gastric cancer cell line (GT) and one cervical cancer cell line (HeLa) in vitro.

The function and evolutionary significance of a triplicated Na,K-ATPase gene in a toxin-specialized insect

Background

The Na,K-ATPase is a vital animal cell-membrane protein that maintains the cell’s resting potential, among other functions. Cardenolides, a group of potent plant toxins, bind to and inhibit this pump. The gene encoding the α-subunit of the pump has undergone duplication events in some insect species known to feed on plants containing cardenolides. Here we test the function of these duplicated gene copies in the cardenolide-adapted milkweed bug, Oncopeltus fasciatus, which has three known copies of the gene: α1A, α1B and α1C.

Results

Using RT-qPCR analyses we demonstrate that the α1C is highly expressed in neural tissue, where the pump is generally thought to be most important for neuron excitability. With the use of in vivo RNAi in adult bugs we found that α1C knockdowns suffered high mortality, where as α1A and α1B did not, supporting that α1C is most important for effective ion pumping. Next we show a role for α1A and α1B in the handling of cardenolides: expression results find that both copies are primarily expressed in the Malpighian tubules, the primary insect organ responsible for excretion, and when we injected either α1A or α1B knockdowns with cardenolides this proved fatal (whereas not in controls).

Conclusions

These results show that the Na,K-ATPα gene-copies have taken on diverse functions. Having multiple copies of this gene appears to have allowed the newly arisen duplicates to specialize on resistance to cardenolides, whereas the ancestral copy of the pump remains comparatively sensitive, but acts as a more efficient ion carrier. Interestingly both the α1A and α1B were required for cardenolide handling, suggesting that these two copies have separate and vital functions. Gene duplications of the Na,K-ATPase thus represent an excellent example of subfunctionalization in response to a new environmental challenge.

Electronic supplementary material

The online version of this article (10.1186/s12862-017-1097-6) contains supplementary material, which is available to authorized users.

Securigenin glycosides as hypoglycemic principles of Securigera securidaca seeds

Seeds of Securigera securidaca (Fabaceae) are used in Iranian folk medicine as an antidiabetic treatment. In this study, the antihyperglycemic activity of chloroform and methanol fractions (CF and MF) from S. securidaca seed extract was investigated and their bioactive constituents were identified. The antidiabetic effects of fractions were assessed by streptozocin-induced diabetic Naval Medical Research Institute mice. The hypoglycemic activity of MF at 100 mg/kg and CF at 400 mg/kg was comparable with glibenclamide (3 mg/kg). MF at 400 mg/kg and CF at 600 mg/kg showed equal hypoglycemic responses to 12.5 IU/kg insulin (P > 0.05). Three cardiac glycosides were isolated as active constituents responsible for the hypoglycemic activity. Securigenin-3- O -β-glucopyranosyl-(1 → 4)-β-xylopyranoside (1) was a major compound in seeds. Securigenin-3- O -inositol-(1 → 3)-β-glucopyranosyl-(1 → 4)-β-xylopyranoside (2) and securigenin-3- O -α-rhamnopyranosyl-(1 → 4)-α-glucopyranoside (3) were found as new natural products. When 1-3 were tested at 10 mg/kg there was a significant reduction of blood glucose levels in diabetic mice, comparable to that of 3 mg/kg glibenclamide (P > 0.05). The hypoglycemic effect was due to an increase in insulin secretion; the insulin levels in the diabetic mice significantly improved and were comparable with those in healthy animals (P > 0.05). Compounds responsible for the hypoglycemic properties of S. securidaca seeds were identified as cardiac glycosides and were found to act via an increase of insulin levels in a diabetic mouse model.

Cytotoxic cardenolides and sesquiterpenoids from the fruits of Reevesia formosana

Bioassay-guided fractionation of the fruits of Reevesia formosana led to isolation of three cardenolides (reevesioside J, reevesioside K, and epi-reevesioside K), three sesquiterpenoids (reevesiterpenol C, reevesiterpenol D, and reevesiterpenol E), and two glycosides (reevesianin A and reevesianin B), along with 46 known compounds. Their structures were determined using spectroscopic techniques. In addition to the reported cytotoxic cardenolides, reevesioside J and strophanthidin exhibited moderate cytotoxicity against the cell lines MCF-7, NCI-H460, and HepG2, with IC50 values of 0.39 ± 0.06 μM and 1.06 ± 0.12 μM for MCF-7, 0.12 ± 0.01 μM and 0.29 ± 0.01 μM for NCI-H460, and 1.09 ± 0.02 μM and 1.72 ± 0.02 μM for HepG2, respectively. Reevesiterpenol E also exhibited the best selective cytotoxicity to the NCI-H460 cell line, with an IC50 value of 3.15 ± 0.22 μM.

Microbial Transformation of 14-Anhydrodigoxigenin by Alternaria alternata

The microbial transformation of 14-anhydrodigoxigenin (1) by Alternaria alternata CGMCC 3.577 led to the production of seven new metabolites, 2-8. Their structures were determined by extensive spectroscopic (CD, IR, 1D- and 2D-NMR, and HR-ESI-MS) data analyses. The reactions in the bioprocess exhibited diversity, including specific oxidation, hydroxylation, reduction, epoxidation, and dehydration. In addition, a hypothetical biocatalytic pathway is proposed.

Cardenolides from the Apocynaceae family and their anticancer activity

Cardenolides, as a group of natural products that can bind to Na(+)/K(+)-ATPase with an inhibiting activity, are traditionally used to treat congestive heart failure. Recent studies have demonstrated that the strong tumor cytotoxicities of cardenolides are mainly due to inducing the tumor cells apoptosis through different expression and cellular location of Na(+)/K(+)-ATPase α-subunits. The leaves, flesh, seeds and juices of numerous plants from the genera of Nerium, Thevetia, Cerbera, Apocynum and Strophanthus in Apocynaceae family, are the major sources of natural cardenolides. So far, 109 cardenolides have been isolated and identified from this family, and about a quarter of them are reported to exhibit the capability to regulate cancer cell survival and death through multiple signaling pathways. In this review, we compile the phytochemical characteristics and anticancer activity of the cardenolides from this family.

Biotechnological Approaches for Biomass and Cardenolide Production in Digitalis purpurea L

Digitalis purpurea L. is one of the main economically viable sources of cardenolides (cardiac glycosides) for the pharmaceutical industry. Nevertheless, production of cardenolides in plants grown by traditional agriculture is not always an efficient process and can be affected by biotic and abiotic factors. This chapter provides two biotechnology strategies for biomass and cardenolide production in D. purpurea. Firstly, we report biomass production using a temporary immersion system (TIS), combined with cardenolide extraction and quantification. Secondly, an efficient protocol for genetic transformation via Agrobacterium tumefaciens is provided. These strategies can be used independently or combined in order to increase the content of cardiac glycosides in D. purpurea and to unravel biosynthetic pathways associated to cardiac glycoside production.

Cytotoxic cardenolides from the latex of Calotropis procera

Three new cardenolides (3, 9 and 10), along with eight known ones, were isolated from the latex of Calotropis procera. The structural determination was accomplished by the 1D- and 2D-NMR spectra as well as HRESIMS analysis. The growth inhibitory activity of the latex and its sub-fractions as well as isolated compounds was evaluated against human A549 and Hela cell lines. The results exhibited that latex had strong growth inhibitory activity with IC50s of (3.37 μM, A-549) and (6.45 μM, Hela). Among the four extracts (hexane, chloroform, ethyl acetate and aqueous), chloroform extract displayed the highest potential cytotoxic activity, with IC50s of (0.985 μM, A-549) and (1.471 μM, Hela). All the isolated compounds displayed various degrees of cytotoxic activity and the highest activity was observed by calactin (1) with IC50s values of (0.036 μM, A-549) and (0.083 μM, Hela). None of these isolated compounds exhibited good antimicrobial activity evaluated by determination of their MICs using the broth microdilution method against various infectious pathogens. The structure-activity relationships for cytotoxic activity were also discussed.

Purification of Δ(5)-3-ketosteroid isomerase from Digitalis lanata

The isomerization of 5-pregnene-3,20-dione into 4-pregnene-3,20-dione was investigated to shed further light on cardenolide biosynthesis and to characterize the enzymes involved in cardenolide formation. It was shown that the Δ(5)-3-ketosteroid isomerase of Digitalis lanata, which catalyzes this isomerization, is an individual enzyme and not, as previously thought, associated with Δ(5)-3β-hydroxysteroid dehydrogenase. The enzyme was purified by fractionated ammonium sulfate precipitation, hydrophobic interaction chromatography and gel filtration. The purification protocol resulted in a 68.1-fold enriched specific enzyme activity with a yield of 2.2%. After an additional chromatofocusing step the 3KSI activity appeared as a single protein band at 17kDa in SDS-PAGE. Plant 3KSI displayed similar properties to microbial 3-ketosteroid isomerases.

Elaeodendron orientale as a source of cytotoxic cardenolides

In the present study, we report six cardiac glycosides (1-6) along with four known ones (7-10) isolated from the leaves and fruits of Elaeodendron orientale. Their stereostructures were elucidated on the basis of spectroscopic analysis, including 1D and 2D NMR, and the absolute configuration of 1 was determined by X-ray diffraction analysis. The compounds were evaluated for growth inhibitory activity against a panel of human cancer cell lines, HeLa, A-549, MCF-7 and HL-60, and normal Vero cells. Four compounds from this series (5 and 7-9, IC50 values ranging from 0.01 to 0.07μM) exhibited cytotoxicity against three of the cancer cell lines assayed that was similar to or higher than the well-known therapies digoxin and digitoxigenin. Taking into account the narrow safety range of cardiac glycosides used in clinic, this series shows a selectivity index higher than 3 for three of the cancer cell lines assayed, increasing their interest for further study.

Studies on the production of Digitalis cardenolides by plant tissue culture I. Determination of digitoxin and digoxin contents in first and second passage calli and organ redifferentiating calli of several Digitalis species by radioimmunoassay

With first and second passage calli induced from seedlings of Digitalis purpurea, D. lanata, D. lutea, D. mertonensis, D. ambigua and D. ferruginea Gigantea and those induced from leaf discs of D. purpurea and D. lanata, the contents of digitoxin and digoxin equivalents were assayed and compared with the contents involved in the inocula. Although the total contents of digitoxin and digoxin equivalents in the first passage calli induced from seedlings varied between zero and nine times as high as in the original seedlings, those in the second passage calli were almost undetectable. The total contents of digitoxin equivalents in the first passage calli induced from leaf discs of D. purpurea were approximately equal to those in the original leaf discs, but those in the second passage calli were less than those in the inocula. In the first passage calli induced from leaf discs of D. lanata, the total contents of digitoxin equivalents decreased but those of digoxin equivalents slightly increased. However, in the second passage calli, the amounts of both cardenolides decreased. Root-forming calli accumulated no more digitoxin nor digoxin equivalents than completely dedifferentiated calli. However, shoot-forming calli accumulated considerable amounts of cardenolides, which were assayed as digitoxin and digoxin equivalents by radioimmunoassay.