Physiological functions of solanaceous and tomato steroidal glycosides

Toxicity assessment of 3-O-[6-deoxy-3-O-methyl-β-D-allopyranosyl-(1 → 4)-β-D-oleandropyranosyl]-17β-marsdenin isolated from Gongronema latifolium leaf on selected brain and kidney function indices in mice

The safety of bioactive compounds, especially those isolated from medicinal plants, is a major concern for health authorities, pharmaceutical industries, and the public. Of recent, anti-tumor pregnane glycosides were isolated from Gongronema latifolium leaf, of which the toxicity of one, 3-O-[6-deoxy-3-O-methyl-β-D-allopyranosyl-(1 → 4)-β-D-oleandropyranosyl]-17β-marsdenin (3DMAOM), has not been evaluated. This study, therefore, evaluated the effects of 3DMAOM on selected brain and kidney function indices in mice. Female Swiss albino mice were randomly administered 5% dimethyl sulphoxide and different doses of 3DMAOM (0.5, 1, 2, and 4 mg/kg body weight) for fourteen (14) days, and their blood, brains, and kidneys were collected for biochemical analysis. There was no significant alteration in the activities of alkaline phosphatase (ALP), acetylcholinesterase, creatine kinase, Na+/K+-ATPase, Ca2+/Mg2+-ATPase, and Mg2+-ATPase in the brain of the treated groups compared to control. Also, no significant changes in the activities of ALP, gamma-glutamyltransferase, Na+/K+-ATPase, Ca2+/Mg2+-ATPase, and Mg2+-ATPase in the kidney of the treated groups compared to control. The plasma concentrations of Na+, K+, Cl-, PO43-, creatinine, and urea of mice were not significantly altered at all doses of the 3DMAOM compared to controls. However, the plasma concentration of Ca2+ was significantly reduced (p < 0.05) at all doses of the 3DMAOM, and the plasma concentration of uric acid was significantly reduced (p < 0.05) at 2 mg/kg body weight of the 3DMAOM compared to controls. These findings suggest that 3DMAOM isolated from Gongronema latifolium leaf may not adversely affect brain function but may affect calcium ion homeostasis in subjects.

Solanum steroidal glycoalkaloids: structural diversity, biological activities, and biosynthesis

Chemical structures of typical Solanum steroidal glycoalkaloids from eggplant, tomato, and potato.

Within- and cross-species predictions of plant specialized metabolism genes using transfer learning

Plant specialized metabolites mediate interactions between plants and the environment and have significant agronomical/pharmaceutical value. Most genes involved in specialized metabolism (SM) are unknown because of the large number of metabolites and the challenge in differentiating SM genes from general metabolism (GM) genes. Plant models like Arabidopsis thaliana have extensive, experimentally derived annotations, whereas many non-model species do not. Here we employed a machine learning strategy, transfer learning, where knowledge from A. thaliana is transferred to predict gene functions in cultivated tomato with fewer experimentally annotated genes. The first tomato SM/GM prediction model using only tomato data performs well (F-measure = 0.74, compared with 0.5 for random and 1.0 for perfect predictions), but from manually curating 88 SM/GM genes, we found many mis-predicted entries were likely mis-annotated. When the SM/GM prediction models built with A. thaliana data were used to filter out genes where the A. thaliana-based model predictions disagreed with tomato annotations, the new tomato model trained with filtered data improved significantly (F-measure = 0.92). Our study demonstrates that SM/GM genes can be better predicted by leveraging cross-species information. Additionally, our findings provide an example for transfer learning in genomics where knowledge can be transferred from an information-rich species to an information-poor one.

A new steroidal glycoside from the fruits of Solanum myriacanthum

A new cholestane-type steroidal glycoside, solamyriaside A (1), was isolated from the fruits of Solanum myriacanthum Dunal (Solanaceae), along with two known steroidal glycosides, namely, solaviaside A (2) and aculeatiside A (3), and three known steroidal alkaloid glycosides, namely, solamargine (4), khasianine (5) and solasonine (6), which were isolated for the first time from this plant. Based on spectroscopic data as well as chemical evidence, 1 was determined to be 3-O-α-L-rhamnopyranosyl-(1→2)-O-[α-L-rhamnopyranosyl-(1→4)]-β-D-glucopyranosyl-22R,25R-cholest-5-ene-3β,16α,22,26-tetraol 26-O-β-D-glucopyranoside. The cytotoxic activity of 1-6 against HL-60 human promyelocytic leukaemia cells was examined. Compounds 4-6 showed cytotoxic activity. Among them, 4 exhibited the strongest activity with an IC₅₀ value of 4.64 ± 0.17 μM, similar to the activity of cisplatin, a positive control.

Tetranychus evansi spider mite populations suppress tomato defenses to varying degrees

Plant defense suppression is an offensive strategy of herbivores, in which they manipulate plant physiological processes to increase their performance. Paradoxically, defense suppression does not always benefit the defense-suppressing herbivores, because lowered plant defenses can also enhance the performance of competing herbivores and can expose herbivores to increased predation. Suppression of plant defense may therefore entail considerable ecological costs depending on the presence of competitors and natural enemies in a community. Hence, we hypothesize that the optimal magnitude of suppression differs among locations. To investigate this, we studied defense suppression across populations of Tetranychus evansi spider mites, a herbivore from South America that is an invasive pest of solanaceous plants including cultivated tomato, Solanum lycopersicum, in other parts of the world. We measured the level of expression of defense marker genes in tomato plants after infestation with mites from eleven different T. evansi populations. These populations were chosen across a range of native (South American) and non-native (other continents) environments and from different host plant species. We found significant variation at three out of four defense marker genes, demonstrating that T. evansi populations suppress jasmonic acid- and salicylic acid-dependent plant signaling pathways to varying degrees. While we found no indication that this variation in defense suppression was explained by differences in host plant species, invasive populations tended to suppress plant defense to a smaller extent than native populations. This may reflect either the genetic lineage of T. evansi-as all invasive populations we studied belong to one linage and both native populations to another-or the absence of specialized natural enemies in invasive T. evansi populations.

Neurotoxicity of the steroidal alkaloids tomatine and tomatidine is RIP1 kinase- and caspase-independent and involves the eIF2α branch of the endoplasmic reticulum

Steroidal alkaloids are a class of natural products that occur in several species of the Solanaceae family. In the case of the tomato plant (Lycopersicon esculentum Mill.), tomatine and its aglycone, tomatidine, are the most representative molecules. These steroidal alkaloids have already shown several potentially useful biological activities, from anticancer to anti-inflammatory or antibacterial. In this work, the toxicity of these molecules in neuronal cells, namely in the neuroblastoma cell line SH-SY5Y, was assessed, emphasis being given to the cellular mechanisms underlying the effects observed. The results show that tomatine/tomatidine-induced cell death is caspase- and RIP1 kinase-independent, as cell death is not prevented by the pan-caspase inhibitor Z-VAD.fmk or by RIP1 inhibitor necrostatin-1. Analysis of Ca²⁺ levels using the fluorescent probe Fura-2/AM indicates that both tomatine and tomatidine have a marked effect upon Ca²⁺ homeostasis by increasing cytosolic Ca²⁺, an event that might be associated with their effect upon the endoplasmic reticulum. We show that the toxicity of these molecules require the PERK/eIF2α branch of the unfolded protein response, but not the IRE1α branch. Given the role of the endoplasmic reticulum in proteostasis, the ability of these molecules to inhibit the proteasome was also evaluated. Tomatine was able to inhibit the chymotrypsin-like catalytic core of purified human 20S proteasome, as shown by its ability to prevent degradation of the fluorogenic substrate Suc-Leu-Leu-Val-Tyr-AMC, thus suggesting that interference with proteostasis can be responsible for the toxicity of these steroidal alkaloids. This study is relevant as it sheds a light regarding the toxicity of molecules present in one of the most consumed plants worldwide.

The bitter side of the nightshades: Genomics drives discovery in Solanaceae steroidal alkaloid metabolism

Steroidal alkaloids (SAs) and their glycosylated forms (SGAs) are toxic compounds largely produced by members of the Solanaceae and Liliaceae plant families. This class of specialized metabolites serves as a chemical barrier against a broad range of pest and pathogens. In humans and animals, SAs are considered anti-nutritional factors because they affect the digestion and absorption of nutrients from food and might even cause poisoning. In spite of the first report on SAs nearly 200 years ago, much of the molecular basis of their biosynthesis and regulation remains unknown. Aspects concerning chemical structures and biological activities of SAs have been reviewed extensively elsewhere; therefore, in this review the latest insights to the elucidation of the SAs biosynthetic pathway are highlighted. Recently, co-expression analysis combined with metabolic profiling revealed metabolic gene clusters in tomato and potato that contain core genes required for production of the prominent SGAs in these two species. Elaborating the knowledge regarding the SAs biosynthetic pathway, the subcellular transport of these molecules, as well as the identification of regulatory and signaling factors associated with SA metabolism will likely advance understanding of chemical defense mechanisms in Solanaceae and Liliaceae plants. It will also provide the means to develop, through classical breeding or genetic engineering, crops with modified levels of anti-nutritional SAs.

Analysis of steroidal alkaloids and saponins in Solanaceae plant extracts using UPLC-qTOF mass spectrometry

Plants of the Solanaceae family are renowned for the production of cholesterol-derived steroidal glycosides, including the nitrogen containing glycoalkaloids and steroidal saponins. In this chapter we describe the use of UPLC (Ultra Performance Liquid Chromatography) coupled with qTOF (Quadrupole Time-of-Flight) mass spectrometry for profiling of these two large classes of semipolar metabolites. The presented method includes an optimized sample preparation protocol, a procedure for high resolution chromatographic separation and metabolite detection using the TOF mass spectrometer which provides high resolution and mass accuracy. A detailed description for non-targeted data analysis and a strategy for putative identification of steroidal glycosides from complex extracts based on interpretation of mass fragmentation patterns is also provided. The described methodology allows profiling and putative identification of multiple steroidal glycoside compounds from the assortment of Solanaceae species producing these molecules.

New spirostanol glycosides from Solanum nigrum and S. jasminoides

A new characteristic steroidal glycoside possessing a hydroxyl group at C-23, inunigroside A (1), was isolated from the withered berries of Solanum nigrum L. On the basis of spectroscopic analysis, the structure of 1 was characterized as (5α,22S,23S,25R)-3β,23-dihydroxyspirostane 3-O-β-lycotetraoside. Next, a major steroidal sapogenol, (22R, 25S)-3β,15α-dihydroxy-spirost-5-ene (3), was obtained from the acid hydrolysate of the methanolic extract of the aerial parts of Solanum jasminoides L. A new bisdesmoside, 3-O-β-D-glucopyranosyl-(1→4)-β-D-glucopyranosyl-(1→4)-β-D-glucopyranosyl (22R,25S)-3β,15α-dihydroxyspirost-5-ene 15-O-α-L-rhamnopyranoside (4), named jasminoside A, was isolated from the methanolic extract of S. jasminoides.

Acid epimerization of 20-keto pregnane glycosides is determined by 2D-NMR spectroscopy

Carbohydrates influence many essential biological events such as apoptosis, differentiation, tumor metastasis, cancer, neurobiology, immunology, development, host-pathogen interactions, diabetes, signal transduction, protein folding, and many other contexts. We now report on the structure determination of pregnane glycosides isolated from the aerial parts of Ceropegia fusca Bolle (Asclepiadaceae). The observation of cicatrizant, vulnerary and cytostatic activities in some humans and animals of Ceropegia fusca Bolle, a species endemic to the Canary Islands, encouraged us to begin a pharmacological study to determine their exact therapeutic properties. High resolution (1)H-NMR spectra of pregnane glycosides very often display well-resolved signals that can be used as starting points in several selective NMR experiments to study scalar (J coupling), and dipolar (NOE) interactions. ROESY is especially suited for molecules such that ωτ(c) ~ 1, where τ(c) are the motional correlation times and ω is the angular frequency. In these cases the NOE is nearly zero, while the rotating-frame Overhauser effect spectroscopy (ROESY) is always positive and increases monotonically for increasing values of τ(c). The ROESY shows dipolar interactions cross peaks even in medium-sized molecules which are helpful in unambiguous assignment of all the interglycosidic linkages. Selective excitation was carried out using a double pulsed-field gradient spin-echo sequence (DPFGSE) in which 180° Gaussian pulses are sandwiched between sine shaped z-gradients. Scalar interactions were studied by homonuclear DPFGSE-COSY and DPFGSE-TOCSY experiments, while DPFGSE-ROESY was used to monitor the spatial environment of the selectively excited proton. Dipolar interactions between nuclei close in space can be detected by the 1D GROESY experiment, which is a one-dimensional counterpart of the 2D ROESY method. The C-12 and C-17 configurations were determined by ROESY experiments.

Anticonvulsant activity of solasodine isolated from Solanum sisymbriifolium fruits in rodents

CONTEXT

Solanum sisymbriifolium Lam. (Solanaceae), commonly known as sticky nightshade, is traditionally used for central nervous system (CNS) disorders. Although solasodine has been isolated from this plant, little is known about its anticonvulsant and CNS depressant actions.

OBJECTIVE

We investigated anticonvulsant and CNS depressant effects of solasodine isolated from S. sisymbriifolium using several experimental models.

MATERIALS AND METHODS

Swiss albino mice (n=6) were employed for pentylenetetrazole (PTZ) and picrotoxin (PCT)-induced convulsions and thiopental-induced sleep time. Different groups of Wistar albino rats (n=6) were subjected to maximal electroshock (MES) test. Solasodine, a steroidal glycoalkaloid, was isolated from dried fruits of S. sisymbriifolium and identified by GC-MS.

RESULTS

The results showed that intraperitoneal (i.p.) injection of solasodine (25 mg/kg) significantly delayed (p < 0.01) latency of hind limb tonic extensor (HLTE) phase in the PCT-induced convulsions. In the MES model, solasodine significantly reduced (p < 0.001) duration of HLTE at 25, 50, and 100 mg/kg, i.p. in a dose-dependent manner. Interestingly, solasodine did not produce any significant reduction in PTZ-induced convulsions. Prior treatment of solasodine (25, 50, and 100 mg/kg, i.p.) significantly potentiated thiopental-provoked sleep in a dose-dependent manner (p < 0.001).

DISCUSSION AND CONCLUSION

Our study, for the first time, shows potent anticonvulsant and CNS depressant activities of solasodine. It is likely that solasodine, in part, is responsible for the anticonvulsant and sedative properties of S. sisymbriifolium. The future study should focus on the exact mechanism of action of solasodine.

Development of plant-based mucosal vaccines against widespread infectious diseases

Mucosal vaccination is a perspective for the control of infectious diseases, since it is capable of inducing humoral and cell-mediated responses. In addition, the delivery of vaccines to mucosal surfaces makes immunization practice safe and acceptable, and eliminates needle-associated risks. Transgenic plants can be used as bioreactors for the production of mucosally delivered protective antigens. This technology shows great promise to simplify and decrease the cost of vaccine delivery. Herein, we review the development of mucosally administered vaccines expressed in transgenic plants. In particular, we evaluate the advantages and disadvantages of using plants for the production of mucosal vaccines against widespread infectious diseases such as HIV, hepatitis B and TB.

C22 isomerization in alpha-tomatine-to-esculeoside A conversion during tomato ripening is driven by C27 hydroxylation of triterpenoidal skeleton

Compositional analysis by liquid chromatography/mass spectrometry of triterpenoid glycosides in different tomato cultivars, ripening stages, and parts of fruits showed that alpha-tomatine was generally most abundant in the flesh of the mature green stage, whereas esculeoside A was predominant in that of the red ripe stage. The sum of these glycoalkaloids was more or less constant, suggesting that alpha-tomatine is converted to esculeoside A during ripening. Besides various substitutions, the C22alphaN --> C22betaN isomerization is an important step in this transformation. By quantum chemical calculations it was shown that hydroxylation at C27 of the triterpenoidal skeleton is the driving force behind the isomerization. For the protonated form of the glycoalkaloid (predominant at the pH of tomato tissue), the C22betaN configuration becomes more favorable than that of C22alphaN, through the extra energy provided by the hydrogen bond between the protonated nitrogen and the lone pair of the oxygen of the C27-OH.

Involvement of ethylene in the accumulation of esculeoside A during fruit ripening of tomato (Solanum lycopersicum)

The composition of glycoalkaloids in tomato fruit changes with ripening. However, it has not been clarified whether the accumulation of glycoalkaloids is controlled by the ripening-inducing phytohormone, ethylene. Here, we report the effect of ethylene on the accumulation of tomato fruit glycoalkaloids. We investigated the effect of exogenously applied ethylene. In response to ethylene treatment, the content of alpha-tomatine decreased, whereas the content of esculeoside A increased. Next, we analyzed the fruits of ripening mutants, rin, nor, and Nr. In fruits of these mutant lines, the level of accumulation of esculeoside A decreased, whereas alpha-tomatine accumulated to higher levels than in wild-type fruit. These results demonstrated that the esculeoside A accumulation was associated with production and perception of ethylene. Additionally, the accumulation profiles of the intermediate metabolites of esculeoside A biosynthesis in ripening mutant fruits suggest that a glycosylation step in the putative pathway from alpha-tomatine to esculeoside A depends on ethylene.

Isolation, characterization, and surfactant properties of the major triterpenoid glycosides from unripe tomato fruits

Various triterpenoid glycosides were extracted from whole unripe tomato fruits ( Lycopersicon esculentum cv. Cedrico), using aqueous 70% (v/v) ethanol to study their surfactant properties. Cation-exchange chromatography using a Source 15S column and subsequent semipreparative HPLC using an XTerra RP18 were employed to purify individual triterpenoid glycosides from the extract. The structure of the purified compounds was established by mass spectrometry and nuclear magnetic resonance spectroscopy. The furostanol glycoside tomatoside A (749 mg/kg of DW) and the glycoalkaloids alpha-tomatine (196 mg/kg of DW) and esculeoside A (427 mg/kg of DW) were the major triterpenoid glycosides present. Furthermore, minor amounts of a new dehydrofurostanol glycoside, dehydrotomatoside, were found. The critical micelle concentrations of the major triterpenoid glycosides, alpha-tomatine, tomatoside A, and esculeoside A, were determined as 0.099, 0.144, and 0.412 g/L, respectively. The results show that tomatoside A, and not the more well-known alpha-tomatine, is the predominant triterpenoidal surfactant in unripe tomato fruits.