Recent progress in the biochemistry of plant steroids other than sterols (saponins, glycoalkaloids, pregnane derivatives, cardiac glycosides, and sex hormones)

Pregnane Glycosides

Pregnane glycosides constitute a class of compounds widely distributed in the plant kingdom. Many of them have shown either anticarcinogenic or cancer inhibitory properties, besides other useful biological activities. New chromatographic techniques and advances in spectroscopic and spectrometric methods have accelerated the purification and structure determination of novel glycosides of this series. A compilation of the pregnane glycosides isolated from 1995 until the middle of 2005, along with their physical data, structures and occurrence are presented in this review, which also summarizes, with suitable examples, recent developments in isolation and purification techniques, and structural elucidation using modern spectrometric methods like ESIMS and tandem mass spectrometry, and 2D NMR spectroscopic strategies. The reported anticancer and other biological activities of pregnane glycosides are also discussed.

Steroidogenesis in plants--Biosynthesis and conversions of progesterone and other pregnane derivatives

In plants androstanes, estranes, pregnanes and corticoids have been described. Sometimes 17β-estradiol, androsterone, testosterone or progesterone were summarized as sex hormones. These steroids influence plant development: cell divisions, root and shoot growth, embryo growth, flowering, pollen tube growth and callus proliferation. First reports on the effect of applicated substances and of their endogenous occurrence date from the early twenties of the last century. This caused later on doubts on the identity of the compounds. Best investigated is the effect of progesterone. Main steps of the progesterone biosynthetic pathway have been analyzed in Digitalis. Cholesterol-side-chain-cleavage, pregnenolone and progesterone formation as well as the stereospecific reduction of progesterone are described and the corresponding enzymes are presented. Biosynthesis of androstanes, estranes and corticoids is discussed. Possible progesterone receptors and physiological reactions on progesterone application are reviewed.

Potato glycoalkaloids and metabolites: roles in the plant and in the diet

Potatoes, members of the Solanaceae plant family, serve as major, inexpensive low-fat food sources providing energy (starch), high-quality protein, fiber, and vitamins. Potatoes also produce biologically active secondary metabolites, which may have both adverse and beneficial effects in the diet. These include glycoalkaloids, calystegine alkaloids, protease inhibitors, lectins, phenolic compounds, and chlorophyll. Because glycoalkaloids are reported to be involved in host-plant resistance and to have a variety of adverse as well as beneficial effects in cells, animals, and humans, a need exists to develop a clearer understanding of their roles both in the plant and in the diet. To contribute to this effort, this integrated review presents data on the (a) history of glycoalkaloids; (b) glycoalkaloid content in different parts of the potato plant, in processed potato products, and in wild, transgenic, and organic potatoes; (c) biosynthesis, inheritance, plant molecular biology, and glycoalkaloid-plant phytopathogen relationships; (d) dietary significance with special focus on the chemistry, analysis, and nutritional quality of low-glycoalkaloid potato protein; (e) pharmacology and toxicology of the potato glycoalkaloids comprising alpha-chaconine and alpha-solanine and their hydrolysis products (metabolites); (f) anticarcinogenic and other beneficial effects; and (g) possible dietary consequences of concurrent consumption of glycoalkaloids and other biologically active compounds present in fresh and processed potatoes. An enhanced understanding of the multiple and overlapping aspects of glycoalkaloids in the plant and in the diet will benefit producers and consumers of potatoes.

Astonishing diversity of natural surfactants: 6. Biologically active marine and terrestrial alkaloid glycosides

This review article presents 209 alkaloid glycosides isolated and identified from plants, microorganisms, and marine invertebrates that demonstrate different biological activities. They are of great interest, especially for the medicinal and/or pharmaceutical industries. These biologically active glycosides have good potential for future chemical preparation of compounds useful as antioxidants, anticancer, antimicrobial, and antibacterial agents. These glycosidic compounds have been subdivided into several groups, including: acridone; aporphine; benzoxazinoid; ergot; indole; enediyne alkaloidal antibiotics; glycosidic lupine alkaloids; piperidine, pyridine, pyrrolidine, and pyrrolizidine alkaloid glycosides; glycosidic quinoline and isoquinoline alkaloids; steroidal glycoalkaloids; and miscellaneous alkaloid glycosides.

Analysis of steroidal lipids by gas and liquid chromatography

This article describes the most commonly used procedures and recent laboratory methodologies using gas and liquid chromatography developed for separation and quantitation of non-saponifiable steroidal lipids from clinical (human) studies, edible fats and oils or fatty foods.

Orthologs in Arabidopsis thaliana of the Hsp70 interacting protein Hip

The Hsp70-interacting protein Hip binds to the adenosine triphosphatase domain of Hsp70, stabilizing it in the adenosine 5'-diphosphate-ligated conformation and promoting binding of target polypeptides. In mammalian cells, Hip is a component of the cytoplasmic chaperone heterocomplex that regulates signal transduction via interaction with hormone receptors and protein kinases. Analysis of the complete genome sequence of the model flowering plant Arabidopsis thaliana revealed 2 genes encoding Hip orthologs. The deduced sequence of AtHip-1 consists of 441 amino acid residues and is 42% identical to human Hip. AtHip-1 contains the same functional domains characterized in mammalian Hip, including an N-terminal dimerization domain, an acidic domain, 3 tetratricopeptide repeats flanked by a highly charged region, a series of degenerate GGMP repeats, and a C-terminal region similar to the Sti1/Hop/p60 protein. The deduced amino acid sequence of AtHip-2 consists of 380 amino acid residues. AtHip-2 consists of a truncated Hip-like domain that is 46% identical to human Hip, followed by a C-terminal domain related to thioredoxin. AtHip-2 is 63% identical to another Hip-thioredoxin protein recently identified in Vitis labrusca (grape). The truncated Hip domain in AtHip-2 includes the amino terminus, the acidic domain, and tetratricopeptide repeats with flanking charged region. Analyses of expressed sequence tag databases indicate that both AtHip-1 and AtHip-2 are expressed in A thaliana and that orthologs of Hip are also expressed widely in other plants. The similarity between AtHip-1 and its mammalian orthologs is consistent with a similar role in plant cells. The sequence of AtHip-2 suggests the possibility of additional unique chaperone functions.

Receptors for mammalian steroid hormones in microbes and plants

Steroids are of universal occurrence, present variously as cell wall constituents and bioregulators. A number of bacteria, fungi, and photosynthetic vascular plants synthesize steroids that are hormonally active in the animal world. The cellular effect of such steroids in microbes and plants appears by and large to be comparable to that in mammals. Available evidence suggests that steroid action in botanical phyla is mediated via receptors organized in a manner similar to that seen in animals. Therefore, the ancestry of ligand induced transactivation via zinc finger proteins appears to date farther back than the early Cambrian burst of metazoan evolution 500 million years ago.

Synthesis and metabolism of vertebrate-type steroids by tissues of insects: a critical evaluation

This review covers the synthesis and the metabolism of vertebrate-type steroids (progesterone, testosterone, estradiol, corticosteroids) by insect tissues and discusses the significance of the reactions for insect physiology. Biosynthesis of vertebrate-type steroids from cholesterol hitherto has been demonstrated in only two insect species, i.e. the water beetle Acilius sulcatus (Coleoptera) and the tobacco hornworm Manduca sexta (Lepidoptera). In Acilius, steroid synthesis is associated with exosecretion (chemical defense). Nothing, however, is known about a physiological role of the C21 steroid conjugate present in ovaries and eggs of Manduca. No synthesis of vertebrate-type steroids was observed in any other insect investigated to date. Most metabolic conversions of steroids by insects concerned oxidoreduction of oxygen groups (hydroxysteroid dehydrogenase activity) and (polar and apolar) conjugate formation. All important enzymatic steps involved in synthesis and catabolism, as known from studies with tissues of vertebrates, were not, or hardly observed. The conclusion is drawn that typical vertebrate-type (C21, C19 and C18) steroids probably do not act as physiologically active substances in insects.

Lipid metabolism in fungi

So far, reviews that have appeared on fungal lipids present data mainly on the lipid composition of these organisms and the influence of lipids on their physiology. These reviews provide little information about the enzymes of lipid metabolism in these organisms and it is assumed, by most workers, that lipid synthesis in all fungi takes place as in Saccharomyces cervesiae, the only fungus in which the complete pathways of phospholipid biosynthesis have been worked out. During the last few years, literature has accumulated on lipid metabolic enzymes of other fungi, as investigators became increasingly interested in this area of research. The present review, after an introduction, will be divided into different sections and each section will deal, comparatively, with various aspects of fungal lipid metabolism and physiology. This review will, therefore, bring out the differences or similarities of lipid metabolism in diverse fungal species.

A possible role of estrogens in carcinogenesis of non-target tissues

The mitogenic action of the estrogen-receptor complex is supposedly similar in both normal and malignant target tissues. As receptors are present in several types of non-target tissues, in the case of lesions at the nuclear acceptor sites, the complex in those might be able to cause successive mitoses. Estrogen-dependent tumors of non-target tissues have been reported by several investigators. In normal and malignant cells of the breast and some other types of non-endocrine cells, the ability to produce their own estrogens (from circulating precursors) has been shown. The locally formed estrogens might have a role in the initiation of some malignant transformations. Indications of this process are the switching to estrogen production of some neoplastic endocrine or undifferentiated cells, certain ectopic effects displayed by some cancerous tissues, and the possible roles of GH, PRL and cholesterol in the development of some malignancies. The present endocrine system for the synthesis of the sexual hormones might be a specialization of a system at the cellular level. Polypeptide hormones might evolve from regulatory parts of cyclases or phosphodiesterases. Traces of the original biological processes might still be maintained by several cell-types.

High-pressure liquid chromatography of steroidal alkaloids

High-pressure liquid chromatography was used to separate the following steroidal alkaloids: tomatidine, solanidine, solasodine, rubijervine, veratramine and jervine. The method was used to prepare crystalline solanidine from a crude mixture of aglycones obtained from Solanum chacoense, and to separate radioactive solanidine from extracts of potato plants fed with [4-C]cholesterol.