Isolation and identification of three ecdysteroid conjugates with a C-20 hydroxy group in eggs of Locusta migratoria

Insect Sterols and Steroids

Insects are incapable of biosynthesising sterols de novo so they need to obtain them from their diets or, in certain cases, from symbiotic microorganisms. Sterols serve a structural role in cellular membranes and act as precursors for signalling molecules and defence compounds. Many phytophagous insects dealkylate phytosterols to yield primarily cholesterol, which is also the main sterol that carnivorous and omnivorous insects obtain in their diets. Some phytophagous species have secondarily lost the capacity to dealkylate and consequently use phytosterols for structural and functional roles. The polyhydroxylated steroid hormones of insects, the ecdysteroids, are derived from cholesterol (or phytosterols in non-dealkylating phytophagous species) and regulate many crucial aspects of insect development and reproduction by means of precisely regulated titres resulting from controlled synthesis, storage and further metabolism/excretion. Ecdysteroids differ significantly from vertebrate steroid hormones in their chemical, biochemical and biological properties. Defensive steroids (cardenolides, bufadienolides, cucurbitacins and ecdysteroids) can be accumulated from host plants or biosynthesised within the insect, depending on species, stored in significant amounts in the insect and released when it is attacked. Other allelochemical steroids serve as pheromones. Vertebrate-type steroids have also been conclusively identified from insect sources, but debate continues about their significance. Side chain dealkylation of phytosterols, ecdysteroid metabolism and ecdysteroid mode of action are targets of potential insect control strategies.

Phytoecdysteroids: Distribution, Structural Diversity, Biosynthesis, Activity, and Crosstalk with Phytohormones

Phytoecdysteroids (PEs) are naturally occurring polyhydroxylated compounds with a structure similar to that of insect molting hormone and the plant hormone brassinosteroids. PEs have a four-ringed skeleton composed of 27, 28, 29, or 30 carbon atoms (derived from plant sterols). The carbon skeleton of ecdysteroid is known as cyclopentanoperhydrophenanthrene and has a β-sidechain on C-17. Plants produce PEs via the mevalonate pathway with the help of the precursor acetyl-CoA. PEs are found in algae, fungi, ferns, gymnosperms, and angiosperms; more than 500 different PEs are found in over 100 terrestrial plants. 20-hydroxyecdysone is the most common PE. PEs exhibit versatile biological roles in plants, invertebrates, and mammals. These compounds contribute to mitigating biotic and abiotic stresses. In plants, PEs play a potent role in enhancing tolerance against insects and nematodes via their allelochemical activity, which increases plant biological and metabolic responses. PEs promote enzymatic and non-enzymatic antioxidant defense systems, which decrease reactive oxygen species in the form of superoxide radicals and hydroxyl radicals and reduce malondialdehyde content. PEs also induce protein biosynthesis and modulate carbohydrate and lipid synthesis. In humans, PEs display biological, pharmacological, and medicinal properties, such as anti-diabetic, antioxidant, anti-microbial, hepatoprotective, hypoglycemic, anti-cancer, anti-inflammatory, antidepressant, and tissue differentiation activity.

Plant ecdysteroids: plant sterols with intriguing distributions, biological effects and relations to plant hormones

The present review summarises current knowledge of phytoecdysteroids' biosynthesis, distribution within plants, biological importance and relations to plant hormones. Plant ecdysteroids (phytoecdysteroids) are natural polyhydroxylated compounds that have a four-ringed skeleton, usually composed of either 27 carbon atoms or 28-29 carbon atoms (biosynthetically derived from cholesterol or other plant sterols, respectively). Their physiological roles in plants have not yet been confirmed and their occurrence is not universal. Nevertheless, they are present at high concentrations in various plant species, including commonly consumed vegetables, and have a broad spectrum of pharmacological and medicinal properties in mammals, including hepatoprotective and hypoglycaemic effects, and anabolic effects on skeletal muscle, without androgenic side-effects. Furthermore, phytoecdysteroids can enhance stress resistance by promoting vitality and enhancing physical performance; thus, they are considered adaptogens. This review summarises current knowledge of phytoecdysteroids' biosynthesis, distribution within plants, biological importance and relations to plant hormones.

Occurrence of phosphorylated castasterone in Arabidopsis thaliana and Lycopersicum esculentum

An in vitro enzyme assay using radioisotope-labeled (3) H-castasterone ((3) H-CS) or (32) P-ATP showed that CS can be phosphorylated by ATP in Arabidopsis and tomato plants. Gas chromatography-mass spectrometry (GC-MS) analysis using non-isotope-labeled CS and ATP revealed that the phosphorylation of CS occurs at the side chain, most likely at the C-23 hydroxyl. The polar fractions than free brassinosteroids (BRs) obtained from extracts of Arabidopsis and tomato showed almost no BRs activity in a rice lamina inclination bioassay. However, the fractions showed increased bioactivity after treatment with wheat germ acidic phosphatase (WGAP). Additionally, CS was identified from the hydrolysate by WGAP using GC-MS analysis in both plants. In contrast, the polar fractions obtained from BR-deficient mutants, Arabidopsis cyp85a2 and tomato d(x) , did not show an increase in biological activity with WGAP treatment, and no free BRs, including CS, were detected in the hydrolysate. This suggests that CS phosphate is a naturally occurring biologically inactive conjugate that is generated when CS is normally synthesized in Arabidopsis and tomato plants. Taken together, these results suggest that phosphorylation of CS is an important conjugation process for the maintenance of the homeostatic level of an active BR and thus the regulation of the growth and development of plants.

Isolation and identification of ecdysteroid phosphates and acetylecdysteroid phosphates from developing eggs of the locust, Schistocerca gregaria

Maturing eggs of the desert locust, Schistocerca gregaria, contain a variety of ecdysteroid (insect moulting hormone) conjugates and metabolites, four of which have been previously isolated from polar extracts and identified as ecdysonoic acid, 20-hydroxyecdysonoic acid, 3-acetylecdysone 2-phosphate and ecdysone 2-phosphate. In the present study we have isolated eight additional ecdysteroids from similar late-stage eggs by high-performance liquid chromatography. The 22-phosphate esters of ecdysone, 2-deoxyecdysone, 20-hydroxyecdysone and 2-deoxy-20-hydroxyecdysone, all of which were first identified as ecdysteroid components of newly-laid eggs of S. gregaria, were identified by co-chromatography with authentic compounds and by physicochemical techniques. The remaining compounds were identified as 3-acetyl-20-hydroxyecdysone 2-phosphate, 3-epi-2-deoxyecdysone 3-phosphate, 3-acetylecdysone 22-phosphate and 2-acetylecdysone 22-phosphate by fast atom bombardment mass spectrometry, p.m.r. spectroscopy and analysis of the steroid moieties after enzymic hydrolysis. The latter two compounds, after isolation, are susceptible to nonenzymic acetyl migration and deacetylation to give mixtures of ecdysone 22-phosphate and its 2- and 3-acetate derivatives. The possible role and significance of these ecdysteroid conjugates with respect to the control of hormone titres in insect eggs is discussed.