A high-performance liquid chromatography method for the purification and analysis of insect ecdysones: Application to measurement of ecdysone titers during pupal-adult development of Heliothis zea

Sterol utilization and metabolism by Heliothis zea

Heliothis zea (corn earworm), an insect that fails to synthesize sterols de novo, was reared on an artificial diet treated with 18 different sterol supplements. Larvae did not develop on a sterol-less medium. delta 5-Sterols with a hydrogen atom, a methylene group, an E- or Z-ethylidene group, or an alpha- or beta-ethyl group (cholesterol, ostreasterol, isofucosterol, fucosterol, sitosterol, and clionasterol, respectively) at position C-24, and delta 5-sterols doubly substituted in the side chain at C-24 with an alpha-ethyl group and at C-22 with a double bond (stigmasterol) supported normal larval growth to late-sixth instar (prepupal: maturity). The major sterol isolated from each of these sterol treatments was cholesterol, suggesting that H. zea operates a typical 24-dealkylation pathway. The sterol requirement of H. zea could not be met satisfactorily by derivatives of 3 beta-cholestanol with a 9 beta, 19-cyclopropyl group, gem dimethyl group at C-4, a delta 5,7-bond or delta 8-bond, or by side chain modified sterols that possessed a delta 25(27)-24 beta-ethyl group, delta 23(24)-24-methyl group or 24-ethyl group, or delta 24(25)-24-methyl or 24-ethyl group. The major sterol recovered from the larvae (albeit developmentally arrested larvae) treated with a nonutilizable sterol was the test compound. Sterol absorption was related to the degree of sterol utilization. The most effective sterols absorbed by the insect ranged from 27 to 66 micrograms per insect, whereas the least effective sterols absorbed by the insect ranged from 0.6 to 6 micrograms per insect. Competition experiments using different proportions of cholesterol and 24-dihydrolanosterol (from 9:1 to 1:9 mixtures) indicated that abnormal development of H. zea may be induced on less than a 1 to 1 mixture of utilizable (cholesterol) to nonutilizable (24-dihydrolanosterol) sterols. The results demonstrate new structural requirements for sterol utilization and metabolism by insects, particularly with respect to the position of double bonds in the side chain and functionalization in the nucleus. The novel sterol specificities observed in this study appear to be associated with the dual role of sterols as membrane inserts (nonmetabolic) and as precursors to the ecdysteroids (metabolic).

Changes in ecdysteroid and juvenile hormone titers in the hemolymph of Galleria mellonella larvae and pupae

The variations in circulating ecdysteroids and juvenile hormones (JH) in Galleria, from the end of the antepenultimate larval stage until emergence of adults, have been determined. The two hormonal families were extracted separately from the same hemolymph sample and quantified by two radioimmunoassays. Juvenile hormone RIA activity was about 35 nM in larvae of the antepenultimate and penultimate stages. It dropped before each molt and increased thereafter. Moreover, it gradually decreased during the last larval instar. In pupae, it was generally low, but it rose drastically during the late pupal development and in young adults. This rise was very much higher in females than in males. Three different RIA-active compounds were found; they were assumed to be JH-I, JH-II, and JH-III according to their retention times in HPLC. The three compounds were present in almost equal concentration in larvae of the penultimate stage: JH-I predominated, however, during the last larval instar. In late pupae, the main hormone was JH-III both in males and in females. There is no clear relationship between ecdysteroid and juvenile hormone changes, except for a female-specific ecdysteroid rise which coincides with the juvenile hormone release in late pupae. This double hormonal stimulation can be involved in the regulation of vitellogenin synthesis and deposition in oocytes.

Biosynthesis and inactivation of ecdysone during the pupal-adult development of the cabbage butterfly, Pieris brassicae L

Injection of labelled ecdysone and 2-hydroxyecdysone into Pieris pupae showed that their catabolism proceeds through 26-hydroxylation followed by conversion into acidic steroids assumed to be 26-oic compounds. This biological system is characterized by the lack of conjugation reactions and by rather long-lived hormones. In vivo biosynthesis of ecdysteroids was investigated by 24 hr [3H]cholesterol labelling, followed by HPLC analysis of the resulting [3H]ecdysone and 20-hydroxyecdysone. Active conversion (up to 0.07% in 24 hours) was observed between 48 hr and 120 hr following pupal ecdysis, a result in good agreement with the variations observed in hormone content. Long-term [3H]cholesterol incorporation experiments made it possible to monitor ecdysteroid dynamics during pupal development. Three periods were observed, corresponding to successive accumulation of ecdysone, 20-hydroxyecdysone and an acidic metabolite. Comparison of these results with those of the experiments involving labelled ecdysone injection shows that the catabolism of injected hormones is not the same as that of endogenous hormones.

Comparison of high-performance liquid chromatography and gas chromatography for the analysis of ecdysteroids

High-performance liquid chromatography (HPLC) with ultraviolet absorption detection, and gas chromatography (GC) with an electron-capture detector have been compared for their convenience in the analysis of ecdysteroids in invertebrate tissues. Analysis by HPLC on reversed-phase materials, including C18, C22 and CN bonded phases, was explored for the separation of both polar ecdysteroids and some of their possible biosynthetic intermediates of lower polarity. The HPLC method was found to be rapid and easy to use, but less sensitive than GC with electron-capture detection. The greater sensitivity and selectivity of GC was found to be important for the more difficult analyses.

Ecdysone 3-epimerase from the midgut of Manduca sexta (L.)

Ecdysone 3-epimerase was partially purified by ammonium sulfate fractionation from the 100,000 g supernate of Manduca sexta midguts. The enzyme converts ecdysone and 20-hydroxyecdysone to their respective 3-epimers, requires NADH or NADPH and O2 for this reaction, and has the following kinetic parameters: for ecdysone, Km = 17.0 +/- 1.4 microM, Vmax = 110.6 +/- 14.6 pmol min-1 mg-1; for 20-hydroxyecdysone, Km = 47.3 +/- 7.5 microM, Vmax = 131.0 +/- 3.5 pmol min-1 mg-1: for NADPH, Km = 85.4 +/- 10.6 microM; for NADH, Km = 51.3 +/- 1.3 microM. The reaction is irreversible and can be inhibited by various ecdysteroids.