Ecdysteroids ecdysone

Insects, crustaceans, platehelminthes, nematodes and annelids use homoses-quiterpenoid epoxides (juvenile hormones) and ecdysteroids (ecdysone, 20-... 

Our present meagre understanding of normal endocrine processes in invertebrates makes the assessment of chemical endocrine disruption in the field difficult (LeBlanc 1999). Steroid roles differ between species and sometimes sexes, and their influence may vary at different developmental stages. In most studies of invertebrates, endocrine disruption appears to involve androgenization rather than oestrogenic effects (see Box 7.2). Arthropods (crustaceans and insects), annelids and molluscs use ecdysteroids, terpenoids and vertebratelike sex steroids for endocrine control. For example, the ecdysteroid ecdysone is naturally converted to 20-hydroxyecdysone (Fig. 7.10), which induces moulting (ecdysis) in both insect larvae and crustaceans. 

It is significant that, although the C27 ecdysteroids ecdysone and 20-hydroxyecdysone are the most commonly found molting hormones in insects, the C28 ecdysteroid, makisterone A, is the major molting hormone of many insects that are unable to dealkylate. In addition, the C29 ecdysteroid, makisterone C, has been identified as a major embryonic molting hormone of a hemipteran that lacks dealkylation capabilities. The ability to synthesize makisterone A is present even in certain insects that ordinarily have adequate cholesterol in their diets as shown for the hemipteran, P. maculiventris, and the higher Diptera. So this appears to be a well-conserved biochemical mechanism. 

Members of the family Amaranthaceae are known to produce ecdysteroids such as 8-ecdysone (19) and inocosterone (20). From petroleum ether extracts of Amaranthus splnosus Linn. Behari and Andhiwal (21) obtained 8-sitosterol (4), stigmasterol (3), campesterol and cholesterol. From the roots of the same species, Banerji (22) isolated two new saponins, a diglucoside and a triglucoside of o-spinasterol. More recently, Roy et al. (23)... 

A recent study differentiated the role of JH and ecdysteroids in the ant Streblognathus peetersi. Ecdysone was correlated with dominant ants and reproduction while JH was more commonly associated with low-ranking ants and sterility (Brent et al., 2006). 

Fig. 4.4. HPLC fractionation of the free ecdysteroid fraction from Moniezia expansa (a) sample 1, 3.3% portion (bj sample 2, 10% portion on a chromatographic system with collection of fractions every minute for the radioimmunoassay (RIA) (ICT-1 antiserum). The positions of authentic ecdysteroids are shown IV, 20, 26-dihydroxyecdysone II, 20-hydroxyecdysone I, ecdysone. (After Mendis et al., 1984.)...

The term ecdysteroid was originally defined as "all compounds structurally related to ecdysone" [4], However, Lafont and Horn [5] differentiated between true ecdysteroids and ecdysteroid-related compounds. True ecdysteroids possess a steroid nucleus with an A/B-cis-ring junction and a 14a-hydroxy-7-en-6-one chromophore, irrespective of their biological activity, while ecdysteroid-related compounds do not fulfil all these criteria. 

Scheme 3). A clone of cells from the midge Cbironomus tentans was found to be resistant to the effects of ecdysteroids because they metabolized 20-hydroxyecdysone rapidly. The initial oxidation product was 20,26-dihydroxyecdysone, but this was oxidized further to 20-hydroxy-26-oxo-ecdysone (21). This aldehyde (21) then formed a tautomeric equilibrium mixture of two cyclic hemiacetals (22) and (23), which were separable, isolated, and their structures determined (Scheme 3) with the use of acetonides (Section 4.03.3.6).32 These are the first examples of ecdysteroids with side-chain hemiacetals. Although 20,26-dihydroxyecdysterone still... 

The steroids known to play major regulatory roles in insect development and metamorphosis all fall into the class of polyhydroxylated ketosteroids called ecdysones (19-22). With the exception of Makisterone A (a C2 ecdysteroid identified from the milkweed bug Oncopeltus fasciatus) the known insect ecdysteroids constitute a group of eight or nine steroids that differ from one another... 

The synthesis of ecdysone, the only ecdysteroid formed by the prothoracic glands, is under the control of the prothoracicotropic... 

Balance between the active and inactive forms of ecdysone and/or other ecdysteroids may be accomplished by the formation of conjugates such as sulfate esters or glucosides (20,27). The sulfation of phenols and a variety of sterols has been 3emonstrated in insect tissues and this, in close association with an appropriate sulfatase, would constitute a readily reversible mechanism whereby the required balance between active and inactive forms of ecdysteroids could be regulated (27). 

Diacylhydrazine insecticides (tebufenozide, methoxyfenozide, halofenozide, and chroma-fenozide) act as nonsteroidal ecdysone agonists. They bind to specific ecdysteroid receptorbinding proteins, interrupting the normal sequence of events. Consequently, they induce an incomplete precocious molt, resulting in the mortality of the larva. 

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