Practical uses for ecdysteroids in mammals including humans: an update

Abstract

Ecdysteroids are widely used as inducers for gene-switch systems based on insect ecdysteroid receptors and genes of interest placed under the control of ecdysteroid-response elements. We review here these systems, which are currently mainly used in vitro with cultured cells in order to analyse the role of a wide array of genes, but which are expected to represent the basis for future gene therapy strategies. Such developments raise several questions, which are addressed in detail. First, the metabolic fate of ecdysteroids in mammals, including humans, is only poorly known, and the rapid catabolism of ecdysteroids may impede their use as in vivo inducers. A second set of questions arose in fact much earlier with the pioneering "heterophylic" studies of Burdette in the early sixties on the pharmacological effects of ecdysteroids on mammals. These and subsequent studies showed a wide range of effects, most of them being beneficial for the organism (e.g. hypoglycaemic, hypocholesterolaemic, anabolic). These effects are reviewed and critically analysed, and some hypotheses are proposed to explain the putative mechanisms involved. All of these pharmacological effects have led to the development of a wide array of ecdysteroid-containing preparations, which are primarily used for their anabolic and/or "adaptogenic" properties on humans (or horses or dogs). In the same way, increasing numbers of patents have been deposited concerning various beneficial effects of ecdysteroids in many medical or cosmetic domains, which make ecdysteroids very attractive candidates for several practical uses. It may be questioned whether all these pharmacological actions are compatible with the development of ecdysteroid-inducible gene switches for gene therapy, and also if ecdysteroids should be classified among doping substances.

Figure 1.

Structures of ligands used for ecdysteroid-inducible gene expression systems in mammalian and plant cells.

Figure 2.

General scheme for ecdysteroid-based gene switches.

Figure 3.

The Invitrogen system for mammalian cells; the elicitor is muristerone A (murA) or ponasterone A (ponA). See text for further details (www.invitrogen.com).

Figure 4.

The RHeoGene system for mammalian cells; the elicitor depicted is the bisacylhydrazine GS-E (1-[3-methoxy-2-ethylbenzoyl]-2-[3,5-dimethylbenzoyl]-2-tert-butylhydrazine). See text for further details (Karns et al., 2001).

Figure 5.

The Syngenta system for plant cells. See text for further details (Martinez et al., 1999a&b).

Figure 6.

Major E and 20E metabolites in Mammals (see text for details). A: E metabolites (2–4) isolated from murine faeces (Girault et al., 1988); B: 20E metabolites (6–8) isolated from rat urine (Ramazanov et al., 1996).

Figure 7.

Three possible ways for a membrane effect of ecdysteroids (adapted from Brann et al., 1995).

Figure 8.

A working hypothesis for ecdysteroid action on mammalian cells: a stimulation of the Akt/PKB pathway would explain a large set of the described effects of 20E on mammals (see text for details). Bad: a proapoptotic factor, which is inhibited upon phosphorylation by Akt; Glut4: glucose transporter type 4; GSK3: glycogen synthase kinase-3; IL3: interleukin-3; INS: insulin; S6K: ribosomal protein S6-kinase.