Ecdysteroid metabolism in mammals: The fate of ingested 20-hydroxyecdysone in mice and rats.

Phytoecdysteroids are molecules derived from sterol metabolism and found in many plants. They display a wide array of pharmacological effects on mammals (e.g. anabolic, anti-diabetic). Although these effects have been long established, the molecular targets involved remain to be identified. Like endogenous steroid hormones and bile acids, which are biochemically related, ingested or injected phytoecdysteroids undergo a set of reactions in mammals leading to the formation of numerous metabolites, only some of which have been so far identified, and it is presently unknown whether they represent active metabolites or inactivation products. In the large intestine, ecdysteroids undergo efficient 14-dehydroxylation. Other changes (reductions, epimerization, side-chain cleavage) are also observed, but whether these occur in the liver and/or large intestine is not known. The purpose of this study was to investigate the pharmacokinetics of 20-hydroxyecdysone (20E), the most common phytoecdysteroid, when administered to mice and rats, using, when required, tritium-labelled molecules to permit metabolic tracking. Bioavailability, the distribution of radioactivity and the kinetics of formation of metabolites were followed for 24-48 hours after ingestion and qualitative and quantitative analyses of circulating and excreted compounds were performed. In mice, the digestive tract always contains the majority of the ingested 20E. Within 30 min after ingestion, 20E reaches the large intestine, where microorganisms firstly remove the 14-hydroxyl group and reduce the 6-one. Then a very complex set of metabolites (not all of which have yet been identified) appears, which correspond to poststerone derivatives formed in the liver. We have observed that these compounds (like bile acids) undergo an entero-hepatic cycle, involving glucuronide conjugation in the liver and subsequent deconjugation in the intestine. Despite the very short half-life of ecdysteroids in mammals, this entero-hepatic cycle helps to maintain their plasma levels at values which, albeit low (≤0.2 µM), would be sufficient to evoke several pharmacological effects. Similar 20E metabolites were observed in mice and rats; they include in particular 14-deoxy-20E, poststerone and 14-deoxypoststerone and their diverse reduction products; the major products of this metabolism have been unambiguously identified. The major sites of metabolism of exogenous ecdysteroids in mammals are the large intestine and the liver. The entero-hepatic cycle contributes to the metabolism and to maintaining a low, but pharmacologically significant, concentration of ecdysteroids in the blood for ca. 24 h after ingestion. These data, together with parallel in vitro experiments provide a basis for the identification of 20E metabolite(s) possibly involved in the physiological effects associated with ecdysteroids in mammals.

The metabolism of 20-hydroxyecdysone in mice: relevance to pharmacological effects and gene switch applications of ecdysteroids.

Ecdysteroids exert many pharmacological effects in mammals (including humans), most of which appear beneficial, but their mechanism of action is far from understood. Whether they act directly and/or after the formation of metabolites is still an open question. The need to investigate this question has gained extra impetus because of the recent development of ecdysteroid-based gene-therapy systems for mammals. In order to investigate the metabolic fate of ecdysteroids in mice, [1α,2α-(3)H]20-hydroxyecdysone was prepared and injected intraperitoneally to mice. Their excretory products (urine+faeces) were collected and the different tritiated metabolites were isolated and identified. The pattern of ecdysteroid metabolites is very complex, but no conjugates were found, in contrast to the classical fate of the (less polar) endogenous vertebrate steroid hormones. Primary reactions involve dehydroxylation at C-14 and side-chain cleavage between C-20 and C-22, thereby yielding 14-deoxy-20-hydroxyecdysone, poststerone and 14-deoxypoststerone. These metabolites then undergo several reactions of reduction involving, in particular, the 6-keto-group. A novel major metabolite has been identified as 2ß,3ß,6α,22R,25-pentahydroxy-5ß-cholest-8(14)-ene. The formation of this and the other major metabolites is discussed in relation to the various effects of ecdysteroids already demonstrated on vertebrates.

Iridoids with anti-inflammatory activity from Vitex peduncularis.

A new iridoid, pedunculariside, together with the known iridoid agnuside were isolated from the butanol extract of Vitex peduncularis stem bark. Both pedunculariside and agnuside showed preferential inhibition of COX-2, with IC50 values of 0.15 +/- 0.21 mg/ml and 0.026 +/- 0.015 mg/ml respectively, while having only small inhibitory effects on COX-1. Both compounds did not exhibit cytotoxicity against vero cells.