Do insect food-derived ecdysteroids appear in the blood of waterfowl, predatory birds, carnivorous mammals and primates?

by Sándor Hornok, Róbert Berkecz, Andor Pitó, Paula Baro, Kathrin M. Röper, József Lanszki, Alexandra Biácsi, Károly Erdélyi, Endre Sós, Viktor Molnár, Endre Papp, Sándor Boldogh, Solt Szabolcs, Gergő Keve, Attila Hunyadi

Arthropod molting hormones, the so-called ecdysteroids were experimentally shown to have anabolic effects in higher vertebrates, promoting energy supply, protein synthesis, and tissue growth. Insectivorous songbirds (Aves: Passeriformes) and bats (Mammalia: Chiroptera) were demonstrated to have naturally acquired ecdysteroids in their blood. However, it is not known if partly insectivorous or artificially insect-fed vertebrates would also have ecdysteroids in their circulation. The aim of this screening study was to clarify this, by collecting blood samples of mammals, birds and reptiles that are wild-living or receive insect diet at zoological gardens, followed by ultra-high performance liquid chromatography and high-resolution quadrupole-orbitrap mass spectrometry analyses. The zoo animal samples originated from one reptilian species (n = 3), as well as one species of insectivorous mammals (n = 8), three species of carnivores (n = 17) and one species of primates (n = 2). Three further species of road-killed mammalian carnivores were sampled postmortem (n = 15). Finally, blood samples were also drawn and analyzed from six species of water-associated (n = 44) and three species of predatory birds (n = 47). Ecdysteroids were detected in two out of 136 samples: from a Common Kestrel (Falco tinnunculus) that contained 58.9 nM 20-hydroxyecdysone (20E), and from a beech marten (Martes foina) that contained 40.9 nM dacryhainansterone (a phytoecdysteroid). Although these concentrations do not mean evidence for sustained biological or anabolic effects, 20E was reported to transactivate estrogen receptors β and α with EC₅₀ values of 13.0 and 25.7 nM, respectively. Accordingly, our results show for the first time that ecdysteroids may be present in pharmacologically relevant concentrations in the blood of predominantly carnivorous species of birds and mammals. However, unlike in songbirds and bats which continuously feed on insects, detectable levels of ecdysteroids appear only rarely in the blood of opportunistic insectivores, therefore their health benefits remain questionable in artificially and occasionally insect-fed zoo animals.