Tigliane metabolites in Hyles frass after feeding experiments with TPA and Euphorbia cyparissias

Abstract

Within the genus Hyles, Euphorbia feeding appears to have evolved twice independently, in H. euphorbiae but also in H. nicaea, a species which had not been studied for its detoxification processes before. Euphorbia is known to contain toxic secondary metabolites, including diterpene esters, preventing most herbivores from feeding on them. We investigated the metabolisation of the standard phorbol ester Phorbol 12-myristate 13-acetate (TPA) and the diterpenes contained in Euphorbia cyparissias by the two species Hyles euphorbiae and Hyles nicaea (subspecies nicaea). For the first time, we report (1) The gut disposition of Hyles n. nicaea for this standard phorbol ester, which is commonly used in cancer and tumour research and (2) The disposition of the food plant tiglinaes of Euphorbia cyparissias after gut passage in both species and (3) Tigliane metabolites in the frass of TPA and of E. cyparissias feeding larvae. For both species around 5–25% of the TPA dose was recovered in the frass of the larvae, along with the metabolites phorbol and phorbol-13-acetate in very small amounts and traces. While the amounts of phorbol found did not differ much between the species frass, phorbol-13-acetate could be found in higher amounts in Hyles n. nicaea frass, indicating a difference in metabolisation. Moreover, enzymatic hydrolysis of TPA to phorbol-13-acetate and phorbol are postulated not to be the main metabolisation pathway, seeing that the amounts found only represent a small fraction of the TPA dose consumed.