Drug metabolism in Lucilia sericata larvae

Abstract

Introduction: Toxicological analysis of post-mortem tissue can confirm whether drugs were implicated in death. Alternative toxicological specimens, such as blowfly larvae (Lucilia sericata) are used when traditional tissue or blood samples are not available for toxicological analysis. Blowfly larvae have a high tolerance to certain drugs, and can grow on tissue spiked with a doses of certain drugs that are lethal to humans. This tolerance suggests that the larvae are able to either metabolise or eliminate the drugs, preventing accumulation within the larvae. However, it is not known whether Lucilia sericata larvae are capable of metabolising drugs. If larvae can metabolise drugs this has significant implications for how future entomotoxicological assays are designed. To investigate whether Lucilia sericata larvae were capable of metabolising, the model drug amitriptyline (AMI) was used. AMI is commonly involved in overdose, and it has a well characterised metabolic pathway.

Aim: To determine whether Lucilia sericata larvae could metabolise the model drug AMI by N-demethylation to nortriptyline (NOR).

Method: Lucilia sericata larvae were reared on AMI-spiked porcine brain tissue (2.5 mg/g). The larvae were washed and frozen at -20 ºC prior to analysis. The biological tissues; porcine brain tissue or Lucilia sericata larvae were homogenized with water (1:10 w/v) and underwent a liquid-liquid extraction (LLE) followed by quantitative analysis using high performance liquid chromatography (HPLC).

Results: The HPLC assay could quantify AMI and NOR from 0.2 µg/mL to 5 µg/mL (R2 > 0.99) extracted from the biological tissues. There was minimal conversion of AMI to NOR within the porcine brain tissue over 123 hours. However, the larvae showed a high tolerance to AMI and partially converted the AMI to NOR in-vivo within 78 hours of exposure to AMI. In contrast, larvae samples taken after 120 hours contained additional metabolites in addition to the NOR.

Conclusion: Lucilia sericata larvae were able to perform N-demethylation using AMI as a model drug. Larvae, when used as an alternative toxicological sample need to be considered metabolically active in comparison to traditional toxicological samples; such as blood or muscle from a cadaver that are no longer metabolically active.