Abstract
The approving agencies for plant protection agents request xenobiotic metabolism and residue studies in rats, farm animals and plants (e.g. EU regulation 1107/2009) according to OECD guidelines. The specific intestinal physiology of ruminants might lead to specific residues, which should be investigated very carefully. Specific aspects of xenobiotic metabolism in ruminants may arise, which are investigated by performing additional in vivo studies. The aim of the present work is to asses a modified rumen simulation system (RUSITEC) for such studies in vitro. Rumen constituents from sheep were incubated over 8 days. Physiological parameters followed by monitoring the pH (6.70 ± 0.07), the redox potential (301 mV ± 30 mV), the microbial composition and determination of β-glucosidase activity. After anequilibration period of three to four days the fermenters were probed with 14C-labelled triazolederivatives, i.e.common metabolites of azole fungicides. Only triazole-alanine was cleaved to 1,2,4-triazole, while triazole-acetic acid and triazole-lactic acid remained stable up to 96 h. Moreover, glycosides are often determined as the main residues in the plants. This analysis showed, that the two glucosides octyl-β-D-glucopyranoside and polydatin were both rapidly cleaved in this rumen in vitro system. These data showed that the modified RUSITEC system is stable, viable and maintained metabolic capacity over a longer period (at least 8 days). This makes many animal experiments obsolete and lead to a significant contribution of the 3R (refine, reduce, replace). The modification of the RUSITEC system enables safe routine use for unlabeled but also for radioactive labelled compounds.
Highlights
In the development of plant protection products extensive tests are required by the approving agencies such as, e.g., the European Food and Safety Agency (EFSA) in Europe and the United States Environmental Protection Agency (US-EPA) in the US, to prove the safety of the product to the environment, animals and humans
The colony forming assay to determine bacterial population showed an increase in colonies from 1.1 × 10E7 colonies/ml at the start of fermentation to 4.1 (± 0.8 SD) × 10E7 after 120 h to 4.8 (± 1.4 SD) × 10E7 after 192 h
The system maintains the particular properties of rumen and, after a pre-incubation time, is stable for up to 192 h
Summary
In the development of plant protection products extensive tests are required by the approving agencies such as, e.g., the European Food and Safety Agency (EFSA) in Europe and the United States Environmental Protection Agency (US-EPA) in the US, to prove the safety of the product to the environment, animals and humans. Xenobiotic metabolism studies in rats, farm animals and plants identify and quantify the active ingredient and its related degradation products, i.e. metabolites. The active ingredient or metabolites of the product may enter the food chain; a detailed assessment of the quality and quantity of the residues is required. The results are compared with the results of rat metabolism studies to determine the appropriate coverage of the relevant metabolites by toxicological studies in rats (EFSA, 2016). If they are not covered, additional toxicological studies are required. All xenobiotic metabolism studies are performed according to OECD TG 417 (rat; OECD, 2010), 503 and 505 (farm animals; OECD, 2007a,b), 501 and 502 (plants; OECD, 2007c,d)
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