Relationship of hepatotoxicity and the target tissue dose of decabrominated diphenyl ether in subacutely exposed Wistar rats

Abstract

Background/Aim. Based on numerous studies in animals, the most prominent toxic effects of decabrominated di-phenyl ether (BDE-209) are observed in the liver, thyroid hormone homeostasis, reproductive and nervous systems. BDE-209 exhibits its toxic effects partly through the aryl hydrocarbon (Ah) receptor and consequent induction of hepatic microsomal enzymes. The aim of this study was to assess the hepatotoxic effect vs target tissue dose of BDE-209 in the subacutely orally exposed Wistar rats. Methods. Effects were examined on male Wistar rats, weighing 200-240 g, exposed to doses of 1,000, 2,000 or 4,000 mg BDE-209/kg body weight (bw)/day by gavage during 28 days. Animals were treated according to the decision of the Ethics Committee of the Military Medical Academy, No 9667-1/2011. Evaluation of the hepatotoxic effect was based on: relative liver weight water and food intake, biochemical parameters of liver function [aspartate amino transferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP), gama glutamyl transferase (γ-GT)], and oxidative stress parameters in liver homogenates [malondialdehiyde (MDA), superoxide dismutase (SOD), -SH] and morphological and pathohistological changes in the liver. For the assessment of internal dose - response relationship, lower confidence limit of Benchmark dose (BMDL) of 5% or 10% i.e. BMDL5 or BMDL10, were calculated using PROAST software. Results. After the application of 1,000, 2,000 or 4,000 mg BDE-209/kg bw/day, the concentrations of BDE-209 measured in liver were 0.269, 0.569 and 0.859 mg/kg of liver wet weight, (ww) respectively. Internal doses correlated with external (r = 0.972; p lt 0.05) according to equation: internal dose (mg BDE-209/kg of liver ww) = 0.0002 ' external dose (mg/kg bw/day) + 0.0622. Hepato-toxicity was demonstrated based on significant increase in AST and γ-GT activities and the degree of histopathological changes. The lowest BMDL5 of 0.07228 mg BDE-209/kg of liver ww, correlating to external dose of 39 mg/kg/day, indicated the increase of AST activity as the most sensitive biomarker of BDE-209 hepatotoxicity in subacutely ex-posed rats. Conclusion. The results of the present work add up to the issue of BDE-209 toxicity profile with a focus on relationship between internal dose and hepatotoxicity. Critical internal dose for the effect on AST of 0.07 mg/kg of liver ww, corresponding to external dose of 39 mg/kg/day, is the lowest dose ever observed among the studies on BDE-209 hepatotoxicity. For the persistent sub-stances with low absorption rate such as BDE-209, critical effect based on internal dose in majority of cases is considered as more precisely defined than the effect established based on external dose, particularly.

Uvod/Cilj. Prema podacima iz brojnih studija na životinjama, dekabromovani difeniletar (BDE-209) najznačajnije toksične efekte ispoljava na jetri, homeostazi hormona štitaste žlezde, reproduktivnom i nervnom sistemu. BDE-209 ispoljava toksične efekte delom preko receptora za aromatične ugljovodonike (Ah) i posledične indukcije mikrozomalnih enzima jetre. Cilj rada bio je procena hepatotoksičnog efekta u odnosu na dozu BDE-209 u ciljnom tkivu kod subakutno oralno eksponovanih Wistar pacova. Metode. Efekti su ispitivani na mužjacima Wistar pacova, mase 200-240 g, koji su putem oralne sonde primali doze od 1 000, 2 000 ili 4 000 mg BDE-209/kg telesne mase (tm) dan, tokom 28 dana. Životinje su tretirane u skladu sa odlukom Etičkog komiteta Vojnomedicinske akademije u Beogradu br. 9667-1/2011. Procena hepatotoksičnih efekata bazirana je na merenju relativne mase jetre, unosa vode i hrane, biohemijskih parametara funkcije jetre [aspartat aminotransferaza (AST), alanin amino-transferaza (ALT), alkalna fosfataza (ALP), gama glutamil transferaza (γ-GT)], parametara oksidativnog stresa u homogenatima jetre [malondialdehid (MDA), superoksid dizmutaza (SOD), -SH)] i morfoloških i histoloških promena na jetri. Za procenu odnosa interna doza - odgovor izračunavana je donja granica pouzdanosti granične Benchmark doze (BMDL) od 5% (BMDL5) ili 10% (BMDL10) primenom PROAST softvera. Rezultati. Koncentracije BDE-209 iznosile su 0,269, 0,569 i 0,859 mg/kg jetre nakon aplikacije 1 000, 2 000, odnosno 4 000 mg BDE-209/kg tm/dan. Interna doza u našoj studiji korelisala je sa eksternom dozom prema jednačini: interna doza (mg BDE-209/kg jetre) = 0,0002 ' eksterna doza (mg/kg tm/dan) + 0,0622 (r = 0,972; p lt 0,05). Hepatotoksičnost je potvrđena na osnovu nalaza o povećanju aktivnosti enzima AST i γ-GT, kao i stepena patohistološkog oštećenja jetre. Najniža BMDL5 u eksperimentu od 0,07228 mg BDE-209/kg jetre, koja koreliše sa eksternom dozom od 39 mg/kg tm/dan izračunata je za aktivnost AST i ukazuje na to da je aktivnost AST ujedno i najosetljiviji biomarker hepatotoksičnosti BDE-209 kod subakutno eksponovanih pacova. Zaključak. Rezultati prezentovane studije daju doprinos pitanju toksikološkog profila BDE-209 sa fokusom na odnos između interne doze i hepatotoksičnih efekata. Kritična interna doza za efekat na AST od 0,07 mg/kg jetre, koja koreliše sa eksternom dozom od 39 mg/kg tm/dan, jeste ujedno i najniža kritična doza do sada definisana za hepatotoksične efekte BDE-209. Kritičan efekat koji se bazira na dozi u ciljnom tkivu u većini slučajeva može se smatrati preciznije definisanim od kritičnog efekta definisanog na bazi oralno primenjene doze, naročito za nedegradabilne supstance sa niskim stepenom apsorpcije, kao što je BDE-209.