Relationships between Tissue Levels of 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), mRNAs, and Toxicity in the Developing Male Wistar(Han) Rat

Abstract

We compared the effects of a single acute dose, or chronic fetal exposure, to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on the male reproductive system of the Wistar(Han) rat. Tissue samples were taken from dams on gestation day (GD)16 and GD21, and from offspring on postnatal days (PND)70 and 120. Steady-state concentration of TCDD was demonstrated in the chronic study: body burdens were comparable in both studies. Fetal TCDD concentrations were comparable after acute and chronic exposure, and demonstrate more potent toxicity after chronic versus acute dosing. In maternal liver, cytochrome P450 (CYP)1A1 and CYP1A2 RNA were induced. In fetus, there was induction of both CYP1A1 and CYP1A2 RNA at medium and high doses, but inadequate evidence for induction at low dose in either study. The low level induction of CYP1A1 RNA at low dose in fetus argues against AhR activation in fetus as a mechanism of toxicity of TCDD in causing delay in balanopreputial separation (BPS), and the greater induction of CYP1A1 RNA in PND70 offspring liver from chronically-dosed dams suggests that lactational transfer of TCDD is crucial to this toxicity. These data characterize the maternal and fetal disposition of TCDD, induction of CYP1A1 RNA as a measure of AhR activation, and suggest that lactational transfer of TCDD determines the difference in delay in BPS between the two studies.

Tracing and analytical results of the dioxin contamination incident in 2008 originating from the Republic of Ireland

“…It is also appears that adverse effects in prenatal rats appear to occur from exposure during a relatively short time window (SCF 2001). Bell et al (2007aBell et al ( , 2007bBell et al ( , 2007c) also compared an acute exposure with a chronic exposure in pregnant rats and confirmed that an acute exposure results in relatively higher exposure of the foetus. However, in these studies the chronic exposure resulted in a delayed puberty in male off-spring at much lower doses than in the pups of mothers exposed to a single high dose.…”

“…The levels of 50, 100 and 200 pg TEQ g -1 , used for the assessment, however, may be a clear underestimation, because higher levels were found in the index loin (433 pg TEQ/g) and also the pooled samples in The Netherlands indicated higher individual levels (around 300 pg TEQ g -1 fat). Moreover, the high levels in the meat also pointed to the possibility of high levels in the liver, an effect well-known in rats exposed to high levels of dioxins (Hurst et al 2000a, Bell et al 2007c. Own data in pork from one of the latest dioxin incidents showed e.g.…”

Evaluation of Incidence Rates in Pre-Clinical Studies Using a Williams-Type Procedure

“…in Kandori et al (2005). Also, markedly unbalanced sample sizes may occur, e.g., n i = 42,...,74 in Bell et al (2007). For this reason, we investigated a number of unbalanced situations (Tables 6 and 7).…”

2-(4-Amino-3-methylphenyl)-5-fluorobenzothiazole is a ligand and shows species-specific partial agonism of the aryl hydrocarbon receptor

“…Total RNA from H4-II-E cells and MCF-7 cells was isolated, quantitated and 50 ng was reverse transcribed into cDNA and quantitative RT-PCR analysis performed essentially as described (Bell et al, 2007), except that confluent cultures were lysed with 0.2 ml of lysis buffer and the amount of cDNA used for multiplex PCRs was 2 ng. PCR efficiencies were empirically determined for each probe, and varied from 109-118% for rat genes and from 110-125% for human genes.The cDNA sequences of the human CYP1A1, -actin and AhR are listed in Table 2.…”

“…The induction of CYP1A1 RNA is a highly sensitive marker of AhR activation (Bell et al, 2007), and measurement of CYP1A1 RNA provides a quantitative measure of AhR activation, that is arguably superior to measuring P450 protein activity, since effects such as regulation of translation, or inhibition of enzyme activity, can vitiate interpretation, and the effects of compound metabolism can be minimised by measuring response at an early time point. This assay thereby enables a quantitative comparison between agonistic and antagonistic activities of AhR ligands.…”