Effect of 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) on Hormones of Energy Balance in a TCDD-Sensitive and a TCDD-Resistant Rat Strain

Abstract

One of the hallmarks of the acute toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is a drastically reduced feed intake by an unknown mechanism. To further elucidate this wasting syndrome, we followed the effects of a single large dose (100 μg/kg) of TCDD on the serum levels of several energy balance-influencing hormones, clinical chemistry variables, and hepatic aryl hydrocarbon receptor (AHR) expression in two rat strains that differ widely in their TCDD sensitivities, for up to 10 days. TCDD affected most of the analytes in sensitive Long-Evans rats, while there were few alterations in the resistant Han/Wistar strain. However, analyses of feed-restricted unexposed Long-Evans rats indicated several of the perturbations to be secondary to energy deficiency. Notable increases in ghrelin and glucagon occurred in TCDD-treated Long-Evans rats alone, which links these hormones to the wasting syndrome. The newly found energy balance regulators, insulin-like growth factor 1 and fibroblast growth factor 21 (FGF-21), appeared to function in concert in body weight loss-induced metabolic state, and FGF-21 was putatively linked to increased lipolysis induced by TCDD. Finally, we demonstrate a reverse set of changes in the AHR protein and mRNA response to TCDD and feed restriction, suggesting that AHR might function also as a physiological regulator, possibly involved in the maintenance of energy balance.

Toxicological characterisation of two novel selective aryl hydrocarbon receptor modulators in Sprague-Dawley rats

“…Typical pattern of body weight loss in TCDD-induced wasting syndrome for comparison with the changes caused by C2 and C4. These data originate from a previous study (Lindén, et al 2014), where TCDD-sensitive L-E rats were exposed to a single ig dose of 100 µg/kg TCDD (no statistical analysis was conducted) b 0,0 5,0e-9 1,0e-8 1,5e-8 2,0e-8 2,5e-8 3,0e-8 3,5e-8 testis a a b Fig. 4 The expression of Cyp1a1 induced by C2 (100 mg/kg/day) and C4 (75 mg/kg/day) vs. controls in liver, duodenum, kidney, lung and testis in S-D rats (n=5-6, mean ± SD).…”

“…This approach was statistically justified as we used a non-parametric approach (Kruskal-Wallis ANOVA) based on rank orders of the values in the experimental and control groups. We further verified the methodology with sera from TCDDsensitive L-E rats collected at 10 days after exposure to 100 µg/kg TCDD or the vehicle (corn oil) (Lindén, et al 2014). The control samples were run on the same ELISA plate and handled identically to the actual samples, except that the non-parametric test in this case was Mann-Whitney U since only two groups were compared.…”

“…2) + (7) + (6) n=5-6 in each group. a The data for the TCDD groups are from a previous study (Lindén, et al 2014), where TCDD-sensitive L-E and TCDD-resistant H/W rats were exposed to a single ig dose of 100 µg/kg TCDD and euthanised at 10 days. The cDNA for these samples had been reverse -transcribed previously, but qPCR was performed with the same primers and in the same conditions as for C2 and C4.…”

“…For comparison of C2 and C4 with TCDD, liver cDNA originating from a previous study (Lindén, et al 2014) was analysed with the same primers and in the same conditions as the samples from the current study. In the Lindén study, TCDD-sensitive L-E and TCDD-resistant H/W rats were exposed to a single ig dose of 100 µg/kg TCDD and euthanised on day 10.…”

“…Han-Wistar rats (Kuopio; H/W; n=5 per group), existing cDNA samples from a previous study were used (Lindén, et al 2014). RT-qPCR on these samples was performed with the same primers and in the same conditions, but for statistical analysis, the data were treated separately.…”