Inflammatory and chloracne-like skin lesions in B6C3F1 mice exposed to 3,3',4,4'-tetrachloroazobenzene for 2 years

Abstract

Exposure to dioxin and dioxin-like compounds (DLCs) has been connected to the induction of chloracne in humans and animals. 3,3',4,4'-Tetrachloroazobenzene (TCAB) is an environmental contaminant that induces chloracne in humans. TCAB has been studied only to a limited extent in laboratory animals. While performing a 2-year gavage study in B6C3F1 mice to evaluate the toxic and carcinogenic effects of TCAB, we also explored potential chloracnegenic properties. Groups of 50 male and 50 female B6C3F1 mice were exposed by gavage to TCAB at dose levels of 0, 3, 10 and 30 mg/kg for 5 days a week for 2 years. The animals developed treatment-related gross inflammatory skin lesions, which were characterized histologically by inflammation, fibrosis, hyperplasia, and ulcers. Additionally, many of the animals developed follicular dilatation and sebaceous gland atrophy, consistent with chloracne-like lesions. This current 2-year study supports recently published papers showing susceptibility to chloracne in mouse strains other than hairless mice. The chloracne-like lesions were not clinically evident; therefore, our study highlights the need for careful examination of the skin in order to identify subtle lesions consistent with chloracne-like changes in rodents exposed to dioxin and DLCs. Since previous short-term studies did not demonstrate any skin lesions, we suggest that reliable assessment of all safety issues involving dioxin and DLCs requires evaluation following chronic exposure. Such studies in animal models will help to elucidate the mechanisms of dioxin-related health hazards.

Fig. 1

Inflammatory skin lesions. (A) Control mouse microscopy. Normal aspect of skin from a control animal. (B) Treated mouse microscopy. Histological section of skin from a female B6C3F1 mouse treated with 30 mg/kg of 3,3′,4,4′-tetrachloroazobenzene in the 2 year study. The mouse exhibited macroscopic ulceration on the torso, which histologically showed chronic active inflammation, epithelial hyperplasia (blue arrow), ulceration (black arrows), and dermal fibrosis (star). H&E.

Fig. 2

Appearance timeline of ulcers/abscesses. Number of animals with grossly observed ulcers/abscesses over the study period.

Fig. 3

Chloracne-like skin lesions. (A, C, E) Control mouse dorsal skin. Histological section from a control male B6C3F1 mouse in the 2-year study with 3,3′,4,4′-tetrachloroazobenzene. Hair follicles exhibit normality; adjacent sebaceous glands can be seen. H&E. (A) Black arrows indicate hair follicles. (C) Black arrows indicate hair follicles. Red arrows indicate sebaceous glands. (E) Black arrows indicate hair follicles. Red arrows indicate sebaceous glands. (B, D, F) Treated mouse dorsal skin. Histological section from male B6C3F1 mouse treated for 2 years with 30 mg/kg 3,3′,4,4′-tetrachloroazobenzene. Note dilation of hair follicles, flattening of lining epithelium and atrophy of adjacent sebaceous glands. No infiltration of inflammatory cells can be discerned. This animal was assigned a moderate degree of hair follicle dilation (i.e., 6 or more follicles segmentally dilated to greater than double the normal diameter within a low magnification field). H&E. (B) Black arrows indicate dilated hair follicles. (D) Black arrows indicate dilated hair follicles. Red arrows indicate atrophic sebaceous glands. (F) Black arrows indicate dilated hair follicles. Red arrows indicate atrophic sebaceous glands.