2-Isopropylthioxanthone (2-ITX), a photoinitiator used in ink for printing of food packaging materials, has been detected in products like milk and fruit beverages. Previous in vitro research demonstrated 2-ITX to 1) exert agonistic effects on the aryl hydrocarbon receptor (AhR), 2) exert antagonistic effects on both the androgen (AR) and estrogen receptor (ER), and 3) to increase aromatase activity. To validate these findings in vivo, male rats were treated by gavage with 50, 150 or 500 mg 2-ITX/kg b.w. per day from postnatal day 23 to 53. For comparison, other groups were treated with 50 ng TCDD/kg b.w./day (AhR agonist), 30 mg bicalutamide/kg b.w./day (Casodex, AR antagonist) or 50 mg flutamide/kg b.w./day (AhR agonist and AR antagonist). 2-ITX, from the lowest dose onwards, decreased the weight of the ventral prostate, and from the middle dose onwards the weight of the seminal vesicles and coagulating gland. The highest dose of 2-ITX reduced the number of spermatozoa in the cauda of the epididymis. Similar effects, but more severe, were induced by flutamide and bicalutamide. Epididymal weight, caput sperm count and preputial separation were negatively affected by Casodex and flutamide but not by 2-ITX. The two highest doses of 2-ITX as well as TCDD increased liver weight. Whole genome mRNA expression profiling of the liver revealed similarity between the effects of 2-ITX and flutamide. In addition, many genes induced by TCDD were also induced by 2-ITX and flutamide. These results demonstrate 2-ITX to express AhR agonistic and AR antagonistic activities, both in vitro and in vivo.
Overall design
Male Wistar rats (PND23, mean body weight (b.w.) 46 g, n = 45 in total) were housed in cages (3 per cage) in a room with controlled temperature (±22°C) relative humidity (±55%) and a 12:12 h light:dark cycle (lights on at 7:00 AM). The rats were fed a phytoestrogen-free diet (Research Diet Services, Wijk bij Duurstede, the Netherlands). Feed and drinking water were provided ad libitum. The body weight of the animals was measured daily. The rats were dosed by oral gavage for 31 subsequent days (PND 23-53) between 9 and 11 AM with either corn oil alone (0.5 ml per 100 g b.w.) for the vehicle control group, or three different doses of 2-ITX (50, 150 or 500 mg/kg b.w./day, further referred to as 2-ITX-50, 2-ITX-150 and 2-ITX-500), or 50 ng/kg b.w./day TCDD (strong AhR agonist), or 50 mg/kg b.w./day flutamide (AR antagonist and AhR agonist) or 30 mg/kg b.w./day Casodex (AR antagonist). Six rats were assigned to each of the six treatment groups; nine rats were assigned to the control group.
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