Sixteen-day and thirteen-week studies
Sixteen-day studies were conducted by giving iodinated glycerol at doses up to 1,000 mg/kg to rats and up to 500 mg/kg to mice. All female rats and 4/5 male mice in the highest dose group died before the end of the studies; there were no dose-related effects on body weights of male or female rats or male mice at the end of the studies. The forestomach of 2/5 female mice that received 500 mg/kg was thickened and granular.
Thirteen-week studies were conducted by administering iodinated glycerol at doses up to 500 mg/kg to rats and mice. During these studies, 3/10 female rats and 1/10 female mice that received 500 mg/kg died. Final mean body weights of rats and mice that received 500 mg/kg were 4% lower than those of vehicle controls for males and 6%-7% lower for females.
Kidney tubular cell lesions, including cortical necrosis, regeneration, and calcification, were observed at increased incidences in the highest dose group of female rats. Lymphoid hyperplasia of the stomach was observed in dosed male and female rats. Kidney tubular cell regeneration was also observed in dosed female mice. Inflammation or abscesses of mild-to-moderate severity and hyperplasia, acanthosis, and/or hyperkeratosis of mild-to-moderate severity were observed in the forestomach of the highest dosed group of female mice.
Two-year studies
Body weight and survival
Two-year studies were conducted by administering 0, 125, or 250 mg/kg iodinated glycerol in deionized water by gavage, 5 days per week for 103 weeks, to groups of 50 male F344/N rats and 50 male B6C3F1 mice. Groups of 50 female F344/N rats and 50 female B6C3F1 mice were administered iodinated glycerol on the same schedule at lower doses of 0, 62, or 125 mg/kg because of the increased severity of kidney and stomach lesions in the 13-week studies. Mean body weights of high dose male rats were 5%-10% lower than those of vehicle controls from week 43 to week 68 and 10%-13% lower from week 72 to the end of the studies. Mean body weights of low dose male rats and high dose female rats were 4%-9% lower than those of vehicle controls from week 88 to the end of the studies. The survival of the high dose group of male rats was considerably lower than that of the vehicle controls after week 86. No other significant differences in survival were observed between any groups of rats of either sex (male: vehicle control, 28/50; low dose, 20/50, high dose, 2/50; female: 31/50; 30/50; 27/50). Mean body weights of dosed and vehicle control male mice were similar. Mean body weights of high dose female mice were 6%-8% lower than those of vehicle controls from week 40 to week 64 and were 9%-13% lower thereafter. No significant differences in survival were observed between any groups of mice of either sex (male: 36/50; 40/50; 32/50; female: 40/50; 33/50; 38/50).
Nonneoplastic and neoplastic effects
The incidence of mononuclear cell leukemia were increased in dosed male rats (vehicle control, 14/50; low dose, 29/50; high dose, 24/50).
Follicular cell carcinomas of the thyroid gland in male rats occurred at an increased incidence in low dose male rats (0/49; 5/49; 1/49). Reduced survival of high dose male rats may have been responsible for the decreased tumor incidence in this group relative to that in the low dose group. Follicular cell carcinomas were observed in one low dose and one high dose female rat. Follicular cell carcinomas of the thyroid gland have been observed in 3/293 water gavage vehicle control male F344/N rats and in 10/1,904 untreated control male F344/N rats.
Adenomas of the nasal cavity were observed in two high dose male rats. Adenomas of the nasal cavity have not been observed in 300 water gavage vehicle control male F344/N rats or in 1,936 untreated control male F344/N rats.
Squamous metaplasia and focal atrophy of the salivary glands were observed at increased incidences in dosed rats (squamous metaplasia--male: 0/48; 47/50; 48/49; female:1/49; 48/50; 49/50; focal atrophy--male: 1/48; 10/50; 30/49; female: 0/49; 4/50; 11/50).
In dosed female mice, adenomas of the anterior pituitary gland were increased (10/47; 15/45; 24/46). The incidences of adenomas of the harderian gland in dosed female mice were increased (6/50; 8/40; 13/50). A carcinoma of the harderian gland was observed in another high dose female mouse.
Dilatation of the thyroid gland follicle and follicular cell hyperplasia were observed at increased incidences in dosed mice (dilatation--male: 0/48; 28/50; 32/50; female: 4/48; 11/48; 10/48; hyperplasia--male: 3/48; 46/50; 34/50; female: 2/48; 25/48; 35/48). The incidences of follicular cell adenomas were 3/48, 6/50, and 0/50 for males and 2/48, 3/48, and 4/48 for females.
Hyperkeratosis and acanthosis of the forestomach were observed at increased incidences in high dose male mice (hyperkeratosis: 0/49; 0/49; 5/50; acanthosis: 0/49; 1/49; 5/50). Squamous cell papillomas were observed in female mice (1/49; 2/50; 5/49). The historical incidence of forestomach squamous cell neoplasms is 4/339 (1.2%) in water gavage vehicle control female B6C3F1 mice and is 18/1,994 (0.9%) in untreated control female B6C3F1 mice. Squamous cell neoplasms were not observed in male mice.
Genetic toxicology
Treatment of the base-substitution mutant S. typhimurium strains TA100 and TA1535 with iodinated glycerol in a preincubational protocol with and without S9 resulted in a dose-related increase in the number of revertant colonies; no increase in revertants was observed with the frame-shift mutant strains TA98 or TA1537. 3-Iodo-1,2-propanediol was also mutagenic in TA100 with or without S9; it was not mutagenic in TA98. Iodinated glycerol increased the number of trifluorothymidine-resistant cells in mouse lymphoma L5178Y/TK+/- assay in the absence of exogenous metabolic activation; it was not tested with activation. Iodinated glycerol induced sister chromatid exchanges (SCEs) and chromosomal aberrations in CHO cells without S9; with S9, the frequency of SCEs was increased more than without S9 but no chromosomal aberrations were induced. No increase in micronucleated polychromatic erythrocytes was observed in the bone marrow of B6C3F1 mice after injection with either iodinated glycerol or 3-iodo-1,2-propanediol.
Conclusions
Under the conditions of these 2-year gavage studies, there was some evidence of carcinogenic activity for male F344/N rats administered iodinated glycerol, as indicated by increased incidences of mononuclear cell leukemia and follicular cell carcinomas of the thyroid gland. Adenomas of the nasal cavity in two high dose male rats may have been related to the administration of iodinated glycerol. There was no evidence of carcinogenic activity for female F344/N rats administered 62 or 125 mg/kg iodinated glycerol by gavage for 103 weeks. There was no evidence of carcinogenic activity for male B6C3F1 mice administered 125 or 250 mg/kg iodinated glycerol by gavage for 103 weeks. There was some evidence of carcinogenic activity for female B6C3F1 mice administered iodinated glycerol, as indicated by increased incidences of adenomas of the anterior pituitary gland and neoplasms of the harderian gland. Squamous cell papillomas of the forestomach may have been related to the administration of iodinated glycerol.
Significant nonneoplastic lesions considered related to exposure of iodinated glycerol were squamous metaplasia and focal atrophy of the salivary gland in male and female rats. Dilatation of the thyroid gland follicle and follicular cell hyperplasia were observed in male and female mice.