2-Hydroxy-4-methoxybenzophenone (HMB) occurs naturally in flower pigments and is synthesized for use in sunscreens, as a UV stabilizer in various cosmetic products, and in plastic surface coatings and polymers. Toxicity studies of HMB were performed in F344/N rats and B6C3F1 mice, by administering HMB in feed and by topical application, in studies of 2 weeks' (5 animals/sex, dose and species) and 13 weeks' (10 animals/sex, dose and species) duration. Assessments included hematology, clinical chemistry, urinalysis, reproductive toxicity, and histopathologic evaluations.
In both 2- and 13-week dosed feed studies, rats received diets containing 0, 3125, 6250, 12500, 25000, or 50000 ppm HMB. One high-dose female rat died during the 2-week study. Body weight gains of high-dose male and female rats were reduced in the 13-week study. Liver and kidney weights were increased in dosed rats in both studies. In the 2-week studies, enlarged livers were associated with a marked hepatocyte cytoplasmic vacuolization in rats receiving diets containing concentrations of 6250 ppm HMB or higher; renal lesions, consisting of dilated tubules and regeneration of tubular epithelial cells, were found primarily in high-dose rats. In the 13-week studies, kidney lesions progressed to include papillary degeneration, or necrosis, and inflammation, while the liver lesion appeared to regress; liver enzymes in serum remained elevated. Rats receiving a diet with 50000 ppm HMB showed markedly lower epididymal sperm density and an increase in the length of the estrous cycle at the end of the 13-week studies.
In 2-week dermal studies, rats received topical applications of 1.25 to 20 mg of HMB in an acetone or lotion vehicle. The only effects noted were small and variable increases in liver and kidney weights, reaching statistical significance primarily in the higher dose groups. In 13-week studies, rats received topical doses from 12.5 to 200 mg/kg HMB in acetone. Kidney weights were elevated in dosed groups of female rats. No other findings were attributed to HMB treatment.
In 2- and 13-week dosed feed studies, mice received feed containing 0, 3125, 6250, 12500, 25000, or 50000 ppm HMB. A dose-related increase in liver weight associated with hepatocyte cytoplasmic vacuolization was the only finding in mice in the 2-week studies. Decreased body weight gains were dose-related in mice in the 13-week studies; mild increases in liver weights were seen in dosed mice of both sexes. Kidney weights were increased variably in dosed females. Microscopic lesions were noted only in the kidneys of males receiving 50000 ppm HMB; these included eosinophilic protein casts in dilated renal tubules and a mild inflammation associated with the dilated tubules. Mice in the highest dose group exhibited a decrease in epididymal sperm density and an increase in length of the estrous cycle.
In 2-week dermal studies, mice received topical applications from 0.5 to 8 mg HMB in an acetone or lotion vehicle. The only effects noted were minimal, variable increases in liver and kidney weights, primarily in the higher dose groups. In 13-week studies, mice received topical doses of 22.75 to 364 mg/kg in acetone. Kidney weights were increased variably in dosed male mice. Epididymal sperm density was decreased at all 3 dose levels evaluated (22.75, 91, and 200 mg/kg).
The genetic toxicity of HMB also was evaluated in mutagenicity studies with Salmonella typhimurium, in cytogenetic studies with Chinese hamster ovary (CHO) cells, and by evaluation of micronucleated erythrocytes in peripheral blood smears from mice in the 13-week studies. HMB was weakly mutagenic in Salmonella with metabolic activation, and induced sister-chromatid exchanges and chromosomal aberrations in CHO cells in the presence of a metabolic activation system. There was no increase in the frequency of micronucleated erythrocytes in the blood of mice receiving HMB.
In summary, HMB produced generally similar effects following topical and oral administration to rats and mice. Consistent findings included decreases in epididymal sperm density, lengthened estrous cycle, and increased liver and kidney weights. Mice in the dosed feed studies exhibited microscopic changes in the kidneys, comprising tubular dilatation with eosinophilic protein casts. Dilatation, tubular regeneration, papillary degeneration, and inflammation were noted in the kidneys of rats; and liver lesions consisting of an apparently reversible hepatocyte cytoplasmic vacuolization occurred in both rats and mice. A no-observed-adverse-effect level (NOAEL) for microscopic lesions was 6250 ppm HMB in the diet for rats and mice. A NOAEL was not reached for decreased epididymal sperm density in the 13-week dermal study in mice (<23 mg/kg/day).