Octahydro-tetramethyl-naphthalenyl-ethanone (OTNE) is a fragrance ingredient that is formed as a mixture of isomers with a basic unsaturated alkyl cyclic ketone structure. The main isomer is 1-(1,2,3,4,5,6,7,8-octahydro-2,3,8,8-tetramethyl-2-naphthalenyl)ethanone (β-isomer). Two other predominant isomers within the mixture are 1-(1,2,3,4,6,7,8,8a-octahydro-2,3,8,8-tetramethyl-2-naphthalenyl)ethanone (α-isomer) and 1-(1,2,3,5,6,7,8,8a-octahydro-2,3,8,8-tetramethyl-2-naphthalenyl)ethanone (γ-isomer). OTNE is used as a perfume ingredient in soap, shampoo, cologne, liquid detergent compounds, and malodor-reducing compounds. Male and female F344/NTac rats and B6C3F1/N mice were administered OTNE (greater than 92.3% pure with respect to the 3 prominent isomers) dermally for 3 months. Genetic toxicology studies were conducted in Salmonella typhimurium, Escherichia coli, and rat and mouse peripheral blood erythrocytes.
Groups of 10 male and 10 female core study rats and mice received no treatment (untreated control) or dermal application of OTNE in 95% aqueous ethanol at concentrations of 0% (vehicle control), 6.25%, 12.5%, 25%, 50%, or 100% (neat) 5 days per week for 3 months. Animals in the 100% OTNE groups were compared to untreated controls, and the remaining dosed groups were compared to the vehicle controls. Groups of 10 male and 10 female special study rats received the same doses for 22 days. Formulations were administered at a volume of 0.5 mL/kg body weight (rats) or 2.0 mL/kg body weight (mice), which resulted in mice receiving higher doses (mg/kg) of OTNE than rats. Dose ranges for rats and mice were estimated as 31.25 to 500 mg OTNE/kg body weight and 125 to 2,000 mg/kg, respectively. All rats and mice survived to the end of the study. Final mean body weights and body weight gains of dosed male and female rats were similar to those of the respective control groups with the exception of the 100% OTNE male rats, which had a statistically significant decrease in mean body weight gain compared to the untreated controls. The final mean body weights of 6.25%, 25%, and 50% OTNE male mice and mean body weight gains of 6.25% and 25% OTNE male mice were significantly less than those of the vehicle control group; those of 100% OTNE male mice were significantly less than those of the untreated controls. Body weights of female mice were unaffected by OTNE treatment. In rats, alanine aminotransferase activities were significantly decreased in all dosed groups of males and in 25% to 100% OTNE females; furthermore, alkaline phosphatase activities were significantly decreased in 100% OTNE males and females. Erythrocyte counts, hemoglobin concentrations, and hematocrit values were significantly decreased in male mice administered 25% OTNE or greater and in 100% OTNE female mice. OTNE exposure via dermal application exhibited the potential to be a reproductive toxicant in male and female B6C3F1/N mice.
In rats, relative liver weights of 50% OTNE males and the absolute and relative liver weights of 100% OTNE males and 50% and 100% OTNE females were significantly greater than those in the respective control groups. In male and female mice, the absolute and relative liver weights of all dosed groups were significantly greater than those of the respective control groups with the exception of the absolute liver weight in 6.25% OTNE males. In addition, the relative kidney weights of 100% OTNE male and female rats were significantly increased, and the absolute thymus weights of 100% OTNE male and female mice and relative thymus weight of 100% OTNE female mice were significantly decreased compared to their respective control groups. Histologically, the incidence of mild centrilobular hypertrophy was significantly increased in male mice treated with 100% OTNE compared to the untreated control group.
In male and female rats administered 12.5% to 50% OTNE, the incidences of minimal to mild hyperplasia and hyperkeratosis (except in 12.5% OTNE males) at the site of application were significantly greater than those in the vehicle control groups; the incidences of these lesions in 100% OTNE males and females were significantly greater than the untreated control incidences.
In the skin of mice at the site of application, the incidences of minimal to moderate hyperplasia and chronic active inflammation were significantly increased in all dosed groups. The incidences of minimal to mild hyperkeratosis were significantly increased in males administered 12.5% OTNE or greater and in all dosed groups of females. The incidences of fibrosis were significantly increased in all dosed groups of males except the 12.5% OTNE group, and in females administered 12.5% OTNE or greater. The incidences of epidermis suppurative inflammation were significantly increased in 100% OTNE males and in females administered 25% OTNE or greater. The incidences of hair follicle hyperplasia were significantly increased in males administered 50% or 100% OTNE and females administered 25% OTNE or greater. Furthermore, the incidences of minimal to mild nonneoplastic lesions noted in the skin adjacent to the site of application of male and female mice were considered secondary to the spread of the test material from the site of application rather than a systemic effect. Incidences of hyperplasia, chronic active inflammation, hyperkeratosis, and fibrosis in the skin adjacent to the site of application were significantly increased in 100% OTNE-treated male and female mice.
OTNE was not mutagenic in Salmonella typhimurium strains TA98, TA100, or TA102, or in Escherichia coli strain WP2 uvrA/pKM101, with or without exogenous metabolic activation. In vivo, increases in micronucleated reticulocytes and mature erythrocytes were observed in female B6C3F1/N mice and in mature erythrocytes in male B6C3F1/N mice following dermal application of OTNE for 3 months. In contrast, no increases in micronucleated reticulocytes were seen in male or female F344/NTac rats following dermal exposure to OTNE for 3 months. In rats, only the very young reticulocyte population is assessed in peripheral blood for micronucleus frequency due to rapid removal of damaged reticulocytes from circulation by the rat spleen.
Under the conditions of these 3-month dermal studies, the major target in F344/NTac rats and B6C3F1/N mice was the skin, site of application. Lesions were more prominent in mice than rats based upon the incidences and severities of hyperplasia, hyperkeratosis, and inflammation of the skin, site of application. Additionally, hepatic lesions were apparent in mice, but not rats. OTNE exhibited the potential to be a reproductive toxicant in male and female mice. These species differences could be attributed to dose, because mice received approximately four times the amount of OTNE on a mg/kg body weight basis than rats. In male and female rats, the lowest-observed-effect level (LOEL) of 12.5% OTNE was based on the increased incidences of skin lesions. In male and female mice, the LOEL was 6.25% OTNE, based on the increased incidences of skin lesions and increased relative liver weights.
National Toxicology Program (NTP). 2016. NTP technical report on the toxicity studies of octahydro-tetramethyl-naphthalenyl-ethanone (OTNE) administered dermally to F344/NTac rats and B6C3F1/N mice. Research Triangle Park, NC: National Toxicology Program. Toxicity Report 92. https://doi.org/10.22427/NTP-TOX-92