4-amino-m-cresol

Endpoint summary

Description of key information

According to the results of the key studies, Toxicokinetics parameters as Absorption, Distribution, Metabolisation and Excretion (ADME) for dermal and inhalation route were determined. The test substance 4 -amino-m-cresol was considered as low bioaccumulable potential substance by oral route and dermal route or intravenously according to the three in vivo key studies (OECD method 417 followed, GLP compliant, Klimisch 1). The excretion rate (mainly by the urine) after exposure was calculated at 92% of bioavailable substance in this routes. In oral route, the absorption rate was defined as 105% (oral gavage). An in vitro key study (Klimisch 2, Acceptable study, followed basic scientific principles or standards, GLP compliant) showed high permeability of the 4-amino-m-cresol accross TC7 cells which are human immortalized intestinal cells. Moreover, the bioavailable fraction of test item which reach the liver can be metabolized in three metabolites : N-acetyl-A074, A074 -glucuronide and N-acetyl-A074 -glucuronide.

According to the dermal abosrption in vitro key study which used the test item diluted at 2% (OECD 418 method followed, Klimisch 1, GLP compliant) was determined at 0.471% using pig skin samples or 0.26% when human skin samples were used. Metabolisation of the test item by skin cells (as keratinocytes or cells in human skin) was showed, the major metabolite found was 4 -(acetylamino)-3 -methyl-phenol (human skin samples in addition with reaction partner) or N-Acetyl-A074 (HaCaT cells).

Key value for chemical safety assessment

Bioaccumulation potential:

low bioaccumulation potential

Absorption rate - oral (%):

105

Absorption rate - dermal (%):

0.471

Additional information

To assess the ADME and toxicokinetics parameters of the registered substance 4-amino-m-cresol, 4 in vitro key studies and 3 in vivo key studies were available.

- One key study (Klimisch 2, no OECD guideline but comparable and scientifically robust method, GLP compliant) used human skin samples to performed a dermal penetration test and metabolism test. A 15 mg/g of test item in typical color cream formulation was used in addition with a reaction partner (4 -amino-2 -hydroxytoluene sulfate, A027). A diffusion cell was used with skin samples. The test item was applied for 1 hours on skin (150 mg). The receptor fluid was collected, extracted and analysed by radio-HPLC approach. The penetration rate was measured at 0.26%±0.09%. Metabolite profile was determined by radio-HPLC and showed the presence of 4 -(acetylamino)-3 -methyl-phenol from the test item (which was completely depleted). (Maas WJM, 2011)

- A Dermal penetration in vitro key study was performed accordingly to OECD 428 method and OECD GLP principles and was quoted as Klimisch 1. Radiolabelled 2 % 4-amino-m-cresol was used in a typical oxidative hair dye formulation in the presence of reaction partner in diffusion cell with pig skin samples as test system. The receptor fluid was sampled at 16, 24, 40, 48, 64 and 72 hours and analysed by means of scintillation counter to determine radioactive concentration. Absorption rate across the pig skin samples were measured at maximuml amount of 1.1410 ± 0.611 µg/cm2 corresponding to 0.471%. Some studies of the same laboratory and experimental conditions were performed with 0.5, 1 or 1.5% of test item were available, and the maxium amount of penetration was dose-related. (Sieber TP, 2007)

- The third in vitro key study was performed to assess metabolism parameters of the test substance using 0.862, 8.62 and 24.6 µL/mL of test item in medium (Acceptable study report, followed scientific principles/standards, Klimisch 2). Substance was incubated with HaCaT cells, an immortalized keratinocyte human cell lines (500 000 cells per well) for 3 and 24 hours. Supernatant was sampled and analysis with HPLC-UV/RAD/Q-ToF-mass spectrometer for quantification and structure elucidation. One metabolite, N-Acetyl A074, was observed in the incubations at both 3 and 24 hour intervals, in all test concentrations. The above results conclude that incubation of 4-amino-m-cresol (A074) with HaCaT cells at concentrations of 7, 70 and 200 µM for 24 hours resulted in formation of N-Acetyl-A074 as a single metabolic biotransformation product. (Obringer, 2013)

- The fourth key study was an in vitro metabolism test performed with Cryopreserved Human Hepatocytes (Acceptable study report, followed scientific principles/standards, Klimisch 2) incubated in suspended hepatocyte or plated hepatocytes for 3 or 24 hours. The test item was used at different dose level : 1 and 10 µg/mL (suspended cells) and 0.862, 8.62, 24.10 µg/mL (plated hepatocytes). Supernatant was sampled and analysis with HPLC-UV/RAD/Q-ToF-mass spectrometer for quantification and structure elucidation. Only one metabolite (A074 glucuronide) was formed in the suspended hepatocyte study. In plated hepatocytes, the metabolites N-Acetyl A074, A074 glucuronide and N-Acetyl A074 glucuronide were observed. The above results conclude that incubation of 4-amino-m-cresol (A074) with suspended human hepatocyte cells at concentrations of 1 and 10 µg/mL for 3 hours resulted in the formation of A074-glucuronide as a single metabolite product.Three metabolites, i.e. N-Acetyl A074, A074 glucuronide and N-Acetyl A074 glucuronide were observed after 24 hour incubation with plated human hepatocytes at 0.862, 8.62 and 24.6 µg/mL. (Krebsfanger N, 2003)

- Three in vivo studies were performed to assess ADME and Toxicokinetics parameters of the registered substance on Wistar female rats. These studies were performed in the same experimental conditions and dose but with differents routes of exposure (oral, dermal and intravenous) . These study followed OECD guideline 417 method, OECD GLP principles, and were quoted as Klimisch 1. The purpose of the entire study was to obtain information on the toxicokinetic parameters of absorption,distribution, metabolism and excretion of the test substance in Wistar rats following a single oral, dermal or intravenous dose. Rats were dosed with 60 mg/kg bw (i.v), 60 mg/kg bw (oral), and 12 and 60 mg/kg (dermal). Radiolabelled test substance was used. (Wenker MAM, 2013)

After oral administration to female Wistar Crl:WI rats, 4-amino-m-cresol was extensively absorbed (105% of the administered dose based on urine data and 86% based on plasma data), extensively metabolized and excreted mainly via the urine(92%). No major accumulation of the test material seems to occur in the body 72 hours after administration (0.82%). At termination of the study of intravenous route, average total radioactivity in blood, carcass plus tissues was 1% of the administered dose indicating no major accumulation of radioactivity after 72 hours. There were no tissues with a residual concentration significantly higher than that observed in blood. The percentage of radioactivity in the carcass was 0.681%. Plasma concentration of test substance equivalents at termination were 0.077 mg/kg. Blood concentration at termination was 3.281 mg/kg (43 times higher than plasma concentrations) indicating distribution of the test substance into the red blood cells. The highest residual concentration was observed in theliver (0.054% of administered dose).

Based on above, dermal absorption of 4-amino-m-cresol was high (36.3% or 0.28 mg/cm2) after 24 h exposure at dose level of 75 mg/kg (0.75 mg/cm2) using DMSO as vehicle and was low (1.05% or 0.001 mg/cm2) after 30 minute exposure at dose level of 15 mg/kg (0.15 mg/cm2) using water based vehicle (color cream formulation). When absorbed, the test substance extensively metabolized and excreted mainly via the urine (32.13%).

Toxicokinetics were measured and calculated for each exposure routes:

	Tmax (hours)	Cmax (mg/kg)	AUC last (hours x mg/kg)	AUC inf  (hours x mg/kg)	T1/2 (hours)	Dose normalized Cmax  (hours x mg/kg)	Dose normalized Auc inf  (hours x mg/kg)	Dose normalized Clast  (hours x mg/kg)	Elimination rate ( per hours)
oral	0.25	89.1	163	167	24	160	2.99	2.93	0.0289
intravenous	ns	ns	189	ns	ns	ns	ns	ns	ns
dermal	2	15.7	81.3	87.4	30.1	236	1.31	1.22	0.023

ns : not specified