2-aminoethanol

Endpoint summary

Link to relevant study record(s)

Reference

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

test procedure in accordance with national standard methods with acceptable restrictions

Objective of study:

toxicokinetics

Qualifier:

no guideline followed

Principles of method if other than guideline:

The absorption, distribution and metabolism of topical [14C]-MEA was studied in vivo, using athymic nude mice and human skin grafted onto athymic nude mice.

GLP compliance:

no

Specific details on test material used for the study:

RADIOLABELLING INFORMATION
- Specific activity: 4 µCi/mmol
- Locations of the label: [1,2-14C]ethanolamine-HCl

Radiolabelling:

yes

Remarks:

C14 ethanolamine

Species:

mouse

Strain:

other: nude

Sex:

not specified

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Harlan Industries
- Weight at study initiation: 30 g

Route of administration:

dermal

Vehicle:

ethanol

Details on exposure:

TEST SITE
- Area of exposure: 1.45 cm²

REMOVAL OF TEST SUBSTANCE
- Washing (if done): none

TEST MATERIAL
- Amount(s) applied (volume or weight with unit): 4 µg

VEHICLE
- Amount(s) applied (volume or weight with unit): 10 µL

USE OF RESTRAINERS FOR PREVENTING INGESTION: no

Duration and frequency of treatment / exposure:

24 hours, single exposure

Dose / conc.:

4 other: µg/animal

Remarks:

radioactive dose of 3.6 µCi to a 1.45-cm²

No. of animals per sex per dose / concentration:

5 animals in total per treatment group

Control animals:

yes

Positive control reference chemical:

Animals were injected intraperitoneally with the labelled test substance.

Details on dosing and sampling:

PHARMACOKINETIC STUDY (Absorption, distribution, excretion)
- Tissues and body fluids sampled : exhaled air, urine, faeces, liver, kidney, lung, brain, heart, muscle

Details on absorption:

The results indicated that topical applied 2-aminoethanol penetrates the skin and is widely distributed in the body, radioactivity being detected in all the tissues and organs examined. Percutaneous penetration of the skin appears however to be relatively slowly, demonstrated by a marked time lag in the initial appearance of labelled carbon dioxide between topical and intraperitoneal treatment. Radioactivity in expired CO2 was detected 5 min after an intraperitonealadministration of 2-aminoethanol, while no radioactivity in expired air was detected during the first 20 min post-topical application.

Details on distribution in tissues:

24% of the applied radioactive dose was recoved in the liver. Further recovery of the administered radioactive dose was at skin administration site (24.3%), as exhaled CO2(over 18%), in urine (4.6%), in kidneys (2.5%) and in feces (1.8%). Lungs, brain, and the heart contained 0.55, 0.27, and 0.15% of the dose, respectively.

Key result

Test no.:

#1

Transfer type:

blood/brain barrier

Observation:

distinct transfer

Details on excretion:

Over 18% of the topical radioactive dose was oxidized to [14]CO2 and 4.6% was excreted in the urine and 1.8% in feces over 24 hr.

Metabolites identified:

yes

Details on metabolites:

The substance is readily metabolized in the skin as well as in other organs and tissues in the mouse. Liver is a major site for metabolism of 2-aminoethanol. Extensive metabolization was indicated by appearance of labelled carbon dioxide in skin and hepatic amino acids, proteins and incorporation into phospholipids, and by recovery of over 18% of radioactive dose as [14]-CO2. Urea, glycine, serine, choline, and uric acid were the urinary metabolites of 2-aminoethanol.

Results summary:

Results details:

Distribution of radioactivity in grafted and ungrafted athymic nude mice 24 h after topical application of ethanolamine (n=5)

Organ/tissue	Human skin grafted nude mouse	ungrafted nude mouse
heart	0.15 ± 0.02	0.13 ± 0.01
brain	0.27 ± 0.07	0.25 ± 0.04
lungs	0.55 ± 0.09	0.63 ± 0.03
kidneys	2.53 ± 0.15	2.24 ± 0.19
liver	24.30 ± 3.82	25.80 ± 4.1
muscle gastroeneminus	398 ± 49*	427 ± 39*
skin application site	18.4 ± 2.7	12.1 ± 0.93
skin untreated	201 ± 34*	275 ± 24
urine	4.60 ± 0.57	5.20 ± 0.72
feces	1.82 ± 0.21	0.98 ± 0.64
cotton swabs	2.85 ± 0.36	3.28 ± 0.25

data represent means ± SE percentage of administered dose; * dpm/mg tissue

Radioactivity in proteins and amino acids isolated from the liver, human skin grafts and mouse skin after topical application

	Liver*	Graft**	Mouse skin**
Protein (dpm/mg)	958, 983	241, 199	119, 157
Amino acids***
Glycine	47.1, 44.6	38.6, 39.4	40.2, 42.8
Serine	22.2, 18.3	traces only	traces only
Glutamic acid	10.2, 8.1	15.4,13.8	15.8, 14.5
Alanine	2.7, 1.9	6.3, 6.4	5.9, 6.5
Aspartic acid	1.4, 1.1	3.1, 4.1	3.8, 3.2
Proline	13.6, 14.9	34.2, 34.9	31.9, 33.1

* individual values from 2 grafted mice

** individual values from 2 grafted mice and two ungrafted mice

*** percentage of radioactivity applied to chromatographic columns

Description of key information

Topically applied MEA penetrates the skin, is widely distributed and is extensively metabolised in the body. A major site for metabolism is the liver. Extensive metabolism was indicated by the incorporation of radiolabelled carbon into hepatic amino acids, proteins and phospholipids. Urea and glycine were the major urinary metabolites of MEA.

Regarding a quantitative figure for dermal absorption, the results of in vivo studies are preferred above the results of in vitro studies. In the in vivo study (Klain, 1985) the potential absorbed dose amounted to about 75% after 24 hours exposure. As workers are not exposed externally for more than 8 hours and assuming that a lower amount of substance was present in the skin (potentially absorbed amount) at t=8 hours compared to t=24 hours and that not the whole amount of substance present in the skin will eventually become systemically available, a correction factor of 2 will be used to derived the dermal absorption figure workers, i.e., 75/2 = 37.5%. For consumers the percentage of 75% is proposed as the default exposure duration for consumers is 24 hours (note that this is a very conservative figure for consumers as consumers will probably not be exposed for 24 hours/day).

Additional information

1. Physical-chemical properties

MEA (MW 61.08 g/mol) is a liquid with a melting point of 14 °C, a boiling point of 167 °C at 1013 hPa and a measured vapour pressure of 0.5 hPa at 25°C. The octanol-water partition coefficient (log Pow) is -2.3 at 20 °C and the substance is fully miscible with water.

 

2. Data from toxicity studies

The systemic effects after acute oral and dermal exposure show that the substance becomes bioavailable and reaches different organs. In the acute oral toxicity study (Myers, 1988) a LD50 of 1089 mg/kg bw was observed. Clinical signs were observed: sluggishness, slight piloerection, slight red crust on perinasal, periocular, or periurogenital fur, pallor, slight emaciation, kyphosis, unkempt appearance. The necropsy revealed mottled or dark red lungs and lesions in stomach, dark red kidneys. Other investigators established an oral LD50 value in rats of 1515 mg/kg bw (BASF AG, 1966). Animals exhibited calm behavior and abdominal position, slight staggering and piloerection, squatting posture. Animals that survived to study termination showed no internal abnormalities at necropsy. The dermal LD50 was 2504 mg/kg bw in rats (Union Carbide, 1988). Clinical signs were noted (erythema, edema, necrosis, ecchymosis, prostration, desquamation, alopecia, scabs, sluggishness, emaciation, ulceration) and animals subjected to a gross pathologic evaluation exhibited salmon-colored to dark red lungs; dark red trachea; mottled dark red thymus; hemorrhaged intestines, kidneys of 1 with a pitted surface, liquid and/or gas filled stomachs and intestines. No evidence of systemic toxicity was reported upon acute inhalation exposure to MEA; the LC50 for 6 hours exposure was > 520 ppm (1300 mg/m³) (Union Carbide, 1988). Exposure of rats to MEA for 28 days by inhalation caused concentration-related lesions in larynx, trachea and lung at 50 and 150 mg/m³(BASF AG, 2010). No systemic effects were observed at the tested concentrations (10, 50 and 150 mg/m³).

 

3. Absorption, distribution, metabolism, excretion

In vivo studies

No information is available on toxicokinetics of MEA regarding the oral and inhalation route.

The absorption, distribution and metabolism of topically administered [¹⁴C]-MEA was studied in vivo, using athymic nude mice and human skin grafted onto athymic nude mice (Klain et al, 1985). The substance was applied at a chemical dose of 4.0 µg and a radioactive dose of 3.6 µCi to a 1.45 cm² graft area, using ethanol as vehicle. The same dose was applied to a similar area of non-grafted mice or administered intraperitoneally to another group of non-grafted mice. Expired air and urine were collected over a period for 24 hours. Radioactivity was determined periodically. At the end of the sampling period skin and selected organs were analysed.

The results indicated that topical applied MEA penetrates the skin and is widely distributed in the body, radioactivity being detected in all the tissues and organs examined. Percutaneous penetration of the skin appears however to be relatively slowly, demonstrated by a marked time lag in the initial appearance of labelled carbon dioxide between topical and intraperitoneal treatment. Radioactivity in expired CO₂was detected 5 min after an intraperitoneal administration of MEA, while no radioactivity in expired air was detected during the first 20 min post-topical application. The substance is readily metabolised in the skin as well as in other organs and tissues in the mouse. Liver is a major site for metabolism, containing over 24% of the applied radioactive dose. Further recovery of the administered radioactive dose was at skin administration site (24.3%), as exhaled CO₂(over 18%), in urine (4.6%), in kidneys (2.5%) and in feces (1.8%). Lungs, brain, and the heart contained 0.55, 0.27, and 0.15% of the dose, respectively. Extensive metabolisation was indicated by appearance of labelled carbon dioxide in skin and hepatic amino acids, proteins and incorporation into phospholipids, and by recovery of over 18% of radioactive dose as¹⁴CO₂. Urea, glycine, serine, choline, and uric acid were the urinary metabolites of MEA.

 

In vitro studies

Skin penetration of MEA was studied in vitro (Klain et al, 1985) by applying 5 µL of solution to 0.8 cm² area of pig skin, resulting in a dose of 4 µg/cm² and a radioactive dose of approximately 0.05 µCi. The results show that percutaneous penetration of MEA was quite slow, with ca. 5% penetrating the skin 50 hours post-application. Ca. 11% was lost from the skin due to evaporation and the bulk of the dose 62% remained in the skin. In separate experiments 7 to 9 times as much radioactivity was recovered from the upper 100 µm layer (mostly epidermis) as compared to the recovery from the remaining dermis. It should be noted that the in vitro penetration rate of MEA in pig skin was considerably slower than the rate observed in the in vivo experiment (see data in vivo). This discrepancy may be due to several experimental variables, including the differences in species, the thickness of the skin, or the presence of the microcirculation system in human or mouse skin which would facilitate the removal of the chemical from the skin.

 

In another study (Sun, 1996) the skin penetration of MEA was tested in an in vitro model with full thickness skin preparations from mice, rats, humans and rabbits. [¹⁴C]-MEA was applied to skin discs as either an undiluted liquid or as an aqueous solution at target doses of 4 mg/cm². An "infinite dose" or an amount of the test compound that would not be entirely absorbed by the skin during the 6 h exposure period was used to allow the calculation of steady-state penetration rates and permeability constants. The steady-state penetration rates were determined to be 42.5, 123.1, 73.8, and 7.9 μg/cm²/h for the undiluted dose of [¹⁴C]-MEA, while the permeability constants were calculated to be 0.42 x 10^-4, 1.21 x 10^-4, 0.72 x 10^-4, and 0.08 x 10^-4cm/hr for rat, mouse, rabbit, and human skin preparations, respectively. Comparing undiluted and water diluted doses of MEA, the results showed that there was generally less skin penetration of the undiluted material than that for the diluted test substance.The results suggest that the potential percutaneous absorption of MEA would be less for humans than it would be for rats, rabbits, and mice.

 

Conclusion

The results indicate that topically applied MEA penetrates the skin, is widely distributed and is extensively metabolised in the body. A major site for metabolism is the liver. Extensive metabolism was indicated by the incorporation of radiolabelled carbon into hepatic amino acids, proteins and phospholipids. Urea and glycine were the major urinary metabolites of MEA.

Regarding a quantitative figure for dermal absorption, the results of the in vivo study are preferred above the results of the in vitro studies. In the in vivo study (Klain, 1985) the potential absorbed dose amounted to about 75% after 24 hours exposure. As workers are not exposed externally for more than 8 hours and assuming that a lower amount of substance was present in the skin (potentially absorbed amount) at t=8 hours compared to t=24 hours and that not the whole amount of substance present in the skin will eventually become systemically available, a correction factor of 2 will be used to derived the dermal absorption figure workers, i.e., 75/2 = 37.5%. For consumers the percentage of 75% is proposed as the default exposure duration for consumers is 24 hours (note that this is a very conservative figure for consumers as consumers will probably not be exposed for 24 hours/day).