Sodium 2-(1-carboxylatoethoxy)-1-methyl-2-oxoethyl isooctadecanoate

Endpoint summary

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

basic toxicokinetics in vitro / ex vivo

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

1979

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Objective of study:

absorption

Qualifier:

no guideline followed

Principles of method if other than guideline:

HAIR
- Principle of test: Samples of hair (tresses) are washed with formula containing ISL and/or commercial shampoo and the ease of removal and uptake of ISL were evaluated.
- Short description of test conditions: Some tresses were damaged with hydrogen peroxide and ammonium hydroxide. Damaged and undamaged tresses were washed with Pationic ISL, a formula where ISL is tagged at 3.5% level, rinsed with tap water, and then re-washed followed by several rinses by immersing in tap water. 3 damaged tresses were also washed using a commercial shampoo to determine the ease of removal of ISL by shampooing. The samples were air dried, pelletized, and radioactivity determined.
- Parameters analysed / observed: Radioactivity (ISL) of each hair sample

SKIN
- Principle of test:
To determine what quantity of ISL applied as an ingredient in an oil-in-water skin cream would be retained on skin
- Short description of test conditions:
5 test areas and varying exposure times, followed by rinsing and biopsy of the exposed skin area. Plugs were taken of the biopsies to obtain samples to be combusted and counted.
- Parameters analysed / observed: ISL as a function of length of exposure, repeated rinsing, and repeated application and rinsing

GLP compliance:

not specified

Specific details on test material used for the study:

SOURCE OF TEST MATERIAL : not reported

RADIOLABELLING INFORMATION
The test substance sodium isostearoyl-2-lactylate (ISL) was prepared with a specific activity of 1,335,947 disintegration/minute/mg by synthesizing with isotopic C14-labeled lactic acid.

STABILITY AND STORAGE CONDITIONS OF TEST MATERIAL : not specified

TREATMENT OF TEST MATERIAL PRIOR TO TESTING : not specified

OTHER SPECIFICS: ISL was chosen as the lactylate to be used after subjective evaluation yielded it had the most promise (not specified as to what constituted the most promise)

All ingredients of the formula that the test substance was a part of and thus was used to wash the hair:
- Lakeway 301-10, 37.5% wt.
- Clindrol 100 LM, 3.0% wt.
- Pationic ISL (test substance), 3.5% wt.
- Methyl paraben, 0.2% wt.
- Deionized water, 56.3% wt.

All ingredients of the cream that the test substance was a part of and thus was used to apply to skin:
- Dehydrag WAXO 5.0 % wt.
- Starfol IPM 2.0 % wt.
- Pationic 145A 2.0 % wt.
- Pationic ISL 3.0 % wt.
- Deionized water 82.6 % wt.
- Propylene glycol 5.0 % wt.
- Sodium citrate 0.2 % wt.
- Methyl paraben 0.2 % wt.

Radiolabelling:

yes

Remarks:

ISL at 3.5%

Species:

other: human (hair); pig (skin)

Sex:

not specified

Details on test animals or test system and environmental conditions:

HAIR TEST
Source: 8-inch long Remy Blue String hair
Details: Some tresses were damaged with hydrogen peroxide and ammonium hydroxide

SKIN TEST
Source: not specified
Details: no details on test animals or environmental conditions reported

Route of administration:

dermal

Vehicle:

water

Remarks:

Formula is 82.6% water

Details on exposure:

SKIN TEST
TEST SITE
- Area of exposure: On each of three test pigs, five areas (3 inches by 3 inches in area) were sheared to remove hair. The areas are noted in a figure: area A = between the ears; area B = left side, anterior dorsal; area C = right side, anterior dorsal; area D = left side, posterior dorsal; area E = right side, posterior dorsal.
- % coverage: not specified
- Type of wrap if used: not specified

REMOVAL OF TEST SUBSTANCE
- Washing (if done): The test area was rinsed by forcing 20-30 mL water from a syringe onto the test area and absorbing the rinse water with aKemwipe.
- Time after start of exposure: varied (see "Duration and frequency of treatment / exposure")

TEST MATERIAL
- Amount(s) applied (volume or weight with unit):
-Base amount of C14-ISL applied was 6.44 mg per 2" by 2" area or 1.61 mg per square inch.
-Volume of C14-ISL cream applied was 100-200 mg

Duration and frequency of treatment / exposure:

- area A: 5 minutes
- area B: 12 hours
- area C: 24 hours
- area D: cream applied and rinsed after 5 minutes; repeat. rinsed once a day for 6 more days (total time of rinse 7 days)
- area E: cream applied and rinsed after 5 minutes; application and rinse repeated for 6 more days (total time of exposure and rinsing 7 days)

Dose / conc.:

100 other: mg

Remarks:

100-200 mg cream applied per 2 inch by 2 inch area

No. of animals per sex per dose / concentration:

3 pigs with 5 test areas each

Control animals:

yes

Positive control reference chemical:

none

Details on dosing and sampling:

TOXICOKINETIC / PHARMACOKINETIC STUDY (Absorption, distribution, excretion)
- Tissues and body fluids sampled: skin and hair
- Time and frequency of sampling: varied for skin test (See "Any other information on materials and methods incl. tables")

Statistics:

Not reported

Type:

absorption

Results:

0.466 mg C14 ISL /g undamaged hair

Type:

absorption

Results:

0.362 mg C14 ISL/g damaged hair

Type:

absorption

Results:

0.193 mg C14 ISL /g damaged and rewashed hair

Type:

other: Retention (area A)

Results:

0.394 mg square inch

Type:

other: Retention (area B)

Results:

0.950 mg square inch

Type:

other: Retention (area C)

Results:

0.802 mg square inch

Type:

other: Retention (area D)

Results:

0.221 mg square inch

Type:

other: Retention (area E)

Results:

0.726 mg square inch

Details on absorption:

HAIR TEST
Initially, 70 mg C14-ISL were available per gram of hair. The results on absorption are based on the average of 6 measurements per treatment (undamaged, damaged, damaged and rewashed) and results were as follows: 0.466 mg C14-ISL/g undamaged hair; 0.362 mg C14-ISL/g damaged hair; 0.193 mg C14-ISL/g damaged and rewashed hair.

SKIN TEST
Application for 5 minutes followed by rinsing (area A): Retention of ~25% of the ISL
Application for 24 hours followed by rinsing (area C): Retention of ~50% of the ISL
Multiple rinsing for six days after one application (area D): Retention of >50% of the ISL
Multiple application and rinsing for 7 days (area E): greater take-up of ISL than area A, demonstrating that multiple applications, even followed quickly by rinsing, result in a cumulative effect

Details on distribution in tissues:

None reported

Metabolites identified:

not specified

HAIR TEST

The bonding strength of ISL to hair is demonstrated by the removal of less than half the original amount of ISL when tresses are rewashed with a commercial shampoo. Results were corrected for background by running a blank and for counting efficiency by comparison with certified C14 benzoic acid.

SKIN TEST

EXCLUSIONS:

For all areas of Pig #2 except area B, the retention values were consistently lower than the other two test animals Pig #2 showed a normal retention of ISL in area B and a comparatively higher average reading for area B than would be expected. Thus, area B was excluded from results / discussion.

Conclusions:

The test item sodium isostearoyl lactylate has shown to demonstrate high protein binding affinity in human hair and pig skin samples. In particular, application of skin cream containing 3.0% radiotagged Pationic ISL on pig skin showed retention of sodium isostearoyl lactylate after rinsing. Multiple applications of the Pationic ISL cream (e.g. over 7 days) resulted in higher retention of sodium isostearoyl lactylate. Also, after application of shampoo containing 3.5% radiotagged Pationic ISL on human hair (Remy Blue String hair), more than half of the original Pationic ISL remained on the hair after washing with commercial shampoo.

Executive summary:

Two in vitro studies were reported by Murphy (1979) with ISL. In the hair test, samples of hair (tresses) are washed with formula containing ISL and/or commercial shampoo and the ease of removal and uptake of ISL were evaluated.

The skin test was conducted to determine what quantity of ISL applied as an ingredient in an oil-in-water skin cream would be retained on skin. This absorption study was conducted to determine what quantity of C14-labeled test substance Sodium isostearoyl lactylate applied in an oil-in-water skin cream could be retained on skin. The cream was applied in five different test areas on pigs with varying exposure times and rinse and re-application methods.

In an hair absorption study, samples initially with 70 mg C14-ISL per gram of hair, the results were as follows: 0.466 mg C14-ISL/g undamaged hair; 0.362 mg C14-ISL/g damaged hair; 0.193 mg C14-ISL/g damaged and rewashed hair.

In the skin study, application for 5 minutes followed by rinsing showed retetnion of about 25% of ISL, application for 24 hours followed by rinsing showed about 50% of ISL, a single application followed by multiple rinsing over 6 days removed less than half the ISL, and multiple applications and rinsing for seven days showed greater take up than area A.

Area	Amount retained (mg square inch)
A	0.394
C	0.802
D	0.221
E	0.726

In conclusion, the test item sodium isostearoyl lactylate has shown to demonstrate high protein binding affinity in human hair and pig skin samples.

Reference 2

Endpoint:

basic toxicokinetics, other

Remarks:

in vivo and in vitro

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

weight of evidence

Justification for type of information:

For justification of read-across please refer to the read-across report attached to IUCLID Section 13.

Reason / purpose for cross-reference:

read-across source

Duration and frequency of treatment / exposure:

in vivo: single dose (oral gavage) and assessed over 48 hours
in vitro: single incubation shaking at 37 °C, aliquots taken at 0, 10, 20, 30, 45, and 60 minutes to be applied to thin-layer plate

Details on absorption:

Not reported

Details on distribution in tissues:

For both mice and guinea pigs, most of the radioactivity was found in the liver, gastrointestinal tract and kidney with only traces of radioactivity in the other tissues (lung, testes, heart and spleen). Total % found in tissues: up to 2.1% in mice and 6.7% in guinea pigs (similar at both concentrations).
See Table 2 in "Any other information on results incl. tables".

Details on excretion:

Mice:
* At 90 mg/kg CSL >97% of the radioactivity was eliminated within 48 hours, most (~77%) being excreted as 14CO2 within 24 hr. Most of the remaining radioactivity was excreted in the urine in 24 hours with only low levels of activity in the faeces and the 48-hr urine.
* At 900 mg/kg CSL, the rate of metabolism to 14CO2 over the first 7 hours was less although the total excreted in 24 hours was similar. The % radioactivity excreted in urine and faeces was similar at both dose levels.

Guinea pigs:
Similar rate and extent of conversion of 14C-CSL to 14CO2 in guinea pig to those in the mouse, but the % excreted dose in the urine of guinea pigs was less (~9%) and the total excreted by all routes in 48 hours was also less.
All of the radioactivity found in the urine was co-chromatographed as lactic acid.

See Table 1 in "Any other information on results incl. tables".

Metabolites identified:

yes

Remarks:

14CO2

Details on metabolites:

In vitro hydrolysis study using liver homogenates of rat, mouse and guinea pig showed rapid hydrolysis of [14C]-CSL. Across all three species, the overall extent of hydrolysis in the liver within 1 hour was similar with 40-60% hydrolysed.
* Slow to no hydrolysis was observed in the blood of rats, mice and one human volunteer.

The livers of all three species readily hydrolysed the compound. The initial rate was highest in the guinea pig (24.7 µmol/g liver/hour) and lowest in the mouse (7.5 µmol/g liver/hour). In all three species, the overall extent of hydrolysis in 1 hour was similar, between 40 and 60% of the compound hydrolysed.
The initial rates of hydrolysis by rat and guinea pig gastrointestinal mucosa are similar and significantly higher than that of the mouse mucosa.
The sample of human duodenal mucosa also hydrolysed CSL but the hydrolysis in 1 hour was less than the extent of hydrolysis achieved by the rat, mouse, or guinea pig mucosa.
Whole blood from rodent species hydrolysed the compound slowly: 0.8 µmol/g blood/hour (rat) and 0.27 µmol/g blood/hour (mouse). The human blood sample yielded no measurable hydrolysis.

Table 1. Excretion of radioactivity by male mice and male guinea pigs given a single oral dose of 14C-labelled CSL or DL-[U14 -C]lactate.

			Radioactivity excreted (% of dose) mean (range) after dosing
Route of excretion	Time from dosing		14C-CSL		14C-Lactate
		Dose (mg/kg)	90	900	325
		Animals/group	4	4	3
Mice
CO2	0-7		69.7 (68.4-71.0)	57.5 (50.7-65.7)	81.3 (75.8-84.9)
	7-24		7.1 (4.2-10.4)	22.3 (12.1-32.9)	8.0 (4.9-12.1)
	24-48		3.4 (1.8-5.8)	2.8 (2.5-3.2)	2.9 (2.6-3.3)
Urine	0-24		14.8 (11.8-17.5)	14.1 (11.9-16.2)	3.4 (3.0-4.5)
	24-48		0.7 (0.3-1.1)	2.1 (0.8-4.1)	0.6 (0.5-0.7)
Faeces	0-24		2.4 (2.0-3.3)	1.8 (1.3-2.1)	0.9 (0.8-1.1)
	24-48		0.3 (0.1-0.6)	0.3 (0.3-0.4)	0.2 (0.2)
Total			98.4 (97.8-99.5)	100.9 (97.2-103.6)	97.3 (96.8-97.8)
Guinea pig
CO2	0-7		63.1 (54.4-67.2)	60.5 (50.6-67.2)	77.6 (74.8-80.4)
	7-24		12.2 (8.3-22.7)	18.1 (13.2-24.4)	4.0 (3.9-4.2)
	24-48		3.5 (2.4-4.4)	3.3 (2.8-4.3)	2.5 (2.0-3.0)
Urine	0-24		9.2 (8.2-11.0)	8.1 (6.4-9.8)	3. (3.1-3.6)
	24-48		0.8 (0.6-1.3)	1.0 (0.3-2.7)	0.4 (0.3-0.4)
Faeces	0-24		3.0 (2.7-3.7)	2.3 (1.8-2.6)	1.6 (1.5-1.6)
	24-48		0.8 (0.6-1.3)	0.6 (0.4-0.7)	0.5 (0.4-0.5)
Total			92.6 (88.8-93.9)	93.9 (89.0-96.0)	89.9 (87.0-92.7)

Table 2. Tissue distribution of radioactivity in male mice and male guinea pigs 48 hours after oral dose of 14C-CSL or control

		14C-CSL		14C-Lactate
	Dose (mg/kg)	90	900	325
Tissue	Animals/group	4	4	3
Mouse
GI tract		0.67 ± 0.15	0.79 ± 0.08	0.84 ± 0.02
Liver		0.79 ± 0.18	0.91 ± 0.05	0.98 ± 0.08
Kidney		0.22 ± 0.03	0.26 ± 0.03	0.21 ± 0.03
Lung		0.04 ± 0.02	0.04 ± 0.01	0.04 ± 0.01
Testes		0.03 ± 0.01	0.03 ± 0.01	0.04 ± 0.02
Heart		0.05 ± 0.04	0.02 ± 0.01	0.03 ± 0.01
Spleen		0.03 ± 0.01	0.02 ± 0.01	0.02 ± 0.01
Total		1.82 ± 0.55	2.07 ± 0.14	2.14 ± 0.09
Guinea pig
GI tract		3.05 ± 0.12	2.01 ± 0.17	1.87 ± 0.04
Liver		2.40 ± 0.79	4.11 ± 3.06	7.87 ± 4.13
Kidney		0.26 ± 0.04	0.24 ± 0.01	0.18 ± 0.01
Lung		0.20 ± 0.05	0.16 ± 0.04	0.10 ± 0.01
Testes		0.06 ± 0.02	0.03 ± 0.01	0.07 ± 0.02
Heart		0.06 ± 0.01	0.06 ± 0.01	0.05 ± 0.02
Spleen		0.04 ± 0.01	0.05 ± 0.02	0.03 ± 0.01
Total		6.07 ± 0.77	6.66 ± 3.03	10.17 ± 4.07

Conclusions:

The in vivo experiments using mice and guinea pigs show that the metabolism and tissue distribution of radioactivity with 14C-CSL were similar to those for an equivalent dose of free 14C-lactate. The biological fate of CSL is comparable in both rodent (rat and mouse) and non-rodent (guinea pig) species. The metabolism in vivo and in vitro show that the compound hydrolyses to stearic and lactic acids by the non-specific carboxylic ester hydrolases and are eliminated along normal physiological routes. CSL is hydrolysed to normal physiological components and is unlikely to present a toxicological problem in terms of its metabolic fate in humans at the dose levels encountered in the human diet.

Executive summary:

Two toxicokinetics studies conducted in vitro and in vivo to compare the in vivo distribution, metabolism and elimination of CSL labelled with 14C-lactic acid with that of 14C-lactic acid alone in addition to an in vitro comparison of the rates of hydrolysis of CSL by gastrointestinal mucosal homogenate (rat, mouse, guinea pig and human), liver homogenate (rat, mouse, guinea pig), whole blood (rat, mouse, man). For the in vivo study, male mice and guinea pigs were given 14C-CSL by oral intubation and housed in all-glass metabolism cages. The radioactivity excreted in expired CO2, urine and faeces, and present in liver, kidneys, heart, lungs, spleen, testes and gastrointestinal tract at post-mortem examination. For the in vitro study, washed livers or intestinal mucosal scrapings from rats, mice and guinea-pigs, human duodenal mucosa, and whole blood from rats, mice, and human volunteers were incubated with 14C-CSL and assayed for 14C-labelled lactate and 14C-CSL by thin-layer chromatography. After hydrolysis plates had been developed, the areas corresponding to lactate and CSL were scraped off and counted. Based on in vivo and in vitro studies, the substance Calcium stearoyl-2 -lactylate has a similar biological fate to lactate in both rodent and non-rodent species. CSL is distributed to tissues similarly to lactate and it is hydrolysed to normal physiological components, thus unlikely to present a toxicological problem in terms of its metabolic fate in humans at the dose levels encountered in the human diet.

This information is used in a read-across approach in the assessment of the target substance. For justification of read-across please refer to the attached read-across report (see IUCLID section 13).

Reference 3

Endpoint:

basic toxicokinetics in vitro / ex vivo

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

supporting study

Justification for type of information:

For justification of read-across please refer to the read-across report attached to IUCLID section 13.

Reason / purpose for cross-reference:

read-across source

GLP compliance:

not specified

Type:

metabolism

Results:

Lactate derived from stearoyl lactylate is metabolized normally after prompt and quantitative release prior to absorption.

Type:

excretion

Results:

Traces of lactate in the faecal fat showed good utilization of the stearic acid moiety and of the calcium.

Type:

excretion

Results:

58% of the C14 in the physical mixture was excreted in the first 24 hours as CO2 through the lungs and 61% of the lactic acid moiety similarly. There was no difference in C14 distribution and excretion in animals receiving lactate in either form.

Details on excretion:

Rats fed the sodium or calcium salt excreted only traces of lactate in the faecal fat showed good utilization of the stearic acid moiety and of the calcium.

Conclusions:

In conclusion it has been shown that calcium stearoyl lactylate will be hydrolised into stearic acid and lactic acid, which gets further metabolised an excreted as CO2.

Executive summary:

In in vitro tests with lipase by Hodge et al. (1961), ready hydrolysis into stearic and lactic acid was observed. Rats fed the sodium or calcium salt excreted only traces of lactate in the faecal fat showed good utilization of the stearic acid moiety and of the calcium.

Experiments comparing the metabolism of a mixture of one stearic acid and C14 labelled lactic acid with stearoyl lactylate containing C14 in the lactic acid moiety, showed that 58% of the C14 in the physical mixture was excreted in the first 24 hours as CO2 through the lungs and 61% of the lactic acid moiety similarly. There was no difference in C14 distribution and excretion in animals receiving lactate in either form. Thus lactate derived from stearoyl lactylate is metabolized normally after prompt and quantitative release prior to absorption.

In conclusion it has been shown that calcium stearoyl lactylate will be hydrolised into stearic acid and lactic acid, which gets further metabolised an excreted as CO2.

This information is used in a read-across approach in the assessment of the target substance.

For justification of read-across please refer to the attached read-across report (see IUCLID section 13).

Description of key information

The toxicokinetic profile of test item sodium isostearoyl lactylate was assessed taking existing studies from the test item as well as from the read-across substances, sodium and calcium stearoyl lactylates (SSL and CSL, respectively), which are structurally and chemically similar to sodium isostearoyl lactylate. For details and justification of read-across please refer to the read-across report attached to IUCLID section 13.

 

Absorption: The test item sodium isostearoyl lactylate has shown to demonstrate high protein binding affinity in human hair and pig skin samples. In particular, application of skin cream containing 3.0% radiotagged Pationic ISL on pig skin showed retention of sodium isostearoyl lactylate after rinsing. Multiple applications of the Pationic ISL cream (e.g. over 7 days) resulted in higher retention of sodium isostearoyl lactylate. Also, after application of shampoo containing 3.5% radiotagged Pationic ISL on human hair (Remy Blue String hair), more than half of the original Pationic ISL remained on the hair after washing with commercial shampoo.

 

Distribution: In the study of Phillips et al. (1981), the distribution, metabolism and elimination of the read-across substance CSL in rodents (rat and mouse) and non-rodents (guinea pig and human) were investigated. 

Total percentages found in tissues 48 hours after oral exposure to 900 mg/kg [¹⁴C]-CSL were 2.1% in mice and 6.7% in guinea pigs. For both species, most of the radioactivity was in the liver, gastrointestinal tract and kidney with only traces of radioactivity in the other tissues (lung, testes, heart and spleen).

 

Metabolism: In vitro hydrolysis study of Phillips et al. (1981) using liver homogenates of rat, mouse and guinea pig showed rapid hydrolysis of [¹⁴C]-CSL. Across all three species, the overall extent of hydrolysis in the liver within 1 hr was similar with 40-60% hydrolysed. It was described in a WHO report that SSL or CSL undergoes hydrolysis mediated by carboxylic ester hydrolases into stearic acid and lactic acid, which gets further metabolised and excreted as CO₂. As the key difference between sodium isostearoyl lactylate and SSL is the branched (for sodium isostearoyl lactylate) vs. linear (for SSL) carbon chain of the fatty acid group of the two lactylates, it is expected that sodium isostearoyl lactylate will also undergo hydrolysis, resulting in isostearic acid and lactic acid/CO₂. It was also shown in the Phillips et al. (1981) study that there was slow to no hydrolysis observed in the blood of rats, mice and one human volunteer.

Overall, it was summarised by Phillips et al. that the biological fate of CSL is comparable in both rodent (rat and mouse) and non-rodent (guinea pig) species and that the metabolism both in vivo and in vitro proceeds with the hydrolysis by carboxylic ester hydrolases of CSL to stearic and lactic acids.

 

Elimination: With mice exposed to 90 mg/kg [¹⁴C]-CSL >97% of the radioactivity was eliminated within 48 hr, most (~77%) being excreted as [¹⁴C]-CO₂ within 24 hr. Most of the remaining radioactivity was excreted in the urine in 24 hr with only low levels of activity in the faeces and the 48-hr urine. At a higher dose of 900 mg/kg [¹⁴C]-CSL, the rate of metabolism to [14C]-CO₂over the first 7 hr was less although the total excreted in 24 hr was similar. The percentage of radioactivity excreted in urine and faeces was similar at both dose levels.

Similar rate and extent of conversion of [¹⁴C]-CSL to [¹⁴C]-CO₂in guinea pig to those in the mouse, but the percentage of excreted dose in the urine of guinea pigs was less (~9%) and the total excreted by all routes in 48 hr was also less.

All of the radioactivity found in the urine was co-chromatographed as lactic acid.

Key value for chemical safety assessment

Bioaccumulation potential:

no bioaccumulation potential