Iodine

Endpoint summary

Description of key information

To determine the sensitising potential of topically applied test item (iodine), a Local Lymph Node Assay was performed in female mice. The study followed guideline EPA OPPTS 870.2600 (2003) and OECD guideline for the Testing of Chemicals No. 429 (2002).

 

For the main study, solutions of 0.25%, 0.5% and 1% test item iodine) in DMSO were applied to the dorsum of both ears one time per day three consecutive days. Control mice were treated with the vehicle (alone) and an additional group with 25% alpha-hexyl cinnamic aldehyde (as positive control). Test item was negative for excessive local irritation (<25% increase in ear thickness) suggesting to be non irritant at the concentrations tested. The stimulation index of the substance was 1.0 at 0.25%, 1.8 at 0.5% and 2.2 at 1%.

 

Based on these results, test item (iodine) is not a considered a dermal sensitizer agent under testing conditions. The EC 3 concentration could not be calculated.

Key value for chemical safety assessment

Skin sensitisation

Link to relevant study records

Reference

Reference 1

Endpoint:

skin sensitisation: in vivo (LLNA)

Type of information:

experimental study

Adequacy of study:

key study

Study period:

From 2010-07-20 to 2010-08-12

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 429 (Skin Sensitisation: Local Lymph Node Assay)

Version / remarks:

2002

Deviations:

yes

Remarks:

The test article characterization was not conducted according to the Good Laboratory Practices. This is not expected to have any impact on the study.

GLP compliance:

yes

Type of study:

mouse local lymph node assay (LLNA)

Specific details on test material used for the study:

Batch No.: Pallets 38361-38380
Purity: 99.8%

Species:

mouse

Strain:

CBA

Sex:

female

Details on test animals and environmental conditions:

TEST ANIMALS
- Source: Harlan Laboratory
- Age at study initiation: Screening (9 wks old), Quantitative Irritation Testing (10 wks old) and Main test (11 wks old)
- Weight at study initiation: 20.4 - 21.2 g for screen animals, 20.3 - 23.1 g for quantitative irritation test (QIT) animals, 21.2 - 25.5 g formain study animals
- Housing: Individual suspended wire-bottom cages
- Diet (e.g. ad libitum): PMI Rodent Chow ad libitum
- Water (e.g. ad libitum): Ad libitum
- Acclimation period: at least 5 days prior to start

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 18-24
- Humidity (%): 44-76
- Air changes (per hr): Not reported
- Photoperiod (hrs dark / hrs light): 12/12

Vehicle:

dimethyl sulphoxide

Concentration:

1, 0.5, and 0.25%

No. of animals per dose:

5 mice per group

Details on study design:

Dosing:
Preliminary Dermal Irritation Screen: Three groups of CBA/J mice (2 animals per group) were treated with increasing concentrations of test item, (5%, 10% and 25%) in DMSO. Treatment was made by topical application of the test article concentrations to the dorsum of each ear once daily for three consecutive days (at approximately the same time each day). The test substance was spread over the entire dorsal surface of the ear using a micropipette at 25μL/ear.
Quantitative Irritation Test (QIT): Six groups of two CBA/J mice per group were treated with six concentrations (0.05%, 0.1 %, 0.25%, 0.5%, 1 % and 2.5%) of the test article in DMSO in the same manner as in the irritation screening study.
Main Test: Five groups of CBA/J mice (5 animals per group) were treated by topical application of the test article concentrations (0.25%, 0.5% and 1.0%), vehicle control or positive control in the same manner as in the screen.
Type and Frequency of Observations:
AII animals in the study were observed once daily throughout the study for clinical signs, either of local irritation at the application site or systemic toxicity, and for mortality
Measurements:
Body weights were recorded on Day 1, immediately prior to dosing, and on Day 6 (prior to sacrifice in the screen, and prior to BrdU injection in the main test). Ear thickness measurements were performed on Day 1 prior to dosing, on Day 3 before the third test article application (approximately 48 hours after the first test article application), and on Day 6 before sacrifice (approximately 120 hours after the first dose and 72 hours after the third dose). Changes in ear thickness on Day 3 and Day 6 relative to Day 1 were expressed as a percent of the Day 1 pre-dose values. Ear thickness increases of 25% or more were considered biologically significant (based on the scientific literature and historical laboratory data) and deemed indicative of a greater than moderate local dermal irritation response.
Node Isolation and Processing:
At 5 hours pre-sacrifice, mice were intraperitoneally injected 200μL of phosphate-buffered saline (PBS) containing BrdU. At sacrifice, each mouse lymph node set were excised and a single-cell suspension of lymph node cells was prepared.

Positive control substance(s):

hexyl cinnamic aldehyde (CAS No 101-86-0)

Statistics:

For each test group, the individual animal stimulation index (SI) values, along with the mean group SI and standard deviation were calculated. Student's t-Test were run to statistically compare each group to the control group.

Positive control results:

alpha-hexyl cinnamic aldehyde stimulation index (SI): 6.4

Parameter:

SI

Value:

1

Test group / Remarks:

0.25% group

Parameter:

SI

Value:

1.8

Test group / Remarks:

0.5% group

Parameter:

SI

Value:

2.2

Test group / Remarks:

1% group

Cellular proliferation data / Observations:

Test Article Formulation and Dosing: The test article formed a homogenous solution in the vehicle, DMSO. No difficulties were experienced with the application of the test article to the ears or with the retention of test article by the ear surface. However, in the screen, test material appeared to stain the ears and hair at the dose sites beginning on Day 2. This did not affect ear measurements.
Body Weights: Body weight changes were noted but were not significant (<2 g).
Mortality and Systemic Observations: AII animals survived the in-life phase of the study and were observed to be normal.

Irritation Screening

Table 1: Results of the initial test irritation

Ear Measurements			Day 1		Day 3		Day 6		Mean Ear Thickness (mm)			%Difference
		AN #	Left	Right	Left	Right	Left	Right	Pre-Dosing (Day 1)	48 Hr (Day 3	End In-Life (Day 6)	Day 3- Day 1		Day 6- Day 1
5% Test item		1	0,18	0,18	0,23	0,23	0,44	0,48	0,18	0,23	0,46	28%^a		156%^a
		2	0,19	0,18	0,23	0,24	0,48	0,44
10%  Test item		3	0,20	0,20	0,31	0,34	0,50	0,48	0,21	0,32	0,47	52%^a		124%^a
		4	0,21	0,21	0,31	0,32	0,41	0,50
25%  Test item		5	0,21	0,20	0,36	0,38	0,54	0,57	0,20	0,36	0,55	80%^a		175%^a
		6	0,19	0,20	0,35	0,36	0,55	0,55
a = an increase in ear thickness of 25% indicates a positive dermal irritation response

Table 2: Results of the quantitative irritation screening

Ear Measurements			Day 1		Day 3		Day 6		Mean Ear Thickness (mm)			%Difference
		AN #	Left	Right	Left	Right	Left	Right	Pre-Dosing (Day 1)	48 Hr (Day 3	End In-Life (Day 6)	Day 3- Day 1		Day 6- Day 1
0.05%  Test item		1	0,19	0,21	0,21	0,21	0,21	0,23	0,20	0,22	0,22	10%		10%
		2	0,20	0,21	0,21	0,23	0,21	0,23
0.1%  Test item		3	0,21	0,20	0,22	0,22	0,20	0,24	0,21	0,22	0,23	5%		10%
		4	0,21	0,22	0,22	0,23	0,24	0,24
0.25%  Test item		5	0,19	0,21	0,19	0,18	0,21	0,22	0,20	0,19	0,23	-5%		15%
		6	0,18	0,20	0,18	0,21	0,23	0,24
0.5%  Test item		7	0,20	0,21	0,21	0,21	0,21	0,22	0,20	0,20	0,22	0%		10%
		8	0,20	0,20	0,21	0,18	0,22	0,22
1%  Test item		9	0,19	0,18	0,19	0,20	0,23	0,22	0,19	0,19	0,22	0%		16%
		10	0,19	0,19	0,19	0,19	0,21	0,23
2.5%  Test item		11	0,20	0,19	0,22	0,21	0,34	0,33	0,20	0,22	0,35	10%		75%^a
		12	0,20	0,19	0,21	0,23	0,35	0,38
a = an increase in ear thickness of 25% indicates a positive dermal irritation response

Main Study

Table 3: Irritation as Measured by Ear Swelling (% Change Day 1 to Day 6) 

DMSO	25% HCA	0.25%  Test item	0.5% Test item	1%  Test item
10.5%	63.2%	15%	15.8%	15%

The EC3, the concentration at which the stimulation index is equal to 3 (calculated to determine skin sensitization potency) could not be calculated for test item.

Interpretation of results:

other: not sensitising

Conclusions:

To determine the sensitising potential of topically applied test item (iodine), a Local Lymph Node Assay was performed in female mice. The study followed guideline EPA OPPTS 870.2600 (2003) and OECD guideline for the Testing of Chemicals No. 429 (2002). The stimulation index of the substance was 1.0 at 0.25%, 1.8 at 0.5% and 2.2 at 1%. The test item (iodine) showed no skin sensitiser potential.

Executive summary:

To determine the sensitising potential of topically applied test item (iodine), a Local Lymph Node Assay was performed in female mice. The study followed guideline EPA OPPTS 870.2600 (2003) and OECD guideline for the Testing of Chemicals No. 429 (2002).

In order to select the doses for the main study, an irritation screening was performed with solutions of 25%, 10%and 5% of test item in dimethyl sulfoxide (DMSO) using two animals per concentration. As irritation was observed (ear swelling > 25%) in the animals, a quantitative irritation test was carried out using 6 concentrations of test item (2 animals per concentration).

For the main study, solutions of 0.25%, 0.5% and 1% test item iodine) in DMSO were applied to the dorsum of both ears one time per day three consecutive days. Control mice were treated with the vehicle (alone) and an additional group with 25% alpha-hexyl cinnamic aldehyde (as positive control). Test item was negative for excessive local irritation (<25% increase in ear thickness) suggesting to be non irritant at the concentrations tested. The stimulation index of the substance was 1.0 at 0.25%, 1.8 at 0.5% and 2.2 at 1%.

Based on these results, test item (iodine) is not a considered a dermal sensitizer agent under testing conditions. The EC 3 concentration could not be calculated.

Reference 2

Endpoint:

skin sensitisation: in vitro

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

an in vitro skin sensitisation study does not need to be conducted because adequate data from an in vivo skin sensitisation study are available

Reference 3

Endpoint:

skin sensitisation: in vivo (non-LLNA)

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

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

Qualifier:

no guideline followed

Principles of method if other than guideline:

In this report, effects of protein iodination on elicitogenic activity in guinea pig iodine allergy model and iodinated protein antigen generation in vitro from iodine-containing chemicals were investigated

GLP compliance:

not specified

Specific details on test material used for the study:

- Source: Katayama Chemical Industries (Osaka, Japan)

Species:

guinea pig

Strain:

Hartley

Sex:

female

Details on test animals and environmental conditions:

Female Hartley strain guinea pigs, at the age of 4 weeks, were purchased from Nippon SLC (Hamamatsu, Japan). They were acclimated for 2 weeks before use.

Reading:

other: Active cutaneous anaphylaxis (ACA) test

Hours after challenge:

0.5

Group:

test chemical

Remarks on result:

other: Provocation of iodine allergy was observed at 0.15 μM, i.e. 38.1 μg and above (0.5, 1.5 μM I2/mg protein), for 1 mg of each of all four proteins: BSA, GSA, HSA, and OVA.

- Effect of protein iodination on the provocation activities of experimental iodine allergy:

Guinea pigs were immunized three times with iodine and active cutaneous anaphylaxis reactions were induced by an intradermal injection of 0.1 mL of a solution containing 10 μg of iodinated protein. Provocation of iodine allergy was observed at 0.15 μM, i.e. 38.1 μg and above, for 1 mg of each of all four proteins: BSA, GSA, HSA, and OVA. The amount of iodine required for PECs to provoke a delayed-type skin reaction was also studied. Guinea pigs immunized three times with iodine were challenged with an intradermal injection of 1E+6 iodinated PECs and the diameters of the areas of erythema at the site of the injection were measured 24 hr later. The amount of iodine necessary to provoke a delayed type allergy reaction was 0.075 μM, i.e. 19.1 μg, for 1E+6 PECs. I-GSA and iodine-containing contrast media did not provoke DTH response.

- Generation of iodine and iodinated protein from potassium iodide and iodinated contrast media by photo-energy. Potassium iodide (KI) in itself, as well as other iodide salts, is not active to react with proteins. Iodide ions (I-) in the salt are to be oxidized to I2, which reacts with proteins. In the first experiment, 5 mL each of a 1% solution of soluble starch was added to equal volumes of 10 mM KI solution and sodium iotalamate preparation and the mixtures were irradiated by UV light at 0.013 mW/cm2 (UV radiometer Topcon UVR-1, Topcon, Tokyo, Japan) in a plastic dish (Falcon 3002) of 6 cm diameter under magnetic stirring. After 14 min of UV light irradiation of the KI/starch solution, 48 μM I2 was produced; 12 hr UV irradiation of the sodium iotalamate/starch solution resulted in 38 μM I2. The violet color disappeared when BSA was added, confirming the presence of I2.

The same experiment was undertaken using a non-ionic contrast medium, iohexol. No color development was observed in the presence of iohexol after 12 hr exposure to UV light under the same experimental conditions. However, after some trials, we found that iohexol also generated 26 μM I2 after 48 hr irradiation at pH 6.5. Thus, the generation of I2 from I- is pH-dependent. Accordingly, I2 generation from KI in 0.1 M phosphate buffer solutions at pH 6.5 and pH 7.2 was studied. The amounts of I2 generated were greater at pH 6.5 than at pH 7.2, the difference indicating that the spontaneous reduction reaction of I2 to I- took place more readily at pH 7.2 than at pH 6.5.

The next experiment was designed to study the effects of X-ray irradiation of potassium iodide solution and iodine-containing contrast media in the presence of protein. Comparative studies on the formation of iodinated protein from sodium iotalamate and GSA at pH 6.5 and pH 7.2 showed that the amounts of iodinated protein generated after irradiation of 7,500 R were 9 μg/mL and 4.2 μg/mL, respectively, which was similar to the results of iodine generation from iodide under UV irradiation when the amounts of iodine generated were greater at pH 6.5 than at pH 7.2. Accordingly, kinetic studies on protein iodination by X-ray irradiation of iotalamate were then performed at pH 6.5. X-ray dose-related generation was observed at doses of 300 R and above. There is a linear dependency for the generation of iodinated protein generation to the dose of photo-energy. Comparing protein iodination induced by nonionic contrast medium, iohexol, with that induced by the ionic contrast medium, sodium iotalamate indicated that the non-ionic contrast medium was much more resistant to protein iodination by X-ray irradiation as in the case of UV irradiation. Rate of iodinated protein synthesis of iohexol expressed by concentration (pg/mL) of iodinated protein per unit irradiation (R) per iodine content (mg/mL) was one-sixth of that of sodium iotalamate.

In order to confirm the involvement of oxidation in the generation of iodinated protein, the effects of the reducing agents, i.e. ascorbic acid, gultathione, Nacetyl- L-cysteine and sodium thiosulfate, were studied. Each of the four reducing agents was added to a twofold-diluted sodium iotalamate preparation at final concentrations of 0 (control), 0.01, 0.1, and 1 mM in the presence of 10 μg/mL GSA, pH 7.2. The X-ray dose was 7500 R. The amount of iodinated GSA generated in the control sample was 4.6 μg/mL. The partial inhibition of iodinated protein formation was observed in the presence of any of the reducing agents at a concentration of 0.1 mM. However, there was no detectable (minimum detectable level was 0.1 μg/mL) iodinated GSA in the samples in which any of the reducing agents were added at 1 mM. It is noteworthy that the iodinated proteins assayed by the sandwich method using anti-diiodotyrosyl residue antibody are of valency greater than 2, and thus are thought to be able to elicit an allergic reaction.

Conclusions:

Active cutaneous anaphylaxis (ACA) and delayed-type hypersensitivity (DTH) tests were performed in guinea pigs immunized with iodine. The amount of iodine (I2) reacted to proteins for giving them an eliciting activity of ACA was ≥ 0.15 μmol for 1 mg of albumin. DTH reactions were provoked by intradermal injection of 1E+6PECs reacted with ≥ 0 .075 μmol of I2.

Executive summary:

In this report, effects of protein iodination on elicitogenic activity in guinea pig iodine allergy model and iodinated protein antigen generation in vitro from iodine-containing chemicals were investigated. Active cutaneous anaphylaxis (ACA) and delayed-type hypersensitivity (DTH) tests were performed in guinea pigs immunized with iodine. The amount of iodine (I2) reacted to proteins for giving them an eliciting activity of ACA was ≥ 0.15 μmol for 1 mg of albumin. DTH reactions were provoked by intradermal injection of 1E+6 PECs reacted with ≥ 0.075 μmol of I2. I2 was generated from a potassium iodide (KI) solution or iodinated contrast media by UV light irradiation. X-ray irradiation of KI and iodinated contrast media in the presence of protein resulted in the generation of iodinated protein antigens. The generation of iodinated protein antigens was inhibited in the presence of reducing agents. Therefore, it is noteworthy that iodine allergy of the present hypothesis is dependent on reactive oxygens.

Reference 4

Endpoint:

skin sensitisation: in vivo (non-LLNA)

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

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

Qualifier:

no guideline followed

Principles of method if other than guideline:

It first studied the specificity of antigen recognition of an antibody obtained by immunizing guinea pigs with iodine to observe whether the antibodies are specific or crossreactive to iodine-containing chemicals and, secondly the mechanism involved in the occurrence of protein iodination from iodine-containing chemicals such as potassium iodide and iodocontrast media in vitro.

GLP compliance:

not specified

Specific details on test material used for the study:

Source: Katayama Chemical Industries (Osaka, Japan)

Species:

guinea pig

Strain:

Hartley

Sex:

female

Details on test animals and environmental conditions:

Female Hartley strain guinea pigs, at the age of 4 weeks, were purchased from Nippon SLC (Hamamatsu, Japan). They were acclimated for 2 weeks before use.

Reading:

other: Active cutaneous anaphylaxis (ACA) test

Hours after challenge:

0.5

Group:

test chemical

Dose level:

Hexaiodotrityrosine

No. with + reactions:

35

Total no. in group:

35

Remarks on result:

positive indication of skin sensitisation

Reading:

other: Active cutaneous anaphylaxis (ACA) test

Hours after challenge:

0.5

Group:

test chemical

Dose level:

Tetraiododityrosine

No. with + reactions:

25

Total no. in group:

35

Remarks on result:

positive indication of skin sensitisation

- Eliciting activity of diiodotyrosine derivatives on iodine allergy in guinea pigs immunized with iodine:

The eliciting activities of tetraiododityrosine and hexaiodotrityrosine were assessed by ACA reactions in five guinea pigs immunized three times with iodine and four control animals. Each guinea pig was challenged with both compounds by intradermal injections of 0.1 mL of fourfold serially diluted saline solution starting from 500 μg/mL to 0.1 μg/mL. Hexaiodotrityrosine showed stronger eliciting activity (p<0.05) than that of tetraiododityrosine. Furthermore, the rates of animals showed that positive skin reactions in immunized animals, were significantly higher with iodinated trityrosine. Moreover, iodinated dityrosine did not elicit a skin reaction in one of the 5 animals even at the highest doses of 50 μg/site.

When these two test samples were injected into normal animals, tetraiododityrosine showed no skin reaction at the highest concentration and hexaiodotrityrosine showed a weak dye leakage at concentrations of 125 μg/mL and higher.

- Sensitizing immunogenicity of hexaiodotrityrosine:

Sensitizing potency of hexaiodotrityrosine was studied. I-GSA 7.2 and iodine were employed as a positive control. Each dose of hexaiodotrityrosine and IGSA 7.2 was emulsified with complete Freund’s adjuvant and injected subcutaneously at a total volume of 1 mL (0.25 mL per site at four separate positions) into the back of the guinea pigs at a dose of 10 mg/animal and 1 mg/animal, respectively. The immunization injections were repeated 3 times at intervals of 2 weeks. The blood was taken from each animal and the serum separated one week after the last sensitization injection. Detection of antibodies was performed by using I-GSA 7.2 and hexaiodotrityrosine as eliciting antigens. No antibody was detected by ASA and PCA reactions in the sera obtained from animals immunized with hexaiodotrityrosine. On the other hand, guinea pigs immunized with iodinated protein, I-GSA 7.2, produced antibodies detected by either iodinated guinea pig serum albumin and hexaiodotrityrosine. Furthermore, no positive PCA reactions were observed in guinea pigs at the sites injected with sera immunized with hexaiodotrityrosine, whereas positive PCA reactions were observed at the sites injected with pooled sera immunized with iodine. Therefore, it is concluded that iodinated trityrosine has no sensitization antigenicity.

- ELISA inhibition studies of erythrosine on reaction of guinea pig anti-iodine antibody to an iodinated protein:

In the first experiment, ELISA inhibition studies were carried out as follows: An equal volume of 20 mM of erythrosine solution in PBS was added to serially diluted anti-iodine antisera, left at 4 ℃ overnight, and then used for ELISA inhibition experiments. Each sample was assayed in duplicate. Erythrosine showed inhibitory activity on the reaction between iodinated protein and anti-iodine antibody. Therefore, the inhibitory activity of erythrosine was compared with that of DIT. Equal volumes of 0.1, 0.3, 1, 3, 10, 30, 100, 300, and 1000 μM erythrosine solutions in PBS was added to 500-fold diluted anti-iodine antisera, left at 4℃overnight, and then used for ELISA inhibition experiments. Each sample was assayed in triplicate. DIT was used as a positive control. The molar inhibitory activity of erythrosine was stronger than that of DIT as the inhibitory curve by erythrosine was shifted to the left compared with that by DIT.

- Provocative activity of erythrosine on passive cutaneous anaphylactic reaction in guinea pigs passively sensitized with guinea pig anti-iodine antisera：

In the preliminary PCA test, Guinea pigs were passively sensitized by intradermal injection of antiiodine antiserum diluted 30- to 3000-fold and challenged with erythrosine at doses of 1 and 10 mg per animal or with 1 mg of I-GSA 7.2 as a positive control. The results indicated that erythrosine at a dose of 10 mg per animal elicited a positive PCA reaction in one of the two animals sensitized with anti-iodine antibody. Therefore, the provocative activity of erythrosine was studied in the animals sensitized with anti-iodine antiserum serially diluted from 5- to 40-fold with saline. Each of the diluted sera was injected intradermally at two sites in every animal. Challenge doses of erythrosine were 1, 5, and 10 mg per animal. Erythrosine was shown to provoke an iodine allergy at the doses of 5 mg/animal and above.

Conclusions:

The present investigation revealed that both tetraiododityrosine and erythrosine had eliciting activities in experimental iodine allergy. The results indicated that both compounds acted as a divalent antigen of experimental iodine allergy.

Executive summary:

The text addressed the hypothesize that iodine allergy is an immune response to iodinated self proteins producedin vivofrom various iodine-containing chemicals. Since an antigenic determinant of experimental iodine allergy is diiodotyrosine (DIT), low molecular weight DIT derivatives having provocative antigenicity without sensitizing immunogenicity.

Tetraiododityrosine and hexaiodotrityrosine provoked dose-dependent skin reactions in guinea pigs previously immunized with iodine. No guinea pigs immunized with hexaiodotrityrosine showed anaphylactic reaction by i.v. challenge with hexaiodotrityrosine and none of their antisera showed positive passive cutaneous anaphylaxis (PCA) reaction in guinea pigs, indicating the non-immunogenic nature of the compound. Erythrosine, one of the color additives having a structure common with DIT, was assessed for its immunological property. Enzyme-linked immunosorbent assay (ELISA) inhibition studies on erythrosine revealed that the inhibitory activity of erythrosine was stronger than that of DIT. Furthermore, erythrosine provoked a PCA reaction in animals sensitized with anti-iodine antisera.

In conclusion, hexaiodotrityrosine is thought to be useful for skin testing of iodine allergy without any fear of sensitization to the allergen.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (not sensitising)

Additional information:

To determine the sensitising potential of topically applied test item (iodine), a Local Lymph Node Assay was performed in female mice. The study followed guideline EPA OPPTS 870.2600 (2003) and OECD guideline for the Testing of Chemicals No. 429 (2002). In order to select the doses for the main study, an irritation screening was performed with solutions of 25%, 10%and 5% of test item in dimethyl sulfoxide (DMSO) using two animals per concentration. As irritation was observed (ear swelling > 25%) in the animals, a quantitative irritation test was carried out using 6 concentrations of test item (2 animals per concentration). For the main study, solutions of 0.25%, 0.5% and 1% test item in DMSO were applied to the dorsum of both ears one time per day three consecutive days. Control mice were treated with the vehicle (alone) and an additional group with 25% alpha-hexyl cinnamic aldehyde (as positive control).

Test item was negative for excessive local irritation (<25% increase in ear thickness) suggesting to be non irritant at the concentrations tested. The stimulation index of the substance was 1.0 at 0.25%, 1.8 at 0.5% and 2.2 at 1%. Based on these results, test item is not a considered a dermal sensitizer agent under testing conditions. The EC 3 concentration could not be calculated.

Sugihara et al (2004) hypothesized that iodine allergy is an immunological response to iodinated self proteins produced in vivo from a variety of chemicals containing iodine. The publication further states that diiodotyrosine (DIT) is an antigenic determinant of experimental iodine allergy. An experiment was designed based on the testing of low molecular weight DIT derivatives that stimulate antigenicity without sensitising immunogenicity. It was determined that tetraiododityrosine and hexaiodotrityrosine triggered a dose dependent skin reaction in guinea pigs that were previously immunised with iodine. None of the tested guinea pigs that were immunized with hexaiodotrityrosine displayed an anaphylactic reaction by intravenous challenge with hexaiodotrityrosine and none of their antisera displayed positive passive cutaneous anaphylaxis (PCA) reaction in guinea pigs, which indicated the non-immunogenic nature of this compound. Erythrosine, a compound with a structure similar to DIT triggered a PCA reaction that was stronger than DIT. Hexaiodotrityrosine is considered to be a useful for the skin testing of iodine allergy without causing sensitisation to the allergen.

Shionoya et al (2004) hypothesised that iodine allergy is an immune response to iodinated autologous proteins that are generated in vivo from organic and inorganic chemicals containing iodine. This publication investigated the effects of protein iodination on elicitogenic activity from iodine containing chemicals in a guinea pig iodine allergy model. Iodinated protein antigen generation in vitro from iodine containing chemicals was also investigated. In the first part of this publication, active cutaneous anaphylaxis (ACA) and delayed type hypersensitivity (DTH) tests were conducted in guinea pigs immunised with iodine. Iodine caused an eliciting activity of ACA when reacting with proteins at a concentration of≥0.15μmol for 1 mg of albumin. DTH reactions were triggered by an intradermal injection of 106 peritoneal exudate cells reacted with≥0.075μmol of I2. In the second part of this publication, I2 was generated from a potassium iodide solution or iodinated contrast media by UV light irradiation. Iodinated contrast media and X-ray irradiation of potassium iodide in the presence of protein resulted in the generation of iodinated protein antigens. It was noted that the production of iodinated protein antigens was inhibited by reducing agents, which suggested that the hypothesis is dependent on reactive oxygens. The study author finalised the publication by stating that further experiments are required. The purpose of the additional experiments would be to investigate human antibodies to iodinated self-protein and the formation of iodinated self-protein antigens in vivo in animals and especially humans.

Respiratory sensitisation

Endpoint conclusion

Endpoint conclusion:

no study available

Justification for classification or non-classification

In the murine local lymph node assay (OECD 429, EPA OPPTS 870.2600), Iodine showed a stimulation index below 3 in all tested concentrations. Thus, based on criteria from Regulation (EC) 1272/2008, iodine is not classified as a skin sensitiser (Skin Sens).

This is further supported from the conclusion in the registration dossier of iodine (including PVP-iodine) as an active substance for biocidal products (Ref: Assessment report, Iodine (including PVP-iodine) Product types 1, 3, 4, 22, 13 December 2013, Sweden), where it is concluded that based on the results from the maximisation test, iodine is not regarded as a skin sensitizer.