Hexamethylene diisocyanate

Neurotoxicity

Administrative data

Endpoint:

neurotoxicity: inhalation

Remarks:

other: Combined Repeated Dose Toxicity Study with the Reproduction/Developmental Toxicity Screening Test

Type of information:

experimental study

Adequacy of study:

other information

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP guideline study

Cross-reference

Reason / purpose for cross-reference:

reference to same study

Data source

Reference

Reference 1

Reference Type:

study report

Title:

Unnamed

Year:

1999

Report date:

1999

Reference 2

Reference Type:

publication

Title:

A combined reproduction, neonatal development, and neurotoxicity study with 1,6-hexamethylene diisocyanate (HDI) in the rat

Author:

Astroff AB et al.

Year:

2000

Bibliographic source:

Reproductive Toxicology 14: 135-146

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

other: OECD Guideline 422 (Combined Repeated Dose Toxicity Study with the Reproduction / Developmental Toxicity Screening Test)

GLP compliance:

yes

Test material

Test material information

Constituent 1

Reference substance name:

Hexamethylene diisocyanate

EC Number:

212-485-8

EC Name:

Hexamethylene diisocyanate

Cas Number:

822-06-0

Molecular formula:

C8H12N2O2

IUPAC Name:

1,6-diisocyanatohexane

Test animals

Species:

rat

Strain:

Sprague-Dawley

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River, Portage, MI
- Age at study initiation: 7-9 wks
- Weight at study initiation: Males: 312-383 g; Females: 201-248 g
- Housing: individual
- Diet: ad libitum (except during the exposure period)
- Water: ad libitum
- Acclimation period: at least 6 days


ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22 +/- 2
- Humidity (%): 40 - 60
- Air changes (per hr): no data
- Photoperiod (hrs dark / hrs light): 12 / 12

Administration / exposure

Route of administration:

inhalation: vapour

Vehicle:

other: air

Details on exposure:

TEST SUBSTANCE GENERATION:
HDI was generated as a vapor by passing filtered, dry air through liquid HDI in a grass bubbler. During vapor generation the bubbler containing HDl was immersed in a constant temperature water bath. The vaporized material was entrained with chamber intake air flow for mixing at the chamber head. Both bubbler temperature and air flow may have been adjusted to maintain desired chamber HDl concentrations and these parameters were monitored continuously with recordings at half-hour intervals (minimum) during eaeh six-hour exposure period.

EXPOSURE SYSTEM:
Chambers: The chambers used in this study were Hazleton H-2000 inhalation exposure chambers which are constructed of stainless steel with clear glass windows. Each chamber has an approximate volume of two cubic meters. The chambers are equipped with stainless steel, wire mesh cage-packs. Each cage-pack is fitted with removable feed troughs and an automatic watering system. The air supplied to the chamber passes through an activated charcoal trap and a HEPA filter before being conditioned to the desired temperature and relative humidity. These chambers have been used
previously for exposure of animals to HDI.

NOMINAL CHAMBER PARAMETERS (During Exposure):
Temperature: 22 ± 2°C; Relative Humidity: 50 ± 10%; Exhaust Flow: 700 ± 100 Lpm; Static Pressure: -0.25 to -1.0 inches of water relative to atmospheric.
To the extent possible these nominal values were maintained during each exposure period. During non-exposure periods (nights) nominal values for each chamber parameter were set to be maintained as Iisted above, with the exception that the range for RH shall be relaxed to be 40 - 70%. This was to accommodate expected inereases in RH due to chamber handling and animal care. The increase to 70% RH is in accordanee with AALAC guidelines governing care of rats.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Chamber samples were collected near the animal's breathing zone using two midget impingers connected in series. Samples were collected at a frequency that ensured that the average daily value was representative of the required concentration. At a minimum, three samples (one for the control
chamber) were collected per chamber per day. An acetonitrile solution (at least 10 mL per impinger) containing N-4-nitrobenzyl-N-n-propylamine (nitro reagent) was used to trap and derivatize HDl to a UV-absorbing compound. All midget impinger samples were assayed by an established high performance liquid chromatography method.

Duration of treatment / exposure:

Chamber samples were collected near the animal's breathing zone using two midget impingers connected in series. Samples were collected at a frequency that ensured that the average daily value was representative of the required concentration. At a minimum, three samples (one for the control
chamber) were collected per chamber per day. An acetonitrile solution (at least 10 mL per impinger) containing N-4-nitrobenzyl-N-n-propylamine (nitro reagent) was used to trap and derivatize HDl to a UV-absorbing compound. All midget impinger samples were assayed by an established high performance liquid chromatography method.

Frequency of treatment:

6 hours/day, 7 days/week

Doses / concentrations

Doses / concentrations 1

Remarks:

Doses / Concentrations:
0, 0.005, 0.050, 0.300 ppm
Basis:
nominal conc.

Doses / concentrations 2

Remarks:

Doses / Concentrations:
0, 0.005, 0.053, 0.299 ppm
Basis:
analytical conc.

No. of animals per sex per dose:

15

Control animals:

yes, sham-exposed

Details on study design:

DOSE SELECTION RATIONALE:
The concentrations of HDl used in this study were based on a 21-day inhalation toxicity study, a 90day inhalation toxicity study, a chronic inhalation toxicity/oncogenicity study, and a sensory irritation study. In the 21-day study, Sprague-Oawley rats were exposed to either 0, 0.005, 0.0175,
0.15, or 0.3 ppm HDl for 5 hours/day, 5 days/week for 3 weeks. Compound-related ocular and nasal irritation were observed in animals exposed to 0.0175, 0.15, and 0.3 ppm on days of exposure only. These findings were not observed during non-exposure days. There were no compound-related effects on body weight, feed consumption, clinical chemistry, hematology, urinalysis, or gross pathology. At 0.3 ppm, liver and kidney weights were decreased in females. The major findings for both sexes were histopathologie lesions of the nasal mucosa and minor changes in the larynx and trachea. This study demonstrated that the target site following HDl exposure was the nasal cavity. In the 90-day study, Fischer 344 rats were exposed to HDl concentrations of 0, 0.01, 0.04 and 0.14 ppm for 6 hours/day, 5days/week for approximately 13 weeks. The only compound-related findings were ocular irritation and histopathologic lesions of the anterior nasal cavity. Both findings were observed at all three concentrations, therefore, a clear NOEL was not established in this study. In the chronic/oncogenicity study, Fischer 344 rats were exposed to HDl concentrations of 0, 0.005, 0.025 and 0.175 ppm for 6 hours/day, 5 days/week for up to 2 years. Animals were evaluated following both one and two years of exposure. A maximum tolerated dose was achieved at the highest concentration based on decreased body weight and slight anemia in the females, and histopathologie lesions of the nasal cavity in both sexes. The lowest concentration (0.005 ppm) was shown to be a NOEL after one year of exposure. However, after two years of exposure 0.005 ppm was considered to be a NOAEL based on the observation of reversible lesions, indicative of responses to non-specific irritation. In the sensory irritation study, female Sprague-Dawley rats were exposed using the head-only technique, to 0, 0.10, 0.21, 0.79, and 4.42 ppm Mondur HX (100% HDl) for three hours. Following exposure the animals were held for a seven-day recovery period. A concentration dependent increase in the respiratory response (sensory irritation) was observed. The severity of the response culminated in the death of two rats at the 4.42 ppm dose level. The RD50 (concentration which was estimated to produee a 50% depression in respiratory frequency) for the last hour of a three-hour exposure was 1.69 ppm. The NOEL for this study was 0.1 ppm. Based on these results, and the projected exposure of the animals for approximately six weeks during the current study, the proposed concentrations were 0, 0.005, 0.05, and 0.3 ppm HDI.

Results and discussion

Any other information on results incl. tables

HDI was administered by inhalation exposure to young-adult male and female Sprague-Dawley rats prior to co-housing and continuing through mating (males) or lactation day 4 (females) at nominal concentrations of 0, 0.005, 0.05 and 0.3 ppm. The first 10/sex/dose level were subjected to neurobehavioral evaluation using a functional observational battery (FOB) and an automated test of activity (figure-eight maze) on three occasions: (1) prior to the initiation of treatment, (2) following approximately two weeks of exposure, and (3) just prior to termination. In summary, the following observations were noted. Compound-related effects involving the FOB were not evident in males or females at any exposure level. Automated measures of activity were not affected by treatment in males or females at any exposure level. Thus, the present study established a NOEL for these neurobehavioral endpoints of 0.3 ppm for males and females.