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Basic toxicokinetics

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Administrative data

Endpoint:
basic toxicokinetics in vivo
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Well documented publication and acceptable for assessment; meets generally accepted scientific standards
Cross-referenceopen allclose all
Reason / purpose:
reference to same study
Reason / purpose:
reference to other study

Data source

Reference
Reference Type:
publication
Title:
Uptake of iron oxide aerosols by mouse airway epithelium
Author:
Watson AY, and Brain JD
Year:
1979
Bibliographic source:
Laboratory Investigation, 40: 450-459

Materials and methods

Objective of study:
other: iron uptake by the airway epithelium
Test guideline
Qualifier:
no guideline followed
Principles of method if other than guideline:
Mice were exposed to an aerosol of iron oxide for 3 hours. Participation of the tracheal and bronchial epithelium in the uptake of iron oxide was investigated immediately following the exposure and at 1 day, 4 days and 7 days postexposure. Two or three animals were sacrificed at each time point for a total of 10 experimental animals.The main objective of the publication was to describe the uptake and transport of submicrometer insoluble particles by the airway epithelium. Iron(III) oxide (Fe203) was selected due to its non-toxic properties.
GLP compliance:
not specified
Remarks:
Study performed before the adoption of GLP principles

Test material

Reference
Name:
Unnamed
Type:
Constituent
Type:
Constituent
Details on test material:
- Name of test material (as cited in study report): iron oxide
-Other: nano spherical iron oxide particles (approx 0.005 µm in diameter); self made material
Radiolabelling:
no

Test animals

Species:
mouse
Strain:
CD-1
Sex:
male
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Charles River Breeding Laboratories, Inc., Wilmington, Massachusetts
- 20 -25 g

Administration / exposure

Route of administration:
inhalation: aerosol
Vehicle:
unchanged (no vehicle)
Details on exposure:
TYPE OF INHALATION EXPOSURE: whole body

GENERATION OF TEST ATMOSPHERE
The generation of the aerosol was done as described by Brain et al. (Environmental Research, 7: 13-26, 1974): submicron iron oxide particles are produced from the combustion of iron pentacarbonyl, Fe(CO)5, yielding to a high purity sample (concentrations of CO less than 5 ppm)

The MMAD was 0.15 µm and GSD 2.2. As stated in the publication the aerosol is a loose, lacy agglomerate of smaller spherical iron oxide particles (approx 0.005 µm in diameter). The particles are electron dense, have a characteristic shape, and are readily distinguished by electron microscopy.

TEST ATMOSPHERE (if not tabulated)

- MMAD (Mass median aerodynamic diameter) / GSD (Geometric st. dev.): 0.15 µm/ 2.2
Duration and frequency of treatment / exposure:
3 h, single period
Doses / concentrations
Remarks:
Doses / Concentrations:
300 mg/m3
No. of animals per sex per dose:
one dose used, 10 animals tested (plus 2 controls)
Control animals:
yes, sham-exposed
Positive control:
no
Details on study design:
Animals were sacrificed immediately after the 3h inhalation exposure, or at 1 day, 4 days and 7 days postexposure (2 or 3 animals per time point; the control animals were killed immediately after exposure). The lungs were fixed in situ by perfusion via the pulmonary arteries. From each animal, one sample of trachea and three samples of large intrapulmonary bronchi were examined with light microscopy, stained with Perl's Prussian staining (modified method, according to Tanaka et al., 1969), and counterstained with 1 per cent basic fuchsin. Thin sections, stained with bismuth subnitrate stain for ferritin, were examined with the electron microscopy. Sections were also examined for their Fe content and every cell was identified. Hemosiderin was quantified and the number of hemosiderin granules were measured.

*Ferric iron stains blue by Perl's method; ferritin and hemosiderin can also be detected.
**Synthesis of ferritin and formation of hemosiderin is stimulated by incorporation of Fe.
Statistics:
3-way analysis of variance

Results and discussion

Preliminary studies:
no data
Main ADME results
Type:
distribution

Toxicokinetic / pharmacokinetic studies

Details on absorption:
no
Details on distribution in tissues:
see below "any other information on materials and methods"
Details on excretion:
no

Metabolite characterisation studies

Metabolites identified:
yes
Details on metabolites:
ferritin and hemosiderin

Any other information on results incl. tables

Perl's positive material was detected in the airway epithelial cells and in the connective tissue with light microscopy, but the form of Fe could not be identified this way.

DISTRIBUTION

Qualitative: Some Fe-oxide particles were detected on the surface of the airway epithelium immediately and after 1 day of exposure, but at 4 days. Particles were observed on the mucous layer, on cell surfaces and between cilia. Electron dense pinocytic material was detected in the apical cytoplasm, of some cells, but Fe oxide was not observed in large phagocytic vesicles. The authors suggest its dissolution in the lumen and uptake from the cell, but this speculation could not be verified.The pinocytic vesicles appeared to migrate from the apical surface to the Golgi complex and the endoplasmic reticulum. Intracellular ferritin and hemosiderin were detected immediately after the 3h exposure to the Fe oxide and at all later time points.

No iron oxide was detected in the connective tissue and between epithelial cells.

Quantitative: Hemosiderin appears in conditions of iron excess, an thus, it was quantified and scored (by electron microscopy) in the sections of the trachea and bronchus, as an indicator of iron uptake by the cells. The results can be seen in Table 1 (attachment below). Each cell section with one or more hemosiderin granules was scored as positive. The percentage of hemosiderin containing cell sections increased significantly over time. Hemosiderin levels were observed also in control animals (killed immediately after exposure), but at significantly lower levels.

Applicant's summary and conclusion

Conclusions:
Interpretation of results (migrated information): other: Nanosize iron oxide particles are pinocytosed by the epithelial cells of the airways and subsequently converted to ferritin and hemosiderin. Quantification of hemosiderin reveals thats that Fe storage increases with time, after exposure to the Fe2O3.
Iron oxide nanoparticles are pinocytised by the epithelial cells of the airways and subsequently give rise to the formation of ferritin and hemosiderin. Quantification of hemosiderin reveals thats that iron storage increases with time, after exposure to the iron(III) oxide (Fe2O3). The study provides some evidence of dissolution of the Fe oxide after entering the cells. However, the very small particle size has to be taken into account.
Executive summary:

Male CD-1 mice were exposed to an aerosol of iron(III) oxide (Fe2O3) at 300 mg/m3 for 3 hours. Uptake by the tracheal and the bronchial epithelium was examined following the exposure and at 1 day, 4 days and 7 days postexposure. Two or three animals were sacrificed at each time point for a total of 10 experimental animals. The findings reveal that iron oxide particles were probably pinocytised by the epithelial cells of the airways and subsequently lead to increase of ferritin and hemosiderin. Quantification of hemosiderin reveals thats that Fe storage increases with time, after exposure to the Fe2O3.