Naphthenic acids, zinc salts, basic

Basic toxicokinetics

Administrative data

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

Not reported

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Study well documented, meets generally accepted scientific principles, acceptable for assessment.

Cross-reference

Cross-reference 1

Reason / purpose for cross-reference:

reference to same study

Cross-reference 2

Reason / purpose for cross-reference:

reference to other study

Data source

Reference

Reference Type:

publication

Title:

Pulmonary clearance and toxicity of zinc oxide instilled into the rat lung

Author:

Hirano S, Higo S, Tsukamoto N, Kobayashi E & Suzuki KT

Year:

1989

Bibliographic source:

Arch. Toxicol. 63(4):336-342

Materials and methods

Objective of study:

toxicokinetics

Principles of method if other than guideline:

Pulmonary toxicity of zinc oxide (ZnO) was evaluated by investigating the metabolic fate and inflammatory potency of ZnO instilled into the rat lung.

GLP compliance:

no

Test material

Test material information

Constituent 1

Details on test material:

- Name of test material (as cited in study report): Zinc oxide
- Obtained from Kanto Chemical Co., Ltd, Tokyo, Japan

Radiolabelling:

no

Test animals

Species:

rat

Strain:

Wistar

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Clea Japan Co., Tokyo
- Weight at study initiation: 250-290 g
- Individual metabolism cages: yes/no
- Diet (e.g. ad libitum): Commercial chow (Oriental Yeast Co., Tokyo), ad libitum
- Water (e.g. ad libitum): Distilled water, ad libitum


ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22 °C
- Humidity (%): 50 %

Administration / exposure

Route of administration:

intratracheal

Vehicle:

other: sterile physiological saline

Details on exposure:

- Preparation of dosing solution: Test material was milled for 5 min with a micro-pulvilizer (P-7, Fritsch Japan Co., Ltd, Yokohama, Japan) and the resulted particles were suspended in sterile physiological saline and sonicated in an ultrasonic cleaner before instillation
- Method of particle size determination: Electron microscope (JSM- 840, JEOL, Tokyo) after collecting the particles on a membrane filter of 0.03 µm pore size (Nuclepore Co., Pleasanton, Calif, USA)
- Particle size: < 2 µm, appeared to form aggregates of 10-20 particles

Duration and frequency of treatment / exposure:

Duration of exposure:
- Time-course experiment: 1/3, 1, 2, 3, 5, 7, 14 and 21 d
- Dose response experiment: 2 d

Frequency of exposure: Single intratracheal instillation of 0.4 mL ZnO suspension

Doses / concentrations

Remarks:

Doses / Concentrations:
- Time-course experiment: 100 µg Zn/rat
- Dose response experiment: 0, 20, 50, 100, 200, 500 and 1000 µg Zn/rat

No. of animals per sex per dose / concentration:

Three

Control animals:

yes, concurrent vehicle

Positive control reference chemical:

No

Details on study design:

None

Details on dosing and sampling:

Time of sacrifice:
- Time-course experiment: 1/3, 1, 2, 3, 5, 7, 14 and 21 d after administration
- Dose response experiment: 2 d after administration

Bronchoalveolar lavage fluid (BALF): BALF was used for measurement of lactate dehydrogenase (LDH) and 13-glucuronidase activity; concentrations of protein and essential elements (S, P, Ca and Mg); and differential cell counts

Organs: Trachea, lung, heart, liver and kidneys were removed, rinsed, blotted and weighed; lung tissues were assayed for metallothionein (MT)

Zinc concentration in BALF pellet, liver and kidney tissues: Measured by an inductively coupled argon plasma-atomic emission spectrometer (JY48PVH, Seiko Instruments & Electronics Co., Ltd, Tokyo)

Statistics:

Two tailed t-test

Results and discussion

Preliminary studies:

Not applicable

Toxicokinetic / pharmacokinetic studies

Details on absorption:

Dose-response experiment: Percentage of Zn retained in the lung increased with the dose, but at doses lower than 50 µg Zn/rat exogenous Zn was not observed 2 d after instillation indicating that the rat lung was able to clear ZnO particles up to a dose of 50 µg Zn/rat at least within 2 d. At doses higher than 200 µg Zn/rat, Zn was retrieved proportionally to the dose of ZnO both in the supernatant and pellet of BALF suggested the role of solubilization of ZnO particles in the bronchoalveolar milieu in the clearance rate of ZnO from the lung.

Details on distribution in tissues:

- No measurable accumulation of Zn was observed in the liver and kidneys even at a dose of 1000 µg Zn/rat
- 20 µg Zn/rat was sufficient to develop maximum responses for β-glucuronidase activity and surfactant content in the bronchoalveolar lavage fluid
- Lactate dehydrogenase activity and protein content in the lavage fluid increased significantly at 20 µg Zn/rat
- Metallothionein (MT) was induced with a peak at 2 d. The content of MT was proportional to the dose of ZnO, but contributed little for the accumulation of Zn in the lung.

Details on excretion:

- ZnO particles were solubilised in the bronchoalveolar milieu and cleared from the lung with a half-life of 14 h.

Toxicokinetic parameters

Test no.:

#1

Toxicokinetic parameters:

half-life 1st: 14 h

Metabolite characterisation studies

Metabolites identified:

no

Details on metabolites:

Not applicable

Any other information on results incl. tables

Table 1. Time-course and dose-response changes in lung wet weight and metallothionein content in the lung

	Time after instillation (days)
	1/3	1	2	3	5	7	14	21
Lung wet weight (g)	0.87	1.33*	1.48	1.41*	1.30*	1.49*	1.24*	1.23
	± 0.04	± 0.04	± 0.19	± 0.04	± 0.10	± 0.07	± 0.02	± 0.13
Metallothionein (µg/lung)	2.2	3.8	7.8*	2.9	2.1	2.6	2	2.3
	± 0.44	± 0.4	± 0.82	± 0.38	± 0.37	± 0.3	± 0.22	± 0.08
	Control	Dose of ZnO (µg Zn/rat)
		20	50	100	200	500	1000	-
Lung wet weight (g)	0.87	1.1	1.46*	1.48	1.39	1.76*	1.99*
	± 0.06	± 0.05	± 0.09	± 0.19	± 0.14	± 0.09	± 0.09
Metallothionein (µg/lung)	2.2	1.7	5.2	7.8*	11*	21*	29*
	± 0.26	± 0.26	± 1.6	± 0.82	± 1.7	± 0.64	± 3.6

Data are presented as means ± SEM

* Significantly different from control value

Bronchoalveolar lavage fluid (BALF):

- Concentrations of protein & essential elements (S, P, Ca and Mg): The protein content increased with the dose and reached a plateau at 200 µg Zn/rat. S, Ca, and Mg content peaked at 2 d and returned to their control levels after 7-14 d, while P content showed a maximum value at 5 d and even at 7 d its content was still 3.8 times higher than the control value. S, Ca and Mg increased with the dose up to 200 µg Zn/rat and appeared to plateau at this dose level. However, the profile of P content again showed a different pattern from those of S, Ca and Mg contents. A dose level of 20 µg Zn/rat produced a maximum response in the P content

- Differential cell counts: Polymorphonuclear leukocytes (PMNs) peaked at 2 d, while 5 d for the macrophages in their peak, cells reached maximum values at 200-500 µg Zn/rat in the dose-response profiles.

Applicant's summary and conclusion

Conclusions:

low bioaccumulation potential based on study results
The results indicated that the rat lung was able to clear ZnO particles up to a dose of 50 g Zn2+/rat at least within two days. No measurable accumulation of Zn was observed in the liver and kidneys even at a dose of 1000 µg Zn2+/rat .

Executive summary:

Pulmonary toxicity of zinc oxide (ZnO) was evaluated by investigating the metabolic fate and inflammatory potency of ZnO instilled into the rat lung.

 

Groups of three rats received single intratracheal instillations of ZnO suspension at a dose of 100 µg Zn/rat in the time-course experiment or received 20, 50, 100, 200, 500 and 1000 µg Zn/rat and were killed 2 d after treatment in the dose-response experiment.

 

ZnO particles were solubilised in the bronchoalveolar milieu and cleared from the lung with a half-life of 14 h. Metallothionein (MT) was induced with a peak at 2 d. The content of MT was proportional to the dose of ZnO, but contributed little for the accumulation of Zn in the lung.

A dose of 20 µg Zn/rat was sufficient to develop maximum responses for β-glucuronidase activity and surfactant content in the bronchoalveolar lavage fluid. Moreover, the activity of lactate dehydrogenase and protein content in the lavage fluid increased significantly at 20 µg Zn/rat.

The results indicated that the rat lung was able to clear ZnO particles up to a dose of 50 g Zn2+/rat at least within two days. No measurable accumulation of Zn was observed in the liver and kidneys even at a dose of 1000 µg Zn2+/rat .