Manganese dioxide

Basic toxicokinetics

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: see 'Remark'

Remarks:

A very well designed and documented study. A clear hypothesis is tested and the results thoroughly analysed and discussed. Restrictions - no claims that the study had been conducted and reported according to internationally accepted guidelines or in compliance with the principles of GLP.

Data source

Reference

Reference Type:

publication

Title:

Influence of the route of administration and the chemical form (MnCl2, MnO2) on the absorption and cerebral distribution of manganese in rats.

Author:

Roels H, Meiers G, Delos M, Ortega I, Lauwerys R, Buchet JP and Lison D

Year:

1997

Bibliographic source:

Arch Toxicol 71:223-230

Materials and methods

Objective of study:

absorption

distribution

Test guideline

Qualifier:

no guideline followed

Principles of method if other than guideline:

Different groups of adult male rats received either MnCl2.4H2O or MnO2 once a week for 4 weeks at a dose of 24.3 mg Mn/kg body wt. (b.w.) by oral gavage (g.) or 1.22 mg Mn/kg b.w. by intraperitoneal injection (i.p.) or intratracheal instillation (i.t.). Four days after the last administration the rats were killed and the concentration of manganese measured in blood, hepatic and cerebral tissues (cortex, cerebellum, and striatum).

GLP compliance:

not specified

Test material

Test material information

Constituent 1

Reference substance name:

Manganese dioxide

EC Number:

215-202-6

EC Name:

Manganese dioxide

Cas Number:

1313-13-9

Molecular formula:

MnO2

IUPAC Name:

dioxomanganese

Test material form:

solid: particulate/powder

Details on test material:

- Name of test material : Manganese chloride and Manganese dioxide
- Physical state: MnCl2 as solution, MnO2 as a powder (particle size D50 3.7 µm)

Radiolabelling:

no

Test animals

Species:

rat

Strain:

Sprague-Dawley

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Age at study initiation: 3 months old
- Weight at study initiation: body wt. 350±450 g
- Housing: housed in an air-conditioned room
- Diet: Fed ad libitum a conventional rat chow diet
- Water: Free access to tap water


ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22 ±2 °C,
- Humidity (%): relative humidity 50 ± 10%
- Photoperiod (hrs dark / hrs light): 12:12 h light/dark cycle

Administration / exposure

Route of administration:

other: oral gavage, intraperitoneal injection and intratracheal instillation

Vehicle:

physiological saline

Details on exposure:

PREPARATION OF DOSING SOLUTIONS:
The MnCl2 solutions and MnO2 suspensions were prepared in 0.9% saline and the pH adjusted to between 6.0 and 6.5 with 0.1 M NaOH. Immediately before use, the preparations were autoclaved and sonicated. During administration, the MnO2 preparations were permanently sonicated and stirred which enabled a reproducible sampling of the aliquots to be administered.

Duration and frequency of treatment / exposure:

once a week for 4 weeks

Doses / concentrations

Remarks:

Doses / Concentrations:
MnCl2, 4H2O or MnO2 at doses of 24.3 mg Mn/kg body wt. (b.w.) by oral gavage (g.) or 1.22 mg Mn/kg b.w. for intraperitoneal injection (i.p.) and intratracheal instillation (i.t.)

No. of animals per sex per dose / concentration:

6 rats per dose group

Control animals:

yes, concurrent vehicle

Details on study design:

- Dose selection rationale: The dose groups were selected on the basis of preliminary experiments which demonstrated the absence of organ toxicity induced by the treatments that might have influenced the absorption rate.

Details on dosing and sampling:

PHARMACOKINETIC STUDY
- Tissues and body fluids sampled: blood, hepatic and cerebral tissues (cortex, cerebellum, and striatum).
- Time and frequency of sampling: Four days after the last administration the rats were killed and the tissues were sampled.

Statistics:

Student's t-test was used for comparison of the means of unpaired data. For multiple comparison ANOVA complemented with Dunnett's or Duncan's tests was performed. The level of statistical significance was taken as P < 0.05.

Results and discussion

Preliminary studies:

A four week observation for signs of toxicity was used as a preliminary study to determine dose selection.

Toxicokinetic / pharmacokinetic studies

Details on absorption:

MnO2 given orally did not significantly increase blood and cerebral tissue Mn concentrations; the low bioavailability is most likely due to the lack of intestinal resorption. Administration of MnO2 i.p. and i.t., however, led to significant increases of Mn concentrations in blood and cerebral tissues. These increments were not significantly different from those measured after MnCl2 administration, except for striatal Mn after i.t. which was markedly less (48%) after MnO2 administration. The liver Mn concentration was not affected by any of the administered treatments. Rats treated i.t. with MnCl2 showed an elective increase of the striatal Mn concentration (205%).

Details on distribution in tissues:

Mn concentrations were significantly increased in the cerebellum (31%), striatum (48%) and cortex (34%) following repeated i.t. installation of MnO2, however no increases in Mn concentration in brain tissues was seen after repeated administration by gavage. A comparison of the blood Mn kinetics immediately after g. and i.t. treatment with MnCl2 or MnO2 indicated that the higher elevation of blood Mn concentration ( > 2000 ng Mn/100 ml) after i.t. administration of MnCl2 could account for the elective uptake of Mn in the striatum observed in repeated dosing experiments. Administration of MnCl2 by g., i.p., and i.t. routes produced equivalent steady-state blood Mn concentrations (about 1000 ng Mn/100 ml), representing increases of 68, 59, and 68% compared with controls, respectively.
It is concluded that the modulation of Mn distribution in brain regions according to the route of administration and the chemical form of the Mn substance may be explained on the basis of different blood Mn kinetics and regional anatomic specificities of the striatal region.

Metabolite characterisation studies

Metabolites identified:

not measured

Any other information on results incl. tables

Four week administration experiment

 No significant effect on body weight gain could be detected after treatment with MnCl₂or MnO₂by gavage, i.p. or i.t. administration. Neither lethality nor signs of toxicity were noted during these treatments. At the end of the 4-week treatment regimen, histological analyses performed on GI tract (gavage), liver (i.p.), and lung (i.t.) tissues did not show any significant alteration, except for some scattered inflammatory foci (macrophages and mononucleated cells) in the lung of rats dosed with MnO₂but not MnCl₂. During the preliminary experiments lung toxicity was checked by monitoring the biological parameters of bronchoalveolar lavages 1 day and 7 days after i.t. instillation. No significant effect of a single instillation of 1.22 mg Mn/kg b.w. either as MnCl₂or MnO₂could be detected on cellular parameters (i.e. total and differential cell counts). Mn concentrations in liver tissue (1500±2000 ng Mn/g tissue wet weight) were not affected after 4 weeks of treatment with MnCl₂or MnO₂.

 

MnCl₂ cohort

An important finding was obtained at the end of the 4 weeks of treatment, viz., the three routes of administration produced similar steady-state increases of Mn in blood (gavage, 68%,P= 0.010; i.p., 59%,P= 0.089; i.t., 68%,P= 0.064). Treatment by oral gavage did not influence the Mn concentration in cerebellum and striatum, and slightly but significantly increased that in the cortex (22%,P= 0.033). Intraperitoneal injection did not change the Mn concentration in cerebellum, whereas that in striatum and cortex was increased by 34% (P= 0.177) and 36% (P< 0.001), respectively. Intratracheal instillation increased the Mn concentrations in the three subregions of the brain. The increases were significant in the cortex (48%,P= 0.027) and striatum (205%,P< 0.001) and approached the level of statistical significance in cerebellum (27%,P= 0.100). In order to take into account some differences noted between the values measured in the respective control groups (gavage, i.p., i.t.), an additional statistical analysis was performed. All control values were pooled to constitute a single overall control group (n= 3 ´ 6) and the increments of tissue Mn concentration in the MnCl₂treated groups were calculated relative to this overall control group. An ANOVA complemented by Dunnett test performed on the increments confirmed the results obtained by the Student's t-test. The effect of the route of administration on the actual concentrations of Mn in cerebral tissues and blood of treated rats was also examined by ANOVA. The multiple range test showed that administration of MnCl₂via oral gavage, i.p. injection, or i.t. instillation produced more or less evenly increased concentrations of Mn in cortex or blood, whatever the route of administration. Only rats treated by i.t. instillation of MnCl₂showed a selectively increased Mn concentration in the striatum. The Mn concentrations in the cerebellum were higher after i.p. or i.t. administration when compared to oral gavage (P< 0.05).

 

MnO₂ cohort

After 4 weeks, the concentration of Mn in blood was significantly increased when administered by the i.p. and i.t. routes, i.e. 79% (P= 0.001) and 41% (P= 0.030), respectively. Administration by gavage did not increase either blood or brain tissue Mn concentrations. Significantly increased Mn concentrations were, however, found in the three brain subregions after i.p. injection (cerebellum, 40%,P= 0.002; striatum, 124%,P< 0.001; cortex, 67%,P< 0.001) and i.t. instillation (cerebellum, 31%,P< 0.001; striatum, 48%,P= 0.001; cortex, 34%,P= 0.013). To take into account differences between the values measured in the respective control groups (gavage, i.p. and i.t.), the same additional statistical approach as mentioned above for the MnCl2 cohort was applied. The ANOVA and Dunnett test performed on the increments again confirmed the results obtained by the Student's t-test. The effect of the route of administration was examined by ANOVA complemented with the multiple range test. The actual Mn concentrations in the cerebral tissues and blood of the treated rats were found not to be significantly increased when MnO2 was given by gavage. The i.p. and i.t. routes produced similar Mn concentrations in both the cerebellum and the cortex, whereas i.t. administration produced a higher striatal Mn concentration (P= 0.059) compared to the two other routes of administration. The Mn concentration in blood was significantly higher after i.p. compared to i.t. administration.

 

Comparison between MnCl₂ and MnO₂ administrations

The effect of the Mn chemical form was studied for each route of administration separately. The comparison (Student's t-test) was performed on the differences between the tissue Mn concentrations in rats (n= 6) treated with either MnCl₂or MnO₂and their respective control mean values (either gavage, i.p., or i.t.). When compared to MnO₂groups, significantly higher increments in cortex and blood Mn concentrations were found after gavage with MnCl₂, while i.t. instillation of MnCl₂produced a significantly greater increment in the striatum. Intraperitoneal injection of MnCl₂did not produce significantly higher increments of Mn concentrations in blood and brain tissues compared to MnO₂.

 

 

Blood Mn kinetics after a single administration

In animals treated with MnCl₂, i.t. instillation of 1.22 mg Mn/kg b.w. was very rapidly followed by a transient rise of the blood Mn concentration. The highest concentration (7050 ng Mn/100 ml) coincided with the first blood sample taken 30 min after dosing with Mn. Although the true peak concentration might occur between 0 and 30 min, it was impossible to sample blood earlier because of experimental constraints. Subsequently, the blood Mn concentrations declined gradually but remained higher than control values (about 500 to 600 ng Mn/100 ml) for at least up to 24 h. By contrast, oral administration of MnCl₂(24.3 mg Mn/kg b.w.) produced a transient rise in blood Mn values which was about five times lower compared with the i.t. route of administration. A peak value of 1660 ng Mn/100 ml was reached after 1 h of dosing followed by a rapid return to control values within 12 h. In animals treated with MnO₂the rise of blood Mn concentrations was strikingly delayed compared to the observations made with MnCl2 and the amplitude of the response was considerably less pronounced. Similarly to MnCl₂, i.t. instillation of MnO₂(1.22 mg Mn/kg b.w.) produced higher blood Mn concentrations than application by oral gavage (24.3 mg Mn/kg b.w.). The onset of increased blood Mn concentration occurred 48 to 72 h after i.t. dosing with MnO₂and after 168 h a peak value of 1760 ng Mn/100 ml (200% increase) was achieved. A more significant delay (96 to 120 h) was observed after gavage administration of MnO₂and the rise in blood Mn concentration after 144 h was only 27% (900 vs 710 ng Mn/100 ml at time 0,P< 0.02). The blood Mn concentration was still slightly increased (830 ng Mn/100 ml) 10 days after dosing but did not significantly differ (P> 0.05) from the control or the t= 0 value. The time course of blood Mn after oral administration of MnO₂most likely reflects a slow and limited transfer of Mn2+ from the GI tract into the circulation.

Applicant's summary and conclusion

Conclusions:

Interpretation of results: low bioaccumulation potential based on study results
It is concluded that the modulation of Mn distribution in brain regions according to the route of administration and the chemical form of the Mn compound may be explained on the basis of different blood Mn kinetics and regional anatomic specificities of the striatal region.

Executive summary:

Different groups of adult male rats received either MnCl2.4H2O or MnO2 once a week for 4 weeks at a dose of 24.3 mg Mn/kg body wt. (b.w.) by oral gavage (g.) or 1.22 mg Mn/kg b.w. by intraperitoneal injection (i.p.) or intratracheal instillation (i.t.). Four days after the last administration the rats were killed and the concentration of manganese measured in blood, hepatic and cerebral tissues (cortex, cerebellum, and striatum).

MnO2 given orally did not significantly increase blood and cerebral tissue Mn concentrations; the low bioavailability is most likely due to the lack of intestinal resorption. Administration of MnO2 i.p. and i.t., however, led to significant increases of Mn concentrations in blood and cerebral tissues. These increments were not significantly different from those measured after MnCl2 administration, except for striatal Mn after i.t. which was markedly less (48%) after MnO2 administration. The liver Mn concentration was not affected by any of the administered treatments. Rats treated i.t. with MnCl2 showed an elective increase of the striatal Mn concentration (205%).

Mn concentrations were significantly increased in the cerebellum (31%), striatum (48%) and cortex (34%) following repeated i.t. installation of MnO2, however no increases in Mn concentration in brain tissues was seen after repeated administration by gavage. A comparison of the blood Mn kinetics immediately after g. and i.t. treatment with MnCl2 or MnO2 indicated that the higher elevation of blood Mn concentration ( > 2000 ng Mn/100 ml) after i.t. administration of MnCl2 could account for the elective uptake of Mn in the striatum observed in repeated dosing experiments. Administration of MnCl2 by g., i.p., and i.t. routes produced equivalent steady-state blood Mn concentrations (about 1000 ng Mn/100 ml), representing increases of 68, 59, and 68% compared with controls, respectively.

It is concluded that the modulation of Mn distribution in brain regions according to the route of administration and the chemical form of the Mn substance may be explained on the basis of different blood Mn kinetics and regional anatomic specificities of the striatal region.