Manganese oxide

Endpoint summary

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

basic toxicokinetics

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

not reported

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

Study conducted to sound scientific principles with a suficient level of detail to assess the reliability of the relevant results. There was a sufficient number of plasma time-points to enable TK calculations to be made. The study was conducted with manganese chloride, which represents a more available form of manganese, rather than with the registered substance itself, the study was assigned a reliability score of 2.

Justification for type of information:

See the read-across report attached in Section 13.

Objective of study:

toxicokinetics

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 417 (Toxicokinetics)

Principles of method if other than guideline:

The toxicokinetics of manganese (Mn) was investigated in male rats either following a single intravenous (iv) or oral dose of MnCl2 (6.0 mg Mn/kg). The plasma concentrations of manganese were quantified by atomic absorption spectrophotometry (AAS).

GLP compliance:

not specified

Radiolabelling:

no

Species:

rat

Strain:

Sprague-Dawley

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Halran Inc., Indianapolis, IN, USA
- Age at study initiation: 2 months
- Weight at study initiation: 210 - 230 g
- Fasting period before study: animals were fasted for 12 hours prior to administration (oral dosing)
- Housing: animals were housed in a temperature controlled room
- Diet:Teklad 4% Mouse-Rat Diet (Teklad, Madison, WI, USA), ad libitum
- Water: tap water, ad libitum

ENVIRONMENTAL CONDITIONS
- Photoperiod (hrs dark / hrs light): 12 hours dark / 12 hours light

Route of administration:

other: oral and intravenous

Vehicle:

other: sterile saline

Details on exposure:

PREPARATION OF DOSING SOLUTIONS:
MnCl2 was dissolved in sterile saline for both iv and oral administration; the test material was dosed at 6.0 mg Mn/kg (1.0 mL/kg) via both routes of administration.

Duration and frequency of treatment / exposure:

Single administration of test material

Remarks:

Doses / Concentrations:
6.0 mg Mn/kg (1.0 mL/kg)

No. of animals per sex per dose / concentration:

not reported

Control animals:

not specified

Details on study design:

- Dose selection rationale: The dose regimen was chosen because it was known to be associated with a significant reduction of succinic dehydrogenase and aconitase in rat brain.

Details on dosing and sampling:

PHARMACOKINETIC STUDY (Absorption, distribution, excretion)
- Tissues and body fluids sampled: Blood (0.3 - 0.5 mL)
- Time and frequency of sampling: 0, 0.05, 0.17, 0.33, 0.5, 1, 2, 4, 8, and 12 h
The blood was centrifuged at 5000 x g for 5 minutes, and the plasma was separated and stored at -20°C prior to analysis.

Statistics:

Statistical analysis for comparison of two means was performed usinf one-way ANOVA. In all cases, a probility level of p < 0.05 was considered as the criterion of significance.

Toxicokinetic parameters:

Tmax: Oral dose MnCl2: 0.25±0.21 h

Toxicokinetic parameters:

Cmax: Oral dose MnCl2: 0.30±0.11µg/mL

Toxicokinetic parameters:

AUC: Oral dose: MnCl2 1.95±0.51 mM·h

Toxicokinetic parameters:

AUC: iv dose MnCl2: 14.8±3.60 mM·h

Metabolites identified:

no

Intravenous (iv) Dosing

After an iv-bolus injection of MnCl₂, the concentration-time profile of manganese in plasma followed a multi-exponential equation:

C(t) = 41.94e^-4.2t + 2.08e^-0.44t

In general, the two-compartment model with first-order elimination from the central compartment provided a good fit to the observed data. Manganese was rapidly eliminated from the plasma with an initial faster phase between 0 and 3 hours and a slower terminal phase between 3 and 12 hours. Accordingly, the first-order initial disposition t_1/2α and the terminal elimination t_1/2ß were estimated to be 0.19h and 1.38h, respectively. By 12 hours, manganese concentrations in plasma were restored to normal levels in all tested animals. Although the total volume distribution (V_ß) of manganese was about 1.16 L/kg, the central volume distribution (V_c) was only 0.14 L/kg, suggesting an extensive distribution of manganese to the peripheral compartment following iv injection of MnCl₂.

 

Oral (op) Dosing

Single oral gavage of MnCl₂ resulted in a rapid appearance of manganese in plasma. The C_max (0.296 µg/mL) was achieved within 0.5 hours of the oral dose. Thereafter, manganese concentrations declined and the terminal phase followed the first-order kinetics. The absolute bioavailability (F) of manganese following oral MnCl₂was 13.2% at a dose of 6 mg/kg. Similar to iv injection, plasma manganese returned to normal levels 12 hours after dosing. Oral dosing of MnCl₂ resulted in a significant increase in terminal t_½ compared to rats receiving iv injection.

Conclusions:

Interpretation of results (migrated information): low bioaccumulation potential based on study results
Upon iv administration of MnCl2, manganese rapidly disappeared from blood with a terminal elimination t½ of 1.83 hours and CLs of 0.43 L/h/kg. The plasma concentration-time profiles of manganese could be described by C = 41.94e-4.2t + 2.08e-0.44t
Following oral administration of MnCl2, manganese rapidly entered the systemic circulation (Tmax = 0.25 h). The absolute oral bioavailability was about 13%.

Executive summary:

The toxicokinetics of manganese (Mn) was investigated in male rats either following a single intravenous (iv) or oral dose of MnCl2 (6.0 mg Mn/kg). The plasma concentrations of manganese were quantified by atomic absorption spectrophotometry (AAS).

Upon iv administration of MnCl₂, manganese rapidly disappeared from blood with a terminal elimination t_½ of 1.83 hours and CL_s of 0.43 L/h/kg. The plasma concentration-time profiles of manganese could be described by C = 41.94e^-4.2t + 2.08e^-0.44t

Following oral administration of MnCl₂, manganese rapidly entered the systemic circulation (T_max= 0.25 h). The absolute oral bioavailability was about 13%.

Reference 2

Endpoint:

basic toxicokinetics in vitro / ex vivo

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

supporting study

Justification for type of information:

See the read-across report attached in Section 13.

Reason / purpose for cross-reference:

read-across source

Toxicokinetic parameters:

Tmax: Oral dose MnCl2: 0.25 ± 0.21 h

Toxicokinetic parameters:

Cmax: Oral dose MnCl2: 0.30 ± 0.11 μg/mL

Toxicokinetic parameters:

AUC: Oral dose MnCl2: 1.95 ± 0.51 mM·h

Toxicokinetic parameters:

AUC: IV dose MnCl2: 14.8 ± 3.60 mM·h

Reference 3

Endpoint:

basic toxicokinetics in vivo

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Well designed documented and reported. Not to GLP.

Objective of study:

distribution

Principles of method if other than guideline:

To determine if olfactory translocation occurs for other solid metal UFPs and assess potential health effects, groups of rats were exposed to manganese (Mn) oxide UFPs (30 nm; approximately 500 microg/m(superscript)3(/superscript)) with either both nostrils patent or the right nostril occluded. Aanalysis of Mn in lung, liver, olfactory bulb, and other brain regions was performed, in addition to gene and protein analyses

GLP compliance:

not specified

Species:

rat

Strain:

Fischer 344

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Harlan (Indianapolis,IN)
- Age at study initiation: 3 months of age
- Weight at study initiation: 200-250g body weight
- Housing: housed in filter-top plastic cages
- Diet (e.g. ad libitum): Purina rodent chow(5001;purina Mills,LLC,St.Louise,MO) was available ad libitum
- Water (e.g. ad libitum): water was available ad libitum
- Acclimation period:1 week


ENVIRONMENTAL CONDITIONS
- Temperature (°C):
- Humidity (%):
- Air changes (per hr):
- Photoperiod (hrs dark / hrs light):


IN-LIFE DATES: From: To:

Route of administration:

other: inhalation and intranasal instillation

Duration and frequency of treatment / exposure:

12 days

Remarks:

Doses / Concentrations:
30 nm;~ 500 μg/m3

No. of animals per sex per dose / concentration:

3

Control animals:

yes

Details on dosing and sampling:

PHARMACOKINETIC STUDY (Absorption, distribution)
- Tissues and body fluids sampled (delete / add / specify): lung, liver, olfactory bulb, and other brain regions
- Time and frequency of sampling: 6 day and 12 days

Statistics:

The results were analysed for statistical differences by one-way analysis of variance with appropriate data transforms using SigmaStat (Systat Software Inc., Point Richmond, CA). Data were appropriately transformed if an analysis of residuals suggested deviations from the assumptions of normality
and equal variance. Differences between groups were further analyzed using Tukey multiple comparisons. Such comparisons were considered statistically significant when p ≤ 0.05.

Preliminary studies:

Studies in monkeys with intranasally instilled gold ultrafine particles (UFPs; <100 nm) and in rats with inhaled carbon UFPs suggested that solid UFPs deposited in the nose travel along the olfactory nerve to the olfactory bulb.

Table 1: Summary of lavage data from 6-and 120day ultrafine Mn oxide exposure in young male F-344 rats

 

		Mn exposure
	Untreated controls	6 days	12days
Total cells(*10^7)	0.680±0.070	0.505±0.049*	0.651±0.069
Percent AM	98.29±1.22	99.44±0.041	99.42±0.052
Percent PMN	0.30±0.12	0.07±0.12	0.11±0.19
Percent lymphocytes	1.04±0.83	0.34±0.42	0.47±0.41
Percent viable	89.83±3.67	92.79±4.83	92.93±0.51
Protein(mg/mL)	0.11±0.01	0.15±0.04	0.15±0.02
LDH(nmol/min/mL)	69.50±6.37	84.13±25.80	79.66±9.32
Β-Glucuronidase(nmol/min/mL)	0.461±0.093	0.497±0.086	0.241±0.048*

Abbreviations: AM, alveolar macrophage; LDH, lactate dehydrogenase; PMN, polymorphonuclear leukocyte.Values are mean± SD; n=6/group for controls and 3/group for Mn-exposed rats.* significantly different from control (p<0.05)

 

 

 

 

Conclusions:

Interpretation of results: bioaccumulation potential cannot be judged based on study results
It was concluded that the olfactory neuronal pathway is efficient for translocating inhaled Mn oxide as solid UFP's to the central nervous system and that this can result in inflammatory changes. We suggest that despite differences between human and rodent olfactory systems, this pathway is relevant in humans.

Additional information

 

TEST MATERIAL: Manganese Oxide (MnO); (EC Number 215-695-8, CAS Number 1344-43-0)

 

The test material, manganese oxide, occurs naturally in the rare mineral manganosite and can also be found in smaller proportions in other manganese minerals such as rhodochrosite. It is a brown/green crystalline powder and particle size analysis has shown that over 10% of the particles were smaller than 100 µm diameter.   

 

Absorption

 

The test material, manganese oxide, has a very low water solubility of 6.6 x 10^-4g/L of manganese in solution at 20.0^oC, which is equivalent to 8.5 x 10^-4g/L of the test material in solution at 20.0^oC based on the manganese content of the test material(O'Connor and Woolley 2009) The test material also has a very low solubility (0.003%) in artificial alveolar based upon the extractable manganese(Anderson 2009). As the test material had greater than 10% of particles less than 100 µm diameter it was subjected to an acute inhalation toxicity (nose only) study in the rat(Griffiths 2010). In order to facilitate aerosolisation and reduce particle size, the test material was ground using a centrifugal ball mill prior to use. A group of 10 rats were exposed to a mean atmosphere concentration of 5.35 mg/L test material with a mean mass median aerodynamic diameter of 3.00 µm and a prediction of 65% of particles being less than 4 µm. The results concluded that the acute inhalation median lethal concentration (4 hr LC₅₀) of manganese oxide was greater than 5.35 mg/L in the rat. As such, although manganese oxide has the potential to be inhaled due to its particle size distribution, it doesn’t exhibit inhalation toxicity at a high dose in the rat. Since the test material has very low solubility (0.003%) in artificial alveolar it is likely that most of the inhaled test material was not absorbed but instead was cleared from the lungs by the mucocilliary elevator into the gastrointestinal (GI) tract. 

 

Manganese oxide has limited solubility (12±4.4%) in artificial gastric juice(Anderson 2009). As the oral absorption of even soluble manganese salts is still relatively low, typically less than 5%, this means that manganese oxide has a relatively low potential for substantial oral absorption ( ≤ 0.5% of any manganese oxide consumed would be absorbed). The acute oral median lethal dose (LD50) of the test material in the female Wistar strain rat was estimated to be greater than 2000 mg/kg bodyweight (Pooles 2009). As such the test material has a very low potential for toxicity by oral absorption. As the test material has a very low solubility in water coupled with its physical inorganic nature (crystalline powder) means that it is very unlikely to be absorbed through the skin. 

 

In conclusion, the test material has a low potential for any absorption by oral ingestion, inhalation or dermal absorption. 

 

Metabolism, Distribution and Excretion

 

Since the test material has a low potential for absorption by any route it means that the test material will not be readily bioavailable. The majority of any test material that is ingested orally is likely to pass through the GI tract unchanged and be excreted in the faeces. Any small amount of manganese from the test material that is absorbed by the gut will enter the essential manganese pool along with that which is absorbed from the daily nutritional requirement of manganese. The circulating amount of manganese will be controlled by the normal homeostatic mechanism provided by the liver that controls the manganese balance. Any test material that is inhaled is likely to be cleared from the lungs by the mucocilliary elevator into the GI tract and again excreted unchanged in the faeces.

 

References

 

Anderson, K. A. (2009). Bioaccessibility of manganese from manganese Materials in Gastric and Lung (Alveolar) Biofluids, Oregon State University.

Griffiths, D. R. (2010). MnO: Acute inhalation Toxicity (Nose Only) Study in the Rat. Project Number 2702/0092.

O'Connor, J. B. and S. M. Woolley (2009). MnO: (Erachem/Eramet): Determination of water solubility - Project Number 2702/0009.

Pooles, A. (2009). MnO: Acute Oral Toxicity in the Rat - Fixed Dose Method. Project number 2702/0084.