Registration Dossier

Toxicological information

Neurotoxicity

Currently viewing:

Administrative data

Endpoint:
neurotoxicity: short-term oral
Type of information:
experimental study
Adequacy of study:
supporting study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: see 'Remark'
Remarks:
Well-documented publication with some restrictions Restrictions: - only six animals per group were tested - only one dose was tested - no positive control was tested - no detailed clinical observations, functional testing or (neuro)histopathology was conducted
Cross-reference
Reason / purpose:
reference to same study

Data source

Reference
Reference Type:
publication
Title:
The similar neurotoxic effects of nanoparticulate and ionic silver in vivo and in vitro
Author:
Hadrup, N. et al.
Year:
2012
Bibliographic source:
NeuroToxicology 33, 416 - 423

Materials and methods

Test guideline
Qualifier:
no guideline followed
Principles of method if other than guideline:
The neurotoxic effects of silver acetate were examined in female Wistar rats. Administered orally by gavage rats (n = 6/group) were given a vehicle control (PVP, 11.5 mg/mL) and 14 mg silver acetate/kg bw/day (equal to 9 mg Ag/kg bw/day) for 28 days. The total brain concentrations of dopamine, noradrenaline and 5-hydroxytryptamine (5-HT) were measured.
GLP compliance:
not specified
Limit test:
no

Test material

Reference
Name:
Unnamed
Type:
Constituent
Test material form:
other: solution
Details on test material:
- Name of test material (as cited in study report): silver acetate (Sigma, St. Louis, prod. no. 204374)
- Analytical purity: 708 µg/mL (with 11.5 mg/mL polyvinylpyrrolidone (PVP))

Test animals

Species:
rat
Strain:
Wistar
Sex:
female
Details on test animals and environmental conditions:
TEST ANIMALS - rats with a specific pathogen-free health status
- Source: Taconic M&B, Lille Skensved, Denmark
- Age at study initiation: 4 weeks old
- Housing: rats were housed two per cage (Macrolon, Buguggiate, Italy)
- Diet (ad libitum): standard diet (Altromin prod. no. 1324, Brogården, Gentofte, Denmark)
- Water (ad libitum): citric acid acidified tap water
- Acclimation period: 1 week

ENVIRONMENTAL CONDITIONS
- Temperature: 22 ± 1°C
- Relative humidity: 55 ± 5%
- Photoperiod (hrs dark / hrs light): 12/12

Administration / exposure

Route of administration:
oral: gavage
Vehicle:
other: polyvinylpyrrolidone (PVP)
Details on exposure:
SILVER SUSPENSIONS
Silver acetate was dissolved in 11.5 mg/mL polyvinylpyrrolidone.

The gavage volume given to the rats was 10 mL/kg.

The rats of the vehicle control group were given 11.5 mg/mL of the vehicle.
Analytical verification of doses or concentrations:
not specified
Details on analytical verification of doses or concentrations:
no data
Duration of treatment / exposure:
28 days
(additional group, used for the vehicle control group to determine an optimal dose, for only 14 days)
Frequency of treatment:
once daily
Doses / concentrations
Remarks:
Doses / Concentrations:
14 mg silver acetate/kg bw/day (equal to 9 mg Ag/kg bw/day)
Basis:
actual ingested
No. of animals per sex per dose:
6 female rats
Control animals:
yes, concurrent vehicle

Examinations

Observations and clinical examinations performed and frequency:
CAGE SIDE OBSERVATIONS: No data

DETAILED CLINICAL OBSERVATIONS: No data

BODY WEIGHT: No data

FOOD CONSUMPTION AND COMPOUND INTAKE (if feeding study):
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: No data
- Compound intake calculated as time-weighted averages from the consumption and body weight gain data: No data

WATER CONSUMPTION AND COMPOUND INTAKE (if drinking water study): No data

OPHTHALMOSCOPIC EXAMINATION: No data
Specific biochemical examinations:
The total brain concentrations of dopamine, noradrenaline and 5-hydroxytryptamine were measured in homogenates. Noradrenaline, dopamine and 5-hydroxytryptamine concentrations were analyzed using high performance liquid chromatography (HPLC) with electrochemical detection. (Lam et al., 1992)*.

*Reference
- Lam, HR, Lof, A. Ladefoged, O. Brain concentrations of white spirit components and neurotransmitters following a three week inhalation exposure of rats. Pharmacol Toxicol 1992: 70: 394-6.
Neurobehavioural examinations performed and frequency:
FUNCTIONAL OBSERVATIONAL BATTERY: No data

LOCOMOTOR ACTIVITY: No data

AUDITORY STARTLE REFLEX HABITUATION: No data

LEARNING AND MEMORY TESTING: No data
Sacrifice and (histo)pathology:
After anaesthethesia in CO2/O2 and euthanasia by decapitation brains were removed and homogenized.
Positive control:
no data
Statistics:
The data are presented as the mean ± standard error of the mean (SEM). For the neurotransmitter measurements significant differences were determined using an ANOVA with a Bonferroni's multiple comparisons test. Statistics were completed using GraphPad Prism 5.0 (GraphPad Software, La Jolla, CA).

Results and discussion

Results of examinations

Clinical signs:
not examined
Mortality:
not examined
Body weight and weight changes:
not examined
Food consumption and compound intake (if feeding study):
not examined
Food efficiency:
not examined
Water consumption and compound intake (if drinking water study):
not examined
Ophthalmological findings:
not examined
Clinical biochemistry findings:
effects observed, treatment-related
Behaviour (functional findings):
not examined
Gross pathological findings:
no effects observed
Neuropathological findings:
not examined
Other effects:
not examined
Description (incidence and severity):
Migrated information from 'Further observations for developmental neurotoxicity study'



Details on results (for developmental neurotoxicity):not applicable (migrated information)
Details on results:
BIOCHEMISTRY
1) Dopamine:
- rats treated with silver acetate for 28 days show an increased dopamine concentration in the brain when compared with the controls (mean ± SEM; Control: 4.0 ± 0.2 nmol/g brain tissue vs. AgAc 9 mg Ag/kg bw/day: 5.3 ± 0.2 nmol/g brain tissue, p < 0.01).

2) 5-hydroxytryptamine:
- The 5-hydroxytryptamine was not increased following silver acetate administration.

3) Noradrenaline
- following 28 days of silver administration, concentration of noradrenaline in the brain were altered. The noradrenaline brain concentration was increased following silver acetate administration (Control: 1.7 ± 0.08 nmol/g brain tissue vs. AgAc 9 mg Ag/kg bw/day: 2.0 ± 0.05 nmol/g brain tissue, p < 0.05)

GROSS PATHOLOGY
The brain weight was not affected by silver acetate treatment.

Effect levels

Based on:
test mat.
Sex:
female
Basis for effect level:
other: Silver acetate affected noradrenaline and dopamine.
Remarks on result:
not measured/tested
Remarks:
Effect level not specified

Any other information on results incl. tables

In vitro examination

- Viability measurements: after 4 hours of incubation with silver acetate the number of dead cells was increased (5 fold) at a concentration of 5 µg Ag/mL. After 24 hours of incubation with 5 µg Ag/mL, the number of dead cells was increased (12 fold) and the number of living cells was decreased (3.5 fold). After 48 hours of incubation, the number of dead cells exposed to 5 µg Ag/mL was increased (23 fold) and the number of living cells was decreased after expsoure to 0.5 and 5 µg Ag/mL (2 and 12 fold, respectively). At 10 µg/mL, silver acetate was highly cytotoxic.

- Necrosis detection: a clear band of HMGB1 protein was seen in the positive control. After 24 hours of incubation, apoptosis, measured with TUNEl staining, was observed in PC12 cells exposed to all doses of silver acetate, except 0.06 µg/mL. Silver acetate (1 µg/mL) apoptosis was inhibited by caspase 8 and 9 inhibitors. Neither the caspase 8 nor the caspase 9 inhibitor affected the control level of apoptpsis observed.

Applicant's summary and conclusion

Conclusions:
According to the authors, silver acetate affected brain neurotransmitter concentrations. Silver acetate affected noradrenaline and dopamine.