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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:
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-referenceopen allclose all
Reason / purpose for cross-reference:
reference to same study
Reason / purpose for cross-reference:
reference to other study

Data source

Reference
Reference Type:
publication
Title:
Bioavailability in the Rat of Zinc and Iron from the Basic Salts Zn5(OH)8Cl2.H2O, Fe(OH)SO4 and Fe4(OH)11NO3.2H2O
Author:
Galvez-Morros M, Garcia-Martinez O, Wright AJA & Southon S
Year:
1992
Bibliographic source:
Food Chem. 43(5):377-381

Materials and methods

Objective of study:
absorption
excretion
Principles of method if other than guideline:
Bioavailability of zinc in Wistar rats from diets containing zinc carbonate was measured.
GLP compliance:
no

Test material

Constituent 1
Chemical structure
Reference substance name:
Carbonic acid, zinc salt, basic
EC Number:
257-467-0
EC Name:
Carbonic acid, zinc salt, basic
Cas Number:
51839-25-9
Molecular formula:
Zn(x/2+y).(OH)x.(CO3)y
IUPAC Name:
zinc hydroxy carbonate
Constituent 2
Chemical structure
Reference substance name:
Zinc carbonate
EC Number:
222-477-6
EC Name:
Zinc carbonate
Cas Number:
3486-35-9
Molecular formula:
CO3.Zn
IUPAC Name:
zinc carbonate
Details on test material:
- Name of test material (as cited in study report): Zinc carbonate
- Specific activity (if radiolabelling): ZnCl2, 3.7-92.5 MBq/mg Zn
- Locations of the label (if radiolabelling): Zn
- Provided by Amersham International, Aylesbury, UK
Radiolabelling:
yes

Test animals

Species:
rat
Strain:
Wistar
Sex:
male
Details on test animals or test system and environmental conditions:
TEST ANIMALS
- Age at study initiation: Adult (experiment 1), immature rats (experiment 2)
- Weight at study initiation: 150-170 g (experiment 1), 75-80 g (experiment 2)
- Fasting period before study: Overnight
- Housing: Singly in polypropylene cages with stainless steel gridded tops and bottoms
- Individual metabolism cages: No
- Diet (e.g. ad libitum): SS control diet (containing FeSO4.7H2O, 174 mg/kg diet equivalent to Fe added at 35 mg/kg), ad libitum for 5 d. After 5 d, rats then received SS diets (in restricted amounts, 20 g/d; 80 to 100% of ad libitum intake), containing Zinc carbonate (25 mg/kg) for a further 14 d, with zinc added at 13 mg/kg and iron added at 35 mg/kg diet.


ENVIRONMENTAL CONDITIONS
- Temperature (°C): 21 °C
- Photoperiod (hrs dark / hrs light): 12/12

Administration / exposure

Route of administration:
oral: feed
Vehicle:
other: cooked starch-sucrose water (1:1:6) paste
Details on exposure:
DIET PREPARATION

Experiment 1:
- Mixing appropriate amounts with (Type of food): 5 g meal of cooked starch-sucrose water (1:1:6) paste containing 130 µg Zn as ZnCO3 extrinsically labelled with 37 kBq 65Zn (ZnCI2, 3.7-92.5 MBq/mg Zn); given to rats for 1 h
- SS control diet (containing FeSO4.7H2O, 174 mg/kg diet equivalent to Fe added at 35 mg/kg), ad libitum was provided 6 h after consumption of the test meal

Experiment 2:
- SS control diet (as in experiment 1), ad libitum for 5 d. After 5 d, rats then received SS diets (in restricted amounts, 20 g/day; 80 to 100% of ad libitum intake), containing Zinc carbonate (25 mg/kg) and Ferrous sulfate (174 mg/kg diet) for a further 14 d.
- At the beginning of the experiment, rats were injected subcutaneously with 37 kBq 65Zn (in 0.2 mL saline) into the scruff of the neck and whole-body counted immediately and then again every day until the end of the experiment
Duration and frequency of treatment / exposure:
Experiment 1: Single exposure, rats were allowed to consume the test meal for 1 h
Experiment 2: Test meal (in restricted amounts, 20 g/day; 80 to 100 % of ad libitum intake), 14 d
Doses / concentrations
Remarks:
Doses / Concentrations:
Experiment 1: ZnCO3, extrinsically labelled with 37 kBq 65Zn
Experiment 2: ZnCO3, 25 mg/kg
No. of animals per sex per dose / concentration:
15
Control animals:
no
Positive control reference chemical:
No
Details on study design:
- Animal assignment: Random
Details on dosing and sampling:
PHARMACOKINETIC STUDY (Absorption, excretion)
- Tissues and body fluids sampled (delete / add / specify): Whole body, faeces, plasma and femur

Experiment 1:
- Time and frequency of sampling: Whole body counted immediately after consuming the meal (Day 0) and then again each day until the end of the experiment (Day 14). Faeces were collected from Day 0 to Day 4, pooled for each rat, and counted for 65Zn.
- Method type(s) for identification: Whole-body radioactivity was measured using an NE 8112 small-animal whole-body gamma counter (NE Technology, Beenham, Berkshire, UK)

Experiment 2:
- Time and frequency of sampling: Whole body counted immediately after injecting 65Zn (Day 0) and then again each day until the end of the experiment. Iron status of rats was assessed via measurement of liver iron content, red blood cell count (RBC), packed cell volume (PCV), mean cell volume (MCV) and haemoglobin (Hb) concentration. Zinc status of rats was assessed via plasma and femur Zinc concentration.
- Method type(s) for identification: Iron (liver) and Zinc (femur) contents were determined by atomic absorption spectroscopy, using a PU 9000 (Pye Unicam, Cambridge, UK). Deproteinated plasma was analysed directly for Zinc. RBC, PCV, MCV and Hb concentration were determined promptly on samples of heparinised whole blood, using a semiautomated Coulter counter (model CBC-5, Coulter Electronics, Luton, UK).
Statistics:
F-test (when the variances differed significantly); t-test (where the variance ratio showed a treatment effect)

Results and discussion

Preliminary studies:
Not applicable

Toxicokinetic / pharmacokinetic studies

Details on absorption:
65Zn absorption (%) = 48.4±3.0
Details on distribution in tissues:
Plasma Zinc = 1.86±0.034 µg/mL
Femur Zinc = 145.8±3.1 µg/g dry wt
Transfer into organs
Observation:
not determined
Details on excretion:
Fractional rate of 65Zn loss/day = 0.0169±0.0005 (experiment 1) & 0.0098±0.0008 (experiment 2)

Metabolite characterisation studies

Metabolites identified:
not measured
Details on metabolites:
Not applicable

Any other information on results incl. tables

Table 1. Experiment 2: Observations in rats fed for 2 wk on SS diets containing ZnCO3 & FeSO4.7H2O

Dietary treatment

Zinc carbonate

Food intake (g)

277.7

Weight gain (g)

102.9

RBC (X 1012/L)

7.00

MCV (GM)< (fl)

62.47

log10MCV

1.7957

PCV (1/L)

0.439

Hb (g/L)

151.0

Liver: dry weight (g)

3.112

Fe (GM) (µg/g dry wt)

223.3

log10Fe concentration

2.3489

Total Fe (GM) (mg)

694.5

log10total iron

2.8417

Experiment 3:

- In this experiment, 65Zn absorption (%) and fractional rate of 65Zn loss/day from [65Zn]Zinc chloride were determined to be 45.1±2.1 and 0.0171±0.0006, respectively.

- Data obtained from the experiment with other salts indicated that the availability of Zinc from Zn5(OH)8CI2.H2O was similar to that from ZnCO3 and ZnCI2, and hence, the basic Zinc salt is of high bioavailability. The availability of iron from the basic iron salts, however, was very poor when compared to ferrous sulphate.

Applicant's summary and conclusion

Conclusions:
Under the test conditions, the test material was determined to possess high bioavailability.
Executive summary:

A study was conducted to determine the bioavailability of Zinc salts in male Wistar rats.

In experiment 1, Zinc absorption from ZnCO3, extrinsically labelled with 65Zn, was measured. In experiment 2, rats were fed ad libitum for 2 wk on semisynthetic diets containing ZnCO3 as the Zinc source (13 mg Zn/kg diet) and FeSO4.7H2O as the iron source (35 mg Fe/kg diet). After 2 wk, rats were sacrificed and the zinc and iron status were determined. Whole body counted immediately after consuming the meal (in experiment 1) or after injecting 65Zn (experiment 2) and then again each day until the end of the experiment.

 

65Zn absorption (%) and fractional rate of 65Zn loss/day from Zinc carbonate was determined to be 48.4±3.0 and 0.0169±0.0005 (experiment 1) or 0.0098±0.0008 (experiment 2), respectively. Plasma and femur Zinc was determined to be 1.86±0.034 µg/mL and 145.8±3.1 µg/g dry wt, respectively.

 

Under the test conditions, the test material was determined to possess high bioavailability. However it must be noted that in this study other zinc compounds were tested and no distinction was made between the different zinc compounds during the observations.