Calcium dihydroxide

Basic toxicokinetics

Administrative data

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

no data available

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

Well documented and scientifically acceptable. Under physiological conditions, the hydroxyl-ions released from calcium dihydroxide following oral adminstration are neutralised in the GI tract and are therefore not relevant for consideration of toxicokinetics. Therefore for assessment of the metabolic fate of the systemically relevant species of calcium dihydroxide following administration via the oral route, the calcium ion Ca2+ is the chemical species of interest. In the current study, calcium was administered in the form of calcium gluconate (plus glycine). Gluconate is an integral component of mammalian energy metabolism and therefore toxicologically not relevant. The objective of the study was the evaluation of the absorption of calcium, including its retention and fate in the human body. In view of the limited relevance of the anionic counter-ions discussed here, calcium released both from calcium dihydroxide and calcium gluconate can be considered as structurally equivalent (analogue), and the results of the study can be used by read-across.

Data source

Reference

Reference Type:

publication

Title:

Bioavailability, biodistribution and toxicity of biocal a new calcium source. Comparative studies in rats.

Author:

Sarabia, M.I.; et al.

Year:

1999

Bibliographic source:

Nutr. Res. 19, 1223-1231

Materials and methods

Objective of study:

other: bioavailablility

Test guideline

Qualifier:

no guideline followed

Principles of method if other than guideline:

Determination of the bioavailability, biodistribution and toxicity of a calcium source.

GLP compliance:

no

Test material

Test material information

Constituent 1

Reference substance name:

"Biocal" (Calcium gluconate plus glycine)

IUPAC Name:

"Biocal" (Calcium gluconate plus glycine)

Constituent 2

Reference substance name:

Calcium gluconate

EC Number:

206-075-8

EC Name:

Calcium gluconate

Cas Number:

299-28-5

IUPAC Name:

calcium bis(2,3,4,5,6-pentahydroxyhexanoate) (non-preferred name)

Details on test material:

- Name of test material (as cited in study report): Calcium gluconate plus glycine ("Biocal")
- Physical state: solid
- Name of test material (as cited in study report): Calcium gluconate
- Physical state: solid

Radiolabelling:

yes

Remarks:

Compounds were intrinsically labeled with 45Ca (specific activity 370 GBq/g).

Test animals

Species:

rat

Strain:

Sprague-Dawley

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Weight at study initiation: 400-450 g for the male and 300-350 g for the female rats
- Fasting period before study: Before the administration of the compounds, the animals were deprived of any solid food for 10 hours. Food was not provided until 1 hour after the compounds intake.
- Housing: Animals were housed in stainless steel cages of 315 mm by 445 mm by 240 mm high with grated floor and a collection tray of the same material.
- Diet: ad libitum; normalised diet (Nutrimentos Diet No.3)
- Water: ad libitum
- Acclimation period:

ENVIRONMENTAL CONDITIONS
- Photoperiod: 12 hours dark/light cycle
No further details are given.

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

not specified

Remarks:

The brief description of the procedure for preparation and adminstration of the test substance suggests that the vehicle may have been water. However, this is in fact not further specified in the publication.

Details on exposure:

Animals were administered by means of a syringe coupled to a gastric catheter, which allowed the intake volume to be standardised to one millilitre.

Duration and frequency of treatment / exposure:

12 days

Doses / concentrations

Remarks:

Doses / Concentrations:
30 mg Ca per kg body weight

No. of animals per sex per dose / concentration:

74 male and 60 female rats

Control animals:

not specified

Positive control reference chemical:

No positive control substance was tested.

Details on study design:

- Bioavailability studies: Carried out with two groups of 7 male rats each. One of them received calcium gluconate as reference standard and the other one calcium gluconate stabilised with glycine.
- Biodistribution studies: Carried out with six groups of 10 rats/sex.
- Toxicity study: In addtion, toxicity of Biocal was investigated using six groups of ten rats/sex, receiving doses of 10, 11, 12, 13, 14 and 15 g Biocal/kg bw.

Details on dosing and sampling:

PHARMACOKINETIC STUDY (Absorption, distribution, excretion)
Bioavailability study
- Tissues and body fluids sampled: urine, faeces
- Time and frequency of sampling: Each rat was placed in a stainless steel metabolic cage, allowing the separation of urine from faeces. The urine was collected for a period of 12 days and its volume was measured daily. Samples of 1 mL were taken in triplicate and were kept for subsequent radioactivity determination.
- Other: Bioavaiability was determined by measurement of 45Ca urine excretion as a function of time and given as the percentage of the total amount of 45Ca activity in urine.

PHARMACOKINETIC STUDY (Absorption, distribution, excretion)
Biodistribution study
- Tissues and body fluids sampled: blood, other tissues
- Time and frequency of sampling: Biological distribution was carried out 12 days after administration of the compounds, in order to determine the calcium biodistribution. The rats received i.v. 1500 I.U. of heparin per kg body weight, then they were anaesthetised with diethyl ether and finally bled by sinus puncture, collecting about 15 mL blood from each rat. Afterwards, liver, spleen, bone, the gut with its content, muscle, lungs, heart, brain and kidneys were removed, washed with isotonic saline solution and weighed.
- Other: The organs were kept for subsequent radioactivity determination. The results were given as percentage of radioactivity concentration, C %.

METABOLITE CHARACTERISATION STUDIES
not examined

Statistics:

The data are presented as mean ± SD. The results were evaluated by one-way analysis of variance (ANOVA). Differences among means were tested using the Student-Newman-Keuls test. Probability levels < 0.05 were considered to be statistically significant.
Toxicity study: LD50 including confidence limits, according to the method by Litchfield and Wilcoxon.

Results and discussion

Preliminary studies:

not performed

Toxicokinetic / pharmacokinetic studies

Details on absorption:

not examined

Details on distribution in tissues:

The highest values of radioactivity concentration were found in bone, giving a value of 97.1 ± 1.3 % for Biocal and 98.7 % for calcium gluconate.

Transfer into organs

Observation:

not determined

Details on excretion:

Bioavailability was expressed as the accumulated percentage of 45Ca excreted in urine as a function of time, giving a value of 2.436 ± 1.337 % for Biocal and 1.241 ± 0.473 % for calcium gluconate. This difference was statistically significant (p<0.05).
Other excretion pathways (e.g. via faeces) were not investigated in this study.

Metabolite characterisation studies

Metabolites identified:

not measured

Details on metabolites:

Not examined.

Any other information on results incl. tables

Toxicity study with 60 female and 60 male rats:

- "Biocal": LD50 = 13.5 g/kg (12.8 -14.3 g/kg)

- Calcium gluconate: LD50 = 10 g/kg

Applicant's summary and conclusion

Conclusions:

Interpretation of results (migrated information): bioaccumulation potential cannot be judged based on study results Estimation of bioaccumulation was not an objective of this study. However, any bioaccumulation potential of calcium can be ruled out beforehand, due to its physiological role as an essential mineral nutrient. Calcium is regulated homeostatically.
The study authors concluded that "calcium from 'Biocal' has a higher bioavailability with the same metabolic behaviour than calcium from calcium gluconate with lower toxicity". However, the assessment of bioavailability only by determination of urinary excrection is not meaningful. Nevertheless, considering the retention of Ca from both sources in bone being 97.1 % (Biocal) and 98.7 % (calcium gluconate) bioavailability values of approximately 99.54 and 99.94 %, respectively, may be derived from this study. It may therefore be concluded that calcium, when available in water-soluble form (the test materials are well soluble in water), is absorbable in the intestine by almost 100 %.