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Basic toxicokinetics

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basic toxicokinetics
Type of information:
experimental study
Adequacy of study:
weight of evidence
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Well documented publication in a peer reviewed journal

Data source

Reference Type:
Phthalate Esters I: Effects on Cytochrome P-450 Mediated Metabolism in Rat Liver and Lung, Serum Enzymatic Activities and Serum Protein Levels
Walseth F., Toftgard R., Nilsen O.G.
Bibliographic source:
Arch Toxicol (1982) 50 : 1-10

Materials and methods

Principles of method if other than guideline:
The study assessed the influence of DMP on liver and lung metabolism. Total protein content as well as the amount of Cyp P450, Cytochrom b5 and cytochrom-c-reductase were analyzed in the two organs. Serum proteins were assessed as markers for liver toxicity. Liver and lung microsomes were isolated, incubated with n-hexane or benzo(a)pyrene, and the rate of metabolite formation was assesssed.
GLP compliance:
not specified

Test material

Constituent 1
Test material form:
Specific details on test material used for the study:
- Name of test material (as cited in study report): dimethylphthalate (DMP)
- Analytical purity: 98-100%

Test animals

Details on test animals or test system and environmental conditions:
- Diet (e.g. ad libitum): ad lib.
- Water (e.g. ad libitum): ad lib.

Administration / exposure

Route of administration:
Duration and frequency of treatment / exposure:
5 days (injections on Days 1, 2, 3, 5, 6, in the morning)
Doses / concentrations
Doses / Concentrations:
3.8mM / kg (738 mg/kg)
No. of animals per sex per dose / concentration:
Control animals:
Details on study design:
Control animals received injections of 0.9% (w/v) sodium chloride

Rat liver and lung microsomal fractions were prepared as previously described by ToftgArd et al . (1980) and Johannesen et al . (1977) respectively .
The microsomes were finally diluted in a 0 .05 M sodium phosphate buffer, pH 7 .4, containing 1 x 10-° M EDTA. The protein concentration in the microsomal preparations was determined by the method of Lowry et al . (1951) using bovine serum albumin as standard . All the microsomal enzyme assays were performed in the morning after storage of the microsomes over night at 4° C. This storage did not influence the measured activities .

The in vitro formation of benzo(a)pyrene metabolites in liver and lung microsomes was assayed by incubating 106 nmol of benzo(a)pyrene added 11 nmol and 33 nmol 14C-labelled benzo(a)pyrene (specific activity 21 .7 mCi/[Lmol) for liver and lung incubations respectively . 0 .75 mg and 3 mg of microsomal protein was used for liver and lung respectively . The incubation time at 37° C was 30 min with a total incubation volume of 1 ml 0 .1 M sodium phosphate buffer, pH 7 .4 .

The in vitro formation of n-hexane metabolites in liver and lung microsomes was assayed by incubating 50 gl of a 8% (v/v) solution of n-hexane with 1 mg of liver or lung microsomal protein for 10 min in a total volume of 3 ml 0 .05 M sodium phosphate buffer, pH 7.7.
Students t-test was used in all group comparisons and p-values less than 0 .05 were considered significant .

Results and discussion

Any other information on results incl. tables

Liver and lung weight were unaffected by treatment.

There was no significant difference in the amount of P450 or cytochrom c reductase in lung or liver, but the amount of cytochrome b5 was increased in the liver (+25%), but not in the lung.

Treatment was DMP had no effect on serum ALAT, ASAT, Alkaline phophatase, albumin, and total protein.

Hydroxylation of benzo(a)pyrene in liver and lung microsomes from rats treated with DMP was not significantly different from controls.

The cytochrome P-450 enzyme system in the lung was ten times more effective than that in the liver as far as metabolism of n-hexane was concerned in control and treated animals.

Hydroxylation of n-hexane was increased in the liver, but not in the lung microsomes from DMP treated rats, indicating that DMP induces specific CAP P450 isoforms (likely 2B6) in the liver, where the major share of DMP is likely metabolised. This matches data from several other studies, that also reported indications of increased liver metabolism after DMP treatment.

Results for DMP differed from those obtained for DBP and DEHP.

Applicant's summary and conclusion