Report No DWI0712

May 1995

Fluoranthene was assessed for induction of DNA repair in hepatocytes following acute oral administration to Specific Pathogen Free outbred albino Hsd/Ola Sprague-Dawley male rats at dosages of 600 and 2000 mg/kg bodyweight. The high dose of 2000 mg/kg chosen for the DNA repair test is the maximum level recommended by the UKEMS and by draft OECD guidelines and is also the OECD and EEC limit dose for acute oral toxicity testing; we consider it to be an appropriate limit for use in this system.

A negative control group was treated with the vehicle, aqueous 1 % methylcellulose and a positive control group was treated with dimethylnitrosamine at 4 mg/kg (for the 2 hour expression) or 2-acetylaminofluorine at 50mg/kg (for the 14 hour expression). Hepatocytes were isolated by enzymatic dissociation a 2 or 14 hours after exposure of the animals to the test substance. Four animals were assessed at each experimental point with the exception that only two animals from the positive control group were assessed at each expression time.

The isolated hepatocytes were allowed to attach to glass coverslips and were cultured in vitro with tritiated (methyl-3H)thymidine a 10 µCi/ml for four hours to 'radiolabel' replicating DNA. The hepatocytes were 'chased' for 24 hours with unlabelled thymidine then they were fixed and processed for autoradiography. DNA repair was assessed by comparing the labelling levels of hepatocyte nuclei from treated animals with control values and with the accompanying cytoplasmic labelling levels (usually a total of 150 cells per animal were examined).

Fluoranthene did not cause any substantial increases in either the gross nuclear grain count or the net nuclear grain count (ie the gross nuclear grain count minus the cytoplasmic grain count) at any dose level at either sampling tie.

Positive control group animals showed a large and highly significant increase (P<0.001) in the net nuclear grain count which was accompanied by a large increase in the gross nuclear grain count.

It is concluded that fluoranthene did not elicit any evidence of DNA-damage in the rat liver in this in vivo test system

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