Statin-induced myopathy in the rat: relationship between systemic exposure, muscle exposure and myopathy.

Rare instances of myopathy are associated with all statins, but cerivastatin was withdrawn from clinical use due to a greater incidence of myopathy. The mechanism of statin-induced myopathy with respect to tissue disposition was investigated by measuring the systemic, hepatic, and skeletal muscle exposure of cerivastatin, rosuvastatin, and simvastatin in rats before and after muscle damage. The development of myopathy was not associated with the accumulation of statins in skeletal muscle. For each statin exposure was equivalent in muscles irrespective of their fibre-type sensitivity to myopathy. The low amount of each statin in skeletal muscle relative to the liver does not support a significant role for transporters in the disposition of statins in skeletal muscle. Finally, the concentration of cerivastatin necessary to cause necrosis in skeletal muscle was considerably lower than rosuvastatin or simvastatin, supporting the concept cerivastatin is intrinsically more myotoxic than other statins.

Point mutation analysis of ras genes in spontaneous and chemically induced C57Bl/10J mouse liver tumours.

The high incidence and profile of ras gene mutations reported in spontaneous and chemically induced liver tumours of the B6C3F1 mouse provides a potential means of determining in vivo genotoxicity and its relevance to carcinogenicity. We analysed spontaneous and chemically induced [with 4-amino-biphenyl (ABP), 2-acetylaminofluorene (AAF) and diethylnitrosamine (DEN)] hepatocellular tumours of the C57Bl/10J mouse for H-ras, K-ras and N-ras gene mutations to see if mutational analysis of the ras genes could be useful for such a determination in this strain. Regions of DNA spanning codons 12, 13 and 61 of the ras genes were amplified from formalin fixed liver tumour sections using the polymerase chain reaction. Mutations were detected using allele specific oligonucleotide probing and confirmed by sequencing. We have found that there are few ras mutations in either spontaneous or chemically induced liver tumours in the C57Bl/10J mouse. Out of 25 spontaneous tumours two contained an A to T transversion and one contained an A to G transition in base 2 of H-ras codon 61 and two contained a G to A transition in base 2 of K-ras codon 13 (the K-ras mutations were only faintly detectable and may be present in a subpopulation of the tumour cells). In the case of the 18 ABP induced tumours one contained a C to A transversion in base 1 of H-ras codon 61, and one contained an A to T transversion in base 2 of H-ras codon 61 and one contained a G to C transversion in base 1 of K-ras codon 13. One C to A transversion in base 1 of H-ras codon 61 was detected out of eight AAF induced tumours. Of the 25 DEN induced tumours, one contained an A to G transition and one contained an A to C transversion in base 2 of H-ras codon 61. The data indicate that at least in hepatocellular tumours of the C57Bl/10J strain and using chronic dosing regimes the ras genes do not represent markers for in vivo genotoxic activity.

Hepatocarcinogenic effect of vinyl carbamate in the C57Bl/10J strain mouse.

The genotoxic carcinogen vinyl carbamate was dosed to C57Bl/10J strain mice for 35 weeks, and the study terminated after week 59. A main study group of 55 males and 50 females was dosed 6 mg/kg vinyl carbamate once weekly by intraperitoneal injection, whilst a reference group of 10 animals/sex were kept undosed. From week 39 onwards there was a high incidence of mortality, which was often associated with acute internal abdominal hemorrhage. Mice of both sexes killed from 34 weeks onwards frequently showed macroscopic evidence of blood-filled, cyst-like structures in the liver. Upon histopathological examination widespread peliosis hepatis was observed with frequent progression to hemangiomata and hemangiosarcomata. Trabecular hepatocellular carcinomata were also apparent, often within the same liver sections and invariably associated with peliosis hepatis. As a consequence of its tumor burden, the liver often showed hepatocyte atrophy, fibrosis, and coagulation necrosis. A small number of livers revealed hepatocellular adenomata and altered hepatocyte foci.

Urinary enzyme assays in toxicological studies in the rat and marmoset.

The relative merits of the automated, fluorimetric assay of urinary enzymes and cell exfoliation were compared with other commonly used tests for renal damage. Two types of nephrotoxic agent were used, causing crystal nephropathy and acute tubular necrosis respectively. Groups of marmosets were given one of two drugs known to cause crystal nephropathy. One agent caused intermittent increases in urinary enzyme excretion and an early increase in cell excretion which was not sustained. The second agent in contrast caused elevated cell and enzyme excretion, increasing throughout the period of administration. A nephrotoxic anti-tumour agent also caused increases in cell and enzyme excretion when given to marmosets. The early changes produced by this agent were studied using catheterised rats. Hourly samples of urine were collected and urinary beta-glycosidase excretion was found to give an early indication of renal damage, which correlated with albuminuria and glycosuria. The fluorimetric assay of urinary enzymes provides a sensitive, non-invasive test of nephrotoxicity.