An evaluation of a low-density DNA microarray using cytochrome P450 inducers.

The aim of this study was to validate a low-density DNA microarray "Rat HepatoChip", which contains 59 genes from a range of potential toxic markers and drug metabolism-related genes. Liver mRNA was isolated from rats dosed with six different chemicals, dexamethasone, troleandomycin, miconazole, clotrimazole, and methylclofanapate, which are all known to induce different cytochrome P450 genes, and isoniazid, which does not cause histopathological changes. Replicate microarrays were used to measure the variability in the chips and in the process. The average variability in signal between different chips observed in triplicate experiments was 33% ranging from 21 to 39% depending on genes. We also demonstrated a strong correlation between the liver histopathology and the gene expression profiles indicating that the gene expression profile reflects histopathological changes. These results suggest that the Rat HepatoChip microarray may provide a fast and effective tool for assessing the toxicity profile of developmental drug candidates during the drug discovery process.

Changes in protein and mRNA levels of growth factor/growth factor receptors in rat livers after administration of phenobarbitone or methylclofenapate.

The effects of phenobarbitone and methylclofenapate were studied on the expression of growth factor and growth factor receptors in livers of male Wistar rats. The major findings were: (1) a significant reduction in epidermal growth factor receptor (EGFR) protein observed with both treatments, and (2) levels of EGFR transcripts were only slightly decreased with both compounds. The reduction in the receptor level therefore does not occur via regulation of transcription. Mannose-6-phosphate receptors (M6PR, also called insulin-like growth factor II receptor) and M6PR transcripts remained unchanged in both experimental groups. Hepatocyte growth factor receptor (HGFR) transcripts were also unchanged in both experimental groups. Transcript levels of transforming growth factor-beta 1 (TGF-beta 1) were lower in both treatment groups compared with the control; the reduction was significant in the methylclofenapate group. This may have relevance to the finding by others that nafenopin, another peroxisome proliferator, suppresses rat hepatocyte apoptosis. Another finding of general interest was that the three "housekeeping genes", namely albumin, actin and glyceraldehyde-3-phosphate dehydrogenase, were influenced by both treatments thus limiting their use as controls for gel loading. The adaptation of a growth regulatory mechanism via EGFR and its ligands may provide conditions such that cells with aberrant growth control have a selective growth advantage over normal cells thus promoting tumorigenesis.