Elevated and Prolonged Lead Exposure in Fisher 344 Rats Leads to Marked Hepatic Differentially Expressed Genes

Purpose: The emergence of DNA chip technology has dramatically increased the number genes that can be studied simultaneously. It has afforded toxicologists the opportunity to study thousands of genes at the same time. Affymetrix DNA Microarray analyses were used to assess hepatic gene expression patterns in Male Fisher 344 rats exposed to 0ppm, 50ppm and 500ppm lead (as acetate).

Methods: Total RNA was isolated and used for cDNA synthesis, as a template for T7 polymerase in the synthesis of cRNA molecules. These cRNA molecules were cleaned up, fragmented and hybridized to GeneChip® Rat Expression Array Set 230 (RAE 230A) and subsequently scanned as described in Affymetrix GeneChip™ one-cycle eukaryotic target labeling assay.

Results: The scatterplot data suggest a greater number of genes were differentially expressed in the 90 days 500 ppm Pb2+ treatment than the other dose groups. Interestingly, 90 days 50 ppm treatment showed less than half the number of genes expressed compared to the 30 days treatment. In contrast, the 90 days 500 ppm group had over one thousand genes differentially expressed at 2-fold and more than twice the number of genes of the other treatment groups at 3-, 5-, and 10-fold levels. Gene precursors for proteins such as FBJ murine osteosarcoma viral oncogene homolog, heat shock protein, protein kinase and proliferating cell nuclear antigen were ten fold up/down-regulated.

Conclusion: In summary, effects associated with lead exposure are dose and time dependent. Response to lead poisoning was observed to be almost similar for the short term treatment period irrespective of lead dose levels. However, when the dose levels were low over long periods of time, toxic effects are minimized due to adaptive response over time. On the contrary, lead exposure for long periods of time results in adverse effects in the form of increase incidence of lead-induced gene expression.