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

Lead contamination of soil and drinking water represent a significant risk to human health, especially for developing infants. Various methods are employed in determining lead intoxication effects on humans using rats as model organisms. In this study 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). Six weeks post-weaning male Fisher 344 rats were exposed to 0 or 50 or 500 ppm Pb2+ through drinking water ad libitum for 30 and 90 days. Two independent experiments were carried out for each time point. Following each exposure period, rats were euthanitized with CO2 and blood was collected for serum analysis by cardiac puncture. Livers were excised and snap frozen in liquid nitrogen. Total RNA was isolated from rat livers using Qiagen RNA Isolation kit. Then cDNA was synthesized for use 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. A total of over 2300 genes were then used in differential gene expression analysis by scatterplot. 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. Using a 2-fold expression difference threshold, genes either up/down-regulated appear to be the same for both treatments during the 30 days exposure period. 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 ATPase inhibitor, heat shock protein and cytochrome P450 were ten fold up/down-regulated.