Two-dimensional electrophoresis of liver proteins: Characterization of a drug-induced hepatomegaly in rats

Two-dimensional electrophoresis (2-DE) of liver proteins was applied to fur ther characterize an unusual drug-induced increase in heptocellular rough e ndoplasmic reticulum (RER) in Sprague-Dawley rats given a substituted pyrim idine derivative. Absolute liver weights of drug-treated rats (9.9 +/- 0.4 g) increased above vehicle-treated controls (7.2 +/- 0.2 g) by 37%. Light m icroscopy revealed diffuse granular basophilia of the hepatocellular cytopl asm, uncharacteristic of hepatocytes and suggested cells rich in ribosomes, which was confirmed by electron microscopy. Immunostaining for cell prolif eration, viz., 5-bromo-2'-deoxyuridine (BrdU) and proliferating cell nuclea r antigen (PCNA), indicated marked hepatocellular proliferative activity. 2 -DE of solubilized liver using an ISO-DALT gel system indicated significant (p < 0.001) quantitative changes in at least 17 liver proteins (12 increas ed, 5 decreased) compared to controls. The protein with the largest increas e was homologous to acute-phase reactant, contrapsin-like protein inhibitor -6. Other markedly upregulated proteins were methionine adenosyltransferase , a catalyst in methionine/ATP metabolism and mitochondrial HMG-CoA synthas e, involved in cholesterol synthesis. The complementary strategies of 2-DE coupled either with database spot mapping or protein isolation and amino ac id sequencing successfully identified a subset of proteins from xenobiotic- damaged rodent livers, the expression of which differed from controls. Howe ver, the current bioinformatics platform for rodent hepatic proteins and li mited knowledge of specific protein functionality restricted application of this proteomics profile to further define a mechanistic basis for this unu sual hepatotoxicity.