Gene Expression Profiling of Rat Livers Reveals Indicators of Potential Adverse Effects

Abstract

This study tested the hypothesis that gene expression profiling can reveal indicators of subtle injury to the liver induced by a low dose of a substance that does not cause overt toxicity as defined by conventional criteria of toxicology (e.g., abnormal clinical chemistry and histopathology). For the purpose of this study we defined this low dose as subtoxic, i.e., a dose that elicits effects which are below the detection of conventional toxicological parameters. Acetaminophen (APAP) was selected as a model hepatotoxicant because (1) considerable information exists concerning the mechanism of APAP hepatotoxicity that can occur following high doses, (2) intoxication with APAP is the leading cause of emergency room visits involving acute liver failure within the United States, and (3) conventional clinical markers have poor predictive value. Rats treated with a single dose of 0, 50, 150, or 1500 mg/kg APAP were examined at 6, 24, or 48 h after exposure for conventional toxicological parameters and for gene expression alterations. Patterns of gene expression were found which indicated cellular energy loss as a consequence of APAP toxicity. Elements of these patterns were apparent even after exposure to subtoxic doses. With increasing dose, the magnitude of changes increased and additional members of the same biological pathways were differentially expressed. The energy loss suggested by gene expression changes was confirmed at the 1500 mg/kg dose exposure by measuring ATP levels. Only by ultrastructural examination could any indication of toxicity be identified after exposure to a subtoxic dose of APAP and that was occasional mitochondrial damage. In conclusion, this study provides evidence that supports the hypothesis that gene expression profiling may be a sensitive means of identifying indicators of potential adverse effects in the absence of the occurrence of overt toxicity.

In vitro gene expression analysis of hepatotoxic drugs in rat primary hepatocytes

“…Therefore, the reason for the lack of the increased oxidative stress related gene was not clear. No decreased genes related to gluconeogenesis or fatty acid synthesis were observed, unlike an in vivo study of APAP (Heinloth et al, 2004). These changes were also not observed in the in vitro study at a low concentration (de Longueville et al, 2003).…”

“…No effects were observed on proliferation-associated genes or antioxidants, unlike CPA (Table 3C). A previous in vivo study showed that oxidative stress in the rat liver represented by an increased Hmox1 was induced by a high dose of APAP but not by low doses (Heinloth et al, 2004) and so it was considered that the lack of oxidative stress in the present study could possibly be from the low concentration. On the contrary, a previous study in rat hepatocytes exposed to a lower concentration (1000 μM) of APAP for 24 h showed induced liver Gst-Ya (de Longueville et al, 2003), which appeared to be consistent with the above-mentioned in vivo study in rats at an intensive dose by Huang and colleagues.…”

“…Decreases of steroid synthesisassociated genes such as LOC191574, Sult1a1, cyp51 and Hmgcr at 24 h were observed. Decreased steroid synthesisassociated genes have also been reported in an in vivo study (Heinloth et al, 2004) but the only commonly affected gene was Sult1a1. These kinds of changes in Cyps and steroid synthesis-associated genes were not observed in the in vitro study at a low concentration of APAP (de Longueville et al, 2003).…”

A Sparse PLS for Variable Selection when Integrating Omics Data

“…Liver Toxicity study In the liver toxicity study (Heinloth et al, 2004), 4 male rats of the inbred strain Fisher 344 were exposed to non-toxic (50 or 150 mg/kg), moderately toxic (1500 mg/kg) or severely toxic (2000 mg/kg) dose of acetaminophen (paracetamol) in a controlled experiment. Necropsies were performed at 6, 18, 24 and 48 hours after exposure and the mRNA from the liver was extracted.…”

New Insights into Functional Aspects of Liver Morphology

“…(Median lobe vessels are yellow, left lobe in blue, caudate sublobes in tan, and right sublobes in white.) teomics technologies (Heinloth et al, 2004;Irwin et al, 2004aIrwin et al, , 2004b, also is a good example for understanding and utilizing "phenotypic anchoring" to better understand genomics data. Previous studies have revealed that there is an unexplained and striking inter-and intralobular variability of acute hepatic necrosis with some regions having massive necrosis and adjacent areas within the lobe or other lobes from the same animal showing no injury at all (Figure 1) (Irwin et al, 2004b).…”