Validation of reference gene stability for APAP hepatotoxicity studies in different in vitro systems and identification of novel potential toxicity biomarkers.
Acetaminophen (APAP) is widely used for the treatment of pain and fever. Although it is safe at therapeutic doses, APAP is toxic at higher doses and can cause severe damage to the liver. To clarify the mechanism of APAP-related liver damage, we attempted the identification of the differential gene expression in response to APAP treatment in hepatic HepG2 cells. In the present study, we used the technique of suppression subtractive hybridization (SSH) for the identification of the differentially expressed genes between untreated and treated cells and identified 14 candidate genes showing increased expression in response to APAP treatment. RT-PCR and real-time RT-PCR analysis confirmed that the expression of two genes was increased within 24 h following APAP treatment. Among them, only lysyl hydroxylase 2 expression was increased in a time- and dose-dependent manner. Furthermore, the expression of lysyl hydroxylase 2 was shown to be increased in the livers of APAP-treated mice compared to untreated controls. The increased expression of lysyl hydroxylase 2 was also observed when the cells were exposed to other hepatotoxins, ethanol and isoniazid. Since lysyl hydroxylase 2 is known to be a key enzyme of liver fibrosis, the increased expression of lysyl hydroxylase 2 may be involved in hepatotoxins-related liver fibrosis.