Purpose: This study was aimed to investigate the effects of a phenolic antioxidant, butylated hydroxyanisole (BHA) and its metabolite, tert-butylhydroquinone (tBHQ) on the induction of HO-1, NQO1 and Nrf2 proteins and their regulatory mechanisms in primary-cultured hepatocytes.
Methods: After exposure of BHA and tBHQ to primary-cultured rat and human hepatocytes and mouse neonatal fibroblasts (MFs), Western blot, semi-quantitative RT-PCR and microarray analysis were conducted.
Results: Induction of HO-1, NQO1 and Nrf2 proteins and activation of ERK1/2 and JNK1/2 were observed after BHA and tBHQ treatments in primary-cultured rat and human hepatocytes. Semi-quantitative RT-PCR study and microarray analysis revealed that HO-1 and NQO1 were transcriptionally activated in primary-cultured rat hepatocytes and a substantial transcriptional activation, including HO-1 occurred in primary-cultured human hepatocytes after BHA treatment. Whereas BHA failed to induce HO-1 in wild-type and Nrf2 knock-out MFs, tBHQ strongly induced HO-1 in wild-type, but not in Nrf2 knock-out MFs.
Conclusions: Our data demonstrate that both BHA and tBHQ are strong chemical inducers of HO-1, NQO1 and Nrf2 proteins in primary-cultured human and rat hepatocytes with the activation of MAPK ERK1/2 and JNK1/2. However, in MFs, BHA failed to induce HO-1, whereas tBHQ strongly induced HO-1 in Nrf2 wild-type but not in Nrf2 knock-out, suggesting that Nrf2 is indispensable for tBHQ-induced HO-1 in MF.