Upregulation of heme oxygenase-1 by brazilin via the phosphatidylinositol 3-kinase/Akt and ERK pathways and its protective effect against oxidative injury.

Heme oxygenase (HO)-1 is a cytoprotective enzyme that is activated by various phytochemicals. We examined the ability of brazilin to upregulate HO-1 expression in auditory cells. We found that brazilin induced the expressions of HO-1 mRNA and protein in concentration- and time-dependent manners. Brazilin induced nuclear factor-E2-related factor 2 (Nrf2) nuclear translocation, and dominant-negative Nrf2 attenuated brazilin-induced expression of HO-1. Brazilin induced a temporary increase in the phosphorylation of Akt. While LY294002, a non-selective phosphotidylinositol 3-kinase (PI3K) inhibitor, was able to reduce brazilin-induced phosphorylation of Akt and the subsequent induction of HO-1. Brazilin activated the extracellular signal-regulated kinase (ERK) and p38 pathways, and the ERK pathway played an important role in HO-1 expression. Brazilin protected the cells against t-butyl hydroperoxide (t-BHP)-induced cell death. The protective effect of brazilin was abrogated by anti-sense oligodeoxynucleotides (ODN) against the HO-1 gene. These results demonstrate that the expression of HO-1 by brazilin is mediated via the PI3K/Akt and ERK pathways, and this expression inhibits t-BHP-induced cell death in House Ear Institute-Organ of Corti 1 (HEI-OC1) cells.