Oxidative stress has been considered as a major cause of cellular
injuries in a variety of clinical abnormalities, especially neural diseases. Our aim of research is to investigate the protective effects and mechanisms of
kaempferol and
rhamnocitrin (kaempferol-7-methyl ether) on oxidative damage in rat
pheochromocytoma PC12 cells induced by a limited supply of serum and
hydrogen peroxide (H2O2). The current result demonstrated that
kaempferol protected PC12 cells from serum deprivation-induced apoptosis. Pretreatment of cells with
kaempferol also diminished intracellular generation of
reactive oxygen species (ROS) in response to H2O2 and strongly elevated cell viability. RT-Q-PCR and Western blotting revealed that
kaempferol and
rhamnocitrin significantly induced
heme oxygenase (HO)-1 gene expression. Addition of
zinc protoporphyrin (Znpp), a HO-1 competitive inhibitor, significantly attenuated their protective effects in H2O2-treated cells, indicating the vital role of HO-1 in cell resistance to oxidative injury. While investigating the signaling pathways responsible for HO-1 induction, we observed that
kaempferol induced sustained extracellular signal-regulated
protein kinase 1/2 (ERK1/2) in PC12 cells grown in low serum medium; while
rhamnocitrin only stimulated transient ERK cascade. Addition of
U0126, a highly selective inhibitor of MEK1/2, which is upstream of ERK1/2, had no effect on
kaempferol- or
rhamnocitrin-induced HO-1
mRNA expression, indicating no direct cross-talk between these two pathways. Furthermore, both
kaempferol and
rhamnocitrin were able to persistently attenuate p38 phosphorylation. Taking together, the above findings suggest that
kaempferol and
rhamnocitrin can augment cellular
antioxidant defense capacity, at least in part, through regulation of HO-1 expression and MAPK signal transduction.