The effect of secoisolariciresinol diglucoside on oxidative stress and inflammation in cardiac iron overload

Abstract

Chronic cardiac iron overload directly correlates with cardiac dysfunction and may ultimately cause heart failure. Although recent studies have suggested that altered calcium homeostasis and increased reactive oxygen species (ROS) play roles in iron overload-induced cardiac dysfunction, the exact mechanism(s) of oxidative stressmediated cardiac inflammation, matrix remodelling and cell death remain unclear. Here we examined iron-induced cardiac damage in terms of oxidative stress, inflammation and apoptosis in an in vitro model of cardiac iron overload using the H9c2 cardiac cells. We also investigated the effect of secoisolariciresinol diglucoside (SDG), a component of flaxseed, on the above mentioned parameters. H9c2 cells were treated with 50 μM iron and a pre-treatment of 500 μM SDG was performed by dissolving SDG into serum- and antibiotic-free Dulbecco's Modified Eagle's Medium and for each treatment type, cells were incubated for 24 hours. Cardiac iron overload resulted in increased intracellular ROS while SDG treatment prevented this increase, as measured by the H2DCFDA assay using flow cytometry. Increased gene expression of inflammatory mediators Tumor Necrosis Factor (TNF)-α, interleukin (IL)-10 and interferon (IFN)γ, as well as matrix metalloproteinases (MMP)-2 and 9, and antioxidants glutathione reductase (GSR), superoxide dismutase (SOD)-2 and peroxiredoxin (Prdx)-6 and a decrease in SOD concentration correlated with increased apoptosis as measured by active caspase 3/7 activity and increase in FOXO3. SDG attenuated the increase of gene expression of inflammatory and apoptosis mediators as well as the increase of caspase 3/7 activity caused by iron treatment. SDG also lead to an increase in gene expression of antioxidants GSR, SOD-2 and Prdx-6 when compared to iron treatment. Cardiac iron overload also resulted in an increase in protein levels of p70S6K1 and a decrease in the AMPK levels. The increase of p70S6 and decrease in AMPK levels was prevented by SDG. Pretreatment with SDG attenuated the iron-induced increases in oxidative stress, inflammation and apoptosis, suggesting a cardio-protective role for SDG against cardiac iron overload.