Suppression of hERG K(+) current and cardiac action potential prolongation by 4-hydroxynonenal via dual mechanisms

Oxidative stress under pathological conditions, such as ischemia/reperfusion and inflammation, results in the production of various reactive chemicals. Of these chemicals, 4-hydroxynonenal (4-HNE), a peroxidation product of ω6-polyunsaturated fatty acid, has garnered significant attention. However, the effect of 4-HNE on cardiac electrophysiology has not yet been reported. In the present study, we investigated the effects of 4-HNE on several cardiac ion channels, including human ether-a-go-go-related (hERG) channels, using the whole-cell patch clamp technique. Short-term exposure to 100 μM 4-HNE (4-HNE(100S)), which mimics local levels under oxidative stress, decreased the amplitudes of rapidly activating delayed rectifier K(+) current (I(Kr)) in guinea pig ventricular myocytes (GPVMs) and HEK293T cells overexpressing hERG (I(hERG)). MS analysis revealed the formation of 4-HNE-hERG adduct on specific amino acid residues, including C276, K595, H70, and H687. Long-term treatment (1–3 h) with 10 μM 4-HNE (4-HNE(10L)), suppressed I(Kr) and I(hERG), but not I(Ks) and I(Ca,L). Action potential duration (APD) of GPVMs was prolonged by 37% and 64% by 4-HNE(100S) and 4-HNE(10L), respectively. Western blot analysis using surface biotinylation revealed a reduction in mature membrane hERG protein after treatment with 4-HNE(10L). Proteasomal degradation inhibitors, such as bortezomib, prevented the 4-HNE(10L)-induced decrease in mature hERG, suggesting a retrograde degradation of membrane hERG due to 4-HNE. Taken together, 4-HNE(100S) and 4-HNE(10L) suppressed I(hERG) via functional inhibition and downregulation of membrane expression of hERG, respectively. The exposure of 4-HNE under pathological oxidative stress may increase the risk of proarrhythmic events via APD prolongation.