Malondialdehyde inhibits cardiac contractile function in ventricular myocytes via a p38 mitogen-activated protein kinase-dependent mechanism

Abstract

(1) Increased oxidative stress plays a significant role in the etiology of cardiovascular disease. Lipid peroxidation, initiated in the presence of hydroxy radicals resulting in the production of malondialdehyde, directly produces oxidative stress. This study was designed to examine the direct impact of malondialdehyde on ventricular contractile function at the single cardiac myocyte level. Ventricular myocytes from adult rat hearts were stimulated to contract at 0.5 Hz, and mechanical and intracellular Ca(2+) properties were evaluated using an IonOptix Myocam system. Contractile properties analyzed included peak shortening amplitude (PS), time-to-PS (TPS), time-to-90% relengthening (TR(90)), maximal velocity of shortening/relengthening (+/-dLdt), and Ca(2+)-induced intracellular Ca(2+) fluorescence release (CICR) and intracellular Ca(2+) decay (tau). p38 mitogen-activated protein (MAP) kinase phosphorylation was assessed with Western blot. (2) Our results indicated that malondialdehyde directly depressed PS, +/-dLdt and CICR in a concentration-dependent manner and shortened TPS without affecting TR(90) and tau. Interestingly, the malondialdehyde-induced cardiac mechanical effect was abolished by both the p38 MAP kinase inhibitor SB203580 (1 and 10 micro M) and the antioxidant vitamin C (100 micro M). Western blot analysis confirmed direct phosphorylation of p38 MAP kinase by malondialdehyde. (3) These findings revealed a novel role of malondialdehyde and p38 MAP kinase in lipid peroxidation and oxidative stress-associated cardiac dysfunction.

Figure 1

(a) Representative traces depicting the effect of malondialdehyde (10⁻⁵ M) on cell shortening in ventricular myocytes. (b) Concentration-dependent response of malondialdehyde (10⁻⁹–10⁻³ M) on peak cell shortening. Data are presented as percent change from basal PS, which was 9.22±0.83%. Mean±s.e.m., n=22 per data group, ^*P< 0.05 vs baseline value.

Figure 2

(a) Representative traces depicting effect of malondialdehyde (10⁻⁵ M) on intracellular Ca²⁺ transient changes (ΔFFI) in ventricular myocytes. (b) Concentration-dependent response of malondialdehyde (10⁻⁹–10⁻³ M) on ΔFFI. Data are presented as percent change from respective basal ΔFFI value. Mean±s.e.m., n=29 per data group, ^*P<0.05 vs baseline value.

Figure 3

Effect of the antioxidant vitamin C and p38 MAP kinase inhibitor SB203580 on malondialdehyde-induced depression of myocyte shortening. Vitamin C (100 μM) or SB203580 (1 and 10 μM) was applied prior to the addition of malondialdehyde (10⁻⁴ and 10⁻³ M). Mean±s.e.m., n=20–23 per data group, ^*P<0.05 vs baseline value.

Figure 4

Effect of malondialdehyde (MDA, 10⁻⁴ M) on phosphorylation of p38 MAP kinase in ventricular myocytes in absence or presence of the p38 MAP kinase inhibitor SB203580 (SB, 1 and 10 μM). (a) Representative gel blot showing p38 MAP kinase phosphorylation (pp-MAPK). (b) Bar graph depicting summary of three different isolations. Mean±s.e.m., ^*P<0.05 vs control (vehicle) group, P<0.05 vs malondialdehyde group.