Mechanical effects of heme-mediated oxidative stress in human cardiomyocytes: implications for systolic function

Introduction: Heme is an essential molecule to aerobic organisms and it is involved in many biological processes. Under pathological conditions, free heme damages lipids, proteins , DNA and produce reactive oxygen species (ROS). In ischemic reperfusion injury, there are an important production of ROS responsible for the contractile dysfunction. In this study we try to explore the effect of free heme on the Ca-dependent active force (Factive).
Methods: We used frozen left ventricular myocardial tissue samples from human donor hearts. Cardiomyocytes were mechanically isolated and permeabilized using Triton X-100. Cardiomyocytes were examined with a set-up that is able to measure Factive and Ca-independent passive force (Fpassive). The Ca sensitivity of Factive (pCa50 ) were also monitored. These mechanical parameters were determined before and after 20 minutes long incubations in relaxing solutions containing Heme (10 µM) and Heme (3 µM )+ hydrogen-peroxide (H2O2, 30 µM). Ellman’s reaction was performed for analyze the SH groups.
Results: After 20 minutes incubation with Heme (10 µM) Factive decreased from 100% to 54% (n=8, P<0.05). H2O2 (30 µM) intensify the damaging effect of heme, Factive decreased with a lower concentration (3 µM) of heme to 77% from 100% (n=8, p<0.05, of Heme + of H2O2). Heme didn’t change the pCa50 in the presence or in the absence of H2O2. Ellman reaction showed that heme cause mainly reversible effects on the SH-group contents (n=3, p<0.05).
Conclusion: These results suggest that free heme alter the function of myofilament proteins which lead to decreased Factive that reflect the heart systolic capabilities and maybe these changes can explain the systolic dysfunction of heart in cardiac ischemic reperfusion injury.