Enhancement of Cellular Antioxidant-Defence Preserves Diastolic Dysfunction via Regulation of Both Diastolic Zn²⁺and Ca²⁺and Prevention of RyR2-Leak in Hyperglycemic Cardiomyocytes

Abstract

We examined whether cellular antioxidant-defence enhancement preserves diastolic dysfunction via regulation of both diastolic intracellular free Zn2+ and Ca2+ levels ([Zn2+]i and [Ca2+]i) levels N-acetyl cysteine (NAC) treatment (4 weeks) of diabetic rats preserved altered cellular redox state and also prevented diabetes-induced tissue damage and diastolic dysfunction with marked normalizations in the resting [Zn2+]i and [Ca2+]i. The kinetic parameters of transient changes in Zn2+ and Ca2+ under electrical stimulation and the spatiotemporal properties of Zn2+ and Ca2+ sparks in resting cells are found to be normal in the treated diabetic group. Biochemical analysis demonstrated that the NAC treatment also antagonized hyperphosphorylation of cardiac ryanodine receptors (RyR2) and significantly restored depleted protein levels of both RyR2 and calstabin2. Incubation of cardiomyocytes with 10 µM ZnCl2 exerted hyperphosphorylation in RyR2 as well as higher phosphorphorylations in both PKA and CaMKII in a concentration-dependent manner, similar to hyperglycemia. Our present data also showed that a subcellular oxidative stress marker, NF-κB, can be activated if the cells are exposed directly to Zn2+. We thus for the first time report that an enhancement of antioxidant defence in diabetics via directly targeting heart seems to prevent diastolic dysfunction due to modulation of RyR2 macromolecular-complex thereby leading to normalized [Ca2+]i and [Zn2+]i in cardiomyocytes.

Intracellular Zn2+ Increase in Cardiomyocytes Induces both Electrical and Mechanical Dysfunction in Heart via Endogenous Generation of Reactive Nitrogen Species

“…Of note, under RNS exposure, the increases in FluoZin-3 intensity, which are associated with changes in [Zn 2+ ] i level, are in similar extent obtained in cardiomyocytes isolated from hyperglycemic heart, as previously demonstrated [25].…”

“…They were fed standard chow ad libitum daily. The blood glucose level of STZdiabetic animals was significantly high compared to control rats while their blood insulin level was markedly lower compared to that of the control rats [25].…”

“…As can be seen in Fig. 1c, ZnPT exposure induced significant prolongations in the repolarizing phase of action potential measured as the repolarizing times at 25, 50, 75, and 90 of full repolarization duration (given as APD 25,50,75,90 ).…”

“…Both twitch activity under isometric condition and action potential data were recorded simultaneously. The parameters of action potential including resting membrane potential, amplitude of action potential, and depolarization phase (TP) and repolarization phases (at 25, 50, 75, and 90 % of full AP duration [APD 25,50,75,90 ]) of action potential were determined. For contractile activity, peak tension of twitch traces (as %), time to maximum contraction (TP), times to half relaxation (DT 50 and DT 90 ), and the rates of changes with time in contraction and relaxation (±dF/dt) were measured.…”

Immuno-spin trapping detection of antioxidant/pro-oxidant properties of zinc or selenium on DNA and protein radical formation via hydrogen peroxide

“…In our previous studies, we have shown that a cellular antioxidantdefence enhancement preserves both systolic and diastolic dyfunctions via regulation of basal-free Zn 2? level and leads to a balanced oxidant/antioxidant level in both heart and circulation and prevented the altered cellular redox state [10,53]. In these studies, incubation of cardiomyocytes with 10 lM ZnCl 2 exerted hyperphosphorylation in cardiac RyR2, as well as higher phosphorylation levels in both PKA and CaMKII in a concentration-dependent manner, similar to hyperglycemia.…”