NOX Inhibition Improves β-Adrenergic Stimulated Contractility and Intracellular Calcium Handling in the Aged Rat Heart

Abstract

Cardiac aging is characterized by alterations in contractility and intracellular calcium ([Ca2+]i) homeostasis. It has been suggested that oxidative stress may be involved in this process. We and others have reported that in cardiomyopathies the NADPH oxidase (NOX)-derived superoxide is increased, with a negative impact on [Ca2+]i and contractility. We tested the hypothesis that in the aged heart, [Ca2+]i handling and contractility are disturbed by NOX-derived superoxide. For this we used adults (≈5 month-old) and aged (20–24 month-old) rats. Contractility was evaluated in isolated hearts, challenged with isoproterenol. To assess [Ca2+]i, isolated cardiac myocytes were field-stimulated and [Ca2+]i was monitored with fura-2. Cardiac concentration-response to isoproterenol was depressed in aged compared to adults hearts (p < 0.005), but was restored by NOX inhibitors apocynin and VAS2870. In isolated cardiomyocytes, apocynin increased the amplitude of [Ca2+]i in aged myocytes (p < 0.05). Time-50 [Ca2+]i decay was increased in aged myocytes (p < 0.05) and reduced towards normal by NOX inhibition. In addition, we found that myofilaments Ca2+ sensitivity was reduced in aged myocytes (p < 0.05), and was further reduced by apocynin. NOX2 expression along with NADPH oxidase activity was increased in aged hearts. Phospholamban phosphorylation (Ser16/Thr17) after isoproterenol treatment was reduced in aged hearts compared to adults and was restored by apocynin treatment (p < 0.05). In conclusion, β-adrenergic-induced contractility was depressed in aged hearts, and NOX inhibition restored back to normal. Moreover, altered Ca2+ handling in aged myocytes was also improved by NOX inhibition. These results suggest a NOX-dependent effect in aged myocytes at the level of Ca2+ handling proteins and myofilaments.

NADPH Oxidase 2 Mediates Myocardial Oxygen Wasting in Obesity

“…This was evident as improved parameters of diastolic and systolic function and reduced concentric remodeling. Therefore, our results are in accordance with many studies where genetic and pharmacological strategies to reduce NOX2 activity have been associated with attenuation of LV dysfunction, pathological remodeling, in models of diabetes [8,9,11,12], sepsis-induced cardiomyopathy [29], pressure overload [45], and in the aged heart [28].…”

“…However, NOX2-signalling has been shown to influence many of the same factors that are believed to contribute to myocardial oxygen wasting in obesity/diabetes. These include changes in mitochondrial function and ROS production [25], as well as altered activity of calcium-handling proteins and impaired calcium homeostasis [26][27][28][29]. In accordance with this, we have also shown an association between cardiac tissue ROS-content and MVO 2 in the hearts from diet-induced obese mice [23], suggesting a role for ROS in myocardial oxygen wasting.…”

“…Additionally, the oxidation of the RYR2 promotes calcium leak and increased calcium sparks, which were also absent in NOX2 KO hearts from mice that were fed a SHFD [44]. Other studies have reported a negative impact of NOX2-derived superoxide following acute exposure to FA load [25] and in other types of heart failure [28]. Our data demonstrating both improved LV function and myocardial energetics may very well be a functional consequence of the improved calcium handling associated with reduced NOX2 activity reported in the studies above.…”

Apocynin Treatment Prevents Cardiac Connexin 43 Hemichannels Hyperactivity by Reducing Nitroso-Redox Stress in Mdx Mice

“…These include other redox-sensitive proteins such as the ryanodine receptor (RyR2) [ 39 , 40 ]. Our group has described that apocynin restores the impaired contractility of mdx mice and in a model of aging by restoring phospholamban phosphorylation [ 11 , 41 ]. Nevertheless, the importance of Cx43 hemichannels in the progression of the dystrophic cardiomyopathy is evidenced by fact that reducing hemichannels permeability reduced the degree of apoptosis in cardiac cells of the mdx hearts, resulting in decreased fibrosis and cardiac hypertrophy.…”

“…), except concentration response curves where standard error is presented. Data from concentration–response experiments were fitted to a sigmoid equation as previously described [ 41 ]. Differences between groups were analyzed by two-way ANOVA, using Newman–Keuls as post-hoc test.…”