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Reduced nerve growth factor (NGF) is associated with cardiac sympathetic nerve denervation in heart failure (HF) which is characterized by increased oxidative stress. Apocynin is considered an antioxidant agent which inhibits NADPH oxidase activity and improves reactive oxygen species scavenging. However, it is unclear whether apocynin prevents reduced myocardial NGF, leading to improvement of cardiac function in HF. In this study, we tested the hypothesis that apocynin prevents reduced myocardial NGF, contributing to amelioration of myocardial apoptosis and failure. Rabbits with myocardial infarction (MI) or sham operation were randomly assigned to receive apocynin or placebo for 4 weeks. MI rabbits exhibited left ventricular (LV) dysfunction, and elevation in oxidative stress, as evidenced by a decreased reduced-to-oxidized glutathione ratio and an increased 4-hydroxynonenal expression, and reduction in NGF and NGF receptor tyrosine kinase A (TrKA) expression in the remote non-infarcted myocardium. Apocynin treatment ameliorated LV dysfunction, reduced oxidative stress, prevented decreases in NGF and TrKA expression and reduced cardiomyocyte apoptosis after MI. In cultured H9C2 cardiomyocytes, hypoxia or hydrogen peroxide decreased NGF expression, and apocynin normalized hypoxia-induced reduction of NGF. Recombinant NGF attenuated hypoxia-induced apoptosis. Apocynin prevented hypoxia-induced apoptosis, and the suppressive effect of apocynin on apoptosis was abolished by NGF receptor TrKA inhibitor K252a. We concluded that apocynin prevented reduced myocardial NGF, leading to attenuation of cardiomyocyte apoptosis and LV remodelling and dysfunction in HF after MI. These findings suggest that strategies to prevent NGF reduction by inhibition of oxidative stress may be of value in amelioration of LV dysfunction in HF.

Increased oxidative stress and myocyte autophagy co-exist in cardiac remodeling. However, it is unclear whether oxidative stress mediates maladaptive myocyte autophagy in pathological ventricular remodeling. In this study, we tested the hypothesis that antioxidants prevent maladaptive myocyte autophagy in pressure overload-induced left ventricular (LV) remodeling. Sprague-Dawley rats underwent abdominal aortic constriction (AAC) or sham operation. The animals were randomized to receive an antioxidant N-acetylcysteine (NAC), an autophagy inhibitor 3-methyladenine (3-MA) or placebo treatment for 2 weeks. We measured LV structure and function by echocardiography and hemodynamics, myocyte autophagy and oxidative stress assessed by 8-hydroxy-2-deoxyguanosine (8-OHdG). AAC rats exhibited increased LV hypertrophy assessed by LV wall thickness and myocyte cross-sectional area. NAC prevented LV hypertrophy in AAC rats. There were no significant differences in LV fractional shortening, end-diastolic dimension and the maximal rate of LV pressure rise among the groups. AAC rats showed an increase in myocardial 8-OHdG that was prevented by NAC. The expression of LC3 II protein, a marker of autophagy, was increased at 2 weeks after AAC. Immunohistochemical scores further confirmed the increase in LC3 expression in AAC rats. The expression of autophagic proteins Beclin1 and Atg12 and ERK activity were also increased in AAC rats. NAC prevented the increases in LC3 II protein, LC3 scores, Beclin1, Atg12 and ERK activity in AAC rats. Inhibition of autophagy by 3-MA prevented LV hypertrophy after pressure overload. These findings suggest that antioxidants may be of value to prevent pressure overload-induced cardiac remodeling through inhibition of maladaptive myocyte autophagy.

NEW FINDINGS What is the central question of this study? Does oxidative stress induce impairment of autophagy that results in myocyte hypertrophy early after pressure overload? What is the main finding and its importance? In cultured myocytes, hydrogen peroxide decreased autophagy and increased hypertrophy, and inhibition of autophagy enhanced myocyte hypertrophy. In rats with early myocardial hypertrophy after pressure overload, myocyte autophagy was progressively decreased. The antioxidant N-acetyl-cysteine or the superoxide dismutase mimic tempol prevented the decrease of myocyte autophagy and attenuated myocyte hypertrophy early after pressure overload. These findings suggest that oxidative stress impairs myocyte autophagy that results in myocyte hypertrophy. ABSTRACT Insufficient or excessive myocyte autophagy is associated with left ventricular (LV) hypertrophy. Reactive oxygen species mediate myocyte hypertrophy in vitro and pressure overload-induced LV hypertrophy in vivo. In the present study, we tested the hypothesis that oxidative stress induces an impairment of autophagy that results in myocyte hypertrophy. H9C2 cardiomyocytes pretreated with the autophagy inhibitor 3-methyladenine were exposed to 10 and 50 μm hydrogen peroxide (H2 O2 ) for 48 h. Male Sprague-Dawley rats underwent abdominal aortic constriction (AAC) or sham operation. The animals were killed 24, 48 or 72 h after surgery. In a separate group, the AAC and sham-operated rats randomly received the antioxidant N-acetyl-cysteine or the superoxide dismutase mimic tempol for 72 h. In H9C2 cardiomyocytes, H2 O2 decreased the ratio of microtubule-associated protein light chain 3 (LC3) II to LC3 I and increased P62 and phosphorylated ERK (p-ERK) proteins and myocyte surface area. 3-Methyladenine further increased H2 O2 -induced p-ERK expression. In rats after AAC, the heart to body weight ratio was progressively increased, the LC3 II/I ratio was progressively decreased, p62 and p-ERK expression was increased, and expression of Beclin1, Atg5 and Atg12 was decreased. N-Acetyl-cysteine or tempol prevented the decreases in the LC3 II/I ratio and Beclin1 and Atg5 expression and attenuated the increases in LV wall thickness, myocyte diameter and brain natriuretic peptide expression in AAC rats. In conclusion, oxidative stress decreases Beclin1 and Atg5 expression that results in impairment of autophagy, leading to myocyte hypertrophy. These findings suggest that antioxidants or restoration of autophagy might be of value in the prevention of early myocardial hypertrophy after pressure overload.

New findings What is the central question of this study? Does NADPH oxidase activation mediate cardiac sympathetic nerve denervation and dysfunction in heart failure. What is the main findings and its importance? Cardiac sympathetic nerve terminal density and function were reduced in heart failure after myocardial infarction in rabbits. The NADPH oxidase inhibitor apocynin prevented the reduction in cardiac sympathetic nerve terminal density and function in heart failure. This suggest that NADPH oxidase activation mediates cardiac sympathetic nerve terminal abnormalities in heart failure. NADPH oxidase may be a potential therapeutic target for cardiac sympathetic denervation and dysfunction in heart failure. Abstract Congestive heart failure (CHF) is characterized by cardiac sympathetic nerve terminal abnormalities, as evidenced by decreased noradrenaline transporter (NAT) density and cardiac catecholaminergic and tyrosine hydroxylase (TH) profiles. These alterations are associated with increased reactive oxygen species (ROS). NADPH oxidase is a major source of ROS in CHF. In this study, we tested the hypothesis that NADPH oxidase activation mediates cardiac sympathetic nerve terminal abnormalities in CHF. CHF was produced by myocardial infarction (MI) in rabbits. Rabbits with MI or a sham operation were randomized to orally receive an NADPH oxidase inhibitor, apocynin (6 mg kg-1 day-1 ), or placebo for 30 days. MI rabbits exhibited left ventricular dilatation, systolic dysfunction, and increases in NADPH oxidase activity and 4-hydroxynonenal expression in the remote non-infarcted myocardium, all of which were prevented by treatment with apocynin. Cardiac catecholaminergic histofluorescence profiles and immunostained TH and PGP9.5 expression were decreased, and the decreases were ameliorated by apocynin treatment. NAT, TH and PGP9.5 protein and mRNA expression were reduced and the reduction was mitigated by apocynin treatment. The effects of apocynin were confirmed by utilizing the NADPH oxidase inhibitor diphenyleneiodonium in a separate experiment. In conclusion, the NADPH oxidase inhibitor apocynin attenuated increased myocardial oxidative stress and decreased cardiac sympathetic nerve terminals in CHF after MI in rabbits. These findings suggest that the activation of NADPH oxidase mediates cardiac sympathetic nerve terminal abnormalities in CHF, and the inhibition of NADPH oxidase may be beneficial for the treatment of heart failure.

Background/Aims: The alterations in myocyte autophagy after myocardial infarction (MI) and the underlying mechanisms have not been fully understood. In this study, we investigated the temporal changes of myocyte autophagy in the remote non-infarcted myocardium in rabbits after MI and the relationships between alterations of myocyte autophagy and left ventricular (LV) remodeling and myocardial oxidative stress. Methods: Rabbits were assigned to MI or sham operation. Rabbits with MI or sham were randomly assigned to receive chloroquine, an autophagy inhibitor, antioxidant vitamins C and E or placebo for 4 weeks. H9C2 cardiomyocytes were subjected to hypoxia or hydrogen peroxide (H2O2) treatment. Results: MI rabbits exhibited progressive increases of LV end-diastolic dimension (EDD), and decreases of LV fractional shortening (FS) and dP/dt over 8 weeks. Myocyte autophagy assessed by the scores of LC3 and Beclin1 expression was progressively decreased at 1, 4 and 8 weeks after MI. The ratio of LC3 II/I and Beclin1 and Atg5 proteins were also decreased at 4 weeks after MI. There was a negative correlation between autophagy and LV EDD and a positive correlation between autophagy and LV FS and dP/dt. The autophagy inhibitor chloroquine worsened LV remodeling after MI. Decreased myocyte autophagy was associated with increased myocardial 4-hydroxynonenal. Antioxidant vitamins C and E prevented the decrease in myocyte autophagy after MI. In cultured H9C2 cardiomyocytes, the LC3 II/I ratio was decreased at 4 and 8 h after exposure to hypoxia, and the change was associated with increased 8-hydroxy-2-deoxyguanosine. A low concentration of H2O2 decreased the LC3 II/I ratio. Conclusion: Progressive reduction in myocyte autophagy in the remote non-infarcted myocardium was associated with myocardial oxidative stress and LV remodeling after MI. Antioxidants prevented the reduction in myocyte autophagy after MI, suggesting that oxidative stress mediates reduction in myocyte autophagy that contributes to post-MI remodeling.