Cardiorespiratory responses, nitric oxide production and inflammatory factors in patients with myocardial infarction after rehabilitation

Highlights

• After cardiac rehabilitation nitrate levels increased in skeletal muscle.

• Body fat correlated inversely with higher NO production in rehabilitated patients.

• Transforming growth factor β was related with decreased inflammation and higher NO.

Abstract

There is evidence that myocardial infarction (MI) patients have an inflammatory process that includes skeletal muscles, and exercise has been reported to reduce some inflammatory markers. The aim of this work was to study NO and some inflammatory markers in quadriceps muscle of MI patients before and after cardiac rehabilitation. Muscle biopsy was obtained in 17 MI patients before and after CR and only once in 11 healthy subjects. Several cardiorespiratory and metabolic parameters were evaluated and skeletal muscle levels of nitric oxide synthases, nitrate, nitrite, nitrotyrosine, tumor necrosis factor alpha (TNF-α), transforming growth factor beta (TGF-β), interleukin- 6 (IL-6) and CD154. After CR there was an increase in maximal oxygen consumption (21.2 ± 1.4 vs 25.7 ± 2.5 mL/kg/min, P < 0.0001); work load (116.2 ± 14.9 vs 140 ± 17 W, P < 0.0001); pulmonary ventilation (59.8 ± 7,5 vs 73.8 ± 11.6 L/min, P < 0.0001); anaerobic threshold (53.8% ± 3.5% vs 60.2% ± 3.3% of maximal VO₂, P < 0.0001), maximal lactatemia (8.1 ± 1.4 vs 9.3 ± 1.5 mmol/L, P < 0.0001), and oxygen pulse (11.7 ± 1.6 vs 14.0 ± 1.9 mL/pulse, P < 0.0001). CSA of type I fibers increased (4380 ± 1868 vs 5237 ± 1530 μm², P = 0.02), and nitrate (18.6 ± 3.04 vs 20.7 ± 2.0 ng/mg, P < 0.001). There was a negative correlation between BMI, fat%, waist and hip circumferences and NO synthase, nitrite and nitrate after CR. The inflammatory mediators were higher in patients than in control subjects and did not change with CR. TGF-β correlated directly with nitrite and nitrate and inversely to other inflammatory factors. In conclusion, there is an increase of nitrate post CR, indicating a more effective NO production. TGF-β was related to anti-inflammatory processes even before CR.

Introduction

Cardiovascular diseases (CVD) are the leading cause of death in the world. According to WHO in 2012, 17.5 million people died from CVD, of which 7.5 million deaths were from coronary artery disease and 6.7 million from cerebrovascular accidents [1]. Exercise based CR programs were developed for patients after acute myocardial infarction (MI) to help them regain their previous exercise capacity and facilitate reintegration into working life. It has been demonstrated that CR is a highly efficient, innocuous and economic therapeutic intervention [2]. There is ample evidence that diet and medical treatment of risk factors play a role in prevention and control of CVD [3]; moreover, CR including its 6 fundamental aspects (patient education, psychological aid, occupational therapy, dietetic orientation, medical treatment and exercise) is crucial in secondary prevention of the disease. Some studies indicate that the modification of risk factors have a very positive impact on morbidity due to cardiac events, both recent and recurrent. After an acute coronary syndrome, the effects seem to be even more pronounced leading to a 40% decline in 6-month mortality [3,4]. Physical training improves exercise capacity more than conventional medical therapy alone [5]. A year program of regular physical exercise in selected patients with stable coronary artery disease (CAD) resulted in higher event-free survival and exercise capacity compared with standard percutaneous coronary intervention [6]. Since 1995, CR participation after acute coronary syndrome and coronary artery bypass grafting is associated with reduced mortality even in the modern era of CAD treatment [7].

Training induces in both healthy subjects and CAD patients an increase in maximal oxygen consumption, which is the product of the capacity of the cardiovascular system to supply oxygen (i.e. cardiac output) and the capacity of skeletal muscles to use oxygen (i.e. arterial-venous oxygen difference). In healthy individuals this increase is approximately produced in equal proportion by central and peripheral adaptations while in CAD subjects impaired cardiac function would place a higher contribution on adaptive changes in the periphery, and consequently demand less effort on cardiac function [8]. Regular physical exercise as part of a multifactorial intervention improves symptom free exercise tolerance and myocardial perfusion. Because no net regression of epicardial coronary stenosis was observed in the majority of patients, and many studies of collateralization in CAD patients have reported that exercise did not improve angiographically detectable collateralization, the current evidence does not firmly support the hypothesis that these beneficial effects of exercise result from a blunted progression and/or an increased regression of coronary lesions, instead it indicates that exercise increases endothelium dependent dilation in the conduit arteries and larger resistance arteries [9], as a result of increased nitric oxide (NO) production and bioavailability [10]. Exercise also produces higher myogenic control, increased metabolic vasodilatation in small resistance arteries, and direct cardiac effects as improved calcium handling, increased P13K activity, reduction of fibrosis and cardiomyocyte apoptosis [4].

Adaptive changes to endurance training in peripheral muscle are: increased oxygen extraction by correcting endothelial dysfunction and increasing basal NO formation [11]; improvement of oxidative metabolism, showed by increase in activity of oxidative enzymes [12]; increased levels of phosphocreatine/inorganic phosphates [13]; changes in mitochondrial ultrastructure [14]; increase of radical scavenger enzyme activity [15]; increase of COX-activity inversely correlated with iNOS expression/iNOS protein content [16]. In addition, there is a reduction of sarcopenia related to attenuation of MuRF-1 expression, a component of the ubiquitin-proteasome system involved in muscle proteolysis [17].

There are several reports of muscle inflammation in general diseases as type II diabetes mellitus [18] and chronic obstructive pulmonary disease (COPD) [19]. Patients with acute coronary syndrome, stable CAD, or chronic heart failure (CHF) showed elevated levels of inflammatory markers in peripheral blood mononuclear cells [20], plasma [21,22] or skeletal muscle [23].

Exercise has been reported to reduce some inflammatory markers in skeletal muscle of CHF patients [23], but not in plasma [22]. Generation of NO is related to inflammatory markers, as demonstrated by the induction of iNOS expression in skeletal muscle by IL-1b and NFkB activation [24].

Most of the work on peripheral effects of exercise on skeletal muscle in patients with CVD has been done ln patients with CHF, however, there is scarce information in MI patients. The hypothesis of the present work is that the improvement in oxygen consumption that is obtained with the rehabilitation program currently used in our University Hospital may be related to an increase in skeletal muscle NO production and to reduction in the muscle inflammatory state. For that purpose, nitric oxide synthases (NOS), nitrate, nitrite, nitrotyrosine, tumor necrosis factor alpha (TNF-α), transforming growth factor beta (TGF-β), interleukin-6 (IL-6) and CD154 were determined, along with several cardiorespiratory and metabolic parameters.