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Plasma Pentraxin 3 Concentration Increases in Endurance-Trained Men

MIYAKI, ASAKO1; MAEDA, SEIJI1; OTSUKI, TAKESHI2; AJISAKA, RYUICHI1

Medicine & Science in Sports & Exercise: January 2011 - Volume 43 - Issue 1 - p 12-17
doi: 10.1249/MSS.0b013e3181e84bce
BASIC SCIENCES
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Introduction: Pentraxin 3 (PTX3), which is mainly produced by endothelial cells, macrophages, and smooth muscle cells in the atherosclerotic region, has a cardioprotective effect. Endurance exercise training has also been known to offer cardioprotection. However, the effect of regular endurance exercise on PTX3 is unknown. This study aimed to investigate whether plasma PTX3 concentrations increase in endurance-trained men. Ten young endurance-trained men and 12 age- and gender-matched sedentary controls participated in this study.

Methods: We measured plasma PTX3 concentrations of the participants in each group. We also determined systemic arterial compliance (SAC) by using simultaneous M-mode ultrasound and arterial applanation tonometry of the common carotid artery and used HDL cholesterol (HDLC) as an index of cardioprotective effect.

Results: Maximal oxygen uptake was significantly higher in the endurance-trained men than that in the sedentary controls. SAC and HDLC were significantly higher in the endurance-trained men than that in the sedentary controls (SAC = 1.74 ± 0.11 vs 1.41 ± 0.09 mL·mm Hg−1, P < 0.05; HDLC = 70 ± 5 vs 57 ± 4 mg·dL−1, P < 0.05). Plasma PTX3 concentrations were markedly higher in the endurance-trained men than that in the sedentary controls (0.93 ± 0.11 vs 0.68 ± 0.06 ng·mL−1, P < 0.05). Relationships between plasma PTX3 concentrations and SAC and HDLC were linear.

Conclusions: This is the first study revealing that endurance-trained individuals had higher levels of circulating PTX3 than sedentary controls. PTX3 may play a partial role in endurance exercise training-induced cardioprotection.

1Division of Sports Medicine, Graduate School of Comprehensive Human Sciences, University of Tsukuba, Tsukuba, Ibaraki, JAPAN; and 2Graduate School of Health and Sport Sciences, Ryutsu Keizai University, Ryugasaki, Ibaraki, JAPAN

Submitted for publication December 2009.

Accepted for publication May 2010.

Address for correspondence: Seiji Maeda, Ph.D., Division of Sports Medicine, Graduate School of Comprehensive Human Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8577, Japan; E-mail: maeda@taiiku.tsukuba.ac.jp.

It is generally accepted that an increase in regular physical activity, especially habitual endurance exercise, reduces cardiovascular risk factors (7,15,16). Endurance exercise training induces increase in both HDL cholesterol (HDLC) (2,30) and arterial compliance (5,6). Increased HDLC and arterial compliance have been recognized as having beneficial cardioprotective effects (20,29).

Recently, pentraxin 3 (PTX3), which is mainly produced by endothelial cells, macrophages, and smooth muscle cells in the atherosclerotic region (21,24), has been identified as a substance playing an important role in cardioprotection and atheroprotection. It has been reported in mice that after transient ischemia in the left anterior descending coronary artery, the area of necrotic heart tissue expanded in PTX3-deficient mice compared with that in the control mice (25), suggesting that PTX3 can prevent ischemic tissue from necrotizing. Furthermore, a previous study demonstrated that PTX3 heals vascular injury via activation of tissue factor (17). Recently, it has been revealed that the mice lacking PTX3 promotes vascular inflammatory response and atherosclerosis (19). These findings suggest that PTX3 has cardioprotective and atheroprotecive effects.

Because PTX3 is implicated in cardioprotection, it is reasonable to hypothesize that PTX3 participates in the mechanisms underlying endurance exercise training-induced cardioprotective effect. However, the relationship between plasma PTX3 concentrations and exercise training-induced cardioprotective effect remains unclear. We hypothesized that endurance-trained individuals have higher levels of plasma PTX3 than sedentary controls, and this increase in PTX3 would partly participate in the mechanism underlying endurance exercise training-induced cardioprotection. To test our hypothesis, we measured plasma PTX3 concentrations, plasma HDLC concentrations, and systemic arterial compliance (SAC) in endurance-trained men. We measured HDLC and SAC as indices of endurance exercise training-induced cardioprotective effect.

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METHODS

Subjects.

All participants in this study were Japanese. Ten young endurance-trained men (19-26 yr) and 12 age- and gender-matched sedentary controls (19-25 yr) participated in this study. All of the endurance-trained men's training was longer than 2 yr. The training mainly consisted of some kind of running training, such as long-distance running and interval training, in which volume and intensity were 5.5 ± 0.3 sessions per week (2.4 ± 0.3 h per session) with a rating of 15-17 on the Borg scale (i.e., hard to very hard). On the other hand, control men had a sedentary lifestyle (no regular physical activity) for at least 2 yr. All subjects were free of signs, symptoms, and history of any overt chronic diseases. None of the participants had a history of smoking, and none were currently taking any medications. In addition, none of the subjects were NSAID or aspirin users. Before all measurements, the subjects refrained from alcohol consumption and intense physical activity (exercise) for 24 h and fasted overnight (12 h) without water. All measurements were performed after a resting period of at least 20 min at a constant room temperature (25°C).

This study was reviewed and approved by the institutional review board at the University of Tsukuba. The study conformed to the principles outlined in the Helsinki Declaration. All potential risks and procedures involved in the study were explained to the subjects, and written informed consent to participate in the study was obtained from all subjects.

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Maximal oxygen uptake.

The maximal oxygen uptake was determined during incremental cycling to exhaustion (3 min at 80 W, with a 30-W increase every 3 min) by monitoring breath-by-breath oxygen consumption and carbon dioxide production (AE280S; Minato Medical Science, Osaka, Japan), heart rate, and ratings of perceived exertion (Borg scale). The values of maximal oxygen uptake were accepted if subjects met at least two of the following criteria: a V˙O2 plateau (<150 mL O2 per minute with an increased work rate), highest respiratory exchange ratio >1.15, peak heart rate within five beats of the age-predicted maximum (220 − age), rating of perceived exertion >19, or extreme fatigue such that the pedaling rate on the bicycle ergometer was <50 rpm.

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SAC

SAC was measured by carotid artery applanation tonometry and Doppler echocardiography as described previously (22). Briefly, carotid artery pressure waveforms were obtained by applanation tonometry (formPWV/ABI; Colin Medical Technology, Komaki, Japan) after a resting period of at least 20 min. At the time of waveform recording, brachial arterial systolic, diastolic, and mean blood pressure (SBP, DBP, and MBP, respectively) were measured by oscillometry (form PWV/ABI; Colin Medical Technology). The pressure signal obtained by tonometry was calibrated by equating the carotid MBP and DBP to brachial artery values. SAC was calculated as follows: SAC = Ad/(dP × R), where Ad is the area under an arbitrary portion of the diastolic pressure waveform, dP is the pressure change in this portion, and R is the systemic vascular resistance given as MBP divided by mean blood flow. The calculation of SAC is based on the assumption that the diastolic pressure decay is a mono-exponential function of time. Mean blood flow was obtained using a Doppler echocardiographic system (EnVisor; Koninklijke Philips Electronics, Eindhoven, The Netherlands) as described previously by our laboratory (22). The insertion point of the aortic valve tips at the end of diastole was defined by two-dimensional imaging in the parasternal long-axis view with a 3.5-MHz transducer, and the M-mode echocardiogram at that level was recorded with the computer. Doppler ultrasonographic flow velocity curves in the ascending aorta were simultaneously obtained using a 1.9-MHz probe held in the suprasternal notch. Mean blood flow was calculated as a product of the aortic cross-sectional area and the mean flow velocity (ImageJ; National Institutes of Health, Bethesda, MD).

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Plasma PTX3 concentration.

All the blood samples were obtained from the antecubital vein by using a 21-gauge needle. Each blood sample was placed in a chilled tube containing ethylenediaminetetraacetic acid (2 mg·mL−1) and was then centrifuged at 2000g for 15 min at 4°C. The plasma was stored at -80°C until the assay. Plasma concentrations of PTX3 were determined using a commercial enzyme-linked immunosorbent assay kit (Quantakine DPTX 30; R&D Systems Inc., Minneapolis, MN). The PTX3 assay was carried out according to the manufacturer's instructions. Briefly, standard or plasma samples assayed in duplicate and 20 μL of which were added to microtiter plate wells coated with a monocronal antibody specific for PTX3, followed by incubation at room temperature for 2 h. The wells were then washed four times with a buffered surfactant solution, and thereafter, 200 μL of anti-PTX3 polyclonal antibody conjugated to alkaline phosphatase was added to each well and incubated for 2 h at room temperature. After appropriate washing, 200 μL of substrate solution was added to each well and incubated again for 30 min at room temperature. The reaction was then stopped by the addition of 2 N sulfuric acid to the wells, and absorbance was measured at 450 nm with corrections set at 540 nm using a microplate reader. The values of plasma PTX3 levels were extrapolated from a curve drawn using standard PTX3. The intra- and interassay coefficients of variation were 3.8% and 6.1%, respectively (values provided by Quantakine DPTX 30; R&D Systems Inc.). The intra-assay coefficient of variation in this study was 5.6%. No significant cross-reactivity or interference with other factors related to PTX3 or other cytokines was observed (information provided by Quantakine DPTX 30; R&D Systems Inc.).

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Blood biochemistry.

The serum concentrations of total cholesterol (TC), LDL cholesterol (LDLC), HDLC, and triglycerides (TG) and the plasma concentrations of glucose (BG) were determined using standard enzymatic techniques. Briefly, TG and TC concentrations were determined by the cholesterol dehydrogenase and glycerol kinase methods, respectively (1,13). LDLC and HDLC concentrations were measured by a direct method (9,31). The BG concentration was assayed by the hexokinase and glucose-6-phosphate dehydrogenase methods (26).

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Statistical analysis.

Student's t-test for unpaired values was used to evaluate the statistical differences between the endurance-trained men and the sedentary controls. Relationships between SAC or HDLC and plasma PTX3 concentrations were analyzed using Pearson's correlation. Data were expressed as means ± SE. Values of P < 0.05 were accepted as significant.

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RESULTS

Table 1 summarizes the characteristics of the endurance-trained men and the sedentary controls. There were no significant differences in age, height, weight, body mass index, TG, TC, LDLC, and BG between the endurance-trained men and the sedentary controls. Table 2 shows the hemodynamics in the endurance-trained men and the sedentary controls. DBP and resting heart rate were significantly lower in the endurance-trained men than that in the sedentary controls. There was no significant difference in SBP and pulse pressure between the two groups. Maximal oxygen uptake was higher in the endurance-trained men than that in the sedentary controls (Table 1). HDLC in the endurance-trained men was markedly higher than that in the sedentary controls (Fig. 1). SAC was significantly higher in the endurance-trained men than that in the sedentary controls (Fig. 2). Figure 3 shows plasma PTX3 concentrations in the two groups. Plasma PTX3 concentrations were higher in the endurance-trained men than that in the sedentary controls. The relationships between plasma PTX3 concentrations and HDLC and SAC were linear (Fig. 4). However, no significant relationship was detected between maximal oxygen uptake and plasma PTX3 concentrations. In the trained group, we found a significant positive correlation between plasma PTX3 concentrations and HDLC (Fig. 5). However, there was no relation between plasma PTX3 concentrations and SAC in the trained group (Fig. 5). In the sedentary controls, plasma PTX3 concentrations were not related to HDLC or SAC (Fig. 5).

TABLE 1

TABLE 1

TABLE 2

TABLE 2

FIGURE 1

FIGURE 1

FIGURE 2

FIGURE 2

FIGURE 3

FIGURE 3

FIGURE 4

FIGURE 4

FIGURE 5

FIGURE 5

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DISCUSSION

In the present study, we determined plasma PTX3 concentrations in endurance-trained men. It was first demonstrated that plasma PTX3 concentrations were markedly higher in the endurance-trained men than that in the sedentary controls. The endurance-trained men also showed clearly higher maximal oxygen uptake, HDLC, and SAC than the sedentary controls. Furthermore, the relationships between plasma PTX3 concentrations and HDLC and SAC were linear. An increase in PTX3 may play a role in the endurance exercise training-induced increase in HDLC and SAC, that is, the cardioprotective effects induced by exercise training.

PTX3 is mainly produced by endothelial cells, macrophages, and smooth muscle cells in the local atherosclerotic region (21,24). However, the role of PTX3 in the cardiovascular system is unclear. Circulating PTX3 concentrations were reported to increase in patients with cardiovascular disease (23,27). Napoleone et al. (17) reported that PTX3 could repair vascular wounds by promoting activation of tissue factor. Peri et al. (23) demonstrated that PTX3 was produced from dying cardiomyocytes but not from necrotic cells in patients with acute myocardial infarction. Recently, it has been demonstrated that PTX3 functions at the crossway between pro- and anti-inflammatory stimuli to balance the overactivation of a pro-inflammatory, pro-atherogenic cascade (19). Namely, the increased levels of PTX3 in cardiovascular disease could reflect a protective physiological response (19). Salio et al. (25) demonstrated that after acute myocardial infarction, the exacerbated heart tissue area in PTX3-deficient mice had expanded compared with that in the control mice. Thus, PTX3 plays a role of repair in cardiovascular injury. Moreover, the recent report showed that the double-knockout mice lacking PTX3 and apolipoprotein E gene developed larger atherosclerosis than the mice lacking only apolipoprotein E (19). Taken together, it is thought that PTX3 has cardioprotective and atheroprotective effects.

The benefit of habitual endurance exercise is recognized as a lifestyle modification worldwide. In epidemiological studies, physically inactive subjects were reported have significantly higher risks of cardiovascular disease, and mortality rates in these subjects were reported to be high (7,15,16). Endurance exercise training produces beneficial cardioprotective effects. Increased HDLC and arterial compliance have been recognized as beneficial cardioprotective effects (20,29). Habitual endurance exercise induces the increase in HDLC and SAC (2,5,6,30). In the present study, HDLC, SAC, and plasma PTX3 concentrations were significantly higher in the endurance-trained men than that in the sedentary controls. Furthermore, we demonstrated that there was a significant positive correlation between plasma PTX3 concentrations and SAC or HDLC. These findings suggest that endurance-trained men have beneficial cardioprotective effects, and PTX3 may partly participate in the mechanism underlying endurance exercise training-induced cardioprotective effect.

It is known that high physical activity and/or endurance exercise training is effective for good health. On the other hand, exercise causes increase in inflammatory factors in various tissues, such as circulating blood, fat, and skeletal muscle (3,10,12,18). A previous study reported that PTX3 is expressed and secreted in vascular walls as a result of the inflammatory response (11). Furthermore, it has been reported that PTX3 is produced via the myeloid differentiation protein 88-interleukin-1 (IL-1) receptor pathway, which induces initial factors for starting inflammatory response (e.g., nuclear factor-kappa B) (25). Myeloid differentiation protein 88 is also known as a necessary factor for vascular remodeling (28). Tumor necrosis factor α and IL-1β are known as triggers of PTX3 production (4,14). On the other hand, anti-atherogenic IL-10 stimulates PTX3 production from dendritic cells and monocytes (8). In addition, PTX3 inhibits pro-atherogenic cytokines interferon-γ production (21). Norata et al. (19) recently reported that PTX3 is a molecule for finely tuning vascular inflammatory response by both pro- and anti-inflammatory factors. Thus, PTX3 is modulated by both pro- and anti-atherogenic factors. PTX3 may be a necessary substance for maintaining vascular homeostasis. Taken together, PTX3 participates in a part of inflammation and plays a role in cardioprotection and atheroprotection. However, the precise roles of PTX3 remain to be elucidated.

There are several limitations of this study that should be emphasized. First, this was a cross-sectional study. Therefore, the results suggesting a role for PTX3 in cardioprotection are preliminary. These findings need to be confirmed in a longitudinal study. Second, the small sample size is clearly one of the limitations of this study. We have demonstrated that plasma PTX3 concentrations, HDLC, SAC, and maximal oxygen uptake were increased in endurance-trained men. Furthermore, the relationships between plasma PTX3 concentrations and HDLC and SAC were linear. However, there was no relation between plasma PTX3 concentrations and maximal oxygen uptake. This may be the influence of a small sample size in the present study. Furthermore, the subjects in this study were young Japanese men. Therefore, these results may not generalize to other populations.

In conclusion, the present study revealed for the first time that circulating PTX3 concentrations are markedly higher in endurance-trained men than that in sedentary controls. We also demonstrated that SAC and HDLC, which are cardioprotective factors, were elevated by the regular endurance exercise. It is possible that PTX3 may partly participate in the mechanism underlying endurance exercise training-induced cardioprotection.

This work was supported by Grants-in-Aid for Scientific Research 21300234 and 21650179 and Grant-in-Aid for JSPS Fellows 21·692 from the Japan Society for the Promotion of Science.

Conflicts of interest: The authors have no financial, consultant, institutional, or other relationships that might lead to bias or a conflict of interest.

The results of the present study do not constitute endorsement by the American College of Sports and Medicine.

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Keywords:

ENDURANCE TRAINING; CARDIOPROTECTION; SYSTEMIC ARTERIAL COMPLIANCE; HDL CHOLESTEROL

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