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 Table of Contents  
ORIGINAL ARTICLE
Year : 2017  |  Volume : 6  |  Issue : 2  |  Page : 44-49

Association of inflammatory cytokines/biomarkers with acute coronary syndrome and its correlation with severity and hospital outcome


1 Department of Cardiology, LPS Institute of Cardiology, GSVM, Kanpur, India
2 Department of Medicine, JNMCH, AMU, Aligarh, Uttar Pradesh, India

Date of Web Publication31-Mar-2017

Correspondence Address:
Nasar Abdali
D 16, Medical College Campus, GSVM, Kanpur - 208 002, Uttar Pradesh
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/2250-3528.203532

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  Abstract 

Objective: Coronary atherosclerosis is one of the major causes of coronary artery disease. Atherosclerosis is an inflammatory process involving vascular wall cells, monocytes, T-lymphocytes, pro-inflammatory cytokines, chemoattractant cytokines (chemokines), and growth factors. The presence of inflammatory cells in the atherosclerotic lesion and elevated levels of the inflammatory markers in peripheral circulation correspond to an active inflammatory process in the body. In view of this background, this study was undertaken to evaluate the association between activation of inflammatory cytokines and acute coronary syndrome (ACS). Furthermore, the correlation of these factors with severity of ACS and in-hospital mortality outcomes was studied.
Study Design: It is a prospective case–control study, including forty cases of ACS (as per the inclusion criteria listed below) and twenty controls. The levels of inflammatory markers interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), and troponin I were estimated in cases and controls. The levels of these markers in the peripheral circulation were also stratified on the basis of the presenting ACS type (unstable angina, non-ST-elevation myocardial infarction, and ST-elevation myocardial infarction). All statistical data were analyzed using SPSS software version 19 Statistical package for windows (Chicago, Inc., IL, USA).
Results: The levels of inflammatory markers such as IL-6, TNF-α, and troponin I were higher in the ACS group than the control, and difference was statistically significant. Furthermore, there was a statistically significant difference in the levels of these markers between the various ACS groups.
Conclusions: The circulating levels of inflammatory markers such as IL-6 and TNF-α are significantly elevated in patients with ACS, supporting the view that inflammatory cytokines are associated with ACS. There is a direct correlation of the levels of IL-6 and TNF-α with the severity of ACS and in-hospital mortality in these cases.

Keywords: Acute coronary syndrome, interleukin-6, tumor necrosis factor-α


How to cite this article:
Razi MM, Abdali N, Asif S M, Azharuddin M. Association of inflammatory cytokines/biomarkers with acute coronary syndrome and its correlation with severity and hospital outcome. J Clin Prev Cardiol 2017;6:44-9

How to cite this URL:
Razi MM, Abdali N, Asif S M, Azharuddin M. Association of inflammatory cytokines/biomarkers with acute coronary syndrome and its correlation with severity and hospital outcome. J Clin Prev Cardiol [serial online] 2017 [cited 2017 Oct 21];6:44-9. Available from: http://www.jcpconline.org/text.asp?2017/6/2/44/203532




  Introduction Top


Coronary atherosclerosis is one of the major causes of coronary artery disease (CAD). Atherosclerosis is an inflammatory process involving vascular wall cells along with activation of markers of inflammation such as the monocytes, T-lymphocytes, pro-inflammatory cytokines, chemoattractant cytokines (chemokines), and growth factors. Atherosclerotic plaques are vulnerable to rupture and thereby associated with serious complications. The presence of inflammatory cells in the atherosclerotic lesions and elevated levels of inflammatory markers in the peripheral circulation correspond to an activation of the inflammatory process in the body.[1],[2],[3],[4]

The fatty streak is the early inflammatory lesion, consisting mainly of monocyte-derived macrophages and T-lymphocytes. Pro-inflammatory stimuli such as oxidatively modified low-density lipoprotein (LDL) cholesterol, free radicals, cigarette smoke, elevated plasma homocysteine, and infectious organisms cause endothelial dysfunction which leads to compensatory responses that alter the normal properties of the endothelium. A cascade of events ensues leading to the development of isolated macrophages, foam cells, fatty streak formation, and finally stable or unstable fibrous plaque. This cascade of events is mediated by pro-inflammatory cytokines, chemoattractant cytokines (chemokines), growth factors, and adhesion molecules produced by activated inflammatory, vascular smooth muscle, and endothelial cells. Pro-inflammatory risk factors cause local (vascular) or systemic (extravascular) inflammation which triggers the production of primary pro-inflammatory cytokines such as interleukin-1a (IL-1) and tumor necrosis factor-alpha (TNF-α). Measurement of these cytokines in serum can provide information about the inflammatory status of an individual.

Markers of inflammation and pro-inflammatory cytokines such as C-reactive protein (CRP), TNF-alpha, and monocyte chemoattractant protein-1 are under evaluation as a marker of monocytes/macrophages activation, soluble IL-2 receptor as a marker of T-lymphocyte activation, and tryptase as a marker of mast cell activation.

Primary pro-inflammatory cytokines and oxidatively modified LDL activating the endothelium also leads to the expression of adhesion molecules that are crucial to the recruitment of inflammatory cells from bloodstream into the vessel wall. These adhesion molecules may be released in soluble form into the bloodstream and can serve as markers of vascular inflammation.

Nucleated cells express heat shock proteins (Hsp), in response to environmental stress. Increased expression of Hsp has been detected in the cells of atherosclerotic lesions, and elevated antibodies against heat shock proteins (Anti-Hsp-Ab) levels have been shown to be associated with human atherosclerosis.

In addition, primary pro-inflammatory cytokines stimulate the production of chemoattractant cytokines (chemokines) which may play a major role in atherogenesis and can be used as markers of inflammation. Moreover, primary pro-inflammatory cytokines stimulate the production of IL-6, a secondary pro-inflammatory cytokine, which in turn stimulates the production of acute phase proteins by the liver. Examples of these proteins include CRP, serum amyloid A (SAA), and fibrinogen. These proteins can be used as markers of inflammation.

CRP is an acute phase protein which increases in various inflammatory and infective states. Increased CRP concentrations may indicate widespread inflammation and instability of atherosclerotic plaques in coronary arteries.[5] [Table 1] enumerates list of major cytokines, their receptors, and cytokine-related inflammatory mediators implicated in the pathophysiology of acute coronary syndrome and related heart failure.[6],[7]
Table 1: List of major cytokines, their receptors, and cytokine-related inflammatory mediators implicated in the pathophysiology of acute coronary syndrome and related heart failure[6],[7]

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Thus, the present study was undertaken with the aim to evaluate the association between inflammatory cytokines and acute coronary syndrome (ACS) and to correlate them with severity of the disease and hospital outcomes.


  Materials and Methods Top


A total of sixty participants, including twenty controls and forty patients of ACS, admitted to the Coronary Care Unit of LPS Institute of Cardiology and J. N. Medical College Hospital were taken for prospective study from the year January 2014 to January 2015. Informed consent was taken from all study participants, and the study protocol was approved by the board of studies of medicine department and the Local Institutional Review Committee.

The diagnosis of ACS was made if two or more of the following criteria were fulfilled.[8]

  • Central chest pain lasting longer than 30 min
  • Typical changes in cardiac Troponin I (cTrop-I)
  • Typical electrocardiogram changes including ST-T changes with or without pathological Q waves in at least two contiguous leads.


Exclusion criteria

  • Patients with a history of recent surgery or trauma within the preceding 2 months
  • Renal insufficiency (creatinine >1.5 mg/dl)
  • Malignancy
  • Febrile disorders (infections) and patients with body temperature >37.5°C
  • Acute or chronic inflammatory diseases
  • Patients with a history of recent infections
  • Patients with known or suspected thrombotic disorders.


The concentration of TNF-α (pg/ml) in serum of patients and healthy controls was determined by use of a commercial ELISA Kit (R and D Systems).

IL 6 concentrations in patients and healthy controls were determined by use of a commercial ELISA Kit (R and D Systems), which employed the quantitative sandwich enzyme immunoassay technique.

All statistical data were analyzed using SPSS software version 19 Statistical package for windows (IBM Corp. Released 2010, Armonk, NY). Continuous variables were expressed as mean ± standard deviation (Gaussian distribution) or range and qualitative data were expressed as percentage. Depending on normality distribution, unpaired t-test for independent samples was used for comparing continuous variables between two groups. Categorical variables were analyzed using Chi-square test. ANOVA was used enabling post hoc comparisons using Bonferroni method, for obtaining P values for comparison between individual groups. All P values were two tailed, and P < 0.05 was considered statistically significant. All confidence intervals were calculated at 95% level.


  Results Top


A total of forty cases and twenty controls with statistically nonsignificant difference regarding age and sex were enrolled in the study. Cases enrolled had more risk factors for ACS as compared to control [Table 2]. Most of the patients enrolled as cases had ST-elevation myocardial infarction (STEMI), followed by unstable angina (USA) and non-ST-elevation myocardial infarction (NSTEMI) with chest pain being the most common presenting complaint [Table 3] and [Table 4]. Serum level of Cardiac biomarkers such as IL-6, TNF-α, and cTrop-I was statistically more significant in cases than in controls with STEMI showing the highest level followed by NSTEMI and USA [Table 5] and [Table 6]. Level of these cardiac biomarkers also correlated well with Killip class [Table 7]. Furthermore, level of these biomarkers has statistically significant impact on patient's hospital outcomes [Table 8].
Table 2: Baseline demographics of the study subjects

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Table 3: Clinical diagnosis at presentation

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Table 4: Presenting symptoms in patients with acute coronary syndrome

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Table 5: Inflammatory markers/markers of myocardial injury in controls and in acute coronary syndrome patients

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Table 6: Inflammatory markers/markers of myocardial injury in patients with different forms of acute coronary syndrome

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Table 7: Inflammatory markers/markers of myocardial injury in acute coronary syndrome patients as per the Killip class at presentation

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Table 8: Inflammatory markers/markers of myocardial injury in acute coronary syndrome patients according to the clinical outcome

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  Discussion Top


Cells of the immune system are widely present in the atherosclerotic plaque and that the disease seems to be driven by inflammatory mechanisms. Moreover, total leukocyte count [9],[10] and levels of systemic inflammatory mediators such as IL-6,[11],[12] fibrinogen,[13] TNF-α,[14] SAA, and CRP have been shown to predict the onset of cardiovascular disease. The inflammatory mediators such as [10] IL-6, fibrinogen, TNF-α, and CRP are acute phase proteins that respond to injury. Synthesis of these factors takes place mainly in the liver, but recently adipose tissue has emerged as another source of cytokines.[15]

In the present study, increased level of TNF-α and IL-6 was seen in different ACS groups which also correlated well with severity of disease. It was seen that its value in different ACS group was maximum in STEMI and minimum in USA and that STEMI had worst prognosis. Maury and Teppo, 1989, have reported that increased levels of TNF-α have been observed after acute myocardial infarction (AMI).[16]

In the present study, the mean value of TNF-α in patients who died was 364.07 ± 41.20 pg/ml and in those who survived was 256.63 ± 78.20 pg/ml, and this difference in the two group was statistically significant (t = 5.35; P < 0.01). Mortality of the patients was directly related to the increased level of TNF-α. Similar observation was reported by Ridker et al., 1997, a follow-up study of 17-months, which showed that the increased levels of TNF-α were associated with increased risk of recurrent coronary events and increased mortality.[17]

In the present study, the mean value of IL-6 in control group, USA, NSTEMI, and STEMI was 5.0560 ± 2.01 pg/ml, 54.36 ± 13.46 pg/ml, 101.22 ± 6.67 pg/ml, and 125.60 ± 28.05 pg/ml, respectively. Its value among ACS group was maximum in STEMI and minimum in USA. As compared to control, the rise in the value of IL-6 was maximum in STEMI followed by NSTEMI and then USA.

As it was seen in the previous study of Biasucci et al., 1996, and Ikonomidis et al., 1999, the patients with stable angina had higher IL-6 concentration than healthy controls and patients with USA had higher IL-6 concentration than patients with stable angina.[18],[19]

In the present study, the mean value of IL-6 in the patients who died was 132.52 ± 27.72 pg/ml and in those who survived was 87.31 ± 33.31 pg/ml. This difference was statistically significant (t = 3.95; P < 0.01) and is in conformation with the previous observation of Biasucci et al.[18] They had reported that the patients with USA and with complicated in-hospital course (urgent need for revascularization) had higher IL-6 concentration both on hospital admission and during the 48 h follow-up compared with those patients with USA and without cardiovascular events during their hospital stay.

In the present study, raised IL-6 at the time of admission was an indicator of adverse in-hospital cardiovascular events. Biasucci et al. have also reported that elevation of IL-6 within the first 2 days of an episode of ACS was associated with adverse in-hospital outcomes.[18] Thus, IL-6 during the first 48 h of an ACS is a good predictor of a major adverse cardiovascular event (MACE) during the 1st month and the 1st year after the initial coronary event. Ridker et al., 2000, and Luc et al., 2000, also showed that patients with persistently elevated IL-6 levels are associated with a worse in-hospital outcome following admission with USA. Further, elevated levels of IL-6 predict the risk of AMI and death but not angina.[11],[20] The risk of MI increased to 38% with each quartile increment of baseline IL-6 levels. This study signifies that mortality was increased with increased levels of IL-6.

In the present study, the mean value of cTrop-I in USA, NSTEMI, and STEMI was 0.1000 ± 0.000 pg/ml, 4.6700 ± 2.8465 pg/ml, and 8.1847 ± 4.3889 pg/ml, respectively. Its value was maximum in STEMI and minimum in USA patients.

In the present study, the mean value of cTrop-I in the patients who died was 8.88 ± 4.82 ng/ml and those that survived was 3.62 ± 4.10 ng/ml, and this difference was statistically significant (t = 2.83; P < 0.05). The increased value of cTrop-I was associated with increased risk of mortality. Our study further strengthens the study by Antman et al., 1996, in which they hypothesized that cTrop-I provides for the early identification of patients at an increased risk of death.[21] The measured value of cTrop-I at concentration of 0.4 mg/L was associated with significantly higher mortality at 42 days than lower concentrations among patients with USA or non-Q-wave infarction. This was an independent predictor of short-term mortality after adjustment for age and the presence of ST-segment depression. Several other clinical outcome-based studies have demonstrated that patients with acute cardiac ischemia in whom CK-MB, cTnI, and/or cTnT was increased, are at increased risk for adverse events including MI or cardiac death.[22],[23] A similar result was also seen in the study of Lindahl et al., 1996, and FRagmin during InStability in Coronary artery disease trial, where the authors measured the incidence of cardiac death at 1 year and found that the risk ranged from 0% to 16% among patients who had elevated troponin and CRP levels.[24] The elevated levels of troponin STEMI patients were found to be associated with increased risk of short-term and long-term MACE and death.

Limitations of the study

Our study had some limitations which merit attention. IL-6 and TNF-α are nonspecific inflammatory markers and do not necessarily indicate an association with CAD. However, in our patients, the levels of the markers were associated with severity of clinical presentation as well as in-hospital mortality. These findings indicate that these markers indeed reflect heightened inflammatory activity in response to an acute coronary event.

Second, the small size of the case and control group which was also not matched with respect to various cardiovascular risk factors needs to be kept in mind. However, a consistent relationship between the levels of inflammatory markers and the severity of coronary event suggests that the elevated levels of the studied inflammatory markers in ACS patients were not just because of greater prevalence of cardiovascular risk factors but more likely reflected the ongoing atherosclerotic activity.


  Conclusions Top


This study once again demonstrates that the circulating levels of inflammatory markers such as IL-6 and TNF-α are significantly elevated in patients with ACS, supporting the view that inflammatory cytokines are associated with ACS. Further, there is a direct correlation between the levels of IL-6 and TNF-α and severity of ACS, including the in-hospital mortality.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

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    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7], [Table 8]



 

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