Myocardial infarction is one of the leading causes of death worldwide. Early diagnosis and management are essential to decrease mortality and morbidity. In clinical practice, many biomarkers are commonly accepted as being essential diagnostic markers of acute MI. However, the early detection of acute MI remains problematic. The development of newer, high-sensitivity assays will create new diagnostic and confirmative tools and facilitate faster decision-making in the emergency department. The American College of Cardiology stated that Troponin I (cTnI) and Creatine kinase (CK-MB), are the marker of choice in diagnosis (1). The elevated cTnI levels are recorded in a high percentage of patients with acute coronary syndromes, even in the absence of elevated CK-MB levels (2). CK-MB is a form of creatine kinase enzyme found primarily in myocardial cells. It is a cardiac biomarker used in the diagnosis of acute MI, myocardial ischemia, or myocarditis (3). CK–MB isoenzyme level, within 24 hours of the onset of the symptoms, has a 98% predictive value for myocardial necrosis (4). Myoglobin (MYO) is a haem protein, present in the cytoplasm of the myocardium and skeletal muscle cells; its plasma concentration is increased 2–3 h post-myocardial ischemic injury (3, 5). The National Academy of Clinical Biochemistry and the American College of Cardiology recommend the use of plasma MYO as an early biomarker of myocardial injury (6).
Many clinical trials indicated that hs-CRP is a risk factor and biomarker with a high predictive value in coronary vascular disease (7-11). H-FABP is a soluble, low molecular-weight protein that is abundant in the cytoplasm of cardiomyocytes. It is one of the biological markers that is early and rapidly released into circulation post-myocardial damage (12). Lp-PLA2 is an enzyme that hydrolyzes oxidized phospholipids. Several pieces of evidence suggested that Lp-PLA2 promoted atherosclerosis by several pathways. Lp-PLA2 concentration in the plasma was significantly elevated in patients with acute myocardial infarction and stable angina pectoris (13, 14). Procalcitonin (PCT), is extremely elevated in patients with severe bacterial infection. It rapidly responded to many stimuli and bacterial toxins and elevated within 2-3 h. It is highly increased in MI and represents an early new biomarker for the diagnosis and guiding the treatment of patients with MI (15). Numerous studies showed that inflammatory cytokines markedly predict MI. Inflammatory cytokines are believed to be part of the pathophysiology of atherosclerosis development. Recently, it was recorded that increasing cytokines promoted the expression of the proatherogenic gene, and stimulated the inflammatory process in the vessel wall. The secretion of cytokines was increased and their expression was accelerated in MI (16-18).  
The study aims to examine the efficacy and diagnostic values of many biomarkers in patients with myocardial infarction in comparison with routinely used markers, (MYO, cTnI, and CK-MB). The establishment of new and sensitivity tests will promote the diagnostic abilities to facilitate fast decisions in the emergency units.
 

Patients with myocardial infarction showed normal random blood sugar (102.6±30.2 vs 98.0±26.2), significantly declined HDL-C (39.8±2.7 vs. 44.7±3.2) and significantly elevated levels of total cholesterol (162.5±9.2 vs. 149.8±8.6), triglycerides (151.3±10.4 vs. 121.9±15.2), LDL (85.9±2.2 vs. 79.8±8.2) and VLDL (32.1±3.9 vs. 24.4±2.9) in comparison with healthy subjects of the same age group (Table 1).
In comparison with healthy control, patients with acute MI also showed significant elevation of the serum levels of cTnI (0.36±0.002 vs. 0.02±0.00), CK-MB (2.67±0.09 vs. 1.8±0.06 ng/mL), MYO (68.2±6.1 vs. 59.4±8.4 ng/mL), CRP (92.7±4.2 vs. 15.1±1.1 nmol/L), H- FABP (7.16±1.3 vs. 4.9±0.6 ng/mL), and PCT (0.048±0.013 vs. 0.012±0.004 ng/mL). However, the serum level of Lp-PLA2 didn’t significantly change in MI in comparison with healthy control (Table 2).
Furthermore, the patients of MI revealed significantly higher serum levels of IL-6 (7.255±3.81 vs. 4.48±1.98 Pg/mL, P<0.05), IL-9 (5.21±0.84 vs. 1.98±0.42 Pg/mL, P<0.05), IL1β (20.11±3.53 vs. 11.71±2.11 nmol/L, P<0.01) and TNF-α) 17.97±2.82 vs. 8.19±1.82 ng/mL, P<0.01) compared with healthy control (Table 3).

Vertically, a similar letter means not significant.
HDL-C: high-density lipoprotein cholesterol, LDL-C: low-density lipoprotein cholesterol, RBS: Random blood sugar, TC: total cholesterol, TG: triglycerides, VLDL-C: very low-density lipoprotein cholesterol.
 
 
Table 2. The levels of biomarkers in the patients with MI compared with healthy control.

Vertically, a similar letter means not significant.
CK-MB: Creatine kinase, CRP hs: Highly sensitive C reactive protein, H-FABP: heart-type fatty acid binding protein, IL6:  Interleukin 6, Lp-PLA2: Lipoprotein-associated phospholipase A2, MYO: Myoglobin, PCT: Procalcitonin, cTnI: Cardiac Troponin I.  
 
Table 3. Serum cytokines levels in patients with MI in comparison with the healthy control group.

Discussion

The current study revealed that patients with acute MI showed significantly elevated levels of cTnI, CK-MB, and MYO. American College of Cardiology and the European Society of Cardiology stated that cTnI and CK-MB were the biomarkers of choice in the diagnosis of MI (9). The elevation of cTnI levels was recorded in a high percentage of acute MI patients, even in the absence of elevated CK-MB levels (2). CK-MB is a cardiac marker used to confirm the diagnosis of acute MI (3). CK–MB determination, within 24 hours of the onset of the symptoms, has a 98% predictive value for myocardial necrosis (4). MYO is rapidly released into the blood; it elevated within 2–3 h post-MI (3, 5, 19). It was also recommended as an early biomarker of myocardial damage (6). 
Our study also showed that patients with acute MI showed significantly elevated levels of serum H-FABP. H-FABP is a sensitive early biomarker, it is elevated 1 h post-AMI (20). It appears that the diagnostic value of H-FABP is much higher than other AMI diagnostic biomarkers (21). H-FABP showed significantly superior sensitivity than cTnI, MYO, and CK-MB, in those with suspected AMI before hospitalization (22).
Furthermore, CRP was also significantly elevated in patients with acute MI in our study, CRP was known as an acute phase protein, and many authors classified CRP as a clinical predictor of MI (23-25). CRP promotes the proliferation and migration of endothelial cells, potentiates the complement system and is involved in the pathogenesis of atherosclerosis (26-28).
The patients with acute MI also showed significantly elevated serum levels of PCT. High serum PCT level is associated with a great degree of inflammation. Thus, the extensive arteriosclerotic plaques are also reflected by higher PCT serum levels. Serum levels in the range of 0.06 to 3 ng/mL indicated arteriosclerosis and represented a valuable diagnostic index, of acute myocardial infarction (15). Like CRP, PCT is not specific and only plays a supplemental role in the cardiovascular system (15, 29).
However, the current study didn’t show significant changes in Lp-PLA2 in acute MI. Lp-PLA2 is the enzyme that is produced mostly by neutrophils and macrophages from atherosclerotic plaques, and after that conveyed to the bloodstream via HDL-C as well as LDL-C (30, 31). It is an important biomarker of inflammation (13). In clinical trial using an Lp-PLA2 inhibitor, showed no benefit in MI patients as a preventive treatment (32). Data analysis revealed that Lp-PLA2 didn’t participate in the pathophysiology of atherosclerosis (33).
Recently, there has been a lot of pieces of evidence proving that inflammation plays a pivotal role in pathophysiology (34). The current research showed that IL-6 was significantly elevated in MI patients. Many previous studies mentioned that IL-6 and soluble IL-6 receptors were increased in acute myocardial infarction, and the IL-6 level was proportional to infarction size and the decline in left ventricular ejection fraction (35-37). IL-6 induced LDL-receptor expression on the macrophage's surface and promoted LDL uptake by macrophage, therefore, accelerating lipid deposition and enhancing foam cell formation (38). It increased matrix metalloproteinase synthesis, degraded the extracellular matrix, and increased the susceptibility of the plaques to rupture (39, 40). IL-6 was also important in cardiac fibroblasts by transiently inducing a hyaluronan-rich matrix that in turn promoted the inflammatory responses, and myofibroblastic phenotype, and initiated the cardio-protective program after AMI (41). Furthermore, the loss of viable myocardium after MI was linked to an inflammatory response. A clinical trial showed that myocardial salvage in patients with acute MI was increased by tocilizumab, which is attached to the IL-6 receptor and inhibited IL-6 signaling (42), and myocardial salvage in patients with acute STEMI was increased by Tocilizumab. Microvascular obstruction was less extensive in the tocilizumab group (43).
Our study also revealed that IL-9 was significantly increased in MI patients. According to previous studies, IL-9 level was increased in different atherosclerotic disorders both systemically and locally in the lesion, in addition to elevation of IL-9 and IL-9R expression, which suggested a role for the IL-9/IL-9R axis in the atherosclerotic process (44, 45).  Elevated circulated IL-9 promoted CD8⁺ T-cell cytotoxicity in AMI patients. The enhancement of CD8⁺ T-cell cytotoxicity induced by CD4⁺ CCR4^- CCR6^- CXCR3^- cells was IL-9 dependent. According to these results, it was suggested that IL-9-secreting CD4⁺ T cells contributed to the pathogenesis of AMI through enhancement of CD8⁺ T-cell cytotoxicity (44).
The significant increase in the level of IL-1β in patients with MI in this study was in line with many other authors. Many studies have suggested that IL-1β was involved in the pathogenesis of atherosclerosis (34, 46-49). Canakinumab, the human monoclonal antibody that selectively neutralizes IL-1β, improved cardiovascular outcomes and prevented the recurrence of cardiovascular events, which provided additional insight into IL-1β-targeted therapies (46-49).
TNF-α was also significantly elevated in MI patients in our study. Previously also recorded that TNF-α was significantly elevated in patients with acute coronary events when the samples of the blood were taken after the occurrence of MI (50-52). The level of TNF-α and its gene expression and subsequently its signaling pathways are changed at different points of the MI pathophysiological process (53). The proatherogenic effects of TNF-α on the endothelium may be attributed to a decrease in the bioavailability of NO, stimulation of vascular superoxide production, decrease of Ca²⁺ uptake by the sarcoplasmic reticulum, decrease of myofilament Ca²⁺ sensitivity, increasing the infiltration of the endothelium by inflammatory cells and inducing of left ventricular dysfunction (54) Furthermore, administration of TNF-α inhibitor during the first week of myocardial infarction reduced the inflammatory cytokines and the infiltration of the inflammatory cells in and around the infarct area (55). Accordingly, serum level of TNF-α was recommended as markers in acute STEMI to follow up the worsening of left ventricular systolic functions, and heart failure (56).

 

Conclusion

Early diagnosis remains the essential principle in the treatment of MI and still needs sensitive diagnostic biomarkers. The present study suggests that in addition to cTnI, CK-MB, and MYO, many other mediators such as CRP, H-FABP, PCT, and cytokines are sensitive, to serve as good indicators for diagnosis of MI and enable clinicians to monitor the cases of MI promptly and develop methods to decrease the adverse post-ischemic effects.

 

Acknowledgements

We thank the dean and the staff of postgraduate department, Faculty of Medicine, Sousse, Tunisia. We thank the patients who participate in this research. We appreciate the efforts of the staff of Nasiriyah Heart Center. 

 

Authors’ Contributions

Amer Muayad Hussein carried out the laboratory investigation. Ernez Hajri Samia and Al-Snafi Ali Esmail participate in opinion, designing, supervision, interpretation, discussion and drafting the manuscript.

 

Ethics approval

The ethical committee at Thi-Qar Health Directorate (2022161 in 31 /5/ 2022) has approved the research, and an informed consents was taken from all participants.  All methods were performed in accordance with the local guidelines and regulations of Ibn El Jazzar Faculty of Medicine, University of Sousse, Sousse, Tunisia and Thi Qar Health directorate.
 

Abbreviations

CK-MB:  Creatine kinase, CRP hs: High sensitive C reactive protein, cTnI: Cardiac Troponin I, HDL-C: high-density lipoprotein cholesterol, H-FABP: heart-type fatty acid binding protein, IL6: Interleukin 6, LDL-C: low-density lipoprotein cholesterol, Lp-PLA2: Lipoprotein-associated phospholipase A2, MI: Myocardial infarction, MYO: Myoglobin, PCT: Procalcitonin, BS: blood sugar, TC: total cholesterol, TG: triglycerides, VLDL-C: very low-density lipoprotein cholesterol.
 
 

Conflicts of Interest

The authors declare no conflicts of interest.

 

Funding

The authors declare that they did not receive financial support from any source/organization.