The association of thiol/disulphide homeostasis with 6-month mortality in patients with acute St-elevation myocardial infarction

Aim: Acute ST-elevation myocardial infarction (STMI) is significant determinant of mortality and long-term mortality rates has not changed significantly over the last two decades. Thiols are an important anti-oxidant mechanism in the body, and excessive reactive oxygen species oxidize the thiol into their disulphide forms. Hence, higher level of disulphide is regarded as an indicator of oxidative stress. In the present paper, we sought to investigate any probable relationship between thiol/disulphide homeostasis and 6-month all-cause mortality among STMI survivors. Material and Methods: 238 consecutive patients with STMI undergoing percutaneous coronary intervension were included. Blood samples for thiol/disulphide homeostasis were drawn on admission. Syntax I and II scores were calculated using the cineangiographic views and relevant patient demographics. Results: 6-month mortality occurred in 25 patients (mortality group), while 213 patients remained alive (non-mortality group). Total thiol, native thiol, disulphide, disulphide/total thiol , disulphide/native thiol and native thiol/total thiol were not different between the mortality and non-mortality groups (p&gt;0.05). Syntax I and II scores were significantly greater in mortality group (26.11±8.06 vs 19.129.80, p=0.029 for Syntax I; 50.1314.59 vs 30.639.79, p&lt;0.001 for Syntax II). Conclusion: Syntax II score, glomerular filtration rate (GFR) and white blood cell count (WBC) were found to predict 6-month mortality.


Introduction
For many years, acute myocardial infarction (AMI) has proved to be a significant determinant of both the morbidity and mortality worldwide, despite advances in interventional cardiology and medical therapy. Although a prominent amelioration in the 30-day mortality rates was achieved in AMI, long-term mortality rates however did not change significantly over the last two decades [1]. Acute ST-elevation myocardial infarction (STMI) is one of the entities comprising the term ''AMI'' , and constitutes nearly one third of the patient population worldwide who admit to the hospital with an AMI [2,3]. Accordingly, new measures and predictors are warranted in order for the physicians to anticipate better the long-term mortality rates among the survivors of an acute STMI, and provide a closer-follow up for them.
Oxidative stress occurs when the generation of reactive oxygen species exceeds the dealing capability of bodily antioxidant defense mechanisms [4]. Oxidative stress and AMI are not mutually exclusive. In this regard, oxidative stress was previously proposed as a major contributor to both the development and progression of vascular atherosclerosis [5].
On the other hand, the ischemic state incited by an acute STMI also generates another milieu of oxidative stress which in turn gives rise to a further impairment in the antioxidant defense mechanisms.
Thiols are sulfhydryl (-SH) containing organic molecules, in which the sulfhydryl is bound to a carbon atom [6]. Moreover, albumin and protein thiols comprise the major source of total thiol mass in the plasma [6]. Thiols serve as a potent antioxidant mechanism in the body. Excessive reactive oxygen species can readily oxidize the thiol groups to transform them into the disulphide forms. Thereby, emergence of higher levels of disulphide forms is regarded as a robust indicator of exposure to oxidative stress [7]. Additionally, this process is reversible, and any tempering in the magnitude of the oxidative stress is likely to initiate the convert the disulphide forms back into their former thiol forms, thus keeping a stable thiol/disulphide homeostasis [8].
Considering the above-mentioned premises, we sought in the present study to investigate any probable relationship between thiol/disulphide homeostasis and 6-month all-cause mortality among the survivors of acute STMI.

Study Population
Our prospective study included a total of 238 consecutive patients (64 female and 174 male) who presented to our hospital with the diagnosis of acute STMI and underwent PCI between January 2018 and October 2018. Acute STMI was defined as the presence of the pertinent criteria as follows: detection of rise and/or fall of cardiac troponins with at least one value above the 99th percentile of the upper reference limit and with at least one of the following features such as ischemia- imaging evidence of new loss of viable myocardium, or new regional wall motion abnormality; and identification of an intracoronary thrombus by angiography [9].
The exclusion criteria for our study were set as follows: the patients with a history of a recent myocardial infarction; those who had received any thrombolytic agent as a pretreatment; those with active infection or chronic inflammatory disease; those with severe hepatic, renal, hematological disease; and, those with any history of neoplasm or rheumatologic disease.
All the study participants underwent a scrutiny including a detailed medical history and a thorough physical examination and recording such baseline demographic features as age, sex, hypertension, chronic obstructive pulmonary disease, peripheral arterial disease, chronic obstructive pulmonary disease, smoking habit, diabetes mellitus, and coronary arterial disease.
Either a written or an oral-witnessed informed consent was obtained from all of the participating patients provided at the emergency service. Our study was performed by complying with the principals by the Declaration of Helsinki and was approved by the local ethics committee.

Echocardiography
Transthoracic echocardiographic evalation of the enrolled patients were performed using Vivid S5 (GE Vingmed Ultrasound AS, Horten, Norway). Left ventricular ejection fraction was calculated using the modified Simpson's rule.
All the conventional echocardiographic examination were performed according to the standards of the American Society of Echocardiography [10].

Intervention
All patients were treated by complying with the recommendations of the STMI guideline [11]. Once the written informed consent for cardiac catheterization was obtained, an emergency coronary angiography was performed in all patients using the standard techniques.
Glycoprotein IIb/IIIa inhibitor (tirofiban) was administered to the patients in the catheterization laboratory at the operator's discretion. Decision regarding the implementation of percutaneous coronary intervention (PCI), coronary artery bypass graft surgery or medical treatment was given by a heart team comprising two cardiologist and one cardiovascular surgeon. All PCIs performed in eligible patients were performed using the standard clinical practice and choice between the alternatives of drug-eluting stent or bare metal stent was at the operator's discretion. Stenting of infarct-related artery was successfully fulfilled in all patients.

Blood Samples and Laboratory Analysis
Blood samples were obtained through venipuncture on admission to the emergency department. The collected blood samples were centrifuged at 1500 g for 10 min to separate the serum. Serum was stored at −80 °C until analysis of thiol/disulfide homeostasis tests.
Routine serum biochemical parameters were measured by using an automated clinical chemistry analyzer (Roche Hitachi Cobas c8000 autoanalyzer, Roche Diagnostic Corp., Mannheim, Germany).
Thiol/disulfide homeostasis test levels were measured using a newly developed, fully-automated and spectrophotometric method by Erel and Neşelioğlu [12].
After determining native and total thiols, the concentration of disulfide was determined using the formula: Disulfide = (total thiol -native thiol) / 2 The ratios of disulfide/total thiol (%), disulfide/native thiol (%) and native thiol/total thiol (%) were calculated using the concentrations of disulfide, native thiol and total thiol, which were previously determined.

Calculation of the SYNTAX I and SYNTAX II Scores
Assessment of the cineangiographic views was performed using Axiom (Siemens Medical Solution, Erlangen, Germany) workstation by two experienced cardiologist blinded to the study data. Each lesion with a diameter stenosis ≥50% in coronary vessels ≥1.5 mm in diameter was scored using the online SYNTAX score calculator (http:// www.syntaxscore.com). If the cardiologists conflict about the lesions, the ultimate score was decided by averaging the scores calculated by each cardiologist. SS1 and SS2 scores were obtained for each patient.

Results
Demographic and clinical characteristics of the study population were given in Table 1 These three variables, namely the Stntax II score, GFR and WBC, which had been found to be significant predictor of mortality, were further evaluated through ROC curve analysis regarding whether we could obtain a cut-off value in the prediction of mortality among the study population.
According to the ROC curve analysis, the optimal cut-off value to predict mortality was 42.7 for the Syntax II score

Discussion
The main findings of our study can be summarized as follows: the admission thiol/disulphide status does not have any significant correlation with the long-term (6 months Aside from the acute coronary syndrome itself, some other clinical conditions as diabetes mellitus [18], hypertension [19], stable coronary arterial disease [20], chronic kidney disease [21], autoimmune diseases [22][23][24][25] implicated in the development of an acute coronary syndrome were also suggested to be associated with lower thiol/disulphide homeostasis.
There are many stress factors, such as ischemia, volume and pressure overload, that may incline the cardiovascular system towards remodeling at cellular levels [26]. Furthermore, cardiovascular remodeling may in turn be related to increased mortality, since adaptive changes in the cardiovascular and coronary arterial system may translate into myocardial fibrosis, positive or negative vascular plaque remodeling and potentially irreversible myocardial or vascular functional deterioration [27,28]. Accordingly, an altered thiol/disulphide homeostasis is very likely to remain incapable of adequately withstanding the oxidative stress milieu like an AMI, and this situation may in part be held responsible with the inappropriate adaptive changes posing an extra risk for future mortality.
Previous studies, in this regard, revealed findings supportive of this premise. In their study, Sivri et al. [16] found a negative correlation between native thiol and the rate of major adverse cardiovascular events (MACE), including mortality, non-fatal MI and acute heart failure, in patients with NSTMI. However, the other thiol/disulphide homeostasis-related parameters did not show such a correlation. In another study by Kundi et al. [29], in-hospital mortality was associated with both lower native thiol/disulphide ratio and higher Syntax I score. Akkuş et al. [30] suggested in their recent study that levels of admission native thiol and total thiol served as independent predictors of MACE, which had included acute coronary syndrome, stroke, and death and target vessel revascularization, during 6 months of follow-up of STMI patients. Contrary to the study by Kundi et al. [29], however, their study failed to yield an association of inhospital mortality with neither native and total thiol levels nor native thiol/disulphide ratio. Aside from the afore-mentioned studies, our study merely investigated all-cause mortality during 6-month follow-op of patients with STMI, and we did not find any correlation between the mortality and admission parameters related to the thiol/disulphide homeostasis. The reason for the lack of such an association can be attributed to the fact that we only evaluated the relationship of the mortality and the admission thiol/disulphide parameters, contrary to MACE in the previous studies.
This study should be interpreted in the light of some limitations. First, our study population is relatively small and future studies conducted on larger populations may yield correlation between the long-term mortality and admission thiol/disulphide status in STMI patients. Secondly, this is a single-center study and demographic, genetic and racial features of our patient cohort display distinctions from that of other centers. Third, we did not correlate our study findings with the other oxidative stress markers.

Conclusion
Admission serum native thiol level, total thiol level, disulphide level, native thiol/total thiol ratio, native thiol/disulphide ratio and total thiol/disulphide ratio cannot be used to identify patients with increased 6-month mortality among the patients with STMI. On the other hand, the Syntax II score, GFR and WBC show robust association with the 6-month mortality rates in the same patient population. However, further studies with larger cohots as well as longer follow-up periods may reveal different results.