Evaluation of thiol disulphide levels in patients with pulmonary embolism

Introduction

PE is a sudden occlusion of a pulmonary artery. This blockage is usually caused by a blood clot coming from a vein in the leg to the lung. PE is a widespread disease with non-specific symptoms that has a potentially high risk of mortality and morbidity. In the United States, 500,000 to 600,000 individuals are diagnosed with PE per year. Many fatal pulmonary embolisms remain undiagnosed because of the lack of routine post-mortem examination, resulting in an underestimation of PE incidence [1], [2], [3], [4]. Two of the most commonly used scoring systems to define PE are the Wells score and the Geneva clinical probabilities. The current standard radiological examination is computed tomography pulmonary angiography (CTPA). Physicians often face diagnostic challenges and CTPA needs to be utilised, even low probability cases [1], [2], [5]. PE risk factors include obesity, immobilisation, cigarette use, cancer, surgery, pregnancy, oral contraceptives or hormone replacement therapies [1], [6]. PE accompanied by shock and heart failure further increases the risk of mortality [7].

Reactive oxygen species (ROS) are unstable species capable of initiating oxidation owing to the existence of unpaired valency shell electrons [1], [8], [9]. ROS is a native by-product of normal oxygen metabolism and plays a significant physiological role in signal transduction. However, they can contribute to the disease mechanisms through the dysregulation of oxidative damage to cellular macromolecules [10], [11]. Smoking, asthma, chronic inflammation are associated with an oxidant-antioxidant imbalance that can be identified in blood [11], [12]. A balance between oxidation and antioxidation is critical in respiratory tissues in the physiopathology of COPD and PE [11], [13]. Experimental evidence [14] indicates the oxidative stress of lung tissue in laboratory animals with PE [15].

As a result of pulmonary circulatory failure due to PE, circulatory instability, hypoperfusion, hypoxia and ischemia occur. All these conditions cause oxidative stress in the organism. Oxidative stress occurs when there is an instability between ROS production and the body’s ability to readily detoxify the reactive mediators or easily repair the resultant damage [14], [15], [16]. Oxidative stress and associated ROS can damage DNA, lipids, and proteins. In events that may cause an acute ischemic condition such as acidosis and hypoxia, the N-terminal end of the albumin is modified and its capacity to bind transition metals such as cobalt and copper is reduced. This modified form of albumin is called Ischemia Modified Albumin (IMA) and accepted as a biochemical test of oxidative stress. When cells of a healthy body are exposed to ROS, antioxidant mechanisms are activated. Therefore, an oxidant-antioxidant balance shifts favouring the oxidant. Thiols contribute to an increase in the amount of antioxidants and their contribution to defense against ROS is great [11], [16], [17].

In response to the damages of reactive oxygen radicals, many different mechanisms in the body control them. These systems complement each other as they play a role in different cells and different free radicals. In biological systems, thiols are bound to albumin and amino acids and contain sulphur [18], [19]. Thiols become oxidised reacting with reactive oxygen radicals thus removing them to prevent tissue damage and the resultant disulphide bonds can be diminished back to thiol groups. So, the thiol-disulphide balance is continued [20]. Oxidative stress can be assessed indirectly by measuring thiol-disulphide levels [13]. The topic of thiol-disulphide balance has garnered interest lately.

Dynamic thiol-disulphide balance can represent the oxidative status of the organism. Studies are showing that thiol disulphide balance is impaired under conditions of increased oxidative stress (pulmonary diseases and pulmonary embolism). Because pulmonary embolism is a disease with high mortality, early diagnosis and treatment are very important in terms of prognosis. Thiol-disulphide balance is a current marker of interest in determining changes in oxidative stress. Compared with conventional oxidative stress markers, the new assay improved by Dr. Erel and Dr. Neselioglu provides a cost-effective, practical and fully automated spectrophotometric analysis that can detect plasma thiol-disulphide homeostasis. Therefore, we purposed to assess the impact of thiol-disulphide levels in the etiopathogenesis of PE, considering that oxidative stress may affect prognosis in PE.

Material and methods

Results

We found significantly lower levels of albumin (3.11±1.03 g/dL), native thiol (195.44±83.3 μmol/L), disulphide (20.42±9.20 μmol/L) and total thiol (236.26±90.66 μmol/L) in patients with PE compared with healthy controls (3.89±0.52, 304.42±62.13, 24.33±8.09, and 353.07±63.58 μmol/L, respectively). Serum IMA levels (0.82±0.16 g/dL) were higher compared with controls (0.67±0.15 g/dL) (Table 1).

Serum albumin levels in patients with PE were strongly correlated with plasma IMA (r=−0.737; p<0.001), native thiol (r=0.762; p<0.001) and total thiol (r=0.822; p<0.001). Serum native thiol strongly correlated with serum total thiol (r=0.981; p<0.001) in patients with PE. Disulphide, native thiol, total thiol and albumin levels of patients with PE were significantly lower than healthy controls and IMA levels of patients with PE were higher than those of healthy controls. In addition, we found that total thiol was negatively correlated with DNT (r=−0.441; p=0.002) and DTT (r=−0.437; p=0.002) ratio in the patients with PE. Some important correlation graphs are given in Figures 1 and 2.

Figure 1:

The correlations between albümin with IMA, NT, TT levels (r=−0.737; p<0.001, r=0.762; p<0.001, r=0.822; p<0.001, respectively).

Figure 2:

The correlations between NT and TT levels (r=0.981; p<0.001).

Diagnostic performance using ROC plots curve indicated that total thiol cut-off values of 296.5 or below could predict PE with 71.4% sensitivity and 82% specificity (area under curve [AUC]=0.848; 95% confidence interval 0.772–0.923) and native thiol cut-off values of 256.65 or below could predict PE with 75.5% sensitivity and 72% specificity (AUC=0.838; 95% confidence interval 0.760-0.917) (Figure 3).

Figure 3:

ROC comparison of TT and NT (AUC for TT=0.848 and NT=0.838).

Diagnostic performance using ROC plots curve indicated that IMA cut-off values of 0.932 or below could predict PE with 95.9% sensitivity and 26.5% specificity (AUC=0.794; 95% confidence interval 0.703–0.885) (Figure 4).

Figure 4:

ROC analyses for IMA (AUC=0.794).

Discussion

Protective mechanism against oxidative cell damage and oxidative stress is the thiol group of the cellular protein [15], [23]. Oxidative stress has been a topic of interest for clinicians for a long time. Notably, it has a critical role in the development of various diseases, like type 1 DM, cancer, atherosclerosis, and HT. Studies have shown that the etiopathogenesis of the disease changes with increased oxidative stress [12], [20]. Accordingly, clinical conditions that influence oxidant-antioxidant balance were excepted from our study. The measurement of thiol-disulphide homeostasis is crucial in explaining the impacts of oxidative stress and for evaluating disease.

Our study found that albumin, native thiol, and total thiol levels were remarkably reduced in patients with PE which was remarkablly related to PE patients. When ROC analysis is analyzed, we can say that total thiol and native thiol have higher sensitivity-specificity according to IMA. The sensitivity and specificity of native thiol for this prediction quite high. Another study revealed that thiol-disulphide homeostasis can be changed during PE and associated with worse haemodynamic parameters and can serve as a prognostic marker for hospital mortality [25].

In our study, the DNT and DTT ratio showing oxidation was significantly higher in PE. There was a negative correlation with DNT and DTT ratio in patients with PE. The increase in DNT and DTT ratios and the decrease in the NTT ratio indicate that the thiol-disulphide balance shifts to the disulphide side, thereby indicating that increased oxidative stress result in PE. In cases where oxidative stress increases, the amount of thiol decreases. Oxidative stress was high, whereas antioxidative parameters were reduced in patients with PE. Strong correlations between the activity of the PE and thiol-disulphide homeostasis indicate that homeostasis may affect the progress of the disease. Parlak et al. reported that the DNT rate was significantly higher in patients with PE [24]. In our study, the rates of DNT and DTT were found to be high in the patient group and our study results are consistent with the literature.

Albumin is one of the most important and most effective antioxidants in plasma. Plasma proteins (especially serum albumin) are very sensitive to oxidation due to free –SH groups. Albumin has an essential role in total antioxidant capacity and its levels reduced because of fast impairment during inflammation and oxidative stress [13], [ 26]. Decreased albumin levels and increased IMA levels indicate that antioxidant capacity shifts towards the oxidant side. We did not find any other studies evaluating IMA levels and thiol-disulphide levels in patients with PE. In this study showed that albumin levels reduced and IMA levels increased in PE. These findings provide a context for understanding the role of the dynamic thiol-disulphide homeostasis and its relation with IMA, an indicator of oxidative stress, in PE patients.

Recently, studies on thiol-disulphide homeostasis have been popular and have gained importance. Kundi et al. [27] expressed that the thiol-disulphide rate riced in acute myocardial infarction, and this rate may enable detection of acute myocardial damage. Koprivica et al. [28] demonstrated the role of oxidative stress in the improvement of endothelial dysfunction in different types of the acute coronary syndrome (ACS). Ates et al. [29] indicated that thiol oxidation increased in type 1 diabetics and this increase was proportional to the severity of the disease. Furthermore, there are some studies evaluating thiol-disulphide homeostasis in patients with preeclampsia and HT [14], [29], [30]. Our results showed a raised thiol-disulphide ratio in patients with PE, which was statistically important, indicating that the decrease in thiols may be crucial factor in the etiology of PE. These results indicate that we can benefit from thiol-disulphide balance in the future stages in estimating the course of the disease by making larger studies.

Conclusion

The measurement of thiol-disulphide homeostasis is crucial for elucidating the effects of oxidative stress and evaluating disease. This study indicated that the oxidative/antioxidative balance shifted to the oxidative side in patients with PE. Our study revealed that thiol-disulphide homeostasis can be altered during PE. It is easily accessible, simple calculated and relatively inexpensive. The results can be supported by studies involving more patients with PE and larger studies can be performed to use thiol disulphide as a prognostic marker.