Thiol-disulfide homeostasis and ischemia-modified albumin in patients with sepsis

Introduction

Sepsis is caused by an uncontrolled inflammatory response following an infection, which can lead to organ dysfunction. It remains a significant cause of mortality in intensive care units worldwide [1]. Although mortality is >10 % in patients with sepsis, comorbidities such as organ transplantation operations, congestive heart failure, cirrhosis, and uncontrolled diabetes mellitus may exacerbate sepsis [2].

In the intensive care unit (ICU), the Sequential Organ Failure Assessment (SOFA) score is used to assess the sepsis status of patients. The SOFA score is a method used to assess organ dysfunction in critically ill patients. It is a good prognostic indicator for the evaluation of the patient during the ICU stay. A SOFA score of 10 and above is independently associated with an increased risk of death in hospitals and in the ICU [3], 4]. The SOFA score is obtained by examining the status of respiratory, coagulation, liver, cardiovascular, central nervous system, and renal organ function. It is calculated 24 h after admission to the ICU and repeated every 48 h. Patients with a SOFA>10 are those who have severe sepsis in the ICU and are associated with more organ involvement [3], 4].

Oxidative stress (OS) is the result of an imbalance between antioxidant and oxidant molecules in the body [5]. Excessive production of reactive oxygen species leads to DNA breaks and oxidation of cell membrane proteins and lipids [6]. The key changes include heightened synthesis of inducible nitric oxide and disruption of mitochondrial electron transport systems [5], 7]. In the body, reactive oxygen molecules transfer an electron to a thiol, which is then oxidized to form a disulfide bond. The formation of disulfide structures is a reversible process. Depending on the OS level, the extent of this conversion can vary. In the context of sepsis, this process contributes to cellular dysfunction, endothelial damage, myocardial depression, and multiple organ failure. These effects may lead to vascular catecholamine unresponsiveness and can indicate potential diseases [8].

Thiols are organic compounds with a carbon-linked sulfhydryl group. Antioxidants containing thiol groups such as glutathione, cysteine, and N-acetyl cysteine are anti-inflammatory molecules against reactive oxygen species formed in inflammation [9]. Thiols play essential roles in cellular processes, including antioxidant defense, inflammation, regulation of enzyme activities, and immunity. They protect the human body against oxidative stress, and this balance is crucial for detoxification and antioxidant protection [10]. This study aims to evaluate thiol/disulfide ratio (TD) and ischemia-modified albumin (IMA) levels in patients diagnosed with sepsis, based on the SOFA score.

Materials and methods

The hospital ethics committee approved the study on September 21, 2023. The research was conducted in the Intensive Care Unit of the Anesthesia and Reanimation Clinic at the University of Health Sciences, Ankara Training and Research Hospital, from October 1, 2023, to October 30, 2024. Patients or their relatives gave informed consent. A total of 66 patients participated in the study, consisting of 29 women (44 %) and 37 men (56 %). The sepsis status of the patients was evaluated with the SOFA score [5], 6]. In our study, the median SOFA score was calculated as 5.83 (Q1:4–Q3:8). 48 (72.7 %) of the patients were evaluated according to SOFA<10, and 18 (27.3 %) were evaluated according to SOFA≥10 on days 0, 3 and 7. The mean age of the patients was 71.7 ± 13.0 years for SOFA<10 and 75.7 ± 11.6 years for SOFA≥10.

The sources of sepsis in patients were lung infections (pneumonia) (48 %), urinary tract infections (25 %), intra-abdominal infections (abscess, peritonitis, 15 %), skin and soft tissue infections (cellulitis, diabetic foot infections, 5 %), infections caused by central venous catheters (5 %), and meningitis and nervous system infections (2 %). Gram-negative bacteria [Klebsiella (20 %), Pseudomonas aeruginosa (15 %), Acinetobacter (15 %) and Escherichia coli (5 %)] were the causative agents in about 45 % (n=30) of the patients and gram-positive bacteria [(Enterococcus (15 %), Staphylococcus aureus (5 %), coagulase-negative Staphylococci (5 %), Streptococcus pneumonia (5 %)] and fungi (5 %) were the causative agents in 35 % (n=23). Gram staining could not be performed in the remaining 20 % (n=13). During treatment, blood, urine, tracheal aspirate, wound site, or surgical debridement cultures were taken from the patients and appropriate antibiotic therapy was administered.

Patients were evaluated clinically on days 0, 3, and 7. Venous blood samples were collected using Becton Dickinson Vacutainer tubes. The first blood sample was taken immediately upon the patient’s arrival, followed by additional samples on days 3 and 7. After blood samples were collected, they were centrifuged at 1,500 g for 10 min to measure TD levels. Serum samples were stored at −80 °C until ready for biochemical analysis. TD levels were measured directly using a new automated spectrophotometric method developed by Erel and Neşelioğlu [8], 9]. Serum IMA, native thiol, and total thiol levels were measured on the same device using an automated analyzer (Siemens ADVIA 1800, Erlangen, Germany). Disulfide concentrations were calculated as half the difference between native thiol and total thiol concentrations. The ratio of disulfides to total thiols, disulfides to native thiols, and native thiols to total thiols was calculated. IMA was determined by the colorimetric albumin cobalt binding assay. The calibrator used in IMA was 1.0 mmol/L mercaptoethanol [11].

Results

This study included 66 patients, 29 females and 37 males. Sepsis patients were classified according to their SOFA score. In intensive care unit patients with less organ involvement, the SOFA score is below 10; in patients with more organ involvement, it is above 10. Our study calculated the median SOFA score as 5.83 (Q1:4–Q3:8). There were no significant differences in body weight, age, or gender between the SOFA groups in our study (p>0.05).

Discussion

In our study, we aimed to investigate the changes in native thiol, total thiol, disulfide, CRP, and PCT in sepsis patients grouped according to SOFA scoring in intensive care units. The findings of our study indicate that IMA and TD change in the pathogenesis of sepsis in patients. Sepsis is a disease that can progress to inflammation in the endothelial system and multiple organ failure triggered by an increase in the synthesis of proinflammatory molecules and monitored in intensive care [12]. Free radicals and reactive products increase during sepsis. TD and IMA changes may help to explain the pathogenesis of sepsis.

In our study, PCT and CRP were examined among acute-phase reactants. Increased CRP level is a classic finding of infection [13]. However, Garnacho-Montero concluded that PCT is a more reliable biomarker than CRP [14]. It was observed that CRP and PCT values changed according to time in SOFA≥10 and SOFA<10 groups (p<0.05). It was observed that CRP and PCT were higher on day 0 (p<0.05). On day 7, CRP and PCT values were significantly lower compared to day 0 and day 3 (p<0.05). It was thought that CRP and PCT decreased after intensive antibiotic treatment starting from day 0.

The imbalance of oxidative balance due to an increase in reactive oxygen species and the inadequacy of antioxidant substances and mechanisms that detoxify them is called OS. Tissue hypoperfusion and multiple organ failure are common in sepsis. It is known that tissue damage is further increased due to oxidative stress in more severe patients with SOFA>10. Another study by Lorente showed that decreased antioxidant status increased oxidative stress and sepsis severity and was associated with mortality [15]. Recent studies indicate that increased disulfide concentrations are linked to OS, while higher native thiol levels may serve as a response to the oxidative environment [16], 17].

Our study found no significant differences in disulfide, total thiol, native thiol, IMA, or native thiol/total thiol ratios values among the SOFA>10 groups (p>0.05). Although not statistically significant, lower values were observed in patients with SOFA>10. These results correlate with previous studies and indicate that oxidant and antioxidant balance is impaired in sepsis [12], 15].

Ayar et al. reported that disulfide, total thiol, and native thiol levels were significantly reduced in children with sepsis [18]. There was no significant difference in the reduced thiol ratio and oxidation-reduction rate between the healthy and sepsis groups. Additionally, levels of native thiol, total thiol, and disulfide were higher in the non-surviving group compared to the surviving group. This suggests that there is no relationship between native thiol, total thiol, disulfide levels, and disease activity in patients with sepsis [18]. Gürü et al. reported that the levels of total thiol and native thiol were low in patients with acquired pneumonia due to oxidative stress (OS) [19]. Parlak et al. investigated the thiol-disulfide balance in adult patients hospitalized with community-acquired pneumonia and compared it to a home control group [20]. Their findings revealed that both native thiol and total thiol levels were significantly lower in the patient group than in the control group. However, there was no significant difference in disulfide levels between the patient and control groups. Interestingly, the study found that the disulfide/total thiol ratio was statistically significantly higher in patients with pneumonia compared to the control group [20]. In patients with SOFA<10, higher native thiol and total thiol values indicate increased antioxidant levels. Ilanbey et al., Gokhan et al., and Baykan et al. obtained the same result in their studies [21], [22], [23].

IMA is formed due to oxidative stress. Increased IMA is an independent predictor of serious cardiac outcomes such as death, myocardial infarction, and refractory ischemia [24]. Worster et al. found that IMA values above 80 U/mL and sensitivity at 6 h was 92.3 % in patients admitted to the emergency department due to cardiac ischemia for serious cardiac outcomes (myocardial infarction, congestive heart failure, serious arrhythmias) [25]. It increases in systemic sclerosis, scleroderma, metabolic syndrome, obesity, acute ischemic stroke patients, end-stage renal disease, acute mesenteric ischemia, arthroscopic knee surgery, DM, post-exercise skeletal muscle ischemia, peripheral vascular diseases, respiratory distress syndrome, obesity, and some cancers. IMA does not increase in immune system disorders, gastrointestinal diseases, and non-ischemic heart diseases [24]. Clinically, the best model recommended for IMA is transient coronary artery occlusion during percutaneous coronary intervention [25].

In our study, IMA values were found to be high on day 0 in SOFA<10 and SOFA≥10 cases. High IMA values on day 0 are used as an indicator of increased oxidative stress or ischemia/reperfusion injury. High IMA levels indicate increased oxidative stress due to ischemia-reperfusion. Higher IMA values on day 0 in patients with SOFA≥10 and SOFA<10 indicate that ischemia was intense (p<0.05) [11]. The albumin cobalt binding test has important analytical and clinical problems. In order to reduce these problems, it has been suggested that IMA results should be interpreted together with plasma albumin concentration. The fact that albumin was not measured in our study creates a limitation in terms of the interpretation of IMA results [26].

Conclusions

When the literature is reviewed, our study is the first to evaluate TD balance on days 0, 3, and 7 of sepsis according to SOFA scoring. The limited number of patients and the single center are the limitations of this study. Nevertheless, it is thought that the mechanisms underlying sepsis change thiol status and IMA in the organism.