The effects of dexmedetomidine on thiol/disulphide homeostasis in coronary artery bypass surgery: a randomized controlled trial

Abstract

Background

Thiol-disulfide homeostasis (TDH) plays a pivotal role in various physiological mechanisms, including antioxidant defence, detoxification, apoptosis, regulation of enzyme activities and cellular signal transduction. TDH can be used as a biomarker to detect oxidative stress (OS) levels and ischemia status in the tissues. Coronary artery bypass grafting (CABG) surgery is a procedure associated with high oxidative stress. Dexmedetomidine, an alpha-2 agonist anaesthetic agent, has antioxidant effects. In this study, the effects of dexmedetomidine on oxidative stress in CABG surgery were investigated.

Methods

Patients who underwent on-pump CABG surgery were divided into two groups: those receiving dexmedetomidine (Group D) and those not receiving dexmedetomidine (Group C). From anesthesia induction to the end of surgery, patients in Group D received intravenous infusions of 0.05–0.2 mcg/kg/min remifentanil and 0.2–0.7 mcg/kg/h dexmedetomidine. Patients in Group C received intravenous infusion of 0.05–0.2 mcg/kg/min remifentanil. Blood samples were collected from the patients 30 min before induction of anesthesia (T1), 30 min after removal of the aortic cross-clamp (T2), and at the end of the surgery (T3). Thiol-disulfide homeostasis (TDH) was assessed using a novel method. A novel automated method enables the determination of native thiols, total thiols and disulfides levels in plasma, allowing the calculation of their respective ratios.

Results

In patients receiving dexmedetomidine, lower postoperative levels of disulfide, disulfide/native thiol, and disulfide/total thiol, along with higher native thiol/total thiol, were observed compared to the control group. (p < 0.05) Postoperative native thiol and total thiol levels were similar for both groups. (p > 0.05)

Conclusions

In our study, through dynamic thiol-disulfide measurements, we found that levels of oxidative stress (OS) were lower in patients who received dexmedetomidine. We believe that the positive effects of dexmedetomidine on OS could be beneficial in CABG surgery. Furthermore, we anticipate that with further studies conducted in larger patient cohorts, the clinical utilization of dexmedetomidine will become more widespread.

Trial registration number

NCT05895331 / 06.07.2023.

Introduction

Thiols are a class of organic compounds that contain sulfhydryl residues (-SH) at their active site. They play a critical role in preventing the formation of an oxidative stress (OS) condition which damage biomolecules in cells. They can interact with oxygen-containing free radicals, forming reversible disulfide bonds. When the OS is terminated, disulfide bonds can be reduced again to thiol groups. This reaction serves as a protective mechanism against the OS. Thiol-disulfide homeostasis (TDH) plays a pivotal role in various physiological mechanisms, including antioxidant defence, detoxification, apoptosis, regulation of enzyme activities and cellular signal transduction. TDH can be used as a biomarker to detect OS levels and ischemia status in the tissues [1]. Total thiols comprise both reduced and oxidized thiols, whereas native thiols comprise only reduced thiols [2]. A novel automated method enables the determination of native thiols, total thiols and disulfides levels in plasma, allowing the calculation of their respective ratios. Decreased native thiols levels and increased disulfide levels signify an escalation in oxidative stress [3].

Coronary artery bypass grafting (CABG) surgery is the sole surgical treatment method for patients with coronary artery disease. In cardiac surgery, oxidative stress may increase due to various factors. Cardiopulmonary bypass (CPB) pump system, ischemia, reperfusion injury, hemolysis, and neutrophil activation are some factors that can lead to oxidative stress [4]. Oxidative stress is a condition associated with comorbidities, surgical procedures, and medications used during the perioperative period [5, 6]. Dexmedetomidine (DEX) is an alpha-2 agonist anesthetic agent with protective effects against apoptosis induced by hypoxia/reoxygenation and cardioprotective properties [7,8,9]. DEX is extensively employed owing to its multifaceted properties, providing sedation, analgesia, anxiolysis, sympatholysis, reduction in postoperative delirium and agitation and contributing to cardiovascular stabilization and the preservation of respiratory function [10, 11].

In this study, we aimed to investigate the hypothesis that the use of dexmedetomidine in patients undergoing major surgery with high oxidative stress, such as CABG surgery, would have positive effects on thiol-disulfide homeostasis.

Methods

Approval was obtained from the Ethics Committee of Ankara Etlik City Hospital (Ethics Committee Approval Number: 035/05.04.2023). (ClinicalTrials ID: NCT05895331/06.07.2023). The study included patients who underwent elective on-pump CABG surgery and were classified as ASA (American Society of Anesthesiologists) class III. Patients under the age of 18, emergency surgeries, patients undergoing off-pump CABG surgery and patients undergoing valve surgery were excluded from the study. The study included 70 patients who underwent elective on-pump CABG surgery between July 15, 2023, and September 15, 2023. Patients were sequentially numbered and randomly assigned to one of two groups using opaque, sealed envelopes: Group D (received DEX) and Group C (did not receive DEX).

In both groups, induction of anaesthesia involved the administration of propofol at a dosage of 2 mg/kg, lidocaine at 1 mg/kg, fentanyl at 1mcg/kg, and rocuronium at 0.6 mg/kg. All patients were routinely administered intraoperative 1 mg/kg methylprednisolone. For maintenance of anaesthesia, patients in group D received 0.8–1.2 MAC sevoflurane, 0.05–0.2 mcg/kg/min remifentanil and 0.2–0.7 mcg/kg/h DEX, while Group C patients received 0.8–1.2 MAC sevoflurane and 0.05–0.2 mcg/kg/min remifentanil. Remifentanil is a medication with anesthetic and analgesic properties. It is routinely used in the maintenance of anesthesia for all patients undergoing CABG surgery. DEX, on the other hand, is an anesthetic agent with sedative, anxiolytic, and analgesic properties, acting as an alpha-2 agonist. The study compared the group of patients receiving standard anesthesia maintenance with a control group to the group of patients receiving DEX as an adjunct in anesthesia maintenance. Patients in both groups were ventilated intraoperatively with volume-controlled ventilation mode, 50% oxygen–50% air, 6 ml/kg tidal volume, and 12 breaths per minute. In both groups, patients underwent the use of the anesthesia machine pump mode during the coronary artery bypass pump process. Patient monitoring interventions included pulse oximetry (SPO2), end-tidal carbon dioxide, heart rate, invasive arterial monitoring, near-infrared spectroscopy (NIRS) monitoring, Bispectral Index (BIS), temperature, and urine output in both groups. Anesthesia was maintained so that the BIS value was between 40 and 60. Age, gender, body mass index (BMI), comorbidities, duration of cross clamp, duration of CPB pump, duration of surgery and intraoperative hemodynamic parameters were recorded for all patients. At the conclusion of the surgery, patients were transferred to the intensive care unit while under endotracheal intubation.

In the study, blood samples were collected from patients 30 min before anaesthesia induction (T1), 30 min after aortic cross-clamp removal (T2) and at the end of surgery (T3) [12]. A blood sample of 3 ml was collected for each time period. The samples were kept at room temperature for 45 min, then centrifuged at 3500 rpm for 10 min and finally stored at -80 °C until the time of measurement.

Thiol-disulfide homeostasis tests were performed using the automated spectrophotometric assay method described by Erel and Neselioglu. This new method is based on the reduction of sodium borohydride (NaBH4) and disulfide bonds to functional thiol groups. With NaBH4, dynamic and reducible disulfide bonds are reduced to functional thiol groups. Unused NaBH4 is removed with formaldehyde after the reaction to prevent further reduction of disulfide bonds and to prevent further reduction of the produced 5,5’-dithiobis-2-nitrobenzoic acid (DTNB). The total thiol content of the samples is measured using Modified Ellman’s reagent, and the disulfide level is calculated according to the following formula: (total thiol - native thiol)/2 [1].

Statistical analysis

SPSS 21.0 (Versinon 22.0, SPSS, Inc, Chicago, IL, USA) program was used for statistical analysis. After applying the Shapiro-Wilk test for normality, Student’s t-test was used if the distribution was normal for the comparison of continuous variables between groups, and the Mann-Whitney U test was used if the distribution was not normal. Chi-square test was used for categorical variables. Results p < 0.05 were considered significant. We performed a sample size calculation using G*Power version 3.1.9.2 based on pilot data obtained from the mean difference in native thiol levels between T1 and T3. In the preliminary study, native thiol levels of difference (mean ± SD) was 58.76 ± 22.58 in Group D and 82.64 ± 38.82 in Group C. Power analysis was performed with the criteria of type 1 error probability (alpha) = 0.05, power(1-beta) = 0.80, and effect size of 0.75, and it was calculated that the minimum required sample size was at least 58 (29 in each group). But 35 patients were enrolled for possible dropouts in each groups.

Results

70 patients aged 18 and older who underwent elective CABG surgery with CPB pump between July 15, 2023, and September 15, 2023 were included in the study. Of these, 7 patients undergoing valve surgery alongside CABG and 3 patients undergoing the reuse of the CPB pump were excluded from the study. Consequently, the study included 60 patients, divided into Group D (30) and Group C (30) (Fig. 1).

Fig. 1

CONSORT diagram of the study

The demographic and clinical characteristics (age, gender, body mass index, chronic diseases), duration of cross clamp, duration of CPB pump, and duration of surgery were similar in both groups. (p > 0.05) (Table 1) Additionally, during the 24-hour postoperative period, inotropic requirements, hemodynamic, and laboratory parameters were similar between the two groups.

The mean remifentanil consumption of the patients was 1.80 ± 0.17 mg in Group D and 1.84 ± 0.21 mg in Group C. There was no difference between both groups (p = 0.366) In Group D, the mean DEX consumption was 146.57 ± 19.52 mcg (Table 1).

Table 1 Demographic and clinic characteristics

Table 2 Thiol/disulfide redox states according to groups

The levels of native thiol, total thiol, disulfide, ratios of disulfide/native thiol, disulfide/total thiol, native thiol/total thiol of the patients in the preoperative (T1), cross clamp removal (T2) and postoperative (T3) periods are shown in Table 2. All of these thiol-disulfide homeostasis values were similar for both groups in the preoperative (T1) and cross clamp removal (T2) period (p > 0.05). Similarly, postoperative (T3) native thiol and total thiol levels were similar (p > 0.05) for both groups. Nevertheless, in Group D, in comparison to Group C, postoperative disulfide levels and ratios of disulfide/native thiol, disulfide/total thiol were lower, while ratio of native thiol/total thiol was higher. (p < 0.05) (Table 2).

The difference in native thiol levels between T1 and T2 was significant between the groups. (p < 0.05) (Group D: 80.53 ± 61.73; Group C: 117.20 ± 77.42).

The differences in total thiol and disulfide levels between T1 and T2 were similar in both groups. (Total thiol levels of difference; Group D: 94.12 ± 66.77; Group C: 127.36 ± 81.48) (Disulfide levels of difference; Group D: 6.79 ± 5.96; Group C: 5.08 ± 4.95). (p > 0.05)

There were no significant differences in T2-T3 total thiol, native thiol, and disulfide levels between the groups. (p > 0.05)

The difference in native thiol and disulfide levels between T1 and T3 was significant between the groups. (Native thiol levels of difference; Group D: 58.69 ± 60.43; Group C: 94.70 ± 66.76) (Disulfide levels of difference; Group D: 4.58 ± 4.46; Group C: 0.67 ± 5.05) (p < 0.05) (Fig. 2).

Fig. 2

Groups comparison of differences in thiol disulfide homeostasis between preoperative (T1) and postoperative (T3) periods

The difference in total thiol levels between T1 and T3 were similar in both groups. (Group D: 67.85 ± 65.01; Group C: 96.05 ± 69.51) (p = 0.110). (Fig. 2)

Discussion

In this study, we aimed to investigate the effects of DEX on thiol-disulfide homeostasis in patients undergoing CABG. In patients receiving DEX, lower disulfide levels and lower disulfide/native thiol and disulfide/total thiol ratios were found in the postoperative period (T3) compared to the control group. Conversely, higher native thiol/total thiol ratios were observed in patients receiving DEX compared to the control group. Additionally, it was observed that there were smaller changes in native thiol levels between the T1-T2 and T1-T3 periods in the DEX group compared to the control group.

In TDH, decrease in native thiol levels indicates an increase in OS. Kutluhan et al. [13] compared the OS effects of propofol and desflurane in their study. In this study, the effects of inhalation and intravenous anesthesia methods on OS were investigated in patients undergoing vertebral surgery. They showed differences in the native and total thiol levels between the groups. In another study comparing sevoflurane and desflurane, a greater decrease in native thiol levels was reported in the desflurane group [14]. In this study, native thiol levels were similar in both groups at T1-T2-T3 times. However, a less prominent decrease in native thiol levels between T1-T2 and T1-T3 times was observed in patients receiving DEX. We attribute this lesser reduction in native thiol levels in Group D to the potential antioxidative properties of DEX.

In TDH, increase in disulfide levels indicate an increase in OS. In addition to native thiols, total thiols and disulfide levels in plasma, the ratios of these parameters affecting TDH have also been investigated in various studies to evaluate the balance between oxidative and antioxidative processes [14,15,16,17]. Akin et al. investigated the effects of general anesthesia versus spinal anesthesia on oxidative stress in patients undergoing cesarean section. They reported lower disulfide, disulfide/native thiol, disulfide/total thiol values, and higher native thiol/total thiol values in the spinal anesthesia group. In our study, we found that the levels of disulfide, disulfide/native thiol, disulfide/total thiol were lower in patients receiving DEX compared to those in the control group. We believe that the reduction of oxidative stress is positively influenced by the intraoperative use of DEX due to its effects on TDH.

There are numerous studies in the literature investigating oxidative stress in cardiovascular surgery through TDH measurements. Sanrı et al. [12] investigated the effects of thiol-disulfide homeostasis in patients undergoing on-pump coronary artery bypass grafting. They reported that increased ratios of disulfide/native thiol, disulfide/total thiol and decreased ratios of native thiol/total thiol were observed after cross clamping in CABG surgery compared to preoperative period. Additionally, a positive correlation between aortic cross-clamp time and disulfide levels was reported in this study. Tanyildiz et al. [18] reported that higher disulfide values in cyanotic patients compared to acyanotic patients in their studies on congenital heart surgery. Our study’s findings are consistent with the studies in the literature. The first study investigated the effect of CABG surgery on oxidative stress. In the other study, the oxidative stress levels of cyanotic and acyanotic patients were compared. In our study, we compared the combination of remifentanil-DEX with remifentanil alone, and found lower levels of oxidative stress with the remifentanil-DEX combination. Izgi et al. [19] reported in their study where they compared remifentanil and DEX in CABG surgery that native thiol levels were higher in the DEX group during the intraoperative cross clamp removal period, while no difference was found in the subsequent intraoperative measurement period. In the current study, they reported that DEX was more successful than remifentanil in reducing oxidative stress [19]. Remifentanil and DEX are drugs with different mechanisms of action [8, 20]. In our study, where remifentanil was used in both groups for anaesthesia maintenance as a component of balanced anaesthesia, the combination of remifentanil and DEX was observed to be more effective in reducing oxidative damage than remifentanil alone. We believe that the additive effects of the different mechanisms of action of remifentanil and DEX contribute to this outcome. Additionally, various studies in the literature suggest that differences in total thiol, native thiol, disulfide, and thiol-disulfide ratios may not consistently occur simultaneously [13, 19, 21, 22]. The reason for this lies in the fact that the different methods and agents investigated can lead to different effects on TDH. TDH has been utilized in numerous studies to assess oxidative stress. Decreased native thiol, total thiol levels, and increased disulfide levels are considered indicative of increased oxidative stress [3].Therefore, when evaluating oxidative stress, we consider that it is essential to comprehensively evaluate thiol, disulfide, their ratios, and the differences in their values over time as a holistic approach.

It has been reported in the literature that dexmedetomidine reduces caspase-3 and apoptosis, increases telomere/telomerase activity, and decreases the formation of free oxygen radicals [23, 24]. We believe these mechanisms contribute to the reduction of oxidative stress by dexmedetomidine. It has been reported that an increase in oxidative stress levels leads to an increase in myocardial damage and impairment in wound healing [25, 26]. Chen et al. [27] reported that dexmedetomidine decreased acute kidney injury in rats by reducing oxidative stress and apoptosis in their studies. Additionally, Tanyıldız and colleagues [18] have reported higher levels of oxidative damage in deceased patients. Furthermore, it has been reported that the level of oxidative stress is associated with the formation of coronary collateral circulation and the development of postoperative atrial fibrillation [24, 25]. We believe that the use of antioxidant-effective treatments during the perioperative period will result in fewer revision surgeries, better wound healing, lower incidence of postoperative complications, hospital stays, and lower mortality rates. We anticipate that the clinical use of DEX, which we found to be effective in reducing oxidative damage in our study, may increase as its use is further investigated in a wider range of patient groups during both intraoperative and postoperative periods.

This study has several limitations. Firstly, the single-center nature of the study is a limitation. Although patient groups were determined through power analysis, multicenter studies involving larger patient populations are needed to determine the rates of complications such as postoperative wound healing and revision surgery associated with DEX. The second limitation is the inability to assess long-term thiol-disulfide homeostasis.

Conclusion

Coronary artery bypass grafting (CABG) surgery is the sole surgical treatment method for patients with coronary artery disease. These patients experience elevated levels of oxidative damage attributed to prolonged exposure to general anaesthesia and the utilization of a CPB pump. Through dynamic thiol-disulfide measurements, we identified a reduction in OS with the use of DEX. We think that the positive effects of DEX on OS may be beneficial in CABG surgery. We believe that reducing oxidative stress could potentially decrease the rates of postoperative complications, length of hospital stay, and mortality. Therefore, we think that DEX should be investigated in multicenter studies involving broader patient populations.