Soluble Urokinase Plasminogen Activated Receptor in Type 2 Diabetes Mellitus Patients Undergoing Coronary Artery Bypass Grafting: A Prospective Interventional Cohort Study

INTRODUCTION

The key role of inflammation in atherosclerosis is well known.^[1] Inflammatory markers have proven to be supportive for the assessment of risk in cardiovascular disease (CVD). Increased levels of high-sensitivity C-reactive protein (hsCRP) have not only been found to be associated with subclinical inflammation but also with increased cardiovascular risk and Framingham Risk Score for risk stratification.^[2] Soluble urokinase plasminogen activator receptor (suPAR) is a new biomarker of prognostic significance in several clinical settings, including CVD.^[2-4] It is bound to uPAR in its membrane and is released with a systemic inflammatory reaction.^[5] Since CVDs represent the inflammatory state, newer evidence shows that the pathophysiological pathway of suPAR is more closely associated with atherosclerosis and subclinical organ damage (SOD) than C-reactive protein (CRP). In addition to this, the plasma suPAR levels are more stable than CRP.^[6] The suPAR level is increased in patients with CVDs, atherosclerosis,^[7] ischemic heart disease,^[7 -9] type 2 diabetes mellitus (T2DM),^[10] poor prognosis,^[11-14] and venous thromboembolism.^[15] Raised suPAR levels also indicate ischemia at the microcirculatory level and help in risk stratification of patients for coronary artery disease on extracorporeal membrane oxygenation.^[16] Anti-inflammatory agents are known to affect suPAR levels but limited literature is available for its guidance in the management of cardiac surgical patients. Therefore, we primarily aimed to assess whether the measurement of suPAR in patients with T2DM undergoing coronary artery bypass grafting (CABG) assists in predicting mortality.

MATERIAL AND METHODS

Patients

We evaluated suPAR in patients with T2DM undergoing elective CABG between September 2022 and January 2024. Randomization into the two groups was done by a sealed envelope technique by a neutral operation theater personnel not knowing about the study; thus the study was blinded. Patients of the study group S (suPAR group) (n = 96) were measured suPAR, hsCRP, and blood sugar, while patients of the control group C (control non-suPAR group) (n = 100) were measured hsCRP and blood sugar only [Flow chart 1].

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Flow chart 1:

Cohort flow diagram.

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RESULTS

The study was conducted on 196 patients of either sex of age at least 18 years or older with T2DM with ASA status III to IV. A total of 196 patients were randomly divided into 2 groups. Patients of the study group (n = 96) were measured suPAR, hsCRP, and blood sugar, while patients of the control group (n = 100) were measured hsCRP and blood sugar only. The majority of patients in both groups belong to the age bracket of 51–70 years, with a mean age of 58.18 ± 9.34 in cases and 59.11 ± 9.89 in controls. Both groups had no significant difference in terms of age (P = 0.249). In both groups, the overwhelming majority of patients were males, with no significant difference in the percentages (P = 0.069). While 10.42% was the mortality rate in cases, it was 10% in controls. However, there was not any significant difference between the two groups [Table 3].

Furthermore, there was no significant difference in the total duration of ventilation (P = 0.149), mean length of ICU stay (P = 0.410) [Table 4], and blood sugar levels in both the groups for up to 48 hours post-surgery [Table 5]. Between T1 and T2 levels of suPAR before surgery and 48 h after surgery, there was a significant difference seen at 2-time intervals, signifying an ischemic and inflammatory effect of CPB (P < 0.001) [Table 6 and Figure 1]. At time T1, the hsCRP values of 0.4 and 0.5 were significantly higher in cases, while all the other values were significantly higher in controls. The mean hsCRP at T1 in cases was 0.77 ± 1.43, which was significantly higher than in controls at 0.50 ± 0.77 (P = 0.050) [Table 7 and Figure 2a]. At time T2, the hsCRP values were similar in both groups. However, values of 6 mg/L and >10 mg/L were significantly higher in controls, while the value of 8 mg/L was higher in cases. The mean hsCRP at T2 in cases was 10.09 ± 2.73, which was not significantly different than in controls at 9.93 ± 2.47 (P = 0.335). This shows that hsCRP values increased significantly post-surgery in both groups [Table 8 and Figure 2b].

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Figure 1:

Graphical representation of mean soluble urokinase plasminogen activated receptor values before surgery and 48 h post-cardiopulmonary bypass. suPAR: Soluble urokinase plasminogen activated receptor, T1: Before surgery, T2: Post 48 hours after cardiopulmonary bypass termination. CPB: Cardiopulmonary bypass.

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Figure 2:

(a) Graphical representation of distribution high senstivity C- reactive protein values before the surgery at time T1 in the two groups. (b) Graphical representation of distribution of high senstivity C-reactive protein values 48 hours post-cardiopulmonary bypass at time T2 in the two.

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Mortality was assessed in the immediate postoperative period. The area under ROC for the parameter suPAR (T1) in predicting mortality is 71%. A threshold of ≥4.9 ng/mL for death yields a sensitivity of 80%, specificity of 74.42%, positive predictive values (PPV) of 26.67%, negative predictive values (NPV) of 96.97%, and accuracy of 75%. The area under ROC for the parameter hsCRP (T1) in predicting mortality is 98.1%. A threshold of ≥1.6 ng/mL for death yields a sensitivity of 100%, specificity of 97.67%, PPV of 83.33%, and accuracy of 97.92%. The area under ROC for the parameter suPAR (T2) in predicting mortality is 96.3%. A threshold of ≥16.25 ng/mL for death yields a sensitivity of 100%, specificity of 91.86%, PPV of 58.82%, and accuracy of 92.71%. The area under ROC for the parameter hsCRP (T2) in predicting mortality is 99.9%. A threshold of ≥ 12.5 for death yields a sensitivity of 100%, specificity of 98.84%, PPV of 90.91%, and accuracy of 98.96% [Table 9 and Figure 3].

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Figure 3:

ROC curve for 30-day post-operative mortality predicted from combinations of soluble urokinase plasminogen-activated receptor and high sensitivity C-reactive protein. ROC: Receiver operating characteristics, T1: Before surgery, T2: Post 48 hrs after cardiopulmonary bypass termination.

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DISCUSSION

Detection of a physiological variable that correlates with cellular hypoperfusion and can be used as an appropriate resuscitation measure is challenging.^[18] Cardiac biomarkers are similar to an intervention.^[19] Lactic dehydrogenase, CK, and Creatine kinase MB (CKMB) have been used in the past but now, troponins are the current standard for diagnosis of myocardial infarction. glycogen phosphorylase isoenzyme BB (GPBB), heart type fatty acid binding protein (HFABP), soluble suppressor of tumorigenicity-2 (sST2), suPAR, and miRNA have proven to be helpful for the diagnosis and treatment of patients suspected of an adverse cardiac event.^[20] Both suPAR and hsCRP have shown prognostic significance in CVDs.^{[11,12,21-23]} However, the association between the biomarkers and prognosis after cardiac surgery has not been established.^[24]

Since suPAR is known to be raised for more than 24 hours in cardiac surgical patients, we measured its levels in the case group before surgery and 48 hours post-CPB. It was seen that 48 h post-CPB, the suPAR levels increased by almost 3 times in the mortality group as compared to less than twice in the survival group [Table 10]. Sehestedt et al. (2011) concluded in their study that raised suPAR levels indicate SOD and cardiovascular injury.^[25] Rasmussen et al. (2021) concluded that a rise in suPAR and hsCRP levels before a cardiac surgical procedure was associated with increased mortality.^[26] Our study aligned with these studies, showing that increased levels of suPAR and hsCRP in the population with T2DM undergoing CABG in the perioperative period indicate an increased risk of mortality in the immediate postoperative period.

AHA states that a biomarker should be synergistic to already known risk factors, helpful in patient management, and should be able to predict possible outcomes.^[27] Increased suPAR and hsCRP both predict adverse cardiovascular events.^[2,28,29]. suPAR is a stable protein and has lesser circadian fluctuations. It is membrane-bound and gets into the bloodstream after getting cleaved from the urokinase-type plasminogen activator receptor. It is found on the surface of various cells, which include inflammatory and endothelial cells.^[6,11,30,31] Its performance also gets enhanced when it is combined with other biomarkers such as procalcitonin and CRP.^[32]

In a healthy adult population, women have increased suPAR levels as compared to men and a positive correlation with age in both men and women has been observed.^[33-38] Gender-specific physiology may be the cause of increased suPAR levels in women.^[39] However, there is a greater annual increase in suPAR levels in men than in women.^[40] Studies have shown both positive and negative correlations between basal metabolic index and suPAR levels.^[33-35,38] However, body mass index (BMI) >35 kg/m⁻² is a known chronic inflammatory state that may lead to increased sugar levels.^[38] Lifestyle choices such as tobacco smoking, unhealthy diet, levels of HDL cholesterol, sedentary lifestyle, and alcohol intake have also been found to affect sugar levels.^[38,40] Furthermore, genetic factors, as well as environmental factors, also affect suPAR levels.^[41]

suPAR levels are reduced by anti-inflammatory agents, leading to a reduced risk of adverse cardiovascular outcomes. Hypolipidemic agents like simvastatin cause decrement in suPAR levels in patients with subclinical aortic stenosis. However, there is no established relation between the effects of hypolipidemic drugs and decreased suPAR levels, leading to lesser mortality and reduced adverse cardiovascular events.^[42] Corticosteroids reduce both inflammation and suPAR levels in patients with chronic obstructive pulmonary disease.^[43] Anakinra, an interleukin (IL)-1 receptor antagonist, has proven efficacy in reducing the acute inflammatory response in acute myocardial Infarction (AMI).^[44] Ridker et al. have shown a reduced incidence of MI with canakinumab, a monoclonal antibody against IL-1β.^[45]Although studies have depicted the effect of anti-inflammatory agents on suPAR levels leading to reduced adverse cardiovascular outcomes, more investigations are required for its use in guiding the treatment of patients with CVD.

CRP is also a protein and it represents acute inflammation. It is also involved in the vascular remodeling process.^[37] During inflammation, the release of proinflammatory cytokines stimulates hepatocytes to produce CRP. Recent data suggest that CRP levels are increased during atherosclerosis.^[46] CRP in small ranges of 0.01–10 mg/L can also be traced with modern high-sensitivity assay techniques, which include immunonephelometry, immunoturbidimetry, high-sensitivity enzyme-linked immunosorbent assay, and resonant acoustic profiling.^[47] Therefore, lesser grades of inflammation can also be detected with these newer high-sensitivity assay techniques. The hsCRP is one of the most commonly used biomarkers for CVD risk prediction across the world. However, hsCRP is not a reliable marker as its levels are affected by several drugs, infections, inflammation, and external stress stimulus.^[48-50]

Raised suPAR levels indicate cardiovascular disorders and more incidence of deaths in the population.^{[28,29,34,51]} The prognostic significance of elevated suPAR levels in cardiac surgical patients and their association with increased postoperative complications is a lesser explored area.^[51] Elevated suPAR levels on the 1^st day after surgery indicate more duration of ventilation and increased duration of ICU stay.^[52] A rise in suPAR levels after the cardiac surgical procedure also depicts an aggravated risk of acute kidney injury.^[53] Interestingly, our study was also in consonance with these facts which have been proven by some small number of studies earlier. However, there was no significant change in patient outcome after including suPAR in known risk models. This proves that perioperative mortality is dependent on other factors.

Our study had some considerable limitations, too. The generalizability to other centers and races was limited because the population assessed was mainly Indians, and the surgical procedures were performed at the same cardiac surgical center. Although the literature has shown suPAR to be associated with low ejection fraction, our study was limited to patients with normal ejection fraction only.^[54] Post-adverse outcomes such as acute kidney injury and stroke were not recorded. Additional information could have also been obtained by recording the cause of death and following the patients for the long term.

CONCLUSION

suPAR, an important biomarker, reflects systemic inflammation leading to the pathogenesis of CVD. Its increased levels (pre-bypass and especially 48 h post-CPB) were associated with increased mortality in T2DM patients undergoing elective on-pump CABG, thereby reflecting more severe disease. However, it lacks consensus reference ranges, and its assays are non-standardized. To summarize, various circulating forms of suPAR and different methods to control them need to be explored for better outcomes after cardiac surgery. suPAR for prognosis of patients having type 2 diabetes mellitus undergoing CABG needs more prospective studies to have a strong relationship between the two.