Validity of Signal Peptide-CUB-EGF Domain-containing Protein-1 (SCUBE-1) in the Diagnosis of Aortic Dissection

1. Introduction

Aortic dissection (AD) is one of the troublesome diagnoses in emergency services. It requres rapid diagnosis and confirmation. The clinical picture beginning with chest pain has to be confirmed using imaging methods. However, the findings are always not clear, and patients can show only a simple finding imitating mere ischemia. Thus, it is possible that AD could be confused with findings suggesting renal colic, rendering the diagnosis a difficult issue. Ultrosonograpy and d-dimer level are also not always helpful. Contrast-induced and invasive tomography may not be applicable for all clinically suspected patients because of side effects and the cost [1]. Therefore, a helpful and noninvasive biomarker is necessary for clinicians to make a clear diagnosis.

Signal peptide-CUB (complement C1r/C1s, Uegf, and Bmp1)-EGF (epidermal growth factor) domain-containing protein 1 (SCUBE-1) is a surface protein secreted during embryogenesis. In recent years, it was demonstrated that this protein can be used for multiple diagnoses, and there are also ongoing studies investigating SCUBE-1.

In the present study, we investigated whether SCUBE-1 protein could be useful for clinicians as a biomarker in the diagnosis of AD.

2. Materials and methods

3. Results

Among the study patients, there were 7 males and 13 females. Among the healthy volunteers, 50% (n = 10) were males and 50% (n = 10) were females. The demographic characteristics of both groups were similar with no statistical differences (p $>$ 0.05). The average duration between the first arrival of patients to the emergency department and the diagnosis was 61.30 $\pm$ 75.13 (range 7 – 310) min, whereas the average time for the arrival of the cardiovascular surgeon was 33.35 $\pm$ 15.89 (range 10 – 65) min. The average hospitalization duration was 4.60 $\pm$ 3.63 (range 0–10) days. Table 1 shows the information regarding the arrival features of patients, vital signs, and their demographic characteristics, including a summary of their diagnosis.

The outcomes of patients were analyzed according to the types of AD, and no statistical significance was found between AD types and mortality. Type 1 AD cases had a statistically significantly high mortality rate (p $<$ 0.001). We also analyzed the correlation between AD types and extravasation state and detected a statistically significantly high relationship in AD type 1 cases (p $<$ 0.001). In addition, mortality rate was significantly higher in cases with extravasation (p $<$ 0.001) (Table 2).

The overall mean SCUBE-1 level of the study subjects was 16.11 $\pm$ 5.33 (range 7.26 – 27.84) ng/dL, with 24.51 $\pm$ 3.01 ng/dL in the patient group and 12.11 $\pm$ 5.31 ng/dL in the control group. The mean SCUBE-1 level in the patient group was found to be significantly higher than that in the control group (p $<$ 0.001). A receiver-operating characteristic (ROC) curve was plotted to determine the specificity and sensitivity of AD diagnosis (with 95% confidence intervals) (Fig. 1), which demonstrated a sensitivity of 95% and a specificity of 76% when the SCUBE-1 level was $>$19.75 ng/dL. On the other hand, a significant correlation was found between AD types and mortality and the extravasation state. However, there were no significant differences in the mean SCUBE-1 levels based on the AD types, outcomes, and extravasation (p $>$ 0.05) (Table 3).

Fig. 1.ROC analysis of subjects’ SCUBE-1 levels.95% sensitivity and 76% specificity were determined on the cut-off value calculated for AD. AUC = 0.863 (95% CI = 0.70–1). AUC = Area under the curve; AD = Aortic dissection; ROC = Receiver-operating characteristic.

4. Discussion

AD comprises the most serious and a life-threatening situation. Although not known clearly, the frequency of AD has been predicted to be 5 – 30 cases in a million population. The diagnosis of AD in emergency services remains a challenging issue. Especially, patients with a history of hypertension are at risk in this context. In the present study, a history of HT was present in 65% of the cases (n = 13). Contrary to the general belief that atypical symptoms are quite common, more than one-third of patients have findings and symptoms secondary to involvement of organ systems. When atypical symptoms are not recognized, potential death is inevitable. These symptoms include 50% pulse deficits, 20% neurological deficits, 5% syncope, and 5% – 10% painlessness [1, 2]. Diagnosis is made using tests such as contrast-enhanced CT angiography, which are expensive and have risks due to radiation and contrast agent. Nonetheless, this test remains the most commonly used diagnostic tool for AD. Hence, diagnostic tests that are inexpensive, noninvasive, and with less risk of complication are necessary. Although d-dimer is a supportive marker for AD, age $>$ 70 years, pregnancy, active malignancy or metastasis, recent surgeries, trauma, deep vein thrombosis, hepatic failure, rheumatoid arthritis, and presence of infection are potential causes of false-positives. In case of warfarin treatment, the presence of small and isolated thrombi and having symptoms lasting longer than 5 days with false-negative outcomes are detected [2]. Furthermore, d-dimer causes confusion for AD diagnosis, and there are also reports of possible d-dimer negativity in patients with AD [3]. There are also reports of patients with negative d-dimer levels but being operated [4]. Ultrasonography (USG) is also a contributory test for the diagnosis. However, emergency physicians have limited experience in this regard. Reliability of USG is variable because it may provide different results depending on the characteristics of patients and the physician experience. A noninvasive and safe diagnostic method useful for making the diagnosis is unavailable, indicating the crucial need for clinical studies.

SCUBE-1 is a cell surface protein released during embryogenesis. Its family members consist of amino-terminal signal peptide, repeated nine copies of EGF-like N terminal, spacer, CUB-domain signal peptide C terminal sequence, and structural cysteine molecules [5]. This protein is expressed on thrombocytes and vascular endothelial cells. It is involved in thrombosis by taking part in the structure of EGF glycoprotein. It also plays a role in thrombin activation and inflammation [6]. In case of vascular damage, there is an increase in the expression of SCUBE-1.

Acıpayam et al. study reported that SCUBE-1can indicate early stages of thrombosis in patients with beta thalassemia [7]. In recent years, this protein has been investigated because of its role in vascular damage and thrombosis. Dia et al. demonstrated that SCUBE-1 expression can be detected 6 h after cardiac ischemia (SCUBE-1 level in patients with ACS: 205 ng/mL), and it has low sensitivity and is a good marker for thrombosis (In our study, the SCUBE-1 level was measured as 27.84 ng/mL in the majority of AD cases.). In the same study, the authors stated that it is a reliable marker for diagnosing ischemic stroke [8]. Moreover, it has been demonstrated that its expression can be detected within 2 h in cases of mesenteric ischemia [9]. A specific biomarker for pulmonary emboli (PE) is also lacking. In this context, in a study conducted by Türkmen et al., it was reported that SCUBE-1 can be used for PE diagnosis as well [10].

AD is a pathology manifested by vascular endothelial damage and thrombi. SCUBE-1 protein is produced from the vascular endothelium, and its levels in the blood increase in cases of vascular structure damage and thrombi [4]. We observed SCUBE-1 levels can increase in AD as well, in our study. This unexpected increase would support the clinical predictivity. A recommended biomarker for AD is lacking, and although determining d-dimer levels is recommended, its diagnostic value is low. Several studies have stated not to use d-dimer positive and negative values for diagnosis, although there are meta-analyses that have indicated using its negative predictive value [1]. In the present study, we determined the AUC value of SCUBE-1 for AD diagnosis as 0.863, in addition to 95% sensitivity and 76% specificity when the SCUBE-1 cut-off level was 19.75 ng/dL. Based on our study results and in comparison with clinical findings, we believe that SCUBE-1 would be a helpful biomarker for clinicians for diagnosing AD.

5. Conclusion

AD is a diagnosis associated with a high mortality rate in emergency services. Therefore, scientific studies are important to help in the diagnosis. We observed that plasma SCUBE-1 levels have high specificity for AD diagnosis and thus can be valuable. We suggest further studies with larger clinical series to support the resuls of our preliminary study.

Limitations

The first limitation of our study was the relatively small numbers of patients and controls, although these numbers were predicted by a power analysis. Next, the average age of the subjects was high in our study, as it is known that AD can also present in younger patients. Finally, according to the manufacturer information on the analysis kit, plasma samples cannot be stored in freezers for more than 2 months. This storage period can be a limitation, although the duration was not expired in our study.

Acknowledgments

We are grateful to Assoc. Prof. Sadık Volkan Emren who works as cardiologist in our hospital for his contributions.

Conflict of interest

None of the authors received any type of financial support that could be considered potential conflict of interest regarding the manuscript or its submission.

Ethical consideration

Approval for conducting the study was obtained from the ethical committee of the university hospital (Izmir Katip Celebi University Clinical Studies Ethics Committee). Ethical committee number: 2019-KAE-0252. Consent forms were obtained from all patients and healthy volunteers or their first-degree relatives. The entire study was conducted according to the criteria of the Declaration of Helsinki.