The effects of serum ischemia modified albumin on diagnosis of cerebral infarction and vertebral basilar artery stenosis

ABSTRACT

Objectives

Serum ischemia-modified albumin (IMA) is higher in patients with cerebral infarction (CI). In this study, we aimed at studying the association between IMA and CI.

Methods

Patients with CI were divided to severe stenosis group and mild stenosis group according to the stenosis of vertebrobasilar artery. Digital subtraction angiography (DSA) and magnetic resonance imaging (MRI) were used for diagnosis. Cobalt-combined with Albumin test was used to determine the serum IMA levels. Serum IMA levels in patients with CI and healthy volunteers were compared by t test. Receiver operating characteristic (ROC) curve was performed for evaluating the diagnostic efficiency of serum IMA for CI. The correlation between IMA level and the National Institute of Health Stroke Scale(NIHSS) score after treatment was analyzed.

Results

Serum IMA levels in patients with CI was increased compared to healthy volunteers(P < .05). Patients in severe stenosis group had a higher serum IMA level than mild stenosis group(P < .05). Serum IMA level at admission was associated with NIHSS score on the 7th day after treatment(P < .05).

Conclusions

Serum IMA level was correlated with vertebrobasilar artery stenosis and  short-term prognosis in patients with acute CI.

KEYWORDS:

• Ischemia modified albumin
• cerebral infarction
• receiver operating characteristic curves
• vertebrobasilar artery stenosis

Introduction

Cerebral infarction (CI), also called ischemic stroke, is one of the most common cerebrovascular diseases. The pathogenesis of CI results from interrupting of blood circulation in brain such as thromboembolism and embolic occlusion. Many factors, including hypertension, coronary heart disease, diabetes, smoking and vertebrobasilar artery stenosis, are identified as risk factors for CI (1). In a previous study, the incidence of patients with vertebrobasilar artery stenosis is as high as 10.9% (2). Early diagnosis and treatment of CI are vital for prognosis of patients. The diagnosis of CI currently relies heavily on imagological examination such as computed tomography (CT), magnetic resonance imaging (MRI), electrical impedance tomography (EIT) (3–5). However, imagological examination is not sensitive for early signs of CI. Therefore, it is urgent to find new biomarkers for early diagnosis of CI.

Ischemia-modified albumin (IMA) was first found in the 1990s, which was formed by human serum albumin after the production of ischemia and hypoxia-free radicals or acidosis. Studies have showed that IMA increases within minutes of the onset of ischemia, with a peak lasting for 6–12 h (6–8). The association between IMA and CI has been reported in previous studies (9–11). For instance, IMA has been considered to be a marker of early diagnosis for CI and acute coronary syndrome (9). Abboud et al. (10) found that serum IMA levels of patients with CI are higher than those in healthy population, and the IMA levels of patients with CI gradually increases within the first 24 h. In a case-control study, serum IMA levels are also higher in patients with CI, cerebral hemorrhage, and subarachnoid hemorrhage than those in healthy persons, but there is no significant difference between patients with CIand those with cerebral hemorrhage (11). It is illustrated that measurement of IMA in patients with acute ischemic stroke (AIS) is helpful to assess the clinical status of patients and predict the prognosis of patients with AIS (12).

Vertebrobasilar artery stenosis is a major source of ischemic stroke. IMA may be a novel biochemical marker that can reflect acute ischemia. However, the association between IMA and vertebrobasilar artery stenosis has not been reported. The purpose of this study was to investigate the possibility of IMA as a rapid biomarker for risk stratification in patients with acute CI and for screening high-risk patients with CI.

Materials and methods

Patients collection

This study was approved by the Ethics Committee of Hangzhou Third People’s Hospital (IRB# 201511). Informed consent was obtained from all participants. From November 2015 to December 2016, 80 patients with acute CI including 37 (46.25%) males and 43 (53.75%) females with a mean age of 62.23 ± 14.12 years in Hangzhou First People’s Hospital were enrolled in this study. Meanwhile, 80 healthy volunteers including 32 (40%) males and 48 (60%) females with a mean age of 62.41 ± 11.23 years participated in the study. These patients and healthy volunteers were all diagnosed by physical examination, cranial CT and MRI. Clinical data included age, gender, smoking history, drinking history, blood pressure and body mass index (BMI) were collected from patients and healthy controls.

Inclusion criteria: 1) confirmation of acute CI at posterior circulation by MRI; 2) adult patients (≥21 years old); and 3) patients with clinical evidence of acute cerebrovascular disease, including unilateral hemiplegia without clear cause (according to NIHSS criteria), aphasia and unconsciousness, 6 h after symptoms started.

Exclusion criteria: 1) patients with cerebral hemorrhage and subarachnoid hemorrhage by cranial CT; 2) patients with malignant tumor, end-stage renal disease, chronic liver disease and autoimmune disease; 3) patents taking drugs such as warfarin, captopril, furosemide and others, which may have an effect on serum IMA levels; and 4) patients with contraindication of whole cerebral angiography.

Digital subtraction angiography and grouping

Whole brain digital subtraction angiography (DSA) was performed in patients with acute CI according to national standards and the guideline of Chinese Radiology Association. Stenosis rate was evaluated according North American Symptomatic Carotid Endarterectomy Trial Collaborators (NASCET) criteria. Stenosis = (1-The narrowest blood flow width of internal carotid artery)/ Stenosis lesion distal to normal internal carotid artery diameter.

Patients with acute CI were divided into two groups according to the stenosis of vertebrobasilar artery: patients with stenosis of vertebrobasilar artery more than 50% were defined as severe stenosis, and others with stenosis of vertebrobasilar artery less than 50% were defined as mild stenosis.

Detection of serum IMA levels

Peripheral venous blood samples were collected from patients and healthy control into tubes with EDTA, immediately after diagnosed for CI. Samples were centrifuged at 3500 rpm/min for 15 min at room temperature. The plasma samples were extracted and frozen below −80°C for use. A Albumin cobalt assay (ACB) was used to determine the serum IMA levels as described in a previous study (13). ACB Assay for IMA was done colorimetrically as follows: 6200 μL of serum was mixed with 50 μl of CoCl2 (1 g/L) vigorously for 10 min, 50 μL of dithiothreitol (DTT) (1.5 g/L) was added and left for 2 min, and 0.9 N NaCl was then added. Plasma albumin levels were measured in a calibrated and well-controlled autoanalyzer using the bromocresol green method (Architect Plus C8000, Abbott, USA). It was read colorimetrically at 470 nm as ABS U/mL (absorbance units). The conditions of patients after treatment were assessed by National Institutes of Health Stroke Scale (NIHSS). The correlation between serum IMA levels at admission and NIHSS after treatment was also analyzed.

Detection of biochemical indicators

Biochemical indicators were detected by an automatic biochemical analyzer (Architect Plus C8000, Abbott, USA) in clinical laboratory of our hospital, including triglyceride (TG), total cholesterol (TC), high density lipoprotein cholesterol (HDL-C), low density lipoprotein cholesterol (LDL-C).

Statistical analysis

Statistical analyses were performed using Statistical Product and Service Solutions (SPSS) version 19.0 (International Business Machines, corp., Armonk, NY, USA). Patient characteristics were described as frequencies (percentages) or means ± standard deviation (SD). Shapiro-Wilk test was used for normality test. Significant differences between groups were assessed by One-way analysis of variance (ANOVA). Chi-square test was used for counting data. The diagnostic efficiency was calculated by receiver operating characteristic curve (ROC). P value <.05 was defined as a statistically significant difference. Figures were drawn by SPSS Statistics and GraphPad Prism (version 8.0 for Windows, Graph Pad Software, San Diego, CA, USA).

Results

Characteristics of patients with CI

The characteristics of 80 patients with CI and 80 healthy volunteers are shown in Table 1. It was indicated that the degree of severe vertebrobasilar artery stenosis was more than 50% (44 of 80 patients), and the degree of mild vertebrobasilar artery stenosis was less than 50% (36 of 80 patients). There were no marked differences between patients with CI and healthy volunteers in variables, including age, gender, BMI, TC, TG, HDL-C and LDL-C (P > .05, respectively).

Table 1. The detailed clinical information of cerebral infarction patients and healthy volunteers (Mean ± SD)

Characters	Healthy volunteers (n = 80)	Cerebral infarction (n = 80)
		All patients (n = 80)	Mild stenosis (n = 36)	Severe stenosis (n = 44)
Age(years)	62.41 ± 11.23	62.23 ± 14.12	61.79 ± 15.11	62.44 ± 13.73
Gender(female/male)	32/48	37/43	16/20	21/23
BMI(Kg/m2)	23.63 ± 2.46	24.56 ± 2.61	23.77 ± 3.11	24.82 ± 3.04
Drinking	32	36	16	20
Smoking	38	51	23	28
Hypertension	/	67	30	37
Diabetes	/	31	12	19
TC(mmol/L)	4.02 ± 1.21	4.78 ± 1.08	4.69 ± 0.92	4.89 ± 1.04
TG(mmol/L)	1.58 ± 0.97	2.42 ± 1.26	2.21 ± 0.84	2.47 ± 1.27
HDL-C(mmol/L)	1.39 ± 1.01	1.35 ± 0.95	1.35 ± 1.14	1.36 ± 0.83
LDL-C(mmol/L)	2.28 ± 1.07	3.51 ± 1.08	3.01 ± 1.18	3.95 ± 1.09

BMI: Body Mass Index; TG: Triglyceride; TC: Total Cholesterol; HDL-C: High Density Lipoprotein Cholesterol; LDL-C: Low Density Lipoprotein Cholesterol.

Serum IMA levels

As shown in Figure 1A, serum IMA levels in patients with CI were increased significantly compared to healthy volunteers (81.85 ± 3.69 U/mL vs. 75.07 ± 4.02 U/mL, P = .00). Serum IMA levels in patients with severe or mild stenosis was higher than those in healthy volunteers (P < .05). In addition, serum IMA levels in severe stenosis group was increased compared to mild stenosis group, and there was a significant difference (83.00 ± 3.38 U/mL vs. 80.43 ± 3.55 U/mL, P = .02) (Figure 1B).

Figure 1. Serum ischemia modified albumin levels in all groups. *: P < .05

ROC curve results

The ROC curve of IMA levels for patients with CI is shown in Figure 2. The area under curve (AUC) value was 0.94 [95% confidence interval (CI): 0.90–0.98, P = .000]. According to the ROC curve, the cutoff value of serum IMA levels for patients with CI was 78.85 U/mL, with 85% sensitivity and 87.5% specificity.

Figure 2. Receiver operator curve of IMA for cerebral infarction. The area under the curve values was 0.94 (95% confidence interval 0.90–0.98, P = .000)

Correlation between NIHSS score and IMA level

On the 7th day after treatment, all patients with acute CI were assessed by NIHSS score. The results of NIHSS score and serum IMA levels are shown in Table 2. Serum IMA levels at admission were associated with NIHSS score on the 7th day after diagnosis (P < .05).

Table 2. Correlation between neurological function score and admission IMA level in patients with acute cerebral infarction treated during 7 days

NIHSS score	1–4 (n = 27)	5–15 (n = 31)	≥16 (n = 22)	P
Serum IMA level at admission	79.36 ± 3.82	81.73 ± 3.76	83.24 ± 4.33	<0.05
Healthy controls	75.07 ± 4.02

Discussion

Ischemic stroke is debilitating. Early diagnosis and treatment of ischemic stroke are vital for the prognosis of the patients. It is very important to identify new biomarkers for early diagnosis of ischemic stroke. Many were investigated but none appeared promising. Ischemia-modified albumin (IMA), a modified type of albumin protein, is a candidate biomarker proposed or used for detection of cardiac ischemia (14,15). Many previous studies have demonstrated that serum IMA level is a highly sensitive marker of early acute myocardial infarction (16–18). Recently, IMA has been reported to be uses for diagnosis in other diseases, such as polycystic ovary syndrome (19), acute pancreatitis (20), and acute pancreatitis (21). In the present study, serum IMA levels increased in patients with CI and vertebral basilar artery stenosis, indicating the use of serum IMA levels for diagnosis of CI.

IMA is associated with tissue ischemia, indicating that IMA may also play a role in the differential diagnosis of acute ischemic cerebrovascular disease. It is shown that serum IMA level was 73 U/mL in patient with TIA and 83 U/mL in patient with cerebral infarction within 3 h after the onset (10). In addition, infarct size was reported to be positively correlated with IMA levels (22). A new study suggested that serum IMA significantly increases after transient ischemic attack (TIA) onset, and IMA is significant associated with the secondary CI. Early detection of IMA is of great value in predicting the secondary CI (23). IMA is regarded as “N-terminal modified” albumin which is generated immediately following myocardial ischemia. The detection of IMA is based on reduced cobalt binding affinity to albumin which is attributed mainly to incapability of cobalt to bind at albumin’s modified N-terminus. In this study, Cobalt-combined with Albumin test also found that the serum IMA levels are higher in patients with CI than those in healthy volunteers.

As a previous study reported, serum IMA was affected by many factors, including serum albumin and serum lipid levels (24). It is reported that serum IMA concentrations is positively associated with TC, TG, and LDL-C concentrations (25). In our study, a similar pattern was observed.

There are several possible explanations for the mechanism of elevated serum IMA levels in patients with acute CI within 24 h (26–30). It was found that the surface of the brain cells is rich in unsaturated fatty acids, causing the brain susceptible for ischemia and hypoxia in brain cells (26,27). It has been demonstrated that reactive oxygen species (ROS) can cause an increase in serum IMA levels within minutes (28). With the aggravation of cerebrovascular disease, cerebral tissue ischemia and hypoxia become more serious, leading to the increase and accumulation of lactic acid, which also promote the production of IMA (29,30). Because of ischemia and hypoxia, neuron necrosis induces mitochondrial capacity obstacles and ion pump deficiency, resulting in IMA formation.

In the present study, serum IMA levels differ between severe stenosis and mild stenosis patients, and they were higher in patients with severe stenosis than those in patients with mild stenosis. To the best of our acknowledge, it is the first study reporting that the correlation of serum IMA levels and the stenosis of vertebrobasilar artery. Severe vertebralbasilar artery stenosis increases the incidence of CI. In addition, we found that serum IMA levels in patients with CI in admission are correlated to NIHSS score on the 7th day after diagnosis. It is indicated that serum IMA levels in patients with CI in admission may be a predictive factor for short-term prognosis.

There were some limitations in present study. Firstly, it was a single center observational study, and the sample size of this study was small. But it was the maximum sample size that could be collected. Multi-center large sample prospective study need to be performed to verify the diagnostic values of IMA. Secondly, serum IMA was only detected in admission, and there was no dynamic detection before and after treatment. It is indicated that serum IMA is associated with the severity of CI. In the next study, the real-time changes of IMA in patients with CI need to be investigated.

Conclusions

To sum up, serum IMA level is associated with the stenosis of vertebrobasilar artery, and may be a biomarker for diagnosing CI.

Compliance with Ethical Standards

The study was approved by the Hangzhou First People’s Hospital. Informed consent was obtained.

Author contributions

CYZ is resposible for the guarantor of integrity of the entire study, study concepts, data acquisition, manuscript review; TC is resposible for the study design, experimental studies, manuscript editing; YHS is resposible for the literature research, manuscript preparation; YZ is resposible for the statistical analysis; YL is resposible for the clinical studies; LN is resposible for the definition of intellectual content, data analysis. All authors read and approved the final manuscript.

Acknowledgments

We thank the participants.

Disclosure statement

The authors declare that they have no conflict of interest.