Introduction

Evaluation of the patients who present to the hospital with a complaint of chest pain or other signs or symptoms suggestive of acute coronary syndrome (ACS) is time-consuming, expensive, and difficult. Millions of patients present annually to hospitals with complaints of chest pain, and many more with other symptoms potentially indicative of ischemia. ¹ Recent literature reports have shown more interest in a new biochemical marker; ischemia-modified albumin (IMA) for the detection of myocardial injury. Special attention is focused on the estimation of IMA tests for the diagnosis and evaluation of patients with myocardial ischemia as well as another acute coronary syndrome in the emergency department. ²

Most biochemical markers are negative in the early phase of acute myocardial ischemia, such as unstable angina (UA), but IMA is highly sensitive and can be detected in the reversible early phase of ACS. ^{3, 4, 5, 6} Many clinical studies have revealed that IMA can be used for early diagnosis of acute myocardial ischemia (AMI), exclusion of ACS, and stratification of ACS risk, so the admission rate of non-ischemic patients and misdiagnosis of individuals at risk for cardiac events can be reduced. ^{7, 8, 9} At present, there is a lack of availability of data about the correlation between serum IMA level and cardiac function changes in patients with UA or stable angina (SA).

Recent studies show that the structure of serum albumin changes when ischemia develops in the body. ¹⁰ From this point of view, studies focusing on a new marker for myocardial ischemia have been carried out. Ischemia Modified Albumin is a new marker used to detect myocardial ischemia and it shows an early change. Myocardial ischemia and accompanying hypoxia induced the structural modifications of human serum albumin (HSA). HSA molecule represents one of the circulating the antioxidant in plasma and plays a vital role in the efficient antioxidant defence of the organism thus having a protective effect. ¹¹

In vivo, studies revealed that serum albumin of individuals with myocardial ischemia exhibits a reduction in its inherent affinity for metal transition ions such as Co(II), Ni(II) and Cu(II) compared to non-ischemic ones. This abnormal molecule of HSA is known as Ischemia-Modified Albumin (IMA) and it is measured by the spectrophotometric Co(II)-albumin binding assay. The concentration of IMA is determined by the addition of a known amount of exogenous Co(II) to a serum sample and measurement of unbounded Co(II) by colourimetric assay using Dithiothreitol (DTT). An inverse relationship exists between the amount of albumin-bound cobalt and the intensity of the colour formation, reported in absorbance units (ABSU). ²

There are several data on IMA in patients with different states with ischemia of non-cardiac origin such as systemic sclerosis ^{12, 13} peripheral vascular disease, skeletal muscle ischemia during arthroscopic knee surgery and exercise induce, but no one concerns diabetes. ¹⁴ Hyperglycemia and oxidative stress can induce chronic ischemia in diabetic patients. It could lead to necrosis of different tissues. ^{15, 16} Chronic hyperglycemia is associated with long-term damage, dysfunction, and failure of the normal functioning of various organs, especially the eyes, kidneys, nerves, heart, and blood vessels. ⁹ The prevalence of diabetes mellitus is rising all over the world and have been increasing rapidly recently in India reaching 1.4 million cases in 2015. ¹⁰ An uncontrolled state of hyperglycemia leads to a variety of complications including peripheral vascular diseases, nephropathy, neuropathy, retinopathy, morbidity, and/or mortality. Type 2 diabetes and its related complications of hypertension, hyperlipidemia and atherosclerotic vascular disease also demonstrated an association of metabolic syndrome with the development of cardiovascular disease (CVD), and more confirmation related to mortality rate increment was given by Type 2 diabetes and their related complications cardiovascular disease remains the leading cause of death, and myocardial infarction (MI) tend to be more extensive and have poorly survival rate than in age, weight and sex-matched in individuals without diabetes. ¹⁷

This case control study was planned to determine IMA level for early detection of myocardial ischemia in acute coronary syndrome with Type-2 Diabetes Mellitus and correlate with control of diabetic status.

Material methods

Study design: A Case-control study was undertaken at GMC, Baramati from 1st of February 20121 to November 2022 with the following criteria.

Inclusion criteria: Standardized clinical data were collected for each patient, which included time of presentation at the emergency department, and the approximate duration of symptoms of acute chest pain.

Exclusion criteria: Patients with liver disorders, autoimmune disorders, pregnant women, and patients with symptoms and signs suggestive of acute mesenteric ischemia, acute renal failure, peripheral vascular disease, or brain ischemia were not enrolled in the study.

Case Selection: Sixty patients with type 2 diabetes mellitus, arrived at the Emergency unit in the hospital suffering from acute chest pain with manifestations suggestive of acute myocardial ischemia, including those such as chest pain, shortness of breath, lower jaw pain, left arm pain, epigastric pain, new or increasing lower extremity edema, palpitations, and other symptoms suggestive of an angina equivalent. The ECG was measured in the ED as part of the standard of care at the GMC & Hospital, Baramati.

Control Group: Sixty healthy volunteers age and sex-matched who didn't have any evidence of diabetes and coronary artery disease were taken as the control group.

Samples processing: Demographic data (sex, age), an ECG and Biochemical data were collected. Blood for IMA and HbA1C levels was collected within two hours of arrival, and IMA risk marker testing was performed before any heparin/thrombolytic treatment was started. Blood samples were collected in tubes containing lithium heparin at the time of the patient's presentation to the emergency department, centrifuged for 5 minutes and preserved at -70 degree.

Results

There were 60 individuals in the control group (mean age 65.24 ± 13.11), and 60 patients in the diabetic group (mean age 59.86 ± 9.03). The comparison of the demographic and laboratory variables is presented inTable 1. These groups were statistically similar in terms of demographic variables (p > 0.05). The creatinin (p = 0.020) and platelet values (p = 0.213) were found to be insignificant predictors for CAD severity. However, the WBC and IMA levels were markedly higher in the patient groups (p = 0.01). The comparison of the laboratory parameters and risk scores between the three groups is presented in Table 1, Table 2.

Values of 80.70 or greater predicted myocardial ischemia with a sensitivity of 93.3% and a specificity of 60% (AUC: 0.92).

The cut-off value for IMA in diagnosing myocardial ischemia in diabetic patients attending ED was 80.70. Values of 80.70 or greater, predicted myocardial ischemia in diabetic patients with a sensitivity of 93% and a specificity of 60% (Area under curve: 0.92, Figure 1).

The IMA level was significantly higher in uncontrolled diabetic patients with acute coronary syndrome compared to controlled diabetic patients with ACS.Table 3

Discussion

The IMA measurement as a marker of myocardial ischemia without myocardial necrosis and/or preceding myocardial necrosis has introduced the hope for improved diagnosis in patients with IHD without or with non-specific ECG changes. ¹¹ IMA has been proven to be an early biochemical marker to detect ischemia in patients with myocardial infarction. ¹⁷ So, Ischemia-modified albumin has been studied primarily in selected populations to display myocardial involvement only in the absence of confounding clinical conditions. IMA increases also in brain ischemia, end-stage renal disease, liver disease, some neoplasms, and infections as well as in patients with peripheral vascular diseases and exercise-induced skeletal muscle ischemia. Recent studies indicate that structural modifications of albumin can occur as the result of endothelial and extracellular hypoxia, acidosis, reduced oxygen tension, various ion-pump disruptions, and generation of reactive oxygen species (ROS). ²

In diabetic patients, hyperglycemia, via several mechanisms (glucose autooxidation, stimulation of the polyol pathway, imbalance between the amount of reduced and oxidized coenzymes forms, nonenzymatic glycation and formation of advanced glycation end-products-AGEs), leads to multiple biochemical sequels resulting in oxidative stress. Reactive oxygen species are well known as a factor responsible for chemical and molecular damage of many biological molecules (proteins, lipids, carbohydrates, DNA, nucleotides) and cell membrane structure. Oxidative stress is important in a variety of physiological (e.g., ageing) and pathological (e.g., atherosclerosis, diabetes) processes. It plays a significant role in pancreatic islet destruction in diabetes type 2 and leads to its late complications. This also causes oxidative protein damage, formation of advanced oxidation protein products (AOPP) and probably IMA. ²

We estimated IMA levels in the plasma of diabetic patients and control subjects using the manual method. We found that the serum levels of IMA were significantly higher in diabetic patients when compared with normal healthy non-diabetic (p-value = 0.003) this agrees with a previous study showing that IMA is a novel marker of tissue ischemia and is accepted as a marker of oxidative stress in type 2 diabetes patients ¹⁸ and others study report that definite and precise mechanisms for IMA production in vivo, it appears to be related to the generation of reactive oxygen species (ROS) due to ischemia-reperfusion that modifies metal binding domains of albumin molecule. ¹⁹ We observed about 75% higher levels of ischemia-modified albumin in the plasma of type 2 diabetic patients in relation to control subjects. This confirms previous, as well as our observations, that increased ROS generation, provoked by hyperglycemia, can cause oxidative protein damage. In the case of albumin decreasing ability to exogenous cobalt binding in plasma has been reported. ^{8, 10} IMA may indicate underlying subclinical disease or vascular dysfunction, what suggested also by Borderie et al. ¹²

In diabetic patients with HbA1c level higher than 7% significant correlation between IMA and HbA1c was found. The binding of glucose to albumin typically occurs in vivo in healthy people and is known to involve the nonenzymatic covalent attachment of glucose to a lysine side chain but increases between two- to threefold in hyperglycemia. Thus, it is possible that patients with a more severe course of disease (poorly controlled diabetes compared to well-controlled diabetes as well as healthy people) could occur greater free radical production, leading to higher IMA concentration. Moreover, diabetic patients exhibit elevated levels of iron and copper ions that, in the presence of glycated proteins, have been shown in vitro to generate ROS. ²⁰ This indicates that IMA level should be considered in the context of well and bad compensated diabetes.

Our current findings, although preliminary, show that chronic oxidative stress provoked by hyperglycemia, in diabetic patients causes the decrease of albumin's ability to exogenous cobalt binding. It supports the hypothesis that the rise in IMA levels may be also of non-cardiac origin. We also reveal higher IMA concentrations in diabetic patients with poor long-term Glycemic control, probably with acidosis, hypertension as well as hypercholesterolemia-LDL compared with baseline.

This may have implications regarding the ability of IMA to detect myocardial ischemia in diabetics. Recently Roy et al. ²¹ suggested and revealed the role of reactive oxygen species, such as superoxide and hydroxyl radicals, generated during myocardial ischemia-reperfusion, on the modification of the N-terminus of albumin and formation of the IMA. A positive IMA value could also help to identify higher-risk individuals, suffering from local or systemic hypoxic conditions, such as acute ischemic stroke, peripheral vascular disease, systemic sclerosis, peripheral vascular intervention, exercise-induced calf-muscle ischemia, and end-stage renal disease.

In this current study, there was a significant difference increase in IMA levels among poorly controlled (HBA1c > 7%) diabetic patients ( mean; 14.70 ± 8.66)when compared with the well-controlled (HBA1c < 7%), diabetic (mean; 3.74 ± 3.68), the patients (long-standing diabetes) duration more than 5 years had higher IMA levels than patients with less than 5 years duration.

Diabetic complications are due to various micro and microangiopathic events producing increased oxidative stress and decreased levels of antioxidants, which can lead to modification of albumin molecule of IMA than patients with less than 5 years duration of diabetes (long-stand diabetes) have a lower than the other one. ²²

Conclusion

We suggest that measurements of IMA in patients with chest pain or signs/symptoms suggestive of acute coronary syndrome cases even in the early phase will help to detect ACS and this is particularly important when patients have type 2 diabetes. Furthermore, there is a positive correlation between HbA1c level with IMA level thus monitoring diabetic control is an important part of the management of acute coronary syndrome. The measurements of IMA can be a very important factor in the correct diagnosis and classification of patients with coexisted diabetes who come to the emergency department with chest pain.

Limitations

• The main limitation of our study was the limited number of cases that reduces the sensitivity and specificity of multivariate analysis.

• Currently no reference standard exists for cardiac ischemia. A combination test of IMA with CK-MB and Troponin I can increase the sensitivity in the early diagnosis of Acute Coronary Syndrome. ²³

• One of the limitations was that the study group was confined to patients with Non-STEMI/USAP. Therefore, our findings cannot be generalized to include all patients with ACS.