Introduction
Cardiovascular disease is the most common cause of death worldwide accounts for approximately 30% deaths worldwide.1 Among which Coronary artery disease due to atherosclerosis is the leading cause of mortality and morbidity in the world and its incidence has shown an upward trend in Indians in the last decade.2,3 In India, coronary heart disease (CHD) has increased about 6 fold in the last 5 0 years to reach 10% prevalence of among 35 to 65 years age group. An early assessment of risk predictors CHD can decrease the morbidity and mortality related to CHD improve the life quality.2
Conventionally the estimation of serum lipids like cholesterol, triglycerides, LDL cholesterol (LDL-C) and HDL cholesterol (HDL-C) are used to assess the risk of CHD. However, the inaccuracies in the correlation between serum lipid profile and CHD, led to the development of better indicators. Among them the estimation of serum apolipoprotein is now increasingly used for risk assessment of CHD.3 Alaupovic found apolipoprotein A-I (Apo A -I), which is one of the components of HDL-C, is a better marker for coronary heart disease.3 Various subfractions of atherogenic LDL -C and protective HDL -C proved as better indicator of coronary heart disease.3
Apo A-I is the major protein constituent of HDL-C. Apo A-I and HDL-C are protective; apolipoprotein B (Apo B) and LDL -C are atherogenic. HDL-C has 2 molecules of Apo A- I, whereas cholesterol content varies in each of these lipoprotein particles. Therefore measuring Apo-AI is a determinant of the number of antiatherogenic particles in circulation, than the cholesterol content, which varies. The atherogenic lipoprotein particles LDL -C, VLDL-C remnants, or IDL -C, and chylomicron remnants each contain 1 molecule of Apo B as the structural protein. The plasma Apolipoprotein concentration reflects the number of atherogenic lipoproteins, and studies in men have demonstrated that Apolipoprotein can be a valuable predictor for CHD 3. Increased Apo B /Apo A-I ratio was also seen in CHD patients 4. With advent of newer assay techniques for these apolipoproteins, they can be accurately used for risk assessment of coronary heart disease. Assessment of apolipoprotein levels is an aid to risk prediction and can be useful in tailoring treatment.4
Aims and Objective
The current study is carried out to evaluate an d compare the efficacy of Apo B and Apo A-I level with LDL-C and HDL-C level as risk factors of coronary heart disease.
Materials and methods
Study design
The study was conducted at the Clinical Chemistry Laboratory of Biochemistry Department at Medical College and S.S.G. Hospital, Baroda after ethical Clearance obtained from the Institutional Ethics Committee for Human Research, Medical College and S.S.G. Hospital, Baroda. Period of data collection was July 2013 to June 2014.
The subjects selected for the study were grouped as follows:
Inclusion criteria
Group I – Control group (n=45)
This group consisted of age and sex matched healthy subjects. They were from medical or paramedical staff and persons coming to hospital for fitness purpose & for routine health check up.
Group II – Patients with Coronary Heart Disease (n=45)
Clinically diagnosed patients of coronary heart disease with age group of 30-65 years with electrocardiographic changes and elevated cardiac biomarkers.
Exclusion criteria
The following patients were excluded from the study:
Patients with coronary artery disease with atrial fibrillation or pacemaker.
Patients with history of stroke, intermittent claudication, peripheral vascular disease, carotid surgery, coronary artery bypasses graft surgery or PTCA.
Patient having H/O chronic alcohol consumption, hepatobiliary disorders or any other acute liver diseases and diabetes mellitus.
After taking informed consent, detailed present and past history was recorded which includes name, age, sex, education, occupation, economic status, nutritional and personal habits, medication and systemic illness. 4 ml venous blood was collected from each case, in plain vacutainer after overnight fast and was subjected for following estimations.
Estimation of serum Apo A-I and Apo B were done by Turbidimetric Immunoassay, serum cholesterol by cholesterol oxidase- peroxidase (CHOD-PAP) enzymatic colorimetric end point method, HDL cholesterol and LDL cholesterol by direct enzymatic method and serum triglycerides by glycerol phosphate oxidase peroxidase (GPO-PAP) enzymatic end point method. All estimations were carried out on fully automated biochemistry analyzer Miura-300.
Statistical analysis
Data analysis was performed with the Microsoft Excel 2010. Comparisons between two groups were made using Student’s t-tests. For all analysis, p < 0.05 was take as statistically significant and p < 0.001 as statistically highly significant. To compare different parameters as risk factor for CHD, Receiver Operating Characteristic (ROC) curve analysis was carried out using MedCalc version 19.1 (free trial version).
Results
Table 1 summarizes results of conventional lipid profile parameters and apolipoproteins in controls and CHD patients. No significant difference was found in total cholesterol (TC), HDL cholesterol and LDL cholesterol levels, only VLDL cholesterol was significantly higher in CHD patients compared to controls (p < 0.05). Apolipoprotein A-1 was lower and Apolipoprotein B was higher in CHD patients compared to controls and the differences were highly significant (p < 0.001).
Table 1
Comparison of serum lipid profile and apolipoproteins between group I and group II
In Table 2, different ratios of lipid profile parameters and apolipoproteins are compared between controls and CHD patients. TC/HDL -C ratio and LDL/HDL -C ratio shows significant difference (p < 0.05) while difference in Apo B/Apo A-I ratio is highly significant (p < 0.001)
Table 2
Comparison of ratio of serum lipid profile and apolipoproteins between group I and group II
To compare different parameters as risk factor for CHD, ROC curve analysis was carried out (Table 3). For S.Apolipoprotein A-I highest area under curve (AUC =0.995 ) was found (Figure 1). AUC for apolipoprotein B(0.888) was also highly significant (p<0.0001)
Table 3
Results of Receiver Operating Characteristic (ROC) curve analysis of conventional lipid profile parameters and Apolipoproteins as CHD risk factor
Discussion
Coronary heart disease has become very prevalent world wide.5 Early identification of risk factors of CHD can help in reducing mortality and morbidity due to CHD.6 In this study an attempt has been made to compare the efficacy of Apo B and Apo A-I level with LDL-C and HDL-C level as risk factors of coronary heart disease. In controls we found mean LDL -C 98.42 ± 15.94 and in CHD patients it was 105.58 ± 24.33 (p=0.102). While apolipoprotein B level was 102.87 ± 16.39 in controls compared to 136.56 ± 21.91 in CHD patients (p<0.001). This indicates increased in apolipoprotein B is better marker for risk of CHD than increased in LDL cholesterol. Similarly we found apolipopro tein AI is better indicator HDL cholesterol for risk prediction of CHD. In similar type of study, Hong LF. et al found Apo B/Apo A-I ratio significantly correlated with severity of coronary artery disease in diabetic people but it does not act as independent risk factor.7 Tamang H et al. concluded Apo B/Apo A-I as better predictor of cardio vascular risk in their study, which is similar to findings of our study.8
Conclusion
In this study we found conventional lipid profile parameters like ratio of Total Cholesterol to HDLc and LDLc to HDLc can be helpful in assessing risk of CHD (p<0.05) and can be used for assessing risk profile of CHD in smaller setups where facilities for apolipoprotein testing are not available. While apolipoprotein levels and Apo B to Apo A-I ratio are definitely of more importance for risk assessment and highly suggestive risk factors for CHD.
