It is now widely accepted that oxidative modification of low density lipoproteins (LDL) convert these native particles into pathogenic , immunogenic [2, 3] and atherogenic [4, 5] particles. Current clinical research addresses the oxidation of LDL as a causative and initiating event in many pathological conditions and the oxidative modification of LDL enhances its atherogenicity .
Ox-LDLs are pathogenic particles, they have a number of biologic activitiesthat contribute to the process of atherosclerotic lesion formation and other diseases. Removal of Ox-LDL from circulating blood is a promising therapeutic strategy against atherosclerosis and many other diseases . This goal cannot be achieved without a better understanding of the processes by which native LDL get oxidized.
In spite of the considerable knowledge and literature that support the correlation between circulating Ox-LDL and many pathologic conditions, to the best of our knowledge, there remains a gap regarding the biochemical status of the blood and the biological conditions of the body that enhance oxidation of native LDL. More understanding of the role of oxidation of lipoproteins may allow more rationally targeted diagnostic and therapeutic procedures in clinical applications.
The chemical composition of LDL makes these particles susceptible to oxidation by different lipid oxidants. The polyunsaturated acyl chains of cholesterol esters, phospholipids and triglycerides are vulnerable to oxidation, as is the sterol of free cholesterol and cholesterol esters.
The apolipoprotein B-100, made of 4536 amino acid residues, with many exposed tyrosines and lysines, which can be directly oxidized or modified by lipid oxidation products. The in vivo mechanism of LDLoxidation remains unclear and there are different mechanisms that may be responsible for the process. They are divided into enzymatic and non-enzymatic processes. The non-enzymatic process of modification involves free transition metal ions such as iron and copper, which are involved in catalyzing lipid peroxidation. The enzymatic process involves a number of different enzyme systems, such as lipoxygenases, myeloperoxidase which catalyses the formation of hypochlorousacid leading to the formation of acetylated LDL, NADPH oxidases, and nitric oxide synthases .
Although native LDL are exposed to all enzymatic and non-enzymatic oxidants, they are protected by a potent array of antioxidants in plasma. Moreover, some of these antioxidants are a part of the LDL composition. The LDL and other biomolecules are protected from free radical attack by the action of antioxidant capacity in the blood.
A healthy aerobic life is characterized by a steady formation of reactive oxygen species (ROS) and reactive nitrogen species (RNS), balanced by a similar rate of their consumption by an enzymatic and non-enzymatic, finely monitored, antioxidant system.
Since enzymatic and non-enzymatic antioxidants work in a network manner to exert their protective effects, no single antioxidant could represent the overall antioxidant status in plasma. Therefore, plasma antioxidant status isthe result of interaction and cooperation of various antioxidants. The concept of total antioxidant capacity (TAC) was developed considering the synergistic role of those antioxidants rather than the simple sum of individual antioxidant action .
Diabetes mellitus (DM) and impaired glucose tolerance (IGT) are associated with many complications including hypertension, renal failure and coronary artery diseases. Previous studies have revealed that the excess of cardiovascular events are observed in patients with type- 2 diabetes and that adequate control of Low Density Lipoprotein cholesterol has been proved to minimize the risk, however, lowering LDL will not be a complete solution. This is clear because at any given level of LDL concentration, there is great variability in the clinical expression of the disease. The atherogenic potential of diabetes could be associated with the modified proteins as the result of glycation and oxidation. The role of Ox-LDL as a residual lipid risk attracts considerable attention . The situations of insufficient and/or inefficient insulin action were reported tocoincide with increased concentrations of the Ox-LDL , however, in which biochemical situation would these native LDL undergo oxidation is not well clarified.
The aim of the current study is to investigate the conditions where LDL undergoes oxidation and the possible role of the parameters of lipid profile (Total Cholesterol, Triglycerides, HDL and LDL) as well as the TAC, in increasing circulating Ox-LDL.
Subjects and methods
This study was conducted in Makkah Al-Mukarama (KSA). The study protocol was approved by the Biomedical Ethics Committee, Faculty of Medicine, Umm Al-Qura University, Makkah, KSA. Ethical approval number 43-01071435.
Participants were selected according to inclusion criteria from patients admitted to the Outpatient department of Diabetes Center in Al-Noor Specialized Hospital (Makkah, KSA) and other residents in the city during the period from May 2012 up to July 2013. Subjects included are adult males, aged 18-55, live in Makkah and agreed to participate in the study. 274 volunteers were subjected to the investigations, they have been informed about the nature of the study and the expected risk and they have signed the ethical consent form. They have also filled out the structured questionnaire. Measurements of weight, height and blood pressure were performed by trained technicians, the Body Mass Index (BMI) was calculated as weight (Kg) divided by height squared (m2).
The studied group was classified into three sub-groups according to the American Diabetes Association (ADA) recommendations for diagnoses of diabetes and classification of glucose tolerance .
Group-I: Control group of non-diabetic normal subjects who met the following criteria:
Fasting blood glucose: <6.1 mmol/l (<110 mg/dl.) and
2-hour postprandial: <7.8 mmol/l. (<140 mg/dl.)
Group-II: Subjects with IGT who met the following criteria:
Fasting blood glucose: <7.0 mmol/l (<126 mg/dl.) and
2-hour postprandial: ≥7.8 mmol/l. (≥140 mg/dl.)
Group-III: cases of type-2 DM and subjects who met the following criteria:
Fasting blood glucose: ≥7.0 mmol/l (≥126 mg/dl.) and/or
2-hour postprandial: ≥ 11.2 mmol/l. (≥200 mg/dl.)
Not categorized as an Insulin Dependent Diabetes Mellitus (IDDM).
Participants who were excluded from the study were those of known history of coronary heart diseases (CHD) or cardiovascular complications of type-2 DM, known IDDM, those who are younger than 18 or older than 55 years old and those with familial hypercholesterolemia.
Information regarding exclusion criteria was obtained from the medical care provider and physicians, patient records or directly from the participants.