ISSN No. 1606-7754                   Vol.15 No.3  December 2007

Combined effects of type 2 diabetes mellitus and cigarette smoking increase the risk of cardiovascular complications
Md. Zakir H. Howlader,1 Md. Rakibul Islam,1 Jahangir Hossain,1 Tanzir A Khan,2 Ahmed F Karim,1 and Yearul Kabir3
Clinical Biochemistry Laboratory, Department of Biochemistry and Molecular Biology, University of Dhaka, , Bangladesh1 IFST, Bangladesh Council of Scientific and Industrial Research, Dhaka2. Department of Family Sciences, College for Women, Kuwait University, Kuwait3.

Abstract

Premature atherosclerosis may result from conditions such as hypercholesterolaemia, diabetes, hypertension and cigarette smoking. Any of these four conditions alone or in combination, stimulates the atherosclerotic process through mechanisms associated with a state of increased vascular oxidative stress. In this study, we investigated the combined effect of type 2 diabetes (DM) and smoking on lipid peroxidation and total antioxidant status, the primary risk factors of atherosclerosis. A total of 85 subjects were included in this study. Out of these, 65 were patients who attended the Bangladesh Institute of Research and Rehabilitation in Diabetes, Endocrine and Metabolic Disorders (BIRDEM) for regular medical check up and 20 were healthy non-smoker volunteers. To investigate the effect of smoking and DM on the risk factors of cardiovascular complications, we divided the study subjects into three groups. Group I consists of healthy non-smoker control subjects, group II was diabetic patients but non-smoker and group III was diabetic and smoker. In group III, the proatherogenic lipid profile (total cholesterol, triglycerides, and LDL cholesterol) increased with a decrease in HDL cholesterol compared to control groups. Thiobarbituric acid reactive substance (TBARS) and lipid hydroperoxide (LHP) increased in group III a sign indicative of increased lipid oxidation. Total antioxidant status (TAS) and antioxidant vitamin (vitamin-C) were significantly lower in group III (p<0.001) compared to other groups.

Keywords: Diabetes mellitus, Cigarette smoking, Oxidative stress, Antioxidant status

Introduction

It is a well established fact that diabetes is a risk factor for cardiovascular disease.1-2 While microvascular complications of diabetes include nephropathy and retinopathy, macrovascular complications resulting in atherosclerotic cardiovascular disease such as coronary artery disease, cerebrovascular disease and peripheral vascular disease are the leading cause of death in the diabetic population.3 Oxidative stress is defined in general as excess formation and/or insufficient removal of highly reactive molecules such as reactive oxygen species (ROS) and reactive nitrogen species (RNS).4-5 ROS include free radicals such as superoxide (ĽO2-), hydroxyl (ĽOH), peroxyl (ĽRO2), hydroperoxyl (ĽHRO2-) as well as non-radical species such as hydrogen peroxide (H2O2) and hydrochlorous acid (HOCl).4,6 RNS include free radicals like nitric oxide (ĽNO) and nitrogen dioxide (ĽNO2-), as well as nonradicals such as peroxynitrite (ONOO-), nitrous oxide ( HNO2 ) and alkyl peroxynitrates ( RONOO ).4,6

Of these reactive molecules, ĽO2-, ĽNO and ONOO- are the most widely studied species and play important role in the development of diabetic cardiovascular complications.

Cardiovascular complications, characterized by endothelial dysfunction and accelerated atherosclerosis are the leading cause of morbidity and mortality associated with diabetes. There is growing evidence that excess generation of highly reactive free radicals, largely due to hyperglycaemia, causes oxidative stress, which further exacerbates the development and progression of diabetes and its complications. Overproduction and/or insufficient removal of these free radicals result in vascular dysfunction, damage to cellular proteins, membrane lipids and nucleic acids.7

Cardiovascular disease (CVD) is a major public health problem and a major source of morbidity and mortality in Bangladesh. The principal manifestations of CVD, such as heart attack and stroke, represent the clinical sequelae of a systemic vascular process known as atherosclerosis. Many studies established that premature atherosclerosis is associated with conditions including hypercholesterolaemia, diabetes, hypertension, and cigarette smoking.8-9 Any of these four clinical conditions, alone or in combination, stimulates the atherosclerotic process through mechanisms associated with a state of increased vascular oxidative stress.10 As a consequence, there is a considerable interest in the study of oxidative stress and antioxidant status of diabetic patients who are in a high risk of CVD.

Chronic cigarette smoking is related to increased free radical production and plasma antioxidant depletion, making it one of the most potent stimuli of the oxidative process observed in humans and in vitro.11-13 Several studies found lower plasma antioxidant concentration in vivo.14-16 Free radicals are non-desirable molecules and they are physiologically generated in an organism and in some conditions their production rate increases in active or passive smoking. There is evidence that smoking is related to increased free radical production and antioxidant depletion.17 Epidemiological studies showed that cigarette smokers consume fewer fruits and vegetables than non-smokers.18-20 They also consume low vitamins supplements than non-smokers.21-23 So the dietary habits for low antioxidant concentration in plasma can not be overruled.

The present study was designed to investigate the effects of cigarette smoking on lipid peroxidation and antioxidant status in the plasma of type 2 diabetic patients.

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