Key words: Risk factor. Hyperhomocysteinemia. Ischemic heart disease. Smoking.

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1 j c p s p September 2004 Volume 14 Number 09 September 2004 Home JCPSP Home Sep JCPSP Contents JCPSP HYPERHOMOCYSTEINEMIA AS A RISK FACTOR FOR ISCHEMIC HEART DISEASE Muhammad Aamir, Abdus Sattar,* Mirza Muhammad Dawood,** Muhammad Dilawar, Aamir Ijaz and Masood Anwar*** ABSTRACT Objective: To determine association of hyperhomocysteinemia with myocardial infarction and conventional risk factors for ischemic heart disease. Design: A non-interventional comparative case control study. Place and Duration of Study: The study was conducted at the department of Chemical Pathology and Endocrinology, Armed Forces Institute of Pathology, Rawalpindi and Armed Forces Institute of Cardiology / National Institute of Heart Diseases, Rawalpindi from January 2001 to June Patients and Methods: A total of 100 hospitalized patients having myocardial infarction (MI) were randomly selected comprising 85 males and 15 females. The average age of the patients was 53 ±4.5 years. A similar number of age and gender-matched healthy controls were also selected. The demographic details, history and clinical examination of both patients and controls were recorded and their blood was collected in fasting state for estimation of serum total cholesterol, plasma glucose and serum total homocysteine. Results: Serum total homocysteine level in controls was significantly lower (10.8 ± 4.1 mmol/l) as compared to patients (18.0 ± 5.9 mmol/l) (p < ). Smoking showed statistically significant association with hyperhomocysteinemic patients (p = 0.04). Conclusion: Ischemic heart disease was associated with moderate hyperhomocysteinemia in our patients and it was also associated with smoking. Key words: Risk factor. Hyperhomocysteinemia. Ischemic heart disease. Smoking. INTRODUCTION Ischemic heart disease (IHD) is the major cause of morbidity and mortality all over the world.1 It is usually attributable to atherosclerotic obstruction of coronary vessels and clinically presents as a spectrum of signs and symptoms ranging from angina pectoris to acute myocardial infarction (AMI), most aptly termed as acute coronary syndrome.2 The age-adjusted incidence of AMI, the most life-threatening form of IHD, is 192/1000

2 male population and 19/1000 female population of Pakistan.3 A number of risk factors are known to predispose to IHD. Some of these cannot be modified, for example, age, gender and family history. Modifiable risk factors include dyslipidemia, hypertension, smoking, diabetes mellitus, obesity, physical inactivity, alcohol consumption and psychological factors.4 These conventional risk factors do not account for all cases of atherosclerotic coronary artery disease (CAD)5 and myocardial infarction (MI) still occurs in individuals having no obvious traditional risk factors.6 Furthermore, among patients of IHD, the risk of recurrent events remains high even after aggressive modification of these factors.7 These observations underscore the need to identify additional risk factors for coronary atherosclerosis. Among the growing list of new risk factors for coronary atherosclerosis, elevated levels of a thiol containing amino acid, homocysteine (Hcy) is increasingly implicated as a potentially reversible risk factor.8 It is formed from intracellular demethylation of essential amino acid methionine and its level in plasma ranges from 5-15mmol/L in fasting state.9 Factors leading to hyperhomocysteinemia include old age, male gender, nutritional deficiency of vitamin B12, vitamin B6 and folic acid,10 renal impairment,11 hypothyroidism12 and genetic deficiency of enzymes like cystathionine b synthetase.13 Modest elevations of Hcy have been associated with the occurrence of cardiovascular disease.14 The recent large European concerted action project confirmed that hyperhomocysteinemia was an independent risk factor for CAD (odds ratio 2.2, 95% CI 1.6 to 2.9) and concluded that an increase of 5 mmol/l in fasting basal plasma Hcy level was associated with a relative risk for CAD of 1.35 (95% CI 1.1 to 1.6) in men and 1.42 (95% CI 0.99 to 2.55) in women.6 The strongest evidence stems from a prospective study involving 14,916 male physicians from United States that showed a three-fold increased risk of having MI in physicians having plasma Hcy 12% above normal as compared to those who had lower levels.15 This study was conducted with the objective to determine association of Hcy with MI and other risk factors for IHD. PATIENTS AND METHODS The proposed study was a non-interventional case control comparative study spanning over a period of six months and carried out at the Department of Chemical Pathology and Endocrinology, Armed Forces Institute of Pathology, Rawalpindi, in collaboration with Armed Forces Institute of Cardiology (AFIC)/National Institute of Heart Diseases (NIHD), Rawalpindi. The study population included 100 hospitalized patients of myocardial infarction along with the same number of healthy age and gender-matched controls. Subjects in renal failure, having thyroid disorders, psoriasis, malignancy and megaloblastic anemia were excluded from the study. The majority of patients as well as controls belonged to middle class socio-economic group and were resident of urban and suburban areas of Rawalpindi district. A verbal consent was obtained from each patient. Recording of demographic details, brief clinical history and physical examination of the subjects followed this. Clinical history included smoking habits of the subjects, presence or absence of diabetes mellitus and hypertension. Smoking habits were defined as current smokers and non-smokers. Subjects were categorized as diabetic if they gave history of diabetes mellitus, with or without treatment and/or if they were found to have symptoms of diabetes with fasting plasma glucose Ž 7.0 mmol/l.16 Physical examination included general physical examination and measurement of arterial blood pressure in the right arm in sitting posture. Average of two readings was used as the estimate of blood pressure. Patients were categorized as hypertensive if they were on hypertensive treatment or if they had a systolic BP > 140 mmhg and /or diastolic BP >90 mmhg.17 A fasting venous blood specimen was collected in a plain tube (without anticoagulant) and glucose bottle, avoiding haemolysis, from each patient as well as control. Blood specimens were transported to the laboratory on ice and serum was separated within one hour of sample collection. Serum total cholesterol and plasma glucose were estimated by commercial kits using CHOD-PAP and GOD-PAP methods respectively on automated chemistry analyser Selectra-II. The subjects were regarded as hypercholesterolemic if their serum total cholesterol was > 5.2 mmol/l.18 An aliquot of serum from each subject was stored frozen at 20 0 C until analysed for Hcy. Serum total Hcy was analyzed in batches by commercial kits using fluorescence polarization immunoassay principle on automated Abbott IMX analyzer. The data was entered and processed on SPSS 10 software. The numerical and categorical data was presented as means and proportions. Mean of serum total Hcy of patients as well as controls was compared using student s t test and p value was calculated for the appropriate degree of freedom. Comparison of mean serum toal Hcy of male patients versus male controls and female patients versus female controls was calculated using student s t test and p value was calculated for appropriate degree of freedom. Hyperhomocysteinemia and other conventional risk factors i.e. smoking, diabetes mellitus, hypertension and hypercholesterolemia between patients and controls were compared using Chi-square (c2) test and p-values were calculated for the appropriate

3 degree of freedom. Association of hyperhomocysteinemia with conventional risk factors in patients was determined using Chi-square (c2) test and p-values were calculated for the appropriate degree of freedom. RESULTS Out of 100 patients of MI included in the study, 85 were males and 15 were females. The average age was 53 ± 4.8 years. These were compared with 100 ages and sex-matched healthy controls. Serum total Hcy level in patients (18.0 ± 5.9 mmol/l) was significantly higher as compared to values (10.8 ± 4.1 mmol/l) in controls (p < ). Table I compares mean Hcy levels between IHD males (20.5 mmol/l) and healthy males (11.3 mmol/l). The difference between these two mean values was statistically significant (p < ). The Hcy levels was (15.2 mmol/l) in IHD females and (8.4 mmol/l) in healthy females, which was statistically significant (p < ). Figure 1 shows comparison of serum total Hcy between patients and controls. Using a Hcy cut off level of 19.0 mmol/l (mean of controls + 2SD), 53 patients and only 3 controls had elevated Hcy levels. Figure 1: Comparison of serum total homocysteine between patients and controls. The statistical comparison of risk factors between patients and controls are summarized in Table I that shows a statistically significant difference between the two for hyperhomocysteinemia (p <0.0001). A statistically significant difference was noted between patients and controls for smoking also (p=0.03). However, no statistically significant difference was observed between patients and controls for hypercholesterolemia (p=0.42), hypertension (p=0.27) and diabetes mellitus (p=0.20). The association of hyperhomocysteinemia with other risk factors of IHD among the patients is shown in Table II. The patients were divided into two groups; group A (n=53), included patients having hyperhomocysteinemia (serum Hcy >19mmol/L); and group B (n=47), included patients having Hcy <19mmol/L. Among the two groups of patients, no statistically significant association was seen between hyperhomocysteinemia and serum total

4 cholesterol, hypertension and diabetes mellitus. Only smoking showed statistically significant association with hyperhomocysteinemic patients (p = 0.04). DISCUSSION Atherosclerotic cardiovascular diseases account for about half of all premature deaths among men in the

5 developed countries as well as in the developing countries Cigarette smoking, hypertension, hypercholesterolemia, and diabetes mellitus are important risk factors for 50-75% of coronary artery disease.5 There has been much recent interest in search for new risk factors and a possible role for sulphur containing amino acid, Hcy. Over the past three decades, the association between elevated serum levels of Hcy and risk of cardiovascular disease has grown from an obscure hypothesis to a major current topic in preventive cardiology.21 Many studies have demonstrated that moderately elevated Hcy level is a risk factor for arterial occlusive disease. In a metaanalysis of 14 case control studies, Boushey and colleagues22 found that an increase of 5 mmol/l in basal total Hcy level was associated with a 60% increase in the odds of CAD among men and an 80% increase in the odds of CAD among women. An increase of 5 mmol/l of plasma Hcy was estimated to increase the risk of CAD by as much as 20 mg/dl increase in cholesterol concentration. The meta-analysis also estimated that approximately 10% of CAD in general population could be attributed to hyperhomocysteinemia. In another prospective cohort study carried out in United States involving 14,916 male US Physicians without prior MI, it was found that those physicians having serum Hcy 12% above normal had a 3-fold increased risk of MI as compared to those who had lower levels even after adjustment of traditional common risk factors.15 The principal observation of this study is that mean of total Hcy of patients of acute MI was significantly higher (18.0 ± 5.9 mmol/l), as compared to age and sex-matched healthy controls (10.8 ± 4.1 mmol/l). This finding is in agreement with studies in the West,23,24 as well as in Pakistan.25 This study, therefore, establishes a positive association between elevated Hcy level and ischemic heart disease. Elevated Hcy level were found in 53% patients of MI in the present study, compared to 40% patients of MI having elevated Hcy level in the West. This difference may be attributable to concurrent covert vitamin deficiencies thought to be much more common in our part of the world.26 Present study also showed that in hyperhomocysteinemic patients, Hcy levels were only moderately elevated. This finding is also in line with recent observations. This indicates that moderately elevated Hcy level is a risk factor for IHD. None of the patient had Hcy level > 100 mmol/l or severe hyperhomocysteinemia. Severe hyperhomocysteinemia is usually caused by genetically determined enzyme deficiencies that usually manifest as life threatening thromboembolic events in early adult life.8 Since the average age of the patients in our study was 53 ± 4.8 years, it is unlikely that elevated Hcy in them was due to enzyme deficiencies. It has also been observed in this study that all hyperhomocysteinemia female patients were in the postmenopausal age group. This finding is in agreement with a recent study, which has found that postmenopausal women with elevated Hcy level have a higher incidence of coronary heart disease.27 An interesting observation was that the upper limit of homocysteine in healthy controls of the study was higher than the upper limit of the healthy population in the West (19 mmol/l vs. 15 mmol/l). This is because prevalence of vitamin B12 and folate deficiency is higher in our part of the world due to increased prevalence of under nutritional state and parasitic infestations.26 In control group, no age related difference in Hcy level was observed. This may again be attributed to vitamin deficiency in our healthy population. One limitation of this study was that serum folate and vitamin B12 of patients as well as controls was not determined as the tests were costly and beyond the scope of present study. The higher upper limit of Hcy in our healthy subjects as compared to western population indicates the need to establish local reference ranges. This study observed more patients with conventional risk factors in hyperhomocysteinemic subjects (Group A, n= 53) than patients having low Hcy level. In spite of this, no association was found between hyperhomocysteinemia and these risk factors except smoking. Although Hcy is regarded as an independent risk factor for IHD,1 a positive association between it and smoking was found in some studies.28,29 Since hyperhomocysteinemia is more commonly seen in our patients, randomised placebo controlled trials may be conducted to ascertain clinical benefits of Hcy lowering therapy in patients of ischemic heart disease. It is prudent to manage hyperhomocysteinemia by adequate nutrition and vitamin supplements. CONCLUSION Ischemic heart disease is associated with moderate hyperhomocysteinemia in our patients and it is not an independent risk factor for ischemic heart disease but is associated with smoking. REFERENCES 1. Robert C, Leslie D, Killian R, Eileen N, Seamus C, Brain F, et al. Hyperhomocysteinemia: an independent risk factor for vascular disease. N Engl J Med

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7 20. Ayub M, Tariq W, Nadeem MA, Irshad H. Risk stratification of patients presenting with first acute myocardial infarction with serum cardiac troponin T. Pak J Cardiol 1999;10(2-3): Stampfer MJ, Malinow MR. Can lowering homocysteine levels reduce cardiovascular risk? N Engl J Med 1995; 332: Boushey C, Beresford SAA, Omenn GS, Motulsky AG. A squantitative assessment of plasma homocysteineas a risk factor for vascular disease: probable benefits of increasing folic acid intake. JAMA 1995; 274: Senaratane MP, Griffiths J, Nagendran J. Elevation of plasma homocysteine levels associated with acute myocardial infarction. Clin Invest Med 2000; 4: Laraqui A, Bennouar N, Meggouh F, Allami A, Kadiri NE, Benkouka F, et al. Homocysteine, lipoprotein (a): risk factors for coronary heart disease. Ann Biol Clin (Paris) 2002; 60: Salah-ud-din M, Karira KA, Motahir AS, Samad A. Serum homocysteine in patients with acute myocardial infarction. Pak J Cardiol 2000; 11: Wald NJ,Watt HC, Law MR, Wein DG, Mc Partlin J, Scolt JM. et al. Homocysteine and ischemic heart disease: results of a prospective study with implications regarding prevention. Arch Intern Med 1998; 158: Ridker PM. Homocysteine and risk of cardiovascular disease among postmenopausal women. JAMA 1999; 281: Kvale G, Tverdal A, Refsum H, Nygard O, Bjartveit K, Ueland PM, et al. Homocysteine and cardiovascular disease: a Norwegian cross-sectional study. In: Bjartveit K, Thelle D, (edi). Third international conference on preventive cardiology. Oslo: 1993; Woo KS, Chook P, Yourg RP, Sandersan JE. Hyperhomocysteinemia in association with smoking is a significant risk factor for CAD in Hong Kong Chinese. New risk factors for coronary heart disease in Asia. Int J Cardiol 1997; 62: (suppl) S Department of Chemical Pathology and Endocrinology, Armed Forces Institute of Pathology, Rawalpindi. *Department of Pathology, Combined Military Hospital, Peshawar. **Department of Pathology, Foundation University Medical College, Rawalpindi. ***Department of Haematology, AFIP, Rawalpindi. Correspondence: Dr. Muhammmad Dilawar, C/o, Armed Forces Institute of Pathology, Rawalpindi, Received July 22, 2003; accepted August 04, 2004.

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