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      Association of Low Red Blood Cell Folate Concentrations with Coronary Artery Disease in Iranians: A Matched Case-Control Study

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          Abstract

          Background: It is not fully established whether the increasing risk of coronary artery disease (CAD) is associated with high plasma homocysteine levels or components of the homocysteine remethylation pathway, e.g. vitamin B<sub>12</sub> or 5-methyltetrahydrofolate (5-MTHF) in plasma and red blood cells (RBC). In this study, we tested the hypothesis that 5-MTHF in RBC, which represents the long-term folate status of individuals, may be a more reliable marker of homocysteine remethylation pathway disturbances, and its deficiency may be associated with CAD in Iranians. Methods: Plasma total homocysteine (tHcy), vitamin B<sub>12</sub>, and plasma and RBC 5-MTHF were measured in 200 angiographically documented patients and 200 controls matched for sex and age. Results: In the plasma, tHcy levels were significantly higher in cases compared to controls (geometric mean 12.9 ± 6.5 vs. 10.6 ± 5.6 µmol/l, p = 0.04). However, RBC 5-MTHF (527.2 ± 185.9 vs. 461.3 ± 117.9 nmol/l, p = 0.007) and vitamin B<sub>12</sub> (254.2 ± 132.8 vs. 182.2 ± 110.4 pmol/l, p = 0.04) were significantly higher in controls than patients. RBC 5-MTHF was a strong and independent predictor of plasma tHcy (β = –0.01, p = 0.003, r<sup>2</sup> = 0.19). Subjects in the lowest quartile of red-cell 5-MTHF had a 2.5-fold increased prevalence of CAD compared to subjects in the highest quartile. The association of CAD in the first quartile with red-cell 5-MTHF remained significant when adjusted for plasma tHcy, vitamin B<sub>12</sub>, hypertension and hypercholesterolemia (odds ratio, OR 2.3, confidence interval: 1.1–3.9, p = 0.01). However, the association between CAD in the highest quartile and plasma tHcy decreased and became insignificant when adjusted for red-cell 5-MTHF, vitamin B<sub>12</sub>, hypertension and hypercholesterolemia (OR 1.27, confidence interval: 0.96–1.69, p = 0.11). Conclusion: In this study, the association between CAD and low RBC 5-MTHF was stronger than with plasma 5-MTHF and plasma tHcy levels, indicating that RBC 5-MTHF may be a more stable parameter to study disturbances in the homocysteine remethylation pathway in Iranians.

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          Most cited references 14

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          Homocysteine and cardiovascular disease: evidence on causality from a meta-analysis

           D. Wald (2002)
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            Folic acid improves endothelial function in coronary artery disease via mechanisms largely independent of homocysteine lowering.

            Homocysteine is a risk factor for coronary artery disease (CAD), although a causal relation remains to be proven. The importance of determining direct causality rests in the fact that plasma homocysteine can be safely and inexpensively reduced by 25% with folic acid. This reduction is maximally achieved by doses of 0.4 mg/d. High-dose folic acid (5 mg/d) improves endothelial function in CAD, although the mechanism is controversial. It has been proposed that improvement occurs through reduction in total (tHcy) or free (non-protein bound) homocysteine (fHcy). We investigated the effects of folic acid on endothelial function before a change in homocysteine in patients with CAD. A randomized, placebo-controlled study of folic acid (5 mg/d) for 6 weeks was undertaken in 33 patients. Endothelial function, assessed by flow-mediated dilatation (FMD), was measured before, at 2 and 4 hours after the first dose of folic acid, and after 6 weeks of treatment. Plasma folate increased markedly by 1 hour (200 compared with 25.8 nmol/L; P<0.001). FMD improved at 2 hours (83 compared with 47 microm; P<0.001) and was largely complete by 4 hours (101 compared with 51 microm; P<0.001). tHcy did not significantly differ acutely (4-hour tHcy, 9.56 compared with 9.79 micromol/L; P=NS). fHcy did not differ at 3 hours but was slightly reduced at 4 hours (1.55 compared with 1.78 micromol/L; P=0.02). FMD improvement did not correlate with reductions in either fHcy or tHcy at any time. These data suggest that folic acid improves endothelial function in CAD acutely by a mechanism largely independent of homocysteine.
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              Plasma homocysteine concentrations and risk of coronary heart disease in UK Indian Asian and European men.

              Reasons for the increase in mortality due to coronary heart disease (CHD) in UK Indian Asians are not well understood. In this study, we tested the hypotheses that elevated plasma homocysteine concentrations are a risk factor for CHD in Indian Asians, and explain part of their increased CHD risk, compared with Europeans. We undertook two parallel case-control studies, one in Europeans and one in Indian Asians. We recruited 551 male cases (294 European, 257 Indian Asian) and 1025 healthy male controls (507 European, 518 Indian Asian). Fasting and post-methionine load homocysteine, vitamin B12 and folate concentrations, and conventional CHD risk factors were measured. Fasting homocysteine concentrations were 8% higher (95% CI 3-14) in cases compared with controls, in both ethnic groups. The odds ratio of CHD for a 5 micromol/L increment in fasting plasma homocysteine was 1.3 (1.1-1.6) in Europeans and 1.2 (1.0-1.4) in Indian Asians. The association between fasting plasma homocysteine and CHD was independent of conventional CHD risk factors in both ethnic groups. Post-load homocysteine concentrations were not significantly different in cases compared with controls. Among the controls, fasting homocysteine concentrations were 6% (2-10) higher in Indian Asians than in Europeans. From the results we estimate that elevated homocysteine may contribute to twice as many CHD deaths in Indian Asians, compared with Europeans. The differences in homocysteine concentrations between the two ethnic groups were explained by lower vitamin B12 and folate levels in Asians. Plasma homocysteine is a novel and independent risk factor for CHD in Indian Asians, and may contribute to their increased CHD risk. Raised homocysteine concentrations in Indian Asians may be related to their reduced vitamin B12 and folate levels, implying that the increased CHD risk in this group may be reduced by dietary vitamin supplementation.
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                Author and article information

                Journal
                JVR
                J Vasc Res
                10.1159/issn.1018-1172
                Journal of Vascular Research
                S. Karger AG
                1018-1172
                1423-0135
                2005
                August 2005
                29 July 2005
                : 42
                : 4
                : 325-330
                Affiliations
                aDepartment of Biochemistry, Faculty of Medicine, and bDepartment of Internal Medicine, Cardiovascular Unit, Shiraz University of Medical Sciences, Shiraz, Iran
                Article
                86460 J Vasc Res 2005;42:325–330
                10.1159/000086460
                15970643
                © 2005 S. Karger AG, Basel

                Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher. Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug. Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.

                Page count
                Tables: 2, References: 27, Pages: 6
                Categories
                Research Paper

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