Paul M. Ridker

Background —It has been hypothesized that postmenopausal hormone replacement therapy (HRT) may increase levels of C-reactive protein (CRP), a marker of inflammation associated with increased risk of future cardiovascular events. However, data evaluating this hypothesis are sparse and limited to older women. Methods and Results —CRP levels were evaluated in a cross-sectional survey of 493 healthy postmenopausal women; mean age was 51 years. Overall, median CRP levels were 2 times higher among women taking HRT than among women not taking HRT (0.27 versus 0.14 mg/dL; P =0.001). This difference was present in all subgroups evaluated, including those with no history of hypertension, hyperlipidemia, obesity, diabetes, or cigarette consumption or a family history of premature coronary artery disease (all P < 0.01). Compared with nonusers of HRT, median CRP levels were higher among women using estrogen alone ( P =0.003) and women using estrogen plus progesterone ( P =0.03); however, there was no significant difference in CRP levels between users of different HRT preparations. In multivariate analysis, the relationship between HRT use and CRP remained significant after control for body mass index, age, diabetes, hypertension, hyperlipidemia, alcohol use, and cigarette consumption ( P =0.001). Conclusions —In this cross-sectional survey, CRP levels were increased among apparently healthy postmenopausal women taking HRT. The potential impact of HRT on inflammatory parameters should be investigated in ongoing clinical trials.

—An elevated plasma concentration of the soluble intercellular adhesion molecule-1 (sICAM-1) is associated with increased risk for future coronary events. However, data exploring the interrelations of sICAM-1 with known cardiovascular risk factors are sparse. We determined sICAM-1 levels in 948 middle-aged men with no prior history of cardiovascular disease. sICAM-1 levels increased with age ( P P P P =0.006). Positive correlations were observed between sICAM-1 and triglycerides ( r =0.15; P r =0.21; P r =0.17; P r =0.09; P =0.02); whereas a negative correlation was observed for high density lipoprotein cholesterol ( r =−0.15; P 4 risk factors, respectively ( P P ≤0.05). sICAM-1 levels are associated with several established cardiovascular risk factors. Further studies will be needed to evaluate whether these associations reflect the role of sICAM-1 as a marker of preclinical atherosclerosis, and whether such interrelations might have a causal basis.

Myocardial infarction often occurs among persons without traditional risk factors, and it has been hypothesized that assessment of "novel" markers may help identify persons who are prone to premature atherothrombosis. However, when considering the clinical utility of screening for any new marker for cardiovascular disease, physicians should consider whether there is a standardized and reproducible assay for the marker of interest; whether there is a consistent series of prospective epidemiologic studies indicating that baseline elevations of the novel marker predict future risk; and whether assessment of the novel marker adds to the predictive value of other plasma-based risk factors, specifically, the ratio of total cholesterol to high-density lipoprotein cholesterol. In this article, these criteria are used to evaluate five promising markers of cardiovascular risk: lipoprotein(a), total plasma homocysteine, fibrinolytic capacity, fibrinogen, and high-sensitivity C-reactive protein. Background is also provided to assist physicians in deciding whether one or more of these novel markers deserve clinical consideration in general outpatient settings.

Several mechanisms have been proposed linking hyperhomocystinemia to vascular damage, and it has been hypothesized that elevated levels of total plasma homocysteine represent an important modifiable risk factor for atherothrombotic disease.^1,2 A number of retrospective and cross-sectional studies provide support for this hypothesis.³ However, because homocysteine levels may increase following acute myocardial infarction (MI)⁴ or stroke,⁵ any observed association could, at least in theory, be a result rather than a cause of acute vascular occlusion.

Background — Chlamydia pneumoniae has been hypothesized to play a role in atherothrombosis. However, prospective data relating exposure to Chlamydia pneumoniae and risks of future myocardial infarction (MI) are sparse. Methods and Results —In a prospective cohort of nearly 15 000 healthy men, we measured IgG antibodies directed against Chlamydia pneumoniae in blood samples collected at baseline from 343 study participants who subsequently reported a first MI and from an equal number of age- and smoking-matched control subjects who did not report vascular disease during a 12-year follow-up period. The proportion of study subjects with IgG antibodies directed against Chlamydia increased with age and cigarette consumption. However, prevalence rates of Chlamydia IgG seropositivity were virtually identical at baseline among men who subsequently reported first MI compared with age- and smoking-matched control subjects. Specifically, the relative risks of future MI associated with Chlamydia pneumoniae IgG titers ≥1:16, 1:32, 1:64, 1:128, and 1:256 were 1.1, 1.0, 1.1, 1.0, and 0.8, respectively (all probability values not significant). There was no association in analyses adjusted for other risk factors, evaluating early as compared with late events, or among nonsmokers. Further, there was no association between seropositivity and concentration of C-reactive protein, a marker of inflammation that predicts MI risk in this cohort. Conclusions —In a large-scale study of socioeconomically homogeneous men that controlled for age, smoking, and other cardiovascular risk factors, we found no evidence of association between Chlamydia pneumoniae IgG seropositivity and risks of future MI.

Background —A single base pair mutation in the prothrombin gene has recently been identified that is associated with increased prothrombin levels. Whether this mutation increases the risks of arterial and venous thrombosis among healthy individuals is controversial. Methods and Results —In a prospective cohort of 14 916 men, we determined the prevalence of the G20210A prothrombin gene variant in 833 men who subsequently developed myocardial infarction, stroke, or venous thrombosis (cases) and in 1774 age- and smoking status–matched men who remained free of thrombosis during a 10-year follow-up (control subjects). Gene sequencing was used to confirm mutation status in a subgroup of participants. Overall, carrier rates for the G20210A mutation were similar among case and control subjects; the relative risk of developing any thrombotic event in association with the 20210A allele was 1.05 (95% CI, 0.7 to 1.6; P =0.8). We observed no evidence of association between mutation and myocardial infarction (RR=0.8, P =0.4) or stroke (RR=1.1, P =0.8). For venous thrombosis, a modest nonsignificant increase in risk was observed (RR=1.7, P =0.08) that was smaller in magnitude than that associated with factor V Leiden (RR=3.0, P Conclusions —In a large cohort of US men, the G20210A prothrombin gene variant was not associated with increased risk of myocardial infarction or stroke. For venous thrombosis, risk estimates associated with the G20210A mutation were smaller in magnitude than risk estimates associated with factor V Leiden.

Based on laboratory and experimental evidence, it has been hypothesized that inflammation plays a fundamental role in atherogenesis and acute thrombosis. From an epidemiologic perspective, corroboration of this hypothesis has been provided by a series of prospective cohort studies which demonstrate that inflammatory parameters (such as fibrinogen, C reactive protein, and serum amyloid A), cellular adhesion molecules [such as intercellular adhesion molecule (ICAM)-1], and cytokines (such as interleukin-6) are all elevated at baseline among patients at risk for future coronary occlusion. Furthermore, data deriving from randomized clinical trials suggest that the efficacy of common preventive agents such as aspirin and hydroxy-methylglutaryl (HMG) CoA reductase inhibition may derive in part from interactions with the inflammatory system. Taken together, these data raise the possibility that therapies targeting chronic low-grade inflammation may provide novel future strategies for cardiovascular disease prevention.

Background —It has been hypothesized that infection with either herpes simplex virus (HSV) or cytomegalovirus (CMV) is associated with atherogenesis. However, prospective data relating evidence of prior exposure to these agents with risks of future myocardial infarction (MI) and stroke are sparse. Methods and Results —In a prospective, nested case-control study of apparently healthy men, the baseline prevalence of antibodies directed against HSV or CMV was similar among 643 men who subsequently developed a first MI or thromboembolic stroke and among 643 age- and smoking-matched men who remained free of reported vascular disease over a 12-year follow-up period. Specifically, the relative risks for future MI and stroke were 0.94 (95% CI, 0.7 to 1.2) for HSV seropositivity and 0.72 (95% CI, 0.6 to 0.9) for CMV seropositivity, after adjustment for other cardiovascular risk factors. These findings were not materially altered in comparisons of early versus late events or in analyses stratified by smoking status. There was no evidence of association between HSV or CMV antibodies and plasma concentration of C-reactive protein, a marker of inflammation that predicts vascular risk in this cohort. Conclusions —Among apparently healthy middle-aged men, IgG antibodies directed against HSV or CMV do not appear to be a marker for increased atherothrombotic risk. The observed possible inverse relationship of CMV with MI and stroke was unexpected and may well be due to chance, because the direction of association is not compatible with the a priori hypothesis based on proposed biological mechanisms or previous cross-sectional and retrospective data.

—Although cellular adhesion molecules (CAMs) are hypothesized to play an important role in atherogenesis, the relationship between CAMs and systemic atherosclerosis is uncertain. Among 92 outpatients (48 men; mean±SD age, 65±9 years), we evaluated the association of soluble vascular CAM-1 (sVCAM-1) and intercellular adhesion molecule-1 (sICAM-1) with carotid intimal-medial thickness (IMT), an index of early atherosclerosis. All subjects underwent a 2-dimensional ultrasound examination of both carotid arteries at the distal common carotid arteries and bifurcation. sVCAM-1 and sICAM-1 levels measured by enzyme-linked immunosorbent assay were significantly correlated with mean IMT of the common carotid artery ( r =0.34 and r =0.30, respectively; P r =0.31 and r =0.26, respectively; P r =0.35, P r =0.16, P =0.13) and bifurcation ( r =0.18, P =0.07) carotid IMT but had minimal effect on the associations between sICAM-1 and carotid measurements ( r =0.32, P r =0.23, P P P <0.15). These associations were minimally affected in analyses adjusting for hypertension, diabetes, smoking, low and high density lipoprotein cholesterol, lipoprotein(a), and homocysteine, or in a subgroup analysis limited to those with no prior history of atherothrombotic disease. These data demonstrate a positive association between serum CAMs with carotid IMT and further support the hypothesis that systemic inflammation may have a role in atherosclerotic lesion development.