Terence M. Doherty

Coronary Calcium Does Not Accurately Predict Near-Term Future Coronary Events in High-Risk Adults

BACKGROUND Prognostic risk models have had limited success in predicting coronary events in subjects with multiple risk factors. We and others have proposed an alternative approach using radiographically detectable coronary calcium. We evaluated and compared the predictive value of these 2 approaches for determining coronary event risk in asymptomatic adults with multiple coronary risk factors. In addition, we assessed the predictive value of a risk model that included calcium score and cardiac risk-factor data. METHODS AND RESULTS We recruited 1196 asymptomatic high-coronary-risk subjects who then underwent risk-factor assessment and cardiac electron-beam CT (EBCT) scanning and were followed up for 41 months with a 99% success rate. We applied the Framingham model and our data-derived risk model to determine the 3-year likelihood of a coronary event. The mean age of our cohort was 66 years, and mean 3-year Framingham risk was 3.3+/-3.6%. Sixty-eight percent (818 subjects) had detectable coronary calcium. There were 17 coronary deaths (1.4%) and 29 nonfatal infarctions (2. 4%). The receiver operating characteristic (ROC) curve areas calculated from the Framingham model, our data-derived risk model, and the calcium score were 0.69+/-0.05, 0.68+/-0.05, and 0.64+/-0.05, respectively (P=NS). When calcium score was included as a variable in the data-derived model, the ROC area did not change significantly (0.68+/-0.05 to 0.71+/-0.04; P=NS). CONCLUSIONS Neither risk-factor assessment nor EBCT calcium is an accurate event predictor in high-risk asymptomatic adults. EBCT calcium score does not add significant incremental information to risk factors, and its use in clinical screening is not justified at this time.

Calcification in atherosclerosis: Bone biology and chronic inflammation at the arterial crossroads

Dystrophic or ectopic mineral deposition occurs in many pathologic conditions, including atherosclerosis. Calcium mineral deposits that frequently accompany atherosclerosis are readily quantifiable radiographically, serve as a surrogate marker for the disease, and predict a higher risk of myocardial infarction and death. Accelerating research interest has been propelled by a clear need to understand how plaque structure, composition, and stability lead to devastating cardiovascular events. In atherosclerotic plaque, accumulating evidence is consistent with the notion that calcification involves the participation of arterial osteoblasts and osteoclasts. Here we summarize current models of intimal arterial plaque calcification and highlight intriguing questions that require further investigation. Because atherosclerosis is a chronic vascular inflammation, we propose that arterial plaque calcification is best conceptualized as a convergence of bone biology with vascular inflammatory pathobiology.

TLR SIGNALING: AN EMERGING BRIDGE FROM INNATE IMMUNITY TO ATHEROGENESIS

Chronic inflammation and disordered lipid metabolism represent hallmarks of atherosclerosis. Considerable evidence suggests that innate immune defense mechanisms might interact with proinflammatory pathways and contribute to development of arterial plaques. The preponderance of such evidence has been indirect clinical and epidemiologic studies, with some support from experimental animal models of atherosclerosis. However, recent data now directly implicate signaling by TLR4 in the pathogenesis of atherosclerosis, establishing a key link between atherosclerosis and defense against both foreign pathogens and endogenously generated inflammatory ligands. In this study, we briefly review these and closely related studies, highlighting areas that should provide fertile ground for future studies aimed at a more comprehensive understanding of the interplay between innate immune defense mechanisms, atherosclerosis, and related vascular disorders.

Electron Beam Computed Tomographic Coronary Calcium as a Predictor of Coronary Events Comparison of Two Protocols

BACKGROUND We assessed the accuracy of two electron beam computed tomography (EBCT) protocols for predicting coronary events. METHODS AND RESULTS In 1994, 24 months after enrollment in a longitudinal study, 326 high-risk adults underwent both 3- and 6-mm image-slice thickness EBCT scanning and were followed up for 32.0+/-4.0 additional months. Events were defined as either coronary death, myocardial infarction, or revascularization. We monitored these subjects for the 32-month postscanning period with yearly phone calls and acquisition of records for all hospital admissions. At the time of scanning, 11 subjects (3%) had already suffered 12 events (5 infarctions and 7 revascularizations) during the 24-month prescanning period. During the postscanning period, 18 subjects (6%) suffered 23 events (5 coronary deaths, 6 infarctions, and 12 revascularizations). Thus, 28 subjects (9%) suffered 35 events. Calcium quantities calculated for both protocols, performed on the same subjects, were sorted in ascending order and divided into equal quartiles. When revascularizations were included, there was a significant trend toward higher frequencies of events with increasing calcium quantity (P<.01). However, coronary death and infarction were not significantly more frequent in higher quartiles. These relationships were preserved in the subjects without prior events at the time of scanning. CONCLUSIONS Calcium quantities from the 3-mm and the more reproducible 6-mm scanning are equally accurate for predicting events. Coronary calcium amount appears to be a weak predictor of coronary death and infarction. Its predictive accuracy is superior for predicting revascularization.

Increased Expression of Membrane Type 3-Matrix Metalloproteinase in Human Atherosclerotic Plaque Role of Activated Macrophages and Inflammatory Cytokines

Background—Matrix metalloproteinases (MMPs) are thought to play a prominent role in atherogenesis and destabilization of plaque. Pericellularly localized membrane-type (MT)-MMPs activate secreted MMPs. We investigated the hypothesis that MT3-MMP is expressed in human atherosclerotic plaques and is regulated by locally produced inflammatory cytokines and oxidized low-density lipoprotein (Ox-LDL). Methods and Results—Expression and cellular localization of MT3-MMP in normal and atherosclerotic human coronary arteries were examined using specific antibodies. Abundant MT3-MMP expression was noted in medial smooth muscle cells (SMCs) of normal arteries. In atherosclerotic arteries, MT3-MMP expression was observed within complex plaques and colocalized with SMCs and macrophages (M&phgr;). Cultured human monocyte-derived M&phgr; constitutively expressed MT3-MMP mRNA and proteolytically active protein, as demonstrated by mRNA analyses, immunoblotting, and gelatin zymography, respectively. Ox-LDL, tumor necrosis factor-&agr;, or macrophage colony-stimulating factor caused dose- and time-dependent increases in steady-state levels of MT3-MMP mRNA in cultured M&phgr;. This correlated with a 2- to 4-fold increase in levels of MT3-MMP immunoreactive protein and enzymatic activity in M&phgr; membranes. Confocal microscopy and flow cytometry confirmed induction and spatial distribution of MT3-MMP protein from intracellular domains to the M&phgr; plasma membrane by Ox-LDL, tumor necrosis factor-&agr;, or macrophage colony-stimulating factor. Conclusions—MT3-MMP is expressed by SMCs and M&phgr; in human atherosclerotic plaques. Proinflammatory molecules cause a progressive increase in the expression of MT3-MMP in cultured M&phgr;. Our results suggest a mechanism by which inflammatory molecules could promote M&phgr;-mediated degradation of extracellular matrix and thereby contribute to plaque destabilization.

Prognostic significance of cardiac cinefluoroscopy for coronary calcific deposits in asymptomatic high risk subjects

OBJECTIVES This research investigated the prognostic significance of radiographically detectable coronary calcific deposits. BACKGROUND Coronary calcific deposits are almost always associated with coronary atherosclerosis. We investigated the association between fluoroscopically determined coronary calcium and coronary heart disease end points at 1 year of follow-up. METHODS This prospective population-based cohort study was conducted in the suburbs of Los Angeles. Fourteen hundred sixty-one asymptomatic adults with an estimated > or = 10% risk of having a coronary heart disease event within 8 years underwent cardiac cinefluoroscopy for assessment of coronary calcium at initiation of the study. Clinical status including angina, documented myocardial infarction, myocardial revascularization and death from coronary heart disease were determined after 1 year. RESULTS The prevalence of calcific deposits was high (47%). A follow-up examination at 1 year was successfully completed in 99.9% of subjects. Six subjects (0.4%) had died from coronary heart disease and 9 (0.6%) had had a nonfatal myocardial infarction. Thirty-seven subjects (2.5%) reported angina pectoris, and 13 (0.9%) had undergone myocardial revascularization. Fifty-three subjects had at least one event during the 1-year period. Radiographically detectable calcium was associated with the presence of at least one of these end points, with a risk ratio of 2.7 (confidence limits 1.4, 4.6). The presence of coronary calcium was an independent predictor of at least one end point when controlling for age, gender and risk factors. However, three deaths due to coronary heart disease and two nonfatal myocardial infarctions occurred in subjects without detectable coronary calcium. CONCLUSIONS The presence of coronary calcific deposits incurs an increased risk of coronary heart disease events in asymptomatic high risk subjects at 1 year. This increased risk is independent of that incurred by standard risk factors.

Ethnic Origin and Serum Levels of 1α,25-Dihydroxyvitamin D3 Are Independent Predictors of Coronary Calcium Mass Measured by Electron-Beam Computed Tomography

BACKGROUND Blacks have been found to have lower amounts of coronary calcium as well as higher levels of the osteoregulatory steroid 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] than whites. We sought to determine if racial differences in coronary calcium mass could be explained by differences in serum levels of 1,25(OH)2D3. METHODS AND RESULTS We evaluated standard coronary risk factors, quantified coronary calcium mass with electron-beam computed tomography (EBCT), and measured serum 1,25(OH)2D3 with radioimmunoassay in 283 high-risk subjects (51 [180%] black, 232 [82%] white). Black subjects had lower masses of coronary calcium than whites (14 versus 47 mg; P=.003). Serum 1,25(OH)2D3 levels were slightly higher in blacks (41 versus 38 pg/mL; P=.05). Log 1,25(OH)2D3 levels were inversely proportional to log-transformed calcium mass (r=-.19; P=.001) in both races. Multivariate linear regression demonstrated that both black race (P=.02) and 1,25(OH)2D3 levels (P=.007) contributed inversely and independently to coronary calcium mass. However, an interaction term of racex1,25(OH)2D3 did not significantly contribute to coronary calcium mass, indicating that other undetermined factors in addition to 1,25(OH)2D3 are responsible for ethnic differences in coronary calcium mass. CONCLUSIONS Both black race and serum levels of 1,25(OH)2D3 are independent negative determinants of coronary calcium mass. Nevertheless, diminished amounts of coronary calcium in blacks are not accounted for by higher 1,25(OH)2D3 levels.

Racial differences in the significance of coronary calcium in asymptomatic black and white subjects with coronary risk factors.

OBJECTIVES To compare the significance of a specific feature of coronary atherosclerosis--coronary calcium--in asymptomatic black and white subjects with coronary risk factors. BACKGROUND The natural history and clinical evolution of coronary atherosclerosis differs between blacks and whites. Differences in the underlying pathobiology of atherosclerosis may be one determinant of the ethnic variability in the clinical manifestation of coronary atherosclerosis. METHODS In 1,375 high-risk but asymptomatic subjects (93 blacks [6.8%] and 1,282 whites [93.2%]) with at least one risk factor but no prior evidence of coronary disease, we assessed coronary risk factors, calculated Framingham risk of a coronary event and evaluated coronary calcium with digital subtraction fluoroscopy. We then followed these subjects clinically for 70 +/- 13 months, noting the occurrence of the following coronary events: death due to coronary heart disease (CHD); myocardial infarction (MI); angina pectoris; and performance of coronary bypass or angioplasty. RESULTS Risk factor profiles were similar in black and white subjects (6-year Framingham risk 15 +/- 7% in blacks, 14 +/- 8% in whites [NS]). Coronary calcium was present in 59.9% of white subjects but only 35.5% of black subjects (p = 0.0001). Nevertheless, after 70 months of follow-up, more blacks than whites (22 blacks [23.7%] vs. 190 whites [14.8%]; p = 0.04) suffered one of the following end points: CHD death, MI, angina or revascularization. The age, gender and coronary risk-adjusted odds ratio of black race for at least one event was 2.16 (95% CI 1.34 to 3.48). CONCLUSIONS Despite having a lowered prevalence of coronary calcium than high risk whites, high risk blacks suffer more CHD events. Coronary calcium therefore does not carry the same pathobiologic significance in blacks that it does in whites, consistent with the concept that there are specific racial differences in the natural history of CHD and its evolution into clinically manifest events.

The NOD/RIP2 Pathway Is Essential for Host Defenses Against Chlamydophila pneumoniae Lung Infection

Here we investigated the role of the Nod/Rip2 pathway in host responses to Chlamydophila pneumoniae–induced pneumonia in mice. Rip2−/− mice infected with C. pneumoniae exhibited impaired iNOS expression and NO production, and delayed neutrophil recruitment to the lungs. Levels of IL-6 and IFN-γ levels as well as KC and MIP-2 levels in bronchoalveolar lavage fluid (BALF) were significantly decreased in Rip2−/− mice compared to wild-type (WT) mice at day 3. Rip2−/− mice showed significant delay in bacterial clearance from the lungs and developed more severe and chronic lung inflammation that continued even on day 35 and led to increased mortality, whereas WT mice cleared the bacterial load, recovered from acute pneumonia, and survived. Both Nod1−/− and Nod2−/− mice also showed delayed bacterial clearance, suggesting that C. pneumoniae is recognized by both of these intracellular receptors. Bone marrow chimera experiments demonstrated that Rip2 in BM-derived cells rather than non-hematopoietic stromal cells played a key role in host responses in the lungs and clearance of C. pneumoniae. Furthermore, adoptive transfer of WT macrophages intratracheally was able to rescue the bacterial clearance defect in Rip2−/− mice. These results demonstrate that in addition to the TLR/MyD88 pathway, the Nod/Rip2 signaling pathway also plays a significant role in intracellular recognition, innate immune host responses, and ultimately has a decisive impact on clearance of C. pneumoniae from the lungs and survival of the infectious challenge.

Staphylococcus aureus Panton-Valentine leukocidin contributes to inflammation and muscle tissue injury.

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) threatens public health worldwide, and epidemiologic data suggest that the Panton-Valentine Leukocidin (PVL) expressed by most CA-MRSA strains could contribute to severe human infections, particularly in young and immunocompetent hosts. PVL is proposed to induce cytolysis or apoptosis of phagocytes. However, recent comparisons of isogenic CA-MRSA strains with or without PVL have revealed no differences in human PMN cytolytic activity. Furthermore, many of the mouse studies performed to date have failed to demonstrate a virulence role for PVL, thereby provoking the question: does PVL have a mechanistic role in human infection? In this report, we evaluated the contribution of PVL to severe skin and soft tissue infection. We generated PVL mutants in CA-MRSA strains isolated from patients with necrotizing fasciitis and used these tools to evaluate the pathogenic role of PVL in vivo. In a model of necrotizing soft tissue infection, we found PVL caused significant damage of muscle but not the skin. Muscle injury was linked to induction of pro-inflammatory chemokines KC, MIP-2, and RANTES, and recruitment of neutrophils. Tissue damage was most prominent in young mice and in those strains of mice that more effectively cleared S. aureus, and was not significant in older mice and mouse strains that had a more limited immune response to the pathogen. PVL mediated injury could be blocked by pretreatment with anti-PVL antibodies. Our data provide new insights into CA-MRSA pathogenesis, epidemiology and therapeutics. PVL could contribute to the increased incidence of myositis in CA-MRSA infection, and the toxin could mediate tissue injury by mechanisms other than direct killing of phagocytes.