Plaque changes and arterial enlargement in atherosclerotic monkeys after manipulation of diet and social environment

Proinflammatory endothelial activation detected by molecular imaging in obese nonhuman primates coincides with onset of insulin resistance and progressively increases with duration of insulin resistance

BACKGROUND

Inflammation and insulin resistance (IR) are associated processes that potentiate risk for cardiovascular disease in obesity. The temporal relation between IR and inflammation is not completely characterized. We hypothesized that endothelial cell adhesion molecule expression in large arteries is an early event that coincides with diet-induced obesity and IR in primates.

METHODS AND RESULTS

Ten adult male rhesus macaques were studied at baseline and every 4 to 6 months on a high-fat diet for 2 years. Truncal fat, carotid intima-media thickness, plasma inflammatory biomarkers, and carotid P-selectin and vascular cell adhesion molecule-1 expression by contrast-enhanced ultrasound molecular imaging were assessed. Intravenous glucose tolerance test was performed at baseline and at 4 and 18 months. A high-fat diet produced a rapid increase (P<0.01) in weight, truncal fat, and degree of IR indicated by the insulin area under the curve and glucose disappearance rate on intravenous glucose tolerance test, all of which worsened minimally thereafter. Molecular imaging detected a progressive increase in endothelial cell adhesion molecule expression over time (5- to 7-fold greater than control agent signal at 2 years; P<0.01). Changes in intima-media thickness were not detected until 2 years and, although there was a trend toward an increase in plasma markers of inflammation (monocyte chemotactic protein-1, C-reactive protein), the pattern of increase varied considerably over time.

CONCLUSIONS

In primates with diet-induced obesity, endothelial inflammatory activation is an early event that occurs coincident with the development of IR and long before any measurable change in carotid intima-media thickness. Endothelial activation is related more to the duration rather than to the severity of IR and is not mirrored by changes in plasma biomarkers.

The monkey puzzle: a systematic review of studies of stress, social hierarchies, and heart disease in monkeys

BACKGROUND

It is often suggested that psychosocial factors, such as stress, or one's social position, may play an important role in producing social gradients in human disease. Evidence in favour of this model of health inequalities has relied, in part, on studies of the health effects of the natural social hierarchies found among non-human primates. This study aimed to assess the strength of this evidence.

METHODOLOGY/PRINCIPAL FINDINGS

A systematic review was carried out to identify all studies of psychosocial factors and coronary artery disease (CAD) in non-human primates. We searched databases (MEDLINE, PsycInfo, EMBASE, and Primatelit from inception to November 2010) to identify experimental and observational studies of the impact of social reorganisation, social instability, and disruption of dominance hierarchies on primate CAD outcomes. We also handsearched bibliographies and examined the citations to those studies in public health articles. Fourteen studies were found which presented evidence on CAD and social status and/or psychosocial stress. These suggested that the association between social status and disease may be sex-specific: in female monkeys dominant status may be protective, with subordinate females having a greater extent of atherosclerosis. In male monkeys the reverse may be the case.

CONCLUSIONS/SIGNIFICANCE

Overall, non-human primate studies present only limited evidence for an association between social status and CAD, Despite this, there is selective citation of individual non-human primate studies in reviews and commentaries relating to human disease aetiology. Such generalisation of data from monkey studies to human societies does not appear warranted.

Mechanisms of plaque stabilization with statins

The traditional view of cardiovascular disease held that the degree of stenosis defined high-risk lesions and that removal of cholesterol shrank these lesions and thereby enlarged the lumen. Advances in understanding of the pathophysiology of the acute coronary syndromes refute this view. We now appreciate that vascular biology determines plaque stability and that statins stabilize plaque by favorably altering this biology. They do so chiefly (but probably not exclusively) by cholesterol lowering. In addition to reducing the cholesterol content of plaque, lipid lowering inhibits inflammation, and decreases collagenolytic activity and thrombotic potential. The role of lipid-independent effects remains unclear because many studies used statin concentrations too high to have any clinical relevance. However, data suggest that statin-induced alterations in the function of small G proteins may contribute to the anti-inflammatory and antithrombotic actions of statins in clinical practice.

Going from immutable to mutable atherosclerotic plaques

Atherosclerotic coronary disease develops over several decades and was once thought to be an inevitable, irreversible consequence of aging. Atherogenesis is an inflammatory response that occurs after injury to the endothelium. Thrombosis, because of either endothelial erosion or plaque disruption, precipitates acute coronary events. Effective lipid lowering with statins has consistently and significantly decreased the risk that acute ischemic events will occur. The beneficial effects of statins likely result not only from their lipid-lowering effects but also from mechanisms that influence plaque behavior. Atherosclerotic plaques are not immutable; rather, their structure and composition can be altered by therapeutic modification. Ample evidence from clinical trials supports statin treatment in patients with stable coronary disease. Results of recent clinical trials support early treatment of high-risk patients with unstable coronary disease; early and aggressive statin treatment resulted in fewer recurrent ischemic events in patients with an acute coronary syndrome. Additional studies are needed to confirm the benefit of early statin treatment in patients with unstable coronary disease and to elucidate the reasons for the occurrence of events in treated patients. Research is also necessary to clarify the role of other lipids, as well as nonlipid risk factors, in the occurrence of acute ischemic events.

Hostility, gender, and cardiac autonomic control

OBJECTIVE

Although considerable evidence implicates hostility in the development of coronary artery disease (CAD), the pathogenic mechanisms remain poorly understood. We have developed a psychophysiological model that holds that altered autonomic nervous system function links psychological traits with CAD outcomes. In laboratory studies, stressors reduce high-frequency (HF) heart period variability, an index of cardiac vagal modulation. With ambulatory electrocardiographic recording, we demonstrated in a predominantly male sample that hostility was inversely associated with HF power, but only during waking hours. These findings are consistent with the hypothesis that hostile individuals experience multiple stressful interpersonal transactions each day, resulting in overall lower HF power during the day but not at night.

METHODS

To further evaluate this hypothesis, we screened 96 subjects using the Cook-Medley Hostility Scale and selected 15 men and 15 women representing a wide distribution of hostility. These subjects were studied in a laboratory session assessing reactivity to psychological and orthostatic challenges with continuous electrocardiographic, blood pressure, and respiration monitoring. We predicted that for men and women, hostility would be inversely related to reductions in HF power in response to challenge.

RESULTS

In response to mental stressors, all measures of heart period variability change were inversely related to hostility as predicted. No such relationships were found for responses to tilt. The data suggested a possible effect of gender on these relationships.

CONCLUSIONS

These data add to the growing body of evidence showing that hostility influences vagal modulation of the cardiovascular system and suggest that altered autonomic control is a pathogenic mechanism linking hostility and CAD.

Improved adenovirus vectors for infection of cardiovascular tissues

To identify improved adenovirus vectors for cardiovascular gene therapy, a library of adenovirus vectors based on adenovirus serotype 5 (Ad5) but carrying fiber molecules of other human serotypes, was generated. This library was tested for efficiency of infection of human primary vascular endothelial cells (ECs) and smooth muscle cells (SMCs). Based on luciferase, LacZ, or green fluorescent protein (GFP) marker gene expression, several fiber chimeric vectors were identified that displayed improved infection of these cell types. One of the viruses that performed particularly well is an Ad5 carrying the fiber of Ad16 (Ad5.Fib16), a subgroup B virus. This virus showed, on average, 8- and 64-fold-increased luciferase activities on umbilical vein ECs and SMCs, respectively, compared to the parent vector. GFP and lacZ markers showed that approximately 3-fold (ECs) and 10-fold (SMCs) more cells were transduced. Experiments performed with both cultured SMCs and organ cultures derived from different vascular origins (saphenous vein, iliac artery, left interior mammary artery, and aorta) and from different species demonstrated that Ad5.Fib16 consistently displays improved infection in primates (humans and rhesus monkeys). SMCs of the same vessels of rodents and pigs were less infectable with Ad5.Fib16 than with Ad5. This suggests that either the receptor for human Ad16 is not conserved between different species or that differences in the expression levels of the putative receptor exist. In conclusion, our results show that an Ad5-based virus carrying the fiber of Ad16 is a potent vector for the transduction of primate cardiovascular cells and tissues.

Lipid lowering reduces proteolytic and prothrombotic potential in rabbit atheroma

Thrombus formation at sites of atheromatous plaque disruption cause most acute coronary events such as myocardial infarction and unstable angina. Lesional macrophages and smooth muscle cells produce matrix metallo-proteinases (MMPs) and tissue factor (TF), the molecules likely contribute to plaque rupture and thrombus formation. Recent clinical studies have suggested that lipid lowering can reduce the incidence of acute coronary events. We have recently determined the effects of long-term dietary lipid lowering on atheroma of high-cholesterol-fed rabbits. Lipid lowering diminished macrophage accumulation, reduced expression and activity of MMPs, and increased interstitial collagen accumulation in rabbit atheroma. Expression and activity of TF in atheroma also substantially decreased during lipid lowering. Dietary lipid lowering also promoted accumulation of mature smooth muscle cells expressing less MMPs and TF in the plaque's fibrous cap. These results suggest potential mechanisms by which lipid lowering reduces acute coronary events in patients by decreasing proteolytic and prothrombotic activity within the atheroma.

Effect of long-term cholesterol-lowering treatment with HMG-CoA reductase inhibitor (simvastatin) on myocardial perfusion evaluated by thallium-201 single photon emission computed tomography

Fifteen patients with either angina pectoris or old myocardial infarction, who had positive 201Tl single photon emission computed tomography (SPECT) imaging and coronary sclerosis of more than 50%, were treated with an HMG-CoA reductase inhibitor (simvastatin) for more than 1 year. They were compared with an untreated control group (n = 25). Total cholesterol decreased 22% and high-density lipoprotein (HDL) increased 9% with simvastatin; both changes were significantly different from those in controls. Long-term simvastatin induced improvement of myocardial perfusion on 201Tl SPECT images both during exercise and at rest, which was also significantly different from controls. In addition, the improvement of myocardial perfusion on 201Tl SPECT images was clearly related to the improvements in cholesterol values, especially nonHDL cholesterol. Thus, the greater the decrease in nonHDL cholesterol, the greater the improvement in myocardial perfusion at rest or during exercise with long-term treatment using an HMG-CoA reductase inhibitor. These findings indicate that the improvements in cholesterol values caused by HMG-CoA reductase inhibitor therapy are related to improvements of myocardial perfusion seen on 201Tl SPECT images.

Thrombosis and coagulation abnormalities in the acute coronary syndromes

The acute coronary syndromes, that include unstable angina, acute myocardial infarction, and many cases of sudden cardiac death, exact a considerable price on society in terms of mortality, morbidity, and health care costs. The coronary atherosclerotic lesion is often an indolent and progressive entity that can destabilize causing an acute syndrome with or without warning. The majority of acute coronary syndromes result from events such as rupture or disruption of the atherosclerotic plaque with intracoronary thrombosis and ischemia of the distal myocardium as a result. Advances in our understanding of the process underlying the acute coronary syndromes has allowed for the identification of targets and rational therapeutic strategies for the prevention and treatment of these syndromes. Many of these therapeutic strategies involve the reversal of prethrombotic forces that often coexist with coronary atherosclerosis. Even with recent advances in our approach to atherosclerosis, intracoronary thrombosis, and the resulting acute coronary syndromes, an unacceptably high event rate persists after these syndromes. Further advances in the prevention and treatment of coronary atherosclerosis and its thrombotic complications depends on a more thorough understanding of the biology of the atherosclerotic plaque and the factors which influence its stability.

Pathophysiology of plaque rupture and the concept of plaque stabilization

Atherosclerosis complicated by plaque rupture or disruption and thrombosis is primarily responsible for the potentially lethal acute coronary syndromes. Plaques with a large extracellular lipid-rich core, thin fibrous cap with reduced collagen content and smooth muscle density, and increased numbers of activated macrophages and mast cells appear to be most vulnerable to rupture. Plaque disruption tends to occur at points at which the plaque surface is weakest and most vulnerable, which coincide with points at which stresses, resulting from biomechanical and hemodynamic forces acting on plaques, are concentrated. Reduced matrix synthesis as well as increased matrix degradation may predispose fibrous caps to rupture spontaneously or in response to extrinsic mechanical or hemodynamic stresses. Modification of endothelial dysfunction and reduction of vulnerability to plaque rupture and thrombosis may lead to plaque stabilization resulting in reduction of the frequency of acute coronary syndromes. This putative concept of plaque stabilization, although attractive, has not yet been rigorously validated in humans. Indirect data from clinical trials involving lipid lowering/modification and lifestyle/risk factor modification, however, provide strong support for this new paradigm. Thus, plaque stabilization may prove to be an important modality for reduction of lethal consequences of coronary atherosclerosis.

Influence of dietary lipids on agonistic and affiliative behavior in Macaca fascicularis

The current study evaluates the hypothesis, derived from previous investigations, that alterations in dietary fat and cholesterol influence the social behavior of monkeys. Subjects were 62 adult male, cynomolgus macaques (Macaca fascicularis) assigned originally to an investigation of atherosclerosis regression. This study thus involves a secondary analysis of data derived from an investigation conducted for another purpose. Animals were housed for 14 months' in social groups of five individuals each and initially fed a diet very high in saturated fat and cholesterol to induce coronary artery atherosclerosis. Monkeys were then exposed for 28 months to one of three conditions; (1) a moderately high-fat, high-cholesterol diet and an unstable social environment (in which monkeys were switched among groups monthly); (2) a low-fat, low-cholesterol diet and an unstable social environment; and (3) a low-fat, low-cholesterol diet and a stable social environment. A comparison of animals living in unstable groups revealed that those consuming the low-fat diet exhibited more overt aggression (P < 0.001) and overt submission (P < 0.01) than did monkeys eating the high-fat diet. A second comparison involved only those animals living in stable social units. These monkeys, while consuming the low-fat diet, engaged in more aggression and submission (P_s < 0.05), spent less time in passive body contact or within touching distance (P_s < 0.001), and spent more time alone (P < 0.001) than they had initially while consuming a very high-fat diet. The current investigation is the first on this topic to include measures of social behavior in animals both before and after a reduction in dietary fat. The findings that such a reduction is associated with increased agonism and decreased affiliation may help explain the epidemiologic association in human beings between low or reduced plasma cholesterol concentrations and a high incidence of violence-related mortality. More generally, the data are consistent with the hypothesis that there is a negative feedback adaptation providing for appropriate changes in behavior in response to periodic dietary privation. © 1996 Wiley-Liss, Inc.

Development of risk factors for cardiovascular disease among women from adolescence to older ages

The development of risk factors for young adults to older ages for women has been evaluated in several studies. The increase in risk factor levels is related to age, weight gain, and diet. The levels of risk factors are related to extent of atherosclerosis, even at relatively young ages. The prevention of increase in risk factors is of primary importance for the future reduction of morbidity and mortality due to cardiovascular disease.

Characterization of mineralocorticoid and glucocorticoid receptors in primate brain

Characteristics of neural corticosteroid receptors were studied in 51 adrenally-intact macaque monkeys using a modification of a corticosteroid receptor assay developed in this laboratory for rodent studies. Using cortisol as a ligand, two receptor subtypes could be distinguished and with similar Kd's to those observed in rodents, as measured with corticosterone. The time course showed maximum binding for mineralocorticoid receptors at 24 h and for glucocorticoid at 4 h. There were regional differences in the number of available binding sites for each receptor type, as well as an inverse correlation between the concentration of cortisol in the blood at the time of death and the number of available binding sites. In general this paper emphasizes the similarities between such receptors in primate and those in other species, similarities that could be detected despite the technical constraints of studying tissue taken from non-adrenalectomized animals.

Neuroendocrine responses to fenfluramine challenge are influenced by exposure to chronic social stress in adult male cynomolgus macaques

This study was designed to investigate the effect of chronic social stress on central serotonergic responsivity in adult male cynomolgus monkeys (Macaca fascicularis). The influences of social stress and dominance status (social rank) on adrenocorticotropin hormone (ACTH) and cortisol responses to acute administration of an indirect serotonergic agonist (fenfluramine) were evaluated in 75 cynomolgus macaques that were housed in five-member social groups for 28 mo. These groups either remained stable in composition (No-Stress) or had their composition periodically reorganized in the first (Early-Stress) or second (Late-Stress) halves of the study. At the end of the 23rd month, a fenfluramine challenge was done. Animals in the Late-Stress condition had significantly higher ACTH responses compared to those in the No-Stress condition (p < .05) and significantly higher cortisol responses compared to those in the Early-Stress condition (p < .05). No differences between dominant and subordinate animals in ACTH or cortisol responses to challenge were identified. These data suggest that social stress produces a "state"-related augmentation of hypothalamic-pituitary-adrenal responsivity to fenfluramine (serotonergic) challenge in cynomolgus macaques.