Reduction of coronary atherosclerosis by moderate conditioning exercise in monkeys on an atherogenic diet

High-Volume Physical Activity and Clinical Coronary Artery Disease Outcomes: Findings From the Cooper Center Longitudinal Study

BACKGROUND

High-volume physical activity (PA) is associated with a higher prevalence of subclinical coronary artery disease (CAD). However, the clinical significance of subclinical CAD among high-volume exercisers remains incompletely understood, and the dose-response relationship between high-volume PA and clinical CAD events remains uncertain.

METHODS

Individual participant data from the Cooper Center Longitudinal Study (1987-2018) were linked to Medicare claims files. PA volume was determined by self-report and categorized as <500, 500 to 1499, 1500 to 2999, and ≥3000 metabolic equivalent of task (MET)-minutes per week. Subclinical CAD (coronary artery calcium [CAC]) was measured by cardiac computed tomography. All other risk factors were measured in the standard fashion. Composite CAD events (acute myocardial infarction and revascularization) and all-cause mortality were determined from Medicare claims files. A multivariable-adjusted proportional hazards illness-death model with random shared frailty was used to estimate the association between PA volume, CAC, and both clinical CAD and death. Heterogeneity in the association between CAC and clinical CAD across levels of PA was determined with multiplicative interaction terms.

RESULTS

We included 26 724 participants (54 years of age; 28% women). Mean exercise volume was 1130 MET-minutes per week, with 1997 (7.5%) reporting ≥3000 MET-minutes per week. After a mean follow-up of 20.5 years, we observed 811 acute myocardial infarction events, 1636 composite CAD events, and 2857 deaths without CAD. Compared with individuals exercising <500 MET-minutes per week, the lowest risk for acute myocardial infarction occurred among individuals with intermediate PA volumes (500-1499 MET-minutes per week: hazard ratio [HR], 0.77 [95% CI, 0.65-0.91]; 1500-2499 MET-minutes per week: HR, 0.78 [95% CI, 0.63-0.95]). There was no association between high-volume PA (>3000 MET-minutesw per week) and risk for acute myocardial infarction (HR, 0.95 [95% CI, 0.72-1.25]). In contrast, the lowest risk for death was observed among the high-volume PA group (HR, 0.71 [95% CI, 0.60-0.83]). CAC (on log scale) was associated with a higher risk for composite CAD across all PA categories, including among the high-volume PA subgroup (HR, 1.29 [95% CI, 1.16-1.44]; P<0.001; Pinteraction= 0.969).

CONCLUSIONS

Compared with low-volume PA, high-volume PA was associated with a lower risk for all-cause mortality but a similar risk for clinical CAD. CAC was associated with an increased risk for clinical CAD regardless of the volume of PA.

Is It Possible to Train the Endothelium?-A Narrative Literature Review

This review provides an overview of current knowledge regarding the adaptive effects of physical training on the endothelium. The endothelium plays a crucial role in maintaining the health of vessel walls and regulating vascular tone, structure, and homeostasis. Regular exercise, known for its promotion of cardiovascular health, can enhance endothelial function through various mechanisms. The specific health benefits derived from exercise are contingent upon the type and intensity of physical training. The review examines current clinical evidence supporting exercise's protective effects on the vascular endothelium and identifies potential therapeutic targets for endothelial dysfunction. There is an urgent need to develop preventive strategies and gain a deeper understanding of the distinct impacts of exercise on the endothelium.

Can the Heart Get an Overuse Sports Injury?

Can the Heart Get an Overuse Sports Injury?Recent studies suggest that vigorous endurance exercise increases markers of cardiomyocyte injury and that lifelong endurance exercise may increase myocardial scarring, coronary artery atherosclerosis, AF, and aortic dilatation. This review summarizes the evidence linking these conditions with physical exertion and an approach to their management.

Molecular Mechanisms of Exercise and Healthspan

Healthspan is the period of our life without major debilitating diseases. In the modern world where unhealthy lifestyle choices and chronic diseases taper the healthspan, which lead to an enormous economic burden, finding ways to promote healthspan becomes a pressing goal of the scientific community. Exercise, one of humanity's most ancient and effective lifestyle interventions, appears to be at the center of the solution since it can both treat and prevent the occurrence of many chronic diseases. Here, we will review the current evidence and opinions about regular exercise promoting healthspan through enhancing the functionality of our organ systems and preventing diseases.

Plasma Proteomic Changes of Atherosclerosis after Exercise in ApoE Knockout Mice

Atherosclerosis is the preliminary cause of coronary artery disease, one of the diseases that account for the largest number of fatal mortalities. Physical activity is an effective strategy to restrain atherosclerosis from deterioration. Evidence indicated that changes in the proteomic profile are highly associated with atherosclerosis development, but the mechanism behind exercise for atherosclerosis amelioration has not yet been investigated from a proteomics perspective. Hence, the proteomic profiles could further elucidate the systematic effects of exercise intervention on ApoE knockout atherosclerotic model and high-fat-diet intervention. In the current study, Apoeem1Narl/Narl mice were randomly allocated into a normal diet (ND), Western diet (WD), and WD with 12-week exercise intervention (WD EX) groups. The plasma proteome between WD and WD EX groups demonstrate the significant difference, and ten major pathways, including cardiovascular disease (CVD)–hematological disease, inflammatory disease, infectious diseases, inflammatory response, cell-to-cell signaling and interaction, connective tissue disorders_inflammatory disease, metabolic disease_organismal injury and abnormalities, cell-to-cell signaling and interaction, connective tissue disorders_inflammatory disease, and endocrine system disorders_gastrointestinal disease, etc., were generated by the IPA analysis. The 15 proteins (MYOCD, PROS1, C2, SERPINA10, CRP, F5, C5, CFB, FGG, CFH, F12, PRDX2, PROZ, PPIA, and HABP2) critically involved in CVD–hematological disease pathway showed significant difference between WD and WD EX groups. In current study, exercise could significantly alleviate the significantly elevated C5 and inflammation induced by the WD group in accordance with amelioration of atherosclerosis. Therefore, exercise could mitigate chemotaxis through the modulation of the C5 level and innate immunity, thereby alleviating the pathogenesis of atherosclerosis in Western-diet-induced obese mice.

Endurance exercise training does not limit coronary atherosclerosis in familial hypercholesterolemic swine

Human studies demonstrate that physical activity reduces both morbidity and mortality of coronary heart disease (CHD) including decreased progression and/or regression of CHD with life-style modification which includes exercise. However, evidence supporting an intrinsic, direct effect of exercise in attenuating the development of CHD is equivocal. One limitation has been the lack of a large animal model with clinically evident CHD disease. Thus, we examined the role of endurance exercise in CHD development in a swine model of familial hypercholesterolemia (FH) that exhibits robust, complex atherosclerosis. FH swine were randomly assigned to either sedentary (Sed) or exercise trained (Ex) groups. At 10 months of age, Ex pigs began a 10 months, moderate-intensity treadmill-training intervention. At 14 months, all pigs were switched to a high-fat, high-cholesterol diet. CHD was assessed by intravascular ultrasound (IVUS) both prior to and after completion of 6 months on the HFC diet. Prior to HFC diet, Ex resulted in a greater coronary artery size in the proximal and mid sections of the LCX compared to SED, with no effect in the LAD. After 6 months on HFC diet, there was a 5-6 fold increase in absolute plaque volume in all segments of the LCX and LAD in both groups. At 20 months, there was no difference in vessel volume, lumen volume, absolute or relative plaque volume in either the LCX or LAD between Sed and Ex animals. These findings fail to support an independent, direct effect of exercise in limiting CHD progression in familial hypercholesterolemia.

Cardiorespiratory Fitness and Atherosclerosis: Recent Data and Future Directions

Historically, the relationship between exercise and the cardiovascular system was viewed as unidirectional, with a disease resulting in exercise limitation and hazard. This article reviews and explores the bidirectional nature, delineating the effects, generally positive, on the cardiovascular system and atherosclerosis. Exercise augments eNOS, affects redox potential, and favorably affects mediators of atherosclerosis including lipids, glucose homeostasis, and inflammation. There are direct effects on the vasculature as well as indirect benefits related to exercise-induced changes in body composition and skeletal muscle. Application of aerobic exercise to specific populations is described, with the hope that this knowledge will move the science forward and improve individual patient outcome.

Molecular Mechanisms for Exercise Training-Induced Changes in Vascular Structure and Function: Skeletal Muscle, Cardiac Muscle, and the Brain

Compared with resting conditions, during incremental exercise, cardiac output in humans is elevated from ~5 to 25 L min(-1). In conjunction with this increase, the proportion of cardiac output directed toward skeletal muscle increases from ~20% to 85%, while blood flow to cardiac muscle increases 500% and blood flow to specific brain structures increases nearly 200%. Based on existing evidence, researchers believe that blood flow in these tissues is matched to the increases in metabolic rate during exercise. This phenomenon, the matching of blood flow to metabolic requirement, is often referred to as functional hyperemia. This chapter summarizes mechanical and metabolic factors that regulate functional hyperemia as well as other exercise-induced signals, which are also potent stimuli for chronic adaptations in vascular biology. Repeated exposure to exercise-induced increases in shear stress and the induction of angiogenic factors alter vascular cell gene expression and mediate changes in vascular volume and blood flow control. The magnitude and regulation of this coordinated response appear to be tissue specific and coupled to other factors such as hypertrophy and hyperplasia. The cumulative effects of these adaptations contribute to increased exercise capacity, reduced relative challenge of a given submaximal exercise bout and ameliorated vascular outcomes in patient populations with pathological conditions. In the subsequent discussion, this chapter explores exercise as a regulator of vascular biology and summarizes the molecular mechanisms responsible for exercise training-induced changes in vascular structure and function in skeletal and cardiac muscle as well as the brain.

Lineage-Specific Changes in Biomarkers in Great Apes and Humans

Although human biomedical and physiological information is readily available, such information for great apes is limited. We analyzed clinical chemical biomarkers in serum samples from 277 wild- and captive-born great apes and from 312 healthy human volunteers as well as from 20 rhesus macaques. For each individual, we determined a maximum of 33 markers of heart, liver, kidney, thyroid and pancreas function, hemoglobin and lipid metabolism and one marker of inflammation. We identified biomarkers that show differences between humans and the great apes in their average level or activity. Using the rhesus macaques as an outgroup, we identified human-specific differences in the levels of bilirubin, cholinesterase and lactate dehydrogenase, and bonobo-specific differences in the level of apolipoprotein A-I. For the remaining twenty-nine biomarkers there was no evidence for lineage-specific differences. In fact, we find that many biomarkers show differences between individuals of the same species in different environments. Of the four lineage-specific biomarkers, only bilirubin showed no differences between wild- and captive-born great apes. We show that the major factor explaining the human-specific difference in bilirubin levels may be genetic. There are human-specific changes in the sequence of the promoter and the protein-coding sequence of uridine diphosphoglucuronosyltransferase 1 (UGT1A1), the enzyme that transforms bilirubin and toxic plant compounds into water-soluble, excretable metabolites. Experimental evidence that UGT1A1 is down-regulated in the human liver suggests that changes in the promoter may be responsible for the human-specific increase in bilirubin. We speculate that since cooking reduces toxic plant compounds, consumption of cooked foods, which is specific to humans, may have resulted in relaxed constraint on UGT1A1 which has in turn led to higher serum levels of bilirubin in humans.

Coronary atheroma regression and plaque characteristics assessed by grayscale and radiofrequency intravascular ultrasound after aerobic exercise

The aim of the present study was to investigate effects of aerobic interval training (AIT) versus moderate continuous training (MCT) on coronary atherosclerosis in patients with significant coronary artery disease on optimal medical treatment. Thirty-six patients were randomized to AIT (intervals at ≈ 90% of peak heart rate) or MCT (continuous exercise at ≈ 70% of peak heart rate) 3 times a week for 12 weeks after intracoronary stent implantation. Grayscale and radiofrequency intravascular ultrasounds (IVUS) were performed at baseline and follow-up. The primary end point was the change in plaque burden, and the secondary end points were change in necrotic core and plaque vulnerability. Separate lesions were classified using radiofrequency IVUS criteria. We demonstrated that necrotic core was reduced in both groups in defined coronary segments (AIT -3.2%, MCT -2.7%, p <0.05) and in separate lesions (median change -2.3% and -0.15 mm(3), p <0.05). Plaque burden was reduced by 10.7% in separate lesions independent of intervention group (p = 0.06). No significant differences in IVUS parameters were found between exercise groups. A minority of separate lesions were transformed in terms of plaque vulnerability during follow-up with large individual differences between and within patients. In conclusion, changes in coronary artery plaque structure or morphology did not differ between patients who underwent AIT or MCT. The combination of regular aerobic exercise and optimal medical treatment for 12 weeks induced a moderate regression of necrotic core and plaque burden in IVUS-defined coronary lesions.

Benefits of exercise training on coronary blood flow in coronary artery disease patients

Every 34 seconds an American experiences a myocardial infarction or cardiac death. Approximately 80% of these coronary artery disease (CAD)-related deaths are attributable to modifiable behaviors, such as a lack of physical exercise training (ET). Regular ET decreases CAD morbidity and mortality through systemic and cardiac-specific adaptations. ET increases myocardial oxygen demand acting as a stimulus to increase coronary blood flow and thus myocardial oxygen supply, which reduces myocardial infarction and angina. ET augments coronary blood flow through direct actions on the vasculature that improve endothelial and coronary smooth muscle function, enhancing coronary vasodilation. Additionally, ET promotes collateralization, thereby, increasing blood flow to ischemic myocardium and also treats macrovascular CAD by attenuating the progression of coronary atherosclerosis and restenosis, potentially through stabilization of atherosclerotic lesions. In summary, ET can be used as a relatively safe and inexpensive way to prevent and treat CAD.

Exercise training in hypertension: Role of microRNAs

Hypertension is a complex disease that constitutes an important public health problem and demands many studies in order to understand the molecular mechanisms involving his pathophysiology. Therefore, an increasing number of studies have been conducted and new therapies are continually being discovered. In this context, exercise training has emerged as an important non-pharmacological therapy to treat hypertensive patients, minimizing the side effects of pharmacological therapies and frequently contributing to allow pharmacotherapy to be suspended. Several mechanisms have been associated with the pathogenesis of hypertension, such as hyperactivity of the sympathetic nervous system and renin-angiotensin aldosterone system, impaired endothelial nitric oxide production, increased oxygen-reactive species, vascular thickening and stiffening, cardiac hypertrophy, impaired angiogenesis, and sometimes genetic predisposition. With the advent of microRNAs (miRNAs), new insights have been added to the perspectives for the treatment of this disease, and exercise training has been shown to be able to modulate the miRNAs associated with it. Elucidation of the relationship between exercise training and miRNAs in the pathogenesis of hypertension is fundamental in order to understand how exercise modulates the cardiovascular system at genetic level. This can be promising even for the development of new drugs. This article is a review of how exercise training acts on hypertension by means of specific miRNAs in the heart, vascular system, and skeletal muscle.

Peripheral circulation

Blood flow (BF) increases with increasing exercise intensity in skeletal, respiratory, and cardiac muscle. In humans during maximal exercise intensities, 85% to 90% of total cardiac output is distributed to skeletal and cardiac muscle. During exercise BF increases modestly and heterogeneously to brain and decreases in gastrointestinal, reproductive, and renal tissues and shows little to no change in skin. If the duration of exercise is sufficient to increase body/core temperature, skin BF is also increased in humans. Because blood pressure changes little during exercise, changes in distribution of BF with incremental exercise result from changes in vascular conductance. These changes in distribution of BF throughout the body contribute to decreases in mixed venous oxygen content, serve to supply adequate oxygen to the active skeletal muscles, and support metabolism of other tissues while maintaining homeostasis. This review discusses the response of the peripheral circulation of humans to acute and chronic dynamic exercise and mechanisms responsible for these responses. This is accomplished in the context of leading the reader on a tour through the peripheral circulation during dynamic exercise. During this tour, we consider what is known about how each vascular bed controls BF during exercise and how these control mechanisms are modified by chronic physical activity/exercise training. The tour ends by comparing responses of the systemic circulation to those of the pulmonary circulation relative to the effects of exercise on the regional distribution of BF and mechanisms responsible for control of resistance/conductance in the systemic and pulmonary circulations.

The cerebral vasculature as a therapeutic target for neurological disorders and the role of shear stress in vascular homeostatis and pathophysiology

It is widely accepted that vascular mechanisms are involved in the genesis of many neurological disorders. In particular, blood-brain barrier (BBB) dysfunction has been related to the severity of Alzheimer's disease, encephalopathy due to meningitis, multiple sclerosis, HIV-associated encephalopathy, epilepsy, gliomas and metastatic brain tumors. The BBB may constitute an important therapeutic target to protect neurons after CNS diseases. Both in vivo and in vitro, the functional phenotype of vascular endothelium is dynamically responsive to circulating cytokines, growth factors and puslatile blood flow (shear stress). Shear stress can play a critical role in vascular homeostasis and pathophysiology; it is a major regulator of remodeling in developed blood vessels and in blood vessels affected by atherosclerotic lesions. The physiological fluid mechanic stimulus, shear stress, could be considered to be an important 'differentiative' stimulus capable of modulating endothelial phenotype in vivo. Endothelial cells undergo cell cycle arrest after exposure to physiological levels of shear stress. As for mature endothelial cells, in which flow mediated shear stress may play a role in the induction, progression and/or prevention of atherosclerosis by changing their function, stress may play a role in endothelial cell differentiation from hemopoietic stem cells and/or from embryonic stem cells. Stem cells may be used to repair vascular damage, including loss of EC, due to a variety of diseases (e.g. myocardial neovascularization by adult bone marrow derived angioblasts). In the brain, it was proposed that neuron-producing stem cells may be used to treat Alzheimer's disease, paralysis, etc. Surprisingly, very few investigators are exploring the use of endothelial precursors to revert or prevent cerebrovascular disease. This review summarizes the most recent data related to cerebral vasculature as a therapeutic target for neurological disorders and the role of shear stress in blood-brain barrier homeostasis and pathophysiology.

Bile acid sequestration normalizes plasma cholesterol and reduces atherosclerosis in hypercholesterolemic mice. No additional effect of physical activity

AIMS

Bile acid sequestrants (BAS) and physical activity (RUN) decrease incidence of cardiovascular events. Both treatments are often prescribed, yet it is not known whether their beneficial effects are additive. We assessed the effects of BAS treatment alone and in combination with RUN on cholesterol metabolism, heart function and atherosclerotic lesion size in hypercholesterolemic mice.

METHODS

Male Ldlr-deficient mice remained either sedentary (CONTROL), were treated with Colesevelam HCl (BAS), had access to a running wheel (RUN), or were exposed to BAS and RUN (BAS RUN). All groups were fed a high cholesterol diet for 12 weeks. Then, feces, bile and plasma were collected. Atherosclerotic lesion size was determined in the aortic arch and heart function by echocardiography.

RESULTS

BAS RUN ran more than RUN (6.4 ± 1.4 vs. 3.5 ± 1.0 km/day, p < 0.05). BAS and BAS RUN displayed ~3-fold reductions in plasma cholesterol levels (p < 0.001), ~2.5-fold increases in fecal neutral sterol (p < 0.001) and bile acid (p = 0.01) outputs, decreases in biliary secretions of cholesterol (~6-fold, p < 0.0001) and bile acids (~2-fold, p < 0.001) vs. CONTROL while no significant effects were observed in RUN. Compared to CONTROL, lesion size decreased by 78% in both BAS and BAS RUN, (p < 0.0001).

CONCLUSION

BAS reduce atherosclerosis in Ldlr-deficient mice, coinciding with a switch from body cholesterol accumulation to cholesterol loss. RUN slightly modulated atherosclerotic lesion formation but the combination of BAS and RUN had no clear additive effects in this respect.

The effect of creatine supplementation on myocardial function, mitochondrial respiration and susceptibility to ischaemia/reperfusion injury in sedentary and exercised rats

AIM

To investigate the effects of dietary creatine supplementation alone and in combination with exercise on basal cardiac function, susceptibility to ischaemia/reperfusion injury and mitochondrial oxidative function. There has been an increase in the use of creatine supplementation among sports enthusiasts, and by clinicians as a therapeutic agent in muscular and neurological diseases. The effects of creatine have been studied extensively in skeletal muscle, but not in the myocardium.

METHODS

Male Wistar rats were swim-trained for 8 weeks, 5 days per week. Hearts were excised and either freeze-clamped for biochemical analysis or perfused on the isolated heart perfusion system to assess function and ischaemia/reperfusion tolerance. Mechanical function was documented in working heart and retrograde mode. The left coronary artery was ligated and infarct size determined. Mitochondrial oxidative capacity was quantified.

RESULTS

Aortic output recovery of hearts from the sedentary controls (CSed) was significantly higher than those from creatine-supplemented sedentary (CrSed), creatine-supplemented exercised (CrEx) as well as control exercised (CEx) groups. Ischaemic contracture of hearts from CrEx was significantly higher than that of CSed. There were no differences in infarct size and mitochondrial oxygen consumption.

CONCLUSION

This study suggests that creatine supplementation has no effects on basal cardiac function but reduces myocardial tolerance to ischaemia in hearts from exercise-trained animals, by increasing the ischaemic contracture and decreasing reperfusion aortic output. Exercise training alone also significantly decreased aortic output recovery. However, the exact mechanisms for these adverse myocardial effects are unknown and need further investigation.

Exercise does not attenuate early CAD progression in a pig model

PURPOSE

This study was designed to examine the effects of high-fat (HF) diet and subsequent exercise training (Ex) on coronary arteries of an animal model of early stage CAD. We hypothesized that HF diet would induce early stage disease and promote a proatherogenic coronary phenotype, whereas Ex would blunt disease progression and induce a healthier anti-inflammatory environment reflected by the increased expression of antioxidant capacity and the decreased expression of inflammatory markers in both the macrovasculature and the microvasculature of the coronary circulation.

METHODS

Immunohistochemistry in left anterior descending and right coronary arteries and immunoblots in left anterior descending and left ventricular arterioles were used to characterize the effects of HF diet and Ex on the progression of coronary atherosclerosis.

RESULTS

Our results revealed that HF diet promoted a proatherogenic coronary endothelial cell phenotype as evidenced by the endothelial expression of inflammatory and oxidative stress markers. Ex did not significantly alter any of these immunohistochemical markers in conduit arteries; however, Ex did increase antioxidant protein content in left ventricular arterioles.

CONCLUSIONS

We conclude that, at this early stage of CAD, Ex did not seem to modify vascular cell phenotypes of conduit coronary arteries from proatherogenic to a more favorable antiatherogenic status; however, Ex increased antioxidant protein content in coronary arterioles. These findings also support the idea that endothelial phenotype expression follows different patterns in the macrovasculature and microvasculature of the coronary circulation.

The coronary circulation in exercise training

Exercise training (EX) induces increases in coronary transport capacity through adaptations in the coronary microcirculation including increased arteriolar diameters and/or densities and changes in the vasomotor reactivity of coronary resistance arteries. In large animals, EX increases capillary exchange capacity through angiogenesis of new capillaries at a rate matched to EX-induced cardiac hypertrophy so that capillary density remains normal. However, after EX coronary capillary exchange area is greater (i.e., capillary permeability surface area product is greater) at any given blood flow because of altered coronary vascular resistance and matching of exchange surface area and blood flow distribution. The improved coronary capillary blood flow distribution appears to be the result of structural changes in the coronary tree and alterations in vasoreactivity of coronary resistance arteries. EX also alters vasomotor reactivity of conduit coronary arteries in that after EX, α-adrenergic receptor responsiveness is blunted. Of interest, α- and β-adrenergic tone appears to be maintained in the coronary microcirculation in the presence of lower circulating catecholamine levels because of increased receptor responsiveness to adrenergic stimulation. EX also alters other vasomotor control processes of coronary resistance vessels. For example, coronary arterioles exhibit increased myogenic tone after EX, likely because of a calcium-dependent PKC signaling-mediated alteration in voltage-gated calcium channel activity in response to stretch. Conversely, EX augments endothelium-dependent vasodilation throughout the coronary arteriolar network and in the conduit arteries in coronary artery disease (CAD). The enhanced endothelium-dependent dilation appears to result from increased nitric oxide bioavailability because of changes in nitric oxide synthase expression/activity and decreased oxidant stress. EX also decreases extravascular compressive forces in the myocardium at rest and at comparable levels of exercise, mainly because of decreases in heart rate and duration of systole. EX does not stimulate growth of coronary collateral vessels in the normal heart. However, if exercise produces ischemia, which would be absent or minimal under resting conditions, there is evidence that collateral growth can be enhanced. While there is evidence that EX can decrease the progression of atherosclerotic lesions or even induce the regression of atherosclerotic lesions in humans, the evidence of this is not strong due to the fact that most prospective trials conducted to date have included other lifestyle changes and treatment strategies by necessity. The literature from large animal models of CAD also presents a cloudy picture concerning whether EX can induce the regression of or slow the progression of atherosclerotic lesions. Thus, while evidence from research using humans with CAD and animal models of CAD indicates that EX increases endothelium-dependent dilation throughout the coronary vascular tree, evidence that EX reverses or slows the progression of lesion development in CAD is not conclusive at this time. This suggests that the beneficial effects of EX in CAD may not be the result of direct effects on the coronary artery wall. If this suggestion is true, it is important to determine the mechanisms involved in these beneficial effects.

The forgotten face of regular physical exercise: a 'natural' anti-atherogenic activity

Humans are not programmed to be inactive. The combination of both accelerated sedentary lifestyle and constant food availability disturbs ancient metabolic processes leading to excessive storage of energy in tissue, dyslipidaemia and insulin resistance. As a consequence, the prevalence of Type 2 diabetes, obesity and the metabolic syndrome has increased significantly over the last 30 years. A low level of physical activity and decreased daily energy expenditure contribute to the increased risk of cardiovascular morbidity and mortality following atherosclerotic vascular damage. Physical inactivity leads to the accumulation of visceral fat and consequently the activation of the oxidative stress/inflammation cascade, which promotes the development of atherosclerosis. Considering physical activity as a 'natural' programmed state, it is assumed that it possesses atheroprotective properties. Exercise prevents plaque development and induces the regression of coronary stenosis. Furthermore, experimental studies have revealed that exercise prevents the conversion of plaques into a vulnerable phenotype, thus preventing the appearance of fatal lesions. Exercise promotes atheroprotection possibly by reducing or preventing oxidative stress and inflammation through at least two distinct pathways. Exercise, through laminar shear stress activation, down-regulates endothelial AT1R (angiotensin II type 1 receptor) expression, leading to decreases in NADPH oxidase activity and superoxide anion production, which in turn decreases ROS (reactive oxygen species) generation, and preserves endothelial NO bioavailability and its protective anti-atherogenic effects. Contracting skeletal muscle now emerges as a new organ that releases anti-inflammatory cytokines, such as IL-6 (interleukin-6). IL-6 inhibits TNF-α (tumour necrosis factor-α) production in adipose tissue and macrophages. The down-regulation of TNF-α induced by skeletal-muscle-derived IL-6 may also participate in mediating the atheroprotective effect of physical activity.

Ca2+ regulatory mechanisms of exercise protection against coronary artery disease in metabolic syndrome and diabetes

Chronic exercise attenuates coronary artery disease (CAD) in humans largely independent of reductions in risk factors; thus major protective mechanisms of exercise are directly within the coronary vasculature. Further, tight control of diabetes, e.g., blood glucose, can be detrimental. Accordingly, knowledge of mechanisms by which exercise attenuates diabetic CAD could catalyze development of molecular therapies. Exercise attenuates CAD (atherosclerosis) and restenosis in miniature swine models, which enable precise control of exercise parameters (intensity, duration, and frequency) and characterization of the metabolic syndrome (MetS) and diabetic milieu. Intracellular Ca(2+) is a pivotal second messenger for coronary smooth muscle (CSM) excitation-contraction and excitation-transcription coupling that modulates CSM proliferation, migration, and calcification. CSM of diabetic dyslipidemic Yucatan swine have impaired Ca(2+) extrusion via the plasmalemma Ca(2+) ATPase (PMCA), downregulation of L-type voltage-gated Ca(2+) channels (VGCC), increased Ca(2+) sequestration by the sarcoplasmic reticulum (SR) Ca(2+) ATPase (SERCA), increased nuclear Ca(2+) localization, and greater activation of K channels by Ca(2+) release from the SR. Endurance exercise training prevents Ca(2+) transport changes with virtually no effect on the diabetic milieu (glucose, lipids). In MetS Ossabaw swine transient receptor potential canonical (TRPC) channels are upregulated and exercise training reverses expression and TRPC-mediated Ca(2+) influx with almost no change in the MetS milieu. Overall, exercise effects on Ca(2+) signaling modulate CSM phenotype. Future studies should 1) selectively target key Ca(2+) transporters to determine definitively their causal role in atherosclerosis and 2) combine mechanistic studies with clinical outcomes, e.g., reduction of myocardial infarction.

Voluntary exercise ameliorates the progression of atherosclerotic lesion formation via anti-inflammatory effects in apolipoprotein E-deficient mice

AIM

A sedentary lifestyle with insufficient exercise is associated with cardiovascular disease. Previous studies have demonstrated that endurance exercise benefits atherosclerosis and cardiovascular disorders; however, the mechanisms by which physical activity, such as voluntary exercise (Ex), produces these effects are not fully understood.

METHODS AND RESULTS

Eight-week-old male apolipoprotein (ApoE)-deficient mice were fed a standard diet (STD) or high fat diet (HFD) for 10 weeks. The HFD+Ex group mice performed Ex on a running wheel for 10 weeks. No significant differences in lipid profiles were observed between the HFD and HFD+Ex groups. Although changes in body and brown adipose tissue weights were comparable between the HFD and HFD+Ex groups, white adipose tissue weight was significantly lower in the HFD+Ex group than in the HFD group. The areas of atherosclerotic lesions in the aortic sinus and thoracoabdominal aorta were significantly reduced in the HFD+Ex group than in the HFD group (p<0.001). There was a strong negative correlation between atherosclerotic areas and the mean running distance per day in the HFD+Ex group (r=-0.90, p=0.01). Endothelial function was significantly preserved in the HFD+Ex group (p<0.05). Serum interleukin-6 and macrophage chemoattractant protein-1 levels were significantly lower and those of adiponectin were significantly higher in the HFD+Ex group than in the HFD group (p<0.05).

CONCLUSIONS

These results suggest that Ex ameliorates the progression of endothelial dysfunction and atherosclerotic lesion formation through anti-inflammatory effects, despite continued consumption of HFD.

Impact of inactivity and exercise on the vasculature in humans

The effects of inactivity and exercise training on established and novel cardiovascular risk factors are relatively modest and do not account for the impact of inactivity and exercise on vascular risk. We examine evidence that inactivity and exercise have direct effects on both vasculature function and structure in humans. Physical deconditioning is associated with enhanced vasoconstrictor tone and has profound and rapid effects on arterial remodelling in both large and smaller arteries. Evidence for an effect of deconditioning on vasodilator function is less consistent. Studies of the impact of exercise training suggest that both functional and structural remodelling adaptations occur and that the magnitude and time-course of these changes depends upon training duration and intensity and the vessel beds involved. Inactivity and exercise have direct "vascular deconditioning and conditioning" effects which likely modify cardiovascular risk.

The effect of physical exercise on endothelial function

Endothelium is essential for maintenance of health of the vessel wall and for the local regulation of vascular tone and structure and haemostasis. Regular physical exercise, which is known to promote a favourable cardiovascular state, may improve endothelial function via several mechanisms. Indeed, it augments blood flow and laminar shear stress, resulting in increased nitric oxide production and bioavailability. In this regard, the beneficial effects of training on endothelial function can be mediated in a number of ways, including synthesis of molecular mediators, changes in neurohormonal release and oxidant/antioxidant balance. On the other hand, physical exercise can also elicit systemic molecular pathways connected with angiogenesis and chronic anti-inflammatory action with consequent modification of the endothelial function. However, its benefit depends on the type and intensity of training performed. While strenuous exercise increases oxidative metabolism and produces a pro-oxidant environment, only regular moderate physical activity promotes an antioxidant state and preserves endothelial function. Thus, exercise may have a beneficial effect on the development of cardiovascular disease through preserving endothelial function.

Plasma nitrate/nitrite levels are unchanged after long-term aerobic exercise training in older adults

Reduced nitric oxide (NO) production and bioactivity is a major contributor to endothelial dysfunction. Animal data suggest that improvements in endothelial function in response to aerobic exercise training may depend on the duration of the training program. However, no studies have examined changes in NO (as assessed by the major NO metabolites, nitrate and nitrite, NO(x)) after long-term training in humans. In addition, aging may impair the ability of the vasculature to increase NO with exercise. Thus, we determined whether 24 weeks of aerobic exercise training increases plasma NO(x) levels in sedentary older adults. We also examined changes in forearm blood flow (FBF) at rest and during reactive hyperemia as a measure of vasomotor function. Plasma NO(x) levels were measured in 82 men and women using a modified Griess assay. FBF was assessed in a subset of individuals (n = 15) using venous occlusion plethysmography. After 24 weeks of exercise training, there were significant improvements in maximum oxygen consumption, HDL cholesterol, triglycerides, and body fat. Changes in plasma NO(x) levels ranged from -14.83 to +16.69 micromol/L; however, the mean change overall was not significant (-0.33 + or - 6.30 micromol/L, p = 0.64). Changes in plasma NO(x) levels were not associated with age, gender, race, HDL cholesterol, triglycerides, body weight, body fat, or maximal oxygen consumption. There were also no significant changes in basal FBF, peak FBF, hyperemic response, total hyperemic flow, or minimum forearm vascular resistance with exercise training. In conclusion, improvements in plasma NO(x) levels and FBF are not evident after long-term training in older adults.

Changes in abdominal aortic diameter in response to the cold pressor test and nitroglycerin: a new noninvasive model for the assessment of endothelial-dependent and endothelial-independent vascular relaxation

Coronary vascular responses to the cold pressor test (CPT) have been shown to parallel changes caused by infusion of acetylcholine. Whereas the CPT is a method of assessing endothelial-dependent vasodilation, nitroglycerin produces endothelial-independent vasodilation. We performed histological studies on autopsy specimens of abdominal aorta and demonstrated that it is predominantly muscular artery. To test the hypothesis that vasodilatory responses of the abdominal aorta to interventions would parallel those of peripheral vessels, 33 normal males without hypertension, diabetes, or hyperlipidemia, and 10 younger male smokers had ultrasound imaging of the abdominal aorta conducted in the control state, 2 minutes after immersion of the hand in cold water and 10 minutes after rewarming the hand (i.e., cold pressor test). The internal diameter of the abdominal aorta at the onset of the QRS complex was determined for each intervention by averaging 4 beats. It was found that the cold pressor test and nitroglycerin resulted in similar degrees of dilation of the abdominal aorta in nonsmoking subjects, and that these responses were attenuated in smokers. Thus, both endothelial-dependent and endothelial-independent vascular relaxation were impaired in smokers.

Gene expression profile of rat left ventricles reveals persisting changes following chronic mild exercise protocol: implications for cardioprotection

Background

Epidemiological studies showed that physical exercise, specifically moderate lifelong training, is protective against cardiovascular morbidity and mortality. Most experimental work has focused into the effects and molecular mechanisms underlying intense, rather than mild exercise, by exploring the acute effect of training. Our study aims at investigating the cardioprotective effect of mild chronic exercise training and the gene expression profile changes at 48 hrs after the exercise cessation. Rats were trained at mild intensity on a treadmill: 25 m/min, 10%incline, 1 h/day, 3 days/week, 10 weeks; about 60% of the maximum aerobic power. By Affymetrix technology, we investigated the gene expression profile induced by exercise training in the left ventricle (LV) of trained (n = 10) and control (n = 10) rats. Cardioprotection was investigated by ischemia/reperfusion experiments (n = 10 trained vs. n = 10 control rats).

Results

Mild exercise did not induce cardiac hypertrophy and was cardioprotective as demonstrated by the decreased infarct size (p = 0.02) after ischemia/reperfusion experiments in trained with respect to control rats. Ten genes and 2 gene sets (two pathways) resulted altered in LV of exercised animals with respect to controls. We validated by real-time PCR the increased expression of four genes: similar to C11orf17 protein (RGD1306959), caveolin 3, enolase 3, and hypoxia inducible factor 1 alpha. Moreover, caveolin 3 protein levels were higher in exercised than control rats by immunohistochemistry and Western Blot analysis. Interestingly, the predicted gene similar to C11orf17 protein (RGD1306959) was significantly increased by exercise. This gene has a high homology with the human C11orf17 (alias: protein kinase-A interacting protein 1 or breast cancer associated gene 3). This is the first evidence that this gene is involved in the response to the exercise training.

Conclusion

Our data indicated that few, but significant, genes characterize the gene expression profile of the rat LV, when examined 48 hrs since the last training section and that mild exercise training determines cardioprotection without the induction of hypertrophy.

Voluntary running suppresses proinflammatory cytokines and bone marrow endothelial progenitor cell levels in apolipoprotein-E-deficient mice

Long-term exercise is associated with reduced atherosclerotic burden, inflammation, and enhanced endothelial progenitor cell (EPC) levels in mice. Infusion of progenitor cells in mice decreases atherosclerosis and suppresses inflammation. The aim of this study was to determine whether exercise-induced enhancement of EPCs is associated with reduced atherosclerosis and inflammation. To study this, 20-week old ApoE(-/-) mice with advanced atherosclerotic lesions (n = 12/group) were randomized to voluntary running or no running for 8 weeks. Exercise led to a potent suppression of elevated circulating proinflammatory cytokines without significant reduction of atherosclerotic lesions. When repeated in ApoE(-/-) mice with early atherosclerotic disease, exercise led to a 62% (p = 0.017) reduction in lesion thickness (intima-to-media ratio) at the aortic root. Interestingly, BM-EPC levels were significantly elevated under proinflammatory conditions seen in ApoE(-/-) mice and decreased in response to exercise, independent of the degree of atherosclerosis. Under early atherosclerotic conditions, long-term exercise reduces atherosclerotic plaque burden and is associated with reduced systemic inflammation. Elevated BM-EPCs seen in atherosclerotic conditions may be a marker of generalized vascular inflammation or injury, and decrease in response to exercise, along with other markers of inflammation.

Time course of change in vasodilator function and capacity in response to exercise training in humans

Studies of the impact of exercise training on arterial adaptation in healthy subjects have produced disparate results. It is possible that some studies failed to detect changes because functional and structural adaptations follow a different time course and may therefore not be detected at discrete time points. To gain insight into the time course of training-induced changes in artery function and structure, we examined conduit artery flow mediated dilatation (FMD), an index of nitric oxide (NO)-mediated artery function, and conduit dilator capacity (DC), a surrogate marker for arterial remodelling, in the brachial and popliteal arteries of 13 healthy male subjects (21.6 +/- 0.6 years) and seven non-active controls (22.8 +/- 0.2 years) studied at 2-week intervals across an 8-week cycle and treadmill exercise training programme. Brachial and popliteal artery FMD and DC did not change in control subjects at any time point. FMD increased from baseline (5.9 +/- 0.5%) at weeks 2 and 4 (9.1 +/- 0.6, 8.5 +/- 0.6%, respectively, P < 0.01), but returned towards baseline levels again by week 8 (6.9 +/- 0.7%). In contrast, brachial artery DC progressively increased from baseline (8.1 +/- 0.4%) at weeks 2, 4, 6 and 8 (9.2 +/- 0.6, 9.9 +/- 0.6, 10.0 +/- 0.5, 10.5 +/- 0.8%, P < 0.05). Similarly, popliteal artery FMD increased from baseline (6.2 +/- 0.7%) at weeks 2, 4 and 6 (9.1 +/- 0.6, 9.5 +/- 0.6, 7.8 +/- 0.5%, respectively, P < 0.05), but decreased again by week 8 (6.5 +/- 0.6%), whereas popliteal DC progressively increased from baseline (8.9 +/- 0.4%) at week 4 and 8 (10.5 +/- 0.7, 12.2 +/- 0.6%, respectively, P < 0.05). These data suggest that functional changes in conduit arteries occur rapidly and precede arterial remodelling in vivo. These data suggest that complimentary adaptations occur in arterial function and structure and future studies should adopt multiple time point assessments to comprehensively assess arterial adaptations to interventions such as exercise training in humans.

Is the anti-inflammatory effect of regular exercise responsible for reduced cardiovascular disease?

Engaging in regular physical activity reduces the risk of developing CVD (cardiovascular disease), but it is not certain to what degree this may be due to the anti-inflammatory effects of exercise. Following acute exercise, there is a transient increase in circulating levels of anti-inflammatory cytokines, whereas chronic exercise reduces basal levels of pro-inflammatory cytokines. Exercise training also induces the expression of antioxidant and anti-inflammatory mediators in the vascular wall that may directly inhibit the development of atherosclerosis. Limited studies in humans and more comprehensive assessments in animal models have confirmed that exercise is atheroprotective and helped identify a number of the mechanisms to explain these effects. This review explores the relationship between systemic and vascular wall inflammation and the role that the anti-inflammatory effects of exercise have on the development and progression of CVD.

Combined Work and Leisure Physical Activity and Risk of Stroke in Men and Women in the European Prospective Investigation into Cancer-Norfolk Prospective Population Study

Most studies to date support a protective role of physical activity in reducing stroke risk. However, they were not able to take into account combined work and leisure activity. We prospectively followed up 22,602 men and women aged 40-79 years, who had no history of stroke and myocardial infarction at baseline, participating in the European Prospective Investigation into Cancer-Norfolk. Participants were categorized into four levels of physical activity based on a validated self-reported questionnaire, which assesses combined work and leisure activities, at baseline during the period from 1993 to 1997. Stroke incidence was ascertained by death certificate and hospital record linkage data up to 2004, average 8.6 years of follow-up. We used the Cox proportional hazards model. There were 361 incident strokes during follow-up (total person years = 195,092). After adjusting for age, sex, systolic blood pressure, body mass index, cholesterol, history of diabetes and smoking, men and women who were physically active were less likely to have a stroke (relative risk = 0.70, 95% CI: 0.49-0.99, p = 0.024) compared to those who were inactive. This highlights the fact that efforts to increase physical activity in both the work place and in leisure time should be encouraged.

Physical training and metabolic supplementation reduce spontaneous atherosclerotic plaque rupture and prolong survival in hypercholesterolemic mice

Moderate physical exercise (PE) combined with metabolic treatment (MT) (antioxidants and l-arginine) are well known to reduce atherosclerotic lesion formation in hypercholesterolemic mice. However, the long-term beneficial effects on unstable atheroma remain poorly understood. We started early PE training in large groups of 6-week-old hypercholesterolemic mice (by graduated swimming) alone or in combination with nutritional supplementation (1.0% vitamin E added to the chow and 0.05% vitamin C and 6% l-arginine added to the drinking water). Inactive controls did not receive PE. The spontaneous development of atherosclerotic plaque rupture (associated with advanced atherosclerosis) and survival rates were evaluated. Moderate PE elicited an increase in plasma levels of nitric oxide. Early combined treatment with PE and MT in the hypercholesterolemic mice significantly reduced lesions (also detected noninvasively at 10 months) and spontaneous atherosclerotic plaque rupture and prolonged survival more effectively than each intervention alone. Thus, early concerted actions of MT and PE improve the natural history of atherosclerotic lesions and reduce the plaque instability in hypercholesterolemic mice.

Exercise and the coronary circulation-alterations and adaptations in coronary artery disease

Coronary vasorelaxation depends on nitric oxide (NO) bioavailability, which is a function of endothelial nitric oxide synthase-derived NO production and NO inactivation by reactive oxygen species. This fine-tuned balance is disrupted in coronary artery disease (CAD). The impairment of NO production in conjunction with excessive oxidative stress promotes the loss of endothelial cells by apoptosis, leads to a further aggravation of endothelial dysfunction and triggers myocardial ischemia in CAD. In healthy individuals, increased release of NO from the vasculature in response to exercise training results from changes in endothelial nitric oxide synthase expression, phosphorylation, and conformation. However, exercise training has assumed a role in cardiac rehabilitation of patients with CAD, as well, because it reduces mortality and increases myocardial perfusion. This has been largely attributed to exercise training-mediated correction of coronary endothelial dysfunction in CAD. Indeed, regular physical activity restores the balance between NO production and NO inactivation by reactive oxygen species in CAD, thereby enhancing the vasodilatory capacity in different vascular beds. Because endothelial dysfunction has been identified as a predictor of cardiovascular events, the partial reversal of endothelial dysfunction secondary to exercise training might be the most likely mechanism responsible for the exercise training-induced reduction in cardiovascular morbidity and mortality in patients with CAD.

Vascular nitric oxide and oxidative stress: determinants of endothelial adaptations to cardiovascular disease and to physical activity

Cardiovascular disease is the single leading cause of death and morbidity for Canadians. A universal feature of cardiovascular disease is dysfunction of the vascular endothelium, thus disrupting control of vasodilation, tissue perfusion, hemostasis, and thrombosis. Nitric oxide bioavailability, crucial for maintaining vascular endothelial health and function, depends on the processes controlling synthesis and destruction of nitric oxide as well as on the sensitivity of target tissue to nitric oxide. Evidence supports a major contribution by oxidative stress-induced destruction of nitric oxide to the endothelial dysfunction that accompanies a number of cardiovascular disease states including hypertension, diabetes, chronic heart failure, and atherosclerosis. Regular physical activity (exercise training) reduces cardiovascular disease risk. Numerous studies support the hypothesis that exercise training improves vascular endothelial function, especially when it has been impaired by preexisting risk factors. Evidence is emerging to support a role for improved nitric oxide bioavailability with training as a result of enhanced synthesis and reduced oxidative stress-mediated destruction. Molecular targets sensitive to the exercise training effect include the endothelial nitric oxide synthase and the antioxidant enzyme superoxide dismutase. However, many fundamental details of the cellular and molecular mechanisms linking exercise to altered molecular and functional endothelial phenotypes have yet to be discovered. The working hypothesis is that some of the cellular mechanisms contributing to endothelial dysfunction in cardiovascular disease can be targeted and reversed by signals associated with regular increases in physical activity. The capacity for exercise training to regulate vascular endothelial function, nitric oxide bioavailability, and oxidative stress is an example of how lifestyle can complement medicine and pharmacology in the prevention and management of cardiovascular disease.

Moderate regular exercise increases basal production of nitric oxide in elderly women

Vascular endothelial cells produce nitric oxide (NO), which is a potent vasodilator substance and is thought to have antiatherosclerotic properties. Therefore, it has also been proposed that NO may be useful to regulate vascular tonus and prevent progression of atherosclerosis. On the other hand, NO activity reduces with aging. We previously reported that the plasma nitrite/nitrate (NOx: the stable end product of NO) concentration was significantly increased by intense aerobic exercise training in healthy young humans. We hypothesized that lifestyle modification (e.g., even mild regular exercise training) can increase NO production in previously sedentary older humans. We measured the plasma NOx concentration before and after a mild aerobic exercise training regimen (cycling on a leg ergometer at 80% ventilatory threshold for 30 min, 5 days/week) for 3 months in elderly women. In addition, we assessed the plasma concentration of cyclic guanosine monophosphate (cGMP), a second messenger of NO, in the same samples. The individual ventilatory threshold increased significantly after the 3-month exercise training. The blood pressure at rest significantly decreased after exercise training. These results suggest that the 3-month exercise training in the older women produced favorable physiological effects. The plasma concentration of NOx significantly increased by the exercise training, and the plasma concentration of cGMP also increased by the exercise training. The present study suggests that even a mild regular aerobic-endurance exercise increases NO production in previously sedentary older humans, which may have beneficial effects (i.e., antihypertensive and antiatherosclerotic effects by endogenous NO) on the cardiovascular system.

Exercise reduces preexisting atherosclerotic lesions in LDL receptor knock out mice

Exercise is recommended both as a prophylactic and also as a therapeutic approach for patients with established coronary artery disease. In this study, we investigated the effect of a normal chow diet, with or without exercise in LDL r-/- mice with preexisting atherosclerotic lesions. A total of 28 LDL r-/- mice (LDL receptor knock out mice, 4-6 weeks old) were fed a high fat, high cholesterol diet (inductive phase). At the end of the 3 months, eight mice were sacrificed, and plasma autoantibodies to oxidatively modified proteins, cholesterol levels, and surface area of the lesions in the aorta were determined. The remaining mice were divided into two groups, and placed on a normal chow diet alone, or normal chow and exercise for three more months (regressive phase). Plasma autoantibodies to oxidatively modified proteins and cholesterol were measured along with the lesion size. Compared to the group of animals at the end of the inductive phase, both the groups of animals in the regressive phase had very low levels of plasma cholesterol and autoantibodies, and almost a 50% reduction in the aortic lesion area. The group that was exercised had the lowest levels of autoantibodies and aortic lesions as compared to the group without the exercise. However, the plasma cholesterol levels were comparable in both groups. This study demonstrates that reduction of preexisting atherosclerotic lesions is accelerated dramatically by exercise in LDL r-/- mice.

Physical activity and atherosclerosis: which animal model?

Atherosclerosis is a progressive disease that is the most important single contributor to human cardiovascular morbidity and mortality. Epidemiologic studies show that physical activity, or routine exercise, reduces the risk of developing cardiovascular disease. The mechanisms through which exercise may function in primary or secondary prevention of atherosclerosis remain largely to be established. Most studies in humans are performed after the onset of clinical signs when disease is well advanced and the prescription of exercise is based on empirical evidence of benefit in secondary prevention. Animal models per-mit the study of the initiation and progression of preclinical stages of atherosclerosis. In order to provide information relevant to treatment and prevention, these models should mimic human disease and interactions of physical activity with disease processes as closely as possible. The purpose of this review is to compare animal models of atherosclerosis and to summarize the available data in those models in regard to the effects of exercise.

Aggressive diets and lipid responses

Poor diet and physical inactivity, the two major contributors to the development of overweight and obesity, have recently been identified as the second most common actual cause of death in the United States. With the increasing awareness of the strong link between obesity and chronic disease, in particular cardiovascular disease, a myriad of diets have surfaced and many of them claim weight loss depends more on the macronutrient composition of the diet than the number of calories consumed. Long-term outcome data, particularly cardiovascular outcome data, on these diets are sparse. This article summarizes previous and recent reports of popular and aggressive diets, such as low-carbohydrate diets, low-fat diets, and very low-calorie diets, addressing their effects on weight loss and focusing on their effects on lipids and lipoproteins.

Effect of exercise training on endothelium-derived nitric oxide function in humans

Vascular endothelial function is essential for maintenance of health of the vessel wall and for vasomotor control in both conduit and resistance vessels. These functions are due to the production of numerous autacoids, of which nitric oxide (NO) has been the most widely studied. Exercise training has been shown, in many animal and human studies, to augment endothelial, NO-dependent vasodilatation in both large and small vessels. The extent of the improvement in humans depends upon the muscle mass subjected to training; with forearm exercise, changes are restricted to the forearm vessels while lower body training can induce generalized benefit. Increased NO bioactivity with exercise training has been readily and consistently demonstrated in subjects with cardiovascular disease and risk factors, in whom antecedent endothelial dysfunction exists. These conditions may all be associated with increased oxygen free radicals which impact on NO synthase activity and with which NO reacts; repeated exercise and shear stress stimulation of NO bioactivity redresses this radical imbalance, hence leading to greater potential for autacoid bioavailability. Recent human studies also indicate that exercise training may improve endothelial function by up-regulating eNOS protein expression and phosphorylation. While improvement in NO vasodilator function has been less frequently found in healthy subjects, a higher level of training may lead to improvement. Regarding time course, studies indicate that short-term training increases NO bioactivity, which acts to homeostatically regulate the shear stress associated with exercise. Whilst the increase in NO bioactivity dissipates within weeks of training cessation, studies also indicate that if exercise is maintained, the short-term functional adaptation is succeeded by NO-dependent structural changes, leading to arterial remodelling and structural normalization of shear. Given the strong prognostic links between vascular structure, function and cardiovascular events, the implications of these findings are obvious, yet many unanswered questions remain, not only concerning the mechanisms responsible for NO bioactivity, the nature of the cellular effect and relevance of other autacoids, but also such practical questions as the optimal intensity, modality and volume of exercise training required in different populations.

Long-term combined beneficial effects of physical training and metabolic treatment on atherosclerosis in hypercholesterolemic mice

The pathogenic mechanisms by which physical exercise influences atherosclerotic lesion formation remain poorly understood. Because vigorous physical training increases oxidative stress, this study tested the hypothesis that graduated and moderate physical exercise together with metabolic intervention (l-arginine and antioxidants) may contribute to increased vascular protection. Exercise training in mice was induced by graduated swimming. In hypercholesterolemic male mice on an atherogenic high-cholesterol diet, graduated and moderate exercise lowered plasma cholesterol and decreased atherosclerotic lesions compared with sedentary control mice. Antioxidants (1.0% vitamin E added to the chow and 0.05% vitamin C added to the drinking water) and l-arginine (6% in drinking water) supplementation to exercising hypercholesterolemic mice further and synergistically reduced atherosclerosis compared with untreated exercised mice. Arterial oxidation-specific epitopes and systemic oxidative stress were reduced by metabolic intervention. Graduated chronic exercise elicited an increase in production of nitric oxide through increased endothelial nitric oxide synthase expression and ameliorated scavenger activities. Thus, metabolic intervention with l-arginine and antioxidants together with graduated and moderate exercise training reduce atherosclerotic lesion formation.

Exercise and the nitric oxide vasodilator system

In the past two decades, normal endothelial function has been identified as integral to vascular health. The endothelium produces numerous vasodilator and vasoconstrictor compounds that regulate vascular tone; the vasodilator, nitric oxide (NO), has additional antiatherogenic properties, is probably the most important and best characterised mediator, and its intrinsic vasodilator function is commonly used as a surrogate index of endothelial function. Many conditions, including atherosclerosis, diabetes mellitus and even vascular risk factors, are associated with endothelial dysfunction, which, in turn, correlates with cardiovascular mortality. Furthermore, clinical benefit and improved endothelial function tend to be associated in response to interventions. Shear stress on endothelial cells is a potent stimulus for NO production. Although the role of endothelium-derived NO in acute exercise has not been fully resolved, exercise training involving repetitive bouts of exercise over weeks or months up-regulates endothelial NO bioactivity. Animal studies have found improved endothelium-dependent vasodilation after as few as 7 days of exercise. Consequent changes in vasodilator function appear to persist for several weeks but may regress with long-term training, perhaps reflecting progression to structural adaptation which may, however, have been partly endothelium-dependent. The increase in blood flow, and change in haemodynamics that occur during acute exercise may, therefore, provide a stimulus for both acute and chronic changes in vascular function. Substantial differences within species and within the vasculature appear to exist. In humans, exercise training improves endothelium-dependent vasodilator function, not only as a localised phenomenon in the active muscle group, but also as a systemic response when a relatively large mass of muscle is activated regularly during an exercise training programme. Individuals with initially impaired endothelial function at baseline appear to be more responsive to exercise training than healthy individuals; that is, it is more difficult to improve already normal vascular function. While improvement is reflected in increased NO bioactivity, the detail of mechanisms, for example the relative importance of up-regulation of mediators and antioxidant effects, is unclear. Optimum training schedules, possible sequential changes and the duration of benefit under various conditions also remain largely unresolved. In summary, epidemiological evidence strongly suggests that regular exercise confers beneficial effects on cardiovascular health. Shear stress-mediated improvement in endothelial function provides one plausible explanation for the cardioprotective benefits of exercise training.

Suppression of skeletal muscle lipoprotein lipase activity during physical inactivity: a molecular reason to maintain daily low-intensity activity

We have examined the regulation of lipoprotein lipase (LPL) activity in skeletal muscle during physical inactivity in comparison to low-intensity contractile activity of ambulatory controls. From studies acutely preventing ambulatory activity of one or both the hindlimbs in rats, it was shown that approximately 90-95 % of the heparin-releasable (HR) LPL activity normally present in rat muscle with ambulatory activity is lost, and thus dependent on local contractile activity. Similarly, approximately 95 % of the differences in LPL activity between muscles of different fibre types was dependent on ambulatory activity. The robustness of the finding that physical inactivity significantly decreases muscle LPL activity was evident from confirmatory studies with different models of inactivity, in many rats and mice, both sexes, three muscle types and during both acute and chronic (11 days) treatment. Inactivity caused a local reduction of plasma [3H]triglyceride uptake into muscle and a decrease in high density lipoprotein cholesterol concentration. LPL mRNA was not differentially expressed between ambulatory controls and either the acutely or chronically inactive groups. Instead, the process involved a rapid loss of the HR-LPL protein mass (the portion of LPL largely associated with the vascular endothelium) by an actinomycin D-sensitive signalling mechanism (i.e. transcriptionally dependent process). Significant decreases of intracellular LPL protein content lagged behind the loss of HR-LPL protein. Treadmill walking raised LPL activity approximately 8-fold (P < 0.01) within 4 h after inactivity. The striking sensitivity of muscle LPL to inactivity and low-intensity contractile activity may provide one piece of the puzzle for why inactivity is a risk factor for metabolic diseases and why even non-vigorous activity provides marked protection against disorders involving poor lipid metabolism.