Chlamydia pneumoniae infection is frequent but not associated with coronary arteriosclerosis in cardiac transplant recipients

We sought to explore the relation between Chlamydia pneumoniae, cytomegalovirus (CMV), and cardiac transplant-associated arteriosclerosis. Serologic evidence of past Chlamydia pneumoniae infection was investigated in 3 patient groups at the time of cardiac catheterization: cardiac transplant recipients (n=49), patients having coronary artery bypass grafting (CABG) (n=39), and a control group free of angiographic coronary artery disease (n=21). High Chlamydia pneumoniae immunoglobulin G titers (> or =1:160) were more frequently observed in cardiac transplant recipients (odds ratio[OR] 13.7; 95% confidence intervals [CI] 1.6 to 117.4, p <0.05) and CABG patients (OR 21.7; 95% CI 1.6 to 287.0, p <0.05) than in controls. However, high Chlamydia pneumoniae titers did not distinguish between cardiac transplant recipients with or without angiographic transplant-associated arteriosclerosis or CABG patients with or without bypass vein graft disease. Furthermore, there was no significant relation between elevated Chlamydia pneumoniae titers and the presence or progression of transplant-associated arteriosclerosis in the subgroup of patients who were also CMV positive. Yet, analysis of the same angiograms demonstrated an association between CMV infection and the recent progression of transplant-associated arteriosclerosis. Thus, patients with cardiac transplantation have evidence of past Chlamydia pneumoniae and CMV infection but Chlamydia pneumoniae does not appear to have an independent role or synergistic relation to CMV in the development of transplant-associated arteriosclerosis.

Estradiol therapy combined with progesterone and endothelium-dependent vasodilation in postmenopausal women

BACKGROUND

Epidemiological studies indicate that estrogen replacement therapy decreases the risk of cardiovascular events in postmenopausal women. Estrogen may confer cardiovascular protection by improving endothelial function because it increases endothelium-dependent vasodilation. It is not known whether progesterone attenuates the beneficial effects of estrogen on endothelial function.

METHODS AND RESULTS

Seventeen postmenopausal women with mild hypercholesterolemia were enrolled in a placebo-controlled, crossover trial to evaluate the effect of transdermal estradiol, with and without vaginal micronized progesterone, on endothelium-dependent vasodilation in a peripheral conduit artery. Brachial artery diameter was measured with high-resolution B-mode ultrasonography. To assess endothelium-dependent vasodilation, brachial artery diameter was determined at baseline and after a flow stimulus induced by reactive hyperemia. To assess endothelium-independent vasodilation, brachial artery diameter was measured after administration of sublingual nitroglycerin. During estradiol therapy, reactive hyperemia caused an 11.1+/-1.0% change in brachial artery diameter compared with 4. 7+/-0.6% during placebo therapy (P<0.001). Progesterone did not significantly attenuate this improvement. During combined estrogen and progesterone therapy, flow-mediated vasodilation of the brachial artery was 9.6+/-0.8% (P=NS versus estradiol alone). Endothelium-independent vasodilation was not altered by estradiol therapy, either with or without progesterone, compared with placebo. There was a modest decrease in total and LDL cholesterol during treatment both with estradiol alone and when estradiol was combined with progesterone (all P<0.001 versus placebo). In a multivariate analysis that included serum estradiol, progesterone, total and LDL cholesterol concentrations, blood pressure, and heart rate, only the estradiol level was a significant predictor of endothelium-dependent vasodilation.

CONCLUSIONS

The addition of micronized progesterone does not attenuate the favorable effect of estradiol on endothelium-dependent vasodilation. The vasoprotective effect of hormone replacement therapy may extend beyond its beneficial actions on lipids.

Effect of direct thrombin inhibition with Bivalirudin (Hirulog) on restenosis after coronary angioplasty

The direct antithrombin, bivalirudin, did not reduce angiographic restenosis measured either as the dichotomous restenosis rate of 62% for bivalirudin and 58% for heparin (p = 0.70), or as the late loss in lumen diameter of 0.44 +/- 0.47 mm for bivalirudin and 0.39 +/- 0.53 mm for heparin (p = 0.62). Direct thrombin inhibition with bivalirudin neither reduces angiographic restenosis nor alters the impact of several established risk factors for restenosis.

Noninvasive assessment of transplant-associated arteriosclerosis

BACKGROUND

Transplant-associated arteriosclerosis is the major limitation to long-term survival in the cardiac transplant recipient, and annual surveillance angiography is used in many centers to monitor its progression. Noninvasive methods would be preferable because angiography is invasive, costly, and insensitive; however, the reliability of such methods has been questioned.

METHODS

All publications relating to the assessment of the cardiac allograft by noninvasive testing were identified through MEDLINE and a review of references from the published literature on transplant-associated arteriosclerosis.

RESULTS

Resting and stress ECG, radionuclide scintigraphy, echocardiography, and positron emission tomography have all been used in cardiac transplant recipients with variable results. Most techniques are insensitive, but this limitation may be improved with pharmacologic stress imaging like dobutamine echocardiography. Although insensitive, some methods have good specificity (i.e., radionuclide scintigraphy). The noninvasive measurement of absolute coronary blood flow is promising as a specific and sensitive technique but is limited by availability and cost.

CONCLUSIONS

In general, noninvasive techniques to assess transplant-associated coronary arteriosclerosis are limited by variable sensitivity and specificity. However, certain methods, such as dobutamine echocardiography and radionuclide scintigraphy, can provide important adjunctive physiologic information to angiography. Such techniques can therefore help to guide the care and treatment of the cardiac transplant recipient with allograft coronary arteriosclerosis.

Noninvasive assessment of endothelium-dependent flow-mediated dilation of the brachial artery

Coronary atherosclerosis is characterized by an early loss of endothelium-dependent vasodilation. However, the methods of assessing coronary endothelial function are invasive and difficult to repeat over time. Recently, a noninvasive ultrasound method has been widely used to measure flow-mediated dilation in the brachial artery as a surrogate test for endothelial function. We seek to further validate this method of measuring vascular function. The brachial artery diameters and blood flow of 20 normal volunteers (10 males and 10 females) were measured using high resolution (7.5 MHz) ultrasound and strain gauge plethysmography. Flow-mediated endothelium-dependent vasodilation was measured in the brachial artery during reactive hyperemia after 5 minutes of cuff occlusion in the upper arm. The brachial artery diameter increased maximally by 9.7 +/- 4.3% from baseline at 1 min after cuff release and blood flow increased by 1002 +/- 376%. Five min of cuff occlusion was sufficient to achieve 97 +/- 6% of maximal brachial artery dilation and degree of dilation was not different whether the cuff was inflated proximally or distally to the image site. The intraobserver variability in measuring brachial diameters was 2.9% and the variability of the hyperemic response was 1.4%. In young, healthy men and women, the baseline brachial artery diameter was the only factor that was predictive of the flow-mediated vasodilation response. The brachial noninvasive technique has been further validated by the determination of flow-mediated dilation. This method of assessing endothelial function may help to determine the importance of vasodilator dysfunction as a risk factor in the development of atherosclerosis.

Vitamin C improves endothelium-dependent vasodilation in patients with insulin-dependent diabetes mellitus

OBJECTIVES

We sought to determine whether the antioxidant vitamin C improves endothelium-dependent vasodilation of forearm resistance vessels in patients with insulin-dependent diabetes mellitus.

BACKGROUND

Endothelium-dependent vasodilation is impaired in patients with diabetes mellitus. Oxidatively mediated degradation of endothelium-derived nitric oxide contributes to abnormal endothelium-dependent vasodilation in animal models of diabetes mellitus.

METHODS

The study group included 10 patients with insulin-dependent diabetes mellitus and 10 age-matched control subjects. Forearm blood flow was determined by venous occlusion plethysmography. Endothelium-dependent vasodilation was assessed by intraarterial infusion of methacholine (0.3 to 10 microg/min). Endothelium-independent vasodilation was assessed by intraarterial infusion of nitroprusside (0.3 to 10 microg/min). Forearm blood flow dose-response curves were determined for each drug infusion before and during concomitant infusion of vitamin C (24 mg/min).

RESULTS

In diabetic subjects, endothelium-dependent vasodilation was augmented by the concomitant infusion of vitamin C (p = 0.001). Endothelium-independent vasodilation was not affected by the concomitant infusion of vitamin C (p = NS). In control subjects, vitamin C infusion did not affect endothelium-dependent vasodilation (p = NS).

CONCLUSIONS

Vitamin C selectively restores the impaired endothelium-dependent vasodilation in the forearm resistance vessels of patients with insulin-dependent diabetes mellitus. These findings indicate that nitric oxide degradation by oxygen-derived free radicals contributes to abnormal vascular reactivity in humans with insulin-dependent diabetes mellitus.

Rationale and design of the Myocardial Ischemia Reduction with Aggressive Cholesterol Lowering (MIRACL) study that evaluates atorvastatin in unstable angina pectoris and in non-Q-wave acute myocardial infarction

The goal of the Myocardial Ischemia Reduction with Aggressive Cholesterol Lowering (MIRACL) study is to determine whether early, rapid, and profound cholesterol lowering therapy with atorvastatin can reduce early recurrent ischemic events in patients with unstable angina or non-Q-wave acute myocardial infarction. Within 1 to 4 days of hospitalization for one of these conditions, 2,100 patients will be randomly assigned to receive atorvastatin, 80 mg/day, or placebo in a double-blind design. Both groups receive dietary counseling. Over a 16-week follow-up period, the primary outcome measure is the time to occurrence of an ischemic event, defined as death, nonfatal acute myocardial infarction, cardiac arrest with resuscitation, or recurrent symptomatic myocardial ischemia requiring emergency rehospitalization. Secondary outcome measures are the time to occurrence and incidence of each of the primary outcome components, as well as nonfatal stroke, worsening angina, congestive heart failure requiring hospitalization, and need for coronary revascularization not anticipated before randomization. The sample size of 1,050 patients in each group is expected to provide 95% power to detect a 30% reduction in the primary outcome measure with a 5% level of significance. The results of the MIRACL study will determine the utility of profound cholesterol lowering as an early intervention in acute coronary syndromes.

Current concepts in cardiovascular pathology: the role of LDL cholesterol in plaque rupture and stabilization

Emerging evidence is redefining traditional concepts of coronary atherosclerosis. Recent data indicate that severe stenoses, the traditional focus of attention, do not cause most coronary events. Rather, interest has increased in the often less stenotic but more vulnerable lesions that are characterized by thin fibrous caps, large lipid accumulations, large numbers of macrophages, and depletion of smooth muscle cells. Such lesions appear prone to rupture, which allows the blood to come into contact with the highly thrombogenic material in the lipid core of the plaque, thereby precipitating thrombosis. The fibrous cap may become weakened through decreased synthesis of the extracellular matrix or increased degradation of the matrix. The cytokine interferon-gamma, produced by T-lymphocytes, inhibits the ability of smooth muscle cells to synthesize collagen, a structurally important component of the fibrous cap. A family of enzymes known as matrix metalloproteinases can degrade all major constituents of the vascular extracellular matrix: collagen, elastin, and proteoglycans. Additional studies on the biochemical mechanisms of atherosclerosis may provide a fuller understanding of the ways in which lipid-lowering therapy can confer clinical benefit.

Central role for CD40/CD40 ligand (CD154) interactions in transplant rejection

Major advances have been made in understanding the expression and function of CD40 and its ligand CD154. It is now clear that CD40/CD154 interactions are critical in many aspects of the immune response, including T cell activation, T cell-dependent macrophage activation, T cell-B cell interactions and endothelial activation. Moreover, increasing evidence supports a central role for CD40/CD154 interactions in the immune processes of allograft rejection. Functional studies using blocking monoclonal antibodies have revealed beneficial effects of interupting CD40/CD154 co-stimulation in animal models of transplantation, particularly in association with interuption of the CD28/B7 pathway. A next step is to develop new therapeutic approaches to interrupting this pathway in humans, either through the development of receptor antagonists or through the understanding of intracellular signaling pathways utilized by these molecules.

CD40 and CD40 ligand (CD154) are coexpressed on microvessels in vivo in human cardiac allograft rejection

BACKGROUND

CD40 is expressed by a wide variety of cells in the immune system, including endothelial cells. It binds to CD40 ligand ([CD40L] CD154), which was originally reported to be restricted in its expression to early-activated T cells. We report here the expression of CD40 and CD40L in human cardiac allografts.

METHODS

A total of 123 consecutive biopsies from 11 human cardiac allograft recipients were analyzed by immunohistochemistry for the expression of CD40 and CD40L. The expression of CD40L was also examined in vitro in homogeneous cultures of umbilical vein endothelial cells by reverse transcriptase-polymerase chain reaction and by flow cytometry.

RESULTS

CD40 was expressed at low levels, and CD40L was minimal or absent in histologically normal biopsies in the absence of CD3+ T-cell infiltrates. In rejection, the expression of CD40 increased on vascular endothelial cells and on graft-infiltrating leukocytes throughout biopsy specimens. Induced expression of CD40 was strongly associated with the presence of CD3+ T-cell infiltrates, acute rejection, and ischemic injury (P<0.05). CD40L was expressed in biopsies with rejection and was prominent on a subset of infiltrating leukocytes as well as on microvascular endothelial cells. In contrast to CD40, staining of endothelial CD40L was focal in most biopsies. Overall, the expression of CD40L correlated with the presence of CD3+ T-cell infiltrates and rejection (P<0.05), but not ischemic injury (P=0.9). To confirm that the endothelium can synthesize CD40L, we also evaluated the expression of endothelial CD40L in vitro. Cultured endothelial cells were found to express little constitutive CD40L that markedly increased after 24 hr of treatment with supernatants from phytohemagglutinin-activated peripheral blood mononuclear cells or by the cytokines tumor necrosis factor-alpha, interleukin-1a, interleukin-4, or interferon-gamma.

CONCLUSION

Both CD40 and CD40L are expressed in vivo on infiltrating leukocytes and on microvascular endothelium in human cardiac allograft rejection. We suggest that endothelial cell CD40 and CD40L play a role in human cell-mediated immune responses such as cardiac allograft rejection.

Role of endothelial dysfunction in coronary artery disease and implications for therapy

Atherosclerosis is a complex process that is characterized by the accumulation of modified low-density lipoprotein (LDL), local inflammatory and immune responses, and reduced nitric oxide bioavailability within the arterial wall. These cellular changes lead to endothelial vasomotor dysfunction, plaque instability, and the development of clinical events such as stable angina and the acute coronary syndromes. The vascular endothelium plays a critical role in modulating both the inflammatory response and vasomotor abnormalities that occur in those with coronary artery disease or risk factors for disease. In these conditions, endothelial cells are activated by cytokines to express cellular adhesion molecules that facilitate the adhesion of leukocytes to the endothelium, and their migration into the subintimal space. Cytokines stimulate inflammatory and smooth muscle cells in the intima to produce degradative enzymes, including metalloproteinases that can weaken the fibrous cap of atherosclerotic lesions and make them vulnerable to rupture. Endothelial cells also regulate vascular tone by the synthesis of nitric oxide. Atherosclerosis and other conventional risk factors for coronary artery disease are associated with endothelial vasodilator dysfunction in the coronary epicardial and resistance vessels, which likely contributes to myocardial ischemia. Several studies have demonstrated that lowering serum total and LDL cholesterol reverses endothelial vasomotor dysfunction, reduces myocardial ischemia, and lowers the risk of the acute coronary syndromes or need for revascularization. Improving endothelial function, for example, by lowering blood cholesterol should now be regarded as a goal of therapy in the treatment of coronary artery disease.

Hemostatic/fibrinolytic predictors of allograft coronary artery disease after cardiac transplantation

Allograft coronary artery disease (CAD) remains the leading cause of morbidity and mortality affecting the long-term survival of patients after cardiac transplantation. Because there is increasing evidence that imbalances in hemostatic and fibrinolytic pathways are associated with graft failure, we hypothesized that atherothrombotic risk factors may contribute to allograft CAD. This study sought to determine if plasma hemostatic and fibrinolytic parameters are associated with the severity of allograft CAD. The extent of allograft CAD was investigated by angiography and intravascular ultrasound (IVUS) in 16 cardiac transplant recipients. Intimal thickening was quantified using IVUS by measuring the intimal index (li = intimal area/[intimal area + luminal area]) in two to five segments of the left anterior descending (LAD) coronary artery. The maximal li per patient was calculated and index to the time post-transplant (Mxli/Yr). Plasma fibrinogen (FGN), tissue-type plasminogen activator (t-PA), plasminogen activator inhibitor-1 (PAI-1), lipoprotein(a) (Lp(a)), and net fibrinolytic activity of plasma were assayed 6-24 months after transplant as indicators of the fibrinolytic system and then correlated with the IVUS measurements. The FGN level correlated with the severity of intimal thickening, Mxli/Yr (r2 = 0.41, p = 0.008), and was inversely correlated with angiographic tertiary vessel filling (r2 = 0.25, p = 0.051). In patients with lower plasma fibrinolytic activity (lytic zone less than 100 mm2), Mxli/Yr was increased eightfold (0.218 +/- 0.137 versus 0.025 +/- 0.021, p = 0.001). t-PA (r2 = 0.0004, p = 0.94), PAI-1 (r2 = 0.008, p = 0.75) and Lp(a) levels (r2 = 0.11, p = 0.21) did not predict Mxli/Yr. Thus, we demonstrate that plasma FGN and net fibrinolytic activity correlate with the degree of intimal thickening measured by IVUS after cardiac transplantation. These data suggest that fibrin deposition may play a role in allograft CAD after cardiac transplantation.

Bivalirudin compared with heparin during coronary angioplasty for thrombus-containing lesions

OBJECTIVES

We investigated whether bivalirudin is more effective than heparin in preventing ischemic complications in high risk patients undergoing coronary angioplasty for thrombus-containing lesions detected by angiography.

BACKGROUND

Heparin is administered during coronary angioplasty to prevent closure of the dilated vessel. Bivalirudin (Hirulog) is a direct thrombin inhibitor that can be safely substituted for heparin during angioplasty. Bivalirudin has several theoretic advantages over heparin as an anticoagulant agent.

METHODS

We performed an observational analysis of the Hirulog Angioplasty Study in which 4,098 patients with unstable or postinfarction angina were randomized to receive either bivalirudin or heparin during coronary angioplasty. The study group for this analysis consisted of 567 patients who had thrombus-containing lesions on angiography. The primary end point was death, myocardial infarction, emergency coronary artery bypass graft surgery or abrupt vessel closure before hospital discharge.

RESULTS

Patients with thrombus-containing lesions had a higher incidence of myocardial infarction (5.1% vs. 3.2%, p = 0.03) and abrupt vessel closure (13.6% vs. 8.3%, p < 0.001) than those without thrombus. In patients with thrombus-containing lesions, however, the incidence of the primary end point was not different between the bivalirudin and heparin treatment groups. Furthermore, no difference in the incidence of ischemic events at 6 months was seen between the treatment groups.

CONCLUSIONS

Bivalirudin is not more effective than heparin in preventing ischemic complications in patients undergoing coronary angioplasty for thrombus-containing lesions detected by angiography. Other approaches, perhaps involving potent anti-platelet agents, should be considered for patients with thrombus-containing lesions.

Vitamin C improves endothelium-dependent vasodilation in forearm resistance vessels of humans with hypercholesterolemia

BACKGROUND

Endothelium-dependent vasodilation is impaired in humans with hypercholesterolemia. Oxidative degradation of endothelium-derived nitric oxide plays a major role in endothelial dysfunction in animal models of hypercholesterolemia. To assess whether this mechanism is relevant to humans, we studied the effect of vitamin C, an antioxidant, on vasodilator function in forearm resistance vessels of patients with hypercholesterolemia.

METHODS AND RESULTS

We studied 11 hypercholesterolemic and 12 healthy control subjects. Forearm blood flow was determined by venous occlusion plethysmography. Endothelium-dependent vasodilation was assessed by intra-arterial infusion of methacholine (0.3 to 10 micrograms/min). Endothelium-independent vasodilation was measured by intra-arterial infusion of nitroprusside (0.3 to 10 micrograms/min) and verapamil (10 to 300 micrograms/min). Forearm blood flow dose-response curves were determined for each drug before and during coadministration of vitamin C (24 mg/min). In hypercholesterolemic subjects, endothelium-dependent vasodilation to methacholine was augmented by coinfusion of vitamin C (P = .001); in contrast, endothelium-independent vasodilation to nitroprusside and verapamil were not affected by coinfusion of vitamin C (P = .8 and P = .3, respectively). In control subjects, vitamin C administration did not alter endothelium-dependent vasodilation (P = .2).

CONCLUSIONS

We conclude that vitamin C improves endothelium-dependent vasodilation in the forearm resistance vessels of patients with hypercholesterolemia. These findings suggest that nitric oxide degradation by oxygen-derived free radicals contributes to abnormal vascular reactivity in hypercholesterolemic humans.

Heat changes in lipid membranes under sudden osmotic stress

Closed lipid vesicles act as osmometers increasing or decreasing their volume under the influence of osmotic gradients. The enthalpy changes accompanying membrane compression or expansion have not been measured yet, and first results obtained with high-sensitivity titration calorimetry are reported here. Phospholipid vesicles suspended in and in equilibrium with an electrolyte or nonelectrolyte with a defined initial concentration of c(i), were injected into a solution with a final concentration of c(f), and the heat changes were monitored with a titration microcalorimeter. Osmotic compression (delta c = c(f) - c(i) > 0) produced an exothermic heat change with deltaH approximately -500 +/- 100 cal/mol and osmotic expansion (delta c < 0) an endothermic heat change with deltaH approximately 1000 +/- 200 cal/mol; both results normalized to a concentration gradient of delta c = 1 M NaCl. The heats of compression and expansion varied linearly with the lipid content and the size of the osmotic gradient but were independent of the vesicle size. The cubic thermal expansion coefficient alpha(v) which equals (1/V)(deltaV/deltaT)p could be derived and was found to be 1.25 x 10(-3) and 2.5 x 10(-3) K(-1) for the compressed and expanded bilayer vesicles, respectively. The entropy changes associated with compression and expansion could be estimated. Compression of the membrane led to a negative entropy change and increased the hydrocarbon chain order. Expansion of the membrane was accompanied by a positive entropy change which can be explained, in part, by more disordered hydrocarbon chains. Vesicle expansion and compression thus appear to be asymmetric as far as the thermodynamic driving force is concerned.

Cell dysfunction in atherosclerosis and the ischemic manifestations of coronary artery disease

Many of the cellular mechanisms and dysfunctions that underlie atherosclerotic plaque formation have been identified, including adverse interactions between atherogenic lipids and the arterial endothelium, loss of endothelium-dependent dilation, accumulation of inflammatory cells and mediators of inflammation in the intima of the arteries, and a decline in anticoagulant defenses. Several studies have shown that these mechanisms, which appear to be active throughout the pathogenesis and progression of atherosclerosis, are reversible within days, weeks, or months with effective lipid-lowering therapy. In addition, the findings of large-scale trials of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors suggest that the rapid improvement observed in trial participants is attributable to a reversal of endothelial and vascular wall dysfunctions rather than to a reduction in plaque size. The accumulated evidence indicates that improved endothelial function can benefit patients who have angina pectoris and/or are at risk for myocardial infarction. Current understanding of the cellular mechanisms of atherogenesis also suggests avenues of future research to refine treatment approaches and further improve outcomes for patients with coronary artery disease.

Effect of cholesterol reduction on myocardial ischemia in patients with coronary disease

BACKGROUND

Cholesterol lowering is associated with a reduction in cardiovascular morbidity and mortality. This study sought to determine whether cholesterol lowering also results in a reduction of myocardial ischemia during daily life.

METHODS AND RESULTS

We enrolled 40 patients with proven coronary artery disease, total serum cholesterol between 191 and 327 mg/dL, and at least one episode of ST-segment depression on ambulatory ECG monitoring. Twenty patients were randomized to an American Heart Association Step 1 diet plus placebo (placebo group) and 20 to the same diet plus lovastatin (treatment group). Serum cholesterol and LDL cholesterol levels and ambulatory monitoring were repeated after 4 to 6 months of therapy. The two groups were comparable with respect to baseline characteristics, number of episodes of ST-segment depression, and baseline serum cholesterol levels. The treatment group had lower mean total and LDL cholesterol levels at study end and experienced a significant reduction in the number of episodes of ST-segment depression compared with the placebo group. ST-segment depression was completely resolved in 13 of 20 patients (65%) in the treatment group versus 2 of 20 (10%) in the placebo group. The treatment group exhibited a highly significant reduction in ischemia (P < .001). By logistic regression, treatment with diet and lovastatin was an independent predictor of ischemia resolution.

CONCLUSIONS

Cholesterol lowering with lovastatin appears to be effective in eliminating myocardial ischemia during daily life in a significant proportion of patients.

Atherogenic lipids, vascular dysfunction, and clinical signs of ischemic heart disease

LDL is oxidized in vascular endothelial cells to a highly injurious product that results in characteristic cell dysfunction(s) in large arteries and resistance vessels. The characteristic dysfunctions (ie, loss of dilation, constriction, thrombosis, and inflammation) operate before and throughout the development of atherosclerosis and particularly during plaque rupture. Although oxidized LDL appears to induce these cell/vessel wall dysfunctions in a time- and concentration-dependent manner, Tamai and colleagues have shown that this interaction can be dynamic in that a reduction in lipids restores endothelium-dependent vasomotor function almost immediately. The same intervention (ie, lipid lowering) also appears to stabilize atheroma in the long term, improves endothelium-dependent vasomotion over months, and results in a reduction in clinical signs of risk in coronary heart disease (ie, ischemia and the need for revascularization). The above leads us to some important but unanswered questions. Can we rely on clinical measures of arterial vasomotor dysfunction to represent the other important cell dysfunctions (eg, inflammation, abnormal growth) while monitoring the response to therapeutic interventions? How can we effectively inhibit oxidation of LDL in the arterial wall, and is this useful in reversing the many cell dysfunctions and clinical sequelae of coronary atherosclerosis? What is the time course for restoration of endothelial dysfunction in the atherosclerotic epicardial coronary arteries in patients with effective lipid-lowering therapy? The intracellular responses to oxidized LDL are so numerous (loss of vasodilation, loss of anticoagulant mechanisms, abnormal inflammation, and growth) that targeting therapies to specific pathways may prove difficult. Parallel efforts in basic physiological and clinical research have resulted in remarkable progress that has improved outcomes in patients with coronary heart disease. We expect that many of the characteristic cell/vessel wall dysfunctions that result from adverse interactions with risk factors are dynamic and can be manipulated in a relatively short time frame. Treatment of atherogenic lipids with other risk factors must be further refined and may well become the cornerstone for effective management of angina, unstable syndromes, and ischemia in addition to the control of important outcomes such as myocardial infarction and coronary death.

Biological mechanisms for the clinical success of lipid-lowering in coronary artery disease and the use of surrogate end-points

The small changes in luminal narrowing observed with lowering total cholesterol are unlikely to be the principal mechanism by which lipid-lowering achieves a reduction in clinical events and revascularization rates. Endothelium dependent vasomotor function, and the cellular characteristics of plaques that seem to be intimately related to rupture and thrombosis, are factors that may explain the clinical success from correcting the dyslipidemias. Dyslipidemias cause endothelial dysfunction that predisposes to vasoconstriction of the epicardial coronary arteries and the resistance vessels relative to metabolic demand. Dysfunctional endothelium also promotes the recruitment of inflammatory cells into the vessel wall which contributes to the activation of vascular smooth muscle cells and sets up an environment within the plaque that predisposes to rupture and a prothrombotic state. Aggressive lowering of total cholesterol, and especially LDL and oxidized LDL, improves coronary endothelial function both of the epicardial and resistance vessels, and leads to a reduction in myocardial ischemia. Lipid-lowering may promote plaque stability in part by reducing the recruitment of inflammatory cells, and possibly by changing the size or consistency of the lipid-rich core of plaques. A thicker fibrous cap and stiffer plaque that is less likely to rupture may result, and in the event that rupture does occur, cholesterol lowering may reduce the formation of overlying thrombus. Testing coronary or peripheral artery endothelial vasomotor dysfunction may be a surrogate measure for assessing the effectiveness of interventions to prevent coronary heart disease. These tests are likely to be used increasingly to identify interventions that deserve greater attention in larger clinical trials, as well as providing mechanisms for any observed clinical benefits.

Flow-induced vasodilation of the human brachial artery is impaired in patients <40 years of age with coronary artery disease

The objective of this study was to determine whether abnormal flow-induced endothelium-dependent vasodilation in the brachial artery identifies young patients with coronary artery disease (CAD). High-resolution ultrasonography was used to measure vascular reactivity in a peripheral conduit vessel, the brachial artery, in 14 young men with CAD and in 11 age-matched, healthy, male volunteers. Endothelium-dependent vasodilation was determined by measuring the change in brachial artery diameter during increases in flow induced by reactive hyperemia. Endothelium-independent vasodilation was assessed by administration of sublingual nitroglycerin. To ascertain whether flow-mediated vasodilation in humans is mediated by endothelium-derived nitric oxide, brachial artery diameter was measured during reactive hyperemia, before and during administration of the nitric oxide synthase antagonist NG-monomethyl-L-arginine (L-NMMA). Brachial artery diameter was also measured during intraarterial infusion of acetylcholine and nitroprusside before and after administration of L-NMMA. Flow-induced vasodilation was less in patients with CAD than in healthy volunteers (1.3 +/- 1.1% vs 6.2 +/- 0.7%, p <0.05). Nitroglycerin increased brachial artery diameter similarly in each subject group (11.3 +/- 1.0% vs 15.8 +/- 1.2%, p =0.05). L-NMMA inhibited flow-mediated vasodilation and the vasodilative response to acetylcholine, but did not affect the response to nitroprusside. It is concluded that abnormal flow-induced endothelium-dependent vasodilation occurs in the brachial artery of young patients with CAD.