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ACC/AHA 2008 Performance Measures for Adults With ST-Elevation and Non-ST-Elevation Myocardial Infarction

ACC/AHA 2008 Guidelines for the Management of Adults With Congenital Heart Disease
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J Am Coll Cardiol, 2004; 43:2225-2232, doi:10.1016/j.jacc.2003.11.065
© 2004 by the American College of Cardiology Foundation
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CLINICAL RESEARCH: TRIGLYCERIDES AND RISK

Impaired intravascular triglyceride lipolysis constitutes a marker of clinical outcome in patients with stable angina undergoing secondary prevention treatment

A long-term follow-up study

Andrei C. Sposito, MD, PhD*, Pedro A. Lemos, MD{dagger}, Raul D. Santos, MD, PhD{dagger}, Whady Hueb, MD, PhD{dagger}, Carmen G. C. Vinagre, PhD{dagger}, Edgard Quintella, MD{dagger}, Otavio Carneiro, MD{dagger}, M. John Chapman, PhD, DSc{ddagger}, Jose A. F. Ramires, MD, PhD, FACC*{dagger} and Raul C. Maranhão, MD, PhD{dagger}§,*

* Heart Institute (InCor), Zerbini Foundation, Brasilia, Brazil
{dagger} Heart Institute (InCor), University of São Paulo Medical School, São Paulo, Brazil
{ddagger} INSERM Unité 551, Hôpital de la Pitié-Salpetriere, Paris, France
§ Faculty of Pharmaceutical Sciences, University of São Paulo, São Paulo, Brazil

Manuscript received January 29, 2003; revised manuscript received November 7, 2003, accepted November 13, 2003.

* Reprint requests and correspondence: Prof. Raul C. Maranhão, Instituto do Coração (InCor), Hospital das Clínicas da Faculdade de Medicina USP, Av. Dr. Eneas Carvalho Aguiar, 44., 05403.900 São Paulo, SP, Brazil.
ramarans{at}usp.br


   Abstract
Top
 Abstract
Methods
 Results
 Discussion
 References
 
OBJECTIVES: We sought to verify whether the intravascular metabolism of chylomicron-like emulsion may predict the clinical evolution of patients with coronary artery disease (CAD) undergoing secondary prevention therapy of CAD.

BACKGROUND: Case-control studies have suggested an association between impaired intravascular catabolism of triglyceride (TG)-rich lipoproteins and CAD. However, evidence is lacking with respect to the potential clinical relevance of this metabolic disorder in CAD patients.

METHODS: During a period of 4.5 ± 0.9 years, we followed up 63 stable CAD patients (mean age 60 ± 10 years) undergoing secondary prevention therapy (low-density lipoprotein cholesterol <100 mg/dl) in whom kinetic studies of the in vivo catabolism of chylomicron-like emulsions were performed. At enrollment into the study, fasting patients were injected intravenously with a chylomicron-like emulsion labeled with radioactive triglyceride (3H-TG) and cholesteryl esters (14C-CE) to evaluate the efficacy of intravascular TG lipolysis.

RESULTS: At baseline, CAD patients displayed a diminished fractional clearance rate (FCR) for 3H-TG (–26%; p = 0.027), for 14C-CE (–37%; p = 0.015), and for delipidation index (DI) (–26%; p = 0.02) as compared with 35 control subjects. During follow-up of secondary prevention therapy, 33% of CAD patients (n = 21) presented with clinically refractory angina and aggravated coronary angiographic severity. The FCR for 3H-TG (–44%; p = 0.005) and DI (–41%; p = 0.006) in those patients with refractory angina was significantly lower than that observed in those with stable evolution. Moreover, in a Cox multivariate regression analysis, the presence of a DI less than the median value was an independent predictor of an unfavorable clinical evolution (adjusted hazard ratio 3.32; 95% confidence interval 1.21 to 9.14; p = 0.020).

CONCLUSIONS: The current study establishes that delayed intravascular TG lipolysis is a strong and independent predictor of evolution to severe angina among patients undergoing secondary prevention therapy of CAD.

Abbreviations and Acronyms
  ACAD = aggravating coronary artery disease
  ACE = angiotensin-converting enzyme
  CAD = coronary artery disease
  CE = cholesterol ester
  CI = confidence interval
  DI = delipidation index
  FCR = fractional clearance rate
  HDL = high-density lipoprotein
  HR = hazard ratio
  LDL = low-density lipoprotein
  LPL = lipoprotein lipase
  SCAD = stable coronary artery disease
  TG = triglyceride
  VLDL = very low-density lipoprotein

Intravascular lipolysis is the rate-limiting step for the hydrolysis and removal of triglyceride (TG)-rich lipoproteins, chylomicrons, and very low-density lipoproteins (VLDL) from the circulation (1,2). Lipoprotein lipase (LPL) is the key enzyme that acts at the endothelial surface of extrahepatic capillaries, releasing large amounts of fatty acids from TG-rich lipoproteins for uptake by cells of neighboring tissues for either energy production or storage. Delayed intravascular lipolysis increases the exposure of arterial wall cells to atherogenic TG-rich lipoproteins, thereby favoring their accumulation within the subendothelial space. In case-control studies with a chylomicron-like emulsion model, we have observed that patients with coronary artery disease (CAD) exhibit delayed intravascular TG lipolysis as compared with subjects without angiographically detectable CAD (3,4). In a recent meta-analysis, carriers of the Gly188Glu, Asp9Asn, and Asn291Ser amino acid-changing mutations in LPL displayed an increased risk of CAD as compared with non-carriers, which may indicate that an impaired intravascular lipolysis could influence the risk of CAD (5). However, evidence to establish the potential clinical impact of impairment in intravascular TG lipolysis in CAD patients undergoing secondary prevention therapy is lacking.

Large clinical trials have shown that cholesterol-lowering treatment with statins reduces total mortality among subjects undergoing primary and secondary prevention therapy. We and others have shown that statin treatment increases the fractional clearance rate (FCR) of native low-density lipoprotein (LDL) and chylomicron-like emulsions via the LDL receptor-dependent pathway (6,7). However, as expected, statins had no effect on the rate of intravascular lipolysis of TG-rich lipoproteins (6,7). Thus, this study was designed to evaluate the clinical impact of such delayed intravascular TG lipolysis in CAD patients who were treated with statins. Our findings indicate that impaired intravascular TG lipolysis has a long-term impact on clinical and angiographic progression of patients with chronic stable CAD.


   Methods
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 Abstract
 Methods
Results
 Discussion
 References
 
Patients.   Between January 1994 and March 1996, 63 patients with CAD (14 women; age range 43 to 70 years) were admitted to the Lipid Research Laboratory of the Heart Institute (São Paulo, Brazil) for determination of the plasma decay curves of doubly radiolabeled chylomicron-like emulsions. Patients originally had been referred to the Outpatient Clinic of the Heart Institute for clinical management of stable angina and had CAD confirmed by coronary angiography performed <6 months before entry into the study. Inclusion criteria were plasma TGs <400 mg/dl and no use of lipid-lowering therapies during the two months preceding enrollment. Subjects with diabetes, those who had high alcohol intakes (>1 drink per day), or those who had liver, renal, thyroid, inflammatory, or neoplastic diseases were not included in the study. Equally, patients with heart failure or severe angina as defined by functional class III or IV were excluded. All enrolled women were required to be postmenopausal, and none were treated with hormonal replacement therapy either before or during the study.

For comparison with the group of CAD patients, the emulsion plasma decay curve was also determined in 35 control subjects (8 women; age range 42 to 71 years). No control subjects were using lipid-lowering drugs, and the data used for this comparison were obtained before the CAD patients were entered into secondary prevention treatment. Normal angiographic examination was necessary for study inclusion of control subjects, and even mild luminal irregularities were considered an exclusion criterion. Coronary angiographies were performed <6 months before enrollment to investigate thoracic pain; control and non-CAD subjects were selected to be comparable on the basis of age, gender, and TG levels. Written, informed consent was obtained from all subjects before entry into the study, and the experimental protocol was approved by the Ethical and Scientific Committee of the Heart Institute in accordance with the Declaration of Helsinki.

Emulsion clearance study.   The chylomicron-like emulsion (final composition: triolein 76.5 ± 4.1%, free cholesterol 1.9 ± 0.3%, cholesteryl oleate 11.2 ± 3%, and phosphatidylcholine 10.4 ± 1.3%; size range from 80 to 110 nm) was made from lipid mixtures emulsified by ultrasonic irradiation and purified by ultracentrifugation in density gradients as described previously (3,4,6,8). 14C-cholesteryl oleate and 3H-triolein (Amersham, Buckinghamshire, United Kingdom) were added to the lipid mixtures for the determination of plasma kinetics. The emulsion was sterilized by passage through a 0.2-µm filter and 3 to 5 mg of total lipid emulsion (200 to 300 µl) containing 74 kBq (2 µCi) of the 14C and 148 kBq (4 µCi) of the 3H label were injected.

Enrolled patients reported to the laboratory by 8:00 AM after a 12-h overnight fast, and blood was collected for lipid and apolipoprotein analysis, as described in the following text. The radiolabeled emulsion was then injected in a bolus (200 to 300 µl) into the antecubital vein. To obtain blood samples for radioactivity measurement, the antecubital vein of the contralateral arm was cannulated and slow infusion of N/saline, without heparin, was started to maintain catheter patency. The total saline volume infused did not exceed 100 ml. Blood samples were collected at pre-established intervals of 2, 4, 6, 10, 15, 20, 30, 45, and 60 min after injection of the emulsion. Blood was collected and radioactivity in the samples was determined using a Packard 1660 TR Spectrometer (Packard, Meriden, Connecticut). The curve calculations of the plasma decay of 14C and 3H radioactivity were made by the non-linear least squares method, as described previously (3,4,6,8–10), and were expressed as the FCR of both radioactive labels. Redgrave and Zech (11) created the delipidation index (DI), which corrects total TG disappearance (lipolysis plus particle uptake) for cholesterol ester (CE) disappearance (particle uptake only). Thus, the DI provides a good estimate of TG lipolysis from plasma by the following formula:

The calculated interassay coefficient of variation for both emulsion label kinetic studies was <3%. The radiological dose injected as emulsion label was evaluated according to the guidelines of the International Commission on Radiological Protection and was below the Annual Limit for Intake of Radionuclide (50 mSv) as previously discussed (3,4,6,8). For each chylomicron-like emulsion kinetic study, the radioactive dose for 14C-CE and 3H-TG was 0.02 mSv and 0.0012 mSv, respectively.

Plasma lipid and apolipoprotein determinations.   Blood samples were collected on tubes containing ethylenediamine tetraacetic acid and centrifuged at 1,500 g for 10 min at 4°C to separate plasma. All lipid determinations were measured directly on plasma samples. Plasma total cholesterol and TGs were determined using enzymatic methods (Roche Laboratories, Basel, Switzerland). High-density lipoprotein (HDL) cholesterol determination was performed by the same method as for total cholesterol after LDL and VLDL precipitation with magnesium phosphotungstate. Very low-density lipoprotein cholesterol and LDL cholesterol were estimated by the Friedewald formula.

Clinical follow-up.   After the baseline emulsion plasma decay study and biochemical determinations, CAD patients received maximal antianginal and secondary prevention therapies, and were clinically followed up for 4.5 ± 0.9 years at the Outpatient Clinic of the Heart Institute. Before entrance (>60 days) and during the study, all patients were on the National Cholesterol Education Program (NCEP) type I diet. No educational program was offered to these patients during the study to increase physical activity. Patients were treated with standardized medical therapy with aspirin (100 mg/day), selective beta-blockers, and isosorbide dinitrate (120 mg/day). The beta-blocker dosage was individually established to obtain a heart rate between 50 and 60 beats/min. When indicated, hypertensive patients were also treated with calcium antagonists and/or angiotensin-converting enzyme (ACE) inhibitors. Treatment with statins was initiated in all CAD patients. Statin dosage was also established individually, with the aim of maintaining plasma LDL cholesterol concentrations <100 mg/dl according to the NCEP-Adult Treatment Panel II guidelines. After six weeks of treatment, the emulsion plasma decay study was re-evaluated in a subset of enrolled patients and is published elsewhere (6,12). Patients were reviewed at regular intervals of four to six months by clinical evaluation and by biological analyses. Neither the patients nor trial participants, including the attending physicians, had any knowledge of the results of the chylomicron-like emulsion kinetics during the study. Angina symptoms were graded according to severity from I to IV as defined by the Canadian Cardiovascular Society. Unstable angina was defined as chest pain at rest lapsing more than 10 min with documented transient ST-segment depression or ST-segment elevation of 0.1 mV in at least two continuous electrocardiographic leads. During the follow-up, two groups of patients were identified:

Aggravating coronary artery disease (ACAD) group—those who evolved to functional class III or IV angina despite the maximal dose of antianginal treatment and were considered as displaying clinically refractory angina. These were then submitted to a new coronary angiography and to a revascularization procedure when indicated.
Stable coronary artery disease (SCAD) group—those whose functional class of angina was unchanged during the follow-up study.

Coronary angiography.   Coronary angiography and left ventriculography were performed according to standard techniques. Lumen narrowing >70% was considered as a significant stenosis. All coronary angiographies were also classified by the Gensini score method. Severe angiographic progression was defined according to the following conditions: 1) the appearance of a coronary stenosis ≥50% at the final angiogram in a vessel segment with no apparent coronary stenosis at the initial coronary angiogram; 2) the appearance of a coronary stenosis ≥70% at the final angiogram in a vessel segment with stenosis <50% at the initial coronary angiogram; or 3) the appearance of a new coronary occlusion.

Echocardiography.   Echocardiographic evaluation was performed annually to detect possible silent deteriorations in ventricular function. M-mode and two-dimensional echocardiography were performed using commercially available machines (ATL Apogee CX and ATL Ultramark 9 HDI CV, Advanced Technology Laboratories, Bothell, Washington) with a 2- to 4-MHz broad-band transducer. The left ventricular ejection fraction and segmental ventricular motion were compared between patient groups.

Statistical analysis.   Data are expressed as mean ± standard deviation, and values of p > 0.05 were considered to be non-significant. The Kolmogorov-Smirnov normality test was applied to evaluate all quantitative variables. Frequencies in the categorical data were compared by the Fisher exact test. Univariate analyses were performed by the paired or unmatched t test for parametric data and by the Wilcoxon signed rank test or the Mann-Whitney U test for non-parametrical data. The correlation analysis was performed by the Spearman correlation test. The Kaplan-Meier time-to-event (clinically refractory angina) technique and the log-rank test were performed to compare the two groups of CAD patients with a DI greater than or less than the median. The Cox proportional hazards regression analysis using a model built by forward stepwise selection of variables was performed to obtain the hazard ratios (HRs) and 95% confidence interval (CI). The SPSS version 8.0 for Windows (Chicago, Illinois) was used to perform statistical calculations.


   Results
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 Abstract
 Methods
 Results
Discussion
 References
 
Baseline characteristics of CAD patients and controls.   Table 1 shows the baseline biological and clinical characteristics of CAD patients compared with control subjects. There was no significant difference between the two groups in age, body mass index (BMI), frequency of hypertension, physical inactivity, smoking habit, ex-smoking habit, or mean plasma levels of TGs, total cholesterol, LDL cholesterol, and VLDL cholesterol. High-density lipoprotein cholesterol was 14% lower (p = 0.012) in the CAD group than in the control group.


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  		Table 1 Baseline Characteristics, Plasma Lipids, and Apolipoproteins and Plasma FCR of the Emulsion Radioactive Lipids of the Study Subjects According to the Presence or Absence of Angiographically Defined CAD

 
Consistent with our previous results, the FCR for 3H-TG was 26% lower (p = 0.027) and the FCR for 14C-CE was 37% lower (p = 0.015) in the CAD group than in the control group (Table 1). To minimize the influence of the uptake of the chylomicron-like particles from the circulation on the plasma decay of 3H-TG, we calculated the DI, which expresses the amount of emulsion TG removed exclusively by lipolysis before the chylomicron-like emulsion is removed from plasma. Patients in the CAD group had a 26% lower DI than the control group (p = 0.02) (Table 1). High-density lipoprotein cholesterol was positively correlated with FCR for 3H-TG (r = 0.4; p = 0.001) and DI (r = 0.6; p = 0.001).

Clinical follow-up.   Complete clinical follow-up was performed in all enrolled patients. After the 4.5 ± 0.9 years of the follow-up period that ensued the emulsion plasma decay study, 21 patients (33%) displayed clinically refractory angina (ACAD group) and 42 (67%) had a stable clinical evolution (SCAD group). At enrollment and before treatment, all CAD patients had class I or II angina, and the frequency of patients with class I and II was similar in the ACAD and SCAD groups (class I: ACAD, n = 6 and SCAD, n = 9; class II: ACAD, n = 15 and SCAD, n = 33; p = NS). The mean anginal class at study initiation was also similar in the two groups (ACAD 1.7 ± 0.5 vs. SCAD 1.8 ± 0.5; p = NS) but became different at the end of the follow-up despite maximal antianginal therapy (ACAD 3.3 ± 0.5 vs. SCAD 1.7 ± 0.6; p < 0.0001). Neither an acute cardiovascular event nor detrimental evolution of systolic ventricular function, as assessed by the segmental ventricular motion or ejection fraction of the left ventricle (Table 2), was documented during the follow-up. The mean follow-up time was similar in both groups (Table 2).


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  		Table 2 Clinical and Kinetic Characteristics of Patients Who Experienced ACAD and of Patients Who Had SCAD

 
As shown in Table 2, there was no significant difference in age, BMI, the frequency of hypertension, physical inactivity, smoking habit, or ex-smoking habit between the ACAD and SCAD groups. During the follow-up, there was no significant modification in the frequency of these risk factors in the two groups. Equally, after statin treatment, mean plasma concentrations of total cholesterol (170 ± 23 mg/dl vs. 162 ± 29 mg/dl; p = NS), TGs (149 ± 81 mg/dl vs. 140 ± 72 mg/dl; p = NS), VLDL (30 ± 16 mg/dl vs. 28 ± 14 mg/dl; p = NS), LDL (96 ± 9 mg/dl vs. 94 ± 11 mg/dl; p = NS), and HDL cholesterol (45 ± 10 mg/dl vs. 44 ± 8 mg/dl; p = NS) were not significantly different between the ACAD and SCAD groups, respectively. The effect of statin treatment to increase FCR-CE (+70%; p = 0.01) and the absence of significant effect on FCR-TG or DI was confirmed in a subset of enrolled patients and was published elsewhere (6,12). There was no difference between the two groups in the use of calcium antagonists or ACE inhibitors.

Figure 1 shows the disappearance curves for mean plasma 3H-TG and 14C-CE in the ACAD group, SCAD group, and control group. The time-course curves revealed a slower decay in the circulating levels of 3H-TG in the ACAD group. In fact, the ACAD group had a significantly lower mean FCR-TG (–44%, p = 0.005) and DI (–41%, p = 0.006) than the SCAD group, thereby indicating a greater delay in the intravascular TG lipolysis in the group of patients who displayed aggravation of angina status (Table 2). There was no difference in the mean FCR-CE between the two groups (Table 2).



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  		Figure 1 Plasma disappearance curves of the emulsion 3H-triglyceride (TG) (A) and 14C-cholesteryl ester (CE) (B) determined in the controls, in patients who presented clinical aggravating coronary artery disease (ACAD), and in those who had evolution of stable coronary artery disease (SCAD).

 
To estimate the relative risk of the delayed intravascular TG lipolysis, we divided the enrolled CAD patients in two subgroups with a baseline DI greater than or less than the median. The Kaplan-Meier analysis revealed that patients with DI less than the median had the highest probability of developing refractory angina during the follow-up period than patients with a DI greater than median (log rank 95% CI 1.39 to 8.24; p = 0.007) (Fig. 2). The Cox proportional hazards regression model was fitted to obtain the HR for the clinical evolution to refractory angina, and the analysis was adjusted for the confounding effects of: post-statin-treatment LDL cholesterol; age; gender; BMI; the presence of clinical risk factors such as hypertension, physical inactivity, smoking or ex-smoking habit; and the use of calcium antagonists or ACE inhibitors. A final model was built by forward stepwise selection of variables, and a DI lower than the median was the only variable identified as an independent predictor of evolution to clinically refractory angina (adjusted HR 3.32; 95% CI 1.21 to 9.14; p = 0.020). None of the other variables, including HDL cholesterol (adjusted HR 0.96; 95% CI 0.86 to 1.11; p = 0.8), was selected for the model. A second modeling using categorical variables composed of statins and their dosages, beta-blockers and their dosages, ACE inhibitors and their dosages, and calcium blockers and their dosages, as potential predictors—plus all the other variables mentioned previously—gave the same final model.



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  		Figure 2 Kaplan-Meier curves of the time elapsed to a refractory angina event in the two groups of patients with delipidation index (DI) above or below the median. CI = confidence interval.

 
Angiographic analysis.   At the initial coronary angiography, there was no difference between the ACAD and SCAD groups either in the frequency of patients with one-, two-, or three-vessel disease or in the angiographic score (Table 2). Because all of the ACAD patients had been submitted to angiographic re-evaluation, we compared the baseline and final angiographies of these patients in order to verify the presence of angiographic progression. Indeed, all of the patients in the ACAD group exhibited angiographic progression as indicated by the increase in the Gensini angiographic score (69 ± 6%; p = 0.013). Nevertheless, we applied a very strict criterion, as defined in the Methods section, with the aim of comparing the kinetic data between the two groups of patients with a marked difference in angiographic progression. By this criterion, in the ACAD group, 11 patients (52%) presented with severe angiographic progression and 10 patients presented with non-severe progression. There was no difference in age (62 ± 9 vs. 61 ± 10; p = NS), BMI (27 ± 3 vs. 26 ± 3; p = NS), frequency of hypertension [3 (30%) vs. 4 (36%); p = NS], physical inactivity [4 (40%) vs. 5 (45%); p = NS], smoking habit [2 (20%) vs. 2 (18%); p = NS], mean total cholesterol (169 ± 20 mg/dl vs. 173 ± 24 mg/dl; p = NS), TGs (148 ± 83 mg/dl vs. 149 ± 72 mg/dl; p = NS), VLDL cholesterol (29 ± 19 mg/dl vs. 28 ± 14 mg/dl; p = NS), LDL cholesterol (95 ± 10 mg/dl vs. 96 ± 8 mg/dl; p = NS), or HDL cholesterol (45 ± 8 mg/dl vs. 44 ± 9 mg/dl; p = NS) between the subgroups with severe versus non-severe angiographic progression, respectively. However, as shown in Table 3, FCR-TG was 35% smaller (p = 0.026) and DI was 40% smaller (p = 0.04) in the group of patients with severe angiographic progression, suggesting an association between the impairment of intravascular TG lipolysis and severity of angiographic progression. No difference was observed in FCR-CE between these two subgroups (Table 3).


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  		Table 3 Gensini Score and Plasma FCR of the Emulsion Triglycerides in ACAD Group Patients Separated According to the Presence or Absence of Severe Angiographic Progression

 

   Discussion
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 Abstract
 Methods
 Results
 Discussion
References
 
The present long-term follow-up study reveals for the first time that an impaired rate of intravascular TG lipolysis is a strong and independent predictor of unfavorable clinical outcome in statin-treated patients with SCAD. In addition, among patients who presented with clinically refractory angina, the impairment in TG lipolysis was related to the degree of coronary lesion progression. This finding provides evidence to support the concept that the intravascular lipolysis rate is implicated in the prognosis of patients with CAD.

Estimation of lipolytic activity has long been made by the assay of post-heparin lipase activity in vitro, whereby a large amount of LPL released from tissue-binding sites is incubated with labeled TG-rich emulsions or lipoproteins to determine the catabolic rate. This technique may well evaluate the functionality of LPL or hepatic lipase but does not reflect intravascular lipolysis activity in vivo. The access of TG-rich lipoproteins to LPL, for example, might be controlled by capillary blood flow. In line with this assumption, the injection of heparin causes a rapid and transitory reduction of plasma TG levels, thereby indicating that the availability of LPL is significantly increased after heparin injection (13,14). Moreover, there is a very weak correlation between post-heparin plasma LPL protein and activity and VLDL TG concentration (r = –0.3; p < 0.05) (15). In this context, we also observed a weak association between post-heparin lipase activity and DI (r = 0.35; p = 0.015), suggesting that modulation of intravascular lipolysis in vivo is not measured in the assay in vitro (R. Santos, unpublished data, 2003). Kinetic analysis of the intravascular catabolism of chylomicron-like emulsions provides a high-resolution view of TG-rich particle metabolism in the circulation. It has been consistently demonstrated that chylomicron-like emulsions compete with native chylomicrons and VLDL for the same lipolytic mechanisms and hepatic receptor sites in a dose-dependent manner in both animal models and human subjects (3,16–20). As for native chylomicrons, emulsion particles undergo a two-step metabolic process, which is mediated by acquired apolipoproteins such as apoCII and apoE (i.e., extensive lipolysis by LPL and rapid uptake of remnants by the liver). Spleen uptake is negligible, indicating that emulsion remnants are not removed to a significant degree by non-physiological routes such as the mononuclear phagocyte system (16,17). Equally, the transfer of cholesteryl ester from the emulsion to native lipoprotein classes by cholesteryl ester transfer protein is minimal: 30 min after the injection <3% of the emulsion cholesteryl esters are found out of the 1.006 g/ml density fraction that corresponds to the emulsion density (3,10). Moreover, the emulsions are composed of homogenous preparations of particles in the size range of small lymph chylomicrons, and the removal of remnants is independent of size within the particle size range of the emulsion preparation (21). Thus, the kinetics of 3H-TG should reflect the combined impact of overall intravascular lipolysis activity in vivo and TG-rich lipoprotein uptake, whereas the DI should reflect TG lipolysis alone.

Consistent with our previous results (3,4), the enrolled CAD patients displayed a reduction of both FCR-TG and FCR-CE when compared with control subjects who did not present with angiographically detectable CAD. Such a finding indicates that in those patients there is a reduction of both intravascular lipolysis and removal of remnants of the chylomicron-like emulsions. During the observation period of 4.5 ± 0.9 years, and despite secondary prevention therapy, 33% of the followed CAD patients presented with clinically refractory angina and angiographic progression of coronary lesions. When we compared the baseline data of these patients with those who displayed a stable clinical evolution, we found a significantly slower intravascular TG lipolysis in those who had an unfavorable outcome. Moreover, in a multivariate analysis, patients who had a DI below the median displayed a three-fold higher risk of developing a clinically refractory angina than those with the DI above the median. This finding is consistent with data from statin clinical trials, suggesting that post-statin-treatment levels of plasma TGs predict the risk of cardiovascular disease (22). Therefore, we may conclude that the persistence of a slower intravascular TG lipolysis and, as a consequence, the elevated circulating levels of TG-rich lipoproteins have a clinical impact in statin-treated patients and should be considered as targets in future CAD prevention trials.

Increased levels of TG-rich lipoproteins have been demonstrated to impair overall artery vasodilator capacity, thereby reducing the post-obstructive reserve of blood flow (23,24). Therefore, patients who presented with a lower rate of intravascular lipolysis should have been more sensitive to the progression of obstructive coronary lesions. On the other hand, a reduced rate of remnant particle uptake (estimated from the measurement of FCR-CE) enhances the residence time of TG-rich lipoproteins, namely VLDL and chylomicrons, in the arterial bed, thereby facilitating their subendothelial migration and favoring plaque progression (25,26). Because these two mechanisms are not mutually exclusive, the clinical aggravation observed in those patients who displayed a more severely impaired intravascular lipolysis may possibly result from the combination of these two mechanisms. Nevertheless, our current findings can support only the mechanisms related to the progression of coronary lesions.

Conclusions.   We presently demonstrate that the DI, the net rate of intravascular TG catabolism from chylomicron-like emulsions, represents a significant and sensitive predictor of clinical progression of CAD in statin-treated patients. Therefore, our findings support the concept that TG-rich lipoproteins, VLDL, chylomicrons, and their remnants are implicated in the pathophysiology of atherosclerosis and highlight the key relationship between intravascular TG lipolysis and progression of CAD.


   Footnotes
 
This study was supported by FAPESP (Fundação de Amparo á Pesquisa do Estado de São Paulo), São Paulo, Brazil (grant no. 99/01229-2). Dr. Maranhão holds a Research Award from Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Brasilia, Brazil.


   References
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 Abstract
 Methods
 Results
 Discussion
 References
 

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  3. Maranhao RC, Feres MC, Martins MT, et al. Plasma kinetics of a chylomicron-like emulsion in patients with coronary artery disease. Atherosclerosis. 1996;126:15–25[CrossRef][Medline]
  4. Sposito AC, Maranhao RC, Vinagre CG, Santos RD, Ramires JA. Effects of etofibrate upon the metabolism of chylomicron-like emulsions in patients with coronary artery disease. Atherosclerosis. 2001;154:455–461[Medline]
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  6. Santos RD, Sposito AC, Ventura LI, Cesar LA, Ramires JA, Maranhao RC. Effect of pravastatin on plasma removal of a chylomicron-like emulsion in men with coronary artery disease. Am J Cardiol. 2000;85:1163–1166[CrossRef][Medline]
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