Primary prevention of coronary heart disease: from controversy to consensus

In recent years, interest has tended to focus on prevention of coronary events in high-risk groups, particularly those with established coronary heart disease. While this is understandable, it has led to a lack of emphasis on primary prevention. Yet it is only by means of primary or even pri-mordial prevention that a substantial reduction in coronary mortality on a population level will be achieved. This becomes clear when we consider that half of all persons who suffer a first myocardial infarction will die within the first month thereafter. Nevertheless, major progress has been made in primary prevention. Reliable risk algorithms have been constructed in Europe (PROCAM) and the U.S., and preliminary analyses on both sides of the Atlantic indicate that these algorithms can be useful applied to populations which are geographically and ethnically distinct from those in which they were derived. A notable trend in recent years is the increasing recognition of the metabolic syndrome with its key components of abdominal obesity, hypertriglyceridemia hypertension, low HDL-C, small, dense LDL, insulin resistance and hyperinsulinemia as being perhaps the most common and dangerous metabolic abnormality of all. Newer risk markers are being evaluated. The position of homocysteine remains unclear. Despite a strong association of elevated homocysteine with risk in case-control studies, prospective investigations have been less convincing. Evidence is beginning to accumulate from cross-sectional and prospective studies that markers of inflammation such as C-reactive peptide may improve our ability to predict risk of coronary events. While these data are encouraging, results of further studies must be awaited before the true place of these markers can be determined. The same can be said of many genetic markers of risk. Though a very large number of association studies have indicated links between a variety of genetic markers and coronary risk, these effects have tended to disappear after controlling for epigenetic and confounding factors and with increasing sample sizes. Finally, much attention is being devoted to non-invasive imaging of the coronary arteries. Such methods hold much promise as a screening test to exclude coronary stenosis in low-risk individuals. However, the measurement of calcium content of the arterial wall by EBCT has yet to prove its usefulness as a predictor of coronary events.

Zinc protoporphyrin and percentage of hypochromic erythrocytes as markers of functional iron deficiency during therapy with erythropoietin in patients with advanced acquired immunodeficiency syndrome

BACKGROUND

We assessed zinc protoporphyrin (ZPP) and the percentage of hypochromic erythrocytes in patients with advanced acquired immunodeficiency syndrome (AIDS) treated with recombinant erythropoietin (rhEPO).

METHODS

Patients received 150 IU rhEPO subcutaneously every second day for 10 days, and 150 IU rhEPO plus 62.5 mg of intravenous iron every second day for an additional 10 days.

RESULTS

Before rhEPO therapy, ZPP was at 64.3 +/- 27.3 micromol/mol heme and the percentage of hypochromic erythrocytes was elevated at 9.7%, indicating mild functional iron deficiency. Ferritin was 1,002 +/- 956 microg/L, with transferrin saturation of 19.1 +/- 9.7%. Under rhEPO alone, ZPP rose to 80.1 +/- 21.6 micromol/mol heme and the percentage of hypochromic red cells rose to 22.9 +/- 4.7%; ferritin fell to 705 +/- 601 microg/L and transferrin saturation fell to 12 +/- 6.3%. When rhEPO was supplemented with iron, ZPP fell to 70.4 +/- 20.5 micromol/mol heme, the percentage of hypochromic red cells fell to 14.7 +/- 3.4%; ferritin was unchanged at 771 +/- 62 microg/L and transferrin saturation rose to 20.5 +/- 5.5%.

CONCLUSIONS

In contrast to ferritin and transferrin saturation, ZPP and the percentage of hypochromic erythrocytes effectively detect the functional iron deficiency under rhEPO therapy in advanced AIDS.

Systemic inflammatory parameters in patients with atherosclerosis of the coronary and peripheral arteries

Plasma concentration of markers of inflammation are increased in patients with atherosclerosis. However, it is unclear whether the pattern and magnitude of this increase vary with the site and extent of disease. In 147 patients undergoing semiquantitative coronary angiography, we measured the acute-phase reactants C-reactive protein (CRP) or serum amyloid A (SAA); the proinflammatory cytokine interleukin 6 (IL-6); the active and total fractions of the anti-inflammatory cytokine transforming growth factor-beta (TGF-beta); the macrophage activation marker neopterin; and the infection marker procalcitonin. Compared with 62 patients without either coronary artery disease (CAD) or peripheral artery disease (PAD), 57 patients with CAD but no PAD showed greater median CRP (0. 4 versus 0.2 mg/dL, P=0.004) and IL-6 (3.8 versus 1.6 pg/mL, P=0. 007) levels and a lower level of active-TGF-beta (57 versus 100 ng/mL, P=0.038). Moreover, CRP, IL-6, and neopterin levels showed a positive and the active TGF-beta level a negative correlation with the extent of coronary atherosclerosis. Compared with these 57 patients with CAD alone, 15 patients with PAD and CAD had higher median levels of SAA (17 versus 7 mg/mL, P=0.008), IL-6 (12 versus 4 pg/mL, P=0.002), neopterin (14 versus 11 mg/dL, P=0.006), and total TGF-beta (11834 versus 6417 ng/L, P=0.001). However, these strong univariate associations of markers of inflammation and atherosclerosis were lost in multivariate analysis once age, sex, and high density lipoprotein cholesterol or fibrinogen were taken into account. Increased plasma levels of CRP, SAA, IL-6, TGF-beta, neopterin, and procalcitonin constitute an inflammatory signature of advanced atherosclerosis and are correlated with the extent of disease but do not provide discriminatory diagnostic power over and above established risk factors.

Apolipoprotein A-I (R151C)Paris is defective in activation of lecithin: cholesterol acyltransferase but not in initial lipid binding, formation of reconstituted lipoproteins, or promotion of cholesterol efflux

ApoA-I(R151)Paris is a natural apolipoprotein (apo) A-I variant that is associated with low levels of high-density lipoprotein cholesterol (HDL-cholesterol) and the partial deficiency of lecithin:cholesterol acyl-transferase (LCAT) in the plasma of heterozygous carriers. We compared the abilities of recombinant normal apoA-I and recombinant apoA-I(R151C)Paris to clear an emulsion of dimyristoylphosphatidylcholine (DMPC), to form reconstituted lipoproteins with dipalmitoylphosphatidylcholine (DPPC), to activate LCAT, and to promote efflux of biosynthetic cholesterol from porcine aortic smooth muscle cells (SMCs) or of exogenous cholesterol from lipid-loaded mouse peritoneal macrophages. Recombinant apoA-I(R151C)Paris occurred in monomeric and dimeric forms at a ratio of 60:40. Normal apoA-I and apoA-I(R151C)Paris cleared DMPC emulsions at equal rates. Both isoforms associated completely with DPPC during cholate dialysis. Normal apoA-I formed one single particle with a mean diameter of 9.3 nm, whereas apoA-I(R151)Paris gave rise to three particles with mean diameters of 9.3 nm (containing 74% of apoA-I), 10.6 nm, and 12.1 nm, respectively. Compared to normal apoA-I, apoA-I(R151C)Paris had a reduced LCAT-cofactor activity with a 60% lower Vmax/Km ratio due to a 50% higher affinity constant, Km. During incubations for 10 min and 360 min, normal apoA-I/DPPC complexes and apoA-I(R151C)Paris/DPPC complexes were equally efficient in releasing biosynthetic cholesterol from SMCs. In the lipid-free form, apoA-I(R151C)Paris induced normal hydrolysis of cholesteryl esters and normal cholesterol efflux from lipid-loaded mouse-peritoneal macrophages. In conclusion, in addition to its ability to form homo- and heterodimers, apoA-I(R151C)Paris is characterized by defective LCAT-cofactor activity but by normal lipid binding and cholesterol-efflux-promoting abilities.

Human macrophages synthesize type VIII collagen in vitro and in the atherosclerotic plaque

Type VIII collagen is a short-chain collagen that is present in increased amounts in atherosclerotic lesions. Although the physiological function of this matrix protein is unclear, recent data suggest an important role in tissue remodeling. Type VIII collagen in the atherosclerotic lesion is mainly derived from smooth muscle cells. We now show that macrophages in the atherosclerotic vessel wall and monocytes in adjacent mural thrombi also express type VIII collagen. We demonstrated this using a novel combined fluorescence technique that simultaneously stains, within the same tissue section, specific RNAs by in situ hybridization and proteins by indirect immunofluorescence. In culture, human monocyte/macrophages expressed type VIII collagen at all time points from 1 h to 3 wk after isolation. Western blotting and immunoprecipitation also revealed secretion of type VIII collagen into the medium of 14-day-old macrophages. Because this is the first report of secretion of a collagen by macrophages, we tested the effect of lipopolysaccharide (LPS) and interferon gamma, substances that stimulate macrophages to secrete lytic enzymes, on macrophage expression of type VIII collagen. LPS and interferon gamma decreased expression of type VIII collagen. By contrast, secretion of matrix metalloproteinase 1 (MMP 1) was increased, indicating a switch from a collagen-producing to a degradative phenotype. Double in situ hybridization studies of expression of type VIII collagen and MMP 1 in human coronary arteries showed that in regions important for plaque stability, the ratio of MMP 1 RNA to macrophage type VIII collagen RNA varies widely, indicating that the transition from one phenotype to the other that we observed in vitro may also occur in vivo.

High risk strategies for atherosclerosis

Calculating a person's chances of developing coronary heart disease (CHD) is not simple, as many risk factors interact in a complex fashion. Thus many markers, though significant in univariate comparisons, are no longer so when multivariate analysis is performed. Those factors contributing independently to risk can be identified only in prospective investigations such as the Münster Heart (PROCAM) or the Framingham studies. In the Münster Heart study, follow-up of middle-aged men for eight years identified the following nine independent risk variables: age, smoking history, personal history of angina pectoris, family history of myocardial infarction, systolic blood pressure, raised plasma low density lipoprotein cholesterol (LDL-C), low plasma high density lipoprotein cholesterol, raised fasting plasma triglyceride and presence of diabetes mellitus. These have been used to generate an algorithm for prediction of first coronary events which is available in interactive fashion on the internet'. Large trials have shown that lowering LDL-C reduces the risk of CHD, and diminishes CHD morbidity and mortality in persons without prior evidence of coronary atherosclerosis (primary prevention). This is even more the case in patients with such evidence (secondary prevention). It appears that lowering of LDL-C also reduces all-cause mortality in secondary prevention.

Obesity, mortality and cardiovascular disease in the Münster Heart Study (PROCAM)

In the Münster Heart Study (PROCAM), 16,288 men aged 40.6 +/- 11.3 years (mean +/- S.D.) and 7328 women aged 36.0 +/- 12.3 years were enrolled between 1979 and 1991. Mean body mass indices (BMIs) were 25.6 +/- 3.3 and 23.8 +/- 4.1 kg/m2 in men and women, respectively. There was a graded and continuous positive interaction in both men and women between BMI, age and serum total cholesterol, low density lipoprotein (LDL) cholesterol, and blood pressure (both systolic and diastolic). High density lipoprotein (HDL) cholesterol tended to increase with age, but decreased in graded fashion with increases in BMI in both sexes. Triglyceride increased with BMI in both sexes and with age in women, but decreased in the older age groups of overweight and obese men. Though fasting blood glucose increased with age and BMI in both sexes, the increase was more marked in women. Among the 10,856 men aged 36-65 years at study entry, 313 deaths occurred within a follow-up period of 7.1 +/- 2.4 years. Among these men, increased mortality was seen at high BMIs in both smokers and non-smokers and was caused by coronary heart disease (CHD). Increased mortality at low BMI was seen in smokers but not in non-smokers and was due to an increase in cancer deaths. The BMI-associated increase in CHD death was completely accounted for by the factors contained in the Münster Heart Study (PROCAM) risk algorithm, indicating that the effect of overweight and obesity on CHD is mediated via other risk factors.

Multiple dysfunctions of two apolipoprotein A-I variants, apoA-I(R160L)Oslo and apoA-I(P165R), that are associated with hypoalphalipoproteinemia in heterozygous carriers

ApoA-I(R160L)Oslo and apoA-I(P165R) are naturally occurring apolipoprotein (apo) A-I variants that are associated with low HDL-cholesterol in heterozygous carriers. We characterized the capacity of these variants to bind lipid, to activate lecithin:cholesterol acyltransferase (LCAT), and to promote efflux of biosynthetic cholesterol from porcine aortic smooth muscle cells (SMCs) or exogenous cholesterol from lipid-loaded mouse peritoneal macrophages. During cholate dialysis, normal apoA-I and both variants associated completely with dipalmitoylphosphatidylcholine (DPPC) and formed rLpA-I of identical size. However, both apoA-I(P165R) and apoA-I(R160L)Oslo showed a reduced capacity to clear a turbid emulsion of dimyristoylphosphatidylcholine (DMPC). Compared to normal apoA-I, the LCAT-cofactor activity of apoA-I(P165R) and apoA-I(R160L)Oslo as defined by the ratio of Vmax to appKm was reduced significantly by 62% and 29%, respectively (here and throughout the text, the apparent Km is given as Michaelis-Menten kinetics do not take particle binding into account and therefore would result in errors with an interfacial enzyme such as LCAT; Vmax estimates are not affected by this error). ApoA-I/DPPC complexes induced biphasic cholesterol efflux from SMCs with a fast and a slow efflux component. Compared to rLpA-I reconstituted with wild type apoA-I, rLpA-I with apoA-I(P165R) or apoA-I(R160L)Oslo were significantly less effective in promoting cholesterol efflux from SMCs in incubations of 10 min duration but equally effective in incubations of 6 h duration. Lipid-free apoA-I did not induce efflux of biosynthetic cholesterol from SMCs but induced hydrolysis of cholesteryl esters and cholesterol efflux from acetyl-LDL-loaded mouse peritoneal macrophages. In the lipid-free form, both apoA-I variants promoted normal cholesterol efflux from murine peritoneal macrophages. We conclude that amino acid residues arginine 160 and proline 165 of apoA-I contribute to the formation of a domain that is very important for initial lipid binding and contributes to LCAT-activation and promotion of initial cholesterol efflux but not to the stabilization of preformed rLpA-I.

Hypochromic red cells and reticulocyte haemglobin content as markers of iron-deficient erythropoiesis in patients undergoing chronic haemodialysis

BACKGROUND

In patients on chronic haemodialysis, because of a non-specific increase in serum ferritin, iron deficiency may be overlooked leading to failure of erythropoietin treatment. A reticulocyte haemglobin content < 26 pg and a percentage of hypochromic red cells > 2.5 have been proposed as markers of iron-deficient erythropoiesis in such subjects, but it is unclear which parameter is superior.

METHODS

We measured haematocrit, reticulocyte haemglobin content, ferritin and the percentage of hypochromic red cells over 10-150 days in 36 chronic haemodialysis patients in a university hospital. Transferrin saturation was also measured in a subset of 25 patients; iron deficiency was defined as a transferrin saturation < 15%.

RESULTS

The diagnostic sensitivity and specificity of a reticulocyte haemoglobin content < 26 pg in detecting iron deficiency were 100% and 73% respectively, compared with 91% and 54% for a percentage of hypochromic red cells > 2.5. Paradoxical reticulocyte haemglobin concentrations occurred on follow-up in five patients receiving 4000 U erythropoietin per haemodialysis (HD). In three patients, reticulocyte haemglobin content exceeded 26 pg despite a persistent lack of iron. In a fourth, iron gluconate (62.5 mg i.v./HD) increased transferrin saturation to 27% and reduced the percentage of hypochromic red cells from 12 to 4, while reticulocyte haemglobin remained > 30 pg. In the final patient, iron gluconate increased transferrin saturation from 8 to 30% and reduced the percentage of hypochromic red cells from 40 to below 5, but reticulocyte haemglobin content remained < or = 26 pg throughout.

CONCLUSIONS

The reticulocyte haemglobin content is superior to the percentage of hypochromic red cells in detecting iron deficiency in haemodialysis patients.

Smoking, lipoproteins and coronary heart disease risk. Data from the Münster Heart Study (PROCAM)

AIMS

The mechanism of the increase in coronary heart disease risk associated with smoking is unclear, but may partly be due to smoking-related changes in intermediate risk factors such as lipid levels, fibrinogen and blood pressure. We therefore examined the distribution of these variables among smokers and non-smokers in the Münster Heart Study.

METHODS

20696 men, aged 41.7+/-2.7 years (mean +/- SD) and 10212 women, aged 37.0+/-2.6 years, were enrolled between 1978 and 1995. Thirty-two percent of women and 36% of men smoked. Compared to non-smokers, mean levels of low density lipoprotein cholesterol, total cholesterol, triglycerides and fibrinogen were increased, respectively, by 1.4%, 0.9%, 15% and 12.1% in male and by 2.0%, 5.5%, 12% and 3.4% in female smokers. Mean high density lipoprotein cholesterol levels, body mass index and blood pressure were reduced, respectively, by 6.4%, 3.8%, and 2% in male, and by 6.7% 1.2% and 2% in female smokers. In the subgroup of 4639 men aged 40 to 65 with 8 years of follow-up, the coronary event rate (definite myocardial infarction, sudden cardiac death) in cigarette smokers was more than twice that of non-smokers with otherwise identical risk factors.

CONCLUSION

In the Münster Heart Study, smoking was associated with adverse changes in lipids (of greater magnitude in women), and fibrinogen (of greater magnitude in men). However, these changes explained only a small part of the smoking-related increase in coronary heart disease risk.

Diagnosis and management of new cardiovascular risk factors

Independent risk factors for coronary heart disease (CHD) can best be identified by means of long-term prospective epidemiological studies. These factors should not be viewed in isolation, but as part of a complex governing a person's global risk of CHD. In the Münster Heart Study (PROCAM), 8-year follow up of a cohort of middle-aged men has led to the identification of nine variables which independently contribute to CHD risk: age, smoking history, personal history of angina pectoris, family history of myocardial infarction (MI), presence of diabetes mellitus, systolic blood pressure and the levels of low density lipoprotein (LDL) cholesterol, high density lipoprotein cholesterol and triglyceride. An algorithm based on these risk factors may be used to calculate an individual's risk of fatal or non-fatal MI and is available in interactive fashion on the website of the International Task Force for Prevention of Coronary Heart Disease at www.chd-taskforce.com. Treatment goals for LDL cholesterol depend on a person's level of risk: for persons with a small increase in risk 160 mg x dl(-1), for those with a moderate increase in risk 135 mg x dl(-1) and for those at high risk, including those with a history of CHD (secondary prevention) 100 mg x dl(-1). Intervention trials indicate that lowering of LDL cholesterol for 5 years produces much of the benefit predicted from the epidemiological data. The place of newer risk markers such as Lp(a), homocysteine, and parameters of clotting and inflammation in risk prediction and management remains to be determined.

Assignment of Tangier disease to chromosome 9q31 by a graphical linkage exclusion strategy

A low level of high density lipoprotein (HDL) cholesterol is a strong predictor of ischaemic heart disease (IHD) and myocardial infarction. One cause of low HDL-cholesterol is Tangier disease (TD), an autosomal codominant inherited condition first described in 1961 in two siblings on Tangier Island in the United States of America. Apart from low HDL-cholesterol levels and an increased incidence of atherosclerosis, TD is characterized by reduced total cholesterol, raised triglycerides, peripheral neuropathy and accumulation of cholesteryl esters in macrophages, which causes enlargement of the liver, spleen and tonsils. In contrast to two other monogenic HDL deficiencies in which defects in the plasma proteins apoA-I and LCAT interfere primarily with the formation of HDL (refs 7-10), TD shows a defect in cell signalling and the mobilization of cellular lipids. The genetic defect in TD is unknown, and identification of the Tangier gene will contribute to the understanding of this intracellular pathway and of HDL metabolism and its link with IHD. We report here the localization of the genetic defect in TD to chromosome 9q31, using a genome-wide graphical linkage exclusion strategy in one pedigree, complemented by classical lod score calculations at this region in a total of three pedigrees (combined lod 10.05 at D9S1784). We also provide evidence that TD may be due to a loss-of-function defect.