American Heart Journal
Volume 146, Issue 6 , Pages 1060-1063, December 2003

Increased levels of pregnancy-associated plasma protein-A in patients with hypercholesterolemia: the effect of atorvastatin treatment☆

  • Tomáš Štulc, MD

      Affiliations

    • Third Department of Internal Medicine, Charles University, Prague, Czech Republic
    • Corresponding Author InformationReprint requests: Tomáš Stulc, MD, 3rd Department of Internal Medicine, U Nemocnice 1, Praha 2, Czech Republic 128 21.
    • ,
  • Ivan Malbohan, MD, PhD

      Affiliations

    • Institute of Clinical Chemistry, First Faculty of Medicine, Charles University, Prague, Czech Republic
    • ,
  • Jan Malík, MD, PhD

      Affiliations

    • Third Department of Internal Medicine, Charles University, Prague, Czech Republic
    • ,
  • Lenka Fialová, MD, PhD

      Affiliations

    • Institute of Clinical Chemistry, First Faculty of Medicine, Charles University, Prague, Czech Republic
    • ,
  • Jiřina Soukupová, PhD

      Affiliations

    • Institute of Clinical Chemistry, First Faculty of Medicine, Charles University, Prague, Czech Republic
    • ,
  • Richard Češka, MD, PhD

      Affiliations

    • Third Department of Internal Medicine, Charles University, Prague, Czech Republic

Received 13 February 2003; accepted 20 May 2003.

Article Outline

Abstract 

Background

Serum levels of pregnancy-associated plasma protein-A (PAPP-A) have recently been linked to plaque instability and are increased in acute coronary syndromes. The relation between PAPP-A levels and coronary risk factors, namely blood lipids, has not been studied to date. We have therefore investigated whether serum PAPP-A levels are increased in asymptomatic hypercholesterolemic subjects and whether PAPP-A levels are influenced by atorvastatin therapy.

Methods

We examined 27 subjects with isolated hypercholesterolemia free of manifest vascular disease and 29 age-matched healthy control subjects. Patients were examined at baseline and after 10 weeks of atorvastatin treatment (20 mg/d).

Results

In untreated hypercholesterolemic subjects, PAPP-A levels were significantly higher than in control subjects (8.02 ± 1.86 mU/L vs 6.50 ± 2.54 mU/L, P = .018). There was no correlation between PAPP-A levels and serum lipid levels. Atorvastatin treatment reduced total and LDL-cholesterol by 31% and 40%, respectively. Despite this profound lipid lowering, there was no significant change in the serum PAPP-A levels.

Conclusions

PAPP-A levels are elevated in hypercholesterolemic subjects without clinical signs of atherosclerosis. PAPP-A may therefore not only reflect plaque instability but also serve as a marker of total atherosclerotic burden in asymptomatic subjects with hyperlipidemia. However, PAPP-A levels are not influenced by atorvastatin treatment.

 

Conventional risk factors often fail to identify patients who eventually develop premature atherosclerosis.1 New markers of atherosclerotic plaque development and activity are therefore sought to identify patients at highest risk of clinical events. Various inflammatory mediators such as C-reactive protein (CRP) and endothelium or monocyte-derived molecules have been linked to both atheroslerosis and acute coronary syndromes.2, 3, 4

Quite recently it has been demonstrated that circulating levels of pregnancy-associated plasma protein A (PAPP-A) are elevated in patients with unstable angina and acute myocardial infarction.5, 6 PAPP-A, a zinc-binding metalloproteinase, has been detected in vascular smooth muscle cells in unstable and eroded atherosclerotic lesions5 and in the arteries after experimental injury.7 It was therefore hypothesized that increased plasma levels of PAPP-A may reflect the instability of atherosclerotic plaques and that PAPP-A might be a novel marker of acute coronary syndromes.5, 8

Hypercholesterolemia is a strong risk factor for premature atherosclerosis, and it is associated with increased serum levels of inflammatory markers.9 Cholesterol lowering is critical treatment in reducing the risk of acute cardiac events; event reduction is accompanied by a decrease of serum inflammatory markers.2, 10, 11 However, the relation between circulating PAPP-A levels and hyperlipidemia has not been studied to date. We have therefore investigated whether serum PAPP-A levels are increased in asymptomatic middle-aged hypercholesterolemic subjects compared with normolipidemic control subjects and whether PAPP-A levels are influenced by atorvastatin therapy.

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Methods 

Subjects and study design 

Patients with primary hypercholesterolemia were included in the study. The subjects were >18 years of age, with serum total cholesterol >7.0 mmol/L after 4 weeks of lipid-lowering diet, without any lipid-lowering medication. Patients with hypertriglyceridemia (triglycerides >4.5 mmol/L), secondary hyperlipidemia, manifest vascular disease or previous history of acute coronary syndromes, diabetes, malignancy or other major disease were excluded. The control group consisted of healthy normolipidemic subjects (total cholesterol <6.0 mmol/L, triglycerides <2.0 mmol/L).

Hypercholesterolemic patients were treated with atorvastatin 20 mg OD for 12 weeks. Clinical and laboratory examinations were performed at baseline and at the end of the treatment period. In the control group, only baseline examination was performed. Blood for laboratory tests was drawn after an overnight fast. All subjects signed an informed consent; the study protocol was approved by the local ethics committee. The study conforms with the principles outlined in the Declaration of Helsinki.

Laboratory measurements 

Serum PAPP-A and high-sensitivity CRP (hsCRP) levels were measured by immunometric assay (PAPP-A and us-CRP kits, Cezanne, France), using time-resolved amplified cryptate emission12 technology (TRACE, Kryptor analyzer, Cezanne, France). The intra-assay and interassay variation coefficient of the PAPP-A measurements in our laboratory were 1.2% and 2.9%, respectively. The sera for the PAPP-A and CRP measurements were stored at −85°C until analysis. Serum total cholesterol, triglyceride, and HDL cholesterol levels were measured using automated analyzer methods; LDL cholesterol concentrations were calculated by using the Friedewald formula. Biochemical markers of renal, liver, and skeletal muscle function included serum transaminases, creatinine, creatine kinase, and a full blood count.

Statistics 

The results are expressed as mean ± SD. For PAPP-A and CRP levels, the Mann-Whitney U test was used to compare the differences between the control subjects and patients; Wilcoxon paired test was used to compare the values before and after treatment. Differences in the remaining variables were tested by the 2-sample or paired t test as appropriate. Spearman correlation was used to test for the relation between variables. All statistical tests are 2-sided.

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Results 

Twenty-nine control subjects and 27 patients with hypercholesterolemia were included in the study; all patients completed the entire treatment period. The average follow-up time was 89 ± 8 days. The treatment was well tolerated; neither serious side effects nor significant change in safety laboratory parameters were noted throughout the study.

Baseline characteristics of the study groups are shown in Table I. The groups were comparable with respect to age, sex, and body mass index. Hypertension and smoking were slightly more frequent among the patients than among the control subjects, but the difference was not statistically significant.

Table I. Baseline characteristics and lipid and CRP results of the study subjects
Control subjectsPatients before treatmentPatients after treatment
Number2927
Sex (male/female)9/208/19
Age (y)47.8 ± 6.552.3 ± 11.5
BMI (kgm−2)25.2 ± 3.426.7 ± 4.3
Hypertension6 (21)9 (33)
Smoking5 (17)9 (33)
TC (mmol/L)5.14 ± 0.728.59 ± 1.60*5.87 ± 1.12‡
LDL-C (mmol/L)2.99 ± 0.646.20 ± 1.39*3.67 ± 0.94‡
HDL-C (mmol/L)1.61 ± 0.321.63 ± 0.321.61 ± 0.33
TG (mmol/L)1.21 ± 0.661.67 ± 0.63†1.33 ± 0.37§
CRP (mg/L)1.11 ± 1.102.21 ± 1.72†1.63 ± 1.65∥

Hypertension and smoking are presented as the number (percentage) of patients with the condition. BMI, Body mass index; TC, total cholesterol; TG, triglycerides; HDL-C, HDL-cholesterol; LDL-C, LDL-cholesterol; CRP, C-reactive protein.

∗ P < .001 patients versus controls.

† P < .01 patients versus controls.

‡ P < .001 patients before versus after treatment.

§ P < .01 patients before versus after treatment.

∥ P < .05 patients before versus after treatment.

Serum levels of total and LDL cholesterol and of triglycerides were higher in the patients than in the control subjects (Table I); all these parameters were significantly reduced by atorvastatin treatment. HDL cholesterol levels were virtually identical in patients and control subjects, and they were not influenced by the therapy.

In untreated patients, PAPP-A levels were significantly higher than in control subjects (8.02 ± 1.86 mU/L vs 6.50 ± 2.54 mU/L, P = .018) (Figure 1). There was no significant change in PAPP-A levels after atorvastatin therapy (8.02 ± 1.86 mU/L vs 7.67 ± 1.89 mU/L, P = .443). CRP levels were also higher in patients at baseline than in control subjects, and the levels were significantly reduced by atorvastatin treatment (Table I). There was no correlation between PAPP-A or CRP levels and serum total, LDL or HDL-cholesterol or triglycerides in either study group.

  • View full-size image.
  • Figure 1. 

    Serum PAPP-A levels in control subjects (circle) and in patients with hypercholesterolemia before (filled square) and after 12 weeks of atorvastatin treatment (open square). Results are shown as individual values and mean ± SD.

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Discussion 

The current study demonstrates for the first time that circulating PAPP-A levels are increased in patients with hypercholesterolemia who are free of clinically manifest atherosclerosis. Our results extend the earlier observations by others that PAPP-A levels are increased in patients with acute coronary syndromes.5, 6

PAPP-A was originally identified in the serum of pregnant women.13 PAPP-A is produced by placental tissue; circulating PAPP-A levels increase during pregnancy and they are used in the fetal diagnosis of Down syndrome.14 Only recently has PAPP-A been identified in nonplacental tissues,15, 16 the concentrations in the sera of nonpregnant human beings being several orders of magnitude lower than during pregnancy.17

The physiological role of PAPP-A is only beginning to be unraveled. PAPP-A is a high-molecular-weight, zinc-binding metalloproteinase, which acts as a specific protease of IGF binding protein-4 (IGFBP-4).15 By degradation of IGFBP-4, PAPP-A releases free IGF-I, making it available for binding to the specific receptors. PAPP-A therefore appears to be a local regulator of insulin-like growth factor (IGF)-I activity, and it may play a role in local proliferative responses. Upregulation of PAPP-A in unstable plaques,5 together with increased circulating levels in hypercholesterolemia and coronary atherosclerosis,5, 6 suggest that the involvement of the PAPP-A/IGF-I system may be clinically relevant.

So far, there are only two studies regarding the relation between serum PAPP-A levels and atherosclerosis. In their pioneering work, Bayes-Genis et al5 observed substantially and significantly higher PAPP-A levels in acute myocardial infarction and in unstable angina than in control subjects (20.6 mIU/L vs 14.9 mIU/L vs 7.4 mIU/L). At autopsy, PAPP-A expression was abundant in unstable atherosclerotic plaques but was much lower in stable plaques. Similarly, Denktas et al6 observed significantly higher serum PAPP-A levels in patients with unstable angina or acute myocardial infarction (7.1 mIU/L) than in control subjects (5.5 mIU/L). Based on these results, it was suggested that increased plasma levels of PAPP-A reflect the instability of atherosclerotic plaques and that PAPP-A might be a specific marker of acute coronary syndromes.5

In our study, however, the serum PAPP-A levels were significantly higher in patients with severe hypercholesterolemia than in the healthy normolipidemic control subjects, despite the absence of clinically manifest atherosclerosis. This suggests that the increase in PAPP-A levels is not limited to patients with acute coronary syndromes but may also reflect the earlier stages of atherosclerotic lesions in subjects with hyperlipidemia, even in the absence of clinical signs of atherosclerosis. The role of PAPP-A in the initiation and progression of stable atherosclerotic lesions therefore deserves further investigation, and circulating PAPP-A might eventually become a novel marker of preclinical atherosclerosis. However, the interpretation of increased PAPP-A levels is difficult. The values reported for patients with acute coronary syndromes by Bayes-Genis et al and by Denktas et al differ substantially, whereas, at the same time, the PAPP-A increase in our hyperlipidemic patients is virtually identical with that reported by Denktas et al for patients with acute coronary syndromes. The reasons for these discrepancies are currently unclear, and the use of PAPP-A as a marker of unstable plaques or preclinical atherosclerosis therefore requires further research and careful evaluation.

Atorvastatin did not change the circulating PAPP-A levels significantly, despite the profound lipid-lowering. This contrasts with the observed decrease in serum CRP levels: in our patients, CRP was twice as high as in control subjects, and it was reduced by 27% after the atorvastatin treatment. The reason for the lack of decrease in PAPP-A levels remains unclear. The association of PAPP-A with acute coronary syndromes and its expression in the unstable plaques5, 6 would suggest that PAPP-A is involved in the plaque inflammatory responses. Plaque inflammation and serum inflammatory markers have been shown to decrease within a short time after lipid-lowering.10, 11 PAPP-A might therefore be expected to follow the similar pattern, but this was not the case in our study. However, as mentioned earlier, the experimental studies suggest that PAPP-A may rather be involved in the plaque proliferative responses than in the plaque inflammation. In the experimental model, the expression of PAPP-A in vascular smooth muscle cells was upregulated in response to balloon injury, which suggests its role in the proliferative repair processes.7 This effect of PAPP-A is probably related to the IGF-I system. IGF-I was shown to support vascular smooth muscle cell proliferation and migration,18 and IGFBP-4 overproduction results in vascular smooth muscle hypoplasia due to IGF-I blockade.19 Proteolytically degrading IGFBP-4, PAPP-A increases the availability of free IGF-I in a paracrine fashion,7, 15 which could contribute to the proliferative processes within the atherosclerotic plaques. The increased expression observed in the unstable plaques may therefore reflect the compensatory reparative activity, which is secondary to matrix degradation in the unstable plaques.

Conclusions 

The emerging role of PAPP-A as a marker of acute coronary syndromes brought about the interest in the novel and unsuspected function of this protease in atherosclerotic plaque biology. In this study, we have demonstrated for the first time that PAPP-A levels are elevated in asymptomatic patients with hypercholesterolemia. PAPP-A may therefore not only reflect plaque instability, as suggested earlier, but also serve as a marker of atherosclerotic burden in subjects with hyperlipidemia, even in the absence of clinical signs of atherosclerosis. Further research is needed to clarify whether PAPP-A might eventually become a clinically useful marker of preclinical atherosclerosis.

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References 

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☆ Supported by grants J 13/98 11110000 2-1 and IGA NB 7392-3.

PII: S0002-8703(03)00446-0

doi:10.1016/S0002-8703(03)00446-0

American Heart Journal
Volume 146, Issue 6 , Pages 1060-1063, December 2003

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