High Lp(a) lipoprotein level in maternal serum may interfere with placental circulation and cause fetal growth retardation

Lipoprotein(a): An underrecognized genetic risk factor for malignant coronary artery disease in young Indians

Malignant coronary artery disease (CAD) refers to a severe and extensive atherosclerotic process involving multiple coronary arteries in young individuals (aged <45 years in men and <50 years in women) with a low or no burden of established risk factors. Indians, in general, develop acute myocardial infarction (AMI) about 10 years earlier; AMI rates are threefold to fivefold higher in young Indians than in other populations. Although established CAD risk factors have a predictive value, they do not fully account for the excessive burden of CAD in young Indians. Lipoprotein(a) (Lp(a)) is increasingly recognized as the strongest known genetic risk factor for premature CAD, with high levels observed in Indians with malignant CAD. High Lp(a) levels confer a twofold to threefold risk of CAD-a risk similar to that of established risk factors, including diabetes. South Asians have the second highest Lp(a) levels and the highest risk of AMI from the elevated levels, more than double the risk observed in people of European descent. Approximately 25% of Indians and other South Asians have elevated Lp(a) levels (≥50 mg/dl), rendering Lp(a) a risk factor of great importance, similar to or surpassing diabetes. Lp(a) measurement is ready for clinical use and should be an essential part of all CAD research in Indians.

Lipoprotein (a): impact by ethnicity and environmental and medical conditions

Levels of lipoprotein (a) [Lp(a)], a complex between an LDL-like lipid moiety containing one copy of apoB, and apo(a), a plasminogen-derived carbohydrate-rich hydrophilic protein, are primarily genetically regulated. Although stable intra-individually, Lp(a) levels have a skewed distribution inter-individually and are strongly impacted by a size polymorphism of the LPA gene, resulting in a variable number of kringle IV (KIV) units, a key motif of apo(a). The variation in KIV units is a strong predictor of plasma Lp(a) levels resulting in stable plasma levels across the lifespan. Studies have demonstrated pronounced differences across ethnicities with regard to Lp(a) levels and some of this difference, but not all of it, can be explained by genetic variations across ethnic groups. Increasing evidence suggests that age, sex, and hormonal impact may have a modest modulatory influence on Lp(a) levels. Among clinical conditions, Lp(a) levels are reported to be affected by kidney and liver diseases.

Lower Incidence of M2/ANXA5 Carriage in Recurrent Pregnancy Loss Patients With Elevated Lipoprotein(a) Levels

This study compared the incidence of M2/ANXA5 haplotype carriage, a documented repeated miscarriage risk factor, in patient groups with normal and elevated lipoprotein(a) (Lp(a)) levels. A total of 138 women with ≥2 consecutive, idiopathic recurrent miscarriages, categorized in patients with elevated (≥30 mg/dL, n = 44) and normal Lp(a) level (<30 mg/dL, n = 94) were recruited at the recurrent pregnancy loss (RPL) clinic of Munich Großhadern University Hospital. A total of 500 fertile women served as controls. All patients were genotyped for ANXA5 promoter haplotypes, genetic frequencies were compared, and odds ratios (ORs) and relative risks of M2 carriers were calculated. Women with M2 haplotype had an almost 2 times higher relative risk of RPL (OR 2.6, 95% confidence interval 1.5-4.6, P = .001) than fertile controls. Furthermore, risk rises to 2.47 in patients having normal Lp(a) levels (OR 3.2, 95% confidence interval 1.7-5.9, P = .001), whereas women with high Lp(a) levels exhibit notably lower apparent RPL risk of 1.39 (OR 1.4, 95% confidence interval 0.5-4.1, P = .659).

Ethnic heterogeneity in the longitudinal effects of placental vascular blood flow on birthweight

OBJECTIVE

Our goals were: (1) to estimate the longitudinal trends in uterine artery (UtArt) and umbilical artery (UmArt) resistance indices (RIs) in different ethnic strata; (2) to estimate time-dependent changes across gestation in the influence of variation in UtArt and UmArt RI on variation in birthweight in different ethnic strata; and (3) to determine the optimum set of UtArt and UmArt RIs for predicting birthweight in different ethnic strata.

STUDY DESIGN

Analyses were carried out on data collected in a prospective study of 535 multiethnic gravidas recruited from the Cedars-Sinai Medical Center (Los Angeles, CA). Baseline maternal characteristics were recorded at time of entry into the study. UtArt and UmArt RIs were measured on 3 occasions during pregnancy (visit 1, 16-20 weeks' gestation; visit 2, 21-29 weeks' gestation; and visit 3, 30-36 weeks' gestation). The outcome for this study was gestational age-adjusted birthweight (aBW).

RESULTS

The average UtArt and UmArt RI decreased steadily across gestation for all ethnicities. The average UtArt RI at each visit and the average rate of change between visits were not significantly different among the ethnicities. However, the UmArt RI measured at visit 3 and its rate of change in the last trimester were significantly different among the ethnic groups (P < .02). After adjustment for traditional risk factors for fetal growth restriction, the magnitude and rate of change of UtArt RI significantly predicted aBW only in Hispanic women, whereas the magnitude and rate of change of UmArt RI predicted aBW only in African American women. The most parsimonious combination of UtArt and UmArt RI measurements at visits 1, 2, and 3 that predicted statistically significant variation in aBW differed by ethnicity.

CONCLUSION

The relationships between aBW and longitudinally collected measures of UtArt and UmArt RI depend on the context defined by ethnicity and time of measurement after adjusting for a parsimoniously selected subset of traditional risk factors.

Risk factors for cardiovascular disease in women with a history of pregnancy complicated by preeclampsia or intrauterine growth restriction

OBJECTIVE

Women with a history of preeclampsia or intrauterine growth restriction (IUGR) have an increased risk for cardiovascular disease in later life. We determined the presence of traditional and novel risk factors for cardiovascular disease in these women.

METHODS

We studied 256 women with a history of preeclampsia and 59 women with a history of intrauterine growth restriction. Fifty-three women with a history of uncomplicated pregnancy served as controls. We determined values for blood pressure, body mass index, concentrations of cholesterol, high-density lipoprotein cholesterol, triglycerides and lipoprotein (a), and insulin resistance.

RESULTS

Women with a history of preeclampsia exhibited more risk factors for future cardiovascular disease such as dyslipidemia, hypertension, obesity, and increased insulin resistance compared with women with a history of uncomplicated pregnancy. Women with a history of IUGR have higher concentrations of cholesterol and show a tendency to higher BMI, higher triglyceride concentrations, and increased insulin resistance as compared with women with a history of normal pregnancy.

CONCLUSIONS

Preeclampsia or IUGR may represent an early marker for increased risk for early cardiovascular disease.

Lipoprotein (a) in pregnancy: a critical review of the literature

In this article the literature on lipoprotein (a) during normal pregnancy and pregnancy complicated by preeclampsia or intrauterine growth restriction is reviewed. MEDLINE, from January 1966 to May 2003, was searched to locate relevant articles in English. Additional publications were identified by reviewing references in selected articles. Studies were reviewed by predefined and strict criteria. It appeared that methodology and results of studies on lipoprotein (a) during normal and complicated pregnancy were very diverse. Lipoprotein (a) increased with advancing gestation or remained unaltered during normal pregnancy. Women with preeclampsia had higher, unaltered or lower lipoprotein (a) concentrations as compared to normal pregnant controls. Only few studies were in agreement with most of the review criteria. In conclusion, published studies on lipoprotein (a) in pregnancy differ substantially in the used methods to measure lipoprotein (a), sample size, study design and ethnicity of the study population. Therefore, these studies yielded conflicting results and no unequivocal view on the role of lipoprotein (a) in normal and complicated pregnancy. Recommendations for future studies are amongst others: the use of an apo(a) independent method for measuring Lp(a), inclusion of sufficient numbers of patients, the use of a longitudinal study design when the objective is to study the changes of Lp(a) during pregnancy and selection of a study population that is ethnically representative for the general population.

Maternal thrombophilia and neonatal thrombosis

In neonates and infants, numerous clinical and environmental conditions lead to elevated thrombin generation and subsequent thrombus formation. Genetic prothrombotic defects (protein C, protein S and antithrombin deficiency, mutations of coagulation factor V and factor II, elevated lipoprotein (a)) have been established as risk factors of thromboembolic events in neonates and infants. The interpretation of the laboratory evaluation relies on age-dependent normal reference values. Because appropriate clinical trials are missing in these age groups, treatment recommendations are adapted from small-scale studies in neonates and infants and from guidelines relating to adult patient protocols. Secondary long-term anticoagulation should be administered on an individual basis.

Lipoprotein(a): an emerging cardiovascular risk factor

Lipoprotein(a) is a cholesterol-enriched lipoprotein, consisting of a covalent linkage joining the unique and highly polymorphic apolipoprotein(a) to apolipoprotein B100, the main protein moiety of low-density lipoproteins. Although the concentration of lipoprotein(a) in humans is mostly genetically determined, acquired disorders might influence synthesis and catabolism of the particle. Raised concentration of lipoprotein(a) has been acknowledged as a leading inherited risk factor for both premature and advanced atherosclerosis at different vascular sites. The strong structural homologies with plasminogen and low-density lipoproteins suggest that lipoprotein(a) might represent the ideal bridge between the fields of atherosclerosis and thrombosis in the pathogenesis of vascular occlusive disorders. Unfortunately, the exact mechanisms by which lipoprotein(a) promotes, accelerates, and complicates atherosclerosis are only partially understood. In some clinical settings, such as in patients at exceptionally low risk for cardiovascular disease, the potential regenerative and antineoplastic properties of lipoprotein(a) might paradoxically counterbalance its athero-thrombogenicity, as attested by the compatibility between raised plasma lipoprotein(a) levels and longevity.

The association between inherited thrombophilia, antiphospholipid antibodies and lipoprotein A levels with obstetrical complications in pregnancy

OBJECTIVES

To evaluate the association between obstetrical complications in pregnancy and thrombophilic factors.

STUDY DESIGN

75 pregnant women with obstetrical complications and 66 controls with live births without obstetrical complications were tested for thrombophilia. All subjects were negative for thromboembolic disease.

RESULTS

The obstetrical complications in the study group were unexplained oligohydramnios = 16 (21%), IUGR = 17 (23%), preeclampsia <32 weeks = 15 (20%), recurrent abortions = 42 (56%), fetal demise = 14 (19%), abruption = 8 (11%). Comparing women with obstetrical complications versus controls, factor V Leiden mutation was present in 7 (10%) versus 1 (2%) P =.064, odds ratio (OR) = 7, 95%, CI = 0.8-58.5, antiphospholipid antibody syndrome in 14 (19%) versus 2 (3%) P =.003, OR = 7, 95% CI = 1.7-35, high lipoprotein A levels 13 (30%) versus 6 (10%) P =.019, OR = 3.8, 95% CI = 1.3-11. In the study group, there was a case each of prothrombin gene mutation, elevated homocysteine level, antithrombin III, protein S&C deficiencies. Major thrombophilia diagnosis was present in 24 (32%) versus 3 (5%) of controls p =.001, OR = 9.8. No association was found with the methylenetetrahydrofolate reductase gene mutation. In 22 women who subsequently became pregnant, prophylactic anticoagulant therapy compared to pretreatment control pregnancies showed 22 versus 11 live births P =.001, 95% CI = 0.3-0.7 and obstetrical complications of 2 (9%) versus 22 (100%) P =.001, OR = 11, 95% CI = 2.9-41.2.

CONCLUSION

An association is suggested between non-thromboembolic pregnancy complications and hypercoagulable disorders. Prophylactic anticoagulant therapy may be associated with improved pregnancy outcome.

The elevated plasma lipoprotein(a) concentrations in preeclampsia do not precede the development of the disorder

We sought to determine whether maternal plasma lipoprotein(a) [Lp(a)] levels are elevated in the second trimester, before the development of preeclampsia and other obstetrical complications, in women at risk. In the first part of the study (cross-sectional), plasma concentrations of Lp(a) were compared among 16 women with preeclampsia, 35 normotensive pregnant women and 18 healthy nonpregnant women. In the second part (nested case-control), blood samples were collected prospectively from 82 women at risk of preeclampsia, at 14-24 weeks of gestation, and Lp(a) levels were compared between those in whom preeclampsia or other obstetrical complications developed and those in whom they did not. In the cross-sectional study, plasma concentrations of Lp(a) were significantly higher in women with preeclampsia than in normotensive pregnant and healthy nonpregnant women (41 +/- 31 vs. 24 +/- 16 and 15 +/- 10 mg/dl, respectively; P=.001). Of the 82 women in the second part of the study, 9 (11%) developed preeclampsia and 19 (23%) had complications such as intrauterine growth restriction, preterm delivery and fetal or neonatal loss. There were no differences in plasma Lp(a) concentrations between the women with preeclampsia and those without complications, though Lp(a) levels were significantly higher in women with other complications than in those with either preeclampsia or uncomplicated pregnancies (40 +/- 29 vs. 17 +/- 13 or 28 +/- 18 mg/dl, respectively; P=.05). In conclusion, elevated plasma levels of Lp(a), associated with clinically established preeclampsia, are not detected before the appearance of the disorder in pregnant women at risk.

Correlation of first trimester placental volume and second trimester uterine artery Doppler flow

Uterine artery Doppler examination can identify impaired trophoblast invasion in the second trimester of pregnancy. High resistance and an early diastolic 'notch' show insufficient physiological conversion of the spiral arteries. Uterine artery Doppler is routinely performed between 22-24 weeks which is relatively late for treatment. In this study we wanted to find out whether women with increased uterine blood flow resistance at 22 weeks already have reduced placental volumes in the first trimester measured with 3D sonography.A total of 1060 women with singleton pregnancies had three dimensional (3D) volume measurements of their placentae between 11-13 weeks and uterine Doppler scans between 21-22 weeks. Stepwise logistic and linear regression analyses were used to show a correlation between placental volume (PV) and a CRL dependent placental quotient (PQ) with uterine perfusion parameters. Uterine perfusion at 21-22 weeks depends significantly on PV or PQ at 11-13 weeks (P< 0.0001 for both) and smoking behaviour (P=0.006). The occurrence of a notch also depends significantly on PV and PQ (P< 0.0001 for both) and also on gravidity (P< 0.0001) and age (P=0.0007) as well as on smoking behaviour (P=0.0094). PV and PQ did not show any dependency on age, gravidity, BMI or smoking habits. Placentae of women with high resistance uterine perfusion in the second trimester are already remarkably small in the first trimester. Placental volumetry is probably an efficient method for early and simple identification of impaired trophoblast invasion.

Lipoprotein (a) levels in normal pregnancy and in pregnancy complicated with pre-eclampsia

Lipoprotein (a) (Lp(a)) is recognised as a risk factor for arterial and venous thrombosis, a property which may relate to its structural similarity to plasminogen. Pregnancy is associated with a hypofibrinolytic state. Elevated Lp(a) may influence fibrinolysis and have an unfavourable role in pregnancy outcome. In this study alterations in plasma Lp(a) concentrations during normal pregnancy was examined, in a detailed longitudinal investigation, in ten women together with changes in other lipid parameters. In addition, Lp(a) concentrations were examined in subjects with pre-eclampsia (n=10) relative to matched controls (n=10), since it has recently been reported that a substantial increase in circulating Lp(a) occurs in this disorder. Lp(a) concentration increased steadily in normal pregnancy between 10 and 35 weeks with a doubling of the median value from 14.5 to 27.0 mg/dl (P=0.01). A significant increase in Lp(a) values was observed in all subjects with increasing gestation (median rise 190%, range 117-340%). This increase was intermediate to those seen in plasma triglyceride and cholesterol. No significant difference in Lp(a) values was observed in subjects with pre-eclampsia, compared with matched normal pregnancy controls (median 14 mg/dl [IQR 4.7-69.0] in pre-eclampsia vs 20 mg/dl [9.0-56. 3] in controls; P=0.57), at a median gestation of 32 weeks. In conclusion, there is a 2-fold increase in Lp(a) during normal pregnancy, which may influence fibrinolysis. Circulating Lp(a) is not significantly elevated in women with pre-eclampsia, and thus is unlikely to play a role in the pathophysiology of this disorder.

Interaction of the protein C/protein S anticoagulant system, the endothelium and pregnancy

Normal pregnancy is associated with significant changes in haemostasis, lipid metabolism and endothelial function. This suggests that maternal adaptation in these systems is required for successful pregnancy outcome. A number of acquired and heritable prothrombotic abnormalities are associated with complications in pregnancy. A common feature of these abnormalities is their ability to alter endothelial function or the protein C/protein S system and increase thrombin generation. In this review the normal function of the endothelium and the protein C/protein S system is detailed. The changes which characterize normal and complicated pregnancies are outlined and the evidence for the impact of heritable and acquired disorders of the protein C/protein S system on pre-eclampsia and fetal loss are discussed.

Standardization and clinical management of lipoprotein(a) measurements

The present article proposes personal suggestions to improve determinations and clinical interpretation of results of lipoprotein(a) assays. Methods and procedures for sampling and quantification of the various isoforms of lipoprotein(a) in serum, plasma and urine are reviewed with the aim of improving the reliability and reproducibility of results and reinforcing the clinical utility of lipoprotein(a) measurements.

Plasma concentrations of Lp(a) lipoprotein and TGF-beta1 are altered in preeclampsia

This study was performed to investigate the possible association between preeclampsia and the plasma concentrations of Lp(a) lipoprotein and TGF-beta1 in a large series of patients. Additionally, correlation between the concentrations of these molecules and the severity of preeclampsia or fetal growth retardation was evaluated. Following clinical examination and biochemical analyses, both electroimmunoassay and RIA technique were used for quantitative determinations of plasma Lp(a) lipoprotein. ELISA technique was used to measure the active form of TGF-beta1 in plasma of pregnant normotensive and preeclamptic women. We examined 154 women with preeclampsia (preeclampsia group) and 76 healthy, pregnant normotensive women (control group). The preeclampsia group was further divided into the following subgroups: mild preeclampsia, severe preeclampsia and preeclampsia with fetal growth retardation. Plasma levels of Lp(a) lipoprotein were lower in the total preeclampsia group as well as in all preeclampsia subgroups (5.45+/-7.41, 5.58+/-8.02, 5.08+/-5.38, and 4.32+/-5.28 mg/dl in the total preeclampsia group, and in subgroups with mild preeclampsia, severe preeclampsia, and preeclampsia with fetal growth retardation, respectively) than in the control group (7.84+/-9.26 mg/dl) as determined by quantitative electroimmunoassay. Corresponding results were obtained with a radioimmunoassay (166.03+/-200.2 U/l in the total preeclampsia group vs. 229.18+/-257.7 U/l in controls). There was good correlation between the two methods used for Lp(a) lipoprotein measurement. The differences between controls and the total preeclampsia group as well as each preeclampsia subgroup were statistically significant by a non-parametric test (one-way Kruskal-Wallis test). Plasma concentrations of the active form of TGF-beta1 were increased in all preeclampsia subgroups as well as in the total group (5.63+/-1.68 ng/ml) compared to controls (4.67+/-1.33 ng/ml). This increase in TGF-beta1 was statistically highly significant. Plasma concentrations of Lp(a) lipoprotein and the active form of TGF-beta1 did not differ significantly between the preeclampsia subgroups. The outcome of this study may suggest involvement of both parameters in the pathophysiology of preeclampsia and may substantiate the notion of a multifactorial etiology of the disease.

Do gonadotropins influence serum lipoprotein(a) concentrations? Observations on children, adolescents and adults

Data from 7045 subjects were examined. The main groups consisted of the following in- and outpatients: 1414 neonates, 2554 children and adolescents (1336 males, 1218 females), 1209 women directly postpartum, 786 non-pregnant women and 1090 men aged between 18 and 100 years of age. Unless otherwise stated, persons were under medical observation or therapy. The results were obtained over a three-year period using an in-house immunoluminometric assay specific for apolipoprotein(a) using two polyclonal antibodies and single lot of reagents to allow for comparability of results. Girls aged between 10 and 12 years of age had significantly higher serum lipoprotein(a) (median 124 mg/l) levels than boys (median 88 mg/l) of the same age (p < 0.05-Mann-Whitney U-test). Post-pubertal lipoprotein(a) concentrations were not significantly different from pre-pubertal levels. Between the ages of 0-9 and 13-17 years there were no statistically significant sex-linked differences in serum lipoprotein(a). In adults, lipoprotein(a) serum levels were significantly higher in women (median 163 mg/l) aged between 50 and 59 years, when compared with men (median 128 mg/l) of the same age group (p = 0.05-Kruskal-Wallis one way ANOVA followed by the Nemenyi test). There was no significant difference in serum lipoprotein(a) concentrations between healthy women (median 91 mg/l), women direct postpartum (median 116 mg/l) and in-patient women (median 117 mg/l) aged between 18 and 41 years of age (p = 0.11-0.96). There was no correlation between maternal lipoprotein(a) and birth weight in mature newborns (r = -0.028-0.085). The results may indicate a direct influence of gonadotropins at puberty and during the menopause which cause an increase in serum lipoprotein(a) concentrations.

High levels of Lp(a) lipoprotein in a family with cases of severe pre-eclampsia

We report a family with two cases of severe pre-eclampsia/eclampsia in which very high levels of Lp(a) lipoprotein were found. The serum level of Lp(a) lipoprotein is genetically determined and the Lp(a) apolipoprotein has a close homology to plasminogen. Very high levels of Lp(a) lipoprotein might interfere with the fibrinolytic/thrombolytic process in man. A previous report suggested that a high maternal serum Lp(a) lipoprotein level can cause fetal growth retardation, and it is proposed that very high levels might lead to increased deposition of fibrin in the uterine spiral arteries in pregnancy, which is central in the pathogenesis of pre-eclampsia. If confirmed, a very high Lp(a) lipoprotein level could be one risk factor for pre-eclampsia that is genetically determined.