Serum Lipid Concentrations Change with Serum Alkaline Phosphatase Activity During Pregnancy

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1 422 Annals o f Clinical & Laboratory Science, vol. 30, no 4, 2000 Serum Lipid Concentrations Change with Serum Alkaline Phosphatase Activity During Pregnancy JongWeon Choi and Soo Hwan Pai Department of Clinical Pathology, College of Medicine, Inha University Hospital, Inchon, Korea Abstract. To investigate the relationship between serum lipids and alkaline phosphatase during normal pregnancy, we measured triglyceride, total cholesterol, HDL-cholesterol, and LDL-cholesterol concentrations and alkaline phosphatase activity in serum samples from 546 apparently healthy pregnant, postpartum, and nonpregnant women. Serum HDL-cholesterol levels did not change significantly during pregnancy, but serum triglyceride, total cholesterol, LDL-cholesterol, and alkaline phosphatase levels increased gradually as pregnancy proceeded, reached maximum values in the third trimester, and returned to nonpregnant levels by wk postpartum. The serum alkaline phosphatase activity averaged 2.1-fold higher in the late third trimester than in the first trimester; the serum triglyceride concentration averaged 2.3-fold higher in the late third trimester than in the first trimester. Compared to the peak values during pregnancy, serum alkaline phosphatase activity averaged 45% lower and serum triglyceride level averaged 47% lower at wk postpartum. The serum alkaline phosphatase activity was correlated with the serum concentrations oftotal cholesterol (r = 0.68, p < 0.01) and triglyceride (r = 0.71, p < 0.01). In short, this study shows that serum triglyceride and total cholesterol levels change in parallel with serum alkaline phosphatase activity during and after normal pregnancy, (received 2 7 April 2000, accepted 9 August 2000) Keywords: serum cholesterol, serum triglyceride, serum alkaline phosphatase, normal pregnancy. Introduction Many physiological alterations occur during gestation. Most pregnant women develop elevated plasma lipid levels during gestation, and the hyperlipidemia increases as the pregnancy progresses [1,2]. In late pregnancy, plasma triglyceride concentrations are increased threefold over the levels in nonpregnant women [3]. In nonpregnant women, an excessive accumulation of lipids in plasma is attended by increased risks of coronary heart disease and other vascular complications. However, the significance of the elevated plasma lipid levels during pregnancy is still unclear [4]. Berge et al [5] reported that maternal hyperlipidemia can influence the risk for cardiovascular disease [5], whereas Piechota and Staszewski [6] concluded that the hyperlipidemia of pregnancy is not atherogenic [6]. Address correspondence to Jong Weon Choi, M.D., Department o f Clinical Pathology, Inha University Hospital, 7-206, 3-ga, Shinheung-dong, Jung-gu, Inchon, , Korea; tel ; fax ; jwchoi@inha.ac.kr. Alkaline phosphatase exists in various tissues, and the total serum alkaline phosphatase level in healthy subjects consists of isoenzymes contributed by the liver, bone, intestine, and placenta. Serum alkaline phosphatase concentrations are elevated in patients with bone diseases characterized by increased osteoblastic activity [7]. However, growing children and pregnant women in the third trimester have physiologically elevated serum alkaline phosphatase levels. In pregnancy, the placental isoenzyme of alkaline phosphatase is recognized as a major cause of the increased level in the maternal circulation [8]. Placental alkaline phosphatase constitutes 40% to 65% of the total serum alkaline phosphatase in the third trimester and returns to normal in about one month postpartum [7]. However, according to Valenzuela et al [9], the amount of bone alkaline phosphatase activity in serum is also elevated during pregnancy because maternal bone formation increases in this period. During and after pregnancy, changes in the concentrations of total cholesterol, triglyceride, and alkaline phosphatase in serum or plasma have been /00/ $1.75; 2000 by the Association of Clinical Scientists, Inc.

2 Serum lipids and alkaline phosphatase during pregnancy 423 described extensively [2,3)9], but few studies have attempted to correlate the serum lipid concentrations and serum alkaline phosphatase activities during pregnancy. Therefore, in the present study, we investigated the relationships between the changes of maternal serum lipid levels and the alterations of serum alkaline phosphatase activities that occur throughout pregnancy and in the puerperium. Materials and M ethods Lipid profiles and alkaline phosphatase activity were measured in serum from 546 healthy women, age yr, including 304 pregnant women, 190 postpartum women, and 52 nonpregnant women (Table 1). Twenty-seven women were excluded from this study for the following reasons: 9 had recent infection, 7 had received blood transfusion, and 11 had complications during pregnancy. Gestational age was determined by sonographic examination and the date of the last menstrual period. Pregnant women were divided into four groups by gestational age: first trimester ( wk, n = 74), second trimester ( wk, n = 83), early third trimester ( wk, n = 71), and late third trimester ( wk, n = 76). Postpartum women were divided into three groups: 4-8 wk postpartum (n = 63), wk postpartum (n = 68), and wk postpartum (n = 59). A control group comprised nonpregnant women (n = 52) without history of pregnancy or recent disease. The subjects were all Korean housewives from middle-class families; there were no significant differences in racial composition, socioeconomic status, or occupation among the groups. The study was approved by the Committee of Ethics of the Inha University Hospital, and informed consent was obtained from all subjects. After the subjects had fasted for > 12 hr, blood (6 ml) was drawn into an evacuated serum separator tube. Serum lipid concentrations and alkaline phosphatase activity were measured with a model 747 automatic chemical analyzer (Hitachi, Inc, Tokyo, Japan) within 4 hr after collection. Triglyceride, total cholesterol, and low- or high-density lipoprotein-cholesterol (HDLcholesterol, LDL-cholesterol) were analyzed by enzymatic colorimetric methods using triglyceride GPO-PAP reagents (Roche Diagnostics GmbH, Mannheim, Germany), SICDIA L T-CHO reagents (Eiken Chemical Industries, Tokyo, Japan), Cholestest- LDL reagents (Daiichi Chemicals, Tokyo, Japan), and Cholestest-HDL reagents (Daiichi), respectively [10-15]. Serum total alkaline phosphatase activity was measured according to the IFCC recommendations [16] using SICDIA L ALP reagents (Eiken) with /»-nitrophenyl phosphate substrate and 2-amino-2- methyl-1-propanol buffer [16]. Data analysis was performed using SAS statistical software (version 6.12; SAS Institute Inc, Cary, NC, USA). Differences of serum lipid concentrations or alkaline phosphatase activity between groups were evaluated by the Mann-Whitney U-test, because most of the analytes showed nongaussian distributions. Correlations between serum lipid levels and alkaline phosphatase activity were assessed by the Pearson correlation coefficients. P values < 0.01 were considered statistically significant. Reference ranges (central 95th percentile confidence intervals) were calculated by nonparametric statistics. Results The concentrations of serum triglyceride, total cholesterol, HDL-cholesterol, and LDL-cholesterol, and the serum alkaline phosphatase activity in the eight groups of women are summarized in Table 1. There were no significant differences in serum total cholesterol, HDL- and LDL-cholesterol, or alkaline phosphatase during the first trimester of pregnancy, compared to nonpregnant women. However, serum triglyceride averaged 1.37 (SD ) mmol/l during the first trimester, which was significantly above the values (0.98 ±0.31 mmol/l) in nonpregnant women. Serum triglyceride levels continued to increase throughout pregnancy, attaining a peak concentration after 32 wk of pregnancy. Serum triglyceride levels declined progressively after delivery, reaching a mean level of 0.95 ±0.23 mmol/l at wk postpartum, which was equivalent to the non-pregnant women. Serum total cholesterol levels began to increase during the second trimester ( mmol/l) and peaked at wk of pregnancy (6.77 ±1.12 mmol/ L). Serum cholesterol levels were still elevated at wk postpartum, but returned to nonpregnant levels by wk after delivery.

3 424 Annals o f Clinical & Laboratory Science Table 1. Changes of serum lipid concentrations and alkaline phosphatase activity during and after normal pregnancy. Population Age (yr) No. of cases Triglyceride Total cholesterol HDLcholesterol LDLcholesterol Alkaline phosphatase (IU/L) Pregnant women 1st trimester ±0.36b ± ± ± ± nd trimester ±0.39b ±0.94b,c ± ± ± Early 3rd trimester b d ± 1.08b ± ± ±74.8b>d Late 3rd trimester ± 0.59b ± 1.12b ± ± 1.25b ±96.3b e Postpartum women 4-8 wk ±0.38b>f ±0.79b ± ± 1.30b ±65.4b>f wk reference range ± 0.34b b ± ± ± wk ± ± ± ± Non-pregnant women (controls) ± ± ± ± ± a central 95% confidence interval, computed by nonparametric method. b p <0.01 vs nonpregnant women, computed by Mann-Whitney U test. c p <0.01 vs 1st trimester, computed by Mann-Whitney U test. d p <0.01 vs 2nd trimester, computed by Mann-Whitney U test. e p <0.01 vs early 3rd trimester, computed by Mann-Whitney U test, f p <0.01 vs late 3rd trimester, computed by Mann-Whitney U test.

4 Serum lipids and alkaline phosphatase during pregnancy 425 No significant differences were noted in serum HDL-cholesterol concentrations during or after pregnancy, but serum LDL-cholesterol levels were significantly higher during the late third trimester and at 4-8 wk postpartum, compared to the nonpregnant controls. Serum alkaline phosphatase activity increased gradually from the second trimester of pregnancy and was twofold higher at wk than during the first trimester; it reached a peak ( IU/L) during the late third trimester. Serum alkaline phosphatase activity began to decrease soon after delivery and by wk postpartum did not differ significandy from the nonpregnant controls. The striking relationship between serum alkaline phosphatase and lipids during pregnancy is illustrated by Fig. 1, which is a plot of the sequential change of the mean triglyceride, total cholesterol, and alkaline phosphatase levels during seven stages from early pregnancy to 24 wk after delivery. The serum triglyceride and total cholesterol concentrations changed in a parallel course to alkaline phosphatase activity during pregnancy and the puerperium. Serum alkaline phosphatase activity at wk of gestation was 2.1- fold higher than during the first trimester. Serum triglyceride and total cholesterol concentrations at wk of gestation were 2.3- and 1.8-fold higher than the corresponding concentrations during the first trimester. Alkaline phosphatase activity at wk after delivery was 45% lower than the peak activity at weeks of pregnancy. Triglyceride and total cholesterol concentrations at wk after delivery were 47% and 29% lower than the corresponding peak concentrations at weeks of pregnancy. Scatter plots of serum triglyceride and total cholesterol concentrations vs serum alkaline phosphatase activity in 494 specimens of serum from pregnant and postpartum women are shown in Figs. 2 o -S "N U QJ <U S 5 ^ Í 1 ct* O <D l-1 d <u.d «rt jy -x o _G a 3 u v C/5 trimester trimester trimester trimester (4-8 wk) (12-16 wk) (20-24 wk) Fig. 1. Changes in the mean values for serum triglyceride concentration (squares), total cholesterol concentration (triangles), and alkaline phosphatase activity (circles) during and after normal pregnancy. The degree of change of alkaline phosphatase activity during each stage was similar to those for triglyceride and total cholesterol concentrations.

5 426 Annals o f Clinical & Laboratory Science Serum triglyceride concentration Fig. 2. Scatter plot that shows the correlation between triglyceride concentration (X-axis) and alkaline phosphatase activity (Y-axis) in 494 serum specimens from pregnant and postpartum women. The equation of the correlation line is Y = X ; r = 0.71 (p = <0.01). and 3. The serum alkaline phosphatase activity was significantly correlated with the concentrations of both triglyceride (r = 0.71, p < 0.01) and total cholesterol (r = 0.68, p< 0.01). Discussion In this study we compared the sequential changes of triglyceride, total cholesterol, HDL-cholesterol, and LDL-cholesterol concentrations in maternal serum during gestation with the corresponding alterations in alkaline phosphatase activity. Our data are in accord with the results of Potter and Nestel [17] and Qureshi et al [18], which showed that concentrations of serum cholesterol and triglyceride increase significandy during the second trimester and reach a maximum in the third trimester of pregnancy. The responses of serum lipid levels during the first trimester of pregnancy have varied in different studies. For example, Martin et al [4] found increased mean serum cholesterol concentration in the first trimester, compared to nonpregnant subjects. Berge et al [5] found that serum total cholesterol was 7% lower and serum triglyceride was 18% lower in the first trimester, compared to pre-pregnancy values [5]. In contrast, in the present study, the triglyceride concentration was 40% higher during the first trimester than in nonpregnant women, and the serum total cholesterol concentration did not differ significantly from nonpregnant controls. The apparent discrepancies among these studies in regard to serum lipid levels during early gestation may reflect differences in age, race, or nutritional status of the populations. The elevation of alkaline phosphatase activity in maternal serum during late pregnancy has been well documented [19] and primarily reflects the presence of placental alkaline phosphatase in the maternal circulation [9,20]. According to Valenzuela et al [9], during the third trimester of pregnancy, total alkaline

6 Serum lipids and alkaline phosphatase during pregnancy o Serum cholesterol concentration Fig. 3. Scatter plot that shows the correlation between total cholesterol concentration (X-axis) and alkaline phosphatase activity (Y-axis) in 494 serum specimens from pregnant and postpartum women. The equation of the correlation line is Y = 82.27X ; r = 0.68 ( p = <0.01). phosphatase concentration consists of isoenzymes contributed by placenta (51%), bone (37%), liver (9%), and intestine (2.5%), whereas in nonpregnant women, it consists of isoenzymes of placenta (1.4%), bone (48%), liver (29%), and intestine (21%). According to Shaper and Patel [20], placental alkaline phosphatase constitutes 59% of the serum total alkaline phosphatase activity during the third trimester of pregnancy, while in nonpregnant women, only 1.8% of serum total alkaline phosphatase activity is attributed to the placental isoenzyme [20]. In the present study, serum alkaline phosphatase activity increased progressively throughout gestation to a peak level at the end of gestation, and then fell to baseline by wk postpartum. As shown in Fig. 1, the changes of serum alkaline phosphatase activity paralled the successive changes of serum triglyceride and total cholesterol concentrations during and after pregnancy. In the entire set of serum specimens from pregnant and postpartum women, serum alkaline phosphatase activity was significantly correlated with the serum triglyceride and total cholesterol concentrations. To the authors knowledge, such correlations between serum lipid levels and alkaline phosphatase activity have not been previously reported in pregnant humans or experimental animals. In conclusion, this study shows that serum triglyceride and total cholesterol concentrations change in association with changes of alkaline phosphatase activity during normal pregnancy. Since the study involved only healthy women, it does not provide insights into the pathophysiological mechanisms or clinical significance of the observed associations. To gain such insights will require further studies in women with complicated pregnancies. Clinicians who use serum lipid profiles as biochemical markers of cardiovascular risks should be aware of the changes of serum lipid concentrations that

7 428 Annals o f Clinical & Laboratory Science occur during normal pregnancy and should defer assays o f serum triglyceride and total cholesterol concentrations until wk postpartum, in order to avoid the influences o f pregnancy. References 1. Jimenez DM, Pocovi M, Ramon-Cajal J, Romero MA, Martinez H, Grande F. Longitudinal study of plasma lipids and lipoprotein cholesterol in normal pregnancy and puerperium. Gynecol Obstet Invest 1988;25: Loke DF, Viegas OA, Kek LP, Rauff M, Thai AC, Ratnam SS. Lipid profdes during and after normal pregnancy. Gynecol Obstet Invest 1991;32: Ordovas JM, Pocovi M, Grande F. Plasma lipids and cholesterol esterification rate during pregnancy. Obstet Gynecol 1984;63: Martin U, Davies C, Hayavi S, Hartland A, Dunne F. Is normal pregnancy atherogenic? Clin Sei 1999;96: Berge LN, Arnesen E, Forsdahi A. Pregnancy related changes in some cardiovascular risk factors. Acta Obstet Gynecol Scand 1996;75: Piechota W, Staszewski A. Reference ranges of lipids and apolipoproteins in pregnancy. Eur J Obstet Gynecol Reprod Biol 1992;45: Pincus MR, Zimmerman HJ, Henry JB. Clinical enzymology. In: Clinical Diagnosis and Management by Laboratory Methods (Henry JB, Ed), Saunders, Philadelphia, 19th ed, 1996; pp Meyer RE, Thompson SJ, Addy CL, Garrison CZ, Best RG. Maternal serum placental alkaline phosphatase level and risk for preterm delivery. Am J Obstet Gynecol 1995;173: Valenzuela GJ, Munson LA, Tarbaux NM, Farley JR. Time-dependent changes in bone, placental, intestinal, and hepatic alkaline phosphatase activities in serum during hum an pregnancy. Clin Chem 1987;33: Allain CC, Poon LS, Chan CS, Richmond W, Fu PC. Enzymatic determination of total serum cholesterol. Clin Chem 1974;20: Wahlefeld AW, Bergmeyer HU, Eds. Methods of Enzymatic Analysis, Academic Press Inc, New York, NY, 2nd ed, 1974; pp Friedwald WT, Levy RI, Fredrickson DS. Estimation of the concentration of low-density lipoprotein cholesterol in plasma without use of the preparative ultracentrifuge. Clin Chem 1972;18: Anon. Report of the National Cholesterol Education Program expert panel on detection, evaluation, and treatment of high blood cholesterol in adults. Arch Intern Med 1988;148: Olson RE. A critique of the report of the National Institutes of H ealth expert panel on detection, evaluation, and treatment of high blood cholesterol. Arch Intern Med 1989;149: Gordon T, Castelli WP, Hjortland MC, Kanel WB, Dawber TR. High density lipoprotein as a protective factor against coronary heart disease. Am J Med 1977; 62: Tietz NW, Rinker AD, Shaw LM. IFCC methods for the measurement of catalytic concentrations of enzymes. Part 5. IFCC method for alkaline phosphatase. J Clin Chem Clin Biochem 1983;21: Potter JM, Nestel PJ. The hyperlipidemia of pregnancy in normal and complicated pregnancies. Am J Obstet Gynecol 1979;133: Qureshi LA, Xi XR, Limbu YR, Bin HY, Chen MI. Hyperlipidaemia during normal pregnancy, parturition and lactation. Ann Acad Med Singapore 1999;28: Okesina AB, Donaldson D, Lascelles PT, Morris P. Effect of gestational age on levels of serum alkaline phosphatase isoenzymes in healthy pregnant women. Int J Gynaecol Obstet 1995;48: Shaper AG, Patel I. Heat-stable serum alkaline phosphatase of pregnancy in African women. Am J Clin Pathol 1969;51: