Journal 01lnternal Medicine 1992: 231 : 623-625

Short communication Plasma concentration levels of apolipoprotein A-I, apolipoprotein B and lipoprotein (a) in Greenland Inuit (Eskimos) L. U. GERDES, E. B. SCHMIDT*, I. C. KLAUSEN, S. D. KRISTENSEN, E. ERNST*, 0. FLEERGEMAN 81J. DYERBERG* From the Department of Internal Medicine and Cardiology A , Aarhus Amtssygehus, University of Aarhus. Aarhus and the 'Department of Clinical Chemistry, Aalborg Hospital, Aalborg, Denmark

Introduction The incidence and mortality from ischaemic heart disease (IHD) is low in native Greenland Inuit (Eskimos) [l,21. Both genetic [3] and environmental factors are important [4], and both may operate through plasma lipoproteins. Thus the Greenlandic Inuit have relatively low plasma concentrations of low-density (LDL) and very-low-density lipoproteins (VLDL), and relatively high concentrations of highdensity lipoproteins (HDL) [5]. In the present study we have measured plasma concentrations of apolipoprotein A-I, apolipoprotein B and lipoprotein (a) i n . 2 0 native Greenland Inuit (Eskimos). Measurements of these protein constituents of HDL and LDL+VLDL. respectively, and of lipoprotein (a) have not previously been reported from studies in Greenland. The results were compared with data from 20 Caucasian Danish controls, matched by sex and age.

Study population and methods

matched healthy Caucasian Danes living in the city of Aalborg, Denmark. All plasma samples were stored at - 80 "C until the present biochemical analyses, and samples were analysed in combined batches to eliminate inter-assay variation. Plasma lipids, lipoproteins and apolipoproteins

Plasma total cholesterol and triglycerides were measured enzymatically (CHOD-PAP and GPO-PAP, Boehringer-Mannheim GmbH. Mannheim, Germany). HDL-cholesterol was measured after precipitation of apo B-containing lipoproteins with dextran and magnesium [71. LDL-cholesterol was calculated by Friedewald's formula as total cholesterol minus HDL-cholesterol minus 0.45 x plasma triglycerides [8]. Apo A-I and apo B were measured by ratenephelometry with commercially available antisera and standards (Orion Diagnostics, Helsinki, Finland ; Boehringer-Mannheim GmbH, Mannheim, Germany). Plasma Lp(a)was measured with a commercial two-site immunoradiometric assay (Pharmacia AB, Uppsala, Sweden).

Subjects

Plasma samples were obtained from 20 healthy Inuit volunteers (9 men and 11 women), 35-51 years of age, belonging to households in the settlement of Igdlorsuit on the west coast of Greenland in 1982 [6]. The results were compared with data obtained from a study conducted in 1982 of 20 sex- and ageAbbreviations: IHD = ischaernic heart disease, LDL = low density lipoprotein, VLDL = very low density lipoprotein, HDL = high density .lipoprotein. apo A-I = apolipoprotein A-I, apo B = apolipoprotein B, Lp(a) = lipoprotein (a), 95% CI = 95% confidence interval.

Statistical methods

Apo A-I and apo B levels were compared in the two groups using the Wilcoxon-Mann-Whitney test, since there are considerable differences in variance in the two samples. All other data were compared by unpaired t-tests. Plasma triglycerides and Lp(a) data were logarithmically transformed to achieve approximate normality of the distributions.

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Fig. 1. Individual plasma concentrations of apolipoprotein A-I, apolipoprotein B, and lipoprotein (a) in Greenland Inuit and Danes. The results are shown with the superimposed box-plots (group medians, interquartile ranges = H-spread. and fences of 1.5 x H-spread). The corresponding group mean values are shown in Table 1.

Table 1 . Plasma apolipoproteins. high- and low-density-lipoprotein cholesterol. total cholesterol and triglycerides. in 20 Inuits and 20 Danish controls Inuit

Danes

Mean value

(95% CI)

Mean value

(95% CI)

P-value

Apo A-I (g I-') Apo B (g I-') Lp(a) (mg d1-7

1.81 0.59 8.14

(1.56-2.07) (0.534.64) (4.91-1 3.49)

1.23 0.88 6.06

(1.15-1.31) (0.774.98) (3.16-1 1.65)

< 0.0001 < 0.0001

HDL-cholesterol LDL-cholesterol

1.57 2.86

(1.37-1.77) (2.49-3.2 3)

1.52 3.89

(1.36-1.68) (3.42-4.37)

0.001

Total cholesterol Triglycerides

4.74 0.68

(4.24-5.25) (0.60-0.76)

5.94 1.09

(5.49-6.39) (0.91-1.29)

< 0.001*

0.462* 0.682 0.001

Lipid values are expressed in mmol I-'. * After logarithmic transformation.

Results and discussion Figure 1 shows the data for the individual measurements of apolipoprotein A-I, apo B and Lp(a), and group mean values are given in Table 1. The mean plasma Apo A-I concentration was statistically significantly higher in Inuits than in Danes, whereas the opposite was true for apo B. The plasma levels of Lp(a) appeared to be slightly differently distributed in the two populations, but the (geometric) mean levels did not differ.

In contrast to the apo A-I levels, the mean HDLcholesterol concentration did not differ greatly in the two samples of subjects (Table l), suggesting the existence of differences in biochemical composition of HDL in the two populations. On the other hand, both the mean LDL cholesterol and mean VLDL cholesterol (as estimated from plasma triglycerides) were lower in Inuits (Table l),corresponding to the lower apo B levels. Despite the small size of the study, the results are consistent with findings from previous studies which

APOLIPOPROTEIN LEVELS IN G R E E N L A N D INUIT

indicate that plasma lipoprotein patterns in Greenlandic Inuit differ from patterns in Danes [S]. The differences appear to be more strongly reflected by plasma apo A-I and apo B concentrations than by the corresponding lipid concentrations, consistent with results obtained from case-control studies which suggest that apolipoproteins are better IHD risk discriminators than lipids [9-131. The distribution of Lp(a)plasma concentrations was less skewed towards zero in Inuits than in Danes (and other populations). This finding has prompted us to investigate the Lp(a) concentrations and the genetically determined polymorphism of apo(a) in a larger study of Inuit [14].

Acknowledgements This study was financially supported by the Danish Heart Association. Lars U l r i i Gerdes was a Postdoctoral Fellow at the University of Aarhus, Denmark. The authors wish to thank Ms Gitte Glistrup Nielsen, Anette Stenderup and Lene Trudsa for their excellent technical assistance.

References 1 Kromann N, Green A. Epidemiologicalstudies in the Upernavik district. Greenland. Incidence of some chronic diseases, 195074. Acta Med Scand 1980; 208: 401-6. 2 Bjerregaard P. Dyerberg 1. Mortality from ischemic heart disease and cerebrovascular disease in Greenland. Int ] Epiderniol 1988; 17: 514-9. 3 Harvald B. Genetic epidemiology of Greenland. Clin Genet 1989; 36: 364-7. 4 Dyerberg 1. Coronary heart disease in Greenland inuit: a

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paradox. Implications for Western diet patterns. Arch Med Res 1989: 48: 47-54. 5 Bang HO, Dyerberg J. Plasma lipid and lipoprotein pattern in Greenlandic West coast Eskimos. Actn Med Scand 1972: 192: 85-94. 6 Jergensen KA. Nielsen AH, Dyerberg 1. Hemostatic factors and renin in Greenland Eskimos on a high eicosapentaenoic intake. Results of the fifth Umanak expedition. Acta Med Scand 1986; 219: 473-9. 7 Warnick GR, Benderson J. Albers JJ. Dextran sulfate-Mg" precipitation procedure for quantitation of high-densitylipoprotein cholesterol. Clin Chern 1982 : 28: 1379-88. 8 Friedewald WT. Levy RI. Frederickson DS. Estimation of the concentration of low-density lipoprotein cholesterol in plasma, without the use of the preparative ultracentrifuge. Clin Cbem 1972: 18: 499-502. 9 Avogaro P. Bon GB. CazzolatoC, Rorai E. Relationship between apolipoproteins and chemical components of lipoproteins in survivors of myocardial infarction. Atherosclerosis 1980; 37: 69-76. 10 Durrington PN. Hunt L. Ishola M, Kane J , Stephens WP. Serum apolipoproteins A1 and B and lipoproteins in middleaged men with and without previous myocardial infarction. Br Heart 1 1986: 56: 206-12. 11 Kottke BA. Zinmeister AR. Holmes DR, Kneller RW. Hallaway BJ, Mao SIT. Apolipoproteins and coronary artery disease. Mayo Clin Proc 1986: 61 : 313-20. 12 Johansson S. Bonjers G. Fager G et al. Serum lipids and apolipoprotein levels in women with myocardial infarction. Arteriosclerosis 1988 : 8: 742-9. 13 Barbier M. Wile D, Trayner 1. Aber VR. Thompson CR. High prevalence of hypertriglyceridemia iind apolipoprotein abnormalities in coronary heart disease. Br Heart 1 1988; 60: 39 7-40 3. 14 Klausen IC. Gerdes LU. Schmidt EB, Dyerberg 1. Hansen PS. Faergeman 0 . Lipoprotein (a) polymorphism in west Greenland Eskimos is consistent with low rates of ischaemic heart disease. 9 t h International Symposium on Atherosclerosis. Chicago, 1991. Received 3 May 1991, accepted 11 November 1991. Correspondence ; Lars Wick Gerdes. MD. Medicinsk-Kardiologisk afdeling A, Aarhus amtssygehus. DK-8000 Aarhus C. Denmark.

Plasma concentration levels of apolipoprotein A-I, apolipoprotein B and lipoprotein (a) in Greenland Inuit (Eskimos).

Journal 01lnternal Medicine 1992: 231 : 623-625 Short communication Plasma concentration levels of apolipoprotein A-I, apolipoprotein B and lipoprote...
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