Serum lipoproteins in patients with myocardial infarction

Atherosclerosis, 74 (1988) 65-74 Ekvier Scientific Publishers Ireland, Ltd.

65

ATH 04215

Ritva Kauppinen-Miikelin and Esko A. N&ki& TEird hqmrtment of Mtdicine, University of

$

Hehinki, 00290 Helsinki 29, JWand

(Rhved 20 January, 1988) (Revised, rec4zived22 JuBe, 1988) (Accepted 28 June, 1988)

The lipid and lipoprotein profile was examined in male patients with acute myocardial infarction (AMI) at the time of infarction (group A) and in male patients who had survived AMI 2-3 years before the study (group B), and compared to that of healthy ciontrols. The myocardial infarction (MI) patients exhibited similar total cholesterol and LDL-cholesterol levels as the controls. However, the LDL mass concentration was higher in patients than in controls (P < 0.01 for group A, P =zO.Qol for group B). In composition, patients’ LDL in both groups was rich in protein and triglycerides but poor in cholesterol. The compositional changes in patient LDL were evident at all levels of LDL-cholesterol. The mean total HDL and HDL, mass concentrations were lower in patients than in controls (B < O.!Xll for both groups), but there was no difference in XDL, levels. Upon admission to hospital the patients with AMI at the time of examination (group A) had higher serum total triglyceride concentration than controls, but on the fasting morning samples serum triglyceride and VLDL lipici levels did not differ between patients and controls. Patients who had survived AMI 2-3 years prior to study (group B) exhibited higher serum total triglyceride and VLDL levels than the control subjects. On stepwise dk +minant analysis, HDLz protein concentration was the single best variable for distinguishing between patients and controls. The most parameter was the HDL/LDL protein ratio or the HDLJLDL protein ratio. powerful di &minatory

Key words: Lipids; Lipoprotein; Myocardial infarction

In t ?kxased 21 September, 1986. Correspondence to: Ritva Kauppinen-MZWin, Third Department of Medicine, Central University Hospital, University of He&r&i, Haartmaninkatu 4, SF-00290 Helsinki. Finland. Tel. 358-G-4711. Abbrmiatiom: AMZ = acute myocardial infarction; HL = bepatic lipase; II-ID = ischemic heart disease; LCAT = 1ecitbin:cholesterol acyltransferase; LPL = lipoprotein lipase;

MI= myocardial infanxion.

OR

Hyperlipidemia, hypertension and smoking are the major risk factors for ischemic heart disease (II-ID), which is the leading cause of death among middle-aged men in Western countries. Indepeu dent positive associations between total and low density lipoprok (LDL)-cholesterol levels and

0021-9150/8b/$O3.50 0 1988 Elsevier Scientific Publishers Ireland. Ltd.

66 IHD have been established in numerous epidemiological and clinical studies [l-4]. In contrast, high levels of high density lipoprotein (HDL)-cholesterol are protective [5-71. Relationships between elevated serum total and very low density lipoprotein (VLDL) triglyceride concentrations and IHD has remained ambiguous [8-111. In 1971, Alaupovic [12] suggested that apolipoproteins should be considered in the evaluation of lipoprotein disorders. Since then, abnormalities in the composition of lipoproteins, in addition to dyslipoproteinemias, have been found to be associated with IHD [13]. The plasma total apo B and LDL apo B levels have been reported to correlate positively with IHD [4,14-171. It has been proposed that apo B concentration is a better discriminator between patients with IHD and healthy controls than LDL-cholesterol concentration [14,16,17]. The HDL apo A, total plasma apo A-I and HDL apo A-I levels have been shown to correlate negatively with IHD [4,7,14]. In some studies, apo A-I levels have distinguished coronary patients from healthy controls better than HDL-cholesterol [14,17,18] but also contrasting results have been reported [19]. Obviously, there is so far not enough data to define whether apo A-I or apo B is the better marker for IHD [4,14]. Since only a few studies have included measurements of all lipoprotein components and comparisons of lipoprotein mass concentrations, the present study was undertaken to examine the lipid - .,‘X.El DEJOGIUPHIC CONTROLS

DATA RELATING TO PATIENTS AND

Mean f SD.

No. Age (yrs) -ge Height&m) range Weight (kg) range RBW (%) range

Group A

Group B

Controls

116 50.4 f 6.8 * 34-59 174.5+6.4 * 160-192 78.9 f 10.8 57-108 113.8f13.3

105 53.0f6.1 *** 32-62 173.3k5.8 *** 158-190 81.3f13.1 56-130 118.Qf15.6 *

78.3-158.8

87.9-161.4

50 47.0 * 8.5 30-62 176.9f6.1 165-194 80.7kll.2 63-113 112.6k14.5 86.3-157.6

* P < 0.05, * * P -c 0.01, * * * P -z 0.001 for the difference between patients and controls.

and lipoprotein status as a whole by a case-control method in patients with MI, both in acute phase and in the postinfarction phase. The study aimed to asscyp changes in both the concentrations and composr:ron of lipoproteins in patients with IHD in comparison to healthy subjects. It was hoped by conducting analyses in patients with AM1 immediately upon admission to hospital to find lipoprotein patterns still largely similar to those preceding infarction, because the lipoprotein patterns in MI patients in the postinfarction period may greatly be different from those before the acute event because of medication and changes in life style, e.g., in diet, exercise habits, smoking, etc. Subjects and methods Patients There were two patient groups. The first study group (A) was formed from consecutive male patients aged under 60 years admitted to Jorvi Hospital, Espoo, Finland, because of definite AM1 between January 1981 and October 1982. Blood samples for lipoprotein analyses were obtained from all patients with chest pain suggestive of AM1 within the first 2 h at hospital. However, only patients who met criteria unequivocally indicative of AM1 were included in the study. These criteria included a positive ECG finding (Minnesota codes i-i, i-2-l to I-2-8, 3-2, 5-I and 7-I) [20] and a rise (> 10 U/l) in creatine phosphokinase MB fraction (CK-MB). The duration of chest pain before admission averaged 14 h (range 1-96 h). One hundred and sixteen men fulfilled the required criteria and formed the study group. The demographic data relating to the patients are shown in Table 1. Fifty men (50.5% of those with a known history of angina and 43.1% of all patients) had experienced angina pectorls before their AMI. Thirty-two patients (27.6%) had previously diagnosed hypertension. One patient had diabetes. Regular medication (drugs taken daily) was taken by 41 patients (35.3%). Twenty-seven patients (23.3%) took /?-blockers (pindolol, metoprolol, atenolol, timolol, propranolol, sotalol, acebutolol, alprenolol) and 20 (17.2%) diuretics (&&ides, furosemide, triamterene, chlortalidone, spironolactone). The prevalence of smoking in group A men was 77.0% (smoking more than 1 cigarette a day).

67 The second study group (B) included patients who had been treated in Jorvi Hospital because of unequivocai AM1 in 1978 and 1979, i.e. 2-3 years before the study, and who at that time were aged under 60. Hospital records revealed in this age category 159 patients who met the AMI criteria mentioned above. Of these, 21 (13.2%) had died before the study3 one patient was excluded be. L;o”JT: -7.--- Gr” &@ascy

&;lJ

32 p++,;

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participate or could not be contacted. Therefore, the final study group consisted of 105 men (66% of patients discbarged and 76% of eligible subjects). The demographic data relating to these patients are shown in Table 1. None of the patients had suffered acute re-infarction during the 6 months preceding the study. Thirty-five patients (33.3%) had hypertension and 12 patients (11.4%) had diabetes (insulin- or noninsuiin-dependent). At the time of examination 92 patients (87.6%) were on regular medication. Seventy-four patients were taking /I-blockers (pindolol, metoproloi, propranolol, a;renoloI, sotaIo1) and 35 diuretics (thiatides, triamterene, furosemide, ChIortaIidone). The prevalence of smoking was 44.8%. The control group was formed from the staff of the Helsinki University Central Hospital, from office-staff at a large metals company (Gy W&tsiIgi Ab) and from policemen in Helsinki city who responded to a written invitation. The invitations -_--wc*e delivered h the industrial b&th cere =nters* AII control subjects were free of clinical manifestations of IHD. The demographic data relating to tbe controls are shown in Table 1. None of the controIs were on regular medication and 35% were smokers. Demographic data Relative body weight (RBW) was calculated as follows: mw

_ -

weight(kg)* 100

9&

height (cm) - 105

Chemical methoa3 Nonfasting venous blood samples from patients in study group A were taken immediately on admission to hospital. A second blood sample was drawn either next morning, after a 10-h overnight

fast, or during the morning of the second day in hospital if the patient arrived during the night. The first sample was missed for one subject and the second for * 9 subjects. Blood samples were taken from group B patients and control subjects as out+a?ients after 10-h overnight fsl. Serum was immediately separated and stored at 4” C for l-4 days before ultracentrifugation. L~~~iCkLl fractions were separated from sera by a sequential ultracentrifugation technique [21] using a Beckman L 70 ultracentrifuge and Type 50 Ti Beckman rotor (Beckman Instruments Inc., Palo Alto, CA, USA). Chylomicrons were fiist removed at a density of 1.006 g/ml by centrifuging for 30 min at 20000 X g. Thereafter, VLDL were flotated up by ultracentrifuging for 18 h at 96000 x g at a density of 1.006 g/ml The density of the bottom fraction was raised to 1.063 g/mI with a solution containing NaCl (55 g/I), KBr (109 g/I) and EDTA (0.1 g/l)_ LDL were isolated by spinning for 24 h at 105 000 x g. A sample of the LDL bottom fraction was taken to represent total HDL. Thereafter, the density of the LDL bottom fraction was raised to 1.125 g/mI with NaCl(153 g/l) and KBr (354 g/I) solutions. HDL, were isolated by ultracentrifuging the mixture for 48 h at 105000 x g using Type TFI’ 45.6 rotor (Kontron Ltd., Zurich, Switzerland). FinaIIy, the density of the infranatant was adjusted to 1.210 g/mI and I-IDL, were isolated by spinning for 65 h at 105000 x g. The recoveries of cholesterol, triglycerides and phospholipids averaged 94.8% f 4.4% (SD), 96.7 + 7.5% and 95.8 f 5.2% respcctively. Respective corrections were made to VLDL, LDL and HDL fractions so that totd recovery amounted to 100%. Cholesterol concentrations in whole sera and in the isolated lipoprotein fractions were rneaswd by an enzymatic calorimetric method [22] using kit No. 187313 of Boehringer Mannheim GmbH. Triglyceride concentrations were determined by an enzymatic method [23] using kit NO. 297771 of Boehringer Mannheim GmbH. Lipid phosphorus WAS ~IX~JGXXI by the method of Bartlett [24]. pr* t&n was measured by the method described by Ka&yap et al. [25]. The relative proportions of the lipid and protein components in each lipoprotein fraction were calculated as percentages of the total mass of

lipoprotein. The sum of the concentrations of cholesterol, triglyceride, phospholipid and protein in the lipoprotein fractions were taken to equal the total lipoprotein mass, expressed as mg/dl. Since fatty acids esterified with cholesterol were omitted from this calculation, the values are 5-10% lower than the true mass. Statistical methods Data processing was carried out by computer, using BMDP statistical software [26]. Analysis of covariance was used to test the equality of means between patients and controls, with age and RBW as covariates, and to test the independence of variables. Stepwise logistic regressio;a analysis was used when regression slopes were unequal (for serum triglycerides and VLDL triglycerides and protein between group A patients and controls). Discriminant analysis between patients and controls was performed stepwise (F-to-enter limit 4.0, F-to-remove limit 3.996). Logarithmic transformation was performed for parameters which were not normally distributed (skewness/S.E. or kurtosis/S.E. > /2/). The issue of multiple hypothesis-testing is a controversial problem in statistical inference. The author holds the view that in the case of unrelated hypotheses it is immaterial how many hypotheses are tested within the study data, and thus no modification of the P-value is necessary [27]. Should the reader wish to adopt a ‘frequentist’

401 60

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100

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1

t40 LDL cholesterol

I

ia0 (mgldl)

I 220

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statistical viewpoint, then one can control the overall ‘experiment-wise’ type I (alpha) error-rate by setting the ‘test-wise’ level equal to the alpha divided by the number of tests carried out (the Bonferroni adjustment). If, e.g., 10 tests were done in the study, the interpretation of an observed P-value of 0.05 would be translated to a more conservative value of P = 0.005. The study protocol had been approved by the Jorvi Hospital Ethical Committee. Results Lipid and lipoprotein concentrations and kpaprotein compositions Group A patients. The mean serum total cholesterol concentration did not differ between group A men and the control men either, when the samples of the patients were taken upon admission to hospital (224.4 + 3.9 mg/dl vs. 221.3 f 5.1 mg/dl) or they were drawn on the first morning after AMI (211.2 + 4.1 mg/dl vs. 221.3 f 5.1 mg/dl). Nonfasting serum samples of group A patients exhibited higher mean serum total triglyceride concentration than the samples of the controls (167.9 f 9.9 mg/dl vs. 128.0 str 11.0 mg/dl, P c 0.001). However, there was no difference in serum total triglyceride levels between patients and controls, when the fasting morning values of the patients were compared with those of controls (123.3 + 5.3 mg/dl vs. 128.0 f 11.0 mg/dl).

1 260

50

150 LDL cholesterol

250

350

(mpldl)

Fig. 1. Relationshipbetween LDL-cholestcrol and LDL protein concentrations in group A patients and controls (left), and in group B patients and controls (right). a, patients; o, controls. LDL protein (mg/dl) = 32.1+ 0.4 x LDL-cholesterol (mg/dl), for group A. LDL pro”ti (mg/dl) = 37.8 +0.4X LDL-cholesterol (mg/dl), for group B. LDL protein (.mg/dl) = 5.3 +0.5 x LDL-cholesterol (mg/dl), for controls. P = 0.396 for difference between slopes of group A patients and controls, P = 0.371 for difference between slopes of group B patients and controls.

69 TABLE 2 CONCENTRATIONS OF VLDL, LDL AND HDL AND THEIR LIPID AND PROTEIN CONSTITUENTS (mg/dI) IN GROUP A PATIENTS ON ADMISSION (NONFASTING), ON THE FIRST OR SECOND MORNING AFTER AM1 (FASTING), IN GROUP B PATIENTS (FASTING) AND IN CONTROLS (FASTING)

Meanf SEM. Group A

TotaI VLDL Cholesterol TrigIycerides PhosphoIipids protein

Total LDL Cholesterol TrigIyceridti Phospholipids protein

Total HDL CholesteroI Triglycerides PhosphoIipids PrObill

Group B (n = 101)

an admission (n = 109)

Fasting (n = 105)

165.7* Zl.li 89.5f: 26.4* 28.7&

11.2 1.6 * 7.2 1.9 * 1.4 ***

127.8 f 6.7 17.81 i.8 63.3 f4.1 19.5 f 1.2 28.0f1.4 ***

242.9 f 33.6 * 135.7f 40.0$33.6+

393-l+ 158.6* 37.6f 9998+ 97.1*

7.6 ** 3.5 1.4 *** 21*** 20 ***

376.2 + 8.0 * 151.2 f 3.7 3fi7+1.3 *** 93.0 f 2.2 95.3k1.9 ***

259.2f 40.2f 22.9& 59.0f 137.1 f

4.8 1.0 0.8 1.6 3.0

260.3*4.7 42.6fl.O 23.4kO.7 55.7k1.5 138.6f2.5

*** *** ** ***

*** *** *** ***

r

17.0 2.8 _9.9 2.9 1.8

ControIs (n = 50)

*** -__. a* *** ***

131.3 f I6.6* 76.Sk 20.9& 17.3*

421.0f10.3 166.2+ 4.7 46.2f 1.8 105-4 + 2.8 103.2* 2.6

***

348.4+ 10.2 153.3* 4.4 29.3f 1.6 87.3f 3.0 78.5* 2.8

258.4* 40.1* 22.Oi 60.1 f 136,2f

*** ***

4.9 0.9 0.6 1.6 2.7

*** ** ***

* ***

305.6& 51.4* 22.2* 66.lf 165.9*

14.2 1.8 9.1 2.2 1.3

6.1 1.6 0.9 2.1 3.1

* P c 0.05, * * P -z 0.01, * * * P c 0.001 for the difference between patients and contrc9ls.

Table 2 shows the mean concentrations of VLDL, LDL and HDL lipids and protein in group A men and in control men. LDL-cholesterol levels

did not separate patients and controls. However, the mean LDL mass concentration was higher in patients than in controls. Hyperapobetalipopro-

TABLE 3 CONCENTRATIONS OF I-II& AND HDL, AND THEIR LIPID AND PRGTEIN CONSTITUENTS (mg/dI) IN GROUP A PATIENTS ON ADMISSION (NONFASTING), ON THE FIRST OR SECOND MOFWING AFTER AM1 (FASTING), IN GROUP B PATIENTS (FASTING) AND IN CONTROLS (FASTING) Mean+SEM. Group B (n = 92)

Group A On admission (n = 109) TotaI HDL, CholesterOl Triglycerides PInxsphoIipids Protein TotaI IiDLs Cholesterol TrigIyceridea PhosphoIipids protein

97.7f4.1 18.01tO.9 10.6f0.5 25.6k1.4 43.5f1.8

*** *** ** *** **+

161.2f 3.7 22.1f0.5 ** 12.0f0.5 ** 33.4*0.7 93.7f2.8

Fasting (n = 104)

Controls (n = 50)

*** ***

86.253.6 **+ 16.5kO.8 *** 9.250.4 +*= 22.7&1.2 *** 37..8f 1.7 * * *

136.9 f 6.0 27.0f 1.5 12.9f0.6 33.0*1.9 64.0* 2.5

165.7 f_ 3.1 24.3 * 0.5 12.3f0.5 *** 32.3kO.7 96.8f2.0

172.6 f 2.9 13.4 f 0.4 12.7 f 0.4 * + * 37Af0.7 * * 98.6 f 1.9

168.7 f 3.8 24.4 f 0.6 9.3f0.1 33.1 f 1.0 101.9f2.5

94.5f4.2 18.2fl.O 11.1 f0.4 23.3f1.4 41.91t1.9

++* ***

* P < 0.05, * * P -z 0.01, * * * P -c 0.001 for the difference between patients and Control.

70 teinemia, i.e. LDL protein concentration greater or equal to 120 mg/dl (according to Sniderman et al., see ref. 16) was present in 14 patients (12.1%). Figure 1 shows that group A patients exhibited higher LDL protein concentrations than controls at all LDL-cholesterol levels, this was particularly obvious at LDL-cholesterol levels between 100 and 200 mg/dl. The total HDL and HDLz lipid and protein concentrations and mass concentrations were lower in patients than in controls, whereas the HDL, mass concentration was normal in group A patients (Tables 2 and 3). The differences in HDLand HDL,-cholesterol, phospholipid, protein and mass concentration.; between patients and controls remained significant even when VLDL triglyceride concentration was taken into account on analysis of covariance. LDL contained more protein (24.8 f 0.3% vsl. 22.5 f 0.48, P e 0.001) and triglycerides (9.6 f 0.3% vs. 8.4 f 0.48, P -K0.05) but less cholesterol (40.2f0.3% vs. 44.1+0.4%, P
very similar to those obtained for comparison between group A and the controls (Tables 2 and 3). LDL triglyceride, phospholipid and protein concentrations and LDL mass concentration were higher in patients than in controls, although LDL-cholesterol concentration did not differ. Again LDL protein level was higher in patients than in controls at all levels of LDL cholesterol (Fig. I). Sixteen patients of group B (15.2%) had LDL protein concentration greater or equal to 120 mg/dl. Total HDL and HDLz lipid and protein concentrations and mass concentrations were lower in patients than in controls, whereas there was no difference in HDL, mass concentrations. LDL composition of the group B patients showed very similar changes to those of group A patients, containing more protein (24.7 + 0.3% vs. 22.3 f 0.4%, P-c 0.001) and triglycerides (11.1 f 0.4% vs. 8.4 f 0.48, P < 0.001) and less cholesterol (39.1 f 0.4% vs. 44.1 + 0.4%, P -z O.OOl) than control LDL. Like in group A patients, the LDLcholesterol/LDL protein ratio was lower in group B men than in controls at LDL-cholesterol levels below 160 mg/dl(l.48 f 0.04 vs. 1.97 + 0.05, P < 0.001) as well as above 160 mg/dl(l.77 f 0.06 vs. 2.03 + 0.06, P < 0.05). In group B patients HDL, contained more phospholipids (25.7 + 0.5% vs. 23.4 f 0.5%, P < 0.01) than control HDL2. Patient HDL, contained more triglycerides (7.4 _t 0.3% vs. 5.6 f 0.4%, P < 0.01) and phospholipids (21.7 f 0.3% vs. 19.6 + 0.4%, P c 0.001) and less protein (57.0 f0.4% vs. 60.3 f0.4%, P ~0.001) than control HDL,. Discriminatory powers of various lipoprotein variables On stepwise discriminant analysis, HDL, protein concentration allowed the best separation between group A patients and controls followed by HDL, phospholipids and LDL protein concentration (Table 4). When HDL/LDL-cholesterol, HDL/L-DL protein and HDLJLDL protein ratios were included in the analysis, discrimination was best with the HDL/LDL protein ratio (Wilks’ lambda 0.67, approximate F-statistic 74.9, degrees of freedom 1,154). HDL, protein concentration appeared to be the best parameter for distinguishing also between group B patients and controls (Table 4). If HDL/LDL cholesterol,

71 TABLE 4 DISCRIMINATION BETWEEN GROUP A AND B PATIENTS AND CONTROLS (STEPWISE DISCRIMNANT ANALYSIS) Discriminant analysis includes lipoprotein variables for which patients and controls differed significantly in anatysis of variance. Age md RBW are included. WilkST lambda

Approximate

Degrees

of F-statistic freedom

GroupA HDL, protein HDLl phospholipids LDL protein HJ3L cholesterol VLDL protein VLDL triglycerides Total triglycerides

0.78 0.68 OS9 0.53 0.51 0.49 0.44

43.2 35.6 35.3 33.7 28.7 26.4 27.4

(1,154) (2,153) (3,152) (4,151) ~5,150) (6,149) (7,148)

Group B HDL, protein HDLl phospholipids HDLz cholesterol LDL protein VLDL protein VLDL triglycerides

0.64 0.58 0.51 0.46 0.44 0.42

77.3 50.6 44.5 40.5 35.1 32.0

(1,139) (2.138) (3,137) (4,136) (5,135) (6,134)

HDL/LDL protein and HDLJLDL protein ratios were included, the highest degree of discrimination between patients and controls arose from the HDLJLDL protein ratio (Wilks’ lambda 0.58, approximate F-statistic 101.4, degrees of freedom 1,139).

For group A patients with acute myocardial infarction nonfasting serum samples upon admission to hospital were chosen to be preferred for several reasons. First, except for total triglycerides and VLDL, the concentrations of lipoproteins are not affected by the degree of fasting [28,29]. Instead, serum total cholesterol, LDL-cholesterol, whole plasma apo B and LDL ago B concentrations have been shown to fall during the days immediately after AMI [30-321, whereas HDLchoIestero1 concentration remains stable [30] or decreases [31]. Accordingly, there was a small decline in totaI cholesterol, total phospholipids, LDL-cholesterol, LDL phospholipids, LDL pro-

tein and in HDL phospholipids (in both subfractions) and a small rise in HDL and HDL,cholesterol and in HDL, protein in addition to the fall in serum total triglycerides and VLDL in the fasting morning samples of group A patients compafed to the nonfasting admission samples (data not shown). The increase in HDL, protein concentrations most probably reflects rises in ape SAA, an acute phase protein known to be bound to HDL, [33]. The decline in serum total triglycerides and VLDL is most probabiy largely due to the fact that nonfasting and fasting values were compared, but the changes in the other lipoproteins may be mostly caused by the acute event of infarction. Thus, the nonfasting admission values probably deflect the red situation in group A patients better than the fasting morning values. Moreover, apart from triglyceride and VLDL, the results were similar when comparison was made between the fasting morning values of group A and the controls. Unlike patients in many previous studies [1,2,9] the MI patients in the present study exhibited no difference in total or LDL-cholesterol concentrations as compared to healthy controls. This unexpected finding is of special interest and requires careful consideration. It may be partly explained by following possibilities. The values for the group A patients, although obtained immediately on admission to hospital, may not reflect .true pre-infarction lipid status but be altered due to the acute event. The cholesterol levels of the patients might have been higher in the earlier years than at present, if the patients had changed recently their living habits as a result of general health education or for personal reasons. A considerable proportion of the group A patients (50.5%) had suffered from angina before their AMI. At least these subjects are likely to have changed their life style during the years preceding AMI. Life style change during the years after MI is even more plausible in group B patients. Since polygenic hypercholesterolemia is common in Finland, differences in cholesterol levels between IHD patients and healthy people are less likely to become evident in Finnish population than in populatknis with a lower average cholesterol level. However, a markedly high cholesterol level appears a risk factor for IHD also in Finnish population [34]-

72 Since 1970s cholesterol levels in Finland have declined [35], and it seems that the frequency of clearly hypercholesterolemic subjects with AMI in Finland, at least in &h&i area, is aho IlOW lower than it used to be. Inspite of similar LDL-cholesterol levels the patients had higher LDL protein concentrations and higher LDL mass concentrations than controls. Thus, the MI patients showed a compositional change in their LDL, which was evident at all LDGcholesterol levels. LDL particles in the present patients were protein- and triglyceride-rich and cholesterol-poor, in comparison with those in controls. Similar changes in LDL composition have recently been detected in hypertriglyceridemia [36,37]. Triglyceride-enrichment of LDL occurs also in postprandial lipemia [38]. However, the group A patients were not hypertriglyceridemic, and group B patients were probably not more in postprandial lipemic state than the controls. Therefore, it is relevant to ask why the present patients with normal or only slightly elevated triglyceride levels had protein-enrichment in their LDL. The explanations can be only speculative. One possibility could be overproduction of apo B, which could occur also directiy in LDL fraction. However, VLDL-independent production of LDL has been described only in familial hypercholesterolemic subjects 1391. Another explanation is that more cholesterol than usually is removed during the VLDL-LDL cascade. In contrast, it is also possible that the turnover of LDL is increased, so that LDL stays less time in the circulation to acquire cholesterol. KesWemi and G.rundy [40] found, indeed, higher synthetic rates and a shorter residence time for LDL apo B in coronary heart disease patients than in normal controls, and a positive correlation between the fractional catabolic rate of LDL apo B and the ratio of protein to cholesterol in LDL. It is possible that an increase of the LDL mass (which may also mean increased numbers of LDL particles in the circulation) promote atherosclerosis by enhancing the binding of LDL to arterial wall cells or its infiltration into cells. In addition, the compositional change in patients’ LDL may be atherogenic. Kecent studies have provided evidence that LDL enriched in protein may be more atherogenic than normal LDL j15,16,41].

In accordance with the many earlier studies [5,7] the present data revealed significantly lower HDL-cholesterol and total HDL levels in MI patients than in controls. In previous studies, reductions of either HDL,-cholesterol [4] or *of both HDL*- and HDL,-cholesterol [42] have occurred in male patients with IHD. Current data showed lower mass concentrations of HDL, in MI patients than in controls, whereas HDL, levels were similar. It remains speculative whether the production of HDL is impaired or the catabolism is enhanced, and why there is a change in the distribution of HDL subfractions towards HDL, in male MI patients. According to current view lipoprotein lipase (LPL) induced VLDL hydrolysis is linked to HDL, formation. In addition, the LCAT has a role in the conversion of HDL, to HDL2, whereas the conversion of HDL, to HDL, depends on the lipid transfer reaction and hepatic lipase (HL) activity [43]. There were no differences in the LPL or HL activities between group B patients and the controls (data not shown, lipase activities were not examined in group A patients) and we do not have data on LCAT or lipid transfer activities. It is possible that the patient HDL,, rich in triglycerides and phospholipids, is a better substrate for HL than control HDLz [38]. Therefore, patient HDL, may be more readily converted to HDL, than control HDL,. Thirty-five percent of group A patients and 87% of group B patients had regular medication, whereas control subjects did not use drugs. The patients used mainly /&blockers and diuretics, which are known to affect cholesterol, triglyceride and HDL-cholesterol concentrations [44]. In this study, the results were, however, similar as presented when, a subgroup of group A formed from patients with no regular medication was compared with the control group. The number of group B patients without medication was too small for a reliable testing. Differences in dietary habits, physical activity, smoking habits, etc. between patients and controls are likely, and probably contribute to the observed changes in lipoprotein levels. Notably, the design of this study does not allow to differentiate the impact of deleterious living habits and constitutional, probably genetically determined, factors on lipid and lipoprotein patterns in coronary patients.

73 In conclusion, at least in the Helsinki area in Finland determination of lipoprotein protein concentrations seems to give a better indication of the atherogenicity of the lipid and lipoprotein profile than determination of lipoprotein cholesttzol concentrations. HDL protein, HDL, protein and LDL protein concentrations and HDL/LDL protein ratio appear to be parameters which distinguish reliably patients with IHD from healthy controls. It is important to note that some coronary patients have normal total cholesterol and LDLcholesterol level%but yet elevated concentrations of LDL particles. In such patients, the LDL appears to be enriched in protein and triglycerides. It is possible that these structural changes of LDL render it more atherogenic.

Professor Esko NikkiE died on September 21, 1986. The final preparation of this manuscript has been carried out after his death with the kind help and criticism of Associate Professor Maja-Riitta Taskinen, M.D., to whom I wish to express my gratitude. The author is grateful to Mrs. Leena Lehikoinen, Mrs. Sirkka Mannelin and Mrs. Sirkka-Liisa Runeberg for excellent technical assistance. This investigation was supported by grants from the Finnish Heart Foundation, the Finnish Foundation for Cardiovascular Research and the Research and Science Foundation of Farmos, which are gratefully acknowledged. This study has also been supported by the Finnish State Medical Research Council (Academy of Finland). References

severity of angiographically defined coronary artery disease, Atherosclerosis, 49 (1983) 1. 5 Heiss. 6.. Johnson, N.J., Reiland, S., Davis, C.E. and TYO~, HA., The epidemiology of plasma high-density hpoprotein cholesterol levels. The Lipid Research Chn& Program Prevalence Study, Circulation, 62 (Suppl. Iv) (1980) 116. 6

7

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9

10

11

12 13

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