- Email: [email protected]
Lack of association of lipoprotein (a) with coronary heart disease in Spaniard type 2 diabetic patients
Diabetes Research and Clinical Practice 35 (1997) 135% 141
Lack of association of lipoprotein (a) with coronary heart disease in Spaniard type 2 diabetic patients F. Relimpio
a,*, A. Pumar a, F. Losada a, C. Montilla R. Astorga a a Servicio de Endocrinologia, Hospital Universitario b Servicio de Bioquimica Clinica, Hospital Universitario
b, F. Morales a, D. Acosta a,
Virgen del Rocio, Seville, Spain Virgen de1 Rocio, Seville, Spain
Received 29 May 1996; received in revised form 24 November 1996; accepted 23 December 1996
Abstract We tried to elucidate the possible relationship between lipoprotein (a) levels and coronary heart disease by assessing the presence of lipoprotein (a) covariates in NIDDM. We selected 41 type 2 diabetic patients with coronary heart disease and 82 type 2 diabetic patients free from cardiovascular disease. They were adjusted for age, sex and duration of diabetes. Routine chemical analysis was carried out using standard procedures, HbA,, by HPLC and lipoprotein (a) and urinary albumin excretion rate by immunonephelometry. No difference has been found in lipoprotein (a) levels between both groups of patients (18 [144.25] mg/dl in cases vs. 23 [197.25] mg/dl in controls (median [range]), Mann-Whitney U-test, P > 0.1). No association has been found between coronary heart disease and lipoprotein (a) levels greater than 30 mg/dl (Pearson’s x ‘, P > 0.1). Significant and independent linear relationships have been found between the square root of lipoprotein (a) levels, serum creatinine and total cholesterol (multiple r*: 0.15, P < 0.001). Patients treated with insulin had greater square root of lipoprotein (a) levels, even after adjusting for serum creatinine and total cholesterol (5.87 f 0.35 vs. 4.76 f 0.36 (mean f S.E.), ANCOVA, P < 0.05). These data do not show an association between symptomatic coronary heart disease and lipoprotein (a) in NIDDM. Significant and independent relationships have been found between this variable and serum creatinine, total cholesterol and insulin therapy. 0 1997 Elsevier Science Ireland Ltd. Keywords: Lipoprotein Insulin therapy
(a); Diabetes
mellitus
(non-insulin-dependent);
Abbreviations: lp(a), lipoprotein (a); NIDDM, non-insulindependent diabetes mellitus; UAER, urinary albumin excretion rate; CHD, coronary heart disease. * Corresponding author. Present address: Endocrinologia, Centro de Especialidades Virgen de 10s Reyes, Marques de Paradas s/n, 41001 Seville, Spain. Fax: + 34 5 4248111; email: [email protected]
heart disease; Microalbuminuria;
1. Introduction Lipoprotein (a) is a subtype of the LDL molecule in which apoprotein (a), a large glyco-
0168-8227/97/$17.00 0 1997 Elsevier Science Ireland Ltd. All rights reserved. PI1 SO1 68-8227(97)01369-7
Coronary
136
F. Relimpio
et al. /Diabetes
Research
protein, is covalently bound to the apo B [l]. Its clinical interest lies in its recognition as an independent risk factor of atherosclerotic vascular disease in the general population [2]. NIDDM is a condition associated with a high cardiovascular risk [3]. The main determinants of atherosclerotic cardiovascular disease in NIDDM seem to be partly the same risk factors that confer a high cardiovascular risk in the general population [4]. Notwithstanding, considerable controversy exists in other aspects, such as the role played by glycemic control or the trend to cluster around other risk factors. Likewise, controversy exists about’ the recognition of high lipoprotein (a) (lp(a)) levels as an independent cardiovascular risk factor in this condition [5-l 51 and its putative relationships with mode of treatment [14,16] or the presence of diabetic kidney disease [6,8,15,17]. Therefore, the present case-control study was designed in order to elucidate if there is a relationship between lp(a) levels and coronary heart disease (CHD) in NIDDM. Our objective was also to assess the presence of lp(a) covariates in this very condition.
2. Patients and methods The patients studied belong to an on-going cohort of type 2 diabetic patients followed-up in our out-patient diabetes unit. Forty-one consecutive patients with CHD have been studied. For each case, two controls, adjusted for gender, age and duration of diabetes have been selected from the same cohort. The diagnosis of NIDDM was based upon current WHO criteria. Only four cases had an age less than 40 years and none required insulin. The first firm indication of hyperglycemia (fasting blood glucose > 7.8 mmol/l) or a diagnostic oral glucose tolerance test was used to compute the duration of diabetes. The ocurrence of gestational diabetes mellitus was taken as the starting point of the disease, only if the persistence of glucose tolerance abnormalities had occurred after delivery, without the need to continue insulin therapy or to use it in 2 years time after delivery. A thorough clinical interview
and Clinical
Practice
35 (1997)
135- 141
was performed in order to ascertain clinical status, current therapies and cardiovascular situation. Information was mainly received directly from patients and families, although clinical records were also used. The hypolipidaemic drugs used belonged to the groups of 3-hydroxy-3methylglutaryl coenzyme A reductase inhibitors, fibrates or bile acid sequestrants. Postmenopausal replacement hormonal therapy was not used. Two patients (a case and a control) were receiving thyroid hormone for primary hypothyroidism and benignant nodular thyroid disease, respectively. Two patients in the control group had chronic viral hepatitis secondary to B-virus infection in non-advanced stage (mild hypertransaminasemia). For the purpose of the present study, CHD was established: if hospital-requiring myocardial acute infarction or angina pectoris had been diagnosed by a cardiologist; if the patient had been submitted to invasive coronary procedures (bypass surgery or percutaneous transluminal angioplasty) or if a stress testing had been positive. The absence of that complication was assessed by a negative answer to a questionnaire in which symptoms induced by daily-life physical efforts were asked for, and a normal resting ECG. The presence of laser-treated diabetic retinopathy was assessed from ophthalmologic records or reported by the patient. The presence of essential hypertension was established if there was the need to take anti-hypertensive drugs or if there was confirmed evidence of resting recordings yielding systolic blood pressure greater than 160 mmHg and/or diastolic blood pressure greater than 90 mmHg. Having taken the morning anti-hypertensive treatment (if needed), and after a lo-min rest period in the sitting position, systolic and diastolic pressures (fifth phase) were measured twice to the nearest 5 mmHg and then averaged. Readings were taken 5 min apart using an appropiately sized cuff. Height and weight were measured with the subjects wearing light clothes, without shoes. The body-mass index (BMI) was calculated as weight (kg) divided by height (m’). The waist-tohip ratio (WHR) was calculated by dividing the waist circumference (at the umbilicus) by the hip circumference (at the bitrochanteric level). The main demographic features of cases and controls are shown in Table 1.
F. Relimpio Table Main
1 demographic
and analytical
et al. /Diabetes
features
of patients
Research
and Clinical
belonging
to both
groups
Cases (n = 41) Age (years) Known Gender
duration of diabetes (male/female)
(years)
Essential hypertension (n, ‘%) Current smoking habit (n. “/;I) Hypolipidaemic drug-treated (n, %) Insulin-treated (n, %) Insulin dose (U/kg) Laser-requiring (n, ‘Xl) BMI (kg/m*) WHR Systolic blood pressure (mmHg) Diastolic blood pressure (mmHg) Fasting blood glucose (mg/dl) HbA,, (‘X1) Total serum cholesterol (mg/dl) HDL-cholesterol (mg/dl) Non-HDL-cholesterol (mg/dl) Triglycerides (mg/dl) Apoprotein A, (mg/dl) Apoprotein B (mg/dl) Lipoprotein (a) (mg/dl) UAER category(normo/micro/macroalbuminuric) Serum creatinine (mg/dl) Serum uric acid (mg/dl) a Matching b Differences
criteria. assessed by the Mann-Whitney
2.1. Biochemical
Practice
35 (1997)
135-141
of study Controls
(n = 82)
63.75 * 8.76
62.93 + 11.62
12.60 k 9.67 16125
11.93*9.31 32/50
35 (85.4) 4 (9.8) 13 (31.7) 23 (56.1) 0.56 If: 0.2 IO (24.4) 30.57 + 4.56 I .05 * 0.07 15Ok22.19 80.85 * 1 I .77 198.95 + 62.3 7.46 + 1.59 215.36 + 32.38 49.79 + 12.06 164.79 f 33.39 164 [314] 144.95 f 22.06 112.95 k 22.16 18 [144.25] 22/10/2 0.97 * 0.35 5.48 i 1.68
137
42 (51.2) 13 (15.9) 22 (26.8) 40 (48.8) 0.5 * 0.13 17 (20.7) 29.54 k 4.63 1.03 * 0.08 149.04 + 18.14 83.22 + 9.37 185.97 k 68.35 7.47 * 2.12 215.54 f 40.63 53.63 + 13.09 160.5 k 38.45 135 [479] 148.64 + 23.12 112.25 + 27.41 23 [197.25] 4912019 0.92 +- 0.36 4.95 + 1.52
P-value d ‘I ‘I P
U-test.
measurements
Blood samples for biochemical determinations were taken from an antecubital vein after a 10-h fast, before the morning drug intake or insulin administration. Blood glucose was measured by the hexokinase method (Gluco-quanta Glucose, BoehringerMannheim; normal values 75 110 mg/dl). Serum creatinine was determined by an enzymatic calorimetric test (Creatinine-PAPa, Boehringer-Mannheim; normal values 0.55 1.1 mg/dl in men, and 0.550.9 mg/dl in women). The urinary albumin excretion rate (UAER) was measured in overnight (10 h) sterile non-ketotic urine collections using laser immunonephelometry (Behring nephelometer analyzer). For the purpose of the present study, those patients having an UAER lower than 20 pg/min have been considered normoalbuminuric, those having an
UAER > 20 and < 200 pg/min have been considered microalbuminuric and those having UAER values > 200 ,ugg/min have been considered macroalbuminuric. HbA,, was measured by HPLC (HPLC autoanalyzer, DIC (Menarini); normal values up to 5.5%). Total serum cholesterol was analyzed by a fully-enzymatic method (CHOD-PAP@‘, BoehringerMannheim; normal values 150-250 mg/dl). HDL-cholesterol was measured after precipitation of VLDL and LDL with phosphotungstic acid and magnesium chloride. Serum triglycerides were measured by an enzymatic method (GPO-PAP”, BoehringerMannheim; normal values 60- 160 mg/dl). Apolipoproteins A, and B were determined by immunoturbidimetric assay (Tina-quanta Apolipoprotein A, and Apolipoprotein B, respectively, Boehringer-Mannheim; normal values 104-202 mg/dl for males and 108-225 mg/dl for
138
F. Relimpio
et al. /Diabetes
Research
females in the first case and 666133 mg/dl for males and 60- 117 mg/dl for females in the second). Serum uric acid was measured by means of an enzymatic calorimetric test (Uric Acid PAP@) Boehringer-Mannheim; normal values 3.4-7 mg/ dl for males and 2.4-5.7 mg/dl for females). Lp(a) was measured by means of an immunonephelometric assay (N Antiserum to Human Lp(a), Behring, Marburg, Germany, lower limit of detection: 9.5 mg/dl). 2.2. Statistical
and Clinical
Practice
35 (1997)
135-141
Table 2 Bivariate correlation analysis (Spearman correlation coefficients) between lipoprotein (a) and those variables in which a significant result was found Variable
P-value
Creatinine Systolic blood pressure Total cholesterol HDL cholesterol Apoprotein A,
0.22 0.18 0.21 0.18 0.22
<0.05 <0.05 < 0.05 < 0.05 < 0.05
analysis
Normality was evaluated by the KolmogorovSmirnov test. For every quantitative variable, group differences were assessed by means of ttests, one-way ANOVA or Mann-Whitney Utests, depending on data distribution. Pearson’s x2 or Fisher’s exact test (depending on cell sizes) were used to evaluate the association of categorical variables to CHD. Bivariate correlations have been sought by using the Spearman correlation. Stepwise multiple regression analysis has been used to assess the independent relationship of lp(a) with those variables found to have a significant Spearman correlation. An ANCOVA model has been built to assess the independent effect of a categorical variable and two lp(a) covariates upon lp(a) levels. For stepwise multiple regression analysis, one-way ANOVA, and ANCOVA the square root of lp(a) has been taken in order to overcome difficulties derived from the skewness of data distribution. All variables are expressed as mean k S.D., except those in which normality could not be assumed, in which median (range) is expressed. All contrasts are two-tailed. A P < 0.05 was considered significant. All statistical calculations have been made by means of the statistical software package SPSS for Windows 5.0.1 using a PC.
3. Results A lp(a) level below the lower limit of detection was found in 36 patients (29.3%) (15 patients with CHD (36.6%) and 21 controls (25.6%) Pearson’s x2, non-significant). A lp(a) level greater than 30
mg/dl was found in 49 patients (39.8%) (17 patients with CHD (41.5%) and 32 controls (39%), Pearson’s x2, non-significant). A significant difference in lp(a) levels between patients with CHD and controls has not been found (Table 1). The performance of the former analysis, considering separately those patients submitted/not submitted to hypolipidaemic drugs, yielded essentially the same results. Only the presence of essential hypertension has been significantly different in both groups of study (Table 1). Lp(a) levels showed significanty positive Spearman correlations with serum creatinine, total cholesterol, HDL-cholesterol, apoprotein A, values and systolic blood pressure (Table 2). A stepwise multiple regression analysis using the square root of lp(a) levels as the dependent variable, and the covariates as independent variables was performed. Only serum creatinine and total cholesterol were selected by this procedure as being independently related to the dependent variable (Table 3). Lp(a) levels were significantly greater in patients treated with insulin (33 [197.25] vs. 14.5 [126.25] mg/dl, (median [range]), Mann-Whitney U-test P < 0.01). Likewise, a significant association was found between insulin treatment and Table 3 Stepwise multiple regression analysis (taking lipoprotein (a) as the dependent variable) Step
Variable
Multiple
1 2
Creatinine Total cholesterol
0.08 0.15
Y*
the square
root
T
P-value
3.21 3.10
of
F. Relimpio Table 4 Square root category Albumin
of lipoprotein
excretion
Normoalbuminuria Microalbuminuria Macroalbuminuria One-way
ANOVA,
(a) according
the albumin
Square root of lipoprotein
category
(n = 71) (n = 30) (n = 11) factor
et al. /Diabetes
Research
excretion
(a)
5.04 * 3.03 5.67 k 3.07 6.45 + 3.06
effect non-statistically
significant.
lp(a) levels greater than 30 mg/dl (Pearson’s x2 = 6.46, P < 0.05). Patients treated with insulin also had almost significantly greater serum creatinine levels and significantly greater total cholesterol levels (data not shown). To assess the independence of the relationship between insulin treatment and lp(a) levels from the covariates, an ANCOVA model has been used, considering the square root of lp(a) as the dependent variable, insulin therapy as the grouping factor and total cholesterol and serum creatinine as covariates. The linear relationship between each covariate and the square root of lp(a) levels was not significantly different in those treated with insulin from those not receiving exogenous insulin. After adjusting for serum creatinine and total cholesterol, those patients treated with insulin had significantly greater square root of lp(a) levels (5.87 + 0.35 vs. 4.76 + 0.36 (mean f SE.), P < 0.05). After categorizing patients according to their UAER, a trend was seen towards greater square root of lp(a) levels in those patients with macroor microalbuminuria, but without reaching statistical significance (one-way ANOVA, Table 4).
4. Discussion Data presented in this study do not find a relationship between CHD and lp(a) levels in NIDDM. Weak, although significant and independent correlations have been found between lp(a) levels and serum creatinine and total cholesterol. Insulin treatment was associated with higher lp(a) levels, even after adjusting for the effect of covariates.
and Clinical
Practice
35 (1997)
135-141
139
The sample was extracted from a clinic-based NIDDM cohort in Southern Spain. Gender, age and duration of diabetes were carefully adjusted for. It is because all the analytical procedures are well-standardized with commercially-available methods performed in the central laboratory and no change in the main procedures has been perfomed while the study was made, that the study group was analyzed following a homogeneous clinical/biochemical protocol. No significant differences were found in the variables analyzed in the present study between patients with CHD and controls except for the prevalence of hypertension. Detection bias can be excluded, as the whole cohort is sequentially submitted to blood pressure measuring. Nevertheless, patients with CHD had non-significant trends towards: (1) a greater frequency of insulin treatment and laser therapy, (2) greater adiposity, (3) nonHDL-cholesterol, (4) triglycerides and (5) uric acid values, (6) lower HDL-cholesterol and apoprotein A, values. The presence of CHD could have impacted in many ways upon modifiable risk factors. This fact could explain the absence of significant differences in classical risk factors for CHD between both groups of study. Lp(a) levels in patients with CHD were not significantly different from controls. Likewise, an association between the study group membership and a lp(a) level greater than 30 mg/dl or a lp(a) level below the lower limit of detection was not found. The influence of hypolipidaemic drugs can be discarded because of the similar rates of use between patients with CHD and controls, the absence of nicotinic acid in both groups of study and the similar results obtained when the analysis is performed separately in patients submitted/not submitted to those agents. It is unlikely that the low frequency of use of thyroid hormones and the minimal prevalence of mild hepatic disease in the control group could alter the results. In addition, no woman was submitted to postmenopausal replacement hormone therapy, which has altered lp(a) levels [18]. According to current thinking, lp(a) levels are relatively stable and are under strong genetic influence [19,20]. Thus, it is unlikely that dietary, life-style and pharmacological modifications, undertaken because of the presence
140
F. Relimpio
et al. /Diabetes
Research
of CHD, could influence lp(a) levels. Nevertheless, the association between CHD and lp(a) levels in NIDDM is currently far from clear. There are data supporting [4- 1 l] and denying [ 12- 151 such an association. Different ethnic background, study design, biochemical methods or end-point definition could account for discrepant results. In fact, if type 2 diabetic patients with high lp(a) levels had a worse prognosis with respect to CHD (and hence a greater early mortality), a transversal case-control design would infrarepresent those patients, and a possible association between CHD and lp(a) levels could be missed. Another source of concern is the confounding effect of ‘silent CHD’, a prevalent condition in type 2 diabetic patients. In this case our results would deny an association between overt, symptomatic CHD and lp(a) levels in NIDDM. Nevertheless, a study acomplishing the exclusion of silent CHD did not find greater lp(a) levels in type 2 diabetic patients with CHD (although such an association was significant when a cut-off lp(a) level of 30 mg/dl was used) [7]. It seems that only longitudinal studies can determine whether a high lp(a) level poses a significant cardiovascular risk to type 2 diabetic patients. A non-significant trend towards greater lp(a) levels in macro- and microalbuminuric patients was found. This trend has been reported previously in studies analysing a smaller sample [ 17,211. Moreover, a significant relationship between lp(a) levels and UAER category has been found in another study with a greater sample size [14]. The accordance of present data with previously reported findings, and the significant and independent relationship found between lp(a) and serum creatinine raise the question of an existing association between kidney function and lp(a) levels in NIDDM which could have passed undetected due to insufficient sample size. In any case, the association between lp(a) levels and micro/ macroalbuminuria would be consistent with the proposal that elevation of lp(a) occurs as part of non-specific hepatic protein synthesis, triggered by albumin loss in order to maintain constancy of plasma oncotic pressure [22]. An independent relationship was detected between lp(a) levels and total cholesterol in the
and Clinical
Pructice
35 (1997)
135-141
present study. Similar magnitude relationships between lp(a), total- and LDL-cholesterol have been found in one study [14], and with apoprotein B levels in another [7]. Due to its well-established inaccuracies in NIDDM [23], the Friedewald’s expression has not been used to compute LDLcholesterol in the present study. A significant relationship between lp(a) levels and insulin treatment was found. Long duration of diabetes is usually associated with greater frequency of insulin need and diabetic kidney disease. Moreover, patients treated with insulin in the present study had significantly greater total cholesterol and serum creatinine levels. So, the association found between lp(a) levels and insulin treatment could be confounded by these two covariates. Notwithstanding, after adjusting for serum creatinine and total cholesterol, patients treated with insulin had significantly greater lp(a) levels. Similar findings have previously been reported [ 14,161. This issue raises the possibility that in insulin-requiring type 2 diabetic subjects, the summation of endogenous and exogenous insulin could result in higher insulin plasma levels. Whether or not insulin (exogenous or endogenous, subcutaneously or portally delivered) augments the synthesis and secretion of lp(a) by the liver remains a subject for further investigation. In summary, these data do not find an association between symptomatic CHD and lp(a) in NIDDM. Significant and independent relationships have been found between this variable and serum creatinine, total cholesterol and insulin therapy. Significant questions remain about the variability of lp(a) in NIDDM. If this variable is only under genetic influence, it could be suggested that high lp(a) levels could predict individuals deemed to suffer a worse outcome (more frequent insulin need and diabetic kidney disease). On the contrary, it could be suggested that the influence of altered milieu upon lp(a) levels is more important than was previously suspected.
References [I]
Utermann, G. (1989) Science 246, 904-910.
The
mysteries
of lipoprotein
(a).
F. Relimpio
et al. /Diabetes
Research
Scanu, A., Lawn, R.M. and Berg, K. (1991) Lipoprotein (a) and atherosclerosis. Ann. Int. Med. 115, 2099218. J., Vaccaro, O., Neaton, J.D., Wentworth, D. [31 Stamler, and Group, M.R. (1993) Diabetes, other risk factors, and I2 year cardiovascular mortality for men screened in the Multiple Risk Factor Intervention Trial. Diabetes Care 16, 4344444. G. and Schutle, H. (1988) The Prospective [41 Assmann, Cardiovascular Miinster (PROCAM) Study: prevalence of hyperlipidemia in persons with hypertension and/or diabetes mellitus and the relationship to coronary heart disease. Am. Heart J. 116, 171331724. E., Neel, D., Cohen, D., [51 Velho, G., Erlich, D., Turpin, Froguel, P. et al. (1993) Lipoprotein (a) in diabetic patients and normoglycemic relatives in familial NIDDM. Diabetes Care 16, 7422747. B.H., Leurs, P.B., Sels, J.P., [61 Heesen, B.J., Wolffenbuttel, Menheere, P.P., Jackie-Beckers, SE. et al. (1993) Lipoprotein (a) levels in relation to diabetic complications in patients with non-insulin-dependent diabetes. Euro J. Clin. Invest. 23, 580-584. J., Huby, T., James, R.W., Erlich, D., [71 Ruiz, J., Thillet, Flandre. P. et al. (1994) Association of elevated lipoprotein (a) levels and coronary heart disease in NIDDM patients. Relationship with apolipoprotein (a) phenotypes. Diabetologia 37, 5855591. J.D. PI Jenkins, A.J., Steele, J.S., Janus, E.D., Santamaria, and Best, J.D. (1992) Plasma apolipoprotein (a) is increased in type 2 (non-insulin-dependent) diabetic patients with microalbuminuria. Diabetologia 35, 10555 1059. G.F., Gwilym, R.M., Mazurkiewicz, J., and [91 Watts, Coltart, J. (I 995) Independent correlation between plasma lipoprotein (a) and angiographic coronary artery disease in NIDDM. Diabetes Care 18, 2344236. T., Okubo, M., Nakanishi, K. et []Ol Hiraga, T., Kobayashi, al. (1995) Prospective study of lipoprotein (a) as a risk factor for atherosclerotic cardiovascular disease in patients with diabetes. Diabetes Care 18, 241-244. Vll James, R.W., Boemi. M., Sirolla, C., Amadio, L. et al. (1995) Lipoprotein (a) and vascular disease in diabetic patients. Diabetologia 38, 71 l-714. S.M., Moss, S.E., Klein, B.E.K. and Klein, R. [I21 Haffner, (1992) Lack of association between lipoprotein (a) concentrations and coronary heart disease mortality in diabetes: the Wisconsin epidemiologic study of diabetic retinopathy. Metabolism 41, 194- 197.
PI
and Clinical
Practice
3.5 (1997)
135-141
141
L., Mykklnen, L., Karonen, S.L. and [I31 Niskanen, Uusitupa, M. (1993) Apolipoprotein (a) levels in relation to coronary heart disease and risk factors in type II (non-insulin-dependent) diabetes. Cardiovasc. Risk Factors 13, 2055210. P., Derue, G., Novik, u41 Heller, F.R., Jamart, S.J., Honore, V., Galanti, L. et al. (1993) Serum lipoprotein (a) in patients with diabetes mellitus. Diabetes Care 16, 819823. A.I., Gall, M.-A., Rossing, P., 1151 Nielsen, F.S., Voldsgaard, Hommel, E., Andersen, P. et al. (1993) Apolipoprotein (a) and cardiovascular disease in type 2 (non-insulin-dependent) diabetic patients with and without diabetic nephropathy. Diabetologia 36, 4388444. P. et al. (1994) U61Gruden, G., Veglio, M., Cavallo-Perin, Lipoprotein (a) and insulin treatment in NIDDM patients. Diabetes Care 17, 1075-1076. G., Veglio, M., Cavallo-Perin, P. et al. (1994) 1171 Gruden, Lipoprotein (a) in non-insulin-dependent diabetic patients with normoand microalbuminuria. Horm. Metab. Res. 26, 4899490. R., Paoletti, R., Meschia, M., U81Soma, M., Fumagdlli, Maini, M.C., Crosignani, P., Ghanem, K., Gaubatz, J. and Morrisett, J.D. (1991) Plasma lp (a) concentration after oestrogen and progestagen in postmenopausal women. Lancet 337, 612. A.D. and Durrington, P.N. (1990) Lipoprotein [I91 MBewu, (a) structure, properties and possible involvement in thrombogenesis and atherogenesis. Atherosclerosis 85, I 14. P-I Scanu, A.M. (1992) Genetic basis and pathophysiological implications of high plasma Lp(a) levels. J. Intern. Med. 231, 6799683. J.L., Senti, M., Rubies-Prat, J. et al. (1994) PII Reverter, Relationship between lipoprotein profile and urinary albumin excretion in type II diabetic patients with stable metabolic control. Diabetes Care 17, 189- 194. (a) P21Jenkins, A.J., Best, J.D. (1995) The role of lipoprotein in the vascular complications of diabetes mellitus. J. Intern. Med. 237, 359-365. J., Reverter, J.L., Senti, M. et al. (1993) I231 Rubies-Prat, Calculated low-density lipoprotein cholesterol should not be used for management of lipoprotein abnormalities in patients with diabetes mellitus. Diabetes Care 16, 1081~ 1086.
Lack of association of lipoprotein (a) with coronary heart disease in Spaniard type 2 diabetic patients F. Relimpio
a,*, A. Pumar a, F. Losada a, C. Montilla R. Astorga a a Servicio de Endocrinologia, Hospital Universitario b Servicio de Bioquimica Clinica, Hospital Universitario
b, F. Morales a, D. Acosta a,
Virgen del Rocio, Seville, Spain Virgen de1 Rocio, Seville, Spain
Received 29 May 1996; received in revised form 24 November 1996; accepted 23 December 1996
Abstract We tried to elucidate the possible relationship between lipoprotein (a) levels and coronary heart disease by assessing the presence of lipoprotein (a) covariates in NIDDM. We selected 41 type 2 diabetic patients with coronary heart disease and 82 type 2 diabetic patients free from cardiovascular disease. They were adjusted for age, sex and duration of diabetes. Routine chemical analysis was carried out using standard procedures, HbA,, by HPLC and lipoprotein (a) and urinary albumin excretion rate by immunonephelometry. No difference has been found in lipoprotein (a) levels between both groups of patients (18 [144.25] mg/dl in cases vs. 23 [197.25] mg/dl in controls (median [range]), Mann-Whitney U-test, P > 0.1). No association has been found between coronary heart disease and lipoprotein (a) levels greater than 30 mg/dl (Pearson’s x ‘, P > 0.1). Significant and independent linear relationships have been found between the square root of lipoprotein (a) levels, serum creatinine and total cholesterol (multiple r*: 0.15, P < 0.001). Patients treated with insulin had greater square root of lipoprotein (a) levels, even after adjusting for serum creatinine and total cholesterol (5.87 f 0.35 vs. 4.76 f 0.36 (mean f S.E.), ANCOVA, P < 0.05). These data do not show an association between symptomatic coronary heart disease and lipoprotein (a) in NIDDM. Significant and independent relationships have been found between this variable and serum creatinine, total cholesterol and insulin therapy. 0 1997 Elsevier Science Ireland Ltd. Keywords: Lipoprotein Insulin therapy
(a); Diabetes
mellitus
(non-insulin-dependent);
Abbreviations: lp(a), lipoprotein (a); NIDDM, non-insulindependent diabetes mellitus; UAER, urinary albumin excretion rate; CHD, coronary heart disease. * Corresponding author. Present address: Endocrinologia, Centro de Especialidades Virgen de 10s Reyes, Marques de Paradas s/n, 41001 Seville, Spain. Fax: + 34 5 4248111; email: [email protected]
heart disease; Microalbuminuria;
1. Introduction Lipoprotein (a) is a subtype of the LDL molecule in which apoprotein (a), a large glyco-
0168-8227/97/$17.00 0 1997 Elsevier Science Ireland Ltd. All rights reserved. PI1 SO1 68-8227(97)01369-7
Coronary
136
F. Relimpio
et al. /Diabetes
Research
protein, is covalently bound to the apo B [l]. Its clinical interest lies in its recognition as an independent risk factor of atherosclerotic vascular disease in the general population [2]. NIDDM is a condition associated with a high cardiovascular risk [3]. The main determinants of atherosclerotic cardiovascular disease in NIDDM seem to be partly the same risk factors that confer a high cardiovascular risk in the general population [4]. Notwithstanding, considerable controversy exists in other aspects, such as the role played by glycemic control or the trend to cluster around other risk factors. Likewise, controversy exists about’ the recognition of high lipoprotein (a) (lp(a)) levels as an independent cardiovascular risk factor in this condition [5-l 51 and its putative relationships with mode of treatment [14,16] or the presence of diabetic kidney disease [6,8,15,17]. Therefore, the present case-control study was designed in order to elucidate if there is a relationship between lp(a) levels and coronary heart disease (CHD) in NIDDM. Our objective was also to assess the presence of lp(a) covariates in this very condition.
2. Patients and methods The patients studied belong to an on-going cohort of type 2 diabetic patients followed-up in our out-patient diabetes unit. Forty-one consecutive patients with CHD have been studied. For each case, two controls, adjusted for gender, age and duration of diabetes have been selected from the same cohort. The diagnosis of NIDDM was based upon current WHO criteria. Only four cases had an age less than 40 years and none required insulin. The first firm indication of hyperglycemia (fasting blood glucose > 7.8 mmol/l) or a diagnostic oral glucose tolerance test was used to compute the duration of diabetes. The ocurrence of gestational diabetes mellitus was taken as the starting point of the disease, only if the persistence of glucose tolerance abnormalities had occurred after delivery, without the need to continue insulin therapy or to use it in 2 years time after delivery. A thorough clinical interview
and Clinical
Practice
35 (1997)
135- 141
was performed in order to ascertain clinical status, current therapies and cardiovascular situation. Information was mainly received directly from patients and families, although clinical records were also used. The hypolipidaemic drugs used belonged to the groups of 3-hydroxy-3methylglutaryl coenzyme A reductase inhibitors, fibrates or bile acid sequestrants. Postmenopausal replacement hormonal therapy was not used. Two patients (a case and a control) were receiving thyroid hormone for primary hypothyroidism and benignant nodular thyroid disease, respectively. Two patients in the control group had chronic viral hepatitis secondary to B-virus infection in non-advanced stage (mild hypertransaminasemia). For the purpose of the present study, CHD was established: if hospital-requiring myocardial acute infarction or angina pectoris had been diagnosed by a cardiologist; if the patient had been submitted to invasive coronary procedures (bypass surgery or percutaneous transluminal angioplasty) or if a stress testing had been positive. The absence of that complication was assessed by a negative answer to a questionnaire in which symptoms induced by daily-life physical efforts were asked for, and a normal resting ECG. The presence of laser-treated diabetic retinopathy was assessed from ophthalmologic records or reported by the patient. The presence of essential hypertension was established if there was the need to take anti-hypertensive drugs or if there was confirmed evidence of resting recordings yielding systolic blood pressure greater than 160 mmHg and/or diastolic blood pressure greater than 90 mmHg. Having taken the morning anti-hypertensive treatment (if needed), and after a lo-min rest period in the sitting position, systolic and diastolic pressures (fifth phase) were measured twice to the nearest 5 mmHg and then averaged. Readings were taken 5 min apart using an appropiately sized cuff. Height and weight were measured with the subjects wearing light clothes, without shoes. The body-mass index (BMI) was calculated as weight (kg) divided by height (m’). The waist-tohip ratio (WHR) was calculated by dividing the waist circumference (at the umbilicus) by the hip circumference (at the bitrochanteric level). The main demographic features of cases and controls are shown in Table 1.
F. Relimpio Table Main
1 demographic
and analytical
et al. /Diabetes
features
of patients
Research
and Clinical
belonging
to both
groups
Cases (n = 41) Age (years) Known Gender
duration of diabetes (male/female)
(years)
Essential hypertension (n, ‘%) Current smoking habit (n. “/;I) Hypolipidaemic drug-treated (n, %) Insulin-treated (n, %) Insulin dose (U/kg) Laser-requiring (n, ‘Xl) BMI (kg/m*) WHR Systolic blood pressure (mmHg) Diastolic blood pressure (mmHg) Fasting blood glucose (mg/dl) HbA,, (‘X1) Total serum cholesterol (mg/dl) HDL-cholesterol (mg/dl) Non-HDL-cholesterol (mg/dl) Triglycerides (mg/dl) Apoprotein A, (mg/dl) Apoprotein B (mg/dl) Lipoprotein (a) (mg/dl) UAER category(normo/micro/macroalbuminuric) Serum creatinine (mg/dl) Serum uric acid (mg/dl) a Matching b Differences
criteria. assessed by the Mann-Whitney
2.1. Biochemical
Practice
35 (1997)
135-141
of study Controls
(n = 82)
63.75 * 8.76
62.93 + 11.62
12.60 k 9.67 16125
11.93*9.31 32/50
35 (85.4) 4 (9.8) 13 (31.7) 23 (56.1) 0.56 If: 0.2 IO (24.4) 30.57 + 4.56 I .05 * 0.07 15Ok22.19 80.85 * 1 I .77 198.95 + 62.3 7.46 + 1.59 215.36 + 32.38 49.79 + 12.06 164.79 f 33.39 164 [314] 144.95 f 22.06 112.95 k 22.16 18 [144.25] 22/10/2 0.97 * 0.35 5.48 i 1.68
137
42 (51.2) 13 (15.9) 22 (26.8) 40 (48.8) 0.5 * 0.13 17 (20.7) 29.54 k 4.63 1.03 * 0.08 149.04 + 18.14 83.22 + 9.37 185.97 k 68.35 7.47 * 2.12 215.54 f 40.63 53.63 + 13.09 160.5 k 38.45 135 [479] 148.64 + 23.12 112.25 + 27.41 23 [197.25] 4912019 0.92 +- 0.36 4.95 + 1.52
P-value d ‘I ‘I P
U-test.
measurements
Blood samples for biochemical determinations were taken from an antecubital vein after a 10-h fast, before the morning drug intake or insulin administration. Blood glucose was measured by the hexokinase method (Gluco-quanta Glucose, BoehringerMannheim; normal values 75 110 mg/dl). Serum creatinine was determined by an enzymatic calorimetric test (Creatinine-PAPa, Boehringer-Mannheim; normal values 0.55 1.1 mg/dl in men, and 0.550.9 mg/dl in women). The urinary albumin excretion rate (UAER) was measured in overnight (10 h) sterile non-ketotic urine collections using laser immunonephelometry (Behring nephelometer analyzer). For the purpose of the present study, those patients having an UAER lower than 20 pg/min have been considered normoalbuminuric, those having an
UAER > 20 and < 200 pg/min have been considered microalbuminuric and those having UAER values > 200 ,ugg/min have been considered macroalbuminuric. HbA,, was measured by HPLC (HPLC autoanalyzer, DIC (Menarini); normal values up to 5.5%). Total serum cholesterol was analyzed by a fully-enzymatic method (CHOD-PAP@‘, BoehringerMannheim; normal values 150-250 mg/dl). HDL-cholesterol was measured after precipitation of VLDL and LDL with phosphotungstic acid and magnesium chloride. Serum triglycerides were measured by an enzymatic method (GPO-PAP”, BoehringerMannheim; normal values 60- 160 mg/dl). Apolipoproteins A, and B were determined by immunoturbidimetric assay (Tina-quanta Apolipoprotein A, and Apolipoprotein B, respectively, Boehringer-Mannheim; normal values 104-202 mg/dl for males and 108-225 mg/dl for
138
F. Relimpio
et al. /Diabetes
Research
females in the first case and 666133 mg/dl for males and 60- 117 mg/dl for females in the second). Serum uric acid was measured by means of an enzymatic calorimetric test (Uric Acid PAP@) Boehringer-Mannheim; normal values 3.4-7 mg/ dl for males and 2.4-5.7 mg/dl for females). Lp(a) was measured by means of an immunonephelometric assay (N Antiserum to Human Lp(a), Behring, Marburg, Germany, lower limit of detection: 9.5 mg/dl). 2.2. Statistical
and Clinical
Practice
35 (1997)
135-141
Table 2 Bivariate correlation analysis (Spearman correlation coefficients) between lipoprotein (a) and those variables in which a significant result was found Variable
P-value
Creatinine Systolic blood pressure Total cholesterol HDL cholesterol Apoprotein A,
0.22 0.18 0.21 0.18 0.22
<0.05 <0.05 < 0.05 < 0.05 < 0.05
analysis
Normality was evaluated by the KolmogorovSmirnov test. For every quantitative variable, group differences were assessed by means of ttests, one-way ANOVA or Mann-Whitney Utests, depending on data distribution. Pearson’s x2 or Fisher’s exact test (depending on cell sizes) were used to evaluate the association of categorical variables to CHD. Bivariate correlations have been sought by using the Spearman correlation. Stepwise multiple regression analysis has been used to assess the independent relationship of lp(a) with those variables found to have a significant Spearman correlation. An ANCOVA model has been built to assess the independent effect of a categorical variable and two lp(a) covariates upon lp(a) levels. For stepwise multiple regression analysis, one-way ANOVA, and ANCOVA the square root of lp(a) has been taken in order to overcome difficulties derived from the skewness of data distribution. All variables are expressed as mean k S.D., except those in which normality could not be assumed, in which median (range) is expressed. All contrasts are two-tailed. A P < 0.05 was considered significant. All statistical calculations have been made by means of the statistical software package SPSS for Windows 5.0.1 using a PC.
3. Results A lp(a) level below the lower limit of detection was found in 36 patients (29.3%) (15 patients with CHD (36.6%) and 21 controls (25.6%) Pearson’s x2, non-significant). A lp(a) level greater than 30
mg/dl was found in 49 patients (39.8%) (17 patients with CHD (41.5%) and 32 controls (39%), Pearson’s x2, non-significant). A significant difference in lp(a) levels between patients with CHD and controls has not been found (Table 1). The performance of the former analysis, considering separately those patients submitted/not submitted to hypolipidaemic drugs, yielded essentially the same results. Only the presence of essential hypertension has been significantly different in both groups of study (Table 1). Lp(a) levels showed significanty positive Spearman correlations with serum creatinine, total cholesterol, HDL-cholesterol, apoprotein A, values and systolic blood pressure (Table 2). A stepwise multiple regression analysis using the square root of lp(a) levels as the dependent variable, and the covariates as independent variables was performed. Only serum creatinine and total cholesterol were selected by this procedure as being independently related to the dependent variable (Table 3). Lp(a) levels were significantly greater in patients treated with insulin (33 [197.25] vs. 14.5 [126.25] mg/dl, (median [range]), Mann-Whitney U-test P < 0.01). Likewise, a significant association was found between insulin treatment and Table 3 Stepwise multiple regression analysis (taking lipoprotein (a) as the dependent variable) Step
Variable
Multiple
1 2
Creatinine Total cholesterol
0.08 0.15
Y*
the square
root
T
P-value
3.21 3.10
of
F. Relimpio Table 4 Square root category Albumin
of lipoprotein
excretion
Normoalbuminuria Microalbuminuria Macroalbuminuria One-way
ANOVA,
(a) according
the albumin
Square root of lipoprotein
category
(n = 71) (n = 30) (n = 11) factor
et al. /Diabetes
Research
excretion
(a)
5.04 * 3.03 5.67 k 3.07 6.45 + 3.06
effect non-statistically
significant.
lp(a) levels greater than 30 mg/dl (Pearson’s x2 = 6.46, P < 0.05). Patients treated with insulin also had almost significantly greater serum creatinine levels and significantly greater total cholesterol levels (data not shown). To assess the independence of the relationship between insulin treatment and lp(a) levels from the covariates, an ANCOVA model has been used, considering the square root of lp(a) as the dependent variable, insulin therapy as the grouping factor and total cholesterol and serum creatinine as covariates. The linear relationship between each covariate and the square root of lp(a) levels was not significantly different in those treated with insulin from those not receiving exogenous insulin. After adjusting for serum creatinine and total cholesterol, those patients treated with insulin had significantly greater square root of lp(a) levels (5.87 + 0.35 vs. 4.76 + 0.36 (mean f SE.), P < 0.05). After categorizing patients according to their UAER, a trend was seen towards greater square root of lp(a) levels in those patients with macroor microalbuminuria, but without reaching statistical significance (one-way ANOVA, Table 4).
4. Discussion Data presented in this study do not find a relationship between CHD and lp(a) levels in NIDDM. Weak, although significant and independent correlations have been found between lp(a) levels and serum creatinine and total cholesterol. Insulin treatment was associated with higher lp(a) levels, even after adjusting for the effect of covariates.
and Clinical
Practice
35 (1997)
135-141
139
The sample was extracted from a clinic-based NIDDM cohort in Southern Spain. Gender, age and duration of diabetes were carefully adjusted for. It is because all the analytical procedures are well-standardized with commercially-available methods performed in the central laboratory and no change in the main procedures has been perfomed while the study was made, that the study group was analyzed following a homogeneous clinical/biochemical protocol. No significant differences were found in the variables analyzed in the present study between patients with CHD and controls except for the prevalence of hypertension. Detection bias can be excluded, as the whole cohort is sequentially submitted to blood pressure measuring. Nevertheless, patients with CHD had non-significant trends towards: (1) a greater frequency of insulin treatment and laser therapy, (2) greater adiposity, (3) nonHDL-cholesterol, (4) triglycerides and (5) uric acid values, (6) lower HDL-cholesterol and apoprotein A, values. The presence of CHD could have impacted in many ways upon modifiable risk factors. This fact could explain the absence of significant differences in classical risk factors for CHD between both groups of study. Lp(a) levels in patients with CHD were not significantly different from controls. Likewise, an association between the study group membership and a lp(a) level greater than 30 mg/dl or a lp(a) level below the lower limit of detection was not found. The influence of hypolipidaemic drugs can be discarded because of the similar rates of use between patients with CHD and controls, the absence of nicotinic acid in both groups of study and the similar results obtained when the analysis is performed separately in patients submitted/not submitted to those agents. It is unlikely that the low frequency of use of thyroid hormones and the minimal prevalence of mild hepatic disease in the control group could alter the results. In addition, no woman was submitted to postmenopausal replacement hormone therapy, which has altered lp(a) levels [18]. According to current thinking, lp(a) levels are relatively stable and are under strong genetic influence [19,20]. Thus, it is unlikely that dietary, life-style and pharmacological modifications, undertaken because of the presence
140
F. Relimpio
et al. /Diabetes
Research
of CHD, could influence lp(a) levels. Nevertheless, the association between CHD and lp(a) levels in NIDDM is currently far from clear. There are data supporting [4- 1 l] and denying [ 12- 151 such an association. Different ethnic background, study design, biochemical methods or end-point definition could account for discrepant results. In fact, if type 2 diabetic patients with high lp(a) levels had a worse prognosis with respect to CHD (and hence a greater early mortality), a transversal case-control design would infrarepresent those patients, and a possible association between CHD and lp(a) levels could be missed. Another source of concern is the confounding effect of ‘silent CHD’, a prevalent condition in type 2 diabetic patients. In this case our results would deny an association between overt, symptomatic CHD and lp(a) levels in NIDDM. Nevertheless, a study acomplishing the exclusion of silent CHD did not find greater lp(a) levels in type 2 diabetic patients with CHD (although such an association was significant when a cut-off lp(a) level of 30 mg/dl was used) [7]. It seems that only longitudinal studies can determine whether a high lp(a) level poses a significant cardiovascular risk to type 2 diabetic patients. A non-significant trend towards greater lp(a) levels in macro- and microalbuminuric patients was found. This trend has been reported previously in studies analysing a smaller sample [ 17,211. Moreover, a significant relationship between lp(a) levels and UAER category has been found in another study with a greater sample size [14]. The accordance of present data with previously reported findings, and the significant and independent relationship found between lp(a) and serum creatinine raise the question of an existing association between kidney function and lp(a) levels in NIDDM which could have passed undetected due to insufficient sample size. In any case, the association between lp(a) levels and micro/ macroalbuminuria would be consistent with the proposal that elevation of lp(a) occurs as part of non-specific hepatic protein synthesis, triggered by albumin loss in order to maintain constancy of plasma oncotic pressure [22]. An independent relationship was detected between lp(a) levels and total cholesterol in the
and Clinical
Pructice
35 (1997)
135-141
present study. Similar magnitude relationships between lp(a), total- and LDL-cholesterol have been found in one study [14], and with apoprotein B levels in another [7]. Due to its well-established inaccuracies in NIDDM [23], the Friedewald’s expression has not been used to compute LDLcholesterol in the present study. A significant relationship between lp(a) levels and insulin treatment was found. Long duration of diabetes is usually associated with greater frequency of insulin need and diabetic kidney disease. Moreover, patients treated with insulin in the present study had significantly greater total cholesterol and serum creatinine levels. So, the association found between lp(a) levels and insulin treatment could be confounded by these two covariates. Notwithstanding, after adjusting for serum creatinine and total cholesterol, patients treated with insulin had significantly greater lp(a) levels. Similar findings have previously been reported [ 14,161. This issue raises the possibility that in insulin-requiring type 2 diabetic subjects, the summation of endogenous and exogenous insulin could result in higher insulin plasma levels. Whether or not insulin (exogenous or endogenous, subcutaneously or portally delivered) augments the synthesis and secretion of lp(a) by the liver remains a subject for further investigation. In summary, these data do not find an association between symptomatic CHD and lp(a) in NIDDM. Significant and independent relationships have been found between this variable and serum creatinine, total cholesterol and insulin therapy. Significant questions remain about the variability of lp(a) in NIDDM. If this variable is only under genetic influence, it could be suggested that high lp(a) levels could predict individuals deemed to suffer a worse outcome (more frequent insulin need and diabetic kidney disease). On the contrary, it could be suggested that the influence of altered milieu upon lp(a) levels is more important than was previously suspected.
References [I]
Utermann, G. (1989) Science 246, 904-910.
The
mysteries
of lipoprotein
(a).
F. Relimpio
et al. /Diabetes
Research
Scanu, A., Lawn, R.M. and Berg, K. (1991) Lipoprotein (a) and atherosclerosis. Ann. Int. Med. 115, 2099218. J., Vaccaro, O., Neaton, J.D., Wentworth, D. [31 Stamler, and Group, M.R. (1993) Diabetes, other risk factors, and I2 year cardiovascular mortality for men screened in the Multiple Risk Factor Intervention Trial. Diabetes Care 16, 4344444. G. and Schutle, H. (1988) The Prospective [41 Assmann, Cardiovascular Miinster (PROCAM) Study: prevalence of hyperlipidemia in persons with hypertension and/or diabetes mellitus and the relationship to coronary heart disease. Am. Heart J. 116, 171331724. E., Neel, D., Cohen, D., [51 Velho, G., Erlich, D., Turpin, Froguel, P. et al. (1993) Lipoprotein (a) in diabetic patients and normoglycemic relatives in familial NIDDM. Diabetes Care 16, 7422747. B.H., Leurs, P.B., Sels, J.P., [61 Heesen, B.J., Wolffenbuttel, Menheere, P.P., Jackie-Beckers, SE. et al. (1993) Lipoprotein (a) levels in relation to diabetic complications in patients with non-insulin-dependent diabetes. Euro J. Clin. Invest. 23, 580-584. J., Huby, T., James, R.W., Erlich, D., [71 Ruiz, J., Thillet, Flandre. P. et al. (1994) Association of elevated lipoprotein (a) levels and coronary heart disease in NIDDM patients. Relationship with apolipoprotein (a) phenotypes. Diabetologia 37, 5855591. J.D. PI Jenkins, A.J., Steele, J.S., Janus, E.D., Santamaria, and Best, J.D. (1992) Plasma apolipoprotein (a) is increased in type 2 (non-insulin-dependent) diabetic patients with microalbuminuria. Diabetologia 35, 10555 1059. G.F., Gwilym, R.M., Mazurkiewicz, J., and [91 Watts, Coltart, J. (I 995) Independent correlation between plasma lipoprotein (a) and angiographic coronary artery disease in NIDDM. Diabetes Care 18, 2344236. T., Okubo, M., Nakanishi, K. et []Ol Hiraga, T., Kobayashi, al. (1995) Prospective study of lipoprotein (a) as a risk factor for atherosclerotic cardiovascular disease in patients with diabetes. Diabetes Care 18, 241-244. Vll James, R.W., Boemi. M., Sirolla, C., Amadio, L. et al. (1995) Lipoprotein (a) and vascular disease in diabetic patients. Diabetologia 38, 71 l-714. S.M., Moss, S.E., Klein, B.E.K. and Klein, R. [I21 Haffner, (1992) Lack of association between lipoprotein (a) concentrations and coronary heart disease mortality in diabetes: the Wisconsin epidemiologic study of diabetic retinopathy. Metabolism 41, 194- 197.
PI
and Clinical
Practice
3.5 (1997)
135-141
141
L., Mykklnen, L., Karonen, S.L. and [I31 Niskanen, Uusitupa, M. (1993) Apolipoprotein (a) levels in relation to coronary heart disease and risk factors in type II (non-insulin-dependent) diabetes. Cardiovasc. Risk Factors 13, 2055210. P., Derue, G., Novik, u41 Heller, F.R., Jamart, S.J., Honore, V., Galanti, L. et al. (1993) Serum lipoprotein (a) in patients with diabetes mellitus. Diabetes Care 16, 819823. A.I., Gall, M.-A., Rossing, P., 1151 Nielsen, F.S., Voldsgaard, Hommel, E., Andersen, P. et al. (1993) Apolipoprotein (a) and cardiovascular disease in type 2 (non-insulin-dependent) diabetic patients with and without diabetic nephropathy. Diabetologia 36, 4388444. P. et al. (1994) U61Gruden, G., Veglio, M., Cavallo-Perin, Lipoprotein (a) and insulin treatment in NIDDM patients. Diabetes Care 17, 1075-1076. G., Veglio, M., Cavallo-Perin, P. et al. (1994) 1171 Gruden, Lipoprotein (a) in non-insulin-dependent diabetic patients with normoand microalbuminuria. Horm. Metab. Res. 26, 4899490. R., Paoletti, R., Meschia, M., U81Soma, M., Fumagdlli, Maini, M.C., Crosignani, P., Ghanem, K., Gaubatz, J. and Morrisett, J.D. (1991) Plasma lp (a) concentration after oestrogen and progestagen in postmenopausal women. Lancet 337, 612. A.D. and Durrington, P.N. (1990) Lipoprotein [I91 MBewu, (a) structure, properties and possible involvement in thrombogenesis and atherogenesis. Atherosclerosis 85, I 14. P-I Scanu, A.M. (1992) Genetic basis and pathophysiological implications of high plasma Lp(a) levels. J. Intern. Med. 231, 6799683. J.L., Senti, M., Rubies-Prat, J. et al. (1994) PII Reverter, Relationship between lipoprotein profile and urinary albumin excretion in type II diabetic patients with stable metabolic control. Diabetes Care 17, 189- 194. (a) P21Jenkins, A.J., Best, J.D. (1995) The role of lipoprotein in the vascular complications of diabetes mellitus. J. Intern. Med. 237, 359-365. J., Reverter, J.L., Senti, M. et al. (1993) I231 Rubies-Prat, Calculated low-density lipoprotein cholesterol should not be used for management of lipoprotein abnormalities in patients with diabetes mellitus. Diabetes Care 16, 1081~ 1086.