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Low serum adiponectin is independently associated with both the metabolic syndrome and angiographically determined coronary atherosclerosis
Clinica Chimica Acta 383 (2007) 97 – 102 www.elsevier.com/locate/clinchim
Low serum adiponectin is independently associated with both the metabolic syndrome and angiographically determined coronary atherosclerosis☆ Christoph H. Saely a,b , Lorenz Risch a,c,⁎, Guenter Hoefle a , Philipp Rein a,b , Axel Muendlein a , Thomas Marte a,b , Stefan Aczel a,b , Peter Langer a , Heinz Drexel a,b,d a
Vorarlberg Institute for Vascular Investigation and Treatment (VIVIT), Carinagasse 47, A-6800 Feldkirch, Austria b Department of Medicine, Academic Teaching Hospital Feldkirch, Feldkirch, Austria c Division of Clinical Biochemistry, Biocenter, Innsbruck Medical University, Innsbruck, Austria d University for Human Sciences, Triesen, Principality of Liechtenstein Received 20 March 2007; received in revised form 30 April 2007; accepted 30 April 2007 Available online 10 May 2007
Abstract Background: We aimed at investigating serum adiponectin in patients with the metabolic syndrome (MetS), in patients with angiographically diagnosed coronary artery disease (CAD), and in patients who had both, the MetS and CAD. Methods: We enrolled 687 consecutive patients undergoing coronary angiography for the evaluation of CAD. Results: From our patients, 178 had neither the MetS (Adult Treatment Panel III definition) nor significant CAD (MetS−/CAD−), 91 had the MetS, but not significant CAD (MetS+/CAD−), 251 did not have the MetS but had significant CAD (MetS−/CAD+), and 167 had both, the MetS and significant CAD (MetS+/CAD+). Serum adiponectin was highest (12.1 ± 8.3 μg/ml) in MetS−/CAD− subjects. It was significantly lower in MetS+/CAD− (9.5 ± 7.3 μg/ml; p = 0.001) and in MetS−/CAD+ patients (9.2 ± 5.3 μg/ml; p b 0.001) and lowest in MetS+/CAD+ patients (6.7 ± 3.8 μg/ml) in whom it was significantly lower than in MetS−/CAD−, MetS+/CAD−, and MetS−/CAD+ patients (p b 0.001 for all comparisons). In analysis of covariance the MetS and significant CAD proved associated with serum adiponectin in a mutually independent manner. Conclusions: Low serum adiponectin is independently associated with both the MetS and coronary atherosclerosis. © 2007 Published by Elsevier B.V. Keywords: Serum adiponectin; Metabolic syndrome; Coronary artery disease; Coronary angiography; Insulin resistance
1. Introduction Adiponectin is an adipokine that is abundantly expressed in human adipose tissue and directly sensitizes the body to insulin. Hypoadiponectinemia, caused by interactions of genetic and environmental factors, is considered to play an important causal role in obesity and insulin resistance [1,2].
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This work has been supported by grants from the following institutions: Innovationsstiftung of the Liechtenstein Global Trust (LGT) Bank, Bendern, Principality of Liechtenstein; Fachhochschule Dornbirn, Dornbirn, Austria; Vorarlberger Industriellenvereinigung, Bregenz, Austria; Vorarlberger Landeskrankenhaus-Betriebsgesellschaft, Feldkirch, Austria. ⁎ Corresponding author. VIVIT, Carinagasse 47, A-6800 Feldkirch, Austria. Tel.: +43 5522 303 2670; fax: +43 5522 303 7533. E-mail address: [email protected] (L. Risch). 0009-8981/$ - see front matter © 2007 Published by Elsevier B.V. doi:10.1016/j.cca.2007.04.029
The central role of insulin resistance in the pathophysiology of the metabolic syndrome (MetS) and the close relation between insulin resistance and serum adiponectin levels implies an association of the clinical category of the MetS with serum adiponectin. Indeed, several studies have found low serum levels of adiponectin in patients with the clinical entity of the MetS [3–14]. Further, adiponectin exerts direct anti-atherogenic and antiinflammatory effects [15–20]. Low serum adiponectin therefore is considered to play an important role in atherogenesis. Concordantly, low serum adiponectin has been described in patients with coronary artery disease (CAD) [21–25]. Because of its twofold association with both the MetS and CAD, low adiponectin may be hypothesised to be a common soil for both entities. However, the prevalence of the MetS among patients with coronary atherosclerosis typically is high,
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and it is unknown in as far the high prevalence of the MetS among patients with CAD accounts for low serum levels of adiponectin in these patients. We therefore aimed at investigating serum adiponectin in patients with the MetS, in patients with angiographically diagnosed CAD and in patients who had both, the MetS and CAD. 2. Materials and methods 2.1. Study subjects We enrolled 687 consecutive Caucasian patients who were referred to coronary angiography for the evaluation of established or suspected CAD from October 1999 through October 2000. Patients with type 1 diabetes and patients who had suffered myocardial infarctions or acute coronary syndromes within three months prior to the baseline angiography were not enrolled. Information on conventional cardiovascular risk factors (history of smoking, hypertension, and established diabetes mellitus) was obtained by a standardized interview, and systolic/diastolic blood pressure was measured by the Riva-Rocci method under resting conditions in a sitting position at the day of hospital entry at least 5 h after hospitalization. Diabetes mellitus was diagnosed according to WHO criteria [26] and hypertension was defined according to the Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure [27]. Height and weight were recorded and BMI was calculated as body weight (kg)/height (m)2. According to National Cholesterol Education Programme Adult Treatment Panel III (ATP-III) criteria [28], the MetS was diagnosed in the presence of any three of: waist circumference N102 cm in men and N88 cm in women, triglycerides ≥150 mg/dl (1.7 mmol/l), HDL cholesterol b 40 mg/dl (1.0 mmol/ l) in men and b50 mg/dl (1.3 mmol/l) in women, blood pressure ≥ 130/≥85 mm Hg, or fasting glucose ≥ 110 mg/dl (6.1 mmol/l). Using International Diabetes Federation (IDF) criteria [29], the MetS was diagnosed in patients who had a high waist circumference (≥ 94 cm in men and ≥80 cm in women) plus any two of: triglycerides ≥ 150 mg/dl (1.7 mmol/l) or specific treatment for this lipid abnormality, HDL cholesterol b 40 mg/d (1.0 mmol/l) in males and b50 mg/dl (1.3 mmol/l) in females or specific treatment for this lipid abnormality, systolic blood pressure ≥ 130 or diastolic blood pressure ≥ 85 mm Hg or treatment of previously diagnosed hypertension, and fasting plasma glucose ≥ 100 mg/dl (5.6 mmol/l) or previously diagnosed type 2 diabetes. From our patients, 66.2% were on aspirin, 32.3% on statins, 3.1% on fibrates, 12.4% on calcium antagonists, 48.2% on beta blocking agents, 36.4% on angiotensin converting enzyme inhibitors, and 4.1% on angiotensin II blocking agents. Among patients with diabetes, 41.4% were not receiving any antidiabetic medication, and 35.5%, 32.9%, 25.0%, and 1.3% were receiving – alone or in combination – sulfonylurea, biguanides, insulin, and alpha-glucosidase inhibitors, respectively. Coronary angiography was performed with the Judkins technique. Coronary stenoses with lumen narrowing of 50% or more were considered significant, and coronary arteries were defined as normal in the absence of any visible lumen narrowing at angiography, as described previously [30]. The present study complies with the Declaration of Helsinki; the Ethics Committee of the University of Innsbruck approved this study, and all participants gave written informed consent.
2.2. Measurement of biochemical variables Adiponectin was measured by a commercially available sandwich ELISA (human adiponectin ELISA; BioVendor Laboratory Medicine, Inc., Brno, CZ) from venous fasting serum samples stored at −80 °C at the day of collection. Measurements of serum adiponectin were done in duplicate from these samples. Linearity and the analytical sensitivity of our test system were assessed by diluting materials with known analyte concentrations. For investigation of analytical interference the Clinical Laboratory Standardization Institute (CLSI) protocol (EP7-A2) was employed. The performance characteristics of our assay including inter-assay and intra-assay imprecision were assessed in patient samples and control
material, as reported elsewhere [31]. In brief, the employed assay exhibited interand intra-assay CV's of 5.2–13.5%, depending on the adiponectin concentration of the assayed material. The lower limit of detection was 0.038 μg/mL. The serum levels of triglycerides, total cholesterol, low density lipoprotein (LDL) cholesterol, and high density lipoprotein (HDL) cholesterol were determined by using enzymatic hydrolysis and precipitation techniques (Triglycerides GPO-PAP, CHOD/PAP, QuantolipLDL, QuantolipHDL; Roche, Switzerland) on a Hitachi-Analyzer 717 or 911. Glucose levels were measured enzymatically from venous fluoride plasma by the hexokinase method (Roche, Switzerland) on a Hitachi 717 or 911, and serum insulin was measured by an enzyme immunoassay on an AIA 1200 (Tosoh). To measure insulin resistance we used the homeostasis model assessment (HOMA) [32] which has been shown to be a reliable estimate of insulin resistance both among non-diabetic patients and patients with type 2 diabetes [33]. Patients with diabetes who were receiving insulin treatment (n = 40) were excluded from the calculation of insulin resistance.
2.3. Statistical analysis Between-group differences were tested for statistical significance with the Mann–Whitney–U and Kruskal–Wallis tests for continuous variables and with the chi-squared test for categorical variables. Adjustments for multiple comparisons were performed with the Hochberg correction where appropriate. Spearman rank correlation coefficients were calculated. Analyses of covariance (ANCOVA) were performed using the general linear model approach. Results are given as mean ± standard deviation if not denoted otherwise. Statistical significance was defined as two-tailed p value b 0.05. All statistical analyses were performed with the software package SPSS 15.0 for Windows (SPSS, Inc., Chicago, IL).
3. Results 3.1. Patient characteristics Overall, the characteristics of our study population were characteristic for a cohort undergoing coronary angiography for the evaluation of CAD, with a preponderance of male gender (68.7%), and a high prevalence of type 2 diabetes (22.1%), hypertension (53.4%), and smoking (58.8%). From our patients, 258 (37.6%) had the MetS as defined by ATP-III criteria, and in 418 patients (60.8%) coronary angiography revealed significant CAD. When both the coronary state and the presence of the MetS according to ATP-III criteria were considered, 178 had neither the MetS nor significant CAD (MetS− /CAD−), 91 had the MetS, but not significant CAD (MetS+/CAD−), 251 did not have the MetS but had significant CAD (MetS−/CAD+), and 167 had both, the MetS and significant CAD (MetS+/CAD+). Table 1 summarizes the characteristics of our patients in these four groups. 3.2. Adiponectin in subgroups Serum adiponectin was lower in patients who had the ATPIII MetS than in patients without the metabolic syndrome according to ATP-III criteria (7.7 + 5.9 vs. 10.5 ± 7.6 μg/ml; p b 0.001). It was also lower in patients who had significant CAD at angiography than among those without such lesions (8.1 ± 5.4 vs. 11.4 ± 8-8 μg/ml; p b 0.001). When both the presence of the MetS and the presence of significant CAD were considered, serum adiponectin was highest (12.1 ± 8.3 μg/ml) in MetS−/CAD− subjects. It was significantly lower in MetS+/
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CAD− (9.5 ± 7.3 μg/ml; p = 0.001) and in MetS−/CAD+ patients (9.2 ± 5.3 μg/ml; p b 0.001) and lowest in MetS+/ CAD+ patients (6.7 ± 3.8 μg/ml) in whom it was significantly lower than in MetS−/CAD−, MetS+/CAD−, and MetS−/CAD+ patients (p b 0.001 for all comparisons; Fig. 1). 3.3. Results of ANCOVA Analysis of covariance adjusting for age, gender, smoking, and LDL cholesterol showed that the ATP-III MetS (p b 0.001) and CAD (p b 0.001) were associated with serum adiponectin levels in a mutually independent manner. An interaction term MetS ⁎ significant CAD was not significant (p = 0.798). Additional adjustment for treatment with statins, fibrates, ACE inhibitors, and AT-II blocking agents did not significantly affect these results (p b 0.001 for the associations of both CAD and the MetS with serum adiponectin). Subgroup analyses showed that the MetS and CAD after adjustment for age, gender, smoking, and LDL cholesterol were associated with serum adiponectin in a mutually independent manner both among men (pb 0.001 and p b 0.001, respectively) and women (p =0.033 and p =0.032, respectively), and among patients with type 2 diabetes (p b 0.001 and p= 0.047) as well as among non-diabetic individuals (p = 0.010 and p b 0.001, respectively). 3.4. Individual metabolic syndrome traits When compared to subjects who did not meet the respective criteria for the individual ATP-III metabolic syndrome stigmata,
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serum adiponectin levels were lower in patients who met the criteria for high waist circumference (8.6 ± 5.9 vs. 9.7 ± 6.7 μg/ml; p = 0.039), high fasting glucose (8.5 ± 6.3 vs. 9.9 ± 6.6 μg/ml; p b 0.001), high triglycerides (7.3 ± 4.0 vs. 10.8 ± 7.4 μg/ml; p b 0.001), and low HDL cholesterol (7.4 ± 4.6 vs. 10.5 ± 7.1 μg/ ml; p b 0.001). Serum adiponectin was not significantly different in patients who met the blood pressure criterion than in those who did not (9.4 ± 6.7 vs. 9.5 ± 6.0 μg/ml; p = 0.366). Analysis of covariance adjusting for age, gender, smoking, and for the presence of significant stenoses confirmed the associations between serum adiponectin levels and the MetS traits high waist circumference (p b 0.001), high fasting glucose (p = 0.011), high triglycerides (p b 0.001), and low HDL cholesterol (p b 0.001). When all MetS traits were entered simultaneously into the model, the waist criterion (p = 0.009), the high triglycerides criterion (p = 0.001) and the low HDL cholesterol criterion (p = 0.012) were independently associated with low serum levels of adiponectin. 3.5. Insulin resistance Serum adiponectin was significantly and inversely correlated with HOMA insulin resistance scores (r = − 0.297; p b 0.001). This measure of insulin resistance like serum adiponectin was significantly associated with the MetS (ATP-III definition) but unlike adiponectin was not associated with the presence of significant CAD: Both among patients with significant CAD and among subjects who did not have significant CAD, HOMA insulin resistance scores were higher in patients with the MetS (5.5 ± 4.8 vs. 2.6 ± 2.6; p b 0.001 and 5.05 ± 3.7 vs. 2.3 ± 2.0;
Table 1 Characteristics of the study cohort
n Age (years) Male gender (%) BMI (kg/m2) Hypertension (%) Smoking (%) Type 2 diabetes (%) Total cholesterol (mg/dl) LDL cholesterol (mg/dl) HDL cholesterol (mg/dl) Triglycerides (mg/dl) Fasting glucose (mg/dl) HOMA Insulin resistance HbA1c (%) Apolipoprotein A1 (mg/dl) Apolipoprotein B (mg/dl) LDL peak particle diameter (Å) Systolic blood pressure (mm Hg) Diastolic blood pressure (mm Hg) Statins (%) Fibrates (%) ACE inhibitors (%) Angiotensin II blocking agents (%) Adiponectin (μg/ml)
CAD−/MetS−
CAD−/MetS+
CAD+/MetS−
CAD+/MetS+
p-value
178 62 ± 11 48.9 26.2 ± 4.0 44.4 44.4 7.9 222 ± 41 135 ± 34 58 ± 16 121 ± 61 104 ± 30 2.3 ± 2.0 5.8 ± 0.6 162 ± 31 111 ± 24 261 ± 5 133 ± 22 78 ± 11 18.0 1.7 30.3 4.5 12.1 ± 8.3
91 60 ± 10 41.8 30.1 ± 4.1 69.2 58.2 37.4 218 ± 46 128 ± 37 44 ± 12 211 ± 152 129 ± 36 5.0 ± 3.7 6.4 ± 1.2 141 ± 29 116 ± 26 257 ± 7 144 ± 21 84 ± 13 22.0 3.3 44.0 3.3 9.5 ± 7.3
251 64 ± 10 79.3 25.9 ± 3.5 45.4 59.4 13.5 216 ± 40 133 ± 34 50 ± 11 132 ± 72 105 ± 26 2.6 ± 2.6 6.0 ± 0.8 146 ± 24 112 ± 24 260 ± 5 133 ± 20 77 ± 12 37.8 1.6 32.3 2.8 9.2 ± 5.3
167 62 ± 10 77.2 28.5 ± 4.2 66.5 73.7 41.9 214 ± 49 124 ± 37 40 ± 11 230 ± 111 134 ± 43 5.5 ± 4.8 6.6 ± 1.3 143 ± 25 118 ± 27 255 ± 6 143 ± 19 81 ± 11 44.9 6.6 44.9 6.0 6.7 ± 3.8
b0.001 b0.001 b0.001 b0.001 b0.001 b0.001 0.375 0.158 b0.001 b0.001 b0.001 b0.001 b0.001 b0.001 0.139 b0.001 b0.001 0.001 b0.001 0.019 0.007 0.416 0.001
BMI denotes body mass index, LDL low density lipoprotein, HDL high density lipoprotein, and HOMA homeostasis model assessment; ACE angiotensin converting enzyme; to convert values for fasting plasma glucose to mmol/l multiply by 0.0555, to convert values for triglycerides to mmol/l multiply by 0.0113, and to convert values for total cholesterol, LDL cholesterol, or HDL cholesterol to mmol/l multiply by 0.0259; p values are given for the overall difference between study groups.
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4. Discussion
Fig. 1. Serum levels of adiponectin in patients who had neither the metabolic syndrome nor significant coronary artery disease (MetS−/CAD−), in patients who had the metabolic syndrome, but not significant coronary artery disease (MetS+/CAD−), in patients who did not have the metabolic syndrome but had significant coronary artery disease (MetS−/CAD+), and in patients with both, the metabolic syndrome and significant coronary artery disease (MetS+/CAD+).
p b 0.001, respectively), whereas they were similar in patients with significant CAD and in patients without significant CAD both among patients with the metabolic syndrome (p = 0.831) and among individuals who did not have the metabolic syndrome (p = 0.481). When entered simultaneously in an ANCOVA model adjusting for age, gender, smoking, LDL cholesterol and for the presence of significant CAD, insulin resistance and the clinical entity of the MetS independently from each other proved significantly associated with serum levels of adiponectin (p = 0.002 and p = 0.001, respectively). 3.6. IDF definition of the MetS The prevalence of the MetS according to the IDF definition was 47% (n = 323); 150 patients had neither the IDF MetS nor significant CAD, 119 had the IDF MetS, but not significant CAD, 214 did not have the IDF MetS but had significant CAD, and 204 had both, the IDF MetS and significant CAD. As with the ATP-III definition of the MetS, serum adiponectin was highest (12.4 ± 8.7 μg/ml) in IDF MetS−/CAD− subjects. It was significantly lower in MetS+/CAD− (9.7 ± 6.9 μg/ml) and in MetS−/CAD+ patients (9.2 ± 5.5 μg/ml) and lowest in MetS+/CAD+ patients (7.3 ± 4.0 μg/ml) who had significantly lower serum adiponectin than MetS−/CAD−, MetS+/CAD−, and MetS−/CAD+ patients (p b 0.001 for all comparisons). Like the ATP-III MetS, the IDF MetS in multivariate analysis adjusting for age, gender, smoking, and LDL cholesterol and the presence of significant CAD proved significantly and independently associated with serum levels of adiponectin (p b 0.001 for the associations of both CAD and IDF MetS with serum adiponectin). As for the ATP-III metabolic syndrome definition, additional adjustment for treatment with statins, fibrates, ACE inhibitors, and AT-II blocking agents did not significantly affect these results (p b 0.001 for the associations of both CAD and IDF MetS with serum adiponectin).
From our results we conclude that low serum adiponectin is independently associated with both the MetS and the angiographically determined presence of CAD: Serum levels of adiponectin are highest in patients who have neither the MetS nor significant CAD at angiography, are intermediate in patients who have either CAD or the MetS, and are lowest in patients with both the MetS and CAD. This is the first report on the association between adiponectin serum levels and the MetS in patients characterized by coronary angiography. Previous studies had addressed the association between serum levels of adiponectin and the MetS in other patient populations and, importantly, without taking into consideration the coronary artery state [3–14]. In line with other reports [4,11,12,34] serum adiponectin in our investigation was significantly associated with the MetS irrespective of whether we applied ATP-III or IDF criteria for the diagnosis of the MetS. Only few reports on the association between adiponectin serum levels and angiographically determined CAD are available from the literature. One study had found lower serum adiponectin in patients with angiographically proven CAD than in healthy blood donors [23], and two further investigations had shown significant associations between low serum adiponectin and the presence and extent of CAD in angiographied patient populations [21,22]. In extension to these findings our data show that the association between serum adiponectin and angiographically determined CAD is independent from the presence of the MetS: both among patients with the MetS and among patients without the MetS, serum adiponectin is decreased in those with significant CAD at angiography. Similar as with the clinical entity of the MetS, associations between serum adiponectin and biomarkers of insulin resistance have been reported in the literature [35,36]. Our investigation over and above these previous observations demonstrates hat the association between serum adiponectin and insulin resistance is independent of the angiographically determined coronary state. Moreover, this is the fist report which shows that insulin resistance and the clinical entity of the MetS are associated with serum adiponectin values in a mutually independent manner. This is an interesting parallel to our previously published observation that insulin resistance and the MetS independently from each other predict future vascular events [37]. Insulin resistance and the entity of the MetS, though pathophysiologically and clinically closely associated, are not simply interchangeable terms. Screening for CAD and for the MetS is important. CAD is the leading cause of mortality worldwide, and, due to the current epidemic of obesity and sedentary lifestyle in industrialized countries, the prevalence of the MetS is very high in large parts of the world. Indeed, according to the ATP-III definition, about one-fourth of middle-aged men and women in the U.S. have the MetS [38]. Moreover, individuals with the MetS face a strongly increased risk of cardiovascular events. A biomarker such as adiponectin that is independently associated with both the presence of the MetS and the presence of CAD thus appears
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most interesting for clinical application as a metabolic and vascular risk marker. From the individual MetS stigmata all except the high blood pressure trait were significantly associated with low serum adiponectin. When the five ATP-III MetS components were entered simultaneously into one ANCOVA model, the waist criterion and the dyslipidemic MetS traits proved independently predictive of adiponectin serum levels. These results are well in line with those from a previous investigation in Korean patients: Also in this investigation, significant associations between serum adiponectin and all MetS traits except high blood pressure were observed; concordant with our results the association was strongest between serum adiponectin and the low HDL cholesterol trait of the MetS in this study. Previous studies have reported that administration of statins [39], fibrates [40], ACE inhibitors, or AT-II blocking agents [41] increases plasma adiponectin levels in human subjects. However, in our investigation the prevalence of these medications tended to be higher in study subgroups with CAD or with the metabolic syndrome, in which adiponectin was low. Therefore, and because adjustment for medication use did not significantly affect the mutually independent associations of CAD and the MetS with serum adiponectin, differences in medication use between study subgroups do not explain our observation that low serum adiponectin is independently associated with both the MetS and angiographically determined coronary atherosclerosis. Our investigation is characterized by the typical limitations and strengths of studies enrolling patients who undergo coronary angiography for the evaluation of CAD. The angiographical characterization of the coronary artery state was an essential feature of our study design. Of course, patients undergoing coronary angiography for the evaluation of CAD are a selected group of patients the results from which are not necessarily applicable to the general population. However, the population we chose to investigate is at a high vascular risk and therefore deserves particular clinical attention. We did not measure adiponectin isoforms. In the light of our results a future investigation addressing the respective associations of the MetS and of CAD with HMW adiponectin isoforms would be of interest. In conclusion we found that low serum adiponectin is independently associated with both the MetS and coronary atherosclerosis. This observation contributes significantly to the understanding of the pathophysiology of hypoadiponectinemia. Clinically, adiponectin, as a biomarker that is strongly and independently associated with both the presence of the MetS and the presence of angiographically determined CAD is a most interesting candidate for metabolic and vascular risk stratification. 5. List of abbreviations
MetS CAD WHO ATP-III IDF
Metabolic Syndrome Coronary Artery Disease World Health Organisation Adult Treatment Panel III International Diabetes Federation
CLSI LDL HDL HOMA ANCOVA HMW
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Clinical Laboratory Standardization Institute Low Density Lipoprotein High Density Lipoprotein Homeostasis Model Assessment Analysis of Covariance High Molecular Weight
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Low serum adiponectin is independently associated with both the metabolic syndrome and angiographically determined coronary atherosclerosis☆ Christoph H. Saely a,b , Lorenz Risch a,c,⁎, Guenter Hoefle a , Philipp Rein a,b , Axel Muendlein a , Thomas Marte a,b , Stefan Aczel a,b , Peter Langer a , Heinz Drexel a,b,d a
Vorarlberg Institute for Vascular Investigation and Treatment (VIVIT), Carinagasse 47, A-6800 Feldkirch, Austria b Department of Medicine, Academic Teaching Hospital Feldkirch, Feldkirch, Austria c Division of Clinical Biochemistry, Biocenter, Innsbruck Medical University, Innsbruck, Austria d University for Human Sciences, Triesen, Principality of Liechtenstein Received 20 March 2007; received in revised form 30 April 2007; accepted 30 April 2007 Available online 10 May 2007
Abstract Background: We aimed at investigating serum adiponectin in patients with the metabolic syndrome (MetS), in patients with angiographically diagnosed coronary artery disease (CAD), and in patients who had both, the MetS and CAD. Methods: We enrolled 687 consecutive patients undergoing coronary angiography for the evaluation of CAD. Results: From our patients, 178 had neither the MetS (Adult Treatment Panel III definition) nor significant CAD (MetS−/CAD−), 91 had the MetS, but not significant CAD (MetS+/CAD−), 251 did not have the MetS but had significant CAD (MetS−/CAD+), and 167 had both, the MetS and significant CAD (MetS+/CAD+). Serum adiponectin was highest (12.1 ± 8.3 μg/ml) in MetS−/CAD− subjects. It was significantly lower in MetS+/CAD− (9.5 ± 7.3 μg/ml; p = 0.001) and in MetS−/CAD+ patients (9.2 ± 5.3 μg/ml; p b 0.001) and lowest in MetS+/CAD+ patients (6.7 ± 3.8 μg/ml) in whom it was significantly lower than in MetS−/CAD−, MetS+/CAD−, and MetS−/CAD+ patients (p b 0.001 for all comparisons). In analysis of covariance the MetS and significant CAD proved associated with serum adiponectin in a mutually independent manner. Conclusions: Low serum adiponectin is independently associated with both the MetS and coronary atherosclerosis. © 2007 Published by Elsevier B.V. Keywords: Serum adiponectin; Metabolic syndrome; Coronary artery disease; Coronary angiography; Insulin resistance
1. Introduction Adiponectin is an adipokine that is abundantly expressed in human adipose tissue and directly sensitizes the body to insulin. Hypoadiponectinemia, caused by interactions of genetic and environmental factors, is considered to play an important causal role in obesity and insulin resistance [1,2].
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This work has been supported by grants from the following institutions: Innovationsstiftung of the Liechtenstein Global Trust (LGT) Bank, Bendern, Principality of Liechtenstein; Fachhochschule Dornbirn, Dornbirn, Austria; Vorarlberger Industriellenvereinigung, Bregenz, Austria; Vorarlberger Landeskrankenhaus-Betriebsgesellschaft, Feldkirch, Austria. ⁎ Corresponding author. VIVIT, Carinagasse 47, A-6800 Feldkirch, Austria. Tel.: +43 5522 303 2670; fax: +43 5522 303 7533. E-mail address: [email protected] (L. Risch). 0009-8981/$ - see front matter © 2007 Published by Elsevier B.V. doi:10.1016/j.cca.2007.04.029
The central role of insulin resistance in the pathophysiology of the metabolic syndrome (MetS) and the close relation between insulin resistance and serum adiponectin levels implies an association of the clinical category of the MetS with serum adiponectin. Indeed, several studies have found low serum levels of adiponectin in patients with the clinical entity of the MetS [3–14]. Further, adiponectin exerts direct anti-atherogenic and antiinflammatory effects [15–20]. Low serum adiponectin therefore is considered to play an important role in atherogenesis. Concordantly, low serum adiponectin has been described in patients with coronary artery disease (CAD) [21–25]. Because of its twofold association with both the MetS and CAD, low adiponectin may be hypothesised to be a common soil for both entities. However, the prevalence of the MetS among patients with coronary atherosclerosis typically is high,
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and it is unknown in as far the high prevalence of the MetS among patients with CAD accounts for low serum levels of adiponectin in these patients. We therefore aimed at investigating serum adiponectin in patients with the MetS, in patients with angiographically diagnosed CAD and in patients who had both, the MetS and CAD. 2. Materials and methods 2.1. Study subjects We enrolled 687 consecutive Caucasian patients who were referred to coronary angiography for the evaluation of established or suspected CAD from October 1999 through October 2000. Patients with type 1 diabetes and patients who had suffered myocardial infarctions or acute coronary syndromes within three months prior to the baseline angiography were not enrolled. Information on conventional cardiovascular risk factors (history of smoking, hypertension, and established diabetes mellitus) was obtained by a standardized interview, and systolic/diastolic blood pressure was measured by the Riva-Rocci method under resting conditions in a sitting position at the day of hospital entry at least 5 h after hospitalization. Diabetes mellitus was diagnosed according to WHO criteria [26] and hypertension was defined according to the Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure [27]. Height and weight were recorded and BMI was calculated as body weight (kg)/height (m)2. According to National Cholesterol Education Programme Adult Treatment Panel III (ATP-III) criteria [28], the MetS was diagnosed in the presence of any three of: waist circumference N102 cm in men and N88 cm in women, triglycerides ≥150 mg/dl (1.7 mmol/l), HDL cholesterol b 40 mg/dl (1.0 mmol/ l) in men and b50 mg/dl (1.3 mmol/l) in women, blood pressure ≥ 130/≥85 mm Hg, or fasting glucose ≥ 110 mg/dl (6.1 mmol/l). Using International Diabetes Federation (IDF) criteria [29], the MetS was diagnosed in patients who had a high waist circumference (≥ 94 cm in men and ≥80 cm in women) plus any two of: triglycerides ≥ 150 mg/dl (1.7 mmol/l) or specific treatment for this lipid abnormality, HDL cholesterol b 40 mg/d (1.0 mmol/l) in males and b50 mg/dl (1.3 mmol/l) in females or specific treatment for this lipid abnormality, systolic blood pressure ≥ 130 or diastolic blood pressure ≥ 85 mm Hg or treatment of previously diagnosed hypertension, and fasting plasma glucose ≥ 100 mg/dl (5.6 mmol/l) or previously diagnosed type 2 diabetes. From our patients, 66.2% were on aspirin, 32.3% on statins, 3.1% on fibrates, 12.4% on calcium antagonists, 48.2% on beta blocking agents, 36.4% on angiotensin converting enzyme inhibitors, and 4.1% on angiotensin II blocking agents. Among patients with diabetes, 41.4% were not receiving any antidiabetic medication, and 35.5%, 32.9%, 25.0%, and 1.3% were receiving – alone or in combination – sulfonylurea, biguanides, insulin, and alpha-glucosidase inhibitors, respectively. Coronary angiography was performed with the Judkins technique. Coronary stenoses with lumen narrowing of 50% or more were considered significant, and coronary arteries were defined as normal in the absence of any visible lumen narrowing at angiography, as described previously [30]. The present study complies with the Declaration of Helsinki; the Ethics Committee of the University of Innsbruck approved this study, and all participants gave written informed consent.
2.2. Measurement of biochemical variables Adiponectin was measured by a commercially available sandwich ELISA (human adiponectin ELISA; BioVendor Laboratory Medicine, Inc., Brno, CZ) from venous fasting serum samples stored at −80 °C at the day of collection. Measurements of serum adiponectin were done in duplicate from these samples. Linearity and the analytical sensitivity of our test system were assessed by diluting materials with known analyte concentrations. For investigation of analytical interference the Clinical Laboratory Standardization Institute (CLSI) protocol (EP7-A2) was employed. The performance characteristics of our assay including inter-assay and intra-assay imprecision were assessed in patient samples and control
material, as reported elsewhere [31]. In brief, the employed assay exhibited interand intra-assay CV's of 5.2–13.5%, depending on the adiponectin concentration of the assayed material. The lower limit of detection was 0.038 μg/mL. The serum levels of triglycerides, total cholesterol, low density lipoprotein (LDL) cholesterol, and high density lipoprotein (HDL) cholesterol were determined by using enzymatic hydrolysis and precipitation techniques (Triglycerides GPO-PAP, CHOD/PAP, QuantolipLDL, QuantolipHDL; Roche, Switzerland) on a Hitachi-Analyzer 717 or 911. Glucose levels were measured enzymatically from venous fluoride plasma by the hexokinase method (Roche, Switzerland) on a Hitachi 717 or 911, and serum insulin was measured by an enzyme immunoassay on an AIA 1200 (Tosoh). To measure insulin resistance we used the homeostasis model assessment (HOMA) [32] which has been shown to be a reliable estimate of insulin resistance both among non-diabetic patients and patients with type 2 diabetes [33]. Patients with diabetes who were receiving insulin treatment (n = 40) were excluded from the calculation of insulin resistance.
2.3. Statistical analysis Between-group differences were tested for statistical significance with the Mann–Whitney–U and Kruskal–Wallis tests for continuous variables and with the chi-squared test for categorical variables. Adjustments for multiple comparisons were performed with the Hochberg correction where appropriate. Spearman rank correlation coefficients were calculated. Analyses of covariance (ANCOVA) were performed using the general linear model approach. Results are given as mean ± standard deviation if not denoted otherwise. Statistical significance was defined as two-tailed p value b 0.05. All statistical analyses were performed with the software package SPSS 15.0 for Windows (SPSS, Inc., Chicago, IL).
3. Results 3.1. Patient characteristics Overall, the characteristics of our study population were characteristic for a cohort undergoing coronary angiography for the evaluation of CAD, with a preponderance of male gender (68.7%), and a high prevalence of type 2 diabetes (22.1%), hypertension (53.4%), and smoking (58.8%). From our patients, 258 (37.6%) had the MetS as defined by ATP-III criteria, and in 418 patients (60.8%) coronary angiography revealed significant CAD. When both the coronary state and the presence of the MetS according to ATP-III criteria were considered, 178 had neither the MetS nor significant CAD (MetS− /CAD−), 91 had the MetS, but not significant CAD (MetS+/CAD−), 251 did not have the MetS but had significant CAD (MetS−/CAD+), and 167 had both, the MetS and significant CAD (MetS+/CAD+). Table 1 summarizes the characteristics of our patients in these four groups. 3.2. Adiponectin in subgroups Serum adiponectin was lower in patients who had the ATPIII MetS than in patients without the metabolic syndrome according to ATP-III criteria (7.7 + 5.9 vs. 10.5 ± 7.6 μg/ml; p b 0.001). It was also lower in patients who had significant CAD at angiography than among those without such lesions (8.1 ± 5.4 vs. 11.4 ± 8-8 μg/ml; p b 0.001). When both the presence of the MetS and the presence of significant CAD were considered, serum adiponectin was highest (12.1 ± 8.3 μg/ml) in MetS−/CAD− subjects. It was significantly lower in MetS+/
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CAD− (9.5 ± 7.3 μg/ml; p = 0.001) and in MetS−/CAD+ patients (9.2 ± 5.3 μg/ml; p b 0.001) and lowest in MetS+/ CAD+ patients (6.7 ± 3.8 μg/ml) in whom it was significantly lower than in MetS−/CAD−, MetS+/CAD−, and MetS−/CAD+ patients (p b 0.001 for all comparisons; Fig. 1). 3.3. Results of ANCOVA Analysis of covariance adjusting for age, gender, smoking, and LDL cholesterol showed that the ATP-III MetS (p b 0.001) and CAD (p b 0.001) were associated with serum adiponectin levels in a mutually independent manner. An interaction term MetS ⁎ significant CAD was not significant (p = 0.798). Additional adjustment for treatment with statins, fibrates, ACE inhibitors, and AT-II blocking agents did not significantly affect these results (p b 0.001 for the associations of both CAD and the MetS with serum adiponectin). Subgroup analyses showed that the MetS and CAD after adjustment for age, gender, smoking, and LDL cholesterol were associated with serum adiponectin in a mutually independent manner both among men (pb 0.001 and p b 0.001, respectively) and women (p =0.033 and p =0.032, respectively), and among patients with type 2 diabetes (p b 0.001 and p= 0.047) as well as among non-diabetic individuals (p = 0.010 and p b 0.001, respectively). 3.4. Individual metabolic syndrome traits When compared to subjects who did not meet the respective criteria for the individual ATP-III metabolic syndrome stigmata,
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serum adiponectin levels were lower in patients who met the criteria for high waist circumference (8.6 ± 5.9 vs. 9.7 ± 6.7 μg/ml; p = 0.039), high fasting glucose (8.5 ± 6.3 vs. 9.9 ± 6.6 μg/ml; p b 0.001), high triglycerides (7.3 ± 4.0 vs. 10.8 ± 7.4 μg/ml; p b 0.001), and low HDL cholesterol (7.4 ± 4.6 vs. 10.5 ± 7.1 μg/ ml; p b 0.001). Serum adiponectin was not significantly different in patients who met the blood pressure criterion than in those who did not (9.4 ± 6.7 vs. 9.5 ± 6.0 μg/ml; p = 0.366). Analysis of covariance adjusting for age, gender, smoking, and for the presence of significant stenoses confirmed the associations between serum adiponectin levels and the MetS traits high waist circumference (p b 0.001), high fasting glucose (p = 0.011), high triglycerides (p b 0.001), and low HDL cholesterol (p b 0.001). When all MetS traits were entered simultaneously into the model, the waist criterion (p = 0.009), the high triglycerides criterion (p = 0.001) and the low HDL cholesterol criterion (p = 0.012) were independently associated with low serum levels of adiponectin. 3.5. Insulin resistance Serum adiponectin was significantly and inversely correlated with HOMA insulin resistance scores (r = − 0.297; p b 0.001). This measure of insulin resistance like serum adiponectin was significantly associated with the MetS (ATP-III definition) but unlike adiponectin was not associated with the presence of significant CAD: Both among patients with significant CAD and among subjects who did not have significant CAD, HOMA insulin resistance scores were higher in patients with the MetS (5.5 ± 4.8 vs. 2.6 ± 2.6; p b 0.001 and 5.05 ± 3.7 vs. 2.3 ± 2.0;
Table 1 Characteristics of the study cohort
n Age (years) Male gender (%) BMI (kg/m2) Hypertension (%) Smoking (%) Type 2 diabetes (%) Total cholesterol (mg/dl) LDL cholesterol (mg/dl) HDL cholesterol (mg/dl) Triglycerides (mg/dl) Fasting glucose (mg/dl) HOMA Insulin resistance HbA1c (%) Apolipoprotein A1 (mg/dl) Apolipoprotein B (mg/dl) LDL peak particle diameter (Å) Systolic blood pressure (mm Hg) Diastolic blood pressure (mm Hg) Statins (%) Fibrates (%) ACE inhibitors (%) Angiotensin II blocking agents (%) Adiponectin (μg/ml)
CAD−/MetS−
CAD−/MetS+
CAD+/MetS−
CAD+/MetS+
p-value
178 62 ± 11 48.9 26.2 ± 4.0 44.4 44.4 7.9 222 ± 41 135 ± 34 58 ± 16 121 ± 61 104 ± 30 2.3 ± 2.0 5.8 ± 0.6 162 ± 31 111 ± 24 261 ± 5 133 ± 22 78 ± 11 18.0 1.7 30.3 4.5 12.1 ± 8.3
91 60 ± 10 41.8 30.1 ± 4.1 69.2 58.2 37.4 218 ± 46 128 ± 37 44 ± 12 211 ± 152 129 ± 36 5.0 ± 3.7 6.4 ± 1.2 141 ± 29 116 ± 26 257 ± 7 144 ± 21 84 ± 13 22.0 3.3 44.0 3.3 9.5 ± 7.3
251 64 ± 10 79.3 25.9 ± 3.5 45.4 59.4 13.5 216 ± 40 133 ± 34 50 ± 11 132 ± 72 105 ± 26 2.6 ± 2.6 6.0 ± 0.8 146 ± 24 112 ± 24 260 ± 5 133 ± 20 77 ± 12 37.8 1.6 32.3 2.8 9.2 ± 5.3
167 62 ± 10 77.2 28.5 ± 4.2 66.5 73.7 41.9 214 ± 49 124 ± 37 40 ± 11 230 ± 111 134 ± 43 5.5 ± 4.8 6.6 ± 1.3 143 ± 25 118 ± 27 255 ± 6 143 ± 19 81 ± 11 44.9 6.6 44.9 6.0 6.7 ± 3.8
b0.001 b0.001 b0.001 b0.001 b0.001 b0.001 0.375 0.158 b0.001 b0.001 b0.001 b0.001 b0.001 b0.001 0.139 b0.001 b0.001 0.001 b0.001 0.019 0.007 0.416 0.001
BMI denotes body mass index, LDL low density lipoprotein, HDL high density lipoprotein, and HOMA homeostasis model assessment; ACE angiotensin converting enzyme; to convert values for fasting plasma glucose to mmol/l multiply by 0.0555, to convert values for triglycerides to mmol/l multiply by 0.0113, and to convert values for total cholesterol, LDL cholesterol, or HDL cholesterol to mmol/l multiply by 0.0259; p values are given for the overall difference between study groups.
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4. Discussion
Fig. 1. Serum levels of adiponectin in patients who had neither the metabolic syndrome nor significant coronary artery disease (MetS−/CAD−), in patients who had the metabolic syndrome, but not significant coronary artery disease (MetS+/CAD−), in patients who did not have the metabolic syndrome but had significant coronary artery disease (MetS−/CAD+), and in patients with both, the metabolic syndrome and significant coronary artery disease (MetS+/CAD+).
p b 0.001, respectively), whereas they were similar in patients with significant CAD and in patients without significant CAD both among patients with the metabolic syndrome (p = 0.831) and among individuals who did not have the metabolic syndrome (p = 0.481). When entered simultaneously in an ANCOVA model adjusting for age, gender, smoking, LDL cholesterol and for the presence of significant CAD, insulin resistance and the clinical entity of the MetS independently from each other proved significantly associated with serum levels of adiponectin (p = 0.002 and p = 0.001, respectively). 3.6. IDF definition of the MetS The prevalence of the MetS according to the IDF definition was 47% (n = 323); 150 patients had neither the IDF MetS nor significant CAD, 119 had the IDF MetS, but not significant CAD, 214 did not have the IDF MetS but had significant CAD, and 204 had both, the IDF MetS and significant CAD. As with the ATP-III definition of the MetS, serum adiponectin was highest (12.4 ± 8.7 μg/ml) in IDF MetS−/CAD− subjects. It was significantly lower in MetS+/CAD− (9.7 ± 6.9 μg/ml) and in MetS−/CAD+ patients (9.2 ± 5.5 μg/ml) and lowest in MetS+/CAD+ patients (7.3 ± 4.0 μg/ml) who had significantly lower serum adiponectin than MetS−/CAD−, MetS+/CAD−, and MetS−/CAD+ patients (p b 0.001 for all comparisons). Like the ATP-III MetS, the IDF MetS in multivariate analysis adjusting for age, gender, smoking, and LDL cholesterol and the presence of significant CAD proved significantly and independently associated with serum levels of adiponectin (p b 0.001 for the associations of both CAD and IDF MetS with serum adiponectin). As for the ATP-III metabolic syndrome definition, additional adjustment for treatment with statins, fibrates, ACE inhibitors, and AT-II blocking agents did not significantly affect these results (p b 0.001 for the associations of both CAD and IDF MetS with serum adiponectin).
From our results we conclude that low serum adiponectin is independently associated with both the MetS and the angiographically determined presence of CAD: Serum levels of adiponectin are highest in patients who have neither the MetS nor significant CAD at angiography, are intermediate in patients who have either CAD or the MetS, and are lowest in patients with both the MetS and CAD. This is the first report on the association between adiponectin serum levels and the MetS in patients characterized by coronary angiography. Previous studies had addressed the association between serum levels of adiponectin and the MetS in other patient populations and, importantly, without taking into consideration the coronary artery state [3–14]. In line with other reports [4,11,12,34] serum adiponectin in our investigation was significantly associated with the MetS irrespective of whether we applied ATP-III or IDF criteria for the diagnosis of the MetS. Only few reports on the association between adiponectin serum levels and angiographically determined CAD are available from the literature. One study had found lower serum adiponectin in patients with angiographically proven CAD than in healthy blood donors [23], and two further investigations had shown significant associations between low serum adiponectin and the presence and extent of CAD in angiographied patient populations [21,22]. In extension to these findings our data show that the association between serum adiponectin and angiographically determined CAD is independent from the presence of the MetS: both among patients with the MetS and among patients without the MetS, serum adiponectin is decreased in those with significant CAD at angiography. Similar as with the clinical entity of the MetS, associations between serum adiponectin and biomarkers of insulin resistance have been reported in the literature [35,36]. Our investigation over and above these previous observations demonstrates hat the association between serum adiponectin and insulin resistance is independent of the angiographically determined coronary state. Moreover, this is the fist report which shows that insulin resistance and the clinical entity of the MetS are associated with serum adiponectin values in a mutually independent manner. This is an interesting parallel to our previously published observation that insulin resistance and the MetS independently from each other predict future vascular events [37]. Insulin resistance and the entity of the MetS, though pathophysiologically and clinically closely associated, are not simply interchangeable terms. Screening for CAD and for the MetS is important. CAD is the leading cause of mortality worldwide, and, due to the current epidemic of obesity and sedentary lifestyle in industrialized countries, the prevalence of the MetS is very high in large parts of the world. Indeed, according to the ATP-III definition, about one-fourth of middle-aged men and women in the U.S. have the MetS [38]. Moreover, individuals with the MetS face a strongly increased risk of cardiovascular events. A biomarker such as adiponectin that is independently associated with both the presence of the MetS and the presence of CAD thus appears
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most interesting for clinical application as a metabolic and vascular risk marker. From the individual MetS stigmata all except the high blood pressure trait were significantly associated with low serum adiponectin. When the five ATP-III MetS components were entered simultaneously into one ANCOVA model, the waist criterion and the dyslipidemic MetS traits proved independently predictive of adiponectin serum levels. These results are well in line with those from a previous investigation in Korean patients: Also in this investigation, significant associations between serum adiponectin and all MetS traits except high blood pressure were observed; concordant with our results the association was strongest between serum adiponectin and the low HDL cholesterol trait of the MetS in this study. Previous studies have reported that administration of statins [39], fibrates [40], ACE inhibitors, or AT-II blocking agents [41] increases plasma adiponectin levels in human subjects. However, in our investigation the prevalence of these medications tended to be higher in study subgroups with CAD or with the metabolic syndrome, in which adiponectin was low. Therefore, and because adjustment for medication use did not significantly affect the mutually independent associations of CAD and the MetS with serum adiponectin, differences in medication use between study subgroups do not explain our observation that low serum adiponectin is independently associated with both the MetS and angiographically determined coronary atherosclerosis. Our investigation is characterized by the typical limitations and strengths of studies enrolling patients who undergo coronary angiography for the evaluation of CAD. The angiographical characterization of the coronary artery state was an essential feature of our study design. Of course, patients undergoing coronary angiography for the evaluation of CAD are a selected group of patients the results from which are not necessarily applicable to the general population. However, the population we chose to investigate is at a high vascular risk and therefore deserves particular clinical attention. We did not measure adiponectin isoforms. In the light of our results a future investigation addressing the respective associations of the MetS and of CAD with HMW adiponectin isoforms would be of interest. In conclusion we found that low serum adiponectin is independently associated with both the MetS and coronary atherosclerosis. This observation contributes significantly to the understanding of the pathophysiology of hypoadiponectinemia. Clinically, adiponectin, as a biomarker that is strongly and independently associated with both the presence of the MetS and the presence of angiographically determined CAD is a most interesting candidate for metabolic and vascular risk stratification. 5. List of abbreviations
MetS CAD WHO ATP-III IDF
Metabolic Syndrome Coronary Artery Disease World Health Organisation Adult Treatment Panel III International Diabetes Federation
CLSI LDL HDL HOMA ANCOVA HMW
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Clinical Laboratory Standardization Institute Low Density Lipoprotein High Density Lipoprotein Homeostasis Model Assessment Analysis of Covariance High Molecular Weight
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