Downloaded from http://jim.bmj.com/ on September 5, 2016 - Published by group.bmj.com
ORIGINAL ARTICLE
Sex-Specific Predictors of Metabolic Syndrome Independent of Its Components Altan Onat, MD,* Günay Can,† Hakan Çakır,‡ Fatma Özpamuk-Karadeniz,§ Yusuf Karadeniz,k Hüsniye Yüksel,* Barış Şimşek,¶ and Evin Ademoğlu# Abstract: To what extent is the metabolic syndrome (MetS) determined beyond its recognized components? In 1702, middle-aged men and women without MetS at baseline, MetS development was identified in 546 participants at a mean of 10.1-year follow-up. Participants subsequently developing MetS had, beyond higher values of MetS traits, significantly higher total and low-density lipoprotein cholesterol, apolipoprotein B, C-reactive protein (CRP), γ-glutamyl transferase (GGT), and lower high-density lipoprotein cholesterol. Females were significantly more frequent never smokers and males had lower values of total testosterone. In logistic regression analyses, adjusted for sex, age, and smoking status, MetS was predicted disparately in the sexes, whereas males exhibited, beyond abdominal obesity, CRP, GGT, and sex hormone-binding globulin (SHBG) as independent predictors, abdominal obesity was not an independent predictor in females in whom other than age, CRP conferred MetS risk, whereas SHBG was and current smoking tended to be protective. A surrogate of hepatic steatosis proved a major mediator of abdominal obesity in determining incident MetS (relative risk, 5.6 [95% confidence interval, 3.4-9.3]) in each sex. We confirm that GGT and SHBG are novel independent MetS determinants. Hepatic steatosis is the major predictor of MetS mediating adiposity in each sex. Abdominal obesity is not an independent determinant in Turkish women in whom autoimmune activation seems to prevail before MetS development. Key Words: abdominal obesity, GGT, inflammation, metabolic syndrome, serum SHBG (J Investig Med 2015;63: 796–801)
T
he metabolic syndrome (MetS) is a cluster of multiple metabolic abnormalities around central obesity and insulin resistance. Proinflammatory and prothrombotic states are essential features, beyond its 5 components. The National Heart, Lung, and Blood Institute/American Heart Association modified the dysglycemia criterion of the Adult Treatment Panel-III definition of MetS, lowering it to 100 mg/dL.1 Its close association with the risk of type 2 diabetes and cardiovascular disease constituting a growing problem worldwide renders it clinical and prognostic significance.2 Except for the thresholds of abdominal obesity and low highdensity lipoprotein (HDL) cholesterol, a sex difference among the MetS components has not been generally recognized, although From the Departments of *Cardiology and †Public Health, Cerrahpaşa Medical Faculty Istanbul University, Istanbul; ‡Department of Medicine, Darıca Training and Research Hospital, Kocaeli; §Department of Cardiology, Balıklıgöl State Hospital; kDepartment of Internal Medicine, Mehmet Akif İnan Training and Research Hospital, Şanlıurfa; ¶Siyami Ersek Center for Cardiovascular Surgery, Cardiovascular Division; and #Biochemistry Department, Istanbul Medical Faculty, Istanbul University, Istanbul, Turkey. Received January 12, 2015, and in revised form March 29, 2015. Accepted for publication April 6, 2015. Reprints: Altan Onat, MD, Cerrahpaşa Medical Faculty, Nisbetiye cad. 59/24, Etiler 34335, Istanbul, Turkey. E-mail: [email protected]. Competing interest: The authors declare no competing interests. Copyright © 2015 by The American Federation for Medical Research ISSN: 1081-5589 DOI: 10.1097/JIM.0000000000000203
796
such difference has been expressed for certain ethnicities. The difference has been attributed to related hormonal regulation of body fat distribution and attendant metabolic abnormalities.3 However, experience from the Turkish Adult Risk Factor (TARF) study disclosed that sex also affects the response of proinflammatory state to central obesity and the associated impaired function of HDL particles, women being influenced more pronouncedly by this process. Moreover, the association of serum C-reactive protein (CRP), the main inflammatory mediator or marker, is largely independent of the ATP-III MetS components in men, but not in women.4 Autoimmune activation in relation to diabetes and coronary heart disease (CHD) has been observed among Turks much more frequently in the female sex. A sex difference has been reported also regarding new onset diabetes among 6547 individuals with incident diabetes, wherein, compared with men, women had lower hemoglobin A1c and higher LDL cholesterol and pulse pressure, differences that decreased over time.5 Obesity and insulin resistance are believed to be at the core of most cases of MetS, yet further research is required to truly understand the pathophysiology behind the syndrome and the gene-environment interactions increasing susceptibility.6 Whether other inflammation biomarkers (apolipoprotein [apo] B, fibrinogen, lipoprotein [Lp] a) are independently and smoking status uniformly relevant to MetS incidence needs to be examined more adequately in various ethnicities and Lp phenotypes. It is likely that atherogenic small dense LDL particles lie underneath these associations, which may uncover the clustering of inflammatory mediators with ATP-III–defined MetS. It has been proposed that nonalcoholic fatty liver disease and pediatric MetS are interrelated and have common pathophysiological features.7 Several studies on TARF participants indicated that factors (apoB,8 CRP,9 SHBG,10 γ-glutamyltransferase [GGT],11 Lp[a])12 beyond the MetS components were of independent relevance relative to MetS or cardiometabolic risk. We, therefore, aimed to investigate these and some other variables regarding their independent predictive value of risk for MetS. We further studied the predictive value for MetS between a surrogate of hepatic steatosis (HS)13 and abdominal obesity and/or sex proteins. Because it is established that a sex difference exists among Turkish adults with respect to determinants of cardiometabolic risk,14,15 we stratified the prospective analyses for incident MetS to sexes. Findings shed light to the mediators for MetS beyond its components and the sex-specific timing of autoimmune activation.
SUBJECTS AND METHODS Population Sample The TARF study is a prospective survey on the prevalence of cardiac disease and risk factors in adults in Turkey carried out periodically almost biennially since 1990 in 59 communities scattered throughout all geographical regions of the country.16 It comprises a representative sample of the Turkish adult population. Because combined HDL cholesterol and waist circumference determinations were first made in the survey 1997/1998, participants Journal of Investigative Medicine • Volume 63, Number 6, August 2015
Copyright © 2015 American Federation for Medical Research. Unauthorized reproduction of this article is prohibited.
Downloaded from http://jim.bmj.com/ on September 5, 2016 - Published by group.bmj.com
Journal of Investigative Medicine • Volume 63, Number 6, August 2015
included in this and subsequent surveys were eligible. These consisted of 3510 subjects of whom 1230 (35%) with prevalent MetS and 578 (16.5%) with no follow-up were excluded. Thus, the sample was formed by 1702 participants free of MetS at baseline. The sample was composed of 62% with entry in 1998 and 20% in the survey 2000, the remaining 18% entered in years 2002 to 2008. Follow-up extended to the survey 2012 to 2013. The survey conformed to the principles embodied in the Declaration of Helsinki and was approved by the Istanbul University Ethics Committee. All individuals gave written consent to participation. Data were obtained by history of the years via a questionnaire, physical examination of the cardiovascular system, sampling of blood, and recording of a resting electrocardiogram.
Measurements of Risk Variables Blood pressure (BP) was measured in the sitting position on the right arm, and the mean of 2 recordings at least 5 minutes apart was recorded. Waist circumference was measured with a tape (Roche LI95 63B 00), the subject standing and wearing only underwear at the level midway between the lower rib margin and the iliac crest. Self-reported cigarette smoking was categorized into never smokers, former smokers (discontinuance of 3 months or more), and current smokers (regularly 1 or more cigarettes daily). Plasma concentrations of total and HDL cholesterol, fasting triglycerides, and glucose were determined in the 1998 survey by the enzymatic dry chemistry method using a Reflotron apparatus. Low-density lipoprotein cholesterol values were computed according to the Friedewald formula when accompanying triglycerides were less than 4.5 mmol/L. In the subsequent surveys, all biochemical parameters were assayed in a central laboratory. Blood samples were shipped to Istanbul to be stored in deep freeze at −75°C, until analyzed. Concentrations of SHBG and total testosterone were determined by the electrochemiluminescence immunoassay ECLIA on Roche Elecsys 2010 (Roche Diagnostics, Mannheim, Germany). Serum concentrations of apoA-I, apoB, Lp(a), and high-sensitivity CRP were measured by the Behring kits and nephelometry by BN ProSpec analyzer (Siemens Healthcare Diagnostics, Germany). Serum GGT activity was assayed by the kinetic method using Glucana as substrate (Thermo Trace, Noble Park, Victoria, Australia). Plasma fibrinogen was assayed by the modified Clauss method using Behring Fibrintimer II coagulometer and Multifibren U kit. Serum MIF protein concentrations were assayed with commercially available human ELISA kit (Quantikine ELISA R&D Systems, Minneapolis, MN, catalog no. SMF00B).
Definitions Conditions of individuals with diabetes were diagnosed with criteria of the American Diabetes Association,17 namely when plasma fasting glucose was 126 mg/dL or greater (or 2-hour postprandial glucose >200 mg/dL) and/or the current use of diabetes medication. Individuals with MetS were identified when 3 of the 5 criteria of the National Cholesterol Education Program (ATP III) were met, modified for prediabetes (fasting glucose 100–125 mg/dL), and furthered for abdominal obesity using as cut point of 95 cm or more in men, as assessed in the TARF study.18 For women, the cut point of 88 cm or more was retained on the basis of own prospective analyses. No MetS denoted any participant not meeting full criteria for MetS.
Estimation of HS by an Algorithm We estimated via a previously reported algorithm based on body mass index (BMI), waist circumference, triglycerides, and GGT to detect fatty liver13 using the following equation:
Metabolic Syndrome and Independent Predictors
HS = (e0.953 loge triglycerides +0.139 BMI + 0.718 loge GGT + 0.053 waist circumference − 15.745)/(1 + (e0.953 loge triglycerides + 0.139 BMI + 0.718 loge GGT + 0.053 waist circumference − 15.745) 100). In agreement with the authors, we used an index of less than 30 to indicate absence of HS, 60 or greater presence of HS, and 30 to 59 probable presence of HS.
Data Analysis Descriptive parameters were shown as mean (SD) or in percentages. Two-sided t tests and Pearson χ2 tests were used to analyze the differences in means and proportions between groups. Due to the skewed distribution, log-transformed values were used for triglycerides, CRP, GGT, MIF protein, and Lp(a) for analyses. Estimates (and 95% confidence intervals [CI]) for relative risk (RR) of the dependent variable were obtained by the use of multiple logistic regression analyses in models that controlled for potential confounders and expressed in terms of 1-SD increment. A value of P
ORIGINAL ARTICLE
Sex-Specific Predictors of Metabolic Syndrome Independent of Its Components Altan Onat, MD,* Günay Can,† Hakan Çakır,‡ Fatma Özpamuk-Karadeniz,§ Yusuf Karadeniz,k Hüsniye Yüksel,* Barış Şimşek,¶ and Evin Ademoğlu# Abstract: To what extent is the metabolic syndrome (MetS) determined beyond its recognized components? In 1702, middle-aged men and women without MetS at baseline, MetS development was identified in 546 participants at a mean of 10.1-year follow-up. Participants subsequently developing MetS had, beyond higher values of MetS traits, significantly higher total and low-density lipoprotein cholesterol, apolipoprotein B, C-reactive protein (CRP), γ-glutamyl transferase (GGT), and lower high-density lipoprotein cholesterol. Females were significantly more frequent never smokers and males had lower values of total testosterone. In logistic regression analyses, adjusted for sex, age, and smoking status, MetS was predicted disparately in the sexes, whereas males exhibited, beyond abdominal obesity, CRP, GGT, and sex hormone-binding globulin (SHBG) as independent predictors, abdominal obesity was not an independent predictor in females in whom other than age, CRP conferred MetS risk, whereas SHBG was and current smoking tended to be protective. A surrogate of hepatic steatosis proved a major mediator of abdominal obesity in determining incident MetS (relative risk, 5.6 [95% confidence interval, 3.4-9.3]) in each sex. We confirm that GGT and SHBG are novel independent MetS determinants. Hepatic steatosis is the major predictor of MetS mediating adiposity in each sex. Abdominal obesity is not an independent determinant in Turkish women in whom autoimmune activation seems to prevail before MetS development. Key Words: abdominal obesity, GGT, inflammation, metabolic syndrome, serum SHBG (J Investig Med 2015;63: 796–801)
T
he metabolic syndrome (MetS) is a cluster of multiple metabolic abnormalities around central obesity and insulin resistance. Proinflammatory and prothrombotic states are essential features, beyond its 5 components. The National Heart, Lung, and Blood Institute/American Heart Association modified the dysglycemia criterion of the Adult Treatment Panel-III definition of MetS, lowering it to 100 mg/dL.1 Its close association with the risk of type 2 diabetes and cardiovascular disease constituting a growing problem worldwide renders it clinical and prognostic significance.2 Except for the thresholds of abdominal obesity and low highdensity lipoprotein (HDL) cholesterol, a sex difference among the MetS components has not been generally recognized, although From the Departments of *Cardiology and †Public Health, Cerrahpaşa Medical Faculty Istanbul University, Istanbul; ‡Department of Medicine, Darıca Training and Research Hospital, Kocaeli; §Department of Cardiology, Balıklıgöl State Hospital; kDepartment of Internal Medicine, Mehmet Akif İnan Training and Research Hospital, Şanlıurfa; ¶Siyami Ersek Center for Cardiovascular Surgery, Cardiovascular Division; and #Biochemistry Department, Istanbul Medical Faculty, Istanbul University, Istanbul, Turkey. Received January 12, 2015, and in revised form March 29, 2015. Accepted for publication April 6, 2015. Reprints: Altan Onat, MD, Cerrahpaşa Medical Faculty, Nisbetiye cad. 59/24, Etiler 34335, Istanbul, Turkey. E-mail: [email protected]. Competing interest: The authors declare no competing interests. Copyright © 2015 by The American Federation for Medical Research ISSN: 1081-5589 DOI: 10.1097/JIM.0000000000000203
796
such difference has been expressed for certain ethnicities. The difference has been attributed to related hormonal regulation of body fat distribution and attendant metabolic abnormalities.3 However, experience from the Turkish Adult Risk Factor (TARF) study disclosed that sex also affects the response of proinflammatory state to central obesity and the associated impaired function of HDL particles, women being influenced more pronouncedly by this process. Moreover, the association of serum C-reactive protein (CRP), the main inflammatory mediator or marker, is largely independent of the ATP-III MetS components in men, but not in women.4 Autoimmune activation in relation to diabetes and coronary heart disease (CHD) has been observed among Turks much more frequently in the female sex. A sex difference has been reported also regarding new onset diabetes among 6547 individuals with incident diabetes, wherein, compared with men, women had lower hemoglobin A1c and higher LDL cholesterol and pulse pressure, differences that decreased over time.5 Obesity and insulin resistance are believed to be at the core of most cases of MetS, yet further research is required to truly understand the pathophysiology behind the syndrome and the gene-environment interactions increasing susceptibility.6 Whether other inflammation biomarkers (apolipoprotein [apo] B, fibrinogen, lipoprotein [Lp] a) are independently and smoking status uniformly relevant to MetS incidence needs to be examined more adequately in various ethnicities and Lp phenotypes. It is likely that atherogenic small dense LDL particles lie underneath these associations, which may uncover the clustering of inflammatory mediators with ATP-III–defined MetS. It has been proposed that nonalcoholic fatty liver disease and pediatric MetS are interrelated and have common pathophysiological features.7 Several studies on TARF participants indicated that factors (apoB,8 CRP,9 SHBG,10 γ-glutamyltransferase [GGT],11 Lp[a])12 beyond the MetS components were of independent relevance relative to MetS or cardiometabolic risk. We, therefore, aimed to investigate these and some other variables regarding their independent predictive value of risk for MetS. We further studied the predictive value for MetS between a surrogate of hepatic steatosis (HS)13 and abdominal obesity and/or sex proteins. Because it is established that a sex difference exists among Turkish adults with respect to determinants of cardiometabolic risk,14,15 we stratified the prospective analyses for incident MetS to sexes. Findings shed light to the mediators for MetS beyond its components and the sex-specific timing of autoimmune activation.
SUBJECTS AND METHODS Population Sample The TARF study is a prospective survey on the prevalence of cardiac disease and risk factors in adults in Turkey carried out periodically almost biennially since 1990 in 59 communities scattered throughout all geographical regions of the country.16 It comprises a representative sample of the Turkish adult population. Because combined HDL cholesterol and waist circumference determinations were first made in the survey 1997/1998, participants Journal of Investigative Medicine • Volume 63, Number 6, August 2015
Copyright © 2015 American Federation for Medical Research. Unauthorized reproduction of this article is prohibited.
Downloaded from http://jim.bmj.com/ on September 5, 2016 - Published by group.bmj.com
Journal of Investigative Medicine • Volume 63, Number 6, August 2015
included in this and subsequent surveys were eligible. These consisted of 3510 subjects of whom 1230 (35%) with prevalent MetS and 578 (16.5%) with no follow-up were excluded. Thus, the sample was formed by 1702 participants free of MetS at baseline. The sample was composed of 62% with entry in 1998 and 20% in the survey 2000, the remaining 18% entered in years 2002 to 2008. Follow-up extended to the survey 2012 to 2013. The survey conformed to the principles embodied in the Declaration of Helsinki and was approved by the Istanbul University Ethics Committee. All individuals gave written consent to participation. Data were obtained by history of the years via a questionnaire, physical examination of the cardiovascular system, sampling of blood, and recording of a resting electrocardiogram.
Measurements of Risk Variables Blood pressure (BP) was measured in the sitting position on the right arm, and the mean of 2 recordings at least 5 minutes apart was recorded. Waist circumference was measured with a tape (Roche LI95 63B 00), the subject standing and wearing only underwear at the level midway between the lower rib margin and the iliac crest. Self-reported cigarette smoking was categorized into never smokers, former smokers (discontinuance of 3 months or more), and current smokers (regularly 1 or more cigarettes daily). Plasma concentrations of total and HDL cholesterol, fasting triglycerides, and glucose were determined in the 1998 survey by the enzymatic dry chemistry method using a Reflotron apparatus. Low-density lipoprotein cholesterol values were computed according to the Friedewald formula when accompanying triglycerides were less than 4.5 mmol/L. In the subsequent surveys, all biochemical parameters were assayed in a central laboratory. Blood samples were shipped to Istanbul to be stored in deep freeze at −75°C, until analyzed. Concentrations of SHBG and total testosterone were determined by the electrochemiluminescence immunoassay ECLIA on Roche Elecsys 2010 (Roche Diagnostics, Mannheim, Germany). Serum concentrations of apoA-I, apoB, Lp(a), and high-sensitivity CRP were measured by the Behring kits and nephelometry by BN ProSpec analyzer (Siemens Healthcare Diagnostics, Germany). Serum GGT activity was assayed by the kinetic method using Glucana as substrate (Thermo Trace, Noble Park, Victoria, Australia). Plasma fibrinogen was assayed by the modified Clauss method using Behring Fibrintimer II coagulometer and Multifibren U kit. Serum MIF protein concentrations were assayed with commercially available human ELISA kit (Quantikine ELISA R&D Systems, Minneapolis, MN, catalog no. SMF00B).
Definitions Conditions of individuals with diabetes were diagnosed with criteria of the American Diabetes Association,17 namely when plasma fasting glucose was 126 mg/dL or greater (or 2-hour postprandial glucose >200 mg/dL) and/or the current use of diabetes medication. Individuals with MetS were identified when 3 of the 5 criteria of the National Cholesterol Education Program (ATP III) were met, modified for prediabetes (fasting glucose 100–125 mg/dL), and furthered for abdominal obesity using as cut point of 95 cm or more in men, as assessed in the TARF study.18 For women, the cut point of 88 cm or more was retained on the basis of own prospective analyses. No MetS denoted any participant not meeting full criteria for MetS.
Estimation of HS by an Algorithm We estimated via a previously reported algorithm based on body mass index (BMI), waist circumference, triglycerides, and GGT to detect fatty liver13 using the following equation:
Metabolic Syndrome and Independent Predictors
HS = (e0.953 loge triglycerides +0.139 BMI + 0.718 loge GGT + 0.053 waist circumference − 15.745)/(1 + (e0.953 loge triglycerides + 0.139 BMI + 0.718 loge GGT + 0.053 waist circumference − 15.745) 100). In agreement with the authors, we used an index of less than 30 to indicate absence of HS, 60 or greater presence of HS, and 30 to 59 probable presence of HS.
Data Analysis Descriptive parameters were shown as mean (SD) or in percentages. Two-sided t tests and Pearson χ2 tests were used to analyze the differences in means and proportions between groups. Due to the skewed distribution, log-transformed values were used for triglycerides, CRP, GGT, MIF protein, and Lp(a) for analyses. Estimates (and 95% confidence intervals [CI]) for relative risk (RR) of the dependent variable were obtained by the use of multiple logistic regression analyses in models that controlled for potential confounders and expressed in terms of 1-SD increment. A value of P
