ECTOPIC FAT AN IMPORTANT FEATURE OF INTRAABDOMINAL OBESITY

ECTOPIC FAT: AN IMPORTANT FEATURE OF INTRA-ABDOMINAL OBESITY IN TYPE 2 DIABETES Marja-Riitta Taskinen, MD, Ph. D Professor of Medicine, Division of Cardiology Helsinki University Hospital Helsinki, Finland

What Is Ectopic Fat Accumulation? Caloric intake and/ or Energy expenditure Positive energy balance Lipid overflow into liver, pancreas, muscle and heart FFA Inflamed adipose tissue Imbalance between loading and export of lipids results in ectopic fat accumulation at organs FFA: free fatty acids Source: www. myhealthywaist. org

Why Is the Fatty Liver Dangerous for Cardiovascular Health Risk? Glucose VLDL HDL ALT The fatty liver : overproduction of cardiometabolic risk factors Fibrinogen CRP § Obesity § Genetic predisposition § Fat in the diet? § Fructose? PAI-1 FVII ALT: alanine aminotransferase CRP: C-reactive protein FVII: factor VII Source: www. myhealthywaist. org PAI-1: plasminogen activator inhibitor-1

Determination of Liver Fat Content Using Magnetic Resonance Spectroscopy Water peak Liver fat 6% Liver fat 28% Triglyceride peak Reproduced by permission of the American Diabetes Association. Copyright© 2000 American Diabetes Association. From Ryysy L et al. Diabetes 2000; 49: 749 -58 Source: www. myhealthywaist. org

Regulation of Lipid Metabolism in the Liver Free fatty acid flux Dietary fatty acids § De novo lipogenesis § Fatty acid oxidation § VLDL assembly VLDL secretion Source: www. myhealthywaist. org

The Atherogenic Lipoprotein Triad Lifestyle Large VLDL § Insulin resistance § Type 2 diabetes § FCH subjects § Low HDL subjects Genes Small, dense LDL Increased CAD Risk HDL CAD: coronary artery disease Source: www. myhealthywaist. org FCH: familial combined hyperlipidemia

VLDL 1 TG production (mg/kg/day) Relationship Between VLDL 1 Production Rate and Plasma VLDL 1 Triglyceride (TG) Pools 600 r=0. 62, p<0. 001 400 200 0 0 10 20 30 40 50 60 VLDL 1 TG pool (mg/kg) VLDL 1 TG production rate is the predictor for VLDL 1 TG pool size Adapted from Adiels M et al. Arterioscler Thromb Vasc Biol 2005; 25: 1697 -703 Source: www. myhealthywaist. org

600 r=-0. 56, p<0. 005 500 400 300 200 100 0 22 23 24 25 26 27 LDL size (nm) 28 29 30 VLDL 1 TG production (mg/kg/day) VLDL 1 Triglyceride (TG) Production Is Linked With Detrimental Changes of LDL Size and HDL Cholesterol 600 r=-0. 64, p<0. 001 500 400 300 200 100 0 0. 7 0. 9 1. 1 1. 3 1. 5 1. 7 HDL cholesterol (mmol/l) Adapted from Adiels M et al. Diabetologia 2006; 49: 755 -65 Source: www. myhealthywaist. org

VLDL 1 TG production (mg/kg/day) Relationship Between VLDL 1 Triglyceride (TG) Production and Liver Fat Assessed Using Proton Spectroscopy 600 r=0. 58, p<0. 01 400 200 0 0 5 10 15 20 25 Liver fat (%) Liver fat content is the driving force for VLDL-TG overproduction Adapted from Adiels M et al. Diabetologia 2006; 49: 755 -65 Source: www. myhealthywaist. org

Defective Regulation of VLDL Metabolism by Insulin in Type 2 Diabetic Patients 1000 FFA VLDL 1 apo B production Oxidation mg/day De novo lipogenesis FA Remnants -51% 500 TG 0 CE Controls Type 2 diabetes Degradation VLDL 1 MTP VLDL 2 Apo B § Insulin fails to suppress VLDL 1 apo B production. IDL LDL § Accumulation of VLDL 1 particles. HL LPL HL IDL Apo B: apolipoprotein B VLDL 2 LPL CE: cholesteryl ester FA: fatty acid FFA: free fatty acids HL: hepatic lipase LPL: lipoprotein lipase MTP: microsomal triglyceride transfer protein TG: triglycerides LDL Small, dense LDL Source: www. myhealthywaist. org LPL Adapted from Malmströn R et al. Arterioscler Thromb Vasc Biol 1997; 17: 1454 -64

Characteristics of the Subjects Low liver fat (n=10) Body mass index (kg/m 2) 26. 0 2. 9 Subcutaneous fat (cm 3) 2150 730 Intra-abdominal (visceral) fat (cm 3) 1600 880 Liver fat (%) 2. 1 1. 5 M value (mg/kg/min) 6. 4 1. 8 Fasting triglycerides (mmol/l) 1. 4 0. 5 HDL cholesterol (mmol/l) 1. 4 0. 2 LDL size (nm) 26. 6 0. 8 * p<0. 05 ** p<0. 01 High liver fat (n=10) 28. 4 2420 2480 11. 4 4. 0 2. 0 1. 1 25. 3 3. 6 520 860* 4. 5*** 2. 1* 0. 8 0. 3** 1. 1** *** p<0. 001 Adapted from Adiels M et al. Diabetologia 2007; 50: 2356 -65 Source: www. myhealthywaist. org

High Liver Fat: Lack of VLDL 1 Suppression in Response to Insulin % of total VLDL at baseline VLDL 1 triglyceride production rate 100 61%, p<0. 01 75 Low liver fat <5. 5% High liver fat >5. 5% 50 25 0 0 200 400 600 Time (minutes) Adapted from Adiels M et al. Diabetologia 2007; 50: 2356 -65 Source: www. myhealthywaist. org

Normal Production and Suppression of VLDL 1 Particles in Normal Healthy Subjects by Insulin Apo B: apolipoprotein B Insulin Low liver fat MTP: microsomal triglyceride transfer protein TG: triglycerides TG MTP VLDL 1 Apo B VLDL 2 Adapted from Adiels M et al. Diabetologia 2007; 50: 2356 -65 Source: www. myhealthywaist. org

Overproduction and Dysregulation of VLDL 1 Particles in Type 2 Diabetes Insulin High liver fat Apo B: apolipoprotein B TG: triglycerides TG Apo B VLDL 1 VLDL 2 High liver fat is linked with hepatic insulin resistance and overproduction of large VLDL particles Adapted from Adiels M et al. Diabetologia 2007; 50: 2356 -65 Source: www. myhealthywaist. org

Why People With a Big Waist do not all Have Dyslipidemia? Metabolic syndrome? Elevated VLDL 1 concentrations Insulin resistance? Normal lipid profile Intra-abdominal (visceral) obesity Source: www. myhealthywaist. org Insulin resistance Intra-abdominal (visceral) obesity The atherogenic triad Low HDL Small, dense LDL particles

Sources of Fatty Acids for Liver and VLDL Triglycerides (TG) FFA POOL 2 CM 1 FA STORAGE? β-ox TG 4 LIVER TG 2 DNL Apo B 5 GLUCOSE INSULIN 3 VLDL TG Apo B: apolipoprotein B -ox: -oxidation CM: chylomicron DNL: de novo lipogenesis FA: fatty acids FFA: free fatty acids Adapted from Adiels M et al. Arterioscler Thromb Vasc Biol 2008; 28: 1225 -36 Source: www. myhealthywaist. org

Palmitate rate of appearence (µmol/minute) Whole-Body Palmitate Rate of Appearance in Obese Subjects Without and With Nonalcoholic Fatty Liver Disease (NAFLD) * Normal IHTG NAFLD n=14 Liver fat (%) 3. 4 ± 0. 4 BMI (kg/m 2) 35. 3 ± 1. 3 *Significantly different from the normal IHGT group, p<0. 05 n=14 22. 7 ± 2. 0 36. 8 ± 1. 2 IHTG: intrahepatic triglycerides The rate of the release of fatty acids from adipose tissue is increased in obese subjects with NAFLD Adapted from Fabbrini E et al. Gastroenterology 2008; 134: 424 -31 Source: www. myhealthywaist. org

VLDL Triglyceride (TG) Secretion Rate Is Increased in Obese Subjects With Nonalcoholic Fatty Liver Disease (NAFLD) 30 * (µmol/minute) 25 * 20 Systemic plasma FFA Nonsystemic fatty acids 15 10 5 0 * Normal IHGT Liver fat (%) 3. 4 ± 0. 4 BMI (kg/m 2) 35. 3 ± 1. 3 NAFLD 22. 7 ± 2. 0 36. 8 ± 1. 2 BMI: body mass index FFA: free fatty acids IHTG: intrahepatic triglycerides *Significantly different from the normal IHGT group, p<0. 05 Fatty acids derived from nonsystemic sources are the major factors responsible for the increase in VLDL TG secretion Adapted from Fabbrini E et al. Gastroenterology 2008; 134: 424 -31 Source: www. myhealthywaist. org

Sources of Fatty Acids for Liver Fat and VLDL Triglycerides § Increased rate of free fatty acid flux from adipose tissue results in increased rate of hepatic free fatty acid uptake. § Intrahepatic de novo lipogenesis is enhanced in subjects with nonalcoholic fatty liver disease (NAFLD). § The production and secretion of large VLDL particles correlate with liver fat content. § Basal hepatic lipid oxidation seems to be unaltered in subjects with NAFLD. Overproduction of VLDL particles is NOT able to adequately compensate for increase of hepatic triglyceride production liver fat accumulation

Regulation of DNL by SREBP 1 -C, Ch. REBP and LXRs in Liver ACC: acetyl-Co. A carboxylase Ch. REBP: carbohydrate-responsive element-binding protein DGAT: diacylglycerol acyltransferase DNL: de novo lipogenesis ELOVL 6: long-chain elongase FAS: fatty acid synthase GK: glucokinase GPAT: mitochondrial glycerol 3 -phosphate acyltransferase L-PK: liver-pyruvate kinase LXR: liver X receptors SCD 1: stearoyl-Co. A desaturase SREBP-1: sterol regulatory element-binding protein 1 TG: triglycerides Adapted from Postic C and Girard J. J Clin Invest 2008; 118: 829 -38 Source: www. myhealthywaist. org

Mechanisms Leading to Insulin Resistance in the Liver Akt: protein kinase B DAG: diacylglycerol FA: fatty acids Acylcarnitine FA LPA: lysophosphatidic acid m. TOR: mammalian target of rapamycin TG Fatty acyl-Co. A β-oxidation Acetyl-Co. A FA CO 2 Fatty acyl-Co. A Akt Fatty acyl-Co. A PA NFĸB PKC m. TOR PKC: protein kinase C TG: triglycerides ? Insulin resistance DAG Fatty acyl-Co. A PA: phosphatidic acid Ketones Acylcarnitines Ceramide G-3 -P LPA NFk. B: nuclear factor-kappa B TG Adapted from Fabbrini E et al. Hepatology 2010; 51: 679 -89 Source: www. myhealthywaist. org

Consequences of Ectopic Fat Accumulation: Insulin Resistance, Dyslipidemia, NAFLD and Left Ventricular Dysfunction Glucose production FFA Subcutaneous fat Oxidation Intra-abdominal (visceral) fat FFA Ch. REBP SREBP-1 c DNL TG TG Insulin VLDL LV dysfunction CAD risk factor? Glucose Atherogenic dyslipidemia CAD: coronary artery disease Glucose uptake Ch. REBP-1 c: carbohydrate-responsive element-binding protein-1 c DNL: de novo lipogenesis FFA: free fatty acids NAFLD: nonalcoholic fatty liver disease SREBP-1: sterol regulatory element-binding protein 1 TG: triglycerides Adapted from Fabbrini E et al. Hepatology 2010; 51: 679 -89 Source: www. myhealthywaist. org

Fat in Cardiomyocyte Low myocardial TG content High myocardial TG content H 2 O CH 2 H 2 O CH 3 • Adapted from Mc. Gavock JM et al. Circulation 2007; 116: 1170 -5 x 50 CH 2 + CH 3 6 5 4 3 ppm 2 1 0 TG: triglycerides Source: www. myhealthywaist. org

Cardiac Steatosis – a Component of Ectopic Fat Obese Impaired glucose tolerance Myocardial triglycerides (fat/water ) Lean Intra-abdominal 54 ± 39 (visceral) fat (cm 2) Hepatic fat (fat/water) 1. 1 ± 0. 9 * 120 ± 53* 132 ± 36* 4. 3 ± 5. 2 8. 3 ± 11. 1* Type 2 diabetes * 160 ± 65* 8. 9 ± 8. 8* *p<0. 05 vs. lean Adapted from Mc. Gavock JM et al. Circulation 2007; 116: 1170 -5 Source: www. myhealthywaist. org

Myocardial Fat and Coronary Heart Disease § Proton magnetic resonance spectroscopy is technically challenging but a powerful research tool. § Is accumulation of myocardial triglycerides related to diastolic dysfunction? - More rigorous characterization of diastolic function needed. § No data available on the relationship between myocardial fat and coronary heart disease. § Determinants of myocardial triglyceride accumulation are largely unknown. § Data on responses of myocardial triglycerides to pharmacological interventions are non-existing.

Why Is Ectopic Fat Accumulation a Health Hazard? Caloric intake and/ or Energy expenditure Positive energy balance Lipid overflow into liver, pancreas, muscle and epicardium FFA Inflamed adipose tissue Ectopic fat accumulation results in lipotoxicity at organ levels with deleterious consequences at cardiovascular disease health. FFA: free fatty acids Source: www. myhealthywaist. org

My Warmest Thanks to my Collaborators "Current players" Gothenburg Anne Hiukka Eeva Leinonen Sakari Mänttäri Aino Soro-Paavonen Sanni Söderlund Jukka Westerbacka Hannele Yki-Järvinen Martin Adiels Jan Boren Sven-Olofsson Glasgow Muriel Caslake Chris J. Packard Philip Steward "The ladies of the lab" Imaging team Hannele Hilden Virve Naatti Helinä Perttunen-Nio Nina Lundbom Jesper Lundbom Antti Hakkarainen