The Emerging Role of Adipose

Tissue

Gareth Denyer

University of Sydney, Australia

Obesity in Australia

Epidemiology of obesity World perspective

• 50% European adults 35-65 years old are overweight or obese

• More men overweight, more women obese• In Western countries, inversely associated with socio-

economic status

For Aus stats: www.asso.org.aunavigate to fast facts

Male Class V

Male Class I

Female Class V

Female Class I10

20

30

‘93 ‘06

UK Foresight study

The Propaganda

• We are second only to USA• 52% of Australian women & 67% Australian men

are overweight or obese. – 2.5 times higher than in 1980.

• Childhood obesity in Australia one of the highest amongst developed nations. – 25% overweight or obese.

• Health crisis costing $1.5 billion a year in direct health costs

• “Fattest people are getting fatter faster”• “2050 90% adults and 40% children overweight”

From www.asso.org.au

Alternative View

• The recent rise is not as rapid as before– Greatest rise was 15 years ago

• Speakman Int J Obes (2008) 32 1611-7– We are all just reaching our ‘set point’– Previously exercise and low-calorie foods

kept us below the set point– In the past, only the very rich were fat!– In developing nations, higher classes fatter

Health Risks of Obesity in AdultsNurses’ Health Study (women 30 to 55 yr)

Health Professionals Follow-up Study (men 45-60 yr)

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Type 2 diabetes Hypertension Heart Disease Cholelithiasis

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Women Men

Morbidity and Mortality

• Increased mortality and morbidity– >20% of deaths from coronary heart disease– >70% of cases of Type 2 diabetes

• Chronic Disease– Dyslipidemia– Arthritis– PCOS - polycistic ovarian disease– Sleep apnoea– Hypertension– NAFLD/NASH

• non-alcoholic fatty liver disease, steatohepatitis

Circulating CVD factors characteristic of obesity

• High cholesterol– Low HDL, high LDL

• Other dyslipidemia– Triglyceride concentration– Small, dense LDLs– Elevated apoB

• Prothrombotic factors• High Systolic Blood

Pressure• Proinflammatory markers

Health concerns associated with childhood obesity are similar to adults

Ebbeling. Pawlak, Ludwig: Lancet, 2002

In NSW – 25% of boys and 23% of girls are overweight or obese (2004)

Social and Cultural Impact

• Obviously very difficult to do these studies– All MUST be adjusted for socioeconomic status– But several done in Australia

• Employment– wage ‘penalty’ of up to 12%

• Health Care– reluctance to seek health care services– reluctance for doctors to discuss weight with patients

• ‘too difficult’, ‘non-compliant’

• Education– lower university and tertiary education attendance

• Relationships– interesting studies with assessment of ‘blind’ interactions vs

photo-prompted

Social Networkschildren – peer harassment and rejection

Problem with BMI?

• Classification by Body Mass Index (BMI)• obese > 30 kg/m2

• overweight > 25 kg/m2

– May not apply to all ages and shapes

• Waist & waist:hip ratio– Alert –

• Men > 94 cm (37 in), WHR > 0.95• Women > 80 cm (32 in), WHR > 0.8

– Action – • Men > 102 cm (40 in)• Women > 88 cm (35 in)

Apple or Pear? Vague (1947)

Distinct Depots of Fat

10 60

% fat

VA

T (

area

, cm

2 )250

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20 30 40 50

150

♀

♂

Men have more visceral fat

Racial Differences too…

Lancet, 2003

% fat and VISCERAL FAT also higher per BMI in Caucasian men, African American women and both genders of Asian’s and Indians

Abdominal Adiposity

Visceral fat is independently linked with heart disease

Obesity and Coronary Artery Disease

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Donahue RP, Lancet 1987;1(8537):821-4Donahue RP, Lancet 1987;1(8537):821-4 Honolulu Heart Study: 7692 men, 12 yr follow-up

Visceral Fat and Glucose Intolerance

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Upper Body Obesity

Lower Body Obesity

Controls

Despres et al (1995) Int J Obes 19; S76

Visceral/Subcutaneous

• Fat distribution– gluteo-femoral fat – no problems– abdominal viscera - diabetes & coronary artery

disease. • independent of age, overall obesity or the amount of

subcutaneous fat.

• New definition of obesity? – based on the anatomical location of fat rather than

on its volume,

• Metabolic Obesity– visceral fat accumulation in either lean or obese

individuals

The Old (!!) view Adipose as Connective Tissue

• “The individual cells fill up with fat and the cytoplasm and the nucleus are pressed to the edge of each cell membrane.”

• “Adipose can be found under the skin, on the heart, and around the kidneys. It serves to protect, insulate, and store fat.”

Metabolic Warehouse?

Uptake of Fat after a meal

Synthesis of Fat in response to insulin

Releasing fatty acids into the bloodstream during starvation and exercise

Very dynamic – huge fluxes after meals & during starvation

Adipocyte size is very flexible

Obesity - Metabolic InflexibilityF

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elea

se (

nmol

/ml/m

in)

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Time after meal (min)

Meal (100 g carbohydrate)

normal

obese

Activity of Visceral fat in fasted subjects

Obese vs. normal

• Less suppression after meal• Continual release even when fed• Less release during fasting

NEFA Control

• Fatty acid buffering is reduced in obesity– Overspills into the other tissues– inappropriate accumulation of fat in muscles

and liver– leading to insulin resistance and steatosis

• Visceral fat especially good at releasing NEFA– Into portal circulation so to liver first– especial effect on glucose and VLDL output

New viewLargest Endocrine Organ!!

Adipocytes

Leptin

Fat Storage

Energy Intake Metabolic Rate

Hypothalamus

Leptin Receptors

LIPOSTATADIPOSTAT

Early Enthusiasm for Leptin

Before AfterPeople without leptin are hyperphagic

..and they respond to leptin injections

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Leptin

So could leptin injections be the ‘cure’ for obesity?

Leptin and Obesity

• Obese people higher blood [leptin] – More and bigger WAT cells– Leptin higher in women– Sex hormone interactions

• Extra leptin is ineffective– leptin-resistant… why?– Small changes in leptin

may not be meaningful• Rather than a excess of

leptin telling us to stop eating, a lack of leptin may tells us to start eating

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eptin

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Adipokines – molecules secreted by adipose tissue

• Leptin receptors are like cytokine receptors– Adipocytokines… Adipokines

• Many more discovered!– Affecting more than just appetite and

metabolic rate– Over 50 known protein and signal molecules

Lots of Adipokines

angiotensin

BLOOD PRESSUREleptin

APPETITELIPID METABOLISM

Cholesterol ester transfer protein

complement proteins (adipsin)

IMMUNITY

adiponectinresistinvisfatin

INSULIN SENSITIVITY

PAI-I (plasminogen activator inhibitor-I)

HEMOSTASISTNF-αInterleukin-6

C-reactive protein

INFLAMMATORY CYTOKINES

VEGF

ANGIOGENESIS

CELL ADHESIONintercellular adhesion

molecule -1

WAT is not all Adipocytes

• Other cells comprise adipose tissue– stromal-vascular cells– pre-adipocytes (stem cells)– macrophages

• Macrophages also secrete a range of cytokines– So the adipokines coming

from WAT may not always be adipocyte-derived

– Resistin best example• rodents in adipocytes,

macrophages in humans

Obesity as Inflammation

• Big fat cells and big fat pads produce large amounts of adipokines– except adiponectin

• adiponectin produced by small fat cells

• As fat stores get bigger– increased mix of inflammatory cytokines– increased blood coagulation potential– increased blood pressure

• WAT is potentially the BIGGEST endocrine organ!– Affecting many tissues and homeostatic processes

Adipokines of Interest

• Inflammatory cytokines – the link between adiposity and heart disease?

• Interleukin-6 – high in obese. More from visceral.• Plasminogen activator inhibitor 1 (PAI-1) – high in obese• C-reactive protein - liver and also in adipose tissue

• Adipokines that affect insulin sensitivity – the link between adiposity and Type II diabetes?

• TNF-α – insulin resistance in muscle (IRS interference)• visfatin – produced by visceral fat• adiponectin – produced by small adipocytes

• Inflammatory and resistance markers especially raised in VISCERAL ‘obesity’– but cause or effect?

Macrophages

• 10% of cells in WAT– Much higher in obese fat pads– More “activated” in obese– Even fuse to form giant – multinuclear cells

• Source?– Stem cells in WAT can become macrophages– But likely to be trapped by increased local expression

of ICAM-1• Macrophages really similar to adipocytes

– Both can carry fat (remember foam cells)• May be there to mop up fat from large, burst cells

Average adipocyte area (µm2)

% m

acro

phag

es

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Dying Fat Cells

Macrophages (green)Cluster around fat cell

Macrophage Infiltration

Not all adipokines are proteins…

• Cell 134, 933–944, September 19, 2008

Systemic lipid profiling also led to identification of C16:1n7-palmitoleate as an adipose tissue-derived lipid hormone that strongly stimulates muscle insulin action and suppresses hepatosteatosis.

WAT affects other tissues

• WAT is the most insulin sensitive tissue– Although total responsiveness is not great– Metabolically relatively inactive – Glucose disposal slow in comparison to muscle– Low contribution to glucose disposal on a whole body

basis• BUT fatty acid and adipokine release affects

insulin action in other tissues• Even in normal weight people, WAT can be

25% of body weight– Can range from 3% (male elite athlete) to 70% (very

obese)

Examples

• Anti-diabetic thiazolidinedione drugs– increase insulin sensitivity in WAT– Change the adipokine profile– Increase production of new fat cells which

produce adiponectin

• Knockout of GLUT-4 in WAT– Widespread insulin resistance in muscle and

liver– Even though WAT size unaffected

Effects of WAT loss

• Lipodystrophy– Lack of adipose tissue

• Accompanied by – Insulin resistance– Type II diabetes– Dyslipidemia (high triglycerides, low HDL)– Hepatic and muscle fat accumulation

• Hepatic steatosis and cirrhosis

– Some sexual abnormalities• Lack of ovulation, infertility• Excess of male hormones hirsuitism

Lipodystrophies

• Inherited– Defects in genes that control adipocyte development

• Acquired– HIV patients receiving protease inhibitors

• >100,000 protease-induced lipodystrophies in USA• Impairment of adipocyte differentiation• But only in some depots

– Loss of subcutaneous fat in face, arms, legs

– Others depots compensate

– Exaggerated shapes (eg, thin, drawn face, very wide hips)

– Sleep apnoea after HIV treatment• International Journal of STD & AIDS 2006; 17: 614–620

Transplantation

• Removal of fat from one site– Compensatory increase in size of other depots– Dynamic

• In hibernating animals or animals in which fat is laid down ‘seasonally’ the “correct” level of fat is re-made

• Grafting experiments– Pads grafted are not ‘noticed’ by the animal

• No compensatory changes – not ‘lipostatically’ active

– UNLESS…• Donor pads are grafted touching another pad… • Implies paracrine interactions between the pads

Whole Body Effects

• Transplant WAT into lipoatrophic animals– Restores glucose tolerance– But the transplanted fat has to be good “quality”

• Small, active adipocytes good• Triglyceride laden, old adipocytes do not help

• Transplantation of young, insulin sensitive adipocytes into insulin resistant animals– Restores glucose tolerance

• Subcutaneous/visceral transplants– Show depots are intrinsically distinct – More subcutaneous improves insulin sensitivity

Does fat cell number change?

• Nature 2008 June 5; 453(7196) p783-7

The number of fat cells stays constant in adulthood in lean and obese individuals, even after marked weight loss.

The number of adipocytes is set during childhood and adolescence.

Approximately 10% of fat cells are renewed annually at all adult ages and levels of BMI.

obese

lean

Spalding, 2008 Nature

Hyperplasia and Hypertrophy

weight gain

weight loss

regain

even with 6 months calorie restriction, no apoptosis

larger potential for fat deposition?

adipocytes

HYPERTROPHY

cell number constant

HYPERPLASIA??

Stages of Weight Gain

• Involves both hyperplasia and hypertrophy– Hypertrophy occurs first– Then pre-adipocytes proliferate– Then differentiation into new adipocytes– NB. Large adipocytes secrete factors which initiate

differentiation

• Specific depots have different types of growth– Some evidence that visceral fat cells may get larger– … whereas subcutaneous may proliferate more

Fat Cell Size

• Large cells– Increased secretion of inflammatory adipokines

• Young, small cells– Increased secretion of adiponectin

• Small cells that used to be big?• Hypoxic fat cells

– Poor blood supply to extremities in fat pads– Inflammatory adipokine profile– E.g., CCL5

Current Research

• Study fat cells as they change their size• Techniques

– Microarrays to study gene expression– Proteomics to study protein changes

• Models– Cell culture

• Problem with lifespan

– Isolated adipocytes… from different depots• Fractionate into large/small

– Whole animal - diets• Difficult to distinguish effects of diet from effects of changing cell

size• Cell size macrophage accumulation adipokines

Serendipity…

Our colleagues in Pharmacology were looking at the ability of adipose tissue to take up and release THC

tetrahydrocannabinol

Vehicle control

THC does NOT cause weight gain

BUT…….

Adipocytes much larger!

And more macrophages…

What’s Happening?

• No increased caloric intake

• Larger, fewer cells

• Repackaging?– Fat from dying cells redistributed?– Would expect to see re-esterification of fat– This requires glycerol 3-phosphate

PEPCK vital in glyceroneogenesis

Over-expression causes more fat accumulation

THC increases PEPCK

Gene Expression changes with THC treatment

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Therapy in Australia

• Diet and Lifestyle

• Drugs

• Bariatric Surgery

Lifestyle Managementdiet and physical activity

• How much weight loss is appropriate to aim for?• ‘ideal’ weight probably unachievable

– MAINTAIN (don’t put on more)• this may be the best option

– LOSE 5-10%• even this results in 20% less mortality, 10 mmHg

drop in blood pressure, 15% lowering of lipids/cholesterol, etc

Dietary Therapy for Obesity: An Emperor With No Clothes Hypertension. June 2008;51:1426-1434

“In an era when we pride ourselves on practicing evidence-based medicine, why then does dietary and behavioral therapy still reign?”

“Over 5 decades, it has been demonstrated repeatedly that dietary therapy fails…”

Why bother with lifestyle?

• General pessimism regarding ability to maintain reduced weight with lifestyle changes alone

• US NHANES study – 1310 people who lost 10% BW– 60% maintained weight loss at 1 yr

• Factors predicting weight maintenance– Close monitoring of food intake– Regular exercise– Regular monitoring of weight

Voelker R 2007, JAMA V298, pp 272-3Voelker R 2007, JAMA V298, pp 272-3

Bariatric Surgery

• Manipulation of the Digestive system– Malabsorbtive

• shorten the digestive tract• by-pass the small intestine or parts of it

– Restrictive• reduce the size of the stomach

http://www.bariatricsurgeons.com/options.htm

Banding

Laproscopic adjustable gastric band (LAGB)

Minimally invasive

Adjustable (even reversible)

O’Brien & Dixon (2006) in Clinical Obesity, Kopelman et al

Small Bowel By-Pass

O’Brien & Dixon (2006) in Clinical Obesity, Kopelman et al

Stapling & Biliopancreatic By-Pass

O’Brien & Dixon (2006) in Clinical Obesity, Kopelman et al

Still 250 ml stomach

Banding

• Convenient– 35 min operation– Inexpensive, Not permanent

• Safe – 0.05% deaths– Late complications common (15%)

• Slippage, infection, stomach erosion, leakage

• Relatively slow weight loss– But >50% excess weight (EW) loss over 2 years

• Some lose 120% EW

– But easy to ‘cheat’

Roux en Y (Gastric Bypass)

• Small stomach, less digestive juice– Restriction and malabsorbtion

• 80% excessive weight loss• Stop diabetic medication

– 85% cure from Type II diabetes– IN TWO DAYS!!!!– “Metabolic Surgeons”

• All other obesity related problems affected– Angina, hypertension, sleep apnoeas, arthiritis

• Skin excess a big disadvantage– Also hair thinning, gall stones

• 90 min operation, 0.5% deaths– Cutting and joining… Leak 2% – Cheating still possible if force stomach to stretch!

Diabetes Reversal

• Very rapid– Within a few days– Even before any significant weight loss– Same applies to sleep apnoea

• Mechanism?– Food-gut interactions affecting incretin

secretion?– Intestinal gluconeogenesis appears to be key

• Cell Metab 2008 Sep 8(3):201-11

– But still not clear how the communication works

N Eng J Med 357;8 (2007)

Sustained Weight Loss

N Eng J Med 357;8 (2007)

Short vs Long term costs?

Costs of Surgery soon Recouped

• Diabetes Care 2009;32:567-574 and 580-584.

• Randomised controlled study in Melbourne• Looking at Type 2 diabetes in obese patients

– Surgery vs drug/diet interventions

• Surgically induced weight loss is cost-effective relative to conventional therapy – in the short term (2 years)– projected over a patient's lifetime

Bariatric Surgery in Australia

• 1996 frequency was 1.2 per 100,000– In 2006 it was 36 per 100,000

• In 2008 12,000 banding operations performed• Many see as the ONLY option

– Ensures compliance– Reversal of diabetes

• Can we persevere with lifestyle therapy?• Surely this can’t be the answer….

– And would we recommend it for children?!