BIOKIMIA OBESITAS

ANNISA HANIFWATI

• Referensi :- Clinical Biochemistry review Vol 25, Aug 2004- Textbook of Biochemistry Illustrated Review

Fifth edition, Lippincott’s 2010- Biochemistry of Leptin, Shaliana, National Dairy

Research India- The Biochemistry of Obesity, Rick Voake MD- Medical Biochemistry 4th ed,2002,NV Bhagavan

• THE CLINICAL BIOCHEMISTRY OF OBESITY

ABSTRACT OBESITY:

- RESULT OF EXCESSIVE ENERGY INTAKE COMPARE TO ENERGY USAGE ( DECREASED PHYSICAL ACTIVITY)

- PHYSICAL CONSEQUENCES OF OBESITY : ARTHRITIS, INSULIN RESISTANCE, DIABETES, FATTY LIVER, CAD, HYPERTENSION, PCOS

- PATOPHYSIOLOGICAL MECHANISME : COMBINATION OF TOXIC METABOLIC EFFECTS OF FFA & ADIPOKINES

• INTRODUCTIONOBESITY : INCREASED ADIPOSE TISSUE MASSADIPOSE TISSUE :- STORAGE TISSUE FOR TRIACYLGLICEROL- AN ENDOKRIN ORGAN, RELEASING ADIPOKINES

. DEFINITION OBESITASWHO GUIDELINE 1985: BMI>25 : OVERWEIGHT

>28,5 : OBESE (WOMEN) >30 : OBESE (MEN)

BMI: calculated as weight (kg) divided by height squared (m2)

• ACQUIRES CAUSE OF OBESITY- CHILDREN : INCREASED ENERGY INTAKE (SUGAR), DECREASED PHYSICAL

ACTIVITY- CUSHING SYNDROME : TRUNCAL / VISCERAL OBESITY- HYPOTHYROIDISME : RARE CASE OF OBESITY, WEIGHT GAIN IS DUE TO

WATER RETTENTION, WHICH IS REVERSIBLE AFTER THYROID HORMON THERAPY

- NORMALLY :SIGNAL FROM THE GUT & ADIPOSE TISSUE ARE INTEGRATED IN HTE CNS TO AFFECTS APPETITE & ENERGY HOMEOSTASIS & LIMIT WEIGHT GAIN

- PATHOLOGICAL OBESITY:FAILURE OF HOEMOSTATIC MECHANISME

• GENETIC CAUSE OF OBESITY- THRIFTY GENE HYPOTHESIS : CERTAIN POPULATIONS MAY HAVE GENES

THAT DETERMINE INCREASED FAT STORAGE, IN A MODERN ENVIRONMENT RESULT IN OBESITY & DM TYPE 2

- SINDROMA PRADER-WILLI, SINDROM ANGELMAN, SINDROM WILSON-TURNER

. LEPTIN ASSOCIATED GENES- LEPTIN SECRETED FROM ADIPOCYTES INTO THE CIRCULATION TRANVERSE

INTO THE CNS- BINDS TO LEPTIN RECEPTOR IN HIPOTALAMUS- LEPTIN STIMULATES PRODUCTION OF ALFA MSH & ACTH. MSH BIND TO

MELANOCORTIN RESEPTOR IN HIPOTALAMUS, CAUSE DECREASE FOOD INTAKE

- MUTATION OF SISTEM ( LEPTIN, RESEPTOR, MSH), CAUSE OBESITY (RARE/ UNCOMMON)

- OBESITY : USUALLY HIGH LEPTIN, BUT LEPTIN RESISTEN, CAUSE DEFICIENCY LEPTIN

. OBESITY & INSULIN RESISTANCE :- OBESITY & DM TYPE 2: INSULIN RESISTEN- DM TYPE 2 : OVERWEIGHT, OBESE > 90%- PREECED THE ONSET DM TYPE 2: WEIGHT GAIN & INSULIN RESISTEDM- CURRENT THEORIES : DM TYPE 2 DEVELOP WHEN PANCREATIC BETA CELL

OUTPUT CAN NO LONGER SATISFY THE DEMAND, IMPOSED BY INCREASED INSULIN RESISTEN

• FFA PARADIGMA LINKING OBESITY TO INSULIN RESISTANCE- ELEVATED CELLULER LEVEL OF FFA : PRODUCE INSULIN, RESISTANCE IN SKELETAL

MUSCLE&LIVER, REDUCE BETA CELL FUNCTION, CAUSE LIPOTOXICITY

. CAUSATIVE FACTOR INVOLVED IN HEPATIC INSULIN RESISTANCE :- HEPATIC FFA- TRIGLYCERIDE ACCUMULATION

. INSULIN RESISTENT MUSCLE CHARACTERISED BY :- LOWERED ABILITY TO OXIDISE FFA

.

• IMBALANCE BETWEEN FFA UPTAKE- OXIDASI- PROMOTING ACCUMULATION OF LIPID & TRIACYLGLYCEROL IN SKELETAL

MUSCLE, CAUSE INSULIN RESISTANCE

. FFA : - BLOCK INSULIN SIGNALLING PATHWAY - LEAD INSULIN RESISTEN

. ADIPOKINE PARADIGMA LINGKING OBESITY TO INSULIN RESISTAN- ADIPOSE TISSUE : AN ENDOKRINE ORGAN- ADIPOKINES : ADIPOSE TISSUE-DERIVED HORMONES&INFLAMMATORY

CYTOKIN- DYSFUNCTION OF ADIPOSE TISSUE CAUSING SYSTEMIC INSULIN RESISTEN

• LEPTIN- DISCOVERD IN 1994- LEPTIN : DECREASE NEUROPEPTIDE Y IN HIPOTALAMUS, SHOULD

SUPPRESS APPETITE- LEPTIN PRODUCE BY ADIPOSE TISSUE, PLACENTA, BONE MARROW,

SOMACH, MUSCLE, BRAIN

Theodor Hanekamp © 2003 14

LeptinLeptin: • encoded by the OB (obese gene)• protein is 167 amino acid residues long• generated mainly in adipose tissue• messenger “reduce fuel intake”• increases heart rate, blood pressure, thermogenesis• acts on leptin receptors

Leptin receptor• encoded by the DB (diabetic gene) in mice• located mainly in the hypothalamus• also expressed in cells of the adrenal cortex & beta-cells• binding of hormone to receptor reduces appetite

Theodor Hanekamp © 2003 15

Leptin deficient mice

Leptin –deficient homozygous mice (ob gene)• behave like mice that are constantly starving • are 3 times bigger than normal• can’t stay warm• resemble diabetic mice(DB)• are insulin-resistant• db/db mice are obese and diabetic

ob/ob

OB/ob or OB/OB

Theodor Hanekamp © 2003 16

Leptin cascadeAppetite suppressing

neuropeptides( -MSH) -melanocyte-stimulating

hormone (POMC)Proopiomelanocortin (CRH) Corticotropin –releasing hormone (CART) Hypothalamic peptide

Appetite stimluating neuropeptides

(NPY) Neuropeptide Y

BIOCHEMICAL MEDIATOR OF OBESITY

BIOCHEMICAL MEDIATOR OF OBESITY

The regulation of intake & expenditure is achieved by coordinating the effect of endocrine mediators & neural signal that arise from adipose tissue, endocrine gland, neurological & gastrointestin system. All of the information finally is integrated by the CNS

• One of the most significant mediator of the energy store in the adipose tissue is leptin (from the Greek), leptin meaning thin. Leptin is a protein of 167 amino acid residues that is synthesized in adipocytes. Its syntesis is increased by insulin, glucocorticoid, &estrogen & is decreased by beta adrenergic agent. The role of leptin in obesity comes from studies in rodent.

• In genetically obese mice (ob/ob) the observed gross obesity is due to abscense of leptin production in adipocytes. Leptin action on energy metabolisme is mediated by receptor in many cells and it bind spesifically to a receptor in the hypotalamus.

• The action of leptin involves at least 2 pathways.

• During starvation &weight loss, adipose tissue is decreased, low level of leptin. Low leptin leads to production of neuropeptide Y, which is syntesized in the arcuate nuclues of hypotalamus & transported axonally to the paraventricular nucleus. Neuropeptide Y binds to its reseptor & functions as a potent appetite stimulant.The effect is increased appetite, decrease energy expenditure, increase parasympathetic activity

• An opposite, when the leptin level rise, mediated by melanocyte-stimulating hormon (MSH), that bind melanocortin 4 receptor (MC4R). MSH binding to MCR4 initiates biological response: decrease appetite, increase energy expenditure & increase symphatetic activity

• Most obese human, plasma level of leptin are high due to excess adipose tissue. Inspite of abundant leptin, there is continued overeating

• Inheritage obese disorder : hyperphagia lead obesity, hypogonadisme, mental retardation (Willi Prader syndrom, 1 of 10.000-20.000 birth). Delete in chromosom 15

• THE BIOCHEMISTRY OF OBESITY

The Hypothalamic-Leptin Axis• Feedback system• Allows the fat cells to tell the brain to quit

seeking more food when too much fat is present.

• Allows the brain to adjust the metabolic rate to control energy use.

Lustig, Ped Annals, 35:12 Dec 2006

Physiological effects of LeptinRegulation of food intake ,energy expenditure and body weight .Thermogenesis .Reproductive function .Supressed bone formation .Directly act on the cells of liver and muscles .Related to inflammatory response .Contribute to early hematopoiesis.

The Hypothalamic-Leptin AxisHow it works:

• When excess fat builds up in the fat cell, leptin is produced and enters the bloodstream.

• Leptin receptors in the hypothalamus are triggered.

• This shifts the hypothalamus into “Spend Energy” mode.

• Leptin changes SLOWLY (days to weeks)

Lustig, Ped Annals, 35:12 Dec 2006

“Spend Energy” Mode• Appetite reduction (Don’t

need to waste time looking for more food)

• Increase sympathetic tone to skeletal muscle increasing ATP and mitochondrial proteins (Muscles are prepared to function optimally)

Lustig, Ped Annals, 35:12 Dec 2006

• Increase TSH to increase thyroid output and increase baseline energy expenditure

• Beta-adrenergic stimulus to fat cells increases lypolysis (Break out stored energy for immediate use)

“Conserve Energy” ModeAppetite increases (Need

to seek more food for energy)

Decrease sympathetic and increase vagal tone to slow down muscle function

Increase fat absorption by fat cells

Lustig, Ped Annals, 35:12 Dec 2006

Vagus increases peristalsis and insulin production (for food processing)

Vagus nerve also slows heart rate and myocardial oxygen consumption

What if leptin feedback is blocked?Hypothalamus is tricked into thinking that

there is no leptin being released from fat cells.It then sends Orexin-A all over your brain,

making you think you are starving.The hypothalamus is stuck in “conserve

energy” mode, increasing appetite, slowing down metabolic rate, increasing fat storage.

Your brain is constantly “starving” even though the fat cells are busting at the seams!

Orexin-A (hypocretin-1)• Small peptide hormone released by the

hypothalamus to act on the rest of the brain.• It signals hunger, after the hypothalmus is

stimulated by ghrelin from the stomach• It also signals wakefulness, so that your brain

stays awake long enough to seek food, and not to hibernate!

• Another reason obese children don’t sleep well

Energy in = Energy out ???• Obese children are “leptin resistant” (leptin

receptors are blocked)• They are stuck in “Conserve Energy” mode• Their brains are starving, so they are

constantly seeking more food• Yet very little of that energy is available for

activity, since it is routed away into the fat cells.

What blocks leptin?• Brain damage to the leptin receptor area: hypothalamic

obesity syndrome• Insulin excess blocks leptin receptors• (Fructose is what leads to insulin excess)

Lustig, Ped Annals, 35:12 Dec 2006

What blocks leptin?• Brain damage to the leptin receptor area: hypothalamic

obesity syndrome• Insulin excess blocks leptin receptors• (Fructose is what leads to insulin excess)

Lustig, Ped Annals, 35:12 Dec 2006

Insulin excess blocks leptin

Lustig, Ped Annals, 35:12 Dec 2006

Insulin excess blocks leptin• Insulin receptors in the brain share the same

substrate as leptin receptors• When there is excess insulin, it hogs all the

substrate, leaving none for leptin to use.• Leptin attaches to the receptor, but nothing

happens.

In the hyperinsulin state

• Even high levels of leptin have no effect on the hypothalamus

• Known as “leptin resistance”• Occurs in a large percentage of overweight

children and adults

• CAUSA HYPERINSULINEMIA :- HIGH FAT DIET- LOW FIBER DIET- SLEEP DEPRIVATION- HIGH FRUCTOSA

Fructose:A major cause of hyperinsulinemia

• Fructose is absorbed from the intestine and enters the liver without insulin regulation, AND it does not suppress ghrelin (hunger hormone).

• It is then converted into acetyl-CoA, which floods the Kreb cycle, forcing excess production of FFA, triglycerides and VLDL lipoproteins.

Review:

What fructose becomes in your liver• FFA (free fatty acids, the building blocks of all

lipids)• VLDL lipoproteins and triglycerides (the nasty

lipids most associated with cardio- vascular disease)

• Uric acid (oxidative stress, vascular inflammation)

Fiber is also a factor

• Fiber adds bulk to foods, so the stomach turns off ghrelin sooner

• Fiber slows absorption of sugar in the gut• Fiber binds to bile acids, reducing fat

absorption from the gut • Fruits and veggies are a good source

Fructose:A major cause of hyperinsulinemia

• All this excess fat production leads to fatty liver which causes hepatic insulin resistance

• Fructose also activates the enzyme jnk-1 which causes hepatic inflammation, and more insulin resistance

• Faulty feedback to the liver results in massive insulin production, leptin resistance, and obesity

Fiber is also a factor

• Fiber adds bulk to foods, so the stomach turns off ghrelin sooner

• Fiber slows absorption of sugar in the gut• Fiber binds to bile acids, reducing fat

absorption from the gut • Fruits and veggies are a good source

Other symptoms of fructose poisoning• Diabetes (hyperinsulin state, insulin resistance)• Cardiovascular disease • Hypertension (renovascular damage)• Fatty liver • Hyperlipidemia• Increased BMI from excess lipid stored in fat cellsSound familiar?

Metabolic Syndrome = Fructose Poisoning

• With higher BMI, other symptoms can evolve• PCOS (polycystic ovary syndrome)• Acanthosis nigricans• Diabetic complications• Elevated CRP, endothelial damage

• BIOCHEMISTRY OF LEPTIN

How leptin works ?

Role of leptin in regulation of food intake and body weight

Decrease hunger and food consumption - inhibition of neuropeptide Y synthesis .

Food intake linked to its ability to regulate the neuroendocrine system .

Neuropeptide Y36 a.a residue produce in the arcuate nucleus of the hypothalamus . Rich in tyrosine residues .

Appetite stimulating hypothalamic peptide

Contd.Found in many organ, high level of NPY are found in brainstem and hypothalamus .

Stimulates leptin production in adipose tissue by increasing food intake and insulin secretion.

Action through the parasympathetic nervous system.

Role of leptin in lipid metabolismInhibits intracellular lipid concentration

Activate 5 –AMP-activated protein kinase (AMPK) Inhibits acetyl coenzyme-A carboxylase (ACC)

Increase in fatty acid oxidation and reducing the fat tissue in muscles and liver

.Increase insulin sensitivity .

Inducers and suppressers of leptin expression Inducers Effect Species

Feeding + Rodent + man

Glucocorticoids + Rodent + man

Insulin + Rodent

C or + Man

Cytokines + Rodent

Obesity + Rodent + man

Fasting - Rodent + man

Pertussis toxin - Rodent

-receptor antagonists - Rodent

Thiazolidinediones - Rodent

cAMP - Rodent

Feedback loop• Food intake trigger the output of glucocorticoids and

insulin

• Favour fat accumulation & increase leptin

• Leptin travels to hypothalamus

• Regulate body mass & control body energy intake , energy expenditure

• NPY also regulate body fat mass

Obesity• Main focus of leptin research.

• Dramatic effects on obesity in mice.

• In human a body mass index over 27.3 for man & 27.8 for women.

• Hypothalamic insensitivity to leptin – fundamental mechanism of obesity.

Leptin resistance

Mutation of the gene for leptin receptors in the brain

Post receptor abnormalities in leptin signal transduction

Impaired leptin transport across blood- brain barrier

What about humans:• Human fat cells also manufacture leptin protein

(167 a.a )

Mutation in gene for leptin or its receptor are rarely found in obese people

High blood conc. leptin indicates leptin resistance

Extreme obesity in 5 members of two families that are homozygous for mutation in their leptin gene –like ob/ob mice.

Extreme obesity among three members of a family homozygous for mutation in leptin receptor gene-like db/db mice.

Only moderate obesity in people heterozygous for leptin gene.

Recombinant human leptin available.

The 16 september 1999 issue the New England Journal of Medicine reports- 9 year old girl homozygous for frame shift mutation leptin gene.

Contd.

Contd.

• Factor in obesity - -3 adrenoreceptor

• Defect contribute leptin resistance/leptin expression

• A paradox exists-comparison between mouse & human research cannot be made

Future prospects• More focus on leptin receptor & involvement

in leptin resistance

• Relation to reproduction

• Mechanisms involved in regulation of leptin