Glucose Regulation by Dr Sarma

download report

Transcript Glucose Regulation by Dr Sarma

www.drsarma.in

Glucose Homeostasis Counter Regulation Dr.Sarma.R.V.S.N

M.D., (Med) M.Sc., (Canada) Consultant Physician and Chest Specialist

BioEd Online

Glucose Equilibrium – A Wonder !!

Normal Blood Glucose

Fasting state : 60 to 100 mg%

Postprandial : 100 to 140 mg %

What keeps the blood glucose in such a narrow range?

Why are we not becoming hypoglycemic when we fast?

Why is our blood sugar not shooting up to very high levels after a rich meal ?

What are the regulatory and counter regulatory hormones ?

2

Glucose Equilibrium – A Wonder !!

Normal Blood Glucose

Fasting state : 60 to 100 mg%

  

Postprandial : 100 to 140 mg %

Let us grasp some of the fascinating

What keeps the blood glucose in such a narrow range?

answers !!

Why are we not becoming hypoglycemic when we fast?

Why is our blood sugar not shooting up to very high levels after a rich meal ?

What are the regulatory and counter regulatory hormones ?

3

Glucose Homeostasis Research Timeline

1552BC 1 st Century AD 1776 18 th Century 1869 1889 1921-23 1983 2001           

1552 BC: Ebers Papyrus in ancient Egypt. First known written description of diabetes.

1 st Century AD: Arateus — “Melting down of flesh and limbs into urine.” 1776: Matthew Dobson conducts experiments showing sugar in blood and urine of diabetics.

Mid 1800s: Claude Bernard studies the function of the pancreas and liver, and their roles in homeostasis.

1869: Paul Langerhans identifies cells of unknown function in the pancreas. These cells later are named “Islets of Langerhans.” 1889: Pancreatectomized dog develops fatal diabetes.

1921: Insulin “discovered” — effectively treated pancreatectomized dog.

1922: First human treated with insulin. Eli Lilly begins mass production.

1923: Banting and Macleod win Nobel Prize for work with insulin.

1983: Biosynthetic insulin produced.

2001: Human genome sequence completed.

4

Cell growth and energy metabolism

Carbohydrates Glucose Pyruvate Fatty acids Fats Amino acids TCA Cycle Kreb’s Cycle Proteins ATP 5

Intermediary Metabolism of Fuels 6

Intermediary Metabolism of Fuels Clinical Pearl 1. All the fuels are inter changeable in the body 2. It is the total calorie restriction that is important in Obesity and T2D 7

Glucose-6-Phosphate – The Central Molecule 8

Glucose-6-Phosphate – The Central Molecule Clinical Pearl G-6-Phosphate is the Center Stage for CHO Metabolism Glucose-6-Phosphate dehydrogenase (G6PD) is the crucial enzyme 9

Homeostasis of Glucose Counter Regulation Mechanisms

      A steady maintenance of blood glucose with in a narrow range Fasting state and fed states – their effects on BG Rate of glucose appearance R a Rate of disappearance R d must be in balance Blood Glucose (BG) = R a R d Control systems  Glucose Receptors, GLUT 1-14     Controlling Hormones, Insulin, Glucagon, Cortisol, Epinephrine etc., Insulin Signaling sequences, Glucagon signaling Effector Cells – Muscles, Liver, Brain, Heart and Adipose tissue Feedback loops   Negative feedback Positive feedback

10

Homeostasis of Glucose Counter Regulation Mechanisms

      A steady maintenance of blood glucose with in a narrow range Fasting state and fed states – their effects on BG Rate of glucose appearance R a Rate of disappearance R d

Clinical Pearl

a R d Control systems  Glucose Receptors, GLUT 1-14     Controlling Hormones, Insulin, Glucagon, Cortisol, Epinephrine etc., Insulin Signaling sequences, Glucagon signaling Effector Cells – Muscles, Liver, Brain, Heart and Adipose tissue Feedback loops   Negative feedback Positive feedback

11

Normal, Hyper and Hypoglycemic states Ra Ra is the rate of appearance of Glucose 100 mg Rd Rd is rate of disappearance of Glucose Ra 200 mg Rd Ra Ra > Rd; Ra 200 mg

or Rd When Ra = Rd; It is Euglycemic state Ra 50 50 Rd

m g Rd m g Rd Ra < Rd; Ra

or Rd

HYPERGLYCEMIA HYPOGLYCEMIA 12

Effect of CHO intake on Glucose Metabolism Gluconeogen esis Lipolysis Ra Glycogenoly sis GLUCAG ON Exogenous CHO Rd INSULIN 13

Glucose Homeostasis Lower Blood Glucose

 cells release Glucagon stimulate glycogen breakdown and gluconeogenesis

Food Higher Blood Glucose Between meals

 -cells release insulin stimulate glucose uptake by peripheral tissues

14

High blood glucose affects the size of beta cells 15

Pancreatic Hormones Pancreas

Exocrine Pancreas – P Lipase, P amylase etc

Endocrine Pancreas – Islets of Langerhans

Hormones secreted are –

Alpha cells – Glucagon

 

Beta cells – Insulin C cells - Somatostatin

  

D cells - Somatostatin E cells - ?? Function F cells - Pancreatic polypeptide (PPP) 16

Regulation of Blood Glucose levels

Glucose is the major source of energy for cells

Blood Glucose (BG) regulated by Insulin & Glucagon 17

18

Glucose Homeostasis Chart Condition High Blood Sugar

Toxic to the cells - AGP

Low Blood Sugar

Energy needs unmet

Receptor Glucose transporter Glucose transporter Control Center

-cell of the pancreas

-cell of the pancreas Effector Insulin Glucagon Result Glucose uptake by muscle/fat tissue Lowers blood glucose Liver breaks down glycogen to glucose Raises blood glucose 19

The Six Mechanisms of Transport - CM 2 1 3 6 5 4 20

Membrane Transport Proteins 21

Channel Proteins 22

Cell Membrane - Transporters 23

ATP Powered Receptors 24

Glucose Transport

FIRST STEP

GLUCOSE ABSORPTION IN THE GI TRACT

25

Intestinal Cell Transport 26

Intestinal Cell Transport Clinical Pearl New approach in T2D, MS and Obesity - GLUT-2 Blockers 27

The First Messengers from GI tract

THE MESSERGERS

INCRETINS – GLP1 and GIP_

28

Entero-Insular Axis of Secretion Insulin secretion is also increased

By intestinal polypeptide hormones

GLP-1 (glucagon like peptide) [exendin-4]

Glucose-dependent insulinotropic peptide(GIP)

GLP-1 and GIP are called Incretins

Cholecystokinin and by pancreatic Glucagon.

Insulin secretion is decreased by pancreatic somatostatin.

29

Entero-Insular Axis of Secretion Insulin secretion is also increased

By intestinal polypeptide hormones

Glucose-dependent insulinotropic peptide(GIP)

 

Cholecystokinin and by pancreatic Glucagon.

Insulin secretion is decreased by pancreatic somatostatin.

30

Response to Elevated Blood Glucose In the post prandial state (after a meal)

Remember there are two separate signaling events

First signal is from the ↑ Blood Glucose to pancreas

To stimulates insulin secretion in to the blood stream

The second signal from insulin to the target cells

Insulin signals to the muscle, adipose tissue and liver to permit to glucose in and to utilize glucose

This effectively lowers Blood Glucose 31

Response to Elevated Blood Glucose In the post prandial state (after a meal)

 

↑ Blood Glucose to pancreas

2. Secreted Insulin must trigger Glucose uptake –

Second signal The second signal from insulin to the target cells

3. T2D may result from failure of either or both to permit to glucose in and to utilize glucose

This effectively lowers Blood Glucose 32

Glucose induced Insulin secretion

Glucose enters the beta cells through uniporter GLUT 2

 

Oxidative phosphorylation ATP closes the ATP gated K + channel and depolarizes the cell membrane

 

Depolarization opens the voltage gated Ca + channels Ca + enters the beta cells

This leads to exocytosis of Insulin and secretion 33

Glucose induced Insulin secretion

Glucose enters the beta cells Closure of K ATP

Channels by Glucose is

Oxidative phosphorylation +

Depolarization opens the Insulin is necessary to let in glucose

Ca + enters the beta cells

This leads to exocytosis of Insulin and secretion 34

K + ATP Channel Closed by ↑ BG and SU 35

K + ATP Channel Closed by ↑ BG and SU Clinical Pearl 1. SU Group close K ATP Insulin Channels – Secrete 2. Differences in action of SU are because of the differences in their action on K ATP Channels 3. Gliclazide and Glimiperide just hit the SUR closure and stop 36

Intricacies in the Beta Cell 37

K + ATP – Sulfonylurea Receptor

  

K + ATP channel has two sub units – Kir6.2 and regulatory sulfonylurea receptor(SUR) ATP gated K + channel is coupled to SUR K + channel can be closed independently of glucose

This leads to increased insulin secretion

SUR1 are ATP binding transporters superfamily 38

K + ATP – Sulfonylurea Receptor

K + ATP channel has two sub closer of the SUR

ATP gated K + channel is Beta cells independently of glucose 3. This is the cause of late hypoglycemia with these

This leads to increased SUs

K + channel can be closed insulin secretion 4. Beta cell apoptosis sets in fast after a few years of

SUR1 are ATP binding use transporters superfamily 39

(F)PHHI

(Familial) Persistent Hyperinsulinemic Hypoglycemia of Infancy

Unregulated insulin secretion

Profound hypoglycemia and brain damage

Manifests at birth or at first year of life

Under diagnosed

Probably the cause of undiagnosed postnatal deaths

 

Defect is K ATP Channels mutation – Persistent closure with continuous trigger for Insulin release

Treatment is pancreatectomy – (95% of pancreas) 40

K + ATP Channel Opening is Cardio-protective 41

K + ATP Channel Opening is Cardio-protective Clinical Pearl 1. Glibenclamide, Tolbutamide close the SUR in myocardium 2. This effect is deleterious to heart in ischemia 42

Tyrosine Kinase Pathway - Insulin 43

Tyrosine Kinase Pathway - Insulin Clinical Pearl 1. Tyrosine Kinase (TK) phosphorylation is the fundamental step 2. Its failure stops further cascade of intracellular signals 3. This is one of the possible mechanisms of Insulin Resistance 4. PPAR- Gamma (Pioglitazone) enhances TK signaling pathway 44

Insulin Receptor (IR)

Insulin Receptor is a tyrosine kinase.

Consists of 2 units -dimerize when bound with insulin.

Inside cell - auto phosphorylation occurs,

Increasing tyrosine kinase activity.

Insulin Receptor phosphorylates intracellular signaling molecules.

Stimulates insertion of GLUT-4 proteins

which let in glucose

Stimulate glycogen, fat and protein synthesis.

45

Insulin + 3 HN S S S S -S-S NH 3 +  -subunits

EXTRACELLULAR

OOC + 3 HN S S S S COO NH 3 + Plasma membrane Tyrosine kinase domain OOC COO  -subunits Transmembrane domain

CYTOPLASM Figure 2.

The insulin receptor. Insulin binding to the  -chains transmits a signal through the transmembrane domain of the  -chains to activate

46

the tyrosine kinase activity

1 Extracellular

insulin binds

2

IRTK (L) activated IRTK (R)

3

phosphorylated/ activated OP OP L R

P P Cytoplasm P P

ADPs Phosphorylation catalyzed by IRTK (L)

Figure 3.

Activation of the tyrosine kinase domains of the insulin receptor by

47

insulin binding, followed by interchain autophosphorylation

1 Extracellular

insulin binds

2

IRTK (L) activated IRTK (R)

3

phosphorylated/ activated

4

IRTK (L) phosphorylated L

Cytoplasm

R ATPs OP OP

P P P P

PO ADPs ADPs OP OP Phosphorylation catalyzed by IRTK (L)

Figure 3.

Activation of the tyrosine kinase domains of the insulin receptor by

48

insulin binding, followed by interchain autophosphorylation

Insulin Signaling – TK Receptor phosphorylation Binding of insulin to the TK Receptor causes

Transphosphorylation of tyrosines on the receptor

Phosphotyrosine residues bind to

IRS-1 (insulin receptor substrate – adopter protein) 49

Insulin Receptor (IR)

A key regulator of growth signaling 

IR is hetero-tetramer

Insulin binding induces conformation change and stimulation of receptor Tyrosine kinase activity

IR auto-phosphorylates and phosphorylates downstream second messengers, like IRS (Insulin Receptor Substrate)

Obesity down regulation of IR

Diabetes up regulation of IR 50

Epidermal Growth Factor (EGF) Receptor

Auto-phosphorylation of TK (Obesity)

Receptor tyrosine kinases

The interaction of the external domain of a receptor tyrosine kinase with the ligand, often a growth factor, up regulates the enzymatic activity of the intra cellular catalytic domain, which causes tyrosine phosphorylation of cytoplasmic signaling molecules.

51

Epidermal Growth Factor (EGF) Receptor

Auto-phosphorylation of TK (Obesity)

Receptor tyrosine kinases 1. Up regulation of TK receptor signal Clinical Pearl

The interaction of the external domain of a receptor tyrosine kinase with the ligand, often a growth factor, up regulates the enzymatic

(autophosphorylation) in obesity 2. Leads to Glucose entry into cells with out insulin

tyrosine phosphorylation of cytoplasmic signaling molecules.

52

Insulin Signaling – PKB and MAPK pathways

Ras independent signaling – The PKB Signaling and

Ras dependent – The MAPK Signaling

Ras independent through activation of Protein Kinase B

Responsible for immediate non-genomic effects

Ras dependent – Activation of

Mitogen Activated Protein Kinase (MAPK) pathway

Responsible for genomic effects 53

Insulin Signaling – PKB and MAPK pathways 54

Insulin Signaling – PKB and MAPK pathways Clinical Pearl 1. Ras independent signaling cascade – PI3P – PKB 2. Ras dependent signaling cascade – MAP Kinase 55

Glucose Uniporter - GLUTs 56

Glucose Uniporter - GLUTs Clinical Pearl 1. Translocation of GLUT-4 to cell surface is crucial for Glu. uptake 2. Insulin resistance is usually due to failure of this step 57

Ras Independent – PI3K - PKB Signaling

IRS1 binds PI3 kinase through SH2 domain

This phosphorylates PIP2 to PIP3

Increased concentration of PIP3 recruits

PKB to the plasma membrane

PKB is phosphorylated by

two membrane associated kinases PKC λ and ξ

Active PKB is released into the cytosol

Where it translocates glucose transporter (GLUT-4)

GLUT-4 (uniporter) moves on to the membrane

GLUT-4 lets Glucose in and increases glucose uptake 58

PIP Signaling Pathway 59

Ras - Independent Insulin Signaling 60

Insulin and PI3K Signaling 61

Ras Independent Extracellular Space

= GLUT-4

Cytoplasm

Active IRTK  IRS tyr-OH ATP 

[1]

IRTK

Figure 5.

Mechanism for insulin to mobilize GLUT-4 transporter to the plasma membrane in muscle & adipose ADP  catalyzed IRS IRS  IRS  IRS  +  tyr-OP IRS  tyr-

OP

IRS tyr-OP PIP 3 tyr-OP tissue.

IRS

, insulin-receptor substrate;

IRTK,

insulin receptor tyrosine kinase;

PI-3K

, phosphatidyl-inositol kinase;

PDK

; phospholipid-dependent kinase

PKB

, protein kinase B PDK GOLGI PKB PO PO p85 PI 3K

[4] [2]

membrane OP OP activated by docking active IRS PIP 2 signals Golgi to traffic GLUT-4 to

62

Ras Dependent – MAPK Signaling At the same time…

Phosphorylated insulin receptor binds

to adapter protein SHC through GRB2

GRB2 also has SH3 domains that bind and activates Sos

Binding of Sos to inactive Ras causes a

conformational change that permits release of

GDP and binding of GTP (activation of Ras)

Sos is a GEF for monomeric G protein Ras

Sos dissociates from activated Ras

Linking insulin receptor to Ras 63

Ras - Dependent Insulin Signaling 64

Ras Dependent – MAPK Signaling

Activated Ras passes the signal to raf kinase

Raf activates a cascade of kinases (MAP Kinase cascade)

Mitogen Activated Protein Kinases (MAP Kinases)

Highly conserved kinase cascades

Last kinase in the cascade has to be double phosphorylated

It has high specificity (since it is double phosphorylation) 65

Ras Dependent

Glucose GLUT-4 Glucose transport (muscle/adipose)

Extracellular

PO PO OP OP Activated IRTK

Cytoplasm

metabolic responses Activation of protein phosphatase

Dephosphorylation of:

glycogen synthase glycogen phosphorylase phosphorylase kinase acetyl CoA carboxylase hormone-sensitive lipase phosphofructokinase-2 pyruvate kinase HMG CoA reductase regulatory kinases

Protein synthesis Cell growth and replication Signal transduction (e.g., phosphorylation of IRS, SHC, PLC)

KINASE CASCADE

(protein phosphorylation)

NUCLEUS

DNA synthesis mRNA synthesis mitogenic response

66

Ras Dependent – MAPK Signaling

MAPK regulates the activity of transcription factors

Active MAPK translocates to the nucleus

It phosphorylates several transcription factors

And production of more GLUT4 67

Glucose Entry in to the Cell

Insulin/GLUT4 is not the only pathway

Insulin-dependent, GLUT 4 - mediated

Cellular uptake of glucose into muscle and adipose tissue (40%)

Insulin-independent glucose disposal (60%)

GLUT 1 – 3 in the Brain, Placenta, Kidney

SGLT 1 and 2 (sodium glucose symporter)

Intestinal epithelium, Kidney 68

Fatty Acid Dysregulation impairs Insulin action 69

Fatty Acid Dysregulation impairs Insulin action

Clinical Pearl

1.Excess FFA – cause dysregulation of IR 2.GLUT-4 function is impaired – Insulin Resistance

70

Cyclic AMP Pathway - Glucagon

 Off switch  PDE inactivates cAMP  PDE stops signal transduction.

 Caffeine inhibits PDE!

71

Glucose controls Insulin and Glucagon release 72

Liver and Kidney

Major source of net endogenous glucose production

Accomplished by gluconeogenesis and glycogenolysis when glucose is low

And of glycogen synthesis when glucose is high.

Can oxidize glucose for energy and convert it to fat which can be incorporated into VLDL for transport.

73

Metabolic Effects of Insulin - in the Liver 74

Muscle

Can convert glucose to glycogen.

Can convert glucose to pyruvate through glycolysis further metabolized to lactate or transaminated to alanine or channeled into the TCA cycle.

In the fasting state, can utilize FA for fuel and mobilize amino acids by proteolysis for transport to the liver for gluconeogenesis.

Can break down glycogen

But cannot liberate free glucose into the circulation.

75

Metabolic Effects of Insulin - in the Muscle 76

Adipose Tissue (AKA fat)

Can store glucose by conversion to fatty acids and combine these with VLDL to make triglycerides.

In the fasting state can use fatty acids for fuel by beta oxidation.

77

Effects of Insulin - in the Adipose tissue 78

Metabolic Effects of Glucagon 79

Insulin – Anabolic and Glucagon - Catabolic

Metabolic Action Glycogen synthesis Glycolysis (energy release) Lipogenesis Protein synthesis Glycogenolysis Gluconeogenesis Lipolysis Ketogenesis Insulin ↑ ↑ ↑ ↑ ↓ ↓ ↓ ↓ Glucagon ↓ ↓ ↓ ↓ ↑ ↑ ↑ ↑

80

Glucose Uniporters - GLUTs

Transport can work in both directions

81

The GLUT – Glucose Transporters

14 transporters of Glucose are identified

Their genes are located and cloned

The function of some is yet under evaluation

Some genetic defects produce specific diseases like GLUT-1-DS

In breast and prostate cancer GLUT- 11 is hyper expressed and supplies the high needs of glucose to the cancer cells. – Anti GLUT – 11 drugs might be a therapeutic approach for these cancers.

82

The GLUT – Glucose Transporters

14 transporters of Glucose are identified

  

Their genes are located and cloned The function of some is yet under evaluation 1. GLUT -1 DS – a genetic disorder of Glucose metabolism GLUT-1-DS Clinical Pearl

2. Anti GLUT -11 drugs in breast & prostate Ca are underway expressed and supplies the high needs of glucose to the cancer cells. – Anti GLUT – 11 drugs might be a therapeutic approach for these cancers.

83

Glucose Transporter Proteins - GLUTs

GLUT - 1 - Responsible for feeding muscle during exercise (that is how exercise lowers blood glucose) Placenta, BB, RBC, Kidney and many tissues. Low in liver. Mainly “house keeping”

GLUT – 2 – Uniporter of glucose into the beta cells and stimulates insulin secretion. Beta cells of pancreas. Liver, small intestinal epithelium, Kidney. Has high Km (60 mM). Never saturates.

GLUT - 3 the tissues. Abundant in neuronal tissue, placenta and kidney. It feeds the high glucose requirement with out insulin.

– Insulin independent glucose disposal in to 84

Glucose Transporter Proteins - GLUTs

  

GLUT - 1 - Responsible for feeding muscle during Clinical Pearl Placenta, BB, RBC, Kidney and many tissues. Low in 1. The GLUT-3 Receptors are Insulin independent 2. In brain GLUT-3 mediate glucose uptake Liver, small intestinal epithelium, Kidney. Has high 3. In placenta also GLUT-3 mediate Glucose uptake 4. Foetal growth is not affected very much in IR insulin.

independent glucose disposal in to 85

Glucose Transporter Proteins – GLUTs contd..

GLUT – 4 – Insulin dependent – It is the main channel for glucose entry into cells. Muscle, Heart and adipose tissues depend on GLUT –4 for glucose entry in to cells

GLUT – 5 – Rich in small intestine and conduct absorption of dietary glucose and fructose transport. Mediate glucose for spermatogenesis

GLUT – 6 – Pseudo gene – Mediates none so far

GLUT – 7 – Only in liver endoplasmic reticulum and it conducts glucose back out – G6P transporter in ER

SGLT 1 and 2 - Sodium - Glucose symporter in the intestinal epithelium and renal tubular epithelium 86

Glucose Transporter Proteins – GLUTs contd..

 

GLUT – 4 – Insulin dependent – It is the main channel for glucose entry into cells. Muscle, Heart and adipose tissues depend on GLUT –4 for glucose entry in to cells GLUT – 5 – Rich in small intestine and conduct 1. GLUT-4 is main Glucose transporter in all tissues Clinical Pearl

 

Insulin conducts glucose back out – G6P transporter in ER

SGLT 1 and 2 - Sodium - Glucose symporter in the intestinal epithelium and renal tubular epithelium 87

Brain

Converts glucose to CO2 and H2O.

Can use ketones during starvation.

Is not capable of gluconeogenesis.

Has no glycogen stores.

88

Know Our Brain !!

Brain is the major glucose consumer

Consumes 120 to 150 g of glucose per day

Glucose is virtually the sole fuel for brain

Brain does not have any fuel stores like glycogen

Can’t metabolize fatty acids as fuel

Requires oxygen always to burn its glucose

Can not live on anaerobic pathways

One of most fastidious and voracious of all organs

Oxygen and glucose supply can not be interrupted 89

Know Our Brain !!

    

Brain is the major glucose consumer

   

Oxygen and glucose supply can not be interrupted 90

Second Signaling

Now Insulin that is secreted in to the blood starts the second signaling event

Insulin binds to the Insulin Receptors (IR) on the muscle and fat cells

Muscle and fat cells increase glucose uptake

This leads to lowering of blood glucose 91

Insulin – C peptide

Insulin is dimer of two peptides

Each peptide consists of A and B chains

A has 21 amino acids

B has 30 amino acids

2 chains are linked by pair of S – S bonds

C peptide has 35 amino acids and is cleaved 92

Insulin – C peptide

Insulin is dimer of two chains Clinical Pearl

peptides

Each peptide consists of 1. Insulin Analogs are substitutions of AA in α and ß A has 21 amino acids RAIA, LAIA B has 30 amino acids

2 chains are linked by pair of S – S bonds

C peptide has 35 amino acids and is cleaved 93

Preproinsulin – Proinsulin – Insulin 94

Preproinsulin – Proinsulin – Insulin Clinical Pearl 1. C – Peptide assay is simpler, less costly than Insulin assay 2. It is the surrogate for endogenous Insulin secretion 3. It is not affected by exogenously administered Insulin 4. It is not largely influenced by food intake 95

PPAR Family of Nuclear Receptors Peroxisome Proliferator Activated Receptors 96

PPAR Family of Nuclear Receptors Peroxisome Proliferator Activated Receptors Clinical Pearl 1. PPAR alpha are essential regulators of serum lipids 2. PPAR gamma are essential for Insulin Sensitivity 3. In Insulin Resistance the PPAR Gamma are inactivated 4. Glitazones enhance the PPAR Gamma activity 97

The Role of Pancreas Insulin

Hypoglycemic hormone

Beta cells of pancreas

Two chain polypeptide – Anabolic in nature

Receptor interactions

Intracellular interactions

Transporters

Clinical correlation 98

Insulin - Mechanism of action

Insulin binds to its trans-membrane receptor.

β subunits of the receptor become phosphorylated

Receptor has intrinsic tyrosine kinase activity.

Intracellular proteins are activated/inactivated—

IRS-1, IRS-2 and seven PI-3-kinases

GLUT-4, Transferrin, LDL-R, IGF-2-R move to the cell surface.

Cell membrane permeability increases:

Glucose, K+, amino acids, PO4 enter 99

Insulin Insulin Release

In a 24 hour period, 50% of the insulin secreted is basal and 50% is stimulated.

The main stimulator for secretion is glucose.

Amino acids also stimulate insulin release, especially lysine, arginine and leucine.

This effect is augmented by glucose.

100

Control of Insulin Secretion

Glucose interacts with the GLUT-2 transporter on the pancreatic beta cell.

Glucose enters the cell releases - hexokinase→ G-6-P

Increased metabolism of glucose → ATP →

Excess of ATP- blocks ATP dependent K channels →

Membrane depolarization →

↑ Cytosolic Ca++ →

This stimulates degranulation and

Releases ↑ insulin secretion.

101

Control of Insulin Secretion Insulin secretion is also increased by

Growth hormone (acromegaly)

Glucocorticoids (Cushings’)

Prolactin (lactation)

Placental lactogen (pregnancy)

Sex steroids 102

Regulation of Insulin Secretion Summary of feedback mechanism for regulation

blood glucose

↓ ↑

insulin

↓ ↑

transport of glucose into cells,

gluconeogenesis,

glycogenolysis

↓ ↓

blood glucose

↓ ↓

insulin 103

Role of Insulin Metabolic Effects of Insulin

Main effect is to promote storage of nutrients

Paracrine effects

Decreases Glucagon secretion

Carbohydrate metabolism

Lipid metabolism

Protein metabolism and growth 104

Role of Insulin Carbohydrate metabolism

Increases uptake of glucose

Promotes glycogen storage

Stimulates glucokinase

Inhibits gluconeogenesis

Inhibits hepatic glycogenolysis

Inactivates liver phophorylase 105

Sources of Glucose in to blood

Glucose is derived from 3 sources

Intestinal absorption of dietary carbohydrates

Glycogen breakdown in liver and in the kidney.

Only liver and kidney have glucose-6-phosphatase.

Liver stores 25-138 grams of glycogen, a 3 to 8 hour supply.

Gluconeogenesis, the formation of glucose from precursors

These include lactate and pyruvate, amino acids (alanine and glutamine), and to a lesser degree, from glycerol 106

Fasting State

Short fast

Utilizes free glucose (15-20%)

Break down of glycogen (75%)

Overnight fast

Glycogen breakdown (75%)

Gluconeogenesis (25%)

Prolonged fast

Only 10 grams or less of liver glycogen remains.

Gluconeogenesis becomes sole source of glucose

Muscle protein is degraded for amino acids.

Lipolysis generates ketones for additional fuel.

107

Role of Insulin Lipid Metabolism

Insulin promotes fatty acid synthesis

Stimulates formation of α-glycerol phosphate

α-glycerol phosphate + FA CoA = TG

TG are incorporated into VLDL and transported to adipose tissues for storage.

Insulin inhibits hormone-sensitive lipase,

Thus decreasing fat utilization.

108

Role of Insulin

Protein Metabolism and Growth

Increases transport of amino acids

increases mRNA translation and new Proteins,

A direct effect on ribosomes

Increases transcription of selected genes,

Especially enzymes for nutrient storage

Inhibits protein catabolism

Acts synergistically with growth hormone 109

Role of the Pancreas Lack of insulin

Occurs between meals, and in diabetes.

Transport of glucose and amino acids into the cells decreases, leading to hyperglycemia.

Hormone sensitive lipase is activated,

Causing TG hydrolysis and FFA release.

↑ FFA conversion in liver →

Phospholipids and cholesterol →

Lipoproteinemia,

FFA breakdown leads to ketosis and acidosis.

110

Insulin Resistance

Associated with obesity

Underlying metabolic defect in

Type 2 diabetes

Polycystic ovarian disease

Associated with

Hypertension, gout, high triglyceride

30% of general population 111

What causes insulin resistance?

Decreases in receptor concentration

Decreases in tyrosine kinase activity,

Changes in concentration and phosphorylation of IRS-1 and IRS-2,

Decreases in PI3-kinase activity,

Decreases in glucose transporter translocation,

Changes in the activity of intracellular enzymes.

112

What causes insulin resistance?

    

Decreases in receptor concentration Clinical Pearl

1. T2D is mostly a question of Insulin Resistance feature in T2D 113

The Role of Pancreas Other pancreatic hormones

Somatostatin

14 amino acid paracrine factor

Potent inhibitor of glucagon release

Stimili: glucose, arginine, GI hormones

It is anti GH (somatotrophin) in its actions

Pancreatic polypeptide

36 amino acids, secreted in response to food

Glucagon 114

Counter Regulatory Hormones

Early response

Glucagon

Epinephrine

Delayed response

Cortisol

Growth hormone 115

Counter Regulatory Hormones

Glucagon

 

Acts to increase blood glucose Secreted by alpha cells of the pancreas

 

Chemical structure 29 amino acids Derived from 160 aminoacid proglucagon precursor

GLP-1 (Glucagon Like Peptide -1)

The most potent known insulin Secretagogue

It is made in the intestine by alternative processing of the same precursor

Intracellular actions 116

Role of Glucagon

Metabolic Effects of Glucagon

Increases hepatic glycogenolysis

Increases gluconeogenesis

Increases amino acid transport

Increases fatty acid metabolism ( ketogenesis ) 117

Role of Glucagon

  

Increases hepatic glycogenolysis 1. Glucagon is the treatment for hypoglycemia

2. Glucagon Kit – 1 mg s/c or IM or IV injection

– ketogenesis ) 3. In 2 to 3 minutes recovery 4. Costs Rs. 400 per dose 118

Glucagon Secretion Stimulation of Glucagon secretion

Blood glucose < 70 mg/dL

High levels of circulating amino acids

Especially arginine and alanine

Sympathetic and parasympathetic stimulation

Catecholamines

Cholecystokinin, Gastrin and GIP

Glucocorticoids 119

Responses to decreasing Glucose levels

Response ↓ ↑ ↑ ↑ ↑ Insulin Glucagon Epinephrine Cortisol, GH Glycemic theshhold 80 - 85 mg% 65 - 70 mg% 65 - 70 mg% 65 - 70 mg% Food ingestion 50 - 55 mg% Physiological effects ↑ R a ↑ R ↑ R a a (↓ R d ) ↓ R d Role in counter regulation Primary First Defense Primary Second Defense Critical Third Defense Not Critical ↑ R a ↓ R d ↑ Exogenous Glucose < 50mg% no cognitive change

120

Role of Epinephrine Epinephrine

The second early response hyperglycemic hormone.

This effect is mediated through the hypothalamus in response to low blood glucose

Stimulation of sympathetic neurons causes release of epinephrine from adrenal medulla .

Epinephrine causes glycogen breakdown, gluconeogenesis, and glucose release from the liver.

It also stimulates glycolysis in muscle

Lipolysis in adipose tissue,

Decreases insulin secretion and

Increases glucagon secretion.

121

Role of Cortisol and GH

These are long term hyperglycemic hormones

Activation takes hours to days.

Cortisol and GH act to decrease glucose utilization in most cells of the body

Effects of these hormones are mediated through the CNS.

122

Cortisol

Cortisol is a steroid hormone

It is synthesized in the adrenal cortex.

Synthesis is regulated via the hypothalamus (CRF) and anterior pituitary (ACTH).

Clinical correlation: Cushing’s Disease 123

Growth Hormone (GH)

GH is a single chain polypeptide hormone.

Source is the anterior pituitary somatotrophs.

It is regulated by the hypothalamus.

GHRH has a stimulatory effect.

Somatostatin (GHIF) has an inhibitory effect.

Clinical correlation: Gigantism and Acromegaly cause insulin resistance.

Glucose intolerance—50%

Hyperinsulinemia—70% 124

What is T2D or T1D ?

125

Normal, T2D and T1D Normal Subject High blood glucose Detected by

-cells Type 2 Diabetes (T2D) High blood glucose Blood glucose remains high Poor function of

-cells Type 1 Diabetes (T1D) High blood glucose

-cells destroyed by autoimmune reaction Blood glucose remains high No

-cells to detect & respond

-cells release insulin

-cells release of insulin is inadequate or inefficient Insulin secretion is nil Peripheral cells respond to insulin & take up glucose Lower blood glucose Peripheral cells poorly respond to insulin and glucose up take is poor Peripheral cells have no insulin to respond and take up glucose Blood glucose remains high Blood glucose remains very high 126

Type 2 Diabetes Mellitus Peripheral Tissue Insulin Resistance v. Time Time in years

-cell Insulin Production v. Time Time in years Disease Progression Diabetic Pre-Diabetic Normal Glucose Homeostasis Birth 127

T2D – It is Question of Balance !

PERIPHERAL INSULIN RESISTANCE Non-Diabetic State ß-CELL MASS & FUNCTION Diabetic State 128

Pathology of Type 2 Diabetes 129

Time Sequence of Events in T2D 130

Insulin Kinetic Defect in T2D 131

Natural History of T2D Plasma Glucose 120 (mg/dL) Obesity IGT * Diabetes Uncontrolled Hyperglycemia Post-meal Glucose Fasting Glucose Relative

-Cell Function 100 (%) Insulin Resistance Insulin Level -20 *IGT = impaired glucose tolerance -10 0 10 Years of T2D 20 30 132

Net Beta Cell Mass

Replication  -cell mass

133

Net Beta Cell Mass

Replication

Clinical Pearl 1. Crucial determinant of the course of T2D patient 2. Beta cell apoptosis is the cause of secondary OHA failure

 -cell mass

134

Net Beta Cell Mass THE FORMULA FOR ß-CELL MASS (Mitogenesis + Size + Neogenesis) - Apoptosis = Growth Increased ß-mass (i.e. compensation for insulin resistance): (Mitogenesis + Size + Neogenesis) > Apoptosis Decreased ß-mass (i.e. Type-2 diabetes): Apoptosis > (Mitogenesis + Size + Neogenesis) 135

Approaches to lower Blood Glucose 136

Approaches to lower Blood Glucose Clinical Pearl 1. Various approaches to treat T2D and T1D 2. To restore normoglycemia is the goal 3. These approaches have additive effect 137

Evolution of the Modern Cardio-metabolic Man

Grotesque not in physical appearance alone !!

138

Fatty Acid Oxidation - What is the Switch ?

Glucose Stearoyl CoA Desaturase (SCD) Thrifty Gene Hypothesis 139

Fatty Acid Oxidation - What is the Switch ?

Glucose Clinical Pearl SCD SWITCH MANIPULATION might be the answer Stearoyl CoA Desaturase (SCD) Thrifty Gene Hypothesis 140

The Web of Cardio-metabolic pathogenesis 141

Leptin

Produced almost exclusively by adipose tissues

Regulates appetite via ‘satiety signal’ to Hypothalamus

Has beneficial effects on muscle fat oxidation and insulin resistance

These are compromised by Leptin insensitivity

Has a suggested role in the development of various cardiac risk factors – including high blood pressure 142

Adipsin (ASP)

ASP – Acylation Stimulation Protein

Role in the uptake and esterification of Fatty Acids

Facilitates fatty acid storage through Triacylglycerols

Stimulates Triacylglycerol synthesis via Diacylglycerol Acyl Transferase (DGAT)

Stimulates translocation of GLUT to cell surface

ASP release is induced by HDLc 143

Adiponectin

Significant homology to complement factor C1q

Accumulates in vessel walls in response to ET injury

Reduced in obesity

Weight loss causes increase in its levels

Reduced in patients with CAD

Beneficial effects on CAD may be through

Inhibition of mature macrophage function

Modulation of endothelial inflammatory response

Inhibition of TNFα induced release of adhesion molecules 144

WISH YOU ALL A HAPPY NEW YEAR 145