www drsarma in Glucose Homeostasis Counter Regulation Dr

www. drsarma. in Glucose Homeostasis Counter Regulation Dr. Sarma. R. V. S. N M. D. , (Med) M. Sc. , (Canada) Consultant Physician and Chest Specialist Bio. Ed Online

Glucose Equilibrium – A Wonder !! n Normal Blood Glucose Fasting state : 60 to 100 mg% n Postprandial : 100 to 140 mg % n n What keeps the blood glucose in such a narrow range? n Why are we not becoming hypoglycemic when we fast? n n 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 !! n Normal Blood Glucose Fasting state : 60 to 100 mg% n Postprandial : 100 to 140 mg % n Let us grasp some of the fascinating n What keeps the blood glucose in such a narrow range? answers !! n n n 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 1552 BC 1 st Century AD 1776 18 th Century 1869 1889 1921 -23 1983 2001 n 1552 BC: Ebers Papyrus in ancient Egypt. First known written description of diabetes. n 1 st Century AD: Arateus — “Melting down of flesh and limbs into urine. ” n 1776: Matthew Dobson conducts experiments showing sugar in blood and urine of diabetics. n n Mid 1800 s: 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. ” n 1889: Pancreatectomized dog develops fatal diabetes. n 1921: Insulin “discovered” — effectively treated pancreatectomized dog. n 1922: First human treated with insulin. Eli Lilly begins mass production. n 1923: Banting and Macleod win Nobel Prize for work with insulin. n 1983: Biosynthetic insulin produced. n 2001: Human genome sequence completed. 4

Cell growth and energy metabolism Carbohydrates Glucose Pyruvate Co A Fatty acids Fats Amino acids Ac ety l-C o. A 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 T 2 D 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 (G 6 PD) is the crucial enzyme 9

Homeostasis of Glucose Counter Regulation Mechanisms n A steady maintenance of blood glucose with in a narrow range n Fasting state and fed states – their effects on BG n Rate of glucose appearance Ra n Rate of disappearance Rd must be in balance n Blood Glucose (BG) = Ra n - Rd Control systems n Glucose Receptors, GLUT 1 -14 n Controlling Hormones, Insulin, Glucagon, Cortisol, Epinephrine etc. , n Insulin Signaling sequences, Glucagon signaling n Effector Cells – Muscles, Liver, Brain, Heart and Adipose tissue n Feedback loops n Negative feedback n Positive feedback 10

Homeostasis of Glucose Counter Regulation Mechanisms n A steady maintenance of blood glucose with in a narrow range n Fasting state and fed states – their effects on BG n Rate of glucose appearance Ra n Rate of disappearance Rd must be in balance n n Clinical Pearl INSULIN GLUCAGON Blood Glucose (BG) = Rv/s R a d and Rd V/s Ra Control systems n Glucose Receptors, GLUT 1 -14 n Controlling Hormones, Insulin, Glucagon, Cortisol, Epinephrine etc. , n Insulin Signaling sequences, Glucagon signaling n Effector Cells – Muscles, Liver, Brain, Heart and Adipose tissue n Feedback loops n Negative feedback n Positive feedback 11

Normal, Hyper and Hypoglycemic states Ra Ra is the rate of appearance of Glucose 100 mg Rd Ra Ra 200 mg Rd Rd is rate of disappearance of Glucose When Ra = Rd; It is Ra Euglycemic state Ra Rd Ra > Rd; Ra ↑or Rd↓ HYPERGLYCEMIA 50 m g Rd Ra < Rd; Ra ↓or Rd ↑ HYPOGLYCEMIA 12

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

Glucose Homeostasis Lower Blood Glucose -cells release Glucagon stimulate glycogen breakdown and gluconeogenesis Between meals -cells release insulin stimulate glucose uptake by peripheral tissues Higher Blood Glucose Food 14

High blood glucose affects the size of beta cells 15

Pancreatic Hormones Pancreas n Exocrine Pancreas – P Lipase, P amylase etc n Endocrine Pancreas – Islets of Langerhans n Hormones secreted are – n n n 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 n Glucose is the major source of energy for cells n Blood Glucose (BG) regulated by Insulin & Glucagon 17

Regulation of beta-cell –size by the and level Glucagon of blood glucose Glucose Homeostasis Insulin 18

Glucose Homeostasis Chart Condition Receptor High Blood Sugar Toxic to the cells - AGP Energy needs unmet Glucose transporter Control Center -cell of the pancreas Effector Result Low Blood Sugar -cell of the pancreas Insulin Glucagon 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 T 2 D, MS and Obesity - GLUT-2 Blockers 27

The First Messengers from GI tract THE MESSERGERS INCRETINS – GLP 1 and GIP_ 28

Entero-Insular Axis of Secretion Insulin secretion is also increased n By intestinal polypeptide hormones n GLP-1 (glucagon like peptide) [exendin-4] n Glucose-dependent insulinotropic peptide(GIP) n GLP-1 and GIP are called Incretins n Cholecystokinin and by pancreatic Glucagon. n Insulin secretion is decreased by pancreatic somatostatin. 29

Entero-Insular Axis of Secretion Insulin secretion is also increased n By intestinal polypeptide hormones n Pearl GLP-1 (glucagon Clinical like peptide) [exendin-4] Newn Glucose-dependent Drugs for T 2 D- Incretin (GLP-1 peptide(GIP) and GIP) Function insulinotropic Enhancers n GLP-1 and GIP are called Incretins n n 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) n Remember there are two separate signaling events n First signal is from the ↑ Blood Glucose to pancreas n To stimulates insulin secretion in to the blood stream n The second signal from insulin to the target cells n n 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) n Clinical Pearlsignaling events Remember there are two separate 1. First Insulin secretion must be triggered – First Signal signal is from the ↑ Blood Glucose to pancreas n 2. To Secreted must trigger Glucose uptake – stimulates. Insulin insulin secretion in to the blood stream Second signal n n The second signal from insulin to the target cells 3. T 2 D may result from failure of either or both n n Insulin signals to the muscle, adipose tissue and liver to permit to glucose in and to utilize glucose This effectively lowers Blood Glucose 32

Glucose induced Insulin secretion n n n 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 through uniporter GLUT 2 Pearl n Clinical n Oxidative phosphorylation Closure of KATP Channels by Glucose is + n ATP closes the ATP gated K fundamental Glucose is necessary to Insulin is necessary channel and depolarizes the cell membrane stimulate Insulin Depolarization opens the to let in glucose voltage gated Ca+ channels n n n 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 KATP Channels – Secrete Insulin 2. Differences in action of SU are because of the differences 3. in their action on KATP Channels 4. 3. Gliclazide and Glimiperide just hit the SUR closure and stop 36

Intricacies in the Beta Cell 37

K+ ATP – Sulfonylurea Receptor n n n K+ ATP channel has two sub units – Kir 6. 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 SUR 1 are ATP binding transporters superfamily 38

K+ ATP – Sulfonylurea Receptor K+ ATP channel has two sub Clinical Pearl units – Kir 6. 2 and regulatory sulfonylurea receptor(SUR) Tolbutamide cause prolonged n 1. Glibenclamide, closer of the SUR n ATP gated K+ channel is coupled to SUR 2. This causes prolonged and intense pressure on + n K channel can be closed Beta cells independently of glucose 3. This is the cause of late hypoglycemia with these n This leads to increased insulin SUs secretion 4. Beta cell apoptosis sets nin. SUR 1 fast are after few years of ATPabinding use transporters superfamily 39

(F)PHHI n (Familial) Persistent Hyperinsulinemic Hypoglycemia of Infancy n Unregulated insulin secretion n Profound hypoglycemia and brain damage n Manifests at birth or at first year of life n Under diagnosed n Probably the cause of undiagnosed postnatal deaths n Defect is KATP Channels mutation – n Persistent closure with continuous trigger for Insulin release n 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) n Insulin Receptor is a tyrosine kinase. n Consists of 2 units -dimerize when bound with insulin. n Inside cell - auto phosphorylation occurs, n Increasing tyrosine kinase activity. n Insulin Receptor phosphorylates intracellular signaling molecules. n Stimulates insertion of GLUT-4 proteins n which let in glucose n Stimulate glycogen, fat and protein synthesis. 45

+ Insulin 3 HN NH 3+ S S -S-S- -subunits EXTRACELLULAR -OOC + 3 HN S S Plasma membrane Tyrosine kinase domain -OOC COONH 3+ CYTOPLASM Transmembrane domain COO- -subunits 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

Extracellular 2 1 IRTK (L) insulin activated binds L IRTK (R) 3 phosphorylated/ activated OP OP R P Cytoplasm P P ATPs 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

Extracellular 2 1 IRTK (L) insulin activated binds L IRTK (R) 3 phosphorylated/ activated 4 IRTK (L) phosphorylated PO OP OP R ATPs P Cytoplasm P P PO P OP OP P P ADPs ATPs ADPs 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 n Transphorylation of tyrosines on the receptor n Phosphotyrosine residues bind to n IRS-1 (insulin receptor substrate – adopter protein) 49

Insulin Receptor (IR) A key regulator of growth signaling n n n 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) n Obesity down regulation of IR n 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, upregulates 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. 2. The interaction of the external domain of a receptor tyrosine kinase Clinical Pearl with the ligand, often a growth factor, up. Up regulation of TK receptor regulates the enzymatic (autophosphorylation) in obesityactivity of the intra cellular catalytic domain, Leads to Glucose entry into cells with out insulin which causes tyrosine signal phosphorylation of cytoplasmic signaling molecules. 52

Insulin Signaling – PKB and MAPK pathways n Ras independent signaling – The PKB Signaling and n Ras dependent – The MAPK Signaling n Ras independent through activation of Protein Kinase B n Responsible for immediate non-genomic effects n Ras dependent – Activation of n Mitogen Activated Protein Kinase (MAPK) pathway n 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 – PI 3 P – 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 – PI 3 K - PKB Signaling n IRS 1 binds PI 3 kinase through SH 2 domain n This phosphorylates PIP 2 to PIP 3 n Increased concentration of PIP 3 recruits n PKB to the plasma membrane n PKB is phosphorylated by n two membrane associated kinases PKC λ and ξ n Active PKB is released into the cytosol n Where it translocates glucose transporter (GLUT-4) n GLUT-4 (uniporter) moves on to the membrane n GLUT-4 lets Glucose in and increases glucose uptake 58

PIP Signaling Pathway 59

Ras - Independent Insulin Signaling 60

Insulin and PI 3 K Signaling 61

Ras Independent Extracellular Space = GLUT-4 Cytoplasm IRS Active IRTK PO PO OP OP tyr-OH ATP [1] IRTK Figure 5. Mechanism for insulin to mobilize GLUT-4 transporter to the plasma membrane in muscle & adipose tissue. IRS, insulin-receptor substrate; IRTK, insulin receptor tyrosine kinase; PI-3 K, phosphatidyl-inositol kinase; PDK; phospholipid-dependent kinase PKB, protein kinase B catalyzed IRS p 85 [2] activated by docking IRS PIactive IRS tyr-OP IRS 3 K IRSactive tyr-OP PIP 2 PIP IRS 3 tyr-OP + [4] signals Golgi to traffic GLUT-4 to PDK PKB membrane ADP GOLGI 62

Ras Dependent – MAPK Signaling At the same time… n Phosphorylated insulin receptor binds n to adapter protein SHC through GRB 2 n GRB 2 also has SH 3 domains that bind activates Sos n Binding of Sos to inactive Ras causes a n conformational change that permits release of n GDP and binding of GTP (activation of Ras) n Sos is a GEF for monomeric G protein Ras n Sos dissociates from activated Ras n Linking insulin receptor to Ras 63

Ras - Dependent Insulin Signaling 64

Ras Dependent – MAPK Signaling n Activated Ras passes the signal to raf kinase n Raf activates a cascade of kinases (MAP Kinase cascade) n Mitogen Activated Protein Kinases (MAP Kinases) n Highly conserved kinase cascades n Last kinase in the cascade has to be double phosphorylated n It has high specificity (since it is double phosphorylation) 65

Ras Dependent Glucose Extracellular GLUT-4 PO PO Glucose transport (muscle/adipose) Activated IRTK metabolic responses Activation of protein phosphatase OP Cytoplasm OP Signal transduction (e. g. , phosphorylation of IRS, SHC, PLC) Dephosphorylation of: KINASE CASCADE glycogen synthase (protein phosphorylation) glycogen phosphorylase mitogenic Cell growth phosphorylase kinase response acetyl Co. A carboxylase and replication hormone-sensitive lipase NUCLEUS phosphofructokinase-2 pyruvate kinase DNA synthesis HMG Co. A reductase regulatory kinases m. RNA synthesis Protein synthesis 66

Ras Dependent – MAPK Signaling n MAPK regulates the activity of transcription factors n Active MAPK translocates to the nucleus n It phosphorylates several transcription factors n And production of more GLUT 4 67

Glucose Entry in to the Cell n n n Insulin/GLUT 4 is not the only pathway Insulin-dependent, GLUT 4 - mediated n Cellular uptake of glucose into muscle and adipose tissue (40%) Insulin-independent glucose disposal (60%) n GLUT 1 – 3 in the Brain, Placenta, Kidney n SGLT 1 and 2 (sodium glucose symporter) n 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 n Off switch n PDE inactivates c. AMP n PDE stops signal transduction. n Caffeine inhibits PDE! 71

Glucose controls Insulin and Glucagon release 72

Liver and Kidney n n 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 n n n 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. n Can break down glycogen n But cannot liberate free glucose into the circulation. 75

Metabolic Effects of Insulin - in the Muscle 76

Adipose Tissue (AKA fat) n n 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 Insulin Glucagon Glycogen synthesis ↑ ↓ Glycolysis (energy release) ↑ ↓ Lipogenesis ↑ ↓ Protein synthesis ↑ ↓ Glycogenolysis ↓ ↑ Gluconeogenesis ↓ ↑ Lipolysis ↓ ↑ Ketogenesis ↓ ↑ 80

Glucose Uniporters - GLUTs Transport can work in both directions 81

The GLUT – Glucose Transporters n 14 transporters of Glucose are identified n Their genes are located and cloned n The function of some is yet under evaluation n n 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 n 14 transporters of Glucose are identified Their genes are located and cloned Clinical Pearl n The function of some is yet under evaluation 1. GLUT -1 DS – a genetic disorder of Glucose n Some genetic defects produce specific diseases like metabolism GLUT-1 -DS 2. Anti GLUT -11 drugs in breast & prostate Ca are n Inunderway 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. n 83

Glucose Transporter Proteins - GLUTs n n n 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 m. M). Never saturates. GLUT - 3 – Insulin independent glucose disposal in to the tissues. Abundant in neuronal tissue, placenta and kidney. It feeds the high glucose requirement with out insulin. 84

Glucose Transporter Proteins - GLUTs n n n GLUT - 1 - Responsible for feeding muscle during exercise (that is how exercise. Clinical lowers blood glucose) Placenta, BB, Pearl RBC, Kidney and many tissues. Low in liver. Mainly 1. The GLUT-3 Receptors are Insulin “house keeping” independent GLUT – 2 – Uniporter of glucose into the beta cells and stimulates insulin secretion. Beta cellsglucose of pancreas. Liver, 2. In brain GLUT-3 mediate uptake small intestinal epithelium, Kidney. Has high Km (60 m. M). 3. Insaturates. placenta also GLUT-3 mediate Glucose Never uptake GLUT - 3 – Insulin independent glucose disposal in to the tissues. Abundant in neuronal placenta andmuch kidney. in 4. Foetal growth is nottissue, affected very It feeds IR the high glucose requirement with out insulin. 85

Glucose Transporter Proteins – GLUTs contd. . n n n 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 – G 6 P transporter in ER SGLT 1 and 2 - Sodium - Glucose symporter in the intestinal epithelium and renal tubular epithelium 86

Glucose Transporter Proteins – GLUTs contd. . n 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 Clinical Pearl n n GLUT – 5 – Rich in small intestine and conduct absorption 1. GLUT-4 isand main Glucose transporter in all of dietary glucose fructose transport. Mediate glucose tissues for spermatogenesis GLUT 6 – Pseudo gene – Mediates none so signaling far 2. It–cannot function without TK of GLUTInsulin – 7 – Only in liver endoplasmic reticulum and it conducts glucose back out – G 6 P transporter in ER SGLT 1 and 2 - Sodium - Glucose symporter in the intestinal epithelium and renal tubular epithelium 87

Brain n Converts glucose to CO 2 and H 2 O. n Can use ketones during starvation. n Is not capable of gluconeogenesis. n Has no glycogen stores. 88

Know Our Brain !! n Brain is the major glucose consumer n Consumes 120 to 150 g of glucose per day n Glucose is virtually the sole fuel for brain n Brain does not have any fuel stores like glycogen n Can’t metabolize fatty acids as fuel n Requires oxygen always to burn its glucose n Can not live on anaerobic pathways n One of most fastidious and voracious of all organs n Oxygen and glucose supply can not be interrupted 89

Know Our Brain !! n Brain is the major glucose consumer n Consumes 120 to 150 g of glucose per day Clinical Pearl Glucose is virtually the sole fuel. Insulin for brain 1. Brain does not need for glucose n Brainuptake does not have any fuel stores like glycogen n Can’t metabolize fatty acids as fuelmediate it without 2. The GLUT-3 Receptors Insulin n Requires oxygen always to burn its glucose n Can 3. not on anaerobic pathways In live hypoglycemia we need to give Glucose only n One of most fastidious and voracious of all organs n n Oxygen and glucose supply can not be interrupted 90

Second Signaling n n 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 n n Insulin is dimer of two peptides Each peptide consists of A and B chains n A has 21 amino acids n B has 30 amino acids n n 2 chains are linked by pair of S – S bonds C peptide has 35 amino acids and is cleaved 92

Insulin – C peptide n Clinical Pearl 1. Insulin Analogs are chains Insulin is dimer of two peptides Each peptide consists of A substitutions AA in α and ß and Bof chains n n A has 21 amino acids 2. Insulin Glargine, Insulin aspart, Insulin lispro etc. , n B has 30 amino acids RAIA, LAIA n n 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 n Hypoglycemic hormone n Beta cells of pancreas n Two chain polypeptide – Anabolic in nature n Receptor interactions n Intracellular interactions n Transporters n Clinical correlation 98

Insulin - Mechanism of action n Insulin binds to its trans-membrane receptor. n β subunits of the receptor become phosphorylated n Receptor has intrinsic tyrosine kinase activity. n Intracellular proteins are activated/inactivated— n IRS-1, IRS-2 and seven PI-3 -kinases n GLUT-4, Transferrin, LDL-R, IGF-2 -R move to the cell surface. n Cell membrane permeability increases: n Glucose, K+, amino acids, PO 4 enter 99

Insulin Release n n 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 n Glucose interacts with the GLUT-2 transporter on the pancreatic beta cell. n Glucose enters the cell releases - hexokinase→ G-6 -P n Increased metabolism of glucose → ATP → n Excess of ATP- blocks ATP dependent K channels → n Membrane depolarization → n ↑ Cytosolic Ca++ → n This stimulates degranulation and n Releases ↑ insulin secretion. 101

Control of Insulin Secretion Insulin secretion is also increased by n Growth hormone (acromegaly) n Glucocorticoids (Cushings’) n Prolactin (lactation) n Placental lactogen (pregnancy) n 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 n Main effect is to promote storage of nutrients n Paracrine effects n Decreases Glucagon secretion n Carbohydrate metabolism n Lipid metabolism n Protein metabolism and growth 104

Role of Insulin Carbohydrate metabolism n Increases uptake of glucose n Promotes glycogen storage n Stimulates glucokinase n Inhibits gluconeogenesis n Inhibits hepatic glycogenolysis n Inactivates liver phophorylase 105

Sources of Glucose in to blood n Glucose is derived from 3 sources n Intestinal absorption of dietary carbohydrates n Glycogen breakdown in liver and in the kidney. n Only liver and kidney have glucose-6 -phosphatase. n Liver stores 25 -138 grams of glycogen, a 3 to 8 hour supply. n Gluconeogenesis, the formation of glucose from precursors n These include lactate and pyruvate, amino acids (alanine and glutamine), and to a lesser degree, from glycerol 106

Fasting State n n n Short fast n Utilizes free glucose (15 -20%) n Break down of glycogen (75%) Overnight fast n Glycogen breakdown (75%) n Gluconeogenesis (25%) Prolonged fast n Only 10 grams or less of liver glycogen remains. n Gluconeogenesis becomes sole source of glucose n Muscle protein is degraded for amino acids. n Lipolysis generates ketones for additional fuel. 107

Role of Insulin Lipid Metabolism n Insulin promotes fatty acid synthesis n Stimulates formation of α-glycerol phosphate n α-glycerol phosphate + FA Co. A = TG n TG are incorporated into VLDL and transported to adipose tissues for storage. n Insulin inhibits hormone-sensitive lipase, n Thus decreasing fat utilization. 108

Role of Insulin n Protein Metabolism and Growth n Increases transport of amino acids n increases m. RNA translation and new Proteins, n A direct effect on ribosomes n Increases transcription of selected genes, n Especially enzymes for nutrient storage n Inhibits protein catabolism n Acts synergistically with growth hormone 109

Role of the Pancreas Lack of insulin n n Occurs between meals, and in diabetes. Transport of glucose and amino acids into the cells decreases, leading to hyperglycemia. n Hormone sensitive lipase is activated, n Causing TG hydrolysis and FFA release. n ↑ FFA conversion in liver → n Phospholipids and cholesterol → n Lipoproteinemia, n FFA breakdown leads to ketosis and acidosis. 110

Insulin Resistance n n Associated with obesity Underlying metabolic defect in n Type 2 diabetes n Polycystic ovarian disease Associated with n Hypertension, gout, high triglyceride 30% of general population 111

What causes insulin resistance? n Decreases in receptor concentration n Decreases in tyrosine kinase activity, n Changes in concentration and phosphorylation of and IRS-2, n Decreases in PI 3 -kinase activity, n Decreases in glucose transporter translocation, n Changes in the activity of intracellular enzymes. IRS-1 112

What causes insulin resistance? n Decreases in receptor concentration n Decreases in tyrosine kinase activity, n 1. T 2 D in is concentration mostly a question of Insulinof Changes and phosphorylation and. Resistance IRS-2, n Decreases PI 3 -kinase activity, Insulin resistance are 2. Drugsinwhich improve n crucial Decreases in glucose transporter translocation, n 3. Quantitative deficiency is only a late feature Changes in the activity of intracellular enzymes. Clinical Pearl IRS-1 in T 2 D 113

The Role of Pancreas Other pancreatic hormones n n Somatostatin n 14 amino acid paracrine factor n Potent inhibitor of glucagon release n Stimili: glucose, arginine, GI hormones n It is anti GH (somatotrophin) in its actions Pancreatic polypeptide n n 36 amino acids, secreted in response to food Glucagon 114

Counter Regulatory Hormones n Early response Glucagon n Epinephrine n n Delayed response n Cortisol n Growth hormone 115

Counter Regulatory Hormones n n n Glucagon n Acts to increase blood glucose n Secreted by alpha cells of the pancreas n Chemical structure 29 amino acids n Derived from 160 aminoacid proglucagon precursor GLP-1 (Glucagon Like Peptide -1) n The most potent known insulin Secretagogue n It is made in the intestine by alternative processing of the same precursor Intracellular actions 116

Role of Glucagon n Metabolic Effects of Glucagon Increases hepatic glycogenolysis n Increases gluconeogenesis n Increases amino acid transport n Increases fatty acid metabolism (ketogenesis) n 117

Role of Glucagon n Metabolic Effects of Glucagon Clinical Pearl Increases hepatic glycogenolysis 1. Glucagon is the treatment for hypoglycemia n Increases gluconeogenesis 2. Increases Glucagon Kitacid – 1 transport mg s/c or IM or IV injection n amino – n Increases fatty acid metabolism (ketogenesis) n 3. In 2 to 3 minutes recovery 4. Costs Rs. 400 per dose 118

Glucagon Secretion Stimulation of Glucagon secretion n Blood glucose < 70 mg/d. L n High levels of circulating amino acids n Especially arginine and alanine n Sympathetic and parasympathetic stimulation n Catecholamines n Cholecystokinin, Gastrin and GIP n Glucocorticoids 119

Responses to decreasing Glucose levels Response Glycemic theshhold Physiological effects Role in counter regulation ↓ Insulin 80 - 85 mg% ↑ Ra (↓ Rd) Primary First Defense ↑ Glucagon 65 - 70 mg% ↑ Ra ↑ Epinephrine 65 - 70 mg% ↑ Ra ↓ Rd Critical Third Defense ↑ Cortisol, GH 65 - 70 mg% ↑ Ra ↓ Rd Not Critical ↑ Food ingestion 50 - 55 mg% ↑ Exogenous Glucose Primary Second Defense < 50 mg% no cognitive change 120

Role of Epinephrine n n 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. n It also stimulates glycolysis in muscle n Lipolysis in adipose tissue, n Decreases insulin secretion and n Increases glucagon secretion. 121

Role of Cortisol and GH n n These are long term hyperglycemic hormones Activation takes hours to days. n Cortisol and GH act to decrease glucose utilization in most cells of the body n Effects of these hormones are mediated through the CNS. 122

Cortisol n Cortisol is a steroid hormone n n n 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) n GH is a single chain polypeptide hormone. n Source is the anterior pituitary somatotrophs. n It is regulated by the hypothalamus. n GHRH has a stimulatory effect. n Somatostatin (GHIF) has an inhibitory effect. n Clinical correlation: Gigantism and Acromegaly cause insulin resistance. n Glucose intolerance— 50% n Hyperinsulinemia— 70% 124

What is T 2 D or T 1 D ? 125

Normal, T 2 D and T 1 D Normal Subject High blood glucose Type 2 Diabetes (T 2 D) High blood glucose Type 1 Diabetes (T 1 D) High blood glucose -cells destroyed by autoimmune reaction Detected by -cells release insulin Peripheral cells respond to insulin & take up glucose Lower blood glucose Blood glucose remains high Poor function of -cells No -cells to detect & respond -cells release of insulin is inadequate or inefficient Insulin secretion is nil 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

Peripheral Tissue Insulin Resistance v. Time -cell Insulin Production v. Time Relative Insulin Resistance -cell Insulin Production Type 2 Diabetes Mellitus Time in years Disease Progression Age Diabetic Pre-Diabetic Normal Glucose Homeostasis Time in years Birth 127

T 2 D – It is Question of Balance ! Non-Diabetic State PERIPHERAL INSULIN ß-CELL MASS RESISTANCE & FUNCTION Diabetic State ASS M L L ß-CE ON NCTI U F & IN SUL N I L A HER P I R E PE ANC T S I RES 128

Pathology of Type 2 Diabetes 129

Time Sequence of Events in T 2 D 130

Insulin Kinetic Defect in T 2 D 131

Natural History of T 2 D Obesity IGT* Diabetes Uncontrolled Hyperglycemia Post-meal Glucose Plasma Glucose Fasting Glucose 120 (mg/d. L) Relative -Cell Function Insulin Resistance 100 (%) Insulin Level -20 *IGT = impaired glucose tolerance -10 0 10 20 Years of T 2 D 30 132

Net Beta Cell Mass Replication Neoformation Apoptosis -cell mass 133

Net Beta Cell Mass Replication Clinical Pearl 1. Crucial determinant of the course of T 2 D patient 2. Beta cell apoptosis is the cause. Apoptosis of Neoformation Apoptosis secondary OHA failure Neoformation -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 T 2 D and T 1 D 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 Co. A Desaturase (SCD) Thrifty Gene Hypothesis 139

Fatty Acid Oxidation - What is the Switch ? Glucose Clinical Pearl SCD SWITCH MANIPULATION might be the answer Stearoyl Co. A Desaturase (SCD) Thrifty Gene Hypothesis 140

The Web of Cardio-metabolic pathogenesis 141

Leptin n Produced almost exclusively by adipose tissues n Regulates appetite via ‘satiety signal’ to Hypothalamus n n n 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) n ASP – Acylation Stimulation Protein n Role in the uptake and esterification of Fatty Acids n Facilitates fatty acid storage through Triacylglycerols n Stimulates Triacylglycerol synthesis via Diacylglycerol Acyl Transferase (DGAT) n Stimulates translocation of GLUT to cell surface n ASP release is induced by HDLc 143

Adiponectin n Significant homology to complement factor C 1 q n Accumulates in vessel walls in response to ET injury n Reduced in obesity n Weight loss causes increase in its levels n Reduced in patients with CAD n Beneficial effects on CAD may be through Inhibition of mature macrophage function n Modulation of endothelial inflammatory response n Inhibition of TNFα induced release of adhesion molecules n 144

WISH YOU ALL A HAPPY NEW YEAR 145