Endocrine versus exocrine pancreas a Pancreatic islets represent 1 - 2 % of pancreas, but blood flow through them represents 10 - 15 %. pp nsulin Characteristics - Polypeptide - Secretory granules - free insulin and C-peptide - Two types of secretory granules: - Quickly secretable (5 %) - Reserve pool (95 %) - Half-time 3 - 8 min - Degradation - liver ( up to 50 %), kidneys, target tissues (insulin proteases) Insulin secretion Insulin and C-peptide (approx. 1:1) C-peptide = sign of pancreatic secretory capacity (half-life approx. 35 min) - Possible biologic activity - Regulation of renal functions - Potential role in nervous system 10 min Nucleus Endoplasmic reticulum Molecular forms of insulin Pre-proinsulm Constitutive pathway Regulated pathway Cell membrane Clinical relevance - insulin structure and analogues Cld-FA RELATIVE EFFECTS OF INSULIN ANALOGS Fast-acting analogues IriSLlh lispro Insulin aspart Long-acting analogues Inaďin gia'gine Deiemir Insulin > 5 Impart, glul.v.nc. I.tp.ol-- '\ Inhaled invulin- «>^jl Short (regular)- — Inltrnvpdutr (MPH)--- ......iimilin analog | <*'^. Long (jtargine, deternir) — • - • ■ ^vT------------- 1-1-r 8 10 12 14 Time (hours) -I-1-r 16 18 20 Figure I. Representative time action profiles of selected exogenous insulins. Source: References 25. 26. nsulin secretion 300-1 250-200 150-100-50- Insulin concentrations (pM) in portal vein Combination of increase in absolute secretion and in pulse frequency i Fasting Post-Meal Pulsatile secretion - Maintaining maximal biological response - Suppression of liver gluconeogenesis - Uptake adipocytes Biphasic insulin release glucose t (min) 1. pool 2. pool Secretion of insulin by individual (3 cells is synchronized Secretion of insulin is pulsatile and shows rhytmicity. Stimulation of insulin secretion by glucose is biphasic. Glucose exhibits incretin effect. Biphasic insuline secretion ::o; Time (min) secretion - „normal" and obese ■—• Normal « Obese £ 2.2- 3.0 2 B 2.2 IB 14 I 0 0 8 0.2 160 140 120 100 50 BO 40 H) 11 • Normal • Obese 0600 1000 1400 1800 2200 0200 0600 3 60- NSi\ ■ Normal Obese I I I 0800 1200 1600 2000 2400 0400 Clock lime (hoursy CO T3 CO I T3 C CO C o '+-> cu u cu 1/1 1/1 cu CO to Normal Obese 600- 0600 1200 1800 2400 0600 0600 1200 1800 2400 0600 Clock time 51 Regulation of insulin secretion Glucose (3 cells = neuroendocrine integrator, response to: - Plasmatic concentrations of substrates (AA, Glu) - PC of hormones (insulin, GLP-1, somatostatin, adrenaline) - PC of neurotransmitters (noradrenaline, acetylcholine) Endoplasmic reticulum . Glu Production of ATP - change in ATP/ADP ratio - closure of ATP-sensitive K+IC - inhibition of K+ efflux - depolarization - opening of voltage-gated Ca2+ IC - exocytosis AA - Leu, Arg, Lys - Generation of ATP - Direct depolarization of plasmatic membrane Modification of mRNA translation - Glu-(+) mRNA Other: - GH, VIP, secretin, gastrin, glucocorticoids, prolactin, placental lactogene, sex hormones Glucose is the main stimulus for insulin secretion. Glucose has a permissive effect on secretion of other insulin secretion modulators. it (ID Nucleus ^| W Glucose transporter Glucose DAI 1 Glucose-6-phosphate Glucokinase Mitochondrion Intracellular-* Ca2+ stores Insulin containing ~J q granules ^ q Amino acids Ketoacids Acetylcholine (+) CCK (+) Glucagon (+) GLP-1 (+) Epinephrine (-) Norepinephrine (-) Somatostatin (-) ° o Insulin, o secretion dJ5 Voltage-dependent Ca2+channel ATP-sensitive K* channel Ca2t Depolarization Physiologie effects of insulin Immediate effects - Seconds - Modulation of K+and Glu transport Early effects - Several minutes - Regulation of metabolic activity Medium-term effects - Minutes to hours - Regulation of metabolic activity Delayed effects - Hours to days - Cell growth - Cell differentation Effect of insulin on target tissue is anabolic and is mediated by insulin receptor. Insulin receptor Characteristics - 2 a and 2 (3 subunits - TK activity - Phosphorylation of IRS 1-4 (insulin receptor substrate) - Interaction with other cell substrates - PI3K (phosphatydylinositol-3-kinase) - MAPK (mitogen-activated protein kinase) PI3K i PI3P PI2P Pl-dependent kinase Proteinkinase B Metabolic effects - transport of Glu, glycolysis, glycogen synthesis, proteosynthesis regulation Cell growth, strong antiapoptotic signal MAPK I N Endocytosis of IR Pro-pro I iterative effects of insulin and cell differentiation : Number of available IR is influenced by exercise, diet, insulin itself and by other hormones. Obesity and chronic hyperinsulinemia causes significant decrease in number of IR, exercise and starvation significant increase in number of IR. I a subunits = Ligand binding (3 subunits = TK activity [ Endosome acidification Phosphoryl-^+ ation ^ Insulin ^ dissociation Degradation of insulin t Glucose uptake & T Glycolysis T Glycogen synthesis & i Gluconeogenesis LT Lipogenesis & i Lipolysis T Protein synthesis & i Proteolysis _Cell survival/growth_^ mmediate effects of insulin of target tissues Utilization of glucose - Approx. 40 % of glucose in body - Approx. 80-90% skeletal muscles - Adipose tissue - adipocytes - GLUT4 While GLUT1 is responsible for basal uptake of glucose by skeletal muscles and adipocytes, GLUT4 is stimulated by insulin and is responsible for insulin-stimulated uptake of glucose. Transporter Expression Function GLUTI - Ubiquitous - Ery, endothelial cells (CNS), placenta, kidneys, colon - Skeletal muscles and adipocytes - Basal uptake of Glu GLUT2 - (3 cells of pancreas - Liver, small intestine, kidneys - Glu sensor - Uptake of Glu during high concentrations of circulating Glu GLUT3 - Primarily neurons - Placenta, liver, epithelial cells of GIT - Basal uptake of Glu - Essential role in CNS GLUT4 - Skeletal muscles and adipocytes - Vesicles! - Insulin-stimulated uptake of Glu GLUT5 Jejunum, sperms Transport of Fru Utilization of glucose is the main immediate effect of insulin. Effect of insulin on glucose uptake ~ 6 CO cd XL co CD o o _g O 5 -4 - 3 H 2 1 H 0 - Splanchnic Adipose Muscle Brain Controls I Type 2 diabetics Early and medium-term effects of insulin - Determined by phosphorylation of enzyme connected to metabolic pathways. - Skeletal muscles, adipose tissue, liver Production of ketone bodies (-) - Dephosphorylation of hormone-sensitive lipase (inhibition of triglyceride utilization and cleavage to FFA and glycerol) - Activation of acetylcoenzyme A carboxylase (lipogenesis) - Antagonization of catecholamines effect on lypolysis (phosphorylation and activation of phosphodiesterase = decreased intracellular cAMP) Utilization of glucose - liver - Stimulation of expression of enzymes connected to Glu utilization (glucokinase, pyruvate kinase) and lipogenic enzymes - Inhibition of enzymes connected to Glu production (phosphoenolpyruvate carboxykinase, glucose-6-phosphatase) - Stimulation of glycogen synthesis - Stimulation of malonylcoenzyme A synthesis - inhibition of ketone bodies synthesis Glycogenolysis Glycogen IG Glycogen I I synthase Glycogen Phosphorylase t G Glucose- 1-P Gluconeogenesis (2) Pyruvate i (2) Oxaloacetate I I ^ PEP carboxykinase f G (2) PEP Í (2) 3-Phosphoglycerate t (2) 1,3-Bisphosphoglycerate I Fructose-1,6-bisphosphate J Fructose-1.6-b,sphosphate tG Fructose-6-phosphate Í Glucose-6-phosphate • . Glucose-6-phosphatase f G II i Glucose nsulin and skeletal muscles (+) uptake of glucose (GLUT4) (+) glycogen synthesis (+) transport of AA (+) translation of mRNA (-) degradation of proteins (+) preference of fat reserves mechanism - mTOR phosphorylation Myocyte P KB/Akt © Uptake (D Activation (3) Intracellular trafficking and distribution @ Mitochondrial transport and oxidation p70S6K 1_ Extracellular space y mTOR Intracellular space 4E-BP1 T elF4G J t muscle protein synthesis Insulin and liver GLUT2 = Glu entry in hepatocytes Role of hexokinase - production of Glu-6-P and maintaining Glu gradient (+) lipid synthesis (+) proteosynthesis (-) ketogenesis Direct effects of insulin I Glycogenolysis IGluconeogenesis Indirect effects of insulin I Decrease free fatty acid flux to liver I Glucagon secretion Insulin Gluconeogenesis Insulin — Adipose tissue Glucagon Free + fatty acid Glucose Glucose Fed-state versus fasted-state glycemia 3 1/5 c Fed-state Fasted-state; Exercise Insulin Epinephrine Glycerol Lactate L Amino acids -Glucagon Norepinephrine? NEFA c o 0> orq O 3 0> 3 Q. 0> Q. 3 fl> glycemia Delayed insulin effects - Synthesis of lipogenic enzymes - Inhibition of gluconeogenesis enzymes - MAPK cascade - Pro-growth effect - (+) cell growth - Mitogenic effect Clinical relevance - Hyperinsulinemia - DM2 - Increased risk of cancer - Endometrium - Breast - Colon - Kidney - Proliferation of smooth muscle - Hypertension - Atherosclerosis - Dyslipidemia - Vascular diseases Blood Vessel Lumen Insulin Insulin Insulin VCAM-1 Hypoglycemia (-) insulin secretion (+) glucagon and adrenaline secretion (liver) (+) GH and Cortisol (decreased utilizatio of Glu) Neurogenic Sweaty Hungry Tingling Shaky/tremulous Heart pounding Nervous/anxious Blood sugar low (p< 0.001) Neuroglycopenic Warm Weak Difficulty thinking/confused Tired/drowsy Faint Dizzy Difficulty speaking Blurred vision ADB PAB Hypo Pgyziologic mechanisms preventing hypoglycemia Vegetative nervous system represents an important mechanism preventing hypoglycemia. Peripheral sensors Decreased glucose (PNS) + * * + Increased sympathoadrenal outflow f 1 1 ' ^____L.^ ^ (SNS) ^ if* Adrenal A A A medulla * Increased NE Increased ACh •<------/j ) - - - (palpitations, (sweating, hunger) \K_y tremor, arousal) i Hr1 Decreased Increased insulin glucagon I I (Lost in T1 DM) (Lost in T1 DM) Liver Increased epinephrine I I (Often attenuated in T1 DM) (Often attenuated in T1 DM) Increased neurogenic symptoms Increased glycogenolysis Increased gluconeogenesis LMuscle Kidney Fat Increased 'actate, __ amino acids, ^ I alveerol ▼ ▼ Increased lactate amino acids, glycerol Increased glucose production I Decreased glucose clearance I Increased Increased ingestion of carbohydrates glucose J Hyperglycemic effect of adrenaline Adrenaline prepares body to immediate performance, it mobilizes energetic substrate -glucose - as a source of energy. t Epinephrine r~ Liver Pi I Pancreatic islets \P I Muscle Fat I Insulin t Glucagon Pi Pi,Ps t Glycogenolysis \(f t Gluconeogenesisj ^ t Lactate and Alanine (?W 1 Í Glycolysis I Glucose Í Lipolysis / transport I ....................7ft I Glycerol NEFA t Glucose production t Glucose i Glucose utilization _i Diabetes mellitus type 1 Gut Muscle Glucose Ketones Kidney Glucose Ketones Triglyceride Genetic predisposition Environmental trigger (virus?) I Islet cell-directed antibodies T-cell-mediated ß-cell injury FFA Regulatory • T-cells?- DKA trigger (illness?) Adipose tissue CO E O I CD. 100-1 50 o4 Impaired 1st-phase insulin secretion Stable \. diabetes Unstable diabetes ^--- 4-► I I I I i' 8 10 Time (yrs) DM1 is associated with mobilization of substrates for gluconeogenesis and ketogenesis from muscle and adipose tissue, increased gluconeogenesis and ketogenesis in the liver, as well as disturbed substrate intake by peripheral tissues. Diabetes mellitus type 2 Clinical relevance Insulin resistance - Mutation in IR gene Defects in insulin secretion - Mutation in insulin gene (proinsulin) - Mutation in mitochondrial genes - MODY (Maturity-onset diabetes of the young) - HNF-4a (MODY 1) - Glucokinase (MODY 2) - HNF-la (MODY 3) - IPFl(MODY4) - HNF-lß (MODY 5) - NeuroDl/BETA2 (MODY 6) Glucose Endoplasmic reticulum ATP-sensitive K+ channel O Insulin secretion O DM2 is multifactorial disease connected with resistence of peripheral tissues (muscles, adipose tissue) to insulin, disturbed insulin secretion (under glycemia influence) and increased glucose production in liver. Diabetes mellitus typu 2 Proteins - Protein catabolism - Negative nitrogen balance Lipids - Lipid catabolism with production of ketone bodies - Decreased synthesis of FA and triglycerids - Increased concentration of free FA - FA catabolism, production of ketone bodies Hyperglycemia - Glycosuria, osmotic diuresis and polyuria - Increased plasma osmolality, polydipsia, ADH - Dehydratation - Decreased blood pressure and volume of ECF Polyphagy Ketoacidosis - Metabolic acidosis - Hyperventilation - Acidification of urine - Hyperkalemia - consequences glucose concentration KEY I Range for diagnosis I of pre-diabetes Glucagon Characteristics - Peptide hormone (29 AA) - Syntesized as proglucagon - Pancreas - Enteroendocrine eels in GIT - CNS - Alternative splicing creates other peptides, most important GLP-1 - Short half-life (5-10 min) - Degradation in liver Secretion - (+)AA - (+) hypoglycemia Receptors - Liver, (3 cells, kidneys, heart, adipose tissue, blood vessels, CNS, stomach, adrenal glands Functions - Glucose homeostasis - insulin antagonism Glucagon release is stimulated by: ■ Hypoglycemia ■ Epinephrine ((52) ■ Vagal stimulation Glucagon Glucagon release is inhibited by: • Hyperglycemia • Somatostatin I ^ Mobilizace Ca2+ Receptor PGC-1 -* PEPCK G-6-Pase I Glycolysis v Glycogenosis T Gluconeogenesis a Phosphorylasc Glycogenolysis . T Phosphorylase Kinase | " b Glucagon T Hepatic glucose output Proglucagon - alternative splicing Glicentin - L-cells (small intestine) Preproglucagon - Stimulation of insulin secretion - Inhibition of stomach secretion - Trophic effect in intestine PS Oxyntomodulin - colon (anorexigenic factor) - Postprandial secretion - Increased energy expandituree - (+) glucose tolerance GRPP (inhibition of Glu-stimulated insulin secretion, modulator of energy metabolism) IP-1, IP-2 L-cells (modulation of insulin secretion?) a-cell Glicentin-related pancreatic peptide Intervening peptide 1 Major proglucagon fragment GLP-1 Psck2 dominant Glucagon GRPP IP1 GLP-2 Psck1/3 dominant GLP-1 GLP-2 ] Glucagon IP1 GLP-1 JPxJ GLP-2 (I GRPP; Glucagon IP1 GLP-1 j GLP-2 JI Glucagon IP1 Oxyntomodulin GRPP Glucagon IP1 Glicentin GLP-land GLP-2 Charakteristics Neuroendocrine L cells CNS - Caudal NTS-viscerosensoric information - Activation of POMC neurons - Inhibition of food intake (anorexigenic factor) - Induction of satiety = quick modification of food intake based on metabolic substrates (glucose), hormones (leptin) and neuropeptides. Clinical relevance - Agonists of GLP1R- treatment of DM2 - Exenatid, lixisenatid - Liraglutid - Albiglutid, dulaglutid - Inhibitors of dipeptidyl peptidase 4 (DPP4) - sitagliptin, vildagliptin, saxagliptin, alogliptin, linagliptin - DM2 GLP-1 and GLP-2 show incretin effect preparing insulin secretion in dependence on glucose presence in GIT lumen. Functions - GLP-1 (GLP1R) - (+) insulin secretion - (-) glucagon secretion - Stimulation of neogenesis and proliferation of pancreatic isles - Inhibition of (3 cell apoptosis Functions-GLP-2 (GLP2R) - Inhibition of antrum motility - Inhibition of gastric juice secretion stimulated by food - Trophic effect (small intestine, colon) - Inhibition of enterocyte apoptosis - Stimulation of blood flow and nutrient absorption GLP-1 GLP-2 Glucagon - secretion and its regulation T-type Ca2+ IC TTX-sensitive Na+ IC Activation of L-/N-type of Ca2+ IC Influx Ca2+ Secretion of glucagon - exocytosis Repolarization - KDR IC KATP IC - dependence on Glu! 1. Low concentration Glu - open 2. High concentration Glu - change ATP/A DP - closed T-type Ca2+ channel TTX-sensitive Na+ channel L- or N-type Ca2+ channel lucagon secretion requires depolarizing cascade which ends with Ca2+ influx and glucagon secretion. Physiologie effects of glucagon Target enzyme Metabolic response (+) Glu-6-phosphatase expression Glu entering circulation (-) glucokinases Lower rate of Glu entering glycolytic cascade (+) phosphorylation (activation) of glycogen Phosphorylase Stimulation of glycogenolysis Inhibition of glycogen synthase Inhibition of glycogen synthesis Inactivation of phosphofructokinase 2, activation of fructose-6-phosphatase Inhibition of glycolysis, stimulation of gluconeogenesis Inhibition of pyruvate kinase Inhibition of glycolysis (ÍhslJ -—-u I Glycerol Adipocyte [* J——- Gluconeogenesis Acetyl coenzyme A 3-ß-hydroxybutyrate Malonyl CoA (FA synthesis) Oxatoacetate Citrate Krebs cycle Other effects Stimulation of phosphorylation (activation) of hormone-sensitive lipase and lipolysis - substrates for gluconeogenesis and antibody production FFA as a source of energy mainly for skeletal muscles arget organ for glucagon effect is liver, where it stimulates gluconeogenesis and glycogenolysis, thus increasing glycemia ntegrated effect of glucagon - insulin Orbital prefrontal cortex I I I r I Glucose Physiology Medial prefrontal cortex Pancreatic islets ß-cells —► i Insulin ■ F a-cells —► í Glucagon % <- Hippocampus Dorsal midline thalamus Brain stem _L Amygdala t Sympathoadrenal activity + i Insulin + Í Glucagon 7 Somatostatin Characteristics - Peptide hormone (14 AA) - Secretion stimulated by: - food rich in lipids (FFA) - food rich in saccharides (Glu) - food rich in proteins (AA - Leu, Arg) Functions - Paracrine effect - (-) insulin, glucagon, PP - Inhibition of practically all exocrine and endocrine GIT functions - Inhibition of motility Clinical relevance - Somatostatin analogues and insulin/glucagon producing tumors Glucose rine Glucose Insulin Role of paracrine cholinergic signaling in somatostatin secretion - paracrine effect of acetylcholine stimulates insulin secretion, but also secretion of somatostatin. Pancreatic polypeptide - PP Characteristics - Peptide hormone (36 AA) - Secretion stimulated by: - Food (proteins), distention of stomach - Exercise - Direct vagal stimulation - Insulin-induced hypoglycemia - Secretion inhibited by: - Hyperglycemia - Bombesin, somatostatin - Receptors: - Stomach, small intestine, colon, pankreas, prostate, enteric NS, CNS Functions - Inhibition of pancreatic exocrine secretion - Inhibition of gallbladder contraction - Modulation of stomach secretion - Modulation of stomach motility - Regulation of food intake? PVN Activity of hepatic vagal nerve energy expenditure T gallbladder motility J pancreatic exocrine secretion 1 gastric emptying 1 Pancreatic polypeptide stimulates energy consumption through sympathetic stimulation of brown adipose tissue. It also modulates secretion of CCK and inhibits ghrelin secretion. Amylin Characteristics - Peptide hormone (37 AA) - ß cells, stomach, proximal small intestine - Posttranslational modification (amidation) - Secretion together with insulin and C-peptide - Increase after application of: - p.o. and p.e. glucose Function - Slowing of emptying of stomach on vagal basis - Inhibition of glucagon secretion (postprandial) - Muscles - Inhibition of glycogen synthesis Stimulation of glycogenolysis, glycolysis and lactate production food 0 intake Clinical relevance - Increased plasmatic concentration during obesity, gastric diabetes and DM2 - Analogue of amylin DM1 and DM2 therapy (pramlintid) -amylin-deficient states glucagon © release pancreas amylin • Adiposity • Nociception • Maternal behaviors • Neurogenesis • Anxiolytic/antidepressant • Bone homeostasis