The ROLE of GLUCAGON in DIABETES An Update
The ROLE of GLUCAGON in DIABETES : An Update Pierre Lefèbvre Cairo, Egypt, September 2007
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1923 Murlin et al The discovery
1942 Czyste Hospital Warsaw Ghetto Studies on « Hunger’s disease » by Dr Emil Apfelbaum et al
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1949 Foà* et al Cross-circulation experiments *Only Author I know to have published a paper when in utero …
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Paradoxical hyperglycemia in the dog receiving PDV blood Insulin-induced hypoglycemia in the « donor » dog 11
1959 -1960 Unger et al The first polypeptide radio-immunoassay
Roger UNGER 13
1973 14
Topics · Importance of glucagon for the maintenance of glucose homeostasis · The physiology of glucagon production and how glucagon exerts its effects · Abnormalities of glucagon secretion in patients with T 2 DM 15
Pancreatic Islet Hormones Are Critical for Normal Glucose Tolerance -Cells Insulin + Glucagon – Glucose uptake HGO = hepatic glucose output Adapted from Unger RH. Metabolism. 1974; 23: 581– 593 + HGO 16
The Physiological Balance Between Insulin and Glucagon is Essential for Normal Metabolic Control – + Insulin* Glucose Glucagon* (plasma concentration) – + *Insulin and glucagon secretion are also influenced by other nutrients, hormones, and neural input Adapted from Berne RM, Levy MN, eds. Physiology. St. Louis, Mo: Mosby, Inc; 1998: 822– 847 17
Glucagon is Important to Maintain Adequate FPG Levels Between Meals Glucose production = Glucose utilization α-Cell Glucagon + 10 g/h Blood glucose 4. 5 mmol/L (81 mg/d. L) 4 g/h 6 g/h Adapted from Unger RH. Diabetes. 1983; 32: 575– 583 18
Normal Reciprocal Response of Insulin and Glucagon in Persons Without Diabetes Postprandial Insulin and Glucagon Responses in Persons Without Diabetes mg% CHO Meal 120 100 80 Glucose μU/m. L 120 80 Insulin 40 pg/m. L 0 120 110 Glucagon 100 90 – 60 0 CHO = carbohydrate Adapted from Unger RH, et al. N Engl J Med. 1971; 285: 443– 449 60 120 Time (min) 180 240 19
Topics · Importance of glucagon for the maintenance of glucose homeostasis · The physiology of glucagon production and how glucagon exerts its effects · Abnormalities of glucagon secretion in patients with T 2 DM 20
α-Cell Function is Regulated by Nutrient, Neural and Hormonal Influences Stimulatory Factors (↑ Glucagon) Inhibitory Factors (↓ Glucagon) · Hypoglycaemia · Glucose · Protein meal · Carbohydrate meal · Amino acids · Ketones · Stress; adrenaline (epinephrine) · Insulin · Sympathetic/parasympathetic nerves · Somatostatin · GIP · GLP-1 Adapted from Dunning BE, et al. Diabetologia. 2005; 48: 1700– 1713 21
Glucagon Stimulation of Hepatocytes Leads to Increased Hepatic Glucose Production Glucagon + + - Glycogenolysis Gluconeogenesis Glycolysis Glucose Glycogenesis HGP TCA = trichloroacetic acid Adapted from Mc. Murry J, et al. Fundamentals of General, Organic, and Biological Chemistry. 4 th ed. Upper Saddle River, NJ: Prentice Hall; 2006 Jiang G, Zhang BB. Am J Physiol Endocrinol Metab. 2003; 284: E 671 -E 678 22
Glucagon From α-Cells is Responsible for 75% of HGP START INFUSION* N = 8† Net Splanchnic Glucose Production (mg/min) 150 75% in HGP 100 50 <. 01 – 30 0 <. 01 30 60 <. 01 90 <. 01 vs baseline 120 Time (min) HGP = hepatic glucose production *Somatostatin and insulin were delivered to induce selective glucagon deficiency †Healthy, non-obese men age 18– 30 Adapted from Liljenquist JE, et al. J Clin Invest. 1977; 39: 369– 374 23
Changes in Glucagon/Insulin Ratio Regulate HGO and Glycogen Synthesis in Normal Physiology Glucagon/Insulin ratio* HGO (mg/kg. min)*† Liver Glycogen (mmol/L)* (n= 6) (n= 8) 2. 5 – 40 – 350 – 2. 0 – 300 – 1. 5 – 20 – 250 – 10 – 200 – 0. 5 – | 0 | 120 | 240 | 360 Minutes | | 480 600 0 – | 0 | 120 | 240 | 360 | | 480 600 Minutes HGO = hepatic glucose output *All measurements made after a standard mixed meal in healthy volunteers ages 18– 40 years †HGO completely suppressed after 30 minutes of meal intake Adapted from Taylor R, et al. J Clin Invest. 1996; 97: 126– 132 150 – | 0 | 120 | 240 | 360 | | 480 600 Minutes 24
Topics · Importance of glucagon for the maintenance of glucose homeostasis · The physiology of glucagon production and how glucagon exerts its effects · Abnormalities of glucagon secretion in patients with T 2 DM 25
Pancreatic Islet Morphology: Structural Defects are Evident in T 2 DM Normal T 2 DM β-Cells (insulin) Amyloid plaque α-Cells (glucagon) • Disorganised and misshapen • Marked reduction in β-cell number • Amyloid plaques T 2 DM = type 2 diabetes mellitus Adapted from Rhodes CJ. Science. 2005; 307: 380– 384 26
Islet Dysfunction Leads to Hyperglycaemia in T 2 DM pancreatic islet -cell hypertrophy Fewer -cells Insufficient insulin + Excess glucagon – ↑ Glucose Less effective glucose uptake HGO = hepatic glucose output Adapted from Unger RH. Metabolism. 1974; 23: 581– 593 ↑ HGO 27
In T 2 DM, Insufficient Insulin and Elevated Glucagon Secretion Result in Hyperglycaemia CHO meal mg/d. L 400 300 NGT T 2 DM 200 100 Glucose μU/m. L 0 150 100 Insulin 50 NGT T 2 DM pg/m. L 0 150 Glucagon 125 NGT T 2 DM 100 75 – 60 0 60 120 Time (min) Adapted from Müller WA, et al. N Engl J Med. 1970; 283: 109– 115 180 240 28
Decreased Glucose Disposal and Increased HGP Contribute to Increased FPG in T 2 DM 2. 8 Diagnosis 2. 4 Glucose Clearance 2. 0 (m. L/kg • min) 1. 6 Impaired insulin-mediated glucose disposal 1. 2 0. 8 50 100 150 200 250 4. 5 4. 0 3. 5 Glycogenolysis and 3. 0 Gluconeogenesis (mg/kg • min) 2. 5 2. 0 1. 5 1. 0 300 Excessive glucagon-mediated glucose output 50 100 150 200 250 300 FPG (mg/d. L) HGP = hepatic glucose production; FPG = fasting plasma glucose; T 2 DM = type 2 diabetes mellitus Adapted from De. Fronzo RA. Diabetes. 1988; 37: 667– 687 29
Suppression of Endogenous Glucose Production is Impaired in T 2 DM Meal NGT (n= 12) Endogenous Glucose (µmol/min/kg) 18 T 2 DM (n= 18) 14 10 6 2 -30 -15 0 30 60 90 120 150 180 210 240 270 300 Time (minutes) HGO = hepatic glucose output Adapted from Kelley D, et al. Metabolism. 1994; 43: 1549– 1557 30
α-Cell Sensitivity to Glucose is Reduced in T 2 DM 180 NGT* (n = 8) T 2 DM (n = 8) AGRarg (pg/m. L) 150 - 120 - 90 - 60 PG 50 30 0 100 200 300 400 500 600 700 Plasma Glucose Level (mg/d. L) AGRarg= mean acute glucagon response to arginine from 2 to 5 min; PG 50 = plasma glucose level required for half-maximal suppression of AGRarg T 2 DM = type 2 diabetes mellitus; *Healthy men ages 18– 29 Adapted from Ward WK, et al. J Clin Invest. 1984; 74: 1318– 1328. Dunning B, et al. Diabetologia. 2005; 48: 1700– 1713 31
In Patients with T 2 DM, Suppression of Glucagon Reduces Glycogenolysis and Plasma Glucose Levels Glucagon Glycogenolysis§ Glucose (n= 9) † † 100 50 -g glucose ↓ 12 Glucose (mmol/L) 150 4, 500 dpm/kg/min Glucagon (ng/L) 200 50 -g glucose ↓ 3, 000 ‡ ‡ 1, 500 0 -60 0 60 120 180 240 300 360 Time (min) 50 -g glucose‡ ↓ 10 8 6 4 0 60 120 180 240 300 360 -60 0 60 Time (min) Non-suppressed glucagon 120 180 240 300 360 Time (min) Suppressed glucagon †P <0. 0001 between groups; ‡P <0. 001 between groups §As assessed by [14 C] glucose appearance Protocol: somatostatin and insulin delivered to mimic glucagon deficiency, then glucagon infused to simulate a non-suppressed day, or delayed by 2 hours to create transient glucagon deficiency (suppressed day) Adapted from Shah P, et al. J Clin Endocrinol Metab. 2000; 85: 4053– 4059 32
Effect of a glucagon monoclonal antibody on glucose excursion during an OGTT m In ob/ob mice. Data from Sorensen et al , Diabetes 2006, 55: 2843 -2848
Hyperglucagonemia is a feature of all forms of diabetes « Dual A- and B-cell abnormality » ? A-cell insulin resistance ? Hyperglycemia-induced desensitization of the A-cell (Glucotoxicity ? ) 35
An alternative hypothesis* -Insulin and glucagon are secreted in a pulsatile manner -Normal intra-islet insulin pulsatility helps avoiding excessive glucagon release -Normal insulin pulsatility is lost in diabetes Thus, loss of normal intra-islet insulin pulsatility may be involved in the hyperglucagonemia of diabetes *Lefèbvre, Paolisso and Scheen 1991 36
Lelio ORCI 37
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Pulsatile insulin and glucagon-induced glucagon release* Nine Type 1 diabetic patients Very small insulin infusion given either continuously (circulating insulin levels ~15 µU/ml) or same total amount of insulin given in 13 min pulses and both compared to saline infusion No significant effect on blood glucose After 52 minutes, 5 gm iv arginine pulse and evaluation of integrated glucagon response *Paolisso et al , JCEM 1988, 66: 1220 -26 40
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New support for the intra-islet insulin hypothesis MEIER JJ, KJEMS LL, VELDHUIS JD , LEFEBVRE PJ and BUTLER PC : Postprandial Suppression of Glucagon Secretion Depends on Intact Pulsatile Insulin Secretion : Further Evidence for the Intraislet Insulin Hypothesis* *Diabetes , 55: 1051 -1056, 2006 43
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Glucagon pulses in the basal state prior to alloxan in a representative pig 45
GLUCAGON Pulse mass, height and interval in the fasting state and after a meal studied both before and after alloxan in 7 pigs* *Meier et al , 2005 submitted 46
Mean cross-correlogramms between insulin and glucagon concentrations time series in 7 pigs studied over 90 min after a test meal, each prior and after alloxan treatment. The relationship between insulin and glucagon levels is significant before but disappears after alloxan 47
« Forward » and « reverse » cross-As. Pen analyses imply that, in the post-prandial state, pulsatile insulin secretion directly suppresses glucagon secretion, but that this association is lost after a ~60% reduction in beta cell mass 48
In conclusion It is confirmed that glucagon is secreted in distinct pulses both in the fasting state and after a meal In healthy minipigs, suppression of glucagon secretion after a meal is likely accomplished, at least in part, by increased insulin secretion This action of insulin is lost in the minipig alloxan model of Type 2 diabetes mellitus in which post-prandial insulin secretion is impaired as a consequence of an ~60% decrease in beta-cell mass We conclude that post-prandial hyperglucagonemia in diabetes is likely due , at least in part, to impaired insulin secretion leading to a loss of intra-islet driven suppression of glucagon secretion 49
Potential Clinical Consequence: The best way to normalize the hyperglucagonemia of diabetes may be to restore normal insulin secretion , including pulsatility … Increase in amplitude of insulin pulses, without changes infrequency, reported by a 6 wk GLP 1 infusion in 5 old patients with T 2 DM by Meneilly et al JCEM, 2005, 90: 6251 -56 50
Glucagon: Summary · Glucagon plays an essential role in glycaemic control · α-Cell sensitivity to glucose is impaired in T 2 DM, resulting in excessive glucagon secretion · Excessive glucagon secretion contributes to hyperglycaemia in both IGT and T 2 DM · Lowering glucagon levels will be a valuable therapeutic target in the treatment of T 2 DM IGT = impaired glucose tolerance; T 2 DM = type 2 diabetes mellitus 51
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