Insulin

Lecture Classes for BNS 1st Year
Maharajgunj Nursing Campus

1. Insulin For BNS I st Year Dr. Pravin Prasad I st Year Resident, MD Clinical Pharmacology Maharajgunj Medical Campus 5 th October, 2015( Asoj 18, 2072); Monday

2. Insulin: Introduction Ref: http://www.sedico.net/English/SedicoInformationCenter/DiabetesCenter/Pancreas/insulinoma1_e.htm Two chain polypeptide having 51 amino acids (AA), held together by 2 sulphide bonds A-chain 21 AA B-chain 30 AA Molecular Weight: 6000 Pork insulin more homologous to human insulin Secreted by β -cells of pancreatic islets as Preproinsulin (110 AA) After removal of 24 AA, proinsulin is formed. C-peptide is split by proteolysis and both fragments are stored in granules within the cell. Both are secreted together in the blood Human proinsulin

3. Regulation of Insulin Secretion Basal condition ~1U/ hr ; larger quantity following meals Regulated by following Mechanisms: Chemical Hormonal Neural

4. Chemical Regulation of Insulin Secretion Beta cells have glucose sensing mechanism activated by: Entry of glucose into beta cells (aegis of glucose transporter GLUT1) Phosphorylation of glucose by glucokinase Upon activation, it indirectly inhibits the ATP-sensitive K + channels (K + ATP ) Partial depolarization of the β -cells Increases Ca 2+ availability (increased influx, decreased efflux and release from intracellular stores) Exocytotic release of insulin from storing granules. Response varies when nutrients are given orally and parenterally

5. Hormonal and Neural Regulation of Insulin Secretion Hormonal Regulation Intra-islet pancreatic interaction Growth Hormone, Corticosteroids and Thyroxine shows effect in on insulin release in response to glucose. Neural Regulation On stimulation of Insulin Release Adrenergic alpha 2 Decreases Adrenergic beta 2 Increases Cholinergic ( muscuranic ) (Ach or vagal mediated) Increases Primary Central site of regulation of insulin secretion: Hypothalamus ( Ventrolateral nuclei  and Ventromedial nuclei  )

6. Histology Of Pancreas

7. Insulin as an Anabolic Hormone: Actions Glucose transport across cell membrane Expression of glucose transporters into the membrane Intracellular utilization of glucose Effects on gluconeogenesis Effects on Lipid metabolism Effect on Very Low Density lipoprotein and Chylomicrons Effects on Protein Metabolism

8. Insulin: How it Acts

9. Insulin: How it acts Binds to alpha subunit of receptor tyrosine kinase (RTK) present in cell membrane  Activates tyrosine kinase activity of beta subunit  phosphorylates tyrosine residue present on eachother , Insulin Receptor Substrate proteins (IRS1, IRS2) Activates a casacade of phosphorylation and dephosphorylation reactions  Amplification of signals  stimulation and inhibition of enzymes responsible for rapid action of insulin Translocation of glucose transporter GLUT4 to plasma membrane and expression of genes directing synthesis of GLUT4 is promoted Long term effects exerted by generation of transcription factors promoting proliferation and differentiation of specific cells

10. Insulin: Its Fate Distributed only extracellularly Degraded if given orally Injected insulin/insulin released from pancreas: metabolised in liver (kidney and muscles also contributes) Biotransformation results into reduction of disulphide bonds: chains are separated.

11. Insulin: Its Preparations Older commercial preparations: beef and pork insulin, ~1% (10,000 ppm) other proteins ( proinsulins , polypeptides, pancreatic proteins, insulin derivatives) Newer preparations: single peak and monocomponent , highly purified pork/beef insulin, recombinant human insulin/insulin analouges , <10 ppm proinsulin

12. Insulin: Its Preparations Regular Insulin: Soluble, buffered neutral pH of unmodified insulin stabilized by a small amount of zinc Given sub cutaenously , slow absorption, peak activity after 2-3 hrs , lasts for 6-8 hrs Needs to be injected ½ - 1 hr before meal: else risk of early postprandial hyperglycaemia and late postprandial hypoglycaemia Cannot be mixed with insulin glargine / detemir

13. Insulin: Its preparations Lente Insulin Neutral Protamine Hagedorn (NPH) Insulin or Isophane Insulin Insulin-zinc preparation Insulin- Protamine preparation Combination of Ultralente (large particles, crystalline, practically insoluble, long acting) and semilente (small particles, amorphous, short acting); Ratio 7:3 Protamine sufficient to complex all insulin molecules Neutral pH Combined with regular insulin in the ratio 70:30 or 50:50 Injected twice daily s.c. before breakfast and before dinner

14. Insulin Analouges Insulin lispro : Weak hexamers , dissociates rapidly Quick and more defined peak Injected immediately before or even after meal: better control of meal-time glycaemia and lower incidence of post prandial hypoglycaemia Multiple injections, fewer incidence of hypoglycaemia Insulin aspart : Similar to insulin lispro Insulin glulisine : Used for continuous subcutaneous insulin infusion (CSII)

15. Insulin Analouges Insulin glargine : Remains soluble at pH4, precipitates at neutral pH Delayed onset of action, maintained for up to 24hrs: “smooth peakless effect” Insulin detemir : Binds to albumin and action is prolonged Twice daily dose is required

16. Insulin: Unwanted Efects Hypoglycaemia Seen more in labile diabetes patients Sympathetic symptoms and neuroglucopenic symptoms Hypoglycaemic unawareness Local Reactions Swelling, stinging, erythema; Lipodystrophy Allergy Utricaria , angioedema, anaphylaxis Edema

17. Uses of Insulin Diabetes Milletus : Mandatory in Type 1 DM (Insulin Dependent DM), post pancreatectomy diabetes, gestational diabetes ( 0.4-0.8 u/Kg/day) Some cases of Type 2 DM (Non Insulin dependent DM): not controlled by diet/exercise, failure of OHA, under weight, temporary situtations , during complications (0.2-1.6 U/kg/day) Given as Split-mix regimen and Basal Bolus regimen Diabetes Ketoacidosis Regular insulin, 0.1-0.2 U/kg i.v. bolus followed by 0.1U/kg/ hr infusion- adjusted according to the fall in blood glucose levels Hyperosmolar (non ketotic ) Hyperglycaemic Coma

18. Insulin Regimens Split-mixed Regimen Basal Bolus Regimen Regular insulin with lente or isophane (30:70 or 50:50) Long acting insulin ( Insulin glargine ) and short acting insulin ( lispro / aspart ) injected separately Injected Before Breakfast and Before Dinner Long acting insulin ( glargine ) injected daily (before breakfast/ before bed time) with 2-3 meal time injections with rapid acting insulin ( lispro / aspart ) Only two daily injections required Better round the clock euglycaemia Post lunch glycaemia not adequately controlled Late postprandial hypoglycaemia may occur 3-4 daily injecctions More demanding and expensive Higher incidence of severe hypoglycaemia Best avoided in young and children and elderly