Insulin Flashcards
- Insulin nearly absent
- Autoimmune destruction of pancreatic B cells
- Plasma glucagon elevated
- Occurs mainly in adolescents
Type I diabetes
Exogenous insulin given to type I diabetes patients for what?
- Prevent ketosis
- Reduce hyperglucagonemia
- Reverse catabolic state
- Abnormal insulin secretion and resistance to insulin action at tissues
- Associated with obesity and metabolic syndrome
- Deficiency in pancreatic B cell response to glucose, worsened by hyperglycemia
Type II diabetes
How do you treat Type II diabetes in the early and late stages?
Early: Noninsulin anti diabetic drugs
Late: Drug regimen with addition of insulin
Type _____ diabetes is caused by elevated blood glucose due to other reasons such as pancreatectomy, pancreatitis, non pancreatic disease, drug therapy, etc.
3
- Gestational diabetes
- Abnormality in glucose levels beginning during pregnancy (7%)
- Placenta/placental hormones creaste insulin resistance (most prominent in last trimester)
Type 4 diabetes
HbA1c tests for what?
- A1c measures the “glycosylated” hemoglobin
- A1c is correlated with mean blood glucose
Pt at goal: test 2xs a year
Pt not at goal: test 4xs a year
What is the stepped care approach for type 2 diabetes?
- Lifestyle changes: diet, exercise, smoking, lipids
- Single oral agent
- Combination oral therapy
- Oral therapy plus insulin
- Insulin
How is insulin formed?
Proinsulin produced by pancreatic B cells are packaged into granules where its hydrolyzed into insulin and C peptide. Insulin is stored in crystals with a ratio of 2 atoms of zinc with 6 atoms of insulin
Insulin high secretion rate is released in response to what 4 factors?
- Glucose
- Other sugars (ex: Mannose)
- Certain amino acids (ex: Leucine, arginine)
- Vagal nerve activity
Give MOA of Insulin.
- Hyperglycemia
- Increased intracellular ATP
- Higher intracellular ATP closes ATP-dependent K+ channels
- Decrease in outward K+ movement causes depolarization which opens calcium channels
- Increase in intracellular calcium
- Intracellular 2nd messengers modulate release of cyclic AMP (cAMP), inositol triposphate (IP3), and diacylglycerol (DAG).
- Release of Insulin
What organ/organs clears insulin from the body?
- Liver: 60% of insulin released from pancreas
- Kidney: 35-40% of endogenous insulin (in insulin-treated diabetics - subcutaneous injections - the kidney may clear as much as 60%)
How is insulin degraded?
Cleavage of sulfide linkage between A and B chains space and then further degraded by proteolysis
What is the composition of insulin?
Two heterodimers that contain an alpha subunit (extracellular: recognition site) and a beta subunit that spans the membrane and contains a tyrosine kinase..
The subunits combine to form either homodimers or heterodimers, resulting in the disulfide-linked transmembrane insulin receptor.
Insulin binds to ___ subunit.
Alpha
___ subunit increases tyrosine kin as activity, resulting in auto-phosphorylation.
Beta
-Phosphorylated beta subunit promotes aggregation of heterodimers and stabilizes the receptor kinase activated state
What causes a change in the affinity of insulin receptors?
- Decreased affinity: caused by some hormonal agents (hydrocortisone)
- Increased affinity: caused by growth hormone
What glucose transporter is most important in lowering blood glucose and where does it act?
GLUT4 - found in muscle and adipose cell membranes and is inserted from storage vesicles.
Where are GLUT2 glucose transporters found?
Pancreatic B cells and liver
-Abnormalities in these transporters may contribute to reduced insulin secretion in type 2 diabetes
Endogenous insulin reaches the liver first. What does it do in the liver?
Increases glucose storage as glycogen through the insertion of additional GLUT2 glucose transport molecules in cell plasma membrane
Insulin resets liver to “fed” stat which influences what factors?
- Glycogenolysis
- Ketogenesis
- Gluconeogenesis
Also causes decreased protein catabolism.
What are the actions insulin has on muscle cells?
- Protein synthesis
2. Glycogen synthesis (Glucose transport into muscle cells facilitates GLUT 4 transporters into plasma membrane)
What are the actions of insulin on adipose cells?
Reduces free fatty acids in circulation by promoting triglyceride storage via these 3 mechanisms:
- Lipoprotein Lipase induction
- Enhance glucose transport (GLUT4 transporters)
- Reduces intracellular lipolysis of stored triglyceride
Goal in treating insulin is to control both basal and postprandial (after meal) glucose levels, minimizing _____________.
Hypoglycemia
What are the rapid-acting insulins?
- Insulin lispo
- Insulin aspart
- Insulin glulisine
When are Insulin lispro peak serum values?
Within 1 hr - much more rapid than hexametric human insulin.
New, monomeric insulin analog, recombinant technology, interchange of two amino acids near the B chain terminal, rapid acting
Insulin Lispro
When should Insulin Lispro be given?
- Injected immediately before a meal (Postprandial glucose control)
- Preferred for infusion devices
- Duration of action is no more than 3-4 hours