Insulin pharmacology

A PowerPoint presentation on "Insulin Pharmacology" suitable for undergraduate medical students

1. INSULIN
PHARMACOLOGY
Dr. D. K. Brahma
Associate Professor
Department of Pharmacology
NEIGRIHMS, Shillong

2. Background
Discovered by Banting and Best - 1921
Fredrick G. Banting & Charles H. Best -
Canadian Scientist – Extracted Insulin from Dog
pancreas
2 chain Polypeptide – 51 amino acids & MW
6000
Chain-A has 21 and Chain-B has 30 amino
acids – connected by two disulfide bonds
Source: Porcine, Bovine and Human (Pork =
human)
Synthesized in β cells of islets of pancreas –
single chain 110 amino acids (Preproinsulin)
Proinsulin – 86 amino acids
Connecting “C” peptide (35 amino acids)
removed by proteolysis in Golgi apparatus –
Insulin
Source: https://www.researchgate.net/figure/268872215_fig3_Figure-3-Structure-of-
pro-insulin-showing-C-peptide-and-the-A-and-B-chains-of-insulin

3. Diabetes Mellitus
•Hyperglycaemia, glycosuria, hyperlipidaemia, negative nitrogen balance
and ketonaemia
•Pathological changes: thickening of capillary basement membrane,
increase in blood vessel wall matrix, and cellular proliferation
•Consequences: Lumen narrowing, atherosclerosis, sclerosis of
glomerular capillaries, retinopathy, neuropathy and peripheral vascular
insuffficency
•Causes of pathological changes: Enhanced non-enzymatic glycosylation
of tissue proteins and accumulation of large amounts of sorbitol
•Glycosylated haemoglobin (HbA
1c
) – Index of protein glycosylation

4. Diabetes Mellitus - Types
•Type I: Insulin dependent DM (IDDM) / Juvenile onset diabetes – low circulating insulin level –
prone to ketoacidocis
–destruction of β cells in pancreatic islets
–Type IA – antibodies destroying β cells
–Type IB: Idiopathic, no β cell antibody detectable
–Low degree of genetic predisposition
•Type II Noninsulin-dependent DM (NIDDM): no loss of moderate loss of β cell, low/normal/high
insulin in circulation, no anti- β-cell antibody – genetic predisposition
•Causes: (1) Abnormality in gluco-receptor in β cell – needs higher conc. of glucose; (2)
Relative β cell deficiency
–Down regulation of insulin receptors in peripheral tissues
–Many Hypertensives are hyperinsulinaemic – normoglycaemic but dyslipidaemia,
hyperuricaemia, abdominal obesity (metabolic syndrome) – Insulin Resistance
–Excess of hyperglycamic hormones
•Other Types: Type III (!) – LADA and MODY; Type IV – Pancreactomy and gestational diabetes
mellitus (GDM)

5. Regulation of Secretion
Basal condition – 1 U per hour – more after meals
Regulated by – Chemical, hormonal and neural mechanisms
3. Neural: Sypmpathetic and vagal Nerve influennce in islets – (i) alpha-2 stimulation decreases insulin release (predominant)
(ii) beta-2 cell stimulation increases Insulin release; (3) Vagal stimulation increases Insulin relese – IP3DAG
1. Chemical (glucosensor) 2. Hormonal
Glucokinase
Glucosensor
Source: Essentials of Medical pharmacology by KD
Tripathi – 7
th
Edition, JAYPEE, 2013
Source: https://courses.washington.edu/conj/bess/humoral/humoralregulation.htm

6. Actions of Insulin
Meal derived glucose, amino acids, fatty acids and fuel storage
Major anabolic hormone – synthesis of glycogen, lipids and proteins
1.Facilitates glucose transport across cell membrane – skeletal muscle and fats - Liver, brain,
RBC, WBC and renal medullary cells are independent
2.Intracellular utilization of glucose – phosphorylation to form Glucose-6-PO4 – increased
production of glucokinase – also glycogen synthase
3.Inhibits gluconeogenesis from protein, FFA and glycerol (diverted to liver) – by decreasing
synthesis of (gene mediated) phosphoenol pyruvate carboxykinase.
4.Inhibits lipolysis in adipose tissues – favours triglyceride synthesis – in diabetes, increased FFA
and glycerol (Acetyl-CoA) – ketone bodies
5.Facilitates amino acid entry and their synthesis to protein – also inhibits protein breakdown in
muscles and other cells – in its absence excess pyruvate, glucose and urea (negative nitrogen
balance)

7. Insulin - mechanism of action
T – Tyrosine residue; GLUT4 – Glucose
transporter, IRS – Insulin receptor substrate
protein, T-PrK – Tyrosine protein kinase,
Ras – Regulator of cell division and
differentiation
Source: Essentials of Medical pharmacology by KD Tripathi – 7
th
Edition, JAYPEE, 2013

8. Fate of Insulin
Distributed only extracellularly – given
orally gets degraded in GIT
Secreted and injected Insulin –
metabolized in liver, kidneys and muscles
First pass metabolism - 50% of Insulin
passing through portal vein
Degradation after receptor mediated
internalization
Biotransformation – sulfide bonds are
reduced – chain A and B are separated –
broken down to amino acids
Source - https://www.slideshare.net/aishahadalicia/insulin-and-its-mechanism-of-
action-31298888

9. Preparations of Insulin
Classically – produced from beef and pork pancreas
Contains 1% (10, 000 ppm) other proteins – proinsulin, polypeptides,
pancreatic proteins etc.) – potentially antigenic
Replaced with highly purified pork/beef insulin/recombinant human
insulin/insulin analogues
Single peak and Monocomponent insulin (MC) – proinsulin <10 ppm –
stable, less resistance and lipodystrophy
Unitage/Assay: I U reduces fasting rabbit blood sugar by 45 mg/dl or
potency to induce hypoglycaemic convulsion in mice
I mg of International Standard of Insulin = 28 units
Radioimmunoassay or enzyme immunoassay

10. Types of preparations – Regular (Soluble) Insulin
Buffered neutral pH solution unmodified insulin stabilized by small
amount of zinc
Forms hexamers around zinc ions – released slowly and gradually by
dilution on SC administration
Peak onset 2- 3 hours and lasts for 6-8 hours
Drawbacks:
Before meals – early postprandial hyperglycaemia and late post
prandial hypoglycaemia – injected ½ to 1 hour before
Do not provide basal level of action – interdigestive period
Slow onset of action is not applicable for IV injection
Long acting – modified or retard preparations

11. Insulin preparations - Purified
Rendered insoluble - complexed with protamine or excess zinc
Lente (Insulin-zinc suspension): 2 types
Ultrelente: Large particle size, crystalline and insoluble in water – long acting Semilente: Small particle
size, amorphous – short acting; Lente: 7:3 ratio mixture
Isophane (Neutral Protamine Hagedorn or NPH) insulin: Protamine added just
sufficient to complex all insulin molecules
Neither are in free form – neutral pH
On injection: dissociate slowly intermediate action
Used in combination with regular insulin in 70:30 ratio or 50:50
Injected twice daily before breakfast and dinner (split-regimen)
Available preparations: Highly purified MC pork regular insulin, highly purified MC pork
lente, Highly purified MC NPH, highly purified regular insulin and Isophane (30:70
ratio)

12. Human Insulin
Same amino acid sequence as human insulin - produced by recombinant DNA
technology
In Escherichia coli – proinsulin recombinant bacteria (prb) and in yeast – precursor
yeast recombinant (pyr) or by enzymatic modification of porcine insulin
Human actrapid (regular insulin) – 40 U/ml
Human monotard (lente), human insulatard (NPH), Human mixtard (30:50), Insuman
(50:50)
Advantages: More water soluble and hydrophobic, more rapid absorption than porcine
or bovine, more defined peak, shorter duration of action

13. Insulin analogues
Recombinant DNA technology, modified pharmacokinetic – greater stability and
consistency
Insulin lispro: Reversing Proline and lysine at B 28 and B 29 position – quick acting,
just before meals
Insulin aspart: B 28 is replaced by aspartic acid – mimics physiological insulin
Insulin glulisine: Replacing aspartic acid at B 23 by lysine and glutamic acid replacing
lysine at B 29 – continuous SC insulin infusion (CSII)
Insulin glargine: Long- acting – precipitates at neutral pH on SC injection – depot
created – slow dissociation – 24 hours low blood level – usually at bed time

14. Reactions and Drug Interactions (DIs)
HYPOGLYCAEMIA: Labile diabetics
Causes: Injection of large doses, missing a meal after injection, vigorous exercise
Symptoms: Sweating, anxiety, palpitation, tremor – counter regulatory; dizziness,
headache, behavioural changes, visual disturbances, hunger, fatigue, weakness,
muscular incoordination etc. - due to deprivation - Below < 40 mg/dl – seizure and
coma
Treatment: Glucose orally and IV – Glucagon – 0.5 to 1 mg IV
Local reactions (swelling), lipodystrophy, Allergy, Oedema
Drug Interactions: Beta blockers (beta-2; prolong hypoglycaemia), Thiazides, diuretics,
steroids, OCPs (raises blood sugar), acute alcohol ingestion (hypoglycaemia –
glycogen depletion), Lithium and aspirin (hypoglycaemia – enhance insulin
secretion)

15. Uses of Insulin
Purpose: Restore metabolism to normal, avoid symptoms due to hyperglycaemia and
glycosuria and prevent complications
Indications: Type 1 DM, Post pancreatectomy diabetes and gestational diabetes; Type
2 DM: Not conrolled by diet and exercise, failure of oral hypoglycaemics, under wight,
tide over crisis and complications (ketoacidosis)
Treatment: According to requirement and convenience of each patient – by testing
urine and blood glucose level
Type 1: usually 0.4 to 0.8 U/kg/day (severity and obesity)
Target: obtain basal control – no single daily dose of long/intermediate/short acting ones can fulfill
Multiple (2 – 4) injections daily of long and short acting or Long acting with Oral hypoglycaemics (meal
time)
Conventionally, split-mixe d re gime : mixture of regular with lente/isophane (30:70 or 50;50) – before
breakfast and before dinner

16. Uses of Insulin – contd.
Basal bolus regime: 3 - 4 daily injections - a long acting (glargine) insulin before
breakfast or before bed time with 2-3 meal time injections of short rapidly acting (lispro
or aspart)
Other uses: Diabetic Ketoacidosis (Coma), Hyperosmolar (non-ketotic
hyperglycaemic) coma
Insulin resistance: Type 2 DM, Age, large body fats, pregnancy, OCPs – acromegally,
Cushing`s syndrome, phaeochromocytoma etc.
Acute Insulin resistance: Infection, trauma, surgery, stress etc.
Newer Insulin Delivery devices: Insulin syringe, Pen devices, inhalled insulin, Insulin
pumps (CSII) etc.

17. Summary of Insulin preparations
Short acting: Regular soluble insulin – clear appearance; 6-8 hours – can be mixed
with others except glargine
Intermediate acting: Lente, NPH or Isophane – cloudy; 20-24 hours - Regular
Long acting: Glargine and detemir – clear; 24 hours – cannot be mixed with others
(can be combined)
Rapid acting: lispro, aspart, glulisine – clear; 3-5 hours – can be mixed with Regular
and NPH

18. Thank you
Insulin prefilled syringe
Insulin pump