Chapter 60 – Insulin, Oral Hypoglycaemic Agents and the Pharmacology of the Endocrine Pancreas

Insulin

Prevalence of diabetes mellitus (DM) has increased over the past decades. Obesity↑. Consequences of prolonged hyperglycemia and dyslipidemia:

o Accelerated atherosclerosis.o Chronic kidney disease.o Blindness.

HISTORYo 1869 – Paul Langerhans discovers that the pancreas has 2 types of cells: acinar (which secrete

digestive enzymes) and the cells concentrated in islets (which had another fxn).o 1889 – Minowski and von Mering showed that taking out the pancreas in dogs could produce a

DM type of disease.o 1900s – Gurg Zuelzer tried to treat a diabetic patient w/ extracts of pancreas.o 1911 – E.L. Scott got alcoholic extracts of the pancreas and treated some diabetic dogs. Lacked

measures of control of blood glucose.o 1916-1920 – Nicolas Paulesco discovers that pancreatic extracts lower gluconuria and ketonuria in

dogs.o Frederick Banting and Charles Best – Ligating the pancreatic duct, they destroyed the acinar cells,

but left the islet cells intact. They extracted the remaining tissue w/ ethanol and acid. First patient was Leonard Thompson (14 years old). Daily injections of insulin helped

him reduce his blood glucose to normal levels. Stable extracts of insulin soon were obtained and patients were treated. NOBEL PRIZE IN MEDICINE AND PHYSIOLOGY 1923.

CHEMISTRYo Abel – Purifies insulin. o 1960 – Sanger determines AA sequence of insulin. First artificial synthesis (1963).o 1972 – Hodgkin et al elucidate insulin’s 3D structure.o Humans: 1 insulin gene and 1 protein product.o Preproinsulin – has a single chain and 110 AAs.

It translocates through the rER membrane. It has a 24-AA signal peptide in its N-terminus. This peptide is CLEAVED → It is now

called PROINSULIN. The signal sequence is a requirement for translocation into the lumen of the rER.

o Proinsulin folds and disulphide bonds form. Transport to the Golgi complex → secretory granules. Some proinsulin is secreted by the β cells (incomplete conversion of proinsulin to insulin).

Conversion to insulin. 4 basic AAs and the connector peptide (C Peptide) are removed by proteolysis.

o Equimolar amounts of C peptide and insulin are released into the circulation. (Index for insulin secretion).

The protein now has the A and B chains of the insulin molecule. It also has 1 intrasubunit and two intersubunit disulphide bonds.

A Chain of insulin: 21 AAs. B Chain of insulin 30 AAs. Mass: 5734 Da. The chains are inactive by themselves. N-terminus –B1 AA →B30 AA. C-Terminus – A21 AA → A1 AA.

o Insulin has variations that cause ≠s in biological potency and immunogenicity.o 3D structure.

Each chain has α-helical regions in each of the chains. It can exist as a monomer, dimer or hexamer. Zn2+ molecules coordinated in the hexamer: that’s how it is stored in the β cells of the

pancreas. (Zn2+ facilitates hexamer formation and storage & conversion of proinsulin to insulin).

1

The monomer is most likely the biologically active form of insulin and the one that is in the circulation.

o Interaction w/ the receptor b/c of 12 invariant residues on both chains. GlyA1, GluA4, GlnA5, TyrA19, AsnA21, ValB12, TyrB16, GlyB23, PheB24, PheB25 and TyrB26. Binding to surfaces at the N-and C-terminal regions of the α subunit of the receptor. The more affinity insulin has for its receptor, the more potent it will be in causing a

response in glucose metabolism. Human, bovine and porcine insulins are equipotent.o Family: Insulin-like Growth Factors (IGFs).

IGF-1 and IGF-2 (also called somatomedins) have homologous structures to proinsulin. However, unlike proinsulin, they keep their C peptide and are produced in many tissues (not just the pancreas).

Fxn is to regulate growth, and to mediate the action of GROWTH HORMONE. Receptors of IGF-1 and insulin are closely related. (Can bind to each other’s receptors).

Synthesis, Secretion, Distribution, and Degradation of Insulin

Insulin Production

Islet of Langerhans has 4 types of cells, each of which synthesizes a distinct hormone.o α cell: Glucagon.o β CELL: Insulin. (60-80% of the islet; located in the central core). 1ary glucose sensor. (Amilina)o δ cell: Somatostatin.o PP or F cell: Pancreatic polypeptide.

Cells connected by tight junctions that allow small molecules to pass and facilitate coordinated control of groups of cells.

Arterioles enter the islets and branch out in the core; they form capillaries and coalesce into venules.o BLOOD FLOW: β CELLS → α Cells → δ Cells.

Up to 20% of immunoreactive insulin in plasma is, in reality, proinsulin and intermediates. Conversion of proinsulin to insulin:

o 2 Ca2+-dependent endopeptidases (PC2 and PC3).o PC2- cleaves A chain-C peptide jxn.o PC3- cleaves B chain-C peptide jxn.

REGULATION OF INSULIN SECRETIONo Goal: stable concentrations of glucose in blood during fasting and feeding.o Mediators: nutrients, GI hormones, pancreatic hormones, and autonomic neurotransmitters.

Cause ↑insulin secretion: Glucose. AAs. Fatty acids. Ketone bodies. Stimulation of β2 adrenergic receptors and CN X stimulation.

Cause ↓ insulin secretion: Stimulation of α2 adrenergic receptors. (α2 agonists like clonidine and

guanadrel)o They reduce cAMP concentration by binding to a G-protein coupled

receptor. Any condition that stimulates the sympathetic nervous system.

o Hypothermia, exercise, hypoxia, hypoglycaemia, surgery or burns. Therefore β-blockers (propranolol) decrease insulin production and α2 receptor

antagonists increase insulin production. Some of these mediators affect both biosynthesis and secretion of insulin, while others,

like the Ca2+ concentration outside the cell, only affect secretion and not biosynthesis.o Glucose

Promotes the secretion of insulin in a greater extent when taken orally.

2

Orally, glucose also causes the secretion of GI hormones and stimulation of CN X.

GI hormones that promote Insulin Secretion: Gastrin, Secretin, Cholecystokinin, Vasoactive Intestinal Peptide, Gastrin-Releasing Peptide, Enteroglucagon, Gastrointestinal Inhibitory Peptide (GIP) and Glucagon-like Peptide 1 (GLP-1).

How does glucose promote insulin secretion? Hyperpolarised β cell: No insulin secretion. Depolarised β cell: Insulin

secretion. Glucose depolarises β cell. Glucose enters the β cell (facilitated transport –GLUT2, a transporter). Glucokinase phosphorylates Glucose to Glucose-6-Phosphate (G-6-P).

o GLUCOKINASE It’s a hexokinase expressed only in tissues involved in the

regulation of glucose metabolism. It’s the glucose sensor. There are mutations in the glucokinase gene that cause a

maturity-onset diabetes of the young (MODY2). It takes more glucose to stimulate insulin release.

Increase in IC glucose and G-6-P means that MORE ATP CAN BE PRODUCED. (ATP in the cell > ADP in the cell).

The increased concentration of ATP inhibits an ATP-sensitive K+ channel and, because the K+ flux decreases, the Vm rises and a voltage-sensitive Ca 2+ channel opens.

The ATP-sensitive K+ channel (4 Kir 6.2 and 4 SUR-1 subunits).o The Kir 6.2 subunit is the one that causes it to close when IC ATP

rises.o SUR-1

Inhibitors (Channel closes): Sulfonilureas and meglitinides. This causes insulin production b/c the channel closes in response to the inhibitor.

Activators (Channel opens): ADP, Diazoxide. (Decrease in insulin secretion b/c the cell remains hyperpolarised if the K+

flux doesn’t decrease). Consequences of the opening of this voltage-sensitive Ca2+ channel:

o Increase in the secretion of insulin.o Activates phospholipases.

More production of eicosanoids and IP3. IC Ca2+ stores are mobilised.

Other ways the voltage-gated Ca2+ channel can be opened:o ACh & Cholecystokinin stimulate Phopholipase C, which opens the

channel.o Hormones that increase IC concentrations of cAMP. They bind to a G-

protein coupled receptor and stimulate adenynyl cyclase. Glucagon GIP GLP-1

o Biphasic secretion of insulin: Peak after 1-2 minutes (short phase). Long phase: takes longer to peak, but its effect lasts longer.

o Rate of secretion of insulin and glucagon are reciprocal. (Insulin affects α cell). Glucagon stimulates the release of somatostatin by the δ cell, which may suppress

insulin secretion a little bit. (However, it must reach the circulation and go back around to the α and β cells in order to do that).

Insulin can inhibit the rate of glucagon release in a paracrine manner. DISTRIBUTION AND DEGRADATION OF INSULIN.

o Fasting: 40 µg of insulin every hour. Peripheral concentration: 0.5 ng/ ml.

3

After eating, the insulin concentration rises first in the portal blood and then, to a smaller extent, in the peripheral circulation.

o Half-life of insulin in plasma is about 5 to 6 minutes in people w/ uncomplicated diabetes. Less in people w/ anti-insulin Igs.

o Half-life of proinsulin is longer (17 min). 10% of immunogenic “insulin” in plasma. INSULINOMA: Proinsulin production is increased. 2% as potent as insulin.

o The liver doesn’t clear C peptide as fast as it clears insulin, so C peptide concentrations in plasma are higher than the concentrations of insulin. C peptide also has a longer half-life than insulin (30 minutes).

o Degradation: Liver, kidneys and muscle. Liver: Insulin gets to the portal vein and goes to the liver and 50% of the insulin secreted

by the pancreas is destroyed in the liver at this stage so it never gets to the general circulation.

Degraded in the hepatocyte’s cytoplasm and membrane.o Cytoplasm: receptor-mediated endocytosis. (Endosomes &

lysosomes). About 50% of the internalised insulin is degraded. Kidneys: Filtered by the glomeruli and reabsorbed/degraded by the tubules.

If renal fxn is severely impaired, that affects IMMENSELY the rate of degradation of insulin. Hepatic fxn cannot compensate.

Endothelial cells internalise but don’t degrade insulin b/c this internalisation is part of the transcytosis (the process of bringing insulin from the intravascular to the EC space).

Degrading enzyme: Thiol metalloproteinase (hepatocytes). Most of the degradation happens in the cytoplasm.

CELLULAR ACTIONS OF INSULINo Target tissues: Liver, muscle and fat. (Insulin also exerts effects on other cells).o Controls the uptake, use and storage of cellular nutrients.

Anabolic actions Stimulation of IC use of glucose, AAs and fatty acids.

Catabolic actions Inhibits IC use of glycogen, fats and proteins.

How? It stimulates the transport of substrates and ions into the cells, helps proteins to translocate btn IC compartments, activates specific enzymes, changes the amount of proteins by altering the rates of gene transcription and specific mRNA translation.

o Fast action (seconds or minutes). Other effects might take hours. Activation of glucose and ion transport systems. Covalent modification of enzymes Some effects on gene transcription.

REGULATION OF GLUCOSE TRANSPORTo B/C OF INSULIN, GLUCOSE GETS TRANSPORTED INTO MYOCYTES AND

ADIPOCYTES.o GLUT-1 through GLUT-5 are the main glucose transporters. (Na+-independent facilitated

transport). Integral-membrane glycoproteins w/ 12 membrane-spanning α-domains. When insulin enters the cell, it stimulates the movement of vesicles containing GLUT-4

and GLUT-1 towards the cell membrane. As a result, more glucose gets transported into the cell.

If there’s no insulin, the transporters return to the cytoplasm (TYPE 2 DM). REGULATION OF GLUCOSE METABOLISM

o Glucokinase (Hexokinase IV): phosphorylates glucose into Glucose-6-Phosphate (G-6-P). Facilitated diffusion of glucose into cells along a downhill gradient. Associated w/ GLUT-2 transporter in liver and pancreas. There is 1 glucokinase gene, but different exons and promoters are used by pancreas and

liver.

4

Liver: glucokinase gene is regulated by insulin.o Hexokinase II: Associated w/ GLUT-4 in skeletal and cardiac muscle. Regulated transcriptionally

by insulin.o G-6-P may enter several pathways:

Isomerizes to G-1-P and is stored as glycogen. Glycolytic pathway → ATP. Pentose phosphate pathway: Provides NADPH for reductive syntheses, metabolism of

CYP and maintenance of reduced glutathione.o Affects cells via the activity of protein kinases and phospho-protein phosphatases.

REGULATION OF GENE TRANSCRIPTIONo More than 100 genes are known to be regulated by insulin.

Ex. Inhibits genes for gluconeogenesis. (Type 2 DM: Liver overproduces glucose). THE INSULIN RECEPTOR

o Insulin binds to its receptor on different types of cells like (but not limited to) liver, muscle and fat cells.

o A transmembrane glycoprotein composed of 2 α subunits and 2 β subunits. β-α-α-β heterotetramer.

Subunits derived from a single-chain precursor. α domains are entirely extracellular. (Insulin-binding domain). β subunits have tyrosine-protein-kinase activity.

o Insulin binds → receptors aggregate and are internalised rapidly. Receptor dimerization is essential for signal transduction.

o Tyrosine Phosphorylation and the Insulin Action Cascade Insulin receptor: tyrosine-kinase receptor. Much like other growth factor receptors. Autophosphorylation → tyrosine-kinase activity can happen towards IRS-1 to 4 and Shc. Tyrosine phosphorylated IRS: Signalling cascades.

They interact w/ SH2 Domains and recruit proteins like SHP2, Grb2 and SOS. MAP Kinases and PI3 Kinases are activated.

IGF-1 receptor resembles insulin receptor (similar signalling pathways). They bind each other’s ligands.

Target tissues = DISPLACEMENT OF THE GLUT-4 TRANSPORTER. The tyrosine kinase activity of the insulin receptor is REQUIRED FOR SIGNAL

TRANSDUCTION. (An insulin receptor incapable of autophosphorylation is biologically inert).

Polymorphism in IRS-1 is associated w/ insulin resistance and increased risk of type 2 DM. Inhibits insulin-receptor tyrosine kinase.

Diabetes Mellitus and the Physiological Effects of Insulin

Characteristic of all types of DM: o Hyperglycemia, altered metabolism of lipids, ketones, proteins and CHs and a greater risk of

complications from CV disease. o Insulin resistance: a decrease in the response of peripheral tissues to insulin.o Symptoms: Polyuria, polydipsia, unexplained weight loss.o Diagnosis

Random (OR 2 hrs after OGL) plasma glucose concentration > 200 mg/dl. Fasting plasma glucose concentration > 126 mg/dl

Normal actions of insulino Inhibits hepatic glucose production.o Stimulates the uptake and metabolism of glucose by muscle and adipose tissue (at higher

concentrations of glucose).o Inhibits lipase in adipose tissue (inhibits hydrolysis of triglyceride stores).

Reduces concentrations of glycerol and free fatty acids. (↓ gluconeogenesis). In diabetics, there is ↑ gluconeogenesis and ketogenesis.

5

o Stimulates AA uptake and protein synthesis. (Lowers plasma AAs, including alanine and glutamine, which are needed for gluconeogenesis). If it’s not there, it prevents gluconeogenesis.

Increased gluconeogenesis in diabetics results in production and excretion of urea and ammonia. Diabetes causes decreased protein synthesis and proteolysis.

o Normally, insulin enhances the transcription of lipoprotein lipase in the endothelium. This results in the release of Intermediate-Density Lipoproteins, which are converted into LDL.

Diabetics: HypertriglyceriDEMIA and hypercholesterolemia often occur. Ketone bodies are produced by the liver

o Oxidation of free fatty acids → Acetyl CoA → acetoacetate and β-hydroxybutyrate.o Mitochondria

Acetyl CoA + carnitine esters→ fatty esters (acyclarnitine transferase, AcT) Fatty acid synthesis causes the production of malonyl CoA. This inhibits AcT.

Insulin increases the concentration of malonyl CoA. Insulin decreases hepatic concentration of carnitine esters.

o Prevents the production of ketone bodies.o T1 DM: Favours ketogenesis → ketonemia and acidosis.

Glucagon opposes the hepatic effect of insulin: there is gluconeogenesis and glycogenolysis.o Hyperglucagonemia =

↑ hepatic glucose production. ↓ peripheral glucose uptake. ↓ conversion of glucose → glycogen.

Vascular changes in diabeteso Narrowing of the vessel lumina= inadequate perfusion of critical regions of certain organs.

Expansion of matrix in vessel walls, in the basement membrane of the retina and in the mesangial cells of the renal glomerulus.

o Major complications’ Premature atherosclerosis. Intercapillary glomerulosclerosis. Retinopathy. Neuropathy. Ulceration and gangrene of the extremities.

Most diabetic complications arise from prolonged exposure of tissue to elevated glucose concentrations (Diabetes Control and Complications Trial, DCCT).

o Intensive therapy w/ insulin reduced the mean risk for the development of retinopathy, nephropathy and neuropathy.

It also rduced the development of hypercholesterolemia, macrovascular disease. Improving day-to-day glycemic control can reduce and slow the development of diabetic

complications dramatically. It increased the risk of hypoglycaemia (<50 mg/dl). CAREFULLY MONITOR glycemic

control in kids. Careful – older patients are more susceptible to the consequences of

hypoglycaemia.o Toxic effects of hyperglycaemia.

Accumulation of non-enzymatically glycosylated products and osmotically active sugar alcohols (sorbitol) in tissues.

May form cross-linked proteins ADVANCED GLYCOSYLATION END PRODUCTS.

May be directly responsible for expansion of the vascular complications of diabetes.

Modified cellular proliferative activity in vascular lesions in diabetics.o Macrophages have receptors for advanced glycosylation end products.o They produce more cytokines (TNF-α and IL-1)o Degradation in mesenchymal cells; proliferative cascades in endothelial

cells.

6

Production of sorbitol by aldose reductase is dependent on glucose concentration. Increased sorbitol concentration in lens, retina, arterial wall and Schwann cells of peripheral nerves causes tissue damage.

Neuropathy: + GLUCOSE than myoinositol inside the cell = altered nerve function.

Cellular metabolism is affected directly by glucose. Glycosylated Haemoglobin (Haemoglobin A1C) is a measure of glycemic state because

it’s proportional to the glucose concentration and to the time the haemoglobin has been exposed to glucose.

Rise in Haemoglobin A1C from 5 to 10%. TYPE 1 DM (T1 DM, 5% of all US/UK diabetics; higher prevalence in northern Europe)

o Immune response against β cell. (1A). Igs against islet cells, against insulin (IAAs), against heat-shock protein 65, GAD

antibodies, etc. However, the presence of IAAs ALONE confers only a small risk for T1 DM. IAAs +

islet cell IGs = VERY HIGH RISK FOR THE DISEASE. The presence of more than 1 form of Igs is a more powerful predictor of the

development of the disease.o HLA (Human leukocyte antigen) alleles in the B and DR loci.

90% of T1 Diabetics have the HLA-DR3 or HLA-DR4 alleles (40% of general population).

HLA-DR2 means LESS risk for T1A DM.o Both humoral and cell-mediated immune mechanisms in the aetiology of T1A DM. o The destruction of β cells may occur over months or years before the onset of the disease.o 10% of Type I diabetics DON’T HAVE AUTOIMMUNE INSULITIS (T1B DM).o Absolute insulin deficiency.

TYPE 2 DM (T2 DM)o Incidence increases w/ age. Ethnicity: African-Americans, Hispanics and Native Americans.o Incidence is higher in southern Europe.o Positive family history of T2 DM is predictive for the disease.o Persons >20% over ideal body weight: risk factor. (80-90% of US diabetics are obese).o Comorbidity and associated conditions

Impaired glucose tolerance. Diabetes Hypertension Hyperlipidemia.

o β-cell defect. ↓tissue sensitivity to insulin. About 50% reduction of β-cell mass. However, their insulin concentration in plasma can be normal.

In these patients, more proinsulin is secreted. Proinsulin ALONE makes up about 20% of circulating immunoreactive insulin

o Defects in insulin secretion. First-phase defect after IV glucose challenge.

o β-cell abnormalities may be secondary to desensitization by chronic hyperglycemia.o Severely hyperglycemic patients are hypoinsulinemic.o Likely that several genes are involved. T2 DM is a multifactorial, heterogenous disease.

About 220 million people w/ DM in the world today. Both types increasing in frequency. Risk factors for DM type 2: Sedentary lifestyle, increasing age, obesity, low birth weight. Secondary diabetes associated w/ chronic pancreatitis (toxic factors in tropical countries). Mutations in the insulin gene. MODY (Maturity-Onset Diabetes of Youth).

o MODY-2: mutation in the glucokinase gene. Autosomal dominant.

7

Insulin Therapy

Treatment for T1 AND T2 DM. Sometimes, it’s administered IV or IM. Most of the time, it’s subcutaneous. Subcutaneous insulin injection does not reproduce the normal cycle of rise and fall of insulin

concentrations after a meal. Subcutaneous insulin injection is released straight into the peripheral circulation instead of being released

into the portal circulation. Therefore, the subcutaneous injection does not have any effect on hepatic metabolism (which would normally be stimulation of uptake of glucose into hepatocytes and inhibition of gluconeogenesis and glycogenolysis).

Classification according to duration of actiono Shorto Intermediateo Long

Classification according to species of origin: human or porcine (which only differ in 1 AA).o Mid-1970s – Monocomponent porcine insulins.o Late 1970s – Development of biosynthetic human insulin.o Human insulin is more soluble.

UNITAGEo 1 UNIT – Amt of insulin required to lower blood glucose in a fasting rabbit to 45 mg/dl.o International standard: Mix of bovine and porcine insulin containing 24 units/mg.o Commercial preparation: 100 units / mL (3.6 mg /ml).

CLASSIFICATION OF INSULINSo Short and rapid-acting

Regular, crystalline zinc insulin. Buffer at neutral pH (storage for days at room temp). Acts quick but effect doesn’t a lot. Inject 30-45 min before meals. (Can be given in a subcutaneous injection pump). Rapid fall in blood glucose. Insulin is cleared quickly. Baseline glucose level w/in 2 to 3 hours. (Counter-regulatory hormones). IV infusion for diabetics w/ ketoacidosis, during labour, perioperative patients

and patients in ICU. Usually given in combination w/ an intermediate or long-acting preparation. Is a hexamer: slows absorption.

Lispro and Aspart: Retain monomeric or dimeric configuration (hexamers do not associate). Short-acting analogs.

Absorbed 3X more quickly than human insulin. Earlier hypoglycaemic response.

15 minutes before meals. Lispro: Dissociates into monomers almost as soon as it’s injected.

o Hypoglycemia is reduced. Glucose control is improved. Lispro is very similar to aspart in its effects.

Glulysine Time-action similar to insulin aspart and lispro. Can be administered by continuous subcutaneous insulin infusion pump. Immediately before or after a meal. After a meal= based on food consumed.

Inhaled insulin (clinical trials) – high patient satisfaction, similar incidence of hypoglycaemia. Smoking increases absorption of inhaled insulin.

o Intermediate-acting: Dissolve more gradually; effect lasts longer. May be used in combination w/ regular (soluble) insulin. Once a day before breakfast or 2X a day. Before bedtime (T2 DM) helps normalise

fasting blood glucose. Neutral Protamine Hagedorn (NPH)

Insulin suspended in a complex w/ Zn and protamine. Phosphate buffer. Does not slow the absorption of the fast-acting insulin.

8

Lente Insulin Crystallised (ultralente) + amorphous (semilente) insulins. Acetate buffer.

Human vs. porcine immediate-acting preparations. Human: More rapid onset and shorter duration of action. If taken before dinner,

the effect may not last long enough to prevent hyperglycemia in the morning.o Long-acting

Ultralente insulin Long half-life= difficult to determine optimal dosage. Doses adjusted according to the fasting blood glucose concentration.

Protamine zinc insulin (Not used a lot today). Glargine

Human insulin long-acting analog. Stabilised hexamer. pH = 4.0. Cannot be mixed w/ lispro, aspart or regular insulin (b/c these have a pH of 7). Less hypoglycaemia. Doesn’t have a huge peak of absorption. Once daily at any time during the day and injected anywhere. Can be combined w/ various oral antihyperglycaemic agents (sulfonylureas,

metformin, etc). Slower onset and a prolonged peak of action. Provide low basal concentrations of insulin throughout the day. Will not control postprandial glucose elevations in insulin-deficient T1 or T2 DM.

o Insulin detemir - binds to albumin. 2X a day, reduced prevalence of hypoglycaemia (compared w/ NPH).

Intermediate or long-acting insulin in most patients. Human Proinsulin (Very good intermediate-acting insulin) & Porcine proinsulin affect hepatic glucose

production.o High incidence of MI in HPI-treated patients.

The kinetics of insulin action vary VERY widely.o Rate of subcutaneous absorption.

Indications and Goals for Therapy

Patients for whom insulin therapy is imperative:o ALL T1 DM patients.o Patients w/ T2 DM not controlled adequately by diet and/or oral hypoglycaemic agents.o Patients w/ postpancreatomy or gestational diabetes.o To manage diabetic ketoacidosis.o Perioperative management of T1 AND T2 DM.o Hyperglycemic, nonketotic coma.

Goal: Normalise blood glucose and all other aspects of metabolism.o Coordinate diet, exercise and insulin.o 90<Fasting blood glucose<120 mg/dL.o 2-hr postprandial value<150 mg/dL.o Haemoglobin A1C <6.5% (<7%)

DAILY REQUIREMENTSo Normal production in healthy people: 18-40 units/day (0.2-0.5 units/kg of weight per day).

Half in response to meals, half in the basal state.o Nondiabetic, obese and insulin resistant people produce up to 4X more insulin or more.o T1 DM

Dose of insulin: 0.6 – 0.7 units/kg of body weight per day (More for obese patients). If the patient requires less than 0.5 units/kg every day, he/she may have some endogenous

production of insulin or may be more sensitive to insulin (good physical conditioning).o Basal dose (40%-60% of the daily dose).

9

Suppresses lipolysis, proteolysis, and hepatic glucose production.o Postprandial dose is required for disposition of nutrients after meals. (Usually given before meals).o Euglycaemia is achieved w/ combinations of intermediate or long-acting insulins w/ regular

insulins.o Dosage regimens:

Inject a mixture of regular and intermediate-acting insulins before breakfast and before dinner.

The dose before dinner may be divided into a dose of regular insulin before dinner and a dose of intermediate-action insulin before bedtime if one dose before dinner didn’t control glycaemia during the night and until the morning.

o DAWN PHENOMENON: Increased requirement for insulin in the early morning.

Basal administration of long-acting insulin (before breakfast or at bedtime) and preprandial injections of a short-acting insulin.

o 50% OF β-CELL SECRETORY CAPACITY IS LOST FOR EVERY 6 YEARS OF T2 DM. Interest in including insulin therapy earlier in the treatment of T2 DM. Difficult to achieve euglycaemia only w/ oral antihyperglycemic agents.

Introduce basal-acting insulin. Measure C peptide to see how much insulin the patient is still producing or IF

he/she is still producing insulin at all. Maybe add in an insulin sensitiser?

o Careful monitoring of therapeutic end points. Home glucose monitors.

Factors That Affect Insulin Absorption

Site of Injectiono Abdomen, buttock, anterior thigh or dorsal arm.o Absorption is quicker from abdomen. Slowest in the thigh.

Rotation of injection site (to avoid lipohypertrophy). Patient may rotate injection throughout entire abdomen.

o Preferable to select a consistent injection site for each component of insulin treatment. Type of Insulin Subcutaneous blood flow

o Increased by massage, hot baths, exercise.o The more blood flow, the faster the absorption.o If the patient is upright, subcutaneous blood flow to abdomen decreases.

Smoking Regional Muscular Activity. Volume and Concentration of the Injected Insulin – Mixture of insulins that have a different duration of

action changes the duration of action and the time of absorption.o Regular insulin and NPH in different ratio. o Pen devices containing different mixtures of insulins.

Depth of Injection Subcutaneous insulin administration results in formation of anti-insulin IgGs. Human insulin is

immunogenic. o Some patients have high titers of Igs against insulin and the insulin becomes longer-acting.

Foetal hyperglycemia (Igs against insulin cross the placenta).o Only human insulin can be used during pregnancy.

Continuous Subcutaneous Insulin Infusion (CSII)

CSII therapy is not suitable for all patients b/c it demands considerable attention.o However, it may be preferable to several daily injections.

10

o Constant basal infusion w/ the option of different infusion rates during the day. This helps avoid the dawn phenomenon and is useful in the injection of short-acting doses programmed according to the size and nature of a meal.

Unique problemso All insulin short-acting → Insulin deficiency & ketoacidosis may develop rapidly if therapy is

interrupted accidentally.o Pump failure, dislodgement of the needle, aggregation of insulin in the infusion line, etc.o Subcutaneous abscesses and cellulitis.

Adverse Reactions

HYPOGLYCAEMIAo Causes

Unusually large dose Incorrect timing btn the time of peak delivery of insulin and food intake Other factors that increase sensitivity to insulin or that increase glucose uptake. Vigorously trying to achieve euglycaemia.

o Must always be considered when looking at the benefits of intensive therapy.o Physiological responses to hypoglycaemia

↓ insulin secretion Release of Counter-regulatory hormones: epinephrine, glucagon, growth hormone,

cortisol and norepinephrine. T1 DM: Glucagon response becomes deficient but epinephrine compensates.

o If the epinephrine pathway of counter-regulation fails, the patient is more susceptible to hypoglycaemia. (Autonomic diabetic neuropathy, hypoglycaemic unawareness, and altered thresholds for and deficient release of counter-regulatory hormones).

Symptoms: Sweating, hunger, paresthesias, palpitations, tremor, anxiety (Autonomic symptoms)

difficulty in concentrating, confusion, weakness, drowsiness, a feeling of warmth, dizziness, blurred vision and loss of consciousness (neuroglycopaenic symptoms).

SEVERE: Convulsions and coma.o Home glucose monitoring when the patient feels suggestive symptoms of hypoglycaemia.

Nocturnal hypoglycaemia should be suspected if there are morning headaches, night sweats or symptoms of hypothermia.

Somogyi phenomenon: Hypoglycaemia at night causes there to be a counter-regulatory response, which could cause hyperglycaemia in the morning.

However, neuroendocrine counter-regulation starts failing w/ the progression of the disease, so nocturnal hypoglycaemia may not be what causes morning hyperglycaemia.

Treatment of morning hyperglycemia More long or intermediate-acting insulin at night (or at bedtime).

o Carry some form of easily ingested glucose. ID Card or bracelet w/ pertinent medical information. INSULIN ALLERGY AND RESISTANCE

o Have decreased w/ the use of recombinant human insulin.o Occur as a result of reactions to the small amounts of aggregated or denatured insulin in all

preparations, to minor contaminants or to components added to insulin in its formulation.o Allergy: IgE-mediated. Local cutaneous reactions. Rare = life-threatening systemic responses.o IgG antibodies – resistance.o Measure IgG and IgE for insulin.o Antihistamines in cutaneous reactions. Glucocorticoids to insulin-resistant patients (w/ Anti-

insulin IgGs). LIPOATROPHY AND LIPOHYPERTROPHY

11

o Lipoatrophy is the atrophy of subcutaneous fat (at the site of the insulin injection). A variant of an immune response to insulin.

o Lipohypertrophy is the enlargement of subcutaneous fat deposits. Insulin has local lipogenic action in high concentrations. If the patient injects him/herself in the same site. Use other injection sites.

o Rare w/ more purified preparations. INSULIN OEDEMA

o Diabetic patients w/ severe hyperglycaemia or ketoacidosis that is controlled w/ insulin may develop oedema, abdominal bloating and blurred vision. Weight gain of 0.5-2.5 kg.

o Retention of Na+. Usually goes away on its own.

Insulin Treatment of Ketoacidosis and Other Special Situations

Patients w/ ketoacidosis require IV insulin.o 0.1 units/kg per hour.o Blood glucose will fall 10% per hour.o Administration of glucose along w/ insulin to prevent hypoglycaemia and to allow clearance of all

ketones.o Appropriate replacement of fluid and electrolytes.o Administer insulin subcutaneously at least 30 min before IV therapy is discontinued.

IV insulino Perioperative period and during childbirth.o During surgery: To maintain stable plasma glucose, fluid and electrolyte balance.

Variable-rate regime Glucose-insulin-potassium infusion method.

DRUG INTERACTIONS AND GLUCOSE METABOLISMo Drugs that cause hypoglycaemia or hyperglycaemia.

Hypoglycaemia β blockers

o Inhibition of the effects of catecholamines on gluconeogenesis and glycogenolysis.

o Prevent some of the symptoms associated w/ the fall in blood glucose. Salicylates

o Enhance pancreatic β-cell sensitivity to glucose and potentiate insulin secretion.

Some drugs only potentiate the actions of sulfonylureas. Hyperglycaemia

Direct effects on peripheral tissues that counter the actions of insulino Epinephrine, glucocorticoids, atypical antipsychotics (clozapine and

olanzapine), and drugs used in highly active antiretroviral therapy. Inhibit insulin secretion directly

o Phenytoin, clonidine, Ca2+ channel blockers (nifedipine, ,verapamil). NEW FORMS OF INSULIN THERAPY

o New insulins, routes of administration (nasally, orally, rectally, by inhalation), intraperitoneal delivery devices, implantable pellets, closed-loop artificial pancreas, islet cell and pancreatic transplantation and gene therapy.

o New Routes of Delivery: Inhalated insulin is prepared when adjuvants like mannitol, glycine and sodium citrate are

added to insulin (+ absorption in respiratory mucosa). Quick absorption (similar to regular insulin).

Insulin is not well absorbed by the intestine, which is why oral preparations haven’t been successfully synthesized.

o Transplantation And Gene Therapy

12

Segmental pancreatic transplantation is successful but it’s complicated and only considered in patients w/ advanced disease and complications.

Islet-cell Transplants: less complicated, based on protocols for islet preparation and a regimen for glucocorticoid-free immunosuppressive regimen.

Gene therapy in rodents: Hepatocytes transdifferentiate into a fxnal endocrine pancreas.Oral Hypoglycaemic Agents

HISTORYo Sulfonylureas were discovered accidentally in 1942 by Janbon and colleagues.

Carbutamide was the first clinically useful sulfonylurea for the treatment of diabetes. Tolbutamide (1950s) and others followed.

o 1997 – Repaglitinide New class: Meglitinides (Benzoic Acid Derivatives).

Insulin secretagogue.o Guanadine found in the plant Galega officinalis

1920s – Biguanides began to be investigated. METFORMIN – Now used extensively.

o Thiazolidinedineones – Insulin sensitizers. Bind to peroxisome proliferator-activated receptors (PPARγ). Results in + glucose uptake

in muscle and – endogenous glucose production. Troglitazone, rosiglitazone and pioglitazone.

Sulfonylureas

CHEMISTRYo Two generations of agents.

First generation: Tolbutamide, acetohexamide, tolazamide and chlorpropamide. Second generation: Glyburide(glybenclamide), glipizide, gliclazide, glimepiride.

o Substituted arylsulfonylureas.

Mechanism of Action

Stimulate insulin release from the pancreatic β cells.o May also reduce hepatic clearance of insulin.

Initially, when a sulfonylurea is given, the insulin concentration in plasma increases, but, in a few months, the insulin concentration goes back to its pre-treatment levels. (The glucose levels stay the same, however).

o Less plasma glucose means insulin levels don’t need to be as high to affect target tissues.o Chronic hyperglycemia (before treatment) severely impacts insulin secretion.

Less receptors for sulfonylureas on β cells means the drug has less effect on insulin secretion. If chronic treatment is stopped, the β cells will regain their initial responsiveness to the drug.

May or may not have extrapancreatic effects.

Absorption, Fate, and Excretion

Effectively absorbed from the GI Tract.o Food and hyperglycemia can reduce their absorption. Hyperglycemia inhibits gastric and intestinal

motility. o Given 30 minutes before eating.

Largely bound to plasma proteins. Half-lives:

o Tolbutamide, tolazamide and acetohexamide: 4-7 hrs.o Chlorpropamide: 24-48 hrs.

Second-generation is about 100 times more potent. Short half-lives, but long-lasting effects. All metabolised by the liver – metabolites excreted in the urine. Use w/ caution in patients w/ renal or hepatic insufficiency.

13

Adverse Reactions

May cause hypoglycaemic reactions including coma. o If a patient has hepatic or renal insufficiency, the drug gets cleared more slowly, and if it’s a

longer-acting drug (like chlorpropamide), the risk of hypoglycaemic effects is greater.o 2nd Generation: Long action does not necessarily mean more risk of hypoglycaemia.

The body’s inhibition of the production of insulin is its defence against hypoglycaemia, and it occurs w/ some long-acting sulfonylureas but not w/ others.

Glucagon is reduced by some long-acting sulfonylureas but not by others.o Can present w/ acute neurological symptoms (like a stroke). Check plasma glucose level (elderly

patients). Treat for a longer time if the patient has been taking a long-acting sulfonylurea. Drugs that potentiate the effect of these drugs usually slow their clearance, or displace them from binding

proteins (Other sulfonylureas, clofibrate, and salicylates). Other drugs might DIRECTLY cause hypoglycaemia.

Nausea and vomiting, cholestatic jaundice, agranulocytosis, aplastic and haemolytic anemias, generalised hypersensitivity reactions and dermatological reactions.

o Chlorpropamide: Hyponatremia – Potentiates effect of ADH on the renal collecting duct. (To patients w/ diabetes insipidus, this may actually be an advantage).

There is no excess risk of CV disease when treating w/ sulfonylureas of first or second generation.o Some, like glimepiride, may even cause some CV benefits (ischaemic preconditioning).

Therapeutic Uses

If a healthier diet alone doesn’t work, adding a sulfonylurea is appropriate to control T2 DM.o Continue to control diet.

Don’t prescribe to T1 DM patients, to pregnant/lactating women, and to patients w/ hepatic or renal insufficiency.

50-80% of patients respond initially to oral hypoglycaemic agents.o 5-10% of these patients will go back to having hyperglycaemia:

Change in drug metabolism. Change in diet. Worse status of β cells.

o Most of these patients will eventually require insulin. Initial dose of tolbutamide: 500 mg (Max effective dose: 3000 mg).

o Tolazamide (Max dose of 1000 mg), Chlorpropamide (Max dose of 750 mg): 100-250 mg.o Taken 2X a day, before breakfast and dinner.

Glyburide: 2.5-5 mg / day. Max dose of 20 mg. Glipizide: 5 mg / day. Max dose of 40 mg. Gliclazide: 40-80 mg / day. Max dose of 320 mg. Glimepiride: 0.5 mg/day. Max dose of 8 mg. Combination of insulin and sulfonylureas help in T2 but not T1 DM patients.

o Good results if there is still some β-Cell activity and if the patient has had DM for only a short time.

Meglitinides

Repaglinide

Insulin Secretagogue. A derivative of Benzoic Acid. Closes ATP-dependent K+ channels (see page 3) on the β cells, which depolarises the cell and causes

insulin production. Peak blood levels and half-life: 1 hr. Multiple pre-prandial uses.

14

Metabolism in the liver yields inactive derivatives. Use w/ caution in patients w/ hepatic & renal insufficiency. Major side effect is hypoglycaemia.

Nateglinide

Derived from D-Phenylalanine. Blocks ATP-sensitive K+ Channels (like repaglinide and the sulfonylureas). More rapid but less sustained secretion of insulin. T2 DM – Reduces postprandial elevations in glucose levels. Dose: 120 mg (1 to 10 minutes before a meal). Use w/ caution in patients w/ liver and kidney insufficiency. May cause less hypoglycaemia than repaglinide and the sulfonylureas.

Biguanides

Metformin – Widely used in Europe and Canada.o Alone or in combination w/ a sulfonylurea. Improves glycaemic control and lipid concentrations

in patients who respond poorly to diet or to a sulfonylurea alone. Phenformin – withdrawn in many countries b/c it caused lactic acidosis. MECHANISM OF ACTION

o It’s an ANTIHYPERGLYCAEMIC agent, NOT a HYPOGLYCAEMIC agent like the sulfonylureas and the meglitinides.

o Generally does not cause hypoglycaemia (even in large doses).o DECREASES HEPATIC GLUCOSE PRODUCTION (Gluconeogenesis).o INCREASES THE ACTION OF INSULIN IN MUSCLE AND FAT.

Activates an AMP Kinase. ABSORPTION, SECRETION AND DOSING.

o Absorbed in the small intestine. o Doesn’t bind to plasma proteins.o Excreted unchanged in the urine.o 2.5 g of metformin / day.

3X (w/ meals).

Precautions and Adverse Effects

Don’t prescribe to patients w/ renal impairment, hepatic disease, a past history of lactic acidosis, cardiac failure or chronic hypoxic lung disease.

Discontinue b4 IV contrast media are injected and b4 any surgical procedure. (Risk of lactic acidosis).o Should be discontinued until renal fxn is determined to be normal.

Discontinue if the plasma lactate levels exceed 3 Mm, if the patient has a MI or septicemia. Acute side effects:

o Diarrhoea, abdominal discomfort, nausea, metallic taste and anorexia.o Decreased absorption of vitamin B12 (counter w/ a B12 supplement).

DOES NOT PROMOTE WEIGHT GAIN and reduces triglycerides by 15-20%. Decreases Haemoglobin A1C (less risk of microvascular complications).

The only therapeutic agent that reduces macrovascular events in T2 DM. Combination w/ sulfonylurease, thiazolizinediones and/or insulin.

Thiazolidinediones

3 agents: troglitazone (severe hepatic toxicity), rosiglitazone, and pioglitazone. Lower Haemoglobin A1C. Combination w/ insulin or oral hypoglycaemic agents. Increase HDL.

15

Mechanism of Action

Selective agonists for nuclear peroxisome proliferator-activated receptor γ (PPARγ) which activates insulin-responsive genes that regulate CH and lipid metabolism.

o ↑ Insulin sensitivity in peripheral tissues. (BUT, PPARγ is virtually absent in skeletal muscles). Maybe the activation of PPARγ in adipocytes reduces the flux of fatty acids into muscle

(↓ insulin resistance). Activates adipocyte hormones/adipokines (like adiponectin).

Increases AMP Kinase (just like metformin).o May lower glucose production by the liver.o Increase glucose transport into myocytes and adipocytes (synthesis and translocation of specific

forms of glucose transporters). REQUIRE SOME ENDOGENOUS INSULIN PRODUCTION FOR THEIR ACTION.

Absorption, Excretion, and Dosing

Rosiglitazone and pioglitazone (1X a day; absorbance in 2 hrs; max effect in 6-12 weeks). Metabolised by the liver.

o Don’t administer to patients w/ hepatic disease. Any drug that may interact w/ CYP 2C8 (metabolic enzyme for rosiglitazone) and w/ CYP 3A4

(pioglitazone) will have interactions w/ the thiazolidinediones.

Precautions and Adverse Effects

Liver fxn should be monitored, even if pioglitazone and rosiglitazone don’t have much of a problem w/ hepatotoxicity. (It could occur, though).

o Even having abnormal liver fxn tests should be a “red flag” for discontinuing the drugs. Anaemia, weight gain, oedema, and plasma volume expansion. Don’t use in patients w/ Heart Failure (NYHA level 3 and 4).

o The thiazolidinediones can cause heart failure if the patient has abnormal cardiac fxn to begin with.

Peripheral oedema independent of heart failure (reduction in renal Na+ excretion or increase in vascular permeability).

o Should be treated and the thiazolidinedione should be discontinued.

α-Glucosidase Inhibitors

Inhibit the enzyme α-glucosidase in the intestinal brush border, which slows the absorption of CHs in the intestine. As a result, the rise in plasma glucose after a meal (T1 AND T2 DM) is blunted. Administer before a meeal.

Do NOT result in hypoglycaemia. Can improve Haemoglobin A1C in severely hyperglycaemic T2 DM patients.

o If the hyperglycaemia is not that severe, the drugs are less potent than other oral antidiabetic agents.

May be considered as monotherapy in elderly patients or in patients w/ predominantly postprandial hyperglycaemia. Used in combination w/ other antidiabetic agents and/or insulin.

ACARBOSE, MIGLITOL Side effects: Malabsorption, flatulence, diarrhoea and abdominal bloating.

o Titrate dose slowly: 25 mg for the first 4-8 weeks. Raise the dose every 4-8 weeks. MAX DOSE: 75 mg before a meal.

Reduction in the incidence of Type 2 DM.

16

# of individuals w/ impaired glucose tolerance (pre-diabetes) >= # of diabetics. Impaired Glucose Tolerance (IGT)

o 100 mg/dl <Fasting Plasma Glucose Concentration<126 mg/dlo 140 mg/dl<2-hr value in OGTT<199 mg/dl.

IGT → DIABETES is 9% to 15%. US: 60% of all people are overweight or obese. Childhood obesity is also a troubling issue.

o The incidence of T2 DM in US children has multiplied by 10 in the past generation. Diet and weight loss were a protective factor against diabetes. Metformin, acarbose and troglidazone reduce the progression of diabetes. Angiotensin-Converting Enzyme Inhibitors are associated w/ a decreased incidence of

DM.

Glucagon-Like Peptide 1 (GLP-1)

Glucose-Dependent Insulinotropic Polypeptide (GIP) and GLP-1 o Released from the GI tract.o Augment glucose-dependent insulin secretion.

GLP-1 works better at augmenting glucose-dependent insulin secretion in T2 DM patients than GIP.o Reduces glucagon secretion.o Slows gastric emptying.o Decreases appetite.o Therefore, it may not only help to reduce prosprandial glucose levels, but also to induce weight

loss. GLP-1 is rapidly inactivated by the dipeptidyl peptidase IV (DPP-IV) Enzyme. It must, then, be infused

continuously. o GLP-1 receptor agonists that are resistant to the actions of DPP-IV.

Clinical trials Exendin-4.

o Lowers Haemoglobin A1C.o Promotes weight loss.o 2X daily injections. Combined w/ other agents.o Side effects: Nausea, sometimes hypoglycaemia.

NN2211o Also must be injected. Nausea and hypoglycaemia.o Lowers Haemoglobin A1C.

o DPP-IV inhibitors. Similar effects to the GLP-1 analogs. Less nausea. Theoretical concern about the long-term safety of these compounds: DPP-IV can

metabolise a wide range of peptides, not just GLP-1. If there is a lot of endogenous GLP-1 production, the DPP-IV inhibitors become less

potent.

17