Insulin & Drugs for Type 2 Diabetes (Crider)

What is the strucutre of ATP-sensitive K+ channels?

-4 pore forming Kir6.x subunits joined together with -4 regulatory SURx subunits

What are the first generation sulfonylureas?

-Acetohexamide -Chlorpropamide -Tolazamide -Tolbutamide

Be able to recognize the acidic function and the lipophilic groups for a first generation sulfonylurea.

-Acidic group: middle S-N bond of sulfonylurea -2 lipophilic groups on each end of sulfonylurea

Have a general understanding of the structures of nateglinide and rapaglinide, how these compounds differ from sulfonylureas, and what possible advantage they have over sulfonylureas.

-Carboxylic acid + amide -More rapid onset -Shorter duration of action -May mimic a more physiological pattern of insulin release

What are the second generation sulfonylureas?

-Glipizide -Glyburide -Glimepiride

What is the role of phenol in the formulation of insulin degludec?

-Injected SC in a formulation with Zn & phenol as dihexamer conformation. -After injection, the phenol diffuses out & the hexamers change to a multi-hexamer chain conformation. -With slow release of Zn, the chains break down to dimers which will rapidly dissociate into absorbable monomers. phenol is used to stabilize the structure by binding to hydrophobic pockets. As phenol diffuses away, the dihexamers undergo a conformational change forming multihexamers

Have a general knowledge concerning the structure of the insulin products: insulin aspart

-Insulin + Asp at 28 -Contains Zn++

Have a general knowledge concerning the structure of the insulin products: insulin glargine

-Insulin + Gly at G-21 + Arg at R-31 + Arg at R-32 -Replacement of Asn with Gly at G-21 on A-chain -Addition of 2 Arg residues R-31 & R032 on B-chain --> raises isoelectic point -Clear solution with pH of 2 (more stable) -Stabilized insulin hexamer -Prolonged & predictable absorption

Have a general knowledge concerning the structure of the insulin products: insulin lispro

-Insulin + Lys at 28 + Pro at 29 + Asn instead of Asp at 3 -Contains Zn++

Have a general knowledge concerning the structure of the insulin products: insulin detemir

-Insulin + Lys at 29 -Removal of The B30 -Associates at injection site -Strongly bound to plasma proteins -Myristic Acid attached to the amino group of Lys B29 -Highly lipophilic -Forms dexamers & dihexamers at the injection

Have a general knowledge concerning the structure of the insulin products: insulin glulisine

-Insulin + Lys at 3 + Glu at 29 -Does not contain Zn++

Have a general knowledge concerning the structure of insulin degludec and why this product has a long-duration of action.

-Multi-hexamer formation coupled with protein binding -Extremely stable & predictable release pattern -Forms multihexamers in SC tissue = prolonged absorption -Lipophilic side chain enhances protein binding = long duration of action

What is involved in the conversion of benzylic methyl groups to carboxylic acid metabolites?

-P-450 -Alcohol dehydrogenase -Aldehyde dehydrogenase

What are the Type 2 antidiabetic agents?

-Thiazolidindiones (TZDs) -Sulfonylureas & related insulinotropes or secretagogues -Biguanides -alpha-Glucosidase inhibitors -Amylin analogs -GLP-1R agonists -DPP4 inhibitors -SGLT2 inhibitors

Understand the reason that sulfonylureas are weak acids.

-the sulfonyl group exerts an electron withdrawing effect, thus activating the NH proton -upon ionization, the resulting anion is stablizied by resonance onto both oxygen atoms of the sulfonyl group & the carbonyl group of the urea group

Quick summary of regulation of insulin release from pancreatic beta cells

1) Glucose enters the pancreatic beta cell by GLUT2 2) Increase ATP levels 3) ATP binds to K+ channel 4) K+ channel closes 5) Depolarization via increase in trapped intracellular K+ 6) Increase in calcium influx 7) Insulin secretion from beta cells

What is the pathway of regulation of insulin release from pancreatic beta cells?

1) Glucose enters the pancreatic beta cell by means of the GLUT2 transporter 2) Increase glucose metabolism raises ATP levels 3) ATP binds to the K+ channel favoring closing 4) K+ closing traps a greater portion of K+ ions within the cell, rendering the intracellular environment less negative vs extracellular fluids (depolarization) 5) Depolarization increases Ca++ influx 6) Increases Ca++ causes insulin exocytosis

Be able to describe the synthesis of insulin from preproinsulin.

1) Preproinsulin -proteolytic cleavage -24 amino acids 2) Proinsulin -folding & disulfide bond formation -Endopeptidases 3) Insulin

How is tolbutamide metabolized?

1) para-methyl group on the far left is rapidly metabolized by CYP2C9 to give a hydroxymethyl metabolite (OH-methyl) that retains some activity 2) The alcohol is oxidized further by a combination of alcohol and aldehyde dehydrogenase to give an inactive carboxylic metabolite

What is the approximate daily dose of Glimepiride?

1-2 mg

What is the approximate daily dose of Glipizide?

10 mg

What is the approximate daily dose of Tolbutamide?

1000-1500 mg

A-chain of human insulin has ___ amino acids

21

What is the approximate daily dose of Chlorpropamide?

250-375 mg

What is the approximate daily dose of Tolazamide?

250-375 mg

B-chain of human insulin has ___ amino acids

30

Insulin detemir is ____ potent than human insulin

4x less

What is the approximate daily dose of Glyburide?

5 mg

What is the approximate daily dose of Acetohexamide?

500-750 mg

Be able to describe the chemical structure of insulin.

A-chain: 21 amino acids (internal S-S bond C6-C11) B Chain: 30 amino acids (S-S bond C7 & C7 of A-Chain & S-S bond of C19 & C20 of A-Chain)

A-chain of human insulin has a S-S bond at ____

C6-C11

B-chain of human insulin has a S-S bond at ____

C7 & C7 of A-chain C19 & C20 of A-chain

What is nateglinide metabolized by?

CYP 2C9 & 3A4

What is repaglinide metabolized by?

CYP3A4 & 2C8

What is the brand name for insulin aspart?

Fiasp

_____ acts like ATP in that it binds to K+ channel to cause depolarization --> influx of Ca++ --> release of insulin

Glyburide

What is the brand name of insuline glargine?

Lantus

What is the brand name of insulin detemir?

Levemir

Insulin aspart is formulated containing _____ & ____

Nicotinamide & L-Arg

Are the disulfide linkages formed in proinsulin?

No

Is a sulfonylurea group essential for binding to the sulfonylurea receptor?

No

Have a general understanding of the SUR1-Kir6.2 binding site in pancreatic β-cells.

Ok

Understand that insulin self associates into hexamers and that only insulin monomers and to a much lesser extent dimers can pass through capillary walls.

Ok

Nateglinide is the ____ enantiomer

R

Which meglitinide has a shorter half life?

Repaglinide

What are Meglitinides?

Repaglinide & Nateglinide

Recognize the differences in binding between rapaglinide and nateglinide at the ATP-sensitive potassium channel.

Repaglinide is a B-ligand that binds at the B site Nateglinide is an A-ligand that binds at the A side Both have an acidic group that binds to the anionic site

Understand the difference in metabolism between tolbutamide and chlorpropamide.

Review slide 23

Have a general understanding of how glipizide, glyburide, and glimepiride are metabolized.

Review slide 24

Repaglinide is the ___ enantiomer

S (+)

Be able to recognize the structure of a sulfonylurea

SO2 + urea

If given the structure, be able to recognize the structural difference between first and second generation sulfonylureas.

Second generation sulfonylureas have a lot larger structures

Understand that the SUR1-Kir6.2 receptor in pancreatic β-cells contains a binding site A (on the SUR1) and a binding site B (on the SUR1-Kir6.2) site.

Slide 30

Have a general understanding of the differences in binding of glimepiride and tolbutamide at the SUR1-Kir6.2 receptor.

Tolbutamide: -highly selective for the A site -sulfonylurea binds to the anionic site -benzene ring binds to the phenyl binding site Glyburide/glimepiride: -binds to A + B sites -much more potent than tolbutamide -binds more specifically, but not selectively

What is the structure of insulin hexamer?

Two Zn++ coordinated to 6 His residues on the B-chain 3 coordinated H2O molecules

What does nicotinamide cause in insulin aspart?

a decrease in chemical stability causing increased levels of high molecular weight proteins

Understand the reason that insulin detemir is a long-acting insulin preparation.

amide between lys side chain of Lys 29 on the B-chain & the carboxylic acid of myristic acid --> creates highly lipophilic area --> highly bound to plasma proteins such as albumin --> long-acting

PC3 cleaves at _____ & ______

arginine & arginine

Preproinsulin is synthesized in the ____

beta-cells of the pancreas

How is preproinsulin converted to proinsulin?

by catalytic removal of 24 amino acids from the N-terminal end

Be able to recognize a benzylic carbon

carbon alpha to a benzene ring

Understand the benzylic methyl groups usually are metabolized to ________.

carboxylic acid metabolites (COOH)

Where are Kir6.2/SUR2A found?

cardiomyocytes

What do compounds that bind at the SUR do?

close the channel & stimulate insulin secretion

What do alpha-glucosidase inhbitors do?

decrease glucose absorption

What do biguanides do?

decrease hepatic glucose production & enhances peripheral glucose uptake

The amino acid substitutions on the rapdily-acting insulins have been made at regions on the peptide that _____

do not bind to the insulin receptor

Why is insulin detemir less potent than human insulin?

due to steric effect of the myristic acid at the insulin receptor

How is proinsulin converted to insulin?

endopeptidases PC2 & PC3 cleave the connecting peptide (C-chain)

Meglitinide are ____ protein bond

extensively

Regular insulin self associated in a ____ form

hexamer

What does L-Arg cause in insulin aspart?

improves chemical stability

Where does the conversion from preproinsulin to proinsulin occur?

in the rough endoplasmic reticulum

What do thiazolidindiones do?

increase insulin sensitivity & peripheral glucose uptake

____ bind to A, B, or A+B sites

insulinotropes

What happens to the connecting peptide once insulin is formed?

it is processed via folding & disulfide bond formation

What must happen before insulin can be absorbed through blood capillaries?

it must dissociate into dimers & then monomers

PC2 cleaves at _____ & _____

lysine & arginine

Be able to give a possible explanation why nateglinide may have less cardiovascular side effects compared to rapaglinide.

may be due to lack of selectivity at Kir6.2-ATP channels of repaglinide in the pancreas

At low physiological conditions, insulin is found in the _____ form

monomer

Only the ____ form of insulin is able to interact with insulin receptors

monomer

The rapidly acting insulins exist as the ____ form at the injection site

monomer or dimer

The second generation sulfonylureas are _____ potent than first generation compounds

more

Insulin degludec forms ___ in the SC tissue

multihexamers therefore, absorption is prolonged

B-ligands is ___selective in closing pancreatic ATP-sensitive K+ channels

non-

What is the selecitivity of repaglinide?

non-selective for pancreatic KATP

Insulin degludec has ____ daily dosing

once

Where are Kir6.2/SUR1 found?

pancreatic Beta-cells

What does Kir stand for?

potassium inward rectifier channel

Insulin glargine _____ when injected SC

precipitates

Meglitinides are _____ absorbed

rapidly

Tolbutamide is a _____ acting sulfonylurea

short

What on the structure of insulin detemir contibutes to the strong binding to albumin?

the lipophilic side chain

Where is repaglinide eliminated?

through the bile

Where are Kir6.1/SUR2B found?

vascular myocytes

A-ligands is ___selective in closing pancreatic ATP-sensitive K+ channels

very