Pancreatic Hormones and Insulin Receptor Agonists

Hongmei Li

Mar. 21th, 2006

The bulk of the pancreas is an exocrine gland secreting pancreatic fluid into the duodenum after a meal.

Inside the pancreas are millions of clusters of cells called islets of Langerhans. The islets are endocrine tissue containing four types of cells. In order of abundance, they are:

beta cells, which secrete insulin and amylin; alpha cells, which secrete glucagon; delta cells, which secrete somatostatingamma cells, which secrete a polypeptide.

Pancreatic Hormones

Insulin Amylin Glucagon Somatostatin Pancreatic Polypeptide

A chain

B chain

Beta cells have channels in their plasma membrane that serve as glucose detectors. Beta cells secrete insulin in response to a rising level of circulatingglucose.

Insulin is a small protein consisting of an A chain of 21 amino acids linked by two disulfide (S—S) bridges to a B chain of 30 amino acids.

Insulin affects many organs:

It stimulates skeletal muscle fibers.

It stimulates liver cells.

It acts on fat cells

It inhibits production of certain enzyme.

In each case, insulin triggers these effects by binding to the insulin receptor.

glucoseuptake

glycogen synthesis

protein synthesis

amino acids uptake

enzymeproduction

glycogenbreaking

fat synthesis

Pancreatic Hormones

Insulin Amylin Glucagon Somatostatin Pancreatic Polypeptide

β Amylin

Amylin is a peptide of 37 amino acids.

It inhibits the secretion of glucagon; It slows the emptying of the stomach; It sends a satiety signal to the brain.

All of its actions tend to supplement thoseof insulin, reducing the level of glucose inthe blood.

Pancreatic Hormones

Insulin Amylin Glucagon Somatostatin Pancreatic Polypeptide

αGlucagon

Glucagon, a polypeptide of 29 amino acids, acts principally on the liver.

It stimulates the conversion of glycogen into glucose. It stimulates the conversion of fat and protein into intermediate metabolites that are ultimately converted into glucose.

Glucagon secretion is stimulated by low levels of glucose in the blood; inhibited by high levels, and inhibited by amylin.

Pancreatic Hormones

Insulin Amylin Glucagon Somatostatin Pancreatic Polypeptide

δ Somatostatin

Somatostatin consists of two polypeptides,

one of 14 amino acids and the other of 28.

They work together to reduce the rate at

which food is absorbed in the intestine.

Pancreatic Hormones

Insulin Amylin Glucagon Somatostatin Pancreatic Polypeptide

γPancreatic Polypeptide by Gamma Cells

The gamma cells of the islets secrete a 36-amino-acid pancreatic polypeptide, which reduces appetite.

The insulin receptor (IR) is a transmembrane glycoprotein, composed of 2α and 2β domains.

. Its intracellular tyrosine

kinase domain is activated by binding of insulin, leading to a cascade of signaling events.

Who need insulin medicine

Type I (insulin dependent) diabetes patients whose body produces no insulin.

Type 2 diabetes patients that do not always produce enough insulin.

Treatment

subcutaneous injection

Stage 1 Insulin was extracted from the glands of cows and pigs. (1920s)

Stage 2 Convert pig insulin into human insulin by removing the one amino acid that distinguishes them and replacing it with the human version.

Insulin drug evolution

Stage 3 Insert the human insulin gene into E. coli and culture the recombinant E.coli to produce insulin (trade name = Humulin®). Yeast is also used to produce insulin (trade name =

Novolin®) (1987).

Recombinant DNA technology has also made it possible to manufacture slightly-modified forms of human insulin that work faster (Humalog® and NovoLog®) or slower (Lantus®) than regular human insulin.

Types of insulin

• Regular insulins

• Insulin analogs

• Pre-mixed insulin

Short peptide mimics

Regular insulins:

Human insulin: Humulin® (from E.coli),

Novalin® (from yeast) NPH - neutral protamine Hagedorn (NPH),

protamine mixed. Lente® insulin / Ultralente® insullin-

zinc added

Types of insulin

• Regular insulins

• Insulin analogs

• Pre-mixed insulin

Short peptide mimics

Insulin Analogs:

Fatty Acid Acylated insulins

Insulin Lispro (Humalog®) (1996)

Insulin Aspart (NovoLog®) (2000)

Insulin Glargine (Lantus®) (2002)

Insulin Detemir (Levemir®) (Jun.,2005)

Insulin Glulisine (Apidra®) (Jan., 2006)

Amino Acid Substitutons

A- chainPosition

B- chain Position

Source/Type

A21 B3 B28 B29 B30 B31 AndB32

Human Asn Asn Pro Lys Thr

Aspart Asn Asparticacid

Lys Thr

Lispro Asn Lys Pro Thr

Glulisine Asn Lys Pro Glu Thr

Glargine Gly Pro Lys Thr Arg

Detemir Lys Myristicacid

rapid-acting

long-acting

Types of insulin

• Regular insulins

• Insulin analogs

• Pre-mixed insulin

Short peptide mimics

Types of insulin

• Regular insulins

• Insulin analogs

• Pre-mixed insulin

Short peptide mimics

Insulin receptors were used as targets to screen surrogate peptides in random peptide phage display libraries.

Short surrogate peptides

IR

Short surrogate peptides

H2C-D117: 14 a.a. RP9-S371: 16 a.a. 20E2-D118: 24 a.a.

Future Directions for new IR agonists

Increased Stability Less Variability High Selective Action Ultra Rapid Onset Ultra Long Activity W/O side effects

References

Renuka C. P. et.al (2002) J. Biol. Chem. 277, 22590–4 Zoltan V. AND William C. D. (2001) Pharm. Rev. 52, 1-9 Lauge S. et. Al (2003) PNAS 100, 4435-9 Mark R. B. (1997) J. of Clin. Endoc.& Met. 82, 3-7 Gianni C. (1992) FEBS 307, 66-70 Irl B. H., (2001) Clin. Diabetes 19, 146-7 BRUCE W. B. and POUL S. (2001) Diabetes care 24,69-72 http://www.indstate.edu/thcme/mwking/diabetes.html