1ACE = Angiotensin I Converting Enzyme

10 ACE inhibitors available in US: benazepril, captopril, enalapril, fosinopril,

lisinopril, moexipril, perindopril, quinapril, ramipril and trandolapril.

ACE inhibitors were the 4th most prescribed drug class in the U.S (159.8 million Rx

in 2008).

Lisinopril was the 2nd most prescribed drug in the US (75.5 million Rx in 2008).

2Endogenously generated peptides are involved in the physiology and pathology of all major organ

systems and play important roles in many processes. These include neurotransmission, immune

function, cell proliferation, pain/analgesia, fluid balance in the kidney, endocrine functions, reproduction,

contraction/relaxation of all types of smooth muscle, regulation of the cardiovascular system,

satiety/obesity, etc.

31. TO MIMIC THE ACTION OF A PEPTIDE:

A. Administer the Peptide (See next page for advantages/disadvantages). Non-peptide agonists can be effective drugs, however rational design of these drugs is generally not possible. Requires random/large scale screening approach.

B. Block the Degradation by Peptidase(s) - This is a good strategy because the level of the peptide can be specifically increased at its normal site(s) of action and peptidase inhibitors can be synthesized with good stability and bioavailability. Disadvantages include: 1) Blocking one peptidase may interfere with the metabolism of more than one peptide; 2) Inhibition ofmore than one peptidase may be needed to block the degradation of a peptide 3) Enhancing general levels of a peptide with multiple actions may produce side-effects.

2. TO BLOCK THE ACTION OF A PEPTIDE:

A. Use a Receptor Antagonist This is an excellent approach because the specific actions of a peptide mediated by a single receptor type can be blocked, leading to the potential for few unwanted side effects. However, many peptide receptor antagonists are themselves peptides and suffer from the disadvantages listed above. Development of non-peptide antagonists may with good bioavailability and stability is possible, but is still not a straightforward process.

B. Block the Synthesis/Processing of the Peptide This is also an excellent approach and one exemplified by the development of Angiotensin Converting Enzyme (ACE) inhibitors. In this approach, all the actions of the peptide can be blocked and enzyme inhibitors can be synthesized with high affinity, specificity and bioavailability. However, disadvantagesinclude the following: 1) Cannot block a specific action of a peptide if it acts on more than one receptor. 2) Intermediate forms of a peptide that build up when processing is blocked may have their own biological activity. 3)Processing enzymes may process other peptide hormones. (ACE inhibitors do not suffer this disadvantage as the Renin-Angiotensin system specifically processes and generates only angiotensin and not other peptides).

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6Top Left: Schematic diagram of the structure of human ACE. The majority of the ACE

molecule projects into the extracellular space and is boud to the plasma membrane via a

C-terminal transmembrane spanning helix, followed by a short 30 residue cytoplasmic

tail. The two homologous active site domains are denoted by the HEMGH sequence

which contains two zinc-binding histidine residues and the catalytic glutamic acid. The

distribution of carbohydrate is shown for all 17 potential Asn-linked glycosylation sites.

The extent of actual glycosylation varies from tissue to tissue and may not involve all

potential sites.

Top Middle: Superposition of the crystal structures of the N-domain (blue) and C-

domain (pink) showing the similarity of their primarily alpha-helical structures. Active site

zinc ion is shown in green.

Top Right: Space filling model of the C-domain of ACE showing the deep central groove

containing the active site and bound inhibitor lisinopril (yellow).

Bottom: Model of two possible orientations of the N- and C-domain in the ACE

holoenzyme.

7A common misconception is that peptidases are peptide-specific, perpetuated by the

names given to some of the enzymes (e.g., Angiotensin I Converting Enzyme,

Enkephalinase, etc.). Peptidases recognize amino acids around the peptide-bond

being hydrolyzed and therefore can potentially cleave many different peptides.

Clinically used ACE inhibitors:

-In 1974, Cushman and Ondetti at Bristol-Meyers Squibb used a model based on the structure of

carboxypeptidase A and a snake venom peptide that inhibited ACE to synthesize captopril, which

contained a free SH group to bind the active site zinc. This was the first clinically used ACE inhibitor. When the X-ray crystal structure of ACE was finally determined in 2003, it turned out to

have no homology to carboxypeptidase A.

-Because the -SH group can cause rash and taste disturbances at higher doses, second

generation ACE inhibitor enalaprilat used a -COOH group instead of SH to bind zinc. Most ACE

inhibitors use a free COOH group to bind zinc, except fosinopril,which uses phosphinic acid.

However, the free COOH or phosphinic acid group causes poor absorption, so they are synthesized the prodrug esters which is absorbed well and converted by esterases to the active

drug. Only Lisinopril and Captopril are active compounds that do not require conversion.

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9Angiotensin Converting Enzyme (ACE) plays a central role in the control of peptide hormones that

regulate blood pressure. Thus, ACE inhibitors are effective antihypertensive agents.

Inhibitors of other steps in the pathway are also effective antihypertensives. These include Renin

inhibitors (Aliskiren, brand name Tekturna) and angiotensin receptor antagonists (the sartans e.g., Losartan).

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An additional mechanism by which ACE inhibitors can work involves the angiotensin metabolite,

Angiotensin 1-7 (1 residue shorter than angiotensin II). This metabolite can be generated directly

from angiotensin I by endopeptidases such as neutral endopeptidase, prolylendopeptidase and

thimet oligopeptidase.

Angiotensin 1-7, acting through its receptor (also called the Mas receptor), has effects opposite to

those of angiotensin II and thereby is a negative regulator of the renin-angiotensin system.

ACE inhibitors promote angiotensin 1-7 generation via 2 mechanisms: 1) increasing angiotensin

1 levels by inhibiting conversion to angiotensin II increases substrate concentration and thus

conversion by endopeptidases. 2) by blocking ACE metabolism of angiotensin 1-7 into the inactive

metabolite angiotensin 1-5.

From Hypertension Primer, 4th Edition, edited by JL. Izzo, Jr., DA. Sica, HR. Black

Publisher: Lippincott Williams & Wilkins; (November 1, 2007)

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From Hypertension Primer, 4th Edition, edited by JL. Izzo, Jr., DA. Sica, HR. Black

Publisher: Lippincott Williams & Wilkins; (November 1, 2007)

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Side Effects/Contraindications

CommonCommon Dry Cough 5 20% of patientsp Not dose-related; occurs within 1 wk. 6 mo. Women > men May Require cessation of therapyMay Require cessation of therapy

Fetopathic Potential Not teratogenic in 1st trimester

De elopmental defects in 2nd or 3rd trimester Developmental defects in 2nd or 3rd trimesterRare Angioneurotic Edema (or Angioedema) Angioneurotic Edema (or Angioedema) ~0.1 - 0.5% of patients Not dose-related; occurs within 1st week Severe swelling of mouth tongue lips airway Severe swelling of mouth, tongue, lips, airway may be life-threatening

Side Effects/Contraindications

RareRare Hypotension First dose effect in patients with elevated PRA, salt depletion, CHFp , p ,

Hyperkalemia In patients with renal insufficiency, diabetic nephropathy

A t R l F il Acute Renal Failure Patients with renal stenosis, heart failure, volume depleted

Skin Rash Extremely Rare (reversible) Alteration/loss of taste Neutropenia Glycosuria Hepatotoxicity

Drug Interactions

Antacids Antacids May reduce bioavailability of ACE inhibitors

Capsaicin May worsen ACE inhibitor-induced cough

NSAIDs May reduce antihypertensive response to ACE inhibitors

K+ sparing Diuretics or K+ supplements K -sparing Diuretics or K supplements May exacerbate ACE inhibitor-induced hyperkalemia

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Novel and Unexpected Functions of ACE

and ACE inhibitors

ACE inhibitors potentiate B2 bradykinin receptor signaling by inducing crosstalk between ACE and

B2 receptor. (Erds EG, Deddish PA, and Marcic BM. Potentiation of Bradykinin Actions by ACE Inhibitors. Trends Endocrinol Metab 10: 223-229, 1999.)

ACE inhibitors bind directly to B1 kinin receptors and induce high output nitric oxide production in

endothelial cells. (Ignjatovic T, Tan F, Brovkovych V, Skidgel RA, and Erds EG. Novel mode of action of angiotensin I converting enzyme inhibitors: direct activation of bradykinin B1 receptor. J Biol Chem 277: 16847-16852, 2002)

ACE itself is a signaling molecule that can be phosphorylated, activating JNK kinase and gene

transcription in response to ACE inhibitors. (Kohlstedt, K., Brandes, R. P., Muller-Esterl, W., Busse, R. and Fleming, I. Angiotensin-converting enzyme is involved in outside-in signaling in endothelial cells. Circ. Res. 94, 60-7, 2004).

Ki iA i t i

Other antihypertensive drugs that interfere with the Renin-Angiotensin System

KininogenAngiotensinogen

Renin Kallikrein

Angiotensin I(Inactive)

Bradykinin B2 Receptor

ACE

(Inactive)

Angiotensin II

AT1 Receptor

Angiotensin IIBradykinin(1-7)

(Inactive)Angiotensin

ReceptorAntagonists

(the sartans

Vasodilation

Na+ Excretion

Receptor

Vasoconstriction

Aldosterone release Blood

(the sartans , e.g. Losartan)

Na+ RetentionBlood Pressure

Other antihypertensive drugs that interfere with the Renin-Angiotensin System

Ki iA i t i KininogenAngiotensinogen

Renin KallikreinRenin

Inhibitor

Angiotensin I(Inactive)

Bradykinin B2 Receptor

Aliskiren

ACE

(Inactive)

Angiotensin II

AT1 Receptor

Angiotensin IIBradykinin(1-7)

(Inactive)

Vasodilation

Na+ Excretion

Receptor

Vasoconstriction

Aldosterone release BloodNa+ Retention

Blood Pressure