Vasoconstriction in human coronary arteries (5-HT receptor – 5-HT)

Drug Discovery Assay – reference number: B003

Overview

Assay Description

The experiment assesses whether test articles cause vasoconstriction in human coronary arteries with 5-HT as a reference compound. Coronary arteries supply blood to the myocardium. Changes in blood flow and vascular tone can greatly affect cardiac function; even a brief reduction in coronary blood flow can induce dysfunction of the heart.

Figure 1: Cumulative concentration response curve to 5-HT in isolated human coronary artery, demonstrating a concentration dependent contractile response. The Log EC₅₀ = −7.1 ± 0.16M (83nM) (mean ± S.E.M), with a maximum contractile response of 74.16 ± 8.8% at 3 × 10⁻⁶M.

Testing Information

Introduction

The specific results that will be provided are the effects of increasing concentrations of test articles on the contractile state of human isolated coronary arteries.

Test Article Requirements

Test article(s) to be provided by the Sponsor in storable aliquots at required test concentrations with information on diluent vehicle used. Stock solutions are prepared in distilled water unless otherwise requested. Bath volumes are 5mL; sponsor to provide sufficient test article to run the entire study.

Suggested Testing

In duplicate and 6 concentrations

Study Outline

Rationale and Experimental Design

The purpose of this assay is to determine whether test articles cause vasoconstriction in human coronary arteries.

Exclusion Criteria

No specific exclusion criteria are in place other than to reject macroscopically diseased/necrotic tissue. Furthermore, tissues which do not respond to the standard pharmacology checks will be excluded.

Standardisation and Qualification

All individual vessels are initially processed through standardisation and qualification procedures to ensure functionality, prior to starting the study protocol.

Vessels are processed through a standardisation procedure to reduce signal variability prior to pharmacological intervention. This ensures that vessels are maintained under appropriate physiological tension throughout the experiments.

Following standardisation, vessels are “woken up” by 2 successive high potassium salt solution challenges with washes and recovery periods following each challenge. This process standardises the basal resting tone and ensures robust contractile responses.

Vessels are then challenged with an appropriate vasoconstrictive agent before endothelial function is assessed by the addition of the appropriate endothelial dependent vasorelaxant agent. Test tissues are then washed, and the responses allowed to return to baseline.

Vessels which pass the standardisation and qualification pass/fail criteria will then progress to the study protocol.

Agonist Constriction Assays

To assess their ability to elicit vasoconstriction, 6 point cumulative concentration response curves (CCRC’s) will be performed for each test article. These CCRC’s will be performed from resting baseline tension. A positive control compound and representative test article vehicle CCRC will also be run to allow direct comparison with test articles.

An example of the conditions assessed for 3 test articles are detailed below (each condition will be run in duplicate vessels):

• Representative test article vehicle CCRC

• Positive control CCRC

• Test article 1 CCRC

• Test article 2 CCRC

• Test article 3 CCRC

Supplementary Option

To assess the involvement of a specific receptor subtype in any observed responses, the concentration of test article eliciting the largest response can subsequently (following a wash out and recovery period) be tested in the presence of a specific antagonist. This supplementary option will incur an extra charge.

Antagonist Constriction Assays

Option 1 – IC₅₀ Determination

To assess the ability of each test article to antagonise an agonist mediated vasoconstriction response, 6 point cumulative concentration response curves (CCRC’s) will be performed for each test article. These concentration response curves (CCRC’s) will be performed following pre−constriction with an appropriate vasoconstrictive reference agonist. A positive control compound and representative test article vehicle CCRC will also be run to allow direct comparison with test articles.

An example of the conditions assessed for 3 test articles are detailed below (each condition will be run in duplicate vessels):

• Representative test article vehicle CCRC

• Test article 1 CCRC

• Test article 2 CCRC

• Test article 3 CCRC

• Positive control CCRC

Option 2 – pA₂ Determination

To assess the ability of a test article to antagonise an agonist mediated vasoconstriction response; 6 point cumulative concentration response curves (CCRC’s) will firstly be performed for the vasoconstrictive reference agonist.

Following a wash out and recovery period, vessels will be incubated with the test article (3 different concentrations of test item will be assessed), positive control or test article vehicle before the same 6 point cumulative concentration response curve will be repeated for the reference agonist.

An example of the conditions assessed for 3 test articles are detailed below (each condition will be run in duplicate vessels):

• Representative test article vehicle

• Test article 1 concentration 1

• Test article 1 concentration 2

• Test article 1 concentration 3

• Test article 2 concentration 1

• Test article 2 concentration 2

• Test article 2 concentration 3

• Test article 3 concentration 1

• Test article 3 concentration 2

• Test article 3 concentration 3

• Positive control

Analysis

Responses shall be expressed either in milligrams or grams tension, or as a % of the maximal contractile response (e.g. KPSS). Statistical analysis (where appropriate) will be performed using GraphPad Prism, with the results being shown in graphical form in the final report.

Case study: Response of cultured isolated human coronary arteries to 5-HT

The concentration-dependent effects of serotonin (5-hydroxytryptamine) in human isolated coronary arteries, set up in REPROCELL Biopta's wire myographs, are shown in the graph below. The graph also highlights REPROCELL Biopta's ability to culture blood vessels in order to look at the effect of test compounds over a 2-3 day period. Human coronary arteries show robust contractile responses to 5-HT after 24 and 48 hours of culture.

The location of the concentration-effect curve is consistent with historical data from Biopta’s uncultured vessels and now provides us with a protocol to explore the longer-term effects of drug treatment on vasoactive pathways; invaluable for exploring both efficacy and safety mechanisms.

Human coronary arteries show robust contractile responses to 5-HT after 24 and 48 hour culture periods.