Cardiovascular models

Non-clinical drug evaluation

Toxicology, pharmacokinetics, chemistry, safety pharmacology, and pharmacodynamics.

Species selection

• Humans average 70 bpm with a 200 ms action potential and 93 mmHg.

• Rats around 580 bpm and 111 mmHg.

• Dogs around 105 bpm and 128 mmHg.

• Mice around 340 bpm and 11 mmHg.

Non-clinical experimental models

Specific methodology applied on a biological system

• In vivo: clinical data, animal models

• Ex vivo: isolated organs

• Ex vivo/in vitro: cellular models

• In vitro: molecular models (biochemistry)

Pathological model

Mimic the pathology in experimental models

• In vivo: genetic selection, genetic manipulation, administration of a toxic or pharmacological compound, surgery

• Ex vivo: an organ from patients or an animal model

• Ex vivo/ in vitro: primary cell culture from patients or animal models, cell lines, reprogrammed stem cells (iPS), engineered tissue

• In vitro: modified recombinant protein with mutation

Proof of concept

• Demonstrate efficacy of the therapeutic strategy in a non-clinical model of the pathology

• Then, a 1st trial in humans

Organ perfussion

Driven by arterial blood pressure (Pa)

• Right heart: low-pressure system

• Left heart: high-pressure system

Blood pressure

• Systolic pressure (120 mmHg, when blood is ejected into arteries)

• Diastolic pressure (80 mmHg, pressure between heartbeats)

Hemodynamics recording (BP recording)

• Invasive: catheterism

• Non-invasive: sphygmomanometer

Catheterism

• Advantages: direct mesurement, collection of blood samples

• Limits: anesthesia may be required (influence heart rate and blood pressure), risk of complications: thrombosis, infection

Sphygmomanometer

• Advantage: recording in vigil (non-anesthetized) animals

• Limit: indirect mesurement

Catheterism method

• Placing a fluid-filled catheter into an artery, connected to a pressure transducer.

• Generates an arterial pressure trace providing systolic, diastolic, mean arterial pressure, pulse pressure, and heart rate.

• Measure specific pressures, such as right ventricle systolic pressure in nicotine-exposed mice.

Tail cuff method (CODA system)

• Tail-cuff placed on the tail to occlude the blood flow. Upon deflation, one of several types of noninvasive blood pressure sensors, placed distal to the occlusion cuff, can be used to monitor the blood pressure.

• Animals are vigil.

• Necessitates a habituation period (generally 5 consecutive days, with “real” measurement on day 6-7)

• Limit: provides with a snapshot of BP value; no long-term monitoring

Radiotelemetry

• Implanting a pressure probe and transmitter.

• It allows for direct, continuous monitoring of blood pressure and circadian rhythms in conscious, free-moving animals

• Limited by battery life.

• Experimental designs using this method must carefully control treatment timing, doses, and positive controls.

Experimental design

• 5 experimental groups

• Treatment parameters: dose, route, frequency, vehicle, timing

Echocardiography

• Non invasive technique to explore cardiac morphology and function using ultra sounds

• A probe emits ultrasounds at high frequency (15-40 MHz) toward the organs

• The probe receives back the echoes, which are translated in electrical signal and amplified.

• Used for morphological exploration of the heart chambers and large vessels

• Conducted on anaesthetized, unconscious animals (typically using isoflurane, a gaseous anaesthetics)

Echocardiography B-mode

2D morphological images to measure dimensions and calculate left ventricle (LV) volumes, LV mass, stroke volume, ejection fraction, and cardiac output.

Echocardiography M-mode

Motion mode displays the movement of the anterior and posterior walls over time, used to measure LV internal diameters during systole and diastole.

Echocardiography Doppler-mode

Uses pulse wave and color Doppler to visualize blood flow velocity, which serves as a crucial indicator of diastolic function

Echocardiograms uses

Measure the effects of inotropic drugs, like omecamtiv mecarbil, which increases fractional shortening in rats and dogs.

Electrocardiogram

Maps the heart's electrical pathways.

• P wave represents atrial depolarization

• QRS complex represents ventricular depolarization

• T wave represents ventricular repolarization

ECG Recording

• External electrodes or implanted radiotelemetry

• Yields data on heart rate, arrhythmias, and ischemia

Safety pharmacology

• Before human trials, investigates the potential unwanted effects of a drug at therapeutic and supra-therapeutic doses

• A core battery of tests evaluates the central nervous system, respiratory function, and cardiovascular function, with a heavy emphasis on arrhythmogenic potential

Long QT syndrome

• A slower cardiac action potential repolarization leads to a prolonged QT interval on an ECG

• Trigger "Torsades de pointes" (a dangerous arrhythmia) and sudden death

• Can be inherited or drug-induced (iatrogenic) by pharmacological inhibition of the hERG K+ channel, which blocks the repolarizing potassium efflux

ICH S7B Guidelines

Risk evaluation of ventricular repolarization

Arterial hypertension

• Hypertension is defined as systolic blood pressure > 140 mmHg and/or diastolic > 90 mmHg

• Affects 30–45% of adults globally

• Major risk factor for cardiovascular and renal events, ischemic heart disease, and stroke

Models for arterial hypertension

Mimic this pathology using genetic selection, neurohormonal stimulation, dietary changes, or genetic manipulation

Spontaneous hypertensive rat (SHR)

• Genetic model of hypertension that naturally develops chronic hypertension leading to left ventricular hypertrophy and ultimately heart failure over a period of two years

• Hypertensive development begins around 5–6 weeks of age, reaching systolic pressures between 180 and 200 mmHg in the adult age phase.

• Starting between 40 and 50 weeks, SHR develops characteristics of cardiovascular disease, such as vascular and cardiac hypertrophy

• Control: Wistar-Kyoto rats

Stroke prone SHR (SHRSP)

• Further development of SHR that has even higher blood pressure than SHR and a strong tendency to die from stroke

• 80% in males, 60% in females

• Extensive arteriosclerosis

• Control strain: Wistar Kyoto

Dahl salt-sensitive rat model

• An inbred strain that develops hypertension and heart failure when exposed to high-salt diets, characterized by metabolic disturbances such as insulin resistance and dyslipidemia

• Suppressed plasma renin activity (due to high Na reabsorption), low aldosterone

• Diastolic heart failure, nephropathy

• Control strain: normal rat, with a high salt diet

• Mimics salt-sensitive HT in patients

Transgenic hypertension model

Transgenic rats, overexpression of a gene involved in BP regulation

• TGR(mREN2)27 transgenic rat, resulting in severe hypertension

• Double transgenic: human renin and angiotensinogen. Test antihypertensive effect of the human renin inhibitor

Advantage of studying conscious animals

• Anesthetics actively influence and alter fundamental cardiovascular parameters, including heart rate and blood pressure

• Studying conscious, "vigil" animals provides a much more accurate, unconfounded picture of the animal's true physiological baseline and the actual pharmacodynamic effects of the drug over an extended period

Important parameters to be examined to explore the effect of a drug on the cardiovascular system

1. Blood pressure: via catheter or tail cuff, asses wether a drug is a vasodilator (lowers BP) or a vasoconstrictor (raises BP)

2. Heart rate: via pressure tracing or electrocardiogram (ECG). Determine if a drug causes dangerous tachycardia (abnormally fast) or bradycardia (abnormally slow)

3. QT interval: via ECG. Total time for ventricular depolarization and repolarization. Prolongation of the intervals indicates a risk of fatal arrhythmias

4. Ejection fraction (EF) / stroke volume (SV): in vivo echocardiography. Evaluates drugs’ inotropic effect (how strongly it impacts the heart muscle’s ability to contract).

   1. SV: amount of blood pumped per beat

   2. EF: percentage of the blood the left ventricle pumps out with each contraction

Cardiac repolarization tests

• Patch clamp: electrophysiology to study the drug's effect directly on specific ion channels expressed in cell lines

• ECG: check for a prolongation of the QT interval or the onset of arrhythmias