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The chronic administration of isoproterenol via an implanted osmotic pump has been used widely to mimic advanced heart failure in mice. Here, we describe detailed methods in surgical mini-pump implantation for the continuous isoproterenol administration over 3 weeks, as well as, echocardiographic assessment for the successful model creation.
Isoproterenol (ISO), is a non-selective beta-adrenergic agonist, that is used widely to induce cardiac injury in mice. While the acute model mimics stress-induced cardiomyopathy, the chronic model, administered through an osmotic pump, mimics advanced heart failure in humans. The purpose of the described protocol is to create the chronic ISO-induced heart failure model in mice using an implanted mini-pump. This protocol has been used to induce heart failure in 100+ strains of inbred mice. Techniques on surgical pump implantation are described in detail and may be relevant to anyone interested in creating a heart failure model in mice. In addition, the weekly cardiac remodeling changes based on echocardiographic parameters for each strain and expected time to model development are presented. In summary, the method is simple and reproducible. Continuous ISO administered via the implanted mini-pump over 3 to 4 weeks is sufficient to induce cardiac remodeling. Finally, the success for ISO model creation may be assessed in vivo by serial echocardiography demonstrating hypertrophy, ventricular dilation, and dysfunction.
Heart failure with reduced ejection fraction (HFrEF) is accompanied by a well-recognized compensatory response of the sympathetic nervous system to maintain cardiovascular homeostasis1. Hemodynamic stress and deleterious effects on the heart and circulation were observed with chronic activation. These have become the cornerstone of contemporary pharmacotherapy for heart failure and are important mechanisms in the progression of heart failure and therapeutic antagonism of neurohormonal systems1.
Several mouse models are available for basic investigations of heart failure. Genetic models are attractive for exploring molecular therapies and investigating signaling pathways. However, these models may not be relevant to common forms of heart failure. Other common models include left anterior descending (LAD) artery ligation, transaortic constriction (TAC), and isoproterenol (ISO), each aiming at a different pathological etiology2,3,4,5,6. LAD artery ligation induces an anterior wall myocardial infarction thus creating a model specific for ischemic cardiomyopathy. TAC induces acute pressure overload to create a hypertensive model of heart failure. Although the pressure gradient can be measured, allowing for the stratification of hypertrophy, the acute onset of hypertension lacks direct clinical relevance4. Both LAD and TAC models require a high level of surgical expertise to execute. Acute ISO model of heart failure mimics stress-induced cardiomyopathy, also known as Takotsubo disease, which is characterized by a marked increase in catecholamines and activity in the left ventricle that mimics acute myocardial infarction7,8. In contrast, chronic ISO models of heart failure present symptoms characteristics of advanced heart failure, with chronically elevated levels of catecholamines1. The advantages of the chronic ISO model are that it provides chronic adrenergic stimulation that mimics advanced heart failure and that it is relatively easy to create. The investigator should choose a model that best recapitulates their pathology of interest.
The overall goal of this method is to induce heart failure in mice using an implanted mini pump that releases ISO continuously to mimic chronic sympathetic activation found in heart failure patients1. The method is simple and reproducible. Although there is clear variation among mouse strains, ISO administered over 3 to 4 weeks at 30 mg/kg/day is sufficient to induce cardiac remodeling in most mice. Specifically, ISO leads to a pro-hypertrophic compensatory phase during week 1 followed by wall thinning, ventricular dilation and decrease in systolic function by week 2 and 32. Success for the ISO model creation can be assessed in vivo by serial echocardiography demonstrating hypertrophy, dilation, and ventricular dysfunction, as well as ex vivo via histological and molecular assessment of harvested cardiac tissue for intramyocardial lipid accumulation, fibrosis, ER stress, apoptosis, and gene expression9,10,11,12.
This protocol adheres to the animal care guidelines of the University of California, Los Angeles (ARC protocol #2010-075). Readers are advised to adhere to their own IACUC-approved protocol, as peri-procedure mouse care and analgesia management may be institution-specific.
1. Preparation of isoproterenol osmotic pump
NOTE: This procedure has been applied successfully on 9+ week-old female mice weighing 18+ g from over 100 inbred mouse strains, as well as, in male mice in a subset of strains. There is no maximum body weight limit for this procedure. Always include age-matched controls, as it is unknown whether the age of treatment affects isoproterenol-induced susceptibility to heart failure development.
2. Preparation of surgical instruments
3. Isoproterenol osmotic pump surgical implantation
4. Echocardiographic assessment under anesthesia
NOTE: Echocardiographic assessment can be performed repeatedly to monitor serial cardiac remodeling over several weeks. We performed echocardiographic measurements at weekly intervals over 3 weeks.
In our previously published study, we administered an ISO dosage of 30 mg/kg/d over 21 days via the osmotic pump across 105 Hybrid Mouse Diversity Panel (HMDP) strains2,13. We assessed outcomes using echocardiogram performed at baseline, week 1, 2 and 3 of ISO treatment (Figure 1). Similar to a prior study where the authors studied the impact of isoproterenol among 23 mouse strains14, we observed striking inte...
We have applied this method to over 100+ strains of inbred mice to assess cardiac outcomes due to chronic beta-adrenergic stimulation2,13. Significant differences in susceptibility to isoproterenol are known to exist among mouse strains and may be customized to the strain of interest as needed16. This may be due to the variation in beta-adrenergic receptor function between mouse strains17, strain-dependent differenc...
The authors have nothing to disclose.
The authors acknowledge NIH K08 HL133491 for funding support.
Name | Company | Catalog Number | Comments |
Micro-Osmotic Pump System with Flow Moderator in Place | Alzet | Model 1004 | Includes filling tube, flow moderator and pump body |
(-)-Isoproterenol hydrochloride | Sigma-Aldrich | 16504-1G | (-)-Isoproterenol hydrochloride is a powder that needs to be stored at -20°C. |
1 ml sterile syringe | VWR | BD309602 | |
30 W LED Fiber optic O-ring light microscope illuminator | AmScope | SKU: LED-30WR | |
5-0 COATED VICRYL (polyglactin 910) Suture | Ethicon | J303H | 5-0, absorbable |
Fine Scissors - Sharp | FST | 14060-09 | |
Glass beads | FST | 18000-46 | |
Hot bead sterilizers | FST | 18000-50 | |
Iris forceps | WPI | 15915 | |
Look Sharpoint 6-0, 18" Black Nylon Monofilament Suture | LOOK | AA-2176 | 6-0, non-absorbable |
Needle holder | WPI | 15926 | |
Normal Saline, 0.9% NaCl | Fisher | 89167-772 |
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