An Improved Method for Rapid Intubation of the Trachea in Mice

Summary

This article presents a rapid and simple method for administering bleomycin directly into the mouse trachea via intubation. Key advantages of this method are that it is highly reproducible, easy to master, and does not require specialized equipment or lengthy recovery times.

Abstract

Despite some anatomical and physiological differences, mouse models continue to be an essential tool for studying human lung disease. Bleomycin toxicity is a commonly used model to study both acute lung injury and fibrosis, and multiple methods have been developed for administering bleomycin (and other toxic agents) into the lungs. However, many of these approaches, such as transtracheal instillation, have inherent drawbacks, including the need for strong anesthetics and survival surgery. This paper reports a quick, reproducible method of intratracheal intubation that involves mild inhaled anesthesia, visualization of the trachea, and the use of a surrogate spirometer to confirm exposure. As a proof of concept, 8-12 week old C57BL/6 mice were administered either 2.0 U/kg of bleomycin or an equivalent volume of PBS, and both damage and fibrotic endpoints were measured post-exposure. This procedure allows researchers to treat a large cohort of mice in a relatively short period with little expense and minimal post-procedure care.

Introduction

In spite of some anatomical and physiological differences,¹ murine models continue to be invaluable for modeling human biology and disease pathogenesis.² From a husbandry standpoint, mice are easy to handle, have a low breeding time, an accelerated lifespan, and are relatively inexpensive to house. With the development of diverse genetic strains and strategies (e.g., conditional knock-outs, reporter mice, lineage-tracing approaches, etc.), as well as the wide range of available reagents (e.g., antibodies, recombinant proteins, inhibitors, etc.), mice have become an essential model vertebrate organism to uncover human homeostasis....

Protocol

The Institutional Animal Care and Use Committees (IACUC) at the University of Washington and Cedars-Sinai Medical Center have approved the animal work necessary for these studies.

1. Preparation

1. Sterilize both the blunt end forceps and the depressor via autoclave.
2. Using a biological safety cabinet, prepare a working stock of BLM in PBS from the lyophilized powder.  Sonicate the solution for 10 min at 35 Khz to assure even mixing.
   Note: A total volume of between 30 and 45 µl is recommended to prevent pipetting variation on the low end, and suffocation with larger volumes.
3. Prepare a clean workspace that includes ap....

Results

Intubated mice were monitored daily for weight loss and distress, and sacrificed 4, 10 or 17 days later via intraperitoneal injection of 2.5% 2,2,2-tribromoethanol. Bronchoalveolar lavage (BAL) was collected in three washes of PBS as described elsewhere ²¹, and the right lung was fixed in 10% formalin, paraffin embedded, and stained with Masson's Trichrome by the University of Washington Histology and Imaging Core ²².

Discussion

In instances where aerosolization is impractical due to limited reagent availability, safety, or cost, direct tracheal administration is a superior method for delivery of exogenous agents into the lungs.¹⁶ Transtracheal instillation has been widely used to accomplish this; however, as with all surgical intervention, it also carries with it the potential for complications caused by the procedure itself, and not necessarily the agent being instilled.¹³ For these reasons, it has become.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Bleomycin For Injection, 30 units/vial	APP Pharmaceuticals, LLC	103720	For best results, BLM should be suspended in PBS, aliquoted, and stored as single use lyophilzed aliquots
Blunt End Forceps
Tongue Depressor (i.e. bent Valleylab Blade Electrode, 2.4")	Covidien	E1551G	Before use, create a 45 degree bend 1.5 cm  from the blade tip. A suitable depressor can also be created from any metal implement of similar dimensions.
Exel Safelet Catheter 22G X 1"	Exel International	26746
1 ml Slip-tip Disposable Tuberculin Syringe (200/sp, 1600/ca)	BD	309659
0.2 ml Pipettor and Filter Tips
Fiber-Lite Illuminator. Model 181-1: Model 180 mated with Standard Dual Gooseneck illuminator	Dolan Jenner Industries, Inc.	181-1	Lower output LED illuminators are not recommended as they fail to suficiently illuminate the trachea.
Intubation Board			See Diagram 1.
Colored Label Tape: 0.5 in. Wide	Fisherbrand	15-901-15A
Oxygen
Phosphate-Buffered Saline, 1X	Corning	21-040-CV	Product should be sterile
Non-Sterile Silk Black Braided Suture Spool, 91.4 m, Size 4-0	Harvard Apparatus	517698
Table Top Anesthesia Machine Isoflurane	Highland Medical Equipment		http://www.highlandmedical.net/
Slide Top Induction Mouse Isoflurane Chamber	MIP / Anesthesia Technologies	AS-01-0530-SM
FORANE (isoflurane, USP) Liquid For Inhalation 100 mL	Baxter	1001936040
Nanozoomer Digital Pathology system	Hamamatsu
IgM ELISA Quantification Kit	Bethyl Laboratories	E90-101