Name: simple continuous glucose monitoring in freely moving mice
Uploaded: 2023-02-24T13:35:00
Description: Watch this Scientific Journal Video about Simple Continuous Glucose Monitoring in Freely Moving Mice at JoVE.com

We thank Dvir Mintz DVM and the veterinary and husbandry staff in the animal facility, as well as members of our group, for fruitful discussions. This study was supported by an Israel Science Foundation grant 1541/21 awarded to D.B.Z. D.B.Z. is a Zuckerman STEM faculty.

The experiments were approved by the Hebrew University&#39;s Institutional Animal Care and Use Committee (IACUC).
NOTE: All tools must be sterilized, and handling of the cannula must be performed using a sterile technique. The protocol below is fine-tuned to a specific CGM. The protocol can be adapted to other CGMs.
1. Analgesic administration before the procedure
<ol>
	<li>Administer 5% dextrose and 0.45% saline with meloxicam at 5 mg/kg body wei...

<ol>
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This protocol offers a simple, inexpensive method to monitor glucose levels in mice that does not require challenging microsurgery and does not involve bleeding or handling the mice. The method is easy to implement in every facility and does not cause mortality, pain, or excessive discomfort to the mice. The most critical step in the protocol is inserting the cannula of the glucose sensor under the skin of the mouse. The addition of a few sutures allows the cannula to stay in place for a longer time. The sensors are smal...

Diabetes mellitus (DM) is a devastating disease characterized by high blood glucose levels. Type 1 DM can be a result of an autoimmune attack on the insulin-producing beta cells in the pancreas. Type 2 DM and gestational DM, on the other hand, are characterized by a failure of the beta cells to secrete sufficient insulin in response to a rise in glucose levels1. The mouse is a common model organism used to study DM since it has similar physiology, and its normal glucose levels are close to those of humans. Furthermore, specific mouse strains may develop DM due to mutations in key signaling pathways or following exposure to specific diets, which enables disease modeling2,3,4.
Blood glucose is commonly measured in mice using glucometers designed for patients by extracting a small drop of blood (1-2 &#181;L) from the tip of the tail of the mouse. This method causes stress and requires handling of the mouse, which affects the glucose levels and prohibits the measurement of blood glucose levels in freely behaving mice or when the researcher is not close by5. Bleeding the mice may cause stress to nearby mice, particularly to mice of the same cage whose glycemia has not been measured yet, thus affecting the results. Mice respond differently depending on the handler, and the person measuring glucose may affect the glucose levels of the mice. These pitfalls call for careful experimental design and underlie some inconsistencies between experiments.
It is possible to measure glucose in freely moving mice with no bleeding by implanting glucose sensors into the aortic arch of the mice using state-of-the-art telemetry6. The resulting measurements are very good and can be sustained over a long period, but it is challenging to implant these sensors, and the telemetry system is expensive, leading to a moderate adoption of this methodology and no adoption in non-specialized labs. Subcutaneous or other glucose sensors that are tailored to the dimensions of the mice and their physiology have been developed in recent years, but these again require highly skilled experts and are in some cases costly6,7,8,9,10.
Commercial continuous glucose monitors (CGMs) that were originally developed to monitor the glucose levels of DM patients offer another option to measure glucose in freely moving mice, with lower cost and technical expertise requirements than implanted probes. Such probes have been used in basic research by a few labs5,11,12,13,14,15&#160;including our colleagues who used this protocol16. These devices typically include a sensor, a mounting device, a receiver, and a software application. The sensor has a cannula guiding the enzymatic glucosensor, adhesive tape, an energy source, short-term memory, and a wireless communication module that stores and sends the data to the receiver. The receiver can show the current glucose levels and sends the data to a server; this receiver can be a cellphone. The software application provides data for the patient and the medical care team on the glycaemia of the patient. In patients, the sensor is attached easily using the mounting device. The cannula is inserted subcutaneously by pressing the mounting device against the skin, and the sensor stays in place with the help of adhesive tape.
This is a detailed protocol for adapting a commercial CGM device to measure glucose levels in mice. This protocol describes how to surgically insert the glucose sensor and attach it to the mouse. Scripts for basic data analysis and data visualization are provided. The potential pitfalls, troubleshooting, and examples of standard results are provided. The protocol below is specific for a certain CGM but can be easily adapted to other types of commercial CGMs as they become available.

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			<td>2%&#160; Chlorhexidine Gluconate and 70%&#160; Isopropyl Alcohol</td>
			<td>3M</td>
			<td>ID&#160;7000136290</td>
			<td></td>
		</tr>
		<tr>
			<td>5% Dextrose and 0.45% Sodium Chloride Injection, USP</td>
			<td>Braun</td>
			<td>L6120</td>
			<td></td>
		</tr>
		<tr>
			<td>Castroviejo needle holder</td>
			<td>FST</td>
			<td>12061-02</td>
			<td></td>
		</tr>
		<tr>
			<td>Extra Fine Bonn scissors</td>
			<td>FST</td>
			<td>14084-08</td>
			<td></td>
		</tr>
		<tr>
			<td>FreeStyle Libre 1 reader</td>
			<td>Abbott</td>
			<td>ART27543&#160;</td>
			<td></td>
		</tr>
		<tr>
			<td>FreeStyle Libre sensor</td>
			<td>Abbott</td>
			<td>ART36687</td>
			<td></td>
		</tr>
		<tr>
			<td>FreeStyle Libre sensor applicator</td>
			<td>Abbott</td>
			<td>ART36787</td>
			<td></td>
		</tr>
		<tr>
			<td>Gauze pads</td>
			<td>Sion medical</td>
			<td>PC912017</td>
			<td></td>
		</tr>
		<tr>
			<td>Graefe Forceps</td>
			<td>FST</td>
			<td>11052-10</td>
			<td></td>
		</tr>
		<tr>
			<td>Hair Removal Cream</td>
			<td>Veet</td>
			<td>3116523</td>
			<td></td>
		</tr>
		<tr>
			<td>High-fat high-sucrose diet</td>
			<td>Envigo Teklad diets</td>
			<td>TD.08811</td>
			<td></td>
		</tr>
		<tr>
			<td>Isoflurane, USP Terrell</td>
			<td>Piramal</td>
			<td>26675-46-7</td>
			<td></td>
		</tr>
		<tr>
			<td>Meloxicam 5 mg/mL</td>
			<td>Chanelle Pharma</td>
			<td>08749/5024</td>
			<td></td>
		</tr>
		<tr>
			<td>MiniARCO Clipper kit</td>
			<td>Moser</td>
			<td>CL8787-KIT</td>
			<td></td>
		</tr>
		<tr>
			<td>PROLENE Polypropylene Suture 5-0</td>
			<td>Ethicon</td>
			<td>8725H</td>
			<td></td>
		</tr>
		<tr>
			<td>Puralube Opthalmic Ointment</td>
			<td>Perrigo</td>
			<td>574402511</td>
			<td></td>
		</tr>
		<tr>
			<td>Q-tips&#160;</td>
			<td>B.H.W</td>
			<td>271676</td>
			<td></td>
		</tr>
		<tr>
			<td>SomnoSuite Low-Flow Anesthesia System</td>
			<td>Kent Scientific</td>
			<td>SOMNO</td>
			<td></td>
		</tr>
	</tbody>
</table>

simple continuous glucose monitoring in freely moving mice

Mice are a common model organism used to study metabolic diseases such as diabetes mellitus. Glucose levels are typically measured by tail-bleeding, which requires handling the mice, causes stress, and does not provide data on freely behaving mice during the dark cycle. State-of-the-art continuous glucose measurement in mice requires inserting a probe into the aortic arch of the mouse, as well as a specialized telemetry system. This challenging and expensive method has not been adopted by most labs. Here, we present a simple protocol involving the utilization of commercially available continuous glucose monitors used by millions of patients to measure glucose continuously in mice as a part of basic research. The glucose-sensing probe is inserted into the subcutaneous space in the back of the mouse through a small incision to the skin and is held in place tightly using a couple of sutures. The device is sutured to the mouse skin to ensure it remains in place. The device can measure glucose levels for up to 2 weeks and sends the data to a nearby receiver without any need to handle the mice. Scripts for the basic data analysis of glucose levels recorded are provided. This method, from surgery to computational analysis, is cost-effective and potentially very useful in metabolic research.

Surgical outcome 
Results from eight HSD:ICR mice (aged 8 weeks) fed a high-fat high-sucrose diet (HFHS) for 18 weeks and five lean HSD:ICR mice (aged 12 weeks) are shown. The device we used stores data for up to 8 h. Access to the local animal facility was restricted to 07:00-19:00, thus prohibiting data collection during the late P.M. hours, when the mice are active. The mice were, therefore, placed in a room with reverse lighting for 7 days before the surgical procedure, with dark hours between 8...

Watch this Scientific Journal Video about Simple Continuous Glucose Monitoring in Freely Moving Mice at JoVE.com

Simple Continuous Glucose Monitoring in Freely Moving Mice

Here, we describe a simple method to implant a commercial continuous glucose monitor designed for patients onto mice and provide the scripts to analyze the results.

Mice are a common model organism used to study metabolic diseases such as diabetes mellitus. Glucose levels are typically measured by tail-bleeding, which ...

Our protocol offers a simple inexpensive method to monitor glucose levels in mice. The main advantage of this technique is that it does not require challenging microsurgery, and does not involve bleeding, or handling the mice. This method can be used to identify elusive glucose management phenotypes in mouse models of obesity and diabetes.While attempting this protocol, the most critical step is the insertion of the cannula under the skin, and tightening of the inner sutures in order to keep the cannula in place. To begin shave the midline of the back of the anesthetized mouse, and use a depilatory cream to ensure complete hair removal. Open and load the sensor.Then mount the sensor onto the sensor mounting device to expose the sensor's tape and cannula side. The cannula is void from the needle. Suture two 5-0 taper point sutures to the tape on both sides of the cannula.For the dorsal skin preparation, make a two millimeter incision in the center of the shaved area above the spine using sharp scissors. Briefly insert small forceps with a blunt edge under the skin to form a small subcutaneous pocket, so that the cannula can be inserted easily into the pocket. Pass a suture through the skin on each side of the incision.For the sensor insertion, remove the sensor completely from the sensor mounting device and hold the sensor with forceps to keep the surrounding tape from sticking to itself. Carefully insert the cannula into the subcutaneous pocket. Pull the sutures on each side, and tighten and tie them to attach the sensor firmly in place.This will prevent the cannula from slipping out of the subcutaneous pocket once the adhesive tape loosens over time, Cut the ends of the sutures and discard them. Attach adhesive tape surrounding the sensor, and make eight discontinuous sutures around the sensor attaching the border of the sensors taped to the skin. Activate the sensor.Once the cannula is inserted, and the CGM is successfully activated, collect the data using the receiver. The raw output data of three days from a single mouse using the code provided is shown here. The axis parameters, and all the other parameters can be modulated in the code.Here, the data for three days are shown for clarity. Making a subcutaneous pocket and the addition of a few sutures allows the sensor's cannula to stay in place for a longer time. The continuous data acquired using this technique allowed us to uncover an elusive metabolic phenotype in a specific mouse strain.

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