Macrophages are vital cells in the immune system, playing diverse roles in tissues such as pathogen clearance, tissue repair, and immune regulation. Under certain pathological conditions, such as chronic inflammation, autoimmune diseases, or tumor progression, abnormal activation or dysfunction of macrophages can adversely affect the organism. Clodronate Liposomes are a class of agents capable of specifically depleting or eliminating macrophages. Currently, Clodronate Liposomes represent the most mature, convenient, and cost-effective tool for macrophage depletion. They can effectively clear macrophages in various tissues and compartments in animal models, including the liver, spleen, lungs, and bloodstream, making them the most widely used method for macrophage depletion today.
Literature Examples of Common Applications
01. Adipose Tissue
Source: PMID 21931688
This study aimed to investigate whether obesity-related adipose tissue inflammation, specifically the infiltration of macrophages into adipose tissue, is a cause of insulin resistance and the development of type 2 diabetes.
Mouse Strain: Male C57BL/6J mice.
Experimental Method: Mice were divided into two groups: normal diet and high-fat diet (DIO), fed with standard chow and high-fat diets, respectively. DIO mice were injected with either Clodronate Liposomes or PBS Liposomes (control). Experiments were conducted 6 to 7 days after the first injection.
Administration Route: Intravenous (IV) injection.
Dosage: Two injections at approximately 110 mg/kg, with a three-day interval.
Detection Methods: Metabolic parameter testing (blood glucose, plasma insulin levels, liver weight, and triglyceride content), hyperinsulinemic-euglycemic clamp test, histological examination, and RT-qPCR.
Results: The study demonstrated that reducing macrophages in visceral adipose tissue improved metabolic profiles and insulin sensitivity in DIO mice, which could be partly attributed to increased adiponectin levels.
Figure 1. Effect of clodronate liposomes on macrophage depletion in adipose tissue of DIO mice.
02. Liver
Source: PMID 31996460
The authors depleted macrophages via intraperitoneal (IP) injection of Clodronate Liposomes and subsequently injected bone marrow-derived macrophages via tail vein prior to ischemia-reperfusion injury (IRI) to study the role and potential molecular mechanisms of macrophages in liver IR damage.
Mouse Strain: Male C57BL/6 mice (6-8 weeks old).
Administration Route: Intraperitoneal (IP) injection.
Dosage: 400 μL/mouse.
Administration Protocol: Following Clodronate Liposome injection, mice were given drinking water containing ampicillin (1 mg/mL) until the end of the experiment to prevent infection.
Detection Methods: Immunohistochemistry (Figure 2-A) and flow cytometry (Figure 2-G) performed 48 hours post-injection.
Figure 2. Impact of Roquin-1 on liver ischemia-reperfusion (IR) injury.
03. Tumors
Source: PMID 31933479
The authors depleted macrophages in mice via IP injection of Clodronate Liposomes at specific doses and frequencies based on previous research and experimental designs to investigate the impact of macrophages on tumor metastasis.
Mouse Strain: NSG mice.
Administration Route: Intraperitoneal (IP) injection.
Dosage: Three times a week at 6.5 mL/kg.
Detection Methods: Bioluminescence imaging (BLI), immunofluorescence, and RT-qPCR.
Results: Macrophage depletion using Clodronate Liposomes resulted in a significant reduction in the number of metastatic lesions in the liver and lungs in orthotopically transplanted MYC/Twist1-HCC mice, indicating that macrophages play a crucial role in tumor metastasis.
Figure 3. Twist1 induces MYC-HCC metastasis via a macrophage-dependent mechanism.
04. Embryonic Microglia
Source: PMID 29559892
This study explored the effects of in utero administration of a microglia-depleting agent (a type of brain macrophage) on improving neurodevelopmental outcomes in rat fetuses infected with Cytomegalovirus (CMV).
Animal Strain: Wistar rats (RCMV-1 145-147-gfp).
Administration Route: Intrauterine embryonic intracerebroventricular injection.
Dosage: 0.5 μL/injection.
Administration Protocol: On embryonic day 15, the experimental group received simultaneous injections of Clodronate Liposomes (0.5 μL/injection) and rat CMV (1.75×10³ pfu). The control group received PBS liposomes (0.5 μL/injection). Dams were administered doxycycline (200 mg/kg feed) throughout gestation.
Detection Methods: Immunohistochemistry, tissue clearing, flow cytometry, confocal microscopy, and RT-qPCR.
Results: Depletion of microglia using Clodronate Liposomes and maternal doxycycline treatment were both associated with significantly improved survival rates, better weight gain, enhanced sensorimotor development, and a reduced risk of seizures.
Figure 4. Clodronate liposomes deplete microglia and reduce CMV dissemination in the developing brain.
05. Gastrointestinal Tract
Source: PMID 36263186
This study aimed to investigate the role and mechanism of TMP195 (a selective class IIa histone deacetylase [HDAC] inhibitor) in colorectal cancer (CRC) treatment. Given the close relationship between HDACs and cancer, as well as the association of class IIa HDAC inhibitors with immune function, researchers specifically focused on the effect of TMP195 on M1 macrophage polarization and its potential therapeutic efficacy when combined with PD-1 blockade therapy.
Mouse Strain: C57BL/6 mice.
Administration Route: Intraperitoneal (IP) injection.
Dosage: 200 μL/dose.
Administration Protocol: Injections began two days prior to MC38 cell inoculation, administered every three days at 200 μL/dose until the mice were euthanized.
Detection Methods: Colitis-associated colorectal cancer model, flow cytometry, histopathology and immunostaining, RT-qPCR, and ELISA.
Results: Partial depletion of macrophages using Clodronate Liposomes abolished the anti-tumor effects of TMP195, suggesting that the efficacy of TMP195 may be macrophage-dependent.
Figure 5. Macrophage depletion attenuates the therapeutic efficacy of TMP195 against colorectal cancer.
Figure 6. Flow cytometric analysis of M1 macrophage and T lymphocyte infiltration.
06. Brain Microglia
Source: PMID 30980832
This study investigated the effects of immediate microglial depletion following traumatic brain injury (TBI) on cellular and behavioral pathology in a rat model.
Animal Strain: Sprague-Dawley rats.
Administration Route: Intracranial injection.
Dosage: 10 μL.
Administration Protocol:
Preoperative Anesthesia: Animals were anesthetized with isoflurane (5% induction, 1-2% maintenance). Sutures were removed, the incision reopened, the skull cleaned, and the animal placed in a stereotaxic frame.
Drilling: A burr hole was drilled into the skull. A 10 μL Hamilton® 80000 1701N syringe was used to slowly inject 10 μL of liposome suspension (liposome size = 2 μm) into the cerebral cortex and thalamus.
Postoperative Care: Animals recovered in individual cages for at least 60 minutes before being returned to their dams. Surgery and postoperative recovery were conducted on a heating pad maintained at 37°C to preserve body temperature.
Note: Coordinates for the two injection sites were based on the third edition of the Paxinos and Watson Rat Brain Atlas: Cortex (-1.5 mm AP, 1.7 mm ML, 1.7 mm DV); Thalamus (-3.5 mm AP, 1.7 mm ML, 3.5 mm DV).
Detection Methods: Neuropathological evaluation and electrophysiological testing.
Figure 7. Microglial activation in the cortex following clodronate-induced depletion.
07. Alveolar Macrophages
Source: PMID 22110592
This study investigated the impact of pulmonary ischemia on alveolar macrophages. In a mouse model, the left pulmonary artery was completely occluded, isolating the left lung from the systemic circulation until new systemic vessels entered the lung parenchyma 5-7 days later. Clodronate Liposomes were used to deplete monocytes/macrophages to evaluate the effects on angiogenesis.
Mouse Strain: C57BL/6 mice.
Administration Route: Intraperitoneal (IP) injection combined with intratracheal administration.
Dosage: 100 μL.
Animal Model Protocol:
Preparation: Male C57BL/6 mice (5-6 weeks old) were used according to protocols approved by the Johns Hopkins University Animal Care and Use Committee.
Anesthesia: Mice were anesthetized with 2% isoflurane.
Tracheal Intubation: Anesthetized mice were intubated and connected to a ventilator (120 breaths/min, 0.2 mL tidal volume).
Left Pulmonary Artery Ligation (LPAL): A lateral thoracotomy was performed. The left pulmonary artery was identified and ligated to cut off blood supply to the left lung, simulating ischemia. The thoracic incision was closed, the endotracheal tube removed, and the mice were allowed to recover.
Sample Collection: Mice were euthanized via cervical dislocation at various time points post-LPAL. Lung tissues were collected for bronchoalveolar lavage (BAL), cell counting, flow cytometry, immunohistochemistry, and immunofluorescence staining.
Administration Protocol: Clodronate Liposomes or control PBS liposomes were administered either in a long course (24 hours before LPAL, and on days 1, 5, and 9 post-LPAL) or a short course (24 hours before and 24 hours after LPAL).
Detection Methods: Flow cytometry.
Results: Flow cytometric analysis confirmed a reduction in macrophage numbers following Clodronate Liposome treatment. Both short-course and long-course Clodronate Liposome treatments resulted in a significant decrease in total macrophage numbers in lung tissues.
Figure 8. Changes in macrophage numbers in ex vivo left lung tissues post-LPAL.
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