Establishing a Silicosis Rat Model via Exposure of Whole-Body to Respirable Silica

Using this protocol of silicosis rat model, it is possible to closely mimic the pathological process of human silicosis. This technique is easy to perform cost effectively with good repeatability, and there is no trauma to the animal. The established rat model in this study contributes to early identification, accurate diagnosis, and treatment of silicosis.

To begin, place the silica particles in an agate mortar and grind for 1.5 hours before each animal exposure. Then weigh 30 grams of the ground silica in an electronic balance and place it in a glass container. Bake at 180 degrees Celsius for six hours in an electric-heating, air-blowing dryer to eliminate pathogens from the surface of the silica particles.

Set up the silica exposure controller by connecting the injection and the generator systems. Then place the weighed silica in the generator and confirm that the pipeline connection is proper. The power cord is connected, and the power supply is normal.

After ensuring the valves of the inhalation chamber are closed, turn on the exhaust gas discharge device and the air source to confirm that the inside of the shielding cabinet is in a negative pressure state. Check the silica concentration in the cabinet with a calibrated atmospheric sampler following the manufacturer's instructions. For gravimetric determination, use a digital, single-pan, analytical balance and weigh down the silica.

Place the rat in the cage, then place 10 rats in the inhalation chamber and close the inhalation compartment and the screened cabinet doors. Then proceed with the silica inhalation experiment as planned. On completion of the experiment, close the mixed gas flow control valve and open the pure gas flow valve to inject the gas into the inhalation chamber.

After 20 minutes, close the pure air flow valve. Open the door and take the cage out of the inhalation chamber. Then take the rats out of the cage and take them back to the pathogen-free room.

Next, remove the rat rack and the branch pipe components in sequence and place them in the sink for cleaning. After rinsing, close the automatic cleaning valve and open the hatch. Then wipe the inner wall with a clean cloth to dry the tank.

Finally, disinfect the tank with 75%ethanol and close the exhaust gate. Next, quickly open the door of the inhalation cabin to evaporate the moisture so that the inside of the inhalation cabin remains dry. The rats exposed to silica for two and 24 weeks revealed alveolar wall thickening after two weeks of silica inhalation, whereas the alveolar structure disappeared, and large areas of fibrosis formed after 24 weeks.

Further, the silica particles were seen trapped in the macrophages of the lung lobes observed through a polarized light microscope. Immunohistochemical staining of CD 68 in the lung revealed the dynamic evolution of silicotic nodules from two to 24 weeks. As the exposure time increased, the area of the nodules also gradually increased, and the adjacent silicotic nodules fused into larger nodules.

Multiple fibrotic lesions of varying sizes were formed in the lungs of rats exposed to silica compared with the control rats. However, no significant differences in the kidney, liver, and spleen were found between the rats with silicosis and the control. But interestingly, bone loss was observed in rats with silicosis.

The most important thing in this protocol is ensuring that the silica is well-ground, and the concentration is constant before starting the procedure.