By Pawel Slabiak • June 14, 2023
Center for Advanced Imaging Innovation and Research
Histology slide of a rat knee.
Cartilage cells, called chondrocytes, seen ex vivo through fluorescence microscopy. Each cell is approximately 8-10 microns in diameter, about the size of a droplet of fog.
An in vivo MRI showing P15-1 accumulation in knee cartilage of a rat with an ACL injury.
In vitro fluorescence microscopy of chondrocytes viewed on a lab computer.
The imaging modalities the team used included: • confocal fluorescence microscopy (in vitro) • fluorescence microscopy (in vitro) • optical imaging (in vivo) • ultrasound (in vivo) • MRI (in vivo) • fluorescence microscopy (ex vivo) • electron microscopy (ex vivo)
Chondrocyte in normal conditions.
Chondrocyte in inflammatory media.
All protocols involving the use of animals were approved by the NYU Grossman School of Medicine Institutional Animal Care and Use Committee.
Syringe with P15-1
Rat under general anesthesia
Initially, the research team had relied on anatomical landmarks for aim but only half the injections succeeded. With ultrasound guidance, the success rate exceeded 90 percent.
Lower intensity in the control knee indicates that healthy cartilage is retaining less of the P15-1 peptide.
Cartilage in the knee with an ACL rupture shows high retention of P15-1 days after injection.
MRI shows a post-injection change in a metric known as T1 relaxation in the cartilage of the knee with an ACL rupture. No such change is observed in the control knee. The conclusion is that P15-1 accumulates in the injured joint and that MRI can be used to image this process.
Each cryosection is 10 microns thin.
A section of a healthy control knee seen under a fluorescence microscope with tenfold magnification.
A section of a knee with a ruptured ACL, showing damaged cartilage and white areas with accumulated P15-1.
At 40-fold magnification, chondrocytes in a knee with an ACL rupture appear bright with P15-1.
White arrows point to chondrocytes in the cartilage and the area where cartilage meets subchondral bone, highlighting bright spots with concentrated P15-1.
Layers of chondrocytes seen through a fluorescence microscope as its focus travels from the surface of cartilage to 605 microns down into the tissue.
Ex vivo fluorescent microscopy (top) and in vivo MRI of P15-1 retention in knee cartilage.
Credits: Knee photo by Yuri Arcurs/Shutterstock. Research images courtesy of Amparo Ruiz. Photography, text, and production by Pawel Slabiak.