They don't say what is injected, calling it only a "gerozyme inhibitor". Original article appears to be:

https://www.science.org/doi/10.1126/science.adx6649

Inhibition of 15-hydroxy prostaglandin dehydrogenase promotes cartilage regeneration Mamta Singla https://orcid.org/0000-0002-6408-1167, Yu Xin Wang https://orcid.org/0000-0001-8440-9388, Elena Monti https://orcid.org/0000-0002-3767-0855, Yudhishtar Bedi https://orcid.org/0000-0002-1213-4116, [...] , and Nidhi Bhutani https://orcid.org/0000-0002-7494-5870

FTFA: "Both systemic and local inhibition of 15-PGDH with a small molecule inhibitor (PGDHi) led to regeneration of articular cartilage and reduction in OA-associated pain."

"PGDHi" is a name for both the process "15-hydroxyprostaglandin dehydrogenase inhibition" and any inhibitor.

This link(a PDF file) shows PGDHi's are powerful stuff:

https://www.biorxiv.org/content/biorxiv/early/2025/04/17/202...

"PGDHi" could be prostaglandin-E2 (dinoprostone):

https://en.wikipedia.org/wiki/Prostaglandin_E2

which was used in:

https://med.stanford.edu/news/all-news/2025/06/muscle-aging....