I just googled it with quotes (i.e. "osteoblastin") and came up with one maybe research article, a bunch of stuff about the AAMC #9, and a whole lot of gibberish. Which suggests to me that it's either a made up hormone/enzyme for the MCAT, or something that's not necessary to know b/c it's not studied very much.
So perhaps just read as "enzyme/hormone X" instead of "osteoblastin" if you're looking at it on a practice test.