In vitro chondrogenesis stimulated by extracts of gall bladder epithelium.

Living adult gall bladder epithelium has previously been shown to initiate in vivo ectopic cartilage and/or bone formation. In the present study, we demonstrate that solubilized extracts of gall bladder, which have never been inductive when tested in vivo, do in fact contain a factor that stimulates chondrogenesis in stage 24 chick limb bud mesenchymal cell cultures. These 4 M guanidinium chloride soluble, cold water soluble protein fractions initiate a dose-dependent increase in the amount of cartilage formed following an 8-10 day continuous exposure as evidenced by the presence of greater numbers of chondrocytes when viewed with phase optics, more intense toluidine blue metachromatic staining in fixed plates and elevated 35S-sulfate incorporation into the cell layer (as a maker for proteoglycan biosynthesis). The factor(s) responsible for this activity binds to DEAE anion-exchange resins, is stable to heat (100 degrees C for 10 min) and 2-mercaptoethanol reduction but is labile to trypsin digestion. These results emphasize the importance of in vitro test systems to identify bioactive agents which may otherwise go undetected using an in vivo implantation assay.