Background and objectives: BMP-2 is similar to BMP-4 in the structure and both of them belong to the TGF-β superfamily. The expensiveness of BMP-2 motivated us to search the substitute. In the attempt to substitute BMP-2 with BMP-4 for the tissue-engineering of cartilage, we made pellets of 6 groups with the addition of BMP-4, BMP-2, and insulin into the medium.
Methods: The combinations were as following: M4OO (BMP-4 in the medium), M2OO (BMP-2 in the medium), OOO (no growth factor), M4MO (BMP-4 and insulin in the medium), M2MO (BMP-2 and insulin in the medium), and OMO (insulin in the medium). We harvested the pellet of tissue-engineered cartilage at the end of 3rd week of 3D culture in vitro.
Results: Gross pictures could hardly tell any difference among 6 groups though the pellet of M2MO seems larger than the pellets of other groups. BMP-2 could increase the total cell number with the supplement of insulin. (M2MO > OMO, p < 0.01). Insulin really changed the total cell numbers ( p < 0.01), regardless of addition of any other growth factors, while BMP-4 alone (M4OO) could not make difference from BMP-4 with insulin (M4MO) in total cell numbers ( p > 0.05). For GAG production, BMP-2 was significantly different from BMP-4 and control group ( p < 0.01) while BMP-4 had no additive effect on GAG production at all. Insulin was able to increase the GAG production significantly either with or without BMP-2 family ( p values < 0.01). The histological sections stained by the Toluidine blue also showed the consistent image of the GAG production, with the strongest metachromasia in the section of M2MO group.
Conclusions: Insulin possesses the strong effects on GAG production with or without BMP-2, while we could not use BMP-4 to substitute the BMP2.
Key words: BMP-2; BMP-4; insulin; chondrogenesis; chondrocyte