[Skeletal effects of thiazolidinediones]

Thiazolidinedione (TZD), a new class of anti-diabetic agents, is known to promote adipocytic differentiation by activating peroxisome proliferator-activated receptor-gamma (PPAR gamma). In the bone marrow, osteoblasts and adipocytes are derived from common mesenchymal stem cells or stromal cells, which also play crucial roles in the generation of osteoclasts from their progenitor hematopoietic cells. Recent in vitro studies demonstrated that TZDs promote adipocytic differention of the stromal cells. However, whether or not this affects osteoblastic differentiation is unclear. On the other hand, TZDs clearly inhibit osteoclast-like cell formation and bone resorption in vitro. These results indicate that TZDs have direct effects on bone cells. However, little is known about their in vivo effects on bone. Our recent study demonstrated that troglitazone, a TZD, decreased bone resorption markers before it affected glycemic indices in type2 diabetics, suggesting TZDs affects bone in vivo and may be beneficial for bone health in type2 diabetics.