The expression of the fibrillar collagen genes during fracture healing: heterogeneity of the matrices and differentiation of the osteoprogenitor cells.

The cells that express the genes for the fibrillar collagens, types I, II, III and V, during callus development in rabbit tibial fractures healing under stable and unstable mechanical conditions were localized. The fibroblast-like cells in the initial fibrous matrix express types I, III and V collagen mRNAs. Osteoblasts, and osteocytes in the newly formed membranous bone under the periosteum, express the mRNAs for types I, III and V collagens, but osteocytes in the mature trabeculae express none of these mRNAs.

Radiolabeling, stability, and body distribution in rats, of low molecular weight polylactide homopolymer and polylactide-polyethyleneglycol copolymer.

In order to study its fate in vivo, a low molecular-weight polylactide homopolymer was derivatized with a p-methoxyphenyl moiety, so as to make it susceptible to radiolabeling with 125I. A low molecular weight polylactide-polyethyleneglycol copolymer capped with ap-methoxyphenyl residue was also synthesized. The derivatized polymers were successfully [125I]iodinated in organic medium.

Molecular failure of apoptosis: inappropriate cell survival and mutagenesis?

Since cell death by apoptosis is achieved through complex interactions between numerous molecular components, cells may fail to die when stimulated because of molecular abnormalities in the apoptosis pathway or in its control mechanisms. Such inappropriate cell survival is well established when apoptosis is suppressed by elevated expression of bcl-2, at least for some cell types. Many cells undergo apoptosis at moderate levels of DNA damage and suppression of such apoptosis might be expected to increase the rate of mutation because of the persistence of cells with damaged DNA.

Exogenous fibroblast growth factors-1 and -2 do not accelerate fracture healing in the rabbit.

Both fibroblast growth factors-1 (acidic FGF) and -2 (basic FGF) increase the proliferation of osteoblasts and chondrocytes in vitro and FGF-2 stimulates angiogenesis and bone formation in vivo. To test their effects on rabbit tibial fracture-healing under stable and unstable mechanical conditions, 3 micrograms of either FGF-1 or FGF-2 was injected around rabbit tibial fractures on day 4 after fracture. Neither growth factor had a significant effect on either the size of, or the amounts of bone and cartilage in, the 10-day callus irrespective of the mechanical conditions under which the fracture was healing.