Peripheral aromatization of androgens exert estrogenic actions in many tissues. Recently in situ production of estrogens by aromatase was detected in human bone and cultured osteoblasts and has been proposed to participate in the maintenance of bone mass. We examined aromatase expression by immunohistochemistry and mRNA in situ hybridization in 16 cases of tibia (female 2 male, 14 female, 62 ؎ 5.2 years old) and quantified the level of aromatase mRNA in 28 cases of rib, femur, and lumbar vertebrae (16 male, 12 female, 58.0 ؎ 11.3 years old) by reverse transcriptase-polymerase chain reaction (RT-PCR) in order to study whether or not and in which cell types aromatase was expressed in human bone tissues. We also studied alternative use of multiple exons 1 of its gene and immunolocalization of type I 17␤-hydroxysteroid dehydrogenase (HSD), which converts estrone produced by aromatase to estradiol. Strong aromatase immunoreactivity and mRNA hybridization as well as type I 17␤-HSD immunoreactivity were detected in lining cells, osteoblasts, chondrocytes of articular cartilage, and adipocytes adjacent to bone trabeculae in all the cases examined. Amounts of aromatase mRNA varied greatly among the subjects (11.25 ؎ 9.77, 0.61-42.84 attomol/ng of total RNA). The amount of aromatase expression was not correlated with age or gender of the subjects but positively correlated with the degree of osteroporotic changes evaluated by radiological findings of lumbar vertebrae. Analysis of multiple exons 1 revealed that 1b or fibroblast type was predominantly (23/26) utilized as a promoter of aromatase gene expression. These results demonstrated that aromatase is expressed widely in human bone tissue and may play important roles in maintenance of human bone

Octacalcium phosphate (OCP) is thought to be a precursor of the mineral crystals in biological apatite. Synthetic OCP has been shown to be converted into an apatite structure when implanted in murine calvarial bone, to enhance bone regeneration more than synthetic hydroxyapatite (HA), and to degrade faster than biodegradable beta-tricalcium phosphate. This study was designed to investigate whether OCP implantation enhances the formation and resorption of new bone (remodeling) concomitant with OCP degradation when implanted intramedullary in a rabbit femur for 12 weeks, compared to sintered HA ceramic. Histological and histomorphometric analyses using undecalcified specimens showed that the area of bone apposition was significantly higher on OCP than on HA between 2 and 3 weeks, whereas it subsequently became smaller on OCP than on HA. The area attacked by multinucleated giant cells, including tartrate-resistant acid phosphatase (TRAP)-positive cells, was significantly higher for OCP than for HA at 8 weeks. Radiography revealed resorption of OCP but not of HA. The results disclose some osteoconductive characteristics of synthetic OCP in the bone marrow space: (1) enhancement of bone regeneration at the initial bone apposition stage and (2) stimulation of resorption of the newly formed bone coupled with OCP biodegradation mediated by TRAP-positive osteoclast-like cells. These results suggest that synthetic OCP would be a more useful bone substitute than HA in implant applications where rapid bone formation and concomitant implant resorption are important considerations.

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To evaluate the effect of capacitively coupled electric fields (CCEF) on delayed union of fractures, an experimental model of delayed union was produced in the radius of rabbits, and the process of healing was investigated by radiography, bone mineral density (BMD) measured with dual energy x-ray absorptiometry, and histological survey. It was confirmed radiographically and histologically that callus formation was enhanced in the group treated with CCEF. After stimulation, the average BMD increased more than 18% compared with the controls. Our experiment on a delayed union model suggests that CCEF is effective for the treatment of delayed union of fractures.