Gail I. Anderson

Plasminogen Activator System in Osteoclasts

To determine which genes of the plasminogen activator (PA) system were expressed in osteoclasts, RNA extracted from microisolated mouse osteoclasts was used as template for reverse transcribed polymerase chain reaction (RT‐PCR) with gene‐specific primer pairs. Using this approach, the expression of RNAs for tissue‐type plasminogen activator, urokinase‐type plasminogen activator, plasminogen activator inhibitor‐1, plasminogen activator inhibitor‐2, protease nexin, and urokinase receptor isoform 1 (uPAR1) were detected in mouse osteoclasts. The expression of uPAR RNA in osteoclasts was confirmed by in situ hybridization with a uPAR1 probe. RNA encoding the uPAR isoform 2 was not detected in mouse osteoclasts, but a novel unspliced uPAR RNA variant was detected in these cells. The novel uPAR variant and uPAR1 RNA were also detected in mouse calvarial osteoblasts, kidney, muscle, and the mouse macrophage cell line J774A.1 by RT‐PCR. The presence of RNAs for most of the components of the PA system in osteoclasts suggests that it may have a functional role in this cell type.

Bone growth is enhanced by novel bioceramic coatings on Ti alloy implants

Calcium phosphate ceramics are widely used as coating materials to orthopedic implants and are found to enhance initial bony ingrowth by stimulating osseous apposition to the implant surface. In this study, two novel calcium orthophosphate materials were selected for coating onto the commonly used orthopedic implant material Ti-6Al- 4V. One was calcium alkali orthophosphate with the crystalline phase Ca10[K/Na](PO4)7 with a small addition of SiO2 (AW-Si) and the other was calcium orthophosphate composed of 70 mol % fluorapatite, Ca10(PO4)6F2 and 30 mol % CaZr4(PO4)6 (FA7Z). The coated implants were placed in cortical and cortico-cancellous bone of sheep femur for six weeks. Retrieved samples were tested for osseointegration and mechanical strength. It was found that both coatings produced enhanced bone/implant contact rate compared to the control when implanted in cortico-cancellous bone. This study demonstrates that the two coatings have the capability of encouraging bone growth, and hence the potential for being used as coating materials on Ti implants.

The effect of Gu-Sui-Bu (Drynaria fortunei) on bone cell activity

We investigated the effects of Gu-Sui-Bu using in vitro bone cell cultures. Primary rabbit and mouse marrow cells were cultured with or without five different concentrations of Gu-Sui-Bu extract. Osteoclast numbers were assessed using tartrate-resistant acid phosphatase (TRAP) positive cell counts and for function, osteoclast resorption pits on bovine bone slices were performed. Alkaline phosphatase (AP) positive cell counts and mineralized nodule formation were examined to assess osteoblast function with Gu-Sui-Bu. TRAP+ osteoclast numbers increased, as did the number and size of resorption pits with 0.001 mg/ml of extract. Low doses of extract did not alter AP+ colony number or mineralized nodule formation, but both were inhibited by doses of 0.1 mg/ml or higher. The highest dose of extract (10 mg/ml) inhibited proliferation of all cell types. At 0.01 and 0.001 mg/ml doses, RANKL increased over time; however, osteoprotegerin levels only increased at doses > or = 0.1 mg/ml. Resorption pit formation was decreased without alteration in mature multinucleated (TRAP+) cell counts only at the highest dose of the putative active ingredient of Gu-Sui-Bu. In summary, lower concentrations of Gu-Sui-Bu extract had positive effects on osteoclast proliferation, survival and resorptive activity that may be mediated through enhanced prostaglandin secretion. However, high doses of extract proved detrimental to osteoclast and osteoblast survival. No effect of low doses of Gu-Sui-Bu extract was seen in osteoblast cultures. High doses of the putative active ingredient of Gu-Sui-Bu showed mild inhibition of mouse osteoclast function.

The effect of partial vs. full hydroxyapatite coating on periprosthetic bone quality around the canine madreporic femoral stem

While hydroxyapatite coatings have been shown to enhance osseointegration of metal prostheses, the optimal extent of the coating over the femoral stem component remains unclear. In this study, we investigated the effect of the application of hydroxyapatite to the proximal half of the femoral stem vs. full hydroxyapatite coating on the madreporic-surfaced femoral stems in a canine model over time. Total hip arthroplasties were performed on 22 dogs. Fifteen had half-HA coated stems, and seven had fully HA coated stems. The dogs were followed for 3 weeks, 3 months, or 1 year postoperatively. Micromotion near the femoral component was assessed at three levels along the medial aspect of the stems. Percent bone apposition, trabecular strut width, connectivity index, and cortical porosity measurements were performed at five levels and in four quadrants about the femoral stems. Micromotion was greater adjacent to the half-coated stems at 3 weeks postoperatively only. There was a trend to decreased micromotion from proximal to distal in both stem types. Both designs fixed proximally and tended to load share laterally more than in the other three quadrants. Fully HA coated stems induced greater percent bone apposition, wider trabecular struts, and more connectivity compared to half-HA coated stems.