The use of heparan sulfate to augment fracture repair in a rat fracture model

Fracture healing is a complex process regulated by numerous growth and adhesive factors expressed at specific stages during healing. The naturally occurring, cell surface-expressed sugar, heparan sulfate (HS), is known to bind to and potentiate the effects of many classes of growth factors, and as such, may be a potential candidate therapy for enhancing bone repair. This study investigated the local application of bone-derived HS in the repair of rat femoral fractures. After 2 weeks, there was a significant increase in the callus size of rats administered with 5 mu g HS compared to the control and 50 mu g HS groups, presumably due to increased trabecular bone volume rather than increased cartilage production. In addition, 5 mu g HS increased the expression of ALP, Runx2, FGF-1, IGF-II, TGF-beta 1, and VEGF. It is hypothesized that these increases resulted from changes in HS-mediated receptor/ligand interactions that increase local growth factor production to augment bone formation. The findings of this study demonstrate the anabolic potential of HS in bone repair by recruiting and enhancing the production of endogenous growth factors at the site of injury. (c) 2006 Orthopaedic Research Society.

Effect of cyclic pneumatic soft tissue compression on simulated distal radius fractures

We investigated the effect of pneumatic pressure applied to the proximal musculature of the sheep foreleg on load at the site of a transverse osteotomy of the distal radius. The distal radii of 10 fresh sheep foreleg specimens were osteotomized and a pressure sensor was inserted between the two bone fragments. An inflatable cuff, connected to a second pressure sensor, was positioned around the proximal forelimb musculature and the leg then was immobilized in a plaster cast. The inflatable cuff was inflated and deflated repeatedly to various pressures. Measurements of the cuff pressure and corresponding change in pressure at the osteotomy site were recorded. The results indicated that application of pneumatic pressure to the proximal foreleg musculature produced a corresponding increase in load at the osteotomy site. For the cuff pressures tested (109.8-238.4 mm Hg), there was a linear correlation with the load at the osteotomy site with a gradient of 12 mm Hg/N. It is conceivable, based on the results of this study, that a technique could be developed to provide dynamic loading to accelerate fracture healing in the upper limb of humans.

In vitro heterogeneity of osteogenic cell populations at various equine skeletal sites

Bone cell cultures were evaluated to determine if osteogenic cell populations at different skeletal sites in the horse are heterogeneous. Osteogenic cells were isolated from cortical and cancellous bone in vitro by an explant culture method. Subcultured cells were induced to differentiate into bone-forming osteoblasts. The osteoblast phenotype was confirmed by immunohistochemical testing for osteocalcin and substantiated by positive staining of cells for alkaline phosphatase and the matrix materials collagen and glycosaminoglycans. Bone nodules were stained by the von Kossa method and counted. The numbers of nodules produced from osteogenic cells harvested from different skeletal sites were compared with the use of a mixed linear model. On average, cortical bone sites yielded significantly greater numbers of nodules than did cancellous bone sites. Between cortical bone sites, there was no significant difference in nodule numbers. Among cancellous sites, the radial cancellous bone yielded significantly more nodules than did the tibial cancellous bone. Among appendicular skeletal sites, tibial metaphyseal bone yielded significantly fewer nodules than did all other long bone sites. This study detected evidence of heterogeneity of equine osteogenic cell populations at various skeletal sites. Further characterization of the dissimilarities is warranted to determine the potential role heterogeneity plays in differential rates of fracture healing between skeletal sites.

Cyclic pneumatic soft-tissue compression accelerates the union of distal radial osteomoties in an ovine model

The aim of this randomised, controlled in vivo study in an ovine model was to investigate the effect of cylic pneumatic pressure on fracture healing. We performed a transverse osteotomy of the right radius in 37 sheep. They were randomised to a control group or a treatment group where they received cyclic loading of the osteotomy by the application of a pressure cuff around the muscles of the proximal forelimb. Sheep from both groups were killed at four or six weeks. Radiography, ultrasonography, biomechanical testing and histomorphometry were used to assess the differences between the groups. The area of periosteal callus, peak torsional strength, fracture stiffness, energy absorbed over the first 10° of torsion and histomorphometric analysis all showed that the osteotomies treated with the cyclic pneumatic pressure at four weeks were not significantly different from the control osteotomies at six weeks.

Efficacy of B vitamins in lowering homocysteine in older men - Maximal effects for those with B-12 deficiency and hyperhomocysteinemia

Background and Purpose - A higher plasma concentration of total homocysteine (tHcy) is associated with a greater risk of cardiovascular events. Previous studies, largely in younger individuals, have shown that B vitamins lowered tHcy by substantial amounts and that this effect is greater in people with higher tHcy and lower folate levels. Methods - We undertook a 2-year, double-blind, placebo-controlled, randomized trial in 299 men aged >= 75 years, comparing treatment with a daily tablet containing 2 mg of folate, 25 mg of B-6, and 400 mu g of B-12 or placebo. The study groups were balanced regarding age (mean +/- SD, 78.9 +/- 2.8 years), B vitamins, and tHcy at baseline. Results - Among the 13% with B12 deficiency, the difference in mean changes in treatment and control groups for tHcy was 6.74 mu mol/L (95% CI, 3.94 to 9.55 mu mol/L) compared with 2.88 mu mol/L (95% CI, 0.07 to 5.69 mu mol/L) for all others. Among the 20% with hyperhomocysteinaemia, the difference between mean changes in treatment and control groups for men with high plasma tHcy compared with the rest of the group was 2.8 mu mol/L (95% CI, 0.6 to 4.9 mu mol/L). Baseline vitamin B12, serum folate, and tHcy were significantly associated with changes in plasma tHcy at follow-up (r = 0.252, r = 0.522, and r = -0.903, respectively; P = 0.003, <0.001, and <0.001, respectively) in the vitamin group. Conclusions - The tHcy-lowering effect of B vitamins was maximal in those who had low B12 or high tHcy levels. Community-dwelling older men, who are likely to be deficient in B12 or have hyperhomocysteinemia, may be most likely to benefit from treatment with B vitamins.

Homocysteine-lowering therapy in renal disease

Hyperhomocysteinemia is a potential risk factor for vascular disease and is associated with endothelial dysfunction, a predictor of adverse cardiovascular events. Renal patients (end-stage renal failure (ESRF) and transplant recipients (RTR)) exhibit both hyperhomocysteinemia and endothelial dysfunction with increasing evidence of a causative link between the 2 conditions. The elevated homocysteine appears to be due to altered metabolism in the kidney (intrarenal) and in the uremic circulation ( extrarenal). This review will discuss 18 supplementation studies conducted in ESRF and 6 in RTR investigating the effects of nutritional therapy to lower homocysteine. The clinical significance of lowering homocysteine in renal patients will be discussed with data on the effects of B vitamin supplementation on cardiovascular outcomes such as endothelial function presented. Folic acid is the most effective nutritional therapy to lower homocysteine. In ESRF patients, supplementation with folic acid over a wide dose range ( 2 - 20 mg/day) either individually or in combination with other B vitamins will decrease but not normalize homocysteine. In contrast, in RTR similar doses of folic acid normalizes homocysteine. Folic acid improves endothelial function in ESRF patients, however this has yet to be investigated in RTR. Homocysteine-lowering therapy is more effective in ESRF patients than RTR.

Acute exposure to cyclosporine does not increase plasma homocysteine in rats

There is interest in the postulate that cyclosporine a (CsA) contributes to the elevated homocysteine levels seen in organ transplant recipients, as hyperhomocysteinemia is now considered an independent risk factor for cardiovascular disease (CVD) and may partially explain the increased prevalence of CVD in this population. The main purpose of this investigation was to determine the effect of CsA administration on plasma homocysteine. Eighteen female Sprague Dawley rats (4 months old) were randomly assigned to either a treatment or a control group. For 18 days the treatment group received of CsA (25 mg/kg/d) while the control group received the same volume of the vehicle. Blood samples obtained following sacrifice to measure CsA, total homocysteine, and plasma creatinine. There were no significant differences in plasma homocysteine (mean values SD: treatment = 4.79 +/- 0.63 mu mol/L, control = 4.46 +/- 0.75 mu mol/L; P = .37). Homocysteine was not significantly correlated with final CsA concentrations (r = .17; P = .69). There was a significant difference in plasma creatinine values between the two groups (treatment = 60.44 +/- 7.68 mu mol/L, control = 46.33 +/- 1.66 mu mol/L; P < .001). Furthermore, plasma homocysteine and creatinine were positively correlated with the treatment group (r = .73; P < .05) but not the controls (r = -.10; P = .81). In conclusion, CsA does not influence plasma homocysteine concentrations in rats.