Biochemical characterization of fracture callus proteoglycans

Biochemical and density assessment of the new bone in late remodeling after callus distraction

Biochemical changes in a canine bone-lengthening model were characterized 5 months after surgery. The mineral content and the total amount of EDTA-extractable noncollagenous proteins, insulin-like growth factor-I, and osteocalcin were determined for the lengthened callus, and a gradient density fractionation analysis of bone powder particles was performed. The results were compared with two other areas of the lengthened tibia and one region of the contralateral tibia. The mineral and osteocalcin contents showed significant decreases, whereas the hydroxyproline concentration was significantly increased. Neither the insulin-like growth factor-I content nor the concentration of EDTA-extractable proteins was significantly different in any of the examined regions.

Calcium-dependent neutral proteinase (calpain) in fracture healing in rats

Calpain refers to Ca(2+)-dependent neutral cysteine proteinase, which originally was thought to be an intracellular proteinase but recently has been shown to function extracellularly as well. This report describes the immunohistochemical demonstration of calpain and biochemical changes in the amount of calpain during fracture healing in rats. The tibiae of 6-week-old Wistar rats were fractured, and calluses were obtained 5-28 days after fracture. A frozen section of the fracture callus was stained by the immunoperoxidase method with use of polyclonal antibodies of calpains I and II. Positive staining was noted with the anti-calpain II antibody in the perivascular areas, chondrocytes, and cartilage matrix in calluses at 5, 7, and 10 days. Less intense staining was seen in older calluses. The caseinolytic activity of calpain II reached its maximum on the 5th day, was high on the 7th and 10th days, and decreased rapidly thereafter. The quantity of calpain II was dependent on the process of fracture healing. It was concluded that calpain was working as one of the matrix proteinases in fracture callus.

Autoradiographic study of the effects of pulsed electromagnetic fields on bone and cartilage growth in juvenile rats

Application of pulsed electromagnetic fields (PEMF) has been used in growth and repair of non-union bone fractures. The similarities between the fibrocartilage callus in non-union bone fractures and the secondary cartilage in the mandibular condyle, both histologically and functionally, lead naturally to study the effects of PEMFs on growth in the condyle. The purposes of this study were: (1) to describe the effects of PEMFs on the growth of the condyle using autoradiography, [3H]-proline and [3H]-thymidine, and (2) to differentiate between the effects of the magnetic and electrical components of the field. Male pre-adolescent Sprague-Dawley rats (28 days old) were divided into three experimental groups of five animals each: (1) PEMF-magnetic (M), (2) PEMF-electrical (E) and (3) control, and were examined at three different times-3, 7 and 14 days of exposure. Each animal was exposed to the field for 8 h per day. Histological coronal sections were processed for quantitative autoradiography to determine the mitotic activity of the condylar cartilage and the amount of bone deposition. The PEMF (magnetic or electrical) had statistically significant effects only on the thickness of the articular zone, with the thickness in the PEMF-M group being the most reduced. Length of treatment was associated with predictable significant changes in the thickness of the condylar cartilage zones and the amount of bone deposition.(ABSTRACT TRUNCATED AT 250 WORDS)

Neutral protein-degrading enzymes in experimental fracture callus: a preliminary report

The process of endochondral fracture healing is biochemically similar to growth plate calcification. Recent studies have identified potentially important roles for proteoglycan-degrading enzymes in the growth plate. The purpose of the study described herein was to identify, in healing fractures, neutral enzyme activities capable of degrading proteoglycans and other matrix proteins. Two sets of 60 male Sprague-Dawley rats underwent the production of closed femoral fractures. Calluses were retrieved at timed intervals, and cell and matrix vesicle fractions were prepared for electron microscopy, neutral peptidase, and alkaline phosphatase assays. In another group of 10 animals, fractions were prepared from 14-day calluses and examined for proteoglycanase activity. In the cell fractions, alkaline phosphatase, alanyl-beta-naphthylamidase, aminopeptidase, and endopeptidase activities showed somewhat parallel distributions peaking at approximately 14-17 days. In the matrix vesicle fractions, similar relative distributions were observed for alkaline phosphatase and endopeptidase. However, here the peak activities occurred up to 3 days later than they did in the cell fractions. Significant proteoglycanase activity was confirmed in both cell and matrix vesicle fractions. These findings are consistent with the hypotheses that (a) neutral peptidases, by virtue of their temporal expression in parallel with alkaline phosphatase, may be involved in preparing fracture callus matrix for calcification; and (b) matrix vesicles may convey certain of these enzymes to sites of both matrix degradation and calcification, since the same activities found in cells are found in matrix vesicles a few days later. The possibility that some of these enzymes are involved in growth factor activation remains to be investigated.

Pulsed electromagnetic fields alter phenotypic expression in chondroblasts in tissue culture

We hypothesize that pulsed electromagnetic fields (PEMF) alter phenotypic expression of chondroblasts by promoting the production of alkaline phosphatase (AP) and altering the structure of proteoglycans. Chondroblasts from the hypertrophic zone of tibial epiphyses (HC), sternum (SC), and skin fibroblasts (F) were cultured from 16 day chick embryos. Cultures were randomly designated control (C) or experimental (E). E received PEMF for 24 h in a 6 h on, 6 h rest sequence. The controls were in the same incubator shielded by Mu metal. Assays for AP activity were performed and normalized to protein content. Proteoglycan synthesis assay involved labeling with 35S fractionating in a 5% to 20% surcrose gradient determining total protein and chondroitin sulfate content. PEMF showed no change of AP activity on F. A high AP basal activity was found in HC, but was not increased above the control. PEMF increased AP in the SC samples (E/C ratio). The sucrose gradient data showed a shift in peaks for SC only altering the ratio of carbohydrate to protein for the SC. Analysis of carbohydrate and protein indicated that the effect was decreased synthesis or degradation of protein. We conclude that PEMF alters the phenotypic expression of sternal chondroblasts in our in vitro system.