Sclerostin antibody treatment enhances bone strength but does not prevent growth retardation in young mice treated with dexamethasone

OBJECTIVE

Exposure to supraphysiologic levels of glucocorticoid drugs is known to have detrimental effects on bone formation and linear growth. Patients with sclerosteosis lack the bone regulatory protein sclerostin, have excessive bone formation, and are typically above average in height. This study was undertaken to characterize the effects of a monoclonal antibody to sclerostin (Scl-AbI) in mice exposed to dexamethasone (DEX).

METHODS

Young mice were concomitantly treated with DEX (or vehicle control) and Scl-AbI antibody (or isotype-matched control antibody [Ctrl-Ab]) in 2 independent studies. Linear growth, the volume and strength of the bones, and the levels of bone turnover markers were analyzed.

RESULTS

In DEX-treated mice, Scl-AbI had no significant effect on linear growth when compared to control treatment (Ctrl-Ab). However, in mice treated with DEX and Scl-ABI, a significant increase in trabecular bone at the femoral metaphysis (bone volume/total volume +117% versus Ctrl-Ab-treated mice) and in the width and volume of the cortical bone at the femoral diaphysis (+24% and +20%, respectively, versus Ctrl-Ab-treated mice) was noted. Scl-AbI treatment also improved mechanical strength (as assessed by 4-point bending studies) at the femoral diaphysis in DEX-treated mice (maximum load +60% and ultimate strength +47% in Scl-AbI-treated mice versus Ctrl-Ab-treated mice). Elevated osteocalcin levels were not detected in DEX-treated mice that received Scl-AbI, although levels of type 5b tartrate-resistant acid phosphatase were significantly lower than those observed in mice receiving DEX and Ctrl-Ab.

CONCLUSION

Scl-AbI treatment does not prevent the detrimental effects of DEX on linear growth, but the antibody does increase both cortical and trabecular bone and improves bone mechanical properties in DEX-treated mice.

Effect of alloxan-diabetes on multiple forms of hexokinase in adipose tissue and lung

Comparison has been made of the effect of alloxan-diabetes on the multiple forms of hexokinase (EC 2.7.1.1) in adipose tissue and lung. Types I and II hexokinase were distinguished in adipose tissue by their different stabilities to heat treatment, which made it possible to determine the activity of each form spectrophotometrically; additional confirmatory evidence was obtained from starch-gel electrophoresis. Type II hexokinase was markedly depressed in adipose tissue from alloxan-diabetic rats. Lung contained types I, II and III hexokinase, type I predominating. There was no significant change in the pattern of these multiple forms of hexokinase in lung from alloxan-diabetic rats. These results are discussed in relation to current ideas that the insulin-sensitivity of a tissue may be correlated with the content of type II hexokinase.

A rapid and cost-effective method for analysis of three common genetic risk factors for thrombosis

A simple, rapid and cost-effective method for the analysis of three of the most widely screened genetic risk factors for thrombosis has been established. The protocol developed uses blood spots stored on filter paper (Guthrie spots) as well as DNA extracted from anticoagulated blood. The use of Guthrie spots taken at birth enables the retrospective study of patients who develop thrombotic complications without necessitating resampling. Following isolation of DNA, conventional fluorescence-labelled polymerase chain reaction (PCR) is performed using a thermostable DNA polymerase. Denatured, single-stranded PCR products are analysed on a semi-automated capillary-based genetic analyser, the data being stored electronically. This sensitive protocol obviates the need for endonuclease digestion and the associated gel running and documentation, and leads to a reduction in the recurrent costs of laboratory consumables.

Effects of hyaluronan on models of immediate and delayed hypersensitivity in the rat

Others have previously shown that superoxide dismutase conjugated with hyaluronan (HA) retains enzymic activity but is non-immunogenic. Whether HA could be widely used to prevent sensitisation to protein/polypeptide therapeutics is not known. In this study we investigated the effects of HA on bovine serum albumin (BSA) and methylated BSA pleural reactions in sensitised rats (active Arthus and delayed hypersensitivity reactions respectively) and on a reverse passive Arthus reaction in which rats received an intravenous injection of rabbit immunoglobulin and intrapleural challenge with goat anti rabbit immunoglobulin. HA suppressed the active Arthus and delayed hypersensitivity models when administered at the time of sensitisation but only the delayed hypersensitivity model at the time of intrapleural challenge. HA did not modulate the reverse passive Arthus reaction. The results show no evidence that simple mixing of HA with antigens masks antigenic determinants. However, HA appeared to have suppressive effects on both antibody and cell-mediated immune reactions. Therefore it may not be necessary to conjugate protein/polypeptide therapeutics to HA in order to prevent immune sensitisation.

The effects of cyclooxygenase 2 inhibitors on cartilage erosion and bone loss in a model of Mycobacterium tuberculosis-induced monoarticular arthritis in the rat

Selective cyclooxygenase 2 (COX 2) inhibitors NS-398 and nimesulide were investigated for their effects on patellar cartilage and bone content in a model of Mycobacterium tuberculosis (M.tb)-induced monoarticular arthritis in the rat. The protective/destructive properties of these nonsteroidal antiinflammatory drugs (NSAIDs) were compared with piroxicam, known to accelerate cartilage breakdown and reduce bone erosion in this model in comparison to untreated arthritic controls. Male CFHB Wistar rats were injected intraarticularly with heat killed M.tb into the left stifle joint, resulting in loss of patellar cartilage glycosaminoglycans (GAG), bone erosion and inflammation. The right stifle joint received saline. Animals were dosed daily, p.o., with NS-398 (1, 10 mg/kg), nimesulide (0.5, 5 mg/kg) or piroxicam (10 mg/kg). Four days after M.tb injection, patellar GAG content, bone weight and joint swelling were measured in drug-treated animals and untreated arthritic controls. Changes in the left joint were compared to the right. The expression and distribution of COX 2 protein was determined by immunocytochemistry in synovial tissue from arthritic controls over the time course. Focal accumulations of inflammatory cells were positively immunolabelled for COX 2 in the synovium from the left stifle joint of untreated arthritic animals, 6 h after injection of M.tb. Labeling of inflammatory cell infiltrates increased and was widespread in the synovium at 24 h. By day 4 fibroblasts were positively labelled for COX 2 in addition to polymorphonuclear and mononuclear leukocytes. Piroxicam and nimesulide at the higher dose significantly exacerbated M.tb-induced cartilage GAG loss while NS-398 was without effect. Both COX 2 inhibitors did not alter M.tb-induced patellar bone loss. In contrast, piroxicam significantly reduced bone loss. All COX inhibitors significantly reduced joint swelling. In conclusion, the selective inhibition of COX 2 may result in the amelioration of synovitis with a lowered risk of NSAID-induced cartilage damage in rheumatic disease.