No abstract

While effects of inhaled corticosteroids on serum markers of bone metabolism in normal and asthmatic subjects have been reported, there are little data on the direct effects of these corticosteroids on end-organs such as bone. The results presented here compare the effects of budesonide and its epimers (22S- and 22R-budesonide), fluticasone and dexamethasone on growth and differentiation of cultured human bone cells. Osteoblast-like cells were cultured from human foetal bone chips grown to confluence and used at first subculture. At concentrations of 10(-11)-10(-7) M each corticosteroid (CS) caused a dose-dependent decrease in [3H]thymidine incorporation into deoxyribonucleic acid (DNA), median effective concentration (EC50): fluticasone (0.06 nM) >22R (0.26 nM) >22S (0.4 nM) >budesonide (0.47 nM) >dexamethasone (1.5 nM). Each CS resulted in a dose-dependent increase in alkaline phosphatase activity, EC50: fluticasone (0.14 nM) >22R (0.2 nM)=22S (0.2 nM) >budesonide (0.4 nM) >dexamethasone (1.6 nM). The 1,25 dihydroxyvitamin D3 (1,25(OH)2D3)-stimulated osteocalcin production was decreased in the presence of each CS, EC50: fluticasone (0.02 nM) >22S (0.1 nM) >22R (0.2 nM) >budesonide (1.0 nM) >dexamethasone (1.8 nM). In human bone cells the potencies of fluticasone and budesonide in relation to dexamethasone are not dissimilar to those derived from human lymphocytes in vitro.

Nitric oxide (NO) is synthesised by a group of enzymes called nitric oxide synthases (NOS) and oxidizes to its stable end-products nitrite (NO2-) and nitrate (NO3-) We have previously reported in an in vivo rat model that NO is an important regulator for rat bone fracture healing. This study examines the effects of NO on alkaline phosphatase (ALP) activity in a rat fracture callus explant culture system. Explants of rat femoral fracture callus from days 4, 7, 14 and 28 post fracture induced NO2 release and ALP activity in a biphasic temporal manner, with the highest activity on day 7 and the lowest activity on day 14. Inhibition of NOS by co-incubation with an NOS inhibitor, S-(2-aminoethyl) isothiouronium bromide hydrobromide (AETU), inhibited ALP activity by an average of 50% at each time point (P <0.01). Supplementation with NO donor 3-morpholinosydnonomine hydrochloride (SIN-1) at low doses (25 and 0.025 microM) increased ALP activity by 20% (P < 0.01). ALP mRNA and histochemical ALP activity were localised to osteoblast-like and chondrocyte-like cells within fracture callus. The current study provides evidence that NO plays a regulatory role in ALP activity during rat fracture healing.