Bone forming cells needs sufficient PS-341 concentration glucocorticoid availability for normal bone development, but mature osteoblast

and osteocytes do not require endogenous glucocorticoids.2 Circulating active steroids have negative correlations with bone mineral density (BMD) of the lumbar spine.3 At molecular level, glucococorticoid signaling is mediated via the glucocorticoid receptor (GRα), which is expressed in tissues responsive to glucocorticoid action including osteoblasts. Patients with endogenous glucocorticoid excess develop osteoporosis mainly due to rapid suppression of bone formation.4-6 Glucocorticoids inhibit osteoblast functions by promoting apoptosis of osteoblasts and mature osteocytes together with the inhibition Inhibitors,research,lifescience,medical of cell proliferation and differentiation.7,8 Increase in osteoclastic activity which causes

the increase in bone resorption also contributes to the development of osteoporosis due to excess of glucocorticoids.9 Bone tissue response to glucocorticoids does not correlate with serum levels of active Inhibitors,research,lifescience,medical glucocorticoid, but it is strongly correlated with the serum levels of the inactive glucocorticoid, cortisone.10 This indicates Inhibitors,research,lifescience,medical that there may be a local factor that modulates the sensitivity of glucocorticoids in the tissue. 11β-hydroxysteroid dehydrogenase has been shown to be regulating glucocorticoid action in the tissue at the pre-receptor level. This enzyme is found in almost all glucocorticoids target tissues including the skeletal tissues. There are two isoenzymes of 11β-hydroxysteroid dehydrogenase, 11β-HSD1 and 11β-HSD2 with 11β-HSD1 being the predominant isoenzyme expressed in human osteoblasts and osteoclasts.11 It interconverts inactive cortisone to active glucocorticoids, cortisol. The activity and synthesis of 11β-HSD1

depends on the glucocorticoids Inhibitors,research,lifescience,medical concentration in the tissues. Both dehydrogenase and reductase activities are present in adult bones, but the 11β-HSD1 activity in adult human osteoblast is primarily reductase, which converts cortisone into biologically active cortisol. In contrast, dehydrogenase activity converts active glucocorticoids to inactive metabolite. Bone tissue cells can self-regulate the local Inhibitors,research,lifescience,medical concentration of active glucocorticoids Pim phosphorylation by modulating the expression and activity of 11β-HSD1.12 At the physiological levels of endogenous glucocorticoids, 11β-HSD1 activity is predominantly reductase in order to generate active glucocorticoids. However, with excessive levels of glucocorticoids, particularly with some synthetic steroids, dehydrogenase activity is diverse ranging from increase to attenuation of active glucocorticoids local availability.13 Liquorice and its derivatives, carbenoxolone and glycyrrhetinic acid (GCA), inhibit 11β-HSD activity.14 Treatment with carbenoxolone led to a significant fall in bone resorption markers, but did not show any effect on bone formation markers.13 Glycyrrhetinic acid was also shown to totally inhibit 11β-HSD 1 activity in an ‘in vitro’ study.