The glucocorticoid-induced leucine zipper gene (GILZ) expression decreases after successful treatment of patients with endogenous Cushing's syndrome and may play a role in glucocorticoid-induced osteoporosis.

CONTEXT: Glucocorticoid-induced bone loss is a serious complication in patients with endogenous Cushing's syndrome. However, the mechanism(s) by which excess glucocorticoids influence bone metabolism is not completely understood. OBJECTIVE: The aim of the study was to investigate the functional role of glucocorticoid-induced leucine zipper (GILZ) in bone remodeling with special focus on glucocorticoid-induced osteoporosis (GIO). PATIENTS: Nine patients with endogenous Cushing's syndrome participated in the study. RESEARCH DESIGN AND METHODS: We analyzed bone biopsies from Cushing's patients before and after treatment to screen for expressional candidate genes with putative roles in GIO. Microarray analysis combined with real-time RT-PCR revealed that the gene encoding GILZ ranked among the topmost regulated genes and was selected for functional characterization in vitro. RESULTS: GILZ mRNA was expressed by human fetal osteoblasts (hFOB), human mesenchymal stem cells (hMSC), osteoblasts differentiated from hMSC, and osteoclasts. GILZ was increased by dexamethasone in a time- and dose-dependent manner in hFOB. Inhibition of GILZ in hFOB cells by small interfering RNA decreased typical osteoblast-related genes, suggesting a physiological role in promoting osteoblast maturation. Our data further support a functional role for GILZ in normal bone remodeling by modulating expression of TNF-(ligand) receptor superfamily/osteoprotegerin in favor of increased ratio in hFOB. Finally, osteoclasts exposed to conditioned media from GILZ-silenced hFOB indicated effects on osteoclast activity. CONCLUSION: Taken together, these results implicate the transcription factor GILZ in the pathophysiology of GIO by regulating osteoblast maturation and bone turnover.

Restoration of the coupling process and normalization of bone mass following successful treatment of endogenous Cushing's syndrome: a prospective, long-term study.

OBJECTIVE: Endogenous Cushing's syndrome (CS) is associated with bone loss and an increased risk of fractures. However, the long-term outcome of treatment on bone health has not been adequately clarified. DESIGN: We followed 33 patients with active CS prospectively before and twice after treatment (mean follow-up 33 (n = 25) and 71 months (n = 18), respectively). The patients were compared to age-, sex- and body mass index (BMI)-matched controls, also followed longitudinally. METHODS: Bone mineral indices (bone mineral density (BMD), bone mineral content (BMC) and bone area) were evaluated in the lumbar spine (LS), femoral neck (FN), and total body (TB) by dual-energy X-ray absorptiometry (DXA). Biochemical markers of bone turnover were assessed by serum levels of osteocalcin and C-terminal telopeptides of Type-1 collagen (CTX-1). RESULTS: Mann-Whitney rank sum tests showed that BMD of the LS, FN and TB was reduced by 14.8% (P < 0.001), 15.7% (P < 0.001), and 9.2% (P < 0.001) in CS vs. controls at baseline, with markedly reduced serum osteocalcin (P = 0.014) and increased CTX-1 (P = 0.012) levels, but no correlation between markers. At first follow-up, BMD was increased in LS (7.9%, P < 0.001) and FN (3.5%, P = 0.003) compared to baseline. The time-dependent rise in BMD (LS (r = 0.59; P = 0.002) and FN (r = 0.52; P = 0.007); Spearman's rank correlation), in CS was paralleled by increased osteocalcin (275%, P < 0.001) and correlation between biochemical markers (r = 0.92, P < 0.001; Pearson's correlation). TB BMD did not increase significantly before the second follow-up, when BMD Z-scores were normalized in all three compartments. CONCLUSION: Our observations demonstrate restoration of coupled bone remodeling and normalization of bone mineral density in all measured skeletal compartments of treated CS patients after prolonged recovery, first significant in predominantly trabecular bone (i.e. lumbar spine).

Low-dose GH improves exercise capacity in adults with GH deficiency: effects of a 22-month placebo-controlled, crossover trial.

Fifty-five patients with adult-onset GH deficiency (mean age, 49 years) were enrolled in a placebo-controlled, crossover study to investigate the effects of GH therapy on exercise capacity, body composition, and quality of life (QOL). GH and placebo were administered for 9 months each, separated by a 4-month washout period. GH therapy was individually dosed to obtain an IGF-I concentration within the normal range for age and sex. The final mean daily dose of GH was 1.2 IU/day for men and 1.8 IU/day for women. Mean IGF-I concentration at baseline was higher in men than in women (95+/-33 vs 68+/-41 microg/l respectively; P < 0.04) and increased to a similar level on GH therapy. Body fat mass was reduced by 1.9+/-2.9 kg and lean body mass was increased by 1.8+/-2.8 kg (P = 0.0001 for each) with GH treatment. Total and low-density cholesterol levels decreased. Absolute maximal oxygen uptake increased by 6% (P = 0.01), relative to body weight by 9% (P = 0.004), and there was a trend toward increased endurance performance by 7% (P = 0.07). There were no significant effects on QOL. In conclusion, treatment with a low, physiologic dose of GH produced positive effects on body composition and lipids and improved exercise capacity, likely to be of clinical relevance. No changes in QOL were seen, possibly because of a good QOL at baseline.

Raised serum levels of interleukin-8 and interleukin-18 in relation to bone metabolism in endogenous Cushing's syndrome.

OBJECTIVE: It is well known that patients with endogenous Cushing's syndrome (CS) have decreased bone mass and enhanced risk for osteoporotic fractures, secondary to decreased bone formation and increased bone resorption. Immunological mediators, such as cytokines, have recently been shown to influence bone metabolism, and in the present study we examined serum levels of several cytokines, with known or potential effects on bone homeostasis, in 33 consecutive recruited untreated CS patients and 33 age-, sex- and body mass index-matched healthy controls. METHODS: Cytokine levels were measured by enzyme immunoassay and bone mass by dual-energy X-ray absorptiometry. RESULTS: Our main findings were (i) interleukin (IL)-8 and IL-18 levels were significantly increased in CS patients compared with controls. (ii) Levels of both IL-8 and IL-18 were positively correlated to serum cortisol. (iii) For serum levels of the 'classical' resorptive cytokines, i.e. IL-6 and tumor necrosis factor alpha, no significant differences were found between CS patients and controls. (iv) Raised IL-18 levels were correlated with decreased osteocalcin levels in CS patients. CONCLUSIONS: Our results demonstrated that CS patients have markedly elevated levels of the proinflammatory cytokines IL-8 and IL-18 in spite of high levels of the immunosuppressive hormone cortisol. These cytokines may be involved in the pathogenesis of disturbed bone homeostasis in CS.