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Alkaptonuria (AKU) is a rare disorder characterized by the deficiency of the enzyme homogentisate 1,2-dioxygenase and consequent homogentisate accumulation, which leads to progressive and severe osteoarthopathy starting from the second decade of life. Thus, in AKU patients, bone involvement represents an important clinical issue, which we investigated. Serum levels of receptor activator of NF-κB ligand (RANKL), osteoprotegerin, sclerostin, Dickkopf-1, and bone remodeling markers were measured in nine AKU patients (two children and seven adults) and 22 controls, together with lumbar spine bone mineral density (LS-BMD) and femoral-BMD. In the two AKU children, the average of LS-BMD and femoral-BMD Z-scores were within the normal range, but reduced with respect to the controls. Otherwise, in the adult AKU patients, LS-BMD T-score was inside the normal range, but femoral-BMD T-score reached osteopenic levels. Consistently, in AKU adults, higher RANKL and C-terminal telopeptide of collagen type 1 and lower osteoprotegerin levels were observed than in controls. Otherwise, spontaneous osteoclastogenesis was already evident in peripheral blood mononuclear cell cultures from AKU children, together with a high percentage of circulating osteoclast precursors. Osteoclastogenesis was sustained by the high levels of tumor necrosis factor-α, RANK, RANKL, and LIGHT. In conclusion, the altered osteoclastogenesis was observed already in AKU children, despite the absence of evident injury. Thus, a preventive approach in young patients, targeting osteoclast activity, may prevent the macroscopic bone disease that appears in adult AKU.

Subjects with hypergonadotropic hypogonadism due to Turner's syndrome show low cortical mineral density, osteoporosis and risk of fractures. It is not clear if this bone fragility derives from chromosomal abnormalities or is the result of inadequate bone formation due to estrogen deficiency. The aim of this study was to investigate the cellular mechanisms underlying bone fragility in subjects with Turner's syndrome before induction of puberty and after hormonal replacement therapy (HRT). For this purpose, we have evaluated the osteoclastogenic potential of non-fractioned and T-cell depleted cultures of peripheral blood mononuclear cells (PBMCs) belonging to girls with Turner's syndrome who had not been treated with HRT yet, girls and young women who were on HRT and age-matched controls. Untreated subjects showed high FSH serum levels, whereas the other subjects displayed normal FSH serum levels. T-cell immunophenotype was analyzed through flow cytometry. Biochemical and DXA analyses were performed. Spontaneous osteoclastogenesis in non-fractioned and T-cell depleted cultures of PBMC belonging to girls with high FSH levels was more evident than in cultures of subjects with normal FSH levels. In the former, osteoclastogenesis was sustained by monocytes expressing high levels of c-fms, TNF-α and RANK, and T-cells producing high RANKL and TNF-α; in the latter it was supported by T-cells expressing high RANKL levels. CD4+CD25high T-cells were reduced in all subjects, whereas CD3+/CD16+/CD56+ NKT-cells were increased in those with high FSH levels. High RANKL and CTX levels were detected in the sera. Bone impairment was already detectable by DXA in subjects aged under 10, although it became more evident with aging. In conclusion, our results demonstrated that bone fragility in subjects with Turner's syndrome is associated to enhanced osteoclastogenesis. This process seems to be due to high FSH serum levels before HRT, whereas it is caused by high RANKL during HRT.

Background/Objectives Calcific aortic valvular disease (CAVD) is an actively regulated process characterized by the activation of specific osteogenic signaling pathways and apoptosis. We evaluated the involvement in CAVD of the TNF-related apoptosis-inducing ligand (TRAIL), an apoptotic molecule which induces apoptosis by interacting with the death receptor (DR)-4 and DR5, and whose activity is modulated by the decoy receptor (DcR)-1 and DcR2. Methods Sections of calcific and normal aortic valves, obtained at surgery time, were subjected to immunohistochemistry and confocal microscopy for TRAIL immunostaining. Valvular interstitial cells (VICs) isolated from calcific (C-VICs) and normal (N-VICs) aortic valves were investigated for the gene and protein expression of TRAIL receptors. Cell viability was assayed by MTT. Von Kossa staining was performed to verify C-VIC ability to produce mineralized nodules. TRAIL serum levels were detected by ELISA. Results Higher levels of TRAIL were detected in calcific aortic valves and in sera from the same patients respect to controls. C-VICs express significantly higher mRNA and protein levels of DR4, DR5, DcR1, DcR2 and Runx2 compared to N-VICs. C-VICs and N-VICs, cultured in osteogenic medium, express significantly higher mRNA levels of DR4, Runx2 and Osteocalcin compared to baseline. C-VICs and N-VICs were sensitive to TRAIL-apoptotic effect at baseline and after osteogenic differentiation, as demonstrated by MTT assay and caspase-3 activation. TRAIL enhanced mineralized matrix nodule synthesis by C-VICs cultured in osteogenic medium. Conclusions TRAIL is characteristically present within calcific aortic valves, and mediates the calcification of aortic valve interstitial cells in culture through mechanism involving apoptosis.