Citations

Abstract Motivation: Using stable isotopes in global proteome scans, labeled molecules from one sample are pooled with unlabeled molecules from another sample and subsequently subjected to mass-spectral analysis. Stable-isotope methodologies make use of the fact that identical molecules of different stable-isotope compositions are differentiated in a mass spectrometer and are represented in a mass spectrum as distinct isotopic clusters with a known mass shift. We describe two multivariable linear regression models for 16O/18O stable-isotope labeled data that jointly model pairs of resolved isotopic clusters from the same peptide and quantify the abundance present in each of the two biological samples while concurrently accounting for peptide-specific incorporation rates of the heavy isotope. The abundance measure for each peptide from the two biological samples is then used in down-stream statistical analyses, e.g. differential expression analysis. Because the multivariable regression models are able to correct for the abundance of the labeled peptide that appear as an unlabeled peptide due to the inability to exchange the natural C-terminal oxygen for the heavy isotope, they are particularly advantageous for a two-step digestion/labeling procedure. We discuss how estimates from the regression model are used to quantify the variability of the estimated abundance measures for the paired samples. Although discussed in the context of 16O/18O stable-isotope labeled data, the multivariable regression models are generalizable to other stable-isotope labeled technologies. Contact: eckel@mayo.edu

Abstract A case of granulomatous slack skin disease is presented in which we studied the possible involvement of extrarenal 1,25(OH)2D in the pathogenesis of the patient's hypercalcemia. Immunolocalization of 1α-OH in skin showed simultaneous dysregulation in epithelial and granulomatous cells. Introduction: Granuloma-forming diseases such as sarcoidosis are associated with extrarenal synthesis of active 1,25-dihydroxyvitamin D [1,25(OH)2D]. Here we describe a case of granulomatous slack skin disease in which we have studied the possible involvement of extrarenal synthesis of 1,25(OH)2D in the pathogenesis of the patient's hypercalcemia. The aim of the study was to clarify the etiology of hypercalcemia in this patient. Materials and Methods: This was a case study of a 19-year-old man with a T-cell lymphoproliferative disorder diagnosed as granulomatous slack skin disease who presented with hypercalcemia and raised serum 1,25(OH)2D. Analysis of expression of the enzyme 25-hydroxyvitamin D 1α-hydroxylase (1α-hydroxylase), which catalyzes synthesis of 1,25(OH)2D, was carried out by immunohistochemical analysis of involved and uninvolved skin. Approval was granted by the Mayo Foundation Institutional Review Board and Biospecimens Subcommittee. Results: In uninvolved skin, expression of 1α-hydroxylase was confined to the basal layer of the epidermis, whereas slack skin showed overexpression of the enzyme in dermal granulomata and basal cells of the epidermis. Conclusions: Hypercalcemia associated with granulomatous slack skin syndrome seems to be caused by dysregulation of 1α-hydroxylase expression in both epidermal and dermal granulomatous cells. This contrasts with psoriasis and sarcoidosis of the skin, in which overexpression of the enzyme is restricted to keratinocytes and granulomata, respectively.

Abstract We used QCT scans obtained in 687 men and women, 21–97 years of age, to estimate the factor of risk for vertebral fracture, Φvert, defined as the ratio of spinal loading to vertebral strength. With age, vertebral strength declined and Φvert increased significantly more in women than men. Age- and sex-specific differences in Φvert closely resembled previously reported vertebral fracture incidence. Introduction: Despite the high prevalence of vertebral fractures, little is known about the interaction between spinal loading and vertebral fragility. Materials and Methods: We assessed the ratio of spinal loading to vertebral strength (i.e., the factor of risk, Φvert) in an age- and sex-stratified population-based sample of 700 women and men 21–97 years of age. We measured volumetric BMD (vBMD, mg/cm3) and cross-sectional area (CSA, cm2) of the midvertebral bodies of L1–L3 using QCT and computed vertebral compressive strength from these data using engineering beam theory. A biomechanical model of the trunk was used to estimate compressive forces applied to the L3 vertebral body during standing, bending forward, and bending forward while lifting 10 kg. The factor of risk for fracture, Φvert, was computed as the ratio of spinal compressive force to vertebral strength for each activity. Results: Men had a higher vertebral strength at all ages, largely because of their greater CSA. Whereas both sexes exhibited a marked decline in vertebral compressive strength with age (p < 0.001), the decline was greater in women than men (−43% versus −31%, p = 0.008). Compressive forces on L3 were greater in men than women, because of their greater body weight and height. For both sexes, forces during bending and lifting were 8-fold higher than those experienced during upright standing. For all activities, Φvert increased with age, but significantly more so in women than men (p < 0.001). For bending and lifting, Φvert-bending exceeded 1.0 in 30% of women and 12% of men ≥50 years of age, values that are similar to the reported frequency of vertebral fracture. Conclusion: These findings illustrate potential mechanisms underlying vertebral fractures and provide strong rationale for further evaluation of this QCT-based biomechanical approach for assessment of fracture risk.