25-hydroxyvitamin D levels and bone histomorphometry in hemodialysis renal osteodystrophy

25-hydroxyvitamin D levels and bone histomorphometry in hemodialysis renal osteodystrophy.BackgroundThe importance of 25-hydroxyvitamin D (25-OHD) serum levels in hemodialysis chronic renal failure has not been so far histologically evaluated. Information still lacking relate to the effect of 25-OHD deficiency on serum parathyroid hormone (PTH) levels and on bone and its relationship with calcitriol levels.MethodsThis retrospective study has been performed on a cohort of 104 patients on hemodialysis from more than 12 months, subjected to transiliac bone biopsy for histologic, histomorphometric, and histodynamic evaluation. The patients, 61 males and 43 females, mean age 52.9 ± 11.7 years, hemodialysis length 97.4 ± 61.4 months, were treated with standard hemodialysis and did not receive any vitamin D supplementation. Treatment with calcitriol was not underway at the time of the biopsy. Transiliac bone biopsies were performed after double tetracycline labels. In addition, serum intact PTH (iPTH), alkaline phosphatase, and 25-OHD were measured. Calcitriol serum levels was also measured in a subset of patients (N = 53). The patients were divided according to serum 25-OHD levels in three groups: (1) 0 to 15 (15 patients), (2) 15 to 30 (38 patients), and (3) >30 ng/mL (51 patients).ResultsThere was no significant difference in average age, hemodialysis age, serum PTH [490 ± 494, 670 ± 627, and 489 ± 436 pg/mL, respectively (mean ± SD)], alkaline phosphatase, and calcitriol between the three groups. The parameters double-labeled surface, trabecular mineralizing surface, and bone formation rate were significantly lower in group 1 than in the other groups (P < 0.03, < 0.03, and < 0.02, respectively). Osteoblast surface and adjusted apposition rate were borderline significantly lower in group 1 (P < 0.06 and < 0.10). There was no statistical difference in the biochemical and bone parameters between groups 2 and 3. A positive significant correlation was found between several bone static and dynamic parameters and 25-OHD levels in the range 0 to 30 ng/mL, showing a vitamin D dependence of bone turnover at these serum levels. However, actual evidence of an effect on bone of 25-OHD deficiency was found at serum levels below 20 ng/mL. With increasing 25-OHD levels beyond 40 ng/mL, a downslope of parameters of bone turnover was also observed.ConclusionSince PTH serum levels are equally elevated in low and high 25-OHD patients, while calcitriol levels are constantly low, an effect of 25-OHD deficiency (group 1) on bone, consisting of a mineralization and bone formation defect, can be hypothesized. The effect of vitamin D deficiency or bone turnover is found below 20 ng/mL. The optimal level of 25-OHD appears to be in the order of 20 to 40 ng/mL. Levels of the D metabolite higher than 40 ng/mL are accompanied by a reduction of bone turnover

Immunohistochemical localization and mRNA expression of matrix Gla protein and fetuin-A in bone biopsies of hemodialysis patients

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Understanding Nanocalcification: A Role Suggested for Crystal Ghosts

The present survey deals with the initial stage of the calcification process in bone and other hard tissues, with special reference to the organic-inorganic relationship and the transformation that the early inorganic particles undergo as the process moves towards completion. Electron microscope studies clearly exclude the possibility that these particles might be crystalline structures, as often believed, by showing that they are, instead, organic-inorganic hybrids, each comprising a filamentous organic component (the crystal ghost) made up of acidic proteins. The hypothesis is suggested that the crystal ghosts bind and stabilize amorphous calcium phosphate and that their subsequent degradation allows the calcium phosphate, once released, to acquire a hydroxyapatite, crystal-like organization. A conclusive view of the mechanism of biological calcification cannot yet be proposed; even so, however, the role of crystal ghosts as a template of the structures usually called “crystallites” is a concept that has gathered increasing support and can no longer be disregarded

A MORFOLOGIC STUDY OF BONE AND ARTICULAR CARTILAGE IN OCHRONOSIS

An ochronotic femoral head has been studied morphologically under the light and the electron microscope. Its articular cartilage showed the alterations already reported in the literature, mainly consisting of erosions of the surface, pigment accumulation in chondrocytes and intercellular matrix, chondrocyte degeneration, the formation of pigmented, calcified and uncalcified microshards, and the presence of granulation tissue with macrophagic cells. The changes in bone were less severe than those in cartilage. Pigment was present in the calcified matrix. This did not seem to disturb the organization of the bone tissue, although it was diffusely osteoporotic, perhaps because of limb disuse. The preservation of calcified matrix might depend on the fact that its collagen fibrils are encrusted by mineral substance, which avoids the dangerous effects that the deposition of ochronotic pigment induces in the fibrils of soft connective tissues. On the other hand, the newly formed osteoid matrix remains uncalcified for too short a time to be modified by the pigment. Diffuse or granular pigmentation was found in a few osteocytes, while several of them were condensed or reduced to cellular fragments. Bone resorption often occurred near these osteocytes. However, this did not seem to alter the degree of bone remodelling, possibly because of the relatively low numbers of degenerated or dead osteocytes. Pigment was also contained in the cytoplasmic vacuoles of otherwise active osteoclasts, whereas it was not found in osteoblasts. On the whole, ochronosis in bone seems to induce the same changes as in other connective tissues. However, their severity appears to be limited by calcification, which prevents modifications in collagen fibrils, and by bone remodelling, which to some extent eliminates the oldest, pigment-richest parts of the tissue

PTH and bone markers of renal osteodystrophy in predialysis chronic renal failure.

[No abstract available