Activity of osteoclastic bone resorption in primary hyperparathyroidism --- a comparative electron microscopic and histomorphometric study

A predator-prey based mathematical model of the bone remodelling cycle: exploring the relationship between the model parameters and biochemical factors

Bone remodelling is a vital process which enables bone to repair, renew and optimize itself. Disorders in the bone remodelling process are inevitably manifested in bone-related diseases, such as hypothyroidism, primary hyperparathyroidism and osteoporosis. In our previous work, a predator-prey based mathematical model was developed to simulate bone remodelling cycles under normal and two pathological conditions, hypothyroidism and primary hyperparathyroidism, for trabecular bone at a fixed point. However, the biochemical meanings of the model parameters were not fully explored. This article first extends the previous work by proposing relationships between the model parameters and biochemical factors involved in the bone remodelling process and by examining whether those relationships do predict the behaviours observed in vivo. The model is then applied to the simulation and investigation of bone remodelling of postmenopausal osteoporosis. The proposed connections are supported by good agreement between the model simulations and published experimental observations for the normal condition and all three pathological variations in bone remodelling.

The osteocyte: an endocrine cell ... and more

Few investigators think of bone as an endocrine gland, even after the discovery that osteocytes produce circulating fibroblast growth factor 23 that targets the kidney and potentially other organs. In fact, until the last few years, osteocytes were perceived by many as passive, metabolically inactive cells. However, exciting recent discoveries have shown that osteocytes encased within mineralized bone matrix are actually multifunctional cells with many key regulatory roles in bone and mineral homeostasis. In addition to serving as endocrine cells and regulators of phosphate homeostasis, these cells control bone remodeling through regulation of both osteoclasts and osteoblasts, are mechanosensory cells that coordinate adaptive responses of the skeleton to mechanical loading, and also serve as a manager of the bone's reservoir of calcium. Osteocytes must survive for decades within the bone matrix, making them one of the longest lived cells in the body. Viability and survival are therefore extremely important to ensure optimal function of the osteocyte network. As we continue to search for new therapeutics, in addition to the osteoclast and the osteoblast, the osteocyte should be considered in new strategies to prevent and treat bone disease.

Teriparatide following bisphosphonates: initial and long-term effects on microarchitecture and bone remodeling at the human iliac crest

Since the approval of teriparatide for clinical application, a number of iliac crest studies have focused on increases in bone volume or changes in structural parameters with microCT and numerical changes in histomorphometry. This investigation is based on individual histopathological observations related to early and late effects of teriparatide treatment in humans. A total of 44 (18 paired) iliac crest biopsies (ICB) from 41 patients receiving teriparatide (10 months +/- 6 months) following bisphosphonate (BP) treatment were investigated for hematopoietic changes, bone turnover, and description of microarchitectural changes using histology and selective microCT. Fully 71% of the ICB showed a normal or high bone turnover; 56% of the paired ICB presented an increase in bone turnover following teriparatide treatment. Early teriparatide stimulation (<1 month) resulted in peritrabecular fibroblast-like formations. Rare findings (<9%) included reactive hematopoietic changes, osteoidosis, endosteal fibrosis, microcallus, or woven bone. Round mast cells were frequently observed within marrow spaces. A total of 14% had an increase in cortical porosity, approximately 20% demonstrated signs of intratrabecular resorption sites. Teriparatide treatment resulted in an increase in remodeling units as early as 1 week after the first application with a continuous stimulation up to 18 months of rhPTH treatment despite previous BPs. Subgroups of patients developed increased cortical and/or intratrabecular resorption pattern, with unclear biomechanical significance. This mechanism could potentially result in new trabecular structures with an increase in trabecular number. Some individuals presented histological findings (e.g., fibrosis) that may require adjustment of treatment that could be of importance for clinical efficacy.

[Morphologic changes in iliac crest trabecular bone in primary hyperparathyroidism and their significance for diagnosis]

Iliac crest bone biopsy specimens of 391 patients with surgically proven primary hyperparathyroidism were investigated. In 60 unselected cases quantitative analysis of trabecular bone changes was performed. The age of the patients ranged between 12 and 85 years. The observed morphological findings were divided into four stages. In a few cases no differences from normal bone tissue could be observed. In 46% occurrence of a nonspecific increase of osteoid seams, osteoblasts, and osteoclasts was observed. Of the cases 50% showed a specific, but very often mild endosteal fibrosis. Only in 4% was there a severe fibroosteoclasia with development of so-called brown tumors. The quantitative analysis showed an increase of trabecular bone mass as well as of remodeling surfaces. But there was an overlap of up to 25% with the normal controls. The results demonstrate the influence of parathyroid hormone peptides on bone morphology. However, the investigation of a bone biopsy specimen is not generally very useful for diagnostic purposes.

Histomorphometric analysis of bone changes in surgically proven primary hyperparathyroidism and nephrolithiasis--the importance of bone biopsy in diagnosis

The morphologic changes in trabecular bone were studied in 60 patients with surgically proven hyperparathyroidism and in 69 patients with nephrolithiasis. The hyperparathyroid bone lesions showed substantial variation in their extent. Four, typical stages were defined. The structure of trabecular bone remained intact in most cases. Bone turnover is significantly higher in the patients with primary hyperparathyroidism. Fifty percent of all patients with nephrolithiasis had bone changes similar to those found in the surgically proven hyperparathyroidism group. In 50% of so-called asymptomatic cases of hyperparathyroidism, the iliac crest biopsy is a useful supplement to clinical and hormonal data in deciding whether to operate on the parathyroid glands. In about 45% of cases, however, no definite diagnoses is possible. The determination of serum parathyroid hormone in primary hyperparathyroidism has a greater importance for diagnostic purposes than morphologic investigation of the bone biopsy.