IntroductionMechanical loading of bone tissue is a prerequisite for the maintenance of bone structure. Experimental and clinical observations demonstrate that immobilisation of healthy individuals disturbs bone metabolism leading to increased bone resorption, decreased bone formation, and loss of bone mass mainly in weight bearing skeletal regions Dehority et al., 1999;Vico et al., 1987). Mechanical strain, transmitted into bone tissue via muscle force interacts with the impact of gravity (g) in an osteoanabolic manner. Therefore, bone loss occurs during long term periods of living in a micro-g environment, e.g. during space flights (Carmeliet and Bouillon, 1999) although the functional integrity of the neuro-muscular-skeletal system is not impaired. It is unclear how bone tissue perceives mechanical loading and whether gravitation exerts its anabolic effects directly on bone cells or indirectly on bone tissue by increasing the impact of muscle-and weight-induced forces on bone.Mechanical forces are absorbed by the bone matrix and transformed into deformation. Deformation of the bone matrix is perceived by bone cells via adhesion molecules which modulates osteoblast metabolism (Liegibel et al., 2002). Deformation of the interconnecting porous bone tissue also induces fluid shifts within the osteocytic lacunae and canaliculi. There is evidence that fluid flow may be more important for an osteocytic response AbstractDeformation of the bone matrix by mechanical strain causes fluid shifts within the osteocytic canaliculi which affect osteocytic cell metabolism. We applied low fluid shear (1 ± 63 Pa for 10 ± 48 h) to human osteoblastic cells (HOB) in vitro to study its impact on cell proliferation and differentiated functions. Proteins involved in translating the physical force into a cellular response were characterised. Low fluid shear stress stimulated proliferation of HOB 1.2-fold when stress was applied intermittently for 24 h. Shear stress also increased differentiated cellular properties such as alkaline phosphatase (ALP) activity (121% of control), fibronectin (FN) and fibronectin receptor (FNR) expression (290 % and 200%, respectively). Prostaglandin E 2 (PGE 2 ) and TGFb1 release into the medium were significantly stimulated when shear stress was applied for 6 ± 12 h and 24 ± 48 h, respectively. TGFb1 + 2 neutralising antibodies or the presence of indomethacine inhibited the mitogenic effect of fluid shear and reduced ALP activity to its control level. Furthermore, TGFb treatment induced a dose-dependent increase in FN and FNR expression. Therefore, fluid shear stress of low magnitude (a) suffices to affect HOB metabolism and (b) regulates anchorage of HOB via FN and FNR by stimulating osteoblastic PGE 2 and TGFb secretion.

Osteocytes are the most abundant bone cells, playing important roles in tissue maintenance. Little is known of how they react in vivo to cancer stress. Here we present a comparative study of the effect of a bone-residing tumour (myeloma) and metastases of bone-remote cancers on osteocytes. While no differences in morphology of the bone are seen, the changes in the transcriptome of osteocytes are specifically related to the tumour stress present. Screening approximately 22 000 genes in osteocytes prepared from cryosections of native bone using laser-supported microdissection, we observed approximately 1400 and approximately 1800 gene expression differences between osteocytes dissected from normal bone compared with those associated with metastases and multiple myeloma, respectively. The genes up-regulated due to the stress exerted by metastases were repressed by multiple myeloma and vice versa, indicating stress-specific footprints in the transcriptome of osteocytes. Functionally, the stressors seem to impose selective pressures on signalling pathways such as that of TGFbeta, a major player in bone biology. Our data show for the first time that the transcriptome of osteocytes in vivo becomes strongly affected by cancer stress, generating gene expression footprints which, in contrast to comparable morphological changes, appear to relate to the nature of cancer and might thus become helpful in distinguishing different bone diseases.

Induction of matrix synthesis by low-level laser has been demonstrated extensively. However, the question of dose- or power intensity-dependency is under-investigated. To address this issue we chose human osteoblast cell cultures and measured their alkaline phosphatase (ALP) activity after laser irradiation. The cell cultures were irradiated periodically by 690 nm radiation via optical transmission fiber-based laser needles, reaching into the culture dishes. The osteoblasts showed no induction of ALP activity when we used a single laser needle stimulation with a laser irradiance of 51 mW/cm(2), an increase of approximately 43% at 102 mW/cm(2) irradiance (two needles per well) and a ninefold increase at 204 mW/cm(2) irradiance (four needles per well), leaving the temperature of the culture medium unaffected. We concluded that the osteoblastic response in ALP activity to a laser stimulus shows a logarithmic relationship, with a distinct threshold, rather than a linear dose-dependency. Secondly, the laser irradiance, rather than the dose, is relevant for the impact of the laser.

Amylin is a 37-amino-acid peptide related to CGRP and calcitonin. It is co-secreted with insulin from pancreatic beta-cells. Amylin is deficient with type 1 diabetes mellitus. To study the in vivo effects of amylin in humans, diabetic patients are an adequate model of chronic amylin deficiency. We investigated the effect of a 12 months pramlintide therapy (amylin analogue) on bone metabolism in patients with type 1 diabetes mellitus. 23 patients with type 1 diabetes mellitus (age 45.2 +/- 10.3 years, duration of diabetes mellitus 20.7 +/- 9.8 years, 13 male, 10 female) injected themselves 0.1 ml pramlintide, a human amylin analogue, four times per day for a period of 12 months. Bone mineral density measurements of the lumbar spine by dual-energy X-ray absorptiometry (DXA), and biochemical markers of bone metabolism (serum-calcium, PTH, osteocalcin, urinary pyridinium cross-links) were obtained before and one year after starting pramlintide therapy. None of the following parameters changed significantly: bone density, serum calcium, PTH, osteocalcin or pyridinium cross-links. Only osteocalcin decreased from 7.205 ng/ml to 5.825 ng/ml, but this change was not statistically significant. We conclude that a one-year pramlintide therapy does not affect bone density or bone metabolism in patients with type 1 diabetes mellitus without osteopenia (based on the markers used).

Osteoporosis affects approximately 7 million patients in Germany and severely impairs quality of life. The clinical picture, subjective complaints as well as the presence or absence of risk factors are essential to determine the individual risk profile and to decide on possible serum blood tests, osteodensitometry, and X-ray examinations. Back pain or other clinical evidence of impaired bone stability should be evaluated with X-ray studies of the spine. If osteoporosis and an increased risk of fracture are present, treatment is indicated which includes an evidence-based pharmaceutical regimen in order to increase bone stability and to lower the risk of fractures. Drug treatment with adequate calcium and vitamin D supplementation and antiresorptive or osteoanabolic substances, usually for 3-5 years, should be accompanied by pain medication and neuromuscular rehabilitation to help prevent falls and maintain independence of the elderly.