Soluble epoxide hydrolase inhibitor can protect the femoral head against tobacco smoke exposure-induced osteonecrosis in spontaneously hypertensive rats

Exposure to tobacco smoke (TS) has been considered a risk factor for osteonecrosis of the femoral head (ONFH). Soluble epoxide hydrolase inhibitors (sEHIs) have been found to reduce inflammation and oxidative stress in a variety of pathologies. This study was designed to assess the effect of sEHI on the development of ONFH phenotypes induced by TS exposure in spontaneously hypertensive (SH) rats. SH and normotensive Wistar Kyoto (WKY) rats were exposed to filtered air (FA) or TS (80 mg/m3 particulate concentration) 6 h/day, 3 days/week for 8 weeks. During this period, sEHI was delivered through drinking water at a concentration of 6 mg/L. Histology, immunohistochemistry, and micro-CT morphometry were performed for phenotypic evaluation. As results, TS exposure induced significant increases in adipocyte area, bone specific surface (BS/BV), and trabecular separation (Tb.SP), as well as significant decreases in bone mineral density (BMD), percent trabecular area (Tb.Ar), HIF-1a expression, bone volume fraction (BV/TV), trabecular numbers (Tb.N), and trabecular thickness (Tb.Th) in both SH and WKY rats. However, the protective effects of sEHI were mainly observed in TS-exposed SH rats, specifically in the density of osteocytes, BMD, Tb.Ar, HIF-1a expression, BV/TV, BS/BV, Tb.N, and Tb.SP. Our study confirms that TS exposure can induce ONFH especially in SH rats, and suggests that sEHI therapy may protect against TS exposure-induced osteonecrotic changes in the femoral head.

Alendronate decreases TRACP 5b activity in osteoarthritic bone

The activity of a tartrat-resistant acid phosphatase 5B (TRACP 5b), a marker of osteoclast function, was quantified in osteoarthritic bone specimens from patients treated with Alendronate. Prior to total hip replacement, 12 patients were randomized in a bisphosphonate and a control group. The bisphosphonate group received daily oral Alendronate for 50 days before operation. After operation, the femoral heads were harvested. Samples of the anterior femoral head (A1) and the intertrochanteric area (A2) were taken, analyzed with an immunoassay and stained for TRACP 5-positive-cells. The immunoassay revealed that TRACP-5b activity of the bisphosphonate group was significantly increased in A1 compared to A2, but not of the control group. Bisphosphonate treatment decreased enzyme activity compared to the controls: 0.41 U/mg vs. 0.31 U/mg in A1 and 0.26 U/mg vs. 0.18 U/mg in A2 (p<0.05). The histological examination shows significantly less TRACP-positive cells in bisphosphonate-treated bone sections, confirming the results. Our data suggest that bisphosphonates reduce TRACP 5b activity in the intertrochanteric area rather than in the anterior femoral head. Consequently, they are more effective in areas of well-supplied bone than in osteoarthritic bone tissue.

PKC-ζ expression is lower in osteoblasts from arthritic patients: IL1-β and TNF-α induce a similar decrease in non-arthritic human osteoblasts

Protein kinase C (PKC) is a family of enzymes detected in a diverse range of cell types where they regulate various cellular functions such as proliferation, differentiation, cytoskeletal remodelling, cytokine production, and receptor-mediated signal transduction. In this study we have analyzed the expression of 11 PKC isoforms (-alpha, -beta(I), -beta(II), -gamma, -delta, -eta, -theta, -epsilon, -zeta, -iota/lambda, and -micro) in osteoblasts from patients with osteoarthritis (OA) and rheumatoid arthritis (RA) in comparison with osteoblasts from post-traumatic (PT) patients. By Western blotting analysis, nine isoforms, -alpha, -beta(I), -beta(II), -delta, -theta, - epsilon, -zeta, - iota/lambda, and -micro, were detected in osteoblasts. In RA and OA patients, PKC -theta and -micro were greater expressed whereas PKC-epsilon and -zeta decreased when compared with normal cells. The subcellular distribution and quantitative differences were confirmed by immuno-electron microscopy. Furthermore, we demonstrated that treatment with the proinflammatory cytokines, IL-1beta and TNF-alpha, significantly decreased PKC-zeta expression in PT osteoblasts. This suggests that proinflammatory cytokines can modulate the expression of this PKC isoform in osteoblasts in a way which is similar to changes detected in arthritic patients.

Evidence for auto/paracrine actions of vitamin D in bone: 1alpha-hydroxylase expression and activity in human bone cells

Vitamin D is an important regulator of mineral homeostasis and bone metabolism. 1Alpha-hydroxylation of 25-(OH)D3 to form the bioactive vitamin D hormone, 1alpha,25-(OH)2D3, is classically considered to take place in the kidney. However, 1alpha-hydroxylase has been reported at extrarenal sites. Whether bone is a 1alpha,25-(OH)2D3 synthesizing tissue is not univocal. The aim of this study was to investigate an autocrine/paracrine function for 1alpha,25-(OH)2D3 in bone. We show that 1alpha-hydroxylase is expressed in human osteoblasts, as well as the vitamin D binding protein receptors megalin and cubilin. Functional analyses demonstrate that after incubation with the 1alpha-hydroxylase substrate 25-(OH)D3, the osteoblasts can produce sufficient 1alpha,25-(OH)2D3 to modulate osteoblast activity, resulting in induced alkaline phosphatase (ALP) activity, osteocalcin (OC) and CYP24 mRNA expression, and mineralization. The classical renal regulators of 1alpha-hydroxylase, parathyroid hormone, and ambient calcium do not regulate 1alpha-hydroxylase in osteoblasts. In contrast, interleukin (IL)-1beta strongly induces 1alpha-hydroxylase. Besides the bone-forming cells, we demonstrate 1alpha-hydroxylase activity in the bone resorbing cells, the osteoclasts. This is strongly dependent on osteoclast inducer RANKL. This study showing expression, activity, and functionality of 1alpha-hydroxylase unequivocally demonstrates that vitamin D can act in an auto/paracrine manner in bone.

Age-related decrease in the activity of collagenase in the femoral head in patients with hip osteoarthritis

The aim of the study was to evaluate the relation between the activity of collagenase in the subchondral bone of the femoral head and the age of patients with hip osteoarthritis. Thirty-two patients were enrolled into the study. The mean age was 66 (range from 37 to 80 years). Bone samples of the femoral head were harvested during total hip replacement. The activity of collagenase was measured through spectrofluorimetry. We found statistically a significant correlation between collagenase activity in the bone and age. The mean activity of collagenase in younger patients (37-68 years) was 64.17 IU/microg. In older patients (69-80 years), the mean collagenase activity was 52.26 IU/microg. In patients with hip osteoarthritis the activity of collagenase in the subchondral bone of the femoral head tended to decrease with an increase in age.

Detection of living cells in non-processed but deep-frozen bone allografts

Impacted morselized donor bone is successfully used to treat bone loss in revision total hip arthroplasties. It is generally thought, but not proven, that the processing and storage at -80 degrees C of the donor bone kills all cells. Because of the risk of contamination and to increase our understanding about the process of new bone formation after revision total hip arthroplasty, the aim of this study was to investigate whether the donor bone does contain vital cells. Samples from 11 femoral heads were obtained according to the American and European standards of bone banking, and tested for their capacity to give rise to proliferating cells, using tissue culture methods. All bone samples were stored at - 80 degrees C for a minimum of 6 months. Bone sample cores were morselized and cultured for 6 weeks. Inverted phase contrast microscopy was used to evaluate cell growth. DNA marker analysis was used to confirm cellular identity. All bank bone samples gave rise to cell growth. The cell cultures showed osteoblastic characteristics in that they expressed high levels of alkaline phosphatase activity. DNA marker analysis showed identical alleles for cultured cells from frozen bone and freshly obtained buccal cells from the same donor, indicating that the cells growing from the banked bone were indeed originating from the donor tissue. It was therefore concluded that -80 degrees C freezing of bone tissue does not routinely kill cells within the tissue.

Tissue inhibitor of metalloproteinases-4 (TIMP-4) gene expression is increased in human osteoarthritic femoral head cartilage

Tissue inhibitor of metalloproteinases-4 (TIMP-4), the newest member of the TIMP family, blocks the activities of several matrix metalloproteinases (MMPs) implicated in the arthritic cartilage erosion. By utilizing semi-quantitative RT-PCR, immunoblotting, and immunohistochemistry, we investigated whether the TIMP-4 gene is expressed in human non-arthritic and osteoarthritic (OA) cartilage. Directly analyzed femoral head cartilage showed TIMP-4 RNA expression in 2 of 9 non-arthritic and 12 of 14 OA patients. Femoral head cartilage from 6 of 9 OA patients had elevated TIMP-4 protein compared to the low-level expression in 3 of 8 non-arthritic controls. In most patients, there was correlation between TIMP-4 RNA and protein expression. TIMP-4 protein was also detected immunohistochemically in the upper zone of OA cartilage. The widespread TIMP-4 RNA and protein expression and augmentation in femoral OA cartilage suggests its important role in joint tissue remodeling and pathogenesis of OA. Increased TIMP levels in arthritic cartilage may not be a sufficiently effective defense against cartilage resorption by excessive multiple MMPs and aggrecanases.

The relative importance of cysteine peptidases in osteoarthritis

OBJECTIVE

To assess the activity of cysteine peptidases in cultured human articular chondrocytes as well as in osteoarthritic (OA) cartilage and subchondral bone, and to interpret their relative importance in cartilage destruction and remodeling of the subchondral region.

METHODS

Intracellular and secreted cysteine peptidase activity was measured in chondrocytes using fluorimetric assays, and enzymes were immunolocalized using monospecific antibodies. Enzyme histochemistry in normal and OA femoral heads was used to characterize enzymatic activity in full thickness samples containing cartilage and subchondral bone. The zonal distribution of cathepsin activity was measured in tissue slices of normal and OA femoral heads cut parallel to the joint surface, using fluorogenic substrates.

RESULTS

Cathepsins B and L were localized by immunohistochemistry with lysosome-like structures in dedifferentiated chondrocytes. Free cysteine peptidase activity (i.e., not requiring prior activation), secreted and intracellularly stored by chondrocytes, was due to cathepsin B, while cathepsin L contributed a minor fraction of the total activity, and was seen only after activation at acidic pH. Histochemistry and activity measurements confirmed cathepsin B as the major, active cysteine peptidase in OA cartilage, particularly at sites where matrix neosynthesis took place. However, free cathepsin L and/or cathepsin K activity was found subchondrally in association with cathepsin B in osteophytes, in zones undergoing bone remodeling, and at sites of inflammation.

CONCLUSION

Cathepsin B, not cathepsin L or cathepsin K, is a candidate for articular cartilage catabolism in OA. While cathepsin K is the major osteoclastic cysteine peptidase, cathepsin L and cathepsin B may also participate in the remodeling processes of bone as well as in bone erosion by inflammatory cells.

Physiological cell death of chondrocytes in vivo is not confined to apoptosis. New observations on the mammalian growth plate

Chondrocytes at the lower zone of the growth plate must be eliminated to facilitate longitudinal growth; this is generally assumed to involve apoptosis. We attempted to provide definitive electron-microscopic evidence of apoptosis in chondrocytes of physes and chondroepiphyses in the rabbit. We were, however, unable to find a single chondrocyte with the ultrastructure of 'classical' apoptosis in vivo, although such a cell was found in vitro. Instead, condensed chondrocytes had a convoluted nucleus with patchy chromatin condensations while the cytoplasm was dark with excessive amounts of endoplasmic reticulum. These cells were termed 'dark chondrocytes'. A detailed study of their ultrastructure combined with localisation methods in situ suggested a different mechanism of programmed cell death. In addition, another type of death was identified among the immature chondrocytes of the chondroepiphysis. These cells had the same nucleus as dark chondrocytes, but the lumen of the endoplasmic reticulum had expanded to fill the entire non-nuclear space, and all cytoplasm and organelles had been reduced to dark, worm-like inclusions. Since these cells appeared to be 'in limbo', they were termed 'paralysed' cells. It is proposed that 'dark chondrocytes' and 'paralysed cells' are examples of physiological cell death which does not involve apoptosis. It is possible that the confinement of chondrocytes within their lacunae, which would prevent phagocytosis of apoptotic bodies, necessitates different mechanisms of elimination.

Cathepsin B in osteoarthritis: zonal variation of enzyme activity in human femoral head cartilage

OBJECTIVES

To determine the quantitative topographical distribution of cathepsin B in human femoral head cartilage by measuring the zonal variation of enzyme activity in specimens taken from various anatomical regions of normal and osteoarthritic (OA) tissues, and to correlate this parameter with the severity of the OA lesions.

METHODS

OA articular cartilage was obtained at surgery for total hip replacement and control cartilage obtained at postmortem. Cylinders of full thickness cartilage with underlying bone were retrieved with a biopsy trephine. Sections of cartilage were produced by cryocutting the tissue as slices parallel to the articular surface and assayed for cathepsin B with a specific, highly sensitive fluorogenic substrate. The severity of the OA lesions was graded according to the histopathological-histochemical method of Mankin.

RESULTS

Zonal cathepsin B activity of normal cartilage was uniform and low in all regions of the femoral head. In apparently intact OA cartilage and in severely degraded tissue the zonal distribution and the amounts of enzyme were similar to control values. At sites with active disease, cathepsin B activity was much greater than in controls and its irregular zonal distribution correlated with tissue degeneration, hypercellularity, or cloning of chondrocytes as determined histochemically. Particularly high enzyme levels were observed at sites with regenerating cartilage, where some zonal peaks attained 20-fold activity with respect to controls.

CONCLUSION

Cathepsin B may play a role in sustaining the chronicity of OA, not as an initiator, but rather as a perpetuator of the disease and as an antagonist of regeneration.

Cathepsin B in osteoarthritis: cytochemical and histochemical analysis of human femoral head cartilage

OBJECTIVE

To localise the cysteine endopeptidase cathepsin B in chondrocytes and cartilage from normal and osteoarthritic (OA) human femoral heads in order to provide qualitative information on its cellular expression and distribution at possible sites of action.

METHODS

OA articular cartilage was obtained at surgery for total hip replacement; control cartilage was obtained at postmortem. Chondrocytes were isolated by sequential enzymatic digestion and cathepsin B analysed by immunocytochemistry and activity staining with a fluorogenic substrate. Lysosomes were visualised by fluorescence microscopy after staining of living cells with acridine orange. Using a histochemical reaction, enzyme activity was measured in cryosections of full thickness cartilage.

RESULTS

Chondrocytes from normal cartilage contained very few lysosomes and only a minor cell population was cathepsin B positive. A high proportion of chondrocytes from active OA cartilage contained a large number of lysosomes and an excess of cathepsin B in intracellular organelles; the enzyme was stored in an active form. In this respect, OA chondrocytes closely resembled normal cells that had been phenotypically modulated by serial subcultures. No cathepsin B activity could be detected by histochemistry in either chondrocytes or matrix of normal cartilage. While apparently intact and severely degraded OA cartilage was also cathepsin B negative, tissue at sites of active destruction and, particularly, at repair sites was highly positive.

CONCLUSION

The presence and the particular distribution of active cathepsin B in OA cartilage at 'more involved' sites suggest a pathological role for this enzyme in sustaining and perpetuating cartilage degradation. While other stimuli may also be responsible for cathepsin B expression in OA chondrocytes, the similarity with artificially modulated cells indicates fibroblastic metaplasia as a plausible mechanism.

Study of the effect of a glycosaminoglycan-peptide complex on the degradative enzyme activities in human osteoarthritic cartilage

The in vitro collagenolytic and proteoglycanasic activity from human fibrillated osteoarthritic cartilage was determined using labelled proteoglycans and type II collagen as substrates. In vitro, a glycosaminoglycan-peptide complex (GP-C Rumalon) induced a dose-dependent inhibition of both collagenolytic and proteoglycanasic activities while sodium salicylate and indomethacin had only a weak suppressive effect on proteoglycanase. Phospholipase A2 activity was unmodified by GP-C suggesting that the effect of the drug on degradative enzymes was unrelated to prostaglandin formation.

[Regulation of in vitro metabolism of human spongiosa by parathyroid hormone and calcitonin]

A method was developed to investigate in vitro metabolism of human trabecular bone and its hormonal regulation. Human and bovine parathyroid hormone 1-34 caused an increase in the release of calcium and magnesium out of human bone. Human, salmon and porcine calcitonin caused a decrease in the release of calcium and magnesium and inhibited the effect of parathyroid hormone.

The determination of bone viability: a histochemical method for identification of lactate dehydrogenase activity in osteocytes in fresh calcified and decalcified sections of human bone

We have developed a technique for assessing bone viability by the histochemical demonstration of lactate dehydrogenase (LDH) activity in osteocytes. Fresh sawn and ground (75 microns) sections were prepared from femoral heads removed at operation from patients with osteoarthritis of the hip. The sections were decalcified overnight in cold 10% EDTA, pH 7.0. LDH activity was shown by the tetrazolium-formazan reaction with nitroblue tetrazolium as indicator and lithium lactate as substrate. Osteocytes were regarded as viable if their cytoplasm stained dark blue, indicating LDH activity; lacunae containing non-viable osteocytes could be identified by interference contrast illumination. Nearly all osteocytes were viable in the samples studied. Small trabecular fragments, such as could be obtained by needle biopsy, were also suitable for staining after grinding to approximately 50 microns. The method should have application both in research and in diagnosis of ischemic bone disease.

Distribution of 99mTc-phosphate compounds in osteoarthritic femoral heads

In a study of the distribution of 99mTc-polyphosphate and 99mTc-methylene diphosphonate in osteoarthritic femoral heads by macroautoradiography of samples obtained during replacement surgery, the bone-seeking agents were seen to accumulate in the weight-bearing, denuded areas, mainly in the cyst walls and at the osteochondral junctions in the osteophytes. The autoradiographic findings were substantiated by findings from impulse-counting of different zones in the femoral heads that were done on frozen sections. Morphological studies of sections adjacent to the cut surface used for autoradiography showed that the accumulations of the radionuclides were located in areas of new-bone formation, particularly enchondral ossification. This finding was confirmed by histochemical staining for alkaline phosphatase, a marker enzyme for bone mineralization. The over-all distribution of alkaline phosphatase activity in cells roughly paralleled the deposition of the bone-seeking agents.

CLINICAL RELEVANCE

Scintigrams of osteoarthritic joints reflect primarily the rate of osteogenesis in subchondral bone and osteophytes. As the scan is positive even in very early stages in the development of the disease, a more detailed knowledge of the mechanism responsible for an increased uptake of 99mTc-phosphate compounds may, among other things, contribute to the elucidation of the pathogenesis.