Molecular Interactions between Dietary Lipids and Bone Tissue during Aging

Age-related bone disorders such as osteoporosis or osteoarthritis are a major public health problem due to the functional disability for millions of people worldwide. Furthermore, fractures are associated with a higher degree of morbidity and mortality in the long term, which generates greater financial and health costs. As the world population becomes older, the incidence of this type of disease increases and this effect seems notably greater in those countries that present a more westernized lifestyle. Thus, increased efforts are directed toward reducing risks that need to focus not only on the prevention of bone diseases, but also on the treatment of persons already afflicted. Evidence is accumulating that dietary lipids play an important role in bone health which results relevant to develop effective interventions for prevent bone diseases or alterations, especially in the elderly segment of the population. This review focuses on evidence about the effects of dietary lipids on bone health and describes possible mechanisms to explain how lipids act on bone metabolism during aging. Little work, however, has been accomplished in humans, so this is a challenge for future research.

A Jack of All Trades: Impact of Glucocorticoids on Cellular Cross-Talk in Osteoimmunology

Glucocorticoids (GCs) are known to have a strong impact on the immune system, metabolism, and bone homeostasis. While these functions have been long investigated separately in immunology, metabolism, or bone biology, the understanding of how GCs regulate the cellular cross-talk between innate immune cells, mesenchymal cells, and other stromal cells has been garnering attention rather recently. Here we review the recent findings of GC action in osteoporosis, inflammatory bone diseases (rheumatoid and osteoarthritis), and bone regeneration during fracture healing. We focus on studies of pre-clinical animal models that enable dissecting the role of GC actions in innate immune cells, stromal cells, and bone cells using conditional and function-selective mutant mice of the GC receptor (GR), or mice with impaired GC signaling. Importantly, GCs do not only directly affect cellular functions, but also influence the cross-talk between mesenchymal and immune cells, contributing to both beneficial and adverse effects of GCs. Given the importance of endogenous GCs as stress hormones and the wide prescription of pharmaceutical GCs, an improved understanding of GC action is decisive for tackling inflammatory bone diseases, osteoporosis, and aging.

CypD-mPTP axis regulates mitochondrial functions contributing to osteogenic dysfunction of MC3T3-E1 cells in inflammation

Bone is a dynamic organ, the bone-forming osteoblasts and bone-resorbing osteoclasts form the physiological basis of bone remodeling process. During pathological process of numerous inflammatory diseases, these two aspects are uncoupled and the balance is usually tipped in favor of bone destruction. Evidence suggests that the inflammatory destruction of bone is mainly attributed to oxidative stress and is closely related to mitochondrial dysfunction. The mechanisms underlying osteogenic dysfunction in inflammation still need further investigation. Reactive oxygen species (ROS) is associated with mitochondrial dysfunction and cellular damage. Here, we reported an unexplored role of cyclophilin D (CypD), the major modulator of mitochondrial permeability transition pore (mPTP), and the CypD-mPTP axis in inflammation-induced mitochondrial dysfunction and bone damage. And the protective effects of knocking down CypD by siRNA interference or the addition of cyclosporin A (CsA), an inhibitor of CypD, were evidenced by rescued mitochondrial function and osteogenic function of osteoblast under tumor necrosis factor-α (TNF-α) treatment. These findings provide new insights into the role of CypD-mPTP-dependent mitochondrial pathway in the inflammatory bone injury. The protective effect of CsA or other moleculars affecting the mPTP formation may hold promise as a potential novel therapeutic strategy for inflammation-induced bone damage via mitochondrial pathways.

Role of Galectin-3 in Bone Cell Differentiation, Bone Pathophysiology and Vascular Osteogenesis

Galectin-3 is expressed in various tissues, including the bone, where it is considered a marker of chondrogenic and osteogenic cell lineages. Galectin-3 protein was found to be increased in the differentiated chondrocytes of the metaphyseal plate cartilage, where it favors chondrocyte survival and cartilage matrix mineralization. It was also shown to be highly expressed in differentiating osteoblasts and osteoclasts, in concomitance with expression of osteogenic markers and Runt-related transcription factor 2 and with the appearance of a mature phenotype. Galectin-3 is expressed also by osteocytes, though its function in these cells has not been fully elucidated. The effects of galectin-3 on bone cells were also investigated in galectin-3 null mice, further supporting its role in all stages of bone biology, from development to remodeling. Galectin-3 was also shown to act as a receptor for advanced glycation endproducts, which have been implicated in age-dependent and diabetes-associated bone fragility. Moreover, its regulatory role in inflammatory bone and joint disorders entitles galectin-3 as a possible therapeutic target. Finally, galectin-3 capacity to commit mesenchymal stem cells to the osteoblastic lineage and to favor transdifferentiation of vascular smooth muscle cells into an osteoblast-like phenotype open a new area of interest in bone and vascular pathologies.

IL-4/CCL22/CCR4 axis controls regulatory T-cell migration that suppresses inflammatory bone loss in murine experimental periodontitis

Inflammatory bone resorption is a hallmark of periodontitis, and Tregs and Th2 cells are independently associated with disease progression attenuation. In this study, we employed an infection-triggered inflammatory osteolysis model to investigate the mechanisms underlying Treg and Th2 cell migration and the impact on disease outcome. Aggregatibacter actinomycetemcomitans-infected C57Bl/6 (wild-type [WT]) mice develop an intense inflammatory reaction and alveolar bone resorption, and Treg and Th2 cell migration is temporally associated with disease progression attenuation. Tregs extracted from the lesions preferentially express CCR4 and CCR8, whereas Th2 cells express CCR3, CCR4, and CCR8. The absence of CCR5 and CCR8 did not significantly impact the migration of Tregs and Th2 cells or affect the disease outcome. CCR4KO mice presented a minor reduction in Th2 cells in parallel with major impairment of Treg migration, which was associated with increased inflammatory bone loss and higher proinflammatory and osteoclastogenic cytokine levels. The blockade of the CCR4 ligand CCL22 in WT mice resulted in an increased inflammatory bone loss phenotype similar to that in the CCR4KO strain. Adoptive transfer of CCR4(+) Tregs to the CCR4KO strain revert the increased disease phenotype to WT mice-like levels; also, the in situ production of CCL22 in the lesions is mandatory for Tregs migration and the consequent bone loss arrest. The local release of exogenous CCL22 provided by poly(lactic-co-glycolic acid) (PLGA) microparticles promotes migration of Tregs and disease arrest in the absence of endogenous CCL22 in the IL-4KO strain, characterized by the lack of endogenous CCL22 production, defective migration of Tregs, and exacerbated bone loss. In summary, our results show that the IL-4/CCL22/CCR4 axis is involved in the migration of Tregs to osteolytic lesion sites, and attenuates development of lesions by inhibiting inflammatory migration and the production of proinflammatory and osteoclastogenic mediators.

Increased neutrophil infiltration, IL-1 production and a SAPHO syndrome-like phenotype in PSTPIP2-deficient mice

OBJECTIVE

Proline-serine-threonine-phosphatase-interacting protein 2 (PSTPIP2) is involved in macrophage activation, neutrophil motility and osteoclast differentiation. However, the role of PSTPIP2 in inflammation and autoinflammatory diseases is still not clear. In this study, we generated PSTPIP2 knockout (Pstpip2(-/-)) mice to investigate its phenotype and role in autoinflammatory diseases.

METHODS

We constructed a Pstpip2-targeting vector and generated Pstpip2(-/-) mice. The phenotype and immunopathology of Pstpip2(-/-) mice were analysed.

RESULTS

All Pstpip2(-/-) mice developed paw swelling, synovitis, hyperostosis and osteitis, resembling SAPHO syndrome, an inflammatory disorder of the bone, skin and joints. Multifocal osteomyelitis was found in inflamed paws, with increased macrophage and marked neutrophil infiltrations in the bone, joint and skin. Profound osteolytic lesions with markedly decreased bone volume density developed in paws and limbs. Neutrophil-attracting chemokines and IL-1β were markedly elevated in inflamed tissues.

CONCLUSION

Our study suggests that PSTPIP2 could play a role in innate immunity and development of autoinflammatory bone disorders, and may be associated with the pathogenesis of human SAPHO syndrome.

[Investigation of the role of Zn2+ and zinc-containing proteins in the pathogenesis of bone inflammmation (the case of periodontitis)]

The levels of Ag, Al, Bi, Co, Cr, Fe, Mo, Si in osseous tissue of periodontium of domestic cats decreased in case of periodontitis in comparision with those of a healthy animals. At the same time the level of Zn increased dramatically. The level of tagged [14C] glycine in protein of bones of periodontium increased twofold and [35S] methionine 1,54 times which is explained by the fact of predominance of I type collagen in which one third of amino acids is represented by glycine while sulfur-containing amino acids are virtually absent. The latter are contained in non-collagenous proteins of bones of periodontium contributing for its metabolism. The difference in tagged aminoacids inclusion in bones of periodontium is mainly provoked by redistribution of the collagen and non-collagenous proteins.

Rheumatoid arthritis and ankylosing spondylitis - pathology of acute inflammation

Histomorphological analysis of inflammatory lesions in rheumatoid arthritis (RA) and ankylosing spondylitis (AS) display similarities but also major differences. Ankylosing spondylitis is characterised by two key pathological findings: sacroiliac joint and spinal inflammation and new bone formation with the possible consequence of bone fusion, usually in the axial skeleton. In AS the primary site of inflammation is located at the enthesis or subchondral bone marrow with bone marrow oedema, lymphocytic infiltrates, increased osteoclast density and increased microvessel density are typical findings in acute inflammation. In RA joint inflammation has its origin in the synovial membrane of peripheral joints. Osteitis in the subchondral bone marrow reveals similar findings compared to AS and it is suggested to occur secondary to inflammation in the synovial membrane. Structural damage defines the outcome in both diseases. However, in AS it is defined by new bone formation and in RA by the destruction of cortical bone.

Therapeutic strategies against inflammation and bone loss associated with osteomyelitis

Despite current treatment strategies, osteomyelitis is often refractory and recurrent. The bacteria responsible for osteomyelitis can invade bone-forming osteoblasts, which are active participants in the generation of damaging inflammation and bone loss at sites of infection. Therefore, strategies promoting cell-mediated immune responses while limiting inflammation are required for the treatment of chronic bone infections. This review describes the mechanisms utilized by resident bone cells to perceive bacteria, recruit leukocytes to sites of infection and promote osteoclast-mediated bone destruction, as well as novel targets for the therapeutic intervention of these processes.

18F FDG-PET imaging in musculoskeletal infection

(18)F Fluorodeoxyglucose-positron emission tomography (FDG-PET) has become an encouraging imaging modality in musculoskeletal infection. This application has an incremental value in the assessment of both acute and chronic infection and has shown to be more accurate in detecting chronic osteomyelitis than conventional radionuclide imaging. Whether FDG-PET has the potential to replace conventional scintigraphy completely depends on a number of factors, including cost and availability. Conventional radionuclide studies have represented imaging methods of choice in the diagnosis of implant-associated infection in patients with trauma so far. However, nonspecific tissue uptake of imaging agents and limited spatial resolution restrict their usefulness. Magnetic resonance imaging (MRI) and computed tomography (CT) image quality is degraded in the presence of metallic implants due to susceptibility and beam-hardening artifacts, respectively. Although its role is still evolving, FDG-PET imaging will have increased importance in patients with metallic implants used for trauma surgery because FDG uptake is not hampered by metallic artifacts. In contrast to patients with metallic implants, PET may not be as useful in the diagnosis of infection in patients with failed total joint replacements. In this situation, combined 111Indium-labeled leucocyte/(99m)Tc-sulfur colloid marrow imaging still remains the gold standard. This article reviews the currently available literature on FDG-PET and PET/CT in the diagnosis of musculoskeletal infection.

Antimicrobial peptide 99mTc-ubiquicidin 29-41 as human infection-imaging agent: clinical trial

Ubiquicidin (UBI) 29-41 is a cationic, synthetic antimicrobial peptide fragment that binds preferentially with the anionic microbial cell membrane at the site of infection. The current study was conducted to evaluate its potential as an infection-imaging agent in humans.

METHODS

Eighteen patients, 9 female and 9 male (mean age, 31.7 y; range, 5-75 y), with suspected bone, soft-tissue, or prosthesis infections were included in the study. (99m)Tc-UBI 29-41 in a dose of 400 microg/370-400 MBq was injected intravenously in adults. A dynamic study was followed by spot views of the suspected region of infection (target) and a corresponding normal area (nontarget) at 30, 60, 120, and 240 min. The target-to-nontarget ratios were used to find the optimum time for imaging. Whole-body anterior and posterior images were also acquired at 30, 120, and 240 min to study biodistribution. Activity in each organ was expressed as percentage retained dose. Visual score (0-3) was used to categorize studies as positive or negative, with scores of 0 (minimal or no uptake; equivalent to soft tissue) and 1 (mild; less uptake than in liver) being considered negative and scores of 2 (moderate; uptake greater than or equal to that in liver) and 3 (intense; uptake greater than or equal to that in kidneys) being considered positive. Scans were interpreted as true- or false-positive and true- or false-negative on the basis of bacterial culture as the major criterion and the results of clinical tests, radiography, and 3-phase bone scanning as minor criteria.

RESULTS

The biodistribution study showed a gradual decline in renal activity as percentage of administered dose from 6.53% +/- 0.58% at 30 min to 4.54% +/- 0.57% at 120 min and 3.38% +/- 0.55% at 240 min. The liver showed a similar trend, with values of 5.43% +/- 0.76%, 3.17% +/- 0.25%, and 2.02% +/- 0.30% at 30, 120, and 240 min, respectively. Radioactivity accumulated gradually in the urinary bladder, with values of 4.60% +/- 0.92% at 30 min, 23.00% +/- 2.32% at 120 min, and 38.85% +/- 4.01% at 240 min. Of 18 studies performed with 99mTc-UBI 29-41, 14 showed positive findings and 4 showed negative findings. Negative findings were subsequently confirmed to be true negative. The positive findings for 1 scan were interpreted as false positive, as no growth was obtained on bacterial culture and no evidence of infection was found on minor criteria. In 10 cases, the major criterion was used, whereas in 4 cases minor criteria had to be used for interpretation. Quantitative analysis revealed a maximum mean target-to-nontarget ratio of 2.75 +/- 1.69 at 30 min, which decreased to 2.04 +/- 1.01 at 120 min. The overall sensitivity, specificity, and accuracy were 100%, 80%, and 94.4%, respectively. No adverse reactions were observed during image acquisition and within 5 d after the study.

CONCLUSION

99mTc-UBI 29-41 showed promise in localizing foci of infection, with optimal visualization at 30 min.

Roles for NF-kappaB and c-Fos in osteoclasts

NF-kappaB and c-Fos are transcription factors that are activated in immune cells and in most other cell types following stimulation by a variety of factors, including cytokines, growth factors, and hormones. They regulate the expression of a large number of genes, and both are activated in osteoclast precursors after RANKL, IL-1, or TNF bind to their respective receptors. However, of these cytokines, only RANKL is required for the induction of osteoclast formation in vivo. Nevertheless, it is likely that IL-1, TNF, and other cytokines participate in the upregulation of osteoclast formation seen in a variety of conditions that affect the skeleton in which cytokine production is increased, including estrogen deficiency and inflammatory bone diseases. In this review, the RANKL/ OPG/RANK system and roles for NF-kappaB and c-Fos in osteoclasts are reviewed along with our current understanding of how this system may be disrupted in common bone diseases, such as postmenopausal osteoporosis, inflammatory arthritis, and Paget's disease.

Biokinetics of 99mTc-UBI 29-41 in humans

Antimicrobial peptides have been proposed as new agents to distinguish between bacterial infections and sterile inflammatory processes. (99m)Tc-UBI labeled by a direct method has shown high in vitro and in vivo stability, specific uptake at the site of infection, rapid background clearance, minimal accumulation in non-target tissues and rapid detection of infection sites in mice. The aim of this study was to establish a (99m)Tc-UBI biokinetic model and evaluate its feasibility as an infection imaging agent in humans. Whole-body images from 6 children with suspected bone infection were acquired at 1, 30, 120, 240 min and 24 h after (99m)Tc-UBI administration. Regions of interest (ROIs) were drawn around source organs (heart, liver, kidneys and bladder) on each time frame. The same set of ROIs was used for all 6 scans and the cpm of each ROI were converted to activity using the conjugate view counting method. Counts were corrected by physical decay and by the background correction factor derived from preclinical phantom studies. The image sequence was used to extrapolate (99m)Tc-UBI time-activity curves in each organ and calculate the cumulated activity (A). Urine samples were used to obtain the cumulative percent of injected activity (% I.A.) versus time renal elimination. The absorbed dose in organs was evaluated according to the general equation described in the MIRD formalism. In addition, (67)Ga-citrate images were obtained from all the patients and used as a control. Biokinetic data showed a fast blood clearance with a mean residence time of 0.52 h. Approximately 85% of the injected activity was eliminated by renal clearance 24 h after (99m)Tc-UBI administration. Images showed minimal accumulation in non-target tissues with an average target/non-target ratio of 2.18 +/- 0.74 in positive lesions at 2 h. All infection positive(99m)Tc-UBI images were in agreement with those obtained with (67)Ga-citrate. The mean radiation absorbed dose calculated was 0.13 mGy/MBq for kidneys and the effective dose was 4.34 x 10(-3)mSv/MBq.

A genetic approach to inactivating chemokine receptors using a modified viral protein

We have developed a genetic system, called degrakine, that specifically and stably inactivates chemokine receptors (CKR) by redirecting the ability of the HIV-1 protein, Vpu, to degrade CD4 in the endoplasmic reticulum (ER) via the host proteasome machinery. To harness Vpu's proteolytic targeting capability to degrade new receptors, we fused a chemokine with the C terminal region of Vpu. The fusion protein, or degrakine, accumulates in the ER, trapping and functionally inactivating its target CKR. We have demonstrated that degrakines based on SDF-1 (CXCL12), MDC (CCL22) and RANTES (CCL5) specifically inactivate their respective receptor functions. Using a retroviral vector expressing the SDF-1 degrakine, we have established that CXCR4 is required for the homing of hematopoietic stem/progenitor cells (HSPC) to the bone marrow immediately after transplantation. Thus the degrakine provides an effective genetic tool to dissect receptor functions in a number of biological systems in vitro and in vivo.

Targeting cytokines to inflammation sites

To increase the half-life of a cytokine and target its activation specifically to disease sites, we have engineered a latent cytokine using the latency-associated protein (LAP) of transforming growth factor-beta 1 (TGF-beta 1) fused via a matrix metalloproteinase (MMP) cleavage site to interferon (IFN)-beta at either its N or C terminus. The configuration LAP-MMP-IFN-beta resembles native TGF-beta and lacks biological activity until cleaved by MMPs, whereas the configuration IFN-beta-MMP-LAP is active. LAP provides for a disulfide-linked shell hindering interaction of the cytokine with its cellular receptors, conferring a very long half-life of 55 h in vivo. Mutations of the disulfide bonds in LAP abolish this latency. Samples of cerebrospinal fluid (CSF) or synovial fluid from patients with inflammatory diseases specifically activate the latent cytokine, whereas serum samples do not. Intramuscular injection in arthritic mice of plasmid DNA encoding these constructs demonstrated a greater therapeutic effect of the latent as compared to the active forms.

Monocyte chemoattractant protein-1 expression and monocyte recruitment in osseous inflammation in the mouse

In bone, early events in inflammation involve the production and release of primary proinflammatory cytokines, such as interleukin-1 beta. By activation of target cells, these cytokines are thought to induce a second wave of cytokines, including monocyte chemoattractant protein-1 (MCP-1). MCP-1 is a cytokine that stimulates chemotaxis of monocytes. Experiments were undertaken to examine the expression of MCP-1 in bone-associated cells in vivo. To observe in vivo expression of MCP-1, an inflammatory lesion was created in the murine mandible. Immunohistochemistry experiments using specific antibodies to MCP-1 were conducted to identify MCP-1-expressing cells in inflamed and noninflamed bone. We found that osteoblasts were the principal cells expressing MCP-1 in inflamed bone. There was little or no MCP-1 expression in noninflamed bone. Immunohistochemistry experiments were carried out to assess monocyte recruitment during osseous inflammation. The number of MCP-1-positive cells was significantly correlated to the number of monocytes/macrophages present (n = 15; r = 0.69; P < = 0.01). These in vivo results strongly suggest that MCP-1 is an important mediator involved in the recruitment of monocytes/macrophages in inflamed bone.

[A study using nondecalcified bone biopsy of the incidence and presentation forms of renal osteodystrophy]

BACKGROUND

Renal osteodystrophy (ROD) is a common complication of chronic renal failure. Fibrous osteitis and, to a lesser extent, osteomalacia are the predominant lesions. The aim of the present study was to evaluate the prevalence of the different forms of ROD.

METHODS

Nondecalcified bone biopsies were evaluated in 100 patients with end-stage renal disease (57 in pre-dialysis and 43 on hemodialysis) in whom biochemical (calcium, phosphorus, alkaline phosphatase, parathyroid hormone) and histomorphometric studies were carried out. Bone biopsies were classified in four histological groups: mild, fibrous osteitis (FO), osteomalacia (OM) and mixed type (FO + OM).

RESULTS

96% of patients had histological findings of ROD with the following distribution: 41% mild; 30% FO; 14% OM; and 11% mixed. The most advanced types of ROD were seen in interstitial renal diseases. Pre-dialysis OM was associated with metabolic acidosis, a low phosphocalcic product and relative hypophosphoremia. Chronic aluminium poisoning was uncommon (7%) and was basically associated with OM. No instance of aluminium poisoning with osteodystrophy and bone fractures was seen.

CONCLUSIONS

The most severe histological forms of OM were found in hemodialysis patients with persistent hypophosphoremia and associated with osteosclerosis.

The volume of distribution of ceftazidime and albumin in normal, immature and infected bone

The penetration of ceftazidime into bone was determined by measuring the volume of distribution of 14C-ceftazidime in infected and non-infected bone of adult mongrel dogs. The volume of distribution in non-infected cortical bone was 0.114 +/- 0.011 l/kg (mean +/- S.E.M.) and increased significantly in non-infected immature callus to 0.484 +/- 0.13 l/kg (P less than 0.05). In the presence of infection, the volume of distribution in non-infected cortical bone was 0.144 +/- 0.05 l/kg, and significantly higher in infected reactive cortical bone, 0.453 +/- 0.07 (P less than 0.05). We conclude that ceftazidime penetrates infected and non-infected bone and that this penetration is greater into immature bone.

[Rifampicin diffusion in non-infected human bone (author's transl)]

Rifampicin levels in serum, cortical bone and spongious bone were measured by a biological assay in 13 non-infected patients undergoing total replacement of the hip. Samples were collected after 24-72 hours rifampicin administration (daily oral dose: 600 mg). The mean level was 0.67 +/- 0.48 microgram/g in cortical bone and 3.35 +/- 0.72 microgram/g in spongious bone. Rifampicin diffusion was also assessed in normal bone from crista iliaca needle biopsy specimens in 7 patients treated for osteitis or septic arthritis. Bone and serum levels did not appear linearly correlated but, in any case, bone levels were much higher than MIC for Staphylococcus aureus which is usually involved in bone and joint infections.

[Comparative investigations concerning osteotropic radiopharmaceuticals. III. Scanning with 18F and 99mTc-malignant diseases (author's transl)]

Total body scans under identical conditions and using 18F and 99mTc-EHDP were carried out in patients with known, or subsequently proven, metastases. There was no statistical evidence for any difference in the number of scintigraphically demonstrable lesions. Patients with internal prostheses who developed infections of the prosthesis show no significant difference in the uptake of either nucleid. Soft tissue lesions showed a significantly higher uptake of 99mTc-EHDP than of 18F. 18F can be replaced for nearly all problems by 99mTc-EHDP without loss of diagnostic information.