Jari Salo

Acid attack and cathepsin K in bone resorption around total hip replacement prosthesis.

Normal bone remodeling and pathological bone destruction have been considered to be osteoclast‐driven. Osteoclasts are able to attach to bare bone surface and produce an acidic subcellular space. This leads to acid dissolution of hydroxyapatite, allowing cathepsin K to degrade the organic type I collagen‐rich osteoid matrix under the acidic condition prevailing in Howship lacunae. Using a sting pH electrode, the interface membrane around a loosened total hip replacement prosthesis was found to be acidic. Confocal laser scanning disclosed irregular demineralization of the bone surface in contact with the acidic interface. Cathepsin K, an acidic collagenolytic enzyme, was found in interface tissue macrophages/giant cells and pseudosynovial fluid. Tissue extracts contained high levels of cathepsin K messenger RNA (mRNA) and protein. These observations suggest the presence of an acid‐ and cathepsin K‐driven pathological mechanism of bone resorption, mediated not by osteoclasts in subosteoclastic space, but rather by the uncontrolled activity of macrophages in extracellular space.

Bone stress injuries of the lower extremity: a review.

Bone stress injuries can cause long-lasting damage, especially in young athletes and military conscripts, if not diagnosed and treated properly. Diagnosis has been traditionally based on clinical, radiographic and scintigraphic examinations, but MRI has become increasingly important. High resolution MRI is particularly valuable for the grading of bone stress injuries. The clinician should be aware of the wide range of bone stress injuries and available diagnostic methods. Early diagnosis is the prerequisite for avoiding long-lasting complications. Most bone stress injuries heal with closed treatment, but surgery is necessary in some cases. They heal well if the diagnosis is not delayed and the treatment adequate.

Involvement of a disintegrin and a metalloproteinase 8 (ADAM8) in osteoclastogenesis and pathological bone destruction

Objectives: The eventual role of a disintegrin and a metalloproteinase 8 (ADAM8) in osteoclastogenesis was studied in erosive rheumatoid arthritis (RA) and in vitro. Methods: ADAM8 protein and mRNA expression was measured in RA pannus and synovitis and compared to osteoarthritic (OA) synovial membrane. Human monocytes were isolated and stimulated with proinflammatory cytokines and their ADAM8 expression and surface ADAM8 were measured. Human peripheral blood monocytes and RAW 264.7 mouse monocyte/macrophage cells were stimulated to osteclast like-cells, and their expression of ADAM8 and osteoclastic markers (calcitonin receptor, integrin β 3, cathepsin K, TRAP) were analysed. Transfection and small interfering RNA (siRNA) were used to assess the role of ADAM8 in formation of polykaryons. Results: Increased numbers of ADAM8 positive cells were shown particularly in the pannus-cartilage/bone junction close or adjoining to TRAP positive multinucleate cells under formation (60 (2)% in pannus, 47 (2)% in synovitis vs 10 (1)% in OA, p<0.001). Human pannus contained high ADAM8 mRNA copy numbers (23 (7) in pannus, 14 (4) in synovitis vs 1.7 (0.3) in OA, p<0.001). Functional studies in vitro disclosed ADAM8 mRNA and protein, which was first converted to a proteolytically active and then to fusion-active form. Gene transfection and siRNA experiments enhanced and inhibited, respectively, expression of osteoclast markers and maturation of multinuclear cells. Conclusions: ADAM8 may be involved in bone destruction in RA because it is upregulated in RA pannus adjacent to developing erosions and enhances maturation of osteoclast-like cells.

Plasmin-matrix metalloproteinase cascades in spinal response to an experimental disc lesion in pig.

Study Design. Proteinases were immunohistochemically stained to analyze degenerated discs and paradiscal tissues in comparison to contiguous control tissues in an experimental porcine model of intervertebral disc degeneration. Objective. The aim was to analyze plasmin and metalloproteinases known to participate in mutual activation cascades. Summary of Background Data. Comparison of the degenerated discs and paradiscal structures with control tissues disclosed accumulation of plasmin and induction of matrix metalloproteinases (MMP), MMP-1 and MMP-2 in the discs, but some other MMPs in reactive and remodeling tissues. Material and Methods. In 6 domestic pigs, the cranial L4 endplate was perforated to penetrate the nucleus pulposus. Three months later, the animals were killed and the experimental and the contiguous control vertebrae, complete with their intervertebral discs, were excised and subjected to histologic and immunohistochemical examinations. Results. Immunohistochemical analysis disclosed increased expression of MMP-1 and MMP-2 in the traumatized and degenerated intervertebral discs. Some MMPs were also induced in all paradiscal structures (bone marrow, vertebral bone, and spinal ligaments), or decreased in already scarred areas. The common denominator for all the anatomic sites studied was accumulation of plasmin. Conclusion. Fibroblast collagenase (MMP-1) and gelatinase A (MMP-2), capable of degrading native and denatured collagen, were induced in degenerating intervertebral discs. Use of an experimental model enabled demonstration that biomechanical destabilization and degeneration of the disc also affects all other paradiscal structures, which are subjected to proteolysis and/or reparative fibrosis apparently representing remodeling of the spine subjected to pathologic stress. Profiling of various MMPs and plasmin, known to participate in mutual activation cascades, suggests that plasmin could activate pro-MMP-1, pro-MMP-2, pro-MMP-3, pro-MMP-7, pro-MMP-9, and pro-MMP-13 and alone or/and in cooperation with MMP-3 initiate at least 2 mutual MMPs activation cascades driven by activated MMP-3 and MMP-7.

In Vitro Evaluation of a 3D PLGA—TCP Composite Scaffold in an Experimental Bioreactor

A 3D poly(lactic acid-co-glycolic acid)/tricalcium phosphate (PLGA-TCP) composite scaffold, generated with the low-temperature deposition modeling rapid prototyping technique, was tested for its viability in a 3D cell cultivation in vitro. The aim was to find optimal cell culture conditions for the selected scaffold material and to monitor cell division, differentiation, and migration of selected cell types in this environment. In addition, the behavior and cell-matrix interactions of selected cell types were monitored as well as the biodegradation rate of the tested scaffold material. Chinese hamster ovary cells as well as a human cell line 293 epithelial cells were cultured on the scaffolds. A variety of different preconditioning protocols were deployed to prepare the scaffolds before seeding with the cells. Cell cultivations were conducted for 1–4 weeks and the coverage of the luminal surfaces was analyzed with light microscopy. Long cultivation periods were required to achieve partial coverage of the luminal surfaces of the scaffolds. Tissue engineering with 3D cell cultures and biomaterials represents a promising approach for organ manufacturing research. It may have potential for eventual on-demand high-throughput production of artificial tissues but the process has many challenges. The culture system in a well controlled bioreactor environment is discussed.

Bone Substitutes in Clinical Work

Clinical use of bone substitutes is becoming a routine procedure. The ever-increasing variety of commercially- available materials offers many new possibilities, but can be embarrassing, too. Is this material resorbable, does it have compression strength, how can it be applied, is it of living origin etc.? are common questions in the Surgeon’s mind. Last, but not least, what is the price of the selected material. Should I still use the good old method of autologous bone graft, and try to save money? In this paper will try to give an overview of current materials based on the biology and clinical use, not based on commercial or marketing strategies. Bone substitutes can all be classified as osteoconductive, osteo-inductive or osteogenic material. Their clinical use differs in many ways. Osteoconductive materials form a bridge over the bone void area to offer a possibility for bone formation in bony environment without too much scar formation. Osteo-induction is based on the stimulation of mesenchymal stem cells to differentiate and form bone tissue. Osteogenic material works both ways in some extent, and it also has active cells. Traditional osteogenic material, autograft, is facing new challengers as material and tissue technology proceed.