Bio

Professional Education


  • Doctor of Philosophy, University Of Helsinki (2012)
  • Doctor of Medicine, University Of Helsinki (2010)

Stanford Advisors


Publications

Journal Articles


  • Chronic inflammation in biomaterial-induced periprosthetic osteolysis: NF-?B as a therapeutic target. Acta biomaterialia Lin, T., Tamaki, Y., Pajarinen, J., Waters, H. A., Woo, D. K., Yao, Z., Goodman, S. B. 2014; 10 (1): 1-10

    Abstract

    Biomaterial-induced tissue responses in patients with total joint replacement are associated with the generation of wear particles, which may lead to chronic inflammation and local bone destruction (periprosthetic osteolysis). Inflammatory reactions associated with wear particles are mediated by several important signaling pathways, the most important of which involves the transcription factor NF-κB. NF-κB activation is essential for macrophage recruitment and maturation, as well as the production of pro-inflammatory cytokines and chemokines such as TNF-α, IL-1β, IL-6 and MCP1. In addition, NF-κB activation contributes to osteoclast differentiation and maturation via RANK/RANKL signaling, which increases bone destruction and reduces bone formation. Targeting individual downstream cytokines directly (such as TNF-α or IL-1β) may not effectively prevent wear particle induced osteolysis. A more logical upstream therapeutic approach may be provided by direct modulation of the core IκB/IKKα/β/NF-κB signaling pathway in the local environment. However, the timing, dose and strategy for administration should be considered. Suppression of chronic inflammation via inhibition of NF-κB activity in patients with malfunctioning joint replacements may be an effective strategy to mitigate wear particle induced periprosthetic osteolysis.

    View details for DOI 10.1016/j.actbio.2013.09.034

    View details for PubMedID 24090989

  • Novel biological strategies for treatment of wear particle-induced periprosthetic osteolysis of orthopaedic implants for joint replacement. Journal of the Royal Society, Interface / the Royal Society Goodman, S. B., Gibon, E., Pajarinen, J., Lin, T., Keeney, M., Ren, P., Nich, C., Yao, Z., Egashira, K., Yang, F., KONTTINEN, Y. T. 2014; 11 (93): 20130962-?

    Abstract

    Wear particles and by-products from joint replacements and other orthopaedic implants may result in a local chronic inflammatory and foreign body reaction. This may lead to persistent synovitis resulting in joint pain and swelling, periprosthetic osteolysis, implant loosening and pathologic fracture. Strategies to modulate the adverse effects of wear debris may improve the function and longevity of joint replacements and other orthopaedic implants, potentially delaying or avoiding complex revision surgical procedures. Three novel biological strategies to mitigate the chronic inflammatory reaction to orthopaedic wear particles are reported. These include (i) interference with systemic macrophage trafficking to the local implant site, (ii) modulation of macrophages from an M1 (pro-inflammatory) to an M2 (anti-inflammatory, pro-tissue healing) phenotype in the periprosthetic tissues, and (iii) local inhibition of the transcription factor nuclear factor kappa B (NF-κB) by delivery of an NF-κB decoy oligodeoxynucleotide, thereby interfering with the production of pro-inflammatory mediators. These three approaches have been shown to be viable strategies for mitigating the undesirable effects of wear particles in preclinical studies. Targeted local delivery of specific biologics may potentially extend the lifetime of orthopaedic implants.

    View details for DOI 10.1098/rsif.2013.0962

    View details for PubMedID 24478281

  • Mutant MCP-1 protein delivery from layer-by-layer coatings on orthopedic implants to modulate inflammatory response. Biomaterials Keeney, M., Waters, H., Barcay, K., Jiang, X., Yao, Z., Pajarinen, J., Egashira, K., Goodman, S. B., Yang, F. 2013; 34 (38): 10287-10295

    Abstract

    Total joint replacement (TJR) is a common and effective surgical procedure for hip or knee joint reconstruction. However, the production of wear particles is inevitable for all TJRs, which activates macrophages and initiates an inflammatory cascade often resulting in bone loss, prosthetic loosening and eventual TJR failure. Macrophage Chemoattractant Protein-1 (MCP-1) is one of the most potent cytokines responsible for macrophage cell recruitment, and previous studies suggest that mutant MCP-1 proteins such as 7ND may be used as a decoy drug to block the receptor and reduce inflammatory cell recruitment. Here we report the development of a biodegradable, layer-by-layer (LBL) coating platform that allows efficient loading and controlled release of 7ND proteins from the surface of orthopedic implants using as few as 14 layers. Scanning electron microscopy and fluorescence imaging confirmed effective coating using the LBL procedure on titanium rods. 7ND protein loading concentration and release kinetics can be modulated by varying the polyelectrolytes of choice, the polymer chemistry, the pH of the polyelectrolyte solution, and the degradation rate of the LBL assembly. The released 7ND from LBL coating retained its bioactivity and effectively reduced macrophage migration towards MCP-1. Finally, the LBL coating remained intact following a femoral rod implantation procedure as determined by immunostaining of the 7ND coating. The LBL platform reported herein may be applied for in situ controlled release of 7ND protein from orthopedic implants, to reduce wear particle-induced inflammatory responses in an effort to prolong the lifetime of implants.

    View details for DOI 10.1016/j.biomaterials.2013.09.028

    View details for PubMedID 24075408

  • Toll-like receptors in human chondrocytes and osteoarthritic cartilage ACTA ORTHOPAEDICA Sillat, T., Barreto, G., Clarijs, P., Soininen, A., Ainola, M., Pajarinen, J., Korhonen, M., Konttinen, Y. T., Sakalyte, R., Hukkanen, M., Ylinen, P., Nordstrom, D. C. 2013; 84 (6): 585-592

    Abstract

    Degenerating cartilage releases potential danger signals that react with Toll-like receptor (TLR) type danger receptors. We investigated the presence and regulation of TLR1, TLR2, and TLR9 in human chondrocytes.We studied TLR1, TLR2, TLR4, and TLR9 mRNA (qRT-PCR) and receptor proteins (by immunostaining) in primary mature healthy chondrocytes, developing chondrocytes, and degenerated chondrocytes in osteoarthritis (OA) tissue sections of different OARSI grades. Effects of a danger signal and of a pro-inflammatory cytokine on TLRs were also studied.In primary 2D-chondrocytes, TLR1 and TLR2 were strongly expressed. Stimulation of 2D and 3D chondrocytes with a TLR1/2-specific danger signal increased expression of TLR1 mRNA 1.3- to 1.8-fold, TLR2 mRNA 2.6- to 2.8-fold, and TNF-α mRNA 4.5- to 9-fold. On the other hand, TNF-α increased TLR1 mRNA] expression 16-fold, TLR2 mRNA expression 143- to 201-fold, and TNF-α mRNA expression 131- to 265-fold. TLR4 and TLR9 mRNA expression was not upregulated. There was a correlation between worsening of OA and increased TLR immunostaining in the superficial and middle cartilage zones, while chondrocytes assumed a CD166(×) progenitor phenotype. Correspondingly, TLR expression was high soon after differentiation of mesenchymal stem cells to chondrocytes. With maturation, it declined (TLR2, TLR9).Mature chondrocytes express TLR1 and TLR2 and may react to cartilage matrix/chondrocyte-derived danger signals or degradation products. This leads to synthesis of pro-inflammatory cytokines, which stimulate further TLR and cytokine expression, establishing a vicious circle. This suggests that OA can act as an autoinflammatory disease and links the old mechanical wear-and-tear concept with modern biochemical views of OA. These findings suggest that the chondrocyte itself is the earliest and most important inflammatory cell in OA.

    View details for DOI 10.3109/17453674.2013.854666

    View details for Web of Science ID 000328281100014

    View details for PubMedID 24237425

  • The response of macrophages to titanium particles is determined by macrophage polarization ACTA BIOMATERIALIA Pajarinen, J., Kouri, V., Jamsen, E., Li, T., Mandelin, J., Konttinen, Y. T. 2013; 9 (11): 9229-9240

    Abstract

    Aseptic loosening of total joint replacements is driven by the reaction of macrophages to foreign body particles released from the implant. It was hypothesized that the macrophages' response to these particles is dependent, in addition to particle characteristics and contaminating biomolecules, on the state of macrophage polarization as determined by the local cytokine microenvironment. To test this hypothesis we differentiated M1 and M2 macrophages from human peripheral blood monocytes and compared their responses to titanium particles using genome-wide microarray analysis and a multiplex cytokine assay. In comparison to non-activated M0 macrophages, the overall chemotactic and inflammatory responses to titanium particles were greatly enhanced in M1 macrophages and effectively suppressed in M2 macrophages. In addition, the genome-wide approach revealed several novel, potentially osteolytic, particle-induced mediators, and signaling pathway analysis suggested the involvement of toll-like and nod-like receptor signaling in particle recognition. It is concluded that the magnitude of foreign body reaction caused by titanium particles is dependent on the state of macrophage polarization. Thus, by limiting the action of M1 polarizing factors, e.g. bacterial biofilm formation, in peri-implant tissues and promoting M2 macrophage polarization by biomaterial solutions or pharmacologically, it might be possible to restrict wear-particle-induced inflammation and osteolysis.

    View details for DOI 10.1016/j.actbio.2013.06.027

    View details for Web of Science ID 000326902500044

    View details for PubMedID 23827094

  • Macrophages-Key cells in the response to wear debris from joint replacements JOURNAL OF BIOMEDICAL MATERIALS RESEARCH PART A Nich, C., Takakubo, Y., Pajarinen, J., Ainola, M., Salem, A., Sillat, T., Rao, A. J., Raska, M., Tamaki, Y., Takagi, M., Konttinen, Y. T., Goodman, S. B., Gallo, J. 2013; 101 (10): 3033-3045
  • Mutant monocyte chemoattractant protein 1 protein attenuates migration of and inflammatory cytokine release by macrophages exposed to orthopedic implant wear particles. Journal of biomedical materials research. Part A Yao, Z., Keeney, M., Lin, T. H., Pajarinen, J., Barcay, K., Waters, H., Egashira, K., Yang, F., Goodman, S. 2013

    Abstract

    Wear particles generated from total joint replacements can stimulate macrophages to release chemokines, such as monocyte chemoattractant protein 1 (MCP-1), which is the most important chemokine regulating systemic and local cell trafficking and infiltration of monocyte/macrophages in chronic inflammation. One possible strategy to curtail the adverse events associated with wear particles is to mitigate migration and activation of monocyte/macrophages. The purpose of this study is to modulate the adverse effects of particulate biomaterials and inflammatory stimuli such as endotoxin by interfering with the biological effects of the chemokine MCP-1. In the current study, the function of MCP-1 was inhibited by the mutant MCP-1 protein called 7ND, which blocks its receptor, the C-C chemokine receptor type 2 (CCR2) on macrophages. Addition of 7ND decreased MCP-1-induced migration of THP-1 cells in cell migration experiments in a dose-dependent manner. Conditioned media from murine macrophages exposed to clinically relevant polymethylmethacrylate (PMMA) particles with/without endotoxin [lipopolysaccharide (LPS)] had a chemotactic effect on human macrophages, which was decreased dramatically by 7ND. 7ND demonstrated no adverse effects on the viability of macrophages, and the capability of mesenchymal stem cells (MSCs) to form bone at the doses tested. Finally, proinflammatory cytokine production was mitigated when macrophages were exposed to PMMA particles with/without LPS in the presence of 7ND. Our studies confirm that the MCP-1 mutant protein 7ND can decrease macrophage migration and inflammatory cytokine release without adverse effects at the doses tested. Local delivery of 7ND at the implant site may provide a therapeutic strategy to diminish particle-associated periprosthetic inflammation and osteolysis. © 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part A, 2013.

    View details for DOI 10.1002/jbm.a.34981

    View details for PubMedID 24123855

  • SURGERY Adverse reactions to metal-on-metal implants NATURE REVIEWS RHEUMATOLOGY Konttinen, Y. T., Pajarinen, J. 2013; 9 (1): 5-6
  • RANKL in the osteolysis of AES total ankle replacement implants BONE Koivu, H., Mackiewicz, Z., Takakubo, Y., Trokovic, N., Pajarinen, J., KONTTINEN, Y. T. 2012; 51 (3): 546-552

    Abstract

    Peri-implant tissue reactions in failed total ankle replacement (TAR) are characterized by early developing peri-implant osteolysis. The hypothesis of the study was that this reaction is mediated by receptor activator of nuclear factor kappa B ligand (RANKL). Samples of peri-prosthetic tissues from failed TAR implants were stained for macrophages, RANKL, its receptor RANK and osteoprotegerin (OPG), and compared to control samples. The failed TAR implants were surrounded by implant capsule, synovial lining-like interface membrane or necrotic tissues. Infiltrating scavenger receptor I positive CD163(+) macrophages were frequent, in particular around necrotic soft tissues or bone sequestrate, and possibly in part formed due to ischemia and mechanical factors. In contrast, implant-derived wear debris was scanty. Still many RANK(+) macrophages were often seen in close contact with RANKL(+) mesenchymal cells, whereas OPG was mostly located at a distance in vascular endothelial cells. Foreign body giant cells were frequent. RANKL seems to stimulate locally accumulated CD163(+) RANK-expressing cells to fusion, which leads to the local formation of multinuclear foreign body giant cells (and probably of osteoclasts). Therefore, peri-implant osteolysis in early TAR implant failure seems to be caused by the RANKL-driven chronic foreign body inflammation directed against, not implant-derived particles, but against necrotic autologous tissues.

    View details for DOI 10.1016/j.bone.2012.05.007

    View details for Web of Science ID 000307617400029

    View details for PubMedID 22627031

  • Profile of toll-like receptor-positive cells in septic and aseptic loosening of total hip arthroplasty implants. Journal of biomedical materials research. Part A Pajarinen, J., Cenni, E., Savarino, L., Gomez-Barrena, E., Tamaki, Y., Takagi, M., Salo, J., Konttinen, Y. T. 2010; 94 (1): 84-92

    Abstract

    Distinction between the two major complications of total hip replacement surgery, septic bacterial culture-positive and aseptic bacterial culture-negative osteolysis and loosening, is difficult due to the eventual role of bacterial remnants and biofilms, which are recognized by cells provided by toll-like receptors (TLRs) of the innate immune system. It was hypothesized that cell typing and TLR mapping might provide new information on the pathomechanisms of loosening. To test this hypothesis, septic (n = 10) and aseptic (n = 5) interface tissue as well as mildly inflamed osteoarthritic synovial membrane (n = 5) samples were characterized and compared using antibodies against several cell line-specific markers, including fibroblast, monocyte/macrophage, T cell, B cell, plasma cell and neutrophil markers, and TLRs. In osteoarthritic synovium, TLR-positive cells were restricted to surface tissues and only few inflammatory cells were detected, whereas aseptic interface was heavily infiltrated with monocyte/macrophages, which were also the major TLR-positive cell type rendering the tissue reactive to TLR ligands. Interestingly, septic cases contained also neutrophil and lymphocyte infiltrates of which especially B-cell infiltrates might be clinically useful in discriminating the two major complications of the joint replacement surgery. (c) 2010 Wiley Periodicals, Inc. J Biomed Mater Res, 2010.

    View details for DOI 10.1002/jbm.a.32674

    View details for PubMedID 20127718

  • Titanium particles modulate expression of Toll-like receptor proteins JOURNAL OF BIOMEDICAL MATERIALS RESEARCH PART A Pajarinen, J., Mackiewicz, Z., Pollanen, R., Takagi, M., Epstein, N. J., Ma, T., Goodman, S. B., Konttinen, Y. T. 2010; 92A (4): 1528-1537
  • Toll-Like Receptors and Aseptic Loosening of Hip Endoprosthesis-A Potential to Respond against Danger Signals? JOURNAL OF ORTHOPAEDIC RESEARCH Lahdeoja, T., Pajarinen, J., Kouri, V., Sillat, T., Salo, J., Konttinen, Y. T. 2010; 28 (2): 184-190

    Abstract

    Bacterial remnants and subclinical biofilms residing on prosthesis surfaces have been speculated to play a role in hip implant loosening by opsonizing otherwise relatively inert wear particles. The innate immune system recognizes these microbial pathogen-associated molecular patterns (PAMPs) using Toll-like receptors (TLRs). Our objective was to evaluate the possible presence of TLRs in aseptic synovial membrane-like interface tissue. Bacterial culture-negative, aseptic (n = 4) periprosthetic synovial membrane-like tissue was compared to osteoarthritis synovial membrane (n = 5) for the presence of cells positive for all known human functional TLRs, stained using specific antibodies by immunohistochemistry, and evaluated using morphometry. In comparison to osteoarthtritic synovium, the number of TLR-positive cells was found to be increased in the aseptic setting, reflecting the considerable macrophage infiltration to the tissues investigated. Thus aseptic periprosthetic tissue seems to be very reactive to PAMPs. It has been recently recognized that TLR do not only respond to traditional PAMPs, but also to endogenous alarmings or danger signals released from necrotic and activated cells. Alarming-TLR interaction in the periprosthetic tissue might be a novel mechanism of aseptic loosening of endoprosthesis.

    View details for DOI 10.1002/jor.20979

    View details for Web of Science ID 000273675700007

    View details for PubMedID 19725103

  • Microbial antigens mediate HLA-B27 diseases via TLRs JOURNAL OF AUTOIMMUNITY Pollanen, R., Sillat, T., Pajarinen, J., Levon, J., Kaivosoja, E., Konttinen, Y. T. 2009; 32 (3-4): 172-177

    Abstract

    HLA-B27 positive individuals are predisposed to reactive arthritis developing 1-3 weeks after urogenital and gastrointestinal infections. Also ankylosing spondylitis (AS) associates strongly to HLA-B27, but no specific infection, Klebsiella pneumoniae excluded, has been linked to it. Before the discovery of its HLA-B27 association there were many reports suggesting a link between chronic prostatitis in men or pelvic inflammatory disease in women and AS. They have since been forgotten although HLA-B27 did not help to understand, why this disease has an axial and ascending nature. It is proposed that the urogenital organs form a source of damage (or danger)-associated molecular patterns (DAMPs), either exogenous pathogen-associated molecular patterns (PAMPs) from microbes or endogenous alarmins, such as uric acid, released from necrotic cells or urate deposits. DAMPs are slowly seeded from low-down upwards via the pelvic and spinal lymphatic pathways. They reach Toll-like receptors (TLRs) in their target mesenchymal stem cells, which are stimulated to ectopic enchondral bone formation leading to syndesmophytes and bamboo spine. At the same time inflammatory cytokines induce secondary osteoporosis of the spine. This new paradigm places microbes, HLA-B27 and TLRs in the pathogenic centre stage, but without pinpointing any (one) specific pathogen; instead, shared microbial patterns are indicated.

    View details for DOI 10.1016/j.jaut.2009.02.010

    View details for Web of Science ID 000266510300004

    View details for PubMedID 19299108

  • Receptor activator of nuclear factor kappa B ligand in an experimental intervertebral disc degeneration CLINICAL AND EXPERIMENTAL RHEUMATOLOGY Mackiewicz, Z., Salo, J., Konttinen, Y. T., Holm, A. K., Indahl, A., Pajarinen, J., Holm, S. 2009; 27 (2): 299-306

    Abstract

    This study was designed to clarify the role of the receptor activator of nuclear factor kappa B ligand (RANKL) in the process of discus degeneration and spondylarthrosis. It was hypothesized that experimental discus lesion would initiate not only local bone remodelling but also increased osteoclast formation on a location remote to the injury site due to altered spinal biomechanics. It was speculated that these changes in vertebral bone remodelling could be reflected in an increased RANKL expression.The presence of RANKL in the spine was studied in an experimental perforating lesion of the cranial endplate of L4 and the adjoining disc in six domestic pigs and in one human herniated disc. After three months, the experimental and contiguous control vertebrae, complete with intervertebral discs, were subjected for immunohistochemistry.This is the first study to show that RANKL was locally seen (produced) in osteoblasts, fibroblasts replacing annulocytes and mesenchymal bone marrow cells and, in part, apparently bound to the surface of osteoclasts and macrophage-like prefusion macrophages. Such RANKL induction was also seen at sites remote from the experimental lesion driving the whole process. More RANKL-positive cells were found in close proximity to the endplate than in the central parts of the vertebrae. Osteocytes in bone matrix and most bone marrow cells in the marrow microenvironment showed no RANKL staining. Human annulus fibrosus also contained RANKL, RANK and OPG.We have demonstrated that RANKL is produced locally, also in soluble form, at the site of injury and also in intact vertebrae and bony structures likely due to altered biomechanics. It seems to be engaged in bone healing and remodelling, essentially proving our working hypothesis. These secondary bone changes could represent part of the degenerative spine disease (spondylarthrosis). RANKL inhibitors, like recombinant human osteoprotegerin (OPG), could be interesting drugs to test, not only in osteoporosis, but also in spondylarthrosis.

    View details for Web of Science ID 000266096700081

    View details for PubMedID 19473572

Stanford Medicine Resources: