Development of a peri-implantitis model in the rat.

OBJECTIVES: The aim of the present study was to establish a rodent peri-implantitis model induced by a mixed bacterial infection characterized by bone loss and semi-quantitative graduation of peri-implant inflammation in histological sections. MATERIALS AND METHODS: Two titanium implants were implanted in Sprague-Dawley rats, bilaterally in each maxilla. After 3 weeks healing, the rats were randomized into three groups according to different treatments over the next 3 months: Antibiotic-Group with oral lavage of antibiotics; Bacteria-Group with oral lavage of Streptococcus oralis and Aggregatibacter actinomycetemcomitans; and Untreated Group with standard housing and no additional treatment. Maxillae were dissected to perform microscopic and histological analysis of bone height and peri-implant tissues. RESULTS: The bone level, measured at one implant site per animal, in the Bacteria-Group (2.60 ± 0.39 mm) was significantly reduced compared to the Antibiotic-Group (2.29 ± 0.32 mm) after 3 months. The differences of bone height in the Bacteria-Group and the Untreated Group (2.46 ± 0.27 mm) did not reach statistical significance. The inflammatory response with respect to the number of inflammatory cells and fibrous tissue compartments of the peri-implant tissues in the Bacteria-Group was significantly increased compared with the Antibiotic-Group (p < .05). S. oralis and A. actinomycetemcomitans DNAs were detected in the Bacteria-Group. CONCLUSIONS: This rat model of peri-implantitis used oral bacterial lavage for the induction of an inflammatory host response and bone loss. Additional bacterial treatment enhances the peri-implant phenotype, so that significant differences to a reduced bacterial load similar to the human peri-implantitis disease can be identified.

Interleukin-1alpha treatment of meniscal explants stimulates the production and release of aggrecanase-generated, GAG-substituted aggrecan products and also the release of pre-formed, aggrecanase-generated G1 and m-calpain-generated G1-G2.

Pro-inflammatory cytokines induce meniscal matrix degradation and inhibition of endogenous repair mechanisms, but the pathogenic mechanisms behind this are mostly unknown. Therefore, we investigated details of interleukin-1 (IL-1alpha)-induced aggrecan turnover in mature meniscal tissue explants. Fibro-cartilagenous disks (3 mm diameter x 1 mm thickness) were isolated from the central, weight-bearing region of menisci from 2-year-old cattle. After 3 or 6 days of IL-1alpha-treatment, GAG loss (DMMB assay), biosynthetic activity ([(35)SO(4)]-sulfate and [(3)H]-proline incorporation), gene expression (quantitative RT-PCR) and the abundance (zymography, Western blot) of matrix-degrading enzymes and specific aggrecan products were determined. Meniscal fibrocartilage had a 4-fold lower GAG content (per wet weight) than adjacent articular cartilage, and expressed MMPs-1, -2, -3 and ADAMTS4 constitutively, whereas ADAMTS5 m-RNA was essentially undetectable. Significant IL-1 effects were a decrease in biosynthetic activity, an increase in GAG release and in the expression/abundance of MMP-2, MMP-3 and ADAMTS4. Fresh tissue contained aggrecan core protein products similar to those previously described for bovine articular cartilage of this age. IL-1 induced the release of aggrecanase-generated CS-substituted products including both high (>250 kDa) and low molecular weight (about 75 kDa) species. TIMP-3 (but not TIMP-1 and -2 or a broad spectrum MMP inhibitor) inhibited IL-1-dependent GAG loss. In addition, IL-1 induced the release of preformed pools of three known G1-bearing products. We conclude that aggrecanases are responsible for IL-1-stimulated GAG release from meniscal explants, and that IL-1 also stimulates release of G1-bearing products, by a process possibly involving hyaluronan fragmentation.

Tumor necrosis factor alpha-dependent aggrecan cleavage and release of glycosaminoglycans in the meniscus is mediated by nitrous oxide-independent aggrecanase activity in vitro.

INTRODUCTION: Little is known about factors that induce meniscus damage. Since joint inflammation appears to be a causative factor for meniscal destruction, we investigated the influence of tumor necrosis factor (TNFalpha) on glycosaminoglycan (GAG) release and aggrecan cleavage in an in vitro model. METHODS: Meniscal explant disks (3 mm diameter x 1 mm thickness) were isolated from 2-year-old cattle. After 3 days of TNFalpha-treatment GAG release (DMMB assay), biosynthetic activity (sulfate incorporation), nitric oxide (NO) production (Griess assay), gene expression of matrix-degrading enzymes (quantitative RT-PCR, zymography), and immunostaining of the aggrecan fragment NITEGE were determined. RESULTS: TNFalpha induced release of GAG as well as production of NO in a dose-dependent manner, while sulfate incorporation was decreased. TNFalpha increased matrix metalloproteinase (MMP)-3 and a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS)-4 mRNA expression, whereas collagen type I was decreased, and aggrecan, collagen type II as well as MMP-1, -2, -13 and ADAMTS-5 were variably affected. Zymography also showed a TNFalpha-dependent increase in MMP-3 expression, but pre-dominantly in the pro-form. TNFalpha-dependent formation of the aggrecanase-specific aggrecan neoepitope NITEGE was induced. Tissue inhibitor of metalloproteinases (TIMP)-3, but not TIMP-1 or -2 inhibited TNFalpha-dependent GAG release and NITEGE production, whereas inhibition of TNFalpha-dependent NO generation with the NO-synthetase inhibitor L-NMMA failed to inhibit GAG release and NITEGE production. CONCLUSIONS: Our study shows that aggrecanase activity (a) is responsible for early TNFalpha-dependent aggrecan cleavage and GAG release in the meniscus and (b) might be involved in meniscal degeneration. Additionally, the meniscus is a TNFalpha-dependent source for MMP-3. However, the TNFalpha-dependent NO production seems not to be involved in release of proteoglycans under the given circumstances.