Copovidone-related Cutaneous Response in the Dog.

A cutaneous response (localized swelling and/or erythema of the skin) has been noted in dog toxicology studies in which multiple, unrelated compounds were administered orally with copovidone as a vehicle. The response has been noted in studies with 6 different test items that are structurally unrelated and span several different therapeutic indications spanning an approximate 6-year period (2009-2015). A factor common among the studies is the formulation-a copovidone amorphous solid dispersion (ASD). Cutaneous responses have not been observed in dogs administered non-ASD formulations of the same test items but have occasionally been noted in placebo (copovidone control) dogs. Polyvinylpyrrolidone (a polymer of one of the primary components of copovidone) has been reported to result in similar findings in dogs when administered by the intravenous route. Considerations for the role of copovidone and the potential role of histamine in the cutaneous changes are outlined.

Quantification of Hepcidin-related Iron Accumulation in the Rat Liver.

Hepcidin was originally detected as a liver peptide with antimicrobial activity and it functions as a central regulator in the systemic iron metabolism. Consequently suppression of hepcidin leads to iron accumulation in the liver. AbbVie developed a monoclonal antibody ([mAb]; repulsive guidance molecule [RGMa/c] mAb) that downregulates hepcidin expression by influencing the RGMc/bone morphogenetic protein (BMP)/neogenin receptor complex and causes iron deposition in the liver. In a dose range finding study with RGMa/c mAb, rats were treated with different dose levels for a total of 4 weekly doses. The results of this morphometric analysis in the liver showed that iron accumulation is not homogenous between liver lobes and the left lateral lobe was the most responsive lobe in the rat. Quantitative hepcidin messenger RNA analysis showed that the left lateral lobe was the most responsive lobe showing hepcidin downregulation with increasing antibody dose. In addition, the morphometric analysis had higher sensitivity than the chemical iron extraction and quantification using a colorimetric assay. In conclusion, the Prussian blue stain in combination with semi-quantitative and quantitative morphometric analysis is the most reliable method to demonstrate iron accumulation in the liver compared to direct measurement of iron in unfixed tissue using a colorimetric assay.

A retrospective evaluation of species-specific sensitivity for neurological signs in toxicological studies: Is the dog more sensitive than the non-human primate?

Selection of the appropriate non-rodent species in preclinical programs is crucial for good translatability and human safety. There is no data available in the literature which provides exact comparison of dog and non-human primate (NHP) sensitivity regarding neurological signs in toxicological studies. We performed a retrospective analysis of 174 toxicity studies with 15 neuroscience substances. Neurological signs in dogs and NHPs were evaluated in correlation to exposure data. Overall incidence of substance induced convulsions was similar in both species and no gender differences were observed. The reported liability of beagles to spontaneous convulsions was not confirmed in our studies. The symptom tremor showed the best inter-species translatability. The current toxicological study design does not include exposure assessment at the time-point of neurological signs, therefore, we propose to include additional toxicokinetic samples. Our analysis revealed factors including housing, handling, and behavior, which prevents direct species comparison. In addition only one non-rodent species is routinely tested in development programs, therefore data for both species is rare. We however, had sufficient data which enabled comparison for one compound. In the spirit of 3Rs further examples should be evaluated.

Recommendations from a global cross-company data sharing initiative on the incorporation of recovery phase animals in safety assessment studies to support first-in-human clinical trials.

An international expert group which includes 30 organisations (pharmaceutical companies, contract research organisations, academic institutions and regulatory bodies) has shared data on the use of recovery animals in the assessment of pharmaceutical safety for early development. These data have been used as an evidence-base to make recommendations on the inclusion of recovery animals in toxicology studies to achieve scientific objectives, while reducing animal use. Recovery animals are used in pharmaceutical development to provide information on the potential for a toxic effect to translate into long-term human risk. They are included on toxicology studies to assess whether effects observed during dosing persist or reverse once treatment ends. The group devised a questionnaire to collect information on the use of recovery animals in general regulatory toxicology studies to support first-in-human studies. Questions focused on study design, the rationale behind inclusion or exclusion and the impact this had on internal and regulatory decisions. Data on 137 compounds (including 53 biologicals and 78 small molecules) from 259 studies showed wide variation in where, when and why recovery animals were included. An analysis of individual study and programme design shows that there are opportunities to reduce the use of recovery animals without impacting drug development.

Establishment of a new methicillin resistant Staphylococcus aureus animal model of osteomyelitis.

PURPOSE: The increase in methicillin-resistant Staphylococcus aureus (MRSA) infections is currently a major health care problem. Vancomycin is still often the first-line anti-microbiological agent for treating such infections; however, a recent decline in efficacy of vancomycin in MRSA infections has raised concerns and accelerated the search for new antibiotics. The aim of this study was to establish a MRSA peri-implant osteomyelitis animal model for future testing of new anti-microbiological agents under typical MRSA infection conditions. METHODS: Eighteen randomised NZW-rabbits underwent a standardised surgical procedure with the insertion of a femoral bone implant. Animals were then divided into group 1 (MRSA inoculation, no antibiotics; M/N), group 2 (MRSA inoculation, Vancomyin; M/V), and group 3 (no MRSA inoculation, no antibiotics; N/N). The primary study outcome parameters were animal leucocyte count, animal weight, and animal body temperature at one, seven, and 42 days after surgery. Additionally, a histo-morphometrical score was established and adjusted to a modified histological Smeltzer score. RESULTS: Macroscopic and histo-morphometrical findings showed a peri-implant osteomyelitis in group 1 with both increased acute and chronic infection parameters in M/N, as compared to M/V and N/N, indicating that vancomycin treatment prevented typical morphological changes of MRSA peri-implant osteomyelitis. Similarly, there was a reduction in animal weight and increase in leucocyte count and body temperature in group 1 (each p < 0.005). Vancomycin treatment again resulted in significantly reduced leucocyte count and body temperature, and increased animal body weight. CONCLUSIONS: Here we have established a peri-implant MRSA osteomyelitis model that successfully combined clinical and laboratory outcome parameters of infection with histo-morphometrical results; this model appears to be valuable for future experimental use and therapeutic monitoring of new anti-microbiological MRSA drugs.

The inhibin B response to testicular toxicants ethylene glycol monomethyl ether or dibromoacetic acid in male rats.

BACKGROUND: This study was conducted as part of an ILSI-HESIconsortium effort to assess the utility of circulating inhibin B as an early biomarker of testicular toxicity in rats. METHODS: Two known testicular toxicants were selected for use in this study: ethylene glycol monomethyl ether (EGME) and dibromoacetic acid (DBAA). EGME (200 mg/kg/day), DBAA (250 mg/kg/day), or vehicle control (0.2% hydroxypropyl methylcellulose [HPMC]) was administered orally to male rats for 3, 6, or 14 consecutive days. On study days 4, 7, and 15, serum was collected for evaluation of inhibin B levels from all surviving animals and a subset of animals was necropsied from each of the control, EGME, and DBAAgroups. RESULTS: Administration of EGMEresulted in spermatocyte degeneration in late stage tubules and spermatocyte depletion to stage III on day 4, progressing to loss of spermatocytes and round spermatids to stage VI by day 7 and continued germ cell loss and degeneration of elongating spermatids by day 15. Inhibin B levels among EGME-treated animals progressively decreased relative to their respective controls at all time points. Administration of DBAA was associated with spermatid retention at all three time points and abnormal residual bodies at days 7 and 15. Inhibin B levels among DBAA-treated animals decreased progressively relative to their respective controls on days 7 and 15. CONCLUSIONS: Serum inhibin B levels in rats provided a signal of testicular toxicity for each of these known testicular toxicants administered at high levels; however, histopathology provided the earliest evidence of toxic effects.

Implant stability in the treatment of MRSA bone implant infections with linezolid versus vancomycin in a rabbit model.

The increasing prevalence of methicillin-resistant Staphylococcus aureus (MRSA) infections represents a significant healthcare burden. Vancomycin and linezolid exhibit potent clinical and microbiological activity in MRSA infections. Our purpose was to investigate the efficacy of linezolid versus vancomycin in experimental implant infections and the influence on implant stability in a rabbit model. Thirty-six female New Zealand White rabbits received surgical insertion of titanium implants into their distal femurs and were randomly assigned to six groups (A: infected, no treatment; B: infected, vancomycin; C: infected, linezolid; D: no infection, no treatment; E/F: no infection, vancomycin or linezolid, respectively). Antibiotics were administered, and plasma levels determined. Bone-implant specimens were tested for mechanical stability of fixation. Quantitative histomorphometry of bone and soft tissue was performed using computerized image analysis. Plasma levels of linezolid and vancomycin were within the respective therapeutic ranges. Microbiological analysis of specimens from infected rabbits showed MRSA tissue colonization in all untreated animals, in two of six vancomycin-treated animals, and in none of the linezolid-treated animals. Antibiotic treatment improved mechanical stability significantly (p = 0.004) with both vancomycin and linezolid. Mechanical testing correlated with histomorphometry results. A significant negative correlation was found between displacement of the implant and the percentage of calcified tissue around the implant, and a significant positive correlation was found between displacement of the implant and the amount of noncalcified tissue. Our data indicate that both treatment regimens improved implant stability.

Bone Substitute Effect on Vascularization and Bone Remodeling after Application of phVEGF165 Transfected BMSC.

VEGF (vascular endothelial growth factor) promotes vascularization and remodeling of bone substitutes. The aim of this study was to examine the effect of distinct resorbable ceramic carriers on bone forming capacities of VEGF transfected bone marrow stromal cells (BMSC). A critical size defect of the radius in rabbits was filled either by a low surface scaffold called beta-TCP (tricalciumphsphate) or the high surface scaffold CDHA (calcium deficient hydroxy-apatite) loaded with autologous BMSC, which were either transfected with a control plasmid or a plasmid coding for phVEGF165. They were compared to unloaded scaffolds. Thus, six treatment groups (n = 6 in each group) were followed by X-ray over 16 weeks. After probe retrieval, the volume of new bone was measured by micro-CT scans and vascularization was assessed in histology. While only minor bone formation was found in both carriers when implanted alone, BMSC led to increased osteogenesis in both carriers. VEGF promoted vascularization of the scaffolds significantly in contrast to BMSC alone. Bone formation was increased in the beta-TCP group, whereas it was inhibited in the CDHA group that showed faster scaffold degradation. The results indicate that the interaction of VEGF transfected BMSC with resorbable ceramic carrier influences the ability to promote bone healing.

A new porcine in vivo animal model of disc degeneration: response of anulus fibrosus cells, chondrocyte-like nucleus pulposus cells, and notochordal nucleus pulposus cells to partial nucleotomy.

STUDY DESIGN: In vivo animal study. OBJECTIVES: To describe a new porcine disc degeneration model, and to analyze disc remodeling and degeneration after nucleotomy with special view to the different nucleus pulposus (NP) cell types. SUMMARY OF BACKGROUND DATA: Thus far, predominantly smaller animals were used for disc degeneration models; however, such small discs were inappropriate to investigate cell implementation therapies. Though notochordal cells (NCs) are important for disc formation and maintenance, differences in the amount of NCs between human and animal discs have often been neglected. METHODS: Twenty-four Goettingen minipigs underwent partial nucleotomy with a 16G biopsy cannula, to remove approximately 10% of total NP volume. Animals were followed up for 3, or 24 weeks and analyzed by radiographs, MRIs, (immuno)histology, gene expression analysis, and biomechanical testing. RESULTS: Three weeks after nucleotomy disc height was reduced by 26%, and magnetic resonance imaging signal intensity by 40%. At 24 weeks disc height was decreased by 32%. Increased degenerative changes were found in a histodegeneration score 3 and 24 weeks after nucleotomy, as well as considerable NP scarification after 3 weeks. In controls, cytokeratin-8 immunohistochemistry identified NCs in proximity to chondrocyte-like NP cells at approximately equal ratio. After nucleotomy, NCs were considerably reduced to <10% of total NP cells. Matrix genes were upregulated, except for aggrecan that decreased to 35% of initial values 3 weeks after nucleotomy. Matrix degrading factors (matrix metalloproteinases 13 and 3) were continuously upregulated, whereas transcripts of their inhibitors (tissue inhibitors of matrix metalloproteinase 2 and 3) were downregulated. No significant changes in segmental spinal flexibility or bone density were found after nucleotomy. CONCLUSION: We introduced a new disc degeneration model with relatively large discs that could be used for cell therapeutic approaches. The study gives further information about disc remodeling after nucleotomy and indicates the relevance of an altered cellular composition for the development of disc degeneration.

Mesenchymal stem cell differentiation in an experimental cartilage defect: restriction of hypertrophy to bone-close neocartilage.

Mesenchymal stem cells (MSCs) are promising for the treatment of articular cartilage defects; however, common protocols for in vitro chondrogenesis induce typical features of hypertrophic chondrocytes reminiscent of endochondral bone formation. Aim of the study was to compare chondrogenic differentiation of MSCs in vitro and in vivo in experimental full-thickness cartilage defects, asking whether MSCs can differentiate into collagen type X-negative chondrocytes in an orthotopic environment. Cartilage defects in knees of minipigs were covered with a collagen type I/III membrane, and half of them received transplantation of expanded autologous MSCs. At 1, 3, and 8 weeks, morphological and molecular aspects of repair were assessed. The orthotopic environment triggered a spatially organized repair tissue with upper fibrous, intermediate chondrogenic, and low layer hypertrophic differentiation of cells and a trend to more safranin-O and collagen type II-positive samples after MSC transplantation at 8 weeks. Compared to in vitro chondrogenesis, significant lower COL10A1/COL2A1 and MMP13/COL2A1 ratios were obtained for in vivo differentiation. This indicates that, as opposed to in vitro chondrogenic induction of MSCs, the in vivo signaling molecules and biomechanical stimuli provide an appropriate environment for progenitor cells to differentiate into collagen type X-negative chondrocytes. Thus, until better in vitro induction protocols become available for chondrogenesis of MSCs, their predifferentiation before transplantation may be unfavorable.

Secretion of matrix metalloproteinase 3 by expanded articular chondrocytes as a predictor of ectopic cartilage formation capacity in vivo.

OBJECTIVE: Monolayer expansion of human articular chondrocytes (HACs) is known to result in progressive dedifferentiation of the chondrocytes and loss of their stable cartilage formation capacity in vivo. For an optimal outcome of chondrocyte-based repair strategies, HACs capable of ectopic cartilage formation may be required. This study was undertaken to identify secreted candidate molecules, in supernatants of cultured HACs, that could serve as predictors of the ectopic cartilage formation capacity of cells. METHODS: Standardized medium supernatants (n = 5 knee cartilage samples) of freshly isolated HACs (PD0) and of HACs expanded for 2 or 6 population doublings (PD2 and PD6, respectively) were screened by a multiplexed immunoassay for 15 distinct interleukins, 8 matrix metalloproteinases (MMPs), and 11 miscellaneous soluble factors. Cartilage differentiation markers such as cartilage oligomeric matrix protein and YKL-40 were determined by enzyme-linked immunosorbent assay. HACs from each culture were subcutaneously transplanted into SCID mice, and the capacity of the chondrocytes to form stable cartilage was examined histologically 4 weeks later. RESULTS: Whereas freshly isolated (PD0) HACs generated stable ectopic cartilage that was positive for type II collagen, none of the cell transplants at PD6 formed cartilaginous matrix. Loss of the ectopic cartilage formation capacity between PD0 and PD6 correlated with a drop in the secretion of MMP-3 to <10% of initial levels, whereas changes in the other investigated molecules were not predictive. Chondrocytes with MMP-3 levels of >or=20% of initial levels synthesized cartilaginous matrix, whereas those with low MMP-3 levels (<10% of initial levels) at PD2 failed to regenerate ectopic cartilage. CONCLUSION: Loss of the capacity for stable ectopic cartilage formation in the course of HAC dedifferentiation can be predicted by determining the relative levels of MMP-3, demonstrating that standardized culture supernatants can be used for quality control of chondrocytes dedicated for cell therapeutic approaches.

Improved osseointegration of PTFEP-coated titanium implants.

BACKGROUND: Clinical success of bone implants is critically related to the interaction between the implant surface and the surrounding tissue. The polymer poly(bis(trifluoroethoxy)phosphazene) (PTFEP) is a promising, highly biocompatible surface coating which also inhibits the adsorption of granulocytes, macrophages, inflammatory cells, bacteria, and platelets. However, there is limited clinical experience of PTFEP as a coating for bone implants. Therefore PTFEP-coated titanium implants in an animal model were examined. MATERIAL/METHODS: PTFEP-coated titanium cylinders were implanted into the lateral femoral condyles of rabbits. Osseointegration was examined six weeks and six months after implantation using a non-destructive mechanical pull-out measurement and a histological analysis. RESULTS: The results indicate improved osseointegration of PTFEP-coated implants. Six weeks after implantation, the PTFEP-coated implants showed a higher stiffness (pull-out length [pol]=7.1+/-2.0 microm) compared with uncoated cylinders (pol=10.2+/-3.4 microm, p<0.05). Six months after implantation, the mechanical properties of both implants had adjusted, and histological analysis revealed an increased bone-implant interface of PTFEP-coated cylinders compared with the first 6 weeks (17.5% vs. 8.2% in controls, p<0.05). CONCLUSIONS: Taken together, the results of this preliminary study indicate promising applications of PTFEP as a coating material for bone implants.

Comparison of cobalt chromium, ceramic and pyrocarbon hemiprosthesis in a rabbit model: Ceramic leads to more cartilage damage than cobalt chromium.

Cartilage wear after hemiarthroplasty remains a problem in orthopedic surgery. The main cause of cartilage wear, apart from incongruency of the joint partners, is generally considered to be the tribology of the material surfaces. This study evaluates in 27 rabbits the degree of cartilage wear of the tibia plateau after hemiarthroplasty with proximal interphalangeal prostheses made of three different materials [cobalt chromium (CoCr), pyrocarbon (PyCa), and ceramic (Cer)]. Three months after hemiarthroplasty, the articulating tibial cartilage was histomorphologically examined and degenerative damage was graded using the modified Mankin score. The mechanical capacity of the cartilage was assessed by stress relaxation testing. The biomechanical properties of the cartilage were significantly superior in the CoCr group as compared with the Cer group (p < 0.03), indicating less damage to the articulating cartilage surface. The Mankin score showed significantly lower values in the CoCr compared with Cer group (p = 0.011), whereas no differences were found between PyCa and CoCr or PyCa and Cer. In contrast to earlier reports, in this hemiarthroplasty model, the CoCr alloy showed less cartilage damage than a ceramic surface. Further, in vivo experiments are necessary to elucidate the controversial issue of the most suitable material for hemiarthroplasty.

Reduced chondrogenic potential of adipose tissue derived stromal cells correlates with an altered TGFbeta receptor and BMP profile and is overcome by BMP-6.

Recent interest has focused on mesenchymal stem cells (MSC) for tissue engineering and regenerative therapy of cartilage defects. MSC originating from adipose tissue (ATSC) are attractive as they are easily available and abundant. They have similar properties like bone marrow derived MSC (BMSC), except for a reduced chondrogenic potential under standard culture conditions driven by TGFbeta. Aim of this study was to search for possible differences explaining the reduced differentiation capacity of ATSC and to eliminate it by adaptation of induction protocols. Expanded MSC were analyzed for their growth factor and related receptor repertoire and ATSC spheroid cultures were supplemented with BMP-2,-4,-6,-7, TGFbeta, FGFa, FGFb, IGF-1, and PTHrP alone or in combination with TGFbeta. In contrast to BMSC, ATSC showed reduced expression of BMP-2, -4, and -6 mRNA and did not express TGFbeta-receptor-I protein. Consistent with this, increased concentrations of TGFbeta did not improve chondrogenesis of ATSC. BMP6 treatment induced TGFbeta-receptor-I expression and combined application of TGFbeta and BMP-6 eliminated the reduced chondrogenic potential of ATSC inducing a gene expression profile similar to differentiated BMSC. Like in BMSC, chondrogenesis of ATSC was associated with hypertrophy according to premature collagen Type X expression, upregulation of alkaline-phosphatase activity and in vivo calcification of spheroids after ectopic transplantation in SCID mice. In conclusion, a distinct BMP and TGFbeta-receptor repertoire may explain the reduced chondrogenic capacity of ATSC in vitro, which could be compensated by exogenous application of lacking factors. Further studies should now be directed to induce chondrogenesis in the absence of hypertrophy.

Disc distraction shows evidence of regenerative potential in degenerated intervertebral discs as evaluated by protein expression, magnetic resonance imaging, and messenger ribonucleic acid expression analysis.

STUDY DESIGN: An animal model of degeneration was used to determine the effects of disc distraction, and was evaluated with magnetic resonance imaging (MRI) as well as gene and protein expression levels. OBJECTIVE: To investigate gene expression and MRI effects of distraction. SUMMARY OF BACKGROUND DATA: Disc degeneration can result from hyper-physiologic loading. Distracted discs with degeneration showed histologic signs of tissue recovery. METHODS: There were 18 rabbits that underwent 28 days of compression (200 N) to induce moderate disc degeneration followed by 28 days of distraction (120 N; attached and loaded distraction device) or sham distraction (attached but unloaded distraction device). Comparison was performed with 56 days of compressed discs without distraction. Quantitative outcome measures were MRI signal intensity and gene expression analysis to determine: messenger ribonucleic acid levels for extracellular matrix genes, including collagen 1, collagen 2, biglycan, decorin, aggrecan, fibromodulin, and osteonectin; and matrix-regulative genes, including matrix metalloproteinase-13, tissue-inhibitor of matrix metalloproteinase-1, and bone morphogenetic protein (BMP)-2. Immunohistology was performed for collagen 2 and BMP-2 to label cells semiquantitatively by staining of the cell-surrounding matrix. RESULTS: A total of 28 days of compression decreased signal intensity. Distraction over the same period reestablished physiologic signal intensity, however, a persistent reduction was found in sham distraction. Distraction resulted in gene expression up-regulation of collagen 1 (5.4-fold), collagen 2 (5.5-fold), biglycan (7.7-fold), and decorin (3.4-fold), while expression of fibromodulin (0.16-fold), tissue-inhibitor of matrix metalloproteinase-1 (0.05-fold), and BMP-2 (0.15-fold) was decreased, as compared with 56 days compression. Distracted discs showed more BMP-2 (19.67 vs. 3.67 in 56 days compression) and collagen 2 (18.67 vs. 11.33 in 56 days compression) positive cells per field. CONCLUSIONS: Distraction results in disc rehydration, stimulated extracellular matrix gene expression, and increased numbers of protein-expressing cells.

Osteoarthritis: cellular and molecular changes in degenerating cartilage.

Osteoarthritis (OA) is a disease of high ethical and economical importance. In advanced stages, the patients suffer from severe pain and restriction of mobility. The consequence in many cases is an inability to work and often the substitution of the diseased joint with an artificial implant becomes inevitable. As cartilage tissue itself has only very limited capacities of self-renewing, the development of this disorder is chronic and progressive. Generally, OA is diagnosed in more advanced stages, when clinical and radiographic signs become evident. At this time point the options for therapeutic intervention without surgery are limited. It is, therefore, crucial to know about the basic incidents in the course of OA and especially in early stages to develop new diagnostic and therapeutic strategies. Numerous studies on human osteoarthritic tissue and in animal models have addressed various aspects of OA progression to get a better understanding of the pathophysiology of this disease. This review presents an overview on different aspects of OA research and the cellular and molecular alterations in degenerating cartilage.

Changes in gene expression and protein distribution at different stages of mechanically induced disc degeneration--an in vivo study on the New Zealand white rabbit.

The objective of the study was to improve the biological understanding of degenerative disc disease using a rabbit model in which different stages of disc degeneration are induced by variation of the duration of loading with an external compression-device applying 2.4 MPa. Gene expression and protein distribution were analyzed in controls and after 1, 28, and 56 days of hyperphysiologic loading. To evaluate extracellular matrix genes, quantitative real-time reverse-transcriptase polymerase chain reaction was applied for collagen I, collagen II, biglycan, decorin, fibromodulin, fibronectin, aggrecan, and osteonectin. As representatives of catabolic, anticatabolic, and anabolic factors, matrix metalloproteinase-13 (MMP-13), tissue inhibitor of matrix metalloproteinase-1 (TIMP-1), and bone morphogenetic protein-2 (BMP-2) were chosen. To evaluate protein distribution, immunohistochemistry was performed for collagen I, collagen II, and BMP-2/4. Matrix gene expression was characterized by two major developments: collagen I and II, biglycan, and decorin showed early elevation followed by later downregulation to control levels, whereas fibromodulin, fibronectin, aggrecan, and osteonectin showed continuous upregulation or remained at similar levels. Induction of MMP-13 gene expression was found in degenerated discs. TIMP-1 and BMP-2 were elevated immediately after hyperphysiologic loading and presented highest levels in the 56-day group. Immunohistochemistry showed less collagen II and BMP-2/4 positive cells after compression. In conclusion, elevated matrix gene expression represents an early cellular response to hyperphysiologic loading. As degeneration progresses, some matrix genes increase upregulation, whereas others start downregulation. Continuous upregulation of catabolic, anticatabolic, and anabolic factors indicates their important role in the degeneration process.

Osseointegration and mechanical stability of pyrocarbon and titanium hand implants in a load-bearing in vivo model for small joint arthroplasty.

PURPOSE: To test the mechanical stability and histologic osseointegration under load-bearing conditions of 2 different materials, pyrocarbon (Py) and titanium (Ti), in a rabbit model. METHODS: Proximal interphalangeal implants (9 Ti, 8 Py) were placed into rabbit knees and the animals were killed after 3 months. Subsidence was assessed by monthly x-rays. Mechanical stability was measured with a nondestructive pullout test. Implant osseointegration was evaluated by an analysis of the relative implant-calcified bone contact surface on microradiographs and by a histomorphometric analysis of the percentage of bone and connective tissue contact with the implant surface. Histologic examination included assessment of bone apposition on the basis of fluorochromes. RESULTS: Subsidence was found in all 8 Py implants but in none of the Ti group. All 9 Ti implants were mechanically stable; all 8 Py implants were loose. A significantly higher implant-bone contact was found for the Ti group compared with the Py group. Bone apposition increased with time and was highest for the Ti implants 6 weeks after implantation. CONCLUSIONS: In the rabbit model osseointegration of implants was highly dependent on the material. A reliable osseointegration was found for Ti implants. For Py implants no osseointegration or implant stability was achieved. For use of small joints of the hand we therefore recommend Ti-based implants.

Intradiscal pressure measurements in normal discs, compressed discs and compressed discs treated with axial posterior disc distraction: an experimental study on the rabbit lumbar spine model.

Intervertebral disc (IVD) pressure measurement is an appropriate method for characterizing spinal loading conditions. However, there is no human or animal model that provides sufficient IVD pressure data. The aim of our study was to establish physiological pressure values in the rabbit lumbar spine and to determine whether temporary external disc compression and distraction were associated with pressure changes. Measurements were done using a microstructure-based fibreoptic sensor. Data were collected in five control rabbits (N, measurement lying prone at segment L3/4 at day 28), five rabbits with 28 days of axial compression (C, measurement at day 28) and three rabbits with 28 days of axial compression and following 28 days of axial distraction (D, measurement at day 56). Disc compression and distraction was verified by disc height in lateral radiographs. The controls (N) showed a level-related range between 0.25 MPa-0.45 MPa. The IVD pressure was highest at level L3/4 (0.42 MPa; range 0.38-0.45) with a decrease in both cranial and caudal adjacent segments. The result for C was a significant decrease in IVD pressure (0.31 MPa) when compared with controls (P=0.009). D showed slightly higher median IVD pressure (0.32 MPa) compared to C, but significantly lower levels when compared with N (P=0.037). Our results indicate a high range of physiological IVD pressure at different levels of the lumbar rabbit spine. Temporary disc compression reduces pressure when compared with controls. These data support the hypothesis that temporary external compression leads to moderate disc degeneration as a result of degradation of water-binding disc matrix or affected active pumping mechanisms of nutrients into the disc. A stabilization of IVD pressure in discs treated with temporary distraction was observed.

Stimulation of gene expression and loss of anular architecture caused by experimental disc degeneration--an in vivo animal study.

STUDY DESIGN: An external compression model was used to evaluate gene and protein expression in intervertebral discs with moderate disc degeneration. OBJECTIVE: To determine messenger ribonucleic acid and protein expression levels of relevant disc components. SUMMARY OF BACKGROUND DATA: An animal model of mechanically induced disc degeneration was developed and characterized histologically. However, little is known at the molecular level in moderate disc degeneration. METHODS: There were 8 New Zealand white rabbits subjected to monosegmental posterior compression to induce moderate disc degeneration. Twelve animals served as controls or sham controls. Discs were analyzed using immunohistochemistry for collagen type 1 (COL1), COL2, aggrecan, and bone morphogenetic protein-2/4 (BMP-2/4). For gene analysis, conventional and quantitative polymerase chain reactions were used for COL1A2, COL2A1, aggrecan, BMP-2, biglycan, decorin, osteonectin, fibromodulin, fibronectin, matrix metalloproteinase-13 (MMP-13), and tissue inhibitor of MMP-1. Gene expression for nontreated, sham-treated, and compressed discs was quantified in relation to the housekeeping gene glyceraldehyde-3-phosphate dehydrogenase. RESULTS: Immunohistochemistry of compressed discs showed a loss of anular architecture, and a significant reduction of BMP-2/4 and COL2 positive cells. Gene expression analysis showed a significant up-regulation of COL1A2, osteonectin, decorin, fibronectin, tissue inhibitor of MMP-1, BMP-2, and MMP-13 in compressed discs. CONCLUSIONS: Experimental moderate disc degeneration is characterized by a loss of BMP-2/4 and COL2 positive cells, although gene expression of disc constituents, catabolic enzymes, and growth factors is stimulated to reestablish disc integrity.