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Biomedical subjects

J Steinmeyer

Publications and source records attributed to J Steinmeyer.

At least 19 recordsLinked to original sources
PubMed2005

Collagen biosynthesis of mechanically loaded articular cartilage explants.

OBJECTIVE: The purpose of this study was to investigate systematically the effect of load amplitudes, frequencies and load durations of intermittently applied mechanical pressure on the biosynthesis of collagen and non-collagenous proteins (NCP) as well as on the water content of cultured bovine articular cartilage explants. METHODS: Cyclic compressive pressure was applied using a sinusoidal waveform of 0.5 Hz frequency with a peak stress of 0.1, 0.5 or 1.0 MPa for a period of 10s followed by a load-free period of 10, 100 or 1000s. These intermittent loading protocols were repeated for a total duration of 1, 3 or 6 days. During the final 18 h of experiments, the incorporation of [(3)H]-proline into collagen and NCP, the content of water as well as the deformation of loaded explants were determined. RESULTS: Intermittently applied, cyclic mechanical loading of articular cartilage explants consistently reduced the relative rate of collagen synthesis compared to load-free conditions. This reduced proportion of newly synthesized collagen among newly made proteins was independent of the mechanical stimuli applied. The release of newly synthesized collagen and NCP from loaded explants into the nutrient media was unaffected by any of the loading protocols applied. In addition, quantitative data are provided showing that only high amplitudes of loads and frequencies enhanced the water content of the explants. CONCLUSIONS: Previous studies reporting that osteoarthritic cartilage in vivo can synthesize elevated amounts of collagen imply that the loading protocols chosen were inadequate for simulating in vitro osteoarthritic-like alterations of collagen synthesis. In our experiments the collagen biosynthesis of chondrocytes was only minor responsive to alterations in mechanical stimuli, applied over a wide range. Thus, our results imply that the synthesis of these structural macromolecules is under the strict control of normal chondrocytes enabling them to maintain the shape of this physical demanded tissue.

Analysis of Variance↗
PubMed2004

[MRI in the follow-up of matrix-supported autologous chondrocyte transplantation (MACI) and microfracture].

AIM: Matrix-guided autologous chondrocyte implantation (MACI) was compared with microfracture (MFX) to demonstrate the reconstitution of cartilage over a two-year period using the morphological capabilities of MRI. PATIENTS AND METHODS: 27 patients (9 females and 18 males, mean age 33 years) underwent MACI on the knee joint. The defects originated from trauma (15 cases), osteochondritis dissecans (8 cases) and chronic repetitive trauma (4 cases) and were localized at the condyles (24 cases) or patella (3 cases). All patients were examined postoperatively after 1, 3, 6, 12 and 24 months with a 1,5 T unit (Gyroscan, Philips) using proton- and T2w spinecho and T1w fatsuppressed 3D gradientecho sequences. We measured the signal intensities of the implant and neighbouring cartilage to calculate the contrast-to-noise ratio (CNR), and the thickness of cartilage and implant layers to define the defect filling rate. Finally, partial and complete remission was defined on MRI and compared with clinical data and morphology on MRI. Additionally, 7 patients were treated with MFX and, subsequently examined on MRI with the same protocol. RESULTS: After MACI, MRI showed a partial but no complete equilibration of signal intensities of implant and adjacent cartilage over the 1 and 2 year follow-up periods which was shown by reduction of CNR from 21 to 10 on 3D-GE and from 26 to 9 on T2w SE sequences. Continuous growth of the implants resulted in an increased filling of the defects starting at 40% after 0.5 year to 85% after 1 or 2 years. Complete remission was found on MRI in 17/27 cases, and remission rate was influenced by etiology of cartilage defect but not by age and gender of patients or size and location of defects. The Lysholm-Gillquist score improved from 49.7 to 97.3. After MFX equilibration of signal intensities and growth of the regenerating fibrous cartilage was less pronounced and complete remission was found in only 2/7 cases. In addition, the clinical score improved from 45.5 to 74.2. CONCLUSION: Direct imaging of cartilage with MRI and assessment of clinical scores allowed improved documentation of the outcome after MACI and MFX. MRI showed that MACI is superior to MFX concerning rate of complete remissions and filling of the defect with regenerating tissue. Clinical examinations showed better scores for MACI than for MFX.

Adult↗
PubMed2003

Proteoglycan metabolism and viability of articular cartilage explants as modulated by the frequency of intermittent loading.

OBJECTIVE: This study was designed to systematically determine whether and to what extent the frequency of intermittent loading modulates the biosynthesis and release of proteoglycans (PGs), and to assess chondrocyte viability within mature bovine articular cartilage explants exposed to different loading patterns. METHODS: Cultured full-thickness cartilage explants from the weight-bearing area of healthy bovine fetlock joints were exposed to intermittently applied, uniaxial cyclic loads by introducing a sinusoidal waveform of 0.1, 0.5 or 1.0Hz, frequency and a peak stress of 0.5MPa for a period of 6 days. The cyclic loads were applied for 5, 10 or 20s followed by a period of unloading lasting 10, 100 or 1000s. The incorporation of radiolabeled sulfate into glycosaminoglycans (GAGs) during the final 18h, the content of GAGs and DNA, the deformation of loaded explants as well as the viability of chondrocytes within the different zones of explants were determined. RESULTS: PG synthesis and loss of endogenous PGs were non-linearly and independently regulated by the frequency of the chosen intermittent load, whereas the release of newly synthesized PGs remained unaffected. The viability of chondrocytes within the superficial zone decreased drastically under intermittent loading in a manner independent of the frequency applied. CONCLUSIONS: Our results confirm the hypothesis that the frequency of intermittent loading is an important mechanical factor controlling the metabolic activities of chondrocytes. They also implicate that an initially healthy cartilage explant can be mechanically manipulated to generate an in vitro model of degenerative, osteoarthritic-like cartilage.

Animals↗
PubMed2002

Differential effects of nonsteroidal antiinflammatory drugs on the IL-1 altered expression of plasminogen activators and plasminogen activator inhibitor-1 by articular chondrocytes.

OBJECTIVE: To determine the in vitro effects of several nonsteroidal antiinflammatory drugs on the IL-1 altered expression and activity of tPA, uPA and PAI-1 by articular chondrocytes. METHODS: Bovine chondrocytes were cultured in alginate gel beads. Cells were treated with IL-1alpha in the presence or absence of drugs at various concentrations. Expression of mRNA for the plasminogen activators (uPA and tPA) and their inhibitor (PAI-1) were analyzed by RT-PCR-ELISA. The protein content of PAI-1 in culture media was deter mined by ELISA. PA activity was measured by a functional assay. RESULTS: All tested NSAIDs dose dependently inhibited the IL-1 induced mRNA expression of tPA, whereas only indomethacin and tiaprofenic acid were also able to reduce the expression of uPA. Expression of PAI-1 was elevated by IL-1 without an accompanying increase in secreted amounts of the inhibitor. Indomethacin, naproxen and tiaprofenic acid stimulated the release of PAI-1 into culture media, whereas meloxicam also induced expression of PAI-1 above IL-1 stimulated levels. CONCLUSION: In conclusion, our studies indicate that NSAIDs preferentially inhibit tPA expression by bovine articular chondrocytes. By increasing the production of PAI-1 at therapeutical concentrations meloxicam could reduce PA activity, whereas the other NSAIDs tested mainly enhanced the release of this inhibitor from the extracellular matrix. In how far this would affect the enzyme-inhibitor balance within cartilage has to be determined in further studies.

Animals↗
PubMed2001

Effects of tetracyclines on the production of matrix metalloproteinases and plasminogen activators as well as of their natural inhibitors, tissue inhibitor of metalloproteinases-1 and plasminogen activator inhibitor-1.

OBJECTIVE: Evaluation of tetracycline effects on the expression of MMP-1, MMP-3, tissue inhibitor(s) of metalloproteinase-1 (TIMP-1), plasminogen activators (PA), and PA inhibitor-1, which are all involved in the ultimate regulation of MMP activity could provide new insight into how tetracyclines achieve their cartilage preserving effects. MATERIALS AND METHODS: We used bovine articular chondrocytes cultured in alginate gel beads for our studies which were initially treated with 10 microM tetracyclines in the presence of IL-1. Only significant effects were studied at additional concentrations. Expression of mRNA was analyzed by RT-PCR-ELISA. The activity of enzymes and TIMP was measured by functional assays; whereas, the level of PAI-1 was determined by ELISA. RESULTS: Treating chondrocytes with IL-1 induced the expression of MMPs and downregulated TIMP-1 but stimulated both the expression of PAs and PAI-1. When tested at 10 microM only minocycline reduced collagenase activity and expression of MMP-1. Further pharmacokinetic analysis revealed IC50 values of 26 microM and 16 microM for the inhibition of collagenase activity and mRNA expression, respectively. Production of MMP-3 was only decreased by tetracycline (IC50 = 45.4 microM). No effects of tetracyclines could be observed on proteoglycan degradation, TIMP activity and the production of PAs, PAI-1, and TIMP-1. CONCLUSIONS: We conclude that the inhibition of MMPs by tetracyclines occurs mainly via down-regulation of the respective gene expression.

Animals↗
PubMed2001

[Drug therapy of arthrosis].

Osteoarthritis is one of the most common and economically important chronic diseases amongst adults, especially those of a senior age. There now exists a range of effective medications, which either alone or in combination can alleviate the symptoms of the disease and improve the quality of life. Because these medications are not always sufficiently effective and must sometimes be interrupted due to side effects, a large arsenal of active agents is necessary. Alleviation of pain and inhibition of inflammation are the primary goals of pharmacotherapy, whereby the objective is to return an active or transiently painful, decompensated osteoarthritis to a latent (silent, pain-free) condition. This therapeutic goal can almost always be accomplished by using analgesics, nonsteroidal anti-inflammatory drugs (NSAIDs), or intraarticular injection of glucocorticoids. The main problem in administering NSAIDs is their gastrointestinal toxicity,for which a prophylactic medication (e.g., simultaneous application of misoprostol or switching to a COX-2 selective NSAID) should be considered especially with risk groups. The newly developed COX-2 selective NSAIDs represent a true enrichment of our therapeutic options. The spectrum of indications for COX-2 selective NSAIDs should in the future correspond to that of older NSAID preparations, providing that no as yet unknown and serious side effects come to light from their use. Pharmacological results published until now confirm that a clinically relevant analgesic and/or anti-inflammatory effect is associated with the use of SYSA-DOAs (symptomatic slow acting drugs in osteoarthritis). However, no clinical studies exist which can positively confirm prevention of morphologically recognizable cartilage defects in man, or a slowing down or reversal of any progressively developing joint cartilage destruction by any individual medication. Neither the benefits, risks, pharmaceutical quality, nor composition of Orthokin are known, and for this reason its use can not be recommended. Pharmacotherapy should only be considered as one of the three pillars of a long-term,stage-adjusted, and individually customized therapy, the other two of which are represented by nonpharmacological measures and surgical treatment.

Analgesics↗
PubMed2001

Effects of non-steroidal antiinflammatory drugs and dexamethasone on the activity and expression of matrix metalloproteinase-1, matrix metalloproteinase-3 and tissue inhibitor of metalloproteinases-1 by bovine articular chondrocytes.

OBJECTIVE: To determine the in-vitro effects of several non-steroidal antiinflammatory drugs and the glucocorticoid dexamethasone on the IL-1 altered expression and activity of MMP-1, MMP-3 and TIMP-1 by bovine articular chondrocytes. DESIGN: Bovine chondrocytes were cultured in alginate gel beads. Cells were treated with IL-1alpha in the presence of vehicle or drugs at various concentrations. After 48 h mRNA expression of MMP-1, MMP-3, and of the tissue inhibitor of metalloproteinases (TIMP-1) was analysed by RT-PCR-ELISA. The protein synthesis of TIMP-1 and MMP-3 was determined by immunoprecipitation. The activity of enzymes and inhibitors was measured by functional assays. RESULTS: IL-1 increased the expression and activity of MMPs. In contrast, TIMP activity remained unchanged although TIMP-1 expression was down-regulated. All tested NSAIDs and dexamethasone inhibited collagenase activity induced by IL-1. Transcript levels of MMP-1, however, were only reduced by indomethacin, meloxicam, naproxen and dexamethasone. Proteoglycanase activity was only reduced by indomethacin, meloxicam and dexamethasone. These effects were pre-translational as confirmed by immunoprecipitation. The IL-1 decreased expression of TIMP-1 was further reduced by dexamethasone, which resulted in a significant loss of TIMP activity. No effects on TIMP activity or TIMP-1 biosynthesis were observed after treatment of chondrocytes with NSAIDs. CONCLUSION: Our studies clearly demonstrate that marked differences exist between individual NSAIDs with respect to their ability to modulate the imbalance between proteases and inhibitors during OA and RA, suggesting that the respective modes of action are independent of the inhibition of cyclooxygenases. Due to their co-regulation of MMPs and TIMP(s) glucocorticoids should be carefully studied for their overall effect on ECM proteolysis.

Animals↗
PubMed2001

Minocycline inhibits the production of inducible nitric oxide synthase in articular chondrocytes.

OBJECTIVE: To determine the in vitro effects of tetracyclines and nonsteroidal antiiflammatory drugs on interleukin 1alpha (IL-1alpha) induced NO production and biosynthesis of inducible NO synthase (iNOS) by articular chondrocytes. METHODS: Bovine chondrocytes were cultured in alginate beads. Cells were treated with IL-lalpha in the presence or absence of drugs at various concentrations. Expression of mRNA for iNOS was analyzed by reverse transcription polymerase chain reaction-ELISA. Protein synthesis of iNOS was determined by immunoprecipitation. NO production was taken as a measure for the activity of the enzyme. RESULTS: Minocycline dose dependently reduced IL-1 stimulated NO production by inhibition of the mRNA expression (IC50 = 69.9 microM) and protein synthesis (IC50 = 37.11 microM) of iNOS. Diclofenac-Na at a concentration of 10 microM only weakly reduced nitrite accumulation and mRNA expression of iNOS. No effects were observed for tetracycline, doxycycline, and meloxicam. CONCLUSION: Inhibition of iNOS in articular chondrocytes may be a new mechanism by which minocycline could exert its beneficial effects in the treatment of joint diseases.

Animals↗
PubMed2000

Pharmacological basis for the therapy of pain and inflammation with nonsteroidal anti-inflammatory drugs.

Nonsteroidal anti-inflammatory drugs (NSAIDs) belong to the most frequently used drugs. The discovery of an inducible isoform of cyclo-oxygenase (COX-2) has led to an intensive worldwide search and the introduction of selective COX-2 inhibitors. In this review, recent advances in understanding the mechanism of action of NSAIDs and, in this context, clinical findings on NSAID-induced gastrointestinal side effects are summarized. This knowledge is important for the effective treatment of pain and inflammation, as well as for preventing serious and sometimes lethal gastrointestinal side effects.

Animals↗
PubMed1999

The effect of continuously applied cyclic mechanical loading on the fibronectin metabolism of articular cartilage explants.

Articular cartilage serves primarily as a load-bearing material able to regulate its own metabolic activity in response to the mechanical stimuli applied. Fibronectin plays a critical role in the organization and function of the cartilage extracellular matrix. The purpose of this study was to investigate systematically the effect of load magnitude, frequency and duration of loading on the synthesis, content and release of fibronectin and proteins by mature bovine articular cartilage explants using a novel mechanical loading system. Increasing the load magnitude, as well as the duration of loading, inhibited the synthesis and content of fibronectin and proteins; the fibronectin synthesis was more specifically affected than the overall protein synthesis indicating that fibronectin is more responsive to pressure than synthesis of other proteins. Reducing the load frequency did not modulate the inhibitory effect of a given cyclic stress on synthesis and content of fibronectin and proteins even though explants were more compressed. The release of endogenous fibronectin was significantly reduced independent of the applied loading protocols when compared with unloaded controls. This study demonstrates that the magnitude and the duration of loading influences the degree of inhibition of fibronectin and protein synthesis, while loaded explants possess an elevated but limited capacity to bind fibronectin. Compared with other studies, our present results show that the applied load function in particular has a profound effect on the metabolism of chondrocytes.

Animals↗
PubMed1999

Effects of intermittently applied cyclic loading on proteoglycan metabolism and swelling behaviour of articular cartilage explants.

OBJECTIVE: The aim of this study was to evaluate the effect of tissue load, frequency and load duration on the biosynthesis and release of proteoglycans (PGs) as well as on the swelling behaviour of cultured mature bovine articular cartilage superimposed with intermittent loads. METHODS: Cyclic compressive pressure was introduced for 1, 3 or 6 days using a sinusoidal waveform of 0.5 Hz-frequency with a peak stress of 0.1, 0.5 or 1.0 MPa. The loads were applied for a period of 10 seconds (s) followed by a load-free period of 10, 100 or 1000 s. The incorporation of [35S]-SO4 into glycosaminoglycans (GAGs) during the final 18 h, the content of GAGs and DNA as well as the deformation of loaded explants were determined. RESULTS: The PG synthesis is sensitive to changes in the loading conditions applied, whereas the release of newly synthesized PG is not. A maximum PG synthesis is observed at day 3, and under load-free intervals of 100 s. After 6 days of loading the release of endogenous PGs is significantly elevated, the viability of superficial chondrocytes decreased, and cartilage swelling is observed. CONCLUSIONS: Considering numerous reports of elevated PG levels synthesized as well as released from human and experimental osteoarthritic cartilage, our results implicate that degenerative processes can also be mimicked by applying well-defined mechanical conditions as described here.

Animals↗
PubMed1998

Pharmacological effect of tetracyclines on proteoglycanases from interleukin-1-treated articular cartilage.

Based on previous in vivo and in situ studies showing that tetracyclines possess antidegenerative effects on cartilage in conjunction with a reduced proteoglycan (PG) loss from the extracellular matrix, we investigated the effects of doxycycline, minocycline and tetracycline on the degradation and biosynthesis of PGs by bovine articular cartilage explants, both in vitro and in situ. Doxycycline, minocycline and tetracycline dose dependently, although weakly, inhibited PG degrading matrix metalloproteinases (MMPs) in vitro, when tested at concentrations ranging from 1 to 100 microM. Ro 31-4724 proved to be a potent inhibitor of MMP proteoglycanases (IC50 value 1.5 nM). Only at a concentration of 100 microM did doxycycline and minocycline significantly inhibit the interleukin-1 (IL-1)-induced augmentation of PG loss from cartilage explants into the nutrient media. The tetracyclines did not modulate the IL-1-mediated reduced aggregability of PGs, whereas 10 microM Ro 31-4724 partially restored the aggregability of PGs ex vivo. Tetracycline even at this high concentration was ineffective. Compared to the effects of the MMP inhibitor Ro 31-4724, treatment with tetracyclines at therapeutic serum levels of 1 or 10 microM was minimal, with little or no effect on cartilage proteoglycanases and PG biosynthesis. In our experiments, tetracyclines and Ro 31-4724 at doses evaluated had no cytotoxic effects on chondrocytes.

Animals↗
PubMed1997

The proteoglycan metabolism of mature bovine articular cartilage explants superimposed to continuously applied cyclic mechanical loading.

This study describes the effect of load magnitude, frequency and duration on proteoglycan (PG) biosynthesis and loss in mature bovine articular cartilage explants. Cultured full thickness cartilage discs were subjected to a continuously applied, uniaxial compressive cyclic load. The loads were applied using a sinusoidal waveform of 0.001, 0.01, 0.1 or 0.5 Hz-frequency and a peak stress of 0.1, 1.0, 2.5, or 5.0 MPa for a period of 1, 3 or 6 days. Increasing the load magnitude, as well as the duration of loading, reduced the PG biosynthesis. Reducing the load frequency abolished the inhibitory effect of a given load magnitude on PG biosynthesis, even though explants were more compressed. Increasing the load magnitude stimulated the release of newly synthesized PGs from explants, whereas an elevated duration of loading significantly decreased the release of endogenous PGs. Explants loaded for 1 or 3 days were viable as determined biochemically, whereas 6 days of loading resulted in a slightly diminished viability of explants. This study demonstrates that the duration and intensity of loading influences the inhibition of PG biosynthesis, while PG loss is only modulated by the magnitude and duration of loading.

Animals↗
PubMed1997

Pharmacological influence of antirheumatic drugs on proteoglycans from interleukin-1 treated articular cartilage.

The purpose of this study was to examine whether drugs used in the treatment of arthritic disorders possess any inhibitory potential on the proteoglycanolytic activities of matrix metalloproteinases (MMPs), and to determine whether drugs which inhibit these enzymes also modulate the biosynthesis and release of proteoglycans (PGs) from interleukin-1-(IL-1) treated articular cartilage explants. The cartilage-bone marrow extract and the glycosaminoglycan-peptide complex (DAK-16) dose-dependently inhibited MMP proteoglycanases in vitro when tested at concentrations ranging from 0.5 to 55 mg/mL, displaying an IC50 value of 31.78 mg/mL and 10.64 mg/mL (1.9 x 10[-4] M) respectively. (R,S)-N-[2-[2-(hydroxyamino)-2-oxoethyl]-4-methyl-1-oxopentyl++ +]-L-leucyl-L-phenylalaninamide (U-24522) proved to be a potent inhibitor of MMP proteoglycanases (IC50 value 1.8 x 10[-9] M). None of the other tested drugs, such as possible chondroprotective drugs, nonsteroidal anti-inflammatory drugs (NSAIDs), disease modifying antirheumatic drugs (DMARDs), glucocorticoids and angiotensin-converting enzyme inhibitors tested at a concentration of 10(-4) M displayed any significant inhibition. Only U-24522, tested at a concentration ranging from 10(-4) to 10(-6) M, significantly inhibited the IL-1-induced augmentation of PG loss from cartilage explants into the nutrient media, whereas DAK-16 and the cartilage-bone marrow extract were ineffective. DAK-16 and the cartilage-bone marrow extract did not modulate the IL-1-mediated reduced biosynthesis and aggregability of PGs by the cartilage explants. The addition of 10(-5) M U-24522, however, partially maintained the aggregability of PGs ex vivo. In our experiments, both possible chondroprotective drugs as well as U-24522 demonstrated no cytotoxic effects on chondrocytes.

Animals↗
PubMed1997

The proteoglycan metabolism, morphology and viability of articular cartilage treated with a synthetic matrix metalloproteinase inhibitor.

Matrix metalloproteinases (MMP) are among the key enzymes responsible for the proteolytic destruction of articular cartilage during chronic rheumatic diseases. Articular cartilage is one potential target for drugs designed to inhibit the activity of MMPs in order to stop or to slow down the proteolytic destruction of the extracellular matrix of cartilage. The purpose of this study was to investigate the effect of the synthetic inhibitor of MMPs U-24522 for its ability (1) to inhibit in vitro the activity of MMP-proteoglycanases; (2) to modulate the morphology and viability of cartilage explants; and (3) to modify the biosynthesis and release of proteoglycans from articular cartilage explants. U-24522 dose-dependently inhibited the activity of MMP-proteoglycanases and significantly reduced the release of proteoglycans from interleukin-1 treated bovine articular cartilage explants when tested at concentrations ranging from 10(-4) to 10(-9) M. This hydroxamic acid derivative proved not to be harmful to chondrocyte viability and cartilage morphology. In addition, U-24522 had no effect on the rate of proteoglycan biosynthesis of interleukin-1 treated cartilage explants and increased the percentage of newly synthesized proteoglycans to form macromolecular aggregates. Thus U-24522 combines direct inhibitory potential on the activity of MMP-proteoglycanases with the inhibition of interleukin-1 stimulated proteoglycan loss from articular cartilage explants without affecting the morphology, viability and biosynthesis of proteoglycans of bovine articular cartilage explants.

Animals↗
PubMed1997

A computer-controlled mechanical culture system for biological testing of articular cartilage explants.

A computer-controlled mechanical culture system was designed to investigate the interaction between mechanical stimuli and the metabolism of articular cartilage. The main features of this system include the following capabilities: (1) Accurately controlled static, permanent cyclic or intermittent cyclic mechanical loads can be applied; (2) a great variety of different functions to load cartilage explants can be chosen; (3) a wide range of selectable forces (1.0-500 N) and frequencies (up to 5.0 Hz) can be used to load explants; (4) cartilage explants can be cultured and loaded within a standard CO2-incubator for extended time periods; (5) similar culture conditions are provided within the loading chambers as in standard tissue culture plates; (6) simultaneously the applied load and the resulting displacement of specimens is measured, and (7) the load chambers are biocompatible, sterilizable, and non-corrosive. We expect that the newly designed mechanical culture system will increase our understanding on the regulatory role of direct mechanical pressure on the metabolic activities of chondrocytes.

Animals↗
PubMed1997

Intermittent cyclic loading of cartilage explants modulates fibronectin metabolism.

OBJECTIVE: The aim of this study was to evaluate systematically the effect of tissue load, its amplitude, time of intermittence and duration of loading on the biosynthesis and release of fibronectin by intermittently loaded mature bovine articular cartilage explants. METHODS: Cyclic compressive pressure was introduced using a sinusoidal waveform of 0.5 Hz-frequency with a peak stress of 0.1, 0.5 or 1.0 MPa for a period of 10 s followed by an unloaded period lasting 10, 100 or 1000 s. Fibronectin and total proteins were radiolabeled with 10 microCi/ml [3H]-phenylalanine during the final 18 h of the 1, 3 or 6 day experiments. The content of endogenous fibronectin was determined using enzyme-linked immunosorbant assay (ELISA), whereas the viability of explants was measured using sections of cartilage explants stained with fluorescein diacetate and propidium iodide. The deformation of loaded explants was determined using a load-displacement transducer system. RESULTS: The mechanical factor time of intermittence significantly altered the synthesis and release of fibronectin by cartilage explants, whereas the tested range of load magnitudes, as well as the duration of loading, seemed to be of subordinate importance. Loading affected the viability of the superficial zone in the cartilage, whereas the chondrocytes of the intermediate and deep zone remained viable. The compression of loaded explants was dependent on the magnitude of stress, as well as on the duration of unloading between each loading cycle. Synthesis of fibronectin, the retention of newly synthesized fibronectin within the extracellular matrix, and the portion of newly synthesized proteins that were fibronectin was significantly increased in cartilage explants which were cyclically compressed with 0.5 MPa for 10 s followed by a period of unloading lasting 100 s. CONCLUSIONS: Previous studies reporting that cartilage explants of human and animal osteoarthritic joints synthesize and retain elevated amounts of fibronectin imply that in our experiments mechanical stimuli can induce a fibronectin metabolism in vitro which mimics some of the osteoarthritic characteristics.

Animals↗