Ultrastructural changes associated with myocardial apoptosis, in failing rat hearts induced by volume overload

BACKGROUND

Myocardial apoptosis has been discussed to play a pivotal role in the development and progression of congestive heart failure (CHF). However, recently there is doubt on the evidence of myocardial apoptosis in heart failure as information on ultrastructural changes by electron microscopy is still scarce. This project therefore aimed to detect direct morphological evidence of myocardial apoptosis in an experimental heart failure model.

METHOD

Following IRB approval, an aortocaval fistula (ACF) was induced in male Wistar rats using a 16G needle. 28±2days following ACF rats were examined by hemodynamic measurements, Western blot, immunofluorescence confocal and electron microscopic analysis.

RESULTS

Within 28±2days of ACF heart (3.8±0.1 vs. 6.6±0.3mg/g) and lung (3.7±0.2 vs. 6.9±0.5mg/g) weight indices significantly increased in the ACF group accompanied by a restriction in systolic (LVEF: 72±2 vs. 39±3%) and diastolic (dP/dtmin.: -10,435±942 vs. -5982±745mmHg/s) function (p<0.01). Activated caspase-3 was significantly increased in failing hearts concomitant with mitochondrial leakage of cytochrome c into the cytosol. Finally, electron microscopy of the left ventricle (LV) of ACF rats revealed pronounced ultrastructural changes in >70% of examined cardiomyocytes, such as nuclear chromatin condensation, myofibril loss and disarray, contour irregularities and amorphous dense bodies, mitochondriosis and damaged cell-cell-contacts between cardiomyocytes.

CONCLUSIONS

Volume overload induced heart failure is associated with activation of the mitochondrial apoptotic pathway. In addition, electron microscopy of the LV revealed direct ultrastructural evidence of extended myocardial apoptosis in ACF rats.

Identification and characterization of a compound from Cuminum cyminum essential oil with antifibrilation and cytotoxic effect

Amyloid pathology is associated with fibril aggregation of different proteins which results in the progressive damage of affected organs. It is strongly believed that specific small molecules interfere with fibrillation by interacting with the amyloidogenic proteins. We had previously reported the strong and long-term inhibition of fibrillation of hen egg white lysozyme (HEWL) by Cuminum cyminum oil. Herein, it was intended to rationally identify the active anti-amyloidogenic compounds of the oil. After fractionation, the highest inhibitory effect was observed in the toluene-ethyl acetate part of the oil. Gas chromatography-mass spectrometry (GC-MS) analysis of this fraction indicated that eight compounds were predominantly present in the fraction. Unexpectedly, two compounds including terpinolene and limonene, having very similar chemical structures, inhibited and induced fibrillation, respectively. PC12 cells (derived from a transplantable rat pheochromocytoma) were affected by HEWL fibrils, whereas the inhibited forms of fibrils in the presence of terpinolene led to higher levels of viability, as shown by 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT), lactate dehydrogenase (LDH) and flow cytometry assays. Molecular local docking analysis suggested a site of interaction for terpinolene in the flexible cleft of the protein. This interaction site is close to tryptophan -62 and -63 and two other hydrophobic residues in the hot spot regions of the protein. Seemingly, these interactions interrupt protein self-assembly and therefore, fibril formation. Despite previously reported small anti-amyloid molecules which have aromatic flat rings, terpinolene ring is not flat. This functionally durable small molecule may aid us toward developing new anti-amyloidogenic compounds with extended activity.

Is tendinitis an inflammatory disease initiated and driven by pro-inflammatory cytokines such as interleukin 1β?

Tendonitis and tendinitis are terms used to describe an inflamed and painful tendon. Tendinopathy, is a descriptive term for describing clinical conditions arising from tendon injury and overuse both within and around tendons. The aim of this mini-review is to explore the role of pro-inflammatory cytokines, particularly interleukin-1β (IL-1β) in tendon disorders. A number of investigators including our group have proposed that pro-inflammatory cytokines such as IL-1β are initiators of tendinopathies, stimulating inflammation, apoptosis and extracellular matrix (ECM) degradation. This is one of the reasons why IL-1β is frequently used in culture models of tendon inflammation to study the inflammatory and catabolic responses of tenocytes. However, some researchers oppose this view and suggest that although IL-1β may play a role in rheumatoid arthritis (RA) and osteoarthritis (OA), the involvement of IL-1β in the development of tendinopathy is questionable. This mini-review discusses the relevant papers published in this area and summarises the evidence for and against the involvement of pro-inflammatory cytokines such as IL-1β in tendonitis. Reaching a consensus will be important for the development and refinement of biomimetic models of tendon inflammation and the formulation of new therapeutic strategies for the treatment of tendon injuries.

Anti-inflammatory and anti-catabolic effects of TENDOACTIVE® on human tenocytes in vitro

Tendons have a limited capacity for self-repair due to the low density and mitotic activity of tenocytes. Pro-inflammatory cytokines such as interleukin-1β (IL-1β) have been identified as the main initiators of tendinopathies, stimulating inflammation, apoptosis and extracellular matrix (ECM) degradation. The aim of this study was to evaluate the potential of Tendoactive®, a newly developed proprietary nutraceutical formulation that includes mucopolysaccharides, collagen and vitamin C, in an in vitro model of tendon inflammation. The effects of Tendoactive® were studied in primary cultures of human tenocytes treated with IL-1β for up to 72 h. Expression of collagen type I, integrin β1, cyclo-oxygenase-2 (COX-2), caspase-3 and matrix metalloproteinase-1 (MMP-1) was monitored by western blotting. The effects of Tendoactive® on the expression, phosphorylation and nuclear translocation of protein components of the NF-κB system were studied by western blotting and immunofluorescence respectively. Treatment of tenocytes with Tendoactive® suppressed IL-1β-induced NF-κB activation and p65 nuclear translocation. These events correlated with down-regulation of NF-κB targets including COX-2, MMP-1 and activated caspase-3. Tendoactive® also reversed the IL-1β-induced down-regulation of collagen type I and β1-integrin receptor expression. These results indicate that Tendoactive® has nutraceutical potential as an anti-inflammatory agent for treating tendinopathy through suppression of NF-κB mediated IL-1β catabolic signalling pathways in tenocytes.

Biological actions of curcumin on articular chondrocytes

OBJECTIVES

Curcumin (diferuloylmethane) is the principal biochemical component of the spice turmeric and has been shown to possess potent anti-catabolic, anti-inflammatory and antioxidant, properties. This article aims to provide a summary of the actions of curcumin on articular chondrocytes from the available literature with the use of a text-mining tool. We highlight both the potential benefits and drawbacks of using this chemopreventive agent for treating osteoarthritis (OA). We also explore the recent literature on the molecular mechanisms of curcumin mediated alterations in gene expression mediated via activator protein 1 (AP-1)/nuclear factor-kappa B (NF-kappaB) signalling in chondrocytes, osteoblasts and synovial fibroblasts.

METHODS

A computer-aided search of the PubMed/Medline database aided by a text-mining tool to interrogate the ResNet Mammalian database 6.0.

RESULTS

Recent work has shown that curcumin protects human chondrocytes from the catabolic actions of interleukin-1 beta (IL-1beta) including matrix metalloproteinase (MMP)-3 up-regulation, inhibition of collagen type II and down-regulation of beta1-integrin expression. Curcumin blocks IL-1beta-induced proteoglycan degradation, AP-1/NF-kappaB signalling, chondrocyte apoptosis and activation of caspase-3.

CONCLUSIONS

The available data from published in vitro and in vivo studies suggest that curcumin may be a beneficial complementary treatment for OA in humans and companion animals. Nevertheless, before initiating extensive clinical trials, more basic research is required to improve its solubility, absorption and bioavailability and gain additional information about its safety and efficacy in different species. Once these obstacles have been overcome, curcumin and structurally related biochemicals may become safer and more suitable nutraceutical alternatives to the non-steroidal anti-inflammatory drugs that are currently used for the treatment of OA.

Mesenchymal stem cells in connective tissue engineering and regenerative medicine: applications in cartilage repair and osteoarthritis therapy

Defects of load-bearing connective tissues such as articular cartilage, often result from trauma, degenerative or age-related disease. Osteoarthritis (OA) presents a major clinical challenge to clinicians due to the limited inherent repair capacity of articular cartilage. Articular cartilage defects are increasingly common among the elderly population causing pain, reduced joint function and significant disability among affected patients. The poor capacity for self-repair of chondral defects has resulted in the development of a large variety of treatment approaches including Autologous Chondrocyte Transplantation (ACT), microfracture and mosaicplasty methods. In ACT, a cartilage biopsy is taken from the patient and articular chondrocytes are isolated. The cells are then expanded after several passages in vitro and used to fill the cartilage defect. Since its introduction, ACT has become a widely applied surgical method with good to excellent clinical outcomes. More recently, classical ACT has been combined with tissue engineering and implantable scaffolds for improved results. However, there are still major problems associated with the ACT technique which relate mainly to chondrocyte de-differentiation during the expansion phase in monolayer culture and the poor integration of the implants into the surrounding cartilage tissue. Novel approaches using mesenchymal stem cells (MSCs) as an alternative cell source to patient derived chondrocytes are currently on trial. MSCs have shown significant potential for chondrogenesis in animal models. This review article discusses the potential of MSCs in tissue engineering and regenerative medicine and highlights their potential for cartilage repair and cell-based therapies for osteoarthritis and a range of related osteoarticular disorders.

Interleukin-18 induces apoptosis in human articular chondrocytes

Elevated levels of the pro-inflammatory cytokine, interleukin-18 (IL-18) have recently been demonstrated in osteoarthritic cartilage. However, the effects of IL-18 on chondrocyte signalling and matrix biosynthesis are poorly understood. Therefore, the present study was undertaken to further characterize the impact of IL-18 on human articular chondrocyte in vitro. Human articular chondrocytes were stimulated with various concentrations of recombinant human IL-18 (1, 10, 100 ng/ml) for 0, 4, 8, 12, 24, 48, 72 h in vitro. The effects of IL-18 on the cartilage-specific matrix protein collagen type II, the cytoskeletal protein vinculin, the cell matrix signal transduction receptor beta-integrin, key signalling proteins of the MAPKinase pathway (such as SHC (Sarc Homology Collagen) and activated MAPKinase [ERK-1/-2]), the pro-inflammatory enzyme cyclo-oxygenase-2 (COX-2) and the apoptosis marker activated caspase-3 were evaluated by Western blot analysis and immunofluorescence labelling. Morphological features of IL-18 stimulated chondrocytes were estimated by transmission electron microscopy. IL-18 lead to inhibition of collagen type II-deposition, decreased beta-integrin receptor and vinculin synthesis, SHC and MAPKinase activation, increased COX-2 synthesis and activation of caspase-3 in chondrocytes in a time- and dose-dependent manner. Furthermore, chondrocytes treated with IL-18 exhibited typical morphological features of apoptosis as revealed by transmission electron microscopy. Taken together, the results of the present study underline key catabolic events mediated by IL-18 signalling in chondrocytes such as loss of cartilage-specific matrix and apoptosis. Inhibition of MAPKinase signalling is hypothesized to contribute to these features. Future therapeutics targeting IL-18 signalling pathways may be beneficial in rheumatoid arthritis and osteoarthritis therapy.

[The rare malformation of nasal aplasia]

BACKGROUND

After presenting two sisters with the rare form of congenital arrhinia, this syndrome is reviewed, an explanation of the pathogenesis is offered and the therapeutic options of the functional and aesthetic reconstruction are discussed.

DISCUSSION

In cases of congenital arrhinia different degrees of respiratory distress, cyanotic episodes, and impaired food intake are described. Therefore after birth respiration and food intake need to be monitored to alleviate the situation through intubation or tracheotomy. The following conclusions could be made based on the literature overview. Little is known about the pathophysiology and a great variety of therapeutic interventions and reconstruction solutions with a wide spectrum of complications are described. Due to the numerous forms of complications, which need to be compared with the reconstructive results, indications for surgical reconstruction of the airway and plastic reconstruction of the nose during childhood must be defined very stringently.

CONCLUSION

One method to achieve a satisfactory plastic result is with an osseointegrated prosthesis. This facial prosthesis can be inserted without complications and can guarantee an adequate result, whereas no impairment of maxillofacial development was noted.

Mechanisms of apoptosis after ischemia and reperfusion: role of the renin-angiotensin system

BACKGROUND

Apoptosis plays a key role in the pathogenesis of cardiac diseases. We examined the influence of the renin-angiotensin system (RAS) on different regulators of apoptosis using an isolated hemoperfused working porcine heart model of acute ischemia (2 h), followed by reperfusion (4 h).

METHODS AND RESULTS

23 porcine hearts were randomized to 5 groups: hemoperfused non-infarcted hearts (C), infarcted hearts (MI: R. circumflexus), infarcted hearts treated with quinaprilat (Q), infarcted hearts treated with angiotensin-I (Ang I), and infarcted hearts treated with angiotensin-I and quinaprilat (QA). Fas, Bax, bcl-2 and p53 proteins were increased in MI hearts and further elevated by Ang I. Quinaprilat reduced Bax and p53. Bcl-2 was elevated in Q and reduced in QA. An early upregulation of caspase-3 gene and protein expression was detected in MI and Ang I hearts compared to C. Q reduced caspase-3 gene expression, but had no effect on caspase-3 and Fas protein.

CONCLUSIONS

These data suggest that the RAS plays a pivotal role in cardiac apoptosis which is the early and predominant form of death in myocardial infarction. Ischemia/reperfusion induces programmed cell death via extrinsic and intrinsic pathways. Early treatment with quinaprilat attenuated cardiomyocyte apoptosis.

Induction of three-dimensional assembly and increase in apoptosis of human endothelial cells by simulated microgravity: impact of vascular endothelial growth factor

Endothelial cells play a crucial role in the pathogenesis of many diseases and are highly sensitive to low gravity conditions. Using a three-dimensional random positioning machine (clinostat) we investigated effects of simulated weightlessness on the human EA.hy926 cell line (4, 12, 24, 48 and 72 h) and addressed the impact of exposure to VEGF (10 ng/ml). Simulated microgravity resulted in an increase in extracellular matrix proteins (ECMP) and altered cytoskeletal components such as microtubules (alpha-tubulin) and intermediate filaments (cytokeratin). Within the initial 4 h, both simulated microgravity and VEGF, alone, enhanced the expression of ECMP (collagen type I, fibronectin, osteopontin, laminin) and flk-1 protein. Synergistic effects between microgravity and VEGF were not seen. After 12 h, microgravity further enhanced all proteins mentioned above. Moreover, clinorotated endothelial cells showed morphological and biochemical signs of apoptosis after 4 h, which were further increased after 72 h. VEGF significantly attenuated apoptosis as demonstrated by DAPI staining, TUNEL flow cytometry and electron microscopy. Caspase-3, Bax, Fas, and 85-kDa apoptosis-related cleavage fragments were clearly reduced by VEGF. After 72 h, most surviving endothelial cells had assembled to three-dimensional tubular structures. Simulated weightlessness induced apoptosis and increased the amount of ECMP. VEGF develops a cell-protective influence on endothelial cells exposed to simulated microgravity.

Development and phenotypic characterization of a high density in vitro model of auricular chondrocytes with applications in reconstructive plastic surgery

Cultivation of phenotypically stable auricular chondrocytes will have applications in autologous chondrocyte transplantation and reconstructive surgery of cartilage. Chondrocytes grown in monolayer culture rapidly dedifferentiate assuming a fibroblast-like morphology and lose their cartilage-specific pattern of gene expression. Three-dimensional high-density culture models mimic more closely the in vivo conditions of cartilage. Therefore, this study was undertaken to test whether the high-density cultures might serve as a suitable model system to acquire phenotypically and functionally differentiated auricular chondrocytes from porcine cartilage. Freshly isolated porcine auricular chondrocytes were cultured for 7 passages in monolayer culture. From each passage (passage 0 and 1-7) cells were introduced to high-density cultures and examined by transmission electron microscopy. Western blotting was used to analyse the expression of cartilage-specific markers, such as collagen type II and cartilage specific proteoglycan, fibronectin, cell adhesion and signal transduction receptor beta1-integrin, matrix metalloproteinases (MMP-9, MMP-13), cyclo-oxygenase (COX)-2 and the apoptosis commitment marker, activated caspase-3. When dedifferentiated auricular chondrocytes from monolayer passages 0-4 were cultured in high-density culture, they recovered their chondrocytic phenotype and formed cartilage nodules surrounded by fibroblast-like cells and synthesised collagen type II, proteoglycans, fibronectin and beta1-integrins. However, chondrocytes from monolayer passages 5-7 did not redifferentiate to chondrocytes even when transferred to high-density culture, and did not synthesize a chondrocyte-specific extracellular matrix. Instead, they produced increasing amounts of MMP-9, MMP-13, COX-2, activated caspase-3 and underwent apoptosis. Three-dimensional high-density cultures may therefore be used to obtain sufficient quantities of fully differentiated auricular chondrocytes for autologous chondrocyte transplantation and reconstructive plastic surgery.

Hypoxia inducible factor-1 and facilitative glucose transporters GLUT1 and GLUT3: putative molecular components of the oxygen and glucose sensing apparatus in articular chondrocytes

Articular cartilage is an avascular connective tissue in which the availability of oxygen and glucose is significantly lower than synovial fluid and plasma. Glucose is an important metabolic fuel and structural precursor that plays a key role in the synthesis of extracellular matrix macromolecules in articular cartilage. However, glucose concentrations in cartilage can fluctuate depending on age, physical activity and endocrine status. Chondrocytes are glycolytic cells and must be able to sense the quantities of oxygen and glucose available to them in the extracellular matrix and respond appropriately by adjusting cellular metabolism. Consequently chondrocytes must have the capacity to survive in an extracellular matrix with limited nutrients and low oxygen tensions. The molecular mechanisms responsible for allowing chondrocytes to adapt to these harsh environmental conditions are poorly understood. In this article we present a novel "dual" model of oxygen and glucose sensing in chondrocytes based on recent experimental data. This model incorporates the hypoxia-inducible factor alpha (HIF-1alpha) as an oxygen sensor and the hypoxia responsive facilitative glucose transporters, GLUT1 and GLUT3 as putative components of the glucose sensing apparatus in chondrocytes. Recent studies have shown that GLUT1 and GLUT3 are both expressed in chondrocytes and their HIF-1alpha-mediated transcription may be dually stimulated in response to hypoxia and low glucose conditions which in turn promote anaerobic glycolysis in favor of oxidative phosphorylation. This working model provides, for the first time, a unifying hypothesis to explain how chondrocytes might sense and respond to low oxygen tensions and alterations in extracellular glucose.

Expression of the GLUT1 and GLUT9 facilitative glucose transporters in embryonic chondroblasts and mature chondrocytes in ovine articular cartilage

Glucose transport across the chondrocyte membrane is essential for chondrogenesis and the development of the skeletal system. We have previously used RT-PCR to show that fully developed human articular chondrocytes express transcripts for the GLUT1 and GLUT9 glucose transporters. In this study we report on the expression and immunohistochemical localization of the GLUT1 and GLUT9 proteins in embryonic and mature ovine cartilage. We also provide Western blot evidence for GLUT1 and GLUT9 expression in mature ovine chondrocytes. Ovine embryos (developmental stages E32 to E36 and E42 to E45) were obtained from pregnant ewes humanely killed by injection with sodium pentobarbitone. Embryos were fixed and processed for immunohistochemistry. Polyclonal antibodies to GLUT1 and GLUT9 revealed that both transporters are expressed in developing chondrocytes in ovine embryos and in the superficial, middle and deep layers of ovine cartilage from mature animals. GLUT1 expression was observed in erythrocytes and organs including heart, liver, and kidney. GLUT9 was also found in heart, kidney and liver. Western blotting confirmed the presence of the GLUT1 protein which migrated between the 50 and 64 kDa markers and two specific GLUT9 bands migrating under the 50 and 60 kDa markers, respectively. The presence of GLUT1 and GLUT9 in developing joints of ovine embryos suggests that these proteins may be important in glucose delivery to developing chondroblasts. Expression of these GLUT isoforms may be an important bioenergetic adaptation for chondrocytes in the extracellular matrix of developing cartilage.

Interleukin-1beta-induced expression of the urokinase-type plasminogen activator receptor and its co-localization with MMPs in human articular chondrocytes

The urokinase-type plasminogen activator receptor (uPAR) plays a critical role in cartilage degradation during osteoarthritis as it regulates pericellular proteolysis mediated by serine proteinases. Another important family of proteinases responsible for ECM destruction in arthritis are the matrix metalloproteinases (MMPs). MMPs are regulated by IL-1beta, a cytokine that plays a pivotal role in pathogenesis of osteoarthritis. This study was undertaken to address two questions: 1. Is uPAR-expression regulated by proinflammatory cytokines such as IL-1beta? 2. Does a functional co-localization exist between uPAR and MMPs? By immunohistochemical analysis we observed enhanced expression of uPAR on chondrocytes derived from osteoarthritic human cartilage compared to non-osteoarthritic controls. We found an IL-1beta-mediated expression of uPAR by immunoelectron microscopy. Western blot analysis demonstrated that IL-1beta-stimulated expression of uPAR on chondrocytes in vitro increased in a dose-dependent manner. Furthermore, we found a functional co-localization between uPAR and MMP-9 on IL-1beta-stimulated chondrocytes by means of a co-immunoprecipitation assay. Expression of uPAR in osteoarthritic cartilage but not in healthy cartilage suggests that uPAR plays a role in cartilage breakdown. We propose that uPAR-mediated effects e.g. pericellular proteolysis are one of other cytokine (IL-1beta)-mediated events that contribute to the pathogenesis of osteoarthritis. Furthermore, we found that MMPs and uPAR were part of the same cell surface complexes in chondrocytes. This finding underlines a functional interaction between MMPs and the serine proteinase system in the fine regulation of pericellular proteolysis. Interfering with uPAR signaling may present a novel target in arthritis therapy to prevent excessive proteolytic degradation.

Post-genomic applications of tissue microarrays: basic research, prognostic oncology, clinical genomics and drug discovery

Tissue microarrays (TMAs) are an ordered array of tissue cores on a glass slide. They permit immunohistochemical analysis of numerous tissue sections under identical experimental conditions. The arrays can contain samples of every organ in the human body, or a wide variety of common tumors and obscure clinical cases alongside normal controls. The arrays can also contain pellets of cultured tumor cell lines. These arrays may be used like any histological section for immunohistochemistry and in situ hybridization to detect protein and gene expression. This new technology will allow investigators to analyze numerous biomarkers over essentially identical samples, develop novel prognostic markers and validate potential drug targets. The ability to combine TMA technology with DNA microarrays and proteomics makes it a very attractive tool for analysis of gene expression in clinically stratified tumor specimens and relate expression of each particular protein with clinical outcome. Public domain software allows researchers to examine digital images of individual histological specimens from TMAs, evaluate and score them and store the quantitative data in a relational database. TMA technology may be specifically applied to the profiling of proteins of interest in other pathophysiological conditions such as congestive heart failure, renal disease, hypertension, diabetes, cystic fibrosis and neurodegenerative disorders. This review is intended to summarize the strengths and weaknesses of TMA technology which will have an increasingly important role in the laboratories of the post-genomic era.

Cultivation of human tenocytes in high-density culture

Limited supplies of tendon tissue for use in reconstructive surgery require development of phenotypically stable tenocytes cultivated in vitro. Tenocytes in monolayer culture display an unstable phenotype and tend to dedifferentiate, but those in three-dimensional culture may remain phenotypically and functionally differentiated. In this study we established a three-dimensional high-density culture system for cultivation of human tenocytes for tissue engineering. Human tenocytes were expanded in monolayer culture before transfer to high-density culture. The synthesis of major extracellular matrix proteins and the ultrastructural morphology of the three-dimensional cultures were investigated for up to 2 weeks by electron microscopy, immunohistochemistry, immunoblotting and quantitative, real-time PCR. Differentiated tenocytes were able to survive over a period of 14 days in high-density culture. During the culture period tenocytes exhibited a typical tenocyte morphology embedded in an extensive extracellular matrix containing cross-striated collagen type I fibrils and proteoglycans. Moreover, expression of the tendon-specific marker scleraxis underlined the tenocytic identity of these cells. Taken together, we conclude that the three-dimensional high-density cultures may be useful as a new approach for obtaining differentiated tenocytes for autologous tenocyte transplantation to support tendon and ligament healing and to investigate the effect of tendon-affecting agents on tendon in vitro.

Immunohistochemical localization of aquaporin 10 in the apical membranes of the human ileum: a potential pathway for luminal water and small solute absorption

A new member of the aquaporin family (AQP10) has recently been identified in the human small intestine by molecular cloning and in situ hybridization. Ribonuclease protection assay and northern blotting have demonstrated that AQP10 is expressed in the human duodenum and jejunum. However, the subcellular distribution of the AQP10 protein and its plasma membrane polarization have not yet been established. The objective of this study was to determine the distribution of the AQP10 protein in the human ileum by immunohistochemistry and western blotting using a polyclonal antibody raised against a unique 17-amino acid peptide derived from the human AQP10 sequence. The distribution of the AQP1 and AQP3 proteins was also studied by immunohistochemical staining using affinity-purified polyclonal antibodies. Results revealed that the AQP10 protein is preferentially targeted to the apical membrane domain of absorptive intestinal epithelial cells, whereas AQP3 is located in the basolateral membrane of the cells and AQP1 expression is restricted to the mucosal microvascular endothelia. The presence of AQP10 in the apical membrane of intestinal villi suggests that this protein may represent an entry pathway for water and small solutes from the lumen across to the mucosal side.

Expression of the VEGF receptor-3 in osteoarthritic chondrocytes: stimulation by interleukin-1 beta and association with beta 1-integrins

Recent studies have demonstrated enhanced expression of vascular endothelial growth factor and vascular endothelial growth factor receptor (VEGFR)-1 and -2 in chondrocytes of rheumatoid and osteoarthritic cartilage. Since expression of VEGFR-3 ( Flt-4) in chondrocytes has not yet been investigated, we studied the distribution of VEGFR-3 in osteoarthritic cartilage samples by immunohistochemistry and immunoelectron microscopy. Furthermore, we looked for functional colocalization of VEGFR-3 with the signal transduction receptor beta(1)-integrin. Superficial osteoarthritic chondrocytes exhibited VEGFR-3 expression in the cytoplasm and on the cell membrane. Using western blotting we could demonstrate that interleukin-1 beta (IL-1 beta) stimulates the expression of VEGFR-3 in chondrocytes in vitro in a dose-dependent manner. By coimmunoprecipitation assay we found a functional complex between the beta(1)-integrin and VEGFR-3 in IL-1 beta-stimulated chondrocytes indicating that activated VEGFR-3 may interact with beta(1)-integrin and associated subcellular pathways in osteoarthritic chondrocytes. Taken together with results of previous studies showing that beta(1)-integrins were also associated with other surface receptors and proteins in chondrocytes that cause cartilage destruction in arthritis (for example, urokinase-type plasminogen activator receptor and matrix metalloproteinases), we can hypothesize that signal transduction by these receptor complexes via beta(1)-integrins may play a crucial role in pathogenesis of osteoarticular disorders. Further work needs to be done to elucidate downstream signaling events activated by these receptors.

Beta1-integrins co-localize with Na, K-ATPase, epithelial sodium channels (ENaC) and voltage activated calcium channels (VACC) in mechanoreceptor complexes of mouse limb-bud chondrocytes

Interactions between chondrocytes and their extracellular matrix are partly mediated by beta1-integrin receptors. Recent studies have shown that beta1-integrins co-localize with a variety of cytoskeletal complexes, signaling proteins and growth factor receptors. Since mechanosensitive ion channels and integrins have been proposed to participate in skeletal mechanotransduction, in this study, we investigated the possible co-localization of beta1-integrins with two ion channels and a P-type ATPase in mouse limb-bud chondrocytes. The alpha subunits of Na, K-ATPase, the epithelial sodium channel (ENaC) and the voltage activated calcium channel (VACC) were immunostained in organoid cultures derived from limb-buds of 12-day-old mice using well-characterized antibodies. Indirect immunofluorescence revealed abundant expression of beta1-integrins and each of the selected systems in limb-bud chondrocytes. Two-fluorochrome immunostaining demonstrated that beta1-integrin, Na, K-ATPase, ENaC and VACC co-localize in chondrocytes. Co-imunoprecipitation experiments revealed co-localization and association of integrins with ENaC, VACC and Na, K-ATPase. Cellular responses and signaling cascades initiated by the influx of calcium or sodium through putative mechanosensitive channels may be regulated more effectively if such channels were organized around integrins with receptors, kinases and cytoskeletal complexes clustered about them. The close proximity of ATPase ion pumps such as Na, K-ATPase to chondrocyte mechanoreceptor complexes could facilitate rapid homeostatic responses to the ionic perturbations brought about by activation of mechanically gated cation channels and efficiently regulate the intracellular milieu of chondrocytes.

Mechanisms of magnesium-stimulated adhesion of osteoblastic cells to commonly used orthopaedic implants

Poor cell adhesion to orthopaedic and dental implants may result in implant failure. Cellular adhesion to biomaterial surfaces primarily is mediated by integrins, which act as signal transduction and adhesion proteins. Because integrin function depends on divalent cations, we investigated the effect of magnesium ions modified bioceramic substrata (Al(2)O(3)-Mg(2+)) on human bone-derived cell (HBDC) adhesion, integrin expression, and activation of intracellular signalling molecules. Immunohistochemistry, flow cytometry, cell adhesion, cell adhesion blocking, and Western blotting assays were used. Our findings demonstrated that adhesion of HBDC to Al(2)O(3)-Mg(2+) was increased compared to on the Mg(2+)-free Al(2)O(3). Furthermore, HBDC adhesion decreased significantly when the fibronectin receptor alpha5beta1- and beta1-integrins were blocked by functional blocking antibodies. HBDC grown on the Mg(2+)-modified bioceramic expressed significantly enhanced levels of beta1-, alpha5beta1-, and alpha3beta1-integrins receptors compared to those grown on the native unmodified Al(2)O(3). Tyrosine phosphorylation of intracellular integrin-dependent signalling proteins as well as the expression of key signalling protein Shc isoforms (p46, p52, p66), focal adhesion kinase, and extracellular matrix protein collagen type I were significantly enhanced when HBDC were grown on Al(2)O(3)-Mg(2+) compared to the native Al(2)O(3). We conclude that cell adhesion to biomaterial surfaces is probably mediated by alpha5beta1- and beta1-integrin. Cation-promoted cell adhesion depends on 5beta1- and beta1-integrins associated signal transduction pathways involving the key signalling protein Shc and results also in enhanced gene expression of extracellular matrix proteins. Therefore, Mg(2+) supplementation of bioceramic substrata may be a promising way to improve integration of implants in orthopaedic and dental surgery.

Glucose transport and metabolism in chondrocytes: a key to understanding chondrogenesis, skeletal development and cartilage degradation in osteoarthritis

Despite the recognition that degenerative cartilage disorders like osteoarthritis (OA) and osteochondritis dissecans (OCD) may have nutritional abnormalities at the root of their pathogenesis, balanced dietary supplementation programs have played a secondary role in their management. This review emphasizes the importance and role of nutritional factors such as glucose and glucose-derived sugars (i.e. glucosamine sulfate and vitamin C) in the development, maintenance, repair, and remodeling of cartilage. Chondrocytes, the cells of cartilage, consume glucose as a primary substrate for ATP production in glycolysis and utilize glucosamine sulfate and other sulfated sugars as structural components for extracellular matrix synthesis and are dependent on hexose uptake and delivery to metabolic and biosynthetic pools. Data from several laboratories suggests that chondrocytes express multiple isoforms of the GLUT/SLC2A family of glucose/polyol transporters. These facilitative glucose transporter proteins are expressed in a tissue and cell-specific manner, exhibit distinct kinetic properties, and are developmentally regulated. They may also be regulated by endocrine factors like insulin and insulin-like growth factor I (IGF-I) and cytokines such as interleukin 1 beta (IL-1 beta) and tumour necrosis factor alpha (TNF-alpha). Recent studies suggest that degeneration of cartilage may be triggered by metabolic disorders of glucose balance and that OA occurs coincident with metabolic disease, endocrine dysfunction and diabetes mellitus. Based on these metabolic, endocrine and developmental considerations we present a novel hypothesis regarding the role of glucose transport and metabolism in cartilage physiology and pathophysiology and speculate that supplementation with sugar-derived vitamins and nutraceuticals may benefit patients with degenerative joint disorders.

Redifferentiation of dedifferentiated human chondrocytes in high-density cultures

High-density cultures are widely used as an in vitro model for studies of embryonic cartilage formation. In the present study we investigated the suitability of high-density cultures for the redifferentiation of dedifferentiated chondrocytes. When primary human chondrocytes were cultured in alginate beads, some cells emigrated into Petri dishes. These cells were cultured for one to eight passages (each passage lasting about 3 days) in monolayer culture. At each passage, monolayer cells were removed and allowed to grow in high-density cultures at the medium-air interface and subsequently investigated with morphological, immunolocalization and biochemical methods for the production of cartilage-specific markers, i.e. collagen type II and cartilage-specific proteoglycans. When such dedifferentiated chondrocytes from monolayer passages P1-P4 were introduced in high-density culture, they regained a chondrocyte phenotype and formed cartilage nodules surrounded by fibroblast-like cells. Cells were interconnected by typical gap junctions and after a few days in culturing produced cartilage-specific extracellular matrix, notably collagen type II and cartilage-specific proteoglycans. In contrast, cells taken from monolayer passages P5-P8 did not produce these chondrocyte-specific extracellular materials when grown in high-density culture. We conclude that the growth of dedifferentiated chondrocytes in high-density culture promotes their redifferentiation and reveals their chondrogenic potential. Such high-density cultures might serve as a model system to initiate and promote the redifferentiation of chondrocytes and to provide sufficient quantities of differentiated chondrocytes for autologous chondrocyte transplantation.

Integrins and stretch activated ion channels; putative components of functional cell surface mechanoreceptors in articular chondrocytes

Perception of mechanical signals and the biological responses to such stimuli are fundamental properties of load bearing articular cartilage in diarthrodial joints. Chondrocytes utilize mechanical signals to synthesize an extracellular matrix capable of withstanding high loads and shear stresses. Recent studies have shown that chondrocytes undergo changes in shape and volume in a coordinated manner with load induced deformation of the matrix. These matrix changes, together with alterations in hydrostatic pressure, ionic and osmotic composition, interstitial fluid and streaming potentials are, in turn, perceived by chondrocytes. Chondrocyte responses to these stimuli are specific and well coordinated to bring about changes in gene expression, protein synthesis, matrix composition and ultimately biomechanical competence. In this hypothesis paper we propose a chondrocyte mechanoreceptor model incorporating key extracellular matrix macromolecules, integrins, mechanosensitive ion channels, the cytoskeleton and subcellular signal transduction pathways that maintain the chondrocyte phenotype, prevent chondrocyte apoptosis and regulate chondrocyte-specific gene expression.

Effects of the antirheumatic remedy hox alpha--a new stinging nettle leaf extract--on matrix metalloproteinases in human chondrocytes in vitro

Inflammatory joint diseases are characterized by enhanced extracellular matrix degradation which is predominantly mediated by cytokine-stimulated upregulation of matrix metalloproteinase (MMP) expression. Besides tumour necrosis factor-alpha (TNF-alpha), Interleukin-1beta (IL-1beta) produced by articular chondrocytes and synovial macrophages, is the most important cytokine stimulating MMP expression under inflammatory conditions. Blockade of these two cytokines and their downstream effectors are suitable molecular targets of antirheumatic therapy. Hox alpha is a novel stinging nettle (Urtica dioica/Urtica urens) leaf extract used for treatment of rheumatic diseases. The aim of the present study was to clarify the effects of Hox alpha and the monosubstance 13-HOTrE (13-Hydroxyoctadecatrienic acid) on the expression of matrix metalloproteinase-1, -3 and -9 proteins (MMP-1, -3, -9). Human chondrocytes were cultured on collagen type-II-coated petri dishes, exposed to IL-1beta and treated with or without Hox alpha and 13-HOTrE. A close analysis by immunofluorescence microscopy and western blot analysis showed that Hox alpha and 13-HOTrE significantly suppressed IL-1beta-induced expression of matrix metalloproteinase-1, -3 and -9 proteins on the chondrocytes in vitro. The potential of Hox alpha and 13-HOTrE to suppress the expression of matrix metalloproteinases may explain the clinical efficacy of stinging nettle leaf extracts in treatment of rheumatoid arthritis. These results suggest that the monosubstance 13-HOTrE is one of the more active antiinflammatory substances in Hox alpha and that Hox alpha may be a promising remedy for therapy of inflammatory joint diseases.

Co-localization of integrins and matrix metalloproteinases in the extracellular matrix of chondrocyte cultures

Beta1-integrins were found in the cartilage matrix, suggesting their implication in the assembly of its architectural scaffold, but the mechanism for this event is not yet clear. Matrix metalloproteinases (MMPs) may be involved in an integrin-shedding mechanism and matrix beta1-integrins may act to alter MMP activity. To begin to address this question, this study was designed to determine whether beta1-integrins and MMPs are colocalized in the chondrocytes or in the extracellular matrix of cartilage. We investigated high-density cultures of limb buds of 12-day-old mouse embryos by double immunofluorescence, immunoelectron microscopy and by coimmunoprecipitation assays in order to examine the localization of beta1-integrins and matrix metalloproteinases (MMP-1, MMP-3 and MMP-9) in cartilage. It was found, that all investigated MMPs and beta1-integrins were specifically co-localized in high-density cartilage cultures. Immunogold and immunofluorescence labelling of both beta1-integrins and MMPs were observed not only at the surface of chondrocytes but mainly also in the pericellular space and distributed between collagen fibrils in the extracellular matrix (ECM) as well. Results of immunoprecipitation experiments suggest a functional association of MMPs and beta1-integrins in chondrocytes as already described for other cell types. Further investigations are needed to elucidate the functional association between beta1-integrins and MMPs in chondrocytes.

Biochemical changes in Achilles tendon from juvenile dogs after treatment with ciprofloxacin or feeding a magnesium-deficient diet

Quinolones are antibacterial agents that have the potential to induce Achilles tendon disorders - such as tendinitis or even ruptures - in patients treated with these drugs. We studied the effects of ciprofloxacin on several proteins of Achilles tendons from immature dogs, 10- to 11-weeks-old. The dogs were treated orally for 5 days with 30 or 200 mg ciprofloxacin/kg body weight or with the vehicle alone. Since quinolone-like alterations in joint cartilage were observed in magnesium-deficient animals, another group was fed a magnesium-deficient diet for 6 weeks. At necropsy, tendons (n=3 from each group) were frozen and stored until analysis when they were homogenized in a lysis buffer to release a soluble fraction of the tendon proteins. Densitometric analysis of the immunoblots with anticollagen type I, anti-elastin, anti-fibronectin, and antiintegrin antibodies showed a significant reduction of all proteins. For example, collagen type I concentrations (mean +/-SD, arbitrary densitometric units) were 3190+/-217 (controls), 1890+/-468 (30mg/kg), 1695+/-135 (200mg/kg) and 2053+/-491 in the magnesium-deficient dogs. The differences between concentrations in controls and all treated groups were statistically significant (P<0.01, t-test). Similarly, compared with control samples, relative concentrations of other proteins in tendons from ciprofloxacin-treated dogs (30 mg/kg) decreased by 73% (elastin), 88% (fibronectin), and 96% (beta1 integrin) (data from low-dose group only). A very similar pattern of protein alterations was detected in samples from magnesium-deficient dogs. In conclusion, rather low doses of a fluoroquinolone or a diet-induced magnesium deficiency caused similar biochemical alterations in the soluble fraction of proteins from canine tendons. These findings support our hypothesis that quinolone-induced toxic effects on connective tissue structures are due to the magnesium-antagonistic effects of these antibacterial agents. They also indicate that patients with a latent magnesium deficiency could be at an increased risk of quinolone-induced tendon disorders.

Inhibition of mitogen-activated protein kinase kinase induces apoptosis of human chondrocytes

We previously have reported that the mitogen-activated protein kinase (MAPK) pathway is stimulated by adhesion of human chondrocytes to anti-beta(1)-integrin antibodies or collagen type II in vitro. These mechanisms most likely prevent chondrocyte dedifferentiation to fibroblast-like cells and chondrocyte death. To investigate whether this pathway plays an essential role for the differentiation, phenotype, and survival of chondrocytes, we blocked mitogen-activated protein kinase/extracellular signal-regulated kinase (Erk) (MEK), a kinase upstream of the kinase Erk by using U0126. Exposure of chondrocytes to U0126 caused activation of caspase-3 in a dose-dependent manner. Western blot analysis with an antibody specific for dually phosphorylated Erk shows that collagen type II induced phosphorylation of Erk1/2 was specifically blocked by U0126 in a dose-dependent manner. Immunohistochemical analysis showed that treated chondrocytes were caspase-3 positive. In treated chondrocytes, the cleavage of 116-kDa poly(ADP-ribose)polymerase resulted in the 85-kDa apoptosis-related cleavage fragment and was associated with caspase-3 activity. Analysis by electron microscopy showed typical morphological signs of apoptosis, such as crescent-shaped clumps of heterochromatin, and a degraded pericellular matrix. Thus, these results indicate that the MEK/Erk signal transduction pathway is involved in the maintenance of chondrocytes differentiation and survival. These data stimulate further investigations on the role of mitogen-activated protein kinase pathways in human chondrocytes.

Ultrastructure of Achilles tendon from rats after treatment with fleroxacin

Quinolone therapy can be associated with tendon disorders (tendinitis, ruptures), but little is known about possible ultrastructural changes in tendons after exposure to these antimicrobials. We studied the Achilles tendons from fleroxacin-treated adult rats by electron microscopy. Wistar rats were treated orally with single oral doses of 0, 30, 100, 300 or 600 mg fleroxacin/kg body weight (n = 6 per group). The animals were killed 4 weeks after treatment. Achilles tendon samples were collected and tangential sections were made from the distal part of the tendon. Subsequently, tendons were cut crosswise for preparation of ultrathin sections. Samples were fixed by using glutaraldehyde, osmium tetroxide, tannic acid and finally contrasted with uranyl acetate/lead citrate before they were examined by transmission electron microscopy. The rats did not show any general effects such as behavioural changes or body weight changes which could be attributed to the treatment. However, we were able to detect pathological changes even at the lowest dose level (30 mg/kg), which increased in incidence and severity with increasing doses. Tenocytes exhibited degenerative changes such as multiple vacuoles and large vesicles in the cytoplasm that resulted from swelling and dilatation of cell organelles (mitochondria, endoplasmic reticulum). The nucleus became dense and the chromatin had clumped to form rough plaques. The cells detached from the extracellular matrix. Other important findings were a general decrease of the fibril diameter and an increase in the distance between the collagenous fibrils. The finding that these rather low single dose of a fluoroquinolone induce ultrastructural changes in Achilles tendons from rats, which were not associated with clinical symptoms and which were still present 4 weeks after treatment, is of concern. Further toxicological as well as clinical studies are needed to characterize the conditions under which quinolone-induced tendon lesions develop.

Expression of the urokinase-type plasminogen activator receptor in human articular chondrocytes: association with caveolin and beta 1-integrin

The urokinase-type plasminogen activator (uPA) in concert with other proteolytic enzymes plays a critical role in cartilage degradation during osteoarthritis. Urokinase receptor (uPAR), a glycosyl-phosphatidylinositol-linked glycoprotein present on the cell surface of various cell types such as cancer cells, fibroblasts, synoviocytes, and chondrocytes, is a key regulator of the plasmin-mediated pericellular proteolysis. Recently, in arthritic synovial tissue increased uPAR expression has been detected. By immunohistochemical analysis we observed, in addition, enhanced expression of uPAR in chondrocytes of arthritic samples of human cartilage compared to non-arthritic controls. Using in vitro cultured human chondrocytes, we analyzed whether uPAR is associated with structural proteins, which are known to be involved in cell signaling and activation. uPAR in phorbol-12-myristate-13-acetate-stimulated chondrocytes colocalized with caveolin as well as beta 1-integrin, as demonstrated by double immunostaining with specific antibodies. Furthermore, uPAR was present in caveolae-like structures of chondrocytes as detected by immunoelectron microscopy. Finally, both caveolin and beta 1-integrin were coprecipitated with uPAR-specific antibodies from cell extracts suggesting that these proteins may form functional complexes in human chondrocytes. The localization of uPAR in caveolae and its close association with caveolin and beta 1-integrin points to a significance of uPAR-mediated signaling pathways in human chondrocytes.

Extracellular matrix proteins in cardiac fibroblasts derived from rat hearts with chronic pressure overload: effects of beta-receptor blockade

Left ventricular hypertrophy (LVH) is accompanied by progressive accumulations of extracellular matrix proteins. They are produced predominantly by cardiac fibroblasts that surround the cardiac myocytes. The aim of this study was to emphasize the role of a combined approach using both in vivo and in vitro studies to elucidate the effects of carvedilol on cardiac remodeling. We therefore used an established model of supravalvular aortic banding and cardiac fibroblasts. LVH was induced by banding of the ascending aorta. Male Wistar rats were allocated to four groups: sham-operated, sham+carvedilol, aortic stenosis (AS), and AS+carvedilol. Treatment time was four weeks. Fibroblasts were isolated from the entire left ventricle of sham and AS rats. Carvedilol/metoprolol/prazosin were added (0.1, 1.0 and 10 microM; 24 h). In addition, interferon- gamma was applied for 24 h (10, 100 and 1000 IU). AS rats revealed increased LV weights (+27%) and cardiomyocyte widths as compared to sham-operated rats (1.6-fold, P<0.01). Carvedilol reduced LVH by 20%. This finding was accompanied by a decrease of laminin, fibronectin, collagen I and III in vivo. Collagen I/III and fibronectin were increased in fibroblasts of AS v sham rats (P<0.0001, each). Carvedilol reduced collagen I, III and fibronectin by 40/60/35% (0.1 microM; P<0.001) irrespective of LVH. Carvedilol had no effects on collagen IV and laminin. Carvedilol dose-dependently reduced the proliferation rate by 20% at 0.1 microM(P<0.0001). Metoprolol and prazosin had no effect on the expression of extracellular matrix proteins and on the proliferation of the cells of either origin. Interferon- gamma blunted the proliferation rate of cultured fibroblasts and lead to a significant decrease in extracellular matrix deposits. These results indicate that the effects of carvedilol may be due to the antiproliferative or antioxidative properties of this unselective beta-adrenergic receptor antagonist. These changes of the extracellular matrix represent a new mechanism of carvedilol that may contribute to the observed beneficial effects in congestive heart failure.

Developmental toxicity of the HIV-protease inhibitor indinavir in rats

BACKGROUND

Indinavir is an antiviral agent used for the treatment of HIV infection. We studied its developmental toxicity in rats.

METHODS

Pregnant animals were treated orally with 500 mg indinavir/kg body weight (bw) from day 6 to 15 of gestation (once daily) or from day 9 to 11 (twice daily). Fetuses were evaluated for external and skeletal anomalies on day 21 of gestation. In addition, 19 rats were treated from day 9 of gestation to day 24 postnatally with 500 mg indinavir/kg bw once daily; a control group of 17 rats was treated with the vehicle accordingly. Developmental landmarks were recorded. Sixteen offspring each were studied on postnatal days 7, 14, 21, and 35 for hepatic enzyme activity. Liver tissue was examined by electron microscopy.

RESULTS

Fetal examination on day 21 of pregnancy showed no treatment-related effects on number, weight, and viability of the fetuses; however, an increased incidence was noted in the supernumerary ribs and variations of the vertebral ossification centers in both indinavir-treated groups. Postnatal evaluation showed delayed fur development, eye opening, and descensus testis. The most striking finding was unilateral anophthalmia, observed in 7 pups (3%) from 2 out of 19 litters exposed to indinavir, but not in controls. Only minor changes in hepatic monooxygenase activities occurred in dams. Electron microscopy of liver samples showed hepatocellular inclusions of lipids and myelin figure-like structures in maternal livers and infiltration with granulocytes in offspring livers.

CONCLUSIONS

Further studies on reproductive toxicity, including combinations of three or more antiretroviral agents as used therapeutically, are needed to determine the hazards of such a treatment.

Characterization of caveolins from human knee joint catilage: expression of caveolin-1, -2, and -3 in chondrocytes and association with integrin beta1

Interactions between the extracellular matrix (ECM) and chondrocytes are of great importance for structure and function of cartilage. The present study was undertaken to answer the question whether caveolins take part in integrin-mediated cell-ECM interactions in the human cartilage. In samples of human knee joint cartilage, we detected the caveolin subtypes -1, -2, and -3 by immunohistochemical methods. Double-label experiments revealed a colocalization of caveolin with beta1-integrin. Results of immunoprecipitation and immunoblotting assays show that beta1-integrins associate with all three caveolin subtypes in human chondrocytes and indicate that they are part of the same complexes. Furthermore, immunoelectron microscopy shows the localization of beta1-integrin in caveolae-like structures of the cell membrane. The data stimulate further investigations on the role of the caveolin-integrin complex for integrin-mediated signaling pathways in chondrocytes.

Ultrastructure of Achilles tendons of rats treated with ofloxacin and fed a normal or magnesium-deficient diet

Fluoroquinolones can cause tendinitis and tendon rupture. However, toxicological as well as clinical information on quinolone-induced tendopathy is scarce. We performed extensive electron microscopic studies with Achilles tendon specimens from ofloxacin-treated rats. The drug was given at a dose of 1,200 mg/kg (body weight) orally. Juvenile Wistar rats received one or three oral doses each of 1,200 mg of ofloxacin/kg (body weight)/day. Three days after treatment, the tenocytes of their Achilles tendons showed degenerative alterations, such as multiple vacuoles and vesicles in the cytoplasm that had developed due to swellings and dilatations of cell organelles. Other indications of cell degradation were the occurrence of cell debris and cell detachment from the extracellular matrix accompanied by a loss of cell-matrix interaction. The tenocytes of juvenile Wistar rats that had been treated at day 36 with a single oral dose of 1,200 mg of ofloxacin/kg (body weight) and sacrificed either 3 or 6 months later exhibited similar degenerative alterations. The number of degenerative alterations of tenocytes after ofloxacin treatment was considerably higher in rats that had received a magnesium-deficient diet than in rats with normal magnesium status. Of the adult rats that had been treated once, 5 times, and 10 times with ofloxacin and killed 1 day later, only those with the 10-times treatment showed a significantly increased number of degeneratively altered tenocytes. In summary, effects observed in tendons show similar pathological features as described earlier in cartilage, indicating that quinolone-induced arthropathy and quinolone-induced tendopathy probably are different clinical manifestations of the same toxic effect on cellular components of connective tissue structures.

Chondrotoxicity of ciprofloxacin in immature beagle dogs: immunohistochemistry, electron microscopy and drug plasma concentrations

The systemic effects of ciprofloxacin in immature Beagles were studied. Dogs of 10-11 weeks were dosed orally for 5 days with 0 (n=3), 30 (n=5) and 200 (n=5) mg ciprofloxacin/kg body wt. Plasma concentrations were measured by high-performance liquid chromatography (HPLC) 1 h after dosing (assuming to be peak concentrations). In view of the high doses used, the plasma concentrations were rather low and declined during the study period. For example, plasma concentrations in the high dose group were 6.6 +/- 0.9 mg/l (day 1), 3.9 +/- 1.4 mg/l (day 3), and 2.6 +/- 1.6 mg/l (day 5). In control dogs and in dogs treated with the low dose of ciprofloxacin no pathological changes were seen by light microscopy. However, cleft formation and erosions were observed in joint cartilage from two of five dogs treated with 200 mg/kg. It is noteworthy that despite the high dose used cartilage lesions were not detectable in all five dogs of this group by light microscopy. Using antibodies against cell membrane receptors (e.g. the alpha(5)beta(1)-integrin) or matrix components (fibronectin, collagen II) the articular cartilage effects were studied in detail by immunohistochemistry. The most sensitive alteration was an increase in fibronectin which was detectable in the vicinity of the lesions in cartilage samples from the group of dogs administered the high dose. No clear-cut changes were seen with the use of antibodies against other matrix components. Electron microscopy revealed typical alterations in chondrocytes from dogs treated with ciprofloxacin: e.g., swollen mitochondria and enlarged rough endoplasmic reticulum. These changes were much more pronounced in dogs from the high dose group than in dogs from the low dose group. Our main conclusion is that after oral administration ciprofloxacin exhibits rather low chondrotoxicity, even in the most sensitive species known to date. This correlates with the findings in humans that ciprofloxacin seems to be less chondrotoxic than pefloxacin or other quinolones.

Effects of magnesium deficiency on joint cartilage in immature beagle dogs: immunohistochemistry, electron microscopy, and mineral concentrations

Quinolone-induced chondrotoxicity is possibly associated with the magnesium-chelating properties of quinolones. This toxic effect seems to be restricted to a rather short time period during postnatal development as shown in rats and dogs. We studied developmental changes of the integrin pattern on canine chondrocytes (e.g. the alpha(v)beta(3)- or alpha(5)beta(1)-integrin), because integrin function depends on divalent cations, as well as the matrix composition (e.g., collagen type II, fibronectin), in 11-, 18-, and 55-week-old Beagles (n=8) by immunohistochemistry. We also analyzed the magnesium and calcium content by atomic absorption spectroscopy in cartilage and bone and studied the effects of a magnesium-deficient diet on joint cartilage in four immature Beagles (18 weeks old at necropsy). The dogs were fed the magnesium-deficient diet for 40 to 46 days. All dogs exhibited gait alterations ('limping') after 4 weeks on the magnesium-deficient diet. Male, magnesium-deficient dogs exhibited pronounced weakness in their front legs; in one of these dogs the front legs were hyperextended to a 90 degrees angle. We observed no significant differences in the integrin pattern in samples from dogs at different developmental stages or in magnesium-deficient dogs in comparison to age-matched controls. Localization of fibronectin in the joint cartilage was found to vary with the age of the dogs as well as with the site of collection. In the middle zone of immature joint cartilage, corresponding to the predilective site of quinolone-induced cartilage lesions, we observed a slight increase in staining with the fibronectin antibody in some samples from magnesium-deficient dogs. Electron microscopy revealed alterations in chondrocytes from the magnesium-deficient dogs (e.g., swollen mitochondria and enlarged endoplasmic reticulum) which are also seen after treatment with quinolones. In summary, we found no significant differences of the integrin pattern on chondrocytes from joint cartilage of dogs at various developmental stages. However, magnesium deficiency in immature dogs induced similar clinical symptoms as quinolone treatment as well as distinct alterations in chondrocytic fibronectin staining and their ultrastructure. This corroborates our findings in rats where magnesium chelation is an important event in quinolone-induced chondrotoxicity.

Signal transduction by beta1 integrin receptors in human chondrocytes in vitro: collaboration with the insulin-like growth factor-I receptor

We have examined the mechanism by which collagen-binding integrins co-operate with insulin-like growth factor-I (IGF-I) receptors (IGF-IR) to regulate chondrocyte phenotype and differentiation. Adhesion of chondrocytes to anti-beta1 integrin antibodies or collagen type II leads to phosphorylation of cytoskeletal and signalling proteins localized at focal adhesions, including alpha-actinin, vinculin, paxillin and focal adhesion kinase (FAK). These stimulate docking proteins such as Shc (Src-homology collagen). Moreover, exposure of collagen type II-cultured chondrocytes to IGF-I leads to co-immunoprecipitation of Shc protein with the IGF-IR and with beta1, alpha1 and alpha5 integrins, but not with alpha3 integrin. Shc then associates with growth factor receptor-bound protein 2 (Grb2), an adaptor protein and extracellular signal-regulated kinase. The expression of the docking protein Shc occurs only when chondrocytes are bound to collagen type II or integrin antibodies and increases when IGF-I is added, suggesting a collaboration between integrins and growth factors in a common/shared biochemical signalling pathway. Furthermore, these results indicate that focal adhesion assembly may facilitate signalling via Shc, a potential common target for signal integration between integrin and growth-factor signalling regulatory pathways. Thus, the collagen-binding integrins and IGF-IR co-operate to regulate focal adhesion components and these signalling pathways have common targets (Shc-Grb2 complex) in subcellular compartments, thereby linking to the Ras-mitogen-activated protein kinase signalling pathway. These events may play a role during chondrocyte differentiation.

Beta1-integrins in the cartilage matrix

Integrins are cell-surface receptors that mediate cell attachment to extracellular matrix components. The pericellular matrix in cartilage not only is a mechanical framework, but is also important for chondrocyte differentiation and stabilization of the phenotype. The interaction between chondrocytes and pericellular matrix is mediated, in part, by integrin receptors. We have previously demonstrated the presence of beta1-integrins in the cartilage matrix of organoid culture of limb buds from 12-day-old mouse embryos by immunohistological methods. In order to corroborate these findings, we have further investigated the distribution of integrins in the cartilage matrix by immunoelectron microscopy and by immunoprecipitation methods. Cartilage tissue of limb buds of 17-day-old mouse embryos was treated with collagenase and the cell-free and cellular protein-free supernatant was removed and used for immunoprecipitation experiments. Immunoprecipitation with antibodies against beta1-, alpha1-, alpha3-, and alpha5beta1-integrins and collagen type II, followed by immunoblotting with the same antibodies, demonstrated the presence of these integrins and collagen type II in the supernatant. The integrins found in the cartilage matrix could have been either secreted or shed by the cells. The question as to whether they have a function in the cartilage matrix, such as interlinking, in the matrix organization or in the stabilization of matrix components remains to be elucidated.

Malaria circumsporozoite protein inhibits protein synthesis in mammalian cells

Native Plasmodium circumsporozoite (CS) protein, translocated by sporozoites into the cytosol of host cells, as well as recombinant CS constructs introduced into the cytoplasm by liposome fusion or transient transfection, all lead to inhibition of protein synthesis in mammalian cells. The following findings suggest that this inhibition of translation is caused by a binding of the CS protein to ribosomes. (i) The distribution of native CS protein translocated by sporozoites into the cytoplasm as well as microinjected recombinant CS protein suggests association with ribosomes. (ii) Recombinant CS protein binds to RNase-sensitive sites on rough microsomes. (iii) Synthetic peptides representing the conserved regions I and II-plus of the P.falciparum CS protein displace recombinant CS protein from rough microsomes with dissociation constants in the nanomolar range. (iv) Synthetic peptides representing region I from the P.falciparum CS protein and region II-plus from the P.falciparum, P.berghei or P.vivax CS protein inhibit in vitro translation. We propose that Plasmodium manipulates hepatocyte protein synthesis to meet the requirements of a rapidly developing schizont. Since macrophages appear to be particularly sensitive to the presence of CS protein in the cytosol, inhibition of translation may represent a novel immune evasion mechanism of Plasmodium.

Effects of fluoroquinolones and magnesium deficiency in murine limb bud cultures

Quinolone-induced arthropathy is probably caused by a lack of functionally available magnesium in immature joint cartilage. We used an in vitro assay to study the effects of fluoroquinolones on cartilage formation in mouse limb buds from 12-day-old mouse embryos in regular and in magnesium-deficient medium. Omission of magnesium from the medium had no adverse effect on the outcome of the culture: limb buds grew and differentiated well in regular and in magnesium-deficient Bigger's medium. Lack of calcium, however, severely impaired the development of the explants; this result was even more enhanced when both minerals (magnesium and calcium) were omitted. Electron microscopy revealed cell necrosis and deposition of electron-dense material in the vicinity of chondrocytes from limb buds after 6 days in a magnesium-free medium. A series of seven fluoroquinolones was tested at 30, 60, and 100 mg/l medium. At a concentration of 30 mg/l sparfloxacin only had a slight effect on limb development. At concentrations of 60 and 100 mg/l sparfloxacin, temafloxacin and ciprofloxacin impaired limb development in vitro concentration-dependently. The effects were enhanced in a magnesium-deficient medium (concentration of magnesium <10 micromol/l). Fleroxacin, lomefloxacin and ofloxacin impaired limb development only slightly; no significant differences were recognizable between the outcome in regular and in magnesium-deficient medium. Pefloxacin did not show any effect on limb development in both media. Using electron microscopy, very similar alterations as described above for the limbs cultured in magnesium-deficient medium were observed with ofloxacin at a concentration of 30 mg/l, which had no effect on the growth of the explants when evaluated macroscopically. The affinity of six fluoroquinolones to magnesium was determined by the use of a fluorescence assay. The affinity to magnesium correlated with the activity of the drugs in the limb bud assay. We conclude that fluoroquinolones have no effect on murine limb development in vitro at concentrations that are achieved under therapeutic conditions (peak concentrations approx. 1-5 mg/l in plasma). Effects at higher concentrations (60 and 100 mg/l) are slightly enhanced (factor 2) if the magnesium concentration in the medium is low. Macroscopically, limbs develop regularly in a magnesium-free medium, but ultrastructurally typical alterations are exhibited (e.g. cell necrosis and pericellular deposition of electron-dense material).

Chondrotoxicity and toxicokinetics of sparfloxacin in juvenile rats

Sparfloxacin is a fluoroquinolone with improved antibacterial activity against gram-positive pathogens. Like other quinolones, use of this drug is contraindicated in children and adolescents because of its potential chondrotoxicity in juveniles. We performed histological and immunohistochemical studies on the knee joint cartilage in 5-week-old rats after treatment with 600 or 1,800 mg of sparfloxacin/kg of body weight. Treatment with single or multiple oral doses of 600 mg of sparfloxacin/kg was not sufficient to induce joint cartilage lesions. However, five of eight rats treated with a single oral dose of 1,800 mg of sparfloxacin/kg of body weight showed typical cartilage lesions in the femoral part of the knee joint. The concentrations of the drug in plasma measured 0.25, 0.75, 1.5, 3, 6, 12, and 24 h after the administration of an oral dose of 600 mg of sparfloxacin/kg were 6.3 +/- 1.8, 9.2 +/- 1.7, 9.6 +/- 2.7, 13.0 +/- 1.8, 12.3 +/- 1.6, 3.4 +/- 0.4, and 0.30 +/- 0.20 mg/liter, respectively (mean +/- standard deviation [SD]; n = 5 to 6 per group). The concentrations in plasma measured 0.75, 1.5, 3, 6, 24, and 48 h after the administration of an oral dose of 1,800 mg of sparfloxacin/kg were 10.9 +/- 1.5, 15.9 +/- 1.6, 19.1 +/- 1.7, 14.9 +/- 3.1, 4.1 +/- 0.6, and 0.46 +/- 0.37 mg/liter, respectively (mean +/- SD; n = 3 to 4 per group). The concentrations of sparfloxacin in joint cartilage were significantly higher at all time points studied (114.8 +/- 80, 99.4 +/- 31.5, 84.9 +/- 16.8, 44.4 +/- 13.9, and 14.2 +/- 4.8 mg of sparfloxacin/kg at 1.5, 3, 6, 24, and 48 h after the administration of 1,800 mg/kg, respectively). The range of concentrations in bone were similar to the range of concentrations in cartilage (peak, 115 +/- 12 mg/kg after 3 h). Our data indicate that chondrotoxic doses of sparfloxacin in juvenile rats are approximately 300 times higher than the doses of sparfloxacin used therapeutically (1,800 versus approximately 6 mg/kg of body weight), but due to species differences in kinetics, concentrations in plasma differ by a factor of only approximately 15. More data on quinolone concentrations in cartilage from animals and humans could provide a better basis for a reasonable risk assessment.

Inhibition of chondrogenesis by integrin antibody in vitro

Integrins mediate cell attachment to a variety of extracellular matrix proteins. These interactions play an important role in morphogenesis and differentiation. The mediating functions of integrins during chondrogenesis in vitro were investigated by using mesenchymal cells from limb buds of day 12 mouse embryos. The cells were treated with anti-beta 1, -alpha 1, and -alpha 5 integrin antibodies (a) from day 1 to day 3 and (b) from day 3 to day 7 of cultivation. The total culture period was 7 days. The presence of exogenous anti-beta 1, but not -alpha 1 and -alpha 5 integrin antibodies, from day 1 to 3 completely inhibited the differentiation of blastemal cells to chondroblasts and the formation of cartilage matrix. On the other hand, the presence of exogenous anti-beta 1, -alpha 1, and -alpha 5 integrin antibodies from day 3 of cultivation onwards had no effect. Immunoblotting and immunomorphological findings in the cultures treated with anti-beta 1 antibody from day 1 to day 3 revealed a pattern of integrins and collagen composed of beta 1, alpha 1, alpha 5 beta 1 integrins and collagen type I. The cartilage-specific chondroitin sulfate proteoglycan (CSPG) could not be demonstrated in these cultures. The cultures treated later (day 3 to day 7) showed a pattern of beta 1, alpha 3, alpha 5 beta 1, and alpha v beta 3 integrins, collagen types I and II, and CSPG identical to that of the untreated controls. These findings indicate that beta 1-integrins play a crucial role in early cartilage differentiation and point to a possible important cell-matrix interaction in the induction of chondrogenesis.

Molecular anatomy of the perivascular sheath in human placental stem villi: the contractile apparatus and its association to the extracellular matrix

In previous studies, we have shown that smooth muscle cells and myofibroblast subpopulations of the perivascular stem villous sheath of the human placenta contain focal adhesion plaques and talin immunoreactivity. The close association of these cells to elastic and collagen fibres have led to the assumption of a functional myofibroelastic unit within the perivascular stem villous sheath. Interactions between the extracellular matrix and smooth muscle cells depend on a variety of structural protein assemblies. In the present study, we examined, by immunocytochemistry, whether the molecular assembly of extracellular matrix proteins and molecules of focal adhesions, known to be essential for signal transduction in smooth muscle cells, are also found in smooth muscle cells of the perivascular stem villous sheath of the human placenta. Vascular and extravascular smooth muscle cells were immunoreactive for alpha-actinin, vinculin, paxillin and tensin, the integrin chains alpha1 and beta1, and the basement membrane components laminin and heparan/-chondroitin sulfate proteoglycan perlecan. pp125(FAK) did not react. In the extracellular matrix of blood vessel walls and the perivascular stem villous sheath, we found immunoreactivity of fibronectin and collagen types I, VI and undulin (collagen type XIV). From our data we conclude that within the perivascular stem villous sheath, there exists a system of signal transduction molecules, indicating a cross talk between the smooth muscle cells of this sheath and their surrounding extracellular matrix.