Effects of oxygen free radicals on articular chondrocytes in culture: c-myc and c-Ha-ras messenger RNAs and proliferation kinetics

Immunofluorescence localization of prolyl 4-hydroxylase isoenzymes and type I and II collagens in bone tumours: type I enzyme predominates in osteosarcomas and chondrosarcomas, whereas type II enzyme predominates in their benign counterparts

Prolyl 4-hydroxylase is the key enzyme of synthesis of collagens. Hydroxylation of a sufficient number of proline residues to hydroxyproline is necessary for the stability of triple helices in collagenous proteins, because non-hydroxylated non-triple-helical collagen polypeptide chains are degraded intracellularly. We studied 15 primary chondrosarcomas and osteosarcomas, 17 benign bone tumours and one case of fibrous dysplasia and chordoma using immunofluorescence staining with antibodies against the alpha(I) and alpha(II) subunits of type I and II prolyl 4-hydroxylases, and with antibodies against collagen types I and II. Type I prolyl 4-hydroxylase was found to be the predominant isoenzyme in both types of bone sarcoma, whereas the type II enzyme was more readily expressed by benign tumours. A feature of collagen staining, that was common to both sarcoma types, was that collagen types I and II were mainly found within cancer cells and were rarely present extracellularly. Extracellular collagen staining was more obvious in benign tumours. The results show that expression of prolyl 4-hydroxylase isoenzymes is altered in bone sarcomas as compared with normal bone tissue. Chondrous cells, which normally express mainly the type II isoenzyme, switch their expression pattern to that of type I. The findings provide evidence that type I is the major isoenzyme in malignant bone tumours, and probably in malignant neoplasms in general. The pattern of enzyme expression is considered to be associated with dedifferentiation of cancer cells.

Reactive oxygen intermediates involved in cellular regulation

Reactive oxygen intermediates (ROIs) in low concentration, as released permanently by nonphagocytic cells, possess important functions in inter- and intracellular signalling. They lead to alterations in the phosphorylation pattern followed by gene activation, including the expression of proto-oncogenes. Redox-sensitive sites in membrane molecules may trigger adhesion and chemotaxis or open ion channels and activate transport processes across the cytoplasma membrane. ROIs shift the ratio of cyclic GMP to cyclic AMP giving signals to proliferation and differentiation processes. Senescence, apoptosis, and cell death can also be modulated by ROIs, depending on concentration and cell type.

Expression of extracellular matrix genes: transforming growth factor (TGF)-beta1 and ras in tibial fracture healing of lathyritic rats

Experimental osteolathyrism, induced by dietary aminoacetonitrile (AAN), was used to study the effect of altered extracellular matrix on the expression of connective tissue components in long bone healing. AAN inhibits lysyl oxidase, which is needed for the formation of collagen cross-link precursors, and is also shown to act as a regulator of Ras. Fractured tibias in lathyritic rats develop excessive amounts of mechanically weak callus tissue with irregular cartilage and reduced glycosaminoglycan accumulation. Cartilage-specific proteins (collagen types II, IX, and X and aggrecan) were expressed temporally much wider in lathyritic calluses than in the controls, and active transcription was observed even during the fibrous and ossifying stages. Soft connective tissue was still present in 2- and 3-week-old lathyritic calluses and could explain the elevated type III collagen, biglycan, and decorin mRNA levels. Both transforming growth factor (TGF)-beta1 and c-Ha-ras, which control cell growth and differentiation, were upregulated during the cartilaginous stage. The maximal expression of TGF-beta1 preceded that of ras in osteolathyrism.

Oxidative stress and gene regulation

Reactive oxygen species are produced by all aerobic cells and are widely believed to play a pivotal role in aging as well as a number of degenerative diseases. The consequences of the generation of oxidants in cells does not appear to be limited to promotion of deleterious effects. Alterations in oxidative metabolism have long been known to occur during differentiation and development. Experimental perturbations in cellular redox state have been shown to exert a strong impact on these processes. The discovery of specific genes and pathways affected by oxidants led to the hypothesis that reactive oxygen species serve as subcellular messengers in gene regulatory and signal transduction pathways. Additionally, antioxidants can activate numerous genes and pathways. The burgeoning growth in the number of pathways shown to be dependent on oxidation or antioxidation has accelerated during the last decade. In the discussion presented here, we provide a tabular summary of many of the redox effects on gene expression and signaling pathways that are currently known to exist.

Oxidative stress and superoxide dismutase in development, aging and gene regulation

Free radicals and other reactive oxygen species are produced in the metabolic pathways of aerobic cells and affect a number of biological processes. Oxidation reactions have been postulated to play a role in aging, a number of degenerative diseases, differentiation and development as well as serving as subcellular messengers in gene regulatory and signal transduction pathways. The discovery of the activity of superoxide dismutase is a seminal work in free radical biology, because it established that free radicals were generated by cells and because it made removal of a specific free radical substance possible for the first time, which greatly accelerated research in this area. In this review, the role of reactive oxygen in aging, amyotrophic lateral sclerosis (a neurodegenerative disease), development, differentiation, and signal transduction are discussed. Emphasis is also given to the role of superoxide dismutases in these phenomena.

Auto-destruction of the articular cartilage and free radical mediators

The effect of static compression on the release of superoxide (SO) and nitric oxide (NO) from cartilage obtained from rabbit knee joints with tissue defects was studied. The rabbits were divided into two groups: (1) those that had 5 mm diameter full chondral defects (defect group) and (2) those in which chondral defects were filled with autogenous perichondrial grafts (grafted group). Histologically, cartilage was regenerated in the grafted group 3 weeks after the operation, although only a fibrous tissue filled the defects in the defect group even 16 weeks after the operation. A static pressure of 5 kg for 10 minutes applied to the cartilage chips obtained from the area surrounding the defects released significant amounts of SO and NO into the medium. Maximum increases were observed in the defect group 3 weeks after the operation.

Articular chondrocytes and synoviocytes in culture: influence of antioxidants on lipid peroxidation and proliferation

Chondrocytes and synoviocytes are the main cell types in articular joints. Articular cartilage is fed by synoviocytes via synovial fluid and has a low partial oxygen pressure. Thus, chondrocytes show oxygen radical protective mechanisms in vivo and are unprotected against these factors under common culture conditions. We investigated the influence of ascorbic acid, Fe2+, glutathione and alpha-tocopherol on lipid peroxidation and proliferation of rat articular chondrocytes and rabbit synoviocytes (HIG-82) in vitro. A combination of ascorbic acid and Fe2+ induced the production of thiobarbituric acid-reactive material as a marker of radical-mediated lipid peroxidation in homogenates and/or supernatants of cultured chondrocytes and synoviocytes. The amount of lipid peroxidation of chondrocytes was about 3-fold higher than that of synoviocytes. Ascorbic acid or Fe2+ alone had no significant influence on the production of thiobarbituric acid-reactive material. Lipid peroxidation could be abolished by addition of the radical scavenger alpha-tocopherol, whereas glutathione had no effect. 25-50 microM alpha-tocopherol decreased the ascorbic acid-(100 micrograms/ml) and Fe(2+)-(3 microM) induced lipid peroxidation to a basal level. Moreover, ascorbic acid inhibited the proliferation of rat chondrocytes and rabbit synoviocytes measured by [3H]-thymidine incorporation. Alpha-tocopherol and glutathione had no influence on the proliferation of chondrocytes but alpha-tocopherol decreased the growth of synoviocytes and increased the anti-proliferative effect of ascorbic acid on these cells. The importance of these findings for the use of ascorbic acid, glutathione and alpha-tocopherol in chondrocyte and synoviocyte cultures, or the influence of these molecules on the etiology and treatment of articular diseases will be discussed.

Type II transglutaminase expression in rabbit articular chondrocytes in culture: relation with cell differentiation, cell growth, cell adhesion and cell apoptosis

Depending on the cell type studied, the involvement of type II transglutaminase (TGase) has been proposed in almost any event of the cell life such as differentiation, apoptosis, growth, aging, cell morphology and adhesion, metastatic capacity or extracellular matrix stabilization. In order to define the field(s) where this enzyme may be implicated in chondrocytes, type II TGase expression was studied in chondrocytes at different passages which differentiated state was modulated by retinoic acid, dihydrocytochalasin B or staurosporin. Results showed that (i) type II TGase expression is not incompatible with type II collagen expression, a main marker of chondrocyte differentiation (ii) type II TGase expression is higher when cells are in the exponential phase of growth than when growth arrested (iii) a high type II TGase expression does not imply that cells are apoptotic although cell apoptosis correlates with increased type II TGase expression (iv) non-adherent cells do not express type II TGase whereas adherent cells do whatever their differentiation state as assessed by type II collagen synthesis. These results suggest that, in articular chondrocytes, type II TGase is specifically implicated in the cell adhesion capacity.

Retinoic acid modulation of glutathione and cysteine metabolism in chondrocytes

The major objective of this investigation was to determine the thiol status of chondrocytes and to relate changes in the level of glutathione and cysteine to maturation of the cells as they undergo terminal differentiation. Chondrocytes were isolated from the cephalic portion of chick embryo sterna and treated with all-trans retinoic acid for one week. We found that the addition of 100 nM retinoic acid to the cultures decreased the intracellular levels of glutathione and cysteine from 6.1 to 1.6 and 0.07 to 0.01 nmol/microgram DNA respectively; retinoic acid also caused a decrease in the extracellular concentration of cysteine. The decrease in chondrocyte thiols was dose and time dependent. To characterize other antioxidant systems of the sternal cell culture, the activities of catalase, glutathione reductase and superoxide dismutase were determined. Activities of all of those enzymes were high in the retinoic acid-treated cells; the conditioned medium also contained these enzymes and the cytosolic isoenzyme of superoxide dismutase. We probed the specificity of the thiol response by using immature caudal chondrocytes. Unlike the cephalic cells, retinoic acid did not change intracellular glutathione and extracellular cysteine levels, although the retinoid caused a reduction in the intracellular cysteine concentration. Finally, we explored the effect of medium components on chondrocyte thiol status. We noted that while ascorbate alone did not change cell thiol levels, it did cause a 4-fold decrease in the extracellular cysteine concentration. When retinoic acid and ascorbic acid were both present in the medium, there was a marked decrease in the level of glutathione. In contrast, the phosphate concentration of the culture medium served as a powerful modulator of both glutathione and cysteine. Results of the study clearly showed that there is a profound decrease in intracellular levels of both cysteine and glutathione and that thiol levels are responsive to ascorbic acid and the medium phosphate concentration. These findings point to a critical role for thiols in modulating events linked to chondrocyte maturation and cartilage matrix synthesis and mineralization.

Effects of antioxidants on the anti-proliferation induced by protein synthesis inhibitors in human brain tumor cells

The effects of protein synthesis inhibitors (cycloheximide, anisomycin, puromycin and emetine) on the growth of human brain tumor cells were investigated using U-373 MG human astrocytoma and SK-N-MC human neuroblastoma cell lines. These agents inhibited the growth of the tumor cells in a dose-dependent manner. However, these agents did not affect cell viability evaluated by the trypan blue exclusion method, indicating that growth inhibition was due to the inhibition of cell proliferation rather than the induction of cytotoxicity. Anti-proliferation induced by these agents was significantly blocked by the treatments with either free radical scavengers or antioxidants. These results suggest that enhanced oxidative stress may be involved in the anti-proliferation induced by the protein synthesis inhibitors in human brain tumor cells.

Transient mitochondrial transcript level decay in oxidative stressed chondrocytes

Steady-state levels of 12S rRNA and NADH dehydrogenase subunit 4 mRNA (ND4) mitochondrial transcripts were measured on rabbit articular chondrocyte in culture. In pseudosynchronized chondrocytes, changes of mitochondrial RNA levels were observed during the progression of the cells in the cell cycle. Oxidative stress generated by the hypoxanthine-xanthine oxidase system (HX-XO) induced a transient decrease in the levels of both ND4 and 12S rRNA. Mitochondrial RNA levels recovered 24 h after the oxidative stress. These RNA level changes were not associated with modifications in the structure or the copy number of the mitochondrial genome. Furthermore, the decrease in the amount of the mitochondrial transcripts observed may be related to a transient inhibition of mitochondrial transcription since the treatment of cells with ethidium bromide (a mitochondrial transcription inhibitor) resulted in the same decrease in 12S rRNA level as HX-XO treatment alone.

Production of IL-1 and IL-1 receptor antagonist and the pathological significance in lipopolysaccharide-induced arthritis in rabbits

Injection of lipopolysaccharide (LPS) into rabbit knee joints provoked leucocyte infiltration and loss of proteoglycan (PG) from the cartilage. We investigated the role of IL-1 and IL-1 receptor antagonist (IL-1Ra) and its significance in the pathogenesis of LPS-arthritis. Production of IL-1 beta peaked at 6 h (196.7 +/- 89.4 pg/joint) after injection of 10 ng of LPS, while IL-1Ra peaked at 9 h (34.5 +/- 13.4 ng/joint). The amount of IL-1Ra was 180-200-fold molar excess of IL-1, and a large amount of IL-1Ra was sustained for 1 week. Both IL-1 beta and IL-1Ra were mainly produced by synovial exudate cells. Arthritis was reproduced by rabbit IL-1 beta. LPS-induced leucocyte infiltration was inhibited 70-75% by rabbit IL-1Ra. Loss of PG in LPS-arthritis was prevented by IL-1Ra and also by neutrophil elastase inhibitor, and superoxide dismutase. In leucopenic rabbits, injection of LPS induced neither production of IL-1 beta nor loss of PG. Direct injection of inflammatory exudated cells in leucopenic rabbits reproduced loss of PG, and there was only a partial recovery by IL-1Ra. These results suggest that LPS-initiated IL-1 acts as a key mediator in LPS-arthritis and that endogenous IL-1Ra may suppress a part of IL-1 activity at the site, but its amount was too low for suppression of the produced IL-1. Loss of PG is a sequela of infiltrated leucocytes and leucocyte-derived elastase, and superoxide anion may play a pivotal role in the destruction of cartilage.

Inhibition of lung epithelial cell proliferation by hyperoxia. Posttranscriptional regulation of proliferation-related genes

The alveolar surface of the lung is a major target for oxidant injury. After injury, repair of the alveolar epithelium is dependent on the ability of epithelial type 2 (T2) cells to proliferate. The regulation of T2 cell proliferation and the effect of reactive oxygen (O2) species on this lung cell proliferation have not been well defined. To investigate this process we focused on the regulation of two late cell cycle genes, histone and thymidine kinase, in T2 cells and fibroblasts exposed in vitro to varying periods of hyperoxia (95% O2). Hyperoxia for 24 to 48 h arrested cell proliferation in a SV40T-immortalized T2 cell line we have developed and in primary and SV40T-immortalized lung fibroblasts. Despite the cessation of proliferation, histone and TK mRNA continued to be expressed at high levels; mRNA half-lives were markedly prolonged but neither protein was translated. Thus proliferation arrest induced by hyperoxia was associated with posttranscriptional control of at least two late cell cycle-related genes. This form of proliferation arrest is also seen when primary and SV40T-T2 cells but not fibroblasts are serum deprived, suggesting that T2 cells in vitro may be uniquely sensitive to alterations in their redox state and that these alterations in turn affect translational control of a subset of proliferation-related genes.

Toxic effects and detection of oxygen free radicals on cultured articular chondrocytes generated by menadione

The aim of this work was to study the proliferation pathological perturbations of cultured chondrocytes in response to menadione, an oxygen free radicals producing drug. Rabbit articular chondrocytes in monolayer culture were treated with 10(-5) M, 1.5.10(-5) M and 2.10(-5) M of menadione during three days. A dose dependent decrease of the proliferative capacity was observed. Flow cytometry analysis revealed a perturbation of the cell cycle progression consisting in an accumulation of cells in the S and G2 + M phases. This growth perturbation was due to oxygen radicals production since a treatment with catalase suppressed these toxic effects. Furthermore, to identify oxygen derived radicals in the cellular suspension of cultures treated with menadione, we used a technique of spin-trapping coupled with electron spin resonance (ESR). The ESR signal corresponding to the DMPO hydroxyl radical adduct (DMPO-OH) has been detected. The spectra observation indicated the actual production of hydroxyl radical. However, superoxide anions have not been identified; this fact can be explained by the low reactivity of these anions with DMPO and by the decomposition of signal DMPO-OOH to DMPO-OH.

Induction of differentiation in human HL-60 cells by 4-hydroxynonenal, a product of lipid peroxidation

4-Hydroxynonenal (HNE) is the major diffusible toxic product generated by lipid peroxidation of cellular membranes. The level of lipid peroxidation and, consequently, the concentration of its products are inversely related to the rate of cell proliferation and directly related to the level of cell differentiation. In the present paper the effects of HNE on the proliferation and differentiation of the HL-60 human promyelocytic cell line have been investigated. Repeated treatment at 45-min intervals with HNE (1 microM) was performed to maintain the cells in the presence of the aldehyde for 7 1/2 or 9 h. The effect of HNE on cell proliferation and differentiation was compared with dimethyl sulfoxide (DMSO)-treated cells. HNE causes a strong inhibition of cell growth without affecting cell viability. Moreover, HL-60 cells acquire the capability to produce chemiluminescence after soluble (phorbol myristate acetate) or corpuscolate (zymosan) stimulation. The phagocytic ability has also been calculated by counting the number of cells that phagocytize opsonized zymosan. Values were 43 and 55% after 10 or 12 HNE treatments, respectively, and 88% in DMSO-treated cells. Myeloperoxidase activity, 5 days after treatment, decreased by 85% in either HNE- or DMSO-treated cells while acid phosphatase activity increased with respect to untreated cells. Results obtained indicate that HNE at concentrations close to those found in the normal tissues can induce inhibition of proliferation and induction of differentiation in the HL-60 cell line.

Oxidants and antioxidants in proliferative senescence

In terms of the amount of experimental research it has generated the free radical theory of ageing is one of the most popular hypotheses to explain this ubiquitous phenomenon. From the theory two postulates were derived: either cellular defence mechanisms against free radical-dependent oxidants deteriorate during ageing of cells, or essential, unrepairable damages are imparted to the cell by oxidants regardless of the activity of antioxidant defence systems. The many reports dealing with a putative breakdown in antioxidant defence systems failed to positively support this postulate. However, a minor depletion in cellular glutathione by exposure to a model lipophilic peroxide led to a significant decrement in DNA and protein synthesis. In other words, the glutathione redox cycle is intrinsically fallible with respect to defending the cellular DNA replication system against this model lipophilic peroxide. Interestingly, after ageing in culture cells a partial uncoupling of the NADPH-producing and -consuming systems tends to take place. Experiments involving the addition of antioxidants to the culture medium have failed to significantly extend the lifespan of cultured diploid somatic cells. The level of antioxidants appears to be a modulator rather than a primary determinant of cellular ageing in culture. Several lines of evidence suggest that DNA damages accumulate during ageing of the organism, but no oxidant-related DNA damage has been pinpointed in the cultured cell system. Human mutants with defects in antioxidant enzymes have not shown conclusive signs of accelerated ageing. Cells from patients with Werner's syndrome (progeria of the adult), on the other hand, do not suffer from a defect in their antioxidant defence system, nor do they accumulate more than normal amounts of autofluorescent products resulting from lipid peroxidation. The recent finding that Werner's syndrome constitutes a mutator phenotype may prompt the comparison of oxidant- and ageing-related mutation spectra in order to investigate a mutational theory of ageing as a new derivative from the free radical hypothesis.