Involvement of superoxide in the paraquat-induced enhancement of lung collagen synthesis in organ culture

Superoxide-induced Type I collagen secretion depends on prolyl 4-hydroxylases

Reactive oxygen species (ROS) including superoxide (O₂^•-) play an important role in a variety of diseases, including Alzheimer's Disease, cancer, and atherosclerosis. Early reports showed that O₂^•- is a stimulant for collagen synthesis. However, the mechanism remains incompletely understood. Here we showed that LY83583 (6-anilinoquinoline-5,8-quinone), a substance known to induce O₂^•- production by smooth muscle cell (SMC), increases Type I collagen secretion. This effect could be blocked by treating the cells with Tiron, a scavenger for O₂^•-. LY83583-induced Type I collagen secretion required P4HA1 and P4HA2. Knockout of either P4ha1 or P4ha2 greatly reduced LY83583-stimulated Type I collagen maturation whereas silencing of both P4ha1 and P4ha2 completely blocked LY83583-induced Type I collagen maturation. Although significantly more hydroxyproline on purified Type I collagen was detected from LY83583 treated mouse embryonic fibroblast (MEF) cells by mass spectrometry, the level of prolyl 4-hydroxylases was not altered. Thus, LY83583 might increase the enzymatic activity of prolyl 4-hydroxylases to increase Type I collagen maturation. In addition, we found that LY83583 activated prolyl 4-hydrolases differed from ascorbate-activated prolyl 4-hydroxylase in two aspects: (1) LY83583 activated both P4HA1 and P4HA2 involved in collagen maturation whereas ascorbate mainly stimulated P4HA1 in collagen maturation; (2) LY83583 did not induce N259 glycosylation on P4HA1 as ascorbate did. The mechanisms remain to be investigated.

The pathogenesis of cutaneous fibrosis

Cutaneous fibrosis is an integral component of a variety of human disorders including keloids, hypertrophic scar, and most notably, scleroderma. Each has its own etiology and unique clinical characteristics, but all involve the dysregulation of connective tissue metabolism, in particular, the activation of dermal fibroblasts. In this review, we examine various molecular events in scleroderma that may lead to fibroblast activation, and propose a new model to explain the persistence of such activation by scleroderma fibroblasts in the apparent absence of exogenous stimuli.

Oxygen radicals, inflammation, and arthritis: pathophysiological considerations and implications for treatment

A vast amount of circumstantial evidence implicates oxygen-derived free radicals, especially superoxide and hydroxyl radical (and to lesser extent, hydrogen peroxide), as mediators of inflammation and/or tissue destruction in inflammatory and arthritic disorders. The substrates for radical generation, namely properly stimulated phagocytic cells, transition metal catalysts, and (to a limited extent) ischemia, are all amply present, although there is no particular rheumatic disease in which a consistent abnormality of radical generation has been identified. These radical species can clearly degrade hyaluronic acid, modify collagen and perhaps proteoglycan structure and/or synthesis, alter and interact with immunoglobulins, activate enzymes and inactivate their inhibitors, and possibly participate in chemotaxis. In most situations, however, there is ample scavenging ability to detoxify these radicals before they hit their target, and many rheumatic disease drugs can decrease their production and/or effects. Despite the apparent sufficiency of natural scavengers and the lack of direct evidence that oxygen radicals are pathogenetically important, substantial pharmaceutical effort is still being made to develop free radical scavengers as therapeutic agents. Although individual free radicals die out quickly, rheumatologic interest in them has been sustained for nearly two decades.

Cellular and molecular mechanisms of cutaneous aging

There are two major theories of aging: the programmatic theory states that aging is an inherent genetic process, and the stochastic theory states that aging represents random environmental damage. Processes that are associated with cellular damage and aging are the production of free radicals (a process much enhanced after ultraviolet irradiation) and an increasing number of errors during DNA replication. Cellular manifestations of intrinsic aging include decreased life span of cells, decreased responsiveness of cells to growth signals, which may reflect loss of cellular receptors to growth factors, and increased responsiveness to growth inhibitors. All these findings are more pronounced in cells derived from photodamaged skin. Molecular manifestations of intrinsic aging, studied mainly in fibroblasts, are altered membrane composition, adhesion properties, production of extracellular matrix, and activity of the enzyme catalase. Molecular changes as a result of photoaging are less well characterized; published studies mainly target differences in composition of the extracellular dermal matrix.

Increase in lipoperoxides and prolyl hydroxylase activity in rat liver following chronic ethanol feeding

The effect of lipid peroxidation on hepatic collagen synthesis was investigated in male Wistar strain rats after 7 weeks of ethanol feeding. Compared with control rats, the ethanol-fed rats had a significantly higher lipoperoxide content and a significantly lower reduced glutathione content al all times following ethanol treatment. Except for the earliest time (2 days), hepatic prolyl hydroxylase activity was also significantly increased and finally reached up to 214% of the control level. Hepatic hydroxyproline content was slightly increased, but not statistically significant. The lipoperoxides content was significantly correlated with prolyl hydroxylase activity and inversely correlated with reduced glutathione content. These findings were also confirmed in ethanol-pyrazole-treated rats. These results suggest that elevated lipoperoxides mediate an acceleration of collagen synthesis, even at an early stage, in ethanol-induced hepatic injury.

Interactions of vitamin E and penicillamine in the treatment of hereditary avian muscular dystrophy

Our prior work demonstrated that penicillamine treatment of dystrophic chickens delayed the onset of symptoms, partially alleviated contractures, improved muscle function, and lowered serum creatine kinase. Penicillamine, a sulfhydryl compound with reducing properties, also prevented inactivation of glycolytic enzymes by protecting thiol groups. The present study shows that vitamin E enhances the therapeutic effects of penicillamine. Interaction of these two reductants is dose related. With vitamin E as adjunct therapy, the dosage level of penicillamine could be lowered by 50%, thereby minimizing side effects. The therapeutic rationale for two antioxidants is that penicillamine may act primarily in the cytoplasm to prevent oxidative damage, whereas the more hydrophobic vitamin E may protect membrane bilayers. Additionally, penicillamine may prevent collagen cross-linking and, deposition of insoluble collagen in muscle and thus decrease contracture formation. General applications of combined penicillamine and vitamin E therapy are discussed regarding prevention of free radical and oxidative damage in Duchenne dystrophy and a wide range of human diseases.

Pulmonary interstitial fibrosis induced in hapten-immune hamsters

A model for pulmonary interstitial fibrosis (PIF) based on cell-mediated immune response is described. Animals were primed for contact hypersensitivity responses by skin painting with trinitrophenol (TNP), but instead of challenging with the antigen on the skin, animals were challenged with a single intratracheally administered dose of the immunizing hapten. Primed animals developed inflammation followed by pulmonary fibrosis, as determined by histologic examination. Furthermore, immunized animals developed an increase in hydroxyproline (as an indirect measure of collagen synthesis) that could be recovered from the lung by 7 days after an intratracheal challenge with TNP. The increase in hydroxyproline within the lung persisted through 30 days. The response was specific because little or no fibrosis or increase in collagen deposition was observed in immune animals that were challenged with an unrelated hapten (dinitrophenol). Unimmunized animals demonstrated a slight increase in hydroxyproline in the lung 7 days after challenge, but with time the collagen content of these control animals approached normal levels. These studies demonstrate that a specific cell-mediated immune response to a hapten within the lung can induce pulmonary interstitial fibrosis.

Increased prolyl hydroxylase activity and collagen synthesis in hepatocyte cultures exposed to superoxide

Primary monolayer cultures of rat hepatocytes at confluence were exposed to an exogenously added source of superoxide, and its influence on collagen synthesis was examined. Superoxide was generated by the addition of dihydroxyfumarate to the culture medium. Exposure of hepatocytes to dihydroxyfumarate greatly stimulated the activity of prolyl hydroxylase and the synthesis of collagen. A significant increase in prolyl hydroxylase activity was observed with 5 micrograms per ml dihydroxyfumarate in 24 hr relative to that in the untreated cultures. Maximum stimulation of greater than 3-fold compared to the control value was elicited by 25 micrograms per ml dihydroxyfumarate. When scavengers of superoxide such as superoxide dismutase and Cu(Lys)2 were added in the medium, the increase in prolyl hydroxylase activity induced by dihydroxyfumarate was nearly abolished. Experiments with actinomycin D indicated that synthesis of new RNA was involved in the stimulation of prolyl hydroxylase activity. Analysis of collagen synthesis in cultures exposed to dihydroxyfumarate also showed a marked increase compared to that of the untreated cultures. The presence of superoxide dismutase in the medium significantly reduced the increase in collagen synthesis. Our results indicate that superoxide mediates the stimulation of collagen synthesis in hepatocytes. These findings may provide a possible explanation for excess collagen formation during induced liver fibrosis.

Poly(ADP-ribose) synthetase activity during bleomycin-induced lung fibrosis in hamsters

Bleomycin damages cellular DNA and is a potent inducer of pulmonary fibrosis. It has been shown to act through a superoxide-mediated mechanism. We are interested in determining the biochemical mechanisms involved in fibrosis and in this preliminary study we have examined the temporal relationship between early biochemical events associated with DNA damage and fibrosis, in lungs of hamsters after administration of 0.75 unit of bleomycin. The activities of poly(ADP-ribose) synthetase, an enzyme associated with DNA repair, inducible superoxide dismutase (SOD) and prolyl hydroxylase as well as the tissue levels of NAD+ and hydroxyproline in the lung were determined. All three enzyme activities expressed as per milligram DNA or per lung, increased upon bleomycin treatment over the saline-administered controls. Lung poly(ADP-ribose) synthetase activity which is sensitive to DNA breaks, increased first (24% over control in 1 day, P less than 0.0001), attained the maximum value on the 5th day (952% over control, P less than 0.0001), and started to decline thereafter and approached near the control value on 14th day. Bleomycin treatment induced a rapid change in the level of lung NAD+. After 1 day the level of NAD+ was reduced by 42% compared to the control (P less than 0.001), further declined to 65% (P less than 0.001) on the 3rd day, and stayed at that level until the 7th day. On the 14th day, however, the NAD+ level was still lower (29%, P less than 0.05) but approaching the value in the control animals. The activity of prolyl hydroxylase showed significant increase on the 3rd day (50% over control, P less than 0.0001) after bleomycin administration. The enzyme activity continued to increase until the end of the experiment (490% of control, P less than 0.0001, on Day 14). The content of undialyzable hydroxyproline, a marker for collagen, was also increased significantly in the lung tissue on the 3rd day (30% over control, P less than 0.05), continued to increase and reached the highest level on the 14th day (71% over control, P less than 0.001). A significant increase in the activity of SOD (19% over control, P less than 0.001) was seen on the 5th day which continued to increase and attained the highest value on Day 14 (115% over control, P less than 0.0001).(ABSTRACT TRUNCATED AT 400 WORDS)

Mechanism of production of toxic oxygen radicals by granulocytes and macrophages and their function in the inflammatory process

The paper deals with 1) the features of the respiratory burst (increase of the respiration with production of O2 metabolites, O2-, H2O2, OH) of the inflammatory cells; 2) the factors responsible for its activation; 3) the methods for its measurement; 4) the molecular events which take place at the level of the plasma membrane following the interaction between the stimuli and the cell surface (the Ca++ changes, the modification of membrane potential, the activation of phospholipid turnover) and the hypothesis of the activation of the protein kinase C; 5) the nature of the NADPH oxidase whose activation is responsible for the respiratory burst and the production of O2 metabolites; 6) the defensive, toxic, proinflammatory and modulatory effects due to the reactivity of the oxygen metabolites.

Release of amino-terminal procollagen peptides in paraquat-induced acute pulmonary fibrosis

Acute pulmonary fibrosis following intoxication with paraquat is characterized by increased collagen synthesis and deposition in the lungs. In the present study, a chronic lung lymph fistula preparation in sheep was used to investigate the changes in procollagen type III peptide level in the lung lymph in acute pulmonary distress associated with paraquat application. The procollagen type III peptide is supposed to be an indicator of the changing biosynthetic pattern of pulmonary collagen in lung fibrosis. All animals tested showed a progressive pulmonary distress following the application of paraquat characterized by increasing lymph flows and lymph protein flows which monitored the microvascular membrane damage. In parallel to these findings, procollagen peptide levels in the lymph fluid increased, even before manifest biochemically or histologically detectable pulmonary fibrosis occurred. The present results suggest that the release of procollagen type III peptides into lymph fluid is an early indicator of beginning fibrotic tissue disarrangement, even before completed pulmonary fibrosis can be detected by common tissue analysis.

[Physiological and pathophysiological significance of superoxide-radicals and the regulatory role of the enzyme superoxide dismutase (author's transl)]

The monovalent reduction of molecular oxygen, resulting in the formation of superoxide radicals (O(2)) is regarded as to be an ongoing physiological process involved in the respiration and other biological processes of aerobic cells. These reactive oxygen species have been reported to function as cofactors in many biosynthetic reaction steps. Thus, deviations from cellular steady state concentrations may lead to a multiplicity of clinical symptoms or may to a great deal determine the characteristic of a distinct malady. Decrease of cellular O(2)-concentration is discussed in connection with Trisomie 21 and various mental disorders. The role of O(2) in the biochemistry of inflammation, autoimmune diseases, various toxicological cases and the biological aging process is described. Hypothetical considerations concerning the involvement of O(2) in the pathogenetic mechanisms of Morbus Wilson, haemochromatosis, Parkinson syndrome, cataractogenesis and in carcinogenesis are presented. The physiological control of cellular O(2)-concentration is performed by formation rates of the various cellular O(2)-sources and the overall elimination rates of O(2)-consuming reaction steps. Superoxide dismutase (SOD) is of special interest within this cycle because it detoxifies O(2) radicals with velocity rates which are significantly faster than any other pathway involved in O(2) elimination. Thus attempts for a therapeutic interference on tissue levels of O(2)-radicals are mainly based on inhibition or activation of cellular SOD-activities depending on a supposed decrease or increase in cellular steady state concentrations of O(2). The availability of a drug version of SOD and of various synthetic SOD-active compounds allowing a therapeutic decrease of O(2)-tissue levels. Inhibition of cellular SOD is also possible, however, many still unknown toxic side effects should be expected because of unspecific action of the inhibitor available.