Hydroxyproline contents and prolyl hydroxylase activities in lungs of rats exposed to low levels of ozone

Application of Ozone in Medicine

This review deals with the application of ozone in medicine, its effects on the human organism and its use as a therapeutic approach and sterilizing agent. A particular attention is paid to the therapeutic properties, therapeutic dosage and scope of application. Some mechanisms of the ozone effect at exposure on different organs and systems in human body are also considered. Ozone toxicity is reviewed. The ozone use as a sterilizing agent in the pharmaceutical industry and cosmetics, as well as in the food processing industry is discussed.

Exposure of human lung fibroblasts to ozone: cell mortality and hyaluronan metabolism

Exposure of cultures of human lung fibroblasts to 0.5 ppm ozone for 20 h resulted in a significant increase in cellular mortality by 29%; after exposure to 2.5 ppm ozone for 4 h, the increase amounted to 74%. A marked difference in sensitivity to ozone was observed between fibroblast lines from different individuals. This variability in resistance to ozone was more evident after exposure to 0.5 ppm ozone for 20 h, when compared with 2.5 ppm ozone for 4 h. In one fibroblast line, synthesis of hyaluronan was enhanced by exposure to 0.5 ppm ozone for 20 h. The concentrations of hyaluronan in culture media increased in experiments using different fibroblast cell lines, a phenomenon that was obvious both if cell numbers and combined protein concentrations of cells and media are selected as references for hyaluronan concentrations.

Cellular, biochemical and functional effects of ozone: new research and perspectives on ozone health effects

Ozone, a toxic component of photochemical oxidant air pollution, has been the focus of considerable research efforts for several decades. In spite of this large body of work, questions remain as to the potential risks to human health represented by chronic low-level exposure to ozone. Newer studies in animals have provided fundamental information on the range of biochemical, functional and morphologic responses to ozone exposure. While the response to ozone exposure is extremely complex, some generalities have emerged which may aid attempts to apply the results of these studies to decisions regarding the protection of human health.

Biochemical basis of ozone toxicity

Ozone (O3) is the major oxidant of photochemical smog. Its biological effect is attributed to its ability to cause oxidation or peroxidation of biomolecules directly and/or via free radical reactions. A sequence of events may include lipid peroxidation and loss of functional groups of enzymes, alteration of membrane permeability, and cell injury or death. An acute exposure to O3 causes lung injury involving the ciliated cell in the airways and the type 1 epithelial cell in the alveolar region. The effects are particularly localized at the junction of terminal bronchioles and alveolar ducts, as evident from a loss of cells and accumulation of inflammatory cells. In a typical short-term exposure the lung tissue response is biphasic: an initial injury-phase characterized by cell damage and loss of enzyme activities, followed by a repair-phase associated with increased metabolic activities, which coincide with a proliferation of metabolically active cells, for example, the alveolar type 2 cells and the bronchiolar Clara cells. A chronic exposure to O3 can cause or exacerbate lung diseases, including perhaps an increased lung tumor incidence in susceptible animal models. Ozone exposure also causes extrapulmonary effects involving the blood, spleen, central nervous system, and other organs. A combination of O3 and NO2, both of which occur in photochemical smog, can produce effects which may be additive or synergistic. A synergistic lung injury occurs possibly due to a formation of more powerful radicals and chemical intermediates. Dietary antioxidants, for example, vitamin E, vitamin C, and selenium, can offer a protection against O3 effects.

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.

The combination of ozone and silica on the development of pulmonary fibrosis

The biologic interactions of potentially fibrogenic agents commonly occurring as environmental pollutants remain to be rigorously characterized. Two agents that produce pulmonary fibrosis were selected for this study. Separate groups of male Sprague-Dawley rats were intratracheally instilled with 0, 2, 12, and 50 mg silica and then either sham-exposed or exposed to 0.8 ppm ozone 6 h/d, 5 d/w, for 37 exposure days. Interaction was not detected between silica and ozone in the development of pulmonary fibrosis as determined by quantitative biochemical indices (hydroxyproline and lysyl oxidase) or by histopathologic examination of the lungs. Thus, environmentally relevant levels of ozone appear unlikely to affect the progression of a concurrent silicotic lesion.

Alterations in lung structure caused by inhalation of oxidants

Morphometric and morphologic methods have been used to evaluate changes in rat lungs caused by the inhalation of a variety of oxidants. Exposure to 100% oxygen causes diffuse pulmonary injury and leads to death after 66-72 h of exposure. The primary insult leading to death in rats exposed to hyperoxia is injury to pulmonary capillary endothelium. Sublethal exposure to hyperoxia was found to cause diffuse injury to all major components of the alveolar septum and was associated with destruction of approximately 50% of the pulmonary capillary endothelial cells. A corresponding decrease in pulmonary capillary surface area and capillary lumen volume also occurred. Exposure to ozone and to nitrogen dioxide in low concentrations did not cause a diffuse injury throughout the alveolar region of the lung, but rather led predominantly to structural alterations in terminal bronchioles and in their adjacent alveoli. Morphometric evaluation of animals exposed to 0.25 ppm ozone and to 2 ppm NO2 demonstrated quantitatively and qualitatively similar lesions. These lesions primarily involve injury and remodelling of the alveolar epithelium. These changes in the alveolar epithelium were also associated with the recruitment of increased numbers of alveolar macrophages to the proximal alveolar region. The different types of lung injury caused by various oxidants are most likely to be related to differences in their reactivity with tissue components and to differences in concentration, distribution, and diffusion characteristics of the oxidant gases.

Minireview: the health implications of water treatment with ozone

Ozone is a highly efficient disinfectant which may have significant advantages in water treatment compared to chlorine. It has, however, been shown that mutagenic and possibly carcinogenic byproducts may be produced under certain conditions of ozonation. Light chlorination following ozonization may meet the highest standards of disinfection. In addition the destruction of much of the organic matter by prior ozone treatment may well result in less harmful chlorinated and brominated products in the finished water. In many cases ozone treatment alone may suffice. It would be desirable to test with long term in vivo experiments which of the alternatives produces the best combination of microbiologically clean and pleasant water with minimum mutagenic and carcinogenic effect.

Increased aryl hydrocarbon hydroxylase and prolyl hydroxylase activities in lung organ cultures exposed to benzo[a]pyrene

Exposure of neo-natal rat lungs in organ culture to 10--25 microM benzo[a]pyrene (BaP) elevated the activities of aryl hydrocarbon hydroxylase (AHH) and prolyl hydroxylase (PH). Pyrene, a non-carcinogenic hydrocarbon did not elicit this response. Prolyl hydroxylase is an indicator of collagen synthesis and increased PH activity in the lungs reflects increased collagen synthesis. Our studies suggest that the earliest events in BaP-induced lung injury may include altered collagen metabolism.