Asbestos-related cancer and the amphibole hypothesis. The hypothesis is still supported by scientists and scientific data

Extracellular superoxide dismutase in pulmonary fibrosis

Disruption of the oxidant/antioxidant balance in the lung is thought to be a key step in the development of many airway pathologies. Hence, antioxidant enzymes play key roles in controlling or preventing pulmonary diseases related to oxidative stress. The superoxide dismutases (SOD) are a family of enzymes that play a pivotal role protecting tissues from damage by oxidant stress by scavenging superoxide anion, which prevents the formation of other more potent oxidants such as peroxynitrite and hydroxyl radical. Extracellular SOD (EC-SOD) is found predominantly in the extracellular matrix of tissues and is ideally situated to prevent cell and tissue damage initiated by extracellularly produced ROS. EC-SOD has been shown to be protective in several models of interstitial lung disease, including pulmonary fibrosis. In addition, alterations in EC-SOD expression are also present in human idiopathic pulmonary fibrosis (IPF). This review discusses EC-SOD regulation in response to pulmonary fibrosis in animals and humans and reviews possible mechanisms by which EC-SOD may protect against fibrosis.

Extracellular superoxide dismutase inhibits inflammation by preventing oxidative fragmentation of hyaluronan

Extracellular superoxide dismutase (EC-SOD) is expressed at high levels in lungs. EC-SOD has a polycationic matrix-binding domain that binds to polyanionic constituents in the matrix. Previous studies indicate that EC-SOD protects the lung in both bleomycin- and asbestos-induced models of pulmonary fibrosis. Although the mechanism of EC-SOD protection is not fully understood, these studies indicate that EC-SOD plays an important role in regulating inflammatory responses to pulmonary injury. Hyaluronan is a polyanionic high molecular mass polysaccharide found in the extracellular matrix that is sensitive to oxidant-mediated fragmentation. Recent studies found that elevated levels of low molecular mass hyaluronan are associated with inflammatory conditions. We hypothesize that EC-SOD may inhibit pulmonary inflammation in part by preventing superoxide-mediated fragmentation of hyaluronan to low molecular mass fragments. We found that EC-SOD directly binds to hyaluronan and significantly inhibits oxidant-induced degradation of this glycosaminoglycan. In vitro human polymorphic neutrophil chemotaxis studies indicate that oxidative fragmentation of hyaluronan results in polymorphic neutrophil chemotaxis and that EC-SOD can completely prevent this response. Intratracheal injection of crocidolite asbestos in mice leads to pulmonary inflammation and injury that is enhanced in EC-SOD knock-out mice. Notably, hyaluronan levels are increased in the bronchoalveolar lavage fluid after asbestos-induced pulmonary injury, and this response is markedly enhanced in EC-SOD knock-out mice. These data indicate that inhibition of oxidative hyaluronan fragmentation probably represents one mechanism by which EC-SOD inhibits inflammation in response to lung injury.

The epidemiology of mesothelioma

It has been more than 40 years since occupational crocidolite exposure in South African miners was found to be associated with development of malignant mesothelial tumors 30 to 40 years later. Similar cases were not seen in the amosite and chrysotile miners. Since then, epidemiological and toxicological knowledge have increased enormously, but mortality continues to rise steeply (5% to 10% per year) in most industrialized countries. Even with widespread asbestos abatement efforts, this increase is likely to continue in Western Europe and the United State well into the next century, at least until 2020. Unregulated use of asbestos in less industrialized countries may cause the epidemic to continue throughout the next century in those regions. Asbestos abatement seems to be successful as evidenced by a decline in the proportion of patients with peritoneal tumors, which are the most common malignancies in heavily exposed individuals. Whereas in the 1960s peritoneal tumors comprised up to 30% of the total, in recent years the proportion has fallen to about 10%, This changing ratio could also be due to the steady increase in pleural tumors. The difficulty in formulating the connection as to the etiology of mesothelioma resulted from an unforeseeable difference in the carcinogenicity of various asbestos and mineral fiber types and was compounded by the very long latency of the disease. Unfortunately, the use of a single term, "asbestos," to describe at least five fibrous silicate minerals, each with unique physical, chemical, and biological properties and not infrequently and naturally admixed, severely hampered scientific investigation into the occupational health risks. The field became confused and filled with debate. At the heart of the fiber type controversy lies a fundamentally differing view of the importance of biopersistence of various asbestos fibers in carcinogenesis. This review will deal with the epidemiology of mesothelioma with particular attention to the studies that elucidate the impact of various asbestos fiber types on the etiology of the disease.