Fiber induced disease

In Vitro Systems. Different biochemical approaches provide a variety of methods for comparing and evaluating fiber toxicity. Organ cultures, cultured cells, and cells in suspension from humans and animals can be exposed to fibrous materials or, alternatively, cells from treated animals, bacterial cells, and so on can be used. Many hundreds of experiments have been performed, but it is difficult to apply the results, and in many cases extrapolation to humans is not warranted. Nevertheless, cell systems provide excellent data on which to base our understanding of the mechanisms related to fiber-induced disease a few selected examples follow. 

The pleura, principally the parietal pleura, is a main target for asbestos fibers and is involved far more often than the lung parenchyma, despite the fact that the lung is the first organ reached by inhaled fibers. The precise mechanisms of translocation of fibers toward the pleura and the physiopathology of pleural fiber-induced diseases are still not well understood. 

The size of the fibrous particles that appear to induce disease in the animal models is compatible with the measured respiratory range in humans (Lipp-man, 1977). Most particulate deposition takes place not in the upper or conducting portion of the airways but in the alveolar region of the pulmonary tree (the respiratory unit). Some surface deposition may occur at bifurcations in the bronchial tree, but the actual amount at each location is influenced by anatomy, specific to the species—probably to an individual—as well as the variety of fiber. A large proportion of airborne particulates are rejected as part of the normal clearance mechanisms in animals, but in humans clearance mechanisms may be compromised by smoking, for example. We are unaware of any experiments on fiber toxicity using smoking rats ... 

Artvinli, M., and Y. I. Baris (1982). Environmental fiber-induced pleuro-pulmonary disease in an Anatolian village an epidemiological study. Arch. Environ. Health 37 177-181. 

What are the molecular events involved in the development of asbestos-induced respiratory and pleural effects and how are they influenced by fiber dimensions and mineral type Identification of the molecular and cellular events of asbestos-induced disease has been the subject of extensive research within the past two decades (see Mechanisms of Asbestos Toxicity Overview section). However, much remains unknown, and the precise steps in pathogenic pathways are not frilly established. 

Asbestos and silica are naturally occurring minerals that are mined in various forms for numerous commercial purposes (1,2). Asbestos ore breaks down into fiber forms with a crystalline backbone, while silica can be in crystalline or amorphous (noncrystal) particle form. Asbestos is divided mineralogically into the serpentine form known as chrysotile and the amphibole forms that include crocidolite and amosite. Chrysotile constitutes about 95% of the world s use, and the amphibole fibers, approximately the other 5% (1). All the asbestos varieties have been established as causative agents of all the asbestos-induced diseases (i.e., scarring, lung cancer, and mesothelioma), while it is only the crystalline form of silica that causes disease (1,2). 

Another condition due to mutations in the RYRl gene is central core disease. This is a rare myopathy presenting in infancy with hypotonia and proximal muscle weakness. Electron microscopy reveals an absence of mitochondria in the center of many type I (see below) muscle fibers. Damage to mitochondria induced by high intracellular levels of Ca secondary to abnormal functioning of RYRl appears to be responsible for the morphologic findings. 

The fiber of rice bran products, especially the RiceMucil is helpful in maintaining normal gastrointestinal and colon health (Tomlin and Read, 1988). It helps in bowel regularity. Patients with irritable bowel syndrome, inflammatory bowel disease and colitis get excellent relief with RiceMucil . As has been mentioned in the earlier part of this chapter, the fiber of rice bran is non-bloating and lactose free, and the acidic environment the fiber creates during the fermentation of undigested food improves colon health and induces all the healthy enzymes and fnendly bacteria to proliferate (Folino et al, 1995 Life Sciences News Letter, 1999). It has been scientifically demonstrated to have an excellent nutritional support for gut and colon health. 

There is some evidence that long-term cyclic administration of rifaximin combined with fiber supplementation is effective for inducing symptomatic relief in patients with uncomplicated diverticular disease of the colon. A therapeutic gain of approximately 30% compared to fiber supplementation only can be expected. The drug is well tolerated and no relevant side effects have been reported. Symptoms attributed to diverticula (abdominal pain or discomfort, bloating, disturbance of bowel habits) are nonspecific symptoms and are also features of irritable bowel syndrome. It has been suggested that irritable bowel syndrome and diverticular disease of the colon may coexist in many people and when bowel symptoms occur with diverticulosis coli, they may be due to a coexistent irritable bowel rather to the diverticula themselves [47, 48]. This hypothesis is supported by the fact that many patients with symptomatic diverticular disease show co-... 

Another interesting effect related to H3 receptors is its possible interference in the airway microvascular leakage (AML) induced by a variety of stimuli. Activation of H3 receptors inhibits NANC-induced leakage by reducing neuropeptides release from sensory fibers (Ichinose et al., 1990). Hence, H3 receptors may act as a safety device in asthmatic diseases to prevent, not only bronchoconstriction, but also increased airway permeability. On the other hand, it was also demonstrated that H3 receptor activation inhibits sympathetic tone, which, in turn, reduces antigen-induced AML (Danko et al., 1994). Therefore, the authors conclude that the blockade of H3 receptors may have therapeutic potential in inflammatory pulmonary... 

Some investigators have proposed that amphibole asbestos fibers, such as tremolite asbestos, are more potent than chrysotile fibers in inducing fibrotic lung disease and lung cancer (McDonald 1998 McDonald and McDonald 1997 McDonald et al. 1999 Mossman et al. 1990). Others propose that differences in the... 

---