Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “fiber”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,009 records · Page 56Linked to original sources
PubMed2000

Determinants of the pathogenicity of man-made vitreous fibers (MMVF).

INTRODUCTION AND OBJECTIVES: A number of man-made vitreous fibers (MMVF) have been developed over the years to replace asbestos fibres in its uses as insulating material. Concerns have been raised that these man-made fibers may also pose a significant health hazard when inhaled during their manufacture and application. As will be discussed in this brief overview, dose, dimension and durability of fibrous particles are key parameters with respect to the induction of adverse pulmonary effects, including carcinogenicity as well as non-cancer effects. In particular, fiber biopersistence plays a most important role for pulmonary pathogenicities, and consequently biopersistence receives greatest attention in the search of new fibrous materials. METHODS AND RESULTS: Tests to evaluate fiber biopersistence include the administration of fibers by a short-term inhalation (5 days) or intratracheal instillation into rats. Advantages of the inhalation methodology include the even distribution throughout the lung administered by a physiological process. A disadvantage of this method is the limited respirability of long fibers in the rat whereas they are well respirable by humans. Such long fibers ( > 20 microm) have the greatest potential for tumorigenicity and need special consideration in connection with the evaluation of fiber biopersistence. Enrichment of the inhaled aerosol by these long fibers needs to be considered in order to deposit enough of them in the lower respiratory tract of the rat. In contrast, the advantage of the instillation technique is that these long fibers can be delivered to the lung. However, the major disadvantages of intratracheal instillations are the potential of the administered fibers to form clumps and aggregates in the airways and the induction of a major inflammatory response when high-bolus doses are administered. This could influence fiber dissolution in the lungs significantly. CONCLUSIONS: At the same delivered lung dose, a fiber of low biopersistency has the least effect and is, therefore, less likely to induce lung or pleural tumors even under chronic exposure conditions. Respective animal studies with more fibers of different biopersistence have confirmed this general principle. It is very important that, when evaluating and interpreting fiber effects observed in experimental animals, species differences with respect to respirability, lung retention and mechanisms of responses are considered.

Animals↗
PubMed2003

In vitro and ex vivo blood compatibility study of 2-methacryloyloxyethyl phosphorylcholine (MPC) copolymer-coated hemodialysis hollow fibers.

To identify the advantages of 2-methacryloyloxyethyl phosphorylcholine (MPC) copolymer-coated polysulfone (PSf) hollow fibers for hemodialyzer and hemofilter minimodules with hollow fibers were made and blood compatibility was evaluated in vitro and ex vivo. Three types of hollow fibers, i.e., pure PSf (no additives), PSf alloyed with poly(1-vinyl-2-pyrrolidone) (PVPy), and PSf coated with the MPC copolymer, were processed in wet conditions. Commercially available hollow fibers (APS) were used as a control sample. The PSf hollow fibers have a condensed structure. A porous structure was observed when the PVPy was alloyed before wet processing, and no effect of the innercoated MPC copolymer on the porous structure was observed. One-tenth-sized minimodules of the conventional hemodialyzer were fabricated with 200 fibers each. The solute permeability of the hollow fibers was evaluated using 10% bovine serum in a buffer solution containing cytochrome C, which is a model protein of Beta(2)-microglobulin. After circulation for 2.5 h, the solute permeability of APS and PVPy-alloyed PSf hollow fibers decreased to 50% compared with their initial values. In contrast, the value for the hollow fibers innercoated with the MPC copolymer maintained its initial level. The inner surface of the dialysis membranes was observed with a transmission electron microscope and a layer of adsorbed protein on the PSf, APS, and PVPy-alloyed PSf hollow fibers was observed, but not on the MPC copolymer-coated fibers. Blood cell adhesion was then evaluated by circulation of whole rabbit blood without any anticoagulant ex vivo. Many adherent cells were observed on the PVPy-alloyed PSf hollow fibers; however, blood cells did not adhere or aggregate on the MPC copolymer-coated hollow fibers. From these results, we concluded that the in-situ coating of MPC copolymer on PSf hollow fibers is effective in preventing blood coagulation and maintaining the solute permeability of the fibers.

Animals↗
PubMed1981

Retinotopic analysis of fiber pathways is amphibians. I. The adult newt Cynops pyrrhogaster.

The possibility that pathways of retinal fibers within the optic tract and the tectum of the adult newt are retinotopic was examined by selective labeling of the retinal fibers with horseradish peroxidase. Within the optic tract fibers from the ventral, temporal and dorsal retinal quadrants were ordered from the dorsal to ventral edges of th optic tract. The nasal retinal fibers exhibited two different pathways. The fibers from the dorsonasal retina ran along the ventral edge of the optic tract, while the fibers from the ventronasal retina ran along the dorsal edge of the optic tract. Segregation of pathways within the optic tract was incomplete between the nasal and other retinal fibers. The dorsonasal retinal fibers were mixed completely with the dorsal retinal fibers, and the ventronasal retinal fibers were mixed partly with the ventral retinal fibers. Both the dorsal and dorsonasal retinal fibers preferentially entered the lateral tract, and finally projected onto the ventrolateral parts of the middle tectum and of the caudal tectum, respectively. The ventral and ventronasal retinal fibers entered the dorsomedial tract, and projected onto the dorsomedial parts of the middle tectum and of the caudal tectum, respectively. The temporal retinal fibers invaded the nasal tectum directly. Most dorsal, ventral, and nasal retinal fibers ran along the sub-tracts as far as to the level of their terminals, then sharply turned in a direction to the tectum.

Afferent Pathways↗
PubMed1985

Origin of small primary afferent substance P-immunoreactive nerve fibers in the guinea-pig heart.

Primary afferent and substance P (SP)-immunoreactive nerve fibers of the guinea pig and rat heart were investigated by physiological and immunohistochemical methods. Immunohistochemistry revealed abundant SP-positive fibers in the guinea pig atria, with fewer in the ventricles. Only an occasional fiber was seen in the rat atrium or ventricle. Sectioning the vagus nerve did not noticeably influence the supply of SP-immunoreactive nerve fibers in the guinea pig heart. When the atria or ventricles were stimulated, afferent nerve fiber activity was recorded from the second and third thoracic dorsal roots. In guinea pig atria 3 types of fibers were identified on the basis of conduction velocities: A delta 1, A delta 2 and C fibers. Only A delta fibers were identified in the ventricle. By vagal recordings, A delta fibers were demonstrated but a C fiber response could not be shown in this nerve. SP-immunoreactivity in primary afferent fibers was depleted by the neurotoxin capsaicin. Capsaicin treatment also caused a reduction in the conduction velocity of small diameter myelinated A delta 2 (by 29%) and unmyelinated C fibers (by 46%). In the rat heart, evidence for A delta 2 or C fibers was not found. These results indicate that primary afferent and SP-immunoreactive fibers are numerous in guinea pig heart, but few in the rat. It is concluded that most of these fibers have their cell bodies of origin in the dorsal root ganglia.

Animals↗
PubMed2001

Effects of fiber length and volume fraction on the reinforcement of calcium phosphate cement.

A self-setting calcium phosphate cement (CPC) transforms into solid hydroxyapatite during setting at body temperature, and has been used in a number of medical and dental procedures. However, the inferior mechanical properties of CPC prohibits its use in unsupported defects, stress-bearing locations or reconstruction of thin bones. The aim of the present study was to strengthen CPC with fiber reinforcement, to examine the effect of fiber length and volume fraction, and to investigate the reinforcement mechanisms. Previous studies employed either short fibers for random distributions, or continuous fibers that were as long as the specimen size with preferred orientations such as unidirectional alignment. In the present study, a novel methodology was developed in which fibers several times longer than the specimen mold size were randomly mixed with the CPC paste to approximate the isotropy associated with short fibers, and at the same time achieve the high reinforcement efficacy associated with continuous fibers. Carbon fibers of 8 microm diameter were used with fiber lengths ranging from 3 mm to 200 mm, and fiber volume fraction from 1.9% to 9.5%. A three-point flexural test was used to fracture the specimens. Scanning electron microscopy was used to examine crack-fiber interactions and specimen fracture surfaces. The composite containing fibers of 75 mm in length at a volume fraction of 5.7% achieved a flexural strength about 4 times, and work-of-fracture 100 times, greater than the unreinforced CPC. It is concluded that randomly mixing the CPC paste with carbon fibers that were several times longer than the specimen mold size resulted in substantial improvements in strength and fracture resistance; the reinforcement mechanisms were crack bridging and fiber pullout; and fiber length and volume fraction were key microstructural parameters that determined the cement properties.

Journal Article↗
PubMed1986

Probing the mechanism of incorporation of fluorescently labeled actin into stress fibers.

The mechanism of actin incorporation into and association with stress fibers of 3T3 and WI38 fibroblasts was examined by fluorescent analog cytochemistry, fluorescence recovery after photobleaching (FRAP), image analysis, and immunoelectron microscopy. Microinjected, fluorescein-labeled actin (AF-actin) became associated with stress fibers as early as 5 min post-injection. There was no detectable cellular polarity in the association of AF-actin with pre-existing stress fibers relative to perinuclear or peripheral regions. The rate of incorporation was quantified by image analysis of images generated with a two-dimensional photon counting microchannel plate camera. After equilibration of up to 2 h post-injection, FRAP demonstrated that actin subunits exchanged rapidly between filaments in stress fibers and the surrounding cytoplasm. When co-injected with rhodamine-labeled bovine serum albumin as a control, only actin was detected in the phase-dense stress fibers. The control protein was excluded from fibers and any linear fluorescence of the control was demonstrated as a pathlength artifact. The incorporation of AF-actin into stress fibers was studied by immunoelectron microscopy using anti-fluorescein as the primary antibody and goat anti-rabbit IgG coupled to peroxidase as the secondary antibody. At 5 min post-injection, reaction product was localized periodically in some fibers with a periodicity of approximately 0.75 microns. In large diameter fibers at 5 min post-injection, the analog was seen first on the surface of fibers, with individual filaments resolvable within the core. In the same cell, thinner diameter fibers were labeled uniformly throughout the diameter. By 20 min post-injection, most fibers were uniformly labeled. We conclude that the rate of actin subunit exchange in vivo is extremely rapid with molecular incorporation into actin filaments of stress fibers occurring as early as a few minutes post-injection. Exchange appears to first occur in filaments along the surface of stress fibers and then into more central regions in a periodic manner. We suggest that the periodic localization of actin at very early time points is due to a local microheterogeneity in which microdomains of fast vs. slower incorporation result from the periodic localization of actin-binding protein, such as alpha-actinin, along the length of the fiber.

Actin Cytoskeleton↗
PubMed1977

Polymorphism of myosin among skeletal muscle fiber types.

An immunocytochemical approach was used to localize myosin with respect to individual fibers in rat skeletal muscle. Transverse cryostat sections of rat diaphragm, a fast-twitch muscle, were exposed to fluorescein-labeled immunoglobulin against purified chicken pectoralis myosin. Fluorescence microscopy revealed a differential response among fiber types, identified on the basis of mitochondrial content. All white and intermediate fiber but only about half of the red fiber reacted with his antimyosin. In addition, an alkali-stable ATPase had the same pattern of distribution among fibers, which is consistent with the existence of two categories of red fibers. The positive response of certain red fibers indicates either that their myosin has antigenic determinants in common with "white" myosin, or that the immunogen contained a "red" myosin. Myosin, extracted from a small region of the pectorlis which consists entirely of white fibers, was used to prepare an immunoadsorbent column to isolate antibodies specific for white myosin. This purified anti-white myosin reacted with the same fibers of the rat diaphragm that had reacted with the white, intermediate, and some red fibers are sufficiently homologous to share antigenic determinants. In a slow-twitch muscle, the soleus, only a minority of the fiber reacted with antipectoralis myosin. The majority failed to respond; hence, they are not equivalent to intermediate fibers of the diaphragm; despite their intermediate mitochondrial content. Immunocytochemical analysis of two different musles of the rat has demonstrated that more than one isoenzyme of myosin can exist in a single muscle, and that individual fiber types can be recognized by immunological differences in their myosin. We conclude that, in the rat diaphragm, there are at least two immunochemically distinct types of myosin and four types of muscle fibers: white, intermediate, and two red. We suggest that these fibers correspond to the four types of motor units described by Burke et al. (Burke, R. E., D. N. Levine, P. Tsairis, and F. E. Zajac, III 1973. J. Physiol. (Lond) 234:723-748.)in the cat gastrocnemius.;

Adenosine Triphosphatases↗
PubMed1991

Comparison of charge movement components in intact and cut twitch fibers of the frog. Effects of stretch and temperature.

Charge movements were measured in frog intact fibers with the three-microelectrode technique and in cut fibers with the double Vaseline gap technique. At 13-14 degrees C, the ON segments of charge movement records from both preparations showed an early I beta component and a late I gamma hump component. When an intact fiber was cooled to 4-7 degrees C, the time-to-peak of I gamma (tp,gamma) was prolonged, but I gamma still appeared as a hump. Q-V plots from intact fibers at 4-7 degrees C were fitted with a sum of two Boltzmann distribution functions (method 1). The more steeply voltage-dependent component, identified with Q gamma, accounted for 32.1% (SEM 2.2%) of the total charge. This fraction was larger than the 22.6% (SEM 1.5%) obtained by separating the ON currents with a sum of two kinetic functions (method 2). The total charge in cut fibers stretched to a sarcomere length of 3.5 microns at 13-14 degrees C was separated into Q beta and Q gamma by methods 1 and 2. The fraction of Q gamma in the total charge was 51.3% (SEM 1.7%) and 53.7% (SEM 1.8%), respectively, suggesting that cut fibers have a larger proportion of Q gamma:Q beta than intact fibers. When cut fibers were stretched to a sarcomere length of 4 microns, the proportion of Q gamma:Q beta was unchanged. Between 4 and 13 degrees C, the Q10 of l/tp,gamma in intact fibers was 2.33 (SEM 0.33) and that of 1/tau beta was less than 1.44 (SEM 0.04), implying that the kinetics of I gamma has a steeper temperature dependence than the kinetics of I beta. When cut fibers were cooled from 14 to 6 degrees C, I gamma in the ON segment generally became too broad to be manifested as a hump. In a cut fiber in which I gamma was manifested as a hump, the Q10 of l/tp,gamma was 2.08 and that of l/tau beta was less than 1.47. Separating the Q-V plots from cut fibers at different temperatures by method 1 showed that the proportion of Q gamma:Q beta was unaffected by temperature change. The appearance of I gamma humps at low temperatures in intact fibers but generally not in cut fibers suggests an intrinsic difference between the two fiber preparations.

Animals↗
PubMed2002

Asbestos fibers contributing to the induction of human malignant mesothelioma.

UNLABELLED: To elucidate the features of the asbestos fibers contributing to the induction of human malignant mesothelioma, we used high-resolution analytical electron microscopy to determine the type, number, and dimensions of asbestos fibers in lung and mesothelial tissues in 168 cases of mesothelioma. RESULTS: 1. Asbestos fibers were present in almost all of the lung and mesothelial tissues from the mesothelioma cases. 2. The most common types of asbestos fibers in lung were either an admixture of chrysotile with amphiboles, amphibole alone, and occasionally chrysotile alone. In mesothelial tissues, most asbestos fibers were chrysotile. 3. In lung, amosite fibers were greatest in number followed by chrysotile, crocidolite, tremolite/actinolite, and anthophyllite. In mesothelial tissues, chrysotile fibers were 30.3 times more common than amphiboles. 4. In some mesothelioma cases, the only asbestos fibers detected in either lung or mesothelial tissue were chrysotile fibers. 5. The average number of asbestos fibers in both lung and mesothelial tissues was two orders of magnitude greater than the number found in the general population. 6. The majority of asbestos fibers in lung and mesothelial tissues were shorter than 5 micro m in length. CONCLUSIONS: 1) Fiber analysis of both lung and mesothelial tissues must be done to determine the types of asbestos fibers associated with the induction of human malignant mesothelioma; 2) short, thin asbestos fibers should be included in the list of fiber types contributing to the induction of human malignant mesothelioma; 3) RESULTS support the induction of human malignant mesothelioma by chrysotile.

Asbestos↗
PubMed2003

Subgroup B and F fiber chimeras eliminate normal adenovirus type 5 vector transduction in vitro and in vivo.

Altering adenovirus vector (Ad vector) targeting is an important goal for a variety of gene therapy applications and involves eliminating or reducing the normal tropism of a vector and retargeting through a distinct receptor-ligand pathway. The first step of Ad vector infection is high-affinity binding to a target cellular receptor. For the majority of adenoviruses and Ad vectors, the fiber capsid protein serves this purpose, binding to the coxsackievirus and adenovirus receptor (CAR) present on a variety of cell types. In this study we have explored a novel approach to altering Ad type 5 (Ad5) vector targeting based on serotypic differences in fiber function. The subgroup B viruses bind to an unidentified receptor that is distinct from CAR. The subgroup F viruses are the only adenoviruses that express two distinct terminal exons encoding fiber open reading frames. We have constructed chimeric fiber adenoviruses that utilize the tandem fiber arrangement of the subgroup F genome configuration. By taking advantage of serotypic differences in fiber expression, fiber shaft length, and fiber binding efficiency, we have developed a tandem fiber vector that has low binding efficiency for the known fiber binding sites, does not rely on an Ad5-based fiber, and can be grown to high titer using conventional cell lines. Importantly, when characterizing these vectors in vivo, we find the subgroup B system and our optimal tandem fiber system demonstrate reduced liver transduction by over 2 logs compared to an Ad5 fiber vector. These attributes make the tandem fiber vector a useful alternative to conventional strategies for fiber manipulation of adenovirus vectors.

Adenoviridae↗
PubMed1987

Mechanical properties of skinned single fibers of identified types from rat diaphragm.

Maximum isometric tension (Po), maximum velocity of shortening (Vmax), and tension-pCa (i.e., -log[Ca2+]) relationships were determined in single skinned fibers from rat diaphragm. Histochemistry (myosin-ATPase) and sodium dodecyl sulfate (SDS) gel electrophoresis were performed on these same fibers to determine fiber type and protein composition. Physiologically fast fibers were found to have larger cross-sectional areas (CSA) and produced more tension per CSA and were less sensitive to [Ca2+] than physiologically slow fibers. Fast fibers were typed histochemically as type II and contained myosin heavy chains (MHC) and light chains (LC) of the fast type, whereas the slow fibers contained slow MHC and LC. There were also corresponding differences in the regulatory protein composition of these two fiber types. The histochemical sections confirmed a significant fiber size difference between the type IIa and IIb fibers. When fiber size was used to separate the fast fibers into two groups, type IIb fibers were found to have significantly greater Vmax and tension per CSA than the type IIa fibers. Although there were no noticeable differences in MHC composition between the type IIa and IIb fibers, there were some differences in the myosin LC and regulatory protein content.

Animals↗
PubMed1986

SDH activity and cross-sectional area of muscle fibers in cat diaphragm.

The succinate dehydrogenase (SDH) activity and cross-sectional area of individual muscle fibers in the cat diaphragm were quantified using a computerized image-processing system. The population distributions of fiber-SDH activities and cross-sectional areas showed considerable range within each diaphragm. Despite an overlap in the distribution of SDH activities between fast-twitch (i.e., those staining darkly for myosin ATPase) and slow-twitch (i.e., those staining lightly for myosin ATPase) fibers, differences between the two populations of fibers were observed. Fast-twitch fibers generally had lower SDH activities and greater cross-sectional areas than slow-twitch fibers. However, the range of SDH activities and cross-sectional areas of fast-twitch fibers was much greater than in slow-twitch fibers. The population distributions of SDH activities and cross-sectional areas of both fast- and slow-twitch fibers were unimodal. The unimodal distribution of SDH activities in fast-twitch fibers suggested that these fibers could not be clearly subdivided into two groups based on differences in their oxidative capacity (i.e., high- and low-oxidative fibers). These results were discussed in the context of the classification of fast-twitch glycolytic and fast-twitch oxidative-glycolytic fibers using qualitative histochemistry. In addition, the functional significance of the unimodal distribution of oxidative capacities in fast-twitch fibers was discussed in relation to the distribution of fatigue properties in fast-twitch motor units. A significant negative correlation between cross-sectional area and SDH activity in both fast- and slow-twitch fibers was also observed. The importance of this negative correlation in relationship to the diffusion of energy substrates for oxidative metabolism was discussed.

Adenosine Triphosphatases↗
PubMed1992

Rat soleus muscle fiber responses to 14 days of spaceflight and hindlimb suspension.

Morphological and enzymatic responses in fibers expressing fast, slow, or both types of myosin heavy chain (MHC) were studied in rats after 14 days of spaceflight (COSMOS 2044) or hindlimb suspension. Although the percentage of slow-twitch fibers was unchanged, a higher percentage of fibers that expressed both slow and fast MHC was observed in flight and suspended rats than in synchronous ground-based controls. The soleus was 25 and 34% smaller than control after 14 days of flight and suspension, with the reduction in fiber cross-sectional area (CSA) being greater in slow- than in fast-twitch fibers in both experimental groups. The activities of succinate dehydrogenase (SDH) and alpha-glycerophosphate dehydrogenase (GPD) were not significantly affected by flight or suspension. The total SDH activity (i.e., SDH activity x CSA) decreased significantly in the slow-twitch fibers of the flight and the fast-twitch fibers of the suspended rats, in large part due to fiber atrophy. A shift in MHC expression in 14 and 9% of the fibers in flight and suspended rats occurred without a change in myosin adenosinetriphosphatase activity. The SDH and GPD activities of the fibers that expressed both slow and fast MHC were slightly higher than the slow-twitch fibers and slightly lower than the fast-twitch fibers. These data indicate that events were initiated within 14 days of spaceflight or suspension that began to reconfigure the protein profiles of 9-14% of the slow-twitch fibers from typical slow-twitch toward those of fast-twitch fibers, while all fibers were dramatically losing total protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphatases↗
PubMed1995

SDH and actomyosin ATPase activities of different fiber types in rat diaphragm muscle.

In the rat diaphragm muscle, the histochemical classification of type I, IIa, IIb, or IIx fibers was correlated with myosin heavy chain (MHC) immunoreactivity. Expression of MHC isoforms in single dissected fibers was also assessed electrophoretically. Most fibers (approximately 86%) expressed a single MHC isoform, and when present, coexpression of MHC-2X and MHC-2B isoforms was most prevalent. Type I and IIa fibers were the smallest, type IIb fibers were the largest, and type IIx fibers were intermediate. Succinate dehydrogenase (SDH) and calcium-activated myosin adenosinetriphosphatase (actomyosin ATPase) activities were measured with quantitative histochemical procedures. Type I and IIa fibers had the highest SDH activities, followed in rank order by type IIx and IIb fibers. Type I fibers had the lowest actomyosin ATPase activity, followed in rank order by type IIa, IIx, and IIb fibers. Across all fibers, there was an inverse relationship between fiber SDH activity and cross-sectional area and a positive correlation between fiber actomyosin ATPase activity and cross-sectional area. The SDH and actomyosin ATPase activities of muscle fibers were also inversely correlated. These phenotypic differences in SDH and ATPase activities may be important in determining the contractile and fatigue properties of different fiber types in the rat diaphragm muscle.

Animals↗
PubMed1991

Postnatal changes in the distribution of succinate dehydrogenase activities among diaphragm muscle fibers.

The distributions of oxidative capacities among type-identified muscle fibers in the developing cat diaphragm were examined by quantifying succinate dehydrogenase (SDH) activity using a microdensitometric procedure. Animals were studied during the first six weeks of postnatal development and compared to adults. Muscle fiber SDH activities were initially low during the first 2 postnatal wk, then increased to their highest values between 3 and 6 wk. Thereafter, fiber SDH activities declined to adult values. At each age, the distributions of SDH activities for both type I and II fibers were unimodal. Thus, no objective basis exists for subclassifying type II fibers based on differences in oxidative capacity. Fibers could be subclassified as type IIA, IIB, or IIC based on the acid pH lability of ATPase staining. In neonates, approximately 90% of all fibers were classified as type IIC. Thereafter, the proportion of IIC fibers decreased while the proportions of type I, IIA, and IIB increased. Adult fiber type proportions were reached by 6 wk of age. The SDH activity of type I fibers was generally higher than that of type II fibers at all ages, although there was considerable overlap in the distributions of SDH activities among type I and II fibers. The SDH activity of type IIC fibers was also higher than that of either type IIA or IIB during development. Only in the adult diaphragm was the SDH activity of type IIA fibers higher than that of type IIB. At no age could type IIA, IIB, or IIC fibers be discriminated based solely on differences in oxidative capacity.

Adenosine Triphosphatases↗
PubMed1980

Experimental approaches for exposure to sized glass fibers.

A number of studies have shown that glass fibers induce both malignant mesothelioma and fibrosis in rats and that these reactions may be primarily a function of the physical properties of the fiber. However, these studies were carried out with fibers having broad size distributions and used methods of administration which bear little resemblance to the way man is exposed. To better characterize the health effects of glass fibers, techniques have been developed to expose rats to glass fibers of defined sizes by intratracheal instillation of aqueous suspensions and by "nose only" inhalation exposure, and to determine the deposition, translocation, and ultimate fate of these fibers in the rat. The fibers have known size distributions with geometric mean diameters of 1.5 micrometers (sigma g = 1.1) and lengths of either 5 micrometers (sigma g = 1.49) or 60 micrometers (sigma g = 3.76). The fibers have been activated with neutron irradiation. Of the several resulting radionuclides, 65Zn appeared to be the most suitable for long-term clearance studies by use of in vivo whole body radioassay techniques. A fluidized bed aerosol generator has been developed to expose rats by "nose only" inhalation to approximately 500 fibers/cm3. The generator and exposure system permits reuse of fibers which pass through the exposure chamber and produces no significant alteration of the fiber size distribution. Rats were exposed by intratracheal instillations to 20 mg of the longer fibers and to equal numbers (2 mg) and equal mass (20 mg) of the shorter fibers. Through approximately 19 weeks little difference was observed in the whole rat clearance rate of long versus short fibers in the initial exposure group. Histopathology, however, showed differences at this time with the short fibers apparently successfully phagocytized by alveolar macrophages and cleared to the lymph nodes, while the long fibers were not.

Aerosols↗
PubMed1994

Review of animal/in vitro data on biological effects of man-made fibers.

This paper reviews the investigations with man-made fibers (MMF). Insulation woods: glasswool (GW), rockwool (RW), slagwool (SW), glass microfibers (GMF), glass filaments (GFiI), and refractory ceramic fibers (RCF) have been used in experimental animals and in in vitro cell systems. A large heterogeneous number of fibers, methods of fiber preparation, size selection, aerosolization, fiber size, and fiber burden measurement were noted, rendering difficult a comparison between results. By inhalation, RCF and asbestos used as positive controls produced a significant tumor increase. In some studies, a low tumor yield was found after inhalation of insulation wools; when all inhalation data were gathered, a significant tumor increase was found with GW. However, it is difficult to draw definitive conclusions on the potential of other fiber types because, in addition to the different compositions of the fibers, differences in fiber number and sizes existed, especially in comparison with asbestos. Moreover, experiments using inoculation, especially by the intraperitoneal route revealed a carcinogenic potential of all fibers types but GFiI and SW. In these two groups a small number of animals has been investigated and the fiber characteristics were sometimes irrelevant. So far, a relationship between the carcinogenic potency and fiber dimensions has been established. Other fiber parameters may be of importance (surface chemistry, biopersistence, fiber structure, for example) but further investigations are necessary to determine the correlations between these parameters and tumor incidence. In vitro experiments have emphasized the fiber characteristics identified in vivo as playing a role in the carcinogenic potency and should be developed as a better approach of the mechanistic effects of MMF.

Administration, Inhalation↗
PubMed1994

Dual pH durability studies of man-made vitreous fiber (MMVF).

Dissolution of fibers in the deep lung may involve both extracellular and intracellular mechanisms. This process was modeled in vitro for each environment using an experimental flow-through system to characterize both total dissolution and specific chemical changes for three representative MMVF's: a glasswool, a slagwool, and a refractory ceramic fiber (RCF). Synthetic physiological fluids at pH 4 and at pH 7.6 were used to simulate macrophage intraphagolysosomal, and extracellular environments, respectively. Actual commercial fiber, sized to rat-respirable dimension, having an average fiber diameter of 1 micron and an average length between 15 and 25 microns, was used in the experiments. Fiber dissolution was monitored through change in chemistry of the fluid collected after percolation at a constant rate through a thin bed of sample. There are great differences in total fiber dissolution rates for the different fibers. Slagwool and RCF dissolve more rapidly at pH 4 than at pH 7.6, while the reverse is true for glasswool. Dissolution is sometimes accompanied by a noticeable change in fiber morphology or dimension, and sometimes by no change. There is strong dependency on pH, which affects not only total fiber dissolution, but also the leaching of specific chemical components. This effect is different for each type of fiber, indicating that specific fiber chemistry largely controls whether a fiber dissolves or leaches more rapidly under acidic or neutral conditions. Both total dissolution rates and calculated fiber composition changes are valuable guides to interpreting in vivo behavior of man-made vitreous fibers, and demonstrate the usefulness of in vitro acellular experiments in understanding overall fiber persistence.

Animals↗