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At least 235 records · Page 13Linked to original sources
PubMed1992

Effect of a dietary fiber (beet fiber) on dimethylhydrazine-induced colon cancer in Wistar rats.

The modifying effect of a dietary fiber, Fibeta (beet fiber), on experimentally induced colorectal cancer was studied in Wistar rats. The rats were fed a powdered semisynthetic casein-based diet in which the carbohydrate pool was substituted with Fibeta as the sole source of fiber. Dimethylhydrazine dihydrochloride (DMH-2HCl) was used as initiator in a dose of 20 mg/kg body wt and given by gavage once a week for 10 weeks. Throughout the experiment the rats were offered the diets with different levels of fiber in a preinitiation period of 8 weeks, during the initiation, or in a 30-week postinitiation period. The study was terminated after one year. A protective effect of the fiber was not found at any stage of the colorectal carcinogenic process. Even though differences (not statistically significant) in tumor incidences were seen, these did not reflect any effect of the high or low fiber intake during the study. Analysis for volatile fatty acids in cecal content showed that continuous feeding with a fiber-rich diet resulted in significant increase in most of the volatile fatty acids. The relative change was highest for butyric acid. These findings do not support the hypothesis that butyric acid has a protective effect on colorectal cancer. The tumor yield in the present study was low compared with that reported in the literature, and possible causes for this are discussed.

Animals↗
PubMed2001

Biopersistence, fiber length, and cancer risk assessment for inhaled fibers.

We briefly review the evidence that the carcinogenic risk posed by inhaled fibers depends principally on the lung burden of long fibers. We use a deposition clearance model to generate time-dependent lung burdens in rats of a dozen long fibers for various exposure concentrations. Together with a previously estimated potency factor for long fibers, we use the generated lung burdens to estimate risks of lung cancer associated with inhaled fibers in rats. Over a broad range of exposure concentrations, excess risk is a linear function of exposure concentration. Excess risk of lung cancer is also a linear function of weighted half-life for fibers for which the weighted half-life is short compared to the life span of the rat. We propose an approach to estimating human lung cancer risk associated with inhaled fibers from animal studies.

Administration, Inhalation↗
PubMed2006

Occupational exposure to carbon/coke fibers in plants that produce green or calcined petroleum coke and potential health effects: 2. Fiber concentrations.

We monitored exposure to various fibers among workers in eight plants operated by ConocoPhillips that produce green or calcined petroleum coke. Carbon/coke and other fibers, including calcium silicate, cellulose, gypsum, and iron silicate, were found in occupational samples. Carbon/coke fibers were found in bulk samples of calcined petroleum coke, the probable source of these fibers in occupational samples. Time-weighted average (TWA) total fiber concentrations were approximately lognormally distributed; 90% were < or = 0.1 f/ml. Although consistently low, TWA total fiber concentrations varied with plant, job (tasks), and type of coke. This was expected given the substantial differences in plant configuration, technology, and workplace practices among refineries and carbon plants. Carbon/coke fibers (identified and measured using transmission electron microscopy [TEM]) were found at all plants producing all types of calcined coke and not detected at any plant producing only green coke. Approximately 98% of all carbon/coke TWAs were < or = 0.1 f/ml. Analysis of task length average (TLA) data by various statistical techniques indicates that the average carbon/coke TLA is certainly < or = 0.05 f/ml and probably < 0.03 f/ml.

Calcium Compounds↗
PubMed1989

Blood glucose response to pea fiber: comparisons with sugar beet fiber and wheat bran.

Two new fiber types, pea fiber (PF) and sugar beet fiber (BF), were compared with wheat bran (WB) to investigate the effect on postprandial blood glucose and serum insulin responses in normal subjects. The control meal consisted of 150 g ground beef mixed with 50 g glucose and 20 g lactulose. Only addition of PF (15 g pure fiber) reduced the area under the incremental blood glucose curve significantly (by 65%, p less than 0.05). None of the fibers affected the area under the insulin-response curve significantly although it was reduced by all fibers. Mouth-to-cecum transit time, assessed by the hydrogen breath technique, was decreased by WB and BF, (p less than 0.05) but not by PF. PF is palatable and may prove beneficial as a fiber supplement for diabetics.

Adult↗
PubMed2000

Hepatic LDL receptor mRNA in rats is increased by dietary mushroom (Agaricus bisporus) fiber and sugar beet fiber.

Plasma cholesterol concentration is reduced by feeding some dietary fibers and mushroom fruit body, but the mechanism is not fully understood. We examined the effects of mushroom (Agaricus bisporus) fiber and sugar beet fiber on serum cholesterol and hepatic LDL receptor mRNA in rats. Rats were fed a cholesterol-free diet with 50 g/kg cellulose powder (CP), 50 g/kg mushroom (Agaricus bisporus) fiber (MSF) or 50 g/kg sugar beet fiber (BF) for 4 wk. There were no significant differences in the body weight, food intake and cecum weight among the groups. The relative liver weight in the CP group was significantly greater than that in the MSF and BF groups. The cecal pH in the CP and MSF groups was significantly higher than that in the BF group. Cecal acetic acid, butyric acid and total short-chain fatty acid (SCFA) concentrations in the BF group were significantly higher than those in the other groups. The serum total cholesterol, VLDL + intermediate density lipoprotein (IDL) + LDL cholesterol concentrations in the CP group were significantly greater than those in the MSF and BF groups. The HDL cholesterol concentration in the MSF group was significantly lower than that in the CP group. The hepatic LDL receptor mRNA level in the MSF and BF groups was significantly higher than that in the CP group. The results of this study demonstrate that mushroom fiber and sugar beet fiber lowered the serum total cholesterol level by enhancement of the hepatic LDL receptor mRNA.

Agaricales↗
PubMed2001

Pseudoasbestos bodies and fibers in bronchoalveolar lavage of refractory ceramic fiber users.

Refractory ceramic fibers (RCF) are widely used to replace asbestos in applications requiring high heat resistance. Ferruginous bodies mimicking asbestos bodies (ABs) have been detected in the lungs of RCF production workers. This raises the question about their presence in other occupational groups and whether "typical ABs" still reflect past asbestos exposures in all settings. An AB counting by phase-contrast light microscopy and a screening test by analytical electron microscopy were systematically performed on all bronchoalveolar lavage fluids (BALF) submitted to our laboratory in 1992 through 1997 (n = 1,800). When RCF were detected in electron microscopy, the structures considered as "typical ABs" were marked under light microscopy and prepared for further chemical and structural analysis. Pseudo-ABs on RCF were detected in samples from nine subjects (0.5%). All of them had worked either as foundry workers, steel workers, or welders. In these subjects, alumino-silicate fibers compatible with RCF accounted for 42% of the core fibers analyzed, other nonasbestos fibers for 28%, and asbestos fibers for 30%. ABs thus remain a valid marker of asbestos retention but attention must be paid to a possible occurrence of pseudo-asbestos bodies on RCF and other nonasbestos fibers in end-users of refractory fibers.

Adult↗
PubMed2005

Contractile properties of mouse single muscle fibers, a comparison with amphibian muscle fibers.

Single fibers, 25-40 microm wide and 0.5-0.7 mm long, were isolated from the flexor digitorum brevis muscle of the mouse. Force and movement were recorded (21-27 degrees C) from the fiber as a whole and, in certain experiments, from a short marked segment that was held at constant length by feedback control. The maximum tetanic force, 368+/-57 kN/m2 (N = 10), was not significantly different from that recorded in frog muscle fibers at equal temperature. However, the rising phase of the tetanus was considerably slower in the mammalian fibers, 202+/-20 ms (N = 17) being required to reach 90% of maximum tetanic force as compared with 59+/-4 ms (N = 20) in the frog muscle fibers. Similar to the situation in frog muscle fibers, the force-velocity relation exhibited two distinct curvatures located on either side of a breakpoint near 80% of the isometric force. Maximum speed of shortening was 4.0+/-0.3 fiber lengths s(-1) (N = 6). The relationship between tetanic force and sarcomere length was studied between 1.5 and 4.0 microm sarcomere spacings, based on length-clamp recordings that were free of 'tension creep'. There was a flat maximum (plateau) of the length-tension relation between approximately 2.0 and 2.4 microm sarcomere lengths. The descending limb of the length-tension relation (linear regression) intersected the length axis (zero force) at 3.88 microm and reached maximum force at 2.40 microm sarcomere length. The slope of the descending limb is compatible with a thick filament length of 1.63 microm and an average thin filament length of 1.10 microm. These values accord well with recent electron microscope measurements of myofilament length in mammalian muscle.

Animals↗
PubMed2004

Saccharification of Okara fiber by plant dietary fiber hydrolases.

In this paper, the saccharification process of okara fiber with pectinase, xylanase and cellulase was investigated as a preliminary attempt to effectively utilize okara fiber. The solubilization of okara fiber was raised in proportion to the number of enzymes used; that is, by a single enzyme, two enzymes and three enzymes, in that order. The saccharification of okara fiber was much more completed by a combination of pectinase, xylanase and cellulase than by using individual preparations. This multi-enzyme system liberated sugars equivalent to 80% of the original okara fiber by weight. Moreover the structure of okara fiber gradually disintegrated by hydrolytic reactions with pectinase, xylanase and cellulase in turns. These results suggest that the saccharification of okara fiber progresses by the cooperative action of pectinase, xylanase and cellulase.

Cellulase↗
PubMed1999

Intermittent loading of teeth restored using quartz fiber, carbon-quartz fiber, and zirconium dioxide ceramic root canal posts.

PURPOSE: The purpose of the investigation was to compare the performances of teeth restored with quartz fiber, carbon-quartz fiber, and zirconium-dioxide posts covered with all-ceramic crowns when subjected to a cyclic loading test performed in a wet environment. MATERIALS AND METHODS: Forty single-rooted human lower premolars having similar dimensions were endodontically treated and mounted in acrylic resin blocks with a simulated periodontal ligament. The teeth were divided into three experimental groups and one control group. Post holes 8 mm long were prepared in the roots of the experimental groups in which quartz fiber, carbon-quartz fiber, and zirconium dioxide posts were cemented. In the control group, no posts were used. The crown buildup was made with composite resin. The teeth were covered with all-ceramic crowns and intermittently loaded at an angle of 45 degrees to the long axis of the tooth at a frequency of two loads per second. RESULTS: Only one failure (root fracture + post fracture) was observed in each of the fiber post groups, while in the zirconium dioxide post group, six failures were observed (one crown fracture and 5 root fractures + post fractures). The Kaplan-Meier analysis of the three experimental groups showed that the survival rate of zirconium dioxide posts was significantly lower than that of both types of fiber post. All the experimental groups showed a survival rate higher than that of the control group. CONCLUSION: Fiber posts reduced to a minimum the risk of root fractures of teeth restored with composite cores and Empress crowns under the present experimental conditions (intermittent loading in a wet environment).

Aluminum Silicates↗
PubMed2006

Comparison of experimental and numerical muscle fiber conduction velocity (MFCV) distribution around the end-plate zone and fiber endings.

BACKGROUND: The distribution of muscle fiber conduction velocity (MFCV) estimated from surface myoelectric signals differs depending on the recording electrode locations. It is assumed in this study that the irregular values of MFCV may be estimated around the end-plate zone and the fiber endings due to effect of unique interference property of myoelectric signals, and its hypothesis is confirmed experimentally and numerically in consideration of the waveform characteristics of surface myoelectric signals. MATERIAL/METHODS: In experimental study, the surface myoelectric signals are recorded by array electrodes during voluntary isometric contraction in biceps brachii muscle. In the numerical study, the surface myoelectric signals in consideration of the interference property of some motor unit activities are calculated from the current dipole model which simulated the firing features of muscle fiber from end-plate zone to fiber endings. MFCV is estimated by the technique of cross-correlation. Maximum correlation coefficient (Rxy(Ts)) and amplitude ratio (AMPratio) are used to evaluate similarity and attenuation rate between traveling signals. RESULTS: In both results of experimental and numerical studies, the MFCV significantly increase when both Rxy (Ts) and AMPratio decrease around the end-plate zone and fiber endings although three parameters denote constant values in the locations other than the end-plate zone and the fiber endings. The high correlativity is recognized between the experimental and numerical data for MFCV, Rxy (Ts), and AMPratio. CONCLUSIONS: Therefore, it is demonstrated by experimental and theoretical studies that MFCV, Rxy(Ts), and AMPratio are influenced by irregular waveform properties depending on both positions of the end-plate and fiber endings.

Action Potentials↗
PubMed1982

Complement activation in muscle fiber necrosis: demonstration of the membrane attack complex of complement in necrotic fibers.

The membranolytic C5b-9 complement membrane attach complex (MAC) is assembled after activation of either the classic or the alternative complement pathway. The quaternary configuration of the MAC macromolecule presents neoantigenic determinants not present on precursor molecules. Consequently, antibodies specific for these neoantigen(s) do not detect nonspecifically bound native complement precursors of MAC. By means of antibodies rendered specific for MAC neoantigen(s), MAC was localized by the immunoperoxidase reaction in cryostat sections of human muscle. In 66 biopsy specimens containing necrotic muscle fibers (Duchenne dystrophy, 13; other dystrophies, 15; inflammatory myopathies, 31; miscellaneous myopathies, 7) all of the necrotic fibers reacted for MAC neoantigen(s). C3 and C9 were also consistently localized in necrotic fibers, but localization of C1q, C4, and IgG was variable and often did not exceed background staining. None of the nonnecrotic fibers reacted for immunoglobulin or complement. Detection of MAC neoantigen(s) in necrotic fibers in a wide variety of muscle disease unambiguously shows that (1) the lytic complement pathway is consistently activated and participates in muscles fiber necrosis in vivo, and (2) complement reaction products are generated than can stimulate cellular infiltration and phagocytosis of the necrotic fiber. The findings also suggest that cell necrosis in general may involve participation of complement.

Antigens↗
PubMed1992

Differences in fiber number and fiber type proportion within fascicles. A quantitative morphological study of whole vastus lateralis muscle from childhood to old age.

Data are presented on the number of fibers and the proportion of different fiber types within fascicles of whole vastus lateralis muscles from 5 male children, 5 to 15 years of age, and compared with results from 25 male adults, middle aged and old individuals. The results verify a difference in the proportion of fibers with different properties within a fascicle. The proportion of type 2 (fast twitch) fibers on the border of fascicles is larger than the proportion internally: the children have (P less than 0.01) greater difference than the adults and the middle aged, whereas the old have (P less than 0.001) less difference than the other age groups. The mean number of fibers per fascicle increases (P less than 0.05) from childhood to adult age, and thereafter reduces (P less than 0.01). The results imply that fascicles continuously rearrange during the normal growth and development and the normal aging process. It is argued that the causes of the difference in fiber type proportions within fascicles are local factors in the muscle, secondary to the overall age related functional demands put on the fiber population.

Adolescent↗
PubMed2005

Mechanical properties and in vitro degradation of bioresorbable fibers and expandable fiber-based stents.

Bioresorbable polymeric support devices (stents) are being developed in order to improve the biocompatibility and drug reservoir capacity of metal stents, as well as to offer a temporary alternative to permanent metallic stents. These temporary devices may be utilized for coronary, urethral, tracheal, and other applications. The present study focuses on the mechanical properties of bioresorbable fibers as well as stents developed from these fibers. Fibers made of poly(L-lactide) (PLLA), polydioxanone (PDS), and poly(glycolide-co-epsilon-caprolactone) (PGACL) were studied in vitro. These fibers combine a relatively high initial strength and modulus together with sufficient ductility and flexibility, and were therefore chosen for use in stents. The effect of degradation on the tensile mechanical properties and morphology of these fibers was examined. The expandable stents developed from these fibers demonstrated excellent initial radial compression strength. The PLLA stents exhibited excellent in vitro degradation resistance and can therefore support body conduits such as blood vessels for prolonged periods of time. PDS and PGACL stents can afford good support for 5 and 2 weeks, respectively, and can therefore be utilized for short-term applications. The degradation resistance of the stents correlates with the profile of mechanical property deterioration of the corresponding bioresorbable fibers.

Absorbable Implants↗
PubMed1975

An analysis of nuclear numbers in individual muscle fibers during differentiation and growth: a satellite cell-muscle fiber growth unit.

A numerical analysis of changes in the populations of nuclei in individual, intact muscle fibers was made to study how multinucleation arises during normal differentiation and growth. Gastrocnemius muscle fibers from pre- and post-natal mice were isolated with guanidine (Cardasis and Cooper, '75) and examined. Satellite cells associated with muscle fibers were first observed at 19 days of gestation. The number of nuclei per muscle fiber (muscle + satellite cell nuclei) averages 83 at this age, 157 at birth and continues to increase to 354 by 63 days of age. However, the rate of increase during growth is not constant. Estimates of satellite cell and muscle nuclei in histological cross sections indicate that there is a decrease in the percentage of satellite cells from 32% at birth to 6% in the adult. However, the numbers of satellite cells associated with individual muscle fibers, calculated from these percentages and the nuclear counts on whole fibers, decreases only between 2 and 4 weeks of age. Cytosine arabinoside was injected subcutaneously during the first two weeks of age. Pairs of satellite cells, abnormal nuclei and elevated percentages of satellite cells were observed. This evidence as well as the numerical analysis of nuclear populations in whole fibers lends further support to the hypothesis that satellite cells account for the increase in muscle nuclei from birth to maturity.

Animals↗
PubMed1987

Distribution and innervation of short, interdigitated muscle fibers in parallel-fibered muscles of the cat hindlimb.

The cat hindlimb contains several long, biarticular strap muscles composed of parallel muscle fascicles that attach to short tendons. Three of these muscles--sartorius, tenuissimus, and semitendinosus--were studied by dissecting individual gold-stained fibers and determining the surface distribution of acetylcholinesterase-stained end-plate zones. In each muscle, fascicles were composed of muscle fibers that ran only part of the fascicle length and tapered to end as fine strands that interdigitated with other tapering fibers within the muscle mass. Most muscle fibers measured 2-3 cm in length. Fascicles of muscle fibers were crossed by short transverse bands of endplates (1 mm wide by 1-5 mm long) that were spaced at fairly regular intervals from the origin to the insertion of the muscle. The endplate pattern suggested that the fiber fascicles were organized into multiple longitudinal strips. In the sartorius, the temporospatial distribution of electromyographic (EMG) activity evoked by stimulating fine, longitudinal branches of the parent nerve confirmed that each strip was selectively innervated by a small subset of the motor axons. These axons appeared to distribute their endings throughout the entire length of the fascicles, providing for synchronous activation of their in-series fibers.

Action Potentials↗
PubMed2002

Indices of fiber biopersistence and carcinogen classification for synthetic vitreous fibers (SVFs).

It is generally accepted that the biopersistence of a synthetic vitreous fiber (SVF) is an important determinant of its biological activity. Experimental protocols have been developed to measure the biopersistence of an SVF from short-term inhalation experiments with rats. Clearance kinetics of long (>20 microm) fibers (those believed to have greatest biological activity) have been approximated by one- or two-pool models. Several measures or indices of biopersistence have been proposed in the literature of which three, the weighted half-time (WT(1/2)), the time required to clear 90% of long fibers (T(0.9)), and the so-called slow-phase half-time (T(2)), have been investigated in some detail. This paper considers both one- and two-pool models for long fiber clearance, characterizes the properties of these candidate indices of fiber biopersistence, identifies measures with potentially superior statistical properties, suggests possible cutoff values based on the relation between biopersistence and the outcome of chronic bioassays, and offers comments on the selection of efficient experimental designs. This analysis concludes that WT(1/2) and T(0.9) are highly correlated, are efficient predictors of the outcome of chronic bioassays, and have reasonable statistical properties. T(2), although perhaps attractive in principle, suffers from some statistical shortcomings when estimated using present experimental protocols. The WT(1/2) is shown to be directly proportional to the cumulative exposure (fiber days) after the cessation of exposure and also the mean residence time of these fibers in the lung.

Animals↗
PubMed1980

Organization of chromatin during spermiogenesis: beaded fibers, partly beaded fibers, and loss of nucleosomal structure.

The aggregation of chromatin during spermiogenesis in the house cricket and many other animals is an orderly process involving the formation of a series of long, thick, well defined structures. The differentiation of chromatin preliminary to the development of such unusual structures is given attention here. Examination of nuclei after lysis and spreading indicated that fibers with closely spaced nucleosomes, like the fibers of somatic chromatin, make up the chromatin in all stages of early spermiogenesis and most of middle spermiogenesis. The thick structures of late spermatids cannot be formed by aggregation of fibers of this somatic type, however; just before thick structures form, chromatin fibers lose the nucleosomal structure. During the process, fibers with nucleosomes spaced at irregular intervals and with long stretches of smooth thin fiber are found, as if nucleosomes at one site on a fiber are broken down independently of those at adjacent sites. Since prior studies of cricket proteins have indicated that somatic histones persist during the stages when nucleosome structure disappears, the observations imply that the histones which are organized in nucleosomes during early stages must become incorporated into different kinds of nucleoprotein complexes during succeeding stages of spermiogenesis.

Animals↗
PubMed1979

Fiber composition, fiber size and enzyme activities in vastus lateralis of elite athletes involved in high intensity exercise.

In order to determine the influence of an extensive history of participation in high intensity activity on muscle fiber type, fiber size, and metabolic profile, elite ice hockey players were selected for investigation from three different leagues. Biopsy samples from the vastus lateralis muscle were obtained from different groups of players prior to and following the season and compared with control subjects. No significant differences were found in the percentage (49.6 vs. 43.8%) or the size of the ST fibers between the elite athletes and the control group, nor was there any significant alteration following the season of play in these variables. For the FT fiber subgroups, a reduction in the FTb (12.2 vs. 3.9%) and an increase in FTa (38.0 to 45.2%) fiber populations occurred over the season. Similarly, increases in fiber area were observed for both FT subgroups pre to post season. Of the enzymes studied only 3-hydroxyacyl CoA dehydrogenase was elevated in the post season measures, while total phosphorylase and phosphofructokinase were significantly lower. The metabolic pattern exhibited does not appear to be substantially different from what would be expected from an untrained group of similar fiber distribution.

Adolescent↗