Letter: Penetration of asbestos through the digestive tract of rats

Chrysotile fibers penetrate Escherichia coli cell membrane and cause cell bursting by sliding friction force on agar plates

A mixture (50 microl) consisting of Escherichia coli cells, chrysotile fibers, and 200 mM NaCl was added to 2% agar plates and spread with a plastic stir stick. An apparatus was developed to generate a sliding friction force on the surface of the plate by applying a fixed vertical reaction force to the stir stick while turning the plate. This operation was defined as chrysotile-exposure. The number of living cells, expressed as colony forming units, was reduced in proportion to the duration of chrysotile-exposure. The decrease in the number of living cells was greater following 120 s of chrysotile-exposure than crocidolite- or amosite-exposure. There was no decrease in the number of living cells exposed to chrysotile on 0.5% agar even after 120 s. The number of living cells after chrysotile-exposure decreased with increasing chrysotile concentration. Leakage of beta-galactosidase from cells increased with increasing duration of chrysotile-exposure. Transmission and scanning electron microscopy observation of E. coli revealed chrysotile penetration of the cell membrane. These results show that chrysotile fibers destroy cells by penetration. The driving force for the chrysotile penetration was the sliding friction force, as the number of living cells following chrysotile-exposure decreased with increasing exposure times, but did not decrease following chrysotile-exposure on a low concentration of agar, which provided cells with low sliding friction force.

The oral absorption of micro- and nanoparticulates: neither exceptional nor unusual

This mini-review covers some of the historical and recent arguments over the experimental evidence on the uptake by and translocation from the intestinal mucosa of microparticulates after oral administration. It is concluded that there is now no dispute over the fact that this is a normal occurrence. Particulate uptake does take place, not only via the M-cells in the Peyer's patches and the isolated follicles of the gut-associated lymphoid tissue, but also via the normal intestinal enterocytes. Factors affecting uptake include particle size, surface charge and hydrophobicity and the presence or absence of surface ligands. The covalent attachment of lectin or invasion molecules to the surface of carrier particles leads to greater systemic uptake. Whether or not the route can be utilized for the routine administration of therapeutic agents which are not normally absorbed from the gut is not yet proven. Many studies show that 2-3% of the ingested dose of submicron particles can be absorbed. The increasing diversity of carrier systems, which includes dendrimers and liposomes, needs to be exploited fully. More also must be learned about the inter- and intra-subject variability of lymphoid tissue so that appropriate selectivity can be achieved through the design of specific carriers.

Is there transplacental transfer of asbestos? A study of 40 stillborn infants

An autopsy study was conducted to investigate whether there is transplacental transfer of asbestos in humans. The asbestos burden of lung, liver, skeletal muscle, and placenta digests of 40 stillborn infants was determined using a bleach digestion method. The fibers detected in the tissue digests were characterized as to the type of asbestos, using electron microscopy, energy-dispersive x-ray analysis, and selected-area diffraction analysis. Placental digests of 45 full-term, liveborn infants were similarly processed as controls. Low levels of small, thin, uncoated asbestos fibers were detected in the placentas and organs of 37.5% of the stillborn infants (15 of 40). The fiber sizes ranged from 0.05 to 5.0 microns in length and 0.03 to 0.3 micron in width, with a mean length of 1.15 microns and a mean width of 0.069 micron. Maximum numbers of fibers were found in the lungs (mean 235,400 fibers/g; n = 10), followed by liver (mean 212,833 fibers/g; n = 6), placenta (mean 164,500 fibers/g; n = 4), and skeletal muscle (80,000 fibers/g; n = 1). The fibers were detected at all stages of gestation and showed no association with gestational age. A significant association was found between fiber presence and working mothers, and positive but nonsignificant associations were found with maternal history of drug abuse, previous abortions, and fetal maceration. No association was found between premature rupture of membranes and fiber presence. No fibers were detected in the 45 placentas of the liveborn control infants. There was a highly significant difference in the asbestos fiber counts of the placentas of the stillborn and liveborn infants (P < .001). Our studies demonstrate the presence of short and thin asbestos fibers in stillborn infants and their positive association with working mothers.

Oxidative damage in Alzheimer's dementia, and the potential etiopathogenic role of aluminosilicates, microglia and micronutrient interactions

While evidence implicating free radical oxidative processes in the etiopathogenesis of Alzheimer's dementia is accumulating, the specific cellular and biochemical mechanisms involved remain to be identified. The potential pathogenic role of microglial cells in neurodegenerative processes is indicated by the finding that purified murine microglial cells exposed in vitro to various model aluminosilicate particles stimulate the generation of tissue-injurious free radical reactive oxygen metabolites. Analogous inorganic aluminosilicate deposits have been reported to occur in the core of the characteristic senile plaques found in the brains of Alzheimer disease subjects. The possible modulation of free radical oxidative activity by antioxidant micronutrients and pharmacological agents, provides a rational basis for further preventative and therapeutic clinical investigations.

Cephaloconiosis: a free radical perspective on the proposed particulate-induced etiopathogenesis of Alzheimer's dementia and related disorders

By analogy to the etiology of the pneumoconioses, exogenous dust-induced diseases of the lung, and endogenous crystal-induced arthropathies such as gout, it is proposed that Alzheimer's dementia and allied disorders are causally related to the accumulation of fibriform inorganic deposits within the brain. Hence the neonosological term 'Cephaloconiosis'. It is proposed that: 1) either by the extrinsic migration or intrinsic formation and deposition of insoluble and persistent inorganic reactive nidi, the particle-induced generation of tissue-damaging free-radical oxygen metabolites by stimulated brain glial macrophage-type and allied phagocytic cells, provides a rationale for the etiopathogenesis of neurodegenerative processes; 2) the modulation of the injurious oxidative metabolic reaction by micronutrient and pharmacological antioxidant agents is a rational and potentially feasible strategy for future therapeutic clinical investigations.

The uptake and translocation of latex nanospheres and microspheres after oral administration to rats

Non-ionic and carboxylated fluorescent polystyrene microspheres (100, 500 nm, 1 and 3 microns in diameter), were fed by gavage (2.5% w/v; 1.25 mg kg-1) daily for 10 days to female Sprague Dawley rats. Peyer's patches, villi, liver, lymph nodes and spleen of animals fed the non-ionic microspheres from 100 nm to 1 micron showed unequivocal evidence of uptake and translocation of the particles. Heart, kidney and lung showed no evidence of the presence of microspheres. Carboxylated microspheres were taken up to a lesser degree than the non-ionised particles. Experiments with 125I radiolabelled 100 nm and 1 micron particles showed a higher uptake of the smaller particles, which were concentrated in GI tissue and liver. Particles were not distributed randomly in the tissues, but were concentrated at the serosal side of the Peyer's patches and could be seen traversing the mesentery lymph vessels towards the lymph nodes. The results demonstrate a need to re-examine the possibilities of particulate oral delivery, as well as the potential toxicity of ingested particulates.

Intestinal transport of some macromolecules in food

This review focuses on the intestinal transport of macromolecules in food. Although it is known that neonates have the ability to absorb proteins from the intestine as a means of passive immunization, it has generally been assumed that adults do not retain this capability. A number of studies have shown that the adult mammalian small intestine is capable of transporting a variety of macromolecules in food to a very limited extent. The evidence demonstrating the transport of test substances in the micron-size range across the adult intestinal epithelial barrier is examined for a number of food substances and environmental contaminants. It will be shown that macromolecules can be transported across this barrier by endocytosis; by uptake into the gut-associated lymphoid tissue, and possibly by uptake into the goblet cells. It is considered highly unlikely that large micron-sized particles pass between intestinal cells due to the integrity of the tight junctions between cells that exclude particles in this size range. Quantitative estimates for macromolecular uptake are included along with a discussion of the physiological parameters influencing macromolecular transport.

Asbestos exposure and gastrointestinal malignancy review and meta-analysis

The epidemiologic literature linking asbestos exposure with gastrointestinal malignancy is reviewed. Problems in comparing studies are discussed, appropriate strategies for comparison are developed, and study results are pooled using a model which accounts for both intrastudy and interstudy variability. Stratification of cohorts by dose reveals that significant asbestos exposure, as indicated by a lung cancer standardized mortality ratio (SMR) of at least 200, is associated with an elevated gastrointestinal cancer of SMR for five of six points examined [corrected].

Asbestos bodies in a bile duct cancer after occupational exposure

A case of asbestosis after 5 years of occupational asbestos exposure is presented. At the postmortem examination, cholelithiasis and a cancer developing from the cystic duct were found and identified histologically as a squamous cell carcinoma. After digesting the tumor tissue, short asbestos bodies and fragments could be identified having a similar shape as those observed in the lung. The possible role of asbestos in the carcinogenesis of the observed bile duct cancer is proposed. The digestive examination of all malignant tumors of any origin after an asbestos exposure is suggested for the identification of the possible presence of ingested asbestos fibers, and to obtain further comprehensive human pathological data.

The effects of long-term ingestion of asbestos on the colon of F344 rats

Weanling F344 rats, which were fed a diet containing 10% chrysotile (B), were studied over their life-time to determine the effects of ingested asbestos on the colon. Control groups consisted of rats fed a diet containing a 10% nonnutritive cellulose or a standard laboratory rat diet. The pathological findings in the colons of 501 rats (189 on asbestos diet, 197 on fiber control diet, and 115 on standard control diet), are reported here. Epithelial tumors of the colon (eight adenocarcinomas and one adenoma) were found in nine of the rats on study. Four of the tumors were in asbestos-fed rats, two tumors were found in the non-nutritive cellulose controls, and three tumors were found in the standard laboratory rat diet controls. The probability (based on actuarial analysis) of developing adenoma or adenocarcinomas during the 32 months of the study were 7.4% for the asbestos-fed group, 3.5% for the fiber control diet and 4.0% on the standard control diet. In addition, one malignant mesothelioma of the type induced by intraperitoneally administered asbestos was found in the asbestos-fed group. Non-neoplastic lesions of the colon were also evaluated. The cumulative risk for development of any colon-associated lesion (non-neoplastic plus neoplastic lesions) was greatest for asbestos-fed rats (17.9%), compared to 13.6% for those fed the fiber control diet and 8.2% for those fed the standard control diet. The colon tissue levels of adenosine, 3'-5'-cyclic monophosphate (cAMP) were significantly lower in the animals fed asbestos compared to the control diets. Chrysotile fibers were seen by electronmicroscopy (e.m.) in six of ten ashed colon specimens of rats fed the asbestos diet. Although the differences in numbers of tumors between the animals fed asbestos and the controls were not statistically significant at the 5% level, we felt that the combination of observations including 1) evidence of increased probability of asbestos-fed animals to develop colon lesions in general; 2) evidence of a special type of mesothelioma in rats fed asbestos; 3) evidence for a cell regulator defect (lowered cAMP levels) in colon tissues of animals fed asbestos; and 4) evidence for asbestos fiber penetration of the colonic mucosa (e.m. studies) suggest that ingested asbestos is not inert in the colon.

Ingested mineral fibers: elimination in human urine

Sediment in human urine examined by transmission electron microscopy contains amphibole fibers which originate from the ingestion of drinking water contaminated with these mineral fibers. The ingestion of filtered water results in the eventual disappearance of amphibole fibers from urine. These observations provide the first direct evidence for the passage of mineral fibers through the human gastro-intestinal mucosa under normal conditions of the alimentary canal.

An outbreak of pleural mesothelioma and chronic fibrosing pleurisy in the village of Karain/Urgüp in Anatolia

The 575 inhabitants of the remote Anatolian village of Karain suffered 11 deaths from pleural mesothelioma in 1975/76 and there were five cases of fibrosing pleurisy. In the previous five years there had been 25 cases of mesothelioma. Calcified pleural plaques were common on survey radiography. Asbestos does not occur in the local soil or rock, nor is it handled in the village, but a few fibres were found in the water. Fibres were also found in the pleural tissue of two of five cases examined. Inhabitants of the neighbouring villages are free of mesothelioma.

Asbestos and embryonic development

Chrysotile asbestos was administered to pregnant CD-1 mice in their drinking water and to Day 4 blastocysts during culture. Administration to pregnant mice did not affect embryo survival. In vitro administration of asbestos did not interfere with embryo implantation upon transfer of blastocysts to recipient females but did result in a decrease in postimplantation survival. These studies did not demonstrate asbestos to be teratogenic whether administered to the dam or to the blastocyst in vitro.

Asbestiform amphibole minerals: detection and measurement of high concentrations in municipal water supplies

Ashestiform amphibole minerals, which have been demonstrated to be associated with human health problems, have been detected in substantial quantities in municipal water supplies taken from western Lake Superior Water. The total concentrationl of amphibole minerals in the Duluth, Minnesota, water supply, as measured by x-ray diffraction for daily samples of suspended solids averages 0.19 milligram per liter with large fluctuations due to seasonal and climatological effects on lake circulation. Electron microscopic examination of these water samples confirms the presence of asbestiform amphibole fibers. A conservatiue estimate of the fiber count for 1973 Duluth water supply samples is (1 to 30) x 10(6) amphibole fibers identifiable by electron diffraction per liter of water with a mass concentration of 1 to 30 micrograms per liter.