Ingested mineral fibers: elimination in human urine

Occupational Asbestos Exposure and Kidney Cancer: Systematic Review and Meta-analysis of Cohort Studies

OBJECTIVES

An estimated 125 million workers are exposed to asbestos worldwide. Asbestos is classified by the International Agency for Research on Cancer as a Group 1 carcinogen. The association between occupational asbestos exposure and kidney cancer is not well established however. This study aimed to determine the mortality and incidence of kidney cancer in workers who have been exposed to asbestos. We performed a systematic review and meta-analysis to evaluate the association between occupational asbestos exposure and kidney cancer.

METHODS

Medline, EMBASE, and Web of Science were searched according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines for articles on occupational asbestos exposure and kidney cancer. The studies reported the standardized mortality ratio (SMR) or standardized incidence ratio (SIR) of kidney cancer in workers exposed to asbestos. SMRs or SIRs with its 95% confidence interval (CI) were pooled using a fixed-effect model.

RESULTS

Forty-nine cohort studies involving 335 492 workers were selected for analysis. These studies included 468 kidney cancer deaths and 160 incident cases. The overall pooled-SMR of kidney cancer was 0.95 (95% CI: 0.86-1.05), with no significant heterogeneity (PQ = 0.09, I2 = 24.87%). The overall pooled-SIR of kidney cancer was 0.95 (95% CI: 0.79-1.11), with no significant heterogeneity (PQ = 0.68, I2 = 0.00%). Subgroup analysis did not find any increased association with occupational asbestos exposure. There was no evidence of publication bias with Egger's test P values of 0.08 for mortality studies and 0.99 for incidence studies.

CONCLUSIONS

This systematic review and meta-analysis did not show evidence of association between occupational asbestos exposure and kidney cancer mortality or incidence.

Predicting Long-Term Asbestos Prevalence in Human Lungs, Lymph Nodes, and Remote Organs from Short-Term Murine Experiments

Inhalation of asbestos fibers leads to a suite of fatal diseases that can manifest years, if not decades, after cessation of exposure. The first phase of disease progression occurs as fibers are transported from point of entry in the lungs throughout the entire body. A mathematical model is developed for the disposition of non-chrysotile asbestos in the body and, except for exposure levels, is parameterized by published data on short-term rat experiments. Asbestos exposure in individual humans is determined by matching published long-term lung data for nine patients. The resulting model predicts transport of fibers within the lymphatic system and prevalence of fibers in lymph nodes for these patients with reasonable accuracy. Model predictions for remote organs are compared against published observations. The model consists of a system of globally stable differential equations, and a sensitivity analysis was conducted. The model indicates that fiber density in lymph nodes is correlated with total exposure, level times duration, no matter whether there is a long-term, low-level exposure or short-term, high-level exposure. The model predicts that levels of sequestered asbestos reach steady state within five years of cessation of exposure, a timeline previously not known. The model suggests that the time to steady state is short compared to onset of disease, and that delayed onset of related disease may be a function of chemical and biological processes not in this model.

Exposure to asbestos and the risk of colorectal cancer mortality: a systematic review and meta-analysis

Asbestos exposure is associated with mesothelioma and cancer of the lung, larynx and ovary. However, the association between asbestos exposure and colorectal cancer is controversial despite several systematic reviews of the literature, including a number of meta-analyses. We performed a systematic review and meta-analysis to evaluate quantitatively the association between exposure to asbestos and colorectal cancer. We searched for articles on occupational asbestos exposure and colorectal cancer in PubMed, EMBASE and Web of Science published before April 2018. In total, 44 articles were selected and 46 cohort studies were analysed. The overall pooled risk estimates and corresponding 95% CIs of the association between occupational asbestos exposure and colorectal cancer were calculated using a random-effects model. Subgroup analyses and sensitivity tests were also performed. There was a significantly increased risk of colorectal cancer mortality among workers exposed to asbestos occupationally, with an overall pooled SMR of 1.16 (95% CI: 1.05 to 1.29). The pooled SMR for colorectal cancer was elevated in studies in which the asbestos-associated risk of lung cancer was also elevated (1.43; 95% CI: 1.30 to 1.56). This implies that the risk of colorectal cancer mortality increases as the level of asbestos exposure rises. A sensitivity analysis showed robust results and there was no publication bias. Although the effect size was small and the heterogeneity among studies was large, our findings indicate that occupational exposure to asbestos is a risk factor for colorectal cancer.

Morphological and chemical mechanisms of elongated mineral particle toxicities

Much of our understanding regarding the mechanisms for induction of disease following inhalation of respirable elongated mineral particles (REMP) is based on studies involving the biological effects of asbestos fibers. The factors governing the disease potential of an exposure include duration and frequency of exposures; tissue-specific dose over time; impacts on dose persistence from in vivo REMP dissolution, comminution, and clearance; individual susceptibility; and the mineral type and surface characteristics. The mechanisms associated with asbestos particle toxicity involve two facets for each particle's contribution: (1) the physical features of the inhaled REMP, which include width, length, aspect ratio, and effective surface area available for cell contact; and (2) the surface chemical composition and reactivity of the individual fiber/elongated particle. Studies in cell-free systems and with cultured cells suggest an important way in which REMP from asbestos damage cellular molecules or influence cellular processes. This may involve an unfortunate combination of the ability of REMP to chemically generate potentially damaging reactive oxygen species, through surface iron, and the interaction of the unique surfaces with cell membranes to trigger membrane receptor activation. Together these events appear to lead to a cascade of cellular events, including the production of damaging reactive nitrogen species, which may contribute to the disease process. Thus, there is a need to be more cognizant of the potential impact that the total surface area of REMP contributes to the generation of events resulting in pathological changes in biological systems. The information presented has applicability to inhaled dusts, in general, and specifically to respirable elongated mineral particles.

Novel Iodinated Diterpenes from a Marine Cyanobacterium and Red Alga Assemblage

[structure: see text]. Tasihalides A and B have been isolated from an assemblage of a marine cyanobacterium, belonging to the genus Symploca, and an unidentified red alga. The gross structures and relative stereochemistries of these diterpenes were elucidated by spectroscopic means. In addition to possessing a novel cage structure, the tasihalides represent the only examples of iodinated diterpenes in nature.

Probing the binding of indolactam-V to protein kinase C through site-directed mutagenesis and computational docking simulations

Protein kinase C (PKC) comprises a family of ubiquitous enzymes transducing signals by the lipophilic second messenger sn-1, 2-diacylglycerol (DAG). Teleocidin and its structurally simpler congener indolactam-V (ILV) bind to PKC with high affinity. In this paper, we report our computational docking studies on ILV binding to PKC using an automatic docking computer program, MCDOCK. In addition, we used site-directed mutagenesis to assess the quantitative contribution of crucial residues around the binding site of PKC to the binding affinity of ILV to PKC. On the basis of the docking studies, ILV binds to PKC in its cis-twist conformation and forms a number of optimal hydrogen bond interactions. In addition, the hydrophobic groups in ILV form "specific" hydrophobic interactions with side chains of a number of conserved hydrophobic residues in PKC. The predicted binding mode for ILV is entirely consistent with known structure-activity relationships and with our mutational analysis. Our mutational analysis establishes the quantitative contributions of a number of conserved residues to the binding of PKC to ILV. Taken together, our computational docking simulations and analysis by site-directed mutagenesis provide a clear understanding of the interaction between ILV and PKC and the structural basis for design of novel, high-affinity, and isozyme-selective PKC ligands.

Mesothelioma: cases associated with non-occupational and low dose exposures

OBJECTIVES

To estimate the importance of low dose exposure to asbestos on the risk of mesothelioma.

METHODS

A review of the literature.

RESULTS AND CONCLUSIONS

There is no evidence of a threshold level below which there is no risk of mesothelioma. Low level exposure more often than not contains peak concentrations which can be very high for short periods. There might exist a background level of mesothelioma occurring in the absence of exposure ot asbestos, but there is no proof of this and this "natural level" is probably much lower than the 1-2/million/year which has been often cited.

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.

Asbestos and kidney cancer: the evidence supports a causal association

The role of asbestos in the etiology of lung cancer and of mesothelioma of the pleura and peritoneum has been well documented. The evidence for a causal association between asbestos and other human cancers is not as extensive but suggests that asbestos may be carcinogenic at several different sites. This paper is concerned specifically with a possible causal association between asbestos and human kidney cancer. A review of the evidence to date indicates that only three human studies have sufficient statistical power to detect an excess mortality from kidney cancer among workers exposed to asbestos. All three were occupational cohort studies, and two of these gave strong direct evidence for such an excess; a study of U.S. insulators (kidney cancer SMR = 2.22, 90% CI 1.44-3.30), and a study of U.S. asbestos products company workers (kidney cancer SMR = 2.76, 90% CI 1.29-5.18). The third study, of Italian shipyard workers, reported excess mortality from "cancers of the kidney, urinary bladder, and other urinary organs" (SMR = 1.98, 90% CI 1.42-2.70). Further support for a causal association includes studies finding asbestos fibers in human kidneys and urine, as well as reports of kidney tumors in two animal bioassays. It is concluded that asbestos should be regarded as a probable cause of human kidney cancer.

Asbestos: toxicology and risk assessment for the general population in The Netherlands

Within the scope of the preparation of Integrated Criteria Documents for priority compounds in The Netherlands, the possible health effects of oral and inhalatory exposure to asbestos for the general population were evaluated. It was concluded from the results of experiments in animals that exposure to asbestos by the oral route is not carcinogenic and is not expected to present a health risk to the general population. Inhaled asbestos, however, is distinctly carcinogenic to man, giving rise to lung tumours, and mesotheliomas of the pleura and peritoneum. Chrysotile asbestos appears to be less potent in inducing mesotheliomas than the amphiboles, but all types of asbestos appear to have a similar potency for inducing lung cancer. The risk of mesothelioma is not expected to be influenced by smoking, whereas the risk of lung cancer is expected to be ten times higher in smokers than in non-smokers exposed to the same asbestos concentrations. Risk-assessment models for the inhalatory route, for the general population, are based on linear non-threshold extrapolation of occupational exposure to much lower environmental concentrations. These models give only a rough approximation of the risk of environmental exposure to asbestos. In accordance with the Air Quality Guidelines of the World Health Organization (World Health Organization, 1987), it was estimated that an extra risk of lung cancer of one in 10(6) (in the general population, with 30% smokers) may be presented by lifetime exposure to asbestos fibres longer than 5 microns, measured by electron microscopy, at concentrations of 100-1000/m3. It was further estimated that an extra risk of mesothelioma of one in 10(6) may be presented by lifetime exposure to 10-100 amphibole fibres/m3 or to a range of 100-10000 chrysotile fibres/m3 (fibres longer than 5 microns). From the current asbestos concentrations, the risk of mesothelioma for the general population in The Netherlands appears to be negligible; the extra risk of lung cancer is expected to be higher than 1 in 10(6) near asbestos sources, whereas it appears to be negligible in background areas and in most large cities and industrial areas. However, it must be borne in mind that the validity of the risk figures given is difficult to judge.

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.

Acute myelocytic leukemia after exposure to asbestos

While the carcinogenicity of asbestos has been established in malignant mesotheliomas and lung cancers, and has recently been suspected in several other types of cancer, asbestos has not been implicated in the pathogenesis of acute leukemias. This article includes two cases of acute myelocytic leukemia in individuals with a long history of exposure to asbestos. Significant numbers of asbestos bodies were detected in specimens of their lungs and bone marrow. In addition, the kind of asbestos in both organs was crocidolite, which is implicated in carcinogenesis. No asbestos bodies were detected in the bone marrow specimens from a control group consisting of ten patients with lung cancer with similar occupational histories. The role of asbestos exposure in the development of leukemia requires further study.

Migration of ingested asbestos

Tissue samples from one test and one control baboon were analyzed by transmission electron microscopy for the presence of chrysotile and crocidolite asbestos. The test animal had been gavaged with cumulative doses of 800 mg each of chrysotile and crocidolite asbestos. An earlier evaluation of these tissues led to the conclusion that ingested asbestos fibers do not penetrate the gastrointestinal tract of the baboon and migrate systemically. However, the present study involved more sensitive methodology, and penetration and migration were clearly demonstrated by the recovery of significant levels of asbestos from test stomach, heart, spleen, pancreas, and blood samples.

The use of asbestos-cement pipe for public water supply and the incidence of cancer in selected communities in Utah

We tested the hypothesis that there is an association between the use of asbestos-cement piping for drinking water supplies and the incidence of gastrointestinal and kidney cancer. Cancer incidence in 14 Utah communities that had used predominantly asbestos-cement piping for transporting their drinking water supplies for 20 years or more were compared to 27 Utah communities that had never used asbestos-cement piping. Cancer incidence was tabulated for 11 cancer sites for the years 1967-1976. Increased Standard Incidence Ratios (SIRs) were found for cancer of the kidney in men (SIR 192) and leukemia (a control site) in women (SIR 203). No increased SIRs were found for the opposite sex at these sites or for the other gastrointestinal sites singly or in combination. There was no increase in age-adjusted cancer incidence for the 11 sites in 4 of the 14 study communities that had used asbestos-cement piping for 30 years or more. Limitations of the study were that the water supplies were nonaggressive, and leaching from the pipes was minimal if at all. Furthermore, the latent period for observation was very short, suggesting that these results should be considered preliminary.

Chronic effects of dietary exposure to amosite asbestos and tremolite in F344 rats

Carcinogenesis bioassays of blocky (nonfibrous) tremolite and amosite asbestos alone or in combination with the intestinal carcinogen 1,2-dimethylhydrazine dihydrochloride (DMH) were conducted with male and female Fischer 344 rats. The minerals were administered at a concentration of 1% in pelleted diet for the entire lifetime of the rats starting with the dams of the test animals. One group of amosite rats also received chrysotile asbestos via gavage during lactation. Group sizes varied from 100 to 250 animals. The offspring from mothers exposed to tremolite or amosite asbestos were smaller at weaning than those from untreated mothers and remained smaller throughout their life. The administration of dimethylhydrazine (DMH) did not affect body weight gain, either in amosite-exposed or nonexposed animals. Survival was comparable in the tremolite and control groups. The amosite-exposed rats showed enhanced survival compared to the untreated controls. DMH exposure reduced survival by approximately one year, although the amosite plus DMH groups survived slightly better than the DMH alone groups. No toxicity or increase in neoplasia was observed in the tremolite-exposed rats compared to the controls. Significant increases (p less than 0.05) in the rates of C-cell carcinomas of the thyroid and monocytic (mononuclear cell) leukemia in male rats were observed in amosite-exposed groups. However, the biological significance of the C-cell carcinomas in relation to amosite asbestos exposure is discounted because of a lack of significance when C-cell adenomas and carcinomas were combined and the positive effect was not observed in the amosite plus preweaning gavage group. The biological significance of an increased incidence of mononuclear cell leukemia is questionable, because of a lack of statistical significance in the amosite group when evaluated using life table analysis, lack of significance when compared to the tremolite control group, and the fact that no toxic or neoplastic lesions were observed in the target organs, i.e., gastrointestinal tract and mesothelium. DMH caused a high rate of (62-74%) of intestinal neoplasia in amosite and nonamosite-exposed groups. Neither an enhanced carcinogenic nor protective effect was demonstrated by exposure to amosite asbestos.

Local immune response to repeated topical antigen application in the simian labial mucosa

Minor salivary glands of the oral mucosa in healthy monkeys (Macaca fascicularis and Macaca mulatta) contain organized structural units suitable for recognizing and processing antigens. A previous study of M. fascicularis monkeys provided experimental evidence of retrograde access of oral antigens deep into the minor salivary glands. The present study aimed at exploring the possible immune response of simian oral mucosa to repeated topical application of a chemically defined antigenic solution at the labial and gut mucosa. Ten female M. fascicularis animals were challenged topically at the lower lip mucosa at weekly intervals for a variable period of 4 to 8 weeks with a solution consisting of horseradish peroxidase, ferritin, and special India ink. Transmission electron microscopic examination of immunohistochemically treated sections of the labial glands revealed the presence of plasma cells containing specific anti-horseradish peroxidase antibody. These cells resided in the interacinar regions. Enteric and gut priming with the same antigen in four other monkeys, bypassing the oral mucosa, failed to reveal the presence of horseradish peroxidase-positive plasma cells in the labial mucosa of any of the four animals, although in one animal such cells could be identified in a mesenteric lymph node. This is suggestive of the existence, at least in primates, of a local immune response of the oral mucosa independent of systemic involvement.

An investigation of the penetration of ingested asbestos into the normal and abnormal intestinal mucosa of the rat

To characterize the tissue response associated with the presence of asbestos fibres in the gastro-intestinal wall, duodenal tissues of Wistar rats were examined by light microscopy following injection of a suspension containing amosite fibres into the wall of the duodenum. Intestinal tissues were also examined by light microscopy following oral administration of amosite for 5 days to healthy animals and for up to 7 days to animals with induced gastro-intestinal ulcers. Injection of amosite into the wall of the gastro-intestinal tract resulted in granulomatous lesions characterized by large numbers of macrophages containing crystals with the polarizing characteristics of amosite fibres. Examination by polarizing light microscopy following ingestion of asbestos revealed no such lesions or other histopathological abnormalities in the gut wall of the healthy animals and no intracellular fibres were observed in the animals with ulcers. Light microscopy, therefore, yielded no pathological evidence of widespread transmigration of asbestos from the gastro-intestinal tract of rats, even under conditions of mucosal loss. Further studies involving analysis by electron microscopy are under way.

Biological effects of ingested amosite asbestos, taconite tailings, diatomaceous earth and Lake Superior water in rats

Because amphibole fibers were found in Lake Superior and in Duluth municipal water, this study was initiated to evaluate the carcinogenicity of ingested asbestos. Groups of 22-30 Sprague-Dawley rats were fed asbestos and related materials during their lifetime and were examined at autopsy after spontaneous death. Test materials were unfiltered Duluth city tap water, municipal water reservoir sediment suspension, taconite plant tailings, amosite asbestos (a "low-dose" group at 20 mg/rat . day an a high-dose group at 300 mg/rat . day) and diatomaceous earth; a control group drank fiber-free well water or filtered city tap water. Autopsy studies revealed no significant increase in the incidence of malignant tumors in any experimental group compared with that in the control group.

Ultrastructural and Energy dispersive analysis of inorganic inclusions in a muscle biopsy

A muscle biopsy that, by light microscopy, exhibited mild atrophy consistent with chronic denervating disease was submitted for ultrastructural analysis. Inorganic structures within the tissue were defined by energy dispersive analysis as aluminosilicates, magnesium silicates, and iron deposits. These structures were localized in the interstitial (intercollagenous) area and in high concentrations within degenerated muscle bundles. An alteration of the blood/muscle barrier has obviously occurred; however, the extent to which the end result commonly occurs in humans is unknown. Clarification of the question raised by this observation will have to be derived from animal studies, and clinicians must have an awareness of the need for electron microscopy/energy-dispersive x-ray analysis in muscle biopsies from patients with similar therapeutic backgrounds.

The need to control asbestos fibers in potable water supply systems

Occupational studies have shown that asbestos is a human carcinogen. Because many inhaled asbestos fibers deposited in the lung are cleared and swallowed, workers are also exposed through ingestion. Of the millions of current and former workers who have been heavily exposed to asbestos, one in ten will die from cancer of the gastrointestinal tract. A number on the order of 1 in 1,000 ingested asbestos fibers penetrate the digestive tract and ingested fibers have been recovered in such tissues as kidney, intestine, liver, and urine. One animal study showed tumor production related to ingestion of asbestos-containing material but, in general, the results of seven animal feeding studies have been inconclusive. A statistically significant relationship between male lung and stomach cancer and female peritoneal, gall bladder, and esophageal cancer and asbestos counts in drinking water was determined in one epidemiology study. Increased rates for male stomach and lung, and female pancreatic cancer related to asbestos in drinking water were reported in another study but possible occupational exposure made it difficult to draw conclusions. Data on excess gastrointestinal cancer among occupational groups has been used to estimate that drinking water containing 300,000 asbestos fibers per liter over a lifetime will result in one additional cancer among 100,000 people.

Asbestos fibers in normal and cancerous human kidneys

Exposure of general population of ubiquitously present asbestos has led investigators to monitor its health effects. This pilot study was undertaken to see if there was an association between kidney cancer and fiber concentration in the kidney. Results of transmission electron microscopic (TEM) analysis for asbestos fibers in normal and cancerous human kidney tissues collected from three Chicago hospitals are presented. Chrysotile fibers were recovered from autopsy or surgery tissues of normal and cancerous kidneys. The study did not indicate a definite association between carcinoma and fiber load of kidney of humans exposed to nonoccupational asbestos.

Intestinal barrier to large particulates in mice

Intestinal barrier function in mice was assessed after acute or chronic oral administration of 15.8- and 5.7-micron synthetic spherical particles. The results failed to confirm previous reports that ingested particles rapidly appear in blood. Furthermore, 15.8-micron particles did not accumulate in intestinal Peyer's patches, mesenteric lymph nodes, or other organs of the reticuloendothelial system, even after the maximum dosage of 8 X 10(6) particles per day for 60 d. However, the 5.7-micron particles were demonstrated in Peyer's patches, mesenteric lymph nodes, and lungs after the maximum dosage of 4.5 X 10(8) particles per day for 60 d. At 77 d after the termination of ingestion, 5.7-micron particles were still present in these tissues. The 5.7-micron particles were not found in spleen; retention in liver was equivocal. The site of uptake of particles capable of penetrating the intestinal mucosa appears to be the Peyer's patches. It is suggested that most absorbed particles are sequestered in Peyer's patch macrophages. Particles that escape sequestration are transported by lymph rather than by portal blood. The findings indicate that hazards associated with intestinal uptake of large (> 5 micron) particulates exist, but that the frequency of such penetration is still unclear.