Daños para la salud tras exposición laboral a nanopartículas / Adverse health effects due to occupational exposure to nanoparticles

Introducción: La exposición a nanopartículas ha aumentado en los últimos años de forma significativa debido a su utilización en muchos sectores industriales y en el ámbito doméstico. Se prevé que el empleo en la industria de la nanotecnología aumente hasta alcanzar los 10 millones de puestos de trabajo en el mundo. A pesar del número creciente de industrias y trabajadores dentro del sector, todavía no existen muchos estudios que aborden aspectos toxicológícos, la vigilancia de la salud y la higiene industrial en el sector de la nanotecnología. Objetivo: Revisar la literatura científica reciente buscando evidencias sobre posibles efectos tóxicos y daños sobre la salud tras exposición laboral a nanopartículas. Metodología: Se realizaron búsquedas bibliográficas en las siguientes bases de datos bibliográficas: MEDLINE (PUBMED), OSH UPDATE, IBECS, LILACS, SCIELO y CISDOC. Se revisó la literatura científica en busca de posibles efectos en la salud de la exposición a las nanopartículas. Resultados: Se incluyeron en el estudio un total de 11 artículos científicos que cumplian los requisitos y analizaban los efectos de la toxicidad tras exposición a nanopartículas en poblaciones humanas, 4 sobre toxicidad respiratoria, 2 dermatológica, 3 de ambas exposiciones en la misma muestra y 2 estudios emulando en laboratorio exposiciones a partículas ultrafinas en ambiente laboral. Conclusiones: Aunque no existe mucha literatura científica que estudie este tipo de relación y se hace necesario promover más estudios que profundicen sobre la materia, los trabajos existentes apuntan a que puede existir alguna relación entre la exposición a nanopartículas y problemas de toxicidad respiratoria y/o dermatológica (AU)

Introduction: Exposure to nanoparticles has increased in recent years significantly due to its use in many industries and in the home. It is expected that employment in the nanotechnology industry will increase to 10 million jobs in the world. Despite the growing number of nanoparticles-related industries and workers, there are very few published studies that address toxicity, health surveillance and industrial hygiene in the field of nanotechnology. Objective: To review recent scientific literature for evidence on possible toxic effects and health damage after occupational exposure to nanoparticles. Methods: We searched the literature for the following bibliographic databases: MEDLINE (PubMed), OSH UPDATE, IBECS, LILACS, SciELO and CISDOC. Scientific literature was reviewed for possible health effects of exposure to nanoparticles. Results: We found 11 scientific articles that met the requirements and analyzed the effects of toxicity following exposure to nanoparticles in human populations, 4 on respiratory toxicity, 2 on dermatologic toxicology, 3 on both (respiratory and dermatologic on the same sample), and 2 laboratory studies simulating exposure to ultrafine particles in the workplace. Conclusions: Despite the lack of literature on this topic and the need for more studies to go deeper into this subject, available studies suggests that there may be some relationship between exposure to nanoparticles and respiratory and/or dermatology toxicity (AU)

The clonal origins of dysplasia from intestinal metaplasia in the human stomach.

BACKGROUND & AIMS: Studies of the clonal architecture of gastric glands with intestinal metaplasia are important in our understanding of the progression from metaplasia to dysplasia. It is not clear if dysplasias are derived from intestinal metaplasia or how dysplasias expand. We investigated whether cells within a metaplastic gland share a common origin, whether glands clonally expand by fission, and determine if such metaplastic glands are genetically related to the associated dysplasia. We also examined the clonal architecture of entire dysplastic lesions and the genetic changes associated with progression within dysplasia. METHODS: Cytochrome c oxidase-deficient (CCO⁻) metaplastic glands were identified using a dual enzyme histochemical assay. Clonality was assessed by laser capture of multiple cells throughout CCO⁻ glands and polymerase chain reaction sequencing of the entire mitochondrial DNA (mtDNA) genome. Nuclear DNA abnormalities in individual glands were identified by laser capture microdissection polymerase chain reaction sequencing for mutation hot spots and microsatellite loss of heterozygosity analysis. RESULTS: Metaplastic glands were derived from the same clone-all lineages shared a common mtDNA mutation. Mutated glands were found in patches that had developed through gland fission. Metaplastic and dysplastic glands can be genetically related, indicating the clonal origin of dysplasia from metaplasia. Entire dysplastic fields contained a founder mutation from which multiple, distinct subclones developed. CONCLUSIONS: There is evidence for a distinct clonal evolution from metaplasia to dysplasia in the human stomach. By field cancerization, a single clone can expand to form an entire dysplastic lesion. Over time, this field appears to become genetically diverse, indicating that gastric cancer can arise from a subclone of the founder mutation.

A methodological approach to tracing cell lineage in human epithelial tissues.

Methods for lineage tracing of stem cell progeny in human tissues are currently not available. We describe a technique for detecting the expansion of a single cell's progeny that contain clonal mitochondrial DNA (mtDNA) mutations affecting the expression of mtDNA-encoded cytochrome c oxidase (COX). Because such mutations take up to 40 years to become phenotypically apparent, we believe these clonal patches originate in stem cells. Dual-color enzyme histochemistry was used to identify COX-deficient cells, and mutations were confirmed by microdissection of single cells with polymerase chain reaction sequencing of the entire mtDNA genome. These techniques have been applied to human intestine, liver, pancreas, and skin. Our results suggest that the stem cell niche is located at the base of colonic crypts and above the Paneth cell region in the small intestine, in accord with dynamic cell kinetic studies in animals. In the pancreas, exocrine tissue progenitors appeared to be located in or close to interlobular ducts, and, in the liver, we propose that stem cells are located in the periportal region. In the skin, the origin of a basal cell carcinoma appeared to be from the outer root sheath of the hair follicle. We propose that this is a general method for detecting clonal cell populations from which the location of the niche can be inferred, also affording the generation of cell fate maps, all in human tissues. In addition, the technique allows analysis of the origin of human tumors from specific tissue sites.

Analysis of the clonal architecture of the human small intestinal epithelium establishes a common stem cell for all lineages and reveals a mechanism for the fixation and spread of mutations.

Little is known about the clonal structure or stem cell architecture of the human small intestinal crypt/villus unit, or how mutations spread and become fixed. Using mitochondrial DNA (mtDNA) mutations as a marker of clonal expansion of stem cell progeny, we aimed to provide answers to these questions. Enzyme histochemistry (for cytochrome c oxidase and succinate dehydrogenase) was performed on frozen sections of normal human duodenum. Laser-capture microdissected cells were taken from crypts/villi. The entire mitochondrial genome was amplified using a nested PCR protocol; sequencing identified mutations and immunohistochemistry demonstrated specific cell lineages. Cytochrome c oxidase-deficient small bowel crypts were observed within all sections: negative crypts contained the same clonal mutation and all differentiated epithelial lineages were present, indicating a common stem cell origin. Mixed crypts were also detected, confirming the existence of multiple stem cells. We observed crypts where Paneth cells were positive but the rest of the crypt was deficient. We have demonstrated patches of deficient crypts that shared a common mutation, suggesting that they have divided by fission. We have shown that all cells within a small intestinal crypt are derived from one common stem cell. Partially-mutated crypts revealed some novel features of Paneth cell biology, suggesting that either they are long-lived or a committed Paneth cell-specific long-lived progenitor was present. We have demonstrated that mutations are fixed in the small bowel by fission and this has important implications for adenoma development.

Mechanisms of field cancerization in the human stomach: the expansion and spread of mutated gastric stem cells.

BACKGROUND & AIMS: How mutations are established and spread through the human stomach is unclear because the clonal structure of gastric mucosal units is unknown. Here we investigate, using mitochondrial DNA (mtDNA) mutations as a marker of clonal expansion, the clonality of the gastric unit and show how mutations expand in normal mucosa and gastric mucosa showing intestinal metaplasia. This has important implications in gastric carcinogenesis. METHODS: Mutated units were identified by a histochemical method to detect activity of cytochrome c oxidase. Negative units were laser-capture microdissected, and mutations were identified by polymerase chain reaction sequencing. Differentiated epithelial cells were identified by immunohistochemistry for lineage markers. RESULTS: We show that mtDNA mutations establish themselves in stem cells within normal human gastric body units, and are passed on to all their differentiated progeny, thereby providing evidence for clonal conversion to a new stem cell-derived unit-monoclonal conversion, encompassing all gastric epithelial lineages. The presence of partially mutated units indicates that more than one stem cell is present in each unit. Mutated units can divide by fission to form patches, with each unit sharing an indentical, mutant mtDNA genotype. Furthermore, we show that intestinal metaplastic crypts are clonal, possess multiple stem cells, and that fission is a mechanism by which intestinal metaplasia spreads. CONCLUSIONS: These data show that human gastric body units are clonal, contain multiple multipotential stem cells, and provide definitive evidence for how mutations spread within the human stomach, and show how field cancerization develops.

Surgery and hematogenous dissemination: comparison between the detection of circulating tumor cells and of tumor DNA in plasma before and after tumor resection in rats.

BACKGROUND: To examine the effects of the surgical manipulation of tumors on the hematogenous dissemination of tumors, we compared rates of detection of tumor-derived DNA in the buffy coat and in plasma from tumor-bearing rats before and after tumor resection. METHODS: We injected DHD/K12-PROb cells subcutaneously into BD-IX rats. Three weeks later, we removed the tumors surgically. Group PERI was sacrificed 3 hours after surgery, group POST-2 was sacrificed 2 weeks later, group POST-4 was sacrificed another 2 weeks later, and group POST-LONG was sacrificed when rats were close to death. In group PERI, four perioperative blood samples were taken. In the other groups, only one blood sample was taken per rat, immediately before euthanasia. We used polymerase chain reaction to detect tumor-derived DNA in buffy-coat, plasma, and lung samples. RESULTS: In group PERI, tumor DNA in plasma was more frequent than circulating tumor cells at all perioperative time points. The difference was statistically significant 3 hours after surgery (P = .035). In group POST-2, there was no detectable metastasis or tumor DNA in blood samples. There were lymphatic and lung metastases in most animals in group POST-4 and in all animals in group POST-LONG. In the last two groups, the frequencies of tumor DNA in the buffy coat and in plasma were similar. CONCLUSIONS: In our animal model, the hematogenous dissemination of tumors due to surgery seemed to be more closely related to tumor-derived cell-free DNA than to circulating tumor cells. In addition, the surgical resection of primary tumors did not inhibit the development of metastases.

Detection of circulating tumor cells and of tumor DNA in plasma during tumor progression in rats.

The role and clinical significance of circulating tumor cells and of tumor DNA in the plasma have not yet been clarified. In the present study, we compared rates of detection of tumor-derived DNA in the buffy coat to those in plasma from tumor-bearing rats, and we attempted to correlate these rates with the progression of tumors. We injected DHD/K12-PROb cancer cells subcutaneously into BD-IX rats and divided the animals into six groups according to the time between the injection of tumor cells and euthanasia. After euthanasia, macroscopic metastases were assessed and samples of blood and lung were collected. We used mutant allele-specific amplification by PCR to detect tumor-derived DNA. We detected tumor DNA in lung samples from the first week after inoculation, in plasma from the third week and in the buffy coat from the fifth week. All animals analyzed on the 11th week had macro- or micrometastases in their lungs. Regardless of group, the rate of PCR-positive plasma samples was significantly higher than that of circulating tumor cells (P=0.005). In animals with metastases, this difference was also statistically significant (P=0.008). However, neither the detection of tumor DNA in the plasma nor the presence of circulating tumor cells was strongly correlated with the presence of metastases. Thus, cell-free tumor DNA was detected sooner and more frequently than circulating tumor cells and the dissemination of tumor DNA in the plasma seems to be much more common than detectable hematogenic tumor cells during the spread of colorectal cancer.