Fiberglass & DNA Damage

Fiberglass Mutilates DNA

Accelerated cell growth likely precursor to cancer

By Robert Horowitz
Three different kinds of glass fibers were poisonous to cells and damaged DNA in studies performed by a team of doctors at NIOSH, the medical research arm of the U.S. Department of Labor. Damaged DNA can unleash a process of accelerated and even unrestrained cell growth, and the new research shows cells with fiberglass-damaged DNA exhibited these tendencies. Although the exact mechanism by which cancers and tumors grow is not yet deciphered, damaged DNA and abnormal cellular reproduction is widely thought to be the first step.

Additional research on glass fiber geno- and cytotoxicity is currently on hold because of a lack of money at NIOSH (National Institute for Occupational Safety and Health) and the Department of Labor. A final decision on whether to continue glassfiber experiments-and when-is pending. The newly-elected Republican Congress headed by Newt Gingrich, however, is threatening to completely eliminate NIOSH.

NIOSH researchers set out to answer three questions about glass fibers: whether they can introduce a transformation in the structure and form of cells, whether the induction of "morphological" changes could be related to fiber size, and whether cells thus transformed would exhibit accelerated, tumor-like (neoplastic), growth.

"These results indicate that glass fibers are capable of transforming mammalian (BALB/c-3T3) cells in vitro as a function of their physical properties and that glass-fiber-induced transformed cells possess neoplastic characteristics."

The experiment used three types of glass fibers, one microfiber from Manville, plus a microfiber and a general building insulation fiber manufactured by Owens Corning. The fibers were precision milled to lengths and widths known to cause cancer.

Prior research with cells from the lung of a Chinese hamster demonstrated the respirable portion of Manville glass fibers caused breakage and fragmentation of chromosomes. NIOSH researchers used a technique called micronucleus assay to further explore this phenomenon. "The micronucleus assay is one of the most frequently used short-term assay systems for the detection of genotoxic agents and potential carcinogens," they say.

Micronuclei are fragments of cell nucleus; oftentimes these fragments either do not have the correct number of chromosomes, or the chromosomes are damaged in some way. This does not always prevent the cell from duplicating itself, however, and passing along its incorrect genetic information.

Both Manville and Owens Corning microfibers (average diameters .2 and .18 micron respectively) caused micronucleated and multinucleated cells, with those cells given higher fiber doses exhibiting rates of chromosomal damage as much as five times higher than positive controls-cells treated with a substance known to damage DNA. As the dosage of fibers increased, the total number and percentage of cells with damaged DNA increased commensurably. This is the sought-after dose-response relationship which researchers deem critical. The larger fibers (average diameter 7.3 microns) did not appear to damage chromosomes in the first study.

Researchers stated the mutated genetic information is due to damage to the "spindle," a colorless, narrow structure in the cell nucleus, along which the chromosomes line up to divide during cell duplication.

In a second experiment using a different type of cell, NIOSH researchers confirmed glass fibers cause cell transformation, with the number and percentage of transformed cells clearly related to the amount of fibers administered and their size. Small, very thin fibers, as expected, were the most damaging. In this study, all three fibers exhibited cytotoxic tendencies; that is, they were poisonous to cells. The survival rate of the cells was inversely related to the higher dosage of fiberglass. The rate of cell transformation was also related to dosage, with the large fibers showing a rate of transformation not as high as the microfibers, but significantly higher than control groups.

The researchers then tested the transformed cells to see whether they multiplied, or formed colonies, in agar, a gel-like algae extract. Compared to cells which did not have altered chromosomes, the fiberglass-transformed cells exhibited a greatly enhanced growth ability in the agar. This was measured in two ways, one called "anchorage independent growth" and the other called "transfection-mediated transformation." Both types of growth were indicated at levels deemed to be significant through the use of the Poisson regression equation, a common technique for determining whether a particular statistic could occur by pure chance.

"The study showed that DNA from all glass-fiber-transformed cells significantly increased morphological transformation (p < 0.01), indicating that the transformed cells carried transforming genes," according to the study. "Since both anchorage-independent growth and transfection-mediated transformation were found in the glass-fiber-transformed cells, these findings suggest that transformed cells induced by glass fibers may possess neoplastic properties."

Next, the researchers used blot analysis and other techniques to determine whether glass fibers could be activating oncogenes, portions of DNA which seem to encourage prolific cell growth and tumor formation. To counteract oncogenes, DNA also contains genes which suppress cell replication and tumor growth. The researchers believe that oncogene activation resulted from glass fiber intrusion into cells. They also noted that the DNA transformation resulting from fiberglass damage was "morphologically indistinguishable" from DNA mutated by a human bladder carcinoma.

To summarize their work, the researchers offered the following discussion:

"Results from these studies clearly demonstrate that glass fibers induced transformation in a concentration-dependent manner. However, there are differences in transforming activity among the three different glass fibers studied, in which the sample of the shortest microfibers showed the highest transforming potency, whereas the sample of the thick and longest length showed the lowest activity. This seems to indicate that the glass fiber induced transformation may be related to fiber size. These observations are comparable to previous findings using other transformation systems, which showed that both thin and thick glass fibers induced cell transformation in culture Syrian hamster embryo cells, and that the cell transforming activity was higher with thin than with thick glass fibers..."

"All transformed foci induced by three different glass fibers showed typical characteristics of morphological transformation, such as random cellular orientation, cell piling up and high saturation density. The transfection study revealed that DNAs from glass fiber-transformed cells induced transfection-mediated transformation in host NIH-3T3 cells, suggesting that the cells transformed by glass fibers contain transforming genes. Furthermore, soft-agar cloning analysis provided evidence that glass fiber-induced transformed cells possessed another transformed property, anchorage independent growth. It has been reported that the ability to grow in soft agar is correlated well with tumorogenicity in vivo. Our study, therefore, indicated that transformed cells induced by glass fibers contain many of the characteristics of neoplastic transformation.

"Carcinogenesis has been proposed to be a multi-step process, and it may involve the activation of oncogenes and/or the inactivation of tumor-suppresser genes. The actual mechanism of cell transformation induced by glass fibers is unknown. With the Syrian hamster embryo cell system, Oshimura et al. showed that glass fibers were positive in inducting both morphological transformation and chromosomal changes. Recent studies by Liu et al. showed that glass fibers are capable of inducing micronuclei in V79 cells.

"Using kinetochore analysis, this group further demonstrated that glass-fiber-induced micronuclei resulted from spindle fiber damages. Based on these findings, it can be postulated that cell transformation induced by glass fibers may be related to chromosomal abnormalities. It has also been reported that transfection-mediated transformation often results from the transference of activated proto-oncogenes present in donor DNAs to their respect host cells. Since positive results were found for gene transfection with DNAs from glass-fiber-transformed cells, transforming genes derived from the alteration of proto-oncogenes and/or tumor suppresser genes may also contribute to cell transformation induced by glass fibers. To provide insight into the mechanisms of potential glass fiber carcinogenesis, molecular analyses of these genes in glass-fiber-induced transformed cells are now in progress."

But, in fact, such research is not in progress. Dr. Wen-Zong Whong, spokesman for the group of researchers, told VOF he is now working on studies to define the carcinogenic potential of silica. The directive to switch topics came from NIOSH supervisors; Whong hopes to continue his work on fiberglass. The studies which have been completed, he noted, will be published sometime in 1995.

"Clearly, fiberglass remains an important area" for research, said Dr. Greg Wagner, Director of the NIOSH Division of Respiratory Disease Studies. But the "priority of funding reflects the paucity of funding," he told VOF. The decision whether to fund additional research on fiberglass has not yet been made, Wagner said, and public interest in fiberglass research could influence the decision. VOF's testimony in at a Department of Labor priorities meeting in Washington D.C. in November, he recalled, was a step toward that end.

Dr. Whong and company's current research on silica could result in improved test systems to learn about cancer-causing mechanisms, noted Wagner, which would benefit future work on glass fiber carcinogenicity.

But there is some concern about whether NIOSH will be around at all in a few years, if the conservative majority in Congress follows through on its threat to place a moratorium on all new regulations and consolidate or eliminate agencies. including NIOSH.

"It's a pretty serious threat," said Wagner. "I don't know what is going to happen."

The studies cited in this report are all a product of: NIOSH, Division of Respiratory Disease Studies, NIOSH, Morgantown WV 25605 USA. They are:

  • Whong, WZ; Liu, YQ, et al: Induction of micronucleated and multinucleated cells by glass fibers in cultured mammalian cells.
  • Ong, T; Gao, HG, et al: Glass-fiber induced Cell Transformation and Oncogene Activation in BALB/c-3T3 Cells.
  • Gao, GH; Whong, et al: Morphological Transformation Induced by Glass Fibers in BALB/c-3T3 Cells.

 


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