Mutagenicity of diesel exhaust particles from an engine with differing exhaust after treatments

This study was conducted to investigate the effects of engine operating conditions and exhaust aftertreatments on the mutagenicity of diesel particulate matter (DPM) collected directly in an underground mine environment. A number of after-treatment devices are currently used on diesel engines in mines, but it is critical to determine whether reductions in DPM concentrations result in a corresponding decrease in adverse health effects. An eddy-current dynamometer was used to operate naturally aspirated mechanically controlled engine at several steady-state conditions. The samples were collected when the engine was equipped with a standard muffler, a diesel oxidation catalytic converter, two types of uncatalyzed diesel particulate filter systems, and three types of disposable diesel particulate filter elements. Bacterial gene mutation activity of DPM was tested on acetone extracts using the Ames Salmonella assay. The results indicated strong correlation between engine operating conditions and mutagenic activity of DPM. When the engine was fitted with muffler, the mutagenic activity was observed for the samples collected from light-load, but not heavy-load operating conditions. When the engine was equipped with a diesel oxidation catalyst, the samples did not exhibit mutagenic activity for any of four engine operating conditions. Mutagenic activity was observed for the samples collected when the engine was retrofitted with three types of disposable filters and sintered metal diesel particulate filter and operated at light load conditions. However, those filtration systems substantially reduced the concentration-normalized mutagenic activity from the levels observed for the muffler.

Higher pulmonary dead space may predict prolonged mechanical ventilation after cardiac surgery

Children undergoing congenital heart surgery are at risk for prolonged mechanical ventilation and length of hospital stay. We investigated the prognostic value of pulmonary dead space fraction as a non-invasive, physiologic marker in this population. In a prospective, cross-sectional study, we measured pulmonary dead space fraction in 52 intubated, pediatric patients within 24 hr postoperative from congenital heart surgery. Measurements were obtained with a bedside, non-invasive cardiac output (NICO) monitor (Respironics Novametrix, Inc., Wallingford, CT). Median pulmonary dead space fraction was 0.46 (25-75% IQR 0.34-0.55). Pulmonary dead space fraction significantly correlated with duration of mechanical ventilation and length of hospital stay in the entire cohort (r(s) = 0.51, P = 0.0002; r(s) = 0.51, P = 0.0002) and in the subset of patients without residual intracardiac shunting (r(s) = 0.45, P = 0.008; r(s) = 0.49, P = 0.004). In a multivariable logistic regression model, pulmonary dead space fraction remained an independent predictor for prolonged mechanical ventilation in the presence of cardiopulmonary bypass time and ratio of the partial pressure of arterial oxygen to the fraction of inspired oxygen (OR 2.2; 95% CI 1.14-4.38; P = 0.02). The area under the receiver operator characteristic curve for this model was 0.91. Elevated pulmonary dead space fraction is associated with prolonged mechanical ventilation and hospital stay in pediatric patients who undergo surgery for congenital heart disease and has additive predictive value in identifying those at risk for longer duration of mechanical ventilation. Pulmonary dead space may be a useful prognostic tool for clinicians in patients who undergo congenital heart surgery.

Pseudo tamponade soon after cardiac surgery: a report of three cases

OBJECTIVE

To describe a syndrome suggestive of tamponade but secondary to increased intra-thoracic pressure due to undetected dyssynchronous expiratory efforts in mechanically ventilated patients soon after cardiac surgery.

METHODS

A retrospective chart review of three patients immediately after cardiac surgery.

RESULTS

All patients developed the tetrad of decreased blood pressure, increased central venous pressure, decreased cardiac index and decreased urine output soon after cardiac surgery without other obvious reasons. In all patients, tamponade was suspected. In all cases, physical examination found no marked evidence of patient-ventilator dyssynchrony but evidence of abdominal muscle tensing and intermittent expiratory efforts not in synchrony with the ventilator cycle. In all patients, sedation and muscle relaxation led to a decrease in central venous pressure, improved blood pressure and improved cardiac index and urine output with full resolution of the syndrome. All patients were successfully extubated within 24 hours of surgery.

CONCLUSIONS

In some postoperative cardiac surgery patients expiratory efforts which are not in synchrony with mechanical ventilation and not immediately obvious to clinicians or intensive care unit nurses can simulate tamponade. Greater awareness of this syndrome may decrease the chance of diagnostic error.

Failure of continuous cardiac output measurement using the PiCCO Device during induced hypothermia: a case report

Continuous cardiac output measurement using pulse contour analysis is a technique gaining widespread acceptance in intensive care units. We report a case where a pulse contour analysis computer (PiCCO, Pulsion Medical Systems, Munich, Germany) failed to calibrate in a patient who was undergoing induced hypothermia for anoxic brain injury. Despite several attempts to calibrate, using increased cold injectate volumes and exchanging both the PiCCO device and the arterial catheter, we were unable to correct the calibration problem and hence were unable to monitor cardiac output. Subsequent rewarming of the patient allowed calibration of the arterial waveform and continuous cardiac output measurement. We were unable to find any previous reports of this problem using a PiCCO device, although similar problems with thermodilution cardiac output estimation using the pulmonary artery catheter during hypothermic cardiopulmonary bypass have been documented.

Microcystic Adnexal Carcinoma of the Eyebrow

PURPOSE

To describe a case of the largest reported microcystic adnexal carcinoma of the eyebrow in an 89-year-old woman and to review the literature regarding the periorbital occurrence of this tumor.

METHODS

Case report and literature review.

RESULTS

This case was treated with primary excision and radiotherapy, with no clinical signs of recurrence in the past 6 months.

CONCLUSIONS

Microcystic adnexal carcinoma is a rare tumor; however, because of its aggressive local infiltration, ophthalmologists should consider this diagnosis and complete surgical excision. Long-term data are needed to establish outcomes from the different treatment options.

Latanoprost in port wine stain related paediatric glaucoma

AIM

To evaluate the efficacy of latanoprost (Xalatan) as adjunctive therapy in port wine stain related paediatric glaucoma.

METHODS

A retrospective non-randomised study. Patients with previous surgical intervention and medical treatment were included. Measurements were recorded from clinic and/or examination under anaesthetic (EUA) visits. A successful outcome was considered to be patients who required no further intervention following initiation of latanoprost, with stable glaucoma factors as well as drop in intraocular pressure.

RESULTS

14 patients and 17 eyes were reviewed in total. The mean age of glaucoma diagnosis was 2.59 years (0.1-5.25 years) and of commencing latanoprost was 6.8 years (1.40-12.90 years). Percentage success at 1 month, 3 months, 6 months, and 1 year was 70.6%, 64.7%, 58.9%, and 47.1%, respectively, of eyes treated which translated to 71.4%, 64.2%, 57.1%, and 50% respectively of patients treated.

CONCLUSIONS

A trial of latanoprost as adjunctive therapy in patients with port wine stain related glaucoma may temporise the need for surgery; with 50% of patients being controlled at 1 year follow up. Lack of efficacy was detected as early as 1 month following commencement of treatment.

Deep venous thrombosis following uneventful phacoemulsification

We report a case of deep venous thrombosis following uneventful phacoemulsification and intraocular lens implantation. To our knowledge, this is the first report of such a case. It highlights the challenge of managing perioperative anticoagulation.

Proto-oncogene amplification and overexpression in cadmium-induced cell transformation

Cadmium (Cd) is an essential material used in the battery, metal-coating, and alloy industries. In addition to these industrial uses, it is also a component of cigarette smoke. Therefore, exposure to cadmium is widespread and presents a considerable health concern. Cadmium is known to be a carcinogen; however, the possible mechanism of carcinogenesis with regards to the activation and inactivation of cancer-related genes has not yet been fully elucidated. In this study, amplification, expression, and point mutation of cancer-related genes associated with Cd-induced cell transformation in BALB/c-3T3 cells were studied. Six proto-oncogenes (K-ras, c-myc, c-fos, c-jun, c-sis, and erbB), as well as the p53 tumor suppressor, were investigated for gene amplification using differential polymerase chain reaction (PCR), while the expression of the proteins produced by these genes was evaluated by Western blot analysis. Point mutations in K-ras and p53 were studied by PCR restriction fragment length polymorphism analysis and DNA sequencing. There were no point mutations observed in codons 12, 13, and 61 of K-ras or in exons 4-10 of p53 and no observed differences in the levels of any of the proteins studied. Among 10 Cd-induced transformed cell lines, significant gene amplification was found for c-myc and c-jun in 50% and 80% of the cell lines, respectively. Chromosome painting was performed to confirm that this amplification was not simply due to additional copies of the chromosomes carrying these oncogenes. In addition, reverse-transcription PCR (RT-PCR) was performed to confirm increased expression of c-myc and c-jun. These results suggest that cell transformation induced by Cd may be attributed, at least in part, to gene amplification of c-myc and c-jun and that some of the Cd-transformed cells may possess neoplastic potential resulting from genomic instability.

Effects of phospholipid surfactant on apoptosis induction by respirable quartz and kaolin in NR8383 rat pulmonary macrophages

Apoptosis was measured in rat alveolar macrophage NR8383 cells challenged in vitro with respirable quartz or kaolin dust and with the dusts pretreated with dipalmitoyl phosphatidylcholine (DPPC) to model conditioning of respired dusts by interaction with a primary phospholipid component of pulmonary surfactant. Quartz dust is known to induce apoptosis in vitro and in vivo. For this study, quartz and kaolin were compared as dusts of similar cytotoxicity in some in vitro assays but of differing pathogenic potential: quartz can cause significant pulmonary fibrosis while kaolin generally does not. NR8383 cells exposed to native quartz at concentrations from 50 to 400 microg/ml for 6 h showed a dose-dependent increase in apoptosis measured by the TdT-mediated dUTP-fluorescein nick end labeling (TUNEL), cell death ELISA, and DNA ladder formation assays, while native kaolin induced significant response only at the higher concentrations and only in the TUNEL and ELISA assays. For cell challenge from 6 h to 5 days at 100 microg/ml of dust, quartz was active at all times while kaolin was active only at 5 days. DPPC pre-treatment suppressed quartz activity until 3 days and kaolin activity through 5 days. Cellular release of lactate dehydrogenase, measured in parallel experiments to compare dust apoptotic and necrotic activities, indicated that components of serum as well as surfactant may affect kaolin in vitro expression of those activities.

Gene expression profile in BALB/c-3T3 cells transformed with beryllium sulfate

Differential gene expression was studied to understand the potential molecular mechanism responsible for cell transformation and tumorigenesis induced by beryllium. Cell lines were derived from tumors developed in nude mice injected subcutaneously with BALB/c-3T3 cells morphologically transformed with beryllium sulfate. Using the Atlas mouse 1.2 cDNA expression microarray, the expression profiles of 1176 genes, belonging to several different functional categories, were studied in the tumor cells as well as in the nontransformed control cells. Expression of 18 genes belonging to two functional groups was found to be consistently and reproducibly different (at least twofold) in the tumor cells compared with the control cells. The functional groups and the differentially expressed genes are as follows: The cancer-related genes (nine genes) were the ets-related transcription factor activated by ras, colony-stimulating factor, A-myb, sky, cot1, c-fos, c-jun, c-myc, and R-ras proto-oncogenes. The DNA synthesis, repair, and recombination genes (nine genes) were the DNA replication licensing factor MCM4, the DNA replication licensing factor MCM5, the DNA mismatch repair gene PMS2, the DNA excision repair gene, the DNA mismatch repair gene MSH2, the ultraviolet excision repair gene Rad23 DNA ligase 1, Rad51, and Rad52. The differential gene expression profile was confirmed with reverse transcription-polymerase chain reaction using primers specific for the differentially expressed genes. In general, expression of the cancer-related genes was upregulated, while expression of genes involved in DNA synthesis, repair, and recombination was downregulated in the tumor cells compared with the control cells. Using c-fos and c-jun, two of the differentially expressed genes, as model genes, we have found that in the nontransformed BALB/c-3T3 cells, the beryllium-induced transcriptional activation of these genes was dependent on pathways of protein kinase C and mitogen-activated protein kinase and independent of reactive oxygen species. These results indicate that beryllium-induced cell transformation and tumorigenesis are accompanied by and are possibly a product of alterations in expression of genes related to cancer and to DNA synthesis, repair, and recombination.

Development of a fungus-specific PCR assay for detecting low-level fungi in an indoor environment

A fungus-specific PCR assay using only one primer set has been developed for detecting indoor fungi. Four fungal primer sets, NS3/NS4, NS5/NS6, FF1/FR1 and FF2/FR1, were tested with DNA from humans, rats, mice, bacteria, pollens and six commonly found fungal species (Alternaria chamydospora, Aspergillus flavus, Candida famata, Cladosporium fermentans, Penicillium chrycoIgenum and Stachybotrys chartarum). Results indicated that, although all four primer sets could amplify the fungal DNA, only FF2/FR1 demonstrated no cross-amplification with non-fungal DNA. In addition, these amplified fragments were sequenced to ensure that they indeed matched known fungal DNA sequences. Furthermore, besides the tested fungi, eighteen more genera of fungal sequences were examined and found to match the FF2/FR1. Here, the method of bead-beating was identified as the most effective way for spore breakage and fungal DNA release. The PCR amplification efficiency and potential inhibition were examined using different process solutions and preparation procedures. It was found that, when using 20% nutrient media and homogenization-first procedure, a higher amplification efficiency with less inhibition was achieved. Although positive bands were observed at 0.2 fungal spore/reaction using the homogenization-first procedure, the sensitivity of this assay would be two fungal spores/reaction for environmental samples.

Analysis of K-ras and p53 mutations in mesotheliomas from humans and rats exposed to asbestos

Malignant mesothelioma is known to be associated with asbestos exposure. However, the mechanism of mesothelial carcinogenesis in relation to the activation of proto-oncogenes or inactivation of tumor suppressor genes remains unclear. In this study, the PCR-Primer Introduced Restriction Site (PCR-PIRS) assay was employed to examine mutations in the K-ras proto-oncogene in mesothelioma tissues from workers exposed to asbestos and from rats treated with asbestos. Mutations in exons 5-8 of the p53 tumor suppressor gene were determined by direct DNA sequence analysis. Results of the PCR-PIRS analysis revealed no mutations in codons 12, 13 or 61 of the K-ras gene in any of the 17 human or 22 rat mesothelioma tissue samples. These results were confirmed by direct DNA sequence analysis. No mutations were found in exons 5-8 of the p53 gene in any of the mesothelioma tissue samples analyzed. These results and the results reported by others indicate that the K-ras proto-oncogene and p53 tumor suppressor gene may not play a critical role in the induction of mesothelioma by asbestos either in humans or in rats.

Induction of DNA adducts in vivo in rat lung cells by fume condensates of roofing asphalt

Many workers in the highway construction and roofing industries are potentially exposed to asphalt fumes. However, little is known regarding the carcinogenic hazards of these fumes to the exposed workers. Previous studies have shown that condensates of asphalt fumes are weakly mutagenic to bacteria and are capable of inducing micronucleus formation in cultured mammalian cells. In this study, the induction of DNA adducts in vivo in lung and white blood cells (WBCs) of rats by fume condensates of type I and type III roofing asphalts was investigated using 32P-postlabeling analysis. Male CD rats (3/group) received 3 intratracheal instillations of fume condensates in a 24-h period. DNA from both lung cells and WBCs were isolated and used to detect DNA adducts. Condensates of both roofing asphalt fumes caused DNA adduct formation in rat lung cells in a similar dose-related manner. Under the conditions studied, however, neither type I nor type III fume condensate induced DNA adducts in WBCs. These results indicate that 1) condensates of fumes from both type I and type III have similar genotoxic activity, 2) chemicals in the condensates of roofing asphalt fumes can covalently bind to the DNA of rat lung cells, and 3) WBCs may not be a suitable surrogate for lung cells in DNA adduct studies of workers exposed to roofing asphalt fumes.

Effects of simulated pulmonary surfactant on the cytotoxicity and DNA-damaging activity of respirable quartz and kaolin

Respirable-sized quartz and kaolin dusts were pretreated with simulated pulmonary surfactant dispersions of dipalmitoyl phosphatidylcholine (DPPC) in saline to model the conditioning of particles depositing in alveolar regions of the lung. DPPC-treated and untreated dusts were used to challenge lavaged rat pulmonary alveolar macrophages in vitro. Cytotoxicity was determined over a 5-d period using both total and viable cell counts from a fluorescence-based viability assay. DNA damage, as an indication of genotoxicity, was determined over a 7-d period by the single-cell gel electrophoresis assay. Untreated quartz and kaolin both expressed a significant and potent cytotoxicity, which increased with concentration and time. DPPC-surfactant pretreatment delayed significant expression of this cytotoxicity until 3 to 5 d after challenge. Untreated quartz also caused DNA damage, which increased with concentration and time. DPPC-surfactant treatment of quartz delayed most DNA damage expression to 5 and 7 d. Untreated kaolin expressed weaker activity for DNA damage, significant at the highest concentration through 5 d, and at the higher concentrations on d 7. Surfactant treatment delayed most kaolin activity for DNA damage to 7 d after challenge.

Neoplastic potential of rat tracheal epithelial cell lines induced by 1-nitropyrene and dibenzo(a,i)pyrene

Our previous study showed that both 1-nitropyrene (1-NP) and dibenzo(a,i)pyrene (DBP) induced enhanced growth variants (EGVs) in primary cultures of rat tracheal epithelial (RTE) cells exposed in vivo. Cell lines were established from some of the EGVs. Further studies, using anchorage-independent growth in soft agar and tumorigenicity in athymic nude mice, were performed to determine the neoplastic potential of EGVs induced by 1-NP and DBP. Results show that three of five from DBP- and five of five from 1-NP-induced cell lines displayed anchorage-independent growth. The colony forming efficiency (CFE) from DBP-induced cell lines was 0.067 per thousand and CFE from 1-NP-induced cell lines was 0.151 per thousand. There is a significant difference between the two CFEs (mu = 12.08, P<0. 01). Two of five DBP- and five of five 1-NP-induced cell lines produced squamous cell carcinomas (SCC) in nude mice. The rate of tumorigenicity counted by injected sites was 20% (6/30) for DBP-induced cell lines and 57% (17/30) for 1-NP-induced cell lines. There is a significant difference between the results of tumorigenicity from the cell lines induced by the two different compounds (chi(2)=8.53, P<0.01). Neither of the two cell lines from spontaneously developed foci grew in soft agar or produced SCC in nude mice. It seems that the neoplastic potential of transformed RTE cells induced by 1-NP was higher than that of DBP.

Induction of micronuclei in V79 cells by fractions of roofing asphalt fume condensate

More than 50,000 workers in the United States are exposed to roofing asphalt fumes that may pose genotoxic and potential carcinogenic hazards. The Type III roofing asphalt is most frequently used in roof-application. Results of our previous studies showed that fume condensates of Type III roofing asphalts induced micronuclei (MN) in vitro in cultured V79 cells and DNA adduct formation in vivo in rat lung cells. In this study, the genotoxicity of whole fume condensates (WFC) of Type III roofing asphalt and its five chemical fractions (A, B, C, D and E) was determined by the micronucleus assay using V79 cells. Linear regressions were determined for the dose response of MN frequencies and percent of binucleated and multinucleated cells (MTC) following the treatment. Results showed that the numbers of micronucleated cells in cultures treated with Type III roofing asphalt WFC and its fractions B, C, D and E were significantly higher than that in the control culture, and that the slopes of the linear regression line for fractions B and C were greater than those for the WFC and fractions D and E. A clear dose response of binucleated cells was also induced by the WFC and fractions B and C. These findings indicate that: (1) WFC and all fractions, except fraction A, induced MN formation in cultured V79 cells; (2) fractions B and C possess the highest genotoxic activity; (3) the roofing asphalt WFC contains chemicals or chemical classes that induce not only chromosomal aberrations but also binucleation in V79 cells.

Genetic alterations of cancer-related genes in glass fiber-induced transformed cells

Our previous studies have shown that glass fibers induced morphological transformation in BALB/c-3T3 cells and that transformed cells possessed preneoplastic properties and transforming genes. In the current study, possible molecular mechanisms of glass fiber-induced cell transformation related to the activation and/or inactivation of cancer-related genes resulting from gene amplification and/or point mutations were investigated. Gene amplification was determined by Southern blot analysis of K-ras, H-ras, c-myc, and c-fos proto-oncogenes. Mutational spectra of the p53 tumor suppressor gene and the K-ras proto-oncogene were characterized by single-stranded conformation polymorphism and DNA sequencing. Southern blot analysis showed that gene amplification was found in 56% (K-ras and c-myc), 67% (c-fos), and 100% (H-ras) of glass fiber-transformed cell lines. DNA sequencing analysis revealed that both transition and transversion mutations occurred and were concentrated in exon 2 of K-ras and exon 4 of p53. In addition, multiple mutations in different codons were found in K-ras and p53 These results suggest that (1) glass fiber-induced cell transformation could be attributed to the activation of the H-ras, K-ras, c-myc, and c-fos proto-oncogenes and/or the inactivation of the p53 tumor suppressor gene by gene amplification and/or point mutations and (2) multiple mutations might be due to genomic instability resulting from chromosomal alterations induced by glass fibers.

Phospholipid surfactant adsorption by respirable quartz and in vitro expression of cytotoxicity and DNA damage

Respirable-sized quartz was treated with a saline dispersion of dipalmitoyl phosphatidylcholine (DPPC), a primary component of pulmonary surfactant, to model the adsorption of phospholipid surfactant onto quartz dust following particle deposition in the bronchoalveolar region of the lung. Control and surfactant-treated dusts were used to challenge lavaged rat pulmonary macrophages in vitro over a 1-week period, to determine the effects of adsorbed surfactant on the expression of quartz cytotoxicity and genotoxicity. DNA damage was determined by the single cell gel electrophoresis 'comet' assay. Untreated quartz induced DNA damage, increasing with dose and with time of incubation of dust with macrophages over a 5 day period. DPPC treatment of quartz suppressed DNA damage through 1 day of macrophage challenge. DNA damage then increased over a 5 day period, to approximately half the positive control (untreated quartz) values. Cytotoxicity was measured by trypan blue dye exclusion and by the Live-Dead fluorescence assay for cell viability. Cytotoxicity of surfactant-treated quartz measured one day after challenge of lavaged macrophages was suppressed to values near those of the negative controls, and then increased over a 1 week incubation period to levels near those expressed by native quartz positive controls. Quartz similarly treated with dioleoyl phosphatidylcholine mixed with DPPC substituted in one acyl group with a boron-containing fluorescent chromophore was used with confocal microscopy to measure particle-associated fluorescent surfactant in cells. Approximately half of the fluorescence intensity was lost over a 1 week period following challenge of lavaged macrophage. Results are discussed in terms of a model of restoration of quartz particle surface toxicity as prophylactic surfactant is removed from particle surface by cellular enzymatic digestion processes.

In vitro and in vivo transformation in rat tracheal epithelial cells exposed to diesel emission particles and related compounds

The rat tracheal epithelial (RTE) cell transformation assay was performed to determine the transforming activity of diesel emission particles (DEPs) and two related compounds, 1-nitropyrene (1-NP) and dibenzo(a,i)pyrene (DBP). RTE cells were treated with these agents in vitro and in vivo. Transformed cells from foci induced by these agents were passaged over 20 times to establish immortal cell lines. Results show that (1) DEPs- and 1-NP-induced cell transformation only with the in vivo exposure (30-75 mg/kg bw DEPs and 15-60 mg/kg bw 1-NP); (2) positive dose-related responses to DBP were found with both in vitro (0.05-0.50 microg/ml) and in vivo (7.5-30 mg/kg bw) exposures; (3) the fraction of transformed foci becoming cell lines was in the order of 1-NP(25/48) > DBP(8/28) > DEPs(0/30). These results indicate that (1) DEPs, 1-NP and DBP are capable of transforming rat tracheal epithelial cells, however, the transforming activity of DEPs and -NP may be dependent on metabolic activation, and (2) transformed cells induced by DEPs have a very low probability, if any, of becoming cell lines.

Preneoplastic potential of morphologically distinct transformed foci induced by 3-methylcholanthrene

Individual variability of scoring foci positive for transformation presents a difficult problem in assessing the transformation assay. In this study, an attempt was made to identify five morphologically distinct types of transformed foci based on size (2-3, 3-4, and > or = 4 mm in diameter), invasiveness (smooth vs. invading margins), and other properties (piling vs. spread) induced by 3-methylcholanthrene in Balb/c-3T3 cells. The transformed focal cells were used in in vitro studies including anchorage-independent analysis, focal reconstruction, gene transfection using NIH-3T3 host cells, and Southern blotting to assess amplification of five proto-oncogenes (K-ras, H-ras, c-fos, c-jun, c-myc) and a tumor suppressor (p53) gene. Results showed that 1) there was a significant increase in anchorage-independent growth of all five types of foci ranging from 7-12%; 2) all five morphological types of transformed foci showed 8-15% focal reconstruction; 3) DNA from all five types of transformed foci induced transformation in NIH-3T3 cells at a level significantly above the control DNA; 4) gene amplification studies indicated amplification in both K-ras and H-ras proto-oncogenes; however, c-fos, c-jun, and c-myc did not show DNA amplification. The tumor suppressor gene (p53) was activated and the increase was up to 3-fold over the normal Balb/c-3T3 DNA. These findings are consistent with our hypothesis that all five morphologically different foci have preneoplastic potential and that any foci of size > or = 2 mm regardless of invasiveness and piling should be scored as positive during the transformation assay.

Studies on the relationship between treatment condition and micronucleus induction in V79 cells exposed to silica and glass fibers

Studies have been carried out to determine the relationship between treatment condition and frequencies of micronucleated cells (MNC) and multinucleated cells (MTC) in Chinese hamster lung fibroblasts (V79 cells) exposed to dusts and fibers. Cells were treated with Min-U-Sil 5 silica or Owens Corning AAA-10 glass fibers under three different conditions: 24-h exposure (24E), 24-h exposure followed by 24-h post-incubation in fresh medium (24E-24P), and 48-h exposure (48E). Results showed that the frequency of MNC increased in a concentration-related manner in silica-treated V79 cells only under the condition of 24E-24P. The increase in MNC frequency after 24-h exposure was not concentration-related. No significant increase in MNC was detected in cells sampled after 48-h treatment. The frequencies of MTC in the treatment groups were higher than that in the control group. However, the increase was not statistically significant. Compared with silica, glass fibers were more active for MTC and MNC induction on a mass basis. The highest response was also observed under the condition of 24E-24P. These results indicate that 24-h exposure followed by 24-h post-incubation is a suitable treatment condition for the micronucleus assay on mineral dusts and fibers.