Construction and application of nasopharyngeal carcinoma-specific big data platform based on electronic health records

OBJECTIVE

To establish a nasopharyngeal carcinoma-specific big data platform based on electronic health records (EHRs) to provide data support for real-world study of nasopharyngeal carcinoma.

METHODS

A multidisciplinary expert team was established for this project. Based on industry standards and practical feasibility, the team designed the nasopharyngeal carcinoma data element standards including 14 modules and 640 fields. Data from patients diagnosed with nasopharyngeal carcinoma who visited Southern Hospital after 1999 were extracted from 15 EHRs systems and were cleaned, structured, and standardized using information technologies such as machine learning and natural language processing. In addition, a series of measures such as quality control and data encryption were taken to ensure data quality and patient privacy. At the platform application level, 10 functional modules were designed according to the needs of nasopharyngeal carcinoma research.

RESULTS

As of 1 October 2022, the Big Data platform has included 11,617patients, of whom 8228 (70.83 %) were male and 3389 (29.17 %) were female, with a median age of 48 years (interquartile range, 40 years). The data in the platform were validated to have a high level of completeness and accuracy, especially for key variables such as social demographics, laboratory tests and vital signs. Currently, six projects involving risk factors, early diagnosis, treatment efficacy and prevention of treatment-related toxic reactions have been conducted on the platform.

CONCLUSIONS

We have established a high-quality NPC-specific big data platform by integrating heterogeneous data from multiple sources in the EHR. The platform provides an effective tool and strong data support for real-world studies of nasopharyngeal carcinoma, which helps to improve research efficiency, reduce costs, and improve the quality of research results. We expect to promote multicenter nasopharyngeal carcinoma data sharing in the future to facilitate the generation of high-quality real-world evidence in nasopharyngeal carcinoma. This article may provide some reference value for other comprehensive hospitals to establish a big data platform for nasopharyngeal carcinoma.

Host-guest binding of tetracationic cyclophanes to photodynamic agents inhibits posttreatment phototoxicity and maintains antitumour efficacy

In the past two decades, photodynamic therapy (PDT) has become an effective method for the treatment of cancer. However, the posttreatment residue of photodynamic agents (PDAs) causes long-term skin phototoxicity. Here, we apply naphthalene-derived, box-like tetracationic cyclophanes, named NpBoxes, to bind to clinically used porphyrin-based PDAs to alleviate their posttreatment phototoxicity by reducing their free content in skin tissues and 1O2 quantum yield. We show that one of the cyclophanes, 2,6-NpBox, could include the PDAs to efficiently suppress their photosensitivity for the generation of reactive oxygen species. A tumour-bearing mouse model study revealed that, when Photofrin, the most widely used PDA in clinic, was administrated at a dose corresponding to the clinical one, 2,6-NpBox of the same dose could significantly suppress its posttreatment phototoxicity on the skin induced by simulated sunlight irradiation, without imposing a negative influence on its PDT efficacy.

Adsorption-Based Detoxification of Endotoxins by Porous Flexible Organic Frameworks

Bacterial lipopolysaccharides (LPS, endotoxins) cause sepsis that is responsible for a huge amount of mortality globally. However, their neutralization or detoxification remains an unmet medical need. We envisaged that cationic organic frameworks with persistent hydrophobic porosity may adsorb and thus neutralize LPS through a combination of cooperative ion-pairing electrostatic attraction and hydrophobicity. We here report the preparation of two water-soluble flexible organic frameworks (FOF-1 and FOF-2) from tetratopic and ditopic precursors through quantitative formation of hydrazone bonds at room temperature. The two FOFs are revealed to possess hydrodynamic diameters, which range from 20 to 120 nm, depending on the concentrations. Dynamic light scattering and isothermal titration calorimetric and chromogenic limulus amebocyte lysate experiments indicate that both frameworks are able to adsorb and thus reduce the concentration of free LPS molecules in aqueous solution, whereas cytokine inhibition experiments with RAW264.7 support that this adsorption can significantly decrease the toxicity of LPS. In vivo experiments with mice (five males per group) show that the injection of FOF-1 at a dose of 0.6 mg/kg realizes the survival of all of the mice administrated with LPS of the d-galactosamine (d-Gal)-sensitized absolute lethal dose (LD₁₀₀, 0.05 mg/kg), whereas its maximum tolerated dose for mice is determined to be 10 mg/kg. These findings provide a new promising sequestration strategy for the development of porous agents for the neutralization of LPS.

A cucurbit[8]uril-stabilized 3D charge transfer supramolecular polymer with a remarkable confinement effect for enhanced photocatalytic proton reduction and thioether oxidation

A water-soluble porous supramolecular polymer is assembled through a CB[8]-based 2 + 2 host–guest binding motif, which can greatly increase the efficiency of photocatalysis.

[Spatial clustering analysis and trend of liver cancer death rate in Shandong province, 1970-2013]

Objective: To explore the spatial clustering and trend of liver cancer mortality in different counties of Shandong province from 1970 to 2013, and provide scientific basis for the development of liver cancer prevention and control plan. Methods: Cancer mortality data were obtained from Shandong Death Registration System and three national death cause surveys in China. Mortality rate and age adjusted mortality rate were used to describe the trend of liver cancer in different years. Difference decomposing method was applied to estimate the contribution of demographic and non-demographic factors to the change of mortality. Software ArcGIS 10.2 was used for spatial analysis, and software SaTScan 9.4 was used for spatial clustering analysis on liver cancer mortality. Results: From 2011 to 2013, the crude mortality rate of liver cancer (29.89/100 000) in Shandong increased by 208.00% and 35.37% respectively compared with that during 1970-1974 (9.72/100 000) and 1990-1992 (22.08/100 000) and was similar to that during 2004-2005 (30.44/100 000). While age standardized mortality rate (ASMR) increased first and then decreased. The ASMR during 2011-2013 (12.62/100 000) increased by 60.97% compared with that during 1970-1974 and decreased by 22.38% and 21.81% compared with that during 1990-1992 and 2004-2005, respectively. According to the difference decomposition analysis on liver cancer mortality in different years, the contribution of population factors to the liver cancer mortality rate increased from 3.38% during 1990-1992 to 29.36% during 2004-2005 and 46.16% during 2011-2013. However, the contribution of non-population factors to the increase of liver cancer mortality decreased. According to the spatial distribution of liver cancer mortality, the crude mortality rate of liver cancer in different counties were quite different, ranging from 9.33/100 000 to 65.33/100 000. Using the spatial scanning statistical software to analyze the spatial clustering of liver cancer mortality, multi areas with high mortality rate of liver cancer were found, and they were mainly distributed in Jiaodong peninsula from 2011 to 2013, covering 20 counties (cities, districts) in Qingdao, Yantai and Weihai. The risk of liver cancer mortality in this area was 1.54 times higher than that in other areas. The spatial clustering distribution of liver cancer mortality during 1970-1974 was significantly different from that during 2011-2013, the areas with high mortality rate during 1970-1974 were mainly distributed in central and western Shandong. Conclusions: There were significant temporal and spatial distribution changes in the mortality rate of liver cancer in Shandong from 1970 to 2013. According to these trends and their geographical and spatial distribution, we should further explore the risk factors of liver cancer, and formulate feasible and area specific prevention and control measures for liver cancer.

[Trend of mortality and decomposition on malignant tumors in Shandong province, 1970-2013]

Objective: To describe the mortality trend of major malignant tumors in Shandong province, from 1970 to 2013. Methods: Data related to cancer mortality were obtained from the Shandong Death Registration System and three nationwide retrospective cause-of-death surveys. Trends of overall mortality and major causes of death were described using the indicators as: mortality rates and age-standardized mortality rates, through comparing the three large-scale mortality surveys in Shandong province. Difference decomposing method was applied to estimate the contribution of demographic and non-demographic factors for the change of mortality. Results: From 1970 to 2013, the crude mortality rate of malignant tumors in Shandong was increasing. The age standard mortality rate was increasing and then decreasing. The composition of cancer deaths in the all-cause-deaths was seen increasing and then decreasing as well. Both demographic and non-demographic factors contributed to the increase of crude cancer mortality rate. With the gradual increase of the proportion of population, its role exceeded the non-demographic factors. The age-standardized mortality rate of malignant tumors in 2011-2013 was lower than that in 2004-2005. Lung cancer mortality rose from the fifth to the first place, with an increase of 6.81 times from 1970-1974 to 2011-2013. Ranking of gastric cancer mortality dropped from first to the third place, with esophageal cancer dropped from second to the fourth. After adjusted by China's standard population in 1964, the mortality rate of lung cancer was still rapidly increasing, but the age-standardized mortality rates of esophageal cancer was gradually decreasing. The crude and age-standardized mortality rates of cervical cancer showed a rapid downward trend, reduced 87.00% and 93.00% respectively from 1970-1974 to 2011-2013. Conclusions: Malignant tumors were still major threats to the residents of Shandong province. The changing trend of different malignant tumors presented an inconsistent nature which called for different intervention strategies be carried out, accordingly.

[Acute toxicity and bio-distribution of silver nitrate and nano-silver with different particle diameters in rats]

Objective: To explore the acute toxic effect and the cumulative target organ of silver nitrate and nano-silver with two different particle diameters in rats. Methods: Thirty-six adult SD rats were divided into small particle size nano-silver group (SNS), large particle size nano-silver group (LNS), silver nitrate group (SN), and control group (C) according to the random number table, with 9 rats in each group. The rats of the four groups were respectively injected with 10 mg/mL nano-silver solution (particle diameter of 20 nm, prepared by saline) in silver dose of 30 mg/kg by tail vein for once, 10 mg/mL nano-silver solution (particle diameter of 100 nm, prepared by saline) in silver dose of 30 mg/kg, 1.67 mg/mL silver nitrate solution (prepared by glucose solution) in silver dose of 3 mg/kg, and 30 mg/mL polyvinylpyrrolidone solution (prepared by saline) in dose of 90 mg/kg. (1) Toxicity test. The general observation was performed within 14 days after injection, and the deviation between value of body mass before injection and each of that on post injection day (PID) 1, 7, and 14 were respectively recorded. On PID 1, 7, and 14, 3 rats of each group were harvested for determination of serum content of alanine aminotransferase (ALT), aspartate aminotransferase (AST), total protein, and albumin by fully automatic biochemical analyzer. Then the rats were sacrificed immediately, and heart tissue, liver tissue, spleen tissue, lung tissue, kidney tissue, and brain tissue were collected to calculate the organ coefficient. Organ samples with obvious changes in organ coefficient were collected for histopathological observation by HE staining, with 3 samples in each group at each time point. (2) Bio-distribution. The specimens of heart, liver, spleen, lung, and kidney of rats from groups SNS, LNS, and SN were collected for detection of silver content by inductively coupled plasma mass spectrometry, with 3 samples in each group at each time point. Data were processed with analysis of variance of factorial design, LSD test, and Dunnett's T3 test. Results: (1) The general condition of rats in groups C and SN after injection were normal. The state of rats of groups SNS and LNS was poor with black secretion in the eye and other phenomena on PID 1, which recovered from PID 3 on. (2) The deviations between values of body mass before injection and that on PID 14 in rats of groups LNS and SN were significantly decreased as compared with deviation of group C (with P values below 0.01), but deviation of group SNS was not significantly changed (P>0.05). The deviations between values of body mass before injection and each of that on PID 1 and 7 in rats in the other three groups were similar to those in group C (with P values above 0.05). (3) Compared with those in group C, the serum content of total protein of rats in group SN on PID 1 was significantly decreased, and liver coefficient was significantly increased (with P values below 0.05). On PID 1, the serum content of ALT of rats in group LNS was (61.0±8.7) U/L, which was significantly higher than that in group C [(40.0±4.6) U/L, P<0.01]. Compared with those in group C [(126.0±3.5) U/L and 4.05±0.23], the serum content of AST of rats in groups SNS and LNS on PID 1[(249.7±107.2) and (237.0±38.3) U/L] was significantly increased, and liver coefficients (3.50±0.38 and 3.31±0.07) were significantly decreased, with P values below 0.05. Compared with those in group C [(69.2±4.8) U/L and 4.32±0.39], the serum content of AST of rats in groups SNS and LNS on PID 7 [(181.0±51.5) and (167.7±16.5) U/L] was also significantly increased, and liver coefficients (3.55±0.18 and 3.62±0.21) were also significantly decreased, P<0.05 or P<0.01. On PID 14, the four liver biochemical indexes in serum and all organ coefficients of rats in the other three groups were similar to those in group C (with P values above 0.05). (4) The liver of rats in group SN had slight degeneration on PID 1, the liver cells around the central vein of liver of rats in group SNS had slight degeneration on PID 7, and the liver cells got severely eosinophilic degeneration in liver of rats in group LNS on PID 7. There was no significant pathological change in the liver of rats in each group at the rest time points. (5) The silver content of lung and kidney in rats of group SNS on PID 1, that of spleen and kidney in rats of group LNS on PID 1, and that of heart and kidney in rats of groups LNS and SNS on PID 7 was significantly less than that of group SN (with P values below 0.05). The silver content of liver and spleen in rats of group SNS on PID 14 was significantly more than that of group SN (with P values below 0.05). Compared with that of group SN, the silver content of lung on PID 1 and liver on PID 7 in rats of group LNS was significantly increased (with P values below 0.05). On PID 14, there was no significant change in the silver content of all organs of rats between group SN and group LNS (with P values above 0.05). The silver content of heart, lung, and kidney on PID 1 and heart on PID 7 in rats of group LNS was significantly more than that of group SNS (with P values below 0.05). On PID 14, the silver content of each organ of rats in group SNS was close to that in group LNS (with P values above 0.05). Conclusions: Silver nitrate and nano-silver with two different particle diameters have a short acute toxic effect on the liver of rats, and the liver has certain ability of self-healing. Nano-silver is mainly accumulated in the liver. The distribution of nano-silver with large particle diameter in organs is more widely than that of nano-silver with small particle diameter.

Association of N-acetyltransferase-2 polymorphism with an increased risk of coronary heart disease in a Chinese population

We investigated the possible correlations between N-acetyltransferase-2 (NAT2) gene polymorphisms and the risk of coronary heart disease (CHD). CHD patients (113) and healthy controls (118) were enrolled from the First People's Hospital of Yuhang between January 2013 and June 2014. The patients were divided into mild CHD (N = 72) and severe CHD (N = 41) subgroups. DNA samples were extracted and the distributions of NAT2 polymorphisms were examined by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). Clinical characteristic indexes of severe CHD patients were also examined for relevant statistical analysis. WT, M1, M2, and M3 alleles were observed in both case and control groups. PCR-RFLP identified a wild-type homozygote, WT/WT; a mutant heterozygote, WT/Mx; and a mutant homozygote, Mx/Mx (x = 1, 2, and 3) variant of the NAT2 genotype. Mx/Mx differed significantly between case and control groups (P < 0.05); the frequencies of all four alleles did not differ significantly between case and control groups (P > 0.05). Slow acetylator genotype frequencies were notably higher in the case group than in the control group (P < 0.05). Individuals with the slow acetylator genotype were at 1.97-times higher risk of CHD and also displayed higher triglyceride and lower high-density lipoprotein cholesterol levels than those with the rapid acetylator genotype (P < 0.05). Therefore, the NAT2 polymorphism was believed to be associated with increased risk of CHD, with the NAT2 slow acetylator genotype serving as a risk factor for severe CHD in a Chinese population.

Effect of bradykinin on renal mesangial cell proliferation and extracellular matrix secretion

Recent studies have found that bradykinin (BK) plays a role in delaying glomerulosclerosis, although the mechanism of this phenomenon remains unclear. Mesangial cell proliferation (MCP) and extracellular matrix (ECM) secretion are important mechanisms for glomerulosclerosis. This study investigated the impact of BK on the platelet-derived growth factor (PDGF)-induced proliferation of mesangial cells, and evaluated its correlations with the extracellular signal-related kinase (ERK) signaling pathway. The results showed that on its own, 10-1000 mg/L BK promoted MCP and ECM secretion and induced ERK phosphorylation. However, BK administration after PDGF pre-incubation inhibited PDGF-induced MCP, ECM secretion, and ERK phosphorylation. The BK B2 receptor-specific antagonist, HOE-140, and tyrosine phosphatase inhibitor (OV) effectively blocked the function of BK. In summary, these results demonstrated that BK has a bidirectional effect on MCP and ECM secretion: when used alone, it promoted effects on these phenomena, but these effects were inhibited when combined with PDGF. This suggests that the role of BK might be achieved through inhibiting activation of the PDGF-induced ERK1/2 pathway.

Long term outcomes and prognostic factors of n0 stage nasopharyngeal carcinoma: a single institutional experience with 610 patients

Treatment responses of N0 stage nasopharyngeal carcinoma were firstly analyzed comprehensively to evaluate long term outcomes of patients and identify prognostic factors. A total of 610 patients with N0 NPC, undergoing definitive radiotherapy to their primary lesion and prophylactic radiation to upper neck, were reviewed retrospectively. Concomitant chemotherapy was administrated to 65 out of the 610. Survival rates of the patients were calculated using the Kaplan-Meier method and compared by log-rank test. Prognostic factors were identified by the Cox regression model. The study revealed the 5-year and 10-year overall, disease-free, disease-specific, local failure-free, regional failure-free, locoregional failure-free and distant metastasis-free survival rates to be 78.7% and 66.8%, 68.8% and 55.8%, 79.9% and 70.4%, 81.2% and 72.5%, 95.8% and 91.8%, 78.3% and 68.5%, 88.5% and 85.5%, respectively. There were 192 patients experiencing failure (31.5%) after radiotherapy or chemoradiotherapy. Of these, local recurrence, regional relapse and distant metastases as the first event of failure occurred in 100 (100/610, 16.4%), 15(15/610, 2.5%) and 52 (52/610, 8.5%), respectively. Multivariate analysis showed that T stage was the only independent prognostic factor for patients with N0 NPC (P=0.000). Late T stage (P=0.000), male (P=0.039) and anemia (P=0.007) were independently unfavorable factors predicting disease-free survival. After treatment, satisfactory outcome wasgenerally achieved in patients with N0 NPC. Local recurrence represented the predominant mode of treatment failure, while T stage was the only independent prognostic factor for overall survival. Late T stage, male gender, and anemia independently predicted lower possibility of the disease-free survival.

Mucosal swabs detect HPV in laryngeal papillomatosis patients but not family members

Seven patients, aged 2-7 years, with active recurrent respiratory papillomatosis (RRP) attending the University of Michigan Pediatric Otolaryngology Clinic were studied to determine if human papillomavirus (HPV) is harbored in sites of the upper aerodigestive tract other than in the laryngeal papilloma itself. We also determined if close family members had detectable virus in their oral cavities. Noninvasive swabs of buccal mucosa, posterior pharynx, nasal vestibule, and tonsillar pillar of patients, as well as buccal mucosa and posterior pharyngeal swabs of family members were studied. Swabs of the patients' papillomas served as the positive controls. HPV was detected using polymerase chain reaction (PCR) amplification and Southern hybridization techniques. Six of seven patients had detectable HPV in papilloma and endolaryngeal swabs. Four were HPV type 6, and two were HPV type 11. The patient whose swab was negative for HPV was found to be biopsy negative for papilloma 3 weeks after a single laser excision which was performed 6 months prior to the endolaryngeal swab. HPV types 16, 18 and 31 were not found in any of the patients. No swabs from other sites in patients or family members were HPV positive despite the presence of adequate DNA in the swabbed material for successful amplification of beta-actin sequences. The absence of HPV (other than in the papilloma itself) in the upper aerodigestive tract of patients and caregivers is consistent with the absence of reported cases of horizontal transmission to siblings or other family members. The findings are also consistent with the conventional view that juvenile respiratory HPV is transmitted vertically from vaginal condylomas in the mother.

Thirteen-week, repeated inhalation exposure of F344/N rats and B6C3F1 mice to ferrocene

Ferrocene (dicyclopentadienyl iron; CAS No. 102-54-5) is a relatively volatile compound used as a chemical intermediate, a catalyst, and an antiknock additive in gasoline. This organometallic chemical is of particular interest because of its structural similarities to other metallocenes, some of which are carcinogenic. F344/N rats and B6C3F1 mice were exposed to 0, 3.0, 10, and 30 mg ferrocene vapor/m3, 6 hr/day, 5 days/week, for 13 weeks. During these exposures, no rats or mice died, nor were any clinical signs of ferrocene-related toxicity observed. At the end of the exposures, male rats exposed to the lowest and highest level of ferrocene had decreased body weight gains compared to filtered-air-exposed control male rats, while body weight gains for all groups of both ferrocene- and filtered-air-exposed female rats were similar. Male mice exposed to ferrocene had no differences in body weight gains, compared to controls, but female mice had decreases in body weight gains at the 10 and 30 mg/m3 exposure levels. There were exposure concentration- and exposure-time-related increases in lung burdens of iron. The mean iron lung burden in rats exposed to 30 mg ferrocene vapor/m3 for 90 days was four times greater than the burden in control rats. No exposure-related changes in respiratory function, lung biochemistry, bronchoalveolar lavage cytology, total lung collagen, clinical chemistry, and hematology parameters were observed. This suggests that the accumulations of iron in lung did not cause an inflammatory response nor any functional impairment of the lung. There were no indications of developing pulmonary fibrosis nor of any hematologic toxicity. No exposure-related gross lesions were seen in any of the rats or mice at necropsy. Exposure-related histopathologic alterations, primarily pigment accumulations, were observed in the nose, larynx, trachea, lung, and liver of both species, and in the kidneys of mice. Lesions were most severe in the nasal olfactory epithelium where pigment accumulation, necrotizing inflammation, metaplasia, and epithelial regeneration occurred. Nasal lesions were observed in all ferrocene-exposed animals and differed only in severity, which was dependent on the exposure concentration. Histochemical stains of these target tissues showed the presence of iron ions. The results suggest that the mechanism of ferrocene toxicity may be the intracellular release of ferrous ion through ferrocene metabolism, followed by either iron-catalyzed lipid peroxidation of cellular membranes or the iron-catalyzed Fenton reaction to form hydroxyl radicals that directly react with other key cellular components, such as protein or DNA.

Functional organization of the Bel-1 trans activator of human foamy virus

Human foamy virus encodes a 300-amino-acid nuclear regulatory protein termed Bel-1 that is required for human foamy virus replication in culture. Bel-1 is a potent trans-activator of gene expression directed by the homologous HFV long terminal repeat as well as the long terminal repeat of human immunodeficiency virus type 1. We have used mutational analysis to define several discrete functional domains within Bel-1. The C-terminal approximately 50 amino acids of Bel-1 are shown to be essential for Bel-1 activity but can be effectively substituted by the C-terminal activation domain of VP16. We therefore conclude that the Bel-1 C terminus forms part of an activation domain. Mutations within a central, approximately 100-amino-acid segment of Bel-1 preclude trans-activation by either Bel-1 or the Bel-1/VP16 chimera. These sequences are therefore proposed to direct the interaction of Bel-1 with its viral DNA target sequences. A short Bel-1 segment located between the activation and binding domains is shown to mediate the nuclear localization of this regulatory protein. Although the functional organization of Bel-1 therefore appears comparable to that reported for other eukaryotic transcriptional activators, Bel-1 does not contain sequences homologous to known transcriptional activation or DNA-binding motifs.

Biological markers of exposure to benzene: S-phenylcysteine in albumin

Results of experiments in our laboratory have shown that benzene is metabolized by animals in part to an intermediate that binds to cysteine groups in hemoglobin to form the adduct S-phenylcysteine (SPC). These results suggested that SPC in hemoglobin may be an effective biological marker for exposure to benzene. However, we could not detect SPC in the globin of humans occupationally exposed to benzene concentrations as high as 28 p.p.m. for 8 h/day, 5 days/week. As another approach, we examined the binding of benzene to cysteine groups of a different blood protein, albumin. To facilitate the process, a new method for the precipitative isolation of albumin from plasma was also developed. The isolated albumin was analyzed for SPC by isotope dilution GC-MS. We used this approach to measure SPC in the albumin of F344/N rats exposed by gavage to 0-10,000 mumol/kg benzene. Amounts of albumin-associated SPC increased as a function of dose, followed by a leveling off in the amount of SPC seen at doses greater than 1000 mumol/kg. Levels of SPC were measured in humans occupationally exposed to average concentrations of 0, 4.4, 8.4 and 23 p.p.m. benzene 8 h/day, 5 days/week. Of nine controls, seven had levels of SPC below the limit of detection (0.1 pmol SPC/mg albumin). SPC increased in the exposed groups linearly, giving a statistically significant slope (P less than 0.001) of 0.044 +/- 0.008 pmol/mg albumin/p.p.m. with an intercept of 0.135 +/- 0.095 pmol/mg albumin. From this study, we conclude that SPC in albumin may prove useful as a biomarker for benzene exposure.

S-phenylcysteine formation in hemoglobin as a biological exposure index to benzene

Benzene is metabolized to intermediates that bind to hemoglobin, forming adducts. These hemoglobin adducts may be usable as biomarkers of exposure. In this paper, we describe the development of a gas chromatography/mass spectroscopy assay for quantitating the binding of the benzene metabolite, benzene oxide, to cysteine groups in hemoglobin. We used this assay to study the hemoglobin adduct, S-phenylcysteine (SPC), in the blood of rats and mice exposed to benzene either by inhalation or by gavage. We were able to detect SPC in the hemoglobin of exposed rats and mice, to show the linearity of the exposure dose-response relationship, and to establish the sensitivity limits of this assay. For the same exposure regime, rats showed considerably higher levels of SPC than did mice. As yet, we have not been able to detect SPC in the globin of humans occupationally exposed to benzene. We attempted to determine whether the SPC found in hemoglobin originated from the metabolism of benzene within or outside of the red blood cell. We hypothesized that the greatest red blood cell metabolism would be associated with peripheral reticulocytes, which retain high metabolic capacity. After exposing rats to benzene, we isolated the red blood cells and used discontinuous Percoll gradients to fractionate them into age groups. No differences in SPC levels were found among any of the fractions, suggesting that the SPC found in globin originates from the metabolism of benzene to benzene oxide in a location external to the red blood cell. To our knowledge, this is the first demonstration of the nonenzymatic binding of the benzene metabolite, benzene oxide, to protein.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of ozone in tracheal cell transformation

This project examined the potential role of ozone as a respiratory carcinogen by characterizing its ability to induce or modulate the preneoplastic transformation of rat tracheal epithelial cells. The chemical reactivity of ozone and the types of damage it can cause suggest that it may have a role in environmental carcinogenesis. Previous reports have described an increase in the incidence and number of lung tumors per animal in strain A mice exposed to ozone. However, the role of ozone in the development of the tumors has not been clear. Ozone also has been reported to act alone and synergistically with ionizing radiation to induce changes related to neoplasia in primary hamster embryo cells and in the mouse C3H/10T1/2 cell line in culture. Few other studies have examined the direct cytotoxic or transforming effects of ozone after in vivo or in vitro exposure of cells, and no studies have been reported on the comparative effects of ozone on respiratory cells exposed in vivo or in vitro. The induction of early preneoplastic changes in populations of rat tracheal epithelial cells by carcinogens can be detected and quantified in vitro after exposures in vivo or in vitro of tracheal epithelial cells. This cell culture and transformation system was used to characterize the transforming potency of ozone. Tracheal epithelial cells were isolated from Fischer-344/N rats that had been exposed for six hours per day, five days per week for one, two, or four weeks to 0, 0.12, 0.5, or 1.0 parts per million (ppm)* ozone (sea-level equivalents). Cell populations were examined in culture for increases in the frequency of preneoplastic variants. Rats exposed to ozone did not exhibit an increase in the frequency of preneoplastic tracheal cells, although exposed tracheas did exhibit dose-dependent morphological changes. Rat tracheal epithelial cells were given single, 40-minute in vitro exposures to concentrations of ozone that did not result in any detectable decrease in colony-forming efficiency (approximately 0.7 ppm) and to concentrations that resulted in approximately a 40% decrease (approximately 10 ppm). Exposed cultures were examined for increases in the frequency of preneoplastic variants. The results of these experiments, like those for the in vivo experiments described above, suggest that a single ozone exposure does not induce preneoplastic variants of rat tracheal epithelial cells. In contrast, cultures of rat tracheal cells exposed to 0.7 ppm ozone twice weekly for about five weeks exhibited approximately a twofold increase in the frequency of preneoplastic variants compared with control cultures.(ABSTRACT TRUNCATED AT 400 WORDS)

Toxicokinetics of inhaled 1,3-butadiene in monkeys: comparison to toxicokinetics in rats and mice

1,3-Butadiene is a potent carcinogen in mice and a weaker carcinogen in rats. People are exposed to butadiene through its industrial use--largely in rubber production (over 3 billion pounds of butadiene were produced in 1989)--and because it is common in the environment, occurring in cigarette smoke, gasoline vapor and in the effluents from fossil fuel incineration. Epidemiological studies have provided some evidence for butadiene carcinogenicity in people. Differences in the uptake and metabolism of inhaled butadiene between rodents and primates, including people, might be reflected in differences in its toxicity. In order to compare uptake and metabolism in primates to that in rodents--for which data were already available--we exposed cynomolgus monkeys (Macaca fascicularis) to 14C-labeled butadiene at concentrations of 10.1, 310 or 7760 ppm for 2 hr. Exhaled air and excreta were collected during exposure and for 96 hr after exposure. The uptake of butadiene as a result of metabolism was much lower in monkeys than in rodents. For equivalent inhalation exposures, the concentrations of total butadiene metabolites in the blood were 5-50 times lower in monkey than in the mouse, the more sensitive rodent species, and 4-14 times lower than in the rat. If the toxicokinetics of butadiene in people is more like that of the monkey than that of rodents, then our data suggest that people will receive lower doses of butadiene and its metabolites than rodents following equivalent inhalation exposures to butadiene. This has important implications for assessing the risk to humans of butadiene exposure based on animal studies.

Two-week, repeated inhalation exposure of F344/N rats and B6C3F1 mice to ferrocene

Ferrocene (dicyclopentadienyl iron; CAS No. 102-54-5) is a relatively volatile, organometallic compound used as a chemical intermediate, a catalyst, and as an antiknock additive in gasoline. It is of particular interest because of its structural similarities to other metallocenes that have been shown to be carcinogenic. F344/N rats and B6C3F1 mice were exposed to 0, 2.5, 5.0, 10, 20, and 40 mg ferrocene vapor/m3, 6 hr/day for 2 weeks. During these exposures, there were no mortality and no observable clinical signs of ferrocene-related toxicity in any of the animals. At the end of the exposures, male rats exposed to the highest level of ferrocene had decreased body-weight gains relative to the weight gained by filtered air-exposed control rats, while body-weight gains for all groups of both ferrocene- and filtered air-exposed female rats were similar. Male mice exposed to the highest level of ferrocene also had decreased body-weight gains, relative to controls, while female mice had relative decreases in body-weight gains at the three highest exposure levels. Male rats had a slight decrease in relative liver weight at the highest level of exposure, whereas no relative differences in organ weights were seen in female rats. Male mice had exposure-relative decreases in liver and spleen weights, and an increase in thymus weights, relative to controls. For female mice, relative decreases in organ weights were seen for brain, liver, and spleen. No exposure-related gross lesions were seen in any of the rats or mice at necropsy. Histopathological examination was done only on the nasal turbinates, lungs, liver, and spleen.(ABSTRACT TRUNCATED AT 250 WORDS)

Globin adducts of benzo[a]pyrene: markers of inhalation exposure as measured in F344/N rats

We have explored methods for determining benzo[a]pyrene (BaP) dosimetry by measuring adduction levels to F344/N rat blood hemoglobin, and have refined and validated an assay that measures the in vivo binding of the 7,8-diol 9,10-epoxide metabolite of BaP to globin. The assay for BaP-globin adducts was based on the release of tetrahydroxy-BaP (BaP-tetrols) from globin by mild acid hydrolysis. After extensive isolation, BaP-tetrols were quantitated by high-pressure liquid chromatography using fluorescence detection. BaP-tetrol levels were measured in rats dosed intraperitoneally with 242, 71 and 24 mumol BaP kg-1 body weight in corn oil. The formation of BaP-tetrols was not linear with dose. The lowest dose yielded adduct levels that represented the limits of sensitivity for the method, as performed in this laboratory. Once this limit of sensitivity was established, the potential use of the assay was assessed by measuring the radiochemical binding of inhaled [14C]BaP or its metabolites to the globin of F344/N rats. Rats were exposed for 4 h per day, 1 day per week, for 12 weeks to pure aerosols of [14C]BaP at a level of 2 mg m-3. At the conclusion of exposure, rats were sacrificed and globin was isolated. The extent of [14C]BaP binding to the globin was determined by liquid scintillation spectrometry. Rats exposed to aerosols of [14C]BaP had statistically increased levels of binding to globin, and the levels were comparable to those observed previously after intragastric administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Disposition of inhaled isoprene in B6C3F1 mice

Isoprene (2-methyl-1,3-butadiene) is the monomeric unit of widely occurring natural products called terpenes. Isoprene is widely used in industry with nearly 1.1 million pounds produced in the United States in 1987. The purpose of this investigation was to determine the toxicokinetics of inhaled isoprene in B6C3F1 mice and to compare the data to previously published toxicokinetic data in F344 rats (A. R. Dahl, L. S. Birnbaum, J. A. Bond, P. G. Gervasi, and R. F. Henderson, 1987. Toxicol. Appl. Pharmacol. 89, 237-248). The comparative toxicokinetics in the two species will be useful for extrapolation of rodent toxicity data to humans. Male B6C3F1 mice were exposed to nominal concentrations of 20, 200, and 2000 ppm isoprene or [14C]isoprene for up to 6 hr. For all exposures, steady-state levels of isoprene were reached rapidly (i.e., within 15 to 30 min) after the onset of exposure. The mean (+/- SE) steady-state blood levels of isoprene (identified by headspace analysis) for the 20, 200, and 2000 ppm exposures were 24.8 +/- 3.3, 830 +/- 51, and 6800 +/- 400 ng isoprene/ml blood, respectively. At the two higher exposure concentrations, the increases in blood levels of isoprene were proportional to the increases in air concentrations of isoprene. There was approximately a 2.3-fold decrease in the retained 14C/inhaled 14C ratio with increasing exposure concentration. Depending on the exposure concentration, from 52% (20 ppm isoprene) to 73% (2000 ppm isoprene) of the metabolite-associated (nonisoprene) radioactivity was excreted in the urine over a 64-hr postexposure period. 14CO2 exhalation after the end of the 6-hr exposure was minimal (2%) at the 20 ppm exposure and increased up to 18% at the higher isoprene exposure concentrations. These data suggest that metabolism of isoprene in mice is nonlinear within the range of exposure concentrations used in this study. Hemoglobin adduct formation reached near-maximum between 200 and 2000 ppm isoprene exposure concentration, consistent with our conclusion that pathways for metabolism of isoprene were saturated. Isoprene metabolites were present in blood after inhalation of isoprene at all concentrations studied. There were substantial differences in the toxicokinetics of inhaled isoprene in mice compared to rats. In mice, fractional retention of inhaled isoprene, which reflects, in part, metabolism of isoprene, was linearly related to exposure concentrations up to 200 ppm but decreased at 2000 ppm; in rats, fractional retention of inhaled isoprene decreased with increasing exposure concentration over a range of exposures from 8 to 1500 ppm.(ABSTRACT TRUNCATED AT 400 WORDS)

Benzene hemoglobin adducts in mice and rats: characterization of formation and physiological modeling

Benzene is a myelotoxin and a human leukemogen. Humans are exposed to this compound, both occupationally and environmentally. This study was conducted to determine whether formation of benzene-derived adducts with blood hemoglobin (Hb) can be used as a biomarker of exposure to benzene. B6C3F1 mice and F344/N rats were given 0.1 to 10,000 mumol [14C]benzene/kg body wt, orally. Twenty-four hours later, animals were euthanized, and globin was isolated from blood samples. The globin was analyzed by liquid scintillation spectrometry for the presence of [14C]benzene-derived adducts. Hb adduct formation was linear with respect to dose for amounts of up to 500 mumol [14C]benzene/kg body wt, for both rodent species. Within this linear dose-response range, mice formed adducts from [14C]benzene approximately 3.5 times less efficiently [0.022 +/- 0.010 (pmol adducts/mg globin)/(mumol/kg body wt dose)] than did rats [0.076 +/- 0.014 (pmol adducts)/(mumol/kg body wt dose)]. Benzene-derived Hb adducts also accumulated linearly when mice and rats were given up to three daily doses of 500 mumol [14C]benzene/kg body wt. These data were used to develop a physiological model for benzene-derived Hb adduct formation. Both first-order and saturable pathways for adduct formation were incorporated. The results showed that the model simulated the levels of Hb adducts in both mice and rats after oral exposures to benzene and predicted the levels of Hb adducts present after inhalation exposure. These studies suggest that Hb adducts might be useful biomarkers for human exposures to benzene.

Species differences in the metabolism and disposition of inhaled 1,3-butadiene and isoprene

Species differences in sensitivity to carcinogenic effects from inhaled 1,3-butadiene might stem, at least in part, from differences in uptake, metabolism, and distribution of 1,3-butadiene. To examine this possibility, rats, mice, and monkeys were exposed to stepped concentrations of 14C-labeled 1,3-butadiene and the chemically related compound, isoprene. Respiratory data were collected during exposure and were used to determine fractional uptake. Rates and routes of excretion of retained radioactivity were also determined and blood levels of potentially toxic metabolites were measured. In some cases, the concentrations of hemoglobin adducts were determined. For rodents, the tissue distribution of metabolites was examined. Some results from these continuing studies to date are: a) mice achieve higher blood concentrations of reactive metabolites than do rats; b) blood levels of toxic metabolites are lower in monkeys than in rodents; c) uptake and retention of 1,3-butadiene is nonlinear in the range where long-term toxicity studies have been conducted; d) the efficiency of production of reactive metabolites decreases with increased inhaled concentrations of 1,3-butadiene; e) repeated exposure to 1,3-butadiene does not induce the metabolism of 1,3-butadiene in rodents; f) hemoglobin adducts of 1,3-butadiene are potential dosimeters of exposure; and g) rats inhaling isoprene produce reactive metabolites analogous to those produced during inhalation of 1,3-butadiene. The available data indicate that major differences in the biological fate of inhaled 1,3-butadiene occur among species, and these differences, at least in part, account for those in species sensitivity to the toxicity of inhaled 1,3-butadiene.

Effect of repeated benzene inhalation exposures on benzene metabolism, binding to hemoglobin, and induction of micronuclei

Metabolism of benzene is thought to be necessary to produce the toxic effects, including carcinogenicity, associated with benzene exposure. To extrapolate from the results of rodent studies to potential health risks in man, one must know how benzene metabolism is affected by species, dose, dose rate, and repeated versus single exposures. The purpose of our studies was to determine the effect of repeated inhalation exposures on the metabolism of [14C]benzene by rodents. Benzene metabolism was assessed by characterizing and quantitating urinary metabolites, and by quantitating 14C bound to hemoglobin and micronuclei induction. F344/N rats and B6C3F1 mice were exposed, nose-only, to 600 ppm benzene or to air (control) for 6 hr/day, 5 days/week for 3 weeks. On the last day, both benzene-pretreated and control animals were exposed to 600 ppm, 14C-labeled benzene for 6 hr. Individual benzene metabolites in urine collected for 24 hr after the exposure were analyzed. There was a significant decrease in the respiratory rate of mice (but not rats) pretreated with benzene which resulted in lower levels of urinary [14C]benzene metabolites. The analyses indicated that the only effects of benzene pretreatment on the metabolite profile in rat or mouse urine were a slight shift from glucuronidation to sulfation in mice and a shift from sulfation to glucuronidation in rats. Benzene pretreatment also had no effect, in either species, on formation of [14C]benzene-derived hemoglobin adducts. Mice and rats had similar levels of hemoglobin adduct binding, despite the higher metabolism of benzene by mice. This indicates that hemoglobin adduct formation occurs with higher efficiency in rats. After 1 week of exposure to 600 ppm benzene, the frequency of micronucleated, polychromatic erythrocytes (PCEs) in mice was significantly increased. Exposure to the same level of benzene for an additional 2 weeks did not further increase the frequency of micronuclei in PCEs. These results indicate that repeated exposures to benzene, such as might be encountered by humans as a result of occupational or environmental exposures, are not likely to change or increase benzene metabolism.

Characterization of hemoglobin adduct formation in mice and rats after administration of [14C]butadiene or [14C]isoprene

Occupational exposures to 1,3-butadiene or isoprene occur through their use in the manufacture of rubber and other related polymer products. The purpose of this study was to determine if butadiene or isoprene administration would result in the formation of adducts with blood hemoglobin (Hb), and if such adducts can be used as a measure of previous exposure(s). Male B6C3F1 mice and male Sprague-Dawley rats were injected intraperitoneally with 1, 10, 100, or 1000 mumol [14C]butadiene or 0.3, 3.0, 300, 1000, or 3000 mumol [14C]isoprene per kilogram body weight. Animals were killed 24 hr later. Globin was isolated from blood samples and was analyzed for 14C by liquid scintillation spectroscopy. Hb adduct formation was linearly related to administered doses up to 100 mumol [14C]butadiene or 500 mumol [14C]isoprene per kilogram body weight for mice and rats, respectively. For [14C]butadiene, the efficiency of Hb adduct formation in mice and rats within the linear response range was 0.177 +/- 0.003 and 0.407 +/- 0.019 (pmol of 14C-adducts/mg globin)/(mumol of retained [14C]butadiene/kg body wt), respectively (mean +/- SE; n = 18). For [14C]isoprene, these values for mice and rats were 0.158 +/- 0.035 and 0.079 +/- 0.016 (pmol of 14C-adducts/mg globin)/(mumol of retained [14C]isoprene/kg body wt), respectively (mean +/- SE; n = 12). Hb adducts also accumulated linearly after repeated daily administration of 100 mumol [14C]butadiene or 500 mumol [14C]isoprene per kilogram body wt to mice and rats, respectively, for 3 days. [14C]Butadiene-derived Hb adducts in blood showed lifetimes of approximately 24 and approximately 65 days for mice and rats, respectively, which correlate with the reported lifetimes for red blood cells in these rodent species. Thus, levels of butadiene- or isoprene-derived adducts on Hb in circulating blood may be a useful measure of prior repeated exposures to these compounds.

Comparison of acute ozone-induced nasal and pulmonary inflammatory responses in rats

The centriacinar pulmonary lesion induced by ozone has been extensively characterized, but little is known about the effects of this oxidant gas in the upper airways. The present study was designed to compare the effects of acute ozone exposure in the nose and lungs of rats. We examined the cellular inflammatory responses in the nasal cavity and lower respiratory tract by means of nasal and bronchoalveolar lavage and morphometric quantitation of neutrophils within the nasal mucosa and pulmonary terminal bronchioloalveolar duct regions (i.e., centriacinar). Rats were exposed to 0.0, 0.12, 0.8, or 1.5 ppm ozone for 6 hr and were sacrificed immediately or 3, 18, 42, or 66 hr following exposure. Eighteen hours after exposure, increased numbers of neutrophils, as compared to controls, were recovered from nasal lavage fluid (NLF) of rats exposed to 0.12 ppm ozone. There was no change in the number of neutrophils recovered from bronchoalveolar lavage fluid (BALF) at any time after exposure. Rats exposed to 0.8 ppm ozone had more neutrophils in NLF than controls immediately after exposure, but no concomitant increase in BALF neutrophils at that time. However, as the number of neutrophils in BALF increased (maximum at 42 hr), the number of neutrophils recovered from NLF decreased (minimum at 42 hr). Rats exposed to 1.5 ppm ozone had no significant increases in nasal neutrophils in NLF at any time after exposure but had greatly increased numbers of neutrophils in BALF 3, 18, and 42 hr after exposure. The number of neutrophils recovered by nasal and bronchoalveolar lavage accurately reflected the tissue neutrophil response at sites within the nasal cavity and lung that were injured by acute ozone exposure. Our results suggest that at high ozone concentrations (0.8 and 1.5 ppm), the acute nasal inflammatory response is attenuated by a simultaneous, competing, inflammatory response within the centriacinar region of the lung. Analysis of nasal lavage fluid for changes in cellular composition may be a useful indicator of acute exposure to ambient levels of ozone, but at higher ozone levels, the nasal cellular inflammatory response may underestimate the effects of ozone on nasal and pulmonary epithelia.

Lung retention and binding of [14C]-1-nitropyrene when inhaled by F344 rats as a pure aerosol or adsorbed to carbon black particles

1-Nitropyrene (NP), as found in the environment, is more typically associated with carbonaceous particles than found as an aerosol of the pure compound. To determine whether (and why) an association with particles resulted in prolonged lung retention of NP, rats were exposed to 14C-NP as a pure aerosol or adsorbed on carbon black particles. Total 14C retained in the lung was greater at all times from 0.5 h to 30 d after exposure to 14C-NP adsorbed to carbon black particles than after exposure to pure 14C-NP (p less than .05). The fraction of total 14C in lung bound to carbon black particles decreased steadily with time after exposure, indicating in vivo removal of NP from the particles. At 0.5 h after exposure, the fraction of the estimated deposited 14C that was covalently bound to lung macromolecules was twofold greater for NP adsorbed on carbon black than for pure NP. Covalently bound 14C in lungs increased with time after exposure to 14C-NP adsorbed to carbon black, reaching levels of approximately 1% of the deposited radioactivity at 7-30 d after exposure, whereas levels of covalently bound 14C declined with time after exposure to pure NP. Thus, at 30 d after exposure, the amount of 14C covalently bound to lung macromolecules was approximately 10-fold greater (p less than .05) in rats that inhaled 14C-NP adsorbed on carbon black particles than in rats that inhaled pure 14C-NP aerosols. These results suggest that association of NP with carbon black particles augments the interaction of reactive metabolites of NP with target macromolecules. This phenomenon is thought to be related to the slow release of NP from carbon black particles, and may augment the biological effects of inhaled NP when adsorbed on carbon black or similar particles in the environment.

Effects of adsorption of benzo[a]pyrene onto carbon black particles on levels of DNA adducts in lungs of rats exposed by inhalation

Exposure of rodents to benzo[a]pyrene (BaP) associated with particles has previously been shown to result in increased retention of BaP and metabolites in lungs. To determine if DNA damage might be enhanced, DNA adducts were measured in lungs of F344 rats following inhalation of pure BaP aerosols or BaP absorbed on carbon black particles. Groups of rats were exposed nose only to filtered air, [14C]BaP (2 mg/m3), or [14C]BaP (2 mg/m3) adsorbed on carbon black (97 mg/m3) (BaP/CB) for 4 hr/day, 1 day/week, for 12 weeks. Groups of rats were terminated at 4, 8, 12, 16, 20, and 24 weeks after the beginning of the 12-week exposure period. Retention of total 14C in lungs was used as an indicator of total reactive metabolites. DNA isolated from lungs was analyzed for adducts using a 32P-postlabeling assay. Inhalation of BaP/CB resulted in 100-fold higher levels of 14C in lungs at the end of the 12-week exposure than did inhalation of pure BaP. The halftime for the decline in 14C levels was 34 +/- 3 weeks (mean +/- SE) for rats exposed to BaP/CB and 6 +/- 2 weeks for rats exposed to pure BaP. At the end of 12 weeks of exposure, DNA adducts in lungs of rats exposed to pure BaP ranged from 2-15 adducts per 10(9) bases (mean = 7, n = 4) and in rats exposed to pure BaP absorbed on carbon black ranged from 10-12 adducts per 10(9) bases (mean = 11, n = 4); DNA adducts in lungs of sham-exposed rats ranged from 0-2 adducts per 10(9) bases (mean = 1, n = 4). The halftimes for the decline in DNA adducts in lungs were 3 +/- 1 weeks (mean +/- SE) for the rats exposed to BaP/CB and 5 +/- 2 weeks for the rats exposed to BaP. One of the DNA adducts found following exposure to both BaP and BaP/CB was tentatively identified as the BaP diol epoxide deoxyguanosine (BPDE) adduct. Levels of both total and BPDE DNA adducts were significantly increased (p less than 0.05) in lungs of rats exposed to both BaP and BaP/CB compared to levels in lungs of sham-exposed rats. There were no significant differences in levels of DNA adducts in lungs of rats exposed to BaP or BaP/CB, although the pattern of adducts was different between the two exposure modes.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of repeated benzene inhalation exposures on subsequent metabolism of benzene

Benzene is a known human leukemogen and animal carcinogen. To better assess the risks associated with benzene exposure, it would be helpful to determine whether repeated inhalation exposures would affect the metabolism of benzene. The purpose of these experiments was to determine if exposure of F344 rats and B6C3F1 mice to 600 ppm benzene, 6 h/day, 5 days/week for 3 weeks, would affect the subsequent in vivo metabolism of inhaled [14C]benzene.

Effects of buthionine sulfoximine on the development of ozone-induced pulmonary fibrosis

The capacity of reduced glutathione (GSH) to protect lung tissue against ozone-induced pulmonary fibrosis was investigated. Male B6C3F1 mice were exposed to 0, 0.2, 0.5, and 1.0 ppm ozone for 23 hr/day for 14 days. During exposures and/or for a period of 90 days after exposures, subgroups of mice at each exposure level were given drinking water containing 30 mM L-buthionine-S,R-sulfoximine (BSO) to lower in vivo levels of GSH. These BSO treatments reduced blood glutamylcysteine synthetase (GCS) activity (regulatory enzyme for GSH biosynthesis) and lung nonprotein sulfhydryl (NPSH) levels in nonexposed animals by approximately half. In contrast, ozone exposures increased blood GCS activity and lung NPSH levels in a concentration-dependent manner, with smaller increases in the BSO-treated mice. Immediately after exposures, an ozone-related inflammatory response was seen in lungs, but no histopathological signs of developing fibrosis were evident. Ninety days later, mice exposed to 1 ppm ozone and not treated with BSO had modest evidence of pulmonary fibrosis. Mice exposed to 1 ppm ozone and treated with BSO during this post-exposure period (regardless of BSO treatment during exposures) showed histopathological evidence of exacerbated pulmonary fibrosis, compared to similarly exposed mice not treated with BSO postexposure. These results indicated that interference with the body's normal defense mechanisms against oxidant damage, including suppression of GSH biosynthesis, exacerbates the subsequent development of pulmonary fibrosis.

Response of rodents to inhaled diluted diesel exhaust: biochemical and cytological changes in bronchoalveolar lavage fluid and in lung tissue

The effect of long-term (24 months) inhalation of diesel exhaust on the bronchoalveolar region of the respiratory tract of rodents was assessed by serial (every 6 months) analysis of bronchoalveolar lavage fluid (BALF) and of lung tissue from F344/Crl rats and CD-1 mice (both sexes) exposed to diesel exhaust diluted to contain 0, 0.35, 3.5, or 7.0 mg soot/m3. The purpose of the study was twofold. One was to assess the potential health effects of inhaling diluted exhaust from light-duty diesel engines. The second was to determine the usefulness of BALF analysis in detecting the early stages in the development of nononcogenic lung disease and differentiating them from the normal repair processes. No biochemical or cytological changes in BALF or in lung tissue were noted in either species exposed to the lowest, and most environmentally relevant, concentration of diesel exhaust. In the two higher levels of exposure, a chronic inflammatory response was measured in both species by dose-dependent increases in inflammatory cells, cytoplasmic and lysosomal enzymes, and protein in BALF. Histologically, after 1 year of exposure, the rats had developed focal areas of fibrosis associated with the deposits of soot, while the mice, despite a higher lung burden of soot than the rats, had only a fine fibrillar thickening of an occasional alveolar septa in the high-level exposure group. Higher increases in BALF beta-glucuronidase activity and in hydroxyproline content accompanied the greater degree of fibrosis in the rat. BALF levels of glutathione (GSH) and glutathione reductase activity increased in a dose-dependent fashion and were higher in mice than in rats. Lung tissue GSH was depleted in a dose-dependent fashion in rats but was slightly increased in mice. This depletion may have played a role in the greater fibrogenic response observed in rats. Other tissue changes in enzymatic activity were small compared to changes observed in BALF. The exposure did not increase the cytochrome P-450 content of the lung in either species. The results suggest that, for the noncarcinogenic health effects reported in this paper, there is a threshold of exposure below which adverse effects were not observed. This threshold was well above environmentally relevant levels of diesel exhaust but may be in the range of some occupational exposures. The analysis of BALF proved a useful adjunct to the chronic toxicity study to quantitate the inflammatory changes accompanying the development of pulmonary disease.

Lung, liver, and kidney as potential target organs after exposure to 1-nitropyrene, as determined by the time course of covalently bound material

Previous studies in which rats were exposed to [14C]-1-nitropyrene by inhalation indicated that lung, liver, and kidney consistently accumulated the highest concentrations of 14C after exposure. The purpose of the study described here was to determine the extent to which this 14C was covalently bound to macromolecules. Male F344/N rats were exposed to 360 ng [14C]-1-nitropyrene/l air for 1 h resulting in an average of 2.2 micrograms 1-nitropyrene deposited per rat. An additional group of rats was given 4.2 micrograms [14C]-1-nitropyrene by gavage. Total 14C in 23 tissues was determined for up to 96 h after inhalation exposure and up to 30 d after gavage. Lung, liver, and kidney contained the highest concentrations of 14C. Samples of these tissues were exhaustively extracted to determine the amount of radioactivity covalently bound to macromolecules. Regardless of the route of administration, the kidneys had the highest concentrations of covalently bound 14C. At 96 h after exposure kidneys had overall mean concentrations of 2.7 pmol bound/g tissue.micrograms nitropyrene administered. The overall mean concentration in liver was 0.18 pmol bound/g.microgram and the overall mean concentration in lung was 0.06 pmol/g.microgram at 96 h after exposure. Covalently bound material persisted in kidneys for the duration of the study (30 d postexposure). The calculated half-time for removal of bound 14C from kidneys was 150 d. These data suggest that kidney should be considered as one of the organs at risk after exposure to nitropyrene by inhalation or ingestion.

The inhalation toxicity of two commercial dyes: solvent yellow 33 and solvent green 3

The quinoline dye 2-(2'-quinolyl)-1,3-indandione or Solvent Yellow 33 (SY) and the anthraquinone dye 1,4-di-p-toluidinoanthraquinone or Solvent Green 3 (SG) are used in many manufactured products including military smoke grenades. During manufacturing, SY or a combination of both SY and SG can be released into the air, exposing factory workers by inhalation to these dye compounds. The potential inhalation toxicity of these compounds was tested by exposing F344/N rats to different concentrations of SY or SY/SG dye mixture (30:70 w/w) for 6 hr/day, 5 days/week for 4 or 13 weeks. In the 4-week studies, rats were exposed to SY aerosols at average concentrations of 10 +/- 5, 51 +/- 10, or 230 +/- 30 mg/m3 (means +/- SD) or SY/SG aerosols at average concentrations of 11 +/- 5, 49 +/- 11, or 210 +/- 50 mg/m3 (means +/- SD). Rats exposed to the highest concentration of SY or SY/SG had body weights that were approximately 8% or 7% less, respectively, than their controls after exposure. Rats exposed to the highest concentration of SY/SG for 4 weeks also had reduced pulmonary gas exchange efficiency, airflow obstruction, mild pulmonary inflammation, slight Type II pulmonary epithelial cell hyperplasia, and proliferation of vacuolated alveolar macrophages. In the 13-week studies, rats were exposed to SY aerosols at average concentrations of 1.0 +/- 0.2, 10.8 +/- 1.8, or 100 +/- 17 mg/m3 (means +/- SD) or SY/SG aerosols at average concentrations of 1.1 +/- 0.5, 10.2 +/- 3.1, or 101 +/- 23 mg/m3 (means +/- SD). Animals exposed to the highest concentration of SY or SY/SG for 13 weeks had body weights that were approximately 5 or 9% less, respectively, than their controls after exposure and had accumulation of vacuolated alveolar macrophages in lungs. Rats exposed to the highest concentration of SY/SG dye mixture for 13 weeks also had indications of mild pulmonary inflammation and slight Type II pulmonary epithelial cell hyperplasia. Very little SY was found in lungs after any exposures, indicating its clearance from lungs was at a rapid rate. However, significant amounts of the SG component of the SY/SG mixture were detected in lungs after each exposure. Lung clearance half-times of SG from the 13-week exposure were estimated to be approximately 280 days. In summary, neither test material appeared to be highly toxic following inhalation. However, the slightly higher toxicity observed for SY/SG over SY alone is probably related to the longer lung retention of the SG component of the dye mixture.

Deposition, metabolism, and excretion of 1-[14C]nitropyrene and 1-[14C]nitropyrene coated on diesel exhaust particles as influenced by exposure concentration

Nitrated polycyclic aromatic hydrocarbons (nitro-PAH) have been detected in the environment, originating from sources such as diesel exhaust emissions and coal combustion fly ash. 1-Nitropyrene (NP) is a predominant mutagenic and carcinogenic nitro-PAH found in diesel exhaust emissions. Since inhalation of NP is a likely route of exposure in humans, it is important to determine the biological fate of inhaled NP both in its pure form and associated with particles. The purpose of this study was to determine the disposition of NP aerosols inhaled by rats. The studies described in this paper were designed to determine the deposition of [14C]NP over a range of exposure concentrations, identify the pathways and half-times for excretion of absorbed NP, and determine the distribution of inhaled NP and metabolites in tissues. Male F344 rats were exposed nose only to various concentrations of NP and NP coated on diesel exhaust particles (50-1100 ng/liter). The results indicate that, over the range of concentrations tested, pathways for excretion of [14C]NP equivalents in urine and feces were independent of the exposure concentration of NP, whether in its pure form or associated with diesel exhaust particles. In all cases, fecal excretion was the major route of elimination of [14C]NP equivalents, with about 2 times more excreted by this route than by urine. The fractional deposition of [14C]NP in the respiratory tract did not appear to be dependent on exposure concentration. Half-times for elimination of 14C in urine and feces were about 15 to 20 hr. In all exposures, 14C was widely distributed in the tissues examined. Analysis of the tissues for NP and its metabolites indicated that within 1 hr after exposure, greater than 90% of the 14C was NP metabolites. Lungs of rats exposed to [14C]NP coated on diesel exhaust particles contained nearly 5 times more 14C than lungs from rats exposed to pure aerosols of [14C]NP (148 vs 29 pmol/g lung) within 1 hr after exposure. This difference was increased to 80-fold at 94 hr after exposure (80 vs 1 pmol/g lung). Long-term clearance half-times of 14C from various tissues were similar. The results demonstrate that particle association of NP significantly alters the biological fate of inhaled NP.

Disposition and metabolism of free and particle-associated nitropyrenes after inhalation

The objective of this project was to determine the biological fate of 1-nitropyrene (NP) aerosols in rats. The results from these studies indicate that, over the range of aerosol concentrations tested, pathways for excretion of 14C-NP equivalents in urine and feces were independent of the exposure concentration of NP, either in its pure form or associated with diesel exhaust particles. In all cases, fecal excretion was the major route of elimination of 14C-NP equivalents, with about 2 times more excreted by this route than by urine. Fractional respiratory tract deposition of 14C-NP did not appear to be dependent on exposure concentration. In most cases, half-times for elimination of 14C in urine and feces were about 15 to 20 hours. In all exposures, 14C was widely distributed in the tissues examined. Analysis of the tissues for NP and metabolites indicated that within 1 hour after exposure greater than 90% of the 14C was associated with NP metabolites. Lungs of rats exposed to 14C-NP coated on diesel exhaust particles contained nearly 5 times more 14C than lungs from rats exposed to pure aerosols of 14C-NP (148 vs 29 pmole g lung) within 1 hour after exposure. This difference was increased to 80-fold at 94 hours after exposure (80 vs 1 pmole g lung). Long-term clearance half-times of 14C from various tissues were similar, with values of about 30 to 50 hours measured. Pre-exposure to diesel exhaust prior to exposure to NP may result in increased retention of a small fraction of the NP. Equilibrium organ concentrations predicted for tissues following continuous exposure to NP suggest that both low inhaled concentrations of NP and association of NP with insoluble diesel particles can result in an increased retention of NP in the lungs above what might be predicted using data obtained from animal studies using high concentrations of pure NP. The liver and kidneys are among the other organs predicted to contain the highest amounts of NP.

Effects of the long-term depletion of reduced glutathione in mice administered L-buthionine-S,R-sulfoximine

Previous methods to deplete in vivo concentrations of reduced glutathione (GSH) have not been able to lower tissue GSH levels for extended periods, have been toxic, and can alter the metabolism of xenobiotics. A possible alternative to lower in vivo concentrations of GSH may be the use of buthionine-S,R-sulfoximine (BSO) in the drinking water of laboratory animals to inhibit the biosynthesis of GSH. It has been previously reported that 20 mM BSO in the drinking water given to mice was able to lower GSH levels in a variety of tissues after 15 days. In order to more fully characterize the in vivo depletion of GSH in tissues by ingestion of BSO and determine if this method would be suitable in studies requiring depressed levels of GSH for extended periods, we added different amounts of this agent to the drinking water given to mice for various times up to 28 days. We found that ingested BSO at the highest concentration used in drinking water (30 mM) was able to maximally lower GSH concentrations in mouse lungs, lung lavage fluid, liver, kidneys, and blood to 59.0 +/- 3.6%, 35.0 +/- 5.1%, 44.3 +/- 1.5%, 69.5 +/- 3.9%, and 70.0 +/- 6.0% of control mice, respectively, for up to 28 days. These lowered concentrations of tissue GSH returned to control levels after mice were returned to untreated drinking water for 7 days. The potential toxicity of such treatments was also evaluated. Levels of alkaline phosphatase, lactate dehydrogenase, glucose-6-phosphate dehydrogenase, glutathione peroxidase, and glutathione reductase in lungs and lung lavage fluid, and total and differential cell counts from lung lavage fluid were not different between control and BSO-treated mice. This showed that BSO treatment did not produce indications of lung injury as measured by these biochemical parameters. Serum aspartyl transferase and gamma-glutamyl transpeptidase activities were unaffected by the BSO treatments, indicating normal liver functions. Lung and liver cytochrome P-450 concentrations were also not different between controls and BSO-treated animals. Thus, BSO in the drinking water of mice was able to effectively lower in vivo levels of GSH without eliciting acute toxic responses.

Contribution of intestinal microfloral metabolism to the total macromolecular covalent binding of 1-nitro-pyrene in the lung and liver of the rat

1-Nitropyrene (NP) is a direct acting mutagen found in diesel exhaust and coal-combustion fly ash. The purpose of this study was to investigate the contribution of gut microfloral metabolism to the macromolecular covalent binding (MCB) of NP and/or its metabolites in lungs and liver of the rat. Normal and antibiotic treated rats were administered [14C]NP and MCB was quantitated at various times in lungs and livers. Abolition of gut microfloral metabolism by antibiotic treatment significantly altered total MCB in lungs. MCB in lungs of antibiotic-treated animals 4 h after oral administration of NP was 0.15 nmol NP equivalents/g and was significantly (P less than 0.05) decreased to less than one-half of control values (0.42 nmol NP equivalents/g). MCB in lungs of antibiotic-treated rats was no different from the controls 1 week after NP administration (0.1 nmol NP equivalents/g). Comparison of livers from control and antibiotic-treated rats demonstrated the same pattern of MCB as lungs but differences were not significant. These results reveal that metabolism by gut microflora may play a role in the activation and covalent binding of NP to macromolecules. However, the alteration of covalent binding observed after antibiotic treatment was a change in the time course of formation and breakdown of covalently bound forms and not an effect on the quantity of bound material remaining at 1 week indicating that gut microfloral metabolism is not an exclusive pathway for bioactivation of NP in the rat.

Excretion and metabolism of 1-nitropyrene in rats after oral or intraperitoneal administration

Many nitro-substituted polycyclic aromatic hydrocarbons (NPAHs) have been identified as environmental pollutants and have been found to be mutagens and carcinogens in bacteria and mammalian systems. They require metabolism to express their biological activity. The metabolism and excretion of 1-nitropyrene (NP), a prevalent NPAH, by Fischer-344 rats after intraperitoneal (ip) or oral administration was studied. Radiolabeled NP was administered to rats (10 mg NP/kg body wt), and urine and feces were collected for 7 days. After ip administration of [14C]NP, 60% of the radioactivity was found in the urine and 20% in the feces. Likewise, 55 and 35% of the orally administered 14C was found in urine and feces, respectively. Both urine and feces were analyzed by high-pressure liquid chromatography for metabolites. The majority of the radioactivity in both urine and feces was associated with very polar metabolites, none accounting for more than 10% of the dose. Small amounts (less than 1% of the dose) of aminopyrene (AP), acetylaminopyrene, and NP were detected. A urinary metabolite (3-8% of the dose) was found that converted to acetylaminopyrene phenol (two isomers) when urine was heated overnight at 37 degrees C at pH 4.5. More of this metabolite (2.2 times) as well as AP (1.8 times), was excreted after oral than after ip administration of NP. The NP metabolites found in this study demonstrate that reduction of the nitro group is a significant route of NP metabolism in rats. Since nitroreduction appears to be necessary in the activation of NPAHs to bacterial mutagens, this indicates that similar metabolic pathways are present in rats (catalyzed by mammalian and/or gut bacterial enzymes) and that activation of NPAHs to carcinogens or toxins by nitroreduction is possible.

Interaction of formaldehyde with glutathione in the isolated/ventilated perfused lung and the isolated perfused liver

The interaction of formaldehyde (CH2O) with reduced glutathione (GSH) was evaluated in aqueous solution and in isolated perfused lungs and livers. Addition of CH2O (0-4.9 mM) to a solution of 0.17 mM GSH in 2 mM EDTA, pH 7.4, resulted in a time- and concentration-dependent depletion of GSH. Perfusion of livers with fortified Krebs-Ringer bicarbonate buffer containing 0.3-4.9 mM CH2O resulted in a dose-dependent depletion of GSH. Perfusion of isolated ventilated lungs with perfusate containing 4.9 mM CH2O resulted in a depletion of GSH to 75% of controls. However, lower concentrations of CH2O in the lung perfusate did not result in depletion of GSH. These results demonstrate that exposure to CH2O in aqueous solution or in the perfused lung and liver is capable of depleting endogenous GSH. However, the concentrations of CH2O required to yield a significant depletion of endogenous GSH exceed those encountered in vivo. Thus, it is unlikely that depletion of GSH by CH2O is a causal factor in formaldehyde-induced toxicity.

Macromolecular weight specificity in covalent binding of bromobenzene

Bromobenzene is a hepatotoxicant that causes centrilobular necrosis. Pretreatment of animals with 3-methylcholanthrene decreases and phenobarbital pretreatment enhances the hepatotoxic action of this compound. We have investigated the macromolecular weight specificity of the covalent interactions of bromobenzene with liver macromolecules following incubation of [14C]bromobenzene in isolated hepatocytes. Hepatocytes were prepared from Fischer-344 rats treated for 3 days with 3-methylcholanthrene, phenobarbital, or normal saline. After a 1-hr incubation, total covalent binding, as measured by sodium dodecyl sulfate-equilibrium dialysis, was twofold less in hepatocytes from 3-methylcholanthrene-treated rats and sixfold greater in hepatocytes from phenobarbital-treated rats, as compared to hepatocytes from control animals. Analysis of the arylated macromolecules by electrophoresis on 15% sodium dodecyl sulfate-polyacrylamide disc gels indicated that in the first 1 to 3 min of incubation substantial amounts of covalently bound radiolabel were associated with macromolecules of between 20,000 and 40,000. The amount of radioactivity associated with these macromolecules rapidly diminished in hepatocytes from control and 3-methylcholanthrene-treated animals. In hepatocytes from phenobarbital-treated animals, the amount of radioactivity associated with macromolecules, 20,000, increased throughout the incubation. The amount of radiolabel associated with macromolecules, 20,000, increased in all incubations. When nontoxic doses of phenylmethylsulfonyl fluoride, a specific inhibitor of serine proteases, were added to control hepatocytes incubated with [14C]-bromobenzene, the decrease in radioactivity associated with larger (greater than 20,000) macromolecules was inhibited and a corresponding lack of increase in radioactivity associated with smaller macromolecules was observed. In hepatocytes from phenobarbital-treated rats, either the rate of adduct formation with higher molecular weight macromolecules greatly exceeded the rate of their breakdown or the phenobarbital treatment compromised the degradation process. The toxicity induced by bromobenzene may result from the covalently bound material altering the biological function of macromolecules. The result of this study suggest that cellular degradation of the arylated macromolecules may be one mechanism of detoxification. Persistence of the arylated macromolecules within the cell may be associated with the toxic action of bromobenzene.

The use of sister-chromatid exchange in Chinese hamster primary lung cell cultures to measure genotoxicity

Primary cell cultures derived from Chinese hamster lung (CHL) were established, and their response for the induction of sister-chromatid exchange (SCE) by direct- and indirect-acting mutagens was characterized. An increase in SCE frequency was induced in CHL cells by 3-methylcholanthrene (MCA), benzo[a]pyrene (BaP), and 2-aminoanthracene (2AA). The SCE frequency increased slightly after exposure to cyclophosphamide, but did not respond to the hepatocarcinogen dimethylnitrosamine (DMN). A slight increase in SCE frequency by DMN was observed in the CHL system with use of Aroclor-1254-induced rat liver homogenate fraction (S9). This response to DMN in CHL cells was lower than that seen when CHO cells were the target in the presence of S9. At low (1) and high (20) passages, the CHL cells responded with a similar dose-related increase in SCE frequency to direct- (ethyl methanesulfonate, EMS) and indirect-(MCA) acting mutagens. This response indicates that even after prolonged culturing in vitro, the cells retained the ability to metabolically activate xenobiotic promutagens. The induction of SCE by MCA occurred at concentrations that also induced macromolecular binding. SCE induction was also examined in primary lung cell cultures from animals exposed by nose-only inhalation to MCA aerosol. A significant increase in SCE frequency above controls was observed in cells from animals after a single exposure to MCA. No detectable increase in SCE frequency was observed after repeated inhalation exposures. Because CHL cells are of lung origin and showed metabolic activity, the CHL system appears to be appropriate for study of the genotoxic potential of inhaled compounds.

Generation and characterization of radiolabeled diesel exhaust

To evaluate the potential health risks associated with increased use of diesel engines, information is needed on the biological fate of inhaled diesel exhaust components. Appropriately radiolabeled exhaust produced by burning radiolabeled fuel could be used to gain this information. The purpose of this study was to characterize different radiolabeled diesel exhausts with respect to their potential use in studies of the biological fate of exhaust carbon particles and particle-associated organic compounds (particle extracts). A single-cylinder diesel engine was used to burn diesel fuel containing trace amounts of 14C-labeled hexadecane, dotriacontane, benzene, phenanthrene or benzo(a)pyrene. Greater than 98% of the 14C in all additives was converted to volatile materials upon combustion. The remainder was distributed in varying amounts between the carbon particles and particle extracts. Aromatic additives labeled carbon particles more efficiently than aliphatic additives. Column chromatography of the particle extracts showed that, in most cases, the majority of the radioactivity eluted in fractions identical to the specific fuel additive employed, suggesting that a large amount of the particle-associated organic compounds consisted of uncombusted fuel constituents. Applying an electrical load to the engine-electrical generator increased carbon particle radioactivity, but had variable effects on the amount of radioactivity in the particle extracts. 67Ga-tetramethylheptanedione was also studied as a fuel additive to label carbon particles. 67Ga was incorporated into the exhaust particles and lung deposition of particles in rats was found to be approximately 10%. However, the 67Ga-radiolabel was found to separate from the particles in vivo, making it an unsuitable radiolabel for studying the long-term lung retention of diesel exhaust carbonaceous particles.

Respiratory tract clearance of 14C-labeled diesel exhaust compounds associated with diesel particles or as a particle-free extract

Radiolabeled diesel exhaust particles or dichloromethane extracts of these particles were intratracheally instilled (10 mg) into Fischer-344 rats and the clearance of 14C radioactivity was measured. Approximately 88% of the 14C radioactivity associated with the particles was soluble in dichloromethane. The clearance of 14C radioactivity from lungs occurred in two phases. The initial, more rapid phase of lung clearance of both particle-associated 14C radioactivity (Particle 14C) and extract-associated 14C radioactivity (Extract 14C) was very similar (t 1/2 approximately equal to 3 hr). However, the second phase of lung clearance of the remaining Particle 14C was much slower (t 1/2 approximately equal to 25 days) than the second phase of lung clearance of the Extract 14C (t 1/2 approximately equal to 2.9 days). Tracheal clearance rates of 14C radioactivity from both instillation studies were both rapid and similar (t 1/2 approximately equal to 10-12 hr). These results indicate that diesel engine exhaust particles reduce the lung clearance rate of the organic compounds associated with these particles. These studies also point to the possibility that the rate limiting step in the lung clearance of organic compounds associated with inhaled diesel exhaust particles may be the rate at which they dissociate from these particles in vivo. This is because the long-term clearance rate of the particle-associated organic compounds was shown here to be much slower than that of the same organic compounds in a particle-free form but not as slow as the lung clearance rate reported for diesel exhaust core particles (T.L. Chan, P.S. Lee, W.E. Hering, J. Appl. Toxicol. 1, 77-82 (1981].(ABSTRACT TRUNCATED AT 250 WORDS)

Lung retention and metabolic fate of inhaled benzo(a)pyrene associated with diesel exhaust particles

Polycyclic aromatic hydrocarbons (PAHs) are a class of compounds considered to have human carcinogenic potential and have been found associated with many respirable, environmental particle pollutants. The effect of these ultrafine, insoluble, carrier particles on the lung retention and metabolic fate of inhaled PAHs was investigated with a radiolabeled model PAH, [3H]benzo(a)pyrene (3H-BaP). Fischer-344 rats were exposed (30 min) by nose-only inhalation to 3H-BaP adsorbed (approximately 0.1% by mass) onto diesel engine exhaust particles. These aerosols were generated in a dynamic aerosol generation system by vapor condensation methods. The total mass concentration of these aerosols was 4-6 micrograms/liter of air with a mass median diameter of 0.14 micron. Lung clearance of the inhaled particle-associated 3H radioactivity occurred in two phases. The initially rapid clearance of this inhaled radiolabel had a half-time of less than 1 hr. The second, long-term component of lung clearance had a half-time of 18 +/- 2 days and represented 50 +/- 2% of the 3H radioactivity that had initially deposited in lungs. In contrast, previous inhalation studies with a pure 3H-BaP aerosol showed that greater than 99% of the 3H radioactivity deposited in lungs was cleared within 2 hr after exposure (Sun et al., Toxicol. Appl. Pharmacol. 65, 231-244, 1982). By HPLC analysis, the majority of diesel soot-associated 3H radioactivity retained in lungs was BaP (65-76%) with smaller amounts of BaP-phenol (13-17%) and BaP-quinone (5-18%) metabolites also being detected. No other metabolites of BaP were detected in lungs of exposed rats. Tissue distribution and excretion patterns of 3H radioactivity were qualitatively similar to previous inhalation studies with 3H-BaP coated Ga2O3 aerosols (Sun et al., 1982). These findings suggest that inhaled PAHs may be retained in lungs for a greater period of time when these compounds are associated with diesel engine exhaust particles. In addition, these compounds retained in lungs can be metabolized in lungs. These results may have significant implications for the health risks that may be involved with human exposure to particle-associated organic pollutants.