Comparison of primary lung tumor incidences in the rat evaluated by the standard microscopy method and by multiple step sections.

The data presented in this paper have been derived from a carcinogenicity experiment with rats as part of a comprehensive research project focused on experimental studies on the toxicity and carcinogenicity of intratracheally instilled granular dusts [Ernst H, Rittinghausen S, Bartsch W, Creutzenberg O, Dasenbrock C, Görlitz B-D et al. Pulmonary inflammation in rats after intratracheal instillation of quartz, amorphous SiO(2), carbon black, and coal dust and the influence of poly-2-vinylpyridine-N-oxide (PVNO). Exp Toxicol Pathol 2002; 54: 109-26; Ernst H, Kolling A, Bellmann B, Rittinghausen S, Heinrich U, Pott F. Pathogenetische und immunbiologische Untersuchungen zur Frage: Ist die Extrapolation der Staubkanzerogenität von der Ratte auf den Menschen gerechtfertigt? Teil II: Histologie. Abschlussbericht. Umweltforschungsplan des Bundesministeriums für Umwelt, Naturschutz und Reaktorsicherheit. November 2005. http://www.umweltdaten.de/publikationen/fpdf-l/3033.pdf]. The results of the standard approach to histological sampling in rodent carcinogenicity inhalation studies were compared to those obtained after supplemental evaluation of step sections at intervals of 250microm through the entire lung. Seven lung tissue specimens (six sections) each of 251 rats (55 rats of the control group, 53 rats of the group treated with quartz DQ 12, 56 rats of the group treated with quartz DQ 12 and PVNO (poly-2-vinylpyridine-N-oxide), 53 rats of the group treated with amorphous SiO(2), and 17 rats each of the groups treated with coal dust and carbon black) were evaluated by light microscopy. At least 60 hematoxylin and eosin (H&E)-stained sections per lung were evaluated of 99 female rats (30 rats of the control group, 7 rats each of the groups treated with quartz, quartz and PVNO, and carbon black, 31 rats of the group treated with amorphous SiO(2), and 17 rats treated with coal dust). For the neoplastic and pre-neoplastic lesions detected in the serial slides an approximate value of the whole tumor volume was calculated. The detection of tumors with a diameter of 0.25mm was possible. Based on the size distribution of 75 tumor volumes, the probability of detecting a tumor was 86% when using 12 sections. The addition of step sections enhanced the tumor detection rate from 17 to a total number of 44 lung tumors in the quartz-treated rats, from 6 to 10 in the quartz- and PVNO-treated rats, from 4 to 11 in the amorphous SiO(2)-treated rats, and from 4 to 10 in the carbon black-treated rats. Both the tumor multiplicity and the number of rats with pre-neoplastic lesions increased. These additional data corroborated the initial findings in all experimental groups and provided statistically significant results confirming the equivocal evidence of carcinogenic activity of amorphous SiO(2) in female Wistar rats. This technique offered accurate information on the incidence, histological type, size, and location of proliferative lesions in the entire lung, but the benefit must be balanced against the extra financial effort.

Lung tumor risk estimates from rat studies with not specifically toxic granular dusts.

Since 1985 several carcinogenicity studies have been published about lung tumors in rats after exposure to respirable granular biodurable particles without known significant specific toxicity (abbreviation of this complex definition by the three letters GBP to substitute the former term inert dusts). During this time, the relevance of the carcinogenicity of GBP in rats was questioned, for example, because no lung tumors from GBP were found in hamsters and carcinogenicity in mice was questionable. However, the carcinogenesis and the tumor risk from quartz appear similar in men and rats, and the effects of GBP in rats appear not to differ, on principle, from that of quartz, but at a much higher dose level. We calculated the excess risk (ER) of GBP in rats from the final results of an instillation study with 16 GBP types in connection with results of inhalation experiments with carbon black, titanium dioxide, and diesel particles. Retained particle volume together with some indicator of particle size was identified as the best suitable dose metric and the dose-response relationships were analyzed on the basis of the multistage model. By relating the results to the available dose-response slopes after inhalation, ER for workplace-like exposure were calculated for three particle size classes and an exposure to 0.3 mg/m(3) (density 2-2.5 g/mL); mean diameter 1.8-4 microm (GBP-fine-large): ER 0.1%; 0.09-0.2 microm (GBP-fine-small): ER 0.2%; 0.01-0.03 microm (GBP-ultra-fine): ER 0.5%.

Pulmonary tumor types induced in Wistar rats of the so-called "19-dust study".

The incidences of primary lung tumor types histologically diagnosed in 28 groups of Wistar rats of the so-called "19-dust study" are described, the total study having been already presented by Pott and Roller (Carcinogenicity study with nineteen granular dusts in rats. Eur J Oncol, 2005; 10: 249-81). Each exposed group was repeatedly instilled intratracheally with a suspension of one type and dose of 13 non-mining dusts differing in at least one of the following properties: chemical composition, density, specific surface area, and mean particle size. Eleven of the 13 dusts were classified as respirable granular bio-durable particles without known significant specific toxicity (abbreviation of the nine-word definition: GBP). In 579 (58%) lungs of 1002 rats which survived more than 26 weeks after the first instillation of GBP, at least one primary lung tumor type was observed, and in 306 (31%) at least two types. Three benign tumor types were diagnosed in the 579 tumor-bearing rats: bronchiolo-alveolar adenoma in 46%, cystic keratinizing epithelioma in 53%, and non-keratinizing epithelioma in 2.6% of the rats. Two of three malignant tumor types (bronchiolo-alveolar carcinoma and squamous cell carcinoma) occurred in 46% and 31% of the tumor-bearing rats, respectively, and adenosquamous carcinoma was diagnosed in 0.9%. Numerous lungs with a malignant tumor also showed one or more benign tumor types. In addition, single or multiple metastases from primary tumors of other sites (mainly carcinoma of the uterus) were diagnosed in 14% of the 1002 lungs. The proportionate incidences of the four predominantly diagnosed tumor types were compared with three summarized experimental groups which were exposed either to carbon black (two size classes), to titanium dioxide (two size classes), or to the total of the other nine GBP. A significant difference was not detected. The combination of dust volume with particle size correlated best with the carcinogenic effect, in contrast to dust mass and surface area.

Pulmonary inflammation in rats after intratracheal instillation of quartz, amorphous SiO2, carbon black, and coal dust and the influence of poly-2-vinylpyridine-N-oxide (PVNO).

Effects of poly-2-vinylpyridine-N-oxide (PVNO) were investigated in numerous in vivo and in vitro studies published in the nineteen sixties and seventies. These studies showed that PVNO inhibited development of fibrosis from quartz dust and improved lung clearance of quartz after inhalation exposure. Ameliorating effects of PVNO were observed also for pulmonary damage from colloidal SiO2 and organic substances, and the fibrogenic inflammation caused by carrageenan. Although it is not proven that silicosis is a precondition for quartz-induced lung tumours, we investigated the hypothesis that PVNO could reduce the lung tumour risk from quartz in rats. A carcinogenicity study was therefore started in rats with the main focus on the quantitative relationships among pulmonary inflammation, fibrosis and neoplasia caused by intratracheal instillation of 3 mg quartz DQ 12 with or without additional subcutaneous PVNO treatment. Other study groups were treated with multiple dust instillations, i.e. 30 instillations of 0.5 mg amorphous SiO2 at intervals of 2 weeks, 10 instillations of 0.5 mg of ultrafine carbon black or 1 mg coal at weekly intervals. The analyses of the bronchoalveolar lavage fluid (BALF) 9 months after start of the life-time study showed that the aim of producing similar levels of increased enzyme concentrations in the four groups treated with quartz/PVNO, amorphous SiO2, carbon black and coal was achieved. A 2.5- to 7.7-fold increase for lactate dehydrogenase (LDH), total protein, alkaline phosphatase and gamma-glutamyl transferase (gamma-GT) was found in these groups as compared to the control. In contrast, quartz treatment without PVNO increased the LDH level up to 24-fold and of total protein to 13-fold. However, the cell counts in the BALF were not so much different in all five groups, i.e. quartz without PVNO (leukocytes: 480.000, PMN: 190.000), quartz with PVNO (leukocytes: 300.000, PMN: 100.000), amorphous SiO2 (leukocytes: 570.000, PMN: 315.000), carbon black (leukocytes: 390.000, PMN: 150.000) and coal (leukocytes: 200.000, PMN: 65.000). Histopathological investigations after four weeks and three months revealed that the used PVNO sample was active in the quartz and amorphous SiO2 groups and markedly reduced the incidences or severity of several pulmonary changes such as macrophage accumulation, inflammatory cell infiltration, interstitial fibrosis, bronchiolo-alveolar hyperplasia, alveolar lipoproteinosis and amorphous SiO2 -induced granulomatous alveolitis/interstitial fibrotic granulomas. Also in the lung-associated lymph nodes (LALN), PVNO treatment significantly reduced the incidence and severity of inflammation in both quartz and amorphous SiO2 groups as evidenced by the presence of well-circumscribed aggregates of intact particle-laden macrophages without signs of degeneration and accompanying granulocytic infiltration and fibrosis. Immunological investigations at the 9 months timepoint on the in vitro production of reactive nitrogen (RNI) or oxygen (ROI) intermediates and tumour necrosis factor (TNF-alpha) from BALF-derived cells indicated a diminished responsiveness to LPS in all particle treatment groups. A diminished production of ROI was also found in the quartz, carbon black, and coal dust groups, respectively, as compared to the values seen in the quartz/PVNO- and amorphous SiO2 treated groups. Treatment with quartz plus PVNO restored the capability of the cells to respond to LPS as compared to the treatment with quartz alone. TNF-alpha production was diminished in the groups treated with quartz, carbon black, and coal dust alone whereas in the quartz/PVNO- and amorphous SiO2-treated groups an elevated TNF-alpha production was seen. These results led to the conclusion that only amorphous SiO2 did not affect the "normal" ability of the cells to respond to LPS and that PVNO protected the cells from a toxic effect of the quartz particles.