Lack of Modifying Effects of Intratracheal Instillation of Quartz or Dextran Sulfate Sodium (DSS) in Drinking Water on Lung Tumor Development Initiated with 4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) in Female A/J Mice

Dynamic assessing silica particle-induced pulmonary fibrosis and associated regulation of long non-coding RNA expression in Wistar rats

BACKGROUND

Exposure to respirable crystalline silica (RCS) can induce accelerated silicosis (AS), a form of silicosis that is more progressive and severe form of silicosis. In this project we aimed to assess processes of silicosis in rats exposed to RCS with focus on the regulation of long noncoding RNAs (lncRNAs).

RESULTS

The results showed that RCS induced acute inflammatory response as indicated by the appearance of inflammatory cells in the lung from the first day and peaked on day 7 of exposure. The fibroblasts appeared along with the inflammatory cells decreasing gradually on day 14. Extensive fibrosis appeared in the lung tissue, and silicon nodules were getting larger on day 28. Interestingly, the number of altered lncRNAs increased with the exposure time with 193, 424, 455, 421 and 682 lncRNAs on day 1, 7, 14, 21, and 28 after exposure, respectively. We obtained 285 lncRNAs with five significant temporal expression patterns whose expressions might correlate with severity of silicosis. KEGG analysis showed that lncRNAs from short time-series expression miner (STEM)-derived data mainly involved in 17 pathways such as complement and coagulation cascades.

CONCLUSIONS

The differential expression profiles of lncRNAs may be potential biomarkers in silicosis through modulating expressions of their relevant genes in lungs of rat and thus warrant further investigation.

Relationship between Lung Carcinogenesis and Chronic Inflammation in Rodents

Simple Summary

Lung cancer is the most common cause of cancer-related deaths worldwide. There are various risk factors for lung cancer, including tobacco smoking, inhalation of dust particles, chronic inflammation, and genetic factors. Chronic inflammation has been considered a key factor that promotes tumor progression via production of cytokines, chemokines, cytotoxic mediators, and reactive oxygen species by inflammatory cells. Here, we review rodent models of lung tumor induced by tobacco, tobacco-related products, and pro-inflammatory materials as well as genetic modifications, and discuss the relationship between chronic inflammation and lung tumor. Through this review, we hope to clarify the effects of chronic inflammation on lung carcinogenesis and help develop new treatments for lung cancer.

Abstract

Lung cancer remains the leading cause of cancer-related deaths, with an estimated 1.76 million deaths reported in 2018. Numerous studies have focused on the prevention and treatment of lung cancer using rodent models. Various chemicals, including tobacco-derived agents induce lung cancer and pre-cancerous lesions in rodents. In recent years, transgenic engineered rodents, in particular, those generated with a focus on the well-known gene mutations in human lung cancer (KRAS, EGFR, and p53 mutations) have been widely studied. Animal studies have revealed that chronic inflammation significantly enhances lung carcinogenesis, and inhibition of inflammation suppresses cancer progression. Moreover, the reduction in tumor size by suppression of inflammation in animal experiments suggests that chronic inflammation influences the promotion of tumorigenesis. Here, we review rodent lung tumor models induced by various chemical carcinogens, including tobacco-related carcinogens, and transgenics, and discuss the roles of chronic inflammation in lung carcinogenesis.

Single Intratracheal Quartz Instillation Induced Chronic Inflammation and Tumourigenesis in Rat Lungs

Crystalline silica (quartz) is known to induce silicosis and cancer in the lungs. In the present study, we investigated the relationship between quartz-induced chronic inflammation and lung carcinogenesis in rat lungs after a single exposure to quartz. F344 rats were treated with a single intratracheal instillation (i.t.) of quartz (4 mg/rat), and control rats were treated with a single i.t. of saline. After 52 or 96 weeks, the animals were sacrificed, and the lungs and other organs were used for analyses. Quartz particles were observed in the lungs of all quartz-treated rats. According to our scoring system, the lungs of rats treated with quartz had higher scores for infiltration of lymphocytes, macrophages and neutrophils, oedema, fibrosis, and granuloma than the lungs of control rats. After 96 weeks, the quartz-treated rats had higher incidences of adenoma (85.7%) and adenocarcinoma (81.0%) than control rats (20% and 20%, respectively). Quartz-treated and control rats did not show lung neoplastic lesions at 52 weeks after treatment. The number of lung neoplastic lesions per rat positively correlated with the degree of macrophage and lymphocyte infiltration, oedema, fibrosis, and lymph follicle formation around the bronchioles. In conclusion, single i.t. of quartz may induce lung cancer in rat along with chronic inflammation.

Rat strain differences in levels and effects of chronic inflammation due to intratracheal instillation of quartz on lung tumorigenesis induced by DHPN

Chronic inflammatory effects of single intratracheal instillation (i.t.) of quartz on rat lung tumorigenesis were examined using 4 different animal models. At first, in order to determine an appropriate dose of quartz i.t. to promote lung tumorigenesis, F344 male rats were administrated single 0, 0.5, 1, 2 or 4 mg quartz/rat after initiation by N-bis(2-hydroxypropyl) nitrosamine (DHPN). Further studies were performed to examine strain differences of the effects of chronic inflammation caused by quartz i.t. in 3 strains of rat, i.e. F344, Wistar-Hannover and SD. Each was instilled with 2mg quartz/rat after DHPN administration and sacrificed in week 24. In addition, strain differences in generation of inflammation were determined at days 1 and 28. Finally, for determination of long-term effects period, F344 and Wistar-Hannover rats were similarly treated, but the experiment was terminated at week 52. In F344 rats, the tumor areas in DHPN treated groups showed a tendency to increase along with the dose of quartz. F344 rats demonstrated the highest and Wistar-Hannover rats the lowest sensitivity to quartz in acute and chronic phases in the 3 strains. In 52 week, in F344 rats, the multiplicity of tumors and the serum concentration of IL-6 in the group treated with DHPN and quartz were significantly increased. The present experiments indicated that chronic inflammation due to quartz instillation exerted promoting effects on lung carcinogenesis in F344, SD and Wistar-Hannover rats. The strain differences in tumor promotion appeared to correlate with inflammatory reactions to quartz and increase of IL-6.

Suppressive oligodeoxynucleotides reduce lung cancer susceptibility in mice with silicosis

Silicosis is an inflammatory lung disease induced by the inhalation of silica-containing dust particles. There is conflicting data on whether patients with silicosis are more susceptible to lung cancer induced by cigarette smoke. To examine this issue experimentally, a model was developed in which one of the most abundant and potent carcinogens present in cigarette smoke [4-(N-methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone (NNK)] was administered to mice at the peak of silica-induced pulmonary inflammation. Results show that the incidence of lung tumors in silicotic mice treated with NNK was significantly increased compared with mice exposed to silica or NNK alone. Synthetic oligonucleotides (ODN) containing repetitive TTAGGG motifs can block pathologic inflammation. We therefore examined whether treatment with these suppressive (Sup) ODN could block silica-induced pulmonary inflammation and thereby reduce susceptibility to lung cancer. Results show that Sup (but not control) ODN inhibit pulmonary fibrosis and other inflammatory manifestations of chronic silicosis. Of greater import, Sup ODN reduced lung tumor incidence and multiplicity in silicotic mice exposed to NNK. These findings establish an experimental model for examining the role of silicotic inflammation in cancer susceptibility and demonstrate that Sup ODN represent a novel therapy for chronic silicosis.

Gender-dependent effects of gonadectomy on lung carcinogenesis by 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) in female and male A/J mice

The present study was conducted to investigate the effects of gonadectomy on lung carcinogenesis in female and male mice, and to determine an association between sex hormone and lung carcinogenesis. Female and male A/J mice were divided into gonadectomized and unoperated control groups and all animals were treated intraperitoneally with 1 or 2 injections of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) at the dose of 2 mg/mouse. The mice were sacrificed 18 or 56 weeks after surgery. Serum levels of estradiol in females and testosterone in males were confirmed to be decreased by gonadectomy. Lung white nodules were detected in all mice of all groups. In the control groups of 18- and 56-week studies, the multiplicities of lung nodules in females were significantly greater than in males. In males in the 56-week study, the multiplicity of macroscopical lung nodules, bronchiolo-alveolar hyperplasias, adenomas and tumors (adenomas and adenocarcinomas) showed significant increase with castration. In females in the 18-week study, the multiplicity of adenomas decreased significantly by ovariectomy. Based on the results of the present study, female A/J mice were confirmed to be more susceptible to NNK-induced lung carcinogenesis than males. Furthermore, it was suggested that the process is inhibited by testosterone and accelerated by estradiol. These findings indicate the possibility that sex hormones play important roles in determining sex differences in lung carcinogenesis in the A/J mice initiated by NNK.