Multi-step lung carcinogenesis model induced by oral administration of N-nitrosobis(2-hydroxypropyl)amine in rats

N-Nitrosobis(2-hydroxypropyl)amine (BHP) was first synthesized by Krüger et al. (1974), and has been shown to primarily induce pancreatic duct adenocarcinomas by a subcutaneous injection in Syrian hamsters. By contrast, the carcinogenic effect of BHP has been indicated at the different target organs in rats, namely the lung. When rats are received by an oral administration of BHP in drinking water for 25 weeks, a high incidence of lung carcinomas are induced, which include adenocarcinomas, squamous cell carcinomas and combined squamous cell and adenocarcinomas. So many similarities are observed in terms of not only histological appearances but also gene alterations between human and BHP-induced rat lung cancers. Moreover, the step by step development of lung lesions, from preneoplastic lesions to cancers in rat lung carcinogenesis by BHP offers a good model to investigate the mechanisms underlying the pathogenesis of lung cancers. Because data for genetic and epigenetic alterations have indeed been accumulated during the BHP-induced rat lung carcinogenesis, we will introduce them in this review and hence demonstrate that this lung carcinogenesis model provides a useful opportunity for the research on the pathogenesis of lung cancers of both humans and rats.

No Mutations of Lysophosphatidic Acid Receptor Genes in Lung Adenocarcinomas Induced by N-Nitrosobis(2-hydroxypropyl)amine in Rats

Lysophosphatidic acid (LPA) is a bioactive phospholipid that stimulates cell proliferation and migration, and protects cells from apoptosis. It interacts with specific G protein-coupled transmembrane receptors. Recently, frequent mutations of the LPA receptor-1 (LPA1) gene were detected in rat lung adenocarcinomas induced by N-nitrosobis(2-hydroxypropyl)amine (BHP). In this study, to evaluate the involvement of other LPA receptor gene alterations during lung carcinogenesis, we investigated mutations of the LPA2, LPA3, LPA4 and LPA5 genes in lung adenocarcinomas induced by BHP in rats. Fifteen male Wistar rats, 6 weeks of age, were given 2000 ppm BHP in their drinking water for 12 weeks and then maintained without further treatment until sacrifice at 25 weeks, and 15 adenocarcinomas were obtained. Genomic DNAs were extracted from frozen tissues, and the LPA2, LPA3, LPA4 and LPA5 genes were examined for mutations, using polymerase chain reaction (PCR)-single strand conformation polymorphism (SSCP) analysis. No mutations of LPA2, LPA3, LPA4 and LPA5 were detected in the 15 adenocarcinomas. These results suggest that alterations due to LPA2, LPA3, LPA4 and LPA5 gene mutations might not be involved in the development of lung adenocarcinomas induced by BHP in rats.

Infrequent mutation of lysophosphatidic Acid receptor-1 gene in hamster pancreatic duct adenocarcinomas and established cell lines

To evaluate the involvement of lysophosphatidic acid receptor-1 (LPA1) gene alteration in pancreatic carcinogenesis, we investigated mutations in the LPA1 gene in hamster pancreatic duct adenocarcinomas (PDAs) and established cell lines. Female Syrian golden hamsters received 30 mg/kg of N-nitrosobis(2-oxopropyl)amine (BOP) followed by repeated exposure to an augmentation pressure regimen consisting of a choline-deficient diet combined with DL-ethionine and then L-methionine and a further administration of 20 mg/kg BOP. A total of 10 PDAs obtained 10 weeks after beginning the experiment and three cell lines established from subcutaneously transplantable PDAs in syngeneic hamsters were examined for mutations using reverse transcription-polymerase chain reaction-single strand conformation polymorphism (RT-PCR-SSCP) analysis. A mutation was detected in only one PDA (1/10, 10%) in the form of a GGA to GTA (Gly to Val) transversion at codon 355, and no mutations were detected in the three cell lines. These results suggest that the LPA1 gene mutation may play roles in a limited fraction of BOP-induced pancreatic duct carcinogenesis in hamsters.

Mutations of lysophosphatidic acid receptor-1 gene during progression of lung tumors in rats

Lysophosphatidic acid (LPA) is a bioactive phospholipid that stimulates cell proliferation, migration, and protects cells from apoptosis. It interacts with specific G protein-coupled transmembrane receptors. In this study, mutations of lysophosphatidic acid receptor-1 (LPA1) gene were investigated to clarify the possible molecular mechanisms underlying the development of lung tumors induced by N-nitrosobis(2-hydroxypropyl)amine (BHP) in rats. Male Wistar rats, 6 weeks of age, were given 2000ppm BHP in their drinking water for 12 weeks and then maintained without further treatment until sacrifice at 25 weeks. Genomic DNAs were extracted from paraffin-embedded tissues and exons 2-4 were examined for mutations, using polymerase chain reaction (PCR)-single strand conformation polymorphism (SSCP) analysis. No LPA1 mutations were detected in 15 hyperplasias, but 2 out of 12 adenomas (16.7%) and 7 out of 17 adenocarcinomas (41.2%). These results suggest that mutations of LPA1 gene may be involved in the acquisition of growth advantage from adenomas to adenocarcinomas in lung carcinogenesis induced in rats by BHP.

Frequent mutations of lysophosphatidic acid receptor-1 gene in rat liver tumors

Lysophosphatidic acid (LPA) is a bioactive phospholipid that stimulates cell proliferation, migration, and protects cells from apoptosis. It interacts with specific G protein-coupled transmembrane receptors, including LPA1 to LPA5. In the present study, to clarify an involvement of LPA1 gene alterations in the development of hepatocellular carcinomas (HCCs) we investigated the LPA1 mutations in rat HCCs induced by exogenous and endogenous liver carcinogenesis models. We induced HCCs in rats with N-nitrosodiethylamine (DEN) and a choline-deficient l-amino acid-defined (CDAA) diet. RNAs were extracted from 15 HCCs induced by DEN and 12 HCCs induced by the CDAA diet. To identify LPA1 mutations, reverse transcription (RT) - polymerase chain reaction (PCR) - single strand conformation polymorphism (SSCP) analysis, followed by nucleotide sequencing, was performed. Missense mutations were detected in 7 out of 15 HCCs (46.7%) induced by DEN. Five out of 12 HCCs (41.7%) induced by the CDAA diet also showed missense mutations. These results demonstrated that mutations in LPA1 gene occur in rat HCCs induced by DEN and the CDAA diet, suggesting that LPA1 mutations may be essentially involved in rat liver carcinogenesis.

Quantitative expression of lysophosphatidic acid receptor 3 gene in porcine endometrium during the periimplantation period and estrous cycle

Lysophosphatidic acid (LPA) belongs to the group of lipid messengers, which act via lysophosphatidic acid receptor 3 coupled to G-proteins. The participation of LPA3 in reproductive biology was revealed in mice and has not been studied in gilts. The present study was performed to evaluate the gene expression of LPA3 by a quantitative real-time PCR technique in the endometrium during different stages of pregnancy (days 6-30) and corresponding days of the estrous cycle (days 2-20) as well as in periimplantation period in pigs with surgically detached uterine horns. Based on the most conserved segments of human and rodent LPA3 we obtained a product containing 619bp (GenBank: EF137953), which exhibited high homology with human and rodents sequences. The highest transcript level was noted on days 10-12 of gestation in comparison to remaining periods and during pregnancy on days: 6-7, 8-9, 10-12 and 13-14 in comparison with the corresponding days of the estrous cycle. Higher mRNA level was noted in the horn containing embryos compared to the contralateral horn, where embryos did not develop. The results imply the important role of receptor LPA3 during early pregnancy.