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

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.

Low carbohydrate diets containing soy protein and fish oil slow the growth of established NNK-induced lung tumors

We recently found that a diet composed of 15% of total calories as carbohydrate (CHO), primarily as amylose, 35% soy protein and 50% fat, primarily as fish oil (FO) (15%Amylose/Soy/FO) was highly effective at preventing lung nodule formation in a nicotine-derived nitrosamine ketone (NNK)-induced lung cancer model. We asked herein whether adopting such a diet once cancers are established might also be beneficial. To test this, NNK-induced lung nodules were established in mice on a Western diet and the mice were then either kept on a Western diet or switched to various low CHO diets. Since we previously found that sedentary mice develop more lung nodules than active mice, we also compared the effect of exercise in this cancer progression model. We found that switching to a 15%Amylose/Soy/FO diet reduced lung nodules and slowed tumor growth with both 'active' and 'sedentary' mice. Ki67, cleaved caspase 3 and Terminal Deoxynucleotidyl Transferase-Mediated dUTP Nick End Labeling assays suggested that the efficacy of the 15%Amylose/Soy/FO in lowering tumor nodule count and size was not due to a reduction in tumor cell proliferation, but to an increase in apoptosis. The 15%Amylose/Soy/FO diet also significantly lowered liver fatty acid synthase and 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3 expression, pointing to a global metabolic switch from glycolysis to fatty acid oxidation. Mice fed the 15%Amylose/Soy/FO diet also had significantly reduced plasma levels of interleukin (IL)-1β, IL-6 and tumor necrosis factor α. These results suggest that the 15%Amylose/Soy/FO diet may slow tumor growth by suppressing proinflammatory cytokines, inducing a metabolic switch away from glycolysis and inducing apoptosis in tumors.

The effect of diet and exercise on tobacco carcinogen-induced lung cancer

In previous studies, we found that low-carbohydrate (CHO) diets reduced the incidence of tumors in mice genetically predisposed to cancer. However, because >90% of human cancers arise via carcinogen-induced somatic mutations, we investigated, herein, the role that different types and levels of CHO, protein and lipid play in lung cancer induced by the tobacco-specific carcinogen, nicotine-derived nitrosamine ketone (NNK) in A/J mice. We found lowering CHO levels significantly reduced lung nodules and blood glucose levels. We also found that soy protein was superior to casein and that coconut oil was ineffective at reducing lung nodules. Diets containing amylose or inulin (at 15% of total calories), soy protein (at 35%) and fat (at 50%, 30% being fish oil) were the most effective at reducing lung nodules. These fish oil-containing diets increased plasma levels of the ketone body, β-hydroxybutyrate, while reducing both insulin and 8-isoprostane in plasma and bronchoalveolar interleukin-12 and lung PGE2 levels. After only 2 weeks on this diet, the levels of γ-H2AX were significantly reduced, 24 hours after NNK treatment. Housing these mice in two-tiered rat cages with exercise wheels led to similar mouse weights on the different diets, whereas keeping mice in standard mouse cages led to both significant weight differences between the low-CHO, soy protein, fish oil diet and Western diet and substantially more lung nodules than in the two-tiered cages. Our results suggest that low-CHO, soy protein, fish oil-containing diets, together with exercise, may reduce the incidence of lung cancer.

HapMap-based study: CYP2A13 may be a potential key metabolic enzyme gene in the carcinogenesis of lung cancer in non-smokers

Background

The aim of this study was to evaluate the association between CYP2A13 polymorphisms and lung cancer susceptibility using the HapMap database.

Methods

A case‐control analysis of 532 subjects with lung cancer and 614 controls with no personal history of the disease was performed. The tag SNPs rs1645690 and rs8192789 for CYP2A13 were selected, and the genetic polymorphisms were confirmed experimentally through real‐time PCR, cloning, and sequencing assay.

Results

SNP frequency in this study was consistent with the HapMap Project database of Han‐Chinese and lung cancer risk was associated with CYP2A13 polymorphisms in non‐smokers. CYP2A13 shares a 93.5% identity with CYP2A6 in the amino acid sequence and the homologous sequences may interfere with the study of SNPs of CYP2A13.

Conclusions

CYP2A13 may be a potential key metabolic enzyme gene in the carcinogenesis of lung cancer in non‐smokers. The common polymorphisms of CYP2A13 may be candidate biomarkers for lung cancer susceptibility in Han‐Chinese.

Different inhibitory potential of sex hormones on NNK detoxification in vitro: A possible explanation for gender-specific lung cancer risk

Smoking women are probably at a higher risk to develop lung cancer than men. Different explanations exist for these findings, a gender-specific impairment of tobacco carcinogen metabolism being one of them. In this study, we examined the inhibition of NNK reduction to NNAL, the first and most important detoxication step of this tobacco-specific carcinogen. It is mediated by different carbonyl reductases of the SDR (CBR1 and 11βHSD1) and AKR (AKR1B10, AKR1C1, AKR1C2 and AKR1C4) superfamilies. Inhibition constants of NNK reduction were determined with male (testosterone) and female (estradiol, progesterone) sex hormones and the contraceptives ethinylestradiol and drospirenone in A549 cells and with purified enzymes. Female sex hormones turned out to be stronger inhibitors than testosterone. The gestagen progesterone and its synthetic derivative drospirenone are the strongest inhibitors with Ki-values similar to hormone levels in pregnant women or women using hormonal contraceptives. Therefore, pregnancy or hormonal contraception may commit these women as high risk groups. The results of this study support the hypothesis that women bear a higher lung cancer risk when smoking because of female sex hormones acting as inhibitors of NNK detoxication.

Dosimetry for lung tumorigenesis induced by urethane, 4-(N-methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone (NNK), and benzo[a]pyrene (B[a]P) in A/JJmsSlc mice

Some chemicals are known to be lung carcinogens in rodents. While many studies using two-stage models have administered medium or high doses to mice, few have tested lower doses. The dose dependence of urethane, 4-(N-methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone (NNK), and benzo[a]pyrene (B[a]P), three well-known lung carcinogens at high doses, has not been sufficiently reported in lower dose ranges. Our study evaluated the tumorigenicity of urethane, NNK, and B[a]P at 26 weeks after a single intraperitoneal administration of each compound within medium to low dose in male and/or female A/JJmsSlc (A/J) mice. Dose-dependent tumorigenesis was demonstrated histopathologically for the three compounds. These results suggested that the tumorigenicity of these chemicals is dose dependent in A/J mice, even at lower doses than previously reported.

Sex-related differences of urethane and sodium valproate effects on Ki-67 expression in urethane-induced lung tumors of mice

The aim of the present study was to evaluate sex differences in tumorigenesis by assessing the number of Ki-67-positive cells [Ki-67(+)] in urethane-induced mice lung tumors and the effect of sodium valproate (NaVP) in BALB/c mice. Gonad-intact and gonadectomized female and male mice were divided into the following groups: i) Treated with urethane, ii) treated with urethane and NaVP and iii) gonad-intact or gonadectomized control. Urethane (total 50 mg/mouse) was injected intraperitoneally. The NaVP 0.4% solution was administered orally for 6 months. Histologically, lung tumors were divided into adenomas and adenocarcinomas and assessed immunohistochemically using antibodies against Ki-67. The Ki-67(+) was calculated per one mm² of a tumor. In adenomas, Ki-67(+) in the urethane-treated gonad-intact males was significantly higher than in females (P=0.001) and in castrated males (P<0.01); Ki-67(+) in adenomas of the urethane-treated gonad-intact males was significantly higher than in urethane-NaVP-treated ones (P<0.04). No significant differences were found in analogous female groups. In adenocarcinomas, Ki-67(+) in urethane-treated gonad-intact males was significantly higher than in females and gonadectomized mice of both sexes (P<0.001), and in ovariectomized females was significantly higher than in ovary-intact group (P=0.01). A significantly higher number of Ki-67(+) cells were observed in gonad-intact adenocarcinomas of the urethane-NaVP-treated females compared with the urethane-treated ones (P<0.001). Comparing between urethane-NaVP-treated gonadectomized males and females in adenocarcinomas, determined that Ki-67(+) was significantly lower in females (P=0.005). In adenocarcinomas, Ki-67(+) in urethane-NaVP-treated gonadectomized males and females was significantly lower than in gonad-intact mice of the same sex (P<0.001). In summary, gonadectomy with NaVP treatment decreased Ki-67(+) in adenocarcinomas for mice of both sexes. The results of the present study indicate sex-related differences in mice lung tumorigenesis, and a sex-related effect of NaVP on progression in urethane-induced BALB/c mice lung tumors.

Sodium Valproate Enhances the Urethane-Induced Lung Adenomas and Suppresses Malignization of Adenomas in Ovariectomized Female Mice

In the present study, the possible effect of sodium valproate (NaVP) on urethane-induced lung tumors in female mice has been evaluated. BALB/c mice (n = 60; 4-6 weeks old, females) were used in the following groups: (1) urethane-treated; (2) urethane-NaVP-treated; (3) only NaVP-treated; (4) control. In the same groups, ovariectomized female mice (n = 60) were investigated. Urethane was given intraperitoneally, with a total dose of 50 mg/mouse. In NaVP-treated mice groups, 0.4% aqueous solution of NaVP was offered to mice ad libitum. The duration of the experiment was 6 months. The number of tumors per mouse in ovariectomized mice and in those treated with urethane and NaVP was significantly higher than in mice treated with urethane only (8.29 ± 0.58 versus 6.0 ± 0.63, p < 0.02). No significant difference in the number of tumors per mouse was revealed while comparing the nonovariectomized urethane- and urethane-NaVP-treated groups (p = 0.13). A significant decrease of adenocarcinoma number in ovariectomized mice treated with a urethane-NaVP as compared with ovariectomized mice treated with urethane only was found (p = 0.031). NaVP together with low estrogen may have a protective effect on the malignization of adenomas in ovariectomized mice.

Effects of 8-methoxypsoralen on the metabolism of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone in mice

8-Methoxypsoralen (8-MOP) is a well established drug in the treatment of various skin diseases. Pretreatment of mice with 8-MOP before administration of 4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) significantly reduced the incidence of NNK-induced tumor. The present study was designed to evaluate the in vivo effects of 8-MOP on the bioactivation of NNK in mice. Decrease in the α-hydroxylation of NNK in mouse blood and tissues was observed as the most pronounced effect of 8-MOP. The catalytic property of cytochrome P450 2A5 (CYP2A5) enzyme in mice was determined by the coumarin 7-hydroxylation reaction, suggesting that 8-MOP produced remarkable inhibition on CYP2A5 in female C57BL/6 mice. These results implied that 8-MOP could prevent NNK-induced mutagenesis and tumorigenesis in mice through the inhibition of NNK α-hydroxylation, which may be achieved through the effect of 8-MOP on the bioactivities of CYP2A5.

Long-Term Chronic Toxicity and Mesothelial Cell Reactions Induced by Potassium Octatitanate Fibers (TISMO) in the Left Thoracic Cavity in A/J Female Mice

The present study was conducted to examine the chronic effects of potassium octatitanate fibers (trade name TISMO; chemical formula K2O·6TiO2) on the mouse lung and thoracic cavity. This method of infusion was employed to examine the direct effects of the fibers to the pleura. In the present study, 52- and 65-week experiments were employed to examine the long-term chronic effects after infusion of fiber-shaped TISMO into the thoracic cavities of A/J mice. Following this infusion, TISMO fibers were observed in the alveoli, indicating penetration through the visceral pleura. The additional histopathological detection of TISMO fibers in the liver, spleen, kidneys, ovary, heart, bone marrow, and brain of TISMO-infused mice indicated migration of the fibers out from the thoracic cavity. Atypical mesothelial cells with severe pleural proliferation were observed, but malignant mesotheliomas were not detected. This study demonstrated that intrathoracic infusion of TISMO fiber did not cause malignant mesothelioma but did cause severe chronic inflammation and proliferation of pleural mesothelial cells.

Evidence supporting product standards for carcinogens in smokeless tobacco products

Smokeless tobacco products sold in the United States vary significantly in yields of nicotine and tobacco-specific nitrosamines (TSNA). With the passage of the Family Smoking Prevention and Tobacco Control Act, the Food and Drug Administration now has the authority to establish product standards. However, limited data exist determining the relative roles of pattern of smokeless tobacco use versus constituent levels in the smokeless tobacco product in exposure of users to carcinogens. In this study, smokeless tobacco users of brands varying in nicotine and TSNA content were recruited from three different regions in the U.S. Participants underwent two assessment sessions. During these sessions, demographic and smokeless tobacco use history information along with urine samples to assess biomarkers of exposure and effect were collected. During the time between data collection, smokeless tobacco users recorded the amount and duration of smokeless tobacco use on a daily basis using their diary cards. Results showed that independent of pattern of smokeless tobacco use and nicotine yields, levels of TSNA in smokeless tobacco products played a significant role in carcinogen exposure levels. Product standards for reducing levels of TSNA in smokeless tobacco products are necessary to decrease exposure to these toxicants and potentially to reduce risk for cancer.