Fish oil supplementation inhibits NNK-induced lung carcinogenesis in the A/J mouse

Fat intake modifies association between cigarette smoking and lung cancer in a prospective cohort study: A potential explanation for the lung cancer paradox

BACKGROUND & AIMS

It remains unclear why the association between cigarette smoking and lung cancer was substantially stronger in Western countries than in Asian countries. As experimental studies have revealed that fat intake modulates tobacco carcinogen metabolism and the growth of transplanted or carcinogen-induced lung tumors in mice, the present study sought to investigate whether the association between cigarette smoking and lung cancer was modified by intake of total fat and types of fat (saturated, monounsaturated, and polyunsaturated fats) in the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial.

METHODS

During a median follow-up of 8.9 years, 1,425 cases of lung cancer were documented from 100,864 participants eligible for the present analysis. Cox proportional hazards regression was used to calculate hazard ratios (HR) and 95% confidence intervals (CI).

RESULTS

After adjustment for established or suspected confounders, the strength of the association between cigarette smoking and lung cancer was remarkably larger among individuals with high fat intake. HRs (95% CIs) comparing current with never smokers were 23.0 (13.4, 39.6), 32.7 (20.3, 52.8), and 59.8 (30.2, 118.2) for the tertile 1 (≤13.48 g/day), tertile 2 (13.49-21.89 g/day), and tertile 3 (≥21.90 g/day) of saturate fat intake, respectively. A similar pattern of the non-significant interaction was observed when the accumulated amount of cigarette smoking (1-19, 20-39, and ≥40 vs. 0 pack-years) was entered into the regression models.

CONCLUSIONS

The present study showed that lung cancer risk associated with both the status and accumulated amount of cigarette smoking was remarkably stronger in individuals with high intakes of fat, particularly saturated fat. However, this interaction was not statistically significant and thus warrants further investigations in other studies.

Aspirin-Triggered Resolvin D1 Reduces Chronic Dust-Induced Lung Pathology without Altering Susceptibility to Dust-Enhanced Carcinogenesis

Simple Summary

Farm workers are at an increased risk of developing acute and chronic lung inflammatory diseases from their everyday exposure to organic dust. Previous investigations have examined the inflammatory effects in mice from single and repetitive exposure to dust from swine confinement facilities, however, no study has explored these effects in a chronic model. To address this research gap, we established a chronic dust exposure mouse model of lung tumorigenesis that was also used to measure the efficacy of omega-3 fatty acid-derived lipid mediators as therapeutics for mitigating these induced responses. Our results from these investigations are the first to evaluate the chronic inflammatory, and carcinogenic effects of these dusts, as well as identify a potential therapeutic strategy for mitigating the inflammatory effects by using an omega-3 fatty acid-derived bioactive lipid mediator.

Abstract

Lung cancer is the leading cause of cancer-related deaths worldwide, with increased risk being associated with unresolved or chronic inflammation. Agricultural and livestock workers endure significant exposure to agricultural dusts on a routine basis; however, the chronic inflammatory and carcinogenic effects of these dust exposure is unclear. We have developed a chronic dust exposure model of lung carcinogenesis in which mice were intranasally challenged three times a week for 24 weeks, using an aqueous dust extract (HDE) made from dust collected in swine confinement facilities. We also treated mice with the omega-3-fatty acid lipid mediator, aspirin-triggered resolvin D1 (AT-RvD1) to provide a novel therapeutic strategy for mitigating the inflammatory and carcinogenic effects of HDE. Exposure to HDE resulted in significant immune cell influx into the lungs, enhanced lung tumorigenesis, severe tissue pathogenesis, and a pro-inflammatory and carcinogenic gene signature, relative to saline-exposed mice. AT-RvD1 treatment mitigated the dust-induced inflammatory response but did not protect against HDE + NNK-enhanced tumorigenesis. Our data suggest that chronic HDE exposure induces a significant inflammatory and pro-carcinogenic response, whereas treatment with AT-RvD1 dampens the inflammatory responses, providing a strong argument for the therapeutic use of AT-RvD1 to mitigate chronic inflammation.

Attenuation of Polycyclic Aromatic Hydrocarbon (PAH)-Mediated Pulmonary DNA Adducts and Cytochrome P450 (CYP)1B1 by Dietary Antioxidants, Omega-3 Fatty Acids, in Mice

Numerous human and animal studies have reported positive correlation between carcinogen-DNA adduct levels and cancer occurrence. Therefore, attenuation of DNA adduct levels would be expected to suppress tumorigenesis. In this investigation, we report that the antioxidants omega 3-fatty acids, which are constituents of fish oil (FO), significantly decreased DNA adduct formation by polycyclic aromatic hydrocarbons (PAHs). B6C3F1 male mice were fed an FO or corn oil (CO) diet, or A/J male mice were pre-fed with omega-3 fatty acids eicosapentaenoic acid (EPA) and/or docosahexaenoic acid (DHA). While the B6C3F1 mice were administered two doses of a mixture of seven carcinogenic PAHs including benzo(a)pyrene (BP), the A/J mice were treated i.p. with pure benzo[a]pyrene (BP). Animals were euthanized after 1, 3, or 7 d after PAH treatment. DNA adduct levels were measured by the ³²P-postlabeling assay. Our results showed that DNA adduct levels in the lungs of mice 7 d after treatment were significantly decreased in the FO or EPA/DHA groups compared with the CO group. Interestingly, both qPCR and Western blot analyses revealed that FO, DHA and EPA/DHA significantly decreased the expression of cytochrome P450 (CYP) 1B1. CYP1B1 plays a critical role in the metabolic activation of BP to DNA-reactive metabolites. qPCR also showed that the expression of some metabolic and DNA repair genes was induced by BP and inhibited by FO or omega-3 fatty acids in liver, but not lung. Our results suggest that a combination of mechanism entailing CYP1B1 inhibition and the modulation of DNA repair genes contribute to the attenuation of PAH-mediated carcinogenesis by omega 3 fatty acids.

Zinc, ω-3 polyunsaturated fatty acids and vitamin D: An essential combination for prevention and treatment of cancers

Zinc, ω-3 polyunsaturated fatty acids (PUFAs) and vitamin D are essential nutrients for health, maturation and general wellbeing. Extensive literature searches have revealed the widespread similarity in molecular biological properties of zinc, ω-3 PUFAs and vitamin D, and their similar anti-cancer properties, even though they have different modes of action. These three nutrients are separately essential for good health, especially in the aged. Zinc, ω-3 PUFAs and vitamin D are inexpensive and safe as they are fundamentally natural and have the properties of correcting and inhibiting undesirable actions without disturbing the normal functions of cells or their extracellular environment. This review of the anticancer properties of zinc, ω-3 PUFAs and vitamin D is made in the context of the hallmarks of cancer. The anticancer properties of zinc, ω-3 PUFAs and vitamin D can therefore be used beneficially through combined treatment or supplementation. It is proposed that sufficiency of zinc, ω-3 PUFAs and vitamin D is a necessary requirement during chemotherapy treatment and that clinical trials can have questionable integrity if this sufficiency is not checked and maintained during efficacy trials.

Algae-Derived Bioactive Compounds with Anti-Lung Cancer Potential

Lung cancer is one of the major causes of death worldwide. Natural molecules with anti-lung cancer potential are of a great interest and considered as very promising alternative to substitute or enhance the efficiency of the conventional drugs. Recently, algae as source of high value-added compounds are considered as very promising source of these bioactive molecules. These are secondary metabolites that consist mainly of derivatives of peptides, carbohydrates, and lipids with various structures. Accordingly, various mechanisms by which different algae molecules demonstrate attenuation of tumor angiogenesis were stated and discussed. The mode of action of the algae bioactives is closely related to their nature and chemical structure. Furthermore, this literature review considers the synergistic effect between microalgae bioactives and conventional drugs and discuss the economic feasibility of producing microalgae bioactives at large scale to conclude with some future perspectives related to algae-based drug discovery.

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.

Effects of Physalis peruviana L on Toxicity and Lung Cancer Induction by Nicotine Derived Nitrosamine Ketone in Rats

Nicotine-derived nitrosamine ketone (NNK) is considered a key tobacco smoke carcinogen inducing lung tumors. Physalis peruviana L (harankash) is considered one plant with marked health benefits. This study aimed to evaluate Physalis peruviana L effect on the toxic effect of NNK induced lung cancer in the rats by using pulmonary histopathological, immunohistochemical and DNA flow cytometric analyses. Sixty adult male rats were divided into four groups, each consisting of fifteen animals. The first group received saline, the second received two successive toxic doses of NNK only while the third received two successive toxic doses of NNK with a single daily dose of Physalis peruviana L. The fourth group received a single daily dose of Physalis peruviana L only. Toxic doses of NNK induced hyperplasia and adenocarcinoma in the lung and positive immunoreactivity for Ki-67 and p53 staining with disturbance of the lung DNA content. Administration of Physalis peruviana L with NNK led to a mild pulmonary hyperplasia and weak expression of Ki-67 and p53 with an improvement in the lung DNA content. Physalis peruviana L may protect against NNK induced lung carcinogenesis due to its antioxidant and anti-proliferative effects.

Fish consumption and lung cancer risk: systematic review and meta-analysis

There is evidence pointing to a possible role of diet on cancer etiology. Prior studies evaluating the relationship between fish consumption and lung cancer risk reported inconclusive results. The aim of this study was to achieve a comprehensive assessment of the relationship between fish consumption and lung cancer risk through systematic review and meta-analysis. Case control and cohort studies up to September 1, 2012 about fish consumption and lung cancer risk were confirmed by an online search. Separate relative risk (RR) or odds ratio (OR) estimates with 95% confidence interval (CI) of the relationship between lung cancer risk and fish consumption level from the included articles were combined by Stata11.0 software. Publication bias was evaluated by Egger's linear regression test and funnel plot. Twenty articles (17 case-control and 3 cohort studies) comprising 8799 cases of lung cancer and 17,072 noncases were included in the final analysis. The pooled results from all studies indicated that high fish consumption was significantly associated with a decreased risk of lung cancer (pooled RR: 0.79; 95% CI: 0.69-0.92). There was heterogeneity among the studies (I(2) = 73%, P < 0.05). Pooled RR in case control and cohort studies were 0.76 (95% CI: 0.63-0.91) and 0.95 (95% CI: 0.73-1.24), respectively. Omission of any single study had little effect on the combined risk estimates. This article had no publication bias. This study identifies a significant association between fish consumption and lung cancer, confirming a protective role of fish in lung cancer. More well-designed prospective studies are required to further verify the effect of fish consumption on lung cancer.

ω-3 polyunsaturated fatty acids inhibit the proliferation of the lung adenocarcinoma cell line A549 in vitro

ω-3 polyunsaturated fatty acids (n-3 PUFA), in particular the marine-derived forms eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), have been demonstrated to affect cancer cell replication, the cell cycle and cell death. Epidemiological studies have also suggested diets rich in n-3 PUFA were inversely correlated with the development of cancer. In the present study, we explored the effects of DHA and EPA on the proliferation activity and apoptosis of the human lung adenocarcinoma cell line A549. A methyl thiazolyl tetrazolium (MTT) assay was used to detect cell proliferation, apoptosis was detected by flow cytometry and morphological analysis was determined by fluorescence microscopy and transmission electron microscopy. A549 cells were treated with different doses of DHA (40, 45, 50 and 55 µg/ml) or EPA (45, 50, 55 and 60 µg/ml) for 24, 48 and 72 h. The results demonstrated that DHA and EPA significantly suppressed the proliferation of A549 cells and induced apoptosis of A549 cells in a dose- and time-dependent manner. The apoptotic phenomenon was also confirmed by fluorescence microscopy and transmission electron microscopy. Furthermore, compared with the control, the formation of autophagosomes was clearly enhanced in DHA‑ or EPA-treated cells. In conclusion, DHA and EPA inhibited the proliferation of A549 cells and induced cell apoptosis and autophagy, which may provide new safe and effective options for the treatment of lung cancer in the future.

Stress response pathways protect germ cells from omega-6 polyunsaturated fatty acid-mediated toxicity in Caenorhabditis elegans

Polyunsaturated fatty acids serve both structural and functional roles as membrane components and precursors for a number of different factors involved in inflammation and signaling. These fatty acids are required in the human diet, although excess dietary intake of omega-6 fatty polyunsaturated fatty acids may have a negative influence on human health. In the model nematode, Caenorhabditis elegans, dietary exposure to dihomo-gamma-linolenic acid (DGLA), an omega-6 fatty acid, causes the destruction of germ cells and leads to sterility. In this study we used genetic and microscopic approaches to further characterize this phenomenon. We found that strains carrying mutations in genes involved in lipid homeostasis enhanced sterility phenotypes, while mutations reducing the activity of the conserved insulin/IGF signaling pathway suppressed sterility phenotypes. Exposure to a mild heat stress prior to omega-6 fatty acid treatment led to an adaptive or hormetic response, resulting in less sterility. Mutations in skn-1 and knockdown of genes encoding phase II detoxification enzymes led to increased sterility in the presence of dietary DGLA. Thus, detoxification systems and genetic changes that increase overall stress responses protect the germ cells from destruction. Microscopic analyses revealed that dietary DGLA leads to deterioration of germ cell membranes in the proliferative and transition zones of the developing germ line. Together, these data demonstrate that specific omega-6 polyunsaturated fatty acids, or molecules derived from them, are transported to the germ line where they disrupt the rapidly expanding germ cell membranes, leading to germ cell death.

Effect of a hyperlipidic diet rich in omegas 3, 6 and 9 on aberrant crypt formation in rat colonic mucosa

PURPOSE

To determine whether a hypercaloric and hyperlipidic diet enriched with polyunsaturated fatty acids influences the formation of aberrant crypt foci (ACF) in colonic mucosa of Wistar rats treated with azoxymethane (AOM).

METHODS

At eight weeks of life, the rats were assigned to four groups: Group I-standard diet (STD) not treated with AOM; Group II-hypercaloric and hyperlipidic diet (FED), not treated with AOM; Group III-STD, treated with AOM; Group IV-FED, treated with AOM. At 16 weeks, the animals were injected intraperitoneal with 0.9% saline solution (Group I and II) or AOM at 15 mg/Kg (Groups III and IV) once a week for two weeks. Fifteen weeks later, the animals were euthanized.

RESULTS

FED promoted weight gain in Groups II and IV compared to Groups I and III, respectively. The groups did not differ with regard to the total number of ACF. The Chi-square test revealed no predominance of the presence of foci with <4 crypts. However, foci with ≥5 crypts were proportionally more prevalent in Group III than in Group IV (p=0.043).

CONCLUSION

The administration of polyunsaturated fatty acids did not interfere with the formation of aberrant crypt foci, but reduced ACF multiplicity, exercising an attenuating effect on carcinogenesis.

Effects of dietary fish oil on the depletion of carcinogenic PAH-DNA adduct levels in the liver of B6C3F1 mouse

Many carcinogenic polycyclic aromatic hydrocarbons (PAHs) and their metabolites can bind covalently to DNA. Carcinogen-DNA adducts may lead to mutations in critical genes, eventually leading to cancer. In this study we report that fish oil (FO) blocks the formation of DNA adducts by detoxification of PAHs. B6C3F1 male mice were fed a FO or corn oil (CO) diet for 30 days. The animals were then treated with seven carcinogenic PAHs including benzo(a)pyrene (BaP) with one of two doses via a single intraperitoneal injection. Animals were terminated at 1, 3, or 7 d after treatment. The levels of DNA adducts were analyzed by the ³²P-postlabeling assay. Our results showed that the levels of total hepatic DNA adducts were significantly decreased in FO groups compared to CO groups with an exception of low PAH dose at 3 d (P = 0.067). Total adduct levels in the high dose PAH groups were 41.36±6.48 (Mean±SEM) and 78.72±8.03 in 10⁹ nucleotides (P = 0.011), respectively, for the FO and CO groups at 7 d. Animals treated with the low dose (2.5 fold lower) PAHs displayed similar trends. Total adduct levels were 12.21±2.33 in the FO group and 24.07±1.99 in the CO group, P = 0.008. BPDE-dG adduct values at 7 d after treatment of high dose PAHs were 32.34±1.94 (CO group) and 21.82±3.37 (FO group) in 10⁹ nucleotides with P value being 0.035. Low dose groups showed similar trends for BPDE-dG adduct in the two diet groups. FO significantly enhanced gene expression of Cyp1a1 in both the high and low dose PAH groups. Gstt1 at low dose of PAHs showed high levels in FO compared to CO groups with P values being 0.014. Histological observations indicated that FO played a hepatoprotective role during the early stages. Our results suggest that FO has a potential to be developed as a cancer chemopreventive agent.

NNK-Induced Lung Tumors: A Review of Animal Model

The incidence of lung adenocarcinoma has been remarkably increasing in recent years due to the introduction of filter cigarettes and secondary-hand smoking because the people are more exposed to higher amounts of nitrogen oxides, especially 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone(NNK), which is widely applied in animal model of lung tumors. In NNK-induced lung tumors, genetic mutation, chromosome instability, gene methylation, and activation of oncogenes have been found so as to disrupt the expression profiles of some proteins or enzymes in various cellular signal pathways. Transgenic animal with specific alteration of lung cancer-related molecules have also been introduced to clarify the molecular mechanisms of NNK in the pathogenesis and development of lung tumors. Based on these animal models, many antioxidant ingredients and antitumor chemotherapeutic agents have been proved to suppress the NNK-induced lung carcinogenesis. In the future, it is necessary to delineate the most potent biomarkers of NNK-induced lung tumorigenesis, and to develop efficient methods to fight against NNK-associated lung cancer using animal models.