https://orcid.org/0000-0002-8833-662X
Abstract
The number of new diagnosed cancer cases and cancer deaths are increasing worldwide. Perfluorinated compounds (PFCs) are synthetic chemicals, which are possible inducers of cancer in human and laboratory animals. Studies showed that PFCs induce breast, prostate, kidney, liver and pancreas cancer by inducing genes being involved in carcinogenic pathways.
This study reviews the association between PFCs induced up-regulation/down-regulation of genes and signaling pathways that are important in promoting different types of cancer. To obtain chemical-gene interactions, an advanced search was performed in the Comparative Toxicogenomics Database platform.
Five most prevalent cancers were studied and the maps of their signaling pathways were drawn, and colored borders indicate significantly differentially expressed genes if there had been reports of alterations in expression in the presence of PFCs.
In general, PFCs are capable of inducing cancer in human via altering PPARα and PI3K pathways, evading apoptosis, inducing sustained angiogenesis, alterations in proliferation and blocking differentiation. However, more epidemiological data and mechanistic studies are needed to better understand the carcinogenic effects of PFCs in human.
Introduction
Cancer
Cancer is increasing worldwide and is among the four major causes of death. About 19.3 million new cancer cases and 10 million cancer deaths were reported in 2020. 1 The most prevalently diagnosed cancers are breast, lung, colorectal, prostate, and stomach cancers, respectively. Most cancer-related deaths were caused by lung, colorectal, liver, stomach, and breast cancers, respectively.1 In general, chemicals, diet, infection, radiation, heredity, physical agents, hormones, and autoimmune disease are the most significant risk factors for cancer.2The rapid development in industrialized countries is resulting in more and more production of environmental pollutants, making the role of chemical compounds in inducing cancer an item of interest. For example, air pollutants are the leading cause of lung cancer.3 There are various signaling pathways involved in the progression of cancers. These pathways include: steroid hormone and nuclear receptor, protein kinase C, Rho/ROCK, mitogen-activated protein kinase (MAPK), Notch, ErbB receptor family, angiogenic, PI3K/AKT/mTOR, Met, insulin-like growth factor receptors, Wnt/β-Catenin, Hedgehog, TGF-β and the SMAD, JAK–STAT, NF-κBandimmune signaling pathways.4
Perfluorinated compounds
Perfluorinated compounds (PFCs), as environmental pollutants, are synthetic chemicals extensively implicated in industrial compounds such as fire-fighting foams, Teflon, paint, and ink5,6 due to their unique amphiphilic properties. PFCs are comprised of a hydrophobic fluorinated carbon backbone with diverse polar terminal groups such as carboxyl, phosphonate, sulfonate, sulfonamide, and alcohol. The taught polar bond between carbon and fluorine atoms gives the fluorocarbon chain more rigidity than the hydrocarbon chain. Thus, PFCs are stable at high temperatures and persistent in the environment.7,8 PFCs mainly contaminate drinking water by contaminating groundwater.9
Perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) are among the most detected PFCs in the environment.10 For example, they have been found in aquatic systems in the Netherlands11 and in water, soil, biota, and sediment samples from the west coast of Korea.12 Studies have proven that PFCs accumulate in humans and animals over time.12–17 In the European general population, concentrations of PFOS and PFOA measured in plasma and serum blood samples were in the range of 1–116 μg/L (19 × 10−4-0.23 μM) and 0.5–40.0 μg/L (12 × 10−4-966 × 10−4 μM), respectively.13 PFOS, PFOA, and perfluorohexanesulphonic acid (PFHxS) with concentrations of 31.1, 11.6, and 2 μg/L (62.18 × 10−3, 28.01 × 10−3, and 5 × 10−3 μM), respectively were measured in serum samples collected from residents of United States and Peru.15 Olsen et al. (2003) reported mean PFOS and PFOA concentrations of 1.32 and 1.78 ppm (2.64 and 4.40 μM), respectively, in the blood serum of workers with occupational exposure to these chemicals.14 In addition, PFCs (such as perfluorobutanesulfonic acid (PFBS) and PFHxS have been detected in women’s blood serum and also in drinking water and groundwater in Sweden.16 Besides their high accumulation potential, PFCs are slowly excreted from the human body with estimated half-lives of 3.4, 2.7, and 5.3 years for PFOS, PFOA, and PFHxS, respectively.18 This means that continuous life-long PFC exposure can result in harmful concentrations due to the constant increase of body burden in the human body.
Toxic effects of PFCs
In experimental studies, both acute and chronic exposures to PFCs have been shown to cause hepatotoxicity, neurotoxicity, immunotoxicity, reproduction and endocrine system toxicity, and development retardation in animal models of vertebrates such as rodents and zebrafish embryos (ZFEs).19,20 For humans, Mancini et al. (2019) showed a linear association between the detected PFOS serum concentrations (17.3–85.3 ng/mL (0.03–0.17 μM)) and estrogen-dependent breast cancer in postmenopausal women.21 Immunotoxic effects in male and female mice exposed to PFOS over 28 days have been shown by Peden-Adams et al. (2008).22 Also, an increased apoptosis in hippocampal cells was observed in mice after exposure to 2.15 and 10.75 mg/kg PFOS.23
Studies showed several toxic effects of PFCs in lab animals.24 However, PFCs health outcomes in humans are not well understood yet. Human studies showed different harmful effects of long-term PFCs exposure, such as dyslipidemia,25,26 immunotoxicity,27 and ulcerative colitis.28
There are conflicting data on the carcinogenic effects of PFCs. For instance, cancers of the prostate, kidney, testis, and thyroid have been reported by Mandel et al. to be associated with exposure to perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) in humans.29 However, the authors indicated that there is “limited evidence” for PFOA carcinogenicity with a positive link towards kidney and testis cancers; therefore, they are “possibly carcinogenic,” as stated in the PFOA IARC monograph.29 Studies showed that the pancreas is one of the targets of PFOA, which results in pancreatic acinar cell hyperplasia.30,31 Biegel et al. (2001) also reported an increase in hepatocellular adenoma, testicular Leydig cell adenoma, pancreatic acinar cell adenoma, pancreatic acinar cell adenoma or carcinoma, and Leydig cell hyperplasia in rats being fed with PFOA for two years.30 Studies have shown that PFOA damage in the liver promotes hepatocarcinogenesis in rodents.32 PFOA and perfluorodecanoic acid (PFDA) increased liver weight, peroxisome proliferation, and oxidative DNA damage in male rats being fed with these chemicals (0.02% PFOA or 0.01% PFDA) for two weeks.33 Abdellatif et al. (1990) reported that PFOA induces liver carcinogenesis in rats via inducing peroxisome proliferation.34On the other hand, a case-cohort study in the Danish general population reported an insignificant association between PFOA and pancreatic cancer.35 They reported no association between PFOA and PFOS serum concentrations and prostate, bladder, pancreatic, or liver cancer.35
A link between PFOA and tumors has been shown in rats fed with PFOAs, which resulted in an increased number of Leydig cells, testosterone-producing cells, in them.32,36 It has been reported that the mechanisms of carcinogenicity of PFOAs are hormone-related and are not DNA-damaging.32 In other words, PFOAs, as non-genotoxic carcinogens, disrupt the cellular processes and pathways rather than directly affecting the DNA. Understanding the underlying mechanisms of action in these pathways would allow us to prevent such cancers. PFOS has been associated with increasing the risks of liver adenomas, while PFOA has been associated with increased risks of liver, pancreas, and testis adenomas. Oral exposure to PFOA in rats has been evaluated in its IARC monograph. As shown in this monograph, the incidence rates of various malignancies were increased by an increased dose of PFOA in the study groups. The list of malignancies with increased risk after exposure includes Leyding cell adenoma, Mammary gland fibroadenoma, Hepatocellular carcinoma or adenoma, and pancreatic acinar cell carcinoma or adenoma. However, the risk of hepatic cancers (all) was lower in the intervention groups with more PFOA exposure.37 However, residence in areas with contaminated water by PFOA did not increase the risks of any cancers in humans, and limited data is available to interpret the association between PFOA-contaminated water consumption and kidney and testicular cancer risks.38
Methods
To obtain chemical-gene interactions, an advanced search was performed in the Comparative Toxicogenomics Database (CTD; http://ctdbase.org/) platform. This platform describes differentially expressed genes (DEGs) in humans and animals after exposure to a a variety of chemical substances. After downloading a full database of chemical-gene interactions, the data were filtered in Microsoft Excel 2013 for PFC nomenclature. The obtained results were searched in the Kyoto Encyclopedia of Genes and Genomes (KEGG) database for any direct involvement in the known pathways of cancers. This resulted in a table comprised of DEGs in pathways in cancers when exposed to different PFCs (Fig. 1). Afterwards, using KEGG pathways and its search tool, each of the DEGs were searched through the pathway and was highlighted as up-regulated or down-regulated in to present a systemic view of interactions.
Pathways in cancer when exposed to different PFCs.
A thorough scholarly search was performed to establish the known involvement of PFCs in different cancers. The keywords malignancy, cancer, neoplasm, tumor, and each one of PFCs were searched in Google Scholar to develop a structure for further analysis.
Meanwhile, to obtain detailed predictions of the potential roles of PFCs in cancers, the top five cancers were searched through KEGG to reveal their detailed pathway map. Each map was searched for the selected DEGs and each DEG was highlighted as up-regulated or down-regulated after exposure to PFCs.
Results
DEGs in cancer related pathways after exposure to PFCs
Figure 1 illustrates pathways involved in cancer (derived from KEGG’s website)39–41 and the differentially expressed genes (DEGs) when exposed to different PFCs.
Breast cancer
Cases of bc are increasing worldwide every year. However, the causing factors are still not well recognized. According to the World Cancer Statistics, bc was the most diagnosed malignancy in 2020.1PFCs are among the potential bc-related factors that need to be investigated.
Various epidemiological studies have been reported to investigate the correlation between the PFCs exposure and increased risks of bc (Table 1). A cohort study in pregnant Danish women investigated the link between perflurooctane-sulfonamide (PFOSA) or PFHxS and premenopausal breast cancer (bc) risk with a 10–15 years follow-up. They reported a weak positive association between PFOSA and bc risk. However, there was a significant association between bc and serum levels of PFOSA in the 5th quintile of the study. On the other hand, PFHxS showed an insignificant association with bc risk.24 Another case–control study was done on the Greenlandic Inuit to assess the effects of PFCs on bc.42The results showed increased bc risk with higher levels of PFOA and PFOS in the serum. A cross-sectional study found an association between bc and PFCs (PFOA, PFHS, PFOS, PFNA, and PFDE) with a positive dose–response relationship.43 A recent study on 150 Filipino women (75 bc cases and 75 controls) found significant associations with bc based on odds ratios for three PFCs, including PFDoA, PFDA, PFHxA (undecafluorohexanoic acid).44Conversely, a cohort study on APFO-exposed workers did not show any association between ammonium perfluorooctanoate (APFO) exposure and bc risk.45 A study in the USA showed an increase in fibroadenima of mammary glands in female rats fed by 300 ppm of PFOA for two years.46
Summary of epidemiologic studies of PFCs and breast cancer.
| Study nature | Studied subjects | PFC studied | Cancer type | Results | Reference |
|---|---|---|---|---|---|
| Case–control | 31 Inuit women with bc and 115 control subjects | PFOA, PFOS, and sums of PFAS groups | bc | A significant association between serum PFC levels and the risk of bc. The level of serum PFCs, might be a risk factor in the development of bc in Greenlandic Inuit. | 42 |
| Cohort incidence study (case-cohort study design) | 250 cases of pregnant bc and 233 controls | PFHxS, PFNA, PFOA, PFOS, PFOSA, and sums of PFAS groups | Premenopausal bc | Weak positive and negative insignificant associations were found between bc risk and levels of PFOSA PFHxS, respectively. This study does not provide convincing evidence for a causal link between PFAS exposures and premenopausal bc risks 10–15 years later | 24 |
| Cross-Sectional | 11,631 United States residents | PFOA, PFHS, PFOS, PFNA, PFDE | Cancers related to deregulation of estrogen receptors (breast, prostatic, uterine, and ovarian cancers) | PFCs were associated with increased odds of ovarian and breast cancers with a positive dose–response relationship. PFOA was more correlated with bc and PFHS more with ovarian cancer. | 43 |
| Case–control | 75 bc cases and 75 controls | PFDoA, PFDA, PFHxA | bc | Three PFAS (PFDoA, PFDA, PFHxA) showed significant associations with bc in Greater Manila Area. | 44 |
| Occupational cohort mortality and incidence study | 9,027 workers (4,668 at exposed plant and 4,359 at unexposed plant); 1,145 deaths at exposed plant and 1,824 at unexposed plant | Primarily PFOA | Cancer categories including all cancers, liver, pancreas, prostate, kidney, breast, and bladder | No markedly elevated SMRs for any cancer site relative to Minnesota population -In comparison with unexposed plant [HRs (95% CIs) relative to unexposed workers]: bladder cancer mortality (8 total deaths) 1st and 2nd exposure quartiles 1.03 (0.27–3.96), 3rd and 4th exposure quartiles 1.96 (0.63–6.15); bladder cancer incidence (40 total cases) 1st exposure quartile 0.81 (0.36–1.81), 2nd exposure quartile 0.78 (0.033–1.85), 3rd exposure quartile 1.5 (0.8–2.81), 4th exposure quartile 1.66 (0.86–3.18) | 45 |
| Case–control | 902 bc cases and 858 controls (California teachers) | Serum concentrations of MeFOSAA, PFHxS, PFNA, PFOA, PFOS, PFUnDA | bc | No association with case status for PFOA, PFOS or other or any of the other examined types of PFAS | 47 |
| Study nature | Studied subjects | PFC studied | Cancer type | Results | Reference |
|---|---|---|---|---|---|
| Case–control | 31 Inuit women with bc and 115 control subjects | PFOA, PFOS, and sums of PFAS groups | bc | A significant association between serum PFC levels and the risk of bc. The level of serum PFCs, might be a risk factor in the development of bc in Greenlandic Inuit. | 42 |
| Cohort incidence study (case-cohort study design) | 250 cases of pregnant bc and 233 controls | PFHxS, PFNA, PFOA, PFOS, PFOSA, and sums of PFAS groups | Premenopausal bc | Weak positive and negative insignificant associations were found between bc risk and levels of PFOSA PFHxS, respectively. This study does not provide convincing evidence for a causal link between PFAS exposures and premenopausal bc risks 10–15 years later | 24 |
| Cross-Sectional | 11,631 United States residents | PFOA, PFHS, PFOS, PFNA, PFDE | Cancers related to deregulation of estrogen receptors (breast, prostatic, uterine, and ovarian cancers) | PFCs were associated with increased odds of ovarian and breast cancers with a positive dose–response relationship. PFOA was more correlated with bc and PFHS more with ovarian cancer. | 43 |
| Case–control | 75 bc cases and 75 controls | PFDoA, PFDA, PFHxA | bc | Three PFAS (PFDoA, PFDA, PFHxA) showed significant associations with bc in Greater Manila Area. | 44 |
| Occupational cohort mortality and incidence study | 9,027 workers (4,668 at exposed plant and 4,359 at unexposed plant); 1,145 deaths at exposed plant and 1,824 at unexposed plant | Primarily PFOA | Cancer categories including all cancers, liver, pancreas, prostate, kidney, breast, and bladder | No markedly elevated SMRs for any cancer site relative to Minnesota population -In comparison with unexposed plant [HRs (95% CIs) relative to unexposed workers]: bladder cancer mortality (8 total deaths) 1st and 2nd exposure quartiles 1.03 (0.27–3.96), 3rd and 4th exposure quartiles 1.96 (0.63–6.15); bladder cancer incidence (40 total cases) 1st exposure quartile 0.81 (0.36–1.81), 2nd exposure quartile 0.78 (0.033–1.85), 3rd exposure quartile 1.5 (0.8–2.81), 4th exposure quartile 1.66 (0.86–3.18) | 45 |
| Case–control | 902 bc cases and 858 controls (California teachers) | Serum concentrations of MeFOSAA, PFHxS, PFNA, PFOA, PFOS, PFUnDA | bc | No association with case status for PFOA, PFOS or other or any of the other examined types of PFAS | 47 |
Summary of epidemiologic studies of PFCs and breast cancer.
| Study nature | Studied subjects | PFC studied | Cancer type | Results | Reference |
|---|---|---|---|---|---|
| Case–control | 31 Inuit women with bc and 115 control subjects | PFOA, PFOS, and sums of PFAS groups | bc | A significant association between serum PFC levels and the risk of bc. The level of serum PFCs, might be a risk factor in the development of bc in Greenlandic Inuit. | 42 |
| Cohort incidence study (case-cohort study design) | 250 cases of pregnant bc and 233 controls | PFHxS, PFNA, PFOA, PFOS, PFOSA, and sums of PFAS groups | Premenopausal bc | Weak positive and negative insignificant associations were found between bc risk and levels of PFOSA PFHxS, respectively. This study does not provide convincing evidence for a causal link between PFAS exposures and premenopausal bc risks 10–15 years later | 24 |
| Cross-Sectional | 11,631 United States residents | PFOA, PFHS, PFOS, PFNA, PFDE | Cancers related to deregulation of estrogen receptors (breast, prostatic, uterine, and ovarian cancers) | PFCs were associated with increased odds of ovarian and breast cancers with a positive dose–response relationship. PFOA was more correlated with bc and PFHS more with ovarian cancer. | 43 |
| Case–control | 75 bc cases and 75 controls | PFDoA, PFDA, PFHxA | bc | Three PFAS (PFDoA, PFDA, PFHxA) showed significant associations with bc in Greater Manila Area. | 44 |
| Occupational cohort mortality and incidence study | 9,027 workers (4,668 at exposed plant and 4,359 at unexposed plant); 1,145 deaths at exposed plant and 1,824 at unexposed plant | Primarily PFOA | Cancer categories including all cancers, liver, pancreas, prostate, kidney, breast, and bladder | No markedly elevated SMRs for any cancer site relative to Minnesota population -In comparison with unexposed plant [HRs (95% CIs) relative to unexposed workers]: bladder cancer mortality (8 total deaths) 1st and 2nd exposure quartiles 1.03 (0.27–3.96), 3rd and 4th exposure quartiles 1.96 (0.63–6.15); bladder cancer incidence (40 total cases) 1st exposure quartile 0.81 (0.36–1.81), 2nd exposure quartile 0.78 (0.033–1.85), 3rd exposure quartile 1.5 (0.8–2.81), 4th exposure quartile 1.66 (0.86–3.18) | 45 |
| Case–control | 902 bc cases and 858 controls (California teachers) | Serum concentrations of MeFOSAA, PFHxS, PFNA, PFOA, PFOS, PFUnDA | bc | No association with case status for PFOA, PFOS or other or any of the other examined types of PFAS | 47 |
| Study nature | Studied subjects | PFC studied | Cancer type | Results | Reference |
|---|---|---|---|---|---|
| Case–control | 31 Inuit women with bc and 115 control subjects | PFOA, PFOS, and sums of PFAS groups | bc | A significant association between serum PFC levels and the risk of bc. The level of serum PFCs, might be a risk factor in the development of bc in Greenlandic Inuit. | 42 |
| Cohort incidence study (case-cohort study design) | 250 cases of pregnant bc and 233 controls | PFHxS, PFNA, PFOA, PFOS, PFOSA, and sums of PFAS groups | Premenopausal bc | Weak positive and negative insignificant associations were found between bc risk and levels of PFOSA PFHxS, respectively. This study does not provide convincing evidence for a causal link between PFAS exposures and premenopausal bc risks 10–15 years later | 24 |
| Cross-Sectional | 11,631 United States residents | PFOA, PFHS, PFOS, PFNA, PFDE | Cancers related to deregulation of estrogen receptors (breast, prostatic, uterine, and ovarian cancers) | PFCs were associated with increased odds of ovarian and breast cancers with a positive dose–response relationship. PFOA was more correlated with bc and PFHS more with ovarian cancer. | 43 |
| Case–control | 75 bc cases and 75 controls | PFDoA, PFDA, PFHxA | bc | Three PFAS (PFDoA, PFDA, PFHxA) showed significant associations with bc in Greater Manila Area. | 44 |
| Occupational cohort mortality and incidence study | 9,027 workers (4,668 at exposed plant and 4,359 at unexposed plant); 1,145 deaths at exposed plant and 1,824 at unexposed plant | Primarily PFOA | Cancer categories including all cancers, liver, pancreas, prostate, kidney, breast, and bladder | No markedly elevated SMRs for any cancer site relative to Minnesota population -In comparison with unexposed plant [HRs (95% CIs) relative to unexposed workers]: bladder cancer mortality (8 total deaths) 1st and 2nd exposure quartiles 1.03 (0.27–3.96), 3rd and 4th exposure quartiles 1.96 (0.63–6.15); bladder cancer incidence (40 total cases) 1st exposure quartile 0.81 (0.36–1.81), 2nd exposure quartile 0.78 (0.033–1.85), 3rd exposure quartile 1.5 (0.8–2.81), 4th exposure quartile 1.66 (0.86–3.18) | 45 |
| Case–control | 902 bc cases and 858 controls (California teachers) | Serum concentrations of MeFOSAA, PFHxS, PFNA, PFOA, PFOS, PFUnDA | bc | No association with case status for PFOA, PFOS or other or any of the other examined types of PFAS | 47 |
Mutations in genes (such as BRCA1 and BRCA2)48 and increased levels of steroid hormones are the known factors causing bc, whereas studies have shown that PFOA is involved in the disruption of both. PFOA has changed the levels of reproductive hormones in humans, rodents, and zebrafish (embryos).49–51 In a study, feeding male and female rats with PFOA for two years in the laboratory resulted in non-neoplastic lesions in mammary glands in the females. The same procedure in another study resulted in an increased rate of mammary fibroadenomas in rats.52 White et al. (2007) showed that feeding mice with PFOA caused a delay in the differentiation of mammary glands in damsand female offsprings.53 In addition, mammary fibroadenoma risk was significantly increased in females treated with both low (30 ppm) and high doses (300 ppm) of APFO.54
Mechanisms involved in PFCs-induced breast cancer in human are listed in Table 2. bc types can be categorized into three major groups based on cell receptors: estrogen receptor-positive (ER+), progesterone receptor positive (PR+), and human epidermal growth factor receptor 2 positive (HER2+), which is also known as erythroblastic oncogene b (ErbB2).4 Estrogen receptor 1 (ESR1) encodes estrogen receptor α (ERα), which is elevated in bc.55 Nearly 70% of BCs are ER+, a condition in which the ER levels are increased; therefore, inhibition of ER is a choice of treatment.56 Steroid hormones bind to the estrogen hormone receptor which is a nuclear receptor and results in gene expression modulation.4 Studies showed that PFOA increases the activity of ESR1 by binding to its protein.57 Both PFOA and PFOS have been reported to increase the level of ESR1 expression in zebrafish.58–60 However, Behr et al. (2018) indicated that PFCs do not affect the expression level of ESR1 in human cell lines (MCF-7, H295R, LNCaP, MDA-kb2).61 1H,1H,2H,2H-perfluorooctan-1-ol (6:2 FTOH) is another PFC that can be found in food packaging, such as fast-food packages.62 Maras et al. (2006) showed that exposure to 6:2 FTOH, 8:2 FTOH, and PFOA resulted in ESR1 up-regulation in MCF-7 cells, while PFOS resulted in down-regulation of ESR1.63 ErbB2 is interlinked with estradiol, involved in cell proliferation, and up-regulated in bc.64 Maras et al. (2006) showed that ErbB2 was down-regulated after exposure to 6:2 FTOH, 8:2 FTOH and PFOA.63 Our data analysis also confirms that PFOA decreases the expression of ErbB2.
Mechanisms involved in PFCs-induced breast cancer in human.
| PFCs | Cell line | Concentration | Mechanism of tumorigenic activity | Reference |
|---|---|---|---|---|
| 6:2 FTOH, and 8:2 FTOH | MCF-7 | 10–30 μM | Up-regulation of trefoil factor 1, progesterone receptor, and PDZK1 and down-regulation of ERBB2 gene expression. Small up-regulation of the estrogen receptor as a consequence of exposures to 6:2 FTOH or 8:2 FTOH. | 63 |
| PFOA | MDA-MB-231 | ≥5 nM | PFOA can stimulate bc cells invasion and up-regulate matrix metalloproteinase-2/−9 expression mediated by activating NF-κB. | 65 |
| PFOS | MCF-10A | 10 | Promotes proliferation through accelerating G0/G1-to-S phase transition of the cell cycle. Altering cyclin D1, CDK6, P27, P53, ERK. Inducing PPARα. Stimulates cell migration and invasion by reducing the levels of E-cadherin, occluding, and β-integrin | 66,67 |
| PFOA | MCF-10A | 100 μM | Promotes proliferation through accelerating G0/G1-to-S phase transition of the cell cycle. Altering cyclin D1, CDK6, P27, P53, ERK. Inducing PPARα. Stimulates cell migration and invasion by reducing the levels of E-cadherin, occluding, and β-integrin. | 67,68 |
| PFHxS | MCF-10A | at 100 μM concentration | Affecting cyclin D1, CDK6, P27, P53, ERK. Inducing PPARα. Altering histone modifications and inducing cell malignance; reducing the levels of E-cadherin and β-integrin. Promoting cell migration and invasion. | 69 |
| Binary PFOS and PFOA mixture | MCF-10A | 500 pM | Induced synergistic effects on cell proliferation mediated by PXR activation, increases cyclin D1 and CDK6/4 levels, decreases p21 and p53 levels. Regulates phosphor-Akt and β-catenin. Alteres histone modifications, epigenetic mechanisms implicated in tumorigenesis, and promotes cell migration and invasion by reducing the levels of occludin. | 70 |
| PFOA | MCF-7 | 10−12 M | Promotes cells growth by phosphorylation of Akt and activation of mTORC1. | 71 |
| PFOA | MDA-MB-231 | 100 μM | Simultaneously with stimulated migration, PFOA upregulated FA2H and activated the transcription of PPARα. | 72 |
| PFCs | Cell line | Concentration | Mechanism of tumorigenic activity | Reference |
|---|---|---|---|---|
| 6:2 FTOH, and 8:2 FTOH | MCF-7 | 10–30 μM | Up-regulation of trefoil factor 1, progesterone receptor, and PDZK1 and down-regulation of ERBB2 gene expression. Small up-regulation of the estrogen receptor as a consequence of exposures to 6:2 FTOH or 8:2 FTOH. | 63 |
| PFOA | MDA-MB-231 | ≥5 nM | PFOA can stimulate bc cells invasion and up-regulate matrix metalloproteinase-2/−9 expression mediated by activating NF-κB. | 65 |
| PFOS | MCF-10A | 10 | Promotes proliferation through accelerating G0/G1-to-S phase transition of the cell cycle. Altering cyclin D1, CDK6, P27, P53, ERK. Inducing PPARα. Stimulates cell migration and invasion by reducing the levels of E-cadherin, occluding, and β-integrin | 66,67 |
| PFOA | MCF-10A | 100 μM | Promotes proliferation through accelerating G0/G1-to-S phase transition of the cell cycle. Altering cyclin D1, CDK6, P27, P53, ERK. Inducing PPARα. Stimulates cell migration and invasion by reducing the levels of E-cadherin, occluding, and β-integrin. | 67,68 |
| PFHxS | MCF-10A | at 100 μM concentration | Affecting cyclin D1, CDK6, P27, P53, ERK. Inducing PPARα. Altering histone modifications and inducing cell malignance; reducing the levels of E-cadherin and β-integrin. Promoting cell migration and invasion. | 69 |
| Binary PFOS and PFOA mixture | MCF-10A | 500 pM | Induced synergistic effects on cell proliferation mediated by PXR activation, increases cyclin D1 and CDK6/4 levels, decreases p21 and p53 levels. Regulates phosphor-Akt and β-catenin. Alteres histone modifications, epigenetic mechanisms implicated in tumorigenesis, and promotes cell migration and invasion by reducing the levels of occludin. | 70 |
| PFOA | MCF-7 | 10−12 M | Promotes cells growth by phosphorylation of Akt and activation of mTORC1. | 71 |
| PFOA | MDA-MB-231 | 100 μM | Simultaneously with stimulated migration, PFOA upregulated FA2H and activated the transcription of PPARα. | 72 |
Mechanisms involved in PFCs-induced breast cancer in human.
| PFCs | Cell line | Concentration | Mechanism of tumorigenic activity | Reference |
|---|---|---|---|---|
| 6:2 FTOH, and 8:2 FTOH | MCF-7 | 10–30 μM | Up-regulation of trefoil factor 1, progesterone receptor, and PDZK1 and down-regulation of ERBB2 gene expression. Small up-regulation of the estrogen receptor as a consequence of exposures to 6:2 FTOH or 8:2 FTOH. | 63 |
| PFOA | MDA-MB-231 | ≥5 nM | PFOA can stimulate bc cells invasion and up-regulate matrix metalloproteinase-2/−9 expression mediated by activating NF-κB. | 65 |
| PFOS | MCF-10A | 10 | Promotes proliferation through accelerating G0/G1-to-S phase transition of the cell cycle. Altering cyclin D1, CDK6, P27, P53, ERK. Inducing PPARα. Stimulates cell migration and invasion by reducing the levels of E-cadherin, occluding, and β-integrin | 66,67 |
| PFOA | MCF-10A | 100 μM | Promotes proliferation through accelerating G0/G1-to-S phase transition of the cell cycle. Altering cyclin D1, CDK6, P27, P53, ERK. Inducing PPARα. Stimulates cell migration and invasion by reducing the levels of E-cadherin, occluding, and β-integrin. | 67,68 |
| PFHxS | MCF-10A | at 100 μM concentration | Affecting cyclin D1, CDK6, P27, P53, ERK. Inducing PPARα. Altering histone modifications and inducing cell malignance; reducing the levels of E-cadherin and β-integrin. Promoting cell migration and invasion. | 69 |
| Binary PFOS and PFOA mixture | MCF-10A | 500 pM | Induced synergistic effects on cell proliferation mediated by PXR activation, increases cyclin D1 and CDK6/4 levels, decreases p21 and p53 levels. Regulates phosphor-Akt and β-catenin. Alteres histone modifications, epigenetic mechanisms implicated in tumorigenesis, and promotes cell migration and invasion by reducing the levels of occludin. | 70 |
| PFOA | MCF-7 | 10−12 M | Promotes cells growth by phosphorylation of Akt and activation of mTORC1. | 71 |
| PFOA | MDA-MB-231 | 100 μM | Simultaneously with stimulated migration, PFOA upregulated FA2H and activated the transcription of PPARα. | 72 |
| PFCs | Cell line | Concentration | Mechanism of tumorigenic activity | Reference |
|---|---|---|---|---|
| 6:2 FTOH, and 8:2 FTOH | MCF-7 | 10–30 μM | Up-regulation of trefoil factor 1, progesterone receptor, and PDZK1 and down-regulation of ERBB2 gene expression. Small up-regulation of the estrogen receptor as a consequence of exposures to 6:2 FTOH or 8:2 FTOH. | 63 |
| PFOA | MDA-MB-231 | ≥5 nM | PFOA can stimulate bc cells invasion and up-regulate matrix metalloproteinase-2/−9 expression mediated by activating NF-κB. | 65 |
| PFOS | MCF-10A | 10 | Promotes proliferation through accelerating G0/G1-to-S phase transition of the cell cycle. Altering cyclin D1, CDK6, P27, P53, ERK. Inducing PPARα. Stimulates cell migration and invasion by reducing the levels of E-cadherin, occluding, and β-integrin | 66,67 |
| PFOA | MCF-10A | 100 μM | Promotes proliferation through accelerating G0/G1-to-S phase transition of the cell cycle. Altering cyclin D1, CDK6, P27, P53, ERK. Inducing PPARα. Stimulates cell migration and invasion by reducing the levels of E-cadherin, occluding, and β-integrin. | 67,68 |
| PFHxS | MCF-10A | at 100 μM concentration | Affecting cyclin D1, CDK6, P27, P53, ERK. Inducing PPARα. Altering histone modifications and inducing cell malignance; reducing the levels of E-cadherin and β-integrin. Promoting cell migration and invasion. | 69 |
| Binary PFOS and PFOA mixture | MCF-10A | 500 pM | Induced synergistic effects on cell proliferation mediated by PXR activation, increases cyclin D1 and CDK6/4 levels, decreases p21 and p53 levels. Regulates phosphor-Akt and β-catenin. Alteres histone modifications, epigenetic mechanisms implicated in tumorigenesis, and promotes cell migration and invasion by reducing the levels of occludin. | 70 |
| PFOA | MCF-7 | 10−12 M | Promotes cells growth by phosphorylation of Akt and activation of mTORC1. | 71 |
| PFOA | MDA-MB-231 | 100 μM | Simultaneously with stimulated migration, PFOA upregulated FA2H and activated the transcription of PPARα. | 72 |
Pierozan et al. demonstrated that PFOS and PFOA can transform normal human breast epithelial cells (MCF-10A, an ERα-positive line) to malignant phenotype through specific mechanisms including acceleration of cell cycle by affecting different regulatory cell cycle proteins (cyclin D1, CDK6, P27, P53, ERK), induction of peroxisome proliferator-activated receptor α (PPARα), stimulation of cell migration and invasion by reducing the levels of E-cadherin, occluding, and β-integrin.66–68 It was also stated that unlike PFOS, the ER was not involved in the effects caused by PFOA in MCF-10A cells.68 In a subsequent study, they found exposure of MCF-10A with 500 pM to 500 μM undecafluorohexanoic acid (PFHxA), hexafluoropropylene oxide-dimer acid (GenX), perfluoro 3,6 dioxaoctanoic acid (PFO2OA), heptafluorobutyric acid (HFBA) and PFBS for 72 h induced no cell alteration. However, exposure to 100 μM PFHxS was shown to affect important regulatory cell-cycle proteins (cyclin D1, CDK6, p27, p53 and ERK) and induced cell proliferation, through activation of the constitutive androstane receptor (CAR) and the PPARα. PFHxS also promoted cell migration and invasion by reducing the levels of E-cadherin and β-integrin.69 Very recently, they revealed synergistic effects of very low concentrations (500 pM) of the binary PFOS and PFOA on MCF-10A proliferation mediated by pregnane X receptor (PXR) activation, an increase in cyclin D1 and CDK6/4 levels, decrease in p21 and p53 levels, and by regulation of phosphor-Akt and β-catenin. The PFAS mixture also altered histone modifications, epigenetic mechanisms implicated in tumorigenesis, and promoted cell migration and invasion by reducing the levels of occluding.70 PPARα is a nuclear hormone receptor plays key roles in regulating the biological activities of cancer cells, such as apoptosis, proliferation, and survival. Therefore, ligands of PPARs can change the behavior of cancer cells.73 Fatty acid 2-hydroxylase (FA2H), a PPARα-regulated gene in ERα-negative human MDA-MB-231 cells, can positively induce the migration of MDA-MB-231 cells.74,75 Sakai et al. (2022) analyzed the effects of PFOA on PPARα transcription and FA2H expression in relation to MDA-MB-231 cell migration and discovered that simultaneously with stimulated migration, PFOA upregulated FA2H and activated the transcription of PPARα.72 Moreover, Charazac et al. (2022) found that low concentration of PFOA (10−12 M) promotes MCF-7 (bc) cells growth through the Akt/mTORC1 pathway.71
Overall, as shown in Fig. 2, it seems that PFCs can play a dual role in bc. Our analysis expects that systemic exposure to PFCs could increase the risk of two bc subtypes; luminal A (ER+ and/or PR+, and HER2-), and to some extent luminal B (ER+ and/or PR+, and HER2+). On the other hand, systemic exposure to PFCs could be beneficial in reducing the risks of the other subtypes of bc, including HER2+ and basal-like/triple negative. Considering the different intensities of up-regulation or down-regulation of DEGs exposed to PFCs, further calculations should be performed to report predictive results in bc cases except luminal A, where the data hereby is conclusively in favor of cancer progression after PFC exposure.
Pathways in breast cancer when exposed to PFCs.
Small cell lung cancer
Lung cancer is the second most diagnosed cancer and the leading cause of cancer-related death worldwide.1 Lung cancer is divided into two types: non-small cell carcinoma (NSCC) and small cell lung carcinoma (SCLC). Compared with NSCC, SCLC is more aggressive and more capable of metastasis.76Smoking is the main cause of SCLC, the most aggressive type of lung cancer.77 Lung is one of the major organs of PFCs accumulation. Perez et al. (2013) reported an average of 263 ng/g of PFCs in the lungs.78
Evidence confirms that PFCs exposure increases the risk of lung cancer. Epidemiological studies have revealed that lung cancer accounts for the highest number of deaths among specific cancer types reported in PFOA occupational mortality studies.79 Vieira et al. (2013) found that PFOA-contaminated water districts show a 20%–30% higher risk for lung cancer, and site-specific cancer odds ratios compared to non-contaminated water districts in the same regions significantly increased.80 Very recently, Moon and Mun performed an analysis applying NHANES data to investigate the potential associations between exposures to PFOA, PFOS, PFHxS, and PFNA, and various types of cancer. The results showed significant links between PFOA and PFNA exposure and an increased risk of lung cancer.81
The findings revealed that exposure of the A549 Lung Carcinoma Cell Line to lower doses of PFOA and PFOS causes cell proliferation, whereas, at higher concentrations, the apoptosis pathway has also been identified. Therefore, exposure to PFOA and PFOS triggers lung cancinogenesis.82 It has been reported that perfluoroalkyl acids (PFAAs) exposure induces protective mitochondrial and endoplasmic reticulum autophagy in A549 lung cells. Moreover, signaling pathways analysis revealed that the compounds activated and inhibited the MAPK and the PI3K/Akt pathways, respectively, showing potency order of PFDA > PFNA > PFOA.83
MYC family is a group of proto-oncogenes including C-MYC, L-MYC, and N-MYC that are highly expressed in different cancers, such as lung, breast, colon, and ovary.84,85Increased expression levels of the MYC family in SCLC result in increased cell proliferation.86 Our data analysis shows that PFNA increases the expression level of MYC. Huang et al. (2014) showed that MYC gene expression level was elevated after exposing L-02 cells (human hepatic cells) to PFOS, which might be the reason for increased apoptosis in the cells.87 However, Ruggero (2009) indicated that MYC increases protein synthesis and decreases apoptosis, leading to the progression of cancers.88
B-cell lymphoma 2 (BCL-2) is an anti-apoptotic gene. Studies showed that BCL-2 inhibits cell death induced by C-MYC.89 Ikegaki et al. (1994) showed that BCL-2 expression was increased in five SCLC cell lines (NCI-H69, 209, 345, 378, and 510), which might result in tumorigenesis.90 Pratients with high BCL-2 expression in their tumors had longer survival in comparison with the patients without BCL-2 overexpression; however, there wasn’t a significant difference in the results.91In a study, PFOA increased apoptosis by decreasing BCL-2 protein levels and increasing Bcl2-associated X (BAX) in SMMC-7721 hepatoma cells.92 Cui et al. (2015) reported that PFOS induced apoptosis in laboratory animals, PFCs showed both up and down-regulation effects on BCL-2. Both PFOS and PFOA resulted in increased levels of BCL-2, BAX, and apoptosis in the zebrafish liver cell line.93 As BCL-2 is an anti-apoptotic protein, the increased level of apoptosis shows that its mRNA is not translated into protein. Heart tissues from weaned rats exposed to PFOS had decreased BCL-2 mRNA expression levels and increased apoptosis.94 PFNA decreased BCL-2 protein level and increased apoptosis in rat splenocytes.95 PFNA had the same effects in zebrafish larvae.96
Considering the known gene-chemical interactions and the pathway map of SCLC, it seems that overall PFCs could work in a cell-tissue-specific manner.
The down-regulation of p21 (a potent cyclin-dependent kinase inhibitor) might play protective roles against the effects of DNA damage in the progression of cells into primary SCLCs. In this stage, the overexpression of MYC would lead into dysregulation of cell cycle. However, the down-regulation of p27 combined with the up-regulation of CDK4/6 might increase the expression of RB, a tumor suppressor gene.
In cell cycle and in the transition state of primary into metastatic SCLCs, further systems biology calculations are needed to assess a conclusive analysis on the effects of PFCs in SCLC. Nevertheless, even in apoptosis, downstream DEGs are in favor of cancer progression and angiogenesis (Fig. 3).
Pathways in small SCLC progressionin the presence of studied PFCs.
Colorectal cancer
Colorectal cancer accounts for 10% of diagnosed cancers and 9.4% of cancer-related deaths.1 Epiregulin (EREG)gene expression is increased in primary and metastatic colorectal cancer.97 The EREG gene encodes epiregulin protein, one of the ligands of epidermal growth factor receptor (EGFR), increased in colorectal cancer.98 Our data analysis shows that PFNA increases the expression of EREG mRNA.
Tessmann et al. (2024) investigated the effect of PFOS exposure on the gene expression profile of intestinal tissues of mice and revealed that PFOS exposure in drinking water remarkably downregulated mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase 2 (HMGCS2), a rate-limiting ketogenic enzyme, in intestinal tissues of mice, and also led to upregulation of β-catenin, c-MYC, mTOR and FASN proteins that involved in colorectal carcinogenesis. Moreover, they proved that shRNA-mediated knockdown of HMGCS2 in a human normal intestinal cell line resulted in enhanced cell proliferation and upregulation of proteins implicated in proliferation, including cyclin D, ERK1/2, survivin, and AKT, along with an increase in lipid accumulation.99 Li et al. (2024) examined the effects of PFOS on the proliferation and migration of colorectal cancer cells and found that PFOS enhanced the growth and migration of HCT116 cells at non-cytotoxic concentrations, promoted the mRNA expression of the migration-related angiogenic cytokines vascular endothelial growth factor (VEGF) and interleukin-8 (IL-8), and activated the up-stream signal pathway PI3K/Akt-NF-κB.100 In another study, PFOA increased colorectal cancer DLD-1 cells invasiveness through activating NF-κB mediated MMP-2/-9 expression.101 Zheng et al. found PFOS and PFOA at 2 μM and 10 μM, respectively, promoted migration of three-dimensional colorectal cancer spheroids through altering epithelial-mesenchymal transition-related metabolic pathways, including fatty acid β-oxidation and synthesis of proteins, nucleotides, and lipids.102
Looking at the pathway map of colorectal cancer, it seems that PFCs affect the main nodes in certain aspects at several time points. According to the timeline of colorectal cancer, the up-regulation of MYC leads normal epithelium into dysplastic aberrant crypt foci (ACF), which are precursors of colorectal cancer. However, to convert dysplastic ACF to an early adenoma, the PI3K-Akt signaling has to be activated, while the key nodes in this pathway are down-regulated by PFCs. Although the down-regulation of ERK (a type of serine/ threonine protein kinase) decreases the oncogenic effect of K-Ras (a part of the RAS/MAPK pathway), the up-regulation of c-MYC might result in proliferation. As mentioned earlier, it should also be considered that PFC exposure might help other oncogenes to develop the carcinoma. In this instance, systems biology calculations must be performed to interpret the effects of PFC exposure on the MAPK signaling pathway. While there is no evidence of the effects of PFCs in the progression of intermediate adenomas into late adenomas, the up-regulation of BCL-2 could inhibit apoptosis in the stage of conversion of late adenoma into Carcinoma. However, PFCs play a dual role in this stage as well. While the downstream nodes in the mTOR signaling pathway are down-regulated, the up-regulation of EREG (ERG in the map) might compensate for much of the effects. Thus, systems biology calculations have to be performed here as well to gain a better analysis (Fig. 4).
Pathways in colorectal cancer progression in the presence of studied PFCs.
Prostate cancer
Prostate cancer is the fourth most prevalently diagnosed cancer and the third cause of cancer-related deaths.1 In a study, workers exposed to PFOA for 10 years showed a 3.3-fold increase in prostate cancer mortality risk compared with the control group.32 The authors suggested that reproductive hormones alteration due to the PFOAs might be the reason for their increased risk of prostate cancer. However, the study is limited by the low number of subjects in the prostate cancer group.32 Studies showed that high amounts of PFOA increase the risk of testicular cancer among adults living near a chemical plant.80 Feeding male rats with 300 ppm of PFOA for 2 years resulted in increased testicular Leydig cell adenoma.54Gilliland and Mandel (1993) showed that there was no association between the duration of exposure and cancer mortality in the workers exposed to PFOA, both in men and women.32 However, they showed a positive link between the duration of work (as the intensity of exposure) and prostate cancer.32 The risk ratio of prostate cancer for men in this study was reported to be 1.13 (95% Cl) for each year, amassing in a risk ratio of 3.3 (95%) for 10 years of work, compared with the workers of other units of the same plant without a long-term exposure to PFOAs.32 The age of subjects was positively associated with prostate cancer mortality risk.32 However, the small number of participants has been the main limitation of this study. For that, the authors have suggested considering the association between PFOA exposure and prostate cancer risk as only a hypothesis that needs further investigation.
Cyclin-dependent kinase inhibitor 1B (cdkn1b) encodes a protein (p27kip1) that functions as a cell cycle inhibitor; therefore, cdkn1b is a tumor suppressor gene.Cdkn1b is mutated in prostate cancer, leading to cdkn1b deletion and cancer progression.103 The decreased cdkn1b protein level in malignancies leads to cell proliferation.104 Studies showed that PFOS decreases the expression of the cdkn1b protein, which will result in cell proliferation and tumor progression.105
APFO is a salt of PFOA that rapidly dissociates to PFOA in physiological media. Moderate and high exposure to APFO increased the risk of prostate cancer in workers of APFO manufacturing facilities compared to cohort.106 Eriksen et al. (2009) showed an insignificant relation between serum PFOA and PFOS levels and prostate cancer risk. However, they showed an increased risk of prostate cancer for the three upper quartiles of PFOS.35
Based on our current knowledge of the DEGs, the stage of prostate cancer reveals another aspect of the long-term effects of PFCs. In the first stages, from proliferative inflammatory atrophy to prostatic intraepithelial neoplasia, the down-regulation of p27 reduces the chances of normal apoptosis and is in favor of cancer progression.
It is interesting to note that while the study has aimed to provide evidence of the underlying mechanisms of PFC carcinogenicity, they might play a protective role in the phase transition of localized into metastatic prostate cancer. Multiple nodes in the PI3K-Akt signaling pathway are down-regulated when exposed to PFCs, increasing the protective effects of tumor suppressor genes such as PTEN or NKX3.1 in leading the cell into cell cycle progression or apoptosis. However, it is worth mentioning that the up-regulation of BCL-2 might decrease the anti-apoptotic effects of PFCs in prostate cancer, making it another calculation mystery solved by systems biology analysis.
In the phase transition from metastatic into androgen-independent prostate cancer, the decreased activity in the PI3K-Akt signaling pathway might also reduce the oncogenic effects of AR when activated by other ligands, as well, by declining the risks of tumor cell survival (Fig. 5).
Pathways in prostate cancer progression in the presence of studied PFCs.
Kidney cancer
Kidneys have been reported as one of the main organs that PFCs are accumulated in. Perez et al (2013) detected high levels of PFOS in kidneys.78 Risk of kidney and testis cancer were investigated as a probable result of exposure to PFOA in the population living near DuPont Teflon-manufacturing plant in Parkersburg, West Virginia.80 A cohort study in Minnesota showed that there is no association between the ammonium salt of PFOA (APFO) exposure and kidney, prostate, or breast cancers.42 However, the risk of kidney cancer was reported to be increased with elevated PFOA exposure according to the IARC monograph.37 In addition, a study at the Dupont chemical plant in West Virginia reported an association between kidney cancer and occupational exposure to PFOA.107 Increased risk of mesothelioma and kidney cancer was also observed with increased PFOA exposure in workers of West Virginia manufacturing fluoropolymer.108 The proof for kidney cancer, presented by Barry et al. (2013)109 and Vieira et al. (2013),80 also is suggestive. Shearer et al. (2021)110 revealed a significant exposure-response trend with PFOA in a case-study, but not other PFAS. In a recent multiethnic cohort study, they reported that PFOA (among White participants) and PFNA (among African American participants) were associated with an increased risk of renal cell carcinoma.111
cdkn1b is related to renal angiomyolipoma (the most common benign tumor of the kidney), and PFOS has been reported to decrease the level of cdkn1b, which could result in cancer cell proliferation107 (Fig. 6).
Pathways in renal cell carcinoma progression in the presence of studied PFCs.
Discussion and conclusion
Cancer is among the principal causes of death with the growing number of newly diagnosed cases.1 Despite the huge number of studies regarding various causes and signaling pathways involved in both inducing and inhibiting cancer, diagnosing and curing patients suffering from malignancies is not well developed. One of the possible inducers of cancer could be PFCs. PFCs are used in various industrial applications such as emulsifiers, surfactants, Teflon, and ink.5 They are found in surface water from the ocean, soil and biota.112These chemicals have toxic effects on both human and lab animals, including zebrafish, mice, and rat.113,114 The Stockholm Convention on Persistent Organic Pollutants (POPs) added PFOS in 2009 to the list of compounds that should be banned worldwide. They also added PFOA to the list of substances to be eliminated in 2004.
To find genes and signaling pathways being affected by PFCs we did a literature survey and summarized the data in the maps using KEGG. PFOS and PFOA were the most studied compounds among all PFCs.
Little is known about different PFCs carcinogenic effects on human. Bonefeld-Jorgensen et al (2014) reported that there is no significant association between PFCs exposure and risk of bc in Danish women with 15 years follow-up in their study, which is suggested to be due to the small sample size.24 By contrast, a study in Greenland showed a positive association between PFCs serum level and bc.39 Women with genetic polymorphisms in CYP1A1 (Val) and CYP17 (A1) and high levels of serum PFOA and PFOS showed increased risk of bc.39
It has been shown that PFOA has changed the levels of reproductive hormones in humans, rodents, and zebrafish (embryos).32Studies showed that both PFOA and PFOS increase the level of ESR1 (ERα is encoded by the gene ESR1) expression in zebrafish.58–60 However, Behr et al. (2018) indicated that PFCs do not affect the expression level of ESR1 in human cell lines (MCF-7, H295R, LNCaP, MDA-kb2).61 Our analysis expects that systemic exposure to PFCs could increase the risk of two bc subtypes; Luminal A (ER+ and/or PR+, and HER2-), and to some extent Luminal B (ER+ and/or PR+, and HER2+) (Fig. 2).
The lung is one of the major organs of PFCs accumulation. Perez et al. (2013) reported an average of 263 ng/g of PFCs in the lungs.78 It has been shown that PFOS decreases the expression of the cdkn1b protein, which will result in cell proliferation and tumor progression.105 Ruggero (2009) indicated that MYC increases protein synthesis and decreases apoptosis, leading to the progression of cancers.88
Both PFOS and PFOA resulted in increased levels of BCL-2, BAX, and apoptosis in zebrafish liver cell line.93 Our data analysis shows that perfuorononanoic acid (PFNA) increases the expression of EREG mRNA. Although the down-regulation of ERK decreases the oncogenic effect of K-Ras, the up-regulation of c-MYC might result in proliferation. Studies showed that high amounts of PFOA increase the risk of testicular cancer among adults living near a chemical plant.80 Our data analysis shows that PFOS decreases the expression of cdkn1b protein, which will result in cell proliferation and tumor progression.105
The mechanism of PFCs induction or inhibition of cancer is not well understood. One suggested mechanism of PFCs-induced liver cancer is PPARα activation. PFOA is an agonist of PPARα and causes hepatocellular proliferation.42 On the other hand, one of the key pathways in cancer is apoptosis (Fig. 1). The ratio of Bax/BCL-2 determines cell apoptosis. Exposure to these PFCs results in an increased level of ROS which up-regulates p53 and then Bax, so the ratio of Bax/BCL-2 increases and results in apoptosis. 3 and 5 mg/kg/day of PFNA decreased BCL-2 and increased apoptosis-inducing factor (AIF) and TNFR1 in rat spleen, showing activation of caspase-independent apoptosis pathway.95 They also showed decreased expression of cleaved caspase3 after exposure to 5 mg/kg/day PFNA. Exposing zebrafish larvae to 0.5, 1, and 5 mg/L PFNA resulted in increased expression of p53, JNK1, and AIF decreased expression of BCL-2.96 Cui et al. (2015) exposed zebrafish liver cell lines to PFOS and PFOA and showed that they both resulted in up-regulation of p53, caspase3, BCL-2, NFκB. Bax expression was up-regulated only after exposure to PFOS. As BCL-2 is anti-apoptotic, flow cytometry showed that it is not translated into proteins, and therefore, exposure to PFOS and PFOA resulted in cell apoptosis.93 More studies are needed to find the effects of PFCs on cancer especially in finding their effects in intracellular signaling pathways.
PFOA activates the PI3K/AKT3 pathway in Gambusia affinis.115 Picomolar concentrations of PFOA cause the proliferation of prostate (DU145) and breast cancer (MCF7) cell lines by the PlexinD1 and Akt/mTORC1 pathways, respectively.71 Moreover, PFOS promotes the migration and proliferation of colorectal cancer cells by activating the upstream signal pathway PI3K/Akt-NF-κB and inducing epithelial-mesenchymal transition.100
The inconsistency in the results of studies is due to the small sample size,24 impurity of compounds, lack of data, and interfering factors. Another important reason could be compounds cell-tissue specific function, as it has been shown that PFCs have different distributions in various tissues,114,116 which needs further targeted studies. More investigations in larger populations with better materials and instruments while considering other factors are needed to obtain more accurate results.
Overall, these findings suggest that PFCs are probably capable of inducing malignancies in both animals and humans. PFCs exert their carcinogenic effects by altering PPARα and PI3K pathways, evading apoptosis, inducing sustained angiogenesis, alterations in proliferation, and blocking differentiation. However, the exact mechanism of their carcinogenicity is not understood well and needs more epidemiologic investigations. These findings are worth considering for the update of the IARC monograph.
Acknowledgments
This work was supported by the Shiraz University of Medical Sciences.
Author contributions
All authors contributed to the study conception and design. The first draft of the manuscript was written by Zahra Dehghani, Farbod Shahabinezhad, Pooria Sabouri, and Afshin Mohammadi Bardbori and all authors commented on previous versions of the manuscript. Sara Ranjbar edited the manuscript. All authors read and approved the final manuscript.
Funding
This work was supported by the Research Grants from the Shiraz University of Medical Sciences, Iran (Grant number: 98-01-05-19487).
Conflict of interest statement. All authors have read the journal’s policy on disclosure of potential conflicts of interest. The authors declare that no competing interest exists.
Availability of data and materials
The datasets generated during and/or analyzed during the current study are available from the corresponding author upon reasonable request.
Ethics approval and consent to participate
Ethics approvals were granted from the Shiraz University of Medical Sciences. Informed consent was obtained from all individual participants included in the study.
