Decreased macrophage phagocytic function due to xenobiotic exposures in vitro, difference in sensitivity between various macrophage models

Per- and polyfluoroalkyl substances alter innate immune function: evidence and data gaps

Per- and polyfluoroalkyl substances (PFASs) are a large class of compounds used in a variety of processes and consumer products. Their unique chemical properties make them ubiquitous and persistent environmental contaminants while also making them economically viable and socially convenient. To date, several reviews have been published to synthesize information regarding the immunotoxic effects of PFASs on the adaptive immune system. However, these reviews often do not include data on the impact of these compounds on innate immunity. Here, current literature is reviewed to identify and incorporate data regarding the effects of PFASs on innate immunity in humans, experimental models, and wildlife. Known mechanisms by which PFASs modulate innate immune function are also reviewed, including disruption of cell signaling, metabolism, and tissue-level effects. For PFASs where innate immune data are available, results are equivocal, raising additional questions about common mechanisms or pathways of toxicity, but highlighting that the innate immune system within several species can be perturbed by exposure to PFASs. Recommendations are provided for future research to inform hazard identification, risk assessment, and risk management practices for PFASs to protect the immune systems of exposed organisms as well as environmental health.

Application of the Key Characteristics of Carcinogens to Bisphenol A

The ten key characteristics (KCs) of carcinogens are based on characteristics of known human carcinogens and encompass many types of endpoints. We propose that an objective review of the large amount of cancer mechanistic evidence for the chemical bisphenol A (BPA) can be achieved through use of these KCs. A search on metabolic and mechanistic data relevant to the carcinogenicity of BPA was conducted and web-based software tools were used to screen and organize the results. We applied the KCs to systematically identify, organize, and summarize mechanistic information for BPA, and to bring relevant carcinogenic mechanisms into focus. For some KCs with very large data sets, we utilized reviews focused on specific endpoints. Over 3000 studies for BPA from various data streams (exposed humans, animals, in vitro and cell-free systems) were identified. Mechanistic data relevant to each of the ten KCs were identified, with receptor-mediated effects, epigenetic alterations, oxidative stress, and cell proliferation being especially data rich. Reactive and bioactive metabolites are also associated with a number of KCs. This review demonstrates how the KCs can be applied to evaluate mechanistic data, especially for data-rich chemicals. While individual entities may have different approaches for the incorporation of mechanistic data in cancer hazard identification, the KCs provide a practical framework for conducting an objective examination of the available mechanistic data without a priori assumptions on mode of action. This analysis of the mechanistic data available for BPA suggests multiple and inter-connected mechanisms through which this chemical can act.

Legacy and emerging per- and polyfluoroalkyl substances suppress the neutrophil respiratory burst

Per- and polyfluoroalkyl substances (PFASs) are used in a multitude of processes and products, including nonstick coatings, food wrappers, and fire-fighting foams. These chemicals are environmentally-persistent, ubiquitous, and can be detected in the serum of 98% of Americans. Despite evidence that PFASs alter adaptive immunity, few studies have investigated their effects on innate immunity. The report here presents results of studies that investigated the impact of nine environmentally-relevant PFASs [e.g. perfluorooctanoic acid (PFOA), perfluorooctane sulfonic acid potassium salt (PFOS-K), perfluorononanoic acid (PFNA), perfluorohexanoic acid (PFHxA), perfluorohexane sulfonic acid (PFHxS), perfluorobutane sulfonic acid (PFBS), ammonium perfluoro(2-methyl-3-oxahexanoate) (GenX), 7H-perfluoro-4-methyl-3,6-dioxa-octane sulfonic acid (Nafion byproduct 2), and perfluoromethoxyacetic acid sodium salt (PFMOAA-Na)] on one component of the innate immune response, the neutrophil respiratory burst. The respiratory burst is a key innate immune process by which microbicidal reactive oxygen species (ROS) are rapidly induced by neutrophils in response to pathogens; defects in the respiratory burst can increase susceptibility to infection. The study here utilized larval zebrafish, a human neutrophil-like cell line, and primary human neutrophils to ascertain whether PFAS exposure inhibits ROS production in the respiratory burst. It was observed that exposure to PFHxA and GenX suppresses the respiratory burst in zebrafish larvae and a human neutrophil-like cell line. GenX also suppressed the respiratory burst in primary human neutrophils. This report is the first to demonstrate that these PFASs suppress neutrophil function and support the utility of employing zebrafish larvae and a human cell line as screening tools to identify chemicals that may suppress human immune function.

Re-evaluation of the risks to public health related to the presence of bisphenol A (BPA) in foodstuffs

In 2015, EFSA established a temporary tolerable daily intake (t-TDI) for BPA of 4 μg/kg body weight (bw) per day. In 2016, the European Commission mandated EFSA to re-evaluate the risks to public health from the presence of BPA in foodstuffs and to establish a tolerable daily intake (TDI). For this re-evaluation, a pre-established protocol was used that had undergone public consultation. The CEP Panel concluded that it is Unlikely to Very Unlikely that BPA presents a genotoxic hazard through a direct mechanism. Taking into consideration the evidence from animal data and support from human observational studies, the immune system was identified as most sensitive to BPA exposure. An effect on Th17 cells in mice was identified as the critical effect; these cells are pivotal in cellular immune mechanisms and involved in the development of inflammatory conditions, including autoimmunity and lung inflammation. A reference point (RP) of 8.2 ng/kg bw per day, expressed as human equivalent dose, was identified for the critical effect. Uncertainty analysis assessed a probability of 57-73% that the lowest estimated Benchmark Dose (BMD) for other health effects was below the RP based on Th17 cells. In view of this, the CEP Panel judged that an additional uncertainty factor (UF) of 2 was needed for establishing the TDI. Applying an overall UF of 50 to the RP, a TDI of 0.2 ng BPA/kg bw per day was established. Comparison of this TDI with the dietary exposure estimates from the 2015 EFSA opinion showed that both the mean and the 95th percentile dietary exposures in all age groups exceeded the TDI by two to three orders of magnitude. Even considering the uncertainty in the exposure assessment, the exceedance being so large, the CEP Panel concluded that there is a health concern from dietary BPA exposure.

Exposure to persistent organic pollutants alters the serum metabolome in non-obese diabetic mice

INTRODUCTION

Autoimmune disorders such as type 1 diabetes (T1D) are believed to be caused by the interplay between several genetic and environmental factors. Elucidation of the role of environmental factors in metabolic and immune dysfunction leading to autoimmune disease is not yet well characterized.

OBJECTIVES

Here we investigated the impact of exposure to a mixture of persistent organic pollutants (POPs) on the metabolome in non-obese diabetic (NOD) mice, an experimental model of T1D. The mixture contained organochlorides, organobromides, and per- and polyfluoroalkyl substances (PFAS).

METHODS

Analysis of molecular lipids (lipidomics) and bile acids in serum samples was performed by UPLC-Q-TOF/MS, while polar metabolites were analyzed by GC-Q-TOF/MS.

RESULTS

Experimental exposure to the POP mixture in these mice led to several metabolic changes, which were similar to those previously reported as associated with PFAS exposure, as well as risk of T1D in human studies. This included an increase in the levels of sugar derivatives, triacylglycerols and lithocholic acid, and a decrease in long chain fatty acids and several lipid classes, including phosphatidylcholines, lysophosphatidylcholines and sphingomyelins.

CONCLUSION

Taken together, our study demonstrates that exposure to POPs results in an altered metabolic signature previously associated with autoimmunity.

A human relevant mixture of persistent organic pollutants induces reactive oxygen species formation in isolated human leucocytes: Involvement of the β2-adrenergic receptor

Exposure to chlorinated (Cl), brominated (Br) and perfluoroalkyl acid (PFAA) persistent organic pollutants (POPs) is associated with immunotoxicity and other adverse effects in humans and animals. Previous studies on POPs have mainly focused on single chemicals, while studies on complex mixtures are limited. Using DCF and luminol assays we examined effects on ROS generation in isolated human neutrophils, monocytes and lymphocytes, after in vitro exposure to a total mixture and sub-mixtures of 29 persistent compounds (Cl, Br, and PFAA). The mixtures were based on compounds prominent in blood, breast milk, and/or food. All mixture combinations induced ROS production in one or several of the cell models, and in some cases even at concentrations corresponding to human blood levels (compound range 1 pM - 16 nM). Whilst some interactions were detected (assessed using a mixed linear model), halogenated subgroups mainly acted additively. Mechanistic studies in neutrophils at 500× human levels (0.5 nM - 8 µM) indicated similar mechanisms of action for the Cl, PFAA, the combined PFAA + Cl and total (PFAA + Br + Cl) mixtures, and ROS responses appeared to involve β2-adrenergic receptor (β2AR) and Ca²⁺ signalling, as well as activation of NADPH oxidases. In line with this, the total mixture also increased cyclic AMP at levels comparable with the non-selective βAR agonist, isoproterenol. Although the detailed mechanisms involved in these responses remain to be elucidated, our data show that POP mixtures at concentrations found in human blood, may trigger stress responses in circulating immune cells. Mixtures of POPs, further seemed to interfere with adrenergic pathways, indicating a novel role of βARs in POP-induced effects.

Bisphenol A, bisphenol S and their glucuronidated metabolites modulate glycolysis and functional responses of human neutrophils

Bisphenol A (BPA) and its main substitute, bisphenol S (BPS), are synthetic organic compounds found in various consumer products, in particular food and beverage containers. Numerous reports have shown a link between bisphenol exposure, human contamination and increased health problems. BPA, BPS and their metabolites are detectable in bodily fluids (blood, urine) and were reported to affect immune cells and their responses. Though, the impact of those chemicals on neutrophils, the most abundant leukocytes in the circulation, remains poorly described. Therefore, we examined the effects of BPA, BPS and their monoglucuronide conjugates on neutrophil energy metabolism and anti-microbial functions, mainly phagocytosis, superoxide anion generation and CXCL8/IL-8 chemokine production. We observed that short and prolonged exposures of neutrophils to these chemicals modulate the basal and the bacterium-derived peptide N-formyl-methionyl-leucyl-phenylalanine-induced glycolysis, with BPS causing the most alterations. The variation in energy metabolism was not associated with dysfunctions in cell cytotoxicity, phagocytosis, nor superoxide anion production upon exposure to bisphenols. In contrast, bisphenols significantly reduced the production of CXCL8/IL-8 by neutrophils, an effect found to be greater with the glucuronidated metabolites. Our study highlights that BPA, BPS and their glucuronidated metabolites alter the energy metabolism and certain anti-microbial responses of neutrophils, with possible health implications. Importantly, we found that BPS and the glucuronidated metabolites of BPA and BPS showed higher endocrine-disrupting potential than BPA. More studies on bisphenols, especially the less-documented BPS and bisphenol metabolites, are needed to fully determine their risks, allow better regulation of these compounds, and restrict their extensive usage.

Prenatal exposure to perfluoroalkyl substances modulates neonatal serum phospholipids, increasing risk of type 1 diabetes

In the last decade, increasing incidence of type 1 diabetes (T1D) stabilized in Finland, a phenomenon that coincides with tighter regulation of perfluoroalkyl substances (PFAS). Here, we quantified PFAS to examine their effects, during pregnancy, on lipid and immune-related markers of T1D risk in children. In a mother-infant cohort (264 dyads), high PFAS exposure during pregnancy associated with decreased cord serum phospholipids and progression to T1D-associated islet autoantibodies in the offspring. This PFAS-lipid association appears exacerbated by increased human leukocyte antigen-conferred risk of T1D in infants. Exposure to a single PFAS compound or a mixture of organic pollutants in non-obese diabetic mice resulted in a lipid profile characterized by a similar decrease in phospholipids, a marked increase of lithocholic acid, and accelerated insulitis. Our findings suggest that PFAS exposure during pregnancy contributes to risk and pathogenesis of T1D in offspring.

Semisynthetic quercetin-quinone mitigates BV-2 microglia activation through modulation of Nrf2 pathway

During brain ageing, microglia, the resident immune cells of the CNS, are immunologically activated and contribute to neuroinflammation, a vicious cycle that supports development of neurological disorders. Therapeutic approaches focus mainly on downregulation of their pro-inflammatory activated state that is associated with health benefits. Electrophilic compounds, such as natural quinones and their reduced pro-electrophilic precursors, flavonoids, represent a wide group of diverse substances with important biological effects. They can cause considerable cytotoxicity when used at higher dosages, but on the other hand, they have versatile health benefits at lower dosages. In this study, we investigated the cytotoxicity and prooxidant profile of synthetic conjugate of two electrophilic compounds, quercetin and 1,4-naphthoquinone, 4'-O-(2-chloro-1,4-naphthoquinone-3-yloxy) quercetin (CHNQ), and its attenuation of inflammatory responses and modulation of Nrf2 pathway in BV-2 microglial cells. CHNQ showed higher cytotoxicity than its precursors, accompanied by promotion of production of reactive oxygen species along with G2/M cell cycle arrest at higher concentrations tested. Nevertheless, at a lower non-toxic concentration, CHNQ, more significantly than did its precursors, downregulated LPS-stimulated microglia cells as documented by decreased iNOS, COX-2 and TNFα protein levels. Moreover, CHNQ most effectively upregulated expression of phase II antioxidant enzyme HO-1 and β5 subunit of constitutive proteasome. The enhanced anti-inflammatory effect of CHNQ was accompanied by prominent increase in cytosolic expression of Nrf2 and c-Jun, however, induction effect on nuclear Nrf2 translocation was comparable to QUER. Moreover, a conditioned medium from activated BV-2 cells co-treated with quercetin and CHNQ maintained viability of neuron-like PC12 cells. The compounds tested did not show any disturbance of phagocytosis of live or dead PC12 cells. The present experimental data predict a preventive and therapeutic potential of semisynthetic derivative CHNQ in ageing and related pathologies, mediated by activation of proteins of the antioxidant response.

Obesity associated with coal ash inhalation triggers systemic inflammation and oxidative damage in the hippocampus of rats

People with large amounts of adipose tissue are more vulnerable and more likely to develop diseases where oxidative stress and inflammation play a pivotal role, than persons with a healthy weight. Atmospheric contamination is a reality to which a large part of the worldwide population is exposed. Half of today's global electrical energy is derived from coal. Each organism, in its complexity, responds in different ways to dietary compounds and air pollution. The objective of this study was to investigate the effects of obesity and coal ash inhalation within the parameters of oxidative damage and inflammation in different regions of the brain of rats. A diet containing high-fat concentration was administered chronically to rats, along with exposure to coal ash, simulating the contamination that occurs daily throughout human life. High-resolution transmission electron microscopy was performed to identify the particles present in coal ash samples. Our results demonstrated that obese rats exposed to coal ash inhalation were more affected by oxidative damage with subsequent systemic inflammation in the hippocampus. Since there is an inflammatory predisposition caused by obesity, the inhalation of nanoparticles increases the levels of free radicals, resulting in systemic inflammation and oxidative damage, which can lead to chronic neurodegeneration.

Bisphenol A promotes macrophage proinflammatory subtype polarization via upregulation of IRF5 expression in vitro

Exposure to environmental endocrine-disrupting chemical Bisphenol-A (BPA) is closely associated with an imbalance of immune homeostasis, but the underlying mechanisms are not fully understood. In the present study, the effects of BPA on the polarization of mouse peritoneal macrophages were investigated in vitro. Environmentally relevant low concentrations of BPA treatment under M1 type polarization conditions increased the number of M1 subtype macrophages, the gene expression of M1 phenotypic marker CD11c and the activity and gene expression of M1 functional marker iNOS, as well as the production of pro-inflammatory cytokines. However, The same dose BPA treatment under M2 type polarization conditions reduced the number of M2 subtype macrophages, the gene expression of M2 phenotypic marker CD206 and the activity and gene expression of M2 functional marker Arg-1, along with the production of anti-inflammatory cytokines. We also identified that the expression of transcription factor IRF5 was upregulated by BPA exposure in M1 macrophages under M1 type polarization conditions. Our results demonstrate that BPA promotes macrophage polarization toward proinflammatory M1 subtype and M1 activity, associated with upregulated expression of IRF5, while BPA inhibits macrophage toward anti-inflammatory M2 subtype polarization. These findings provide new insight into the link between exposure to BPA and impairment of immune functions.

Bisphenol A exhibits cytotoxic or genotoxic potential via oxidative stress-associated mitochondrial apoptotic pathway in murine macrophages

Bisphenol A (BPA) is primarily used in production of polycarbonate plastics and epoxy resins including plastic containers. BPA is an endocrine disruptor and supposes to induce asthma and cancer. However, so far only a few evidences have shown the BPA-induced toxic effect and its related mechanism in macrophages. BPA demonstrated cytotoxic effect on RAW264.7 macrophages in a concentration and time-dependent manner. BPA induces necrosis, apoptosis, and genotoxicity in a concentration-dependent manner. Phosphorylation of cytochrome C (cyto C) and p53 was due to mitochondrial disruption via BCL2 and BCL-XL downregulation and BAX, BID, and BAD upregulation. Both caspase-dependent, including caspase-9, caspase-3, and PARP-1 cleavage, and caspase-independent, such as nuclear translocation of AIF, pathways were activated by BPA. Furthermore, generation of reactive oxygen species (ROS) and reduction of antioxidative enzyme activities were induced by BPA. Parallel trends were observed in the effect of BPA on cytotoxicity, apoptosis, genotoxicity, p53 phosphorylation, BCL2 family expression exchange, caspase-dependent and independent apoptotic pathways, and ROS generation in RAW264.7 macrophages. Finally, BPA-exhibited cytotoxicity, apoptosis, and genotoxicity could be inhibited by N-acetylcysteine. These results indicated that the toxic effect of BPA was functioning via oxidative stress-associated mitochondrial apoptotic pathway in macrophages.

Isolating and culturing of sputum macrophages: A potential ex vivo/in vitro model

PURPOSE

This paper aimed to test whether induced sputum samples acquired from human volunteers could be used to isolate and culture airway macrophages for in vitro exposures. This was assessed in terms of the culturing success rate, culture purity, viability and responsiveness of cultured cells.

MATERIALS AND METHODS

The isolation and culturing procedure was performed over three days. On Day 1, induced sputum samples were obtained, processed and seeded in culture wells. Differential cell counts and viability tests were performed to allow for calculation of viable macrophage numbers and appropriate sample dilution. After a 1 h rest, seeded wells were washed to remove non-adherent cells, resulting in macrophage isolation. Then, cells rested overnight (Day 1-Day 2), before in vitro exposure for 2-24 h (Day 2-Day 3). The criteria for progressing into the culturing procedure was cell viability >40% and total cell number >10⁶. Successful culturing was evaluated based on cell attachment (N = 40). Culture purity by differential cell analysis and viability was monitored during culturing (N = 4-8). Macrophage responsivity was assessed by measurement of inflammatory cytokine gene expression (N = 4) and cytokine levels (N = 6) following in vitro exposure to lipopolysaccharide (LPS) (2-24 h) and live bacteria (S. aureus) (4h).

RESULTS

Overall, 88% (35/40) of the samples acquired were suitable for isolation, and 80% (32/40) were successfully progressed through the 2-3 day culturing protocol. Macrophage purity (88%) and viability (85%) were adequate. Moreover, cultured macrophages were responsive to in vitro stimulation with LPS and viable S. aureus showing positive mRNA responses for TNFα, IL-1β and IL-8 and release of IL-1β, respectively.

CONCLUSION

Sputum macrophage isolation by plate adherence and subsequent culturing of sputum macrophages was successfully performed and represents a promising in vitro model for examination of airway macrophage behavior.