Bisphenol AF exposure causes fasting hyperglycemia in zebrafish (Danio rerio) by interfering with glycometabolic networks

Highlights

• BPAF exposure increases fasting blood glucose levels in zebrafish.

• BPAF exposure promotes gluconeogenesis and inhibits glycogenesis and glycolysis.

• This dysfunctional glycometabolism may be due to the failure of insulin regulation.

Abstract

Bisphenol AF (BPAF), one of the main alternatives to bisphenol A, has been frequently detected in various environmental media, including the human body, and is an emerging contaminant. Epidemiological investigations have recently shown the implications of exposure to BPAF in the incidence of diabetes mellitus in humans, indicating that BPAF may be a potential diabetogenic endocrine disruptor. However, the effects of BPAF exposure on glucose homeostasis and their underlying mechanisms in animals remain largely unknown, which may limit our understanding of the health risks of BPAF. To this end, zebrafish (Danio rerio), an emerging and valuable model in studying animal glycometabolism and diabetes, were exposed to environmentally relevant concentrations (5 and 50 μg/L) and 500 μg/L BPAF for 28 d. Several key toxicity endpoints of blood glucose metabolism were detected in our study, and the results showed significantly increased fasting blood glucose levels, hepatic glycogen contents and hepatosomatic indexes and decreased muscular glycogen contents in the BPAF-exposed zebrafish. The results of quantitative real-time PCR showed the abnormal expression of genes involved in glycometabolic networks, which might promote hepatic gluconeogenesis and inhibit glycogenesis and glycolysis in the muscle and/or liver. Furthermore, the failure of insulin regulation, including plasma insulin deficiency and impaired insulin signaling pathways in target tissues, may be a potential mechanism underlying BPAF-induced dysfunctional glycometabolism. In summary, our results provide novel in vivo evidence that BPAF can cause fasting hyperglycemia by interfering with glycometabolic networks, which emphasizes the potential health risks of environmental exposure to BPAF in inducing diabetes mellitus.

Introduction

Diabetes mellitus, a metabolic syndrome mainly characterized by hyperglycemia, has become the third largest public health issue after cardiovascular disease and cancer in the world. According to the latest data published by the International Diabetes Federation, there were 463 million people suffering from diabetes worldwide in 2019, and this number is estimated to reach 578 and 700 million by 2030 and 2045, respectively (Karuranga et al., 2019). In addition to genetics, obesity, an unhealthy diet, and other intrinsic factors, accumulating evidences have shown that exposure to environmental toxicants, especially endocrine-disrupting chemicals (EDCs), is also a main risk factor responsible for the prevalence of diabetes (Lind and Lind, 2018). As one of the most widespread EDCs, bisphenol A (BPA) has been clearly demonstrated to be positively linked to the development of diabetes in human epidemiological investigations (Rancière et al., 2019; Yang et al., 2021). Moreover, animal model experiments also indicated that exposure to BPA can disrupt animal glucose homeostasis, leading to higher blood glucose levels (i.e., hyperglycemia) (Ahn et al., 2018; Alonso-Magdalena et al., 2010). Due to these adverse health effects of BPA on humans and wildlife, the usage of BPA is gradually being prohibited, and some structural analogs of BPA have been developed to replace it (Park et al., 2018).

Bisphenol AF (BPAF), a fluorinated derivative of BPA, has been widely used as a monomer in the manufacturing of polycarbonate copolymers in high-temperature composites, electronic materials, and gas-permeable membranes (Cao et al., 2017). In China, an annual BPAF production capacity of approximately 100 tons was reported by the largest manufacturer of BPAF (Song et al., 2012). With its widespread application in various industrial fields, BPAF is inevitably discharged into the natural environment and is thus an environmental pollutant of emerging concern (Zhao et al., 2021). For example, in the environmental samples around a BPAF manufacturing plant in China, the concentrations of this chemical were reported to be 15.3 μg/L in river water, 2000 ng/g dry weight (dw) in sediments, 331 ng/g dw in soils, and 739 ng/g dw in indoor dust, respectively (Song et al., 2012). In municipal sewage sludges collected from 30 cities in China, the detection ratio of BPAF was 46.2%, with a maximum concentration of 45.1 ng/g dw (Song et al., 2014). Moreover, BPAF has also been frequently detected in marine organisms (Zhao et al., 2021) and human bodies, with the maximum concentrations of 0.44 and 3.39 ng/mL reported in human plasma and urine, respectively (Asimakopoulos et al., 2016; Jin et al., 2018). Considering its ubiquity and potential human exposure, various toxic effects of BPAF have been reported in recent studies, including endocrine disruption effect (Chen et al., 2018; Jones et al., 2018; Liu et al., 2020) and reproductive toxicity (den Braver-Sewradj et al., 2020), cardiotoxicity (Gu et al., 2020), cytotoxic and genotoxic potential (Hercog et al., 2019; Russo et al., 2018), and developmental toxicity (Liang et al., 2021; Mu et al., 2018). Recently, similar to the negative impacts of BPA, two epidemiological studies showed that urinary BPAF levels were positively associated with the incidence of diabetes and higher plasma glucose levels in humans (Duan et al., 2018; Zhang et al., 2019). These investigations suggested that animal experiments are urgently needed to confirm the specific effects of BPAF on animal glucose homeostasis. However, research on this topic is relatively limited until now, and only a few studies investigated the glycometabolic disorder induced by BPAF in mouse liver (Meng et al., 2018) and in vitro HepG2 cells (Yue et al., 2019). Generally, fasting blood glucose (FBG) levels, rather than hepatic glucose levels, are the major biochemical diagnostic parameter of diabetes (Capiotti et al., 2014). Moreover, blood glucose homeostasis is jointly coordinated by the glucometabolic networks within the liver and muscle, not only by those within the liver (Harfmann et al., 2016; Mizgier et al., 2014). Last but not least, the regulatory role of insulin, as the only hormone able to reduce blood glucose, in glycometabolic networks cannot be ignored (Röder et al., 2016). Given the above, to our knowledge, few studies have systematically investigated the effect and mechanism of BPAF exposure on animal blood glucose balance.

In addition to the advantages of a relatively small size, low breeding costs, high fecundity, a short generation cycle, and genetic tractability, zebrafish (Danio rerio) share highly homologous glycometabolism networks with humans, in terms of gene function (Zhang et al., 2018), and the composition, ontogeny, and function of the involved organ systems (Maddison and Chen, 2017). Accordingly, zebrafish is now becoming a valuable model for diabetes-related researches (Zang et al., 2018; Zhang et al., 2018) and glycometabolism interference investigations of environmental pollutants (Liu et al., 2021; Park et al., 2021). Moreover, the biotransformation of BPAF in zebrafish is very similar to those of humans (Shi et al., 2016; Waidyanatha et al., 2015). In both models, BPAF was predominantly metabolized into BPAF-glucuronide by the glucuronidation reaction (Shi et al., 2016; Waidyanatha et al., 2015). This high conservation of xenobiotic metabolic profiles supports the extrapolation of toxic effects and mechanisms of BPAF from zebrafish to humans. In this study, zebrafish as an animal model were exposed to environmentally relevant concentrations (5 and 50 μg/L) and 500 μg/L BPAF for 28 d. The objective of the present study was to investigate the influence of BPAF exposure on glucose homeostasis by detecting FBG levels in the blood, glycogen levels and the expression of genes encoding key glucose metabolic enzymes in the liver and muscle. Plasma insulin levels and the expression of insulin receptors in target tissues were measured to further explore the underlying mechanisms. Our results will strengthen and enrich our understanding of the potential health risks of BPAF, which is especially important as BPAF exposure may be a potential risk factor for diabetes.