Effects Of Perfluorooctanoic Acid On Gut Microbiota And Microbial Metabolites in C57BL/6J MiceⅠ

Abstract: 

Perfluorooctanoic acid (PFOA) represents an increasing public health concern due to its persistence in the environment and its toxic effects. The gut microbiota is known to produce various metabolites that assist the host to maintain metabolic homeostasis. 

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However, few studies have explored the effects of PFOA on gut microbiota-related metabolites. In the present study, male C57BL/6J mice were exposed to 1 ppm of PFOA in drinking water for four weeks and integrative analysis of the gut microbiome and metabolome was performed to reveal the health effects of PFOA. Our results showed that PFOA disturbed both the gut microbiota composition and the metabolic profiles of the feces, serum, and liver in mice. A correlation was found between Lachnospiraceae UCG004, Turicibacter, Ruminococcaceae, and different fecal metabolites. 

Significant alterations of gut microbiota-related metabolites were induced by PFOA exposure, including bile acids and tryptophan metabolites such as 3-indoleacrylic acid and 3-indoleacetic acid. The findings of this study are helpful in improving the understanding of the health effects of PFOA, which might be mediated through the gut microbiota and its related metabolites.

1. Introduction 

Perfluorooctanoic acid (PFOA) is a manufactured per- and poly-fluoroalkyl substance (PFAS) that is extensively applied in fire-fighting foams, surfactants, surface-protective materials, and other commercial products. In the United States, the existence of PFOA has been found in more than 100 public water systems [1]. PFOA is listed as a Persistent Organic Pollutant in the Stockholm Convention, and its production has been phased out in many countries. However, PFOA is highly persistent in the environment and still threatens both the environment and human health. Humans are exposed to PFOA mainly through consuming contaminated drinking water and food, followed by dermal absorption and inhalation [2].

PFOA was detected in human plasma in a Danish mother–child cohort of 738 pregnant women and their children [3], and in participants enrolled in a Diabetes Prevention Program trial in the US [4]. PFOA is considered to be present in the serum of virtually all people in industrialized countries [5]. The half-life of PFOA in humans has been proposed to be 0.5–1.5 years based on human observational research and clinical studies [6]. In October 2021, the US Environmental Protection Agency (EPA) released the PFAS Strategic Roadmap to protect human health and the environment from the hazards of PFAS. 

The US EPA’s lifetime drinking water health advisory limit for PFOA is 0.004 parts per trillion (ppt). Various health effects have been linked to PFOA exposure. For instance, PFOA stimulated cell viability, inhibited free radical production, and disrupted the redox status in swine granulosa cells, with the potential impairment of reproductive function, which requires an adequate oxidative balance [7]. PFOA can induce gut microbial dysbiosis in mice [8–10]. The gut microbiota is composed of microorganisms living in the gastrointestinal tract, which is an integral part of the host. The composition of the gut microbiota is dynamic and can be affected by many factors, including environmental contaminants, such as pesticides [11,12], heavy metals [13,14], and personal care products [15]. Dysbiosis of the gut microbiota is associated with various diseases, such as ulcerative colitis [16]. 

Higher serum levels of PFOA have been found in patients with ulcerative colitis compared to control subjects [5]. The gut microbiota exerts a remarkable influence on the health and disease states of the host through the production or modification of various metabolites. The metagenome of the gut microbiota has a vast capacity to carry out a wide range of metabolic processes, such as the production of short-chain fatty acids, the production of tryptophan derivatives, and the transformation of primary bile acids to secondary bile acids. 

These gut-microbiota-related metabolites play a key role in maintaining the metabolic homeostasis of the host. As an essential amino acid, tryptophan can be transformed into different tryptophan metabolites by gut microorganisms, such as 3-indoleacrylic acid and 3-indoleacetic acid. Tryptophan metabolites can activate signaling pathways and control the homeostasis and the function of immune cells through transcription factors such as the aryl hydrocarbon receptor (AhR) [17]. Primary bile acids are synthesized in host hepatocytes from cholesterol, which enter the gastrointestinal tract and are modified by the gut microbiota into secondary bile acids. Bile acids are recognized as signaling factors and metabolic integrators, and they have become therapeutic targets for diseases such as metabolic disorders [18]. 

The gut microbiota can influence the bile acid pool; meanwhile, the bile acid pool can modulate the community structure of the gut microbiota [19]. The gut and gut microbiota have a bidirectional relationship with the liver, known as the ‘gut–liver axis’. Gut-derived metabolites and products can be transported to the liver through the portal vein. Meanwhile, the liver secretes bile acids into the intestine to facilitate the digestion of fat and fat-soluble nutrients. The gut microbiota plays a crucial role in maintaining the homeostasis of the gut–l–liver axis and the bile acid pool. 

Gut-microbiota-derived metabolites are also critical in the pathogenesis of liver diseases, such as secondary bile acids [20] and trimethylamine N-oxide (TMAO) [21]. PFOA-induced liver damage can be alleviated by the supplementation of lactic acid bacteria or gastrodin [22,23]. The gut microbiota can influence the metabolic homeostasis of the host by producing gut-microbiota-related metabolites. 

However, an integrative analysis of the gut microbiota and metabolome disturbed by PFOA exposure has not been carried out. In this study, we performed 16S rRNA gene sequencing, in combination with untargeted metabolomics, analysis on fecal, serum, and liver samples from PFOA-treated C57BL/6J mice to reveal the effects of PFOA on the gut microbiota and its related metabolites. The findings of this study are helpful in improving the understanding of the toxic effects of PFOA.

Natural Herbal Medicine For Relieving Constipation-Cistanche 

Cistanche is a genus of parasitic plants that belongs to the family Orobanchaceae. These plants are known for their medicinal properties and have been used in Traditional Chinese Medicine (TCM) for centuries. Cistanche species are predominantly found in arid and desert regions of China, Mongolia, and other parts of Central Asia. Cistanche plants are characterized by their fleshy, yellowish stems and are highly valued for their potential health benefits. In TCM, Cistanche is believed to have tonic properties and is commonly used to nourish the kidney, enhance vitality, and support sexual function. It is also used to address issues related to aging, fatigue, and overall well-being. While Cistanche has a long history of use in traditional medicine, scientific research on its efficacy and safety is ongoing and limited. However, it is known to contain various bioactive compounds such as phenylethanoid glycosides, iridoids, lignans, and polysaccharides, which may contribute to its medicinal effects.

Wecistanche's cistanche powder, cistanche tablets, cistanche capsules, and other products are developed using desert cistanche as raw materials, all of which have a good effect on relieving constipation. The specific mechanism is as follows: Cistanche is believed to have potential benefits for relieving constipation based on its traditional use and certain compounds it contains. While scientific research specifically on Cistanche's effect on constipation is limited, it is thought to have multiple mechanisms that may contribute to its potential to relieve constipation. Laxative Effect: Cistanche has long been used in Traditional Chinese Medicine as a remedy for constipation. It is believed to have a mild laxative effect, which can help promote bowel movements and induce constipation. This effect may be attributed to various compounds in Cistanche, such as phenylethanoid glycosides and polysaccharides. Moistening the Intestines: Based on traditional use, Cistanche is considered to have moisturizing properties, specifically targeting the Intestines. Promoting hydration and lubrication of the Intestines may help soften tools and facilitate easier passage, thereby relieving constipation. Anti-inflammatory Effect: Constipation can sometimes be associated with inflammation in the digestive tract. Cistanche contains certain compounds, including phenylethanoid glycosides and lignans, that are believed to have anti-inflammatory properties. By reducing inflammation in the intestines, it may help improve bowel movement regularity and relieve constipation.