Toxicity, gut microbiota and metabolome effects after copper exposure during early life in SD rats
Introduction
Copper is an essential microelement. It is commonly used as a prosthetic group of most oxidases, such as cytochrome C oxidase and copper oxidase, and contributes to the structural integrity and conformation of the enzyme, thus ensuring normal oxidation-reduction reactions in vivo. A lack of copper can cause anemia (Nakagawa et al., 2014) and peripheral neuropathy (Coyle, 2016), and the pathogenesis of nonalcoholic fatty liver disease (NAFLD) is also related to inadequate copper intake (Laura et al., 2017). However, excessive copper intake or copper excretion disorders can lead to oxidative tissue damage through free radical-mediated pathways (Kadiiska and Mason, 2002), resulting in toxicity, such as indian childhood cirrhosis (Nayak and Chitale, 2013) and Wilson’s disease (Kido et al., 2017). Therefore, copper has both advantages and harms for human health depending on the dose taken. Based on the large amount of data currently available in animal models and cell lines as well as an understanding of copper metabolism processes, the recommended nutrient intake (RNI) of copper is 0.3∼0.8 mg/day, and the tolerable upper intake level (UL) of copper is 2∼8 mg/day (EFSA, 2015).
The gut microbiota play a critical role in human immune regulation, energy balance, information exchange, gastrointestinal development, and other physiological processes and is an integral part of the human body that affects health and disease (Mcfall-Ngai et al., 2013; Rakoff-Nahoum and Medzhitov, 2008). However, imbalances in the microecological system can also cause bacterial ectopic and immune dysfunction and can cause various diseases, such as obesity, inflammatory bowel disease, allergic disease, and irritable bowel syndrome (Villanueva-Millán et al., 2015). Infancy is a critical period for the formation of the gut microbiota, which is characterized by dynamic changes and is susceptible to many factors (Milani et al., 2017). Previous studies have shown that unabsorbed heavy metals may affect gut microbiota by altering the diversity and composition of the gut microbiota and disrupting the balance of the microecological environment in the intestine (Richardson et al., 2018; Wei et al., 2015; Zhai et al., 2017; Zhang et al., 2017). However, the toxicological effects of proper or excessive copper exposure on the establishment of gut microbiota and cometabolism through the gut microbiota during early life are not well understood.
Therefore, the current study was performed in suckling SD rats with a 15 day oral administration of different doses of copper. Blood and liver tissues were collected and analyzed for hematology, serum biochemistry, and histopathology. The gut microbiota was investigated using high-throughput sequencing of 16S rRNA from feces. The metabolomics changes in the fecal samples were characterized by UPLC-Q/TOF. The results provided useful information about the safety and potential risks of copper exposure in early life, which may be helpful for further studies on the dietary intake of copper in infants and young children.
Section snippets
Animal care and treatment
Healthy 1-day-old SD rat pups from 5 mother rats were purchased from Chengdu Dashuo Experimental Animal Co., Ltd. (Chengdu, China). The rat pups were housed in plastic cages with mother rats under standard conditions (living temperature was 22 ± 2 °C with a relative humidity of 55 ± 10 %, and a light/dark period of 12/12 h). Mother rats were fed standard rat food (TROPHIC Animal Feed High-Tech Co., Ltd., China) ad libitum with free access to sterile water. The standard rat food were formulated
Clinical observations
Repeated oral exposure of different doses of copper to suckling SD rats for 15 days caused no mortality. Compared with the control group, the exposure groups exhibited no treatment-related changes in the clinical signs of their behavior, mental state, daily activities or external appearance. In addition, there was no statistically significant difference in the body weight changes of the copper-exposed groups (Supplementary Fig. 1).
Hematology
The hematological parameters of the suckling SD rats are shown
Discussion
Copper, as an essential trace element, is still toxic to animals and humans when taken in acute or chronic overdose. The liver is the first organ to encounter nutrients, drugs and environmental toxicants that enter the hepatic portal vein from the digestive system. Acute or chronic exposure to poisons can cause damage to liver function. The liver is also the center for copper storage and regulation in the body, and excess copper can be excreted through bile to maintain copper homeostasis in the
Conclusion
In summary, repeated oral exposure of copper for 15 consecutive days could induce dose-dependent toxic effects during early life in SD rats. The significant changes in the blood biochemistry indexes and the histopathology of the liver according to the dose of copper suggested that the liver may be the target organ that is affected by copper. In addition, gut microbiota and fecal metabolome analysis further demonstrated the gut microbiota imbalance and the impact on liver damage-related
Declaration of Competing Interest
The authors have declared no conflict of interest.
Acknowledgements
This work was supported by the Science and Technology Program of Sichuan Province (2018HH0089, 2017JY0121) and Chunhui Program Research Project from Education Ministry of China (Z2016118, Z2015124).
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