Full length articleToxic effects of dietary copper and EGCG on bioaccumulation, antioxidant enzyme and immune response of Korean bullhead, Pseudobagrus fulvidraco
Introduction
Copper is a critical essential trace metal in aquatic animals as a cofactor for enzymes involved in the maintenance of various physiological homeostasis and in various metabolisms [1]. However, industrial and aquaculture activities (e.g. the use of pesticides and fertilizers, etc.) could lead to high Cu levels in the aquatic environment and results in excess Cu than the Aquatic organisms require [[2], [3], [4]]. Metal exposure such as copper induce bioaccumulation in specific tissues of fish, and the accumulation by metal exposure is a critical toxic factor causing dysfunctions in fish [5]. In addition, the copper properties to suppress antioxidant responses can induce ROS accumulation, which can cause oxidative stress [6]. The antioxidant response is a major activity to defend against oxidative stress caused by metal exposure, so it can be a major biomarker for fish exposed to Cu. These antioxidant system is composed of enzymes [e.g. superoxide dismutase (SOD) and catalase (CAT), etc.] and small molecules [7]. SOD can convert superoxide anions to hydrogen peroxide, and CAT is decomposes hydrogen peroxide into water and oxygen. Moreover, Cu exposure can affect the immunity in aquatic animals such as immune suppression or immune stimulation [[8], [9], [10]]. The innate immune system is a system that triggers an immune response in the body immediately when exposed to dangerous substances, in which case the reaction usually occurs as a non-specific immune response [11,12]. Lysozyme is the first immune response in living organisms and activates the complement system through opsonization [13]. In addition, Lysozyme is an important immune indicator of toxic effects because it is affected by toxic exposures such as metals [12]. Phagocytosis is a major nonspecific immune response that puts large particles into intracellular vacuoles to eliminate pathogenic microorganisms and has been considered as a major immune indicator to assess the health status and immune capacity of fish [14].
EGCG (Epigallocatechin gallate) is a natural antioxidant that accounts for 50–80% of catechins, known as polyphenols in green tea [15,16]. EGCG has a function of detoxifying heavy metals by being easily combined with toxic substances such as metals by various polyphenol-based components [17,18]. In addition, catechin, which can eliminate active oxygen species such as superoxide and hydroxyl radical in relation to active oxygen species, has been reported to have antioxidant function [19]. These polyphenols and green tea extracts are also used in aquaculture for immune enhancement and improved disease resistance [20]. Although EGCG has been revalued as a functional food as numerous potential medicinal benefits have been scientifically identified, few studies have been conducted to detoxify heavy metals using the fish. Therefore, research is needed to verify the detoxification of EGCG according to metal exposure.
Fish is the major source of trace metals in the human diet. The experimental species of this study were chosen as fish because approximately 90% of the human health risks associated with the consumption of metal-contaminated fish [21]. Korean bullhead, Pseudobagrus fulvidraco is widely known as Yellowhead catfish and is classified as a freshwater fish belonging to the Siluriformes order, Bagridae family and Pseudobagrus genus. This species is nocturnal and distributed in China and Japan etc. and in Korea, the species inhabits the mid- and downstream sands and muds of the streams entering the West and South Seas [22]. The west seas of Korea is requires long-term monitoring to preserve marine ecosystem because is reacts sensitively to environmental changes (such as industrial development and introduce of wastewater by dense population, etc.) as the semi-enclosed sea area [23]. In some areas (i.e. Cheonsu Bay), Cu levels were reported to exceed the threshold effects level (TEL) (20 mg kg−1) by about 1% on average [24]. Furthermore, P. fulvidraco are important ecosystem components and are used as biomarkers because they are sensitive to external factors such as pollution. However, the study about cupper toxicity in the P. fulvidraco have been insufficiently conducted. Therefore, the purpose of this study was to evaluate toxic effects on bioaccumulation, antioxidant and immune responses in the P. fulvidraco, and to verify the detoxification effects of EGCG against copper toxicity.
Section snippets
Experimental animals and conditions
Korean bullhead, Pseudobagrus fulvidraco (mean length 16.9 ± 1.38 cm and, mean weight 53.2 ± 1.22 g) were obtained from a Center of Inland Water Culture of National Fisheries Research Institute. Fish were held for 1 week in freshwater to ensure that all individuals were healthy and also, fed the control diet to 1% of body weight. The water used in the experimental is shown in Table 1 and has a temperature of 18 ± 1 °C, pH 7.0 ± 0.7, dissolved oxygen (DO) 7.5 ± 0.5 mg L−1, and chemical oxygen
Copper bioaccumulation
The Cu accumulation for 4 weeks in intestine, liver and gill of P. fulvidraco is demonstrated in Fig. 1. During the 4 week period, dietary Cu exposure (minimum 700 mg kg−1 to maximum 1100 mg kg−1) was observed to increase Cu concentration in the intestine (17–34 fold), liver (11–22 fold) and gill (7.6–12 fold) of Cu-exposed P. fulvidraco compared to controls. Overall, the Cu accumulation increased with increasing Cu concentration (P < 0.05). The most pronounced Cu accumulation during the 4
Conclusion
We investigated the response of dietary Cu and EGCG on bioaccumulation, oxidative stress and immune response of Korean bullhead, Pseudobagrus fulvidraco. In conclusion, the result of this study demonstrate that dietary Cu exposure at levels higher than 700 mg kg−1 can alter the bioaccumulation and the activity of antioxidant enzymes (SOD and CAT), and immune responses (lysozyme and phagocytosis). For dietary EGCG, all of the bioaccumulation, antioxidant enzymes, and immune responses alleviated
CRediT authorship contribution statement
Huisu Lee: Investigation, Formal analysis, Writing - original draft. Jun-Hwan Kim: Writing - review & editing. Hee-Ju Park: Supervision. Ju-Chan Kang: Supervision.
Acknowledgements
This work was supported by the National Research Foundation of Korean (NRF) grant funded by the Korea government (MSIT) (2020R1A2C1003852).
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