Advances in the Utilization of Zebrafish for Assessing and Understanding the Mechanisms of Nano-/Microparticles Toxicity in Water

Abstract

A large amount of nano-/microparticles (MNPs) are released into water, not only causing severe water pollution, but also negatively affecting organisms. Therefore, it is crucial to evaluate MNP toxicity and mechanisms in water. There is a significant degree of similarity between the genes, the central nervous system, the liver, the kidney, and the intestines of zebrafish and the human body. It has been shown that zebrafish are exceptionally suitable for evaluating the toxicity and action mechanisms of MNPs in water on reproduction, the central nervous system, and metabolism. Providing ideas and methods for studying MNP toxicity, this article discusses the toxicity and mechanisms of MNPs from zebrafish.

Keywords: nano-/microparticles; toxicity evaluation; toxicological mechanism; zebrafish.

Figure 1

The zebrafish can be used for toxicity evaluation and mechanistic studies of the nervous, reproductive, and immune systems of MNPs.

Figure 2

Advantages of zebrafish for toxicity evaluation of MNPs. (A) The blood–brain barrier, central nervous system, and social behavior are similar to those of humans, making it an ideal animal model for studying neurotoxicity; (B) The intestine, liver and kidney are similar to those of humans, which makes them suitable for studying MNPs metabolism and immune diseases; (C) The reproductive and developmental toxicity of MNPs can be easily studied due to the short reproductive cycle of zebrafish and the large number of eggs laid. In addition, the embryos are transparent, so a microscope can be used to observe the cell division and organ formation process; (D) The genome of zebrafish has been fully sequenced, and is highly consistent with the human genome, and can be easily manipulated by genetic manipulation such as gene knockout and gene overexpression.

Figure 3

Evaluation index of MNP toxicity in zebrafish in a water body. (A) Evaluation of the toxicity of MNPs on growth and reproduction by the damage and apoptosis of sperm, testis, and oocytes of adult zebrafish, as well as the increased rate of malformation and mortality of embryos [40,41,42]; (B) Evaluation of the behavioral and neurological toxicity of MNPs by increasing oxidative-stress level and apoptosis in the zebrafish brain, as well as behavioral experiments to detect memory, learning, and mental disorders in zebrafish [43,44,45]; (C) Evaluation of the toxicity of MNPs on the metabolism and immune system by the upregulation of immune-related gene expression and apoptosis, as well as the reduction of hepatic glucose and lipid metabolism, glucose, α-ketoglutarate, and lipid-related indicators [46,47,48].

Figure 4

Diagram of the toxicological mechanism of MNPs in water explored using zebrafish. (A) The mechanism of central nervous toxicity of MNPs: Excessive production of H₂O₂, inactivation of enzyme protein, disruption of the balance between CAT and SOD activities, inhibition of AChE activity, and significant reduction in the activity of GS and GDH, leading to brain neurodegeneration. (B) Mechanism of reproductive toxicity of MNPs: MNPs were transferred to oocytes of adult female zebrafish, causing reduction of GR and GSH contents, leading to oxidative stress in oocytes. At the same time, NF-b and TNF- expression was significantly upregulated, affecting the offspring’s growth and development. (C) Effect of MNPs on zebrafish gut: Increased abundance of Fusobacterium metabolized mucin into short-chain fatty butyrate and induce intestinal inflammation in zebrafish. The number of actinobacteria decreased, foreign bodies accumulated in the intestine, and the number of Firmicutes decreased, all of which resulted in reduced mucus production and damage to the intestinal barrier. (D) The mechanism of metabolic toxicity of MNPs: Reduction of PEP, GK, and PK in the glycolytic pathway led to insufficient glucose and pyruvate production, leading to disorders of glucose metabolism. Additionally, the expression levels of PPAR, ACC1, FAS, FABP6, ACO, CPT1, acat2, ALDH9a1a, ALDH2b, and echs1 genes were reduced, resulting in abnormal lipid metabolism.

Figure 5

Solutions to the limitations of zebrafish. (A) To optimize the zebrafish exposure experiments, larval or adult zebrafish should be exposed to real MNPs in contaminated water. (B) The current unified experimental operating procedures and standards must be strictly followed, and researchers still need to promote the construction of standards, so that the toxicity evaluation of zebrafish as a model organism can be more perfect. (C) The mutual verification mechanism for animal models must be strengthened. (D) Long-term exposure experiments should be carried out to expose adult zebrafish to MNPs over a long period of time and there should be generation studies from adult fish to offspring, and then to offspring adult respawning to comprehensively investigate MNP toxic mechanisms.