Identification and characterization of zebrafish SULT1 ST9, SULT3 ST4, and SULT3 ST5

Comparative analysis of the metabolites and biotransformation pathways of fentanyl in the liver and brain of zebrafish

The rise of fentanyl has introduced significant new challenges to public health. To improve the examination and identification of biological samples in cases of fentanyl misuse and fatalities, this study utilized a zebrafish animal model to conduct a comparative investigation of the metabolites and biotransformation pathways of fentanyl in the zebrafish's liver and brain. A total of 17 fentanyl metabolites were identified in the positive ion mode using ultra-high-pressure liquid chromatography Q Exactive HF Hybrid Quadrupole-Orbitrap mass spectrometry (UHPLC-QE HF MS). Specifically, the zebrafish's liver revealed 16 fentanyl metabolites, including 6 phase I metabolites and 10 phase II metabolites. Conversely, the zebrafish's brain presented fewer metabolites, with only 8 detected, comprising 6 phase I metabolites and 2 phase II metabolites. Notably, M'4, a metabolite of dihydroxylation, was found exclusively in the brain, not in the liver. Through our research, we have identified two specific metabolites, M9-a (monohydroxylation followed by glucuronidation) and M3-c (monohydroxylation, precursor of M9-a), as potential markers of fentanyl toxicity within the liver. Furthermore, we propose that the metabolites M1 (normetabolite) and M3-b (monohydroxylation) may serve as indicators of fentanyl metabolism within the brain. These findings suggest potential strategies for extending the detection window and enhancing the efficiency of fentanyl detection, and provide valuable insights that can be referenced in metabolic studies of other new psychoactive substances.

A prototype of the mammalian sulfotransferase 1 (SULT1) family in Xenopus laevis: Characterization of a biased usage of SULT1 genes located in the S-subgenome

BLAST searches previously carried out against Xenopus genome databases, using the cloned X. laevis cytosolic sulfotransferase 1 (SULT1) cDNA sequence, revealed the presence of more than a dozen members of this gene family. Among them, 11 genes composed of five sets, four pairs and a triplet, were homeologous genes in the X. laevis allotetraploid genome consisting of S- and L-subgenomes (≥83% identity within a set). Phylogenetic and synteny analyses of tetrapod SULT1 genes demonstrated that X. laevis possessed six subfamilies, four of which were related to mammalian SULT1 gene subfamilies, while two were ectothermic vertebrate-specific and amphibian-specific SULT1 gene subfamilies. Five sets of homeologous SULT1 genes were located as a gene cluster, and showed S-subgenome-biased gene expression patterns. Acetylation levels of histone H3 at lysine 9 and H4 were also higher in the homeologous SULT1 genes on the S-subgenome than those on the L-subgenome, however, methylation levels of histone H3 at lysine 9 and DNA methylation levels showed no correlation with their transcript levels. In conclusion, histone modifications such as acetylation may be a key factor that controls the S-subgenome-biased expression of the homeologous SULT1 genes.

Gallic Acid Reverses Neurochemical Changes Induced by Prolonged Ethanol Exposure in the Zebrafish Brain

Gallic acid (GA) is a polyphenolic compound that has attracted significant interest due to its antioxidant action through free radical elimination and metal chelation. Ethanol is a highly soluble psychoactive substance, and its toxicity is associated with oxidative stress. In this context, the purpose of the present study was to investigate the effect of GA on neurochemical changes in zebrafish brains exposed to ethanol. GA was first analyzed in isolation by treating the animals at concentrations of 5, 10, and 20 mg/L for 24 h and 48 h. The results revealed that the group exposed to 20 mg/L over a 24/48 h period exhibited increases in thiobarbituric acid reactive substance (TBA-RS) levels and 2',7'-dichlorofluorescein (DCFH) oxidation, demonstrating a pro-oxidant profile. Moreover, decrease in acetylcholinesterase (AChE) enzyme activity was observed. To investigate the effects of GA after ethanol exposure, the animals were divided into four groups: control; those exposed to 0.5% ethanol for 7 days; those exposed to 0.5% ethanol for 7 days and treated with GA at 5 and 10 mg/L on day 8. Treatment with GA at 5 and 10 mg/L reversed impairment of choline acetyltransferase activity and the damage to TBA-RS levels, DCFH oxidation, and superoxide dismutase activity induced by ethanol. Results of the present study suggest that GA treatment (20 mg/L) appeared to disrupt oxidative parameters in the zebrafish brain. GA treatment at 5 and 10 mg/L reversed alterations to the cholinergic system induced by prolonged exposure to ethanol in the zebrafish brain, probably through an antioxidant mechanism.

Individual and combined mechanistic toxicity of sulfonamides and their implications for ecological risk assessment in the Three Gorges Reservoir Area (TGRA), China

Sulfonamides (SAs) are conventional veterinary antibiotics that pose ecological risks in the aquatic environment. This study aims to evaluate the environmental concerns of SAs in the Three Gorges Reservoir Area (TGRA) and their toxicogenetic implications. Here, we employed various in vitro and in vivo bioassays to determine the combine toxicogenetic effects of SAs, which were further confirmed through applying Combination Index (CI) and Independent Action (IA) models. Among the investigated SAs, sulfamethoxazole (SMX) appeared as the individual chemical with relatively high environmental effects and elevated in vitro and in vivo toxicity. Importantly, exposure to the binary mixtures of SAs induced higher developmental toxicity and significantly perturbed the detoxification pathway in zebrafish, compared to that of individual compound exposure. Moreover, the CI and IA models indicated greater synergistic effects of SAs binary mixtures as SMX-SMR, SMX-ST, and SPY-ST on the Acinetobacter sp. Tox2 at Fa = 0.5. Contrarily, IA model predicted the additive, antagonistic and synergistic effects of SAs mixtures on the transcriptional responses of detoxification pathways in zebrafish, implying the different mode of actions (MoAs) for SAs to induce mixture toxicity in vivo. Thus, the nature of toxicological interactions of SAs should be considered while performing their ecological risk assessment.

A prototype of the mammalian sulfotransferase 1 (SULT1) family in Xenopus laevis: molecular and enzymatic properties of XlSULT1B.S

The cytosolic sulfotransferase 1 (SULT1) proteins are a family of highly divergent proteins that show variable expansion in different species during vertebrate evolution. To clarify the evolutionary origin of the mammalian lineage of the SULT1 family, we compiled Xenopus laevis and X. tropicalis SULT1 (XSULT1) sequences from public databases. The XSULT1 family was found to comprise at least six subfamilies, which corresponded in part to five mammalian SULT1 subfamilies but only poorly to zebrafish SULT1 subfamilies. SULT1C was most highly expanded, and could be divided into at least five subfamilies. A cDNA for X. laevis SULT1B (XlSULT1B.S), a homolog of mammalian SULT1B1, was cloned and its recombinant protein was expressed in a bacterial system. XlSULT1B.S, unlike mammalian SULT1B1, was found to be a monomeric protein of ~34 kDa, and displayed sulfonating activity toward 2-naphthol and p-nitrophenol (pNP). However, we could not detect such sulfonating activity toward any endogenous compounds including thyroid hormones, steroid hormones and dopamine, despite the fact that X. laevis and Rana catesbeiana liver cytosols contained sulfonating activity toward most of these endogenous compounds. At optimum pH (6.4), the Michaelis-Menten constant (K_m) for pNP was two orders of magnitude greater in XlSULT1B.S (1.04 mM) than in the cytosol preparations (8-15 μM). Our results indicate that Xenopus possesses a prototype of the mammalian SULT1 family, and that XlSULT1B.S showed overall similarities in primary sequence to, and significant differences in molecular and enzymatic properties from, mammalian SULT1B1.

Zebrafish (Danio rerio): A valuable tool for predicting the metabolism of xenobiotics in humans?

Zebrafish has become a popular model organism in several lines of biological research sharing physiological, morphological and histological similarities with mammals. In fact, many human cytochrome P450 (CYP) enzymes have direct orthologs in zebrafish, suggesting that zebrafish xenobiotic metabolic profiles may be similar to those in mammals. The focus of the review is to analyse the studies that have evaluated the metabolite production in zebrafish over the years, either of the drugs themselves or xenobiotics in general (environmental pollutants, natural products, etc.), bringing a vision of how these works were performed and comparing, where possible, with human metabolism. Early studies that observed metabolic production by zebrafish focused on environmental toxicology, and in recent years the main focus has been on toxicity screening of pharmaceuticals and drug candidates. Nevertheless, there is still a lack of standardization of the model and the knowledge of the extent of similarity with human metabolism. Zebrafish screenings are performed at different life stages, typically being carried out in adult fish through in vivo assays, followed by early larval stages and embryos. Studies comparing metabolism at the different zebrafish life stages are also common. As with any non-human model, the zebrafish presents similarities and differences in relation to the profile of generated metabolites compared to that observed in humans. Although more studies are still needed to assess the degree to which zebrafish metabolism can be compared to human metabolism, the facts presented indicate that the zebrafish is an excellent potential model for assessing xenobiotic metabolism.

Importance of Toxicokinetics to Assess the Utility of Zebrafish Larvae as Model for Psychoactive Drug Screening Using Meta-Chlorophenylpiperazine (mCPP) as Example

The number of new psychoactive substances (NPS) increases rapidly, harming society and fuelling the need for alternative testing strategies. These should allow the ever-increasing number of drugs to be tested more effectively for their toxicity and psychoactive effects. One proposed strategy is to complement rodent models with zebrafish (Danio rerio) larvae. Yet, our understanding of the toxicokinetics in this model, owing to the waterborne drug exposure and the distinct physiology of the fish, is incomplete. We here explore the toxicokinetics and behavioral effects of an NPS, meta-chlorophenylpiperazine (mCPP), in zebrafish larvae. Uptake kinetics of mCPP, supported by toxicokinetic modeling, strongly suggested the existence of active transport processes. Internal distribution showed a dominant accumulation in the eye, implying that in zebrafish, like in mammals, melanin could serve as a binding site for basic drugs. We confirmed this by demonstrating significantly lower drug accumulation in two types of hypo-pigmented fish. Comparison of the elimination kinetics between mCPP and previously characterized cocaine demonstrated that drug affinities to melanin in zebrafish vary depending on the structure of the test compound. As expected from mCPP-elicited responses in rodents and humans, zebrafish larvae displayed hypoactive behavior. However, significant differences were seen between zebrafish and rodents with regard to the concentration-dependency of the behavioral response and the comparability of tissue levels, corroborating the need to consider the organism-internal distribution of the chemical to allow appropriate dose modeling while evaluating effects and concordance between zebrafish and mammals. Our results highlight commonalities and differences of mammalian versus the fish model in need of further exploration.

Identification and characterization of 5α-cyprinol-sulfating cytosolic sulfotransferases (Sults) in the zebrafish (Danio rerio)

5α-Cyprinol 27-sulfate is the major biliary bile salt present in cypriniform fish including the zebrafish (Danio rerio). The current study was designed to identify the zebrafish cytosolic sulfotransferase (Sult) enzyme(s) capable of sulfating 5α-cyprinol and to characterize the zebrafish 5α-cyprinol-sulfating Sults in comparison with human SULT2A1. Enzymatic assays using zebrafish homogenates showed 5α-cyprinol-sulfating activity. A systematic analysis, using a panel of recombinant zebrafish Sults, revealed two Sult2 subfamily members, Sult2st2 and Sult2st3, as major 5α-cyprinol-sulfating Sults. Both enzymes showed higher activities using 5α-cyprinol as the substrate, compared to their activity with DHEA, a representative substrate for mammalian SULT2 family members, particularly SULT2A1. pH-Dependence and kinetics experiments indicated that the catalytic properties of zebrafish Sult2 family members in mediating the sulfation of 5α-cyprinol were different from those of either zebrafish Sult3st4 or human SULT2A1. Collectively, these results imply that both Sult2st2 and Sult2st3 have evolved to sulfate specifically C₂₇-bile alcohol, 5α-cyprinol, in Cypriniform fish, whereas the enzymatic characteristics of zebrafish Sult3 members, particularly Sult3st4, correlated with those of human SULT2A1.

Updated perspectives on the cytosolic sulfotransferases (SULTs) and SULT-mediated sulfation

The cytosolic sulfotransferases (SULTs) are Phase II detoxifying enzymes that mediate the sulfate conjugation of numerous xenobiotic molecules. While the research on the SULTs has lagged behind the research on Phase I cytochrome P-450 enzymes and other Phase II conjugating enzymes, it has gained more momentum in recent years. This review aims to summarize information obtained in several fronts of the research on the SULTs, including the range of the SULTs in different life forms, concerted actions of the SULTs and other Phase II enzymes, insights into the structure-function relationships of the SULTs, regulation of SULT expression and activity, developmental expression of SULTs, as well as the use of a zebrafish model for studying the developmental pharmacology/toxicology.

Role of SULT-mediated sulfation in the biotransformation of 2-butoxyethanol and sorbitan monolaurate: A study using zebrafish SULTs

2-Butoxyethanol and sorbitan monolaurate are major components of oil dispersants that are applied in large quantities to control oil spill in the aquatic environment. An important question is whether aquatic animals are equipped with mechanisms for the detoxification of these oil dispersant compounds. The current study aimed to examine whether zebrafish cytosolic sulfotransferases (SULTs) are capable of sulfating 2-butoxyethanol and sorbitan monolaurate. A systematic analysis of 18 zebrafish SULTs revealed that SULT3 ST1 showed the strongest sulfating activity toward 2-butoxyethanol, while SULT1 ST3 displayed the strongest sulfating activity toward sorbitan monolaurate. The pH-dependence of these two SULTs in mediating the sulfation of 2-butoxyethanol or sorbitan monolaurate was examined. Taken together, these results implied that SULT-mediated sulfation may function in the detoxification of these two oil dispersant compounds.

The specific alteration of histone methylation profiles by DZNep during early zebrafish development

Early embryo development constitutes a unique opportunity to study acquisition of epigenetic marks, including histone methylation. This study investigates the in vivo function and specificity of 3-deazaneplanocin A (DZNep), a promising anti-cancer drug that targets polycomb complex genes. One- to two-cell stage embryos were cultured with DZNep, and subsequently evaluated at the post-mid blastula transition stage for H3K27me3, H3K4me3 and H3K9me3 occupancy and enrichment at promoters using ChIP-chip microarrays. DZNep affected promoter enrichment of H3K27me3 and H3K9me3, whereas H3K4me3 remained stable. Interestingly, DZNep induced a loss of H3K27me3 and H3K9me3 from a substantial number of promoters but did not prevent de novo acquisition of these marks on others, indicating gene-specific targeting of its action. Loss/gain of H3K27me3 on promoters did not result in changes in gene expression levels until 24h post-fertilization. In contrast, genes gaining H3K9me3 displayed strong and constant down-regulation upon DZNep treatment. H3K9me3 enrichment on these gene promoters was observed not only in the proximal area as expected, but also over the transcription start site. Altered H3K9me3 profiles were associated with severe neuronal and cranial phenotypes at day 4-5 post-fertilization. Thus, DZNep was shown to affect enrichment patterns of H3K27me3 and H3K9me3 at promoters in a gene-specific manner.