Geosmin disrupts energy metabolism and locomotor behavior of zebrafish in early life stages

Histology and transcriptomic analysis reveal the inflammation and affected pathways under 2-methylisoborneol (2-MIB) exposure on grass carp

2-Methylisoborneol (2-MIB) is a common and widely distributed off-flavor compound in water. However, the toxic mechanisms of 2-MIB on aquatic organisms remain largely unexplored. In this study, grass carp larvae were exposed to different concentrations (0, 5, and 20 μg L-1) of 2-MIB for 96 h. The accumulation of 2-MIB in the dorsal muscle was measured. Histological analysis, ultrastructure observations, and transcriptomic sequencing were conducted on the liver tissues. The results showed that 2-MIB accumulated significantly in the fish muscle, with the accumulation increasing as the exposure concentration increased through gas chromatography-mass spectrometry (GC-MS) detection. Histological and ultrastructure observations indicated that 2-MIB caused concentration-dependent inflammatory infiltration and mitochondrial damage in the liver. Transcriptomic analysis revealed lipid metabolism disorders induced by exposure to 2-MIB in grass carp. Additionally, 5 μg L-1 2-MIB affected the neurodevelopment and cardiovascular system of grass carp larvae through extracellular matrix (ECM)-receptor interaction and focal adhesion pathway. Furthermore, several pathways related to the digestive system were significantly enriched, implying that 2-MIB may impact pancreatic secretion function, protein digestion and absorption processes. These findings provide new insights into the potential toxicological mechanisms of 2-MIB.

Comprehensive mRNA and microRNA analysis revealed the effect and response strategy of freshwater fish, grass carp (Ctenopharyngodon idella) under geosmin exposure

Geosmin is an environmental pollutant that causes off-flavor in water and aquatic products. The high occurrence of geosmin contamination in aquatic systems and aquaculture raises public awareness, however, few studies have investigated the response pathways of geosmin stress on freshwater fish. In this research, grass carp were exposed to 50 μg/L geosmin for 96 h, liver tissue was sequenced and validated using real-time qPCR. In total of 528 up-regulated genes and 488 down-regulated genes were observed, includes cytochrome P450 and uridine diphosphate (UDP)-glucuronosyltransferase related genes. KEGG analysis showed that chemical carcinogenesis-DNA adducts, metabolism of xenobiotics by cytochrome P450, drug metabolism-cytochrome P450 pathway was enriched. Common genes from the target genes of microRNAs and differential expression genes are enriched in metabolism of xenobiotics cytochrome P450 pathway. Two miRNAs (dre-miR-146a and miR-212-3p) down regulated their target genes (LOC127510138 and adh5, respectively) which are enriched cytochrome P450 related pathway. The results present that geosmin is genetoxic to grass carp and indicate that cytochrome P450 system and UDP-glucuronosyltransferase play essential roles in biotransformation of geosmin. MicroRNAs regulate the biotransformation of geosmin by targeting specific genes, which contributes to the development of strategies to manage its negative impacts in both natural and artificial environments.

Determination of earthy-musty odors in tap water by gas chromatography‒mass spectrometry with silica solid-phase extraction

This research aimed to develop an effective method for detecting semivolatile earthy-musty odors without using the conventional sample processing equipment used for volatile compounds. The concurrent isolation of 2-methylisoborneol (2-MIB), trans-1,10-dimethyl-trans-9-decalol (geosmin, GSM), 2-isopropyl-3-methoxy pyrazine (IPMP), and 2-isobutyl-3-methoxy pyrazine (IBMP) in tap water was successfully achieved by employing a combination of n-hexane liquid‒liquid extraction (LLE) and silica solid-phase extraction (SPE) techniques. Gas chromatography-mass spectrometry (GC-MS) was utilized for the identification of these targets, with the inclusion of borneol (BN) as an internal reference. This robust method was optimized and validated. It was found that the method showed good linearity in the range of 0.5-100 ng/mL and produced good recoveries (84.6 %-103 %) with satisfactory relative standard deviations (1.50 %-10.1 %). The determined limits of detection (LODs) for the group of four substances were found to vary from 0.3 to 0.9 ng/L, whereas the limits of quantitation (LOQs) exhibited variations between 1 and 3 ng/L. The subsequent implementation of this methodology to evaluate the four previously described off-flavor chemicals in tap water resulted in satisfactory results.

Sodium butyrate alleviates deoxynivalenol-induced porcine intestinal barrier disruption by promoting mitochondrial homeostasis via PCK2 signaling

Deoxynivalenol (DON) is one of the most plentiful trichothecenes occurring in food and feed, which brings severe health hazards to both animals and humans. This study aims to investigate whether sodium butyrate (NaB) can protect the porcine intestinal barrier from DON exposure through promoting mitochondrial homeostasis. In a 4-week feeding experiment, 28 male piglets were allocated according to a 2 by 2 factorial arrangement of treatments with the main factors including supplementation of DON (< 0.8 vs. 4.0 mg/kg) and NaB (0.0 vs. 2 g/kg) in a corn/soybean-based diet. Dietary NaB supplementation mitigated the damaged mitochondrial morphology within the jejunal mucosa and the disrupted gut epithelial tight junctions irritated by DON. In IPEC-J2 cells, we found efficient recovery of the intestinal epithelial barrier occurred following NaB administration. This intestinal barrier reparation was facilitated by NaB-induced PCK2-mediated glyceroneogenesis and restoration of mitochondrial structure and function. In conclusion, we elucidated a mechanism of PCK2-mediated improvement of mitochondrial function by NaB to repair porcine intestinal barrier disruption during chronic DON exposure. Our findings highlight the promise of NaB for use in protecting against DON-induced gut epithelial tight junction disruption in piglets.

Volatile sensation: The chemical ecology of the earthy odorant geosmin

Geosmin may be the most familiar volatile compound, as it lends the earthy smell to soil. The compound is a member of the largest family of natural products, the terpenoids. The broad distribution of geosmin among bacteria in both terrestrial and aquatic environments suggests that this compound has an important ecological function, for example, as a signal (attractant or repellent) or as a protective specialized metabolite against biotic and abiotic stresses. While geosmin is part of our everyday life, scientists still do not understand the exact biological function of this omnipresent natural product. This minireview summarizes the current general observations regarding geosmin in prokaryotes and introduces new insights into its biosynthesis and regulation, as well as its biological roles in terrestrial and aquatic environments.

Elevated temperature decreases cardiovascular toxicity of nanoplastics but adds to their lethality: A case study during zebrafish (Danio rerio) development

To highlight the key role of global warming on the toxicity of contaminants, the cardiovascular toxicity of nanoparticles (NPs) was estimated in developing zebrafish (Danio rerio) at different exposure temperatures, and the toxicity mechanisms were explored via multi-omic analyses. Polystyrene NPs (50 nm) at 0.1 mg·L^-1 entered zebrafish embryos at 24 h post-fertilization and caused cardiovascular toxicity in the developing zebrafish at 27 ℃. This was explained by the down-regulation of the branched-chain amino acid and insulin signaling pathways owing to induced oxidative stress. Elevated exposure temperatures promoted the accumulation of NPs in developing zebrafish, increased the levels of oxidative stress and enhanced the oxidative phosphorylation rate in mitochondria, thus resulting in an additive effect on the mortality of zebrafish larvae. Notably, elevated exposure temperatures reduced the cardiovascular toxicity of NPs, as the effective concentration of NPs for inhibiting embryonic heartbeat rate increased from 0.1 mg·L^-1 at 27 ℃ to 1.0 mg·L^-1 at 30 ℃. Experiments of transgenic zebrafish Tg(myl7:GFP) and multi-omic analyses revealed that elevated temperatures enhanced the myocardial contractility of larvae, thus reducing the cardiovascular toxicity of NPs. However, the health risks of enhanced myocardial contraction caused by NP exposure at elevated temperatures requires further consideration.

Mitochondrial dysfunction in metabolic disorders induced by per- and polyfluoroalkyl substance mixtures in zebrafish larvae

Several per- and polyfluoroalkyl substances (PFAS) have been linked to metabolic disorders in organisms. However, few studies have considered their combined effects, which would be more representative of PFAS occurring in the environment. In this study, zebrafish embryos were exposed to a mixture of 18 PFAS at three environmentally relevant concentrations for 5 days to assess their bioconcentration and metabolic consequences. The burdens of ∑PFAS in zebrafish larvae were 0.12, 1.58, and 9.63 mg/kg in the 0.5, 5, and 50 μg/L treatment groups, respectively. Exposure to the PFAS mixture accelerated hatching and larval heart rates, increased energy expenditure, and reduced ATP levels and glucose contents due to decreased feed intake and glucose uptake. Metabolomic analysis revealed that exposure to the PFAS mixture enhanced glycolysis but inhibited phospholipid synthesis, and significantly increased the expression of lipid metabolism related genes (srebf1, acox, and pparα), which indicated enhanced β-oxidation. The significant changes in mitochondrial membrane potential, mitochondrial content, and the transcription of genes involved in the mitochondrial respiratory chain (mfn2, ndufs1, atp5fa1, and mt-nd1) and mitochondrial DNA replication and transcription (18rs-rrn, and polg1) suggested that exposure to the PFAS mixture could cause mitochondrial dysfunction and further disrupt glucose and lipid metabolic pathways, ultimately causing metabolic disorders in zebrafish larvae. These findings demonstrate the importance of assessing the metabolic effects of PFAS mixtures on early development in wildlife and humans.