Are Fish Populations at Risk? Metformin Disrupts Zebrafish Development and Reproductive Processes at Chronic Environmentally Relevant Concentrations

Are environmental levels of gabapentin (GBP) a cause for concern? Chronic reproductive effects of GBP in zebrafish

GBP, a widely used antiepileptic drug, is frequently detected in aquatic environments due to inefficient removal in wastewater treatment. This study investigates the chronic reproductive toxicity of GBP in zebrafish (Danio rerio), a model species for endocrine disruption. Exposure began at 20 days post-fertilization (dpf), coinciding with sex differentiation, and continued for 130 days at environmentally relevant concentrations (1, 10, and 100 μg/L). Our results demonstrated that chronic GBP exposure, even at 1 μg/L, significantly impaired reproductive health in zebrafish, including gonadal development, reduced fecundity, and even the developmental success in the F1 generation. Gene expression analysis revealed alterations in key genes of the hypothalamic-pituitary-gonadal (HPG) axis, resulting in sex-dependent hormonal dysregulation. These findings highlight the potential ecological risks of GBP contamination, where even low concentrations can profoundly affect fish reproduction. The study emphasizes the need for further research on pharmaceutical pollutants and their long-term impacts, as well as improved wastewater treatment processes to mitigate pharmaceutical contamination in aquatic ecosystems.

Effects of nano- and micro- fibers derived from surgical face masks in Danio rerio

The massive use of surgical face masks during the COVID-19 pandemic has compounded the challenge of plastic waste. Surgical face masks are made of polypropylene (PP) and tend to release nano- and micro- fibers (NMFs). The present study aims to provide insights into the impacts of NMFs in aquatic organisms by evaluating the effects of PP-NMFs derived from the artificial photodegradation of surgical face masks on the model species Danio rerio (zebrafish). The impact of NMFs on embryonic and larval developmental stages has been evaluated by investigating the effects of low (0.2 mg/L), medium (1 mg/L), and high (5 mg/L) NMF levels. Alterations in apical endpoints and transcriptomic analysis were investigated. After 6 days, a significant reduction in the eye area was observed. The upregulation of genes related to the negative regulation of developmental processes could explain the observed alterations, while the downregulation of genes involved in energy-related metabolic processes suggests an energy stress state. Increased mortality occurred between 9 and 12 days, a period when zebrafish make the transition from endogenous to exogenous feeding, suggesting an impairment in foraging behaviour due to NMF exposure. The presented findings demonstrate that environmental levels of NMFs may pose a hazard to aquatic organisms, suggesting the potential for an ecotoxicological risk associated with the improper disposal of surgical face masks.

The toxicity comparison of metformin and its degradant guanylurea through multi-routes exposure experiments using algae and rotifer

Metformin (MET) and its metabolite guanylurea (GUA) are prevalent in aquatic environments, raising concerns about their potential risks to aquatic organisms. However, the toxicity of these compounds through different exposure routes has not been reported. This study evaluated the effects of MET and GUA on the growth of the green algae Tetradesmus obliquus and on life table parameters of the freshwater rotifer Brachionus calyciflorus through various exposure routes, including waterborne, foodborne, and combined waterborne + foodborne. Our results indicated that both MET and GUA, at concentrations of 1 mg/L and 100 mg/L, inhibited algae growth, with GUA causing greater stress than MET. Additionally, compared to waterborne exposure, foodborne and combined waterborne + foodborne exposures of MET and GUA at these concentrations significantly decreased the net reproductive rate (R0), intrinsic rate of population increase (rm), and life expectancy (e0) of B. calyciflorus. Notably, the impact of exposure routes on the life table parameters of B. calyciflorus was generally greater than the impact of exposure concentrations. Therefore, previous studies focusing solely on waterborne exposure may have underestimated the toxicity of MET and GUA.

Do (xeno)estrogens pose a risk to earthworms? Soy isoflavones and estradiol impact gonad structure and induce oxidative stress in Eisenia fetida

Understanding the impact of endocrine disruptor compounds (EDCs) across a wide range of species is crucial, given their ubiquitous presence. Although invertebrate species lack sex steroid hormone pathways, they exhibit sensitivity to EDCs, which could affect population dynamics. This study assessed reproductive endpoints and oxidative stress parameters in Eisenia fetida following exposure to estradiol and soy isoflavones, resembling the concentrations found in livestock manure. The experiment used artificial soil, as recommended by OECD guidelines (7:2:1 sand, kaolin and peat). Adult specimens were randomly divided into seven groups (n = 11/replicate): one control, three estradiol (156.1, 283.4 and 633.8 μg/kg of dry soil) and three soy isoflavones (113.0, 215.3 and 405.0 mg/kg of dry soil) concentrations. After eight weeks, samples were collected for cytological, histological and biochemical analysis. Offspring development was assessed after 12 additional weeks. Higher estradiol and isoflavone concentrations led to lower germ cell number and increased abnormalities, especially in the seminal vesicles and ovaries. Catalase and peroxidase activities were significantly increased in all treated groups. The exposure did not significantly affect the number of E. fetida offspring. These findings highlight E. fetida's sensitivity to EDCs at a biochemical and tissue level, suggesting its use as a bioindicator for assessing EDC contamination in soils.

Common antimicrobials disrupt early zebrafish development through immune-cardiac signaling

The global production and use of antimicrobial chemicals surged during and after the COVID-19 pandemic, yet their developmental toxicity in aquatic organisms at environmentally relevant concentrations remains poorly understood. Here, we investigate and compare the developmental effects of two restricted antimicrobial chemicals-triclosan (TCS) and triclocarban (TCC)-and three alternative antimicrobials-benzalkonium chloride (BAC), benzethonium chloride (BEC), and chloroxylenol (CX)-on zebrafish embryos (Danio rerio) at concentrations of 0.4, 4, and 40 μg L-1. We find that BAC induces the most severe reduction in hatching rates, followed by TCS, TCC, BEC, and CX. BAC also exhibits the strongest inhibition of heart rate, with toxicity levels comparable to those of TCS and TCC. All tested chemicals, except CX, cause significant teratogenic effects. Transcriptomic analysis reveals substantial disruptions in immune-related coagulation cascades and mitogen-activated protein kinase signaling pathways. Further validation via protein-protein interaction network analysis and real-time quantitative polymerase chain reaction confirms that altered expression of key hub genes in these pathways impacts bone and heart development, as well as immune system function, potentially driving developmental toxicity. This study provides the first systematic comparison of developmental toxicity among currently used antimicrobials at environmentally relevant concentrations, revealing that the alternative antimicrobial BAC poses greater developmental risks than the banned TCS and TCC. These findings raise concerns about the safety of BAC as a widespread substitute and highlight the necessity for more rigorous environmental risk assessments of alternative antimicrobials before their large-scale application.

Are Environmental Levels of Nonsteroidal Anti-Inflammatory Drugs a Reason for Concern? Chronic Life-Cycle Effects of Naproxen in Zebrafish

The nonsteroidal anti-inflammatory drug naproxen (NPX) is among the most consumed pharmaceuticals worldwide, being detected in surface waters within the ng to μg/L range. Considering the limited chronic ecotoxicity data available for NPX in aquatic ecosystems, the present study aimed at evaluating its impact in the model organism Danio rerio, following a full life-cycle exposure to environmentally relevant concentrations (0.1 to 5.0 μg/L). An integration of apical endpoints, i.e., survival, growth, and reproduction, with gonad histopathology and gene transcription (RNA-seq) was performed to provide additional insights into the mode of action (MoA) of NPX. NPX decreased zebrafish growth and reproduction and led to histopathological alterations in gonads at concentrations as low as 0.1 μg/L. At the molecular level, 0.7 μg/L of NPX led to a disruption in gonads transcription of genes involved in several biological processes associated with reproduction, mainly involving steroid hormone biosynthesis and epigenetic/epitranscriptomic machineries. Collectively, these results show that environmentally realistic concentrations of NPX affect zebrafish reproduction and associated signaling pathways, indicating that current hazard and risk assessment data for NPX underestimate the environmental risk of this pharmaceutical.

Transcriptome-Guided Characterization of the Environmental Toxicity of Metformin: Disruption of Energy Homeostasis and Inhibition of Embryonic Development of Zebrafish at Environmentally Relevant Concentrations

Metformin has been widely detected in aquatic ecosystems, yet the knowledge of its impact on aquatic organisms, particularly at environmentally relevant concentrations, remains limited. In the present study, we characterized the developmental toxicity of metformin in zebrafish, utilizing a transcriptome-guided toxicological assessment framework. Transcriptomic analysis conducted at metformin concentrations within the μg/L range revealed significant disruptions in biological processes associated with nucleotide, hydrocarbon, and amino acid metabolism, suggesting a significant disturbance in energy homeostasis. This observation was corroborated by energy-targeted metabolomic analysis, wherein a considerable number of metabolites involved in purine metabolism, pyrimidine metabolism, and the citrate cycle displayed significant alterations. Notably, most intermediates in the citrate cycle such as acetyl-CoA exhibited remarkable decreases. Additionally, our study identified significant impediments in zebrafish embryonic development, including decreased yolk extension progress, spontaneous contraction and body length, and increased yolk sac area and yolk/while body lipid content ratio, at metformin concentrations as low as 0.12 μg/L. Furthermore, the disruption of energy homeostasis by metformin was observed to persist into adulthood even after a prolonged recovery period. The present findings highlighted the disruptive effects of metformin on energy homeostasis and embryonic development in teleost at environmentally relevant concentrations, thereby prompting a reevaluation of its environmental risk to nontarget aquatic organisms.

Dinickel enzyme evolved to metabolize the pharmaceutical metformin and its implications for wastewater and human microbiomes

Metformin is the first-line treatment for type II diabetes patients and a pervasive pollutant with more than 180 million kg ingested globally and entering wastewater. The drug's direct mode of action is currently unknown but is linked to effects on gut microbiomes and may involve specific gut microbial reactions to the drug. In wastewater treatment plants, metformin is known to be transformed by microbes to guanylurea, although genes encoding this metabolism had not been elucidated. In the present study, we revealed the function of two genes responsible for metformin decomposition (mfmA and mfmB) found in isolated bacteria from activated sludge. MfmA and MfmB form an active heterocomplex (MfmAB) and are members of the ureohydrolase protein superfamily with binuclear metal-dependent activity. MfmAB is nickel-dependent and catalyzes the hydrolysis of metformin to dimethylamine and guanylurea with a catalytic efficiency (kcat/KM) of 9.6 × 103 M-1s-1 and KM for metformin of 0.82 mM. MfmAB shows preferential activity for metformin, being able to discriminate other close substrates by several orders of magnitude. Crystal structures of MfmAB show coordination of binuclear nickel bound in the active site of the MfmA subunit but not MfmB subunits, indicating that MfmA is the active site for the MfmAB complex. Mutagenesis of residues conserved in the MfmA active site revealed those critical to metformin hydrolase activity and its small substrate binding pocket allowed for modeling of bound metformin. This study characterizes the products of the mfmAB genes identified in wastewater treatment plants on three continents, suggesting that metformin hydrolase is widespread globally in wastewater.

Metformin: update on mechanisms of action and repurposing potential

Currently, metformin is the first-line medication to treat type 2 diabetes mellitus (T2DM) in most guidelines and is used daily by >200 million patients. Surprisingly, the mechanisms underlying its therapeutic action are complex and are still not fully understood. Early evidence highlighted the liver as the major organ involved in the effect of metformin on reducing blood levels of glucose. However, increasing evidence points towards other sites of action that might also have an important role, including the gastrointestinal tract, the gut microbial communities and the tissue-resident immune cells. At the molecular level, it seems that the mechanisms of action vary depending on the dose of metformin used and duration of treatment. Initial studies have shown that metformin targets hepatic mitochondria; however, the identification of a novel target at low concentrations of metformin at the lysosome surface might reveal a new mechanism of action. Based on the efficacy and safety records in T2DM, attention has been given to the repurposing of metformin as part of adjunct therapy for the treatment of cancer, age-related diseases, inflammatory diseases and COVID-19. In this Review, we highlight the latest advances in our understanding of the mechanisms of action of metformin and discuss potential emerging novel therapeutic uses.