Risk assessment of the chiral pesticide fenamiphos in a human model: Cytochrome P450 phenotyping and inhibition studies

Synergistic toxic effects and mechanistic insights of beta-cypermethrin and pyraclostrobin exposure on hook snout carp (Opsariichthys bidens): A biochemical, transcriptional, and molecular approach

The extensive utilization of pesticides results in their frequent detection in aquatic environments, often as complex mixtures, posing risks to aquatic organisms. The hook snout carp (Opsariichthys bidens) serves as a valuable bioindicator for evaluating the impacts of environmental pollutants in aquatic ecosystems. However, few studies examined the toxic effects of pesticides on O.bidens, let alone the characterization of the combined effects resulting from their mixtures. This study aims to elucidate the toxic effects of beta-cypermethrin and pyraclostrobin on O.bidens, individually and in combination, focusing on biochemical, transcriptional, and molecular responses. By organizing and analyzing the toxicogenomic databases, both pesticides were identified as a contributor to processes such as apoptosis, oxidative stress, and inflammatory responses. The acute toxicity test revealed comparable acute toxicity of beta-cypermethrin and pyraclostrobin on O.bidens, with LC50 being 0.019 and 0.027 mg/L, respectively, whereas the LC50 decreased to 0.0057 and 0.0079 mg/L under the combined exposure, indicating potential synergistic effects. The activities of enzymes involved in oxidative stress and detoxification were significantly altered after exposure, with superoxide dismutase (SOD) and catalase (CAT) increasing, while malondialdehyde (MDA) levels decreased. The activity of CYP450s was significantly changed. Likewise, the expression levels of genes (mn-sod, p53, esr, il-8) associated with oxidative stress, apoptosis, endocrine and immune systems were significantly increased. Combined exposure to the pesticides significantly exacerbated the aforementioned biological processes in O.bidens. Furthermore, both pesticides can modify protein activity by binding to the surface of SOD molecules and altering protein conformation, contributing to the elevated enzyme activity. Through the investigation of the synergistic toxic effects of pesticides and molecular mechanisms in O.bidens, our findings highlight the importance of assessing the combined effects of pesticide mixtures in aquatic environments.

Enantioselectivity regulation of antibody against chiral herbicide metolachlor based on interaction at chiral center

Enantioselective antibodies have emerged as great potential biomaterials in the fields of immunoassays and chiral separation. However, cross-reactivity of antibodies to the distomer may severely restrict the application. Comprehending the interaction mechanism between antibodies and enantiomers could be beneficial to produce superior enantioselective antibodies. In this study, a pair of recombinant antibodies (RAbs) against metolachlor enantiomers at chiral carbon (αSS-MET and αSR-MET) were generated and characterized. The αSS-MET-RAb and αSR-MET-RAb showed comparable sensitivity and specificity to the parental monoclonal antibodies by icELISA, with IC50 values of 3.45 and 223.77 ng/mL, respectively. Moreover, the complex structures of RAbs and corresponding eutomer were constructed and analyzed, and site-specific mutagenesis was utilized to verify the reliability of the enantioselective mechanism elucidated. It demonstrated that the strength of the interaction between the chiral center region of eutomer and the antibody was the key factor for the enantioselectivity of antibody. Increasing this interaction could limit the conformational adjustment of the distomer in a specific chiral recognition cavity, thus decreasing the affinity of the antibody to the distomer. This work provided the in-depth analysis of enantioselective mechanism for two RAbs and paved the way to regulate antibody enantioselective performance for immunoassays of chiral compounds.

Human CYP2C19 Substrate and Inhibitor Characterization of Organophosphate Pesticides

CYP2C19 is an important enzyme for organophosphate pesticide (OPP) metabolism. Because the OPPs can be both substrates and inhibitors of CYP2C19, we screened 45 OPPs for their ability to inhibit the activity of this enzyme and investigated the role of CYP2C19 in the metabolism of 22 of these molecules. We identified several nanomolar inhibitors of CYP2C19 as well as determined that thions, in general, are more potent inhibitors than oxons. We also determined that thions are readily metabolized by CYP2C19, although we saw no relationship between IC50 values and intrinsic clearance rates. This study may have implications for mitigating the risk of OPP poisoning.

Dissecting the Enantioselective Neurotoxicity of Isocarbophos: Chiral Insight from Cellular, Molecular, and Computational Investigations

Chiral organophosphorus pollutants are found abundantly in the environment, but the neurotoxicity risks of these asymmetric chemicals to human health have not been fully assessed. Using cellular, molecular, and computational toxicology methods, this story is to explore the static and dynamic toxic actions and its stereoselective differences of chiral isocarbophos toward SH-SY5Y nerve cells mediated by acetylcholinesterase (AChE) and further dissect the microscopic basis of enantioselective neurotoxicity. Cell-based assays indicate that chiral isocarbophos exhibits strong enantioselectivity in the inhibition of the survival rates of SH-SY5Y cells and the intracellular AChE activity, and the cytotoxicity of (S)-isocarbophos is significantly greater than that of (R)-isocarbophos. The inhibitory effects of isocarbophos enantiomers on the intracellular AChE activity are dose-dependent, and the half-maximal inhibitory concentrations (IC₅₀) of (R)-/(S)-isocarbophos are 6.179/1.753 μM, respectively. Molecular experiments explain the results of cellular assays, namely, the stereoselective toxic actions of isocarbophos enantiomers on SH-SY5Y cells are stemmed from the differences in bioaffinities between isocarbophos enantiomers and neuronal AChE. In the meantime, the modes of neurotoxic actions display that the key amino acid residues formed strong noncovalent interactions are obviously different, which are related closely to the molecular structural rigidity of chiral isocarbophos and the conformational dynamics and flexibility of the substrate binding domain in neuronal AChE. Still, we observed that the stable "sandwich-type π-π stacking" fashioned between isocarbophos enantiomers and aromatic Trp-86 and Tyr-337 residues is crucial, which notably reduces the van der Waals' contribution (ΔG_vdW) in the AChE-(S)-isocarbophos complexes and induces the disparities in free energies during the enantioselective neurotoxic conjugations and thus elucidating that (S)-isocarbophos mediated by synaptic AChE has a strong toxic effect on SH-SY5Y neuronal cells. Clearly, this effort can provide experimental insights for evaluating the neurotoxicity risks of human exposure to chiral organophosphates from macroscopic to microscopic levels.

Cytochrome P450 isoforms contribution, plasma protein binding, toxicokinetics of enniatin A in rats and in vivo clearance prediction in humans

Emerging mycotoxins, such as enniatin A (ENNA), are becoming a worldwide concern owing to their presence in different types of food and feed. However, comprehensive toxicokinetic data that links intake, exposure and toxicological effects of ENNA has not been elucidated yet. Therefore, the present study investigated the in vitro (rat and human) and in vivo (rat) toxicokinetic properties of ENNA. Towards this, an easily applicable and sensitive bioanalytical method was developed and validated for the estimation of ENNA in rat plasma. ENNA exhibited high plasma protein binding (99%), high hepatic clearance and mainly underwent metabolism via CYP3A4 (74%). The in-house predicted hepatic clearance (54 mL/min/kg) and observed in vivo rat clearance (55 mL/min/kg) were comparable. The predicted in vivo human hepatic clearance was 18 mL/min/kg. ENNA underwent slow absorption (T_max = 4 h) and rapid elimination following oral administration to rats. The absolute oral bioavailability was 47%. The toxicokinetic findings for ENNA from this study will help in designing and interpreting toxicological studies in rats. Besides, these findings could be used in physiologically based toxicokinetic (PBTK) model development for exposure predictions and risk assessment for ENNA in humans.

Enantioselective inhibition of human CYP2C19 by the chiral pesticide ethofumesate: Prediction of pesticide-drug interactions in humans

Ethofumesate is a chiral herbicide that may display enantioselective behavior in humans. For this reason, the enantioselective potential of ethofumesate and its main metabolite ethofumesate-2-hydroxy to cause pesticide-drug interactions on cytochrome P450 forms (CYPs) has been evaluated by using human liver microsomes. Among the evaluated CYPs, CYP2C19 had its activity decreased by the ethofumesate racemic mixture (rac-ETO), (+)-ethofumesate ((+)-ETO), and (-)-ethofumesate ((-)-ETO). CYP2C19 inhibition was not time-dependent, but a strong inhibition potential was observed for rac-ETO (IC₅₀ = 5 ± 1 μmol L^-1), (+)-ETO (IC₅₀ = 1.6 ± 0.4 μmol L^-1), and (-)-ETO (IC₅₀ = 1.8 ± 0.4 μmol L^-1). The reversible inhibition mechanism was competitive, and the inhibition constant (K_i) values for rac-ETO (2.6 ± 0.4 μmol L^-1), (+)-ETO (1.5 ± 0.2 μmol L^-1), and (-)-ETO (0.7 ± 0.1 μmol L^-1) were comparable to the K_i values of strong CYP2C19 inhibitors. Inhibition of CYP2C19 by ethofumesate was enantioselective, being almost twice higher for (-)-ETO than for (+)-ETO, which indicates that this enantiomer may be a more potent inhibitor of this CYP form. For an in vitro-in vivo correlation, the Food and Drug Administration's (FDA) guideline on the assessment of drug-drug interactions used in the early stages of drug development was used. The FDA's R₁ values were estimated on the basis of the obtained ethofumesate K_i and distribution volume, metabolism, unbound plasma fraction, gastrointestinal and dermal absorption data available in the literature. The correlation revealed that ethofumesate probably inhibits CYP2C19 in vivo for both chronic (oral) and occupational (dermal) exposure scenarios.

Enzymes, Reacting with Organophosphorus Compounds as Detoxifiers: Diversity and Functions

Organophosphorus compounds (OPCs) are able to interact with various biological targets in living organisms, including enzymes. The binding of OPCs to enzymes does not always lead to negative consequences for the body itself, since there are a lot of natural biocatalysts that can catalyze the chemical transformations of the OPCs via hydrolysis or oxidation/reduction and thereby provide their detoxification. Some of these enzymes, their structural differences and identity, mechanisms, and specificity of catalytic action are discussed in this work, including results of computational modeling. Phylogenetic analysis of these diverse enzymes was specially realized for this review to emphasize a great area for future development(s) and applications.