Molecular Modification And Toxicity Risk Prediction On Biotoxicity And Degradation Of Quinolones And Derivatives

Quinolones（QNs）antibiotics are consumed in large quantities in China,accounting for about 15%of the total consumption of antibiotics for human,livestock and poultry use.QNs are difficult to degrade,with a long half-life and low removal rate,which cannot be completely absorbed by organisms and permanently pollute the natural environment such as soil,water and sediment.The biotoxicity of QNs can stress animals and plants to produce different degrees of negative response,and the resistance genes（ARGs）induced by QNs can significantly reduce the effectiveness of antibiotic treatment.In addition,most antibiotics remain active after they are metabolized in organisms,or are converted to more toxic products.In this paper,a variety of environmental effects of QNs were taken as the entry point to study the two-way choice between QNs biotoxicity and genotoxicity,as well as the plant-microbial synergistic degradation effect.The purpose of this study was to reduce the biotoxicity of QNs,improve the genotoxicity and the plant-microbial synergistic degradation effect.Based on molecular docking and molecular dynamics（MD）methods,the revised double-effect 3D-QASR model of a two-way choice between QNs biotoxicity and genotoxicity,and the revised comprehensive effect 3D-QASR model of plant-microbial synergistic degradation were constructed to modify environmental-friendly QNs molecules at the source,and explore the prevention strategies and toxicity risk mechanisms.In this paper,the double-effect 3D-QASR（Co MFA）model of a two-way choice between QNs biotoxicity and genotoxicity was constructed with the variation weighting method.The main parameters of the model were the cross-validated（q²）was 0.767（>0.5）;the optimal principal component（n）was 3;the non-cross-validated（R²）was0.996（>0.8）;the standard error of estimate（SEE）was 0.008（<0.95）;and the correlation coefficient(r²_pred)was 0.967（>0.6）,indicating that the model has good prediction ability,fitting ability,stability and reliability.According to analysis of the CoMFA model force fields and three-dimensional contour（3D-contour）maps,the contribution rates of steric field and electrostatic field were 75.6%and 24.4%,respectively.Enrofloxacin（ENR）and Sparfloxacin（SPA）were used as target molecules to modify related groups near the active sites in single and double modification ways.A total of 46 QNs derivatives with reduced biotoxicity were modified and evaluated for environmental friendliness and functional properties.A total of 8 environmental-friendly QNs derivatives with low biotoxicity and high genotoxicity（the highest variation range were 20.11%and 7.84%,respectively）were screened out.The change rate of parameters（eg.hepatotoxicity,potential developmental toxicity,mutagenicity,rodent carcinogenicity,skin sensitization,skin irritation,eye irritation and rat oral toxicity predicted by pharmacokinetics and toxicokinetics）were defined as the potential toxicity risk of QNs prior to and after modification.After modification,hepatotoxicity and rat oral toxicity of ENR were significantly reduced by 20.65%-221.51%and 40.30%-451.49%respectively,and hepatotoxicity of SPA was reduced by 28.86%-83.05%,most of the derivatives were not mutagenic,sensitive or eye irritating.In addition,based on the mixed toxicity index method and molecular dynamics method,the aided verification prior to and after modification of multiple QNs mixtures in the combined toxicity effects mechanism in the soil environment.The combined toxicity of multiple QNs mixtures significantly reduced up to 38.61%（relative amplitude）,and the application of modified QNs and their derivatives in different soil types has reduced the risk of soil environment,while the risk in farmland soil environment was the lowest,which confirmed that the modified derivatives could be used as theoretical reserve for the replacement of QNs antibiotics in the direction of environment and plant friendliness.Furthermore,this paper explored the molecular modification scheme to improve the plant-microbial synergistic degradation effect of QNs,and proposed the source prevention and control strategies to reduce the residual and hazard of QNs in the plant-soil complex environment,as well as the potential toxicity risk.The comprehensive effect Co MSIA model of QNs plant-microbial synergistic degradation effect was constructed by fuzzy comprehensive evaluation coupled with weighted average method.The main parameters of the model were the cross-validated（q²）was 0.707（>0.5）;the optimal principal component（n）was 8;the non-cross-validated（R²）was 0.999（>0.8）;the standard error of estimate（SEE）was 0.308（<0.95）;and the correlation coefficient(r²_pred)was 0.901（>0.6）,indicating that the constructed model has reliable prediction ability,fitting ability and robustness.According to the Co MSIA model field and 3D-contour maps,the contribution rates of steric field,electrostatic field,hydrophobic field,hydrogen bond acceptor field and hydrogen bond donor field were 19.1%,21.7%,27.4%,22.5%and 9.3%,respectively,indicating that electrostatic field,hydrophobic field and hydrogen bond acceptor field were the main factors affecting the QNs plant-microbial synergistic degradation effect.Norfloxacin（NOR）was used as the target molecule for single and double substitution modifications.A total of 35 NOR derivatives with enhanced synergistic degradation effect（1.32%-21.51%）were modified successfully.The environmental friendliness and functional properties of NOR prior to and after modification were evaluated.Screening 7 environmental-friendly QNs derivatives with moderately improved stability and bactericidal efficacy.In addition,the density functional theory（DFT）was used to simulate the plant and microbial transformation pathways of NOR prior to and after modification,and the reaction energy barrier（ΔE）was calculated to find the most likely plant and microbial degradation pathways of NOR derivatives after modification,and it was inferred that hydroxylation and piperazine ring substitution reactions played a significant role in the transformation process.Finally,based on pharmacokinetics and toxicokinetics prediction of toxicity parameters,it was confirmed that the modified QNs molecules and their transformation products significantly reduced the potential toxicity risk,while the hepatotoxicity of NOR reduced by 238.80%-314.45%,and the hepatotoxicity and rat oral toxicity of derivative D-17 transformation products reduced by 67.93%-139.91%and 24.87%-496.30%,respectively.In this paper,a system of comprehensive screening,evaluation and source prevention which can be applied to reduce the QNs biotoxicity and enhance the genotoxicity,as well as the plant-microbial synergistic degradation effect is established based on theoretical calculation and simulation.It includes comprehensive effects 3D-QSAR model construction,molecular modification,drug environmental friendliness and functional properties evaluation,transformation pathways simulation and potential toxicity risk prediction.And the limitation of traditional 3D-QSAR model was broke by introducing mathematical methods to integrate the single environmental effect into multiple environmental effects.The results of this study provide feasible theoretical ideas,methods and guidance for pollution source prevention and new drug design.