Research On Reproductive Toxicity Of Enrofloxacin In Caenorhabditis Elegans

Antibiotics as the drugs against bacteria have been used in curing diseases and promoting the growth of livestock animals for several decades.Fluoroquinolone antibiotics（FQs）are one of the most popular antibiotics presently used worldwide for human health and animal farming due to their strong antibacterial activity,broad antibacterial spectrum,and low cross-resistance.In fact,those antibiotics were not completely absorbed or metabolized by humans and animals.A substantial proportion（30%-90%）of antibiotics was excreted with the parent form and/or metabolites,and accumulated into the environment owing to their long-term persistence.FQs have been frequently detected at high concentrations in soil and water environment associated with agriculture.FQs’environmental accumulation and ecological risks have aroused people’s great concern,but there are limited studies on the toxicity of FQs to soil animals.On the other hand,although a large number of medical studies have reported the side effects of FQs,previous toxicological studies have mainly been conducted by feeding or administering subcutaneously FQs to mammals,and the relevant studies have ignored non-intake but chronic FQs exposure.Soil nematodes are one of the most abundant and diverse groups of soil biota in terrestrial ecosystems.They are important regulators of soil microbial productivity,nutrient cycling and plant growth,and are considered excellent indicators of soil sustainability.However,up to date,the toxicity of FQs on the soil nematodes is rarely known.Caenorhabditis elegans（C.elegans）is the classical model organism of soil nematodes,which is widely used in environmental toxicology research because of its ease of culture,rapid reproduction and sensitivity to toxins.This study investigated the toxicity of chronic FQs exposure in C.elegans,and explore FQs’environmental risks and potential toxicological mechanisms.The results were described as follows:Results of the individual behaviour experiment showed that C.elegans exposed to FQs exhibited delayed development and shortened body length;slower pharyngeal pumping rate and head thrash frequency;small-brood size and low-egg hatchability.To study the underlying mechanism,we conduct a deep investigation of enrofloxacin（ENR）,one with the most significant toxic effects of the seven commonly used FQs,on nematodes.The concentration-effect curves simulated by the Hill model showed that the half effect concentrations(EC₅₀)of ENR were（494.3±272.9）μmol/kg and（107.4±30.9）μmol/kg for the brood size and the hatchability,respectively.The risk quotients of some soil and livestock samples were calculated based on the threshold value of EC10 for the egg hatchability（2.65μmol/kg）.The results indicated that there was possible reproductive toxicity on the nematodes in certain agricultural soils for the FQs.Differential gene expression between the control and the ENR-exposure group enriched with genes involved in the oxidative stress and cell apoptosis pathways（e.g.,isp-1 and pmk-1 genes）.Enrofloxacin caused concentration-dependent decrease in activity levels of the oxidative stress-related enzymes and the content of glutathione,and an increase in germ cell apoptosis in C.elegans.The antioxidants N-acetyl-L-cysteine（NAC,6.17μmol/kg）andβ-carotene（18.6μmol/kg）can partially rescue the harmful effects of ENR in individual reproduction,enzyme activity,and apoptosis.The above results suggest that ENR-induced reproductive toxicity was related to germ cell apoptosis under oxidative stress.In summary,C.elegans exposed to environmentally relevant FQs exhibited growth toxicity,neurotoxicity and reproductive toxicity.And apoptosis caused by oxidative stress may play a key role in ENR-induced reproductive toxicity in nematodes.The study not only alarm the ecological risks of FQs in the soil environment,but also provides a way to mitigate their toxic effects.