Mechanism Of Neurotoxicity Effects Induced By Heterocyclic Aromatic Amines In Caenorhabditis Elegans

Heterocyclic aromatic amines(HAAs)are a type of heterocyclic compounds formed from free amino acids,creatinine,and other carbohydrates during the thermal processing of food,which are widely found in protein-rich processed meat products.Dietary intake of HAAs is difficult to metabolize in the body and longterm accumulation is potentially harmful to human health.Studies have shown that in addition to carcinogenicity and mutagenicity,HAAs also have potential neurotoxicity and may be related to the pathogenesis of neurodegenerative diseases such as Parkinson’s syndrome(PD)and Alzheimer’s disease(AD).At present,the neurotoxicity and mechanisms of toxicity of many HAAs are still unclear,so it is still necessary to use a suitable biological model to systematically evaluate their neurotoxic effects.Caenorhabditis elegans(C.elegans)is a common model organism that has been widely used for toxicological assessment and mechanistic studies of environmental and food contaminants due to its good physiological structure and clear genetic background.Based on this,a class of HAAs,β-carboline HAAs,including 9H-pyrido[3,4-b]indole(Norharman)and 1-methyl-9H-pyrido[3,4-b]indole(Harman),were selected for this study,which is produced at relatively high levels in thermally processed meat products.C.elegans was selected as the test animal in this study to comprehensively explore the neurotoxic effects induced by HAAs,provide toxicological evidence for the risk assessment of HAAs,and to further investigate the toxicity mechanism of molecular regulation with the help of transcriptomics on a high-throughput sequencing platform,in order to provide data support for the study of the toxicity mechanism of HAAs.The primary study components and results are as follows:(1)Preliminary assessment of the toxic effects of acute and chronic exposure to HAAs of C.elegans.Taking Norharman and Harman as the research objects,the acute lethal toxicity of HAAs on C.elegans was explored by acute exposure for 24 h.The experimentally obtained LC50 values of Norharman and Harman were 64.38 mg/L and 164.26 mg/L,respectively.There was a significant dose-effect relationship between nematode mortality and the concentrations of Norharman and Harman.The following experimental exposure concentrations of 0,0.05,5,and 10 mg/L were selected based on the acute toxicity results and exposure concentrations in foods,and the effects on locomotor behavior,growth,and nematode longevity were tested after acute(24 h)and chronic(6 d)exposures,respectively.The study found that compared with acute exposure,chronic exposure had more significant effects on locomotor behavior,growth,and longevity in C.elegans,showing more obvious toxic effects.(2)The effects of chronic exposure to HAAs on the nervous system of C.elegans were studied.Neurobehavioral indicators of nematodes,including foraging ability and chemotaxis,were measured after chronic exposure.It was found that Norharman and Harman caused a decrease in nematode foraging ability and an increase in chemotaxis index,which affected their normal learning and memory abilities.The biochemical indexes of nematodes were determined.It was found that exposure to two HAAs caused the accumulation of ROS and MDA in C.elegans and reduced the activities of antioxidant enzymes SOD and CAT,indicating that Norharman and Harman can induce oxidative stress in the body,and oxidative stress is one of the reasons for the changes in neurobehavior in C.elegans.In addition,the activity of AChE in C.elegans decreased after chronic exposure,and the content of neurotransmitters including ACh and DA also changed,indicating that Norharman and Harman exposure changed the content of neurotransmitters in vivo,causing neurotoxic effects.The damage to the nervous system of nematodes is another major reason to change the learning and memory abilities.(3)Transcriptomic sequencing was used to analyze the effect of Norharman and Harman exposure on the gene expression of nematodes.The number of differentially expressed genes(DEGs)after Norharman exposure was 1005,with 853 up-regulated genes and 152 down-regulated genes.After Harman exposure,there were 183 DEGs in total,116 of them up-regulated and 67 of them downregulated.Further bioinformatics analyses,such as GO and KEGG,were combined to explore the possible related signaling pathways.The RNA sequencing data revealed that the genes involved in the metabolism of xenobiotics by cytochrome P450,the longevity-regulating pathway,and the axon regeneration pathway played a regulatory role in C.elegans after Norharman and Harman exposure.