Thyroid-disrupting Chemicals: Thyroxine Transport Toxicity-directed Recognition And Their Health Risk On The Aged

Thyroid hormones play important physiological functions in human growth,energy metabolism and nerve development.Thyroid is one of the tissues with the most distributed capillaries in human body,which makes thyroid cells easily exposed to various environmental pollutants.Among the exposed pollutants,thyroid-disrupting chemicals(TDCs)can affect the processes of synthesis,transport,conversion and metabolism of thyroid hormones,thus disrupting hormonal levels and causing a series of health effects.Studies have shown that the sum of toxic effects of known TDCs only accounts for a small part of the total toxicity of the sample,and there are a large number of unknown disruptors.So,targeted analysis of known pollutants can no longer meet the needs of environmental health researches.Effect-directed analysis(EDA),which is in the fronteir of environmental chemistry,uses specific biological toxic effects as indicators to guide component separation,chemical analysis and identification of pollutants.By EDA method,we can efficiently screen unknown substances in samples.Among the 18 thyroid toxicity evaluation methods proposed by the organization of economic cooperation and development,the top three are the transthyretin(TTR)competitive binding experiments.However,this method has the disadvantages of large protein consumption,complex operation,time-consuming,and radioactive hazards.Molecularly imprinted materials are three-dimensional polymers,which are also known as biomimetic antibodies.They can not only selectively enrich target molecules and(or)structural analogues,but also have compatibility with analytical methods such as chromatography.Molecularly imprinted materials have exhibited excellent performances in many fields.Based on this,we innovatively prepared thyroxine imprinted bionic materials in this study,which could replace expensive transport proteins for highly selective recognition and binding of thyroxine and its disruptors.Moreover,the toxic effects of disruptors were revealed by their binding ability.On this basis,the imprinted materials were packed into a column and used as the stationary phase.By chromatographic separation,a new system for identifying and analyzing pollutants with TTR toxicity was established using retention factor as an evaluation index.The system can not only realize the identification and analysis of known/unknown TDCs,but also provide the toxicity factors of chemicals.Subsequently,a cross-sectional study was carried out to investigate the correlation between TDCs exposure and thyroid hormones.In this way,we can evaluate the thyriod toxic effects of TDCs from the macro level.Part ?: Preparation and evaluation of thyroxine imprinted biomimetic materialsObjective: To prepare molecularly imprinted biomimetic materials using thyroxine as the template to replace the expensive transport proteins for highly selective recognition of thyroxine and its disruptors,and to further explore the recognition mechanisms of molecularly imprinted pores.Methods: Atom transfer radical polymerization was used to prepare thyroxine imprinted biomimetic materials on the surface of silica particles.The structures and functional groups of imprinted biomimetic materials were characterized by infrared spectroscopy,X-ray photoelectron spectroscopy,scanning electron microscopy,and thermogravimetric analysis.Then,isothermal adsorption experiments,adsorption kinetics experiments,and selective adsorption experiments were used to evaluate the adsorption performances of imprinted biomimetic materials.The selective binding mechanisms of imprinted biomimetic materials were further explored through model fitting.Results: Imprinted biomimetic materials prepared from commercial functional monomers show poor selective recognition performances,which cannot meet practical application needs.In view of the fact that amino acids are the basic building blocks of transport proteins,we performed affinity chromatography among the amino acid library and tryptophan was found to have the highest affinity for template molecule.On this basis,2-(3-indol-yl)ethylmethacrylamide was synthesized as the functional monomer.The theoretical calculations showed that the interaction energy between functional monomer and template was-82.7 k J mol-1 and the non-covalent interactions were mainly composed of hydrogen bond and halogen bond.Structural characterizations and binding performances showed the successful preparation of imprinted biomimetic materials on the surface of silica particles.The imprinted materials showed high selective recognition ability for template molecule,with a maximum adsorption capacity of 22.2 ?mol g-1 and an imprinted factor of 2.1.The binding mechanisms mainly depended on the hydrogen bond and halogen bond interaction,which were consistent with the theoretical calculations.Conclusion: In this study,the functional monomer with strong interaction with thyroxine was successfully screened and synthesized.Based on this,thyroxine imprinted biomimetic materials were prepared,which were expected to replace the expensive transport proteins for recognition of thyroxine and its disruptors.Part ?: Recognition and analysis of thyroid-disrupting chemicals by the thyroxine transport toxicity-directed methodObjective: To establish a method for identifying and analyzing pollutants with thyroxine transport toxicity using retention factors as evaluation indicators,with the help of imprinted biomimetic recognition and chromatographic separation,and to realize the identification and analysis of known/unknown TDCs.Methods: The imprinted biomimetic materials were packed into a chromatographic column.With the help of chromatographic separation theory,the chromatographic parameters were optimized to achieve high efficiencies for screening of TDCs.A total of 72 typical pollutants reported in the literature were studied.The relative potency(RP)provided by the internationally accepted TTR competitive assays was taken as the gold standard.Then receiver operating characteristic(ROC)curve analysis was used to analyze the consistency of the retention factors and RP values.The sensitivity,specificity,consistency rate and positive predictive value of the newly established screening method to distinguish TTR binders and nonbinders were calculated.On this basis,non-targeted screening and verification of unknown TDCs in dust samples were realized by imprinted biomimetic column separation combined with high-resolution mass spectrometry identification.Results: The composition of the mobile phase had a significant effect on the screening of chemicals.Under the optimal mobile phase(0.05% acetic acid/methanol),TTR binders and non-binders could be well separated.The ROC curve analysis showed that the cutoff point of the retention factor was 0.97,at which the prediction accuracy for distinguishing TTR binders and non-binders was greater than 90%.Moreover,the retention factors and RP values were highly correlated(rs = 0.82).That is to say,the established new method was in good consistency with the international screening method.Furthermore,a total of more than 100 suspicious TTR disruptors were screened by high-resolution mass spectrometry.Preliminary verifications on TBBPS and some of phenolic compounds showed that they all had TTR disrupting effects.The new method successfully realized the screening of TDCs in environmental samples.Conclusion: A method for identifying and analyzing pollutants that interfere with thyroxine transport toxicity was established,which can realize the identification and analysis of known/unknown TDCs.It has the advantages of easay operation,low cost and high throughput and provides new ideas for the identification and analysis of unknown pollutants.Part ? Assocoations between perfluorinated compounds exposure and thyroid hormone levels in the agedObjective: To understand the exposures of perfluorinated compounds in the aged,and to explore their effects on thyroid hormone levels.Methods: A cross-sectional study based on 746 elderly people over 60 years old in a community in Wuhan was conducted.14 PFCs in the plasma of the population were determined by liquid chromatography tandem mass spectrometry.Five thyroid function indicators,including thyroid-stimulating hormone(TSH),thyroxine(T4),triiodothyronine(T3),free T4(FT4)and free T3(FT3)were also tested by enzyme-linked immunoassay.Descriptive analysis was used to investigate the exposure of PFCs in the elderly.Toxic equivalent quantity(TEQ)was used to calculate the TTR disrupting toxicity of the combined exposure of PFCs.Linear additive models were used to test the linear relationship between PFCs and hormones.Then,multiple linear regression models were used to explore the relationships between PFCs exposure and hormone levels.We established models with PFCs concentrations as both quartiles and continuous variables.Subsequently,we stratified the population by gender to explore the effect of gender on the correlation between PFCs exposure and hormone levels.Results: Among the PFCs determined in this research,12 PFCs had detection rates of more than 80%.Among them,the concentrations of perfluorooctanesulfonic acid(PFOS)and perfluorooctanoic acid(PFOA)were the highest,and the median concentrations were 15.12 and 2.60 ng m L-1,respectively.Perfluorodecanoic acid(PFDA),PFOS,and perfluorononanoic acid(PFNA)had negative correlations with TSH level.Each interquartile range(IQR)increases in the concentrations of PFDA,PFOS and PFNA reduced TSH levels by 2.14%(95% CI:-4.02,-0.26),1.78%(95%CI:-3.53,-0.02)and 3.04%(95% CI:-5.53,-0.54).Perfluorotridecanoic acid(PFTr A)had a positive correlation with T4 level and each IQR increase in the concentration of PFTr A increased T4 level by 4.52%(95% CI: 0.25,8.78).Perfluoropentanoic acid(PFPA)had a positive correlation with T3 level and each IQR increase in the concentration of PFPA increased T3 level by 1.14%(95% CI: 0.13,2.15).Perfluorobutanoic acid(PFBA)had a negative correlation with FT4 level,and each IQR increase in the concentration of PFBA decreased FT4 level by 1.89%(95% CI:-3.09,-0.70).There was a negative correlation between the combined exposure index TEQ and TSH level.For every IQR increase in TEQ,the TSH concentration decreases by 1.91%(95% CI:-3.77,-0.06).Conclusion: The exposures of PFCs were common in the elderly population in this study.Exposures to PFCs were associated with decreases in TSH and FT4 levels,and increases in T4 and T3 levels.The results indicate that PFCs may cause thyroid-dusrupting effects in the elderly population.