| Background and purpose: Paraben are alkyl esters of p-hydroxybenzoic acid,which can be divided into Methylparaben,Ethylparaben,Propylparaben and Butylparaben(BuP)according to the ester group they carry.The widespread use of paraben preservatives worldwide has led to their widespread presence in the environment.Parabens have been detected in soil,air,dust,surface water,sediment and biota,but the main sources of paraben exposure are still food,pharmaceuticals,cosmetics and personal care products(e.g.shampoos,body washes,body lotions,sunscreens,etc.).According to the European Union and the U.S.Food and Drug Administration,the concentration of mono-esters of paraben(mainly Propylparaben or BuP)as cosmetic preservatives should not exceed 0.19% and the concentration of mixed esters should not exceed 0.8%.However,some manufacturers do not always follow these regulations,and cosmetics that are not labeled or labeled "paraben free" may also contain parabens.Paraben can be rapidly absorbed by the gastrointestinal tract and subcutaneous adipose tissue after entering the body,then metabolized in the microsomes of the liver,and finally excreted as free or bound substances in the urine,bile and feces.Of these,urinary excretion predominates(>70%,mainly in the first 24 hours)and less than 4% is excreted in the feces,although 2% of paraben remain in the tissues.The high and frequent use of cosmetics and personal care products,as well as the detection of paraben residues in animal tissues,imply that this compound may accumulate in the human body.Studies in both in vivo and in vitro experiments have confirmed that paraben have endocrine disrupting properties and that BuP has been shown to interfere with the function of the endocrine system.Toxic effects on the mammary gland,adrenal glands and reproductive system have been reported in some animal experiments on BuP oral and subcutaneous injections.Regarding the effects of BuP on other endocrine-sensitive targets(e.g.,thyroid),the current study did not show a trend of changes in thyroid function and follicular structure after BuP exposure.Therefore,further study of the effects of BuP on thyroid morphological structure and function in animal experiments and determination of its safe exposure level will not only provide an important basis for the safety and risk evaluation of paraben preservatives,but will also provide an important basis for inferring the risk assessment of thyroid lesions in humans.Methods: 1.Sixteen male SD rats were randomly divided into 2groups equally,and the experimental group was injected subcutaneously with BuP solution at a dose of 100 mg/kg bw/d in the neck,and the control group was injected subcutaneously with the same volume of olive oil as the experimental group.Body weight was recorded daily and clinical signs(such as abnormal behavior,wounds,infection and death)were observed.After 21 consecutive days of subcutaneous injection,the rats were executed to obtain thyroid tissue and serum samples.2.The collected serum samples were tested for T3,T4,free T3,free T4,TSH and TPO-Ab levels by ELISA kits.3.The thyroid tissue samples were examined by light and transmission electron microscopy for follicular structure and ultrastructure.4.Human thyroid cells were used and incubated for 24 hours with different concentrations of culture medium containing BuP(0,10,20,40,60,80 mg/L),the cell viability and proliferation levels were detected by CCK8 and Ed U kits,and the levels of apoptosis-related proteins Caspase3,Bcl2 and Bax,the levels of cell proliferation-related protein PCNA and the levels of channel protein NIS were detected by Western Blot.Results: 1.The thyroid weight of the rats in the experimental group increased by 15.6% compared to the control group.2.Under the light microscope,the thyroid follicles in the experimental group were small and irregularly shaped,and the follicular epithelial cells showed edema and hypertrophy-like changes.The cell morphology was cuboidal-columnar,the follicle local structure was destroyed,the gliosis in some follicles was reduced or disappeared,and a large number of detached follicular epithelial cells were seen in the follicular lumen.3.Under the transmission electron microscope,the thyroid follicular epithelial cells showed moderate to severe edema.The overall cell morphology was columnar,the number of microvilli was sparse,and a large number of microvilli were atrophied and detached.The coarse endoplasmic reticulum was heavily dilated,and a large amount of flocculent material was deposited in the endoplasmic reticulum pool,and most of the ribosomes were shed and destroyed.4.The serum T3,T4,free T3 and free T4 levels decreased and the TSH and TPO-Ab levels increased in the experimental group of rats.5.The tissue NIS level of rats in the experimental group decreased by 26.0% compared with the control group,and the NIS level of human thyroid cells decreased in a dose-dependent manner.6.Western Blot results showed that human thyroid cells incubated with different concentrations of culture medium containing BuP(0,10,20,40,60 and 80 mg/L)for 24 h showed a dose-dependent increase in the levels of apoptosis-related protein Caspase3,a dose-dependent decrease in the levels of Bcl2/Bax and a dose-dependent decrease in the levels of proliferation-related protein PCNA.7.CCK8 and Ed U showed a dose-dependent decrease in thyroid cell viability and proliferative capacity.Conclusion: 1.BuP decreased NIS channel protein levels in rat thyroid tissue and caused a dose-dependent decrease in NIS protein levels in human thyroid cells cultured in vitro,indicating that BuP can reduce iodine uptake in the thyroid by inhibiting or disrupting NIS.2.BuP can cause a decrease in the number of apical microvilli as well as ribosomes in rat thyroid follicular cells,resulting in atrophy,shedding and breakage of microvilli and ribosomes.The junction of microvilli and follicular lumen is the site of iodine activation,and ribosomes on the rough endoplasmic reticulum are the site of thyroglobulin(TG)synthesis,suggesting that BuP can reduce iodine activation and iodination of TG tyrosine residues by disrupting microvilli and ribosomes.3.The serum TPO-Ab level of rats in the experimental group was higher than that in the control group,indicating that BuP could cause thyroid follicle destruction in rats.4.BuP caused a dose-dependent decrease in cell viability and proliferation levels of human thyroid cells.In addition,the levels of PCNA,a protein associated with cell proliferation,were dose-dependently decreased.Apoptosis-related protein Caspase3 levels were dose-dependently increased,and Bcl2/Bax levels were dose-dependently decreased.5.BuP caused a decrease in serum T3,T4,free T3 and free T4 levels and an increase in TSH levels,indicating that BuP can disrupt thyroid hormone homeostasis in rats.6.BuP can cause edema and hypertrophy-like changes in the follicular cells of the rat thyroid gland,ultimately leading to an increase in the weight of the rat thyroid gland. |
PDF Full Text Request