Diisodecyl Phthalate Aggravates Autoimmune Thyroiditis And Its Mechanism

Phthalic acid esters(PAES)are the common widely used plasticizers,which give plastic products flexibility and durability.They are widely used in building materials,food packaging,cosmetics,toys,and medical equipment.But phthalates are also harmful to health.Diisodecyl phthalate(DIDP),as a new type plasticizer,is an environmental and friendly plasticizer with good application prospect because of its high boiling point,low melting point and low toxicity.Epidemiological studies show that plasticizer phthalates can induce thyroid dysfunction,and autoimmune thyroiditis(AIT)is a common cause of thyroid dysfunction.Currently we do not know whether phthalate can affect autoimmune thyroiditis,and what are the molecular mechanisms of toxicological effects.Objectives of this project are: to construct TG-induced model of AIT in rats,and to explore the molecular mechanisms about toxicity of DIDP in AIT.In this study,female Wistar rats were used to establish the AIT animal model with subcutaneous injection of thyroglobulin(TG),gave the DIDP solution for 42 days continuously.Histopathological observation was used,serum thyroglobulin antibody(TGAb),free tetraiodothyronine(FT4)and free triiodothyronine(FT3)were detected,thyroid endoplasmic reticulum stress index was as follows: X-box-binding protein-1(XBP-1),Inositol requiring kinase 1α,IRE-1α)and Activating transcription factor 6(ATF6)were detected.Apoptosis-associated proteins was as follows: C/EBP homologous protein(CHOP),Cysteine aspartate proteinase-12(caspase-12)and Cysteine aspartate proteinase-3(caspase-3)were detected.Th17/Treg immunebalance factor in thyroid tissue was as follows: Retinoic acid receptor associated orphan receptor γt(RORγt),Interleukin 23(IL-23),Forkhead transcription factor 3(Foxp3)and Transcriptional coactivation was caused by the expression of TAZ(TAZ)were detected.Meanwhile,the endoplasmic reticulum stress antagonist 4-phenylbutyric acid(4-PBA)was used to investigate the possible mechanism of thyroid tissue injury induced by DIDP.The results show that when DIDP combined with TG,the level of TGAb was dependent on the exposure dose of DIDP,and showed a significant upward trend.H&E staining showed that 1.5 mg/kg/d DIDP could cause the disorder of thyroid follicles significantly.At the same time,large amounts of inflammatory factors appeared when DIDP combined with TG,which aggravated the destruction of thyroid tissue.Compared with TG group,changes in DIDP(0.15,1.5,15 mg/kg/d)+TG group: thyroid hormone FT4 content was significantly increased,while FT3 content was significantly decreased;The levels of endoplasmic reticulum stress index: XBP-1,IRE-1α and ATF6 were significantly increased,and the expression levels of apoptosis factors: Chop,Casepase12 and Casepase3 were significantly increased,and the levels of Th17/Treg immune balance related factors: RORγt,IL-23 and TAZ were significantly increased,Foxp3 levels were significantly reduced.Compared with DIDP15+TG group,toxicity of the thyroid tissue in DIDP15+TG+4-PBA group was alleviated,tissue damage was improved,FT4 and FT3 changes were slowed down,and XBP-1,IRE-1α,ATF6 levels and CHOP,caspase12,caspase3 expressions were reduced.The expression of RORγt,IL-23 and TAZ was decreased,and the content of Foxp3 was increased.This study shows that DIDP can disturb the Th17/Treg immune balance by activating the endoplasmic reticulum stress pathway,thereby exacerbating autoimmune thyroiditis and leading to thyroid dysfunction.