Effects Of Continuous Intervention With Low Doses Of Bisphenol A On Cardiac Development And Nkx2.5 In The Offspring Of SD Rats

Purpose: Bisphenol A(BPA)is one of the typical environmental endocrine disruptor chemicals(EDCs).Experimental animal studies have found that high doses of BPA interfered with post-fertilization zebrafish can lead to cardiac malformations in their offspring.Studies have demonstrated that pregnant women exposed to plastic water glasses and products during pregnancy have a higher incidence of congenital heart disease(CHD)in their offspring than unexposed pregnant women,suggesting a correlation between BPA exposure and CHD.The safe dose of BPA exposure in humans varies from 5 μg/kg/d to 50 μg/kg/d in different countries or regions,and some studies have found that BPA at doses of 2.5 μg/kg/d and 0.5 μg/kg/d can cause pathological changes in the hearts of experimental animals.The Nkx2.5 gene plays a critical role in human heart development,and its mutation or deletion can lead to a variety of cardiac malformations.Animal studies also revealed that the m RNA expression levels of the Nkx2.5 gene were down-regulated at key developmental stages of Oryzias melastigma larvae embryos after continuous exposure to low concentrations of BPA water throughout the embryonic stage.In this study,we selected the safe doses of BPA exposure in humans from different countries or regions and the low doses of BPA that can cause cardiac alterations in experimental animals,observed the effects of the selected low doses of BPA intervention on the macroscopic,pathological and ultrastructural alterations in the hearts of sprague-dawley(SD)rats’ offsprings after the continuous BPA exposure of SD female rats.To investigate the correlation between the effects of BPA and the expression of Nkx2.5,a key gene for heart development,and to provide an etiological basis for the reduction of birth defects and a reference for safe BPA exposure doses.Methods: We selected 0μg/kg/d,0.5μg/kg/d,2.5μg/kg/d,5μg/kg/d and 50μg/kg/d doses of BPA.SD female rats(F0 generation)were continuously poisoned by gavage from eight weeks of age.After mating and conception with uninfected SD male rats kept at the same time at 11 weeks of age,the F0 generation at 20 days of pregnancy(Gestational day,GD)pregnant rats’ foetal rats and postnatal day(PND)21-day-old rats were dissected to obtain heart specimens.At the same time,female SD rats from the F0 generation(F1 generation)were kept for further poisoning,mated and conceived at 11 weeks of age with uninfected male SD rats of the same age purchased again.The F1 generation GD20 foetal rats and PND21 litters were dissected to obtain heart specimens.The effects of various low doses of BPA on cardiac organ index,septal thickness,cardiomyocyte pathomorphology and ultrastructure of SD female rat offspring after continuous intervention with different low doses of BPA simulating the external environment were observed,as well as the effects of various low doses of BPA on the expression of Nkx2.5 at the RNA and protein levels.Results: 1.50μg/kg/d dose of BPA continuous intervention in SD female rats could cause a decrease in cardiac organ index of their female F0 and F1 offspring GD20 fetuses and PND21 litters,male F0 offspring GD20 fetuses and PND21 litters,and male F1 offspring GD20 fetuses.2.50μg/kg/d dose of BPA continuous intervention in SD female rats could cause significant hypertrophy of cardiomyocytes in their female F0 generation PND21 littermates and male F0 and F1 generation PND21 littermates.3.50μg/kg/d of BPA caused a reduction in Nkx2.5 m RNA and protein levels in the heart tissue of female F0 and F1 offspring PND21 rats after continuous intervention in SD female rats.4.50μg/kg/d of BPA caused disruption of myocardial mitochondrial ultrastructure in F1 offspring PND21 female rats after continuous intervention in SD female rats.Conclusions:Continuous intervention of BPA at a low dose of 50μg/kg/d in SD female rats caused a decrease in cardiac organ index in their female offspring;cardiomyocyte hypertrophy in female and male offspring,with more pronounced effects in females;decreased m RNA and protein expression of Nkx2.5 in heart tissue in female offspring;and myocardial mitochondrial ultrastructure in female littermates altered myocardial mitochondrial ultrastructure in female pups.These effects may cause defects in cardiac development.