Colonic mechanism of serum NAD+ depletion induced by DEHP during pregnancy

Di (2-ethylhexyl) phthalate (DEHP) is a widely used plasticizer in polyvinyl chloride products such as feed piping, packing bag, and medical consumable. Our previous studies have demonstrated that DEHP exposure reduced the concentration of nicotinamide adenine dinucleotide (NAD+) in pregnant mice serum, which cuts off the source of NAD+ to placenta and results fetal growth restriction. However, the mechanism of serum NAD+ depletion by DEHP remains elusive. This study investigated the intestinal mechanism of NAD+ shortage-induced by DEHP in pregnant mice. The transcriptome results implicated that the mRNA level of oxidative response genes Cyp1a1, Gsto2, Trpv1 and Trpv3 were upregulated in colon. These changes induced intestinal inflammation. Transmission Electron Microscopy results displayed that DEHP destroyed the tight junctions and cell polarity of colonic epithelial cells. These dysfunctions diminished the expression of NAD+ precursor transporters SLC12A8, SLC5A8, SLC7A5, and the NAD+ biosynthetic key enzymes NAMPT, NMNAT1-3, and TDO2 in colonic epithelial cells. Analysis of the gut microbiota showed that DEHP led to the dysbiosis of gut microbiota, reducing the relative abundance of Prevotella copri which possesses the VB3 biosynthetic pathway. Therefore, maternal DEHP exposure during pregnancy decreased the transportation of NAD+ precursors from enteric cavity to colonic epithelial cells, and inhibited the synthesis of NAD+ in colonic epithelial cells. Meanwhile, DEHP reduced the NAD+ precursors provided by gut microbiota. Eventually, serum NAD+ content was lowered. Taken together, our findings provide a new insight for understanding the intestinal mechanisms by which DEHP affects serum NAD+ levels.