Effect of di-(2-ethylhexyl)phthalate exposure on lung tissue development in newborn rats

OBJECTIVE: To investigate the role of matrix metalloproteinase 9 (MMP-9), tissue inhibitor of metalloproteinase-1 (TIMP-1), and transforming growth factor-β₁ (TGF-β₁) in the toxic effect of di-(2-ethylhexyl)phthalate(DEHP) on lung development. METHODS: The newborn Sprague-Dawley rats were ip given DEHP 10, 100 and 750 mg·kg^-1 daily, half from the postnatal 1st day to the postnatal 14th day, and the other half from the postnatal 1st day to the postnatal 21st day. All of the rats were sacrificed on the next day after the last DEHP administration. The fresh lung tissue was taken for RNA extraction. The MMP-9, TIMP-1, and TGF- β₁ mRNA expression in lung tissue was measured by real time PCR. The lung tissue morphological changes were observed by HE staining. The protein expression of MMP-9, TIMP-1 and TGF-β₁ in lung tissue was also examined by immunohistochemistry. RESULTS: On the postnatal 14th day, the alveolar growth inhibition and thicker alveolar septa were detected during the morphological examination of DEHP 100 and 750 mg·kg^-1 groups compared with the solvent control group(P < 0.05). The mRNA expression of MMP-9 and TGF-β₁ in DEHP 10, 100 and 750 mg·kg ^-1 groups was increased dosage dependently (r = 0.979, P < 0.01; r = 0.990, P < 0.01), so did the protein expression of MMP-9 and TGF-β₁ of DEHP 10, 100 and 750 mg·kg^-1 groups (r = 0.770, P < 0.01; r = 0.959, P < 0.01). Meanwhile, the expression of TIMP-1 mRNA and protein was decreased (r = 0.770, P < 0.01; r = 0.959, P < 0.01). On the postnatal 21st day, there was no significant change in the ratio of lung interstitial tissue between the solvent control and DEHP groups. The mRNA expression of MMP-9 and TGF-β₁ in DEHP 10, 100 and 750 mg·kg^-1 groups was decreased with the increase in DEHP dose (r = 0.879, P < 0.01; r = 0.904, P < 0.01), like the protein expression(r = 0.935, P < 0.01; r = 0.819, P < 0.01), while the expression of TIMP-1 mRNA and protein was increased (r = 0.819, P < 0.01; r = 0.619, P < 0.01). CONCLUSION: DEHP inhibits the alveoli morphological development of newborn rats by interfering the gene and protein expression of MMP-9, TIMP-1 and TGF-β₁.