Effects of oral administration of di-n-butyl phthalate (DBP) on spermatogenesis and sperm function in mice

Abstract

Di-n-butyl phthalate (DBP), a well-known endocrine disruptor, has been reported to elaborate reproductive toxicity but the mechanism has not been elucidated. The prion like protein doppel (PRND/DPL) is known to have the male reproductive function. To investigate the toxic mechanism of male reproductive dysfunction following oral administration of DBP at 200 mg/kg/day corresponding to LOAEL for spermatogenesis defect was conducted for 28 days in adult male mice. After oral exposure, there were no significant differences at body weight, organ weights except salivary gland, blood glucose level, complete blood count (CBC), serum testosterone level, serum T3 level, serum T4 level and daily sperm production (DSP) between the control group and the DBP group. In cauda epididymal sperms, the DBP group had decreased motility, increased bent tail and abnormal head compared with the control group. Testicular lipid peroxidation (LPO) level was significantly higher in the DBP group than the control group. Prnd mRNA and DPL (PRND) protein expression was decreased at Real-time qPCR and western blot. Testicular mRNA expression of Pou4f1, which is known to bind to the Prnd promoter, is reduced. In the testis, decreased Bcl-2 mRNA expression and increased Trp53 mRNA expression in the DBP group compared with the control group means DBP may cause apoptosis, but mRNA expressions of other apoptotic genes were not significant differences between the control and the DBP group. Testicular mRNA expression of ER stress related genes and protein expression of p-eIF2α, which is related with endoplasmic reticulum (ER)-stress were no significant differences between the two groups. The DBP group’s testis had decreased Sertoli cell related genes Sox9, Sgp1 and Sgp2 mRNA expression, increased expression of Amh and Inha mRNA. There were no significant differences at mRNA expressions of Leydig cell steroidogenesis genes. In conclusion, DBP 200 mg/kg administration for 28 days is considered to have caused abnormalities in sperm morphology and function due to increase in ROS, decrease in Pou4f1, Prnd and Bcl-2 mRNA levels, and decrease in Sertoli cell function. In particular, it is considered that the decrease in Prnd mRNA, DPL protein expression due to DBP exposure reduces sperm motility and increases the number of bent tail and abnormal head sperms. This is considered to be one of the major mechanisms of male infertility induction by exposure to phthalates.