Effects of di-2-ethylhexyl phthalate exposure on liver and glycolipid metabolism in male diabetic rats / 上海预防医学

ABSTRACT

Objective:Phthalates （PAEs） are common environmental endocrine disruptors. In this study， the effects of oxidative stress on liver and nutrient metabolism were determined in male diabetic rats exposed to di-2-ethylhexyl phthalate （DEHP）， and the mechanism of DEHP toxicity was explored. Methods:Thirty-two SPF male Wistar rats aged five weeks， weighing 150-170 g， were fed adaptively for one week to establish the model of type 2 diabetes. The model was established by intraperitoneal injection of streptozotocin （STZ） （25 mg/kg） after feeding with high sugar and high fat diet for four weeks. Second STZ injection was given two days later. The model was considered to be established successfully when the random blood glucose level was found to be higher than 16.7 mmol/L in two separate tests. Twenty diabetic rats were then randomly divided into four groups， including control group （corn oil）， 100， 300 and 900 mg/kg DEHP groups. The rats were treated with DEHP by gavage （5 mL/kg） once a day for 30 days. They were fed with normal diet during the treatment period. Caudal venous blood was collected on the 1st， 14th， and 28th days to measure the random blood glucose level. The changes of glucose tolerance were determined by oral glucose tolerance test on the 29th day. Fasting blood glucose （FPG） was measured on the next day of the last exposure. After the rats were anesthetized with pentobarbital and killed， the liver was weighed， the liver coefficient was calculated and the liver pathological section was made. Blood was taken from the abdominal aorta. The levels of aspartate aminotransferase （AST）， alanine aminotransferase （ALT）， alkaline phosphatase （ALP）， triacylglycerol （TG） and albumin （ALB） in serum were measured by spectrophotometry， and the levels of insulin， glutathione （GSH）， H2O2， malondialdehyde （MDA） and superoxide dismutase （SOD） in fasting serum were measured by radioimmunoassay. Results:There was no significant difference in body weight and random blood glucose in the type 2 diabetic rats exposed to different concentrations of DEHP （all P>0.05）. At each time point of the glucose tolerance curve， the blood glucose value of the exposure groups was higher than that of the control group. A "false plateau period" appeared after the blood glucose value reached or exceeded the upper limit at 15 minutes， and the blood glucose level in each group was higher than that of the control group at 120 minutes. The liver organ coefficient of 300 and 900 mg/kg DEHP groups was higher than that of the control group （both P<0.01）， and the liver organ coefficient was positively correlated with the exposure concentration of DEHP （r=0.80，P<0.000 1）. Under the microscope， the liver cells in diabetic rats were swollen， the cytoplasm was light stained， and there were vacuoles in the cells. The serum ALP level in diabetic rats of 900 mg/kg DEHP group was significantly higher than that in the control group （P<0.01）. The serum ALP level was positively correlated with the concentration of DEHP （r=0.75， P<0.01）. The serum MDA level in diabetic rats of 300 mg/kg and 900 mg/kg DEHP groups was significantly higher than that of the control group （both P<0.01）， and the serum MDA level was positively correlated with the concentration of DEHP （r=0.84， P<0.000 1）. The serum SOD level of 900 mg/kg DEHP group was significantly higher than that of control group （P<0.01）. Conclusion:DEHP exposure could lead to liver damage， abnormal glycolipid metabolism， and increase the level of oxidative stress and antioxidant level in male diabetic rats， but did not show a significant effect on insulin resistance.