Diethylene glycol monobutyl ether (DGBE): two- and thirteen-week oral toxicity studies in Fischer 344 rats

Standard toxicologic endpoints, supplemented by additional examinations, were studied for groups of 10 Fischer 344 rats/sex given drinking water formulated to supply 0, 50, 250, or 1000 mg diethylene glycol monobutyl ether (DGBE)/kg/day for 13 weeks. These dose levels were based upon initial investigations using drinking water formulated to supply 0, 1000, 1500 or 2000 mg DGBE/kg/day for two weeks. All rats survived the respective treatment intervals with no adverse treatment-related in-life effects, including no alterations in a functional observational battery. In both studies, rats given > or = 1000 mg/kg/day consumed less water and feed and weighed slightly less than controls. For rats given > or = 1000 mg DGBE/kg/day, the liver and red blood cells (RBC) were the primary target organs although the effects were slight. In the 13-week study, rats given 1000 mg/kg/day had statistically significant increased relative liver weight (7-10%) and hepatic cytochrome P450s (24-39%) and UGT (approximately 16%) levels along with slight, statistically significant, decreases in serum total protein, cholesterol and aspartate aminotransferase. Histopathologically, very slight hepatocyte hypertrophy and increased individual hepatocyte degeneration were found in females only. At 1000 mg/kg/day, the RBC count, hemoglobin (Hgb) and hematocrit (Hct) were minimally, but statistically significantly, decreased (5.1-8.7%) but RBC morphology, RBC indices, reticuloctye count and bone marrow and spleen histopathology were unaffected. Absolute and relative kidney weights statistically significantly increased (6-13%) with an equivocal increase in minor histopathologic changes typical of early spontaneous nephropathy. There were no adverse effects on urinalysis, clinical chemistry, sperm parameters or testis histopathology. At 250 mg/kg/day, there were equivocal decreases (approximately 2-3%) in RBC count, Hgb and Hct that were statistically significant for the RBC count and Hgb, but these changes were within the historical control range. This dose level was considered the no adverse effect level (NOAEL).