The use of multivariate analysis to compare peroxisome induction data on phthalate esters in rats

This paper contains statistical evaluations of the effect of 9 different plasticizers on rat hepatic peroxisome proliferation. There were 9 21-day feeding studies with one plasticizer in each study. The plasticizers are: di(2-ethylhexyl)phthalate (DEHP), butyl benzyl phthalate (BBP), 711 phthalate (711P), di(n-butyl)phthalate (DBP), di(undecyl)phthalate (DUP), di(isodecyl)phthalate (DIDP), di(isononyl)phthalate (DINP), 610 phthalate (610P), and di(ethylhexyl)adipate (DEHA). For each plasticizer, several dosage (as % of diet) groups, plus a negative control group (0%) and a reference control group (1.2% DEHP) were included. There were 5 males and 5 females, approximately 5 weeks old, per group per plasticizer, for a total of 470 animals. For each animal, body weight and food intake were measured prior to treatment and twice a week during the treatment period. Animals were necropsied at the end of the 21-day treatment period. Selected organs and blood samples of each animal were collected for measuring hepatic enzymes, proteins, fat stains, organ weights and serum fats. The endpoints included electron microscopy examination of liver peroxisome proliferation and liver histological abnormalities. The statistical evaluation utilized a multivariate approach that condensed a complex phenomenon into certain meaningful and simple endpoints for quantitative comparisons. The dose of each plasticizer that would protect 99% and 99.9% of rats against peroxisome proliferation (xx% statistically predicted dose, or xx% SPD) was estimated. Marked differences were seen in the ability of the 9 test compounds to cause hepatic peroxisome proliferation in rats. The graphic ranking of overall potency is, in order from most potent to least potent: DEHP, DIDP, DINP, DBP, DEHA, DUP, BBP, 711P and 610P. The ranking in terms of 99.9% SPD is: DEHP, DINP, DIDP, DBP, 610P, DUP, DBP, 711P and DEHA. It was also found that the histological findings of reduced basophilia or increased eosinophilia were highly correlated with peroxisome proliferation (r = 0.94). The other histological findings were incidental observations for specific plasticizers.