Reversibility and Persistence of Di-2-ethylhexyl Phthalate (DEHP)- and Phenobarbital-Induced Hepatocellular Changes in Rodents

Abstract

The tumor promotion stage of chemical carcinogenesis has been shown to exhibit a persistence of cellular effects during treatment and the reversibility of these changes upon cessation of treatment. Inhibition of gap-junctional intercellular communication and increased replicative DNA synthesis appear to be important in this process. The present study assessed the persistence and reversibility of gap-junctional intercellular communication inhibition, peroxisomal proliferation, and replicative DNA synthesis in livers from male F344 rats and B6C3F1 mice. Dietary administration of 20,000 mg/kg DEHP to male rats for 2 weeks decreased intercellular communication (67% of control) and enhanced replicative DNA synthesis (4.8-fold over control). Elevation of the relative liver weight and the induction of peroxisomal beta oxidation were also observed following treatment with 20,000 mg/Kg DEHP for 2 weeks. Following DEHP administration at a dose of 6000 mg/kg for 18 months, inhibition of gap-junctional intercellular communication persisted, and the relative liver weight and induction of peroxisomal beta oxidation remained elevated in both rats and male B6C3F1 mice. Treatment of rats and mice with phenobarbital for 18 months (500-mg/kg diet) also produced an increase in relative liver weight and a decrease in cell-to-cell communication. In recovery studies in which DEHP was administered to male F344 rats for 2 weeks and then withdrawn, the relative liver weight, rate of peroxisomal beta oxidation, increase in replicative DNA synthesis, and inhibition of gap-junctional intercellular communication returned to control values within 2 to 4 weeks after DEHP treatment ceased. Recovery studies with phenobarbital produced similar results. The primary active metabolite of DEHP, mono-2-ethylhexyl phthalate (MEHP), was detected in the livers of animals treated with DEHP for greater than 2 weeks. However, it could not be detected after removal of DEHP from the diet for 2 weeks. This study demonstrated that inhibition of gap-junctional intercellular communication, along with indicators of peroxisomal proliferation, including increased relative liver weight and enhanced peroxisomal beta oxidation, persist while DEHP treatment continues but reverses when treatment is stopped. Studies with phenobarbital produced a similar pattern of response.

Mode of action and human relevance analysis for nuclear receptor-mediated liver toxicity: A case study with phenobarbital as a model constitutive androstane receptor (CAR) activator

“…The relationship between the observed hepatic effects to PB treatment has been demonstrated in recovery studies in the rat where the effects of PB on liver weight, xenobiotic metabolizing enzymes and inhibition of gap junctional intercellular communication were reversible on cessation of treatment (Crampton et al, 1977; Isenberg et al, 2001; Lake et al, 1978). In addition, the liver lesions produced by PB in the mouse appear to be at least partially reversible.…”

Comparative Effects of Phthalate Monoesters on Gap Junctional Intercellular Communication and Peroxisome Proliferation in Rodent and Primate Hepatocytes

“…Thus, the next objective was to determine whether inhibition of gap junctional intercellular communication was reversible, as was demonstrated in vivo (Isenberg et al, 2001). In these studies, inhibition of gap junctional intercellular communication was nearly completely reversed within 24 h of monoester removal.…”

Liver tumor formation in female rat induced by fluopyram is mediated by CAR/PXR nuclear receptor activation

“…For example, studies have shown that the increase in liver weight and cytochrome P450 enzyme activity induced by phenobarbital (Crampton et al, 1977;Lake et al, 1978) is reversible on cessation of treatment. The reversal of early non-neoplastic hepatic alterations has also been observed with other non-DNA reactive receptor mediated hepatocarcinogens such as metofluthrin (Deguchi et al, 2009);sulfoxaflor (LeBaron et al, 2013) and DEHP (Isenberg et al, 2001). Similarly, data generated for fluopyram demonstrated that the hepatic parameters induced following 28 and 90 days of treatment were reversible.…”