The Effect to Pretreatment on the Biliary Excretion of 2,3,7,8-Tetrachlorodibenzo-p-dioxin, 2,3,7,8-Tetrachlorodibenzofuran, and 3,3',4,4'-Tetrachlorobiphenyl in the Rat

The Effect of Pretreatment on the Biliary Excretion of 2,3,7,8-Tetrachlorodibenzo-p-dioxin,2,3,7,8-Tetrachlorodibenzofuran, and 3,3',4,4'-Tetrachlorobiphenylin the rat. MCKINLEY, M. K., KEDDERIS, L. B., and BIRNBAUM,L. S. (1993). Fundam. Appl. Toxicol. 21, 425–432. The laterally halogenated chemicals 2,3,7,8-tetrachlorodibenzofuran(TCDF) and 3,3',4,4'-tetrachlorobiphenyl (TCB) exhibit the samespectrum of toxic effects as 2,3,7,8-tetrachlorodibenzo-p-dioxin(TCDD), the prototype and most toxic member of the halogenatedaromatic hydrocarbon family. Metabolism of all three compoundsappears to be the rate-limiting step for excretion, which isprimarily via the bile into the feces. Therefore, the biliaryelimination of TCDF, TCDD, and TCB was examined as an indirectmeasure of metabolism. Male F344 rats were anesthetized withpentobarbital, the bile duct was cannulated, and 0.1 µmol[³H]TCDD, [¹⁴C]TCDF, or [¹⁴C]TCB/kg body wt was administerediv. Bile was collected for 0–8 hr while the animals werekept under anesthesia. To determine if TCDF was able to induceits own metabolism in vivo, a single dose of 1.0 µmolTCDF/kg was administered to rats by oral gavage 3 days priorto iv injection of 0.1 or 0.3 µmol [¹⁴C]TCDF/kg. Biliaryexcretion and hepatic concentrations of [¹⁴C]TCDF were significantlyincreased in the pretreated animals. These results suggest anautoinduction of TCDF metabolism. Essentially all biliary [¹⁴C]TCDFradioactivity was attributable to metabolites. High-pressureliquid chromatography profiles of biliary radioactivity from0 to 4 hr were qualitatively different between naive and pretreatedrats. To determine if pretreatment with TCDD altered the metabolismof TCDF and vice versa, a single dose of 1.0 µmol TCDF/kgor 0.1 µmol TCDD/kg was administered by oral gavage 3days prior to iv injection of 0.1 µmol [³H]TCDD or [¹⁴C]TCDF/kg,respectively. TCDD pretreatment increased the metabolism andhepatic concentrations of [¹⁴C]TCDF in pretreated rats, whilebiliary elimination and hepatic concentrations of [³H]TCDD wereunaffected by pretreatment with TCDF. In a fourth experiment,the ability of TCDD to alter the metabolism of TCB, a laterallysubstituted polychlorinated biphenyl (PCB), was examined. Pretreatmentwith TCDD increased the metabolism of [¹⁴C]TCB by approximatelytwofold, but no differences in hepatic concentrations were seendue to the rapid elimination of TCB. Rats pretreated with Aroclor1254, a commercial mixture of PCBs, demonstrated significantlyincreased metabolism of [¹⁴C]TCB compared to the naive group.Therefore, under these experimental conditions, induction ofTCDF metabolism occurred in the rat upon pretreatment with eitherTCDD or TCDF at doses which also elicited enhanced hepatic uptake.TCDD and Aroclor 1254 induced the metabolism of TCB. These findingssuggest that repeated exposure to a chemical or to a mixtureof these halogenated aromatic hydrocarbons can result in morerapid metabolism and elimination from the body than followinga single, acute exposure.     

Effect of Dose, Time, and Pretreatement on the Biliary Excretion and Tissue Distribution of 2,3,7,8-Tetrachlorodibenzo-p-dioxin in the Rat

Effect of Dose, Time, and Pretreatment on the Biliary Excretionand Tissue Distribution of 2,3,7,8-Tetrachlorodibenzo-p-dioxinin the Rat. KEDDERIS, L. B., ANDERSEN, M. E., AND BIRNBAUM,L. S. (1993). Fundam. Appl. Toxicol. 21, 405–411. Previous studies of the effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin(TCDD) pretreatment on the biliary excretion and hepatic dispositionindicated that TCDD did not induce its own metabolic elimination.Pretreatment with TCDD did enhance its hepatic uptake. The presentwork was designed to further examine the effects of dose, time,and pretreatment on the tissue distribution and biliary eliminationof [³H]TCDD. Adult male F-344 rats were administered 0 or 100nmol [¹⁴C]TCDD or [³H]-TCDD/kg body weight po 3 days prior tobile duct cannulation and iv injection of 0 or 1 nmol [³H]TCDDor 1, 10, or 100 nmol [¹⁴C]TCDD/kg. Bile was collected for upto 8 hr while rats were maintained under pentobarbital anesthesia.Biliary TCDD and TCDD metabolites were quantified by liquidscintillation spectrometry. In naive animals which receivedno pretreatment, similar rates of excretion (% dose) were observedfollowing iv administration of 1 nmol [³H]TCDD/kg or 10 or 100nmol [¹⁴C-TCDD/kg. Metabolic elimination of highly purified[³H]TCDD (<99%) appeared to be linear with respect to timewith 0.8% of the dose being excreted in the bile over a 5- to8-hr collection period 0 or 24 hr after iv dosing (1, 10, or100 nmol/kg) and 72 hr after oral dosing (100 nmol/kg). In allgroups, higher concentrations of TCDD were found in liver versusfat, and perirenal fat concentrations were elevated relativeto epididymal fat concentrations, probably reflective of theenhanced blood perfusion of the former tissue. Pretreatmentenhanced hepatic concentrations and decreased fat concentrationsof the challenge dose. The time dependence of factors involvedin the dose-related hepatic accumulation of TCDD dispositionwas illustrated by the elevated liver:fat concentration ratiosobserved at the 100 versus 10 or 1 nmol/kg dose at 30 hr, butnot by 5–6 hr after dosing. In studies designed to evaluatethe role of CYP1A2 in the hepatic disposition of TCDD, pretreatmentwith isosafrole, a selective inhibitor of CYP1A2, diminishedhepatic concentrations of [³H]TCDD. In conclusion, TCDD wasmetabolically cleared at a fairly constant rate over an 80-hrperiod, and the rate of elimination was proportional with regardto dose. Studies with isosafrole suggest that TCDD is boundto CYP1A2 in the liver.     

Toxicity of the Protein Kinase C Inhibitor Safingol Administered Alone and in Combination with Chemotherapeutic Agents

Safingol [(2S,3S)-2-amino-1,3-octadecanediol] potentiates thetoxicity of doxorubicin (DOX) and cisplatin (CIS) against tumorcells in vitro and in vivo. The present studies were conductedin rats and dogs to evaluate safingol toxicity when administerediv as a single agent and to evaluate safingol's ability to potentiatethe toxicity of established chemotherapeutic agents to normaltissues in vivo. In an escalating dose study, dogs were administeredsafingol iv at 5, 10, 20, 30, 40, and 75 mg/kg on Days 1 through6. Necropsies were performed on Day 7. Red urine was observedat 10 mg/kg and higher. Icterus was observed following 40 mg/kgwith additional signs of hypoactivity and anorexia occurringafter 75 mg/kg. Clinical and microscopic pathology revealedmarked hepatotoxicity, venous degeneration and necrosis at injectionsites, and evidence of intra-vascular hemolysis. Doses of 5,20, or 40 mg safingol/kg were utilized in single iv dose ratand dog studies. No evidence of adverse systemic toxicity wasseen up to 20 mg/kg in either species [for rats: C_max = 12,600(males) or 17,133 (females) ng/ml, AUC = 3853 (males) or 4365(females) ng x hr/ml; for dogs: C_max = 2533 ng/ml, AUC = 2851ng x hr/ml (no sex differences)]. Local effects of venous irritationor intravascular hemolysis were observed at all doses in ratsand at 20 and 40 mg/kg in dogs. A dose of 40 mg/kg [for rats:C_max = 31,233 (males) or 91,300 (females) ng/ml, AUC = 11,519(males) or 18,620 (females) ng x hr/ml; for dogs: C_max = 9033ng/ml, AUC = 11,094 ng x hr/ml (combined sex)] was associatedwith clinical pathologic and renal histomorphologic changesconsidered consequent to intravascular hemolysis in both species,lethality and testicular toxicity in rats, and clinical biochemicalchanges indicative of hepatobiliary injury in dogs. Studiesindicated that hemolysis occurred during infusion, was not causedby circulating levels of safingol, and was a function of doseconcentration and vein of delivery. Safingol at 10 or 20 mg/kgwas administered iv to rats 30–60 min prior to myelosuppressiveiv doses of DOX, CIS, or cyclophosphamide (CYP). Hematology,plus renal function and morphology for CIS-treated animals,was assessed 4 and 14 days later. Safingol did not potentiateDOX-, CIS-, or CYP-mediated leukopenia/thrombocytopenia. A minimalenhancement of CIS-mediated decrease in GFR and increase increatinine was observed at 20 mg safingol/kg. Dogs were administered20 mg safingol/kg iv followed 60 min later by 0.5 or 1.25 mgDOX/kg or 0.75 or 2.0 mg CIS/kg. A complete toxicologic assessment4 and 29 days postdose failed to show potentiation of DOX toxicityby safingol or vice versa. A renal lesion was inferred in dogsadministered 20 mg/kg safingol and 2 mg/kg CIS based on minimalto slight renal tubular regeneration observed 4 weeks post-treatment.There were no effects of safingol on the pharmacokinetic profilesof DOX or CIS or vice versa.