Environmental Protection Agency risk assessment--process and toxicologic pathology.

Risk assessment of a pesticide includes the identification of hazard, dose-response, exposure assessment, and risk characterization. Toxicology study reports undergo several levels of scientific and regulatory review in the Environmental Protection Agency's (EPA's) Office of Pesticide Programs. A Health Effects Division (HED) scientist reviews the reports. The resulting Data Evaluation Records are presented to several internal HED Peer Review committees to ensure consistency across chemicals in establishing which hazard end points to use when determining the reference dose and carcinogenicity potential for use in dietary and nondietary risk assessments. There may also be external reviews. The toxicologic pathologist can impact many steps in this process. The noncancer end points are just as important as the cancer end points when evaluating the hazard component of a pesticide. The toxicologic pathologist can assist in the hazard and risk characterization by being clear and concise, carefully defining terms and relating individual lesions to the animal, study, and database as a whole. The preceding will assist the HED in fulfilling EPA Administrator Carol Browner's guidance for risk characterizations that are transparent, clear, concise, and reasonable.

Evaluation of the carcinogenic potential of pesticides. 2. Methidathion.

The carcinogen potential of methidathion, a dimethoxyorganic phosphorus pesticide and cholinesterase inhibitor, was evaluated by the Health Effects Division of the Office of Pesticide Programs using a consensus peer review process and the EPA's guidelines for risk assessment. Methidathion was categorized as a Group C (possible human) carcinogen based upon evidence of an increased incidence of benign and malignant hepatocellular tumors, alone and in combination, in a single study involving male Chr-CD-1 mice. The compound was not carcinogenic in female Chr-CD-1 mice in the same study or in Sprague-Dawley rats of either sex in a second study. Methidathion was not genotoxic in a variety of in vitro or in vivo tests designed to detect DNA damage, chromosome aberrations, gene mutations, and sister chromatid exchange. Although methidathion was identified as being structurally similar to two other organophosphate insecticides, prothidathion and lythidathion, no toxicological data were available on either of these agents for comparative purposes. The biological information on methidathion was reviewed by the agency's FIFRA Scientific Advisory Panel who agreed with the category C designation for methidathion. The data were not found to be sufficient to quantify human risk to methidathion.

In vivo biochemical indices of nephrotoxicity of platinum analogs tetraplatin, CHIP, and cisplatin in the Fischer 344 rat.

In vivo biochemical indices of nephrotoxicity were investigated in Fischer 344 rats treated with a new platinum analog, tetraplatin [tetrachloro(dl-trans)1,2-diaminocyclohexane platinum(IV), NSC-363812], in comparison with rats receiving equimolar dosages of cisplatin and CHIP [cis-dichloro,trans-dihydroxybis-isopropylamine platinum(IV), NSC-256927]. The goals of this study were to assess the comparative nephrotoxicities and to determine which battery of tests might be useful for the assessment of platinum analog-induced nephrotoxicity in future clinical investigations of these drugs. An iv bolus injection of 6.7, 13.3, 26.7, and 53.3 mumol/kg of each drug in saline was administered and assessment of biochemical parameters was conducted for 15 days postinjection. A combination of urinary enzyme and protein excretion rates along with blood urea nitrogen (BUN) determinations was used to assess the nephrotoxicity of these compounds. At equimolar dosages, tetraplatin appeared to be less nephrotoxic than cisplatin, and CHIP was not nephrotoxic. At all dosages tested, cisplatin increased the rate of urinary excretion of protein, lactate dehydrogenase (LDH), and N-acetylglucosaminidase (NAG) between Days 1 and 5. Tetraplatin did not affect these parameters until the 13.3 mumol/kg dosage. Cisplatin had little effect on the excretion rates of the brush border enzymes alkaline phosphatase and maltase, whereas tetraplatin caused an initial elevation with delayed onset of peak excretion rates at 8 days postinjection. Changes in BUN were not evident until after the 13.3 mumol/kg dosage of cisplatin and the 26.7 mumol/kg dosage of tetraplatin. BUN was useful for ranking the relative toxicities of the three compounds tested, but was not as sensitive in detecting the onset of injury that correlated with early histopathological changes. Tetraplatin appeared to be less nephrotoxic than cisplatin on an equimolar basis and the specific manifestations of its toxicity were different from those observed with cisplatin. Urinary excretion rates for LDH, NAG, and protein proved to be sensitive indicators of platinum analog-induced nephrotoxicity. These indices, combined with BUN determinations and functional assessments, facilitated comparisons of the nephrotoxicity induced by cisplatin and tetraplatin in rats.

Comparative toxicity and renal distribution of the platinum analogs tetraplatin, CHIP, and cisplatin at equimolar doses in the Fischer 344 rat.

Tetraplatin [tetrachloro(dl-trans)1,2-diaminocyclohexane platinum(IV), NSC-363812] is a new anticancer platinum drug analog targeted for clinical development because of its effectiveness against cisplatin-resistant tumor cell lines and its improved formulation. The toxicity of tetraplatin was compared at equimolar doses to that of cisplatin [cis-diamminedichlorophatinum(II)] and CHIP [cis-dichloro,trans-dihydroxybis-isopropylamine platinum(IV), NSC-256927]. Adult male Fischer 344 rats received an iv bolus injection of 6.7, 13.3, 26.7, or 53.3 mumol/kg of one of these drugs in saline and were killed on Day 1, 3, 5, 8, or 15 postinjection for assessment of toxicity with emphasis on evaluation of nephrotoxicity. Rats to be killed on Day 15 were housed in metabolism cages for daily urine collection. Tetraplatin was less nephrotoxic than cisplatin at equimolar doses; CHIP was not nephrotoxic at these doses. Renal platinum contents were similar after all three drugs and did not appear to be related directly to the nephrotoxicity. Nephrotoxicity was detected 4-5 days after 6.7 mumol/kg cisplatin, was localized to the corticomedullary junction, and progressed with time and dose. Tetraplatin-induced alterations of renal function were first observed after 13.4 mumol/kg on Day 4 as an elevation of urine volume (up to 10-fold) and a smaller elevation of urinary glucose excretion. Tetraplatin lesions were localized in the mid- and outer cortex and, even at the highest dose, were less severe than those observed with cisplatin. There were other prominent toxic effects of tetraplatin, such as gastrointestinal toxicity and myelosuppression, which indicate that factors other than comparative nephrotoxicity may impact the clinical potential of this new agent.

Transformation and tumor promoter sensitive phosphoproteins in JB-6 mouse epidermal cells: one is also sensitive to heat stress.

JB-6 mouse epidermal cells undergo irreversible transformation when exposed to tumor-promoting agents such as 12-O-tetradecanoyl-phorbol-13-acetate (TPA). Phosphoprotein changes related to transformation were sought in four tumor cell lines related to JB-6 cells. Two dimensional polyacrylamide gel electrophoresis showed altered abundances of five phosphoproteins in the tumor cell lines compared with five untransformed clones. The mol. wt. in Kilodaltons and isoelectric points in pH units were: 120/6.0, 80/4.5, 55/6.5, 37/5.0 and 23-25/4.5. In all four transformants pp80 was markedly decreased and the pp23-25 doublet increased. In two of the four transformants pp120 and pp55 were increased and pp37 decreased. Treatment of untransformed clones with TPA affected only one of the phosphoproteins altered in the transformants. Treatment of untransformed clones with TPA produced a 2-fold increase in pp80 after 5 h. pp80 returned to baseline levels by 24 h and changed little in the continuous presence of TPA for up to 96 h. The increase in pp80 with short term TPA treatment occurred in all of the untransformed clones but none of four transformants. Late preneoplastic (P+) JB-6 cells only require treatment with a tumor promoter to transform. Early preneoplastic (P-) JB-6 cells require prior transfection of DNA from late preneoplastic JB-6 cells to transform in response to tumor promoter treatment. Quantitative analysis of pp80 in early preneoplastic, late preneoplastic, and tumor cell lines showed an inverse relationship between the level of pp80 and degree of preneoplastic progression in these cells. pp80 represents approximately 2% of total cellular phosphoprotein in JB-6 cells, shows microheterogeneity of both mol. wt. and isoelectric point, occurs in the particulate fraction of cells and is readily solubilized by 1% Triton. pp80 is increased by heat stress and shares other properties with the recently described mammalian heat stress protein, hsp 80. pp80's decrease in four out of four tumor cell lines, inverse correlation with stage of preneoplastic progression and responsiveness to TPA in preneoplastic but not in tumor cell line suggest that pp80 may be closely linked to biochemical mechanisms underlying transformation in this cell system.

Amelioration of cisplatin-induced nephrotoxicity by the diuretic acetazolamide in F344 rats.

Renal toxicity following a single iv nonlethal dose (6 mg/kg) of cisplatin (CDDP) was investigated in male F344 rats pretreated with 20 mg/kg of acetazolamide (ACZ) sc 30 minutes before CDDP administration. There was a decrease in nephrotoxicity as indicated by a smaller elevation of BUN, a milder histopathologic lesion, and a more rapid recovery of BUN in ACZ-pretreated animals. Renal platinum content of rats receiving ACZ was significantly lower than that in animals treated with CDDP alone. There was no change in platinum level in the plasma or the liver but there was a decreased platinum excretion in urine during 24 hours after treatment. Reduction of platinum concentration in the kidney might account for protection against the renal toxicity. The diuretic ACZ might be useful in the hydration regimens used clinically to prevent renal toxicity from CDDP.

Effects of the diuretics mannitol or acetazolamide on nephrotoxicity and physiological disposition of cisplatin in rats.

The anticancer drug cisplatin has been known to produce severe renal lesions characterized by high levels of blood urea nitrogen (BUN), toxic nephrosis, and platinum (Pt) retention in the kidney. The effect of IV pretreatment with acetazolamide (ACZ) 30 min before or mannitol (MAN) immediately prior to IP administration of 5 mg/kg cisplatin on Pt excretion, tissue distribution, and nephrotoxicity was investigated in male F344 rats. ACZ pretreatment reduced the cisplatin-induced nephrotoxicity, as indicated by only a slight elevation of BUN, a milder histopathologic lesion, and a more rapid recovery of renal function and structure. Although MAN-pretreated animals exhibited similar changes in BUN to ACZ-pretreated animals, the renal damage was similar to that seen in animals treated with cisplatin alone. A reduction of kidney Pt content was observed with both diuretics, although there was significantly less retention after ACZ pretreatment. The diuretic ACZ was more effective than MAN in reducing the renal lesions induced by cisplatin and it might be clinically useful in preventing cisplatin nephrotoxicity.

Mitigation of intestinal cytotoxicity of cisplatin by EDTA in rats.

Cisplatin (cis-dichlorodiammineplatinum-II), an antitumor agent containing platinum, produced acute necrotizing enteritis in rats. This toxic side effect was significantly reduced by oral treatment with CaNa2EDTA. The protective effect of CaNa2EDTA against intestinal cytotoxicity of cisplatin was dose-related. Based on histopathological evaluation of cell necrosis and mitotic index, it was estimated that pretreatment with CaNa2EDTA in drinking water (75 mM) and by gavage (1.5 g/kg) prevented intestinal cytotoxicity by up to 90% compared with cisplatin controls.