Interpretation of male rat renal tubule tumors

Acute, subchronic toxicity and genotoxicity studies of JointAlive, a traditional Chinese medicine formulation for knee osteoarthritis

AIM

In vivo and in vitro toxicity tests of JointAlive® were studied in animal models to support the safe use of JointAlive® as a drug for knee osteoarthritis treatment.

METHODS

The acute toxicity study in Sprague Dawley (SD) rats was conducted at a 20 g/kg bw/day dose of JointAlive®. For 13-week subchronic toxicity tests, SD rats were orally dosed daily with 0.5, 1.5 and 5 g/kg bw/day of JointAlive®. To assess the potential genotoxicity, Ames test, cellular chromosome aberration and mouse micronucleus test in vivo were carried out.

RESULTS

Based on a lack of notable findings other than histopathology finding of co-incidental prostate inflammation at the high dose, the "No Observed Adverse Effect Level (NOAEL)" of JointAlive® was concluded as 5 g/kg bw/day in males and females. Results also indicated that JointAlive® has no risk of genotoxicity.

CONCLUSIONS

General toxicity and genotoxicity studies empirically demonstrated that JointAlive® poses a low risk of potential health risks, providing safety supports for the application of JointAlive® as a potential drug candidate to treat knee osteoarthritis.

Risk assessments for chronic exposure of children and prospective parents to ethylbenzene (CAS No. 100-41-4)

Potential chronic health risks for children and prospective parents exposed to ethylbenzene were evaluated in response to the Voluntary Children's Chemical Evaluation Program. Ethylbenzene exposure was found to be predominately via inhalation with recent data demonstrating continuing decreases in releases and both outdoor and indoor concentrations over the past several decades. The proportion of ethylbenzene in ambient air that is attributable to the ethylbenzene/styrene chain of commerce appears to be relatively very small, less than 0.1% based on recent relative emission estimates. Toxicity reference values were derived from the available data, with physiologically based pharmacokinetic models and benchmark dose methods used to assess dose-response relationships. An inhalation non-cancer reference concentration or RfC of 0.3 parts per million (ppm) was derived based on ototoxicity. Similarly, an oral non-cancer reference dose or RfD of 0.5 mg/kg body weight/day was derived based on liver effects. For the cancer assessment, emphasis was placed upon mode of action information. Three of four rodent tumor types were determined not to be relevant to human health. A cancer reference value of 0.48 ppm was derived based on mouse lung tumors. The risk characterization for ethylbenzene indicated that even the most highly exposed children and prospective parents are not at risk for non-cancer or cancer effects of ethylbenzene.

Disposition and metabolism of cumene in F344 rats and B6C3F1 mice

Cumene is a high-production volume chemical that has been shown to be a central nervous system depressant and has been implicated as a long-term exposure carcinogen in experimental animals. The absorption, distribution, metabolism, and excretion of [(14)C]cumene (isopropylbenzene) was studied in male rats and mice of both sexes after oral or intravenous administration. In both species and sexes, urine accounted for the majority of the excretion (typically ≥ 70%) by oral and intravenous administration. Enterohepatic circulation of cumene and/or its metabolites was indicated because 37% of the total dose was excreted in bile in bile duct-cannulated rats with little excreted in normal rats. The highest tissue (14)C levels in rats were observed in adipose tissue, liver, and kidney with no accumulation observed after repeat dosing up to 7 days. In contrast, mice contained the highest concentrations of (14)C at 24 h after dosing in the liver, kidney, and lung, with repeat dosing accumulation of (14)C observed in these tissues as well as in the blood, brain, heart, muscle, and spleen. The metabolites in the expired air, urine, bile, and microsomes were characterized with 16 metabolites identified. The volatile organics in the expired air comprised mainly cumene and up to 4% α-methylstyrene. The major urinary and biliary metabolite was 2-phenyl-2-propanol glucuronide, which corresponded with the main microsomal metabolite being 2-phenyl-2-propanol.

Effects of fasting and gender on ochratoxin A toxicokinetics in F344 rats

Ochratoxin A (OTA) is a mycotoxin that causes renal tumors in rats, particularly in males. In previous kinetic studies performed in fed conditions (Vettorazzi et al., 2008), mature F344 male rats presented a significantly lower OTA bioavailability than females and young animals. The objective of the present study was to evaluate two factors which could explain this different kinetic profile: the presence of food and the male-specific protein alpha-2u-globulin. Therefore, a 24h kinetic study has been performed in rats under fasting conditions. Food ingestion has been controlled in both sexes during two months. The presence of alpha-2u-globulin in the urine has been analyzed with SDS-gradient mini-gel electrophoresis. Fasting tends to increase the maximum OTA plasma concentrations and the rate of absorption. The relative bioavailability is significantly increased under fasting conditions only in males. Mature males consumed a higher amount of food but, as the OTA dose administered, it was proportional to body weight. The reason why the OTA bioavailability is more affected in presence of food only in males is unclear. Several possibilities, such as differences in gastric emptying, OTA-food interactions and the involvement of alpha-2u-globulin are discussed.

An adjustment factor for mode-of-action uncertainty with dual-mode carcinogens: the case of naphthalene-induced nasal tumors in rats

The U.S. Environmental Protection Agency (USEPA) guidelines for cancer risk assessment recognize that some chemical carcinogens may have a site-specific mode of action (MOA) involving mutation and cell-killing-induced hyperplasia. The guidelines recommend that for such dual MOA (DMOA) carcinogens, judgment should be used to compare and assess results using separate "linear" (genotoxic) versus "nonlinear" (nongenotoxic) approaches to low-level risk extrapolation. Because the guidelines allow this only when evidence supports reliable risk extrapolation using a validated mechanistic model, they effectively prevent addressing MOA uncertainty when data do not fully validate such a model but otherwise clearly support a DMOA. An adjustment-factor approach is proposed to address this gap, analogous to reference-dose procedures used for classic toxicity endpoints. By this method, even when a "nonlinear" toxicokinetic model cannot be fully validated, the effect of DMOA uncertainty on low-dose risk can be addressed. Application of the proposed approach was illustrated for the case of risk extrapolation from bioassay data on rat nasal tumors induced by chronic lifetime exposure to naphthalene. Bioassay data, toxicokinetic data, and pharmacokinetic analyses were determined to indicate that naphthalene is almost certainly a DMOA carcinogen. Plausibility bounds on rat-tumor-type-specific DMOA-related uncertainty were obtained using a mechanistic two-stage cancer risk model adapted to reflect the empirical link between genotoxic and cytotoxic effects of the most potent identified genotoxic naphthalene metabolites, 1,2- and 1,4-naphthoquinone. Bound-specific adjustment factors were then used to reduce naphthalene risk estimated by linear extrapolation (under the default genotoxic MOA assumption), to account for the DMOA exhibited by this compound.

Effects of oral administration of manganese on the kidneys and urinary bladder of Sprague-Dawley rats

The purpose of this study was to investigate the effect of oral administration of manganese acetate on the kidneys and urinary bladder of Sprague-Dawley (SD) rats. Male and female SD rats (150 to 175 g), 6 weeks old, were administered varying doses of manganese acetate for 63 days by oral gavage. At the end of 63 days, 50% of the animals were sacrificed and kidney tissue was isolated and fixed for histopathological studies (study A). The remaining 50% were cross-mated and dosing ceased. Animals were sacrificed after 2 weeks (study B). Male treated animals were noted to have viscous, gritty urine in the urinary bladder, and the high-dose groups had urinary bladder stones (uroliths). Histopathologically, the most striking lesions were observed in the kidneys and prostate glands of male animals. Mild-to-moderate tubulointerstitial nephritis with tubular proteineous and glomerulosclerosis was observed in animals of all treatment groups. Urolithiasis in the urinary bladder was confirmed in 33% to 66% of treated animals. Female animals did not show a significant difference above controls in renal tissues. Results of this study suggest that male rats are more sensitive to the effects of high levels of manganese given orally than female rats and that the genitourinary structures represent target organs of toxicity.

Potential health effects of gasoline and its constituents: A review of current literature (1990-1997) on toxicological data

We reviewed toxicological studies, both experimental and epidemiological, that appeared in international literature in the period 1990-1997 and included both leaded and unleaded gasolines as well as their components and additives. The aim of this overview was to select, arrange, and present references of scientific papers published during the period under consideration and to summarize the data in order to give a comprehensive picture of the results of toxicological studies performed in laboratory animals (including carcinogenic, teratogenic, or embryotoxic activity), mutagenicity and genotoxic aspects in mammalian and bacterial systems, and epidemiological results obtained in humans in relation to gasoline exposure. This paper draws attention to the inherent difficulties in assessing with precision any potential adverse effects on health, that is, the risk of possible damage to man and his environment from gasoline. The difficulty of risk assessment still exists despite the fact that the studies examined are definitely more technically valid than those of earlier years. The uncertainty in overall risk determination from gasoline exposure also derives from the conflicting results of different studies, from the lack of a correct scientific approach in some studies, from the variable characteristics of the different gasoline mixtures, and from the difficulties of correctly handling potentially confounding variables related to lifestyle (e.g., cigarette smoking, drug use) or to preexisting pathological conditions. In this respect, this paper highlights the need for accurately assessing the conclusive explanations reported in scientific papers so as to avoid the spread of inaccurate or misleading information on gasoline toxicity in nonscientific papers and in mass-media messages.

In vitro uptake of methyl tert-butyl ether in male rat kidney: use of a two-compartment model to describe protein interactions

Methyl tert-butyl ether (MTBE) is a gasoline additive that causes renal tumors in male rats. In the process of measuring chemical specific parameters necessary to develop a quantitative dosimetry model of MTBE in rats, the uptake of MTBE was found to be 5.5 times greater in male than in female F-344 rat kidney homogenate. The objectives of this study were to characterize the factor(s) that influences the high uptake of MTBE into male rat kidney in vitro and to develop a system to evaluate the interaction of MTBE with the male rat-specific protein, alpha 2u-globulin (alpha 2u). The uptake of MTBE in male, but not female, rat kidney homogenate was found to be dependent on protein and chemical concentrations. When [14C]MTBE was incubated with male rat kidney homogenate, radioactivity coeluted with the total protein fraction on a gel filtration column. An interaction between [14C]MTBE and male rat kidney proteins was not found under conditions of dialysis or anion exchange chromatography. A two-compartment vial equilibration model was used to assess the interaction between MTBE and alpha 2u. Using this system, the dissociation constant for MTBE and alpha 2u was estimated to be 2.15 x 10(-4) M, which is in the range of other chemicals known to bind to alpha 2u and cause alpha 2u-mediated nephropathy. d-Limonene oxide was used to validate this two-compartment vial equilibration system. These findings illustrate a technique useful in estimating the dissociation constant for a volatile chemical and a protein, as well as explain the process that contributes to the uptake of MTBE into male rat kidney homogenate in vitro. A description of the weak interaction between MTBE and alpha 2u will be used to refine a physiologically based pharmacokinetic model to describe the target tissue (kidney) concentrations of MTBE.

Review of new evidence regarding the relationship of gasoline exposure to kidney cancer and leukemia

Four new or updated epidemiologic studies were presented at a meeting on the health effects of gasoline exposure held in Miami, Florida, November 5-8, 1991. A focus of these studies was whether there is a relationship between gasoline exposure and kidney cancer and leukemia. For gasoline distribution workers, who have a relatively high exposure, there was some evidence for a kidney cancer relationship in three studies but none in the fourth. There was evidence for an acute myelocytic leukemia relationship in three studies. The fourth study dealt only with kidney cancer. It is possible that the benzene content of gasoline was responsible for the leukemia findings. It is uncertain whether gasoline exposure is a cause of kidney cancer.

Review of the carcinogenic potential of gasoline

This review examines the animal, human, and mechanistic studies that precede the new studies reported in this volume. Wholly vaporized unleaded gasoline was found to produce a dose-dependent increase in renal carcinoma in male rats and an excess above background incidence of hepatocellular tumors in female mice in the high-dose group. Mechanistic studies suggest that gasoline is not mutagenic and that the probable mechanism for the male rat renal tumors involves a rat-specific protein, alpha 2u-globulin, whose binding with highly branched aliphatic compounds results in renal tubule cell death and, in turn, a proliferative sequence that increases renal tubule tumors. Human evidence generated predominantly from studies of refinery workers does not support a kidney or liver cancer risk in humans. The current epidemiologic database is inadequate to access leukemia risk from low-level benzene exposure from gasoline. Studies of gasoline-exposed workers that incorporate quantitative exposure information are needed.