The human relevance of the renal tumor-inducing potential of d-limonene in male rats: implications for risk assessment

FEMA GRAS assessment of natural flavor complexes: Sage oil, Orris Root Extract and Tagetes Oil and related flavoring ingredients

In recent years, the Expert Panel of the Flavor and Extract Manufacturers Association (FEMA) has conducted a program to re-evaluate the safety of natural flavor complexes (NFCs) used as flavor ingredients. This publication, twelfth in the series, details the re-evaluation of NFCs whose constituent profiles are characterized by alicyclic or linear ketones. In its re-evaluation, the Expert Panel applies a scientific constituent-based procedure for the safety evaluation of NFCs in commerce using a congeneric group approach. Estimated intakes of each congeneric group of the NFC are evaluated using the well-established and conservative Threshold of Toxicological Concern (TTC) approach. In addition, studies on the toxicity and genotoxicity of members of the congeneric groups and the NFCs under evaluation are reviewed. The scope of the safety evaluation of the NFCs contained herein does not include added use in dietary supplements or any products other than food. Thirteen (13) NFCs derived from the Boronia, Cinnamomum, Thuja, Ruta, Salvia, Tagetes, Hyssopus, Iris, Perilla and Artemisia genera are affirmed as generally recognized as safe (GRAS) under conditions of their intended use as flavor ingredients based on an evaluation of each NFC and the constituents and congeneric groups therein.

FEMA GRAS assessment of derivatives of basil, nutmeg, parsley, tarragon and related allylalkoxybenzene-containing natural flavor complexes

In 2015, the Expert Panel of the Flavor and Extract Manufacturers Association (FEMA) initiated a program for the re-evaluation of the safety of over 250 natural flavor complexes (NFCs) used as flavoring ingredients in food. In this publication, tenth in the series, NFCs containing a high percentage of at least one naturally occurring allylalkoxybenzene constituent with a suspected concern for genotoxicity and/or carcinogenicity are evaluated. In a related paper, ninth in the series, NFCs containing anethole and/or eugenol and relatively low percentages of these allylalkoxybenzenes are evaluated. The Panel applies the threshold of toxicological concern (TTC) concept and evaluates relevant toxicology data on the NFCs and their respective constituent congeneric groups. For NFCs containing allylalkoxybenzene constituent(s), the estimated intake of the constituent is compared to the TTC for compounds with structural alerts for genotoxicity and when exceeded, a margin of exposure (MOE) is calculated. BMDL₁₀ values are derived from benchmark dose analyses using Bayesian model averaging for safrole, estragole and methyl eugenol using EPA's BMDS software version 3.2. BMDL₁₀ values for myristicin, elemicin and parsley apiole were estimated by read-across using relative potency factors. Margins of safety for each constituent congeneric group and MOEs for each allylalkoxybenzene constituent for each NFC were determined that indicate no safety concern. The scope of the safety evaluation contained herein does not include added use in dietary supplements or any products other than food. Ten NFCs, derived from basil, estragon (tarragon), mace, nutmeg, parsley and Canadian snakeroot were determined or affirmed as generally recognized as safe (GRAS) under their conditions of intended use as flavor ingredients based on an evaluation of each NFC and the constituents and congeneric groups therein.

Application to Butterbur Products of a Suggested Daily Intake-Based Safety Evaluation of Individual Herbal Supplements with Cytochrome P450 Expression as a Major Index

The present paper first proposes a method for ensuring the safety of commercial herbal supplements, termed the suggested daily intake-based safety evaluation (SDI-based safety evaluation). This new method was inspired as a backward analog of the acceptable daily intake (ADI) derivation from the no observed adverse effect level (NOAEL), the basis of food additive risk analysis; namely, rats are dosed with individual herbal supplement products at the SDI for human use multiplied by 100 (the usual uncertainty factor value) per body weight for 8 d. The primary endpoint is the sign of adverse effects on liver, especially gene expression of cytochrome P450 (CYP) isoforms. The proposed method was then applied to three butterbur (Petasites hybridus) products without pyrrolizidine alkaloids but lacking clear safety information. Results showed that two oily products markedly enhanced the mRNA expression of CYP2B (>10-fold) and moderately enhanced that of CYP3A1 (<4-fold) with liver enlargement. These products also caused the renal accumulation of alpha 2-microglobulin. One powdery product showed no significant effect on liver and kidney. The large difference in effects of products was due to the difference in chemical composition revealed by liquid chromatography-mass spectroscopy. The oily and the powdery products required attention in terms of safety and effectiveness, respectively. Finally, the results from the SDI-based safety evaluation of butterbur and other herbal supplement products were grouped into four categories and cautionary notes were discussed. The SDI-based safety evaluation of their products by herbal supplement operators would contribute to safe and secure use by consumers.

Aqueous Chlorination of D-Limonene

Limonene (1-methyl-4-(1-methylethenyl)-cyclohexene) is one of the most widespread monocyclic terpenes, being both a natural and industrial compound. It is widely present in the environment, including in water supplies. Therefore, it may be subjected to aqueous chlorination at water treatment stations during drinking water preparation. Besides, being a component of numerous body care and cosmetic products, it may present at high levels in swimming pool waters and could also be subjected to aqueous chlorination. Laboratory experiments with aqueous chlorination of D-limonene demonstrated the prevalence of the conjugated electrophilic addition of HOCl molecule to the double bonds of the parent molecule as the primary reaction. The reaction obeys the Markovnikov rule, as the levels of the corresponding products were higher than those of the alternative ones. Fragmentation pattern in conditions of electron ionization enabled the assigning of the structures for four primary products. The major products of the chlorination are formed by the addition of two HOCl molecules to limonene. The reactions of electrophilic addition are usually accompanied by the reactions of elimination. Thus, the loss of water molecules from the products of various generations results in the reproduction of the double bond, which immediately reacts further. Thus, a cascade of addition-elimination reactions brings the most various isomeric polychlorinated species. At a ratio of limonene/active chlorine higher than 1:10, the final products of aqueous chlorination (haloforms) start forming, while brominated haloforms represent a notable portion of these products due to the presence of bromine impurities in the used NaOCl. It is worth mentioning that the bulk products of aqueous chlorination are less toxic in the bioluminescence test on V. fischeri than the parent limonene.

Toxicological safety assessment of essential oils used as food supplements to establish safe oral recommended doses

Essential oils (EOs) are increasingly consumed as food supplements. The few published recommended doses available generally lack details both on the methodology used and concentration limits for substances of concern, including genotoxic carcinogens. We propose a tiered approach based on the toxicological evaluation of maximized concentrations of each constituent present in the EO investigated. The genotoxic potential of each constituent is assessed using literature data or QSAR analyses. Genotoxic constituents are evaluated according to the methodology provided in the ICHM7 guideline. A Toxicological Reference Value (TRV) is associated to each non-genotoxic constituent, using one of the following methodologies (decision-tree successive steps): extraction from recognized databases or clinical studies, application of adequate safety factors to NOAELs established in animal studies, read-across analyses and when none was possible, TTC of Cramer classes. An EO recommended dose is considered safe when the safety margin (ratio between TRV and systemic exposure) for all constituents is all at least equal to 1. In conclusion, this methodology has proven to be robust to establish safe recommended doses for EOs used as food supplements, consistent with those publicly available, and avoiding unnecessary dedicated new animal testing.

FEMA GRAS assessment of natural flavor complexes: Eucalyptus oil and other cyclic ether-containing flavoring ingredients

In 2015, the Expert Panel of the Flavor and Extract Manufacturers Association (FEMA) initiated a program for the re-evaluation of the safety of over 250 natural flavor complexes (NFCs) used as flavor ingredients. This publication, the sixth in the series, will summarize the re-evaluation of eight NFCs whose constituent profiles are characterized by significant amounts of eucalyptol and/or other cyclic ethers. This re-evaluation was based on a procedure first published in 2005 and subsequently updated in 2018 that evaluates the safety of naturally occurring mixtures for their intended use as flavoring ingredients. The procedure relies on a complete chemical characterization of the NFC intended for commerce and the organization of its chemical constituents into well-defined congeneric groups. The safety of the NFC is evaluated using the well-established and conservative threshold of toxicological concern (TTC) concept in addition to data on absorption, metabolism and toxicology of the constituents of the congeneric groups and the NFC under evaluation. Eight NFCs derived from the Eucalyptus, Melaleuca, Origanum, Laurus, Rosmarinus and Salvia genera were affirmed as generally recognized as safe (GRAS) under their conditions of intended use as flavor ingredients based on an evaluation of each NFC and the constituents and congeneric groups therein.

D-limonene Inhibits Pentylenetetrazole-Induced Seizure via Adenosine A2A Receptor Modulation on GABAergic Neuronal Activity

Background: Epilepsy is a chronic neurological disorder characterized by the recurrence of seizures. One-third of patients with epilepsy may not respond to antiseizure drugs. Purpose: We aimed to examine whether D-limonene, a cyclic monoterpene, exhibited any antiseizure activity in the pentylenetetrazole (PTZ)-induced kindling mouse model and in vitro. Methods: PTZ kindling mouse model was established by administering PTZ (30 mg/kg) intraperitoneally to mice once every 48 h. We performed immunoblot blots, immunohistochemistry (IHC), and high-performance liquid chromatography (HPLC) analysis after the behavioral study. Results: An acute injection of PTZ (60 mg/kg) induced seizure in mice, while pretreatment with D-limonene inhibited PTZ-induced seizure. Repeated administration of PTZ (30 mg/kg) increased the seizure score gradually in mice, which was reduced in D-limonene (10 mg/kg)-pretreated group. In addition, D-limonene treatment increased glutamate decarboxylase-67 (GAD-67) expression in the hippocampus. Axonal sprouting of hippocampal neurons after kindling was inhibited by D-limonene pretreatment. Moreover, D-limonene reduced the expression levels of Neuronal PAS Domain Protein 4 (Npas4)-induced by PTZ. Furthermore, the adenosine A2A antagonist SCH58261 and ZM241385 inhibited anticonvulsant activity and gamma-aminobutyric acid (GABA)ergic neurotransmission-induced by D-limonene. Conclusion: These results suggest that D-limonene exhibits anticonvulsant activity through modulation of adenosine A2A receptors on GABAergic neuronal function.

Toxicity and human health assessment of an alcohol-to-jet (ATJ) synthetic kerosene

A toxicological investigation was conducted for alcohol-to-jet (ATJ) fuels intended as a 50:50 blend with petroleum-derived fuel Jet Propulsion (JP)-8. The ATJ synthetic paraffinic kerosene (SPK) fuel was produced by Gevo (Englewood CO) and derived either from biomass (bio) or non-biomass sources. All toxicity tests were performed with one or both ATJ fuels following addition of a standard additive package required for JP-8. The primary fuel, Gevo (bio) ATJ SPK produced from biomass-derived iso-butanol, exhibited the same dermal irritation potential in rabbits as JP-8; the non-biomass-derived fuel was less irritating. The Gevo (bio) fuel was non-clastogenic in micronucleus testing with rats and neither version was mutagenic in the bacterial reverse mutation assay. A 90-day study was performed with Gevo (bio) ATJ SPK by exposing male and female Fischer 344 rats to target concentrations of 0, 200, 700 or 2000 mg/m³ of fuel, 6 hr per day, 5 days a week for 69 exposure days and included neurobehavioral assays and reproductive health evaluations in the study design. Results were negative or limited to irritant effects in the respiratory system due to exposure to a vapor and aerosol mixture in the 2000 mg/m³ exposure group. Occupational exposure limits for JP-8 were proposed for these ATJ fuels since these fuels display similar or somewhat lower toxicity than JP-8. As both versions of the Gevo ATJ jet fuel were similar, handling of either fuel alone or in a blend with petroleum-derived JP-8 appears unlikely to increase human health risks for workers.

FEMA GRAS assessment of natural flavor complexes: Lavender, Guaiac Coriander-derived and related flavoring ingredients

In 2015, the Expert Panel of the Flavor and Extract Manufacturers Association (FEMA) initiated a program for the re-evaluation of the safety of over 250 natural flavor complexes (NFCs) used as flavor ingredients. This publication, fifth in the series, evaluates the safety of NFCs containing linalool and/or other characteristic mono- and sesquiterpenoid tertiary alcohols and esters using the safety evaluation procedure published by the FEMA Expert Panel in 2005 and updated in 2018. The procedure relies on a complete chemical characterization of the NFC intended for commerce and organization of the chemical constituents of each NFC into well-defined congeneric groups. The safety of each NFC is evaluated using the well-established and conservative threshold of toxicological concern (TTC) concept in addition to data on absorption, metabolism and toxicology of both the constituent congeneric groups and the NFCs. Sixteen NFCs, derived from the Lavandula, Aniba, Elettaria, Daucus, Salvia, Coriandrum, Ribes, Guaiacum/Bulnesia, Citrus, Pogostemon, Melaleuca and Michelia genera, were affirmed as generally recognized as safe (GRAS) under their conditions of intended use as flavor ingredients based on an evaluation of each NFC and the constituents and congeneric groups therein.

Toxicity and occupational exposure assessment for hydroprocessed esters and fatty acids (HEFA) alternative jet fuels

The U.S. Air Force (USAF) has pursued development of alternative fuels to augment or replace petroleum-based jet fuels. Hydroprocessed esters and fatty acids (HEFA) renewable jet fuel is certified for use in commercial and USAF aircraft. HEFA feedstocks include camelina seed oil (Camelina sativa, HEFA-C); rendered animal fat (tallow, HEFA-T); and mixed fats and oils (HEFA-F). The aim of this study was to examine potential toxic effects associated with HEFA fuels exposures. All 3 HEFA fuels were less dermally irritating to rabbits than petroleum-derived JP-8 currently in use. Inhalation studies using male and female Fischer-344 rats included acute (1 day, with and without an 11-day recovery), 5-, 10- or 90-day durations. Rats were exposed to 0, 200, 700 or 2000 mg/m³ HEFA-F (6 hr/day, 5 days/week). Acute, 5 - and 10-day responses included minor urinalysis effects. Kidney weight increases might be attributed to male rat specific hyaline droplet formation. Nasal cavity changes included olfactory epithelial degeneration at 2000 mg/m³. Alveolar inflammation was observed at ≥700 mg/m³. For the 90-day study using HEFA-C, no significant neurobehavioral effects were detected. Minimal histopathological effects at 2000 mg/m³ included nasal epithelium goblet cell hyperplasia and olfactory epithelium degeneration. A concurrent micronucleus test was negative for evidence of genotoxicity. All HEFA fuels were negative for mutagenicity (Ames test). Sensory irritation (RD₅₀) values were determined to be 9578 mg/m³ for HEFA-C and greater than 10,000 mg/m³ for HEFA-T and HEFA-F in male Swiss-Webster mice. Overall, HEFA jet fuel was less toxic than JP-8. Occupational exposure levels of 200 mg/m³ for vapor and 5 mg/m³ for aerosol are recommended for HEFA-based jet fuels.

FEMA GRAS assessment of natural flavor complexes: Mint, buchu, dill and caraway derived flavoring ingredients

In 2015, the Expert Panel of the Flavor and Extract Manufacturers Association (FEMA) initiated a re-evaluation of the safety of over 250 natural flavor complexes (NFCs) used as flavor ingredients. NFC flavor materials include a variety of essential oils and botanical extracts. The re-evaluation of NFCs is conducted based on a constituent-based procedure outlined in 2005 and updated in 2018 that evaluates the safety of NFCs for their intended use as flavor ingredients. This procedure is applied in the re-evaluation of the generally recognized as safe (GRAS) status of NFCs with constituent profiles that are dominated by alicyclic ketones such as menthone and carvone, secondary alcohols such as menthol and carveol, and related compounds. The FEMA Expert Panel affirmed the GRAS status of Peppermint Oil (FEMA 2848), Spearmint Oil (FEMA 3032), Spearmint Extract (FEMA 3031), Cornmint Oil (FEMA 4219), Erospicata Oil (FEMA 4777), Curly Mint Oil (FEMA 4778), Pennyroyal Oil (FEMA 2839), Buchu Leaves Oil (FEMA 2169), Caraway Oil (FEMA 2238) and Dill Oil (FEMA 2383) and determined FEMA GRAS status for Buchu Leaves Extract (FEMA 4923), Peppermint Oil, Terpeneless (FEMA 4924) and Spearmint Oil, Terpeneless (FEMA 4925).

Limonene Inhibits Methamphetamine-Induced Sensitizations via the Regulation of Dopamine Receptor Supersensitivity

Limonene is a cyclic terpene found in citrus essential oils and inhibits methamphetamine-induced locomotor activity. Drug dependence is a severe neuropsychiatric condition that depends in part on changes in neurotransmission and neuroadaptation, induced by exposure to recreational drugs such as morphine and methamphetamine. In this study, we investigated the effects of limonene on the psychological dependence induced by drug abuse. The development of sensitization, dopamine receptor supersensitivity, and conditioned place preferences in rats was measured following administration of limonene (10 or 20 mg/kg) and methamphetamine (1 mg/kg) for 4 days. Limonene inhibits methamphetamine-induced sensitization to locomotor activity. Expression of dopamine receptor supersensitivity induced by apomorphine, a dopamine receptor agonist, was significantly reduced in limonenepretreated rats. However, there was no significant difference in methamphetamine-induced conditioned place preferences between the limonene and control groups. These results suggest that limonene may ameliorate drug addiction-related behaviors by regulating postsynaptic dopamine receptor supersensitivity.

1,1,1,3,3,3-Hexamethyldisilazane (2018)

1,1,1,3,3,3-Hexamethyldisilazane (HMDZ) is used industrially to treat the surface of silica, as an intermediate adhesion promoter or silylating agent in the semiconductor industry, as a chemical modifier of inorganic fillers, and as a water scavenger silicone sealant. In animal studies, HMDZ is considered to be slightly to at most moderately toxic following acute administration via oral, dermal, and inhalation routes of exposure. HMDZ is neither an eye irritant nor was it dermally irritating under semiocclusive conditions; however, it caused dermal necrosis in two studies under occlusive conditions. HDMZ is not genotoxic or mutagenic in in vitro assays and was not reproductively or developmentally toxic in an inhalation screening study in rats. Short-term and subacute, high-dose inhalation exposure to HMDZ produced respiratory tract irritation, reduced feed consumption, changes in clinical chemistry parameters, and reversible central nervous system depression in rats. In a 90-day inhalation exposure study in rats, HMDZ exposure-related effects were observed in the kidneys of male rats but were determined to be alpha-2µ-nephropathy, thus, not relevant to humans. Based on the results of the 90-day (subchronic) inhalation study, 75 ppm was determined to be the no-observed adverse effect level (NOAEL) and was selected as the point of departure for the derivation of the 8-h time-weighted average (TWA), health-based workplace environmental exposure level (WEEL) value. This subchronic inhalation NOAEL was adjusted to account for duration of exposure, interindividual variability, and intraindividual variability. The resulting 8-h TWA WEEL value of 10 ppm is fully expected to provide a significant margin of safety against any potential adverse health effects in workers following long-term inhalation exposure to HMDZ vapor. A 15-min short-term exposure limit of 50 ppm was also established to protect workers from reversible effects produced by acute, high-dose inhalation of HMDZ vapor. A skin notation (Skin) is warranted because of the potential for the dermal route to significantly contribute to the overall exposure to HMDZ.

FEMA GRAS assessment of natural flavor complexes: Citrus-derived flavoring ingredients

In 2015, the Expert Panel of the Flavor and Extract Manufacturers Association (FEMA) initiated a re-evaluation of the safety of over 250 natural flavor complexes (NFCs) used as flavoring ingredients. This publication is the first in a series and summarizes the evaluation of 54 Citrus-derived NFCs using the procedure outlined in Smith et al. (2005) and updated in Cohen et al. (2018) to evaluate the safety of naturally-occurring mixtures for their intended use as flavoring ingredients. The procedure relies on a complete chemical characterization of each NFC intended for commerce and organization of each NFC's chemical constituents into well-defined congeneric groups. The safety of the NFC is evaluated using the well-established and conservative threshold of toxicological concern (TTC) concept in addition to data on absorption, metabolism and toxicology of members of the congeneric groups and the NFC under evaluation. As a result of the application of the procedure, 54 natural flavor complexes derived from botanicals of the Citrus genus were affirmed as generally recognized as safe (GRAS) under their conditions of intended use as flavoring ingredients based on an evaluation of each NFC and the constituents and congeneric groups therein.

Toxicity and occupational exposure assessment for Fischer-Tropsch synthetic paraffinic kerosene

Fischer-Tropsch (FT) Synthetic Paraffinic Kerosene (SPK) jet fuel is a synthetic organic mixture intended to augment petroleum-derived JP-8 jet fuel use by the U.S. armed forces. The FT SPK testing program goal was to develop a comparative toxicity database with petroleum-derived jet fuels that may be used to calculate an occupational exposure limit (OEL). Toxicity investigations included the dermal irritation test (FT vs. JP-8 vs. 50:50 blend), 2 in vitro genotoxicity tests, acute inhalation study, short-term (2-week) inhalation range finder study with measurement of bone marrow micronuclei, 90-day inhalation toxicity, and sensory irritation assay. Dermal irritation was slight to moderate. All genotoxicity studies were negative. An acute inhalation study with F344 rats exposed at 2000 mg/m³ for 4 hr resulted in no abnormal clinical observations. Based on a 2-week range-finder, F344 rats were exposed for 6 hr per day, 5 days per week, for 90 days to an aerosol-vapor mixture of FT SPK jet fuel (0, 200, 700 or 2000 mg/m³). Effects on the nasal cavities were minimal (700 mg/m³) to mild (2000 mg/m³); only high exposure produced multifocal inflammatory cell infiltration in rat lungs (both genders). The RD₅₀ (50% respiratory rate depression) value for the sensory irritation assay, calculated to be 10,939 mg/m^3, indicated the FT SPK fuel is less irritating than JP-8. Based upon the proposed use as a 50:50 blend with JP-8, a FT SPK jet fuel OEL is recommended at 200 mg/m³ vapor and 5 mg/m³ aerosol, in concurrence with the current JP-8 OEL.

Adverse Phototoxic Effect of Essential Plant Oils on NIH 3T3 Cell Line after UV Light Exposure

AIM

Natural or artificial substances have become an inseparable part of our lives. It is questionable whether adequate testing has been performed in order to ensure these substances do not pose a serious health risk. The principal aim of our research was to clarify the potential risk of adding essential oils to food, beverages and cosmetic products.

METHODS

The toxicity of substances frequently employed in cosmetics, aromatherapy and food industry (bergamot oil, Litsea cubeba oil, orange oil, citral) were investigated using cell line NIH3T3 (mouse fibroblasts) with/without UV irradiation. The MTT assay was used to estimate the cell viability. Reactive oxygen species (ROS) which are products of a number of natural cellular processes such as oxygen metabolism and inflammation were measured to determine the extent of cellular stress. DNA damage caused by strand breaks was examined by comet assay.

RESULTS

MTT test determined EC50 values for all tested substances, varying from 0.0023% v/v for bergamot oil to 0.018% v/v for citral. ROS production measurement showed that UV radiation induces oxidative stress to the cell resulting in higher ROS production compared to the control and non-irradiated samples. Comet assay revealed that both groups (UV, without UV) exert irreversible DNA damage resulting in a cell death.

CONCLUSIONS

Our findings suggest that even low concentrations (lower than 0.0464% v/v) of orange oil can be considered as phototoxic (PIF value 8.2) and probably phototoxic for bergamot oil (PIF value 4.6). We also found significant changes in the cell viability, the ROS production and the DNA after the cells were exposed to the tested chemicals. Even though these substances are widely used as antioxidants it should be noted that they present a risk factor and their use in cosmetic and food products should be minimized.

Safety evaluation and risk assessment of d-Limonene

d-Limonene, a major constituent of citrus oils, is a monoterpene widely used as a flavor/fragrance additive in cosmetics, foods, and industrial solvents as it possesses a pleasant lemon-like odor. d-Limonene has been designated as a chemical with low toxicity based upon lethal dose (LD50) and repeated-dose toxicity studies when administered orally to animals. However, skin irritation or sensitizing potential was reported following widespread use of this agent in various consumer products. In experimental animals and humans, oxidation products or metabolites of d-limonene were shown to act as skin irritants. Carcinogenic effects have also been observed in male rats, but the mode of action (MOA) is considered irrelevant for humans as the protein α(2u)-globulin responsible for this effect in rodents is absent in humans. Thus, the liver was identified as a critical target organ following oral administration of d-limonene. Other than the adverse dermal effects noted in humans, other notable toxic effects of d-limonene have not been reported. The reference dose (RfD), the no-observed-adverse-effect level (NOAEL), and the systemic exposure dose (SED) were determined and found to be 2.5 mg/kg/d, 250 mg/kg//d, and 1.48 mg/kg/d, respectively. Consequently, the margin of exposure (MOE = NOAEL/SED) of 169 was derived based upon the data, and the hazard index (HI = SED/RfD) for d-limonene is 0.592. Taking into consideration conservative estimation, d-limonene appears to exert no serious risk for human exposure. Based on adverse effects and risk assessments, d-limonene may be regarded as a safe ingredient. However, the potential occurrence of skin irritation necessitates regulation of this chemical as an ingredient in cosmetics. In conclusion, the use of d-limonene in cosmetics is safe under the current regulatory guidelines for cosmetics.

Renal biomarker changes associated with hyaline droplet nephropathy in rats are time and potentially compound dependent

Alpha 2u-globulin mediated hyaline droplet nephropathy (HDN) is a male rat specific lesion induced when a compound or metabolite binds to alpha 2u-globulin. The objective of this study was to investigate if the newer and more sensitive renal biomarkers would be altered with HDN as well as be able to distinguish between HDN and oxidative stress-induced kidney injury. Rats were dosed orally for 7 days to determine (1) if HDN (induced by 2-propanol or D-limonene) altered the newer renal biomarkers and not BUN or creatinine, (2) if renal biomarkers could distinguish between HDN and oxidative stress-induced kidney injury (induced by potassium bromate), (3) sensitivity of HDN-induced renal biomarker changes relative to D-limonene dose, and (4) reversibility of HDN and renal biomarkers, using vehicle or 300 mg/kg/day D-limonene with 7 days of dosing and necropsies scheduled over the period of Days 8-85. HDN-induced renal biomarker changes in male rats were potentially compound specific: (1) 2-propanol induced mild HDN without increased renal biomarkers, (2) potassium bromate induced moderate HDN with increased clusterin, and (3) D-limonene induced marked HDN with increased αGST, μGST and albumin. Administration of potassium bromate did not result in oxidative stress-induced kidney injury, based on histopathology and renal biomarkers creatinine and BUN. The compound D-limonene induced a dose dependent increase in HDN severity and renal biomarker changes without altering BUN, creatinine or NAG: (1) minimal induction of HDN and no altered biomarkers at 10 mg/kg/day, (2) mild induction of HDN with increased αGST and μGST at 50 mg/kg/day and (3) marked induction of HDN with increased αGST, μGST and albumin at 300 mg/kg/day. HDN induced by D-limonene was reversible, but with a variable renal biomarker pattern over time: Day 8 there was increased αGST, μGST and albumin; on Day 15 increased clusterin, albumin and Kim-1. In summary, HDN altered the newer and more sensitive renal biomarkers in a time and possibly compound dependent manner.

Toxicological studies on 2,4,6-tribromoanisole

TBA, or 2,4,6-tribromoanisole, is a musty-smelling metabolite of 2,4,6-tribromophenol that is used as a flame retardant and an antifungal agent for wooden pallets and packaging materials. The compound can impart its peculiar, often offensive, odor on product packaging to the concern of consumers for the safety of the package contents. These studies were conducted to evaluate the safety of TBA to humans ingesting products tainted with TBA. In addition to the 28-day oral study, a bacterial reverse mutation study was conducted, and confirmed that TBA was not mutagenic. To evaluate oral safety, TBA was evaluated in single dose and 5-day and 4-week repeated dose oral toxicity studies in rats. The test article, administered in single gavage doses of 2000, 5000 and 7500 mg/kg body weight (bw), in 5 daily repeated doses of 1000, 2000 or 3000 mg/kg bw/day or in 28 daily oral gavage doses of 0 001, 0.01, 100, and 1000 mg/kg bw/day did not result in any deaths. Also, the single and repeat dose studies resulted in no significant differences between control and treated groups on body weight gain, food consumption, clinical observations, blood biochemical values, and hematology findings. Treatment-related adverse findings were only detected in male rats during repeated dose studies and were associated with high plasma concentrations of TBA. The test article-related finding of hyaline droplets in the cortical tubular epithelium of kidneys was associated with increases in α(2 μ)-globulin content in the kidneys as indicated by the intensity of immunohistochemical staining. These findings were correlated with an increased weight of kidneys in males administered 1000mg/kgbw/day for 28days. Chemical induction of hyaline droplets containing α(2μ)-globulin in the renal proximal tubule is a process unique to the male rat and is not relevant for human risk assessment. Findings of increased liver weight with minimal centrilobular to diffuse hepatocellular hypertrophy in males treated with TBA at 1000mg/kg bw/day for 28days were considered to be an adaptive metabolic response to xenobiotic administration. The increased volume of urine, noted in both males and females treated with 1000mg/kg bw/day was considered adaptive and necessary to excrete the high xenobiotic burden resulting from TBA administration. TBA appeared to be highly bioavailable since high concentrations of TBA were detected in plasma, at 1, 4 and 8h after administration of TBA at 100 and 1000mg/kg bw for 1 and 28days. Levels were dose-related but did not clarify the course of TBA elimination with time after administration. These studies indicate that TBA, administered orally to rats, produced male rat-specific, treatment-related toxicity at the highest orally administered dose in repeated dose (5-day at 3000mg/kg bw and 28-day at 1000mg/kg bw) studies. Therefore, the NOAEL for the 28-day oral study was determined to be 1000mg/kg bw/day for the rat.

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.

In vivo Comet assay on isolated kidney cells to distinguish genotoxic carcinogens from epigenetic carcinogens or cytotoxic compounds

The objective of this study was to determine the ability of the alkaline in vivo Comet assay (pH>13) to distinguish genotoxic carcinogens from epigenetic carcinogens when performed on freshly isolated kidney cells and to determine the possible interference of cytotoxicity by assessing DNA damage induced by renal genotoxic, epigenetic or toxic compounds after enzymatic isolation of kidney cells from OFA Sprague-Dawley male rats. The ability of the Comet assay to distinguish (1) genotoxicity versus cytotoxicity and (2) genotoxic versus non-genotoxic (epigenetic) carcinogens, was thus investigated by studying five known genotoxic renal carcinogens acting through diverse mechanisms of action, i.e. streptozotocin, aristolochic acids, 2-nitroanisole, potassium bromate and cisplatin, two rodent renal epigenetic carcinogens: d-limonene and ciclosporine and two nephrotoxic compounds: streptomycin and indomethacin. Animals were treated once with the test compound by the appropriate route of administration and genotoxic effects were measured at the two sampling times of 3-6 and 22-26h after treatment. Regarding the tissue processing, the limited background level of DNA migration observed in the negative control groups throughout all experiments demonstrated that the enzymatic isolation method implemented in the current study is appropriate. On the other hand, streptozotocin, 20mg/kg, used as positive reference control concurrently to each assay, caused a clear increase in the mean Olive Tail Moment median value, which allows validating the current methodology. Under these experimental conditions, the in vivo rodent Comet assay demonstrated good sensitivity and good specificity: all the five renal genotoxic carcinogens were clearly detected in at least one expression period either directly or indirectly, as in the case of cisplatin: for this cross-linking agent, the significant decrease in DNA migration observed under standard electrophoresis conditions was clearly amplified when the duration of electrophoresis was increased up to 40min. In contrast, epigenetic and nephrotoxic compounds failed to induce any signifcant increase in DNA migration. In conclusion, the in vivo rodent Comet assay performed on isolated kidney cells could be used as a tool to investigate the genotoxic potential of a test compound if neoplasic/preneoplasic changes occur after subchronic or chronic treatments, in order to determine the role of genotoxicity in tumor induction. Moreover, the epigenetic carcinogens and cytotoxic compounds displayed clearly negative responses in this study. These results allow excluding a DNA direct-acting mechanism of action and can thus suggest that a threshold exists. Therefore, the current in vivo rodent Comet assay could contribute to elucidate an epigenetic mechanism and thus, to undertake a risk assessment associated with human use, depending on the exposure level.

A classification framework and practical guidance for establishing a mode of action for chemical carcinogens

The recently released U.S. Environmental Protection Agency (U.S. EPA) Supplemental Guidance for Assessing Risk from Early Life Exposure to Carcinogens (SGAC) provides guidance to account for potential increased early life susceptibility to carcinogens that are acting via a mutagenic mode of action. While determination of the mode of carcinogenic action is central to the SGAC procedures and other regulatory risk assessments, little guidance is given as to the approaches, criteria, and nature of the evidence required to define a mutagenic mode of action. The purpose of this paper is to provide a framework along with practical guidance for the process of assigning a mode of action. Strengths, weaknesses, reliability, and choice of a test battery are discussed for select bacterial, cell culture, whole animal and human cell assays. Common confounding factors of induced pathology, cytolethality, and regenerative cell proliferation in rodent cancer bioassays are discussed along with approaches to account for these effects in assigning a mode of action and in risk assessments. Specific examples are given to illustrate the complexity in generating a data set sufficient to move from the default regulatory position of assuming a genotoxic mode of action to actually assigning a nongenotoxic mode of action. A two-part framework is proposed for assigning a mode of action. First, a weight of evidence approach is used to assess mutagenic potential based on results of genetic toxicology test systems. Second, a descriptor is assigned to classify the degree to which mutagenic activity likely played a role in the mode of action of tumor formation. This option provides a more realistic way of describing the mode of action instead of being bound by the strict genotoxic vs. nongenotoxic choices.

Hazard characterisation of chemicals in food and diet. dose response, mechanisms and extrapolation issues

Hazard characterisation of low molecular weight chemicals in food and diet generally use a no-observed-adverse-effect level (NOAEL) or a benchmark dose as the starting point. For hazards that are considered not to have thresholds for their mode of action, low-dose extrapolation and other modelling approaches may be applied. The default position is that rodents are good models for humans. However, some chemicals cause species-specific toxicity syndromes. Information on quantitative species differences is used to modify the default uncertainty factors applied to extrapolate from experimental animals to humans. A central theme for extrapolation is unravelling the mode of action for the critical effects observed. Food can be considered as an extremely complex and variable chemical mixture. Interactions among low molecular weight chemicals are expected to be rare given that the exposure levels generally are far below their NOAELs. Hazard characterisation of micronutrients must consider that adverse effects may arise from intakes that are too low (deficiency) as well as too high (toxicity). Interactions between different nutrients may complicate such hazard characterisations. The principle of substantial equivalence can be applied to guide the hazard identification and hazard characterisation of macronutrients and whole foods. Macronutrients and whole foods must be evaluated on a case-by-case basis and cannot follow a routine assessment protocol.

Pharmaceutical excipient development: the need for preclinical guidance

Pharmaceutical excipients have a vital role in drug formulations, a role that has tended to be neglected as evidenced by the lack of mechanisms to assess excipient safety outside a new drug application process. Currently, it is assumed that an excipient is "approved" when the new drug formulation, of which it is a constituent, receives regulatory acceptance. Existing regulations and guidelines indicate that new (novel) excipients should be treated as new chemical entities with full toxicological evaluation. No guidance is available for potentially useful materials (essentially new excipients) available from other industries, e.g., food additives or for established excipients with a new application, e.g., dose route change. However, despite this situation, drug companies are actively evaluating new materials or applying new uses to established excipients. Recently developed excipients (e.g., materials giving "sugar-free" status to medical preparations, the cyclodextrins, and the hydrofluoroalkane inhalation propellants) and excipients undergoing development (e.g., chitosan, various enteric coating substances, liposomes, polymers derived from glycolic and lactic acids, and vaccine adjuvants) are all discussed. In light of many other areas of drug development having recently benefited from new or updated regulatory guidance, specific guidance to assist companies in the development of their excipients is urgently needed. Also, an excipient testing strategy would be an excellent topic for inclusion for International Conference on Harmonisation (ICH) consideration. Such guidance/discussion would complement the current advances in pharmacopoeial standardization of excipient quality. As a consequence, it may be possible to have excipients reviewed by a committee of an international pharmacopoeia with the safety data assessed by elected experts and published.

A comprehensive approach for integration of toxicity and cancer risk assessments

Experimental observations and theoretical considerations indicate a dose threshold for most chemically induced noncancer toxic effects below which the increased risk of toxicity is zero. Thus, the historical approach for minimizing risk from toxic chemicals has been to experimentally determine a no-observed-adverse-effect-level (NOAEL) and then to apply safety or uncertainty factors to estimate a dose not expected to produce that toxic effect in humans. In contrast, for radiation and chemically induced cancer, it has been assumed that all agents operate by a genotoxic mode of action and that some risk can be assigned to even vanishingly small doses. Accordingly, risk assessments for carcinogens have commonly been based on the assumption that the tumor dose-response curve at low doses is linear and passes through the origin. Mode of action is defined as a fundamental obligatory step in the induction of toxicity or cancer. It is now clear that tumor induction can arise in a variety of ways including not only a DNA-reactive genotoxic mode of action, but also non-DNA-reactive nongenotoxic-cytotoxic and nongenotoxic-mitogenic modes of action. Initial risk assessment approaches that recognized this distinction identified a chemical carcinogen as either genotoxic or nongenotoxic, with no middle ground. The realization that there is a continuum whereby different chemicals can act by a combination of modes of action and the recent explosion of research into molecular mechanisms of carcinogenesis indicate that all relevant information should be integrated into the risk assessment process on a case by case basis. A comprehensive approach to risk assessment demands that default assumptions be replaced with an integrated understanding of the rate-limiting steps in the induction of toxicity or cancer along with quantitative measures of the shapes of those dose-response curves. The examples of more contemporary risk assessments are presented for chloroform and vinyl acetate.

Analysis of alpha2u-globulin in rat urine and kidneys by liquid chromatography-electrospray ionization mass spectrometry

A quantitative method was developed for determination of alpha2u-globulin in urine and kidney samples collected from male rats using liquid chromatography-electrospray ionization mass spectrometry (LC-ESI/MS). Samples prepared from urine and kidney homogenates using size exclusion filters were subject to reversed-phase liquid chromatography and the effluent passed into an electrospray ionization source. Quantitative analysis using external standard calibration was based upon selected ion monitoring of protonated molecular ions by the mass spectrometer. Linear calibration curves were developed over the range of approximately 4. 6-370 microg of alpha2u-globulin/microL for spiked urine standards and over the range of approximately 4.6-550 microg of alpha2u-globulin/microL for spiked kidney standards. The precision (relative standard deviation) for repeated injection (using urine samples) and intra-assay precision (using both urine and kidney samples) were within +/-10.4% and +/-13.2%, respectively. Using spiked urine standards, inter-assay precision, intra-assay accuracy, and inter-assay accuracy were within +/-20%, +/-20%, and +/-15%, respectively. Using spiked kidney standards, intra-assay accuracy was within +/-15%. The limits of detection (LOD) for the determination of alpha2u-globulin in urine and kidney samples were approximately 0.41 pg/nL (1.0 fmol injected) and 25 pg/nL ( approximately 13 fmol injected), respectively. The limits of quantitation (LOQ) for determination of alpha2u-globulin in urine and kidney samples were calculated as 1.4 pg/nL (3.7 fmol injected) and 83 pg/nL (45 fmol injected), respectively. Applicability of the LC-ESI/MS method was demonstrated by determination of alpha2u-globulin in both urine and kidney samples collected from male Fischer 344/N rats dosed intravenously with cis-Decalin at concentrations of 0, 2.5, 5.0, 10, and 20 mg/kg. A dose-dependent relationship was found between the amount of cis-Decalin administered and alpha2u-globulin accumulation in kidney samples, whereas no significant change in the urinary levels of alpha2u-globulin occurred. These observations are consistent with excessive accumulation of alpha2u-globulin occurring in protein droplets in renal proximal tubule epithelial cells as a result of decreased catabolic activity due to formation of ligand-protein complexs with Decalin and its metabolite(s). This report demonstrates that LC-ESI/MS may be routinely applied for quantitative analysis of alpha2u-globulin in rat urine and kidney samples to address alpha2u-globulin accumulation and its role in the development of nephrotoxicity associated with chemical exposures.

Carcinogen risk assessment: a necessary dilemma?

Carcinogen risk assessment is the process by which an attempt is made to estimate human risk due to carcinogens, from the results of animal studies. It is based upon a number of prudent default assumptions, that is, assumptions that cannot be proved scientifically because either the basic concept is philosophical in nature or because the amount of scientific evidence required is too costly to obtain even on a world-wide basis. Recently, scientific effort has shown that more and more examples have been described suggesting these examples do not behave in the way indicated by the default assumptions. Since carcinogen risk assessment processes were initiated, it has been demonstrated that cancer may arise by four or more different mechanisms. It is the purpose of this paper to enquire whether consideration of these basically different mechanisms may facilitate carcinogen risk assessment.

Does the term carcinogen send the wrong message?

The term carcinogen has been used by scientists and health regulatory officials for decades. During the last 20 years there have been attempts to redefine the term to make it more rigorous. But, as predicted two decades ago by a benchmark-setting subcommittee of the National Cancer Advisory Board, advances in scientific understanding have brought about dramatic changes in the way we are able to view the term carcinogen. These changes, their scientific bases and their effect on defining the term carcinogen are described. An alternative to the use of the term carcinogen is suggested by the recently proposed US Environmental Agency's guidelines for cancer risk assessment which appear to be in accord with current scientific understanding and the importance of considering the factors affecting the term carcinogen. The guidelines set forth four questions, the answers to which could, in our judgment, replace the need to define or use the term carcinogen which, in light of new scientific knowledge, has become more misleading than useful.

The FEMA GRAS assessment of furfural used as a flavour ingredient. Flavor and Extract Manufacturers' Association

The Expert Panel of the Flavor and Extract Manufacturers' Association (FEMA) has assessed the safety of furfural for its continued use as a flavour ingredient. The safety assessment takes into account the current scientific information on exposure, metabolism, pharmacokinetics, toxicology, carcinogenicity and genotoxicity. Furfural was reaffirmed as GRAS (GRASr) as a flavour ingredient under conditions of intended use based on: (1) its mode of metabolic detoxication in humans; (2) its low level of flavour use compared with higher intake levels as a naturally occurring component of food; (3) the safety factor calculated from results of subchronic and chronic studies, (4) the lack of reactivity with DNA; and (5) the conclusion that the only statistically significant finding in the 2-year NTP bioassays, an increased incidence of hepatocellular adenomas and carcinomas in the high-dose group of male mice, was secondary to pronounced hepatotoxicity. Taken together, these data do not indicate any risk to human health under conditions of use as a flavour ingredient. This evidence of safety is supported by the occurrence of furfural as a natural component of traditional foods, at concentrations in the diet resulting in a 'natural intake' that is at least 100 times higher than the intake of furfural from use as a flavour ingredient.

The low pH Syrian hamster embryo (SHE) cell transformation assay: a revitalized role in carcinogen prediction

A series of publications of the results of National Toxicology Program (NTP) studies (Tennant et al. (1987) Science, 236, 933-941; Haseman et al. (1990) J. Am. Stat. Assoc., 85, 964-971; Shelby et al. (1993) Environ. Mol. Mutagen., 21, 160-179) show that the commonly used short-term genotoxicity tests are less predictive of rodent carcinogenicity than once thought. These results have fueled a great deal of debate in the field of genetic toxicology regarding appropriate strategies for assessing the potential carcinogenicity of chemicals. The debate has continued in the recent discussion of harmonized genotoxicity test strategies (Ashby (1993) Mutation Res., 298, 291-295 and Ashby (1994) 308, 113-114; Madle (1993) Mutation Res., 300, 73-76 and Madle (1994) 308, 111-112; Zeiger (1994) Mutation Res., 304, 309-314) since the underlying problem still has not been resolved. The underlying problem is the fact that the current short-term genotoxicity tests in any combination do not provide both the necessary high sensitivity and high specificity needed for accurate rodent carcinogen detection. In this discussion, we describe the utility of the newly revised Syrian hamster embryo (SHE) cell transformation assay alone and in combination with the Salmonella mutation assay for improved accuracy of screening of rodent carcinogens relative to standard short-term genotoxicity tests. The accompanying papers provide details of improved methodologies for the conduct of the SHE cell transformation assay and an extensive review of the databases which support our conclusion that the SHE cell transformation assay provides an improved prediction of rodent bioassay results relative to other in vitro genotoxicity test batteries.

Risk assessment and biological mechanisms: lessons learned, future opportunities

During the past decade, toxicological research has been dominated by two themes; investigations to elucidate the mechanisms of action of toxicants and studies to provide information to support improved assessments of human health risks. The conduct of mechanistic investigations was given an early impetus by advances in biochemistry and cell biology and, more recently, by related advances in molecular biology. Research to provide information for improved human health risk assessments was stimulated by the 1983 NAS/NRC report that provided a codified structure for conducting risk assessments. At first glance, it would appear that the two themes are closely related and, indeed, should represent parts of a joined theme. However, examination of the toxicology/risk assessment literature of the past decade indicates that this has not been the case. Reports of mechanistic studies infrequently indicate how the information can be used to provide improved estimates of human risk from exposure to toxicants. If reference is made, it is usually qualitative in nature. Neither is examination of the risk assessment literature reassuring. Mechanistic studies may be cited; however, the final step of the process, risk characterization, is usually dominated by the use of default options grounded in conservative interpretations of generic scientific knowledge. Two examples are reviewed that stand out as illustrations of how mechanistic information can be used to make a difference in risk assessments: (1) consideration of the alpha 2u-globulin-mediated mechanism for evaluating male rat data for relevance in assessing human risks of renal cancer and (2) the use of DNA-protein cross-links as an internal dose metric in cross-species extrapolation of nasal cancer risks from inhaled formaldehyde. This paper reviews past experience on these topics and suggests a strategy for increasing the use of mechanistic information in risk assessments. A key component of the strategy is to use the risk assessment process to identify research needs/opportunities that, if addressed, will reduce the use of default options, thereby reducing the uncertainties in risk assessments. Another component of the strategy is to identify a few chemicals anticipated to exert their effect via different mechanisms and whose mechanisms of dosimetry and disease pathogenesis can be investigated in-depth within a risk assessment framework; this identification will create prototype approaches as alternatives to the use of default options that have major impact on the outcome of the risk assessment process.

The effects of JP-8 jet fuel on male Sprague-Dawley rats after a 90-day exposure by oral gavage

The U.S. Air Force is converting from JP-4 jet fuel to the less volatile JP-8 jet fuel, which is similar to commercial Jet Fuel A. Our previous 90-day inhalation study with JP-8 vapor, using F-344 rats and C57BL/6 mice, resulted in no treatment-related adverse effects other than alpha 2-microglobulin nephropathy in male rats (Mattie et al., 1991). In the present study, male rats were dosed with neat JP-8 (0, 750, 1500, 3000 mg/kg) daily by gavage for 90 days in an effort to characterize the kidney lesion and assess further any additional adverse effects associated with prolonged oral exposure to this fuel. Results of this study revealed a significant dose-dependent decrease in body weights of rats exposed to JP-8. Male rat-specific alpha 2-microglobulin nephropathy was observed by histopathologic examination. A number of significant changes were also seen in blood and urine that were not dose-dependent. Additional treatment-related effects were a gastritis and a perianal dermatitis. Although there were no histopathological or weight changes in the livers of exposed rats, there was an increase in the liver enzymes AST and ALT. The elevated enzymes did not increase with increasing dose of JP-8.

Use of 'secondary mechanism' in the regulation of carcinogens; a chronology

Significantly more willingness to depart from worst case assumptions in the evaluation of carcinogenic risk has developed in the last 30 years. Scientists within regulatory agencies and in the academic community are reaching a consensus on the inadequacy of current test methods and on the need for more mechanistic data to help interpret the carcinogen bioassay. The slow regulatory acceptance of the concept of 'secondary mechanism' in the evaluation of cancer risk from chemicals in the U.S. is illustrated by a chronology of laws, policies, and consensus scientific positions adopted through the years.

A strategy for establishing mode of action of chemical carcinogens as a guide for approaches to risk assessments

The current standard approach for assessing carcinogenic potential is to conduct a near lifetime rodent pathology study with the high dose set to the maximum tolerated dose (MTD) of the test chemical. The linearized multistage model is then used as the default approach to estimate the potential human cancer risk at environmental elvels of the chemical. There is an increasing appreciation in the scientific and regulatory communities that chemical carcinogens differ dramatically in potency, exhibit a high degree of tissue and species specificity, and act through different modes of action. This paper advocates a decision tree strategy for classifying carcinogens that are acting primarily through genotoxic, cytotoxic, or mitogenic pathways. A primary concern is whether the chemical has direct genotoxic potential resulting from DNA reactivity or clastogenicity of the compound or its metabolite(s). Knowledge of the exposure-response curve for cytotoxicity is important because initiation and promotion events may occur secondary to a variety of associated activities such as regenerative cell proliferation. Mitogens indice direct stimulation of growth and may provide a selective growth advantage to spontaneously initiated precancerous cells. Of particular concern is the situation where pathological changes induced during the course of the treatment at high doses near the MTD are absent at lower, environmentally relevant, doses. If the tumor response is coincident with the preceding toxic response, it may not be justified to use the high-dose data in extrapolating to expected responses at low environmental exposures where no induced tissue abnormalities occur. Suggestions are presented for appropriate risk assessment approaches for different modes of action. Examples discussed are formaldehyde, a weakly genotoxic rodent nasal carcinogen; chloroform, a nongenotoxic-cytotoxic rodent liver and kidney carcinogen; and phenobarbital, a nongenotoxic-mitogenic rodent liver carcinogen.

Toxicity and cell proliferation in the liver, kidneys and nasal passages of female F-344 rats, induced by chloroform administered by gavage

Dose-response relationships were determined for the induction of cytolethality and regenerative cell proliferation in the established target organs (liver, kidneys, and nasal passages) of female F-344 rats given chloroform daily by gavage. Rats were administered chloroform dissolved in corn oil at doses of 0, 34, 100, 200 or 400 mg/kg/day for 4 consecutive days or for 5 days/wk for 3 wk. Bromodeoxyuridine (BrdU) was administered through an implanted osmotic pump 3.5 days prior to autopsy to label cells in S-phase. Cells in S-phase were visualized immunohistochemically in tissue sections and the labelling index (LI) calculated as the percentage of cells in S-phase. Mild degenerative centrilobular changes and dose-dependent increases in the hepatocyte LI were observed after administration of 100 mg or more chloroform/kg/day. Rats given 200 or 400 mg/kg/day for 4 days or 3 wk had degeneration and necrosis of the proximal tubules of the renal cortex. Regenerating epithelium lining proximal tubules was seen histologically and as an increase in LI. Dose-dependent increases in LI were observed in the kidneys at doses of 100 mg or more chloroform/kg/day at both 4 days and 3 wk. Two distinct treatment-induced responses were observed in specific regions of the olfactory mucosa lining the ethmoid region of the nose. A peripheral lesion was seen at all doses used and included new bone formation, periosteal hypercellularity and increased cell replication. A central lesion was seen at doses of 100 mg or more chloroform/kg/day and was characterized by degeneration of the olfactory epithelium and superficial Bowman's glands. These observations define the dose-response relationships for the liver, kidneys and nasal passages as target organs for chloroform administered by gavage in the female F-344 rat.

Use of mechanistic information in risk assessment for toxic chemicals

Risk assessment (RA) for toxic chemicals is assumed to be a scientific activity providing a framework of principles for the complication and evaluation of all available scientific information and the rational extrapolation to human health effects in as quantitative terms as possible and with a high degree of certainty. Sensible public health decisions are made more certain through the use of mechanistic information throughout the 4 steps in RA: hazard identification, dose-response assessment, exposure (dose) assessment and risk characterisation. Examples of the use of mechanistic information to assess risks of systemic, developmental/reproductive and neurotoxic effects show how to move away from the presently used threshold/no observable adverse effect/uncertainty factor default methodology towards an evaluation based on all available scientific data. The experience gained in cancer RA in the use of metabolic and tissue binding (receptor) models as well as physiologically based pharmacokinetic (PBPK) and pharmacodynamic (PBPD) models can be transferred to non-cancer RA. A good example is the use of a PBPK model for the hepatoxicity of chloroform. As in cancer RA, as default positions are replaced by biological data the risk assessments become less uncertain when extrapolating between species. Combining information on tissue dosimetry and response data can also provide an estimate of variability within populations, which is impossible with present default type methodology but essential for adequate risk characterisation. Unlike the cancer field there is no single hypothesis for the mechanism of action for the multitude of non-cancer end-points studied.

An introduction to drug disposition: the basic principles of absorption, distribution, metabolism, and excretion

A knowledge of the fate of a drug, its disposition (absorption, distribution, metabolism, and excretion, known by the acronym ADME) and pharmacokinetics (the mathematical description of the rates of these processes and of concentration-time relationships), plays a central role throughout pharmaceutical research and development. These studies aid in the discovery and selection of new chemical entities, support safety assessment, and are critical in defining conditions for safe and effective use in patients. ADME studies provide the only basis for critical judgments from situations where the behavior of the drug is understood to those where it is unknown: this is most important in bridging from animal studies to the human situation. This presentation is intended to provide an introductory overview of the life cycle of a drug in the animal body and indicates the significance of such information for a full understanding of mechanisms of action and toxicity.

Induced regenerative cell proliferation in livers and kidneys of male F-344 rats given chloroform in corn oil by gavage or ad libitum in drinking water

These studies were designed to establish the dose response relationships for the induction of cytolethality and regenerative cell proliferation in the liver and kidneys of male F-344 rats given chloroform by gavage or in drinking water. Rats were administered oral doses of 0, 10, 34, 90 or 180 mg/kg/day chloroform dissolved in corn oil by gavage for 4 days or for 5 days/week for 3 weeks. A second group of rats was given chloroform ad libitum in the drinking water at concentrations of 0, 60, 200, 400, 900 or 1800 ppm for 4 days or 3 weeks. Bromodeoxyuridine (BrdU) was administered via an implanted osmotic pump 3.5 days prior to necropsy to label cells in S-phase. Cells having incorporated BrdU were visualized in tissue sections immunohistochemically and the labelling index (LI) evaluated as the percentage of S-phase cells. Rats treated with 90 or 180 mg/kg/day by gavage for 4 days had mild to moderate degeneration of renal proximal tubules and centrilobular hepatocytes. These alterations were absent or slight after 3 weeks of treatment. LI were increased in the kidney cortex only in the rats treated with 180 mg/kg/day for 4 days. A dose-dependent increase in LI was seen in rat liver after 4 days of treatment with 90 and 180 mg/kg/day by gavage, but the LI remained elevated after 3 weeks of treatment only at the 180 mg/kg/day dose. When chloroform was administered in the drinking water, no microscopic alterations were seen in the kidneys after 4 days of treatment. As a general observation, rats treated for 3 weeks with 200 ppm chloroform and greater had slightly increased numbers of focal areas of regenerating renal proximal tubular epithelium and cell proliferation than were noted in the controls, but no clear dose response relationship was evident. However, the overall renal LI was not increased at any dose or time point. Similarly, only mild hepatocyte vacuolation was observed in rats given 1800 ppm chloroform in the water for 3 weeks with no increase in the hepatic LI at any time point, even though the rats were consuming chloroform at a rate of 106 mg/kg/day at the 1800 ppm drinking water concentration. These data indicate more severe hepatic and renal toxicity when chloroform is administered by gavage than in the drinking water and a different pattern of regenerative proliferation in the kidney.(ABSTRACT TRUNCATED AT 400 WORDS)

Two-generation reproduction study on commercial hexane solvent

The reproductive effects of inhalation exposure to commercial hexane vapors were evaluated in Sprague-Dawley rats. Males and females were exposed to commercial hexane vapor at target concentrations of 0, 900, 3000 or 9000 ppm for 6 h a day, 5 or 7 days a week, over two generations. In addition to pre-breed exposures of 10 weeks' duration, exposures continued through mating, gestation and lactation. At both the F0 breed to produce F1 litters and the F1 breed to produce F2 litters, reproductive parameters were unaffected by commercial hexane exposure. The mating, fertility and gestational indices, as well as litter size and postnatal survival, were not significantly different between exposure groups. However, reductions in body weight and body weight gain were observed in both F1 and F2 litters exposed to 9000 ppm. Effects on body weight were not observed in offspring exposed to the two lower concentrations of commercial hexane. Histopathological examination of selected tissues revealed hyaline droplet nephropathy in adult F0 and F1 males exposed to 9000 ppm. This finding was anticipated and is not believed to be relevant for the assessment of human health effects. No other treatment-related histopathological lesions were observed. Thus, exposure of rats to commercial hexane for two generations resulted in reduced body weight gains at 9000 ppm but no adverse effects on reproduction. These findings suggest that occupational exposure to commercial hexane vapors at currently recommended threshold limit value concentrations (i.e. TLV for n-hexane is 50 ppm and TLV for other hexane isomers is 500 ppm) should not pose a reproductive hazard.

Occupational hydrocarbon exposure and chronic nephropathy

This review aims at discussing the questions raised by the hydrocarbon-related chronic nephropathy and its possible consequence, the hydrocarbon-related chronic renal failure. It has been attempted to adopt the point of view of the clinician. Therefore, the most important part of the review is devoted to a presentation and an analysis of the available data on humans. The main features of the available studies on human subjects are presented, their conclusions discussed in the light of the possible methodological flaws, and practical conclusions drawn. After a discussion of the main difficulties encountered for selecting the suitable exposure indicator, the studies are discussed in order of decreasing quality of the study design (cohort, case-control, cross-sectional studies, and the case reports). It is concluded that a great deal of controversies about chronic hydrocarbon-related nephropathy is explained by differences in the study design and that hydrocarbon-induced nephropathy is probably more than a mere hypothesis, although a causal relationship has not yet been proven. Finally, some practical consequences for dealing with a hydrocarbon-exposed patient diagnosed with a kidney disease and the need for further research are discussed.