Results of long-term carcinogenicity bioassays on tert-amyl-methyl-ether (TAME) and di-isopropyl-ether (DIPE) in rats

Pathologists' perspective on the study design, analysis, and interpretation of proliferative lesions in a lifetime rodent carcinogenicity bioassay of sucralose

Sucralose, a sugar substitute first approved for use in 1991, is a non-caloric sweetener regulated globally as a food additive. Based on numerous experimental animal studies (dating to the 1980s) and human epidemiology studies, international health agencies have determined that sucralose is safe when consumed as intended. A single lifetime rodent carcinogenicity bioassay conducted by the Ramazzini Institute (RI) reported that mice fed diets containing sucralose develop hematopoietic neoplasia, but controversy continues regarding the validity and relevance of these data for predicting health effects in humans. The present paper addresses the controversy by providing the perspective of experienced pathologists on sucralose-related animal toxicity and carcinogenicity data generally, and the RI carcinogenicity bioassay findings specifically, using results from publicly available papers and international regulatory authority decisions. In the authors' view, flaws in the design, methodology, data evaluation, and reporting of the RI carcinogenicity bioassay for sucralose diminish the value of the data as evidence that this agent represents a carcinogenic hazard to humans. This limitation will remain until the RI bioassay is repeated under Good Laboratory Practices and the design, data, and accuracy of the pathology diagnoses and interpretations are reviewed by qualified pathologists with experience in evaluating potential chemically-induced carcinogenic hazards.

Consideration of the variability in control tumor incidence data at the Ramazzini Institute in evaluating treatment-related effects following chemical exposure

The Ramazzini Institute (RI) has been conducting animal carcinogenicity studies for decades, many of which have been considered by authoritative bodies to determine potential carcinogenicity in humans. Unlike other laboratories, such as the U.S. National Toxicology Program (NTP), the RI does not provide a report or record of historical control data. Transparently documenting historical control data is critical in the interpretation of individual study results within the same laboratory. Historical control data allow an assessment of significant trends, either increasing or decreasing, resulting from changes in laboratory methods or genetic drift. In this investigation: (1) we compiled a dataset of the tumors reported in control groups of Sprague-Dawley rats and Swiss mice based on data included in published RI studies on specific substances, and (2) conducted case studies to compare data from this RI control dataset to the findings from multiple RI studies on sweeteners and corresponding breakdown products. We found considerable variability in the tumor incidence across multiple tumor types when comparing across control groups from RI studies. When compared to the tumor incidence in treated groups from multiple studies, the incidence of some tumors considered to be treatment-related fell within the variability of background incidence from the RI control dataset.

Pathologists' perspective on the study design, analysis, and interpretation of proliferative lesions in lifetime and prenatal rodent carcinogenicity bioassays of aspartame

Aspartame, an artificial sweetener commonly used as a sugar substitute, is currently authorized for use in more than 100 countries. Hundreds of studies, conducted in various countries dating back to the 1970s, have shown that aspartame is safe at real-world exposure levels. Furthermore, multiple human epidemiology studies have provided no indication that consumption of aspartame induces cancer. Given the continued controversy surrounding the Ramazzini Institute's (RI) studies suggesting that aspartame is a carcinogenic hazard in rodents and evaluation by the International Agency for Research on Cancer, this report aims to provide the perspective of experienced pathologists on publicly available pathology data regarding purported proliferative lesions in liver, lung, lymphoid organs, and mammary gland as well as their implications for human risk assessment as reported for three lifetime rodent carcinogenicity bioassays of aspartame conducted at the RI. In the authors' view, flaws in the design, methodology and reporting of the RI aspartame studies limit the utility of the data sets as evidence that this agent represents a carcinogenic hazard. Therefore, all three RI studies, and particularly the accuracy of their pathology diagnoses and interpretations, should be rigorously reviewed by qualified and experienced veterinary toxicologic pathologists in assessing aspartame's carcinogenic risk.

Exposure Profile to Traffic Related Pollution in Pediatric Age: A Biomonitoring Study

The aim of this study was to trace an exposure profile to traffic-derived pollution during pediatric age. For this purpose, two biomonitoring campaigns for the determination of urinary (u-) methyl tert-butyl ether (MTBE), ethyl tert-butyl ether (ETBE), tert-amyl methyl ether (TAME), and diisopropyl ether (DIPE) were carried out in two different periods of the year (summer 2017 and winter 2018), among a large sample of healthy children (n = 736; 5–11 years old) living in rural and urban areas in central Italy. The quantification of u-MTBE, u-ETBE, u-TAME, and u-DIPE was performed by HS-SPME-GC/MS technique and information on participants was collected by a questionnaire. u-DIPE concentrations resulted always under the LOQ. u-TAME mean levels were similar in both seasons (18.7 ng L⁻¹ in summer vs. 18.9 ng L⁻¹ in winter), while u-MTBE and u-ETBE levels were, respectively, 69.9 and 423.5 ng L⁻¹ (summer) and 53.3 and 66.2 ng L⁻¹ (winter). Main predictors of urinary excretion resulted the time spent in motor vehicles, being male and younger.

Permitted Daily Exposure for Diisopropyl Ether as a Residual Solvent in Pharmaceuticals

Solvents can be used in the manufacture of medicinal products provided their residual levels in the final product comply with the acceptable limits based on safety data. At worldwide level, these limits are set by the “Guideline Q3C (R6) on impurities: guideline for residual solvents” issued by the ICH. Diisopropyl ether (DIPE) is a widely used solvent but the possibility of using it in the pharmaceutical manufacture is uncertain because the ICH Q3C guideline includes it in the group of solvents for which “no adequate toxicological data on which to base a Permitted Daily Exposure (PDE) was found”. We performed a risk assessment of DIPE based on available toxicological data, after carefully assessing their reliability using the Klimisch score approach. We found sufficiently reliable studies investigating subchronic, developmental, neurological toxicity and carcinogenicity in rats and genotoxicity in vitro. Recent studies also investigated a wide array of toxic effects of gasoline/DIPE mixtures as compared to gasoline alone, thus allowing identifying the effects of DIPE itself. These data allowed a comprehensive toxicological evaluation of DIPE. The main target organs of DIPE toxicity were liver and kidney. DIPE was not teratogen and had no genotoxic effects, either in vitro or in vivo. However, it appeared to increase the number of malignant tumors in rats. Therefore, DIPE could be considered as a non-genotoxic animal carcinogen and a PDE of 0.98 mg/day was calculated based on the lowest No Observed Effect Level (NOEL) value of 356 mg/m³ (corresponding to 49 mg/kg/day) for maternal toxicity in developmental rat toxicity study. In a worst-case scenario, using an exceedingly high daily dose of 10 g/day, allowed DIPE concentration in pharmaceutical substances would be 98 ppm, which is in the range of concentration limits for ICH Q3C guideline class 2 solvents. This result might be considered for regulatory decisions.

Scientific considerations for evaluating cancer bioassays conducted by the Ramazzini Institute

BACKGROUND

The Ramazzini Institute (RI) has completed nearly 400 cancer bioassays on > 200 compounds. The European Food Safety Authority (EFSA) and others have suggested that study design and protocol differences between the RI and other laboratories by may contribute to controversy regarding cancer hazard findings, principally findings on lymphoma/leukemia diagnoses.

OBJECTIVE

We aimed to evaluate RI study design, protocol differences, and accuracy of tumor diagnoses for their impact on carcinogenic hazard characterization.

METHODS

We analyzed the findings from a recent Pathology Working Group (PWG) review of RI procedures and tumor diagnoses, evaluated consistency of RI and other laboratory findings for chemicals identified by the RI as positive for lymphoma/leukemia, and examined evidence for a number of other issues raised regarding RI bioassays. The RI cancer bioassay design and protocols were evaluated in the context of relevant risk assessment guidance from international authorities.

DISCUSSION

Although the PWG identified close agreement with RI diagnoses for most tumor types, it did not find close agreement for lymphoma/leukemia of the respiratory tract or for neoplasms of the inner ear and cranium. Here we discuss a) the implications of the PWG findings, particularly lymphoma diagnostic issues; b) differences between RI studies and those from other laboratories that are relevant to evaluating RI cancer bioassays; and c) future work that may help resolve some concerns.

CONCLUSIONS

We concluded that a) issues related to respiratory tract infections have complicated diagnoses at that site (i.e., lymphoma/leukemia), as well as for neoplasms of the inner ear and cranium, and b) there is consistency and value in RI studies for identification of other chemical-related neoplasia.

Mycoplasma pulmonisand Lymphoma in Bioassays in Rats

Lymphomas were reported to be induced in rats in bioassays of aspartame, methyl- tertiary-butyl ether (MTBE), and other chemicals conducted by a nonprofit cancer research organization. European regulatory authorities concluded that lymphomas in the aspartame study were caused by Mycoplasma pulmonis and suggested that this also was the case for the MTBE bioassay. To assess the role of M. pulmonis in these bioassays, we reviewed the tumor data for the aspartame and MTBE bioassays and, additionally, the organization's bioassay of methanol. For all 3 studies, the most frequently reported hematopoietic neoplasm was lympho-immunoblastic lymphoma, the most frequently affected organ was the lung, and, in almost half of the rats with this diagnosis, the lung was the only affected organ. Lesions diagnosed as lymphoma in published illustrations had pleomorphic cellular morphology and appeared to contain neutrophils. Information from these reports and other sources indicated that lesions typical of M. pulmonis disease were prevalent among the aspartame and MTBE study rats and that the rats were not specific-pathogen-free. Because the lymphoma type, cellular morphology, and organ distribution reported in these studies are atypical of lymphoma in rats, because lymphocyte and plasma cell accumulation in the lung is characteristic of M. pulmonis disease, and because M. pulmonis disease can be exacerbated by experimental manipulations, including chemical treatment, we suggest that a plausible alternative explanation for the reported results of these bioassays is that the studies were confounded by M. pulmonis disease and that lesions of the disease were interpreted as lymphoma.

Evaluation of evidence for infection as a mode of action for induction of rat lymphoma

The European Food Safety Authority (EFSA) released a 2006 report questioning the relationship of aspartame exposure with increased incidence of lymphomas/leukemias in a European Ramazzini Foundation (ERF) rat study. The EFSA report suggested that the lymphoma/leukemia findings were most likely explained by infection in the rat colony. The ERF has also conducted the only available long-term oral study of methyl tertiary-butyl ether (MTBE). Thus, using the EFSA report as support, some have now raised questions about the human relevance of MTBE-associated hemolymphoreticular tumors reported by the ERF in female rats as well as whether their incidence was elevated above background levels. In this report, we discuss the hypothesized mode of action (MOA) of infection-induced lymphoma and its relevance to MTBE-associated lymphomas. We address the relationship of rat strain and study duration to lymphoma susceptibility and review evidence of low background rates of this tumor in control animals at the ERF, similar survival rates for female rats at the ERF and National Toxicology Program (NTP), and chemical- and gender-specificity of tumor induction for this type of tumor in studies at the ERF. We find that the background incidence of hemolymphoreticular tumors in female rats in the MTBE study is consistent with contemporaneous studies at the ERF and that there is an exposure-related effect, which is unlikely to be due to infections. We examine more recent tumor classification schemes for lymphomas, which support the combination of lymphoblastic leukemias and lymphomas reported by Belpoggi et al. ([1995] Toxicol Ind Health 11:119-149; [1998] Eur J Oncol 3:201-206).

Life-span exposure to low doses of aspartame beginning during prenatal life increases cancer effects in rats

BACKGROUND

In a previous study conducted at the Cesare Maltoni Cancer Research Center of the European Ramazzini Foundation (CMCRC/ERF), we demonstrated for the first time that aspartame (APM) is a multipotent carcinogenic agent when various doses are administered with feed to Sprague-Dawley rats from 8 weeks of age throughout the life span.

OBJECTIVE

The aim of this second study is to better quantify the carcinogenic risk of APM, beginning treatment during fetal life.

METHODS

We studied groups of 70-95 male and female Sprague-Dawley rats administered APM (2,000, 400, or 0 ppm) with feed from the 12th day of fetal life until natural death.

RESULTS

Our results show a) a significant dose-related increase of malignant tumor-bearing animals in males (p < 0.01), particularly in the group treated with 2,000 ppm APM (p < 0.01); b) a significant increase in incidence of lymphomas/leukemias in males treated with 2,000 ppm (p < 0.05) and a significant dose-related increase in incidence of lymphomas/leukemias in females (p < 0.01), particularly in the 2,000-ppm group (p < 0.01); and c) a significant dose-related increase in incidence of mammary cancer in females (p < 0.05), particularly in the 2,000-ppm group (p < 0.05).

CONCLUSIONS

The results of this carcinogenicity bioassay confirm and reinforce the first experimental demonstration of APM's multipotential carcinogenicity at a dose level close to the acceptable daily intake for humans. Furthermore, the study demonstrates that when life-span exposure to APM begins during fetal life, its carcinogenic effects are increased.

Determination of low level methyl tert-butyl ether, ethyl tert-butyl ether and methyl tert-amyl ether in human urine by HS-SPME gas chromatography/mass spectrometry

Methyl tert-butyl ether (MTBE), ethyl tert-butyl ether (ETBE) and tert-amyl methyl ether (TAME) are oxygenated compounds added to gasoline to enhance octane rating and to improve combustion. They may be found as pollutants of living and working environments. In this work a robotized method for the quantification of low level MTBE, ETBE and TAME in human urine was developed and validated. The analytes were sampled in the headspace of urine by SPME in the presence of MTBE-d12 as internal standard. Different fibers were compared for their linearity and extraction efficiency: carboxen/polydimethylsiloxane, polydimethylsiloxane/divinylbenzene, and polydimethylsiloxane. The first, although highly efficient, was discarded due to deviation of linearity for competitive displacement, and the polydimethylsiloxane/divinylbenzene fiber was chosen instead. The analysis was performed by GC/MS operating in the electron impact mode. The method is very specific, with range of linearity 30-4600 ng L(-1), within- and between-run precision, as coefficient of variation, <22 and <16%, accuracy within 20% the theoretical level, and limit of detection of 6 ng L(-1) for all the analytes. The influence of the matrix on the quantification of these ethers was evaluated analysing the specimens of seven traffic policemen exposed to autovehicular emissions: using the calibration curve and the method of standard additions comparable levels of MTBE (68-528 ng L(-1)), ETBE (<6 ng L(-1)), and TAME (<6 ng L(-1)) were obtained.