Using mechanistic information to support evidence integration and synthesis: a case study with inhaled formaldehyde and leukemia.

Formaldehyde is one of the most comprehensively studied chemicals, with over 30 years of research focused on understanding the development of cancer following inhalation. The causal conclusions regarding the potential for leukemia are largely based on the epidemiological literature, with little consideration of cancer bioassays, dosimetry studies, and mechanistic research, which challenge the biological plausibility of the disease. Recent reanalyzes of the epidemiological literature have also raised significant questions related to the purported associations between formaldehyde and leukemia. Because of this, considerable scientific debate and uncertainty remain on whether there is a causal association between formaldehyde inhalation exposure and leukemia. Further complexity in evaluating this association is related to the endogenous production of formaldehyde. Multiple modes of action (MOA) have been postulated for the development of leukemia following formaldehyde inhalation that includes unsupported hypotheses of direct or indirect toxicity to the target cell population. Herein, the available evidence relevant to evaluating the postulated MOAs for leukemia following formaldehyde inhalation exposure is organized in the IPCS MOA Framework. The integration of all the available evidence clearly highlights the limited amount of data that support any of the postulated MOAs and demonstrates a significant amount of research supporting the null hypothesis that there is no causal association between formaldehyde inhalation exposure and leukemia. These analyses result in a lack of confidence in any of the postulated MOAs, increasing confidence in the conclusion that there is a lack of biological plausibility for a causal association between formaldehyde inhalation exposure and leukemia.

Megakaryocyte expansion and macrophage infiltration in bone marrow of rats subchronically treated with MNX, N-nitroso environmental degradation product of munitions compound RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine).

Hexahydro-1-nitroso-3,5-dinitro-1,3,5-triazine (MNX), environmental degradation product of munitions hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), causes seizures in rats with acute oral exposure like parent RDX. Our previous studies have additionally reported hematotoxicity with acute MNX exposure manifested as myelosuppression, anemia and splenic hemosiderosis. This study explored whether MNX administered subchronically continued to target bone marrow to elicit peripheral blood cytopenia. Female Sprague-Dawley rats were gavaged daily for 4 or 6 weeks with 47 mg kg-1 day-1 MNX (» LD50 ) or vehicle (5% dimethyl sulfoxide in corn oil) and hematological and clinical chemistry parameters, spleen weights, spleen and bone marrow histopathology and immunohistochemistry with ED1 anti-CD68 macrophage marker were evaluated 24 h after the last dose. Unexpectedly, no decrease in blood erythroid parameters was seen with subchronic MNX and convulsions and tremors ceased after 2 weeks of treatment. Toxicological effects observed were MNX-induced increases in blood granulocyte and platelet counts and in bone marrow megakaryocyte and ED1+ -macrophage density. MNX was without effect on bone marrow cellularity and picrosirius red stained/collagen fiber deposition. Spleen weight increased modestly with extramedullary hematopoiesis evident, but hemosiderin and relative red and white pulp areas were unaffected. Collectively, this study demonstrated that erythroid effects characteristic of acute MNX exposure were not evident with subchronic exposure. However, megakaryocyte proliferation in bone marrow coincident with thrombocytosis after subchronic MNX exposure suggested continued hematotoxicity, but with a qualitatively different outcome. Granulocytosis and increased bone marrow macrophages implicated an inflammatory component in MNX hematotoxicity. Copyright © 2017 John Wiley & Sons, Ltd.

Assessment of clinical chemistry and hematological parameters in female Sprague-Dawley rats following a 7-day oral exposure to three different species of Echinacea.

Echinacea has grown in popularity due to its broad therapeutic benefits. Despite its popularity, comprehensive safety evaluations for three medicinal species are limited. In this study, female Sprague-Dawley rats received oral doses (0, 25, 50, 100, 200 mg/kg/d) of 75% (v/v) ethanol extract from the aerial parts of 9 Echinacea samples of three species - Echinacea purpurea, Echinacea angustifolia, and Echinacea pallida - over a 7-day period. Blood and serum samples, collected twenty-four hours post the final dose, were analyzed for hematology and clinical chemistry parameters. The results revealed varied effects across the tested samples, with many parameters showing no discernible impacts at administered doses. Subtle alterations were observed in parameters such as relative liver weight, alkaline phosphatase (ALP), and platelet count. Parameters like relative spleen weight, alanine transaminase (ALT), glucose, urea, hematocrit, hemoglobin, and RBC count exhibited effects in only one out of the nine samples tested. These findings emphasize the heterogeneity in the effects of Echinacea. While the results suggest that Echinacea samples might be considered relatively safe, potential clinical implications warrant caution and underscore the importance of extended testing. A comprehensive toxicity profile assessment remains paramount to conclusively ascertain the safety of three Echinacea species.

An in vitro approach to determine the human relevance of anti-spermatogenic effects of 4-methylmorpholine 4-oxide, monohydrate (NMMO) in rat reproductive toxicity studies.

Reduced sperm counts have been observed in male rats in an extended one generation reproductive toxicity study (EOGRTS, OECD 443) following repeated administration of 300 mg/kg/day N-Methylmorpholine N-oxide (NMMO). However, no adverse effects on reproductive organs have been reported in studies conducted with NMMO, and the mode of action (MOA) for the effects of NMMO on spermatogenesis is unknown, which complicates the interpretation of these data for human risk assessment. Here, a New Approach Method (NAM) strategy was used to evaluate NMMO MOA and compare interspecies susceptibility for anti-spermatogenic effects using organotypic in vitro assays combined with in vitro metabolism and in vitro to in vivo extrapolation (IVIVE) biokinetic modeling to compare predicted oral equivalent doses (OEDs) in human and rat. Dose-response data were collected in isolated germ cells and in an ex vivo seminiferous tubule model that recapitulates the interaction between the somatic environment and differentiating germ cells to account for potential direct and indirect effects on germ cells. With regard to direct spermatogenic effects, the human isolated germ cell model showed no toxicity at doses ≤300 µM (OED ≤ 86 mg/kg/day). With regard to indirect effects, the rat ex vivo model demonstrated dose-dependent decreases in secondary spermatocyte populations at OEDs ≥89 mg/kg/day, and reduced expression of RNAs specific to several stages of spermatogenesis (spermatogonia, pachytene spermatocytes, round spermatids) at OED = 267 mg/kg/day, consistent with in vivo observations. In contrast, the monkey ex vivo model did not show dose-dependent decreases in these same RNAs, and often demonstrated increased trends instead. These studies demonstrate clear quantitative and qualitative differences in the rat and primate response to NMMO. Furthermore, effects observed in the rat in vitro culture were not observed in the monkey at concentrations equivalent to in vivo doses of up to 1376 mg/kg/day, which is higher than the in vivo dose limit in the EOGRT study, indicating that the isolated findings on spermatogenesis in the rat studies are not likely to be relevant to humans.