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.

Validation of a genomics-based hypothetical adverse outcome pathway: 2,4-dinitrotoluene perturbs PPAR signaling thus impairing energy metabolism and exercise endurance.

2,4-dinitrotoluene (2,4-DNT) is a nitroaromatic used in industrial dyes and explosives manufacturing processes that is found as a contaminant in the environment. Previous studies have implicated antagonism of PPARα signaling as a principal process affected by 2,4-DNT. Here, we test the hypothesis that 2,4-DNT-induced perturbations in PPARα signaling and resultant downstream deficits in energy metabolism, especially from lipids, cause organism-level impacts on exercise endurance. PPAR nuclear activation bioassays demonstrated inhibition of PPARα signaling by 2,4-DNT whereas PPARγ signaling increased. PPARα (-/-) and wild-type (WT) female mice were exposed for 14 days to vehicle or 2,4-DNT (134 mg/kg/day) and performed a forced swim to exhaustion 1 day after the last dose. 2,4-DNT significantly decreased body weights and swim times in WTs, but effects were significantly mitigated in PPARα (-/-) mice. 2,4-DNT decreased transcript expression for genes downstream in the PPARα signaling pathway, principally genes involved in fatty acid transport. Results indicate that PPARγ signaling increased resulting in enhanced cycling of lipid and carbohydrate substrates into glycolytic/gluconeogenic pathways favoring energy production versus storage in 2,4-DNT-exposed WT and PPARα (-/-) mice. PPARα (-/-) mice appear to have compensated for the loss of PPARα by shifting energy metabolism to PPARα-independent pathways resulting in lower sensitivity to 2,4-DNT when compared with WT mice. Our results validate 2,4-DNT-induced perturbation of PPARα signaling as the molecular initiating event for impaired energy metabolism, weight loss, and decreased exercise performance.