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Trichloroethylene-induced formic aciduria in the male C57 Bl/6 mouse

Lookup NU author(s): Dr Paul Keane, Dr Christopher Morris

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Abstract

© 2017 Elsevier B.V. 1, 1, 2-Trichloroethylene (TCE) is of environmental concern, due to evaporation while handling, chemical processing and leakage from chemical waste sites, leading to its contamination of ground water and air. For several decades there has been issues about possible long term health effects of TCE but recently the International Agency for Research on Cancer (IARC) and the US Environmental Protection Agency classified TCE as a human carcinogen. Links having been established between occupational exposures and kidney cancer and possible links to non-Hodgkin lymphoma and liver cancer, but there is more still more to learn. In male rats, TCE produces a small increase in the incidence of renal tubule tumours but not in female rats or mice of either sex. However, chronic renal injury was seen in these bioassays in both sexes of rats and mice. The mechanism of kidney injury from TCE is thought to be due to reductive metabolism forming a cysteine conjugate that is converted to a reactive metabolite via the enzyme cysteine conjugate β-lyase. However, TCE also produces a marked and sustained formic aciduria in male rats and it has been suggested that long term exposure to formic acid could lead to renal tubule injury and regeneration. In this study we have determined if TCE produces formic aciduria in male mice following a single and repeat dosing. Male C57 Bl/6OlaHsd mice were dosed with 1000 mg/kg by ip injection and urine collected overnight 24, 48, 72 and 96 h after dosing. Formic acid was present in urine 24 h after dosing, peaked around 48 h at 8 mg formic acid excreted/mouse, and remained constant over the next 24 h and was not back to normal 96 h after dosing. This was associated with a marked acidification of the urine. Plasma creatinine and renal pathology was normal. Plasma kinetics of formic acid showed it was readily cleared with an initial half-life of 2.42 h followed by a slower rate with a half-life of 239 h. Male mice were then dosed twice/week at 1000 mg/kg TCE for 56 days, as anticipated there was a marked and sustained formic aciduria over the duration of the study. This was associated with acidification of the urine, mild diuresis and a marked fall in urinary ammonia. Six biomarkers of renal injury KIM-1, NGAL, NAG, Cystatin-c, Albumin and IL-18 were measured in urine over time and they all showed a small increase at the later time points indicative of early markers of renal injury. However, there was no histological evidence of renal damage or renal tubule cell proliferation after 8 weeks’ exposure to TCE. The concentration of formic acid in plasma at the end of the study was 1.05 ± 0.61 mM compared to control, 0.39 ± 0.17 mM. In the liver, formic acid was present at a concentration of 1 mM in both control and treated mice while in the kidney it was higher at 2 mM in both treated and controls. We also report that trichloroacetic acid (TCA) a metabolite of TCE also causes formic aciduria, at doses likely to arise in vivo after 1000 mg/kg TCE namely 16 and 32 mg/kg. Urinary formic acid peaked 24 h after dosing at 4 mg formic acid excreted/mouse. Thus, as in male and female rats (Yaqoob et al., 2013) male mice show a marked formic aciduria following TCE which after 8 weeks’ exposure did not produce renal injury, but the small rise in renal biomarkers suggest renal damage may occur following longer exposure. Thus, TCE-induced formic aciduria may be a contributor factor in the chronic renal injury seen in male and female rats and mice.


Publication metadata

Author(s): Lock EA, Keane P, Rowe PH, Foster JR, Antoine D, Morris CM

Publication type: Article

Publication status: Published

Journal: Toxicology

Year: 2017

Volume: 378

Pages: 76-85

Print publication date: 01/03/2017

Online publication date: 04/01/2017

Acceptance date: 03/01/2017

ISSN (print): 0300-483X

ISSN (electronic): 1879-3185

Publisher: Elsevier Ireland Ltd

URL: http://doi.org/10.1016/j.tox.2017.01.004

DOI: 10.1016/j.tox.2017.01.004


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