Characterizing a mouse model for evaluation of countermeasures against hydrogen sulfide–induced neurotoxicity and neurological sequelae

Abstract

Hydrogen sulfide (H S) is a highly neurotoxic gas. It is the second most common cause of gas-induced deaths. Beyond mortality, surviving victims of acute exposure may suffer long-term neurological sequelae. There is a need to develop countermeasures against H S poisoning. However, no translational animal model of H S-induced neurological sequelae exists. Here, we describe a novel mouse model of H S-induced neurotoxicity for translational research. In paradigm I, C57/BL6 mice were exposed to 765 ppm H S for 40 min on day 1, followed by 15-min daily exposures for periods ranging from 1 to 6 days. In paradigm II, mice were exposed once to 1000 ppm H S for 60 minutes. Mice were assessed for behavioral, neurochemical, biochemical, and histopathological changes. H S intoxication caused seizures, dyspnea, respiratory depression, knockdowns, and death. H S-exposed mice showed significant impairment in locomotor and coordinated motor movement activity compared with controls. Histopathology revealed neurodegenerative lesions in the collicular, thalamic, and cortical brain regions. H S significantly increased dopamine and serotonin concentration in several brain regions and caused time-dependent decreases in GABA and glutamate concentrations. Furthermore, H S significantly suppressed cytochrome c oxidase activity and caused significant loss in body weight. Overall, male mice were more sensitive than females. This novel translational mouse model of H S-induced neurotoxicity is reliable, reproducible, and recapitulates acute H S poisoning in humans.

Cobinamide is effective for treatment of hydrogen sulfide–induced neurological sequelae in a mouse model

“…Previous work in our laboratory found that H 2 S inhibits cytochrome c oxidase in multiple brain regions . We investigated cytochrome c oxidase activity in H 2 S‐poisoned mice treated with saline versus those treated with Cob.…”

“…All animal studies were approved by the Iowa State University Institutional Animal Care and Use Committee. Only male mice were used in this study because previous studies showed that male are more sensitive to H 2 S‐induced neurotoxicity than female mice . The 7‐ to 8‐week‐old C57/BL6 male mice were purchased from the Jackson Laboratories (Bar Harbor, ME), and weighed 20–25 g at the beginning of the experiment.…”

“…In this dose–response experiment, we tested the hypothesis that Cob manifests dose‐dependent efficacy for treatment of neurological sequelae in a mouse model of H 2 S‐induced neurological sequelae. To achieve this objective, we used a novel mouse model that was recently published . Briefly, fully conscious and freely moving mice were placed in a whole‐body exposure chamber designed to hold up to 10 mice at a time.…”

“…The real‐time concentration of H 2 S in the exposure chamber was constantly monitored using a H 2 S monitor (Environmental Equipment and Supply, Harrisburg, PA) that was custom designed to measure concentrations of up to 1000 ppm of H 2 S. The H 2 S exposure paradigm used in this experiment is summarized in Figure A. This repeated acute exposure paradigm results in mice with behavioral, biochemical, and neurochemical changes and morphologic lesions recapitulating those of the human condition using a reasonably small number of mice . Detailed justification of this model was provided in an earlier publication in which results of neurological sequelae arising both from a single acute exposure (mimicking a typical human exposure scenario) and from the repeated short‐term acute exposures were reported .…”

“…The striatum was also analyzed for serotonin (5‐HT), its metabolite 5‐HIAA, and NE. Samples were prepared and quantified as described previously . Briefly, neurotransmitters were extracted from different brain regions in 0.2 M perchloric acid solution containing 0.05% Na 2 EDTA, 0.1% Na 2 S 2 O 5, and isoproterenol (internal standard).…”