Document Type

Dissertation - Open Access

Award Date

2021

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry and Biochemistry

First Advisor

Brian A. Logue

Keywords

Aminotetrazole cobinamide, Cyanide, Dimethyl disulfide, Dimethyl trisulfide, Hydrogen sulfide, Methanethiol

Abstract

Toxic inhalation agents (TIAs), (i.e., cyanide (CN) and reduced sulfur compounds (RSCs)), including hydrogen sulfide (H2S) and methanethiol (MT)) are extremely poisonous upon exposure. Many TIAs act by inhibiting mitochondrial cytochrome c oxidase, resulting in cellular hypoxia, cytotoxic anoxia, apnea, respiratory failure, cardiovascular collapse, seizure and potentially death. CN is generated in structural fires and cigarette smoke as well as in mining, electroplating and polymer processing, whereas H2S and MT are found in petroleum, oil and natural gas, waste treatment facilities and decaying organic matter. All are common occupational gas exposure hazards in chemical industries and for first responders, including firefighters, and can be used as suicide, homicide, or chemical warfare agents. Despite many TIAs being on the potential terrorist threat s list and common occupational exposure hazards, there are no FDA-approved intramuscular or oral antidotes for these compounds which are effective in a mass-casualty event. Dimethyl trisulfide (DMTS) has recently gained prominence as a promising next generation CN antidote. DMTS converts CN to less toxic thiocyanate (SCN) forming dimethyl disulfide (DMDS), a relatively toxic compound as a major breakdown product. Another potential antidote, aminotetrazole cobinamide (CbiAT), which is a prodrug of cobinamide (Cbi), can directly bind and detoxify CN, H2S and MT. Both DMTS and CbiAT have significant advantages over current treatments, but there is no method available for the analysis of CbiAT in any biological matrices and the methods available for DMDS and DMTS analysis have significant disadvantages. Hence, in this study, an extremely simple and rapid dynamic headspace (DHS) gas chromatography mass spectroscopy (GC-MS) method was developed for the analysis of DMTS and DMDS from whole blood. The dynamic ranges for DMTS (0.2 – 50 μM) and DMDS (0.1 – 200 μM) were wide and the limits of detection (LODs) (40 and 30 nM, respectively) were excellent. Inter- and intraassay accuracies were within 100±15%, and the precision of <10% relative standard deviation RSD) was excellent. The method performed well during pharmacokinetic analysis of DMTS and DMDS from the blood treated with DMTS. Although preliminary, pharmacokinetic results from DMTS-treated rats showed impressive results, i.e., Cmax and tmax of 0.89±0.09 M and 10 min, respectively, indicating rapid absorption and distribution of DMTS as well as slow elimination (t1/2 = 10.5 hr). The DMDS method was used to analyze the level of formation of DMDS in swine blood after DMTS treatment and found almost 50% conversion of DMTS to DMDS, which indicated about 6.7 times lower blood DMDS concentration than its LD50 value (i.e., 33.7 mg/kg). Understanding the level of formation of DMDS along with the availability of the methods will allow the further development of DMTS as a potential CN countermeasure. Additionally, a liquid chromatography tandem mass spectrometry (LC-MS/MS) method was developed for the analysis of CbiAT in plasma. The method produced an LOD of 0.3 μM with a wide dynamic range from 2 – 500 μM. Inter- and intraassay accuracies (100±12% and 100±19%, respectively) and precision (<12% and <9% RSD, respectively) were good. The developed method was used to analyze CbiAT from treated swine and the preliminary pharmacokinetic parameters showed impressive results, most notably quick absorption, and distribution (Cmax and tmax of 44.7 µM and 4 h, respectively) and slow elimination (t1/2 = 23.7 h). This method can be used for the further development of CbiAT as a potential antidote for CN, H2S and MT poisoning. Overall, multiple methods were developed and validated for the analysis of CN, H2S and MT countermeasures in biological matrices that have significant advantages over current analytical approaches and can be used to perform DMTS and CbiAT drug development studies.

Number of Pages

122

Publisher

South Dakota State University

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Rights Statement

In Copyright