In-vitro mercaptopyruvate sulfurtransferase species comparison in humans and common laboratory animals.

Cyanide is a metabolic poison that inhibits cytochrome c oxidase. Its broad applications in manufacturing and history as an agent of warfare/terror highlight the limitations in approved cyanide antidotes for mass casualties. Sulfanegen, a pre-clinical antidote for cyanide poisoning, exploits an endogenous detoxification pathway and should be amenable to mass-casualty scenarios. Because human studies are unethical, determination of appropriate animal species as models in translational studies for FDA approval under the "Animal Rule" are critical. Here, we compared the specific activities of mercaptopyruvate sulfurtransferase (MST, required for sulfanegen's activity), across common laboratory models of cyanide intoxication, and humans. Human MST activities in erythrocytes (measured as micromole pyruvate/min/106 rbc) were closest to those of Swiss-Webster mice and NZW rabbits. Similar species were selected for a more detailed tissue-specific comparison of MST activities. NZW Rabbits were closest to humans in the liver and kidney mitochondrial fractions, the Swiss-Webster mouse was closest to humans in the liver cytosolic fraction, while C57BL/6 mouse was closest in the kidney cytosolic fraction. These data comparing MST activities in animal models will help justify the use of those specific animals per the animal rule. Interestingly, statistically significant differences were found in MST activities of liver mitochondria between human smokers and non-smokers (p=0.0030).

Development of sulfanegen for mass cyanide casualties.

Cyanide is a metabolic poison that inhibits the utilization of oxygen to form ATP. The consequences of acute cyanide exposure are severe; exposure results in loss of consciousness, cardiac and respiratory failure, hypoxic brain injury, and dose-dependent death within minutes to hours. In a mass-casualty scenario, such as an industrial accident or terrorist attack, currently available cyanide antidotes would leave many victims untreated in the short time available for successful administration of a medical countermeasure. This restricted therapeutic window reflects the rate-limiting step of intravenous administration, which requires both time and trained medical personnel. Therefore, there is a need for rapidly acting antidotes that can be quickly administered to large numbers of people. To meet this need, our laboratory is developing sulfanegen, a potential antidote for cyanide poisoning with a novel mechanism based on 3-mercaptopyruvate sulfurtransferase (3-MST) for the detoxification of cyanide. Additionally, sulfanegen can be rapidly administered by intramuscular injection and has shown efficacy in many species of animal models. This article summarizes the journey from concept to clinical leads for this promising cyanide antidote.

Drug interaction study between bupropion and ticlopidine in male CF-1 mice.

Bupropion is an atypical antidepressant that is biotransformed in humans to its major active metabolite hydroxybupropion by cytochrome P450 2B6 (CYP2B6). Co-administration of bupropion with an inhibitor of CYP2B6 can result in a serious drug interaction, leading to bupropion related adverse effects (e.g. seizures). The antiplatelet agent ticlopidine has been identified as a potent in vitro inhibitor of bupropion hydroxylation, however it is unknown if it interacts in vivo in rodents. In this study we investigated the potential pharmacokinetic (PK) drug interaction between bupropion and ticlopidine in mice. Using a destructive sampling design, male CF-1 mice were administered ticlopidine 1.0 mg/kg daily for 5 d, followed by single-dose bupropion 50 mg/kg. Bupropion and hydroxybupropion levels were measured by HPLC-UV in plasma and brain tissues at 30, 60, 90, 120 and 180 min post-dose, and compared between treatment groups. There was a strong trend in both plasma and brain data towards greater bupropion levels and smaller hydroxybupropion levels in ticlopidine treated mice. Analysis of variance indicated statistical differences (p<0.05) at many time points. The variance associated with the area under the curve was calculated using Bailer's method and significant differences were found between treatment groups. Taken together, the concentration time point statistical analysis followed by PK modeling demonstrate a significant PK drug interaction between bupropion and ticlopidine. To our knowledge, this is the first study to document an in vivo drug interaction between these drugs in mice. Our findings support future in vivo drug interaction studies in mice between bupropion and CYP2B6 inhibitors.