Simultaneous determination of 3-mercaptopyruvate and cobinamide in plasma by liquid chromatography–tandem mass spectrometry

The Antioxidant/Nitric Oxide-Quenching Agent Cobinamide Prevents Aortic Disease in a Mouse Model of Marfan Syndrome

Major pathologic changes in the proximal aorta underlie the life-threatening aortic aneurysms and dissections in Marfan Syndrome; current treatments delay aneurysm development without addressing the primary pathology. Because excess oxidative stress and nitric oxide/protein kinase G signaling likely contribute to the aortopathy, we hypothesized that cobinamide, a strong antioxidant that can attenuate nitric oxide signaling, could be uniquely suited to prevent aortic disease. In a well-characterized mouse model of Marfan Syndrome, cobinamide dramatically reduced elastin breaks, prevented excess collagen deposition and smooth muscle cell apoptosis, and blocked DNA, lipid, and protein oxidation and excess nitric oxide/protein kinase G signaling in the ascending aorta. Consistent with preventing pathologic changes, cobinamide diminished aortic root dilation without affecting blood pressure. Cobinamide exhibited excellent safety and pharmacokinetic profiles indicating it could be a practical treatment. We conclude that cobinamide deserves further study as a disease-modifying treatment of Marfan Syndrome.

Analysis of bisaminotetrazole cobinamide, a next-generation antidote for cyanide, hydrogen sulfide and methanethiol poisoning, in swine plasma by liquid chromatography-tandem mass spectrometry

Cyanide, hydrogen sulfide, and methanethiol are common toxic inhalation agents that inhibit mitochondrial cytochrome c oxidase and result in cellular hypoxia, cytotoxic anoxia, apnea, respiratory failure, cardiovascular collapse, seizure and potentially death. While all are occupational gas exposure hazards that have the potential to cause mass casualties from industrial accidents or acts of terrorism, only cyanide has approved antidotes, and each of these has major limitations, including difficult administration in mass-casualty settings. While bisaminotetrazole cobinamide (Cbi(AT)₂) has recently gained attention because of its efficacy in treating these metabolic poisons, there is no method available for the analysis of Cbi(AT)₂ in any biological matrix. Hence, in this study, a simple and rapid liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed and validated for the analysis of Cbi(AT)₂ in swine plasma. The method is extremely simple, consisting of protein precipitation, separation and drying of the supernatant, reconstitution in an aqueous solvent, and LC-MS/MS analysis. The method produced an LOD of 0.3 μM with a wide dynamic range (2 - 500 μM). Inter- and intraassay accuracies (100 ± 12 % and 100 ± 19 %, respectively) were acceptable and the precision (<12 % and < 9 % relative standard deviation, respectively) was good. The developed method was used to analyze Cbi(AT)₂ from treated swine and the preliminary pharmacokinetic parameters showed impressive antidotal behavior, most notably a long estimated elimination half-life (t_1/2 = 37.5 h). This simple and rapid method can be used to facilitate the development of Cbi(AT)₂ as a therapeutic against toxic cyanide, hydrogen sulfide and methanethiol exposure.

Determination of free cyano-cobinamide in swine and rabbit plasma by liquid chromatography tandem mass spectrometry

In recent years, Cobinamide (Cbi) has shown promise as a therapeutic for cyanide poisoning. There are several forms of Cbi based on the identity of the ligands bound to the cobalt in Cbi and these different forms of Cbi have divergent behavior (e.g., the aquo and hydroxo forms of Cbi readily bind to proteins, limiting their distribution significantly, whereas [Cbi(CN)₂] does not). While current analysis techniques only measure total Cbi, methods to elucidate the behavior of 'available' Cbi versus cyanide-complexed Cbi would be valuable for biomedical and pharmacokinetic studies. Therefore, a method was developed for the analysis of cyanide-complexed Cbi in plasma via liquid chromatography tandem mass spectrometry (LC-MS-MS). Plasma samples were prepared by denaturing proteins with 10% ammonium hydroxide in acetonitrile. The resulting mixture was centrifuged, and the supernatant was removed, dried, and reconstituted. Cyanide-complexed Cbi was then analyzed via LC-MS-MS. The limit of detection was 0.2 μM, and the linear dynamic range was between 1 and 200 μM. The accuracy was 100 ± 17% and the precision, measured by relative standard deviation (%RSD), was ≤18.5%. Carryover, a severe problem when analyzing Cbi via liquid chromatography was eliminated using a polymeric-based stationary phase (PLRP-S) and a controlled washing protocol. The method allowed evaluation of the cyanide-bound and 'available' Cbi from treated animals and, when paired with a method for total Cbi analysis, allows for estimation of Cbi utilization when treating cyanide poisoning.

Methionine restriction leads to hyperhomocysteinemia and alters hepatic H2S production capacity in Fischer-344 rats

Dietary methionine restriction (MR) increases lifespan in several animal models. Despite low dietary intake of sulphur amino acids, rodents on MR develop hyperhomocysteinemia. On the contrary, MR has been reported to increase H₂S production in mice. Enzymes involved in homocysteine metabolism also take part in H₂S production and hence, in this study, the impact of MR on hyperhomocysteinemia and H₂S production capacity were investigated using Fischer-344 rats assigned either a control or a MR diet for 8 weeks. The MR animals showed elevated plasma homocysteine accompanied with a reduction in liver cysteine content and methylation potential. It was further found that MR decreased cystathionine-β-synthase (CBS) activity in the liver, however, MR increased hepatic cystathionine-γ-lyase (CGL) activity which is the second enzyme in the transsulfuration pathway and also participates in regulating H₂S production. The relative contribution of CGL in H₂S production increased concomitantly with the increased CGL activity. Additionally, hepatic mercaptopyruvate-sulphur-transferase (MPST) activity also increased in response to MR. Taken together, our results suggest that reduced CBS activity and S-Adenosylmethionine availability contributes to hyperhomocysteinimia in MR animals. Elevated CGL and MPST activities may provide a compensatory mechanism for maintaining hepatic H₂S production capacity in response to the decreased CBS activity.

Percent residual accuracy for quantifying goodness-of-fit of linear calibration curves

Linear models for calibration curves are overwhelmingly created based on minimization of least squares error, with their goodness-of-fit (GOF) quantified using the square of the correlation coefficient (R²). Yet, R² has well-known disadvantages when used to quantify GOF of calibration curves stemming from its calculation based on the absolute error of the signal (i.e., calculated vs. experimental). These disadvantages are exacerbated when using a geometric series of concentrations for calibration standards (e.g., 1, 2, 5, 10, etc.) and when calibration curves span 2-3 orders of magnitude, which is typical for modern analytical techniques. While there are multiple alternative GOF measures, R² overwhelmingly persists in the field of Analytical Chemistry as the most reported measure of GOF. We evaluated R², alternative GOF measures, and multiple quantitative bias parameters, along with residual analysis, for over 60 experimental calibration curves. R² did a poor job of consistently and accurately quantifying the GOF over the entire calibration curve. This was especially true for situations where the low concentration calibrators were not accurately described by the calibration equation. While other GOF parameters, including the sum of the absolute percent error, mean absolute percent error, and quality coefficient, did a better job of describing GOF of calibration curves, each had significant theoretical and/or practical disadvantages. Therefore, we introduce a descriptive GOF parameter called Percent Residual Accuracy (%RA or PRA) which equally weights the accuracy of all calibrators into a single value, generally falling between 0% and 100%, with 100% representing a perfect fit and a "good" fit for calibration data producing a %RA of 90-100%. The %RA much more effectively described the GOF for the entire calibration range than R², and it similarly quantified GOF as compared to the other GOF parameters tested. With the performance and practical advantages of %RA, we conclude that it is the most advantageous GOF parameter and that it should be reported as a standard GOF measure for calibration curves.