LC-MS/MS analysis of 2-aminothiazoline-4-carboxylic acid as a forensic biomarker for cyanide poisoning

Development and validation of HPLC-UV and LC-MS/MS methods for the quantitative determination of a novel aminothiazole in preclinical samples

Aminothiazoles are the important class of chemical groups which have proven their broad range of biological activities. A novel aminothiazole (21MAT) was quantified in analytical solutions using a high-performance liquid chromatography (HPLC) approach that was developed and partially validated for the analysis of in vitro experimental samples. An isocratic elution on reverse phase Phenomenex® Luna C18 (50 mm × 4.6 mm, 5 μm) column with 55% 0.1% v/v orthophosphoric acid in water and 45% of orthophosphoric acid in acetonitrile at a flow rate of 1 mL/min was used. The analyte was detected at 272 nm. Similar to this, a robust bioanalytical technique, LC-mass spectrometry (LC-MS/MS) was created and verified to measure 21MAT in rat plasma for use in in vitro screening study samples and early-stage pharmacokinetic research. The protein precipitation method was used to extract 21MAT from plasma. The mixture of 95: 5% v/v methanol: acetonitrile and 0.1% v/v formic acid, along with 15% of 5 mM ammonium formate solution, was used to separate the mixture on a reverse phase Waters Xterra RP® C18 (150 mm × 4.6 mm, 5 μm) column at a flow rate of 1 mL/min. Using electro spray ionisation mode in multiple reaction monitoring mode, the analyte and internal standard (a structural analogue) were both identified. According to current criteria, all validation parameters (specificity, selectivity, accuracy, precision, recovery, matrix factor, hemolysis effect, and stability) were evaluated in rat plasma. The area response of 21MAT was found to be linear over the concentration range of 1.25-1250 ng/mL in rat plasma. Both techniques are suitable for use in any format of preclinical research and were sufficiently reliable to measure 21MAT precisely in various matrices. In silico prediction helped in understanding absorption, distribution, metabolism, excretion, and toxicity (ADMET) behaviour of the molecule. Both developed LC-MS/MS and HPLC-UV methods were successfully used to quantify the analyte in in vitro screening study samples.

Can the cyanide metabolite, 2-aminothiazoline-4-carboxylic acid, be used for forensic verification of cyanide poisoning?

PURPOSE

Forensic verification of cyanide (CN) poisoning by direct CN analysis in postmortem blood is challenging due to instability of CN in biological samples. CN metabolites, thiocyanate (SCN-) and 2-aminothiazoline-4-carboxylic acid (ATCA), have been proposed as more stable biomarkers, yet it is unclear if either is appropriate for this purpose. In this study, we evaluated the behavior of CN biomarkers in postmortem swine and postmortem blood to determine which serves as the best biomarker of CN exposure.

METHODS

CN, SCN-, and ATCA were measured in postmortem swine (N = 8) stored at 4 °C and postmortem blood stored at 25 °C (room temperature, RT) and 37 °C (typical human body temperature, HBT).

RESULTS

Following CN poisoning, the concentration of each CN biomarker increased well above the baseline. In postmortem swine, CN concentrations declined rapidly (t1/2 = 34.3 h) versus SCN- (t1/2 = 359 h, 15 days) and ATCA (t1/2 = 544 h, 23 days). CN instability in postmortem blood increased at RT (t1/2 = 10.7 h) and HBT (t1/2 = 6.6 h). SCN- and ATCA were more stable than CN at all storage conditions. In postmortem swine, the t1/2s of SCN- and ATCA were 15 and 23 days, respectively. While both the t1/2s of SCN- and ATCA were relatively lengthy, endogenous levels of SCN- were much more variable than ATCA.

CONCLUSION

While there are still questions to be answered, ATCA was the most adept forensic marker of CN poisoning (i.e., ATCA produced the longest half-life, the largest increase above baseline levels, and most stable background concentrations).

Simultaneous quantification of 2-aminothiazoline-4-carboxylic acid and 2-aminothiazoline-4-oxoaminoethanoic acid utilizing chemical derivatization followed by liquid chromatography-tandem mass spectrometry

Detecting cyanide compounds in postmortem blood samples is an important matter in forensic science because cyanide is often used as a poison for murder or suicide. However, the direct analysis of cyanide itself has practical limitations because of cyanide's volatility and short half-life at ambient temperature. Here, we focused on the relatively stable cyanide metabolites 2-aminothiazoline-4-carboxylic acid (ATCA) and 2-aminothiazoline-4-oxoaminoethanoic acid (ATOEA) as potential markers of cyanide exposure. We developed an analytical method that uses chemical derivatization of the target compounds with 4-bromoethyl-7-methoxycoumarin followed by liquid chromatography coupled with electrospray ionization-tandem mass spectrometry. The recovery rates for pretreatment and calibration curve linearities were good in the concentration range of 20-1000 ng/mL. Using our approach, we were able to detect and quantify both ATCA and ATOEA concentrations in postmortem blood samples, and in our samples the ratio of ATCA and ATOEA was in the range of 4.5-19.1. To our knowledge, this is the first time ATOEA has been successfully detected in human blood samples. In addition, we found that ATCA and ATOEA concentrations were both significantly higher in the blood of fire victims than in the blood of individuals with a non-fire-related cause of death. Also, we found that there was a significant positive correlation between ATCA concentrations and ATOEA concentrations. Together, our present data suggested that ATCA and ATOEA are both potential markers of cyanide exposure.

Quantification of cyanide metabolite 2-aminothiazoline-4-carboxylic acid in postmortem dried blood spot samples by liquid chromatography-tandem mass spectrometry

2-Aminothiazoline-4-carboxylic acid (ATCA), which is produced by the reaction of cyanide with endogenous cystine, is a promising biomarker of cyanide exposure because of its physicochemical stability. Analysis of more stable metabolite than the toxic gas itself is sometimes useful for postmortem diagnosis of gas poisoning. Here, we developed and validated an approach that uses liquid chromatography coupled with electrospray ionization-tandem mass spectrometry for quantifying ATCA in dried blood spot (DBS) samples. The linearity of the calibration curve was good in the concentration range of 20-1500 ng/mL. Our method allows for repeatable and the accurate quantification of ATCA, with intra- and inter assay coefficients of variation of below 7.8 % and below 9.3 %, respectively. In addition, the concentration of ATCA in DBSs remained stable for at least one month when stored at -20°C. Our results indicated that our analytical approach can be used to determine past exposure to higher doses of cyanide. In a comparison of ATCA concentrations in DBSs obtained from cadavers with various causes of death, significantly higher ATCA concentrations were observed in fire victims than in non-fire victims, confirming that fire victims inhale large amounts of cyanide gas. Thus, here we extended the possible uses of DBS for quantification of ATCA to forensic toxicological testing for cyanide poisoning.

The two faces of cyanide: an environmental toxin and a potential novel mammalian gasotransmitter

Cyanide is traditionally viewed as a cytotoxic agent, with its primary mode of action being the inhibition of mitochondrial Complex IV (cytochrome c oxidase). However, recent studies demonstrate that the effect of cyanide on Complex IV in various mammalian cells is biphasic: in lower concentrations (nanomolar to low micromolar) cyanide stimulates Complex IV activity, increases ATP production and accelerates cell proliferation, while at higher concentrations (high micromolar to low millimolar) it produces the previously known ('classic') toxic effects. The first part of the article describes the cytotoxic actions of cyanide in the context of environmental toxicology, and highlights pathophysiological conditions (e.g., cystic fibrosis with Pseudomonas colonization) where bacterially produced cyanide exerts deleterious effects to the host. The second part of the article summarizes the mammalian sources of cyanide production and overviews the emerging concept that mammalian cells may produce cyanide, in low concentrations, to serve biological regulatory roles. Cyanide fulfills many of the general criteria as a 'classical' mammalian gasotransmitter and shares some common features with the current members of this class: nitric oxide, carbon monoxide, and hydrogen sulfide.

Quantification of 2-aminothiazoline-4-carboxylic acid as a reliable marker of cyanide exposure using chemical derivatization followed by liquid chromatography-tandem mass spectrometry

In this research, we have developed a novel and simple liquid chromatography coupled with electrospray ionization-tandem mass spectrometry (LC/ESI-MS/MS) method for quantification of 2-aminothiazoline-4-carboxylic acid (ATCA), which is produced by the direct reaction of cyanide (CN) with endogenous cystine. In forensic science, detection of CN is important because CN is a poison that is often used for murder or suicide, in addition to being produced by the thermal decomposition of natural or synthetic materials. However, because CN disappears rapidly from body tissue, ATCA is thought to be a more reliable indicator of CN exposure. For the method reported herein, human blood samples (20 μL) were subjected to protein precipitation followed by derivatization with 4-bromoethyl-7-methoxycoumarin. Blood spiked with ATCA at concentrations ranging from 50 to 1500 ng/mL was used to prepare a calibration curve (lower limit of quantification; 50 ng/mL, lower limit of detection; 25 ng/mL). Our method uses chemical derivatization, so unlike previously reported methods, it does not require tedious pretreatment procedures, hydrophilic interaction liquid chromatography columns, or specialized equipment. In addition, our method allows for repeatable and accurate quantification of ATCA, with intra- and inter-assay coefficients of variation of below 5.0% and below 6.0%, respectively. We used the method to analyze ATCA in postmortem human blood samples, including samples from people who had intentionally ingested CN or were fire victims. Blood ATCA concentrations were higher among people who had ingested CN or were fire victims than among people in a control group (P < 0.0001). The data reported herein demonstrate that our LC/ESI-MS/MS method can be used to detect and quantify ATCA in postmortem blood samples and that CN exposure strongly affects ATCA concentration, providing a useful tool for detection of CN poisoning.

Performance comparison between solid phase extraction and magnetic carbon nanotubes facilitated dispersive-micro solid phase extractions (Mag-CNTs/d-µSPE) of a cyanide metabolite in biological samples using GC–MS

Dispersive-micro solid phase extraction (d-µSPE) has gained increasing attention due to its convenience, effectiveness, and flexibility for sorbent selection. Among a various selection of materials, magnetic carbon nanotubes (Mag-CNTs) is a promising d-µSPE sorbent with excellent separation efficiency in addition to its high surface area and adsorption capability. In this work, two different surface-modified Mag-CNTs, Mag-CNTs-COOH and Mag-CNTs-SO3H, were developed to facilitate d-µSPE (Mag-CNTs/d-µSPE). The cyanide metabolite, 2-aminothiazoline-4-carboxylic acid (ATCA), was selected to evaluate their extraction performance using gas chromatography–mass spectrometry (GC–MS) analysis. The Mag-CNTs-COOH enabled a one-step derivatization/desorption approach in the workflow; therefore, a better overall performance was achieved. Compared to the Mag-CNTs-SO3H/d-µSPE and SPE workflow, the one-step desorption/derivatization approach improved the overall extraction efficiency and reduced solvent consumption and waste production. Both Mag-CNTs/d-µSPE workflows were validated according to ANSI/ASB 036 guidelines and showed excellent analytical performances. The limit of detection (LOD) and limit of quantitation (LOQ) of ATCA in synthetic urine were 5 and 10 ng/mL, respectively, and that in bovine blood were achieved at 10 and 60 ng/mL. The SPE method’s LOD and LOQ were also determined at 1 and 25 ng/mL in bovine blood samples. The Mag-CNTs/d-µSPE methods demonstrated great potential to extract polar and ionic metabolites from biological matrices. The extraction processes of ATCA described in this work can provide an easier-to-adopt procedure for potential routine forensic testing of the stable biomarker in cyanide poisoning cases, particularly for those cases where the cyanide detection window has passed.

RECiQ: A Rapid and Easy Method for Determining Cyanide Intoxication by Cyanide and 2-Aminothiazoline-4-carboxylic Acid Quantification in the Human Blood Using Probe Electrospray Ionization Tandem Mass Spectrometry

In this study, we developed a rapid and easy method to determine cyanide (CN) intoxication by quantification of CN and 2-aminothiazoline-4-carboxylic acid (ATCA), which is a new and reliable indicator of CN exposure, in the human blood using probe electrospray ionization tandem mass spectrometry (PESI/MS/MS) named RECiQ. For CN, we applied the previously reported one-pot derivatization method using 2,3-naphthalenedialdehyde and taurine, which can directly derivatize CN in the blood. The analytical conditions of the CN derivatization were optimized as a 10 min reaction time at room temperature. In contrast, ATCA could be directly detected in the blood by PESI/MS/MS. We developed quantitative methods for the derivatized CN and ATCA using an internal standard method and validated them using quality control samples, demonstrating that the linearities of each calibration curve were greater than 0.995, and intra- and interday precisions and accuracies were 5.1-15 and 1.1-14%, respectively. Moreover, the lower limit of detections for CN and ATCA were 42 and 43 ng/mL, respectively. Finally, we applied RECiQ to three postmortem blood specimens obtained from victims of fire incidents, which resulted in the successful quantification of CN and ATCA in all samples. As PESI/MS/MS can be completed within 0.5 min, and the sample volume requirement of RECiQ is only 2 μL of blood, these methods are useful not only for the rapid determination of CN exposure but also for the estimation of the CN intoxication levels during an autopsy.

Development of magnetic carbon nanotubes for dispersive micro solid phase extraction of the cyanide metabolite, 2-aminothiazoline-4-carboxylic acid, in biological samples

2-aminothiazoline-4-carboxylic acid (ATCA) is a minor metabolite of cyanide and is suggested to be a promising biomarker for cyanide exposure due to its specificity to cyanide metabolism and its excellent short- and long-term stability during storage. In this study, magnetic carbon nanotubes, including magnetic multi-walled carbon nanotubes (Mag-MWCNT) and magnetic single-walled carbon nanotubes (Mag-SWCNT) were synthesized as a novel sorbent for dispersive micro solid phase extraction (d-μSPE) to extract ATCA from biological matrices. ATCA spiked deionized water samples with the addition of the isotopic internal standard (ATCA - ¹³C, ¹⁵N) were subjected to Mag-CNT/d-μSPE to confirm extraction efficiency of this new technique. The extracted ATCA was derivatized and quantitated using gas chromatography/mass spectrometry (GC/MS) analysis. The extraction parameters were optimized and a detection limits of 15 and 25 ng/mL were obtained for synthetic urine and bovine blood respectively with a linear dynamic range of 30-1000 ng/mL. The optimized Mag-CNT/d-μSPE method facilitated efficient extraction of ATCA using 2 mg of Mag-MWCNT with a 10-minute extraction time. The current assay was also found to be effective for the extraction of ATCA with average recoveries of 97.7 ± 4.0% (n = 9) and 96.5 ± 12.1% (n = 9) from synthetic urine and bovine blood respectively. The approach of using Mag-CNT to facilitate d-μSPE offered a novel alternative to extract ATCA from complex biological matrices.

Theoretical and experimental approach to hydrophilic interaction dispersive solid-phase extraction of 2-aminothiazoline-4-carboxylic acid from human post-mortem blood

In this paper, we proposed an innovative hydrophilic interaction dispersive solid-phase extraction (HI-d-SPE) protocol suitable for the isolation of the potential cyanide intoxication marker, 2-aminothiazoline-4-carboxylic acid (ATCA), from such complicated matrix as post-mortem blood. To create an optimal HI-d-SPE protocol, two sorbents were used: a molecularly imprinted polymer (MIP) and commercially available Oasis-MCX^®. The latter sorbent was identified as more recovery-efficient with higher clean-up abilities in a carefully optimized process. Computational analysis was employed to provide insight into the adsorption mechanism of the two selected sorbents. The theoretical results were in agreement with the experiment regarding the efficiency of the sorbent. HI-d-SPE was successfully applied to the analysis of ATCA in 20 post-mortem blood samples using LC-MS/MS. The analytical performance of the method was finally compared to prior existing methods, in turn revealing its superiority.

Biodegradation of cyanide wastes from mining and jewellery industries

Cyanide, one of the known most toxic chemicals, is widely used in mining and jewellery industries for gold extraction and recovery from crushed ores or electroplating residues. Cyanide toxicity occurs because this compound strongly binds to metals, inactivating metalloenzymes such as cytochrome c oxidase. Despite the toxicity of cyanide, cyanotrophic microorganisms such as the alkaliphilic bacterium Pseudomonas pseudoalcaligenes CECT5344 may use cyanide and its derivatives as a nitrogen source for growth, making biodegradation of cyanurated industrial waste possible. Genomic, transcriptomic and proteomic techniques applied to cyanide biodegradation ('cyan-omics') provide a holistic view that increases the global insights into the genetic background of cyanotrophic microorganisms that could be used for biodegradation of industrial cyanurated wastes and other biotechnological applications.

Epigenome-modifying tools in asthma

Asthma is a chronic disease which causes recurrent breathlessness affecting 300 million people worldwide of whom 250,000 die annually. The epigenome is a set of heritable modifications and tags that affect the genome without changing the intrinsic DNA sequence. These marks include DNA methylation, modifications to histone proteins around which DNA is wrapped and expression of noncoding RNA. Alterations in all of these processes have been reported in patients with asthma. In some cases these differences are linked to disease severity and susceptibility and may account for the limited value of genetic studies in asthma. Animal models of asthma suggest that epigenetic modifications and processes are linked to asthma and may be tractable targets for therapeutic intervention.

Cyanide toxicokinetics: the behavior of cyanide, thiocyanate and 2-amino-2-thiazoline-4-carboxylic acid in multiple animal models

Cyanide causes toxic effects by inhibiting cytochrome c oxidase, resulting in cellular hypoxia and cytotoxic anoxia, and can eventually lead to death. Cyanide exposure can be verified by direct analysis of cyanide concentrations or analyzing its metabolites, including thiocyanate (SCN(-)) and 2-amino-2-thiazoline-4-carboxylic acid (ATCA) in blood. To determine the behavior of these markers following cyanide exposure, a toxicokinetics study was performed in three animal models: (i) rats (250-300 g), (ii) rabbits (3.5-4.2 kg) and (iii) swine (47-54 kg). Cyanide reached a maximum in blood and declined rapidly in each animal model as it was absorbed, distributed, metabolized and eliminated. Thiocyanate concentrations rose more slowly as cyanide was enzymatically converted to SCN(-). Concentrations of ATCA did not rise significantly above the baseline in the rat model, but rose quickly in rabbits (up to a 40-fold increase) and swine (up to a 3-fold increase) and then fell rapidly, generally following the relative behavior of cyanide. Rats were administered cyanide subcutaneously and the apparent half-life (t1/2) was determined to be 1,510 min. Rabbits were administered cyanide intravenously and the t1/2 was determined to be 177 min. Swine were administered cyanide intravenously and the t1/2 was determined to be 26.9 min. The SCN(-) t1/2 in rats was 3,010 min, but was not calculated in rabbits and swine because SCN(-) concentrations did not reach a maximum. The t1/2 of ATCA was 40.7 and 13.9 min in rabbits and swine, respectively, while it could not be determined in rats with confidence. The current study suggests that cyanide exposure may be verified shortly after exposure by determining significantly elevated cyanide and SCN(-) in each animal model and ATCA may be used when the ATCA detoxification pathway is significant.