Non-targeted mercapturic acid screening in urine using LC-MS/MS with matrix effect compensation by postcolumn infusion of internal standard (PCI-IS).

While the targeted analysis of mercapturic acid (MA) metabolites in human urine is used to assess exposure to selected chemicals, this compound class has only rarely been addressed in non-target screening utilizing diagnostic neutral loss liquid chromatography tandem mass spectrometry (LC-MS/MS). Additionally, this type of analysis is severely affected by matrix effects (MEs) causing poor comparability of samples and distortion of signal intensities. However, MEs have been neglected in urinary MA non-target screening so far. Therefore, we developed a non-target screening method relying on neutral loss scanning for MAs using post column infusion of an isotope-labelled standard. For signal correction, we synthesized a structural analogue to MAs, N-acetyl-S-methyl-homocysteine-D3, lacking the characteristic neutral loss of the MAs. For method development, 16 structurally different model MA compounds and 20 spiked urine samples were used. Twelve out of the 16 model compounds could be analysed by the developed method. We found severe matrix effects (largely signal suppression) for the spiked model compounds, with only 34% of all peaks' intensities changing by less than a factor of two. This could be compensated by the post column internal standard infusion with now 68% of all peaks' intensities changing by less than a factor of two. For three compounds, an over-compensation was observed resulting in an increase of signal of up to a factor of 16. In the 20 urine samples, altogether 558 native MAs (between 74 and 175 per sample) could be detected after ME compensation. These results indicate that a large number of so far uncharacterized MAs are present in urine, which yield a potential for biomarker discovery and pattern characterisation. Graphical Abstract.

N-Acetylcysteine (NAC) for the Prevention of Liver Failure in Heat Injury-Mediated Ischemic Hepatitis.

Exertional Heat Illness with associated ischemic hepatitis (IH) is a common occurrence among military trainees; however, few specific therapies exist if unresponsive to appropriate supportive measures. A 27-year-old basic combat trainee presented with altered mental status, renal insufficiency, rhabdomyolysis, and a core temp of 107.9 °F after collapsing during a run, leading to the diagnosis of heat stroke. While the patient's azotemia and creatinine kinase levels rapidly improved with aggressive intravenous hydration, transaminases continued to increase to nearly 155 times the upper limit of normal. Further laboratory evaluation revealed coagulopathy and thrombocytopenia suggestive of acute liver failure (ALF). On hospital day three, the patient was started on N-acetylcysteine (NAC). Evaluation for infectious and autoimmune etiologies of ALF was unremarkable; thus, the patient's symptomatology was attributed to IH resulting from heat stroke. Liver function normalized on NAC. Heat Injury is common among US Army recruits and results in thousands of hospitalizations in recent years. IH is characterized by diffuse hepatocyte necrosis following an episode of hemodynamic instability, and is an established sequela of Heat Injury. The mortality of IH among critically ill patients has been estimated to be as high as 60%, with those demonstrating coagulopathy especially at risk. NAC is shown to improve the transplant-free survival rate in non-acetaminophen related ALF, consistent with its proposed mechanisms of improving hepatic blood flow and conjugating toxic metabolites. NAC therapy should be considered early in the course of heat injury-mediated IH to reduce reperfusion injury, improving transplant free outcomes.

Stability of a flavored formulation of acetylcysteine for oral administration.

PURPOSE: The chemical and physical stability of a flavored solution of acetylcysteine stored at room temperature or under refrigeration for up to 35 days in amber plastic prescription bottles were studied. METHODS: The flavored acetylcysteine solution was prepared by adding a sweetener and a strawberry creamsicle flavoring to acetylcysteine solution 10% to a final nominal acetylcysteine concentration of 86.5 mg/mL. Six identical samples of the formulation were prepared in amber plastic prescription bottles. Three bottles were stored at room temperature (23-25 degrees C) and the other three were stored in the refrigerator (3-5 degrees C). Immediately after preparation and at 7, 14, 21, 28, and 35 days, each sample was assayed in duplicate by high- performance liquid chromatography. Stability was defined as the retention of at least 90% of the initial drug concentration. RESULTS: On day 35, the refrigerated acetylcysteine samples retained 96.7% of their initial concentration. The samples stored at room temperature retained 92.5% of their initial concentration. CONCLUSION: A flavored oral formulation of acetylcysteine 86.5 mg/mL was stable for at least 35 days when stored at room temperature and in the refrigerator in amber plastic bottles.