Falsely increased chloride and missed anion gap elevation during treatment with sodium thiosulfate.

BACKGROUND: Sodium thiosulfate (STS) is used to treat calciphylaxis and cyanide poisoning, but can lead to a serious anion-gap acidosis. We suspected that the calculated anion gap in a patient treated with STS for calciphylaxis was decreased to normal by a falsely increased chloride, and we hypothesized that STS directly interfered with chloride measurements. METHODS: Plasma pools were prepared with 12 concentrations of STS from 0 to 20 mmol/l. Chloride was measured in each sample on 9 analyzers: Architect 16200, StatProfile pHOx Plus, RapidLab 1265®, Vitros 350®, Advia 1800, Roche Modular, iSTAT1, RAPIDpoint 500, and Radiometer ABL735. RESULTS: Statistically significant, dose-dependent increases in reported chloride concentrations were seen with all analyzers except the RAPIDpoint 500 and Vitros. The increases ranged from 5 to 75 mmol/l at the peak thiosulfate concentrations (33 mmol/l) expected in treated patients. The CLIA-allowable error of 5% was exceeded by 4 analyzers (Architect 16200, iSTAT1, StatProfile pHOx Plus, and Radiometer ABL735). The RAPIDpoint 500 showed a 3-mmol/l decrease in measured chloride over the tested range. The Vitros analyzer showed no interference. CONCLUSIONS: Interference of STS in chloride measurement in several common analyzers may lead to erroneous anion-gap calculations and confound the diagnosis of STS-induced anion-gap acidosis.

Targeting the fatty acid biosynthesis enzyme, beta-ketoacyl-acyl carrier protein synthase III (PfKASIII), in the identification of novel antimalarial agents.

The importance of fatty acids to the human malaria parasite, Plasmodium falciparum, and differences due to a type I fatty acid synthesis (FAS) pathway in the parasite, make it an attractive drug target. In the present study, we developed and a utilized a pharmacophore to select compounds for testing against PfKASIII, the initiating enzyme of FAS. This effort identified several PfKASIII inhibitors that grouped into various chemical classes of sulfides, sulfonamides, and sulfonyls. Approximately 60% of the submicromolar inhibitors of PfKASIII inhibited in vitro growth of the malaria parasite. These compounds inhibited both drug sensitive and resistant parasites and testing against a mammalian cell line revealed an encouraging in vitro therapeutic index for the most active compounds. Docking studies into the active site of PfKASIII suggest a potential binding mode that exploits amino acid residues at the mouth of the substrate tunnel.

Investigation into the structure-activity relationship of novel concentration dependent, dual action T-type calcium channel agonists/antagonists.

This paper describes the synthesis and biological evaluation of a series of straight chain analogs of a compound (1) that was previously synthesized in our research program. These compounds, which are T-type calcium channel antagonists, exhibits potent anti-proliferative activity against a variety of cancer cells. A structure-activity relationship of these analogs against a variety of cancer cells has provided insight into a logical pharmacophore for this series of compounds. Furthermore, this series of compounds has presented itself as a set of novel, concentration dependent, dual action agonists/antagonists for the T-type calcium channel.

Design, synthesis, and biological evaluation of novel T-Type calcium channel antagonists.

This paper describes the synthesis of several novel T-type calcium channel antagonists that inhibit calcium influx into the cell, which in turn regulates unknown aspects of the cell cycle pathway that are responsible for cellular proliferation. A library of compounds was synthesized and a brief structure activity relationship will be described. From these studies we have identified a compound (1) that displays anti-proliferative activity in the low micromolar range across a variety of cancer cell lines.

In vitro metabolism of tolcapone to reactive intermediates: relevance to tolcapone liver toxicity.

Tolcapone is a catechol-O-methyltransferase (COMT) inhibitor used for control of motor fluctuations in Parkinson's disease (PD). Since its entry onto the market in 1998, tolcapone has been associated with numerous cases of hepatotoxicity, including three cases of fatal fulminant hepatic failure. The cause of this toxicity is not known; however, it does not occur with the use of the structurally similar drug entacapone. It is known that tolcapone is metabolized to amine (M1) and acetylamine (M2) metabolites in humans, but that the analogous metabolites were not detected in a limited human study of entacapone metabolism. We hypothesized that one or both of these tolcapone metabolites could be oxidized to reactive species and that these reactive metabolites might play a role in tolcapone-induced hepatocellular injury. To investigate this possibility, we examined the ability of M1 and M2 to undergo in vitro bioactivation by electrochemical and enzymatic methods. Electrochemical experiments revealed that M1 and M2 are more easily oxidized than the parent compound, in the order M1 > M2 > tolcapone. There was a general correlation between oxidation potential and the half-lives of the compounds in the presence of two oxidizing systems, horseradish peroxidase and myeloperoxidase. These enzymes catalyzed the oxidation of M1 and M2 to reactive species that could be trapped with glutathione (GSH) to form metabolite adducts (C1 and C2). Each metabolite was found to only form one GSH conjugate, and the structures were tentatively identified using LC-MS/MS. Following incubation of M1 and M2 with human liver microsomes in the presence of GSH, the same adducts were observed, and their structures were confirmed using LC-MS/MS and (1)H NMR. Experiments with chemical P450 inhibitors and cDNA-expressed P450 enzymes revealed that this oxidation is catalyzed by several P450s, and that P450 2E1 and 1A2 play the primary role in the formation of C1 while P450 1A2 is most important for the production of C2. Taken together, these data provide evidence that tolcapone-induced hepatotoxicity may be mediated through the oxidation of the known urinary metabolites M1 and M2 to reactive intermediates. These reactive species may form covalent adducts to hepatic proteins, resulting in damage to liver tissues, although this supposition was not investigated in this study.