1H NMR spectroscopic methods have been applied to compare the in vitro reactivity of the renal papillary nephrotoxin 2-bromoethanamine (BEA) with those of selected halide-substituted nephrotoxic analogues, 2-chloroethanamine (CEA), 2-fluoroethanamine (FEA), and 1-phenyl-2-iodoethanamine (PIEA). The primary 1H NMR-detectable transformation during a 24 h incubation of confluent Madin Darby canine kidney (MDCK) cells with BEA, CEA, and FEA (at concentrations up to the IC50 determined by neutral red uptake) was the appearance in cell culture media of 2-oxazolidone (OX). Additional novel signals assigned as FEA carbamate (N-carbamoyl-2-fluoroethanamine) were observed in media collected following incubation of cells with FEA. We propose that N-carbamate intermediates are formed from the spontaneous reaction of these haloalkylamines with HCO(3-)-buffered growth media and that OX is formed from the carbamate via elimination of the hydrogen halide. Further 1H NMR experiments, conducted for up to 8 h at 25 degrees C on 5 mM solutions of BEA, CEA, and FEA in 2H2O containing a 20-fold excess of HCO3- at pH 7.6, demonstrated a time-dependent decrease in the concentration of the free haloalkylamines accompanied by the production of N-carbamate intermediates and OX. Under these pseudo-first-order reaction conditions, the formation of OX from BEA was complete within approximately 6 h. In similar reaction conditions OX formation from CEA (24 h after initiation) had reached 54% of its final equilibrium concentration. Equivalent experiments demonstrated that PIEA was almost completely converted to 4-phenyl-2-oxazolidinone (PHOX) within 2 h. These observations reveal the strong disposition of this series of haloalkylamines toward reaction with HCO3- and indicate that the compounds in this family may exist only transiently as free amines in vivo, where there will virtually always be excess HCO3-. The physiological relevance of the in vitro findings is further indicated by the NMR-detectable conversion of BEA to OX and also an alkylating aziridine (AZ) moiety in rat plasma containing BEA. The ability to form carbamoylated species and OX (or PHOX) may mediate the toxicity of this series of haloalkylamines and hence is potentially of considerable significance.

Cell cultures are increasingly used in the evaluation of chemically-induced nephrotoxicity. The utili of renal cell culture systems in toxicology would be improved, however, if better characterized and more specific markers of toxicity were available. High resolution proton nuclear magnetic resonance ((1)H NMR) spectroscopy is well suited to the study of toxicological events and has identified many novel markers of nephrotoxicity in vivo. In this study, (1)H NMR spectroscopy has been used to characterize the biochemical composition of two renal cell lines of different nephronal origin, LLC-PK1 (pig proximal tubule) and Madin-Darby canine kidney (MDCK, distal tubule). The early biochemical responses of these cell lines to the model proximal tubular toxin S-(1,2dichlorovinyl)i-L-cysteine (DCVC) and the renal medullary toxin 2-chloroethanamine (CEA) have also been investigated. For each line, 500 MHz (1)H NMR spectra of protein-free acetone extracts of cells and culture medium gave characteristic and reproducible profiles of low MW constituents, including amino and organic acids, glucose and soluble membrane precursors, such as choline and myo-inositol. Treatment-related changes in several low MW compounds not routinely measured in toxicological studies were revealed by NMR specboscopy before marked cytotoxicity was observed by phase contrast microscopy. For example, LLC-PK1 cells treated with 60 μM DCVC showed a marked decrease in intracellular choline levels within 3 h which suggests an effect on the balance of choline synthesis and utilization. Wrthin 9 h of treatment with DCVC there were decreases in intracellular acetate and alanine concentrations which may be indicative of a decrease in fatty acid oxidation and biglyceride metabolism accompanied by an increase in gluconeogenesis. In MDCK cells, 1 h post treatment with 5 mM CEA, intracellular glycine was decreased. This study indicates the potential power and applicability of (1)H NMR spectroscopy for evaluating the biochemical and metabolic effects of toxins in cell culture systems and provides a novel approach to identifying new markers of tissue damage.