ELEVATION OF ENDOGENOUS NUCLEOPHILES IN RAT LUNG BY CYSTEINE AND GLUTATHIONE ESTERS IN-VITRO

In this study, we have compared the uptake of L-cysteine (L-CySH), D-c ysteine (D-CySH), L-cysteine isopropyl ester (L-CIPE) and D-cysteine i sopropyl ester (D-CIPE) in rat lung slices and tracheal sections and d etermined the effectiveness of glutathione (GSH), GSH isopropyl monoes ter, GSH isopropyl diester, gamma-glutamylcysteine (gamma-glu-cys) iso propyl monoester and gamma-glu-cys isopropyl diester to elevate and pr olong intracellular GSH concentrations in rat lung slices. Lung slices were incubated with 1.0 mM of thiol and the concentrations determined intracellularly and extracellularly with time. Slices incubated with GSH, GSH isopropyl diester and gamma-glu-cys isopropyl diester had cel lular GSH concentrations increased by up to 60%, 95% and 58%, respecti vely, whereas GSH isopropyl monoester and gamma-glu-cys isopropyl mono ester did not increase the intracellular GSH concentration. Extracellu larly, the GSH concentration had decreased by 15%, GSH isopropyl diest er by 27%, gamma-glu-cys isopropyl diester by 66% and both isopropyl m onoesters by over 90% at 120 min. Lung slices and tracheal sections in cubated with L- or D-CySH at 37 degrees had increased cellular concent rations of L- and D-CySH which ranged between 0.88-1.25 nmol mg(-1) an d 1.35-2.25 nmol mg(-1), respectively. Reducing the incubation tempera ture to 40 had little effect on the accumulation of D-CySH; however, L -CySH concentrations increased progressively in the trachea and lung t o reach 2.73 and 2.63 nmol mg(-1) at 90 min, respectively. Lung slices incubated with L- or D-CIPE had increased L- or D-CySH concentrations up to a max of 13.7 and 11.1 nmol mg(-1) and tracheal sections up to a max of 5.56 and 11.09 nmol mg(-1). In the lung slice medium, L- and D-CIPE levels had decreased by 75.2% and 74.0% at 90 min, respectively , and from the tracheal section medium, L- and n-CIPE concentrations h ad decreased by 66.7% and 32.7%, respectively. Preincubation of lung s lices and tracheal sections with the carboxylesterase inhibitor, bis ( p-nitrophenyl) phosphate (BNPP), almost completely prevented the disap pearance of L- and D-CIPE extracellularly and greatly reduced the appe arance of cellular Land n-CySH. GSH, GSH isopropyl diester and gamma-g lu-cys isopropyl diester elevated and prolonged GSH concentrations in rat lung slices, but GSH isopropyl monoester and gamma-glu-cys isoprop yl monoester did not increase GSH levels. The uptake of L-CySH, but no t D-CySH, is temperature sensitive in rat lung slices and tracheal sec tions and carboxylesterases appear to have a major influence on the up take and metabolism of L- and D-CIPE by rat lung slices and tracheal s ections. Crown Copyright (C) 1998. Published by Elsevier Science Inc.