Metabolism of Cysteine in Astroglial Cells: Synthesis of Hypotaurine and Taurine

The synthesis of hypotaurine and taurine was investigated in astroglia-rich primary cultures obtained from brains of neonatal Wistar rats using 1 H and 13 C nuclear magnetic resonance (NMR) spectroscopy. Cell extracts of astroglial cultures analyzed by 1 H NMR spectroscopy show prominent signals of hypotaurine. To identify cysteine as precursor for hypotaurine and taurine synthesis in astroglial cells, primary cultures were incubated with [3- 13 C]cysteine for 24 or 72 h. Cell extracts and incubation media were then analyzed with 13 C NMR spectroscopy. Labeled hypotaurine, taurine, glutathione, and lactate were identified in the cell extracts. Within 72 h, 35.0% of the total intracellular hypotaurine and 22.5% of taurine were newly synthesized from [3- 13 C] cysteine. The presence of [1- 13 C]hypotaurine and [1- 13 C]taurine in the incubation medium proves the release of those products of cysteine metabolism into the medium. Minor amounts of the [3- 13 C]cysteine were used for the synthesis of glutathione in astroglial cells or metabolized to [3- 13 C]-lactate, which was found in cell extracts and media. These results indicate that the formation of hypotaurine and taurine is a major pathway of cysteine metabolism in astroglial cells.