The role of aldehyde reductase AKR1A1 in the metabolism of gamma-hydroxybutyrate in 1321N1 human astrocytoma cells

The role of the aldehyde reductase AKR1A1 in the biosynthesis of gamma-hydroxybutyrate (GHB) has been investigated in cell lines using a specific double stranded siRNA designed to knock down expression of the enzyme. This enzyme, along with the aldo-keto reductase AKR7A2, has been proposed previously to be one of the major succinic semialdehyde reductases in brain. The AKR1A1 siRNA was introduced into the human astrocytoma cell line (1321N1) and AKR1A1 expression was monitored using quantitative reverse-transcriptase PCR and Western blots. Results show an 88% reduction in mRNA levels and a 94% reduction in AKR1A1 protein expression 72h after transfection with the siRNA. Aldehyde reductase activity was examined in silenced cells by following the aldehyde-dependent conversion of NADPH to NADP at 340nm. This revealed a 30% decrease in pNBA reductase activity in cell extracts after AKR1A1 silencing. Succinic semialdehyde reductase activity was significantly lower in silenced cells when measured using high concentrations (1mM) of succinic semialdehyde, but not with low concentrations (10μM). The effect of silencing on intracellular and extracellular GHB levels was measured using gas chromatography-mass spectrometry. Results show that AKR1A1 has little effect on the production of GHB, indicating that in this cell line alternative enzymes such as the AKR7A2 are likely to play a more significant role in GHB biosynthesis