Mouse aldo-keto reductase AKR7A5 protects V79 cells against 4-hydroxynonenal-induced apoptosis.

We have developed transgenic Chinese hamster V79 cell lines in order to examine the potential for a mouse aldo-keto reductase, AKR7A5, to protect against the toxicity of 4-hydroxynonenal (4-HNE) and related toxic aldehydes. Stable expression of mouse AKR7A5 in V79 cells conferred four-fold increased resistance to 4-HNE cytotoxicity using the MTT assay compared to empty vector-transfected V79 cells. Cells expressing AKR7A5 showed a decrease in mutation rate compared to control cells in the presence of 4-HNE as measured by HGPRT mutagenicity assay. Furthermore, the cells expressing AKR7A5 showed decreased 4-HNE-induced caspase-3 activity in both a time and dose-dependent manner compared to control cells. These results show that in V79 cells 4-HNE mediates apoptosis via caspase-3 activation and that the AKR7A5 enzyme is able to metabolize 4-HNE in cells, thereby attenuating 4-HNE-induced apoptosis. AKR7A isozymes may therefore be important in protecting against toxic aldehydes derived from lipid peroxidation in vivo.

Substrate specificity of mouse aldo-keto reductase AKR7A5.

We have determined the substrate specificity of a mouse aldo-keto reductase (AKR) AKR7A5, an enzyme that is similar to rat aflatoxin aldehyde reductase (AKR7A1) and to human brain succinic semialdehyde reductase (AKR7A2). Previously, we have shown that the mouse enzyme is present in a range of tissues including liver, kidney, testis and brain, and is able to reduce several carbonyl compounds, including succinic semialdehyde, 2-carboxybenzaldehyde, 4-nitrobenzaldehyde and 9,10-phenanthrenequinone [FEBS Lett. 523 (2002) 213]. It has been suggested that it may represent the mouse equivalent of human succinic semialdehyde reductase which is responsible for the biosynthesis of gamma-hydroxybutyrate. In this study, we show that the enzyme is also able to reduce other aromatic aldehydes such as 4-chloro-3-nitrobenzaldehyde, and 3-nitrobenzaldehyde, and has particular high specific activity towards dicarbonyls such as acenapthenequinone, 2,3-bornanedione (camphorquinone), and phenylglyoxal. It has low specific activity towards ketones, and alpha,beta-unsaturated carbonyls such as acrolein and 4-hydroxynonal. The enzyme is inhibited by several compounds including quercitin, ethacrynic acid, indomethacin and sodium valproate. Developing selective inhibitors may lead to a means of modifying the activity of the enzyme in vivo.

Characterisation of a novel mouse liver aldo-keto reductase AKR7A5.

We have characterised a novel aldo-keto reductase (AKR7A5) from mouse liver that is 78% identical to rat aflatoxin dialdehyde reductase AKR7A1 and 89% identical to human succinic semialdehyde (SSA) reductase AKR7A2. AKR7A5 can reduce 2-carboxybenzaldehyde (2-CBA) and SSA as well as a range of aldehyde and diketone substrates. Western blots show that it is expressed in liver, kidney, testis and brain, and at lower levels in skeletal muscle, spleen heart and lung. The protein is not inducible in the liver by dietary ethoxyquin. Immunodepletion of AKR7A5 from liver extracts shows that it is one of the major liver 2-CBA reductases but that it is not the main SSA reductase in this tissue.