pristanal and Sjogren-Larsson-Syndrome

Phytanic acid (3,7,11,15-tetramethylhexadecanoic acid) is a branched-chain fatty acid which, due to the methyl-group at the 3-position, can not undergo beta-oxidation unless the terminal carboxyl-group is removed by alpha-oxidation. The structure of the phytanic acid alpha-oxidation machinery in terms of the reactions involved, has been resolved in recent years and includes a series of four reactions: (1) activation of phytanic acid to phytanoyl-CoA, (2) hydroxylation of phytanoyl-CoA to 2-hydroxyphytanoyl-CoA, (3) cleavage of 2-hydroxyphytanoyl-CoA to pristanal and formyl-CoA, and (4) oxidation of pristanal to pristanic acid. The subcellular localization of the enzymes involved has remained enigmatic, with the exception of phytanoyl-CoA hydroxylase and 2-hydroxyphytanoyl-CoA lyase which are both localized in peroxisomes. The oxidation of pristanal to pristanic acid has been claimed to be catalysed by the microsomal aldehyde dehydrogenase FALDH encoded by the ALDH10-gene. Making use of mutant fibroblasts deficient in FALDH activity, we show that phytanic acid alpha-oxidation is completely normal in these cells. Furthermore, we show that pristanal dehydrogenase activity is not fully deficient in FALDH-deficient cells, implying the existence of one or more additional aldehyde dehydrogenases reacting with pristanal. Using subcellular localization studies, we now show that peroxisomes contain pristanal dehydrogenase activity which leads us to conclude that the complete phytanic acid alpha-oxidation pathway is localized in peroxisomes.

Topics: Aldehyde Oxidoreductases; Aldehydes; Animals; Fatty Acids; Fibroblasts; Humans; In Vitro Techniques; Liver; Male; Oxidation-Reduction; Peroxisomes; Phytanic Acid; Rats; Rats, Wistar; Refsum Disease; Sjogren-Larsson Syndrome

We investigated the role of microsomal fatty aldehyde dehydrogenase (FALDH) in the conversion of pristanal into pristanic acid. Cultured skin fibroblasts from controls and patients with Sjögren-Larsson syndrome (SLS) who are genetically deficient in FALDH activity were incubated with [2,3-(3)H]phytanic acid. The release of aqueous-soluble radioactivity by the SLS cells was decreased to 25% of normal, consistent with an intact formation of pristanal but a deficiency of further oxidation. SLS cells also accumulated four-fold more radioactivity in N-alkyl-phosphatidyl ethanolamine, which arises from incorporation of free aldehyde into phosphatidyl ethanolamine. Recombinant human FALDH expressed in Chinese hamster ovary cells readily oxidized pristanal and cultured fibroblasts from SLS patients showed a severe deficiency in FALDH activity (13% of normal) when pristanal was used as substrate. Nevertheless, SLS patients did not accumulate phytanic acid in their plasma. We conclude that FALDH is involved in the oxidation of pristanal to pristanic acid and that this reaction is deficient in patients with SLS.

Topics: Aldehyde Oxidoreductases; Aldehydes; Animals; CHO Cells; Cricetinae; Fatty Acids; Fibroblasts; Humans; Microsomes; Oxidation-Reduction; Phosphatidylethanolamines; Phytanic Acid; Recombinant Proteins; Sjogren-Larsson Syndrome