ACCUMULATION OF PHYTANIC ACID ALPHA-OXIDATION INTERMEDIATES IN ZELLWEGER FIBROBLASTS

Phytanic acid (3,7,11,15-tetramethylhexadecanoic acid) and other beta-methyl-branched fatty acids, originating from isoprenoids, cannot be degraded by beta-oxidation but are first shortened by one methylene group in a process called alpha-oxidation. Inherited deficiency of the alpha-oxidation system leads to the accumulation of phytanic acid in patients with Refsum syndrome (for review, see Steinberg (1989)). The subcellular location of alpha-oxidation is still controversial: subcellular fractionation studies showed the activity to be located in the mitochondria (Watkins et al 1990), whereas the fact that patients with a complete deficiency of peroxisomes (Zellweger syndrome) are unable to degrade phytanic acid (Poulos et al 1984) suggests a peroxisomal location. Alpha-oxidation is assumed to consist of three steps, namely alpha-hydroxylation, oxidation of alpha-hydroxyphytanic acid to alpha-ketophytanic acid, and decarboxylation. This sequence was recently questioned by Skjeldal and Stokke (1988), who found that addition of alpha-hydroxyphytanic acid inhibited the alpha-oxidation of phytanic acid (measured as liberation of radioactive CO2 from [1-C-14]phytanic acid) but did not lead to an accumulation of radioactive alpha-hydroxyphytanic acid. We have performed feeding studies with [2,3-H-3]- and [1-C-14]phytanic acid in cultures of normal fibroblasts and of cells from patients with various metabolic diseases, in order to resolve these discrepancies.