STUDIES ON THE OXIDATION OF PHYTANIC ACID AND PRISTANIC ACID IN HUMANFIBROBLASTS BY ACYLCARNITINE ANALYSIS

The cl-oxidation of phytanic acid and the beta-oxidation of pristanitc acid were investigated in cultured fibroblasts from controls and pati ents affected with different peroxisomal disorders using deuterated su bstrates. Formation of [omega-H-2(6)]4,8-dimethylnonanoylcarnitine ([o mega-H-2(6)]C-11-carnitine) from [omega-H-2(6)]phytanic acid and [omeg a-H-2(6)]pristanic acid was used as marker for these processes. Analys is was performed by tandem mass spectrometry. In normal cells, formati on of [omega-H-2(6)]C-11-carnitine from both to [omega-H-2(6)]phytanic acid and [omega-H-2(6)]pristanic acid was observed. When peroxisome-d eficient fibroblasts were incubated with these substrates, [omega-H-2( 6)]C-11-carnitine was not detectable or, in two cases, very low, which results from deficiencies in both peroxisomal alpha- and beta-oxidati on. In cells with an isolated beta-oxidation defect at the level of th e peroxisomal bifunctional protein, formation of [omega-H-2(6)]C-11-ca rnitine could also not be detected. Cells with an isolated defect in t he a-oxidation of phytanic acid, obtained from patients affected with Refsum disease (McKusick 266500) or rhizomelic chondrodysplasia puncta ta (McKusick 215100), did not form [omega-H-2(6)]C-11-carnitine from [ omega-H-2(6)]phytanic acid. The observed formation of [omega-H-2(6)]C- 11-carnitine from [omega-H-2(6)]pristanic acid in these cells is in ac cordance with a normal peroxisomal beta-oxidation in these disorders. This study shows that separate incubation of fibroblasts with [omega-H -2(6) ]phytanic acid and [omega-H-2(6)]pristanic acid, followed by acy lcarnitine analysis in the medium by tandem mass spectrometry, can be used for screening cell lines for deficiencies in the peroxisomal alph a- and beta-oxidation pathways.