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Mechanism of toxicity of the branched‐chain fatty acid phytanic acid, a marker of Refsum disease, in astrocytes involves mitochondrial impairment
Author(s) -
Reiser Georg,
Schönfeld Peter,
Kahlert Stefan
Publication year - 2006
Publication title -
international journal of developmental neuroscience
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.761
H-Index - 88
eISSN - 1873-474X
pISSN - 0736-5748
DOI - 10.1016/j.ijdevneu.2005.11.002
Subject(s) - phytanic acid , biochemistry , mitochondrion , peroxisome , cytosol , fatty acid , reactive oxygen species , biology , chemistry , enzyme , gene
Phytanic acid is a saturated branched‐chain fatty acid, which is formed by bacterial degradation of chlorophyll in the intestinal tract of ruminants. The methyl group in β‐position prevents degradation of phytanic acid by the β‐oxidation pathway. Therefore, degradation of phytanic acid is initiated by α‐oxidation in peroxisomes. The inherited peroxisomal disorder Refsum disease is characterised by accumulation of phytanic acid. Unusually high concentrations of phytanic acid can be found in the plasma of Refsum disease patients, who suffer from neurodegeneration and muscle dystrophy. Phytanic acid has been suggested to be causally involved in the clinical symptoms. To elucidate the pathogenic mechanism, we investigated the influence of phytanic acid in rat hippocampal astrocytes by monitoring the cytosolic Ca 2+ concentration, the mitochondrial membrane potential (Δ ψ m ), the generation of reactive oxygen species as well as the cellular ATP level. In response to phytanic acid (100 μM) cytosolic Ca 2+ was quickly increased. The phytanic acid‐evoked Ca 2+ response was transient and involved activation of intracellular Ca 2+ stores. In isolated rat brain mitochondria, phytanic acid dissipated Δ ψ m in a reversible and dose‐dependent manner. Moreover, phytanic acid released cytochrome c from mitochondria. Depending on the mitochondrial activity state, phytanic acid either stimulated or inhibited the electron flux within the respiratory chain. In addition, phytanic acid induced substantial generation of reactive oxygen species in isolated mitochondria as well as in intact cells. Phytanic acid caused cell death of astrocytes within a few hours of exposure. In conclusion, we suggest that phytanic acid initiates astrocyte cell death by activating the mitochondrial route of apoptosis.