Evidence for increased oxidative stress in peroxisomal D-bifunctional protein deficiency

Peroxisome biogenesis disorders (PBDs) and D-bifunctional protein (D-BP) deficiency are two types of inherited peroxisomal disorders. Patients with a PBD lack functional peroxisomes and patients with D-BP deficiency lack the enzyme, which is responsible for the second and third step of the peroxisomal beta-oxidation. The clinical presentation of these peroxisomal disorders is severe and includes several neurological abnormalities. The pathological mechanisms underlying these disorders are not understood and no therapies are available. Because peroxisomes have been associated with oxidative stress, as oxygen radicals are both produced and scavenged in peroxisomes, we have investigated whether oxidative stress is involved in the pathogenesis of PBDs and D-BP deficiency. We found in D-BP-deficient patients increased levels of thiobarbituric acid-reactive substances (TBARS) and 8-hydroxydeoxyguanosine (8-OHdG), which are markers for lipid peroxidation and oxidative DNA damage, respectively, whereas the levels of the lipophilic antioxidants alpha-tocopherol and coenzyme Q(10) were decreased. In addition, we found in skin fibroblasts from D-BP-deficient patients an imbalance between the activities of the peroxisomal H(2)O(2)-generating straight-chain acyl-CoA oxidase (SCOX) and the peroxisomal H(2)O(2)-degrading enzyme catalase. In conclusion, we have found clear evidence for the presence of increased oxidative stress in patients with D-BP deficiency, but not in patients with a PBD.