(E)-4-Hydroxy-2-Nonenal May be Involved in the Pathogenesis of Parkinson’s Disease

Abstract

( E)-4-Hydroxy-2-nonenal (HNE) is a toxic end-product of the free radical-stimulated peroxidation of phospholoipid-bound arachidonic acid in cell membranes. There is a growing body of evidence to suggest that free radicals may play an important role in the pathology of Parkinson’s disease. HNE is highly electrophilic and is conjugated to reduced glutathione (GSH) by glutathione S-transferase. The depletion of GSH in the substantia nigra of Parkinson’s patients and in the brainstem of mice treated with the neurotoxin N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) prompted this study on the concentrations of HNE in the cerebrospinal fluid (CSF) and plasma of Parkinson’s patients and the brainstem of mice treated with MPTP. HNE was identified and quantitated by a highly specific and sensitive method based on the gas chromatography-negative-ion chemical ionisation mass spectrometry of the O-pentafluorobenzyl oxime derivative using 9 D 3-4-hydroxy-2-nonenal as an internal standard. The mean concentration of HNE in the CSF of patients with Parkinson’s disease was 1.47 ± 0.76 μM (mean ± SD, n = 10), while the concentration in the CSF of a group of control patients was 0.38 ± 0.14 μM ( n = 10; p < .01). The mean concentration of HNE in the plasma of Parkinson’s patients was 0.68 ± 0.15 μM ( n = 20) and the concentration in the control group was 0.47 ± 0 12 μM ( n = 20; p < .05). The mean peak concentration of HNE in the brainstem of mice after a single s.c. dose of MPTP (40 mg/kg) was 3.62 ± 0.36 nM/g wet wt. ( n = 17) at 12 h while the control value was 0.45 ± 0.05 nM/g wet wt. ( n = 20; p < .05). The GSH concentration in the brainstem of MPTP-treated mice at 24 h. was 0.65 ± 0.03 μM/g wet wt. ( n = 14) and the control value was 1.25 ± 0.03 μM/g wet wt. ( n = 20; p < .01). The corresponding concentration of GSH-HNE-conjugate at 24 h was 0.32 ± 0.09 μM/g wet wt. ( n = 12) compared with a control value of 0.05 ± 0.02 ( n = 16; p < .01). After treatment with α-tocopherol (2.35 g/kg s.c. daily × 3) the mean concentration of HNE 12 hr. after MPTP injection was 0.89 ± 0.06 nM/g wet wt. ( n = 18). The HNE concentration in a group not treated with α-tocopherol prior to MPTP injection was 3.49 ± 0.09 nM/g wet wt. ( n = 14; p < .05). The concentration of GSH in the mice pretreated with α-tocopherol before MPTP injection was 1.14 ± 0.02 μM/g wet wt. ( n = 17) at 24 h compared to 0.61 ± 0.02 μM/g wet wt. ( n = 14) in the untreated mice ( p < .05). The direct injection of HNE (1, 10, 100, 1,000 μM) into the substantia nigra caused a dose dependent depletion of GSH in the brainstem of mice. The mean concentration of GSH 24 hr after the injection of 100 μM of HNE was 0.43 ± 0.22 μM/g wet wt. ( n = 4) compared with a control value of 1.48 ± 0.02 μM/g wet wt. ( n = 8; p < .05). The corresponding concentration of GSH-HNE-conjugate was 0.32 ± 0.12 μM/g wet wt. ( n = 4) while the control value was 0.04 ± 0.02 μM/g wet wt. ( n = 8). These data suggest that HNE may be a causeative neurotoxin in Parkinson’s disease and that HNE may also be involved in MPTP toxicity.