The influence and the mechanism of docosahexaenoic acid on a mouse model of Parkinson’s disease

Abstract

This study aimed to investigate the effects of docosahexaenoic acid (DHA) on the oxidative stress that occurs in an experimental mouse model of Parkinson’s disease (PD). An experimental model of PD was created by four intraperitoneal injections of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) (4 × 20 mg/kg, at 12 h intervals). Docosahexaenoic acid was given daily by gavage for 4 weeks (36 mg/kg/day). The motor activity of the mice was evaluated via the pole test, and the dopaminergic lesion was determined by immunohistochemical analysis for tyrosine hydroxylase (TH)-immunopositive cells. The activity of antioxidant enzymes in the brain were determined by spectrophotometric assays and the concentration of thiobarbituric acid-reactive substances (TBARS) were measured as an index of oxidative damage. The number of apoptotic dopaminergic cells significantly increased in MPTP-treated mice compared to controls. Although DHA significantly diminished the number of cell deaths in MPTP-treated mice, it did not improve the decreased motor activity observed in the experimental PD model. Docosahexaenoic acid significantly diminished the amount of cell death in the MPTP + DHA group as compared to the MPTP group. TBARS levels in the brain were significantly increased following MPTP treatment. Glutathione peroxidase (GPx) and catalase (CAT) activities of brain were unaltered in all groups. The activity of brain superoxide dismutase (SOD) was decreased in the MPTP-treated group compared to the control group, but DHA treatment did not have an effect on SOD activity in the MPTP + DHA group. Our current data show that DHA treatment exerts neuroprotective actions on an experimental mouse model of PD. There was a decrease tendency in brain lipid oxidation of MPTP mice but it did not significantly.

Introduction

Parkinson’s disease (PD), first described by James Parkinson in 1817 (Parkinson, 1817), is a neurodegenerative disorder that is characterized by a progressive loss of neuromelanin-containing dopaminergic neurons in the substantia nigra (SN) and a depletion of dopamine (DA) in the striatum. Common parkinsonian symptoms are resting tremor, bradykinesia, rigidity and loss of postural reflexes (Jankovic, 2008). The clinical symptoms appear after 50–60% of neuronal loss, cell death and degeneration of the SN (McGeer et al., 1988), which is mostly age-dependent. A large body of evidence suggests that mitochondrial dysfunction and oxidative stress-mediated mechanisms may be, at least partially, responsible for the degeneration (Schapira et al., 1990).

Further evidence suggests that oxidative stress is a pathogenetic factor for PD, which emerged with the discovery of selective dopaminergic toxins, such as 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) (Burns et al., 1983, Langston et al., 1983). MPTP exposure to monkeys and mice has induced many of the same biochemical and neuropathological changes in the nigrostriatal dopaminergic pathway as found in post-mortem studies of PD patients, such as a loss of dopaminergic cells in the SN that were associated with oxidative stress (Kaul et al., 2003, Przedborski et al., 1996, Zhang et al., 2000). MPTP toxicity involves an increase in reactive oxygen species (ROS) and in damage to mitochondrial DNA (Mandavilli et al., 2000). Although MPTP produces acute intoxication, it is one of the best animal models for studying PD (Zhang et al., 2000).

Studies of post-mortem brains from PD patients clearly indicate that these brains have been subjected to an oxidative challenge (Koutsilieri et al., 2002). Lipid peroxidation levels have been found to be increased in brain tissues from parkinsonian patients (Dexter et al., 1989, Dexter et al., 1994) and MPTP-injected mice (Abdel-Wahab, 2005, Choi et al., 2005, Rajeswari and Sabesan, 2008, Rojas and Rios, 1993, Sankar et al., 2007, Xie et al., 2007). These alterations in the levels of oxidative stress were generally accompanied by changes in antioxidant defense mechanisms (Koutsilieri et al., 2002).

Docosahexaenoic acid (DHA), a major polyunsaturated fatty acid (PUFA) found in the phospholipid fraction of the brain, is essential for normal neural function (Akbar et al., 2005). Docosahexaenoic acid alone constitutes >17% (by weight) of the total fatty acids in the brain of adult rats (Hamano et al., 1996, Hashimoto et al., 2002). PUFA levels were reduced in parkinsonian SN compared to other brain regions and to control tissue (Dexter et al., 1989). Docosahexaenoic acid cannot be synthesized de novo in mammals; therefore, it is most likely obtained through their diet. Studies in animals clearly show that oral intake of DHA can alter brain DHA concentrations and thereby modify brain functions (Bourre et al., 1993, Galli et al., 1971, Levant et al., 2007, Murthy et al., 2002, Pawlosky et al., 2001). This information provides us with an opportunity to use DHA as a nutraceutical or pharmaceutical tool to treat brain disorders such as PD. A neuroprotective action of DHA has been observed in a mouse model of PD (Bousquet et al., 2008). Cansev et al. (2008) has shown that DHA treatment reduced ipsilateral rotations by 47% and significantly elevated striatal DA, tyrosine hydroxylase (TH) activity and TH protein on the lesioned side in a rat model of PD.

One of the first proposed mechanisms for the neuroprotective action of DHA is exerting anti-oxidative activity in vivo (Bazan, 2005, Calon et al., 2004, Hashimoto et al., 2002, Wu et al., 2004, Yavin et al., 2002). Indeed, evidence of DHA increasing glutathione reductase (GR) activity (Hashimoto et al., 2002) and decreasing the accumulation of oxidized proteins (Calon et al., 2004, Wu et al., 2004) as well as lipid peroxide and ROS levels (Hashimoto et al., 2002, Hashimoto et al., 2005) in the brain have been published.

We expect that DHA may have beneficial effects on the symptoms of PD; however, the relationship between DHA and lipid peroxidation/antioxidant enzyme activities in the brain of experimental Parkinson’s has not been investigated. The purpose of this present study is to establish the extent to which alterations in brain lipid peroxidation/antioxidant status occurs in PD and to evaluate whether DHA may help to overcome these alterations.