The inhibitory effect of erucic acid on the polyunsaturated fatty acids in Sprague-Dawley rats
Louw, Aletta Petronella
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X-adrenoleukodystrophy (X-ALD) is a progressive neurodegenerative disorder characterized by the accumulation of saturated unbranched very long chain fatty acids (VLCFA), particularly hexacosanoic acid (C26:0) and tetracosanoic acid (C24:0) in plasma and brain. Peroxisomal β-oxidation is also impaired. It affects the cerebral white matter, spinal cord, peripheral nerves, adrenal cortex and testis (Kemp et al., 2004). It is caused by a defect in the ABCD1 gene, which maps to Xq28 and codes the peroxisomal membrane protein, adrenoleukodystrophy protein (ALDP). To date, there is no effective therapy, except for Lorenzo's oil, which consists of oleic acid (C18:1) and erucic acid (C22:1). Treatment with Lorenzo's oil elicits a good biochemical response and cause a decreased in plasma VLCFA levels in patients. However, improvement of neurological symptoms has not been reported. Treatment of X-ALD with monounsaturated fatty acids such as oleic acid and erucic acid lead to the normalization of C26:0 levels, possibly as a result of competition for the microsomal elongation system (Rizzo et aI., 1986). Erucic acid is a mono-unsaturated omega-9 fatty acid, denoted C22:1ω-9. It is a potent inhibitor of saturated very long chain fatty acids (SVLCFA). Because erucic acid competes for the microsomal elongation system, the inhibition of SVLCFA synthesis can lead to inhibition of polyunsaturated fatty acids that are elongated by the same system. Dosages between 400 mg/kg and 1500 mg/kg erucic acid have been tested by Kramer and co-workers (1992). Spraque-Dawley rats (10 rats per group) have been treated for one week with oils that contained 2.5 to 9% erucic acid concentration. The dosages of 1500 mg/kg and higher produced significantly increased myocardial lipidosis. The aim in this pilot study was to determine the optimum dosage for erucic acid in Sprague-Dawley rats that will lower levels of SVLCFA. A further aim was to assess its effect on the biosynthesis and incorporation of polyunsaturated fatty acids (PUFA) into the plasma and brain phospholipids. Sixty male Sprague-Dawley rats were individually housed in metabolic cages with free access to laboratory food and water. The rats were divided into 5 groups (n = 10 in each) including a control group (n = 10). Dosages of 400mg/kg, 575 mg/kg, 600 mg/kg, 625 mg/kg and 800 mg/kg of erucic acid, dissolved in dimethylsulphoxide (DMSO), were given by gavage to the five groups respectively for 7 days. The control group received the vehicle, DMSO. The rats were decapitated on day 8 and brain and blood samples were collected and frozen at -20°C until assayed. The inhibitory effect of different dosages of erucic acid on total plasma SVLCFA concentrations and concentration ratios was determined using a standardized method employing gas chromatography-mass spectrometry (GC-MS). These results were expressed in μmol/L. For the determination of SVLCFA and PUFA in the plasma and brain phospholipids, gas chromatography-mass spectrometry (GC-MS) and thin layer chromatography (TLC) were used. Fatty acids were expressed as a percentage of the total lipid composition and subsequent ratios were calculated. Statistical comparisons of data between the groups were done using analysis of variance (ANOVA). A dose of 600 mg/kg erucic acid reduced C24:0 and C26:0 levels and decreased the C24:0/C22:0 ratio the most. These reduction were, however, not Significantly different Erucic acid competed with the elongation of EPA (Eicosapentanoic acid) to DPA (Docosapentaenoic acid) in the ω-3 fatty acid pathway, which was seen as a decreased DPA/EPA ratio in the 600 mg/kg erucic acid group. This effect was seen in both the plasma and brain phospholipids. Erucic acid slightly decreased DHA (Docosahexaenoic acid) (ω-3) and AA (Arachidonic acid) (ω-6) concentrations in the plasma phospholipids, but had no influence on DHA levels in the brain phospholipids. A result of concern was the significant increase in arachidonic acid (AA) levels in the brain phospholipids. AA is the precursor to a number of inflammatory mediators, including prostaglandins and leukotrienes that could lead to inflammation. The latter could explain why neurological symptoms persist, and sometimes even progress in patients with symptomatic ALD who use Lorenzo's oil. Therefore, we conclude that erucic acid treatment in Sprague-Dawley rats reduced VLCFA levels in plasma and that this result is promising. Unfortunately concomitant increased levels of AA in the brain is a matter of concern. Further research into the mechanism of action of erucic acid is called for.
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