Interactive Effects of Fish Oil and Methylmercury on the Fatty Acid Profile of Adult Rat Forebrain Phospholipids
Type of DegreeThesis
Nutrition and Food Science
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Docosahexaenoic acid (DHA), a fatty acid found in cold water marine fish is a long chain polyunsaturated fatty acid (LCPUFA). It is important for cognitive and motor function, vision, and infant development. Fish is also the major source of methylmercury (MeHg) exposure, a known environmental pollutant that, when ingested, results in neurological, motor, developmental, and visual deficits. There are similar effects of MeHg toxicity and DHA deficiency, and it is postulated that the detrimental effects of MeHg on neural function could be related to a decrease in DHA in brain phospholipids. The objective of this research is to determine if chronic exposure to MeHg alters the forebrain fatty acid profile of the adult rat, and if dietary fish oil could assist in overcoming the adverse effects of mercury exposure. Female Long-Evans rats, approximately five months old, were assigned a dietary treatment which contained a mixture of four oils: palm, safflower, soybean and either coconut (without n-3 LCPUFA) or fish oil (with n-3 LCPUFA), and three concentrations of mercury as methylmercuric chloride (0.0, 0.5, and 5.0 ppm) dissolved in water. The fish oil diet contained 5% of fatty acids as DHA, whereas the coconut oil diet contained saturated fatty acids in the place of the n-3 LCPUFAs. At 18 months of age the rats were euthanized, tissue samples collected and quick-frozen in liquid nitrogen. Lipids were extracted and phospholipids separated into phosphatidylethanolamine (PE) and phosphatidylcholine (PC) fractions using thin-layer chromatography. These fractions were then analyzed for fatty acid composition using capillary gas chromatography. The differences among groups, main treatment effects, and the interaction between diet and MeHg exposure were assessed using a two way ANOVA procedure with post hoc Tukey’s Studentized Range test. The results were reported as adjusted values and were considered significant at P=0.05. In the adult rat forebrain, chronic MeHg exposure had no significant effects on the alteration of the major LCPUFA; DHA and arachidonic acid (ARA), as well as total n-3 and total n-6 fatty acids. However, there was a dietary effect showing a significant increase in DHA in both the PE (23-30% increase) and PC (25-46% increase) fractions in animals consuming dietary fish oil compared with those consuming the coconut oil diet (P<0.001). There were significant decreases of ARA in both the PE (18-20% decrease) and PC (12-28% decrease) fractions. Also, there were reciprocal effects of total n-3 (net increase) and total n-6 (net decrease) fatty acids in both PE (n-3, 23-31% increase; n-6, 19-24% decrease) and PC (n-3, 26-47% increase; n-6, 28-29% decrease) fractions in response to dietary fish oil. Overall, there was no evidence showing a relationship between LCPUFAs and MeHg toxicity in the adult rat brain.