Identification and uptake of novel oxidized lipid products from omega-3 polyunsaturated fatty acids in food and its potential biological roles in rodents

Abstract

Omega-3 polyunsaturated fatty acids (n-3 PUFAs), eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA) and its oxidized products derived from marine foods are reported to reduce the risk of CVD. Similar effect has been proposed for α-linolenic acid (ALA) and potentially its oxidized products, phytoprostanes (PhytoPs) and phytofurans (PhytoFs) found in plant food source. In this thesis, in-house synthesized standards of novel oxidized products from ALA including five types of PhytoPs and two types of PhytoFs were used for new LC-MS/MS method development. We validated that the developed method was high in linearity, sensitivity, recovery and reproducibility without carryover. This method was further adapted to measure lipid profiles in different metabolic samples and to investigate their biological significance in different experimentations. Firstly, PUFAs and their oxidized products were measured in both marine and plant food sources. Since marine foods, namely fish is commonly cooked, lipid profiles of boiled, pan-fried and oven-baked salmons were compared to the raw type. None of the cooking methods reduced the amount of PUFAs in the salmons and only oven-baking increased the level of oxidized products from n-3 PUFAs without elevating oxidized products from omega-6 (n-6) PUFAs. For plant foods, ALA, PhytoPs and PhytoFs were quantified in nine different common nuts and seeds. No correlation was found between the level of ALA and levels of PhytoPs and PhytoFs. Also, the formation of PhytoPs and PhytoFs were independent from phenolic capacity and antioxidant capacity of the food. Secondly, the study investigated if consumption of cooked n-3 PUFAs-rich food changed the lipid profile of liver and heart tissues compared to raw n-3 PUFAs-rich food. Using fish oil as the supplemental diet, it was revealed that oven-baked fish oil supplementation was able to enhance the level of oxidized products from EPA and DHA as well as those of AA in liver and heart tissues of healthy rat compared to controls, while feeding non-cooked fish oil augmented less of the oxidized products from EPA and DHA, and the levels of oxidized products from AA were unaffected compared to controls. Finally, the effect of ALA supplementation on the lipid profile of heart tissues was investigated in cardiac arrest rat model. Isoproterenol was used to induce myocardial infarction (MI). ALA supplemented by flaxseed, walnut and flaxseed oil reduced heart to body weight ratio, and also plasma LDH activity and troponin (cTnI) reduced significantly, indicating that injury from MI was alleviated. Moreover, n-3 PUFAs and their oxidized products were enhanced by ALA-enriched diets. It was also noted that anti-inflammatory and antioxidant enzyme in the heart tissues were up-regulated by ALA-enriched diets. Overall, dietary n-3 PUFAs from different food sources including ALA from plant food and EPA and DHA from marine food augmented the oxidized products in liver and heart tissues. Further, the ALA-rich diets potentially protected the heart through anti-oxidant and anti-inflammatory properties.