Different Sources of Omega-3 Polyunsaturated Fatty Acids Affects Apparent Digestibility, Tissue Deposition, and Tissue Oxidative Stability in Growing Female Rats

Numerous health benefits associated with increased omega 3 polyunsaturated fatty acid (n3 PUFA) consumption has lead to an increasing variety of available n3 PUFA sources. However, sources differ in the type, amount, and structural form of the n3 PUFAs. Therefore, the objective of this study was to determine the effect of different sources of n3 PUFAs on digestibility, tissue deposition, eicosanoid metabolism, and oxidative stability. Female Sprague-Dawley rats (age 28 d) were randomly assigned (n of10/group) to be fed a high fat 12% (wt) diet consisting of either corn oil (CO) or n-3 PUFA rich flaxseed (FO), krill (KO), menhaden (MO), salmon (SO) or tuna (TO) oil for 8 weeks. Rats were individually housed in metabolic cages to determine fatty acid digestibility. Diet and tissue fatty acid composition was analyzed by gas chromatography and lipid classes using thin layer chromatography. Eicosanoid metabolism was determined by measuring urinary metabolites of 2 series prostaglandins (PGs) and thromoboxanes (TXBs) using enzyme immunoassays. Oxidative stability was assessed by measuring thiobarbituric acid reactive substances (TBARS) and total antioxidant capacity (TAC) using colorimetric assays. Gene expression of antioxidant defense enzymes was determined by real time quantitative polymerase chain reaction (RT PCR). Rats fed KO had significantly lower DHA digestibility and brain DHA incorporation than SO and TO fed rats. Of the n3 PUFA sources, rats fed SO and TO had the highest n3 PUFAs digestibility and in turn, tissue accretion. Higher tissue n3 LC PUFAs had no significant effect on 2 series PG and TXB metabolites. Despite higher tissue n3 LC PUFA deposition, there was no increase in oxidation susceptibility indicated by no significant increase in TBARS or decrease in TAC and gene expression of antioxidant defense enzymes, in SO or TO fed rats. On the basis that the optimal n3 PUFA sources should provide high digestibility and efficient tissue incorporation with the least tissue lipid peroxidation, TO and SO appeared to be the most beneficial of the n3 PUFAs sources evaluated in this study. (Authors abstract)
Currently, various sources of n-3 PUFAs are available with claims that some sources are more beneficial than others. The source of n-3 PUFAs that is most favorable to health should provide high digestibility and efficient tissue incorporation with the least tissue lipid peroxidation. The objective of this study was to determine the effect of different sources of n3 PUFAs on digestibility, tissue deposition, eicosanoid metabolism, and oxidative stability. PUFA digestibility was influenced by the structural form. DHA content was 2 to 4 times higher in KO compared to the other sources of n3 PUFAs.  Further studies are needed to clarify whether different PLs influence fatty acid digestibility. This is important because the source of PUFAs that provides high digestibility also increases tissue deposition. DHA was better incorporated when consumed in TG than PL form. TO with the highest DHA in TG form resulted in the highest brain DHA deposition. KO with the highest DHA in PL form did not result in the highest brain deposition due to reduced DHA digestibility. The amount of dietary fatty acids affected liver deposition. Rats fed FO with the highest ALA content also had the highest liver ALA deposition. Rats fed SO with the highest dietary EPA TG resulted in the highest liver EPA deposition. Feeding rats CO containing ALA and no n3 LC PUFAs resulted in DHA, but no detectable EPA liver deposition.  Feeding rats FO, which is high in ALA, decreased liver ARA, but this was not accompanied by increased EPA deposition.  As the chief site for lipid storage, the fatty acid profile of adipose tissue reflected the diet. Rats fed KO with the highest amount of EPA had the highest adipose tissue EPA deposition. Rats fed FO with the highest amount of ALA content had the highest adipose tissue ALA deposition. There was no significant reduction in the adipose mass of rats fed different n3 PUFA sources. Conversion of ALA to n3 LC PUFAs was less efficient.  However, rats fed FO containing ALA, but no DHA, resulted in DHA deposition in gonadal and not in retroperitoneal adipose tissue. This suggested conversion of ALA to n3 LC PUFAs was less efficient in retroperitoneal adipose compared to gonadal adipose. (Editors comments)