Changes to the fatty acid composition in the phospholipids and
triglycerides of adipose tissue occurred as expected, corresponding to
the content of SFA, MUFA and PUFA in the diets. Membrane phospholipid
fatty acids can modulate cellular signalling pathways by
serving as precursors to fatty acid-derived messengers. For example,
some n6 PUFA are substrates for eicosanoid biosynthesis, which may
drive local tissue inflammation [21]. Despite the large differences in
linoleic acid and ALA intake, there were no changes in arachidonic acid
and only small differences in EPA in phospholipids, suggesting that the
pool of substrates for eicosanoid production was relatively unchanged.
Furthermore, enrichment of n6PUFAintheSafflower and Soybean
Oil diets and a high level of n3 PUFA in the Canola–Flaxseed Oil diet
did not produce changes in protein levels of pro- or anti-inflammatory
adipokines in the adipose tissue of our animals. Although the diets
varied in the amounts and ratios of n6andn3 fatty acids, in
adipose tissue, there were no differences among groups in the n6/
n3 ratio in either phospholipid or triglyceride fatty acids. The sole
exception was the Safflower Oil group, in which the n6/n3 ratio in
adipose tissue was elevated due to the high content of linoleic acid in
the oil. The same is true of the PUFA/SFA ratio in adipose tissue
phospholipid fatty acids, while the triglyceride fatty acid composition
closely reflects the dietary composition of PUFA and SFA. Even though
the n6ton3 ratios varied across the dietary treatments, a dietary
n6/n3 ratio of 8:1 or less did not produce differences in adipose
tissue n6/n3 ratios. However, DHA, the main n3PUFAinadipose
tissue phospholipids was similar across all groups, indicating that the
range of dietary ALA intakes was able to maintain tissue DHA by
elongation and desaturation of ALA. Interestingly, DPA was the major
n3 PUFA in adipose tissue triglycerides, where it was elevated in the
Canola Oil and High Oleic Canola Oil groups compared to the Safflower
Oil group. The findings of Gregory et al. [48] and Pawlosky et al.
[49]
suggest that increased ALA intake elevates tissue DPA due to competition
between EPA and DPA for Elongase2 (Elovl2), the enzyme that
acts on both these substrates in the final steps for conversion to DHA.
The prevalence of DPA in the adipose tissue triglycerides of our
animals fed diets containing ALA may similarly be the result of
competition between EPA and DPA. Overall, the changes in adipose
fatty acid composition were insufficient to alter inflammatory adipokines.
Furthermore, our study indicates that very few obesity-related
parameters were altered by 12 weeks of feeding MUFA- or PUFA-rich
diets containing different proportions of n3andn6PUFAinthe
context of a high-fat diet. The findings of this study parallel those of
Hanke et al. [29],whoinvestigatedtheefficacy of the same diet
regimen for modulating hepatic steatosis. Despite a 20% decrease in
liver lipid concentration and similar changes to the liver fatty acid
composition as observed in the present study, markers of glucose
homeostasis, hepatic inflammation, and fatty acid metabolism exhibited
only minor differences among groups.