Dietary n6/n3 ratio and inflammatory and metabolic profiles of healthy adult C57BL/6 mice
Authors: Castro Natalia Casanova , Mucci Daniela , Fernandes Flávia , do Carmo Maria das Graças Tavares , Sardinha Fátima 
Published: November 2023

Eating habits changed expressively in the past decades worldwide. Marine sources of n3 fatty acids (FA) intake has declined. Meanwhile, consumption of n6 FA, found in most vegetable oils and associated with a proinflammatory state, rises. Inflammation plays an important role in triggering insulin resistance (IR), a risk factor for different metabolic disorders and proinflammatory cytokines, such as tumor necrosis factor α (TNF‐α) and interleukin‐6 (IL‐6) are associated with impaired insulin signaling, thus leading to IR. Hence, alternative sources of n3 FA, such as chia (Salvia hispanica) and rosehip (Rosa rubiginosa) oils, which could improve dietary n6/n3 ratio, may provide health benefits. These seeds are rich in alfa‐linolenic FA (ALA), an essential FA that can be bioconverted into the long‐chain polyunsaturated FA (LCPUFA) eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). These LCPUFA attenuate inflammation, improving insulin sensitivity. We aimed to evaluate the effects of different dietary n6/n3 ratios on glucose tolerance, cholesterol levels, inflammatory status and FA incorporation in the liver of C57BL/6 male mice. The study was approved by CEUA/CCS (INJC016). At 42 days, mice were divided into 5 groups, fed ad libitum isocaloric and normolipidic diets, made with different oils: soy (SG), canola (CaG), chia (ChG), rosehip (RG) and fish (FG). At 196 days, mice were euthanized by decapitation, with no difference in body weight and chow consumption among groups. Glucose tolerance was tested at 180 days, by intraperitoneal load of 2g glucose/kg and evaluation of caudal vein glycaemia after 15, 30, 60, 90 and 120 minutes to set the area under curve (AUC). Total cholesterol (TC) was assessed by enzymatic colorimetric assay. Inflammatory cytokines were measured by multiplex detection immunoassays and gas chromatography determined liver FA profile. Data were analyzed with GraphPad Prism 5.0 and one‐way ANOVA with Tukey's test. AUC and liver TNF‐α and IL‐6 were unaffected by the diet. It has been suggested that higher ingestion of n6 or lower of n3 FA contributes to a shift towards proinflammatory status and IR. Yet, we found similar TNF‐α, IL‐6 and AUC among groups, indicating that dietary n6/n3 ratio could be less relevant to animals that were not subjected to metabolic insult. RG showed the highest levels of IL‐10. It has been described that IL‐10 seems to be able to restore the altered redox equilibrium, a state that could result from oxidation of the unsaturations present in this oil. None of the tested oils was as efficient as fish oil to better bioconvert to DHA, once FG showed highest DHA content. TC levels were lower in FG, with no difference between ChG and RG; SG and CaG presented higher TC. This was accompanied by lower hepatic n6/n3 ratio for ChG and FG. TC was positively correlated with both total n6 and n6/n3 ratio, and inversely with total n3, corroborating current literature. Although chia and rosehip oils weren't as efficient as fish oil to synthesize DHA, they may help to improve cholesterol levels, as does fish oil.

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