Tissue and Circulating Fatty Acids as Biomarkers to Evaluate Long-Term Fat Intake Are Tissue and Sex Dependent in CD-1 Mice

Abstract

Background There is currently no consensus on which tissues are optimal for assessing specific diet-derived fatty acids (FAs) as biomarkers for long-term dietary studies. Objectives This study measured the content of unique diet-derived FAs from dairy, echium, and fish in tissues (adipose, muscle, liver, erythrocyte membranes, and plasma phospholipids, cholesterol esters, triglycerides, and free fatty acids) after long-term feeding in CD-1 mice. Methods Beginning at weaning, mice (n = 10–11/sex/diet) were fed 1 of 4 diets (40% kcal/total energy) that only differed in FA composition: control fat blend (CON), reflecting the FA profile of the average US American diet, or CON supplemented with 30% of fish oil (FO), dairy fat (DF), or echium oil (EO). After 13 mo, tissues were collected to determine FAs via gas–liquid chromatography. Tissue FAs were analyzed via 2-factor ANOVA, and relationships between FA intake and tissue content were assessed with Spearman correlations. Results As anticipated, 20:5n–3 (ω-3) tissue content was ≤32-fold greater in FO- compared with CON-fed mice (P < 0.05). In addition, 20:5n–3 intake strongly correlated with its content in all tissues (ρ = 0.67–0.76; P < 0.05). Echium oil intake also influenced tissue FA content in mice as expected. For example, 18:3n–6 was ≤25-fold greater in adipose, muscle, and liver tissues of EO-fed compared with CON-fed mice (P < 0.05). Tissue content of FAs typically considered biomarkers of dairy fat intake (15:0, 16:1 t9, and 17:0) was often not greater in mice fed DF than other diet groups, although 18:2 c9, t11 content was ≤6-fold greater in tissues from DF-fed compared with CON-fed mice (P < 0.05). The content of dairy-derived FAs in blood fractions of females was up to 2-fold greater compared with males, whereas docosapentaenoic acid content was up to 1-fold greater in all blood fractions and in liver tissue of males compared with females (P < 0.05). In adipose, muscle, and liver tissue, the content of γ-linolenic acid and stearidonic acid was less than 1-fold greater in females than in males (P < 0.05). Conclusions Our study indicates that the distribution of dietary FAs is tissue and sex dependent in aged CD-1 mice. Research using FA biomarkers should assess a combination of FA biomarkers to accurately validate patterns of FA intake and source.

Dietary fat quality impacts metabolic impairments of type 2 diabetes risk differently in male and female CD-1® mice

“…In particular, consumption of echium oil or fish oil had a protective effect against deterioration of glucose tolerance in males. Echium oil is a seed oil that may have unique health properties due to its high content of PUFAs, particularly ∝-linolenic acid and stearidonic acid (both n-3 FAs), as well as -linolenic acid (n-6 FA) (31) . Studies in rodents (42)(43)(44) and humans (45,46) indicate that the primary physiologic benefits of echium oil are its lowering effect on cholesterol and/or triacylglycerol blood concentrations, likely by modulating transcription of hepatic genes related to lipogenesis (42,43) and inflammation (43) .…”

“…Supplementation of the BO-, EO-and FO-diet with 30 % of the respective fat source intentionally sought to represent a dietary pattern whereby an average U.S. American substitutes fat derived from dairy, echium or fish in place of a portion of their typical fat source. In-house preparation and FA analysis of the experimental fat blends (38) and a complete composition and ingredient list of the Inc. § Analysis of FAs was performed via gas-liquid chromatography as described in Unger et al (31) . Data presented as 0 g/kg of diet signify <0•5 g/kg.…”

“…experimental pelleted diets (31) (formulated by Research Diets, Inc. (Brunswick, NJ, USA)) have been previously described.…”

“…We also sought to correlate dietary FA tissue content with metabolic responses to the experimental diets. Previous measurements of diet-derived FAs (percent of total FA methyl esters) into body tissues collected at harvest (14 months of age) have been reported in Unger et al (31) .…”

“…Additionally, the impact of consumption of plant-derived n-3 and n-6 FAs on T2D susceptibility is not clear (26)(27)(28)(29) . Echium oil is a promising source of prohealth FAs (27,30) because of its unusually high content of α-linolenic acid (18:3 n-3), stearidonic acid (18:4 n-3), and -linolenic acid (18:3 n-6) (31) , an n-6 FA with purported anti-inflammatory properties (32) . Importantly, whether or not chronic consumption of beneficial FAs can protect against metabolic abnormalities and disease development during ageing is unclear.…”