Natural Abundance Carbon Isotopic Analysis Indicates the Equal Contribution of Local Synthesis and Plasma Uptake to Palmitate Levels in the Mouse Brain

Abstract

Saturated fatty acids are the most abundant fatty acids in the brain, however, there has been some debate regarding the ability of intact dietary saturated fatty acids to be incorporated into the brain. In the present study, we use compound specific isotope analysis to measure the natural abundance carbon isotopic signature of brain, liver, and blood palmitic acid (PAM) and compare it to the dietary PAM and sugar isotopic signatures to calculate the relative contribution of both the incorporation of intact and endogenously synthesized PAM to these pools. Mice were equilibrated to the study diet, and extracted fatty acids were analyzed with gas chromatography isotope ratio mass spectrometry to determine the carbon isotopic signature of PAM (δ C ). Liver, serum total, and serum unesterified fatty acid δ C ranged between -20.6 and -21.1 mUr and were approximately 8.5 mUr more enriched in C when compared to the dietary PAM signature. Brain δ C was found to be more enriched than liver or blood pools (-16.7 ± 0.2 mUr, mean ± SD). Two end-member-mixed modeling using the carbon isotopic signature of dietary PAM and dietary sugars determined the contribution of synthesis to the total tissue PAM pool to range between 44% and 48%. This suggests that endogenous synthesis and dietary PAM are near equal contributors to brain, liver, and blood PAM pools. In conclusion, our data provide evidence that brain PAM levels are maintained by both local endogenous synthesis and through the uptake of intact PAM from the blood.

Higher Increase in Plasma DHA in Females Compared to Males Following EPA Supplementation May Be Influenced by a Polymorphism in ELOVL2: An Exploratory Study

“…The plasma δ 13 C of FAME was determined by GC‐IRMS, as previously described by our laboratory (Giuliano et al, 2018; Lacombe et al, 2017, 2018; Metherel et al, 2017, 2019a, b). Briefly, the δ 13 C of plasma fatty acids collected by IRMS was normalized and converted to the international reference scale (Vienna Peedee Belemnite) by multipoint linear normalization and reported in mUr.…”

Serum lipid analysis and isotopic enrichment is suggestive of greater lipogenesis in young long‐term cannabis users: A secondary analysis of a case–control study

“…FAMEs were quantified with an SP‐2560 biscyanopropyl siloxane, capillary column (100 m length × 0.25 mm diameter × 0.20 μm film thickness (Supelco, Bellefonte, PA) in a Varian 430 GC (Bruker; Billerica, MA) as previously described (Lacombe et al, 2017, 2018). The column oven program was initially set to 60°C, increased at a rate of 8.5°C/min to 170°C and held for 6.12 min, increased at a rate of 4.3°C/min to 175°C, 1.7°C/min to 185°C, 0.8°C/min to 190°C, and finally increased to 240°C at 8.5°C/min and held for 27.76 min; totaling 60 min.…”

Dairy product consumption is associated with a lowering of linoleic acid within serum TAG in adolescent females with overweight or obesity: a secondary analysis

“…For each dairy product, we measured δ13C of 16:0 and 18:2n-6 in duplicate. Serum δ13C of 16:0 was quantified by multipoint linear regression, normalized, and converted to the international carbon isotope reference scale, Vienna Peedee Belemnite, as described previously (17)(18)(19)(20). FAME reference standards with calibrated δ13C values (USGS70, USGS71, and USGS72; Reston Stable Isotope Laboratory, United States Geological Survey) were used to produce the standard curve and the linear regression equation.…”

“…We looked at the isotopic enrichment of 16:0, which is the main saturated fatty acid in dairy fat, and used 18:2n-6 as a control since dairy fat is very low in 18:2n-6 and thus dairy consumption should not affect serum 18:2n-6 δ13C. FAME δ13C was analysed by GC-isotope ratio mass spectrometry using a Delta V isotope ratio mass spectrometry system (Thermo Fisher Scientific) as described previously (18,19) . For each dairy product, we measured δ13C of 16:0 and 18:2n-6 in duplicate.…”

“…Our group has recently developed a method to trace fatty acid metabolism using natural variations in carbon 13 enrichment (δ13C) called compound-specific isotope ratio analysis (17)(18)(19)(20) . This technique uses variations in the carbon isotopic pools of the food supply to trace fatty acid metabolism.…”