Stable isotope tracer and gas-chromatography combustion isotope ratio mass spectrometry to study the in vivo compartmental metabolism of docosahexaenoic acid.
A gas-chromatography combustion isotope ratio mass spectrometry (GCC-IRMS) method using carbon 13 (13C)-stable isotope to trace n-3 polyunsaturated fatty acids (PUFA) turnover in vivo is presented. Natural 13C abundance of commercial n-3 PUFA was measured from 100 to 300 ng of fatty acids and was -27.58, -27.83, and -28.16 for 22:6n-3, 22:5n-3, and 20:5n-3, expressed as delta 13C /1000 versus Pee Dee Belemnite (PDB), respectively. Precision of delta 13C /1000 values was comparable for the three PUFA and gave relative standard deviations of 0.95-0.97%. Isotope enrichment of 0.0010 at.% could be detected. Triglycerides enriched in [13C]22:6n-3 ([13C]22:6-TG) were synthesized by growing a microalgae on [1-13C]glucose. [13C]22:6n-3 represented 36 wt.% of total triglyceride fatty acids and had an isotope enrichment of 2.0420 at.%, which was the double of natural abundance. The isotope enrichment of 22:6n-3 in lipids from rat lipoproteins and red cells could be followed as a function of time after ingestion of 3 mg [13C]22:6-TG and showed specific patterns according to the lipid compartments. The retroconversion of [13C]22:6n-3 was also detected in HDL phosphatidylcholine by the appearance of [13C]22:5n-3 and [13C]20:5n-3. On the other hand, 22:6n-3 natural 13C abundance in human lipid classes of lipoproteins and blood cells has been measured using 10 ml plasma, even for the more limiting lipid compartments in terms of 22:6n-3 dose size.(ABSTRACT TRUNCATED AT 250 WORDS)
Brossard
N
N
INSERM U 352, Chimie Biologique, INSA-Lyon, Villeurbanne, France.
Pachiaudi
C
C
Croset
M
M
Normand
S
S
Lecerf
J
J
Chirouze
V
V
Riou
J P
JP
Tayot
J L
JL
Lagarde
M
M
D000818:Animals; D002247:Carbon Isotopes; D004281:Docosahexaenoic Acids / Q000097:blood / Q000378:metabolism*; D008401:Gas Chromatography-Mass Spectrometry / Q000379:methods*; D006801:Humans; D050356:Lipid Metabolism; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley
D002247:Carbon Isotopes; D004281:Docosahexaenoic Acids