The production of lipids alternately labelled with carbon-13.

Chlorella cells were shown to have similar fatty acid profiles when grown photoautotrophically or if grown photoheterotrophically with ethanoate (acetate) as carbon source. When supplied with ethanoate labelled with carbon-13 in the methyl group, the alga incorporated it into fatty acids with retention of the sequence of labelling on alternate carbon atoms, thus providing a convenient method for synthesising lipids in a form useful for nuclear magnetic resonance (NMR) studies of lipids in situ in membranes. Marine algae used in fish farming may have higher levels of very highly unsaturated fatty acids; proposals for producing these compounds labelled with carbon-13 are, therefore, presented, based on using centrally labelled glycerol. The scope for producing other substances labelled in a form suitable for NMR studies, such as carotenoids, is discussed.

Solubilization of acyl heterogeneous triacylglycerol in phosphatidylcholine vesicles.

The amount of acyl heterogeneous triacylglycerol (TG(HET)) solubilized by phosphatidylcholine (PC) vesicles, prepared by co-sonication of egg PC and small amounts (<6% w/w) of TG(HET), was determined using (13)C nuclear magnetic resonance (NMR). The acyl chains of TG(HET) were predominantly 16 or 18 carbons in length, 50% saturated, and approximately 21.7% (13)C isotopically enriched at the carbonyl carbon. The (13)C NMR spectra revealed two carbonyl resonances at chemical shift values between PC carbonyls and oil-phase TG carbonyls, confirming the presence of TG(HET) solubilized in PC vesicles. Oil-phase TG carbonyl peaks were present only in spectra of vesicles containing >3 wt % TG(HET). Integration of TG(HET) carbonyl resonances determined that PC vesicles solubilized 3.8 wt % of TG(HET), compared to 2.8 wt % of acyl homogeneous triolein. The difference between the maximum solubility of TG(HET) and that of homogeneous TG (TG(HOM)) with similar acyl chain lengths provides evidence that specific acyl composition, in addition to the acyl chain length of triacylglycerols, affects the solubility of TG in PC vesicles and TG-rich lipoprotein surfaces. Thus, TG(HET) may innately be a better model substrate than TG(HOM) for determination of substrate availability of TG at lipoprotein surfaces.

Integral apolipoproteins increase surface-located triacylglycerol in intact native apoB-100-containing lipoproteins.

High-resolution NMR was used to measure the presence and quantity of triacylglycerol (TAG) in the surface of intact native apolipoprotein B-100-containing lipoprotein particles that are made by chickens in response to estrogen treatment and that in hens are deposited in yolk follicles (VLDLy). Integration of 13C NMR resonances shows that intact VLDLy particles contain more surface TAG (5.1 +/- 0.6 mol%, 6.7 +/- 0.8 weight %) than predicted by apolipoprotein-free models using similarly acyl-heterogenous TAG. Change in downfield chemical shift values of surface to core TAG in VLDLy was 0.8 ppm compared with 1.3 ppm in vesicles prepared with purified egg phosphatidylcholine and TAG isolated from the VLDLy, indicating that reduced surface TAG hydration may contribute to the resistance to lipase hydrolysis characteristic of this lipoprotein species. Apolipoprotein-mediated changes in surface lipid composition and lipid hydration provide possible general mechanisms for selectivity in lipoprotein substrate characteristics.

Pancreatic lipase and its related protein 2 are regulated by dietary polyunsaturated fat during the postnatal development of rats.

The developmental gene expression of pancreatic lipase (PL) and its related proteins (PLRP1 and PLRP2) is anticoordinate. It is unknown whether dietary fat regulates the expression of these proteins in the preweanling stage. For determining the regulation of development and diet on PL, PLRP1, and PLRP2 as early as the suckling period, pregnant (Sprague-Dawley) rats consumed from day 15 (d15) of pregnancy through d9 of lactation a purified low (11% of energy) safflower oil diet [low-fat (LF)]. From d9 of lactation, dams and their respective pups were fed LF, medium-fat (MF; 40% of energy), or high-fat (HF; 67% of energy) safflower oil diets to d56. Milk fatty acid content had 15- to 100-fold less C:10 and 2.6- to 3.3-fold more C18:2 in MF and HF groups. Diet (LF < MF = HF; P < 0.002), postnatal development (d15 < d21 < d28 = d56; P < 0.001), and interaction of diet x development significantly affected PL activity starting as early as d15. PL mRNA levels showed a parallel effect of diet (LF < HF = MF; P < 0.013) and development (P < 0.001). Both PLRP1 and PLRP2 mRNA levels were significantly affected by development (P < 0.001) and had an anticoordinate pattern compared with PL expression (d15 > d21 > d28). Reported for the first time is the significant down-regulation of PLRP2 mRNA levels by high polyunsaturated fat in suckling (d15) rats. In conclusion, PL and PLRP2 gene expression is regulated anticoordinately by the amount of dietary polyunsaturated fat starting as early as the preweanling phase of development.