Potential of atmospheric pressure ionization sources for the analysis of free fatty acids in clinical and biological samples by gas chromatography-mass spectrometry

Because of the central role of fatty acids in biological systems, their accurate quantification is still important. However, the impact of the complex matrix of biologically and clinically relevant samples such as plasma, serum, or cells makes the analysis still challenging, especially, when free non-esterified fatty acids have to be quantified. Here we developed and characterized a novel GC-MS method using pentafluorobenzyl bromide as a derivatization agent and compared different ionization techniques such as atmospheric pressure chemical ionization (APCI), atmospheric pressure chemical photoionization (APPI), and negative ion chemical ionization (NICI). The GC-APCI-MS showed the lowest limits of detection from 30 to 300 nM for a broad range of fatty acids and a similar response for various fatty acids from a chain length of 10 to 20 carbon atoms. This allows the number of internal standards necessary for accurate quantification to be reduced. Moreover, the use of pentafluorobenzyl bromide allows the direct derivatization of free fatty acids making them accessible for GC-MS analysis without labor-intense sample pretreatment.

Human milk fatty acid composition and its association with maternal blood and adipose tissue fatty acid content in a cohort of women from Europe

PURPOSE

Human milk (HM) composition is influenced by factors, like maternal diet and body stores, among other factors. For evaluating the influence of maternal fatty acid (FA) status on milk FA composition, the correlation between FA content in HM and in maternal plasma, erythrocytes, and adipose tissue was investigated.

METHODS

223 European women who delivered at term, provided HM samples over first four months of lactation. Venous blood and adipose tissue (only from mothers who consented and underwent a C-section delivery) were sampled at delivery. FAs were assessed in plasma, erythrocytes, adipose tissue, and HM. Evolution of HM FAs over lactation and correlations between FA content in milk and tissues and between mother's blood and cord blood were established.

RESULTS

During lactation, arachidonic acid (ARA) and docosahexaenoic acid (DHA) significantly decreased, while linoleic acid (LA), alpha-linolenic acid (ALA), and eicosapentaenoic acid (EPA) remained stable. Positive correlations were observed between HM and adipose tissue for palmitic, stearic, oleic, and polyunsaturated fatty acids (PUFAs). Correlations were found between milk and plasma for oleic, LA, ARA, ALA, DHA, monounsaturated fatty acids (MUFAs), and PUFAs. No correlation was observed between erythrocytes and HM FAs. LA and ALA were more concentrated in maternal blood than in infant blood, contrary to ARA and DHA, supporting that biomagnification of LCPUFAs may have occurred during pregnancy.

CONCLUSIONS

These data show that maternal adipose tissue rather than erythrocytes may serve as reservoir of PUFAs and LCPUFAs for human milk. Plasma also supplies PUFAs and LCPUFAs to maternal milk. If both, adipose tissue and plasma PUFAs, are reflection of dietary intake, it is necessary to provide PUFAs and LCPUFAs during pregnancy or even before conception and lactation to ensure availability for mothers and enough supply for the infant via HM.

Perfluorooctane sulfonate (PFOS) disturbs fatty acid metabolism in Caenorhabditis elegans: Evidence from chemical analysis and molecular mechanism exploration

Perfluorooctane sulfonate (PFOS) is a persistent organic pollutant that might induce disorders in fatty acid (FA) metabolism, but the underlying mechanisms remain unresolved. Caenorhabditis elegans (C. elegans) as a model organism can synthesize polyunsaturated FAs de novo via the polyunsaturated FA synthesis pathway. In this study, synchronized L1 C. elegans were exposed to 0, 0.01, 0.1, 0.5 and 1 μM PFOS for 72 h. Gas chromatography-mass spectrometry (GC-MS) was used to establish a sensitive and reliable analysis method for PFASs in exposed nematode, the instrument detection limits of nine fatty acid methyl esters examined ranged between 1.11 and 27.6 ng/mL, with satisfactory reproducibility (RSD < 10%) observed. Methyl pentadecanoate (C15:0) was used as an internal standard, the linearity of the calibration (0.1-10 μg/mL) nine FAs from the nematode were quantitatively analyzed. Comparing with the control group, PFOS exposure caused significantly decreased levels of C18:0 while significantly increased levels of C18:3n6. A decrease in the C18:3n6: C18:2n6 ratio was observed. Consistently, expression of the FA desaturation gene fat-3 was significantly down-regulated. These findings suggest that the FA disorder is associated with decrease in mRNA expression of Δ6-desaturase genes in C. elegans. Simultaneously, the disorders in FA metabolism were found to disrupt mitochondrial function with a reduction in ATP synthesis, as determined by the luciferase method. In summary, the results of the study provide insights into the adverse effects of PFOS on FA metabolism in living organisms.

Protocol for a randomized controlled trial to test the acceptability and adherence to 6-months of walnut supplementation in Chinese adults at high risk of cardiovascular disease

Background

Consumption of nuts improves cardio-metabolic risk factors in clinical trials and relates to lower risk of cardiovascular disease (CVD) in prospective observational studies. However, there has not been an adequately powered randomized controlled trial to test if nuts supplementation actually reduces incident CVD. In order to establish the feasibility of such a trial, the current study aimed to assess the acceptability and adherence to long-term nut supplementation amongst individuals at high CVD risk in China.

Methods

This protocol described a 6-month trial performed in Ningxia Province in China among participants with a history of CVD or older age (female ≥65 years, male ≥60 years) with multiple CVD risk factors. Participants were randomized to control (received non-edible gift), low dose walnut (30 g/d), or high dose walnut (60 g/d) groups in a 1:1:1 ratio. Walnuts were provided at no cost to participants and could be consumed according to personal preferences. Follow-up visits were scheduled at 2 weeks, 3 months and 6 months. The primary outcome was fasting plasma alpha linolenic acid (ALA) levels used as an indicator of walnut consumption. Secondary outcomes included self-reported walnut intake from the 24 h dietary recalls. The target sample size of 210 provided 90% statistical power with two-sided alpha of 0.05 to detect a mean difference of 0.12% (as percent of total fatty acid) in plasma ALA between randomized groups.

Results

Two hundred and ten participants were recruited and randomized during October 2019. Mean age of participants was 65 years (SD = 7.3), 47% were females, and 94% had a history of CVD at baseline. Across the three study groups, participants had similar baseline demographic and clinical characteristics.

Discussion

This trial will quantify acceptability and adherence to long-term walnut supplementation in a Chinese population at high risk of CVD. The findings will support the design of a future large trial to test the effect of walnut supplementation for CVD prevention.

Trial registration

NCT04037943

Protocol version: v3.0 August 14 2019

Supplementary Information

The online version contains supplementary material available at 10.1186/s12937-020-00660-7.

Monoacylglycerol Form of Omega-3s Improves Its Bioavailability in Humans Compared to Other Forms

Numerous benefits are attributed to omega-3 fatty acids (OM3) especially in cardiovascular health. However, bioavailability and clinical efficacy depend on numerous factors, including OM3 form, food matrix effects (especially the lipid content of the diet), and metabolic capacity. Here, we show in humans that a "pre-digested" OM3-sn-1(3)-monoacylglycerol lipid structure (OM3-MAG) has a significantly greater absorption at high therapeutic doses (2.9 g/day) than the most commonly OM3-ethyl ester (3.1 g/day) form (used for the treatment of hypertriglyceridemia), and a comparable profile to other pre-digested OM3 free fatty acids (OM3-FFA) structure (3.2 g/day). Nutritional supplement doses of MAG resulted in similar increases in OM3 blood level, compared to OM3 triacylglycerols (OM3-TAG) supplements in obese subjects (1.2 g/day) under low fat diet, and in children with cystic fibrosis (1.0 g/day). These results suggest that both forms of pre-digested OM3-MAG and OM3-FFA are effectively absorbed and re-incorporated effectively into triacylglycerols inside the enterocytes, before being exported into the chylomicrons lipid transport system. The pre-digested OM3-MAG might provide a more effective therapy in severe cardiovascular conditions where high doses of OM3 are required and a low-fat diet is indicated, which limited digestive lipase activity.

Subclinical Mastitis in a European Multicenter Cohort: Prevalence, Impact on Human Milk (HM) Composition, and Association with Infant HM Intake and Growth

Background: Subclinical mastitis (SCM) is an inflammatory condition of the mammary gland. We examined the effects of SCM on human milk (HM) composition, infant growth, and HM intake in a mother–infant cohort from seven European countries. Methods: HM samples were obtained from 305 mothers at 2, 17, 30, 60, 90, and 120 days postpartum. SCM status was assessed using HM Sodium (Na): Potassium (K) ratio >0.6. Levels of different macro- and micronutrients were analyzed in HM. Results: SCM prevalence in the first month of lactation was 35.4%. Mean gestational age at delivery was lower and birth by C-section higher in SCM mothers (p ≤ 0.001). HM concentrations of lactose, DHA, linolenic acid, calcium, and phosphorous (p < 0.05 for all) was lower, while total protein, alpha-lactalbumin, lactoferrin, albumin, arachidonic acid to DHA ratio, n-6 to n-3 ratio and minerals (iron, selenium, manganese, zinc, and copper) were higher (p < 0.001 for all) in mothers with SCM. There were no differences in infant growth and HM intake between non-SCM and SCM groups. Conclusion: We document, for the first time, in a large European standardized and longitudinal study, a high prevalence of SCM in early lactation and demonstrate that SCM is associated with significant changes in the macro- and micronutrient composition of HM. Future studies exploring the relation of SCM with breastfeeding behaviors and developmental outcomes are warranted.

Free fatty acid profiling in marine algae extract by LC-MS/MS and isolation as well as quantification of the ω-3 fatty acid hexadeca-4,7,10,13-tetraenoic acid

Undaria pinnatifida (Wakame) alga contains high amounts of hexadeca-4Z,7Z,10Z,13Z-tetraenoic acid which was reported to decrease the efficiency of cisplatin chemotherapeutics. To obtain a fatty acid enriched extract of this ω-3 poly-unsaturated fatty acid as an analytical standard, Wakame was used as source material for its extraction. A two-step extraction protocol consisting of a liquid-liquid extraction followed by solid-phase extraction with 3-aminopropyl silica in accordance to a normal-phase elution mode was developed. An ultra high performance liquid chromatography with electrospray ionization tandem mass spectrometry method based on sequential windowed acquisition of all theoretical fragment ion mass spectra allowed a simultaneous comprehensive group selective fatty acids profiling in untargeted manner and quantitative analysis of the targeted fatty acid. Hexadeca-4Z,7Z,10Z,13Z-tetraenoic acid was identified using high-resolution product ion spectra. The quantitative method was based on d5-deuterated hexadeca-4Z,7Z,10Z,13Z-tetraenoic acid which was employed as surrogate calibrant. Preliminary method validation was performed by evaluating detection and quantification limits, linear range, intra-assay and inter-day precision. Finally, a concentration of 421.2 ± 14.9 ng/mL (4% CV) of hexadeca-4Z,7Z,10Z,13Z-tetraenoic acid was determined in the extract which was further used as analytical standard.

Comparison of the Incorporation of DHA in Circulatory and Neural Tissue When Provided as Triacylglycerol (TAG), Monoacylglycerol (MAG) or Phospholipids (PL) Provides New Insight into Fatty Acid Bioavailability

Phospholipids (PL) or partial acylglycerols such as sn-1(3)-monoacylglycerol (MAG) are potent dietary carriers of long-chain polyunsaturated fatty acids (LC-PUFA) and have been reported to provide superior bioavailability when compared to conventional triacylglycerol (TAG). The main objective of the present study was to compare the incorporation of docosahexaenoic acid (DHA) in plasma, erythrocytes, retina and brain tissues in adult rats when provided as PL (PL-DHA) and MAG (MAG-DHA). Conventional dietary DHA oil containing TAG (TAG-DHA) as well as control chow diet were used to evaluate the potency of the two alternative DHA carriers over a 60-day feeding period. Fatty acid profiles were determined in erythrocytes and plasma lipids at time 0, 7, 14, 28, 35 and 49 days of the experimental period and in retina, cortex, hypothalamus, and hippocampus at 60 days. The assessment of the longitudinal evolution of DHA in erythrocyte and plasma lipids suggest that PL-DHA and MAG-DHA are efficient carriers of dietary DHA when compared to conventional DHA oil (TAG-DHA). Under these experimental conditions, both PL-DHA and MAG-DHA led to higher incorporations of DHA erythrocytes lipids compared to TAG-DHA group. After 60 days of supplementation, statistically significant increase in DHA level incorporated in neural tissues analyzed were observed in the DHA groups compared with the control. The mechanism explaining hypothetically the difference observed in circulatory lipids is discussed.