Free Fatty Acid Pool Research Articles

Definition, Pathogenesis, and Natural Progress of Non-alcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease (NAFLD) is emerging as a world-wide health problem and is currently recognized as a hepatic manifestation of metabolic syndrome. It is an umbrella term to describe a wide range of diseases from simple steatosis to non-alcoholic hepatosteatosis (NASH) and NSAH-related liver cirrhosis. NAFLD is mainly associated with insulin resistance which allows increased free fatty acid (FFA) flux to the liver by increasing lipolysis from adipose tissue, triggering macrophage/immune activation, decreasing skeletal muscle glucose uptake, and increasing de novo lipogenesis. Increased FFA pool in the liver, in turn, increases lipotoxic intermediates, such as ceramides, diacylglycerols, and lysophosphatidylcholines, which are responsible for mitochondrial dysfunction and endoplasmic reticulum stress, resulting in inflammation of the liver. When inflammation is severe enough to affect stellate cells, hepatic fibrosis can be induced. (J Korean Diabetes 2014;15:65-70)

Contribution of very low-density lipoprotein triglyceride fatty acids to postabsorptive free fatty acid flux in obese humans

ObjectiveIn the fasting state, plasma free fatty acids (FFA) are thought to derive almost exclusively from adipose tissue lipolysis. However, there are mixed reports as to whether the spillover of fatty acids (FA) from very low-density lipoprotein triglyceride (VLDL–TG) hydrolysis contributes significantly to the plasma FFA pool. Because substantial VLDL–TG fatty acid spillover into the plasma FFA pool would profoundly impact the interpretation of isotope dilution measures of FFA flux, we investigated the contribution of VLDL–TG spillover to plasma FFA appearance. Materials/MethodsEighteen obese adults (15 women) participated in these studies. Each volunteer received a primed, continuous infusion of their own ex-vivo labeled ([1-14C]triolein) VLDL–TG and a continuous infusion of [U-13C]oleate (8nmol·kg fat free mass−1·min−1) to measure VLDL–TG and FFA rate of appearance (Ra), respectively. The presence of 14C-oleate in the plasma FFA–oleate pool was used to calculate the contribution of spillover from VLDL–TG–oleate to the plasma FFA–oleate Ra. ResultsThe spillover rate of VLDL–TG–oleate into plasma FFA–oleate was 6±2μmol/min (7%±2% of [14C]oleate from VLDL–TG) and FFA–oleate flux was 240±61μmol/min. Thus, only 3%±1% of total plasma FFA–oleate appearance could be accounted for by VLDL–TG spillover. ConclusionThe contribution of VLDL–TG spillover to the total plasma FFA pool is negligible and will not materially affect the interpretation of FFA flux measures as an index of adipose tissue lipolysis.

Spillover of Fatty Acids During Dietary Fat Storage in Type 2 Diabetes

Spillover of lipoprotein lipase-generated fatty acids from chylomicrons into the plasma free fatty acid (FFA) pool is an important source of FFA and reflects inefficiency in dietary fat storage. We measured spillover in 13 people with type 2 diabetes using infusions of a [3H]triolein-labeled lipid emulsion and [U-13C]oleate during continuous feeding, before and after weight loss. Body fat was measured with dual energy X-ray absorptiometry and computed tomography. Participants lost ∼14% of body weight. There was an ∼38% decrease in meal-suppressed FFA concentration (P < 0.0001) and an ∼23% decrease in oleate flux (P = 0.007). Fractional spillover did not change (P = NS). At baseline, there was a strong negative correlation between spillover and leg fat (r = −0.79, P = 0.001) and a positive correlation with the trunk-to-leg fat ratio (R = 0.56, P = 0.047). These correlations disappeared after weight loss. Baseline leg fat (R = −0.61, P = 0.027) but not trunk fat (R = −0.27, P = 0.38) negatively predicted decreases in spillover with weight loss. These results indicate that spillover, a measure of inefficiency in dietary fat storage, is inversely associated with lower body fat in type 2 diabetes.

Liver fatty acid binding protein (L-Fabp) modulates murine stellate cell activation and diet-induced nonalcoholic fatty liver disease

Activation of hepatic stellate cells (HSCs) is crucial to the development of fibrosis in nonalcoholic fatty liver disease. Quiescent HSCs contain lipid droplets (LDs), whose depletion upon activation induces a fibrogenic gene program. Here we show that liver fatty acid-binding protein (L-Fabp), an abundant cytosolic protein that modulates fatty acid (FA) metabolism in enterocytes and hepatocytes, also modulates HSC FA utilization and in turn regulates the fibrogenic program. L-Fabp expression decreased 10-fold following HSC activation, concomitant with depletion of LDs. Primary HSCs isolated from L-FABP(-/-) mice contain fewer LDs than wild-type (WT) HSCs, and exhibit up-regulated expression of genes involved in HSC activation. Adenoviral L-Fabp transduction inhibited activation of passaged WT HSCs and increased both the expression of prolipogenic genes and also augmented intracellular lipid accumulation, including triglyceride and FA, predominantly palmitate. Freshly isolated HSCs from L-FABP(-/-) mice correspondingly exhibited decreased palmitate in the free FA pool. To investigate whether L-FABP deletion promotes HSC activation in vivo, we fed L-FABP(-/-) and WT mice a high-fat diet supplemented with trans-fatty acids and fructose (TFF). TFF-fed L-FABP(-/-) mice exhibited reduced hepatic steatosis along with decreased LD abundance and size compared to WT mice. In addition, TFF-fed L-FABP(-/-) mice exhibited decreased hepatic fibrosis, with reduced expression of fibrogenic genes, compared to WT mice. L-FABP deletion attenuates both diet-induced hepatic steatosis and fibrogenesis, despite the observation that L-Fabp paradoxically promotes FA and LD accumulation and inhibits HSC activation in vitro. These findings highlight the importance of cell-specific modulation of hepatic lipid metabolism in promoting fibrogenesis in nonalcoholic fatty liver disease. (Hepatology 2013).

Synthesis of customized petroleum-replica fuel molecules by targeted modification of free fatty acid pools in Escherichia coli

Biofuels are the most immediate, practical solution for mitigating dependence on fossil hydrocarbons, but current biofuels (alcohols and biodiesels) require significant downstream processing and are not fully compatible with modern, mass-market internal combustion engines. Rather, the ideal biofuels are structurally and chemically identical to the fossil fuels they seek to replace (i.e., aliphatic n- and iso-alkanes and -alkenes of various chain lengths). Here we report on production of such petroleum-replica hydrocarbons in Escherichia coli. The activity of the fatty acid (FA) reductase complex from Photorhabdus luminescens was coupled with aldehyde decarbonylase from Nostoc punctiforme to use free FAs as substrates for alkane biosynthesis. This combination of genes enabled rational alterations to hydrocarbon chain length (Cn) and the production of branched alkanes through upstream genetic and exogenous manipulations of the FA pool. Genetic components for targeted manipulation of the FA pool included expression of a thioesterase from Cinnamomum camphora (camphor) to alter alkane Cn and expression of the branched-chain α-keto acid dehydrogenase complex and β-keto acyl-acyl carrier protein synthase III from Bacillus subtilis to synthesize branched (iso-) alkanes. Rather than simply reconstituting existing metabolic routes to alkane production found in nature, these results demonstrate the ability to design and implement artificial molecular pathways for the production of renewable, industrially relevant fuel molecules.

Ethnic variation in the activity of lipid desaturases and their relationships with cardiovascular risk factors in control women and an at-risk group with previous gestational diabetes mellitus: a cross-sectional study

BackgroundLipid desaturase enzymes mediate the metabolism of fatty acids to long chain polyunsaturated fatty acids and their activities are related to metabolic risk factors for Type 2 diabetes (T2DM) and coronary heart disease (CHD). There are marked ethnic differences in risks of CHD and T2DM but little is known about ethnic differences in desaturase activities.MethodsSamples from a study of CVD risk in women with previous gestational diabetes were analysed for percentage fatty acids in plasma free fatty acid, triglyceride, cholesterol ester and phospholipid pools for 89 white European, 53 African Caribbean and 56 Asian Indian women. The fatty acid desaturase activities, stearoyl-CoA desaturase (SCD, calculated separately for C16 and C18 fatty acids), delta 6 desaturase (D6D) and delta 5 desaturase (D5D) were estimated from precursor-to-product ratios and their relationships with adiposity, blood pressure, cholesterol, triglycerides, HDL cholesterol and insulin sensitivity explored. Ethnic differences in desaturase activities independent of ethnic variation in risk factor correlates of desaturase activities were then identified.ResultsThere was significant ethnic variation in age, BMI, waist circumference, blood pressure, serum triglycerides and HDL cholesterol concentrations and insulin resistance. Desaturase activities showed significant correlations, independent of ethnicity, with BMI, waist circumference, triglycerides and HDL cholesterol. Independent of ethnic variation in BMI, waist circumference, triglycerides and HDL cholesterol, SCD-16 activity, calculated from each of the four lipid pools measured, was 18–35 percent higher in white Europeans than in African Caribbeans or Asian Indians (all p < 0.001). Similar, though less consistent differences were apparent for SCD-18 activity. Also independently of risk factor variation, but specifically when calculated from the cholesterol ester and phospholipid, pools, D6D activity was significantly lower in Asian Indians, and D5D activity higher in African Caribbeans.ConclusionsSignificant ethnic differences exist in desaturase activities, independently of ethnic variation in other risk factors. These characteristics did not accord with higher risk of T2DM among African Caribbeans and Asian Indians nor with lower risk of CHD among African Caribbeans but did accord with the higher risk of CHD in Asian Indians.

Intravenous Niacin Acutely Improves the Efficiency of Dietary Fat Storage in Lean and Obese Humans

Spillover of fatty acids released by lipoprotein lipase hydrolysis of meal triglycerides may be a major contributor to the free fatty acid (FFA) pool. We studied lean (n = 6) and overweight and obese (n = 5) subjects during continuous feeding on two occasions: during intravenous infusion of niacin (2.8 mg/min) and saline. After establishment of steady-state chylomicronemia and suppression of adipose tissue lipolysis with a liquid meal, spillover was measured with infusions of [U-13C]oleate and [3H]triolein. Total FFA concentrations were lower during niacin infusion in both lean (50 ± 4 vs. 102 ± 7 μmol/L; P < 0.002) and obese (75 ± 6 vs. 143 ± 13 μmol/L; P < 0.01) subjects. Oleate appearance was lower during niacin infusion than during saline infusion in both lean (21 ± 2 vs. 32 ± 5 μmol/min; P = 0.07) and obese subjects (25 ± 3 vs. 46 ± 8 μmol/min; P < 0.02). Spillover was lower during niacin infusion than during saline infusion in lean (21 ± 4 vs. 29 ± 3%) and obese (21 ± 2 vs. 29 ± 5%) subjects (P < 0.03 for both). In summary, during meal absorption, niacin produces additional suppression of lipolysis and a reduction in fractional spillover compared with saline in both normal and obese subjects. Infusion of intravenous niacin provides a model for acutely improving dietary fat storage, perhaps by suppressing lipolysis in visceral adipose tissue.

Tracking fatty acid kinetics in distinct lipoprotein fractions in vivo: a novel high-throughput approach for studying dyslipidemia in rodent models

Isotopic tracers have been used to examine lipid trafficking for many years, and data from those studies have typically yielded novel insight regarding the pathophysiology of dyslipidemia. Previous experimental designs were suitable for studies in humans because relatively large volumes of plasma could be regularly sampled. We have expanded on the earlier logic by applying high-throughput analytical methods that require reduced sample volumes. Specifically, we have examined the possibility of coupling gel-based separations of lipoproteins (e.g., lipoprint) with LC-MS/MS analyses of complex lipid mixtures as a way to routinely measure the labeling profiles of distinct lipids in discrete lipoprotein subfractions. We demonstrate the ability to measure the incorporation of [U-(13)C]oleate into triglycerides (TG), PLs (PL), and cholesterol esters (CE) in VLDL, LDL, and HDL particles in mice. Although rodent models of dyslipidemia are inherently different from humans because of alterations in enzyme activities and underlying metabolism, rodent models can be used to screen novel compounds for efficacy in altering a given biochemical pathway and therein enable studies of target engagement in vivo. We expect that it is possible to translate our approach for application in other systems, including studies in humans.

Elongase of long chain fatty acids family 6 (ELOVL6) and stearoyl‐CoA desaturase ‐1 (SCD1) indices suggests potential metabolic benefits in patients with a range of liver fat contents

SCD1 and ELOVL6 enzyme activities and dietary fatty acid composition contribute to the balance of monounsaturated (MUFA), polyunsaturated (PUFA), and saturated fatty acids (SFA) in the plasma free fatty acid (FFA) pool. Given the potential lipotoxic effects of SFA, the present study investigated FFA composition in fasted and meal‐fed (42g fat, 100g carbohydrate) nondiabetic, African American and Hispanic adults (n = 14, BMI 35.6 ± 6.8 kg/m2, 47.7 ± 8.5 yrs) with low (&lt; 5.6%) or high (&gt; 5.6%) liver fat. FFA composition (mol %) was determined by GC, substrate oxidation by indirect calorimetry, and substrate metabolism using stable isotopes. Low ELOVL6 index (18:0/16:0) was associated with high postprandial insulin (r = − 0.622, P = 0.02) and lower in those with high liver fat (P = 0.01). Fasting FFA turnover correlated with FFA 18:1n9 (r = +0.694, P = 0.01) and 18:2n6 (r = +0.642, P = 0.01), and negatively with 18:0 (r = −0.731, P &lt; 0.01) and 16:0 (r = −0.731, P &lt; 0.01). Whole body fat oxidation correlated with 16:1n7 (r = +0.646, P = 0.02) and indices of SCD1 including 18:1n9/18:0 ratio (r = +0.558, P &lt; 0.05) and 16:1n7/16:0 (r = +0.633, P = 0.02). Fat oxidation correlated inversely with 18:0 (r = −0.592, P = 0.03). Thus, 18:1n9 may be a biomarker for both greater FFA turnover and disposal. These data support beneficial effects of MUFA over SFA in overweight subjects and a positive influence of ELOVL6 and SCD1 on insulin sensitivity and liver fat.

FadD Is Required for Utilization of Endogenous Fatty Acids Released from Membrane Lipids

FadD is an acyl coenzyme A (CoA) synthetase responsible for the activation of exogenous long-chain fatty acids (LCFA) into acyl-CoAs. Mutation of fadD in the symbiotic nitrogen-fixing bacterium Sinorhizobium meliloti promotes swarming motility and leads to defects in nodulation of alfalfa plants. In this study, we found that S. meliloti fadD mutants accumulated a mixture of free fatty acids during the stationary phase of growth. The composition of the free fatty acid pool and the results obtained after specific labeling of esterified fatty acids with a Δ5-desaturase (Δ5-Des) were in agreement with membrane phospholipids being the origin of the released fatty acids. Escherichia coli fadD mutants also accumulated free fatty acids released from membrane lipids in the stationary phase. This phenomenon did not occur in a mutant of E. coli with a deficient FadL fatty acid transporter, suggesting that the accumulation of fatty acids in fadD mutants occurs inside the cell. Our results indicate that, besides the activation of exogenous LCFA, in bacteria FadD plays a major role in the activation of endogenous fatty acids released from membrane lipids. Furthermore, expression analysis performed with S. meliloti revealed that a functional FadD is required for the upregulation of genes involved in fatty acid degradation and suggested that in the wild-type strain, the fatty acids released from membrane lipids are degraded by β-oxidation in the stationary phase of growth.

Mobilization of lipid reserves during germination of oat (Avena sativa L.), a cereal rich in endosperm oil

Since the cereal endosperm is a dead tissue in the mature grain, β-oxidation is not possible there. This raises the question about the use of the endosperm oil in cereal grains during germination. In this study, mobilization of lipids in different tissues of germinating oat grains was analysed using thin-layer and gas chromatography. The data imply that the oat endosperm oil [triacylglycerol (TAG)] is not a dead-end product as it was absorbed by the scutellum, either as free fatty acids (FFAs) released from TAG or as intact TAG immediately degraded to FFAs. These data were supported by light and transmission electron microscopy (LM and TEM) studies where close contact between endosperm lipid droplets and the scutellum was observed. The appearance of the fused oil in the oat endosperm changed into oil droplets during germination in areas close to the aleurone and the scutellar epithelium. However, according to the data obtained by TEM these oil droplets are unlikely to be oil bodies surrounded by oleosins. Accumulation of FFA pools in the embryo suggested further transport of FFAs from the scutellum. Noticeably high levels of TAG were also accumulated in the embryo but were not synthesized by re-esterification from imported FFAs. Comparison between two oat cultivars with different amounts of oil and starch in the endosperm suggests that an increased oil to starch ratio in oat grains does not significantly impact the germination process.

Assessment of the health and antioxidant trade-off in gilthead sea bream ( Sparus aurata L.) fed alternative diets with low levels of contaminants

The aim of the present work was to analyze the effect of partial and total replacement of fish oil (FO) by a blend of vegetable oils on the health and antioxidant status of gilthead sea bream ( Sparus aurata L.) fed primarily plant protein-based diets. The study included measurements of feed-borne contaminants, gene expression analyses of detoxifying and antioxidant pathways and measures of antioxidant and innate immune descriptors. Polybrominated diphenyl ethers (PBDEs) were almost undetectable in all diets, and the loading-charges of polychlorinated biphenyls (PCBs), dioxin-like PCBs, organochlorine pesticides (OCs), and polycyclic aromatic hydrocarbons (PAHs) were at trace levels decreasing their concentrations according to the level of FO replacement with vegetable oils (0%, 33%, 66%, and 100%). Hepatic detoxifying pathways were down regulated by FO replacement, and the hepatic transcription of cytochrome P450 1A1 and aryl hydrocarbon receptor 1 was significantly reduced in fish fed the 100% vegetable oil diet. Dietary intervention did not alter the hepatic expression of the recycling glutathione reductase, whereas glutathione peroxidase-1 and phospholipid glutathione peroxidase were either down- or up-regulated by total FO replacement. This suggests that vegetable oils prime the in situ repair of peroxidized phospholipids rather than the increased turnover of membrane phospholipids from the undamaged pool of cytosolic free fatty acids. The hepatic expression of non-enzymatic antioxidants (metallothionein, glucose regulated protein 75) was down regulated in fish fed 66% and 100% vegetable oil diets. Hepatic glutathione levels and total plasma antioxidant capacity were also lowest in fish fed high levels of vegetable oils, but the concurrent increase in the GSH/GSSG ratio was interpreted as an index of reduced oxidative stress. This redox balance agrees with the enhanced respiratory burst of blood leucocytes after phorbol myristate acetate stimulation in fish feed the 100% vegetable oil. Total plasma peroxidases and plasma alternative complement pathway were not affected by dietary treatment, whereas plasma lysozyme was significantly decreased in fish fed the 66% vegetable oil diet. Taken together, the results suggest that the health and the antioxidant status of gilthead sea bream was not damaged by high levels of FO replacement in eco-friendly diets, but both the scavenging and production of reactive oxygen species were modulated in concert by complex and nutritionally mediated readjustments.

THE INTRACELLULAR FREE FATTY ACID POOL IN ADIPOSE TISSUE

Journal Article The Intracellular Free Fatty Acid Pool in Adipose Tissue Get access Nutrition Reviews, Volume 20, Issue 5, May 1962, Pages 154–157, https://doi.org/10.1111/j.1753-4887.1962.tb04600.x Published: 01 May 1962

Role of GPR81 in lactate-mediated reduction of adipose lipolysis

Heavy exercise or oxygen deficit often links with higher levels of arterial lactate and lower levels of plasma free fatty acids (FFA). Treatment with lactate reduces circulating levels of FFA in vivo and lipolysis in adipose tissues in vitro. However, the underlying mechanism has remained unclear. Here we employ pharmacological and genetic approaches to show that GPR81, an orphan G-protein-coupled receptor with relatively restricted expression in the adipose tissues, functions as a receptor for lactate and can mediate an anti-lipolytic effect of lactate. GPR81 may thus function as a sensor of lactate that can modulate the FFA pool under exercise or conditions of oxygen deficit.

The signal molecule lysophosphatidylcholine in Eschscholzia californica is rapidly metabolized by reacylation

In cultured cells of California poppy (Eschscholzia californica), lysophosphatidylcholine (LPC) triggers a signal path that finally induces alkaloid biosynthesis. LPC is transiently generated by elicitor-activated phospholipase A(2) of the plasma membrane. Externally added LPC is rapidly acylated by a membrane-bound enzyme that shows the highest specific activity in the purified plasma membrane. The fatty acid incorporated into the sn-2 position of LPC is preferentially linoleic (18:2), which is the most abundant acyl component in the PC species of Eschscholzia cells, but a minor component of the pool of free fatty acids. The fatty acid at the sn-1 position of LPC is less important for substrate specificity. The capacity of LPC acylation by intact cells or isolated plasma membranes by far exceeds the rate of LPC generation by activated phospholipase A(2) and is not limited by the availability of acyl donors. Metabolites other than phosphatidylcholine (PC) were not significantly produced from labeled LPC within 20 min, indicating that lysophospholipases are not significantly contributing to the short-time metabolism of LPC. It is concluded that reacylation to PC is the dominating process in the detoxication of LPC and ensures the transient character of its steady state concentrations, even at maximum phospholipase A(2) activities.

Effects of progressive drought stress on the expression of patatin‐like lipid acyl hydrolase genes in Arabidopsis leaves

Patatin-like genes have recently been cloned from several plant species and found to be involved in stress responses and development. In previous work, we have shown that a patatin-like gene encoding a galactolipid acyl hydrolase (EC 3.1.1.26) was stimulated by drought in the leaves of the tropical legume, Vigna unguiculata L. Walp. The aim of the present work was to study the expression of patatin-like genes in Arabidopsis thaliana under water deficit. Expression of six genes was studied by reverse transcriptase polymerase chain reaction in leaves of plants submitted to progressive drought stress induced by withholding water and also in different plant organs. Three genes, designated AtPAT IIA, AtPAT IVC and AtPAT IIIA, were shown to be upregulated by water deficit but with different kinetics, while the other patatin-like genes were either constitutive or not expressed in leaves. The accumulation of transcripts of AtPAT IIA in the early stages of the drought treatment was coordinated with the upregulation of lipoxygenase and allene oxide synthase genes. AtPAT IIA expression was also induced by wounding and methyl jasmonate treatments. The in vitro lipolytic activity toward monogalactosyldiacylglycerol, digalactosyldiacylglycerol, phosphatidylcholine and phosphatidylglycerol was confirmed by producing the recombinant protein ATPAT IIA in insect cells. The analysis of free fatty acid pools in drought-stressed leaves shows an increase in the relative amounts of trans-3-hexadecenoic acid at the beginning of the treatment followed by a progressive accumulation of linoleic and linolenic acids. The possible roles of AtPAT IIA in lipid signaling and membrane degradation under water deficit are discussed.

Ferrous, But Not Ferric, Iron Maintains Homeostasis in Histoplasma capsulatum Triacylglycerides

Iron is an indispensable micronutrient for virtually all microorganisms, where it acts as a cofactor of many enzymes involved in regulation of multiple cellular and physiological functions. This metal is also considered an important determinant contributing to the pathogenesis of fungal infectious diseases, and therefore the identification of iron-regulated metabolic processes occurring within the invading fungal cell can help the development of new antifungal therapeutic strategies. In this study, we examined relationships between iron availability and neutral storage lipids in Histoplasma capsulatum, a dimorphic fungus responsible for the most common respiratory and systemic mycosis in humans. Yeast cells were grown in a defined minimal medium supplemented with or without iron. Lipids were extracted from cells at the log and late stationary growth phases, then separated by thin-layer chromatography, and fatty acids were analyzed by gas chromatography. A culture age-related decrease in the unsaturated fatty acid content was observed in all four neutral lipid classes examined. Iron-related alterations could be seen in relation to triacylglycerol and free fatty acid pools, whereas no iron-dependent effects were detected in diacylglycerol and steryl ester fractions. Regarding triacylglycerols, the presence of iron positively affected the content of unsaturated fatty acids, and this stabilizing action of iron was notably increased when ferrous ions were added. Subsequent iron uptake studies showed a definite preference of H. capsulatum to acquire iron in its reduced, more soluble, ferrous form, and therefore, the availability of iron may be the underlying reason for the observed iron-maintained homeostasis in H. capsulatum triacylglycerols.

Contribution of Triglyceride-rich Lipoproteins to Plasma Free Fatty Acids

Free fatty acids are the major lipid fuel of the body. Dysregulation of adipose tissue lipolysis results in increased plasma free fatty acid concentrations, and via that mechanism contributes to insulin resistance in obesity and type 2 diabetes mellitus. Adipose tissue hormone sensitive lipase is thought to be responsible for the production of the majority of free fatty acids. However, a separate contribution comes from the action of endothelial lipases, especially lipoprotein lipase, on triglyceride-rich lipoproteins via a process known as spillover. The primary substrate for spillover appears to be chylomicrons derived from dietary fat. The spillover of fatty acids into the free fatty acid pool varies from one tissue to another. For example, spillover is low ( approximately 14%) in the forearm of healthy volunteers, suggesting that triglyceride fatty acid storage is relatively efficient in skeletal muscle. In contrast, spillover appears to be higher in adipose tissue and may also be higher in the splanchnic bed, based on preliminary data. If systemic spillover is increased in insulin resistant states such as diabetes, this could represent a mechanism contributing to the abnormal increases in plasma concentrations of free fatty acids in that condition.

Flavour development via lipolysis of milkfats: changes in free fatty acid pool

SummaryUnder the trade name lipolysed milkfat (LMF), concentrated cheese flavours obtained via enzymatic treatments of cheese (or other dairy substrates) have been made available in increasing numbers. In this research effort, (anhydrous) milkfats from cows, ewes and goats were used as substrates for production of cheesy flavours. Those milkfats were subjected to modifications brought about by ten different (commercial) lipases and one cutinase, and the free fatty acids released were analysed by high performance liquid chromatography. Both the degrees of hydrolysis and the free fatty acid profiles of the final products were similar to those reported for several LMF products, although specific keynotes could be pinpointed. Consequently, those milkfats may represent alternative raw materials for manufacture of cheesy flavours, while contributing to alleviate the problem derived from the increasing surplus of milkfat in Western countries.

Changes in the pool of free fatty acids in ovine, bovine and caprine milk fats, effected by viable cells and cell-free extracts of Lactococcus lactis and Debaryomyces vanrijiae

Lipolysis catalysed by lipases, native or released by natural microflora in milk, plays a key role in development of aroma and flavour throughout cheese ripening. This research effort was aimed at a deeper understanding of the action of two wild strains used in traditional ewe’s milk cheesemaking in Portugal, viz. Lactococcus lactis and Debaryomyces vanrijiae. They were both tested as viable cells and cell-free extracts – using bovine, ovine and caprine milk fat emulsions as model substrates. Hydrolysis reactions were carried out at 30 and 37 °C, in the case of L. lactis and D. vanrijiae, respectively; the contents of short- and medium-chain fatty acids were determined by high pressure liquid chromatography. Our experimental results showed general trends, viz. preferential depletion of medium chain fatty acids throughout the whole reaction time. However, distinct patterns were observed towards different substrates, depending on the source and form of the biocatalyst at stake.