Alpha-linolenic acid: functions and effects on linoleic acid metabolism and eicosanoid-mediated reactions

Bioactivity of Macronutrients from Chlorella in Physical Exercise

Chlorella is a marine microalga rich in proteins and containing all the essential amino acids. Chlorella also contains fiber and other polysaccharides, as well as polyunsaturated fatty acids such as linoleic acid and alpha-linolenic acid. The proportion of the different macronutrients in Chlorella can be modulated by altering the conditions in which it is cultured. The bioactivities of these macronutrients make Chlorella a good candidate food to include in regular diets or as the basis of dietary supplements in exercise-related nutrition both for recreational exercisers and professional athletes. This paper reviews current knowledge of the effects of the macronutrients in Chlorella on physical exercise, specifically their impact on performance and recovery. In general, consuming Chlorella improves both anaerobic and aerobic exercise performance as well as physical stamina and reduces fatigue. These effects seem to be related to the antioxidant, anti-inflammatory, and metabolic activity of all its macronutrients, while each component of Chlorella contributes its bioactivity via a specific action. Chlorella is an excellent dietary source of high-quality protein in the context of physical exercise, as dietary proteins increase satiety, activation of the anabolic mTOR (mammalian Target of Rapamycin) pathway in skeletal muscle, and the thermic effects of meals. Chlorella proteins also increase intramuscular free amino acid levels and enhance the ability of the muscles to utilize them during exercise. Fiber from Chlorella increases the diversity of the gut microbiota, which helps control body weight and maintain intestinal barrier integrity, and the production of short-chain fatty acids (SCFAs), which improve physical performance. Polyunsaturated fatty acids (PUFAs) from Chlorella contribute to endothelial protection and modulate the fluidity and rigidity of cell membranes, which may improve performance. Ultimately, in contrast to several other nutritional sources, the use of Chlorella to provide high-quality protein, dietary fiber, and bioactive fatty acids may also significantly contribute to a sustainable world through the fixation of carbon dioxide and a reduction of the amount of land used to produce animal feed.

The Egg Yolk Content in ω-3 and Conjugated Fatty Acids Can Be Sustainably Increased upon Long-Term Feeding of Laying Hens with a Diet Containing Flaxseeds and Pomegranate Seed Oil

Long-term feeding trials examining the incorporation of conjugated linolenic acids (CLnA) into the diet of laying hens are lacking. In the present study, we compared two diets in sixty-six red Sex-Link hens (33 hens/treatment), fed for 26 weeks. The control diet was high in oleic acid, while the test diet was high in α-linolenic acid (ALA) and punicic acid (PunA). No significant differences were observed between treatments for hens’ performance, egg weight and yolk weight. In contrast, dietary ALA and PunA resulted in a significant increase in n-3 PUFA, rumenic acid (RmA) and PunA contents in egg yolk, as well as in the liver, heart, muscle and adipose tissue of the hens. Other conjugated dienes resulting from the metabolism of PunA or RmA also accumulated in the egg yolk and tissues. Unlike DHA, which was exclusively distributed in phospholipids, ALA, RmA and PunA were preferably distributed in triglycerides.

Is there a beneficial effect of gamma-linolenic acid supplementation on body fat in postmenopausal hypertensive women? A prospective randomized double-blind placebo-controlled trial

OBJECTIVE

Systemic arterial hypertension and obesity are major public health problems that increase risks of serious cardiovascular diseases and kidney failure as well as increase mortality. Substances that can alleviate these problems are desirable. We evaluated the beneficial effects of nutritional supplementation with gamma-linolenic acid in postmenopausal hypertensive women.

METHODS

This was a prospective, double-blind, placebo-controlled, randomized study involving 96 postmenopausal women. Participants were divided into two groups either receiving 1,000 mg of borage oil rich in gamma-linolenic acid + vitamin E (drug) or only vitamin E (placebo) capsules for 6 months. They were followed up monthly to assess the impact on systemic blood pressure and body composition. To verify group homogeneity, Fisher's exact and Student t tests were performed. To evaluate differences in various parameters between the two groups and at various times, repeated measures analysis of variance was performed, with Bonferroni correction.

RESULTS

The power of the test was calculated based on the difference in the mean systolic blood pressure between baseline and after 6 months of treatment in the placebo group and in the drug group. A 92.9% test power was found with a 95% confidence interval. There was a significant reduction in the systolic and diastolic pressure as well as a significant change in waist-hip ratio (P < 0.01) in the drug group as compared with the placebo group.

CONCLUSIONS

Supplementation with borage oil rich in gamma-linolenic acid had significant beneficial short-term effects without showing any adverse effect. There remains a need for further studies to evaluate long-term benefits.

Effects of ammonia stress, dietary linseed oil and Edwardsiella ictaluri challenge on juvenile darkbarbel catfish Pelteobagrus vachelli

A two-stage study was carried out to test the response of juvenile darkbarbel catfish Pelteobagrus vachelli to ammonia stress, dietary lipid and bacterial challenge. At stage 1, the catfish (0.99 ± 0.01 g) fed a commercial diet were exposed to 0.01 and 5.70 mg L(-1) total ammonia nitrogen in nine replicates for 14 days. At stage 2, all fish previously exposed to either low or high ammonia were separately transferred into low ammonia (<0.01 mg L(-1)), and divided into three feeding groups. Fish were then fed three levels of linseed oil (0, 2 and 4%) in triplicate for 46 days. Fish growth performance and immune response were low in high ammonia at stage 1. At stage 2, fish growth and immune response were not significantly different between fish previously exposed to low and high ammonia in all diets. Fish fed 4% linseed oil showed the greatest weight gain, feed efficiency ratio, red blood cells, hemoglobin and hematocrit, and achieved higher lysozyme activity, phagocytic index, respiratory burst and total immunoglobulin than fish fed 0% linseed oil, but did not differ from fish fed 2% linseed oil regardless of previous ammonia exposure. After 14-day infection of Edwardsiella ictaluri, cumulative mortality of fish previously exposed to low ammonia was lower than that of fish exposed to high ammonia in all diets. Cumulative mortality of fish fed 0% linseed oil was highest, but the antibody titer of fish fed 4% linseed oil was highest regardless of previous ammonia treatments. This study indicates that ammonia stress has a lasting effect even after ammonia is lowed, but the adverse effect on fish can be mitigated through manipulation of dietary oil inclusion, especially under the challenge of pathogenic bacteria.

Characterization of Longissimus thoracis, Semitendinosus and Masseter muscles and relationships with technological quality in pigs. 2. Composition of muscles

The composition of three porcine muscles (Longissimus thoracis: LT, Semitendinosus: ST, Masseter: MS) was characterized and its link with muscle quality was evaluated. The LT muscle had a higher content of tyrosine, tryptophan, and carbohydrates and a lower content of vitamin E and haem iron than the MS muscle, while the ST had similar composition to MS but a lower content of haem iron. Large differences between muscles were observed in relative amounts of most of the major fatty acids. The LT muscle had higher saturated fatty acids (SFA) and n-6:n-3 fatty acid ratio, and lower polyunsaturated fatty acids (PUFA), PUFA:SFA ratio, unsaturation index and average fatty acid chain length than the ST and MS muscles. Muscle pH, redness and chroma were positively correlated with vitamin E and unsaturated lipids and negatively correlated with tyrosine, tryptophan, carbohydrates and saturated lipids, whereas muscle lightness and expressible juice showed similar correlations but an opposite sign with these variables.

Characterization of the n-3 polyunsaturated fatty acid enrichment in laying hens fed an extruded flax enrichment source

The time required to reach a plateau of n-3 polyunsaturated fatty acid (PUFA) concentration in plasma and egg yolk and dynamics of the enrichment process were examined in laying hens. A group of 75 Lohmann White Leghorn layers (65 wk) were fed one of 3 diets: control, moderate, or high n-3 PUFA-enriched diet for 18 d. Diets provided similar ME and CP and contained 0, 7.5%, or 15% LinPRO (source of n-3 PUFA), respectively. Prior to dietary treatment, baseline values were established for the BW, fatty acid composition in egg yolk on a whole-egg basis, and in plasma. These measurements were repeated at 6, 12, and 18 d of feeding. Enzymatic conversion rates of linolenic acid (LNA) to long-chain fatty acids were calculated. Data were analyzed with Proc Mixed of SAS, and broken stick analysis was used to determine n-3 PUFA plateau using the NLIN procedure of SAS (P < 0.05). The total egg yolk n-3 PUFA reached a plateau of 343.7 mg/egg and 272.9 mg/egg after 6.6 and 5.9 d on the high and moderate diets, respectively. In blood plasma, the n-3 PUFA concentrations reached saturation in 7.2 d with 0.93 mg/mL and 0.67 mg/mL on high and moderate diets, respectively. The transfer efficiency of total n-3 PUFA from the diet to the egg yolk was calculated as 55.6% in control birds, 30.5% in moderate birds, and 22.2% in high birds, demonstrating reduced transfer efficiency of n-3 PUFA as inclusion in the feed increases. Final egg yolk n-3 PUFA concentrations had a CV of 16.5% compared with 28.5% for plasma. After 12 d, the long-chain n-3 PUFA [eicosapentaenoic acid (EPA), docosapentaenoic acid (DPA), and docosahexaenoic acid (DHA)] were significantly higher in egg yolk from hens on the moderate and high enriched diets compared with those from hens fed the control diet, whereas in plasma values did not differ. Broken stick analysis of egg enrichment indicated that high birds reached the target threshold of 300 mg of total n-3 PUFA/egg in 5 d. A significant increase in EPA, DPA, and DHA and reduction in arachidonic acid content in egg yolks from hens fed enriched diets compared with the control diet confirms competition for enzymes during postabsorptive modification of these fatty acids. This work contributes to the understanding of individual hen effects on n-3 PUFA absorption and the effect of level of dietary enrichment with an extruded flax product on final yolk n-3 PUFA concentration.

Effects of dietary n-6:n-3 ratio on immune and reproductive systems of pullet chicks

The objective of this study was to examine the effects of dietary n-6:n-3 ratio on immune and reproduction systems of Leghorn pullet chicks. A total of 216 Hy-Line W-36 pullet chicks (1 d old) were randomly assigned to 3 diets (n-6:n-3 ratios of 10, 6, and 2) until 22 wk of age. The Optomega-50 (Optivite International Ltd., Nottinghamshire, UK) containing 50% salmon fish oil was used as an n-3 source. Pullets were injected with SRBC suspension at 6 and 9 wk and anti-SRBC titers were measured 7 and 14 d after each immunization. The antibody (Ab) titers for Newcastle disease (ND), avian influenza, infectious bronchitis (IB), and infectious bursal disease (IBD) were determined at 4, 6, 10, 14, and 18 wk of age. Pullets fed diet with the n-6:n-3 ratio of 2 had higher feed consumption and lower BW gain (P < 0.05) compared those fed diets with the ratios of 6 and 10. The results demonstrated that the different dietary n-6:n-3 ratios did not have a significant effect on the anti-SRBC titers in pullets serum (P > 0.05). The Ab production against avian influenza vaccine was increased in pullets fed diet containing the n-6:n-3 ratio of 10 at wk 10 and 14 and increased for ND at only 14 wk (P < 0.05). On the other hand, the Ab response to IBD (14 wk) and IB (14 wk) vaccines was increased when pullets were fed diet containing a ratio of 6 (P < 0.05). The pullets fed diet with the n-6:n-3 ratio of 2 showed lower egg production and late sexual maturity (P > 0.05) whereas ovary weight (P = 0.01) and number of large yellow follicles (P = 0.049) were significantly decreased at first oviposition. Our results revealed that the supplementation of Optomega-50 as a source of n-3 to decrease the n-6:n-3 ratio in diet significantly increased Ab production for ND, IB, and IBD in pullet chicks with slight reduction in reproductive organs weight at early production.

The influence of dietary supplementation of arachidonic acid on prostaglandin production and oxidative stress in the Pacific oyster Crassostrea gigas

In a previous study, dietary supplementation with arachidonic acid (ARA) to oysters Crassostrea gigas increased haemocyte numbers, phagocytosis, and production of reactive oxygen species level (ROS) by haemocytes (Delaporte et al., 2006). To assess if the observed stimulation of these cellular responses resulted from changes of ARA-related prostaglandin (PG) production, we analysed prostaglandin E2 metabolite (PGEM) content on the same oysters fed three levels of ARA. Dietary supply of polyunsaturated fatty acids (PUFA) could also induce an oxidative stress that could similarly increase cellular responses; therefore, two indicators of oxidative stress were analysed: peroxidation level and antioxidant defence status. Together the observed positive correlation between ARA and PGEM levels and the absence of lipid peroxidation and antioxidant activity changes supports the hypothesis of an immune stimulation via PG synthesis. Although ARA proportion in oyster tissues increased by up to 7-fold in response to ARA dietary supplementation, peroxidation index did not change because of a compensatory decrease in n-3 fatty acid proportion, mainly 22:6n-3. To further confirm the involvement of PG in the changes of haemocyte count, phagocytosis and ROS production upon ARA supplementation, it would be interesting to test cyclooxygenase and lipooxygenase inhibitors in similar experiments.

Fatty acid and vitamin E composition of intramuscular fat in cattle reared in different production systems

The aim of this study was to evaluate the fatty acid composition of intramuscular fat and the vitamin E content of beef from different production systems. Four cattle production systems were used: cattle reared under intensive conditions and fed concentrate (INT1) from Spain, cattle raised at pasture and supplemented with concentrate (SUP1) from the United Kingdom, cattle raised at pasture and on corn silage (SUP2) from Germany and cattle reared under extensive conditions slaughtered at two and three years old (EXT2 and EXT3) from Uruguay. The highest proportion and content (mg per 100g of muscle) of linoleic acid (C18:2n-6) and arachidonic acid (C20:4n-6) and the lowest saturated fatty acids (SFA) was found in INT1 beef. In contrast, beef reared under extensive conditions showed the highest proportion and content of linolenic acid (C18:3n-3), docosapentaenoic acid (DPA, C22:5n-3) and eicosapentaenoic acid (EPA, C20:5n-3), and SUP1 and SUP2 beef showed the highest level of palmitic acid (C16:0) and SFA. Beef from intensive system (INT1) had the lowest P/S (PUFA/SFA) ratio, whereas beef from extensive system (EXT2 and EXT3) had the lowest n-6/n-3 ratio. The results of the PCA (principal components analysis) of fatty acid composition showed that beef from intensive system (INT1) was clearly differentiated from the other meats and was located with the C18:2n-6 and C20:4n-6 and the n-6/n-3 ratio. EXT2 and EXT3 beef were located with C18:3n-3 and long chain fatty acids. Beef from extensive systems had the highest concentration of vitamin E (3.91mg α-tocopherol/kg muscle).

Essential fatty acid synthesis and its regulation in mammals

The tissue content of highly unsaturated fatty acids (HUFA) such as arachidonic acid and docosahexaenoic acid is maintained in a narrow range by feedback regulation of synthesis. Delta-6 desaturase (D6D) catalyzes the first and rate-limiting step of the HUFA synthesis. Recent identification of a human case of D6D deficiency underscores the importance of this pathway. Sterol regulatory element binding protein-1c (SREBP-1c) is a key transcription factor that activates transcription of genes involved with fatty acid synthesis. We recently identified sterol regulatory element (SRE) that is required for activation of the human D6D gene by SREBP-1c. Moreover, the same SRE also mediates the suppression of the D6D gene by HUFA. The identification of SREBP-1c as a key regulator of D6D suggests that the major physiological function of SREBP-1c in liver may be the regulation of phospholipid synthesis rather than triglyceride synthesis. Peroxisome proliferators (PP) induce fatty acid oxidation enzymes and desaturases in rodent liver. However, the induction of desaturases by PP is slower than the induction of oxidation enzymes. This delayed induction may be a compensatory reaction to the increased demand of HUFA caused by increased HUFA oxidation and peroxisome proliferation in PP administration. Recent studies have demonstrated a critical role of peroxisomal beta-oxidation in DHA synthesis, and identified acyl CoA oxidase and D-bifunctional protein as the key enzymes.

Delayed induction of delta-6 and delta-5 desaturases by a peroxisome proliferator

Delta-6 desaturase (D6D) is the key enzyme for the synthesis of highly unsaturated fatty acids (HUFA) such as arachidonic acid (AA) and docosahexaenoic acid (DHA) in mammals. Transcription of D6D gene is activated by both sterol regulatory element binding protein-1c (SREBP-1c) and peroxisome proliferators (PP). This response of D6D is paradoxical because SREBP-1c transactivates genes for fatty acid synthesis in liver, while PP induce enzymes for fatty acid oxidation. We hypothesized that the induction of D6D gene by PP is a compensatory response to the increased HUFA demand caused by peroxisome proliferation and induction of fatty acid oxidation. We investigated the time-course effects of a PP, Wy14643, on the induction of HUFA metabolizing genes and HUFA profile in rat liver. The mRNA of fatty acid oxidation enzymes in the Wy14643 fed group became significantly higher than controls at 4 h and reached maximum within 28 h. In contrast, the mRNA of delta-6 and delta-5 desaturases in the Wy14643 group was not significantly higher than control at 4 h and took >28 h to reach the maximum. Despite the induction of HUFA synthetic pathway, the concentration of end products (AA and DHA) remained unchanged throughout the 4-day period in liver phospholipids and non-esterified fatty acids. Taken together, this study supports our hypothesis and suggests that peroxisome proliferation and induction of fatty acid oxidation enzymes are the major mechanisms of the induction of HUFA synthesis by PP.

Metabolism and functions of highly unsaturated fatty acids: an update

This review briefly examines the recent progress in knowledge about the synthesis and degradation of highly unsaturated fatty acids (HUFA) and their functions. Following the cloning of mammalian Delta6-desaturase (D6D), the D6D mRNA was found in many tissues, including adult brain, maternal organs, and fetal tissue, suggesting an active synthesis of HUFA in these tissues. The cloning also confirmed the long-postulated hypothesis that the same pathway is followed in n-6 and n-3 HUFA synthesis. Dietary n-6 and n-3 HUFA both induce fatty acid oxidation enzymes in peroxisomes when compared to their respective precursor polyunsaturated fatty acids. This suggests that peroxisomes may be the primary site of HUFA degradation when HUFA are supplied in excess from the diet. Peroxisome proliferators strongly induce the enzymes for the HUFA synthesis. The mechanism of this induction is currently unknown. Recent studies revealed new HUFA functions that are not mediated by eicosanoids. These functions include endocytosis/exocytosis, ion-channel modulation, DNA polymerase inhibition, and regulation of gene expression. These new discoveries will enable us to re-examine the underlying mechanisms for the classical symptoms of essential fatty acid deficiency as well as vitamin E deficiency. Progress has also been made in understanding the mechanism by which dietary HUFA reduce body fat deposition. One mechanism is induction of genes for fatty acid oxidation, which is mediated by peroxisome proliferator-activated receptor-alpha. Another likely mechanism is that HUFA suppress genes for fatty acid synthesis by reducing both mRNA and protein maturation of sterol regulatory element binding protein-1.

Linoleic acid uptake by isolated enterocytes: influence of alpha-linolenic acid on absorption

In a previous study we showed that intestinal uptake of alpha-linolenic acid (18:3n-3) was carrier-mediated and we suggested that a plasma membrane fatty acid protein was involved in the transport of long-chain fatty acids. To further test this hypothesis, the mechanism of linoleic acid (18:2n-6) uptake by isolated intestinal cells was examined using a rapid filtration method and 20 mM sodium taurocholate as solubilizing agent. Under these experimental conditions transport of [1-14C]linoleic acid monomers in the concentration range of 2 to 2220 nM was saturable with a Vm of 5.1 +/- 0.6 nmol/mg protein/min and a Km of 183 +/- 7 nM. Experiments carried out in the presence of metabolic inhibitors, such as 2,4-dinitrophenol and antimycin A, suggested that an active, carrier-mediated mechanism was involved in the intestinal uptake of this essential fatty acid. The addition of excess unlabeled linoleic acid to the incubation medium led to a 89% decrease in the uptake of [1-14C]linoleic acid, while D-glucose did not compete for transport into the cell. Other long-chain polyunsaturated fatty acids added to the incubation mixture inhibited linoleic acid uptake by more than 80%. The presence of alpha-linolenic acid (18:3n-3) in the incubation medium caused the competitive inhibition (Ki = 353 nM) of linoleic acid uptake. The data are compatible with the hypothesis that intestinal uptake of both linoleic, and alpha-linolenic acid is mediated by a membrane carrier common to long-chain fatty acids.

Phospholipid molecular species from human placenta lipids

The phospholipid molecular species from a large-scale preparation of human placenta lipids were analyzed. The major placental phospholipids were choline glycerophospholipids (CPL) (53.2 wt%), sphingomyelin (21.7 wt%) and ethanolamine glycerophospholipids (EPL) (14.6 wt%). 1,2-Diacyl-glycerophosphocholine was the most abundant subclass of CPL (91.7 mol%), while EPL contained 1,2-diacyl (54.6 mol%) and 1-alk-1'-enyl-2-acyl (43.8 mol%) subclasses. The level of polyunsaturated fatty acids (PUFA) in total phospholipids was remarkably constant (38.4-39.9 mol%) within all placental batches tested. The long-chain PUFA, mainly 20:4n-6 and 22:6n-3 of the n-6 and n-3 series, respectively, were found in high proportion in all phospholipid classes, especially in EPL (46.7 mol%) and in inositol glycerophospholipids (IPL) (39.9 mol%). CPL and serine glycerophospholipids were much richer in 18:1n-9 and 18:2n-6. High levels of molecular species with arachidonic acid in the sn-2 position were found particularly in 1-alk-1'-enyl-2-acyl-glycerophosphoethanolamine (with 24.0 mol% 16:0 and 22.0 mol% 18:0 in sn-1 position) and in 1,2-diacyl glycerophosphoinositol with 42.6 mol% 18:0 in sn-1 position. EPL subclasses were rich in 22:6n-3, which occurs mainly as 16:0/22:6n-3 (11.7 mol%) in the plasmalogen form and as 18:0/22:6n-3, 16:0/22:6n-3 and 18:1/22:6n-3 in the diacyl forms. Based on their availability and composition, placental phospholipids could be of interest, for example, for supplementing artificial milk preparations with n-3 and n-6 long-chain PUFA for newborn infants with insufficiently developed 18:2n-6 and 18:3n-3 desaturation/elongation.