Metabolism of alpha-linolenic acid in humans

Alpha-linolenic acid (18:3n-3) is essential in the human diet, probably because it is the substrate for the synthesis of longer-chain, more unsaturated n-3 fatty acids eicosapentaenoic acid (20:5n-3) and docosahexaenoic acid (22:6n-3) which are required for tissue function. This article reviews the recent literature on 18:3n-3 metabolism in humans, including fatty acid beta-oxidation, recycling of carbon by fatty acid synthesis de novo and conversion to longer-chain polyunsaturated fatty acids (PUFA). In men, stable isotope tracer studies and studies in which volunteers increased their consumption of 18:3n-3 show conversion to 20:5n-3 and 22:5n-3, but limited conversion to 22:6n-3. However, conversion to 18:3n-3 to 20:5n-3 and 22:6n-3 is greater in women compared to men, due possibly to a regulatory effect of oestrogen, while partitioning of 18:3n-3 towards beta-oxidation and carbon recycling was lower than in men. These gender differences may be an important consideration in making dietary recommendations for n-3 PUFA intake

Biochemical analysis of proteolytic fragments from desmosomal glycoproteins

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Conversion of alpha-linolenic acid to palmitic, palmitoleic, stearic and oleic acids in men and women

The purpose of this study was to determine whether adult humans can recycle carbon from alpha-linolenic acid (18:3n-3) into saturated (SFA) and monounsaturated (MUFA) fatty acids. Six men and six women consumed 700 mg [U-13C]-18:3n-3. Blood was collected over 21 days and breath over 24h. [13C]-labelled SFA and MUFA were detected in plasma phosphatidylcholine (PC) and triacylglycerol (TAG). Total labelled fatty acid incorporation into SFA and MUFA was five- and 25-fold greater in PC than TAG in men and women, respectively. [13C]-16:0 was the major labelled fatty acid in both fractions. Total [13C] incorporation into SFA and MUFA was 20% greater in men than women, and related positively (r(2) = 0.35, P<0.05) to the fractional recovery of labelled 18:3n-3 as 13CO2 on breath. These results suggest that the extent of partitioning towards beta-oxidation and carbon recycling may regulate the availability of 18:3n-3 for conversion to longer-chain fatty acids

Maternal diet as a modifier of offspring epigenetics

There has been a substantial body of evidence, which has shown that genetic variation is an important determinant of disease risk. However, there is now increasing evidence that alterations in epigenetic processes also play a role in determining susceptibility to disease. Epigenetic processes, which include DNA methylation, histone modifications and non-coding RNAs play a central role in regulating gene expression, determining when and where a gene is expressed as well as the level of gene expression. The epigenome is highly sensitive to a variety of environmental factors, especially in early life. One factor that has been shown consistently to alter the epigenome is maternal diet. This review will focus on how maternal diet can modify the epigenome of the offspring, producing different phenotypes and altered disease susceptibilities

Lack of effect of meal fatty acid composition on postprandial lipid, glucose and insulin responses in men and women aged 50-65 years consuming their habitual diets

The aim of the study was to determine the effect of consuming meals with different fatty acid compositions on the postprandial changes over 6 h in plasma triacylglycerol, NEFA, total cholesterol, glucose and insulin concentrations in middle-aged men and women. Men (n 11; 58 (5) years) and women (n 11; 56 (4) years) consumed four test meals with a similar macronutrient energy content in random order: a reference meal based on the habitual pattern of fatty acid intake in the UK, a meal with an increased (155 %) linoleic acid (LA) to alpha-linolenic acid (alphaLNA) ratio (high LA:alphaLNA), a meal with increased (23 %) MUFA content (high MUFA) and a meal with increased (583 %) EPA and DHA content (high EPA+DHA). The high-LA:alphaLNA and high-EPA+DHA meals selectively increased the ratio of LA to alphaLNA (men 341 %; women 310 %) and the EPA+DHA (men 414 %; women 438 %) concentration in plasma triacylglycerol. The high-MUFA meal did not alter the change in MUFA content of the plasma. Plasma triacylglycerol, NEFA, glucose and insulin, but not total cholesterol, concentrations changed significantly after each meal. There was no significant effect of meal fatty acid composition or gender on maximum change in concentration, time to maximum concentration or area under the curve of any of the metabolites measured in the blood. These results suggest that differences in meal fatty acid composition exert little or no effect on postprandial changes in plasma lipids, glucose and insulin concentration

Phospholipid composition of neonatal guinea pig liver and plasma: Effect of postnatal food restriction

Preterm guinea pigs were delivered on day 65 of gestation (term=68 d) and were allowed either free or restricted access to food for the subsequent 48 h. Plasma phosphatidylcholine (PC) concentration increased postnatally from 190 (range 144–307) to 751 (426–1039) and 883 (758–977) μM for fed and starved pups, respectively. Plasma PC composition in both groups of pups was characterized by selective and equivalent relative increases to individual molecular species containing 18∶0 at thesn-1 position. Hepatic PC concentration increased from 6.75 (5.41–8.20) to 8.65 (6.54–10.63) and 9.23 (8.18–10.17) μmol/g for fed and starved pups, respectively, and, under all conditions, hepatic PC molecular composition closely mirrored that of plasma PC. These results support the hypothesis that the molecular species composition of plasma PC for the guinea pig in the immediate postnatal period is determined largely by the composition of the hepatic PC pool destined for lipoprotein secretion. Hepatic PC composition and concentration of the starved neonatal guinea pig were maintained independently of any dietary nutrient intake, at the expense of mobilization of extra hepatic lipid reserves. While this adaptive mechanism has inherent limited survival potential in neonatal starvation, it has implications for studies measuring plasma phospholipid fatty acid compositions as biochemical markers of dietary fat intake in preterm infants

Polyunsaturated fatty acid concentrations in young men and women consuming their habitual diets

Young women of reproductive age appear to have a greater capacity than men to convert the essential fatty acid alpha-linolenic acid to DHA. The purpose of this study was to test the hypothesis that gender-related differences in n-3 PUFA metabolism are reflected in the concentrations of n-3 PUFA in plasma lipids. The subjects were healthy men (n 13) and women (n 23) aged 18-35 years consuming their habitual diet. Dietary habits were assessed by food-frequency questionnaire. Venous blood samples were collected following an overnight fast. For the women, blood collection took place on the tenth day of their menstrual cycle. The fatty acid concentrations of plasma phosphatidylcholine, triacylglycerol, NEFA and cholesteryl esters were determined by gas chromatography. There were no significant differences between men and women in their consumption of protein, carbohydrate, total fat, alcohol, individual fatty acids and selected micronutrients. DHA concentration alone was significantly higher in plasma phosphatidylcholine (31 %, P = 0.02), triacylglycerol (71 %, P = 0.02) and NEFA (33 %, P = 0.01), but not cholesteryl esters, in women compared with men. There were no significant differences between men and women in the concentrations of any other fatty acids measured. Overall, the present data support the suggestion that greater DHA synthesis in women than men results in a higher DHA concentration in plasma lipid