Maternal adipose tissue is a major contributor to breast milk long-chain fatty acids, probably through the pool of plasma NEFA. The fatty acid composition of the erythrocyte membrane (EM) is a biochemical index of the intake of fatty acids not synthesized endogenously and of PUFA and long-chain PUFA fatty acid status. The present study investigated the associations between breast milk fatty acid composition and the composition of plasma NEFA and of EM fatty acids with special reference to PUFA, long-chain PUFA and conjugated linoleic acid (CLA). The detailed fatty acid composition of mature breast milk was also reported. Thirty-three healthy, lactating Brazilian women donated milk samples; of these, twenty-four also donated blood samples in an observational cross-sectional study. Breast milk fatty acid composition presented several associations with NEFA and EM composition, which explained most ($50 %) of the variability of selected milk PUFA, long-chain PUFA and CLA. Milk CLA was associated with fatty acids that are markers of dairy fat intake in the diet, NEFA and EM. In general, breast milk n-3 fatty acids and CLA, but not n-6 fatty acids, were associated with EM composition, whereas both the n-6 and n-3 fatty acids and CLA in milk were associated with NEFA composition, possibly owing to its role as a direct source of fatty acids for breast milk. These findings emphasize the contribution of the NEFA pool derived from the adipose tissue to the long-chain fatty acid composition of breast milk.Fatty acid metabolism: Breast milk fatty acids: Non-esterified fatty acids: Erythrocyte fatty acids: Lactation

We hypothesize that membrane stability of elite swimmers adapted to chronic intense training is dependent on polyunsaturated fatty acids (PUFAs) and tocopherols in blood pools and that the composition of PUFA in plasma nonesterified fatty acids (NEFAs) might be associated with specific subcutaneous fat sites. Our aims were to investigate in male elite swimmers the associations of n-6 and n-3 PUFA and alpha- and gamma-tocopherols with proxies of membrane stability (phase angle and erythrocyte osmotic fragility) and of PUFA in plasma NEFA with specific skinfolds. Brazilian male elite swimmers (n = 20) under regular training for an average of 4.1 h/d and 6.1 d/wk took part in the study. Blood samples were obtained once after 18-hour rest and an overnight fast. Fatty acids were determined in plasma NEFA and erythrocytes by gas chromatolography and tocopherols were determined in plasma and erythrocytes by high-performance liquid chromatography. The status of PUFA was assessed as mean melting point, PUFA index [(Sigman-6 + Sigman-3) / (Sigman-7 + Sigman-9)] and docosahexaenoic acid indices (22:5n-6/22:4n-6 and 22:6n-3/22:5n-6 ratios) calculated from erythrocyte fatty acids. Phase angle was associated with an index of docosahexaenoic acid inadequacy (22:5n-6/22:4n-6; r = -0.53, P = .019) and with 22:5n-3 in erythrocytes (r = 0.51, P = .024), and erythrocyte osmotic fragility was associated with plasma alpha-tocopherol (r = -0.51, P = .05), which is a biomarker of vitamin E status. Plasma NEFAs 18:3n-3 and 20:4n-6 were positively associated with skinfolds of the trunk and arms (r = 0.49-0.59, P = .011-.043). The data presented indicate that n-3 PUFA and vitamin E states possibly improve membrane stability in elite swimmers and that the extent of specific anatomic sites of subcutaneous adipose tissue in the upper body might contribute to the composition of NEFA in the resting state.

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Recebido em 3/6/03; aceito em 18/11/03; publicado na web em 27/05/04 ANALYSIS OF NON-ESTERIFIED FATTY ACIDS IN HUMAN PLASMA BY CAPILLARY GAS-CHROMATOGRAPHY WITH SPLITLESS INJECTION. The aim of the present work was to test the combination of non-esterified fatty acid (NEFA) isolation using fumed silicon dioxide with capillary gas-chromatography (C-GC) with splitless injection for the analysis of NEFAs in human plasma. Injection volume, solvent re-condensation and split purge flow-rate were the parameters evaluated for the analysis of fatty acid methyl esters by C-GC. The use of a solvent re-condensation technique, associated with 1.0 µL injection and a split purge flow rate of 80 mL/min resulted in satisfactory analysis of NEFAs. Fourteen fatty acids were identified in plasma samples, ranging from 2.03 to 184.0 µmol/L. The combination of both techniques proved useful for routine analyses of plasma NEFAs.Keywords: non-esterified fatty acids; capillary gas-chromatography with splitless injection; fumed silicon dioxide. INTRODUÇÃOOs ácidos graxos desempenham importantes funções na fisiologia humana, tais como de substrato energético e na estrutura de membranas celulares 1 . Quando mobilizados do tecido adiposo, os ácidos graxos são transportados no plasma sanguíneo sob a forma não esterificada (ácidos graxos não-esterificados, AGNE), associados à albumina plasmática. Durante o jejum, o tecido adiposo sofre maior mobilização e os AGNE passam a ser o principal substrato energético para o organismo. Sua concentração plasmática total varia de 300 a 2000 µmol/L, no período alimentado e no jejum, respectivamente 1 . Para a determinação da composição dos AGNE é necessário primeiramente separá-los das demais classes de lipídios plasmáticos (triacilgliceróis, fosfolipídios, ésteres de colesterol, dentre outras). O método clássico usado para a separação das diferentes classes de lipídios é a cromatografia em camada delgada que, entretanto, apresenta algumas desvantagens, como elevado tempo de análise e potencial risco de oxidação dos ácidos graxos poli-insaturados 2 . Outros métodos de separação ou isolamento dos AGNE incluem a cromatografia em coluna 3 e a separação em cartuchos de extração em fase sólida 4 . Entretanto, o preparo das colunas é trabalhoso e a reprodutibilidade dos resultados é dependente da habilidade no seu preparo. Já os cartuchos de extração em fase sólida disponíveis comercialmente apresentam custo relativamente elevado para análises de rotina. No método descrito por Polette et al. 5, os AGNE são separados das demais classes de lipídios plasmáticos pelo uso do dióxido de silício fundido ("fumed silicon dioxide", DSF) como agente delipidante. Após agitação do plasma com o DSF, forma-se um gel denso no qual as lipoproteínas são aprisionadas, enquanto os AGNE associados à albumina plasmática permanecem em solução na fase aquosa, que é facilmente separada por centrifugação. Este método, além de ser relativamente rápido e de baixo custo, melhora a recuperação dos analitos, quando comparado à cromatografia em ...

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