Isomeric fatty acids: evaluating status and implications for maternal and child health.

"Isomeric fatty acids" is a term that refers to the trans- and positional isomers formed during hydrogenation of naturally occurring oils. The purposes of this paper are as follows: (i) to summarize potential exposure of infants to isomeric fatty acids by reviewing estimates of isomeric fatty acids in the maternal diet, in human milk, and in infant formula/infant foods, and (ii) to evaluate the evidence for adverse effects of isomeric fatty acids on infant development with respect to growth and essential fatty acid status. Estimates of the intake of trans-fatty acids vary widely both within and across populations. Current estimates of trans-fatty acids in the North American population are 4-11% of total fatty acids or 3-13 g/(person x d), whereas in Mediterranean countries in which olive oil is the primary fat and in Far Eastern countries in which little commercially hydrogenated fat is consumed, per capita consumption of trans-fatty acids is <1-2 g/d. The trans-fatty acid content of human milk reflects the cross-cultural variation in the maternal diet, with trans-fatty acids in human milk samples ranging from 6 to 7% in North America to <0.5% in Hong Kong. Trans-fatty acids are transferred from the maternal diet through the placenta to the developing fetus or through milk to the breast-fed infant. In some studies, plasma trans-fatty acids are inversely related to birth weight and head circumference. The hypothesis that dietary trans-fatty acids could inhibit biosynthesis of long-chain polyunsaturated fatty acids with 20 and 22 carbon atoms and thus affect infant development is supported by studies demonstrating an inverse correlation of plasma trans-fatty acids with n-3 and n-6 longchain polyunsaturated fatty acids in infants. However, no such relationship has been observed in human milk. A definitive answer concerning a potentially adverse effect of dietary trans-fatty acids on infant development awaits future studies.

Arachidonate and docosahexaenoate added to infant formula influence fatty acid composition and subsequent eicosanoid production in neonatal pigs.

As natural components of human milk, arachdonic and docosahexaenoic acids play important roles in neonatal development; thus, addition of these fatty acids to infant formula has been suggested. This study examined the effects of supplementation of infant formula with microbial sources of either arachidonate or docosahexaenoate or both on accretion of these fatty acids in phospholipids and subsequent modulation of eicosanoid production in neonatal pig lung. One-day-old piglets received for 25 d one of four diets (n = 5): 1) standard diet containing a fat blend similar to that of conventional infant formula, 2) diet containing 0.9 g/100 g of total fatty acids as arachidonate, 3) diet containing 0.7 g/100 g as docosahexaenoate, or 4) a diet containing both 1.0 g/100 g as arachidonate and 0.8 g/100 g as docosahexaenoate. Arachidonate supplementation resulted in 30-60% significantly greater arachidonate in lung phosphatidylethanolamine and phosphatidylcholine. In phosphatidylinositol, however, arachidonate was resistant to dietary manipulation. Accretion of docosahexaenoate in all three phospholipid classes was 2.6- to 4.7-fold greater in docosahexaenoate-supplemented groups than in the standard group. Inclusion of arachidonate in the diet augmented both prostacyclin and thromboxane production by 25 to 35%. Docosahexaenoate supplementation resulted in the least eicosanoid production among the treatments, and significant suppression was observed for thromboxane when supplementation with both fatty acids was compared with supplementation with arachidonate alone. Thus, dietary arachidonic acid and docosahexaenoic acid at concentrations only slightly greater than those found in human milk tended to exercise opposing effects on lung eicosanoid production.

Retinal fatty acids of piglets fed docosahexaenoic and arachidonic acids from microbial sources.

Docosahexaenoic acid (DHA, 22:6n-3) and arachidonic acid (AA, 20:4n-6) serve important roles in perinatal visual and neural development. A neonatal pig model was used to determine if dietary supplementation with DHA and AA at slightly greater concentrations than normally found in human milk would influence fatty acid accretion in retina. One-day-old piglets were assigned to one of four diets (n = 5/group): (i) STD, standard diet containing fat similar to infant formula; (ii) STD + DHA, 0.7% of fatty acids as DHA; (iii) STD + AA, 0.9% as AA; and (iv) STD + BOTH, 0.8% as DHA plus 1.0% as AA. After 25 d, fatty acids in retina phosphatidylcholine (PC) and phosphatidylethanolamine (PE) were determined. Supplementation with DHA resulted in approximately twofold increases (P < 0.05) in PC-DHA (4.88% in STD vs. 10.03% in STD + DHA and 9.47% in STD + BOTH). Similarly, AA supplementation increased PC-AA 1.3-1.4-fold (4.47% in STD vs. 6.19% in STD + AA and 5.70% in STD + BOTH). For PE, supplementation with either fatty acid or in combination resulted in no significant increases, except for a 1.2-fold increase in DHA for STD + BOTH (32.66%) vs. STD (28.38%). Thus, PC responded to dietary supplementation, with addition of DHA, AA, or BOTH, resulting in increases in respective fatty acids; PE was less responsive, with only STD + BOTH resulting in increased DHA. No significant competition between DHA and AA in incorporation into phospholipids was observed. In conclusion, consumption of a combination of DHA and AA by neonatal pigs supported accretion of DHA in retina phospholipids, while simultaneously supplying the AA necessary for membrane phospholipids and eicosanoid biosynthesis.

Modulation of avian lung eicosanoids by dietary omega-3 fatty acids.

This study was conducted to determine if dietary omega-3 polyunsaturated fatty acids could modulate lung eicosanoid production. Three groups of chickens were depleted of essential fatty acids by feeding diets containing 1% hydrogenated coconut oil from hatching to 8 wk, followed by repletion for 3 wk with diets containing soybean oil (SBO) and linseed oil (LSO) separately or in combination. The ratio of linoleic acid (18:2 omega 6) to linolenic acid (18:3 omega 3) was 7.48, 1.17 or 0.32, respectively, for diets containing 10% SBO, 5% SBO/5% LSO or 10% LSO. A 10% SBO diet fed for 11 wk served as the control. Production of prostaglandin F2 alpha, prostaglandin E, thromboxane B2 and 6-keto-prostaglandin F1 alpha by incubated lung was lower in birds fed linseed oil, with total prostanoid production being 95, 42 and 22% of control values for the three dietary treatments, respectively. The ratio of arachidonic acid (20:4 omega 6) to linoleic acid (18:2 omega 6) in serum phospholipids followed a similar pattern for the three treatments, with values of 0.96, 0.52 and 0.21. Thus, production of lung prostanoids of the 2-series could be modulated by varying the dietary omega 6/omega 3 ratio. This effect may be due in part to depression of phospholipid arachidonate, the precursor of 2-series eicosanoids.

Conversion of arachidonate to prostanoids by lung microsomes from rats fed varying amounts of vitamin E.

This study was conducted to investigate the effect of dietary vitamin E on prostaglandin (PG) synthesizing activities in the rat lung. Five groups of weanling male rats were fed for 9 wk a vitamin E deficient diet supplemented with 0, 20, 40, 200 and 400 mg-dl-alpha-tocopherol acetate/kg (E0, E20, E40, E200 and E400). Microsomes from lungs of each group were incubated in the presence of [1-14C]-arachidonate. Separation of metabolites was achieved by reversed phase HPLC. Six prostanoids: 6-keto-PGF1 alpha, 6-keto-PGE1, TXB2, PGF2 alpha, PGE2 and PGD2 were eluted isocratically with the solvent system of acetonitrile-water (pH 3.0) (34:66, V/V). Fractions of eluent were collected and the radioactivity of each fraction was determined. The predominant prostanoid synthesized by rat lung microsomes was 6-keto-PGF1 alpha. The specific activity (pmole PG produced/mg protein/min) for the synthesis of 6-keto-PGF1 alpha was 17.6, 29.3, 16.3, 15.3 and 21.2 for the E0, E20, E40, E200 and E400 groups, respectively. Only minor amounts of 6-keto-PGE1, TXB2, PGF2 alpha, PGE2 and PGD2 were synthesized by rat lung microsomes. Although rats fed vitamin E at 20 mg/kg diet showed the highest enzymatic activity for the synthesis of 6-keto-PGF1 alpha, dietary vitamin E had little overall effect on lung microsomal prostanoid biosynthesis.

Effect of maternal dietary linoleic acid and trans-octadecenoic acid on the fatty acid composition and prostaglandin content of rat milk.

The effects of seven levels of dietary linoleic acid (18:2), with and without trans-octadecenoic acid (18:1t), on the fatty acid composition and prostaglandin content of milk were investigated in lactating rat dams. At parturition, 14 groups of 4 rats each were fed diets containing 20% fat, with mixtures of coconut and safflower oils providing seven concentrations of 18:2 ranging from 3.6 +/- 0.5 to 44.5 + 2.3% of total fatty acids. Hydrogenated soybean oil was added such that 18:1t comprised 10.3 +/- 0.3% of total fatty acids. Milk samples were collected on day 12 postpartum for prostaglandin analyses and on day 16 for fatty acid analyses. The relationship of dietary 18:2 to milk 18:2 was linear (r = 0.98; P = 0.0001), with milk 18:2 ranging from 2.6 +/- 0.1% of total fatty acids at the lowest level of dietary 18:2 to 27.9 +/- 1.6% at the highest. Milk 18:1t was highly correlated (r = 0.99; P = 0.0001) with the amount of dietary 18:1t. In rats fed hydrogenated fat, milk 18:1t averaged 7.0 +/- 0.2% of total fatty acids. Transfer from diet to milk was 46.4 +/- 4.2% for 18:2 and 37.5 +/- 1.7% for 18:1t. Mean concentrations of prostaglandin F2 alpha and E in rat milk were 269 +/- 16 pg/mL and 477 +/- 24 pg/mL respectively. There were no significant differences in the concentrations of either prostaglandin relative to 18:1t consumption at any level of 18:2.

The essential fatty acid deficient chicken as a model for cystic fibrosis.

The essential fatty acid deficient (EFAD) chicken was evaluated as a model for cystic fibrosis (CF). Three semipurified diets--(I) 1% hydrogenated coconut oil (HCO), (II) 10% soybean oil + 1% HCO, and (III) 11% HCO--were fed to chickens from hatching to 5, 8, or 11 wk. Groups I and III exhibited poor weight gain and abnormal serum fatty acid patterns characteristic of EFAD. Production of prostaglandin F2 alpha, thromboxane B2, 6-keto-prostaglandin F1 alpha, and prostaglandin E in lung was significantly reduced at 5, 8, and 11 wk in both EFAD groups. Histopathologic examination revealed increased peribronchiolitis in group I compared with II. Incidence of pulmonary lesions in group III was intermediate. These data support the theory that essential fatty acids are necessary to maintain proper lung function. In this respect, the chicken is a good model for studying the relationship between EFAD and pulmonary disease in CF patients.

Use of published analyses of food items to determine dietary trans octadecenoic acid.

To estimate the dietary levels of trans octadecenoic acid (18:1t) in the diets of eight healthy white adolescent girls, diet records were obtained for a 7-day period. Published trans fatty acid values in foods were used to calculate the trans octadecenoic acid present in the diets. The usefulness of this method was tested by comparing the estimated values with values obtained by chemical analysis of diets collected by the duplicate portion technique from the same subjects over the same period of time. There was no significant difference in the values for the trans octadecenoic acid content of the 54 diets used in this study whether the values were calculated from the diet records or determined by chemical analysis. Dietary trans octadecenoic acid averaged 5.3% of total fatty acids by both methods. The mean trans octadecenoic acid in the daily diet was 2.8 gm as calculated from the diet records and 2.6 gm according to actual analysis. Those values were not significantly different. The present study demonstrated that the trans octadecenoic acid content of the diets of a group of adolescent girls can be estimated from diet records using previously published values for individual food items.

Fat in the diets of adolescent girls with emphasis on isomeric fatty acids.

To determine the amount of isomeric fatty acids in the diets of a segment of the American population, daily food intake was collected, using the duplicate portion method, from eight healthy white adolescent girls for 7 days. The fifty-six diets were analyzed for fatty acids by gas-liquid chromatography. The amount of trans isomers of octadecenoic acid (18:1t) in the diets of the eight girls ranged from 3.5 to 8.2% of total fatty acids with an average of 5.3%. Other trans fatty acids included trans isomers of 14:1 and 16:1, and cis,trans and trans,cis isomers of 18:2. No measurable amounts of trans,trans octadecadienoic acid (18:2tt) were found in the diets of the girls. The total trans fatty acid content of the diets averaged 6.5% of total fatty acids. The daily consumption of total trans fatty acids by the eight girls over a 1 wk period averaged 3.1 g, with 2.6 g of this being 18:1t.

The effect of hydrogenated fat in the diet of nursing mothers on lipid composition and prostaglandin content of human milk.

To study the effects of hydrogenated fat in the maternal diet on lipid composition and prostaglandin content of human milk, eight nursing mothers, 2 months postpartum, were provided with two 5-day diets in a cross-over design with an intervening 2-day period. Diets for the two periods were identical except that sources of hydrogenated fat were used in the meals for one period and nonhydrogenated fat in the other. Trans-isomers of octadecenoic acid (18:lt) comprised 11.8% of the total fatty acids in the hydrogenated fat diet compared with 1.0% in the nonhydrogenated fat diet. The 18:lt content of milk collected daily during hydrogenated fat consumption was 6.5% of the total fatty acids and was significantly higher (p less than 0.01) than the 18:lt content (1.8% of the total fatty acids) of milk collected during nonhydrogenated fat consumption. The amount of 18:lt in the milk was positively correlated (r = 0.909) with the 18:lt content in the previous day's diet. Although detectable concentrations of prostaglandins PGF2 alpha and PGE were found in human milk, their concentrations were not affected by hydrogenated fat in the maternal diet.

Effect of alpha-actinin on actin structure. Release of bound nucleotide.

We have examined the alpha-actinin-F-actin interaction by measuring the effect of highly purified alpha-actinin on bound nucleotide exchange in F-actin. Exchange was followed by measuring the release of actin-bound [14C]ADP in the presence of ATP using an ultrafiltration technique. Alpha-Actinin increases by about 60 to 70% the rate of release of F-actin bound nucleotide when incubated for 1 h in the presence of 1 mM ATP/1 mM MgCl2/0.05 mM CaCl2/0.5 mM dithioerythritol/100 mM KCI/20 mM Tris-acetate, pH 7.5, at 37 degrees C. The ability of alpha-actinin to enhance nucleotide exchange was maximal when alpha-actinin was added at a level near 10% of actin present by weight (molar ratio of 1 alpha-actinin to 49 actin monomers). The potentiating effect of alpha-actinin on the nucleotide exchange rate of F-actin was not highly related to the Mg2+: ATP ratio present in the incubation mixture. Alpha-actinin also increased the rate of bound nucleotide exchange of f-actin was present in a reconstituted actomyosin suspension. The results are consistent with th possibility that one alpha-actinin can affect the structure of multiple actin monomers present in an actin filament.