Martha Del Prado

Synthesis of long-chain polyunsaturated fatty acids in lactating mammary gland: role of Δ5 and Δ6 desaturases, SREBP-1, PPARα, and PGC-1

The purpose of this work was to study whether rat lactating mammary gland can synthesize PUFAs through the expression of Δ5 and Δ6 desaturases (Δ5D and Δ6D), whether these enzymes are regulated by the transcription factors sterol-regulatory element binding protein 1 (SREBP-1) and peroxisome proliferator-activated receptor α (PPARα) and the coactivator peroxisome proliferator-activated receptor γ coactivator 1β (PGC-1β), and whether these desaturases are regulated by the lipid concentration in the diet. The results showed that on day 12 of lactation, ∼35% of the linoleic acid in the diet, which is the precursor of PUFAs, is transferred to the mammary gland. There was expression of Δ5D and Δ6D in mammary gland, and it was regulated by the corn oil content in the diet. The higher the corn oil content in the diet, the lower the expression of both desaturases. Induction of Δ5D and Δ6D was associated positively with similar changes in SREBP-1 and PGC-1β. Expression of PPARα was barely detected and was not affected by the corn oil content in the diet, whereas PGC-1β expression increased as the corn oil in the diet increased. These results indicate that the lactating mammary gland has the capacity to synthesize PUFAs and can be regulated by the lipid content in the diet.

Interrelation among dietary energy and fat intakes, maternal body fatness, and milk total lipid in humans

The relationship between maternal dietaryintakes of energy or fat maternal body composition andthe milk fat concentration is an important element inunderstanding the role of breast-milk in infantnutrition. In most studies in both developing anddeveloped countries, no relation between maternal energyintake and milk fat content was observed. In only onepublished study, in which maternal fat intake comprised a very low 5% of calories, was a short termreduction in milk lipid observed in some subjects. Onthe other hand, a positive relation between maternalfatness and milk fat is evident in both well-nourished and under-nourished women when appropriatemethodologies have been used. Low milk fatconcentrations are associated with higher milk volumesprobably because infant demand determines milk intake,compensating, at least partially, for low milk fat. Noimpairment of infant growth was associated with low milkfat, in studies where it has been measured. Themechanism for the relationship between body fat and milk fat is a fertile field for additionalinvestigation.

Effect of dietary levels of corn oil on maternal arachidonic acid synthesis and fatty acid composition in lactating rats.

OBJECTIVE We examined the effect of different amounts of dietary corn oil rich in linoleic acid (LA) on the endogenous synthesis of arachidonic acid (AA), uptake of its precursor LA, and fatty acid composition of tissues involved in the supply of long-chain polyunsaturated fatty acids for milk synthesis. METHODS Female Sprague Dawley rats received one of the following diets during pregnancy and lactation: a low-lipid diet (LLD; 2%), an adequate-lipid diet (ALD; 5%), or a high-lipid diet (HLD; 10%). Lipids were provided by corn oil. On day 12 of lactation we measured the endogenous synthesis of AA and quantified the conversion of (13)C-LA to (13)C-AA and the metabolic fate of (13)C-LA from all dietary groups. RESULTS The LLD rats demonstrated larger amounts of endogenous synthesis of (13)C-AA and more dietary (13)C-LA transferred to the mammary gland (MG) than HLD rats during lactation. The proportion of medium-chain fatty acids was higher in the MG, milk clot, and liver of LLD than of HLD rats. Daily volume and 24-h yield of lipids and energy were lower in LLD rats than in HLD rats. Measurements of milk composition demonstrated that fat concentration significantly increased as lipid concentration increased in the diet. CONCLUSION These results suggest that maternal adaptations used to compensate for diets deficient in long-chain polyunsaturated fatty acids include increased endogenous synthesis of AA and elevated uptake of LA in the MG and increased synthesis of medium-chain polyunsaturated fatty acids. It appears that the MG and liver participate together for AA synthesis for milk when this fatty acid is not provided in the diet.

13C Enrichment of the CO2 in Breast Milk and in the Breath Is Rapidly Modified by Changes in the 13C Content of the Diet

Background: C4 plants (e.g. corn and sugar cane) have greater ¹³C enrichment than C3 plants (e.g. wheat and sugar beet). Objective: To assess whether ¹³C enrichment of CO₂ in the breath and breast milk of women on diets based on C3 and C4 foods changes from one diet to the other. Materials and Methods: Six breast-feeding women were studied at 5-6 months postpartum. They ate a controlled C4 diet on days 1 and 2 followed by a C3 diet on days 3 and 4. Diet duplicates, breast milk on days 2 and 4 and hourly breath samples were collected over 4 days. ¹³C enrichment was measured by isotope-ratio mass spectrometry. Values of δ¹³C were calculated from the international PDBV standard (δ¹³C_PDBV). Differences between means were compared by paired t test or t test for repeated measurements. Results: δ¹³C_PDBV values were significantly higher in the C4 diet than in the C3 diet composites (p < 0.01). In breath CO₂, the δ¹³C_PDBV value was greater on days 1 and 2 (range -15.4 to -13.2, respectively) and declined on days 3 and 4 (range -20.0 to -21.8, respectively, p < 0.01). The lipid and milk serum fractions of breast milk had significantly higher δ¹³C_PDBV on the C3 diet than on the C4 diet (p < 0.01). Conclusions: Subjects eating a C4 diet have a higher δ¹³C_PDBV value in the breath and breast milk fractions, which diminish rapidly on a C3 diet. Further studies focusing on individual nutrients are warranted.

13C-Linoleicacid Oxidation and Transfer into Milk in Lactating Women Witg Contrasting Body Mass Index

The diet of the rural community of San Mateo Capulhuac Mexico, is marginal in energy (45 kcal/kg body weight/day) and protein (0.8 g/kg body weight/day) and low in fat (17% of total energy). The milk lipid concentration in women from this community was positively correlated with maternal weight, body mass index (BMI) and body fat.1 The aim of this study was to investigate differences in the metabolic distribution of dietary lipids between women with a low or a high BMI by following the metabolism of an oral dose of 13C-linoleic acid (LA).