1. Universidad San Pablo-CEU

Endoplasmic reticulum (ER) homeostasis is crucial to appropriate cell functioning, and when disturbed, a safeguard system called unfolded protein response (UPR) is activated. Fructose consumption modifies ER homeostasis and has been related to metabolic syndrome. However, fructose sweetened beverages intake is allowed during gestation. Therefore, we investigate whether maternal fructose intake affects the ER status and induces UPR. Thus, administrating liquid fructose (10% w/v) to pregnant rats partially activated the ER-stress in maternal and fetal liver and placenta. In fact, a fructose-induced increase in the levels of pIRE1 (phosphorylated inositol requiring enzyme-1) and its downstream effector, X-box binding protein-1 spliced form (XBP1s), was observed. XBP1s is a key transcription factor, however, XBP1s nuclear translocation and the expression of its target genes were reduced in the liver of the carbohydrate-fed mothers, and specifically diminished in the fetal liver and placenta in the fructose-fed mothers. These XBP1s target genes belong to the ER-associated protein degradation (ERAD) system, used to buffer ER-stress and to restore ER-homeostasis. It is known that XBP1s needs to form a complex with diverse proteins to migrate into the nucleus. Since methylglyoxal (MGO) content, a precursor of advanced glycation endproducts (AGE), was augmented in the three tissues in the fructose-fed mothers and has been related to interfere with the functioning of many proteins, the role of MGO in XBP1s migration should not be discarded. In conclusion, maternal fructose intake produces ER-stress, but without XBP1s nuclear migration. Therefore, a complete activation of UPR that would resolve ER-stress is lacking. A state of fructose-induced oxidative stress is probably involved.

Scope: One of the features of metabolic syndrome caused by liquid fructose intake is an impairment of redox status. We have investigated whether maternal fructose ingestion modifies the redox status in pregnant rats and their fetuses. Methods and results: Fructose (10% wt/vol) in the drinking water of rats throughout gestation, leads to maternal hepatic oxidative stress. However, this change was also observed in glucose-fed rats and, in fact, both carbohydrates produced a decrease in antioxidant enzyme activity. Surprisingly, mothers fed carbohydrates displayed low plasma lipid oxidation. In contrast, fetuses from fructose-fed mothers showed elevated levels of plasma lipoperoxides versus fetuses from control or glucose-fed mothers. Interestingly, a clearly augmented oxidative stress was observed in placenta of fructose-fed mothers, accompanied by a lower expression of the transcription factor Nuclear factor-erythroid 2-related factor-2 (Nrf2) and its target gene, heme oxygenase-1 (HO-1), a potent antioxidant molecule. Moreover, histone deacetylase 3 (HDAC3) which has been proposed to upregulate HO-1 expression by stabilizing Nrf2, exhibited a diminished expression in placenta of fructose-supplemented mothers. Conclusions: Maternal fructose intake provoked an imbalanced redox status in placenta and a clear diminution of HO-1 expression, which could be responsible for the augmented oxidative stress found in their fetuses.

Fructose consumption from added sugars correlates with the epidemic rise in obesity, metabolic syndrome and cardiovascular diseases. However, consumption of beverages containing fructose is allowed during gestation. We have investigated whether maternal fructose intake produces subsequent changes in cholesterol metabolism of progeny. Carbohydrates were supplied to pregnant rats in drinking water (10% w/v solution) throughout gestation. Adult male and female descendants from fructose-fed, control or glucose-fed mothers were studied. Male offspring from fructose-fed mothers had elevated plasma HDL-cholesterol levels, whereas female progeny from fructose-fed mothers presented lower levels of non-HDL cholesterol versus the other two groups. Liver X-receptor (LXR), an important regulator of cholesterol metabolism, and its target genes such as scavenger receptor B1, ATP-binding cassette (ABC)G5 and cholesterol 7-alpha hydroxylase showed decreased gene expression in males from fructose-fed mothers and the opposite in the female progeny. Moreover, the expression of a number of LXR target genes related to lipogenesis paralleled to that for LXR expression. In accordance with this, LXR gene promoter methylation was increased in males from fructose-fed mothers and decreased in the corresponding group of females. Surprisingly, plasma folic acid levels, an important methyl-group donor, were augmented in males from fructose-fed mothers and diminished in female offspring. Maternal fructose intake produces a fetal programming that influences, in a gender-dependent manner, the transcription factor LXR epigenetically, and both hepatic mRNA gene expression and plasma parameters of cholesterol metabolism in adult progeny. Changes in the LXR promoter methylation might be related to the availability of the methyl donor folate.

Fructose intake from added sugars correlates with the epidemic rise in obesity, metabolic syndrome and cardiovascular diseases. Fructose intake also causes features of metabolic syndrome in laboratory animals. Therefore, we have investigated whether fructose modifies lipidemia in pregnant rats and produces changes in their fetuses. Thus, fructose administration (10% wt/vol) in the drinking water of rats throughout gestation, leads to maternal hypertriglyceridemia. This change was not observed in glucose-fed rats, although both carbohydrates produced similar changes in liver triglycerides and in the expression of transcription factors and enzymes involved in lipogenesis. After fasting overnight, mothers fed carbohydrates were found to be hyperleptinemic. However, after a bolus of glucose, leptinemia in fructose-fed mothers showed no-response, whereas it increased in parallel in glucose-fed and control mothers. Fetuses from fructose-fed mothers showed hypotriglyceridemia and a higher hepatic triglyceride content than fetuses from control or glucose-fed mothers. A higher expression of genes related to lipogenesis and a lower expression of fatty acid catabolism genes were also found in fetuses from fructose-fed mothers. Moreover, although hyperleptinemic, these fetuses exhibited increased tyrosine phosphorylation of the signal transducer and activator of transcription-3 (STAT-3) protein, without a parallel increase in the serine phosphorylation of STAT-3 nor in the suppressor of cytokine signaling-3 (SOCS-3) protein levels whose expression is regulated by leptin through STAT-3 activation. Thus, fructose intake during gestation provoked a diminished maternal leptin-response to fasting and re-feeding, and an impairment in the transduction of the leptin signal in the fetuses which could be responsible for their hepatic steatosis.

To determine whether the composition of long-chain polyunsaturated fatty acids (PUFA) could be modified in the fetus by maternal dietary fatty acids, pregnant Sprague-Dawley rats were fed semi purified diets that differed only in the non-vitamin lipid component. The diets contained either 10 g palm, sunflower, olive or fish oil (FOD)/100 g diet. A total of 5-6 rats were studied in each group. At day 20 of gestation, corresponding to 1.5 days prior parturition, the fatty acids in maternal adipose tissue were closely related to the fatty acid composition in the corresponding diet. An important proportion of arachidonic acid (AA) appeared in maternal liver and plasma, although it was lower in the FOD than in the other groups. Except for saturated fatty acids, the proportion of individual fatty acids in the placenta correlated linearly with that in maternal plasma. Also, PUFA in fetal plasma and liver showed significant correlations with PUFA in maternal plasma. Again, AA showed the lowest proportion in the plasma and liver of the FOD group. Therefore, the maternal dietary fatty acid composition influences maternal and fetal plasma and tissue composition, and an increase in dietary co-3 fatty acids decreases the amount of AA in maternal and fetal tissues.

Una dosis oral de glucosa (2 g/Kg de peso) produjo cambios similares en la glucosa sanguinea de ratas gestantes de 20 dias y virgenes mientras que el aumento en la insulina plasmatica fue mayor en los animales gestantes, indicando resistencia a la insulina. En el presente trabajo se estudia si un ejercicio moderado y aerobio durante la gestación modifica la respuesta a la insulina en la madre. Ratas virgenes y preñadas de 20 días corrieron en una cinta rodante inclinada 10° durante 5 dias/semana a 20 ml mine incremento progresivo hasta 75 min en el dia 20 de ejercicio y/o gestación en que fueron sometidas a un test de tolerancia intravenoso de insulina con 10 IU de insulina porcina/Kg peso. El efecto hipoglucemiante de la insulina intravenosa mostró una mayor respuesta a la insulina en las ratas preñadas ejercitadas con respecto a las no ejercitadas, mientras que no se observa efecto en las ratas virgenes.

By using different experimental designs in the rat we have been able to answer several unanswered questions on the short- and long-term effects of alterations of lipid metabolism during the perinatal stage. The first was to demonstrate the importance of maternal body fat accumulation during the first half of pregnancy, since undernutrition in this critical period when fetal growth is slow, impedes fat depot accumulation and not only restrains intrauterine development but has long-term consequences, as shown by an impaired glucose tolerance when adults. Secondly, undernutrition during suckling has major long-term effect of decreasing body weight, even though food intake is kept normal from the weaning period. Our findings also show that a diet rich in n-3 fatty acids during pregnancy and lactation has adverse effects on offspring development, but cross fostered experiments showed that this effect was a consequence of the intake of these fatty acids during the lactation period rather than during pregnancy. Pups from dams that were fed a fish oil-rich diet during pregnancy and lactation were found to have altered glucose/insulin relationship at the age of 10 weeks. Since a n-3 fatty acid-rich diet decreases milk yield during lactation, additional experiments were carried out to determine whether decreased food intake or altered dietary fatty acid composition, or both, were responsible for the long-term effects on the glucose/insulin axis. Results show that the decreased food intake caused by a n-3 fatty acidrich diet rather than the change in milk composition during suckling was responsible for the reduced pancreatic glucose responsiveness to insulin release at 16 weeks of age. In conclusion, present findings indicate that impaired maternal fat accumulation during early pregnancy and food intake during lactation, rather than a difference in dietary fatty acid composition, have major effects on postnatal development and affect glucose/insulin relationships in adult rats.

La dieta rica en sacarosa (DRS) no modifica el peso corporal de la rata gestante ni de sus fetos. La práctica de un ejercicio aerobio moderado tampoco afecta a estos parámetros con independencia del tipo de dieta que ingieran o de su estado fisiológico. La respuesta metabólica a la DRS es diferente según el metabolito estudiado, así la hipertrigliceridemia es similar en ratas vírgenes y preñad3s, aunque en estas últimas el efecto de la DRS se suma al aumento de triglicéridos característico de la gestación. Los niveles de ácidos grasos libres no se modifican ni en vírgenes ni en preñadas como consecuencia de la DRS. En lo relativo a la glucemia e insulinemia existe una respuesta diferencial a la DRS dependiendo de que los animales estén o no preñados. Finalmente, la práctica de ejercicio reduce considerablemente la insulina en las ratas gestantes alimentadas con DRS o con la DC.

Fundamento y objetivo. El desarrollo fetal requiere un adecuado aporte de ácidos grasos esenciales y de sus derivados de cadena larga. El objetivo de este estudio ha sido determinar en la rata preñada cómo los ácidos grasos esenciales derivados de la dieta son transportados en el plasma materno y de qué forma influyen las variaciones en la composición de los de la dieta sobre el perfil de ácidos grasos en el plasma fetal. Métodos. Desde el inicio de la gestación, las ratas fueron alimentadas con dietas semisintéticas e isocalóricas que contenían como único componente graso no vitamínico un 10% de grasa de palma, aceite de girasol, aceite de oliva o aceite de pescado. Los animales se estudiaron al día 20 de gestación y fueron alimentados ad libitum con la correspondiente dieta. Resultados. Con los cuatro tipos de dietas, los ácidos grasos poliinsaturados se encontraban en plasma preferentemente esterificados y asociados a las distintas lipoproteínas circulantes, y en particular en los triglicéridos de las de densidad < 1,006 y en los fosfolípidos de lipoproteínas de alta densidad, en vez de en forma de ácidos grasos libres. Las diferencias entre los grupos en los ácidos grasos del plasma fetal se asemejan a los del plasma materno, incluida una reducción en la proporción de ácido araquidónico en las ratas alimentadas con la dieta de aceite de pescado con relación a los demás grupos. La proporción de cada uno de los ácidos grasos poliinsaturados en plasma materno se correlacionó linealmente con los del feto, mientras que esto no ocurrió con los ácidos grasos saturados o con el ácido oleico. Conclusión. En la rata gestante, los ácidos grasos poliinsaturados del plasma se transportan preferentemente en los triglicéridos de las lipoproteínas de densidad < 1,006, varían en función de los de la dieta, y determinan los que llegan al feto. A su vez, la dieta de aceite de pescado, rica en ácidos grasos de la serie 0>-3, reduce la proporción de ácido araquidónico, lo cual puede tener consecuencias negativas en el desarrollo posnatal.