María Pilar Navarro

Maillard reaction products modulate gut microbiota composition in adolescents

SCOPE Scarce data are available concerning effects of certain bioactive substances such as Maillard reaction products (MRP) on the gut microbiota composition, and the question of how a diet rich in MRP affects gut microbiota in humans is still open. METHODS AND RESULTS Two experiments were conducted. In expt. 1, adolescents consumed diets either high or low in MRP in a two-period crossover trial; in expt. 2, rats were fed diets supplemented or not with MRP model-systems. Intestinal microbiota composition in fecal (adolescents) or cecal (rat) samples was assessed by qPCR analysis. Negative correlations were found in the human assay between lactobacilli numbers and dietary advanced MRP (r = -0.418 and -0.387, for hydroxymethylfurfural and carboxymethyl-lysine respectively, p < 0.05), whereas bifidobacteria counts were negatively correlated with Amadori compounds intake. In the rat assay, total bacteria and lactobacilli were negatively correlated with MRP intake (r = -0.674,-0.675 and -0.676, for Amadori compounds, hydroxymethylfurfural and carboxymethyl-lysine respectively, p < 0.05), but no correlations were found with bifidobacteria. CONCLUSIONS Dietary MRP are able to modulate in vivo the intestinal microbiota composition both in humans and in rats, and the specific effects are likely to be linked to the chemical structure and dietary amounts of the different browning compounds.

Intake of Maillard reaction products reduces iron bioavailability in male adolescents.

The effects of diets with different Maillard reaction products (MRPs) content on biological iron utilization were compared using in vitro/in vivo assays. Diets were rich (brown diet, BD) or poor (white diet) in MRP. In vitro studies included iron solubility after in vitro digestion of diets and iron transport across Caco-2 cells. In the human assay 18 healthy adolescent males (11-14 years) participated in a 2-wk randomized two-period crossover trial. Subjects collected urine and faeces on the last 3 days of each dietary period, and fasting blood samples were obtained after periods. In vitro dietary iron availability was significantly lower with the BD than the white diet (9.52 and 12.92%, respectively), as a consequence of the lower iron solubility after the in vitro digestion, but not as a result of decreased transport of the remaining soluble iron. The BD consumption increased iron fecal excretion ( approximately 1.4-fold) and significantly decreased its bioavailability ( approximately 2.7-fold), mainly due to the effects found at digestive level. Serum biochemical parameters related to iron metabolism remained unaltered. It is concluded the presence of MRP in the diet negatively affects iron bioavailability. As iron deficiency may be related to learning impairment and to reductions of cognitive and physical functions, possible long-term effects of excessive MRP intake during adolescence warrant attention.

Antioxidant Properties and Metal Chelating Activity of Glucose-Lysine Heated Mixtures : Relationships with Mineral Absorption Across Caco-2 Cell Monolayers

Model Maillard reaction products were generated by heating glucose-lysine mixtures (GL) at 150 degrees C for different times (15, 30, 60, and 90 min). Samples were characterized by free lysine, browning, and UV-visible spectra and assessed for antioxidant properties, metal chelating ability, and effects on mineral absorption across Caco-2 monolayers. It was found that the capacity to retard lipid peroxidation in a model linoleic acid emulsion system increased with heating time up to 60 min and then leveled off, whereas the scavenging activity toward 1,1-diphenyl-2-picryl-hydrazyl (DPPH) radicals increased in early periods of the reaction (15 and 30 min of heating) and decreased thereafter. The iron binding affinity of the different samples was not correlated with antioxidant properties, and iron transport in Caco-2 cells was unchanged between samples. On the contrary, copper chelating activity showed significant correlation with free radical scavenging activity and with copper absorption across intestinal cells. It can be concluded that severe heat treatment of GL mixtures maintained the ability to reduce lipid peroxidation but decreased the free radical scavenging activity. Moreover, antiradical activity, copper chelation ability, and positive effects on copper absorption were correlated and associated to compounds formed at early stages of the Maillard reaction.

Metabolic transit of Nε-carboxymethyl-lysine after consumption of AGEs from bread crust

Our aim was to investigate carboxymethyl-lysine (CML) intake and excretion after feeding rats with diets containing advanced glycation end-products (AGEs) from bread crust (BC) or its soluble or insoluble fractions, and to identify the factors responsible for the effects observed. CML in serum and different tissues was measured to detect possible accumulations. For 88 days, weanling rats were fed with either a control diet or one containing BC, or its soluble low molecular weight (LMW), soluble high molecular weight (HMW) or insoluble fractions. In the last week of the assay, faeces and urine were collected daily and stored as a 1 week pool. After sacrifice, blood was drawn to obtain serum and some organs were removed. CML analysis was performed by HPLC/MS/MS in diets, faeces, urines, serum and tissues. Faecal excretion of CML was strongly influenced by dietary CML levels and represents the major route of excretion (i.e. 33.2%). However, the urinary elimination of CML was probably limited or saturated, especially when more complex compounds were present in the diet. BC consumption increased CML in the cardiac tissue (170 ± 18 vs. 97 ± 3 μmol per mol lysine for BC and control groups), which correlated with the CML intake. The levels of this AGE in bone were unaffected by the dietary treatment, but in tail tendons CML was greatly increased in the animals that consumed the BC diet (102 ± 13 vs. 51 ± 8 μmol per mol lysine for BC and control groups, P = 0.006), which was associated with the intake of soluble LMW compounds present in BC. Despite the CML accumulation detected in different tissues, serum levels of protein-bound CML were unchanged, indicating the importance of measuring the free CML in this fluid as a real index of dietary CML.

A Mediterranean Dietary Style Improves Calcium Utilization in Healthy Male Adolescents

Objective: To examine the effects of consuming a diet based on the Mediterranean patterns on calcium availability and metabolism in male adolescents. Design: A longitudinal study divided into two periods: a 3-day basal period, during which the subjects (n = 20; 12.9 ± 1.14 years) consumed their usual diet (basal diet, BD), and a 28-day nutritional intervention period, in which an intervention Mediterranean-type diet - was consumed (ID). Methods: Dietary calcium utilization was assessed by means of calcium intake in food and calcium output in feces and urine as measured by flame absorption spectrophotometry. In addition, markers of calcium metabolism (serum Ca, parathyroid hormone and total alkaline phosphatase) and bone resorption (urine deoxypiridinoline) were measured. Results: No differences in total calcium intake were found between the two diets, but food sources of dietary calcium varied significantly. Compared with the BD, the consumption of the ID resulted in significant increases in calcium absorption (∼ 40%, p = 0.04) and retention (∼ 80%, p = 0.008), and a considerable decrease in urinary calcium excretion (∼ 40%, p = 0.01).The variations observed in bone markers reflected a higher bone turnover rate after the ID consumption. Conclusions: A varied diet based on Mediterranean diet patterns during adolescence greatly improves dietary calcium utilization, which may help to maximize the peak bone mass and prevent related diseases, such as osteoporosis.

An Advanced Glycation End Product (AGE)-Rich Diet Promotes Nε-Carboxymethyl-lysine Accumulation in the Cardiac Tissue and Tendons of Rats

The purpose of this study was to investigate the intake, excretion, and tissue accumulation of carboxymethyl-lysine (CML), after feeding rats a diet containing advanced glycation end products (AGEs) from a glucose-lysine (GL) model system. Rats were distributed into two groups and assigned to a control diet or a diet including 3% heated GL (GL diet) for three months. Feces and urine were collected over the last week. After sacrifice, serum was obtained and some organs were removed for CML analysis. The percentage of fecal CML was 2.5-fold higher in the animals fed the GL diet (33.2 vs 76.5% for control and GL group), whereby total recovery was 91.8% compared with a level of 54.6% in the animals fed the control chow, evidencing the importance of the chemical form and the net quantity of dietary CML on its elimination. We suggest that dietary dicarbonyl compounds from GL diet or dietary CML itself are responsible for CML accumulation in hearts and tendons. The most significant result of the present study is that the regular consumption of dietary AGEs in healthy individuals promotes CML accumulation in some organs.

Influence of Diets Rich in Maillard Reaction Products on Calcium Bioavailability. Assays in Male Adolescents and in Caco-2 Cells

The effects of the high intake of Maillard reaction products (MRP) on calcium availability in adolescents and across Caco-2 cell monolayers were examined. In a 2 week randomized two-period crossover trial, 18 male adolescents consumed two diets, named white diet (WD) and brown diet (BD), which were poor and rich in MRP, respectively. A 3 day balance was performed at the end of each period, and fasting blood samples were collected. Calcium solubility and absorption across Caco-2 cells were studied after the in vitro digestion of the diets. The in vitro assay showed similar solubility after the in vitro digestion and similar transport across Caco-2 cells. In accordance, calcium bioavailability in adolescents did not vary between the diets (%WD = 40.4 +/- 5.1, %BD = 38.2 +/- 3.6). Serum and urine biochemical parameters related to calcium status and bone metabolism remained unaltered. Only deoxypyridinoline values were significantly lower after consumption of the BD (13.0 +/- 1.1 compared to 18.3 +/- 2.1 nM/Mm Cr in the WD), possibly indicative of less efficient bone turnover during this period. As calcium acquired during adolescence is essential to maximize peak bone mass and to prevent osteoporosis, possible long-term effects of excessive MRP intake during this period warrant attention.

Influence of heat treatment of casein in presence of reducing sugars on Zn solubility and Zn uptake by Caco-2 Cells after in vitro digestion.

The effect of the heat treatment of casein in presence of reducing sugars on some aspects of Zn availability was investigated. Samples were prepared by mixing casein with glucose-fructose, and were used unprocessed (C) or heated (HC). Changes in Zn speciation after the in vitro digestion of the samples, both as part of a diet and in isolation, were studied. The uptake of soluble Zn from the digested samples was investigated in Caco-2 cells. After in vitro digestion, the percentage of precipitated Zn was significantly higher with the HC sample, both when digested alone and as a part of the diet. In assays with Caco-2 cells, a significant decrease in Zn uptake was observed when the uptake buffer contained the sample C digest, by comparison with the control buffer, without casein digest. When the digested heated mixture was added, Zn uptake by the cells was significantly lower than in either of the two other cases. It may be concluded that the heat treatment of casein in the presence of glucose-fructose has a negative effect on Zn availability because, after in vitro digestion, Zn insolubilization was enhanced and Zn uptake by the enterocyte was impaired, compared with the unheated mixture. In addition, the usefulness of Caco-2 cells in this kind of research has been shown.ResumenSe estudia el efecto del calentamineto de la caseína en presencia de azúcares reductores sobre algunos aspectos de la disponibilidad del Zn. Las muestras se preparan mezclando caseína con glucosa-fructosa y se ensayan sin calentar (C) y calentada (HC). En primer lugar, se investigan los cambios en la solubilidad del Zn tras la digestión in vitro de las muestras, aisladas o formando parte de una dieta. En segundo lugar, se llevan a cabo estudios de captación del Zn soluble, obtenido tras la digestión de las muestras aisladas, en células Caco-2. Tras la digestión in vitro, el porcentaje de Zn precipitado es significativamente superior con la muestra calentada, tanto digerida de forma aislada, como formando parte de la dieta. La adición a la solución de captación de la fracción soluble de los digeridos de las muestras HC y C produce un descenso significativo en la captación del Zn en las células Caco-2, más acusado en HC. Se puede concluir que el calentamiento de la caseína en presencia de glucosa-fructosa afecta negativamente la disponibilidad del Zn, porque, tras la digestión in vitro, favorece la insolubilización del elemento y disminuye su captación por el enterocito de forma aun más acusada que la misma mezcla sin tratar. Por otra parte, se comprueba la utilidad de las células Caco-2 en la realización de este tipo de estudios.

Zinc Status in Anorexia nervosa

Some aspects of zinc nutritive status in patients suffering from anorexia nervosa were evaluated. Basic anthropometric measurements, Zn levels in serum, urine and hair as well as serum alkaline phosphatase (ALP) and lactate dehydrogenase (LDH; Zn-dependent enzymes) and delayed dermal hypersensitivity were tested both in patients and in control subjects. The patients showed higher Zn levels in serum (123%), hair (85%) and urine (215%) than controls, whereas ALP and LDH values were 38 and 21%, respectively, lower than those from the control group. Half of the patients showed hypoergy, and less than 50% of them were able to show a normal immune response. These results suggest that Zn-dependent functions may be impaired in anorexia nervosa as a consequence of Zn unavailability.

Oxygen consumption by oak chips in a model wine solution; Influence of the botanical origin, toast level and ellagitannin content.

The botanical origin, toast level and ellagitannin content of oak chips in a model wine solution have been studied in terms of their influence on oxygen consumption. French oak chips released significantly higher amounts of ellagitannins than American oak chips at any toast level. The release of ellagitannins by oak chips decreased as the toast level increased in the French oak but this trend was not so clear in American oak. Oxygen consumption rate was clearly related to the level of released ellagitannins. Therefore, oak chips should be chosen for their potential to release ellagitannins release should be considered, not only because they can have a direct impact on the flavor and body of the wine, but also because they can protect against oxidation.