Dietary bioactive peptides: Human studies.

Current opinion strongly links nutrition and health. Among nutrients, proteins, and peptides which are encrypted in their sequences and released during digestion could play a key role in improving health. These peptides have been claimed to be active on a wide spectrum of biological functions or diseases, including blood pressure and metabolic risk factors (coagulation, obesity, lipoprotein metabolism, and peroxidation), gut and neurological functions, immunity, cancer, dental health, and mineral metabolism. A majority of studies involved dairy peptides, but the properties of vegetal, animal, and sea products were also assessed. However, these allegations are mainly based on in vitro and experimental studies which are seldom confirmed in humans. This review focused on molecules which were tested in humans, and on the mechanisms explaining discrepancies between experimental and human studies.

Iron in child obesity. Relationships with inflammation and metabolic risk factors.

Iron (Fe) sequestration is described in overweight and in its associated metabolic complications, i.e., metabolic syndrome (MetS) and non-alcoholic liver fatty disease (NAFLD); however, the interactions between Fe, obesity and inflammation make it difficult to recognize the specific role of each of them in the risk of obesity-induced metabolic diseases. Even the usual surrogate marker of Fe stores, ferritin, is influenced by inflammation; therefore, in obese subjects inflammation parameters must be measured together with those of Fe metabolism. This cross-sectional study in obese youth (502 patients; 57% girls): 11.4 ± 3.0 years old (x ± SD); BMI z score 5.5 ± 2.3), multivariate regression analysis showed associations between Fe storage assessed by serum ferritin with risk factors for MetS and NAFLD, assessed by transaminase levels, which were independent of overweight and the acute phase protein fibrinogen. Further studies incorporating the measurement of complementary parameters of Fe metabolism could improve the comprehension of mechanisms involved.

Alterations of left ventricular myocardial strain in obese children.

AIMS: Obesity may have implications in the myocardial structural change, which may contribute to mechanical consequences. Using 2D speckle echocardiography, we looked for myocardial changes and investigated their relation to obesity, inflammation, insulin resistance and physical capacity in children with isolated obesity. METHODS AND RESULTS: Standard echocardiography and 2D strain were prospectively performed in obese children and compared them with age- and sex-matched controls. Z-score body mass index (BMI Z-score), ultra-sensitive C reactive protein, indices of insulin resistance (HOMA-IR) and metabolic stress test were assessed in obese children. Thirty-two consecutive obese patients [age: 12.8 (8-17) years; 15 males; BMI Z-score: 5.8 [2.05-8.6)] were compared with 32 controls. Longitudinal strain and circumferential strain were significantly lower in the obese group (respectively -18.0 ± 2.4% vs. -20.6 ± 2.5%; P = 0.0001 and -18.2 ± 3.5% vs. -20.1 ± 2.3%; P = 0.013), while radial strain did not differ. Longitudinal strain was correlated with HOMA-IR (Pearson's rho = -0.39) and with the exercise capacity (Pearson's rho = 0.62). In the multivariate analysis, after adjusting for age, the mean arterial pressure and left ventricular (LV) mass, the BMI Z-score remained independently related to the longitudinal and circumferential strain. CONCLUSION: Childhood obesity may be associated with an early alteration of the longitudinal and circumferential LV strain. These findings have potentially significant clinical implications for the outcomes and follow-up of obese children meriting further studies.

Relationships of cardiorespiratory fitness with metabolic risk factors, inflammation, and liver transaminases in overweight youths.

The aim of this study was to assess the relationships of fatness and fitness with metabolic risk factors, including liver transaminases and inflammation in obese youth, taking in account gender, age, and pubertal stage. 241 children were studied (135 girls), age 11.9 +/- 2.2 years (x +/- SD), Body Mass Index z score 5.4 +/- 2.7. For girls, VO(2max) was significantly associated with insulin (P = .001), Insulin resistance (HOMA-IR) (P = .005), and ALT (P = .012); a relationship was displayed between fibrinogen and age and % fat mass (FM) (P = .008); for boys, relationships were found between VO(2max) and diastolic blood pressure and triglycerides; independent associations were also found between age and insulin, HOMA-IR and HDL cholesterol; fibrinogen and sedimentation rate were related (P

Evolution of fat oxidation during exercise in obese pubertal boys: clinical implications.

In this study, we examined fat oxidation rates during exercise in obese pubescent boys. Three groups of pubescent boys (16 pre-pubescent, Tanner's stage I; 16 pubescent, Tanner's stage III; and 14 post-pubescent, Tanner's stage V) performed a graded test on a leg cycle ergometer. The first step of the test was fixed at 30 W and power was gradually increased by 20 W every 3.5 min. Oxygen consumption (VO(2)) and carbon dioxide production (VCO(2)) were determined as the means of measurements during the last 30 s of each step, which allowed us to calculate fat oxidation rates versus exercise intensity. Between 20 and 50% of peak oxygen consumption (VO(2peak)), fat oxidation rate in relative values (mg . min(-1) . kg FFM(-1)) decreased continuously with pubertal development. In the same way, the maximum rate of fat oxidation occurred at a lower percentage of VO(2peak) (pre-pubescent: 49.47 +/- 1.62%; pubescent: 47.43 +/- 1.26%; post-pubescent: 45.00 +/- 0.97%). Our results confirm that puberty is responsible for a decrease in fat free mass capacities to use fat during exercise. The results suggest that post-pubescent obese boys need to practise physical activity at a lower intensity than pre-pubescent boys to enhance lipolysis and diminish adipose tissue and the consequences of obesity.

Caseinophosphopeptide-bound iron: protective effect against gut peroxidation.

BACKGROUND: Peptides derived from cow's milk proteins have in vitro protective effects on iron-induced peroxidation that could be used to prevent the side effects of iron fortification. The aim of the study was to confirm these properties in an in vivo model of gut peroxidation. METHODS: Iron bound to the 1-25 phosphopeptide of beta-casein [Fe-beta-CPP(1-25)] was compared to an encapsulated ferric pyrophosphate (Fe-P) in the Caco-2 model. Ferrous sulfate (FeSO(4)) was used as control (100 micromol/l iron, n = 6 per group). The concentration of malondialdehyde (MDA), a stable byproduct of lipid peroxidation, was used as the marker of peroxidation. RESULTS: The lowest MDA levels were observed in cells grown with Fe-beta-CPP(1-25) and the highest with Fe-P. Iron absorption of Fe-beta-CPP(1-25) was higher than in the 2 other forms, due to its high cellular uptake and high basolateral transfer, while iron absorption of Fe-P showed high uptake and high cell retention. CONCLUSIONS: The enhancing effect of beta-CPP(1-25) on iron absorption was associated with a protective effect against enterocyte peroxidation, perhaps due to its low storage by enterocytes. These observations support a role for specific milk components in food fortification to prevent iron deficiency.

Association of arterial stiffness and endothelial dysfunction with metabolic syndrome in obese children.

OBJECTIVE: We investigated whether metabolic syndrome, defined in 3 different ways (2 commonly used and 1 novel) is associated with arterial alterations in obese children. STUDY DESIGN: The study group comprised 384 obese children age 2.5 to 18 years. Blood pressure, fasting blood glucose, blood insulin, plasma lipids, and body composition were measured. Noninvasive ultrasound measurements were obtained in 161 patients to investigate arterial mechanical properties and endothelial function. RESULTS: The prevalence of metabolic syndrome was 10.4%. Intima-media thickness correlated positively with low-density lipoprotein cholesterol (r = .21; P < .01) and negatively with high-density lipoprotein cholesterol (r = -.17; P < .05). In adolescents (11 to 18 years), cross-sectional vascular compliance correlated negatively with abdominal fat (r = -.22; P = .02). The only synergistic effects among individual metabolic syndrome components was an effect of insulinemia and systolic blood pressure on cross-sectional compliance (4.05; P < .05). No significant difference in vascular variables was found between the patients with and without metabolic syndrome using any of the 3 definitions. CONCLUSION: Metabolic syndrome in obese children is not related to arterial variables, whereas several of its individual components are associated with vascular alterations. These data suggest that the value of the metabolic syndrome as a predictor of future cardiovascular events in children remains to be prospectively evaluated. In the meantime, individual cardiovascular risk factors should be evaluated and controlled.

Mutational analysis of the pro-opiomelanocortin gene in French obese children led to the identification of a novel deleterious heterozygous mutation located in the alpha-melanocyte stimulating hormone domain.

The pro-opiomelanocotin (POMC) plays a key role in body weight regulation, where its derived peptides mediate leptin action via the hypothalamic melanocortin 4 receptor (MC4R). The pathogenic effects of POMC mutations have been challenged in obesity. Our aim was to assess the relevance of POMC mutations in a cohort of French obese and nonobese children. Direct sequencing of the POMC gene was performed in 322 obese and 363 control unrelated children. Functional studies for the novel Phe144Leu mutation included the response to alpha-melanocyte stimulating hormone (alphaMSH) and a competitive binding assay. POMC mutations were identified in 3.72% of obese [95% confidence interval (CI): 1.66-5.80] and 2.20% of control (95% CI: 0.69-3.71) subjects. The novel mutation located in the alphaMSH region of the POMC gene (Phe144Leu) was found in one obese child and was transmitted by the obese father. Functional studies showed that MC4R activation in response to Leu144alphaMSH was almost completely abolished due to a dramatically altered binding of Leu144alphaMSH to MC4R. The frequency of POMC mutations is not significantly different between obese and control children in our cohort. The novel heterozygous mutation Phe144Leu leading to the absence of melanocortin signaling was associated with early-onset obesity suggesting its pathogenic role.

Comparative capacities of the pig colon and duodenum for luminal iron absorption.

Iron deficiency is the most common human nutritional disorder in the world. Iron absorptive capacity of the small intestine is known to be much limited and therefore large quantities of iron salts must be used to treat iron deficiency. As a result, significant amounts of iron may reach the large intestine. This study compared the capacities of the small and large intestine to transfer luminal iron to the venous blood in relationship with the expression in epithelial cells of proteins involved in iron absorption using a pig model. Intracaecal injection of iron sulphate corresponding with 2.5 and 5.0 mg elemental iron per kg body mass resulted in modest, transient, but significant (p<0.05) increases in iron concentration in the portal blood plasma. By comparing portal blood plasma iron concentrations following injection in the duodenal and caecal lumen, we calculated that 5 h after injection, iron colonic absorption represented approximately 14% of duodenal absorption. Caecal and proximal colon mucosa accumulated iron to a much lower extent than the duodenal mucosa. Isolated colonocytes were found to express divalent metal transporter (DMT1) and ferritin, but to a lesser extent than the duodenal enterocytes. Ferroportin was highly expressed in colonocytes. In these cells as well as in enterocytes ferroportin was found to be glycosylated. In short term experiments and at a concentration in the range of that measured in the aqueous phases recovered from the large intestine luminal content after iron injection, iron sulphate did not alter colonocyte viability. We concluded that the colonic epithelial cells that express proteins involved in iron absorption are able to transfer luminal iron to the venous blood even if its relative participation in the overall intestinal absorption appears to be modest under our experimental conditions.

Lead and aluminium levels in infants' hair, diet, and the local environment in the Moroccan city of Marrakech.

In order to assess the contamination burden of infants from the city of Marrakech (Morocco), hair lead and aluminium concentrations were studied in a sample of 573 infants, aged 0 to 12 months, and correlated with the infants descriptors such as age, gender and the parents occupations. Moreover, the two metals were measured in the local environment (soil, drinking water) and in the food commonly used during weaning. The mean values in children's hair are 6.6 and 9.5 microg/g for lead and aluminium respectively. The higher value for aluminium compared with lead can be explained by the higher levels of aluminium available in both the infant food and the environment. Age, gender, and the parents' occupations influenced significantly lead but not aluminium contents.

Trace element level in infant hair and diet, and in the local environment of the Moroccan city of Marrakech.

A sample of 573 infants (aged 0 to 12 months) from the Moroccan city of Marrakech was studied in order to determine the level of Pb and Al contaminations. Mean values of Pb and Al in children's hair were 6.6 and 9.5 microg/l, respectively. Age, gender, and parents' occupation influenced significantly Pb content but not Al content. Larger mean values were measured for Al compared with Pb. This finding can be explained by a higher level of Al available in both the infant diet (complementary feeding) and the local environmental factors (soil and drinking water). During weaning, beverages like tea, widely used in Morocco, represent an important source of Pb and Al contamination. Al content in drinking water is above the international standard.

[Effects of puberty on glucose-lipid balance during exercise in the obese child]. / Effets de la puberté sur la balance glucido-lipidique lors de l'exercice de l'enfant obèse.

The aim of the present study was to investigate effect of puberty on substrate oxidation rates using a graded exercise test to exhaustion. Two groups of obese adolescent males (34 prepubertal: body mass index (BMI) = 25,94 +/- 2,63; Z-score = 4,43 +/- 1,83; and 26 postpubertal: BMI = 31,14 +/- 4,88; Z-score = 5,264 +/- 1,76) performed an exercise test on a cycle ergometer. The test consisted in a series of graded exercises on a cycle ergometer. Stage duration was 3 min 30 s. Fat and carbohydrate rates were calculated during the last 30 s of each stage using stoichiometric equations, and this permitted us to calculate substrate oxidation according to exercise intensity. Lipid oxidation rates are significantly higher in the postpubertal group. When the fat oxidation rates are reported relative to fat free mass, fat oxidation rates are higher in the prepubertal group. Puberty decreases significantly the capacity of fat free mass to oxidize fat for a same level of exercise.

Iron and exercise induced alterations in antioxidant status. Protection by dietary milk proteins.

Lipid peroxidation stress induced by iron supplementation can contribute to the induction of gut lesions. Intensive sports lead to ischemia reperfusion, which increases free radical production. Athletes frequently use heavy iron supplementation, whose effects are unknown. On the other hand, milk proteins have in vitro antioxidant properties, which could counteract these potential side effects. The main aims of the study were: (1) to demonstrate the effects of combined exercise training (ET) and iron overload on antioxidant status; (2) to assess the protective properties of casein in vivo; (3) to study the mechanisms involved in an in vitro model. Antioxidant status was assessed by measuring the activity of antioxidant enzymes (superoxide dismutase (SOD); glutathione peroxidase (GSH-Px)), and on the onset of aberrant crypts (AC) in colon, which can be induced by lipid peroxidation. At day 30, all ET animals showed an increase in the activity of antioxidant enzymes, in iron concentration in colon mucosa and liver and in the number of AC compared to untrained rats. It was found that Casein's milk protein supplementation significantly reduced these parameters. Additional information on protective effect of casein was provided by measuring the extent of TBARS formation during iron/ascorbate-induced oxidation of liposomes. Free casein and casein bound to iron were found to significantly reduce iron-induced lipid peroxidation. The results of the overall study suggest that Iron supplementation during intensive sport training would decrease anti-oxidant status. Dietary milk protein supplementation could at least partly prevent occurrence of deleterious effects to tissue induced by iron overload.

Milk proteins and iron absorption: contrasting effects of different caseinophosphopeptides.

Clusters of phosphoserine residues in cow milk caseins bind iron (Fe) with high affinity. Casein inhibits Fe absorption in humans, but protein hydrolysis lessens this effect. Phosphopeptides from different caseins gave conflicting results on Fe absorption; release of phosphate residues by intestinal alkaline phosphatase could be a key point of that metabolism. The objectives of this study were to compare the absorption of Fe complexed to caseinophosphopeptides (CPP) of the main cow milk caseins beta-casein (beta-CPP) and alpha(s)-caseins (alpha(s1)-CPP) and to assess the role of alkaline phosphatase on this absorption. Two experimental models were used: an in vivo perfused rat intestinal loop and an in vitro Caco-2 cell culture model. In addition, we determined the effect of an intestinal phosphatase inhibitor on these various forms of Fe. Gluconate Fe was used as control. In both models, uptake and net absorption of Fe complexed to CPP from alpha(S1)-caseins were significantly lower than from Fe complexed to beta-CPP. Inhibition of the intestinal phosphatase significantly increased the uptake and the absorption of Fe complexed to beta-CPP without effect on the other forms of Fe. These results confirm the enhancing effect of beta-casein and its CPP on Fe absorption. The differences between CPP could be explained by their structural and/or conformational features: binding Fe to alpha(S1)-CPP could impair access to digestive enzymes, whereas beta-CPP-bound Fe is better absorbed than its free form. The differences in protein composition between cow and breast milk, which does not contain alpha-casein, could explain some of their differences in Fe bioavailability.

Improved absorption of caseinophosphopeptide-bound iron: role of alkaline phosphatase.

Hydrolysis of proteins could lessen their inhibiting effect on the poor absorption of cow's milk iron (Fe), which is responsible for the high incidence of Fe deficiency worldwide. When bound to Fe, caseinophosphopeptides (CPP) derived from milk proteins resist luminal digestion, enhance Fe solubility and could improve its bioavailability; brush border enzyme alkaline phosphatase activity could influence iron absorption by releasing free Fe; this study assessed its role in the absorption of CPP-bound Fe. Rat duodenal loops were perfused with Fe gluconate or Fe bound to the CPP of beta casein [beta-CN (1-25)], with or without the addition of an inhibitor of alkaline phosphatase, Na2WO4. The uptake of Fe-beta-CN (1-25) was greater than Fe gluconate. Na2WO4 enhanced the uptake of Fe-beta-CN (1-25) and not of Fe gluconate. So the release of free, insoluble Fe, by alkaline phosphatase seems to be prevented by providing Fe in the Fe-beta-CN (1-25) complex form. Its good disappearance rate makes beta-CN (1-25)-bound Fe a candidate for food fortification.

Iron absorption from concentrated hemoglobin hydrolysate by rat.

Although heme iron is highly bioavailable, the low iron content of hemoglobin prevents its use for dietary fortification; on the other hand, purified heme has low solubility and absorption rate. The present study was designed to assess the interactions between concentrated heme iron and peptides released during globin hydrolysis and cysteine and their relation with iron absorption. Hemoglobin was hydrolyzed by pepsin or subtilisin, and then, heme iron was concentrated by ultrafiltration. Iron absorption was studied in a Ussing chamber; gluconate was used as control. Iron uptake from nonconcentrated pepsin hydrolysate and gluconate was lower than from other groups. Cysteine significantly enhanced iron uptake except from the concentrated subtilisin hydrolysate. There was no significant difference between cysteine-supplemented groups. According to the different hydrolysis pathways of enzymes, it is assumed that the presence of hydrophobic peptides and the strength of heme-peptide interactions are both determining factors of heme iron absorption. These interactions occur mainly before iron uptake, as emphasized by the effect of cysteine.

Zinc status and bone mineralisation in adolescent girls.

The aim of the project was to assess the relationship between zinc status and bone mineralisation in pre-menarcheal adolescent girls. One hundred and thirty-nine healthy pre-menarcheal girls (Tanner pubic hair stage < or = 4), aged 12.4 +/- 1.0 years, had two visits at an interval of 2 years. Serum and urine zinc concentrations (Zn S; Zn U; Zn U/ creatinine), insulin-like growth factor 1 (IGF-I), and markers of bone turn-over, i.e. osteocalcin and parathormone (PTH), concentrations were measured at the first visit. Lumbar (L2-L4) bone mineral content and density (BMC, BMD) were measured at both visits. BMC and BMD and their increase at the follow-up after 2 years were compared with biochemical data by multiple regression. The stage of puberty was added as a covariable in the analysis. At the first visit, a significant correlation was found between sexual maturity and initial BMC, BMD, height, weight, and IGF-I. Zn S was negatively correlated with osteocalcin. Zn U showed a positive correlation with BMC, BMD, IGF-I, height, weight, and PTH. At the second visit, sexual maturity showed a positive correlation with BMD and weight increments and a negative one with BMC and height gains. Zn S was significantly related with BMD increase. These correlations suggest that zinc plays a role in normal growth and bone mineralisation during puberty onset.

Biopeptides of milk: caseinophosphopeptides and mineral bioavailability.

The biological and physiological activities of milk proteins are partially attributed to several peptides encrypted in the protein molecules. These peptides can be liberated by enzymatic digestion in vitro and in vivo. Among the biologically active molecules, phosphorylated peptides (caseinophosphopeptides, CPP) are known to exert an effect on calcium metabolism but also on other minerals. While the existing discrepancy on the potential role of CPP on calcium availability has not been clarified, the results of our previous studies showed that a purified phosphopeptide (beta(1-25)) exhibits a positive effect on iron bioavailability in vivo. Here we report the main results on the efficiency of beta(1-25) in the absorption and availability of iron as well as on the mechanism involved.