Localized self-heating in large arrays of 1D nanostructures.

One dimensional (1D) nanostructures offer a promising path towards highly efficient heating and temperature control in integrated microsystems. The so called self-heating effect can be used to modulate the response of solid state gas sensor devices. In this work, efficient self-heating was found to occur at random networks of nanostructured systems with similar power requirements to highly ordered systems (e.g. individual nanowires, where their thermal efficiency was attributed to the small dimensions of the objects). Infrared thermography and Raman spectroscopy were used to map the temperature profiles of films based on random arrangements of carbon nanofibers during self-heating. Both the techniques demonstrate consistently that heating concentrates in small regions, the here-called "hot-spots". On correlating dynamic temperature mapping with electrical measurements, we also observed that these minute hot-spots rule the resistance values observed macroscopically. A physical model of a random network of 1D resistors helped us to explain this observation. The model shows that, for a given random arrangement of 1D nanowires, current spreading through the network ends up defining a set of spots that dominate both the electrical resistance and power dissipation. Such highly localized heating explains the high power savings observed in larger nanostructured systems. This understanding opens a path to design highly efficient self-heating systems, based on random or pseudo-random distributions of 1D nanostructures.

Dietary long-chain polyunsaturated fatty acid supplementation in infants with phenylketonuria: a randomized controlled trial.

BACKGROUND: Pre- and postnatal tissue accretion of long-chain polyunsaturated fatty acids (LCPUFA) has been related to visual and cognitive development in healthy children in several studies. Children with phenylketonuria (PKU) consume diets with very low contents of preformed LCPUFA. We studied prospectively the LCPUFA status in infants with PKU without or with LCPUFA supplementation during the first year of life. SUBJECTS AND METHODS: Infants with PKU were enrolled at diagnosis (<4 weeks of age) and randomized double blind to phenylalanine-free amino acid supplements without LCPUFA (n = 11) or with both arachidonic (AA, 0.46 wt%) and docosahexaenoic acids (DHA, 0.27 wt%) (n = 10). At enrolment and again at 1, 2, 3, 4, 6, 9 and 12 months, plasma phospholipid fatty acids were measured and dietary intakes were calculated from dietary protocols. RESULTS: Unsupplemented patients showed a marked LCPUFA depletion to levels clearly below those observed in healthy breast-fed infants. In contrast, supplemented infants had stable and higher LCPUFA levels than unsupplemented infants, reaching significant differences for AA values at 3, 4 and 6 months, and for DHA values at 1, 3, 4, 6, 9 and 12 months. Plasma phospholipid levels correlated closely with estimated dietary intakes of preformed LCPUFA. CONCLUSION: Low LCPUFA intakes with PKU diets induce marked depletion of AA and particularly of DHA in the first year of life. Thus endogenous synthesis of LCPUFA from precursors supplied by diet seems unable to compensate for low LCPUFA intakes. LCPUFA supplementation of PKU diets during the first year of life effectively enhances LCPUFA status to levels comparable to those of healthy breast-fed infants.

A comparison of the properties of a Bcl-xL variant to the wild-type anti-apoptosis inhibitor in mammalian cell cultures.

The overexpression of bcl-2 and its homologues is a widely used strategy to inhibit apoptosis in mammalian cell culture systems. In this study, we have evaluated the Bcl-2 homologue, Bcl-x(L) and compared its effectiveness to a Bcl-x(L) mutant lacking most of the non-conserved unstructured loop domain, Bcl-x(L)Delta (deletion of amino acids 26 through 83). The cell line, Chinese hamster ovary (CHO), was genetically modified to express constitutively Bcl-x(L) or the Bcl-x(L) variant and subjected to model apoptotic insults including Sindbis virus (SV) infection, gradual serum withdrawal, and serum deprivation. When cells were engineered to overexpress Bcl-x(L)Delta, cell death due to the SV was inhibited, and Bcl-x(L)Delta provided comparable protection to the wild-type Bcl-x(L) even though expression levels were much lower for the mutant. Furthermore, the cells expressing Bcl-x(L)Delta continued to proliferate following infection while CHO-bcl-x(L) ceased proliferation immediately following infection. As a result, total production of a heterologous protein encoded on the SV was highest in cell lines expressing Bcl-x(L)Delta. Cells expressing the variant Bcl-x(L) also continued to proliferate and showed increased viable cell numbers following gradual serum withdrawal. In contrast, wild-type Bcl-x(L) expressing CHO cells were found to arrest growth but maintain viability following serum withdrawal. Interestingly, CHO cells expressing Bcl-x(L)Delta were also able to recover and return to rapid growth rates much faster than either the wild-type CHO-bcl-x(L) or CHO following the replenishment of fresh complete medium containing 10% FBS. Confocal imaging of yellow fluorescent protein (YFP) fused to the N terminus of Bcl-x(L) and Bcl-x(L)Delta indicated dense aggregates of the Bcl-x(L)Delta while the wild-type protein was distributed throughout the cell in a manner resembling transmembrane localization. As an alternative to complete removal of the loop domain, Bcl-x(L) variants were created in which aspartate residues containing potential caspase recognition sites within the loop domain of Bcl-x(L) were removed. Cell populations expressing various Bcl-x(L)-Asp mutants were exposed to an apoptotic spent medium stimulus, and the cells expressing these Bcl-x(L) variants provided increased viabilities as compared to cells containing wild-type Bcl-x(L) protein. These studies indicate that modification of anti-apoptotic genes can affect multiple cellular properties including response to apoptotic stimuli and cell growth. This knowledge can be valuable in the design of improved apoptosis inhibitors for biotechnology applications.

Reduced risk for overweight and obesity in 5- and 6-y-old children by duration of sleep--a cross-sectional study.

OBJECTIVE: To assess the relationship between sleep duration and adiposity in 5- and 6-y-old Bavarian children. DESIGN: Cross-sectional study. SUBJECTS: A total of 6862 German children aged 5-6 y participating in the obligatory health examination in Bavaria, southern Germany. MEASUREMENTS: Routine data were collected on the height and weight of children at the time of school entry in six public health offices in 1999 and in another two in 2000. Body fat mass was estimated by BIA performed in three of those offices. An extensive questionnaire was given to all children's parents in order to assess risk factors for overweight and obesity. The main outcome measures were overweight, defined by a body mass index (BMI) above the 90th centile and obesity, defined by a BMI above the 97th centile for the German children in Bavaria. Excessive body fat was defined as fat mass above the 90th centile for all German children seen in this survey. The main exposure was usual sleeping hours on week days. RESULTS: The prevalence of obesity decreased by duration of sleep: < or =10 h, 5.4% (95% CI 4.1-7.0), 10.5-11.0 h, 2.8% (95% CI 2.3-3.3), and > or =11.5 h, 2.1% (95% CI 1.5-2.9). Similar relations were found with the prevalence of overweight and excessive body fat. These effects could not be explained by confounding due to a wide range of constitutional, sociodemographic and lifestyle factors. The adjusted odds ratio for obesity were: for sleeping 10.5-11.0 h, 0.52 (95% CI 0.34-0.78) and 0.46 (95% CI 0.28-0.75) for sleeping 11.5 h. CONCLUSION: The effect of sleep duration on obesity in children reflects a higher body fat composition and appears to be independent of other risk factors for childhood obesity.

Polyunsaturated fatty acid supply with human milk.

Polyunsaturated fatty acids in human milk may derive from diet, liberation from maternal body stores, or endogenous synthesis from precursor fatty acids. The contribution of each of these sources has not been studied in detail. Although maternal diet is a key factor affecting human milk composition, other factors such as gestational age, stage of lactation, nutritional status, and genetic background are known to influence the fat content and fatty acid composition in human milk. Both linoleic and alpha-linolenic acids, the essential fatty acids, are present in human milk, as are several other n-6 and n-3 longer chain polyunsaturated fatty acids that are required for optimal growth and development of infants. The fatty acid profile of human milk from lactating women of different countries is remarkably stable, but there is variability in some of the components, such as docosahexaenoic acid, which is mainly due to differences in dietary habits. Tracer techniques with stable isotopes have been valuable in assessing the kinetics of fatty acid metabolism during lactation and in determining the origin of fatty acids in human milk. Based on these studies, the major part of polyunsaturated fatty acids in human milk seems not to be provided directly from the diet but from maternal tissue stores.

Evaluation of the Helicobacter pylori stool antigen test (HpSA) for detection of Helicobacter pylori infection in children.

OBJECTIVE: Helicobacter pylori (H. pylori) infection is usually acquired in early childhood. Noninvasive methods for detection of H. pylori infection are required to study its incidence, transmission, and clearance. They should be easy to perform, inexpensive, and have a high diagnostic accuracy, especially in infants and toddlers. Both serology and the 13C-urea breath test (13C-UBT) do not fulfill all these requirements. The aim of this study was to evaluate a new enzyme immunoassay for detection of H. pylori antigen in stool (Premier Platinum HpSA, Meridian Diagnostics, Cincinnati, OH) in a large cohort of children and to compare it to invasive techniques and the 13C-UBT. METHODS: HpSA was performed in 310 stool samples of 274 children divided into three groups. Group A consisted of 145 children and adolescents (0.5-19.8 yr, 66/145 <6 yr) who underwent upper endoscopy for various gastrointestinal symptoms. H. pylori status was defined by histology, culture, and rapid urease test from biopsies of the antrum and corpus. A 13C-UBT was performed in 133 of 145 children. Group B consisted of 22 patients (5.7-16.1 yr) who were retested with both noninvasive tests 8 wk after anti-H. pylori triple therapy. Group C consisted of 129 healthy infants and toddlers (0.9-3.1 yr) who were tested with the 13C-UBT. Children with discrepant or positive test results were retested after 2 and 12 months. Results of the HpSA were read at 450/620 nm by spectrophotometry. An optical density <0.100 was defined as negative, >0.120 as positive, and values between 0.100 and 0.120 were considered as equivocal. RESULTS: In Group A, the HpSA gave false-negative results in five of 45 infected children and false-positive results in four of 100 noninfected children, whereas four patients (2.8%) showed equivocal results. In both infected and noninfected children, no relation between the optical density values and age was found. The 13C-UBT was correct in 132 of 133 children tested. In Group B, there was complete concordance between the HpSA and 13C-UBT: 19 children tested negative and three positive. In Group C, concordant results between the two noninvasive methods were found in 124 of 129 (96%) toddlers (122 negative and two positive). Retesting of five children with discrepant results revealed that, on initial testing, the HpSA was incorrect in two (one false-positive, one false-negative), and the 13C-UBT was incorrect in three (always false-positive). CONCLUSIONS: In symptomatic children, the HpSA revealed a sensitivity of 88.9% (95% CI 77.3-96.3) and a specificity of 94.0% (88.1-97.7) compared to the 13C-UBT, 100% (94.0-100) and 98.9% (94.7-100), respectively. However, in healthy toddlers, the HpSA performed as well as the 13C-UBT with excellent concordance between the two noninvasive tests. There was no age dependency of the stool test results, and changing the cutoff would not have improved accuracy. Thus, the HpSA test seems suitable to monitor the success of anti-H. pylori therapy.

Comparison of Bcl-2 to a Bcl-2 deletion mutant for mammalian cells exposed to culture insults.

Apoptosis has been found to occur in bioreactors as a result of environmental stresses. The overexpression of bcl-2 is a widely used strategy to limit the induction of apoptosis in mammalian cell cultures. In this study, the effectiveness of wild-type Bcl-2 was compared to a Bcl-2 mutant lacking the nonstructured loop domain in two commercially prominent cell lines, Chinese hamster ovary (CHO) and baby hamster kidney (BHK) cells. The generation of a DNA "ladder" and condensation of chromatin indicated that apoptosis occurred in these cell lines following Sindbis virus infection and serum deprivation. When cells were engineered to overexpress the bcl-2 mutant, cell death due to Sindbis virus was inhibited in a concentration-dependent manner. Furthermore, the Bcl-2 mutant provided increased protection as compared to wild-type Bcl-2 following two model insults, Sindbis virus infection and serum deprivation. Total production for a heterologous protein encoded on the Sindbis virus was increased in cell lines expressing the Bcl-2 variants compared to the parental cell line. In order to understand the reasons for the improved anti-apoptosis properties of the mutant, wild-type Bcl-2 and mutant Bcl-2 were examined by Western blot following each model insult. Wild-type Bcl-2 was observed to degrade into a 23 kDa fragment following both Sindbis virus infection and serum withdrawal in both cell lines, while the mutant Bcl-2 protein was not degraded during the same period. The processing of Bcl-2 was found to correlate with reduced cell viabilities following the two external insults to suggest that Bcl-2 degradation may limit its ability to inhibit apoptosis. These studies indicate that the cells regulate anti-apoptosis protein levels and these processing events can limit the effectiveness of cell death inhibition strategies in mammalian cell culture systems.

Physiological aspects of human milk lipids.

Human milk from healthy and well-nourished mothers is the preferred form of feeding for all healthy newborn infants. The nutrient supply with human milk supports normal growth and development of the infant. Here the general characteristics of human milk lipids and recent knowledge on lactational physiology, composition and functional aspects of human milk lipids are discussed. Lipids in human milk represent the main source of energy for the breastfed baby and supply essential nutrients such as fat-soluble vitamins and polyunsaturated fatty acids (PUFA). The essential fatty acids linoleic and alpha-linolenic acids (LA and ALA) are precursors of long-chain polyunsaturated fatty acids (LC-PUFA), including arachidonic (20:4n-6) and docosahexaenoic (22:6n-3) acids (AA and DHA). LC-PUFA serve as indispensable structural components of cellular membranes and are deposited to a considerable extent in the growing brain and the retina during perinatal development. The supply of preformed LC-PUFA with human milk lipids has been related to functional outcomes of the recipient infants such as visual acuity and development of cognitive functions during the first year of life. Recent stable isotope studies indicate that the major portion of milk PUFA is not derived directly from the maternal diet, but stems from endogenous body stores. Thus, not only the woman's current but also her long-term dietary intake is of marked relevance for milk fat composition.

Fat content and fatty acid composition of fresh, pasteurized, or sterilized human milk.

In hospitals, human milk is subjected to heat treatment to reduce risk of transmission of infectious agents such as human immunodeficiency virus (HIV), hepatitis B, cytomegalovirus, and bacterial contamination, especially during feeding of banked milk to preterm infants. Fat losses due to heat treatment have been extensively studied in cow milk but have received little attention in human milk. We studied the effect of human milk pasteurization and sterilization on total fat content available to the infant as well as on fatty acid composition. Milk samples from 12 mothers (days 5-35 of lactation) were divided into three equal parts: one remained fresh, one was pasteurized (62.5 degrees C for 30min), and one was sterilized (120 degrees C for 30min). Fat content was determined gravimetrically, and the contribution of 30 fatty acids was determined by gas chromatography. For investigation of loss of available fat in sterilized milk, milk was collected from two additional mothers and analyzed with a modified extraction method. Total fat content was the same in fresh, pasteurized, and sterilized milk. The available fat content was 3.1+/-0.4g/dL (mean +/- SE) in fresh human milk, 3.1+/-0.4g/dL in pasteurized human milk, and 2.7+/-0.3g/dL (P < 0.001 vs. fresh) in sterilized human milk because of formation of a surface skin and fat adherence to the vial wall after sterilization. The fatty acid composition of 10 saturated, 10 monounsaturated, and 10 polyunsaturated fatty acids of both the n6 and n3 series was not affected by pasteurization. In sterilized milk there was a slight decrease of linoleic acid (C18:2n6; -0.7% vs. fresh; P = 0.006) and arachidonic acid (C20:4n6; -2.5%; P = 0.045). Pasteurization and sterilization do not affect total fat content of human milk, but sterilization may reduce available fat content by >10%. Fatty acid composition of human milk is not changed by pasteurization, but is slightly changed by sterilization.

Does breast-feeding protect against childhood obesity?

The impact of breast-feeding on overweight and obesity in children at school entry was assessed in a cross sectional study in Bavaria in 1997. The school entry health examination enrolled 134,577 children. Data on early feeding were collected in two rural districts (eligible population n=13,345). The analyses were confined to 5 or 6 year old children with German nationality. The main outcome measures were overweight (BMI>90th percentile for all German children seen at the 1997 school entry health examination in Bavaria) and obesity (BMI>97th percentile). Information on breast-feeding was available for 9206 children of whom 56% had been breast-fed for any length of time. In non breast-fed children the upper tail of the BMI distribution was enlarged as compared to the breast-fed children whereas the median was almost identical. The prevalence of obesity in children who had never been breast-fed was 4.5% as compared to 2.8% in ever breast-fed children. A clear dose response effect for the duration of breast-feeding on the prevalence of obesity was found: 3.8%, 2.3%, 1.7% and 0.8% for exclusive breast-feeding for up to 2, 3 to 5, 6 to 12 and more than 12 months, respectively. The results for overweight were very similar. The protective effect of beast feeding on overweight and obesity could not be explained by differences in social class or lifestyle. The adjusted odds ratios of breast-feeding for any length of time was 0.71 (95% CI 0.56-0.90) for obesity and 0.77 (95%CI 0.66-0.88) for overweight. This data set did not allow to adjust for maternal weight, an important risk factor for obesity in children. Maternal overweight, however, could not explain the effect of breastfeeding on overweight and obesity in a similar study. The reduction in the risk for overweight and obesity is therefore more likely to be related to the properties of human milk than to factors associated with breast-feeding. The potential relevance of different components of human milk for the observed reduction in the risk for overweight and obesity is discussed. The preventive effect of breast-feeding on overweight and obesity is an important additional argument for the promotion of breast-feeding in industrialised countries.

Polyunsaturated fatty acid supply with human milk. Physiological aspects and in vivo studies of metabolism.

The origin of polyunsaturated fatty acids (PUFA) in human milk has not been studied in detail. Diet, liberation from maternal stores and endogenous synthesis from precursors may contribute to PUFA present in human milk. Other factors influencing lipid content and fatty acid composition such as gestational age, stage of lactation, nutritional status and genetical background are known. In a series of in vivo studies using stable isotope methodologies we investigated the metabolism of PUFA during lactation. With this techniques the transfer of single dietary fatty acids into human milk, the oxidation and the deposition in tissues were estimated. Our studies demonstrate that the major part of PUFA in human milk seems not to be derived directly from the maternal diet but from body stores. Nevertheless diet is important, because long term intakes affect composition of body stores.

Docosahexaenoic acid transfer into human milk after dietary supplementation: a randomized clinical trial.

Docosahexaenoic acid (DHA) is important for infant development. The DHA transfer from maternal diet into human milk has not been investigated in detail. We studied the effects of DHA supplementation on the fatty acid composition of human milk and the secretion of dietary (13)C-labeled fatty acids, including DHA, into human milk. Ten lactating women were randomized to consume, from 4 to 6 weeks postpartum, an oil rich in DHA (DHASCO, 200 mg of DHA/day) (n = 5) or a placebo oil (n = 5). Dietary intakes were followed by 7-day protocols. On study day 14 a single dose of [U-(13)C]DHASCO was given orally, milk samples were collected over 48 h, and milk production was recorded. Milk fatty acid composition was determined by gas-liquid chromatography and isotopic enrichment was determined by gas chromatography- combustion-isotope ratio mass spectrometry (GC-C-IRMS). Milk DHA content did not differ between the supplemented and placebo group at study entry (0.29 vs. 0.28 wt%, median). After 2 weeks of supplementation the milk DHA content was almost 2-fold higher in the supplemented versus placebo group (0.37 vs. 0.21 wt%, P = 0.003). Cumulative recovery of [(13)C]palmitic, [(13)C]oleic, and [(13)C]docosahexaenoic acids in human milk at 48 h was similar between supplemented and placebo groups (palmitic acid 7.40 vs. 8. 14%, oleic acid 9.14 vs. 9.97%, and docosahexaenoic acid 9.09 vs. 8. 03% of dose, respectively). Notable lower recovery was observed for [(13)C]myristic acid in both the supplemented and placebo groups, 0. 62 versus 0.77% of dose. Dietary DHA supplementation increases the DHA content in human milk. DHA transfer from the diet into human milk is comparable to palmitic and oleic acid transfer.

Breast feeding and obesity: cross sectional study.

OBJECTIVE: To assess the impact of breast feeding on the risk of obesity and risk of being overweight in children at the time of entry to school. DESIGN: Cross sectional survey SETTING: Bavaria, southern Germany. METHODS: Routine data were collected on the height and weight of 134 577 children participating in the obligatory health examination at the time of school entry in Bavaria. In a subsample of 13 345 children, early feeding, diet, and lifestyle factors were assessed using responses to a questionnaire completed by parents. SUBJECTS: 9357 children aged 5 and 6 who had German nationality. MAIN OUTCOME MEASURES: Being overweight was defined as having a body mass index above the 90th centile and obesity was defined as body mass index above the 97th centile of all enrolled German children. Exclusive breast feeding was defined as the child being fed no food other than breast milk. RESULTS: The prevalence of obesity in children who had never been breast fed was 4.5% as compared with 2.8% in breastfed children. A clear dose-response effect was identified for the duration of breast feeding on the prevalence of obesity: the prevalence was 3.8% for 2 months of exclusive breast feeding, 2.3% for 3-5 months, 1.7% for 6-12 months, and 0.8% for more than 12 months. Similar relations were found with the prevalence of being overweight. The protective effect of breast feeding was not attributable to differences in social class or lifestyle. After adjusting for potential confounding factors, breast feeding remained a significant protective factor against the development of obesity (odds ratio 0.75, 95% CI 0.57 to 0.98) and being overweight (0.79, 0.68 to 0.93). CONCLUSIONS: In industrialised countries promoting prolonged breast feeding may help decrease the prevalence of obesity in childhood. Since obese children have a high risk of becoming obese adults, such preventive measures may eventually result in a reduction in the prevalence of cardiovascular diseases and other diseases related to obesity.

Oxidation of an oil rich in docosahexaenoic acid compared to linoleic acid in lactating women.

BACKGROUND: We studied the oxidation of an oil rich in docosahexaenoic acid (DHA; DHASCO((R))) in lactating mothers receiving a dietary DHA supplement or a placebo. The results were compared with the oxidation of linoleic acid. METHODS: Breast-feeding mothers received a dietary supplement (DHASCO; 200 mg DHA/day, n = 5) or a placebo (n = 5) for 14 days. Six weeks post partum all 10 mothers received a single dose of 2 mg/kg body weight uniformly (13)C-labeled DHASCO. In a previously reported study 6 mothers received 1 mg/kg body weight uniformly (13)C-labeled linoleic acid. Breath samples were collected over 48 h after tracer application. The total CO(2) production was measured by indirect calorimetry and the (13)C isotopic enrichment of labeled CO(2) by isotopic ratio mass spectrometry. RESULTS: The oxidation of (13)C-labeled DHASCO in the supplemented and placebo groups was similar. Maximal (13)C enrichment was reached earlier in the group receiving (13)C-DHASCO (median 1.0 vs. 3.0 h in the linoleic acid group). The cumulative (13)C recovery in breath was higher in the DHASCO versus the linoleic acid group until 10 h after tracer application and comparable thereafter. CONCLUSIONS: The difference in oxidation of DHASCO versus linoleic acid after tracer ingestion might be partly due to a faster absorption and oxidation of shorter chain saturated fatty acids contained in DHASCO. The cumulative oxidation of DHASCO and linoleic acid 24 and 48 h after tracer ingestion is similar.

Effects of human milk pasteurization and sterilization on available fat content and fatty acid composition.

BACKGROUND: Human milk is frequently heat treated in hospitals to reduce bacterial contamination, particularly in banked milk fed to preterm infants. Pasteurization and sterilization may induce oxidative losses of unsaturated lipids and vitamins and may inactivate enzymes and immunologic factors. This study was designed to examine the effects of pasteurization and sterilization on milk fat content available to the recipient infant and on fatty acid composition. METHODS: In fresh, pasteurized (62.5 degrees C for 30 minutes), and sterilized (120 degrees C for 30 minutes) milk samples (5 ml) of 12 mothers (days 5-35 of lactation), fat content was determined gravimetrically and the contribution of 30 fatty acids was determined by gas-liquid chromatography. RESULTS: The coefficients of variation for measurements of milk fat content were 0.7% and of fatty acids accounting for more than 0.09% of weight, 0.1-3.0%. Available fat content was 3.1+/-1.4 g/dl (mean +/- SD) in fresh human milk and 3.1+/-1.4 g/dl (not significant) in pasteurized human milk. Fat content declined to 2.7+/-1.1 g/dl (p < 0.001 vs. fresh) in sterilized human milk, because of increased fat adherence to the container surface after sterilization. The percentage composition of saturated, monounsaturated, and polyunsaturated fatty acids of the n-6 (C18:3, C20:2, C20:3, and C22:4) and the n-3 series (C18:3 C20:5, C22:5, and C22:6) was not affected by thermal treatment. Milk sterilization caused a slight decrease of linoleic (-0.7% vs. fresh milk; p = 0,006) and arachidonic (-2,6%; p = 0.045) acids. CONCLUSIONS: Pasteurization of human milk does not influence fat content and composition, but sterilization may reduce available fat content by more than 10%, whereas there are only slight changes in fatty acid composition.

The use of stable isotope techniques for nutritional and metabolic research in paediatrics.

Stable isotope methods are increasingly used in paediatrics for clinical diagnosis and research due to marked improvements in analytical technologies and better availability of suitable tracers. The safety of stable isotopes is of major importance for use in children. Large amounts of deuterium well above the doses applied under clinical conditions may induce adverse effects. In contrast, heavier stable isotopes such as 13C, 15N or 18O do not induce adverse effects even at the highest enrichments obtained, and they are safe. Breath tests with measurements of 13CO2 enrichment after oral application of a tracer can reliably evaluate helicobacter pylori infection and gastric emptying kinetics. Combined with an estimation of total CO2 production, 13CO2 breath tests allow estimation of the absorption and oxidation of 13C-labelled substrates, such as medium- and long-chain triglycerides, and demonstrates the beneficial effect of carnitine supplements on fat oxidation in primary carnitine deficiency. The study of metabolic processes may require the sampling of blood for isotopic analyses of metabolites of the applied tracer. Gas chromatography-isotope ratio mass spectrometry can detect tracer in individual components from small plasma samples. The high precision enabled us to utilize the small differences in natural 13C-enrichment between dietary fats to study fatty acid turnover in term infants, in whom the dietary fat source was switched to corn oil with a slightly higher 13C-content. With this approach we demonstrated active conversion of linoleic into arachidonic acid. We also applied biotechnologically produced, U-13C labelled linoleic and alpha-linolenic acids to infants and detected the conversion of these essential fatty acids to their longer chain polyunsaturated derivatives, with an apparent change of conversion activity with age. Moreover, it has become possible to measure tissue protein synthesis from small biopsy samples obtained in situ without surgery, such as forceps biopsies of rectal tumors. These few examples of recent developments demonstrate the great clinical and scientific potential of stable isotope methods in future paediatric applications.

Safety of stable isotope use.

UNLABELLED: The increased employment of stable isotope tracers for diagnostic and research purposes frequently raises questions on potential risks associated with their use, which is of particular importance in the paediatric age group. Biological effects and the potential of adverse events has been evaluated in a large number of animal and, in part, also human studies. Possible differences in physical, chemical and biochemical behaviour resulting in kinetic and thermodynamic isotope effects between stable isotopes of the same element are related to the relative differences in atomic weight. Deuterium (2H), which differs markedly in mass from the predominant hydrogen isotope 1H, may induce serious side-effects at high concentrations in body fluids. The threshold dose for the occurrence of side-effects lies well above the usual tracer dosages for clinical use. In contrast to deuterium, heavier stable isotopes such as 13C, 15N or 18O that differ relatively little in mass from the predominant isotopes such as 12C, does not show any adverse biological effects even at highest enrichments. CONCLUSION: The doses of stable isotope tracer substances that are used for clinical diagnostic and research purposes appear safe and without any adverse effects. Stable isotope tracers should only be used in children if the trace is safe at the doses applied, and tracer is chemically pure and stable. In the case of intravenous application, the tracer preparation must also be sterile and pyrogen free.

New insights into lipid and fatty acid metabolism via stable isotopes.

UNLABELLED: Dynamic processes are of great interest in the study of lipid and fatty acid metabolism. Their in vivo investigation is now possible with the use of stable isotope tracers and the available sensitive analytical technology. We present some examples demonstrating the assessment of lipid oxidation as well as modulating factors by analysis of the tracer appearance in breath CO2 by isotope ratio mass spectrometry (IRMS). In a child with severe hypertriglycendaemia due to decreased cleavage of chylomicrons, medium-chain triglycerides were oxidised normally, whereas utilisation of long-chain triglycerides was severely disturbed. In another patient with primary carnitine deficiency, the beneficial effect of carnitine supplementation on fat oxidation could be demonstrated. In combination with gas chromatography, the high sensitivity of IRMS may be used for the detection of tracer materials in various plasma metabolites. In a pilot study, we applied C-13C labelled linoleic and alpha-linolenic acids to infants aged 2 weeks and 11 months, respectively. In these subjects, we could show a relative decrease of the conversion of these essential fatty acids to their longer chain polyunsaturated derivatives with age. The ability of term infants aged 19 days to convert linoleic into arachidonic acid was evaluated by using small natural differences in 13C abundance between different foods. Stable isotopes are also suitable for elucidation of new metabolic pathways. As an example, we could show in rats that linoleic and alpha-linolenic acids, which are usually considered to be essential substrates, can be synthesized endogenously from C16 precursors. CONCLUSION: IRMS is well suitable for the clinical investigation of lipid metabolism with stable isotopes in children. With different sample preparation devices, breath CO2 as well as specific plasma components can be analysed. While breath tests are already applied in clinical routing testing, GC-C-IRMS is a promising tool for research.

New insights into the metabolism of long chain polyunsaturated fatty acids during infancy.

Data obtained with stable isotope methodology have demonstrated that preterm and term infants can convert LA and ALA, respectively, to AA and DHA. In addition, they have clarified the pathways by which infants convert LA and ALA to LCPUFA and have demonstrated the importance of factors such as the dietary LA/ALA ratio and postnatal age on biosynthesis of AA and DHA. Further work is needed to clarify the role of other influential factors on endogenous synthesis of LCPUFA and to determine the absolute amounts of endogenous LCPUFA synthesis. Such data are necessary to define more precisely the LCPUFA requirements of growing infants.