Exploring proteins at soft interfaces and in thin liquid films - From classical methods to advanced applications of reflectometry.

The history of the topic of proteins at soft interfaces dates back to the 19th century, and until the present day, it has continuously attracted great scientific interest. A multitude of experimental methods and theoretical approaches have been developed to serve the research progress in this large domain of colloid and interface science, including the area of soft colloids such as foams and emulsions. From classical methods like surface tension adsorption isotherms, surface pressure-area measurements for spread layers, and surface rheology probing the dynamics of adsorption, nowadays, advanced surface-sensitive techniques based on spectroscopy, microscopy, and the reflection of light, X-rays and neutrons at liquid/fluid interfaces offers important complementary sources of information. Apart from the fundamental characteristics of protein adsorption layers, i.e., surface tension and surface excess, the nanoscale structure of such layers and the interfacial protein conformations and morphologies are of pivotal importance for extending the depth of understanding on the topic. In this review article, we provide an extensive overview of the application of three methods, namely, ellipsometry, X-ray reflectometry and neutron reflectometry, for adsorption and structural studies on proteins at water/air and water/oil interfaces. The main attention is placed on the development of experimental approaches and on a discussion of the relevant achievements in terms of notable experimental results. We have attempted to cover the whole history of protein studies with these techniques, and thus, we believe the review should serve as a valuable reference to fuel ideas for a wide spectrum of researchers in different scientific fields where proteins at soft interface may be of relevance.

Effects of Aqueous Isotopic Substitution on the Adsorption Dynamics and Dilational Rheology of ß-Lactoglobulin Layers at the Water/Air Interface.

The effect of the degree of isotopic substitution of the aqueous medium on the adsorption kinetics and the surface dilational rheological behavior at the water/air interface of the globular protein ß-lactoglobulin was investigated. Aqueous solutions with fixed concentrations of 1 µM protein and 10 mM hydrogenous buffer with controlled pH 7 were prepared in H2O, D2O, and an isotopic mixture of 8.1% v/v D2O in H2O (called air contrast matched water, ACMW). Using a bubble shape analysis tensiometer, we obtained various experimental dependencies of the dilational viscoelasticity modulus E as a function of the dynamic surface pressure and of the frequency and amplitude of bubble surface area oscillations, either in the course of adsorption or after having reached a steady state. In general, the results revealed virtually no effect from substituting H2O by ACMW but distinct albeit relatively weak effects for intermediate adsorption times for D2O as the aqueous phase. In the final stage of adsorption, established after around 10 h, the equilibrium adsorption and the dilational rheological behavior of all protein layers under investigation are only very weakly affected by the presence of D2O. The obtained results help to design experimental protocols for protein adsorption studies, for example, by neutron reflectivity.

Investigating the Conformation of Surface-Adsorbed Proteins with Standing-Wave X-ray Fluorescence.

Protein adsorption to surfaces is at the heart of numerous technological and bioanalytical applications, but sometimes, it is also associated with medical risks. To deepen our insights into processes involving layers of surface-adsorbed proteins, high-resolution structural information is essential. Here, we use standing-wave X-ray fluorescence (SWXF) in combination with an optimized liquid-cell setup to investigate the underwater conformation of the random-coiled phosphoprotein ß-casein adsorbed to hydrophilic and hydrophobized solid surfaces. The orientation of the protein, as determined through the distributions of sulfur and phosphorus, is found to be sensitive to the chemical nature of the substrate. While no preferred orientations are observed on hydrophobized surfaces, on hydrophilic Al oxide, ß-casein is adsorbed as a diblock copolymer with the phosphorylated domain I attached to the surface. Our results demonstrate that targeting biologically relevant chemical elements with SWXF enables a detailed investigation of biomolecular layers under near-physiological conditions.

Genome scale analysis of pathogenic variants targetable for single base editing.

BACKGROUND: Single nucleotide variants account for approximately 90% of all known pathogenic variants responsible for human diseases. Recently discovered CRISPR/Cas9 base editors can correct individual nucleotides without cutting DNA and inducing double-stranded breaks. We aimed to find all possible pathogenic variants which can be efficiently targeted by any of the currently described base editors and to present them for further selection and development of targeted therapies. METHODS: ClinVar database (GRCh37_clinvar_20171203) was used to search and select mutations available for current single-base editing systems. We included only pathogenic and likely pathogenic variants for further analysis. For every potentially editable mutation we checked the presence of PAM. If a PAM was found, we analyzed the sequence to find possibility to edit only one nucleotide without changing neighboring nucleotides. The code of the script to search Clinvar database and to analyze the sequences was written in R and is available in the appendix. RESULTS: We analyzed 21 editing system currently reported in 9 publications. Every system has different working characteristics such as the editing window and PAM sequence. C > T base editors can precisely target 3196 mutations (46% of all pathogenic T > C variants), and A > G editors - 6900 mutations (34% of all pathogenic G > A variants). CONCLUSIONS: Protein engineering helps to develop new enzymes with a narrower window of base editors as well as using new Cas9 enzymes with different PAM sequences. But, even now the list of mutations which can be targeted with currently available systems is huge enough to choose and develop new targeted therapies.

ß-Lactoglobulin Adsorption Layers at the Water/Air Surface: 3. Neutron Reflectometry Study on the Effect of pH.

Several characteristics of ß-lactoglobulin (BLG) layers adsorbed at the air/water interface exhibit a strong pH dependence, but our knowledge on the underlying structure-property relations is still fragmental. Here, we therefore extend our recent studies by neutron reflectometry (NR) and provide a comprehensive overview through direct measurements of the surface excess Γ and the layers' molecular structure. This enables comparison with available literature data to draw general conclusions. The NR experiments were performed at various pH values and within a wide range of protein concentrations, CBLG. Adsorption kinetics measurements in air-contrast-matched-water and over a narrow Qz range enabled direct quantification of the dynamic surface excess Γ(t) and are found to be consistent with ellipsometry data. Near the isoelectric point, pI, the rates of adsorption and Γ are maximal but only at sufficiently high CBLG. NR data collected over a wider Qz range and in two aqueous isotopic contrasts revealed the structure of adsorbed BLG layers at a steady state close to equilibrium. Independent of the pH, BLG was found to form dense monolayers with average thicknesses of 1.1 nm, suggesting flattening of the BLG globules upon adsorption as compared with their bulk dimensions (≈3.5 nm). Near pI and at sufficiently high CBLG, a thick (≈5.5 nm) but looser secondary sublayer is additionally formed adjacent to the dense primary monolayer. The thickness of this sublayer can be interpreted in terms of disordered BLG dimers. The results obtained and notably the specific interfacial structuring of BLG near pI complement previous observations relating the impact of solution pH and CBLG on other interfacial characteristics such as surface pressure and surface dilational viscoelasticity modulus.

Specific Ion Effects of Trivalent Cations on the Structure and Charging State of ß-Lactoglobulin Adsorption Layers.

The properties of proteins at interfaces are important to many processes as well as in soft matter materials such as aqueous foam. Particularly, the protein interfacial behavior is strongly linked to different factors like the solution pH or the presence of electrolytes. Here, the nature of the electrolyte ions can significantly modify the interfacial properties of proteins. Therefore, molecular level studies on interfacial structures and charging states are needed. In this work, we addressed the effects of Y3+ and Nd3+ cations on the adsorption of the whey protein ß-lactoglobulin (BLG) at air-water interfaces as the function of electrolyte concentration. Both cations caused very similar but dramatic changes at the interface and in the bulk solution. Here, measurements of the electrophoretic mobility and with vibrational sum-frequency generation (SFG) spectroscopy were applied and consistently showed a reversal of the BLG net charge at remarkably low ion concentrations of 30 (bulk) and 40 (interface) µM of Y3+ or Nd3+ for a BLG concentration of 15 µM. SFG spectra of carboxylate stretching vibrations from Asp or Glu residues of interfacial BLG showed significant changes in the resonance frequency, which we associate to specific and efficient binding of Y3+ or Nd3+ ions to the proteins carboxylate groups. Characteristic reentrant condensation for BLG moieties with bound trivalent ions was found in a broad concentration range around the point of zero net charge. The highest colloidal stability of BLG was found for ion concentrations <20 µM and >50 µM. Investigations on macroscopic foams from BLG solutions revealed the existence of structure-property relations between the interfacial charging state and the foam stability. In fact, a minimum in foam stability at 20 µM ion concentration was found when the interfacial net charge was negligible. At this concentration, we propose that the persistent BLG molecules and weakly charged BLG aggregates drive foam stability, while outside the bulk reentrant zone the electrostatic disjoining pressure inside foam lamellae dominates foam stability. Our results provide new information on the charge reversal at the liquid-gas interface of protein/ion dispersions. Therefore, we see our findings as an important step in the clarification of reentrant condensation effects at interfaces and their relevance to foam stability.

Budgetary Impact of Medicinal Therapies for Rare Diseases in Bulgaria.

BACKGROUND: Rare diseases have been continually outlined as one of the causes for the National Health Insurance Fund's (NHIF) deficit spending in Bulgaria. AIM: To estimate the budgetary impact of rare disease medicinal therapies from NHIF perspective for 2014 and 2016. MATERIALS AND METHODS: Budgetary impact of rare diseases is calculated as a percentage of NHIF total pharmaceutical spending. Total expenditure per ICD-10 code, mean annual number of patients reimbursed and mean annual cost per patient are analysed. RESULTS: Budgetary impact of rare diseases reached a plateau of about 9% of NHIF total pharmaceutical spending for 2014-2016. Mean number of patients reimbursed and mean annual cost per patient increased by median rates of 4.27% and 2.54%, respectively. Glycogen storage disease, neuropathic heredofamilial amyloidosis and C1 esterase inhibitor deficiency stood out, as they had the second, fourth and fifth most expensive medicinal treatment cost. While accounting for only 92 patients in 2016, these three conditions contributed for 22.89% of NHIF total expenditure on rare disease medicinal therapies. For comparison, coagulation defects, with the biggest total cost per indication, had a similar budgetary impact - 24.88%, but for 277 patients reimbursed. CONCLUSIONS: Our study does not support the concerns about uncontrolled growth of expenditures for rare disease medicinal therapies. Nevertheless, there is a need for enhanced post-marketing surveillance and performance-based payment of these treatments. Development, collection and analysis of local real-world data have been increasingly applied as a tool to advance these health policy goals.

Effect of Training at Lactate Threshold Intensity on Maximal Time to Exhaustion, Depression and Anxiety Behaviour of Spontaneously Hypertensive Rats after Kainate-Induced Status Epilepticus.

AIM: The objective of the present study was to investigate the effect of treadmill training at lactate threshold intensity on maximum time to exhaustion (MTE) and heart rate (HR) as well as behavioral changes after kainate (KA)-induced status epilepticus (SE) of spontaneously hypertensive rats (SHRs). MATERIALS AND METHODS: Male SHRs were divided in four groups: two sedentary (vehicle- and KA-treated) and two exercised (vehicle- and KA-treated), respectively. The exercised rats were trained on a treadmill at a speed of 20 m.min-1 and 0° elevation for 40 min.d-1, for 4 wk. Maximal time to exhaustion and HR was measured at the beginning and at the end of the training period. Status epilepticus was evoked in half of the sedentary and trained rats by a repetitive intraperitoneal injection of KA in low subconvulsive doses. The other half of the groups received saline. Sucrose preference test (SPT) for depression-like behavior and hole board test (HBT) for impulsivity were performed a month after KA/veh injection. RESULTS: The maximum time of exhaustion was elongated in the SHRs at the end of the training period in comparison with the beginning. However, no effect on HR was detected in trained rats. Kainate treatment after one month of training alleviated the SE-induced anhedonia in SPT and stereotyped behavior in HBT, respectively. CONCLUSIONS: Taken together, these results demonstrate that exercise exerts a beneficial influence on physical working capacity, depression and impulsive behavior in a co-morbid model of essential hypertension and SE.

Carfilzomib, lenalidomide, and dexamethasone in patients with relapsed multiple myeloma categorised by age: secondary analysis from the phase 3 ASPIRE study.

A primary analysis of the ASPIRE study found that the addition of carfilzomib to lenalidomide and dexamethasone (carfilzomib group) significantly improved progression-free survival (PFS) compared with lenalidomide and dexamethasone alone (control group) in patients with relapsed multiple myeloma (RMM). This post hoc analysis examined outcomes from ASPIRE in patients categorised by age. In the carfilzomib group, 103/396 patients were ≥70 years old, and in the control group, 115/396 patients were ≥70 years old. Median PFS for patients <70 years old was 28·6 months for the carfilzomib group versus 17·6 months for the control group [hazard ratio (HR), 0·701]. Median PFS for patients ≥70 years old was 23·8 months for the carfilzomib group versus 16·0 months for the control group (HR, 0·753). For patients <70 years the overall response rate (ORR) was 86·0% (carfilzomib group) and 66·9% (control group); for patients ≥70 years old the ORR was 90·3% (carfilzomib group) and 66·1% (control group). Within the carfilzomib group, grade ≥3 cardiovascular adverse events occurred more frequently among patients ≥70 years old compared with patients <70 years old. Carfilzomib-lenalidomide-dexamethasone has a favourable benefit-risk profile for patients with RMM, including elderly patients ≥70 years old. TRIAL REGISTRATION: clinicaltrials.gov identifier: NCT01080391.

Economic Burden And Health-Related Quality Of Life Of Patients With Cystic Fibrosis In Bulgaria.

OBJECTIVE: The aim of this study was to determine the economic burden from a societal perspective and health-related quality of life (HRQOL) of patients with cystic fibrosis (CF) in Bulgaria. MATERIALS AND METHODS: We conducted a cross-sectional study of 33 patients with CF and 17 caregivers from Bulgaria. Data on socio-demographic characteristics, health resource utilisation, informal care, labor productivity losses and HRQOL were collected from questionnaires completed by patients or their caregivers. HRQOL was evaluated with the EuroQol 5-domain (EQ-5D-3L) questionnaire. RESULTS: Median annual costs of CF in Bulgaria were € 24 152 per patient in 2012 as a reference year. Median annual costs for children were found to be significantly higher than those for adults - € 31 945 vs. € 15 714 (p = 0.012). This outcome came from statistically significant differences in costs for main informal carer (p < 0.001) and costs for other informal carers (p = 0.022). As a single cost item, drugs had the biggest monetary impact. Median annual drug costs were € 13 059. Bulgarian CF patients showed low HRQOL results - 50 median VAS score and 0.592 median health utilities. A quarter of patients even rated their health state as worse than death. CONCLUSION: CF patients from Eastern Europe remain a vulnerable population with risk factors for worse health outcomes. Our study provided a state-of-the art analysis that facilitates the elaboration, adoption and application of targeted public health policies to tackle CF-related problems at national and European level.

Carfilzomib, lenalidomide, and dexamethasone for relapsed multiple myeloma.

BACKGROUND: Lenalidomide plus dexamethasone is a reference treatment for relapsed multiple myeloma. The combination of the proteasome inhibitor carfilzomib with lenalidomide and dexamethasone has shown efficacy in a phase 1 and 2 study in relapsed multiple myeloma. METHODS: We randomly assigned 792 patients with relapsed multiple myeloma to carfilzomib with lenalidomide and dexamethasone (carfilzomib group) or lenalidomide and dexamethasone alone (control group). The primary end point was progression-free survival. RESULTS: Progression-free survival was significantly improved with carfilzomib (median, 26.3 months, vs. 17.6 months in the control group; hazard ratio for progression or death, 0.69; 95% confidence interval [CI], 0.57 to 0.83; P=0.0001). The median overall survival was not reached in either group at the interim analysis. The Kaplan-Meier 24-month overall survival rates were 73.3% and 65.0% in the carfilzomib and control groups, respectively (hazard ratio for death, 0.79; 95% CI, 0.63 to 0.99; P=0.04). The rates of overall response (partial response or better) were 87.1% and 66.7% in the carfilzomib and control groups, respectively (P<0.001; 31.8% and 9.3% of patients in the respective groups had a complete response or better; 14.1% and 4.3% had a stringent complete response). Adverse events of grade 3 or higher were reported in 83.7% and 80.7% of patients in the carfilzomib and control groups, respectively; 15.3% and 17.7% of patients discontinued treatment owing to adverse events. Patients in the carfilzomib group reported superior health-related quality of life. CONCLUSIONS: In patients with relapsed multiple myeloma, the addition of carfilzomib to lenalidomide and dexamethasone resulted in significantly improved progression-free survival at the interim analysis and had a favorable risk-benefit profile. (Funded by Onyx Pharmaceuticals; ClinicalTrials.gov number, NCT01080391.).

The effect of enteral supplementation of specific neutral and acidic oligosaccharides on the faecal microbiota and intestinal microenvironment in preterm infants.

We aimed to determine the effects of enteral supplementation of a prebiotic mixture of neutral and acidic oligosaccharides (scGOS/lcFOS/pAOS) on the faecal microbiota and microenvironment in preterm infants. Furthermore, we determined the influence of perinatal factors on the development of the faecal microbiota. In a randomised controlled trial, preterm infants with gestational age <32 weeks and/or birth weight <1,500 g received enteral supplementation of scGOS/lcFOS/pAOS or placebo (maltodextrin) between days 3 and 30 of life. Faecal microbiota, as measured with fluorescent in situ hybridisation (FISH), and microenvironment [short-chain fatty acids (SCFAs), pH, sIgA] were measured at four time points: before the start of the study and at days 7, 14 and 30 of life. In total, 113 preterm infants were included. Enteral supplementation of the prebiotic mixture increased the total bacteria count at day 14 (Exp 3.92; 95 % confidence interval [CI] 1.18-13.04, p = 0.03), but not at day 30 (Exp 1.73; 95 % CI 0.60-5.03, p = 0.31). There was a trend toward increased bifidobacteria counts. There was a delayed intestinal colonisation of all bacteria. Enteral supplementation of the prebiotic mixture decreased the faecal pH (Exp 0.71; 95 % CI 0.54-0.93, p = 0.01) and there was a trend toward increased acetic acid compared to the placebo group (Exp 1.09; 95 % CI 0.99-1.20, p = 0.10). There was no effect on sIgA (Exp 1.94; 95 % CI 0.28-13.27, p = 0.50). Antibiotics decreased the total bacteria count (Exp 0.13; 95 % CI 0.08-0.22, p < 0.001). Enteral supplementation of a prebiotic mixture of neutral and acidic oligosaccharides increases the postnatal intestinal colonisation. However, the extensive use of broad-spectrum antibiotics in preterm infants decreased the growth of all intestinal microbiota, thereby, delaying the normal microbiota development.

Insight into reimbursement decision-making criteria in Bulgaria: implications for orphan drugs.

OBJECTIVE: This article's objective is to critically assess the Bulgarian legislation on health technology assessment (HTA). It analyses how innovative therapies and orphan drugs in particular would respond to the regulators' decision-making criteria for reimbursement. MATERIALS AND METHODS: The study features critical analysis of current decision-making criteria for drug reimbursement in Bulgaria, as well as hypothetical scenario planning for orphan medicinal products. RESULTS: The approval for inclusion into the Positive Drug List (PDL) (which is a must for reimbursement) has been reorganised into an assessment scoring system with decision-making criteria (presence of therapeutic alternative, clinical effectiveness, safety, pharmacoeconomics and societal value) divided into weighted indicators. An explicit threshold has been set--a medicinal product must score 60 points at least to be included in PDL. Under the currently defined reimbursement decision-making criteria a hypothetical middle-of-the-road scenario planning shows that an orphan drug would score 20 points for therapeutic alternative, 28 for clinical effectiveness and 12 for safety. It would take no points for pharmacoeconomics and societal value. This leaves the orphan drugs with a total score of 60 points, making the final outcome of real-life assessment and decision-making heavily dependent on small fluctuations. CONCLUSIONS: The current reimbursement decision-making framework in Bulgaria seems to be generalised and not sufficiently transparent. It is unable to precisely assess innovative health technologies. The availability of a therapeutic alternative emerges as a key reimbursement decision-making criterion for orphan drugs, as these innovative products nominally provide the first medicinal therapy alternative to rare diseases.

High-intensity focussed ultrasound (HIFU) treatment in uraemic secondary hyperparathyroidism.

BACKGROUND: The recently developed non-invasive high-intensity focussed ultrasound (HIFU) technique for the destruction of parathyroid adenomas could also be of interest for the treatment of secondary hyperparathyroidism (SHP) in patients with chronic kidney disease (CKD). We conducted a pilot study using this method. METHODS: Five chronic haemodialysis patients with severe SHP underwent one to three HIFU treatments, respectively. They had at least one or two enlarged parathyroid glands, which were accessible to this technique. RESULTS: In Patients 1-I and 5-V, serum intact parathyroid hormone (iPTH) could be successfully reduced in the long run. In Patient 3-N, serum iPTH decreased dramatically down to the normal range but increased again subsequently. In Patients 2-E and 4-D, transient reductions in serum iPTH were also obtained but HIFU failed to correct SHP during follow-up. Serum total calcium and phosphorus decreased in four among the five patients, either transiently or permanently. Serum total alkaline phosphatases were reduced in four of five patients. Side effects included local oedema, transient impairment of vocal cord mobility and bitonal voice. CONCLUSIONS: HIFU treatment may be of help in controlling SHP in selected patients with CKD. Further experience is clearly needed.

Nitric oxide stimulates the production of atrial natriuretic peptide and progesterone by human granulosa luteinized cells with an antiapoptotic effect.

OBJECTIVE: To study the effect of nitric oxide (NO) on atrial natriuretic peptide (ANP) and progesterone (P) production by human granulose luteinized cells (GLC) in vitro and to elucidate their role on the survival of cultured cells. METHODS: Human GLCs were cultured in HAM's F10/10% FCS as monolayers for 24 h. Subsequently GLCs were treated for 24 h with 0.5 mM Sodium Nitroprusside (SNP, NO donor) and 0.5 mM Aminoglutethimide (AG , P450scc inhibitor). The levels of ANP and P were measured in supernatants of cultured cells by proANP(1-98) kit and RIA, respectively. Caspase-3 activity was determined by Ac-DEVD-pNA as substrate. RESULTS: The production of ANP and P was increased by NO as compared to control cells (p<0.05). AG diminished the production of P compared to SNP (p<0.05). The caspase-3 activity was significantly lower in SNP treated cells (p<0.05) and increased significantly after AG treatment compared to control cells (p<0.05). CONCLUSION: NO generated by SNP in human GLCs culture stimulated the production of ANP and P. The higher levels of ANP and P were closely related to significantly lower caspase-3 activity thus showing the role of ANP, P and NO on the survival of preovulatory human follicle.

Recombinant human TSH in radioiodine treatment of differentiated thyroid cancer.

BACKGROUND: Recombinant human TSH (rhTSH) has been developed to facilitate the follow-up for persistent or recurrent differentiated thyroid cancer (DTC), avoiding the hypothyroid symptoms after the withdrawal of Levothyroxine (L-T4) suppressive therapy. MATERIAL AND METHODS: To analyse the effect of rhTSH in providing stimulation of radioiodine uptake (RAIU) for the ablation of thyroid remnant and/or malignant thyroid tissue in patients with metastatic DTC. Ten subjects (4 women, 6 men), mean age 53 years, with DTC (7 papillary, 2 follicular and 1 Hürthle-cell), requiring radioiodine therapy (RIT) were studied. Nine of them had a positive diagnostic whole body scan (dWBS) or CT for thyroid remnant, lymph nodes and/or distant metastases. One patient with an invasive tall cell PTC had an increased serum Tg and a negative dWBS. Serum TSH was measured before and two days after the rhTSH injection. Thyroglobulin measurements were performed before the rhTSH administration, 3 and 6 months after RIT. There were no serious side effects of the rhTSH application. RESULTS: Serum TSH after the rhTSH injection rose to 156.5 +/- +/- 60.9 mIU/L and induced RAIU in 8 out of 10 patients. Basal serum Tg was increased in 6 patients and decreased three months later in 2 of them. The post-therapy WBS (pthWBS) showed: 1) additional metastatic lesions in 3 patients with positive dWBS, 2) lung nodular metastases in 1 patient with negative dWBS, 3) similar image as the dWBS in 4 patients, 4) negative image in 1 patient with positive dWBS. CONCLUSION: RhTSH is a safe and promising method for the stimulation of RAIU in patients with thyroid remnant and/or persistent or recurrent DTC, avoiding L-T4 withdrawal.

Dietary protein precipitation properties have effects on gastric emptying in healthy volunteers.

BACKGROUND & AIMS: Strategies that reduce the size of particles in the stomach accelerate gastric emptying. Partial dephosphorylation of casein reduces the size of protein precipitates (curds) in acid conditions and facilitates peptic digestion. We hypothesized that changing the precipitation properties of casein by partial dephosphorylation would accelerate gastric emptying. METHODS: Eight healthy male volunteers entered a prospective, double blind, randomized study with crossover design. Gastric emptying of milk based formula containing either unmodified or dephosphorylated casein was assessed by scintigraphy. Gastric pH measurements were acquired concurrently. RESULTS: A trend to faster gastric emptying was observed for the unmodified preparation, with lower median half time (unmodified 133; dephosphorylated 214 min, P = 0.09) and area under the curve (unmodified 8425 min%; dephosphorylated 9135 min%, P = 0.08). A positive correlation was found between half time for the dephosphorylated preparation and the treatment effect (r2 = 0.81, P < 0.02). Gastric pH was unaffected. CONCLUSIONS: The study hypothesis was rejected; indeed gastric emptying tended to be faster for the unmodified than the dephosphorylated protein. This effect was more pronounced in subjects with slow gastric emptying on the dephosphorylated preparation. Properties other than the size of protein precipitates determine the rate of gastric emptying for milk based formula.

Dietary threonine reduces plasma phenylalanine levels in patients with hyperphenylalaninemia.

BACKGROUND: In order to achieve normal intellectual development, the plasma phe-nylalanine (PHE) levels of patients with hyperphenylalaninemia should not exceed toxic levels. This goal is usually accomplished by employing special diets in which the patient's protein intake is in the form of PHE-free mixtures of amino acids. There is evidence from our own observations in animals and a preliminary observation in patients with hyperphenylalaninemia that supplemental dietary threonine (THR) might decrease plasma PHE concentrations. METHODS: In this placebo-controlled crossover study, the effect of supplemental oral THR on the plasma amino acid concentrations of 12 patients with hyperphenylalaninemia was investigated. Before starting the first treatment period of this cross-over study, the patients were randomly assigned to one of two groups supplemented either with approximately 50 mg THR/kg per day or with a similar amount of maltodextrin as placebo. After a feeding period of 8 weeks and a wash-out period of 8 weeks, the supplements were crossed over and the study continued for an additional 8 weeks. Blood was obtained at the start and the end of each supplementation period. RESULTS: Dietary THR supplementation of approximately 50 mg/kg per day resulted in a significant decrease of plasma PHE levels ( P = 0.0234). There was a close positive correlation between plasma and urinary PHE concentrations ( P < 0.001) indicating that the lower plasma PHE levels in the THR supplemented patients were not caused by higher urinary excretion of PHE. CONCLUSIONS: The data of the present study show that oral THR supplementation has a clear plasma-PHE-reducing effect but they do not allow any conclusion about the mechanisms responsible for the observed effect. Although it seems attractive on the basis of the present data to use THR supplementation in patients with hyperphenylalaninemia, the mechanism of the observed effect should be clarified before introduction of such a treatment in these patients.

An infant formula free of glycomacropeptide prevents hyperthreoninemia in formula-fed preterm infants.

BACKGROUND: Hyperthreoninemia is a well-known phenomenon in infants fed a whey protein-predominant formula. Sweet whey is commonly used for the production of these whey-predominant infant milk formulas. Sweet whey contains not only whey proteins but also the threonine-rich glycomacropeptide (GMP). In the current study, an experimental formula based on acid whey without GMP and a formula based on sweet whey with GMP (threonine content 17.2% higher than in the experimental formula) but otherwise with identical composition were tested with particular respect to threonine metabolism. METHODS: Fourteen preterm infants appropriate for gestational age were enrolled in this randomized cross-over study. After a feeding period of at least 7 days, the nutrition of each infant was switched to the other formula for the second feeding period. At the end of each feeding period, the concentrations of creatinine and amino acids in the plasma and in the urine were measured. RESULTS: In the plasma, the threonine concentration was significantly lower in the group fed the experimental GMP-free formula than in the group fed the sweet whey formula (P < 0.001). Renal excretion of all essential amino acids was generally very low and less than 2% of the intake, indicating that the kidneys had no marked homeostatic function with respect to plasma amino acid. The plasma concentrations of the threonine metabolites glycine and serine, and that of urea were not influenced by diet. CONCLUSION: Feeding a whey protein-predominant bovine milk produced from acid whey protein reduces significantly the hyperthreoninemia commonly found in formula-fed preterm infants. Thus, acid whey formulas should be recommended for feeding preterm infants.

Postprandial plasma amino acids in preterm infants: influence of the protein source.

Preprandial plasma amino acid concentrations have been used extensively as a marker of the nutritional value of dietary proteins in preterm infants. This study investigated the postprandial plasma amino acid profiles of preterm infants fed with different dietary proteins at similar protein intakes during the first weeks of life. In 12 preterm infants, pre- and postprandial plasma amino acid concentrations were measured before the removal of an indwelling central venous catheter placed for parenteral nutrition. All infants received breast milk until the time of study. At the start day of the study, infants were randomized to receive a test meal of 10 ml/kg, either of breast milk fortified with breast milk protein to reach a protein content of 2.0 g/dl or of a bovine milk preterm formula with a protein content of 2.0 g/dl (whey/casein ratio 60/40). Five samples of 100 microl blood were obtained immediately before and 15, 30, 45 and 60 min after the test meal. The plasma amino acid analysis was performed by a reversed-phase high-performance liquid chromatography based on o-phthaldialdehyde/2-mercaptoethanol pre-column derivatization. In both groups, the plasma amino acid concentrations increased within the first 30 min and the levels did not return to the preprandial baseline during the observation period. Fifteen minutes after the test meal, the plasma levels of all essential amino acids with the exception of histidine were higher in the bovine milk formula fed infants than in the fortified breast milk fed infants. The sum of plasma essential amino acid levels found in the formula fed infants were significantly (p < 0.05) higher than the levels found in the fortified breast milk fed infants at 15, 30 and 45 min. The kinetics of individual amino acids were influenced by the different quality of the protein even when the intakes in the groups were similar, as demonstrated for histidine and phenylalanine. The data indicate that postprandial plasma amino acid concentrations depend significantly on the dietary amino acid source and cannot simply be calculated from the amino acid composition of dietary proteins. Therefore, postprandial plasma amino acid concentrations should be included in the nutritional evaluation of dietary proteins in preterm infants.