Neonatal metabolic acidosis caused by food proteininduced enterocolitis syndrome: a case report

Food protein-induced enterocolitis syndrome (FPIES) is a non-IgE mediated allergic reaction with gastrointestinal symptoms, such as vomiting and diarrhea. FPIES diagnosis is based on clinical criteria and on a food challenge test. It is an unknown disease in neonatal units due to its nonspecific symptoms in newborn infants. An elevated methemoglobin level is a simple way to approach diagnosis. Here we describe a clinical case of a newborn admitted to the emergency department because of dehydration, lethargy, vomiting, diarrhea, severe metabolic acidosis, and a high methemoglobin level. Clinical improvement and complete recovery was achieved after initiation of elemental formula. The diagnostic suspicion was confirmed after a positive challenge test.

[Severe neonatal anemia due to fetomaternal hemorrhage: an ilustrative case]

Fetomaternal transfusion (FMT) is defined by the transfer of fetal blood into the maternal circulation. The incidence of massive FMT is estimated to be approximately 0.2-0.9 % of births. Although a number of etiologies have been associated with FMT, most causes remain unidentified and the pregnancy is usually asymptomatic. The most frequent symptom is the decrease in fetal movements (26 %) in relation to severe anemia. Several diagnostic modalities for FMT are described (Kleihauer stain, flow cytometry). We describe a case of a newborn with chronic anemia secondary to FMT who, after treatment with transfusions of red blood cells, presented volume overload and clinical worsening as a complication. In this case, our patient needed exchange transfusion for definitive improvement without disability.

Microfluidic based contactless dielectrophoretic device: Modeling and analysis

While there have been many attempts at patterning cells onto substrates, a reliable method for trapping cell clusters and forming cell arrays in a predefined geometry remains to be demonstrated. We intend to develop a multielectrode array platform to initially trap cells via dielectrophoresis (DEP) and to later measure their electrical activity. As a first step toward that objective, here we present an interdigitated microfabricated comb structure. We designed an optimal insulation layer via finite element modeling for maximum dielectrophoretic field strength in solution and minimal cell damage. The microfabricated structure was combined with a microfluidic channel to vertically constrain cell position. With the objective of capturing cells onto the substrate, we here show that there is an optimal thickness of dielectric which limits electrolysis in solution and still allows for sufficient dielectrophoretic force on the cells to pull them onto the surface.

Human Vam6p promotes lysosome clustering and fusion in vivo

Regulated fusion of mammalian lysosomes is critical to their ability to acquire both internalized and biosynthetic materials. Here, we report the identification of a novel human protein, hVam6p, that promotes lysosome clustering and fusion in vivo. Although hVam6p exhibits homology to the Saccharomyces cerevisiae vacuolar protein sorting gene product Vam6p/Vps39p, the presence of a citron homology (CNH) domain at the NH(2) terminus is unique to the human protein. Overexpression of hVam6p results in massive clustering and fusion of lysosomes and late endosomes into large (2-3 microm) juxtanuclear structures. This effect is reminiscent of that caused by expression of a constitutively activated Rab7. However, hVam6p exerts its effect even in the presence of a dominant-negative Rab7, suggesting that it functions either downstream of, or in parallel to, Rab7. Data from gradient fractionation, two-hybrid, and coimmunoprecipitation analyses suggest that hVam6p is a homooligomer, and that its self-assembly is mediated by a clathrin heavy chain repeat domain in the middle of the protein. Both the CNH and clathrin heavy chain repeat domains are required for induction of lysosome clustering and fusion. This study implicates hVam6p as a mammalian tethering/docking factor characterized with intrinsic ability to promote lysosome fusion in vivo.

Sorting of mannose 6-phosphate receptors mediated by the GGAs

The delivery of soluble hydrolases to lysosomes is mediated by the cation-independent and cation-dependent mannose 6-phosphate receptors. The cytosolic tails of both receptors contain acidic-cluster-dileucine signals that direct sorting from the trans-Golgi network to the endosomal-lysosomal system. We found that these signals bind to the VHS domain of the Golgi-localized, gamma-ear-containing, ARF-binding proteins (GGAs). The receptors and the GGAs left the trans-Golgi network on the same tubulo-vesicular carriers. A dominant-negative GGA mutant blocked exit of the receptors from the trans-Golgi network. Thus, the GGAs appear to mediate sorting of the mannose 6-phosphate receptors at the trans-Golgi network.

Signal-binding specificity of the mu4 subunit of the adaptor protein complex AP-4

The medium (mu) chains of the adaptor protein (AP) complexes AP-1, AP-2, and AP-3 recognize distinct subsets of tyrosine-based (YXXphi) sorting signals found within the cytoplasmic domains of integral membrane proteins. Here, we describe the signal-binding specificity and affinity of the medium subunit mu4 of the recently described adaptor protein complex AP-4. To elucidate the determinants of specificity, we screened a two-hybrid combinatorial peptide library using mu4 as a selector protein. Statistical analyses of the results revealed that mu4 prefers aspartic acid at position Y+1, proline or arginine at Y+2, and phenylalanine at Y-1 and Y+3 (phi). In addition, we examined the interaction of mu4 with naturally occurring YXXphi signals by both two-hybrid and in vitro binding analyses. These experiments showed that mu4 recognized the tyrosine signal from the human lysosomal protein LAMP-2, HTGYEQF. Using surface plasmon resonance measurements, we determined the apparent dissociation constant for the mu4-YXXphi interaction to be in the micromolar range. To gain insight into a possible role of AP-4 in intracellular trafficking, we constructed a Tac chimera bearing a mu4-specific YXXphi signal. This chimera was targeted to the endosomal-lysosomal system without being internalized from the plasma membrane.

Use of free-hand three-dimensional ultrasound software in the study of the fetal heart

OBJECTIVE

To propose a new approach to the study of the fetal heart using free-hand three-dimensional (3D) ultrasound software.

METHODS

We studied a total of 28 fetuses, of which 26 were normal and two were known to have heart pathology. In all of them a B-mode scan was performed. After obtaining a four-chamber view, and keeping the transducer in the same position, the free-hand 3D-View software was activated. A sequence of frames was stored. Additional information was recorded looking from the four-chamber view towards the outflow tract, and also adding color Doppler.

RESULTS

We obtained a multiplanar display of one B-mode and two perpendicular M-modes in all cases studied. In this multiplanar mode, Y and X axes represent distance and Z axis represents time. We were able to obtain M-modes and a variation of color-M-mode in any desired position. Moving the information along the Z axis, a frame sequence of the B-mode was obtained. Using this approach we observed one case of fetal supraventricular extrasystoles and other having an interventricular septum defect.

CONCLUSIONS

This modality gives a new perspective of fetal heart scanning using the free-hand 3D-View software, in which there is benefit from many of the advantages of the 3D software, although the power of this procedure must be improved.

Positive cooperative effects between receptors induced by an anti-human growth hormone allosteric monoclonal antibody

Monoclonal antibodies (MAb) anti-human growth hormone (hGH) termed MAb AE5, AC8 and F11 recognize a cluster of epitopes left exposed after hormone binding to receptors. Since these MAb were able to produce either positive (MAb AE5) or negative (MAb AC8 and F11) allosteric effects on hGH binding, the purpose of this work was to further characterize MAb behavior. Results indicated a straight correlation between MAb allosteric effects and affinity constant values for binding of different hGH:MAb complexes to lactogenic receptors from rat liver. Affinity of hGH:MAb AE5 as well as hGH:Fab AE5 complexes enhanced proportionally to the fraction of occupied receptors and Hill coefficients higher than 1 were obtained, suggesting the induction of positive cooperative effects between membrane-bound receptors. On the other hand, hGH:MAb AC8 and hGH:MAb F11 complexes binding affinity to lactogenic sites could not be related to receptor occupancy degree. It is proposed that binding of hGH:MAb AE5 complexes to receptors would elicit a conformational change on adjacent receptor molecules leading to an increase of their affinity to bind subsequent hGH:MAb AE5 complexes.

Molecular characterization of the protein encoded by the Hermansky-Pudlak syndrome type 1 gene

Hermansky-Pudlak syndrome (HPS) comprises a group of genetic disorders characterized by defective lysosome-related organelles. The most common form of HPS (HPS type 1) is caused by mutations in a gene encoding a protein with no homology to any other known protein. Here we report the identification and biochemical characterization of this gene product, termed HPS1p. Endogenous HPS1p was detected in a wide variety of human cell lines and exhibited an electrophoretic mobility corresponding to a protein of approximately 80 kDa. In contrast to previous theoretical analysis predicting that HPS1p is an integral membrane protein, we found that this protein was predominantly cytosolic, with a small amount being peripherally associated with membranes. The sedimentation coefficient of the soluble form of HPS1p was approximately 6 S as inferred from ultracentrifugation on sucrose gradients. HPS1p-deficient cells derived from patients with HPS type 1 displayed normal distribution and trafficking of the lysosomal membrane proteins, CD63 and Lamp-1. This was in contrast to cells from HPS type 2 patients, having mutations in the beta3A subunit of the AP-3 adaptor complex, which exhibited increased routing of these lysosomal proteins through the plasma membrane. Similar analyses performed on fibroblasts from 10 different mouse models of HPS revealed that only the AP-3 mutants pearl and mocha display increased trafficking of Lamp-1 through the plasma membrane. Taken together, these observations suggest that the product of the HPS1 gene is a cytosolic protein capable of associating with membranes and involved in the biogenesis and/or function of lysosome-related organelles by a mechanism distinct from that dependent on the AP-3 complex.

Utilization of the indirect lysosome targeting pathway by lysosome-associated membrane proteins (LAMPs) is influenced largely by the C-terminal residue of their GYXXphi targeting signals

A systematic study was conducted on the requirements at the C-terminal position for the targeting of LAMPs to lysosomes, examining the hypothesis that a bulky hydrophobic residue is required. Mutations deleting or replacing the C-terminal valine with G, A, C, L, I, M, K, F, Y, or W were constructed in a reporter protein consisting of the lumenal/extracellular domain of avian LAMP-1 fused to the transmembrane and cytoplasmic domains of LAMP-2b. The steady-state distribution of each mutant form in mouse L-cells was assessed by quantitative antibody binding assays and immunofluorescence microscopy; efficiency of internalization from the plasma membrane and delivery to the lysosome were also estimated. It is found that (a) only C-terminal V, L, I, M, and F mediated efficient targeting to lysosomes, demonstrating the importance hydrophobicity and an optimal size of the C-terminal residue in targeting; (b) efficiency of lysosomal targeting generally correlated with efficiency of internalization; and (c) mutant forms that did not target well to lysosomes showed unique distributions in cells rather than simply default accumulation in the plasma membrane. Interactions of the targeting signals with adaptor subunits were measured using a yeast two-hybrid assay. The results are consistent with the hypothesis that trafficking of LAMP forms in cells through the indirect pathway is determined by the affinities of their targeting signals, predominantly for the mu2 and mu3 adaptors involved at plasma membrane and endosomal cellular sorting sites, respectively.

Mu1B, a novel adaptor medium chain expressed in polarized epithelial cells

The apical and basolateral plasma membrane domains of polarized epithelial cells contain distinct sets of integral membrane proteins. Biosynthetic targeting of proteins to the basolateral plasma membrane is mediated by cytosolic tail determinants, many of which resemble signals involved in the rapid endocytosis or lysosomal targeting. Since these signals are recognized by adaptor proteins, we hypothesized that there could be epithelial-specific adaptors involved in polarized sorting. Here, we report the identification of a novel member of the adaptor medium chain family, named mu1B, which is closely related to the previously described mu1A (79% amino acid sequence identity). Northern blotting and in situ hybridization analyses reveal the specific expression of mu1B mRNA in a subset of polarized epithelial and exocrine cells. Yeast two-hybrid analyses show that mu1B is capable of interacting with generic tyrosine-based sorting signals. These observations suggest that mu1B may be involved in protein sorting events specific to polarized cells.

Altered trafficking of lysosomal proteins in Hermansky-Pudlak syndrome due to mutations in the beta 3A subunit of the AP-3 adaptor

Hermansky-Pudlak syndrome (HPS) is a genetic disorder characterized by defective lysosome-related organelles. Here, we report the identification of two HPS patients with mutations in the beta 3A subunit of the heterotetrameric AP-3 complex. The patients' fibroblasts exhibit drastically reduced levels of AP-3 due to enhanced degradation of mutant beta 3A. The AP-3 deficiency results in increased surface expression of the lysosomal membrane proteins CD63, lamp-1, and lamp-2, but not of nonlysosomal proteins. These differential effects are consistent with the preferential interaction of the AP-3 mu 3A subunit with tyrosine-based signals involved in lysosomal targeting. Our results suggest that AP-3 functions in protein sorting to lysosomes and provide an example of a human disease in which altered trafficking of integral membrane proteins is due to mutations in a component of the sorting machinery.

The medium subunits of adaptor complexes recognize distinct but overlapping sets of tyrosine-based sorting signals

Tyrosine-based sorting signals conforming to the motif YXXO (Y is tyrosine, X is any amino acid, and O is an amino acid with a bulky hydrophobic side chain (leucine, isoleucine, phenylalanine, methionine, valine)) interact with the medium (mu) subunits of clathrin adaptor (AP) complexes. We have analyzed the selectivity of interaction between YXXO signals and the mu1, mu2, and mu3 (A or B) subunits of the AP-1, AP-2, and AP-3 complexes, respectively, by screening a combinatorial XXXYXXO library using the yeast two-hybrid system. All the medium subunits were found to prefer proline at position Y+2, suggesting that YXXO signals are stabilized by a bend in the polypeptide backbone. Other than for this common preference, each medium subunit favored specific sets of residues at the X and O positions; these preferences were consistent with the proposed roles of the different adaptor complexes in rapid endocytosis and lysosomal targeting. A considerable specificity overlap was also revealed by these analyses, suggesting that additional factors, such as the context of the signals, must be important determinants of recognition.

Randomized prospective trial of early versus delayed feeding after percutaneous endoscopic gastrostomy placement

OBJECTIVE

By convention, most clinicians delay feeding through the gastrostomy tube until 24 h after placement. However, evidence is lacking to support the rationale for such a delay in PEG use. This randomized, prospective study was designed to assess the safety of early feeding after PEG placement.

METHODS

One hundred-twelve patients referred for PEG were randomized to begin tube feedings at 4 h (group A) or at 24 h (group B) after placement. All patients received prophylactic antibiotics. Full-strength Isocal was administered with the following schedule: day 1, 100 ml every 4 h for six feedings; day 2, 200 ml every 4 h for six feedings. Immediately before each scheduled feeding, gastric residual volume was recorded and the next feeding was withheld if the residual volume was > 50 percent (gastric retention). Patients were evaluated on day 1, day 2, day 7, and day 30 for major and minor complications.

RESULTS

The two groups were similar with regard to age, gender, baseline nutritional status, and indications for PEG placement. On the first day of feeding, 14 of 57 patients (25%) in group A, but only five of 55 patients (9%) in group B, had evidence of gastric retention, p = 0.029. The proportion of patients with high gastric residual volumes was not significantly different on day two. In group B, one death occurred because of aspiration of gastric contents on day 2. All other complications were minor and did not differ significantly between the two groups.

CONCLUSIONS

Early initiation of PEG feedings is safe, well tolerated, and reduces cost by decreasing hospital stay.

Detection of negative allosteric effects between monoclonal antibodies by using an antigenic model-builder computer program

The ability of monoclonal antibodies (MAb) to bind or not simultaneously to the antigen (Ag) is used to establish antigenic maps considering that two different MAb do not bind to the Ag when the corresponding epitopes are overlapped (steric effect). Nevertheless, MAb inducing negative allosteric effect on the Ag could prevent the binding of the second MAb even if it is directed to a separate epitope. We report here that a knowledge-based expert module included in our previously described antigenic model-builder program (MAPAG) was able to differentiate between steric and negative allosteric effects between some MAb.

Interaction of endocytic signals from the HIV-1 envelope glycoprotein complex with members of the adaptor medium chain family

The envelope glycoprotein (Env) complex of HIV-1 undergoes rapid internalization from the plasma membrane of human cells by virtue of a tyrosine-based endocytic signal (RQGYSPL, residues 704-710) in the cytosolic tail of the protein (J. F. Rowell et al., J. Immunol. 155, 473-488, 1995). Here we demonstrate that this tyrosine-based signal interacts with the mu 2 (medium) chain of the AP-2 clathrin-associated adaptor, a protein complex involved in endocytosis of cell surface receptors. The same signal is also capable of interacting with two other members of the adaptor medium chain family, mu 1 and mu 3A, which are components of the AP-1 and AP-3 adaptor complexes, respectively. Interactions with mu 1 and mu 3A might be responsible for the targeting of the internalized envelope glycoprotein to lysosomes or to the basolateral plasma membrane of polarized epithelial cells. A second potential tyrosine-based signal (LFSYHRL, residues 760-766) also interacts with mu 1, mu 2, and mu 3A, although it is less important for internalization in vivo probably due to its position within the cytosolic tail. Overexpression of chimeric proteins having the HIV-1 Env cytosolic tail increases expression of the transferrin receptor on the cell surface, probably due to saturation of the cellular pool of mu 2 by the overexpressed proteins. These observations suggest that HIV-1 Env utilizes the protein sorting machinery of the host cells for internalization and sorting at various steps of the endocytic and biosynthetic pathways.

Functional domain mapping of the clathrin-associated adaptor medium chains mu1 and mu2

The clathrin-associated adaptors AP-1 and AP-2 are heterotetrameric complexes involved in the recognition of sorting signals present within the cytosolic domain of integral membrane proteins. The medium chains of these complexes, mu1 and mu2, have been implicated in two types of interaction: assembly with the beta1 and beta2 chains of the corresponding complexes and recognition of tyrosine-based sorting signals. In this study, we report the results of a structure-function analysis of the mu1 and mu2 chains aimed at identifying regions of the molecules that are responsible for each of the two interactions. Analyses using the yeast two-hybrid system and proteolytic digestion experiments suggest that mu1 and mu2 have a bipartite structure, with the amino-terminal one-third (residues 1-145 of mu1 and mu2) being involved in assembly with the beta chains and the carboxyl-terminal two-thirds (residues 147-423 of mu1 and 164-435 of mu2) binding tyrosine-based sorting signals. These observations support a model in which the amino-terminal one-third of mu2 is embedded within the core of the AP-2 complex, while the carboxyl-terminal two-thirds of the protein are exposed to the medium, placing this region in a position to interact with tyrosine-based sorting signals.

Monoclonal antibodies to human growth hormone modulate its biological properties

Previous results indicated that monoclonal antibodies (mAbs) termed mAb AE5, mAb AC8 and mAb F11, recognizing the human growth hormone (hGH) region left exposed after binding to lactogenic, somatogenic and hGH-specific receptors, produce allosteric changes in the hormone which modify its binding properties. To study whether these mAbs could also influence hGH biological activity, experiments were carried out with Nb2 cells, a rat lymphoma cell line which proliferates in the presence of lactogenic hormones. Experiments involving previous binding of the hormone to receptors before adding 125I-mAbs indicated that the hGH domain defined by overlapped epitopes AE5, AC8 and F11 is uncovered in hGH when it is bound to the cell membranes. To reveal any alteration in the hGH molecule induced by the mAbs, preformed 125I-mAb:hGH complexes were added to the cell membranes. Data showed that 125I-mAb AE5:hGH complexes bound better to the receptors than free hormone. On the contrary, hGH previously bound to 125I-mAb AC8 or 125I-mAb F11 was poorly recognized by Nb2 receptors. Furthermore, both mAbs AC8 and F11 strongly inhibited 125I-hGH binding to Nb2 cell membranes and hGH-induced Nb2 cell proliferation whereas mAb AE5 enhanced both hormone binding and hGH mitogenic effect. Additionally, since mAb AC8 is directed towards an epitope shared by hGH and human placental lactogen (hPL), it was also shown that this mAb could impair hPL biological activity even though it recognizes the hPL region left exposed in hPL:Nb2 cell receptor complexes. Data presented in this work suggest that mAbs directed to the hGH or hPL regions unmasked after binding to Nb2 cell receptors produce allosteric alterations in the binding properties of these hormones leading to either enhancement or decrease of their biological activities.

MAPAG: a computer program to construct 2- and 3-dimensional antigenic maps

The contact area between an antibody (Ab) and the antigen (Ag) is called antigenic determinant or epitope. The first step in the characterization of an Ag by using monoclonal antibodies (MAb) is to map the relative distribution of the corresponding epitopes on the Ag surface. The computer program MAPAG has been devised to automatically construct antigenic maps. MAPAG is fed with a binary matrix of experimental data indicating the ability of paired MAb to bind or not simultaneously to the Ag. The program is interactive menu-driven and allows the user an easy data handling. MAPAG utilizes iterative processes to construct and to adjust the final map, which is graphically shown as a 2- or a 3-dimensional model. Additionally, the antigenic map obtained can be optionally modified by the user or readjusted by the program. The suitability of MAPAG was illustrated by running experimental data from literature and comparing antigenic maps constructed by the program with those elaborated by the investigators without the assistance of a computer. Furthermore, since some MAb could present negative allosteric effects leading to misinterpretation of data, MAPAG has been provided with an approximate reasoning module to solve such anomalous situations. Results indicated that the program can be successfully employed as a simple, fast and reliable antigenic model-builder.

Allosteric effects of monoclonal antibodies on human growth hormone

We have previously shown that a monoclonal antibody (MAb) recognizing the human growth hormone (hGH) antigenic domain left exposed after binding to lactogenic receptors enhanced hGH binding probably through allosteric effects on the hormone binding site. Since receptors displaying different specificities would not recognize exactly the same hGH region, we explored whether some of our MAb could affect hGH binding to somatogenic receptors from rabbit liver and to human liver hGH-specific receptors. The effect of MAbAE5,AC8 and F11 on hGH binding was measured by determining the formation of 125I-MAb:hGH:receptor complexes using two different experimental approaches. Results from procedure A, which involved the previous binding of the hormone to microsomes before adding 125I-MAb, indicated that the hGH domain defined by epitopes AE5, AC8 and F11 is uncovered in the various hormone:receptor complexes. Procedure B was devised to reveal any alteration in the hGH molecule induced by the MAb. In this case performed 125I-MAb:hGH complexes were added to microsomes. Data showed that 125I-MAb AE5:hGH complexes bound better to the various receptors than 125I-MAb AE5 to hGH:receptor complexes. On the contrary, hGH previously bound to 125I-MAb AC8 or 125I-MAb F11 was less recognized by the receptors than the free hormone. Furthermore, binding of MAb AE5 or MAb F11 to hGH 20 K (a natural hGH variant lacking residues 32-46) also enhanced its affinity to the various receptors whereas MAb AC8 did not inhibit hGH 20 K binding. Results indicated that MAb recognizing the hGH antigenic area that remains unmasked after binding to different membrane-bound receptors are able to affect hormone binding site.(ABSTRACT TRUNCATED AT 250 WORDS)

Somatotropic and lactotropic receptors in transgenic mice expressing human or bovine growth hormone genes

The somatotropic and lactotropic receptors were studied in liver microsomal preparations from transgenic mice carrying the human growth hormone (hGH) or bovine growth hormone (bGH) gene fused to mouse metallothionein-I (MT) or phosphoenolpyruvate carboxykinase promoter/regulator (PEPCK). Specificity studies indicated that, similarly to normal mice, liver microsomes from the transgenic animals possess a mixed population of somatotropic and lactotropic binding sites. In transgenic animals of both sexes, the binding capacity of somatotropic receptors was significantly increased without corresponding changes in affinity. Expression of the MT-hGH hybrid gene was associated with the induction of somatotropic receptors which was approximately twice as great as that measured in animals expressing the MT-bGH hybrid gene. The binding capacity of lactotropic receptors in liver microsomes (quantitated by the use of labelled ovine prolactin) was increased 2-3 fold in transgenic females and approximately 10-fold in transgenic males as compared to the respective normal controls. We conclude that lifelong excess of GH up-regulates hepatic GH and prolactin receptors, and that lactogenic activity of GH is not essential for induction of prolactin receptors in the liver of transgenic mice.

Identification of somatogenic binding sites in liver microsomes from normal mice and transgenic mice expressing human growth hormone gene

Somatogenic binding sites were detected and characterized in microsomal preparations from livers of normal mice and mice expressing metallothionein-I/hGH (mMT/hGH) hybrid gene, using 125I-labelled bovine or human GH, or a photoreactive derivative of hGH (125I-AP-hGH1). Specific binding of 125I-bGH was detected in liver microsomes from both normal and transgenic mice with an apparent Kd of 2 nM. 125I-hGH was partially displaced by bGH. 125I-AP-hGH1 was covalently bound to the microsomal preparations, and bGH prevented the formation of the 130 kDa species with no appreciable effect on 63 kDa and 70 kDa lactogenic complexes.