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Biomedical subjects

A D Lander

Publications and source records attributed to A D Lander.

At least 19 recordsLinked to original sources
PubMed2006

Membrane-associated non-receptors and morphogen gradients.

A previously investigated basic model (System B) for the study of signaling morphogen gradient formation that allows for reversible binding of morphogens (aka ligands) with signaling receptors, degradation of bound morphogens and diffusion of unbound morphogens is extended to include the effects of membrane-bound non-signaling molecules (or non-receptors for short) such as proteoglycans that bind reversibly with the same morphogens and degrade them. Our main goal is to delineate the effects of the presence of non-receptors on the existence and properties of the steady-state concentration gradient of signaling ligand-receptor complexes. Stability of the steady-state morphogen gradients is established and the time to reach steady-state behavior after the onset of morphogen production will be analyzed. The theoretical findings offer explanations for observations reported in several previous experiments on Drosophila wing imaginal discs.

Animals↗
PubMed2004

A multicenter, randomized, double-blind, placebo-controlled trial of the prokinetic agent erythromycin in the postoperative recovery of infants with gastroschisis.

BACKGROUND/PURPOSE: The recovery of gut function after repair of gastroschisis is frequently prolonged, and these infants are prone to complications associated with parenteral nutrition. This trial was designed to investigate the effect of the prokinetic agent, erythromycin, on the attainment of full enteral feeding in infants after primary repair of uncomplicated gastroschisis. METHODS: A multicenter, randomized, double-blind, placebo-controlled trial was used to investigate the effect of enteral erythromycin (3 mg/kg/dose 4 times daily) compared with placebo on the attainment of full enteral feeding tolerance after primary repair of uncomplicated gastroschisis. Eleven neonatal surgical units in the United Kingdom participated in the study. The primary end-point was the time taken to achieve continuous enteral feeding at 150 mL/kg/24 hours sustained for 48 hours. RESULTS: Of 70 eligible infants, 62 were recruited and randomly divided. There were 30 patients in group I (placebo) and 32 in group II (erythromycin). The groups were comparable in terms of mean gestational age, mean birth weight, extent of evisceration, and degree of intestinal peel. There was no statistically significant difference between the 2 groups in the time taken to achieve full enteral feeding (27.2 v 28.7 days; P =.75). Similarly, no significant differences were found in the incidence of catheter-related sepsis, duration of parenteral nutrition, or time to discharge between the 2 groups. CONCLUSIONS: Enterally administered erythromycin at a dose of 3 mg/kg 4 times daily conferred no advantage in the time taken to achieve full enteral feeding after primary repair of uncomplicated gastroschisis.

Double-Blind Method↗
PubMed2003

Giant-cell fibroblastoma in a patient with a bone-marrow transplant.

A case of an epigastric giant-cell fibroblastoma is reported in a 6-year-old girl who had undergone a bone-marrow transplant for severe combined immunodeficiency secondary to adenosine deaminase deficiency. A small subcutaneous nodule had been excised from the epigastrium at age 12 months.

Bone Marrow Transplantation↗
PubMed2002

Basal forebrain cholinergic cell attachment and neurite outgrowth on organotypic slice cultures of hippocampal formation.

Distributions of somata and neurites of cholinergic neurons were studied after seeding dissociated cells onto organotypic slice cultures. Slice cultures were made from hippocampal formation and adjacent cortical regions from rats or mice. Dissociated cell suspensions of basal forebrain tissue from rat or mouse fetuses were seeded onto the slice cultures. Combined cultures were maintained for 1-21 days in vitro. Cultures processed for acetylcholinesterase (AChE) histochemistry demonstrated non-random patterns of cholinergic cells and their neurites. Labeled cells appeared most frequently in the molecular layer of the dentate gyrus, and in the deeper layers of cortical regions adjacent to the hippocampus. Neurites extending from these labeled cells appeared to target the dentate molecular layer and the cortical subplate layer. By 4 days in vitro, AChE-positive basal forebrain cells display several short and thick neurites that appear to be dendrites, and one long process that appears to be an axon. By 5 days in vitro, dendrites are well developed; by 7 days the presumed axon has extended widely over the cortical target zone. These neurites are maintained through 3 weeks in culture. Distributions of cells varied with the age of the slice. AChE-labeled cells were not seen overlying hippocampal tissue when dissociated cells were seeded on slice cultures made from day 0 rats, but a few labeled cells were seen when seeded on slices from day 2 rats. Clear non-random patterns of labeled cells and neurite outgrowth were seen on slice cultures from day 5 or older pups. The non-random distribution seen with AChE-positive neurons was not seen using other techniques that labeled all cells (non-selective fluorescent labels) or all neurons; these techniques resulted in labeled cells scattered apparently homogenously across the slice culture.These studies demonstrate a non-random pattern of attachment or differentiation of basal forebrain cholinergic neurons when these cells are seeded onto cultured cortical slices; this pattern mimics the normal patterns of basal forebrain cholinergic projections to these cortical regions. These data suggest that the factors that normally guide basal forebrain-derived cholinergic axons to their target cells in vivo are present and detectable in this model system.

Acetylcholinesterase↗
PubMed2002

Anterior resection for megarectosigmoid in congenital anorectal malformations.

PURPOSE: The aim of this study was to review the effectiveness of resecting dilated distal bowel in children suffering unmanageable constipation or soiling who have been operated on previously for anorectal malformations. METHODS: A retrospective review was performed of 9 children. Each child underwent excision of dilated bowel to leave normal caliber bowel anastomosed by hand to a rectal reservoir at the peritoneal reflection. The documented follow-up was reviewed. RESULTS: The 9 children had primary surgery for the following anomalies: high (n = 1), intermediate (n = 1), low (n = 3), rectal stenosis (n = 3), and anal stenosis (n = 3), Seven children had persistent fecalomas, and 7 had major problems with soiling. All were on large doses of laxatives, with 5 having regular rectal washouts and 4 having regular enemas. In all radiologic studies there was a prompt change from normal caliber bowel to dilated bowel at the upper limit of the dilatation. The mean age at operation for excision was 4 years, 11 months (range, 11 months to 9 years, 11 months). The mean period of follow-up was 4 years, 7 months (range, 2 years, 3 months to 10 years). Follow-up showed that all children improved. None had major complications. All were having between one and 3 bowel actions per day. Three continued to soil but improved. Of the remaining 6, only 2 required occasional laxatives and had regular spontaneous bowel actions without soiling. No child was having enemas or washouts. CONCLUSION: Anterior resection for the treatment of megarectosigmoid is a safe and effective procedure.

Anal Canal↗
PubMed2001

Glypican-1 is overexpressed in human breast cancer and modulates the mitogenic effects of multiple heparin-binding growth factors in breast cancer cells.

Glypicans are a family of glycosylphosphatidylinositol-anchored cell surface heparan sulfate proteoglycans implicated in the control of cellular growth and differentiation. Here we show that glypican-1 is strongly expressed in human breast cancers, whereas expression of glypican-1 is low in normal breast tissues. In contrast, the expression of glypican-3 and -4 is only slightly increased in breast cancers by comparison with normal breast tissues, and glypican-2 and -5 are below the level of detection by Northern blotting in both normal and cancer samples. Treatment of MDA-MB-231 and MDA-MB-468 breast cancer cells with phosphoinositide-specific phospholipase-C abrogated the mitogenic response to two heparin-binding growth factors, heparin-binding epidermal growth factor-like growth factor and fibroblast growth factor 2. Stable transfection of these cells with a glypican-1 antisense construct markedly decreased glypican-1 protein levels and the mitogenic response to the same heparin-binding growth factors, as well as that to heregulin alpha, heregulin beta, and hepatocyte growth factor. Syndecan-1 was also expressed at high levels in both breast cancer tissues and breast cancer cells when compared with normal breast tissues. There was a good correlation between glypican-1 and syndecan-1 expression in the tumors. However, clones expressing the glypican-1 antisense construct did not exhibit decreased syndecan-1 levels, indicating that loss of responsiveness to heparin-binding growth factors in these clones was not due to altered syndecan-1 expression. Furthermore, 8 of 10 tumors with stage 2 or 3 disease exhibited high levels of glypican-1 by Northern blot analysis. In contrast, low levels of glypican-1 mRNA were evident in 1 of 10 tumors with stage 2 or 3 disease and in 9 of 10 tumors with stage 1 disease. Taken together, these data suggest that glypican-1 may play a pivotal role in the ability of breast cancer cells to exhibit a mitogenic response to multiple heparin-binding growth factors and may contribute to disease progression in this malignancy.

Adult↗
PubMed2001

The primary management of testicular maldescent in gastroschisis.

Gastroschisis (GS) is the commonest abdominal-wall defect in the Western world. The conventional practice has been reduction of the viscera and closure of the abdominal wall as an emergency procedure. The testis is often a part of the prolapsed viscera along with the bowel loops, stomach, fallopian tube, etc. The primary management of prolapsed (PT) (3) and intra-abdominal (5) testes (IAT) in this condition was studied in 16 consecutive male babies with GS, each was managed by simple reposition of the testes and closure of the abdominal wall. The babies were followed up for spontaneous descent of the testes. At 18-month follow-up, all five IAT had descended into the scrotum spontaneously and were palpably normal. Of the three extra-abdominal PT, two had descended into the scrotum and were normal in size and on palpation. One was palpable in the superficial inguinal pouch. Simple reposition of the testes into the abdomen and closure of the abdominal defect is the correct approach for primary management of PT or IAT in a newborn with GS.

Cryptorchidism↗
PubMed2001

Cell surface glypicans are low-affinity endostatin receptors.

Endostatin, a collagen XVIII fragment, is a potent anti-angiogenic protein. We sought to identify its endothelial cell surface receptor(s). Alkaline phosphatase- tagged endostatin bound endothelial cells revealing two binding affinities. Expression cloning identified glypican, a cell surface proteoglycan as the lower-affinity receptor. Biochemical and genetic studies indicated that glypicans' heparan sulfate glycosaminoglycans were critical for endostatin binding. Furthermore, endostatin selected a specific octasulfated hexasaccharide from a sequence in heparin. We have also demonstrated a role for endostatin in renal tubular cell branching morphogenesis and show that glypicans serve as low-affinity receptors for endostatin in these cells, as in endothelial cells. Finally, antisense experiments suggest the critical importance of glypicans in mediating endostatin activities.

3T3 Cells↗
PubMed2001

Postoperative pneumatosis intestinalis in infants does not automatically preclude enteral feeding.

BACKGROUND: A degree of feed intolerance after neonatal abdominal surgery is common but in an otherwise well baby enteral feeding usually is continued at the highest tolerated level. However, the presence of rectal bleeding, pneumatosis intestinalis, or portal vein gas seen on plain abdominal x-rays suggest the possibility of postoperative necrotising enterocolitis. When this happens feedings usually are stopped for 7 to 10 days, and intravenous antibiotics and total parental nutrition are commenced. METHODS: The authors report 12 episodes of rectal bleeding and 11 episodes of pneumatosis intestinalis in 3 infants who previously had undergone neonatal abdominal surgery for intestinal malformations. In 7 of these episodes, feedings were neither stopped nor were antibiotics given. At the time of these 7 episodes, the infants were more than 3 kg in weight, had no significant cardiac or respiratory pathology, were all clinically stable, had no evidence of peritonitis, had no thrombocytopenia, and were greater than 37 weeks postconception. RESULTS: The 3 infants were monitored closely. There were no early or late problems observed attributable to this management. CONCLUSION: Carefully selected clinically stable patients that have postoperative pneumatosis intestinalis or exhibit rectal bleeding may be successfully managed by reduced enteral feedings with no antibiotics. J Pediatr Surg 36:1820-1823.

Anti-Bacterial Agents↗
PubMed2001

Enhanced glypican-3 expression differentiates the majority of hepatocellular carcinomas from benign hepatic disorders.

BACKGROUND/AIMS: Hepatocellular carcinoma (HCC) is a common malignant tumour worldwide, and its differential diagnosis from benign lesions of the liver is often difficult yet of great clinical importance. In the present study, we analysed whether glypican-3 is useful in differentiating between benign and malignant liver diseases and whether it influences the growth behaviour of HCC. METHODS: Northern blot analysis and in situ hybridisation. RESULTS: Northern blot analysis indicated that expression of glypican-3 mRNA was either low or absent in normal liver, in focal nodular hyperplasia (FNH), and in liver cirrhosis. In contrast, expression of glypican-3 mRNA was markedly increased in 20 of 30 and moderately increased in five of 30 HCC samples. The average increase in glypican-3 mRNA expression in HCC was significant compared with expression in normal liver (21.7-fold increase, p<0.01). In comparison with FNH or liver cirrhosis, glypican-3 mRNA expression in HCC was increased 7.2- (p<0.05) and 10.8-fold (p<0.01), respectively. In addition, pushing HCCs exhibited significantly higher glypican-3 mRNA expression than invading tumours (p<0.05). In situ hybridisation analysis demonstrated weak expression of glypican-3 mRNA in normal hepatocytes and bile ductular cells, and weak to occasionally moderate signals in hepatocytes forming nodules of liver cirrhosis and in regenerated hepatic nodules of FNH. In contrast, glypican-3 in situ hybridisation signals were intense in hepatic cancer cells with even higher levels in pushing HCCs than in invading HCCs. CONCLUSIONS: These findings suggest that glypican-3, in many cases, has the potential to differentiate between benign and malignant liver diseases.

Adult↗
PubMed2000

Mechanisms underlying preferential assembly of heparan sulfate on glypican-1.

Glypicans are major cell surface heparan sulfate proteoglycans, the structures of which are characterized by the presence of a cysteine-rich globular domain, a short glycosaminoglycan (GAG) attachment region, and a glycosylphosphatidylinositol membrane anchor. Despite strong evolutionary conservation of the globular domains of glypicans, no function has yet been attributed to them. By using a novel quantitative approach for assessing proteoglycan glycosylation, we show here that removal of the globular domain from rat glypican-1 converts the proteoglycan from one that bears approximately 90% heparan sulfate (HS) to one that bears approximately 90% chondroitin sulfate. Mutational analysis shows that sequences at least 70 amino acids away from the glypican-1 GAG attachment site are required for preferential HS assembly, although more nearby sequences also play a role. The effects of the glypican-1 globular domain on HS assembly could also be demonstrated by fusing this domain to sequences representing the GAG attachment sites of other proteoglycans or, surprisingly, simply by expressing the isolated globular domain in cells and analyzing effects either on an exogenously expressed glypican-1 GAG attachment domain or on endogenous proteoglycans. Quantitative analysis of the effect of the globular domain on GAG addition to proteoglycan core proteins suggested that preferential HS assembly is achieved, at least in part, through the inhibition of chondroitin sulfate assembly. These data identify the glypican-1 globular domain as a structural motif that potently influences GAG class determination and suggest that an important role of glypican globular domains is to ensure a high level of HS substitution of these proteoglycans.

Amino Acid Sequence↗
PubMed2000

Regulation of neurite outgrowth by integrin activation.

During late-embryonic development, retinal neurons lose the ability to attach and extend neurites on the extracellular matrix molecule laminin-1 (LN-1), despite the fact that they retain expression of integrin receptors for LN-1. Here we show that the developmental loss of responsiveness to LN-1 can be reversed by treatments that increase the activation state of integrins. Both extracellular application of Mn(2+) (at micromolar concentrations) and viral-mediated neuronal expression of a constitutively active form of the ras-related GTPase R-ras (R-ras(38V)) potently promoted late-embryonic retinal neurite outgrowth on LN-1 substrata. In both cases, outgrowth was mediated by integrin alpha6beta1 and not alpha3beta1, even though these neurons express alpha3beta1 and use it for outgrowth on other laminin isoforms, as well as on LN-1 that has been proteolytically or conformationally activated (Ivins et al., 1998). Mn(2+)-and to a much lesser extent R-ras(38V)-also reversed the developmental loss of retinal neuron responsiveness to type IV collagen, by promoting the function of integrin alpha1beta1. Interestingly, the responses of other late-embryonic CNS neurons to LN-1 were also enhanced by treatments that activate integrin function, but those of peripheral nervous system neurons (dorsal root ganglion neurons) were either not enhanced (embryonic neurons) or only modestly improved (adult neurons). These results suggest that a developmental decline occurs in the activation state of neuronal integrins, particularly among CNS neurons. Such a decline may underlie some of the intrinsic loss of regenerative ability sustained by CNS neurons during development and may be a valid target for therapeutic intervention.

Animals↗
PubMed2000

Pyloric atresia: five new cases, a new association, and a review of the literature with guidelines.

BACKGROUND/PURPOSE: Pyloric atresia is an uncommon condition occurring in 1 of 100,000 live births. When occurring in isolation, the clinical course usually is uncomplicated after surgical treatment. However, it may occur in association with other congenital abnormalities. The authors present 5 new cases, 3 of associated abnormalities including 1 of esophageal atresia and 2 of agenesis of the gall bladder and malrotation. Agenesis of the gall bladder has not been described previously in combination with pyloric atresia. The literature has been reviewed and guidelines are suggested for the management. METHODS: The case records of 4 neonates who presented to the author's institution between January 1998 and June 1999 and 1 who presented at another center in 1991 were reviewed. A Medline literature search was performed, and guidelines were developed for the management of this condition based on our cases and the literature review. RESULTS: Patients 1 and 5 had no associated anomalies. Patient 2 had associated esophageal atresia, tracheoesophageal fistula, atrial septal defect, crossed renal ectopia, malrotation, and absent gall bladder. Patient 3 had a rectovestibular fistula, vaginal atresia, atrial septal defect, malrotation absent gallbladder, and absent extrahepatic portal vein. Patient 4 had epidermolysis bullosa. Patients 2 and 5 had unremarkable recoveries, patients 2 and 3 had markedly delayed gastric emptying that responded to cisapride. Patient 3 has portal hypertension and remains under close follow-up. Patient 4 died at 22 days of age of pseudomonas sepsis. CONCLUSIONS: Based on our cases and literature review, we have adopted the following guidelines: (1) All children with pyloric atresia should be screened for multiple anomalies. (2) Delayed gastric emptying should be considered early and may respond to prokinetic agents. (3) Association with Epidermolysis bullosa should not preclude surgical treatment. (4) A skin biopsy specimen should be taken at the time of surgery for electron microscopy if there is a family history of epidermolysis bullosa.

Abnormalities, Multiple↗
PubMed1999

Interactions of neural glycosaminoglycans and proteoglycans with protein ligands: assessment of selectivity, heterogeneity and the participation of core proteins in binding.

The method of affinity coelectrophoresis was used to study the binding of nine representative glycosaminoglycan (GAG)-binding proteins, all thought to play roles in nervous system development, to GAGs and proteoglycans isolated from developing rat brain. Binding to heparin and non-neural heparan and chondroitin sulfates was also measured. All nine proteins-laminin-1, fibronectin, thrombospondin-1, NCAM, L1, protease nexin-1, urokinase plasminogen activator, thrombin, and fibroblast growth factor-2-bound brain heparan sulfate less strongly than heparin, but the degree of difference in affinity varied considerably. Protease nexin-1 bound brain heparan sulfate only 1.8-fold less tightly than heparin (Kdvalues of 35 vs. 20 nM, respectively), whereas NCAM and L1 bound heparin well (Kd approximately 140 nM) but failed to bind detectably to brain heparan sulfate (Kd>3 microM). Four proteins bound brain chondroitin sulfate, with affinities equal to or a few fold stronger than the same proteins displayed toward cartilage chondroitin sulfate. Overall, the highest affinities were observed with intact heparan sulfate proteoglycans: laminin-1's affinities for the proteoglycans cerebroglycan (glypican-2), glypican-1 and syndecan-3 were 300- to 1800-fold stronger than its affinity for brain heparan sulfate. In contrast, the affinities of fibroblast growth factor-2 for cerebroglycan and for brain heparan sulfate were similar. Interestingly, partial proteolysis of cerebroglycan resulted in a >400-fold loss of laminin affinity. These data support the views that (1) GAG-binding proteins can be differentially sensitive to variations in GAG structure, and (2) core proteins can have dramatic, ligand-specific influences on protein-proteoglycan interactions.

Animals↗
PubMed1999

Stable transfection of a glypican-1 antisense construct decreases tumorigenicity in PANC-1 pancreatic carcinoma cells.

Glypican-1 belongs to a family of glycosylphosphatidylinositol (GPI)-anchored heparan sulfate proteoglycans (HSPGs) that affect cell growth, invasion, and adhesion. Cell-surface HSPGs are believed to act as co-receptors for heparin-binding mitogenic growth factors. It was reported that glypican-1 is strongly expressed in human pancreatic cancer, and that it may play an essential role in regulating growth-factor responsiveness in pancreatic carcinoma cells. In this study we investigated the effects of decreased glypican-1 expression in PANC-1 pancreatic cancer cells. To this end, PANC-1 cells were stable transfected with a full-length glypican-1 antisense construct. The glypican- antisense transfected clones displayed markedly reduced glypican- protein levels and a marked attenuation of the mitogenic responses to heparin-binding growth factors that are commonly overexpressed in pancreatic cancer: fibroblast growth factor-2 (FGF2), heparin-binding epidermal growth factor (EGF)-like growth factor (HB-EGF), and hepatocyte growth factor (HGF). In addition, glypican-1 antisense-expressing PANC-1 cells exhibited a significantly reduced ability to form tumors in nude mice in comparison with parental and sham-transfected PANC-1 cells. These data suggest that glypican-1 plays an important role in the responses of pancreatic cancer cells to heparin-binding growth factors, and documents for the first time that its expression may enhance tumorigenic potential in vivo.

Animals↗