Search PubMed⌕ Search

Biomedical subjects

R D Christensen

Publications and source records attributed to R D Christensen.

At least 37 records · Page 2Linked to original sources
PubMed2001

Erythropoietin acts as a trophic factor in neonatal rat intestine.

BACKGROUND: Erythropoietin (Epo) receptors are present on enterocytes of fetal and neonatal small bowel but the role of Epo in the bowel is not known. AIMS: We tested the following hypotheses: (1) enterally dosed Epo is absorbed from the intestines of neonatal rats, (2) Epo acts as a trophic factor in developing small bowel, and (3) the trophic effects of Epo are dependent on the route of administration. METHODS: The dose dependent effects of enterally dosed recombinant human erythropoietin (rEpo 0--1000 U/kg/day) were studied in artificially raised rat pups and compared with dam raised controls and dam raised pups given rEpo in rat milk. After one week, reticulocyte counts, haematocrits, and plasma Epo concentrations were measured, and calibrated morphometric measurements of villi were performed. The effects of route of rEpo administration (enteral v parenteral) on erythropoiesis, bowel growth, and disaccharidase activity were studied in nursing pups treated for one and two weeks. RESULTS: Serum Epo concentrations ranged from undetectable (<0.6 mU/ml) to 8.4 mU/ml in control and enterally dosed pups (median 1.8 mU/ml), and from 4.9 to 82.3 mU/ml (median 20.4 mU/ml) in parenterally dosed animals. No increase in haematocrit or reticulocyte count was noted in enterally treated pups compared with controls after up to two weeks of treatment. Small bowel length was greater in rEpo treated pups, and a dose dependent increase in villus surface area which was independent of the route of dosing and associated with increased BrdU uptake was found. CONCLUSIONS: rEpo is not enterally absorbed in an intact and functional form from the intestines of neonatal rat pups. Thus enterally dosed rEpo has no erythropoietic effects. However, rEpo acts as a trophic factor in developing rat small bowel whether given enterally or parenterally.

Animals↗
PubMed2001

The biology of erythropoietin in the central nervous system and its neurotrophic and neuroprotective potential.

This review summarizes published as well as preliminary data on the biology of erythropoietin (Epo) in the developing and mature human central nervous system (CNS). Both Epo receptor (Epo-R) and Epo gene expression underlie developmental changes and a brain-specific regulation. These features suggest a different role of Epo in normal brain development than in neuroprotection and neuronal tissue repair after brain injury. Epo concentrations in the cerebrospinal fluid may have primary paracrine effects. While the transport of Epo across the intact blood brain barrier (BBB) is generally limited in humans, systemically produced or administrated Epo may cross during BBB dysfunction. Summarized data of the in vivo and in vitro effects of Epo in the CNS show significant neuroprotective and neurotrophic effects of this molecule. These effects are mediated by several mechanisms, including the activation of a variety of genes and their consecutive protein production. Therapeutic strategies involving activation of the CNS Epo-R are discussed, including the potential use of Epo mimetic peptides.

Animals↗
PubMed2001

Granulocyte colony-stimulating factor, granulocyte macrophage colony-stimulating factor and neutrophils in the bronchoalveolar lavage fluid of premature infants with respiratory distress syndrome.

BACKGROUND: Granulocyte colony-stimulating factor (G-CSF) and granulocyte macrophage colony-stimulating factor (GM-CSF) promote clonal maturation of neutrophil and macrophage progenitors and increase functional activities of mature cells. The number and activity of neutrophils and macrophages in the lung affect healing and remodeling following respiratory distress syndrome (RDS). QUESTIONS OF THE STUDY: (1) Are G-CSF and GM-CSF present in the airways of preterm neonates with RDS? (2) Do airway G-CSF and GM-CSF concentrations correlate with neutrophil and macrophage number in the bronchoalveolar lavage (BAL) fluid? (3) Are alveolar macrophages a source of airway G-CSF and GM-CSF? (4) Is in vitro expression of G-CSF and GM-CSF by airway macrophages modified by dexamethasone, endotoxin, or hyperoxia? METHODS: Eighteen preterm neonates with RDS requiring mechanical ventilation within the first 24 h of life underwent BAL on days 1, 3, 6, 10, 12, 15, 20, and 28 if still intubated. BAL G-CSF and GM-CSF concentrations were measured by ELISA, and neutrophils and macrophages were counted. Alveolar macrophages were cultured, and G-CSF and GM-CSF expression measured in the presence and absence of dexamethasone, endotoxin, and hyperoxia. RESULTS: G-CSF and GM-CSF were present in the BAL of intubated preterm neonates. In infants who did not develop chronic lung disease (CLD) (n = 5), G-CSF and GM-CSF concentrations were highest in the first days of life, falling thereafter, while in those who did develop CLD (n = 13) these concentrations increased over time. Neutrophil concentrations in BAL fluid followed a similar pattern. Macrophages from BAL were identified as a source of G-CSF and GM-CSF mRNA and protein. G-CSF and GM-CSF expression by these macrophages was increased by endotoxin, decreased by dexamethasone, and unchanged by hyperoxia. CONCLUSIONS: G-CSF and GM-CSF are present in neonatal BAL, and may contribute significantly to the accumulation of alveolar neutrophils.

Bronchoalveolar Lavage Fluid↗
PubMed2001

Fas and Fas ligand expression in maternal blood and in umbilical cord blood in preeclampsia.

The Fas-Fas ligand (FasL) pathway of apoptosis is abnormally activated in diseases associated with impaired immune tolerance or chronic inflammation. Pregnancy-related hypertension is a spectrum of disease that commonly causes significant morbidity in women and in their newborn infants, is associated with generalized inflammation, and may be causally related to impaired maternal-fetal tolerance. Our recent observation of enhanced trophoblast expression of FasL in one form of pregnancy-related hypertension led us to hypothesize that this group of disorders might be associated with abnormal activation of the Fas-FasL pathway. To test this hypothesis, we prospectively quantified soluble and leukocyte-associated Fas receptor and FasL in the maternal and umbilical cord blood (CB) sera of 20 gestations complicated by preeclampsia and of 18 normal control gestations, using ELISA and flow cytometric analyses. We determined higher soluble FasL levels in paired maternal and CB sera of hypertensive gestations compared with control gestations (p < 0.01); in contrast, soluble Fas levels were similar between groups. Surface expression of FasL was lower on maternal (p < 0.01) and CB (p < 0.05) neutrophils from affected gestations, whereas surface Fas expression was lower on maternal (p < 0.02), but not CB, neutrophils and lymphocytes. We conclude that expression of Fas and FasL in sera and on leukocytes is altered in gestations complicated by preeclampsia, and speculate that activation of the Fas-FasL pathway mediates associated pathologic processes in affected women and in their neonates.

Antigens, Surface↗
PubMed2001

A randomized, double-masked, placebo-controlled trial of recombinant granulocyte colony-stimulating factor administration to preterm infants with the clinical diagnosis of early-onset sepsis.

OBJECTIVE: We performed a randomized, double-masked, parallel-groups, placebo-controlled trial of recombinant granulocyte colony-stimulating factor (rG-CSF) administration to 44 preterm neonates who had blood cultures obtained and antibiotics begun because of the clinical diagnosis of early-onset sepsis. Two primary outcome variables were tested 1) mortality and 2) development of nosocomial infections over the 2-week period after dosing. DESIGN AND METHODS: The treatment group (n = 22) received 10 microgram/kg/day of intravenous rG-CSF once daily for 3 days and the placebo group (n = 22) received the same volume of a visually indistinguishable vehicle. Mortality and culture-proven nosocomial infections were recorded. Immediately before the first, second, and third doses, and again 10 days after the first dose, serum concentrations were determined for tumor necrosis factor-alpha, interleukin 6, granulocyte-macrophage colony stimulating factor, and G-CSF, and blood leukocyte counts, absolute neutrophil counts, immature/total neutrophil ratios, platelet counts, and hemoglobin concentrations were measured. RESULTS: The treatment and placebo groups were of similar gestational age (29 +/- 3 vs 31 +/- 3 weeks) and birth weight (1376 +/- 491 vs 1404 +/- 508 g), and had similar Apgar scores and 24-hour Score for Neonatal Acute Physiology scores. The mortality rate was not different between treatment and placebo groups. However, the occurrence of a subsequent nosocomial infection was lower in the rG-CSF recipients (relative risk:.19; 95% confidence interval:.05-.78). rG-CSF treatment did not alter the serum concentrations of the cytokines measured (except for G-CSF). Serum G-CSF levels and blood neutrophil counts were higher in the treatment than in the placebo group 24 hours and 48 hours after dosing. CONCLUSIONS: Administration of 3 daily doses of rG-CSF (10 microgram/kg/day) to premature neonates with the clinical diagnosis of early-onset sepsis did not improve mortality but was associated with acquiring fewer nosocomial infections over the subsequent 2 weeks.

Bacterial Infections↗
PubMed2001

Congenital autoimmune neutropenia in two premature neonates.

Autoimmune neutropenia (AIN) has been reported in infants and children, but not in neonates. AIN is caused by antibodies produced by the patient against their own neutrophils; therefore, it differs from the more common alloimmune neonatal neutropenia and the neonatal neutropenia because of a maternal autoimmune disease in which antineutrophil antibodies of maternal origin cross the placenta. We observed 2 cases of congenital AIN in premature neonates. These are the youngest reported cases, and indicate that AIN can have a prenatal onset. Examination of the bone marrow biopsies revealed an increase in B lymphocytes and myeloperoxidase-positive cells with a maturation arrest at the myelocyte stage. Recombinant human granulocyte colony-stimulating factor effectively treated the neutropenia, as it does in infantile AIN. Ten months after the diagnosis, 1 of the patients still requires recombinant human granulocyte colony-stimulating administration.

Autoimmune Diseases↗
PubMed2000

Human developmental biology of granulocyte colony-stimulating factor.

The availability of granulocyte colony-stimulating factor (G-CSF) has influenced the management of neonates with neutropenia. Since the first use of G-CSF in a neonate with neutropenia, much has been learned about the cellular sources and physiologic roles of G-CSF. This article reviews our present understanding of G-CSF and its cognate receptor in the fetus and neonate.

Aging↗
PubMed2000

A practical approach to evaluating and treating neutropenia in the neonatal intensive care unit.

Neutropenia is a relatively common problem in the NICU, recognized in as many as 8% of patients at some time during their hospital stay. In most instances, neutropenia among NICU patients is of short duration and has little influence on outcome. In other cases it is prolonged and severe, and constitutes a serious antimicrobial defense deficiency. When a neonatologist discovers a low blood neutrophil count, choices must be made regarding further evaluation and treatment. The authors hope that the information provided in this article is useful in making these choices.

Anti-Bacterial Agents↗
PubMed2000

Evaluation and treatment of thrombosis in the neonatal intensive care unit.

Thromboses are infrequent but serious complications of patients in the NICU. Thromboses tend to occur in very sick neonates, particularly preterm neonates, and the majority of such thromboses are related to central vascular catheters. Other risk factors for neonatal thromboses include infants of diabetic mothers, sepsis, small for gestational age, congenital heart disease, maternal antiphospholipid syndrome, and possibly inherited prothrombotic disorders. Appropriate treatment, dosage, and duration of therapy for neonatal thromboses has not been studied in clinical trials. Treatment options include observation, anticoagulation, thrombolysis, and surgical thrombectomy. Regardless of the treatment chosen, all neonates with thromboses require frequent reassessment of the thromboses by angiography, echocardiography, or ultrasound until thrombus resolution occurs.

Anticoagulants↗
PubMed2000

Expression of tissue factor pathway inhibitor in human fetal and placental tissues.

The coagulation system differs markedly between fetuses, neonates, and adults, and fetal and neonatal thrombotic abnormalities are poorly understood. Tissue factor pathway inhibitor (TFPI) is an important inhibitor of the extrinsic pathway of coagulation. To begin examining the role of TFPI in the maternal-fetal relationship, TFPI expression in human fetal and placental tissues was studied by immunohistochemical staining. TFPI was widely expressed in human fetal tissues from 8-24 weeks gestation, particularly in epithelial and endothelial tissues. Fetal liver, lung, kidney, and intestine were notably positive for TFPI staining. Within the tissues, TFPI was expressed in pneumocytes, hepatocytes, renal tubular and glomerular cells, muscle fibers, and enterocytes. In placental tissues, TFPI was expressed in syncytiotrophoblasts, cytotrophoblasts, vascular endothelium, and extravillus trophoblasts from 10 weeks through term. Advancing gestation had little effect on TFPI expression. Further studies are needed to determine the functional role of TFPI in fetal and placental tissues and to define perturbations in its expression during fetal and neonatal disease states.

Endothelium↗
PubMed2000

Dose-response relationship of megakaryocyte progenitors from the bone marrow of thrombocytopenic and non-thrombocytopenic neonates to recombinant thrombopoietin.

Megakaryocyte (MK) progenitors from the marrow of adults undergo dose-dependent clonogenic proliferation in response to recombinant thrombopoietin (rTpo). It is unknown whether progenitors from the marrow of thrombocytopenic neonates display rTpo dose-dependent proliferation and whether they are more or less sensitive to rTpo than progenitors from non-thrombocytopenic neonates or adults. To assess this, we cultured marrow from four thrombocytopenic and four non-thrombocytopenic neonates, and from six healthy adults, in a serum-free system in the presence of increasing concentrations of rTpo (0-100 ng/ml). Marrow from the thrombocytopenic and non-thrombocytopenic neonates generated three times more MK colonies/105 light density cells (129 +/- 39 and 167 +/- 30 respectively) than marrow from adults (54 +/- 30, P < 0.0001) at a rTpo concentration of 50 ng/ml. Neonatal and adult samples had a rTpo dose-dependent increase in MK colonies. However, neonates reached a maximal number of colonies at a rTpo concentration of 10 ng/ml, compared with 50 ng/ml in adults, resulting in a larger area under the rTpo dose-response curve for neonatal progenitors (P = 0. 0047). Neonates also generated more large MK colonies than the adults (24% vs. 2% at 100 ng/ml).

Adult↗
PubMed2000

Pharmacokinetics, pharmacodynamics, and safety of administering pegylated recombinant megakaryocyte growth and development factor to newborn rhesus monkeys.

Thrombocytopenia is common among sick neonates. Certain groups of thrombocytopenic adults respond favorably to the administration of recombinant thrombopoietin or to pegylated recombinant human megakaryocyte growth and development factor (PEG-rHuMGDF), a recombinant human polypeptide that contains the receptor-binding N-terminal domain of thrombopoietin. The effectiveness and safety of such treatment in neonates, however, have not been reported. The purpose of the present study was to determine the biologic activity and safety of PEG-rHuMGDF administration to newborn rhesus monkeys. Eight monkeys were divided into four groups and treated subcutaneously with 0.00, 0.25, 1.00, or 2.50 microg/kg once daily for 7 d. Complete blood counts, serum chemistries, clotting panels, and MGDF levels were followed serially, and hematopoietic progenitor cell assays were performed on bone marrow aspirates before the first dose and again on d 8. Pharmacokinetic evaluations were performed on the animals that received the highest dose of PEG-rHuMGDF. All monkeys had normal growth during the study period, and all chemistries, clotting studies, and blood pressure measurements were normal. The peak serum MGDF concentration occurred at 3 h, and the half-life was 8.4 to 13.0 h. As in adult rhesus monkeys, platelet counts in the treated neonates began to rise on d 6, peaked on d 11, and returned to baseline by d 23. The two highest doses generated an 8- to 12-fold increase in platelets, whereas those treated with 0.25 microg/kg had a 6-fold increase. Other hematologic parameters measured were unaffected. Thus, newborn monkeys responded to doses of PEG-rHuMGDF that were similar to or smaller than (per kilogram body weight) those that are effective in adult animals and did so without obvious short-term toxicity.

Animals↗
PubMed2000

Origin and fate of erythropoietin in human milk.

Erythropoietin (Epo) is a normal constituent of human milk, but the origin and fate of this cytokine in milk are not known. Regarding its origin, we hypothesized that cells of the mammary gland secrete Epo into milk actively and, therefore, that concentrations in milk do not correlate with concentrations in serum. Regarding its fate, we hypothesized that Epo concentrations in milk change with time postpartum and that Epo in milk is protected from digestion in the neonatal gastrointestinal tract. To address these issues, we measured Epo concentrations in 103 milk samples (ELISA), 55 of which were paired with serum. Mammary duct epithelial cells were evaluated as a source of Epo by breast tissue immunohistochemistry and by cell culture. Circulating and milk Epo were compared by Western analysis to detect size differences, possibly reflecting differences in processing. Epo stability in simulated conditions of digestion was evaluated. We observed that milk Epo concentrations increase as a function of duration of breast-feeding and have a negative correlation with serum Epo or milk protein concentration. Mammary duct epithelial cells from breast biopsies of lactating women had marked immunoreactivity to Epo, but such activity was minimal to absent in nonlactating breast tissue. Further evidence that mammary duct epithelia produce Epo was obtained by observing Epo mRNA and protein expression in cultured human mammary epithelial cells. The molecular size of Epo in milk and serum is identical. Recombinant Epo added to human milk or commercial infant formulas was relatively stable in conditions that simulate gastric and small intestinal conditions of newborn infants; however, recombinant Epo added to D(5)W was not protected from digestion. We conclude that Epo concentrations in milk increase as a function of the duration of breast feeding, that Epo is actively secreted into human milk by mammary duct epithelia, and that the Epo within milk is largely protected from digestion.

Adult↗
PubMed2000

Stability of filgrastim and epoetin alfa in a system designed for enteral administration in neonates.

OBJECTIVE: To determine the stability of recombinant granulocyte colony-stimulating factor (rG-CSF, filgrastim) and recombinant erythropoietin (rEpo, epoetin alfa) in a solution designed for enteral administration in the neonatal intensive care unit. DESIGN: Filgrastim and epoetin alfa were added to a solution with NaCl 0.9%, sodium acetate, potassium chloride, and human albumin in concentrations designed to mimic human amniotic fluid. Additionally, the solution was dripped through polyvinyl chloride feeding tubes to simulate feedings, and aliquots were collected before, during, and after priming of the tube. Other aliquots were either frozen immediately, stored at room temperature, or refrigerated for 0, 6, 12, 18, and 24 hours. MAIN OUTCOME MEASURES: Filgrastim and epoetin alfa concentrations in the various aliquots were compared with the concentrations in the original solution. RESULTS: Filgrastim and epoetin alfa concentrations were stable for at least 24 hours when refrigerated and for at least three weeks when frozen. At room temperature, filgrastim was stable for 18 hours and epoetin alfa for 24 hours. Filgrastim concentrations did not vary significantly before, during, or after priming of the feeding tube, whereas epoetin alfa concentrations decreased significantly unless the feeding tube was primed with 10 mL of solution. CONCLUSIONS: Filgrastim and epoetin alfa were stable in our amniotic fluid-like solution. In this respect, our solution is suitable for enteral administration to patients in the neonatal intensive care unit.

Cold Temperature↗
PubMed2000

Granulocyte colony-stimulating factor is present in human milk and its receptor is present in human fetal intestine.

OBJECTIVE: Human milk provides neonates with a meaningful degree of protection from infection, but the responsible mechanisms are not well understood. Discovering these mechanisms is important, because of the possibility of supplementing infant formulas with factors that simulate human milk's protective capacity. We postulated that granulocyte colony-stimulating factor (G-CSF), a cytokine known to augment antibacterial defenses through its salutory effect on neutrophil production, might be one such factor. To test this hypothesis, we quantified G-CSF in milk of healthy women and those with intraamniotic infection, and sought the presence of functional G-CSF receptors (G-CSF-R) in fetal/neonatal intestinal villi. STUDY DESIGN: G-CSF was measured by enzyme-linked immunoassay in 126 milk samples obtained from breast-feeding women, and the concentrations were analyzed according to gestational age, postpartum day of collection (first 2 days vs greater 2 days), and the presence versus absence of intraamniotic infection. G-CSF-R messenger ribonucleic acid transcripts were sought from fetal/neonatal intestine using reverse transcriptase polymerase chain reaction, and localized using in situ RT-PCR. G-CSF-R protein, and specific intracellular signaling proteins (Janus tyrosine kinase-1, Janus tyrosine kinase-2, and tyrosine kinase-2), were sought by immunohistochemistry. RESULTS: All milk samples contained G-CSF, and significantly more G-CSF was contained in milk collected during the first 2 postpartum days than during subsequent days. Milk from women who delivered prematurely had less G-CSF during the first 2 postpartum days than milk from women who delivered at term. When intraamniotic infection was present, the concentration of G-CSF in milk was elevated significantly compared with concentrations in milk of noninfected women. G-CSF concentrations were also higher in milk collected during the first 2 postpartum days from women who had received intrapartum recombinant G-CSF treatment, compared with milk obtained from women with intraamniotic infection, regardless if they delivered prematurely or at term. G-CSF-R messenger ribonucleic acid and protein were expressed on fetal villus enterocytes, and Janus tyrosine kinase-1, Janus tyrosine kinase-2, and tyrosine kinase-2 were present within the cytoplasm of these cells. CONCLUSIONS: Human milk contains substantial quantities of G-CSF. G-CSF-R are abundant on villus enterocytes, and specific proteins associated with G-CSF-R signaling are present in these cells.

Chorioamnionitis↗
PubMed2000

Granulocyte colony-stimulating factor serum and urine concentrations in neutropenic neonates before and after intravenous administration of recombinant granulocyte colony-stimulating factor.

BACKGROUND: Recombinant granulocyte colony-stimulating factor (rG-CSF) has been suggested as a treatment for certain varieties of neonatal neutropenia, but little is known about the pharmacologic disposition of rG-CSF in that population. METHODS: Ten neutropenic neonates were treated with rG-CSF, 10 micrograms/kg intravenously once daily for 3 to 5 days. Serum and urine samples were obtained before rG-CSF dosing and at intervals thereafter for G-CSF quantification by enzyme-linked immunosorbent assay. RESULTS: Five of the neutropenic neonates (termed group 1) were not infected but likely had hyporegenerative neutropenia (4 were born after pregnancy-induced hypertension/intrauterine growth restriction, and 1 had Rh hemolytic disease). Five other infants (group 2) had neutropenia accompanying bacterial sepsis and shock. Before receiving the first dose of rG-CSF, endogenous G-CSF serum and urine concentrations were relatively low in group 1, averaging 130 pg/mL (range: 48-209) in serum and 53 pg/mL (range: 15-141) in urine. Serum concentrations immediately before the final dose were much higher (range: 81-24 835 pg/mL), whereas urine concentrations were unchanged (range: <7 pg/mL-126 pg/mL). In group 2 patients, before receiving the first-dose of rG-CSF, endogenous concentrations were very high, averaging 59 575 pg/mL (range: 20 028-98 280) in serum and 3189 pg/mL (range: 23-4770) in urine. Predose serum concentrations before the final dose (range: 427-14 460 pg/mL) were lower than before the first dose. The area under the concentration curve after the first dose of rG-CSF administration in group 1 was significantly lower than after the first dose in group 2, but no difference in area under the concentration curve was observed between groups 1 and 2 after the last dose of rG-CSF. SPECULATION: The principal means of clearing G-CSF from the serum is by saturable binding to specific G-CSF receptors (G-CSF-Rs). Therefore, the very high G-CSF serum and urine concentrations of group 2 patients before the first rG-CSF dose implies that their G-CSF-Rs were saturated before the dose was given. We speculate that if G-CSF-Rs are saturated with endogenous G-CSF, treatment with rG-CSF will add little or nothing to the granulocytopoietic effort. On this basis, we judge that neonates with septic shock and neutropenia are unlikely to derive benefit from rG-CSF administration.

Enzyme-Linked Immunosorbent Assay↗
PubMed1999

Plasma thrombopoietin concentrations in thrombocytopenic and non-thrombocytopenic patients in a neonatal intensive care unit.

Thrombocytopenia is a frequent occurrence in the neonatal intensive care unit (NICU), but the role of thrombopoietin (Tpo) in the pathophysiology is unknown. We obtained serial plasma Tpo concentrations in 20 thrombocytopenic neonates in our NICU, and performed bone marrow studies in 15. The initial Tpo levels ranged from undetectable (<41 pg/ml) to 1112 pg/ml and did not correlate with gestational age or platelet count. Neonates with decreased marrow megakaryocytes did not have plasma Tpo levels as high as those reported in adults, particularly in small for gestational age infants (Tpo < 300 pg/ml). In 14/15 neonates followed until resolution, the Tpo concentration decreased as the platelet count increased.

Biopsy↗