Platelet-activating factor-induced chloride channel activation is associated with intracellular acidosis and apoptosis of intestinal epithelial cells

Platelet-activating factor (PAF) is a phospholipid inter- and intracellular mediator implicated in intestinal injury primarily via induction of an inflammatory cascade. We find that PAF also has direct pathological effects on intestinal epithelial cells (IEC). PAF induces Cl(-) channel activation, which is associated with intracellular acidosis and apoptosis. Using the rat small IEC line IEC-6, electrophysiological experiments demonstrated that PAF induces Cl(-) channel activation. This PAF-activated Cl(-) current was inhibited by Ca(2+) chelation and a calcium calmodulin kinase II inhibitor, suggesting PAF activation of a Ca(2+)-activated Cl(-) channel. To determine the pathological consequences of Cl(-) channel activation, microfluorimetry experiments were performed, which revealed PAF-induced intracellular acidosis, which is also inhibited by the Cl(-) channel inhibitor 4,4'diisothiocyanostilbene-2,2'disulfonic acid and Ca(2+) chelation. PAF-induced intracellular acidosis is associated with caspase 3 activation and DNA fragmentation. PAF-induced caspase activation was abolished in cells transfected with a pH compensatory Na/H exchanger construct to enhance H(+) extruding ability and prevent intracellular acidosis. As ClC-3 is a known intestinal Cl(-) channel dependent on both Ca(2+) and calcium calmodulin kinase II phosphorylation, we generated ClC-3 knockdown cells using short hairpin RNA. PAF induced Cl(-) current; acidosis and apoptosis were all significantly decreased in ClC-3 knockdown cells. Our data suggest a novel mechanism of PAF-induced injury by which PAF induces intracellular acidosis via activation of the Ca(2+)-dependent Cl(-) channel ClC-3, resulting in apoptosis of IEC.

Polyunsaturated fatty acids block platelet-activating factor-induced phosphatidylinositol 3 kinase/Akt-mediated apoptosis in intestinal epithelial cells

We have shown earlier that platelet-activating factor (PAF) causes apoptosis in enterocytes via a mechanism that involves Bax translocation to mitochondria, followed by caspase activation and DNA fragmentation. Herein we report that, in rat small intestinal epithelial cells (IEC-6), these downstream apoptotic effects are mediated by a PAF-induced inhibition of the phosphatidylinositol 3-kinase (PI 3-kinase)/protein kinase B (Akt) signaling pathway. Treatment with PAF results in rapid dephosphorylation of Akt, phosphoinositide-dependent kinase-1, and the YXXM p85 binding motif of several proteins and redistribution of Akt-pleckstrin homology domain-green fluorescent protein, i.e., an in vivo phosphatidylinositol (3,4,5)-trisphosphate sensor, from membrane to cytosol. The proapoptotic effects of PAF were inhibited by both n-3 and n-6 polyunsaturated fatty acids but not by a saturated fatty acid palmitate. Indomethacin, an inhibitor of prostaglandin biosynthesis, did not influence the baseline or PAF-induced apoptosis, but 2-bromopalmitate, an inhibitor of protein palmitoylation, inhibited all of the proapoptotic effects of PAF. Our data strongly suggest that an inhibition of the PI 3-kinase/Akt signaling pathway is the main mechanism of PAF-induced apoptosis in enterocytes and that polyunsaturated fatty acids block this mechanism very early in the signaling cascade independently of any effect on prostaglandin synthesis, and probably directly via an effect on protein palmitoylation.

The importance of pro-inflammatory signaling in neonatal necrotizing enterocolitis

Despite modern medical advances, necrotizing enterocolitis (NEC) remains a significant cause of morbidity and mortality in neonatal intensive care units, affecting 10% of premature neonates born weighing less than 1500 g. Although many advances have been made in the understanding of NEC, the etiology and pathophysiology remain incompletely understood, and treatment is limited to supportive care. In recent years, many studies have evaluated the inflammatory cascade that is central to the disease process, and research is ongoing into strategies to prevent and/or ameliorate neonatal NEC. In this review, we examine the key points in the signaling pathways involved in NEC, and potential strategies for prevention and treatment of this dreaded disease.

Altered endothelin receptor binding in response to nitric oxide synthase inhibition in the pregnant rat

The authors evaluate the expression of endothelin-1 (ET-1) and its receptors in the uterus and placenta during maternal nitric oxide synthase (NOS) inhibition. Timed-pregnant rats received L-NAME (2.5 mg/kg/h) or saline from day 14 to 21 of gestation. Uterine and placental tissues collected on day 21 were assayed for preproET-1, ET( A), and ET(B) mRNA expression; localization and expression of ET-1 and receptor proteins; and receptor activity. NOS inhibition did not affect preproET-1 mRNA expression in the placenta or uterus. ET(A) expression decreased in the uterine free wall, but no other changes in receptor mRNA expression were observed in the uterus or placenta. ET-1 and receptor proteins were unchanged. Placental ET(A) and ET(B) receptor binding decreased. Uterine ET(A) receptor binding decreased in the placental bed. ET-1, a prominent mediator during NOS inhibition, is not of uterine or placental origin. Reduced receptor binding activity is the primary means by which these tissues regulate their response to ET-1 in the setting of NOS inhibition.

Expression of endothelin 1 and its receptors in the hypoxic pregnant rat

Endothelin 1 (EDN1) plays a primary role in the pathophysiology of hypoxia-induced fetal growth restriction in the rat. In this study we evaluated the effects of chronic maternal hypoxia on the expression of endothelin and its receptors and on receptor binding activity in the uterus and placenta of the rat, in order to elucidate their roles in hypoxia-induced fetal growth restriction. Timed-pregnant Sprague-Dawley rats were maintained in either a normoxic or a normobaric hypoxic (12% O(2)) atmosphere from Gestational Days 18-21. Uterine and placental tissues collected on Gestational Day 21 were assayed for Edn1, Ednra, and Ednrb (endothelin receptors) mRNA expression by real-time quantitative RT-PCR, for localization of EDN1 and its receptors by immunohistochemistry, for EDNRA and EDNRB protein expression by Western blot, and for receptor binding activity by homologous competitive binding assays. EDN1 mRNA expression was significantly increased in the hypoxic placenta, but not in the uterus, compared with normoxic controls. Immunohistochemistry revealed increased EDN1 specifically in the labyrinth of the placenta. Receptor mRNA levels were not significantly affected by hypoxia, but EDNRA protein expression was significantly decreased specifically in the uterine placental beds. Receptor binding decreased significantly in response to hypoxia in all tissues investigated, compared with controls. These results suggest that chronic maternal hypoxia results in increased expression of EDN1 in the placenta but not in the uterus, and that reduced binding activity, rather than regulation of receptor expression, is a mechanism by which these tissues regulate the local hemodynamic response to increased endogenous placental EDN1 in the setting of hypoxia.

Inhibition of nuclear factor-kappaB ameliorates bowel injury and prolongs survival in a neonatal rat model of necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is a major cause of morbidity and death in premature infants. NEC is associated with increased levels of pro-inflammatory cytokines in plasma and tissues that are regulated by the transcription factor nuclear factor-kappaB (NF-kappaB). It remains unknown, however, whether NF-kappaB mediates injury in neonatal NEC. We therefore examined the activation status of NF-kappaB perinatally in the small intestine and in a neonatal rat model of NEC. We found that intestinal NF-kappaB is strongly activated at birth and, in dam-fed newborn rats, is down-regulated within a day. In contrast, NF-kappaB remains strongly activated at both d 1 and d 2 in stressed animals, and this is accompanied by a significant decrease in the levels of the endogenous NF-kappaB inhibitor protein IkappaBalpha and IkappaBbeta at d 2. To determine the importance of elevated NF-kappaB activity in intestinal injury in NEC, we administered the NEMO-binding domain (NBD) peptide that selectively inhibits the critical upstream IkappaB kinase (IKK). NBD but not a control peptide decreased mortality and bowel injury in this model, supporting the hypothesis that bowel injury in NEC results from elevated NF-kappaB activity. Our findings therefore lead us to conclude that selective NF-kappaB inhibition represents a promising therapeutic strategy for NEC.

Polyunsaturated fatty acid supplementation alters proinflammatory gene expression and reduces the incidence of necrotizing enterocolitis in a neonatal rat model

Although supplementation of preterm formula with polyunsaturated fatty acids (PUFA) has been shown to reduce the incidence of necrotizing enterocolitis (NEC) in animal models and clinical trials, the mechanisms remain elusive. We hypothesized that the protective effect of PUFA on NEC may be due to the ability of PUFA to suppress Toll-like receptor (TLR) 4 and platelet-activating factor receptor (PAFR) gene expression (molecules that are important in the pathogenesis of NEC) in epithelial cells. To investigate the efficacy of different PUFA preparations on NEC in a neonatal rat model, we compared the incidence of NEC among the four PUFA supplemented groups--A: arachidonic acid and docosahexaenoic acid (AA+DHA), B: egg phospholipids (EP), C: DHA, and D: control without PUFA. PUFA supplementation reduced the incidence of NEC and inhibited intestinal PAFR and TLR4 gene expression compared with the controls. To validate the in vivo observations, IEC-6 cells were exposed to PAF after pretreatment with AA or DHA. Both AA and DHA supplementation blocked PAF-induced TLR4 and PAFR mRNA expression in these enterocytes. These results suggest that PUFA modulates gene expression of key factors involved in experimental NEC pathogenesis. These effects might in part explain the protective effect of PUFA on neonatal NEC.

Adenosine regulation of alveolar fluid clearance

Adenosine is a purine nucleoside that regulates cell function through G protein-coupled receptors that activate or inhibit adenylyl cyclase. Based on the understanding that cAMP regulates alveolar epithelial active Na(+) transport, we hypothesized that adenosine and its receptors have the potential to regulate alveolar ion transport and airspace fluid content. Herein, we report that type 1 (A(1)R), 2a (A(2a)R), 2b (A(2b)R), and 3 (A(3)R) adenosine receptors are present in rat and mouse lungs and alveolar type 1 and 2 epithelial cells (AT1 and AT2). Rat AT2 cells generated and produced cAMP in response to adenosine, and micromolar concentrations of adenosine were measured in bronchoalveolar lavage fluid from mice. Ussing chamber studies of rat AT2 cells indicated that adenosine affects ion transport through engagement of A(1)R, A(2a)R, and/or A(3)R through a mechanism that increases CFTR and amiloride-sensitive channel function. Intratracheal instillation of low concentrations of adenosine (< or =10(-8)M) or either A(2a)R- or A(3)R-specific agonists increased alveolar fluid clearance (AFC), whereas physiologic concentrations of adenosine (> or =10(-6)M) reduced AFC in mice and rats via an A(1)R-dependent pathway. Instillation of a CFTR inhibitor (CFTR(inh-172)) attenuated adenosine-mediated down-regulation of AFC, suggesting that adenosine causes Cl(-) efflux by means of CFTR. These studies report a role for adenosine in regulation of alveolar ion transport and fluid clearance. These findings suggest that physiologic concentrations of adenosine allow the alveolar epithelium to counterbalance active Na(+) absorption with Cl(-) efflux through engagement of the A(1)R and raise the possibility that adenosine receptor ligands can be used to treat pulmonary edema.

The roles of bacteria and TLR4 in rat and murine models of necrotizing enterocolitis

Bacteria are thought to contribute to the pathogenesis of necrotizing enterocolitis (NEC), but it is unknown whether their interaction with the epithelium can participate in the initiation of mucosal injury or they can act only following translocation across a damaged intestinal barrier. Our aims were to determine whether bacteria and intestinal epithelial TLR4 play roles in a well-established neonatal rat model and a novel neonatal murine model of NEC. Neonatal rats, C57BL/6J, C3HeB/FeJ (TLR4 wild type), and C3H/HeJ (TLR4 mutant) mice were delivered by Cesarean section and were subjected to formula feeding and cold asphyxia stress or were delivered naturally and were mother-fed. NEC incidence was evaluated by histological scoring, and gene expression was quantified using quantitative real-time PCR from cDNA generated from intestinal total RNA or from RNA obtained by laser capture microdissection. Spontaneous feeding catheter colonization or supplementation of cultured bacterial isolates to formula increased the incidence of experimental NEC. During the first 72 h of life, i.e., the time frame of NEC development in this model, intestinal TLR4 mRNA gradually decreases in mother-fed but increases in formula feeding and cold asphyxia stress, correlating with induced inducible NO synthase. TLR4, inducible NO synthase, and inflammatory cytokine induction occurred in the intestinal epithelium but not in the submucosa. NEC incidence was diminished in C3H/HeJ mice, compared with C3HeB/FeJ mice. In summary, bacteria and TLR4 play significant roles in experimental NEC, likely via an interaction of intraluminal bacteria and aberrantly overexpressed TLR4 in enterocytes.

Prostate cancer cells regulate growth and differentiation of bone marrow endothelial cells through TGFbeta and its receptor, TGFbetaRII

BACKGROUND

The underlying mechanisms permitting prostate cancer bone metastasis are poorly understood. We previously showed that the highly metastatic prostate cancer cell line, PC-3, inhibits bone marrow endothelial (HBME-1) cell growth in collagen gels and induces them to differentiate into cords, resembling angiogenesis in vivo.

METHODS

cDNA microarray analysis was performed to identify cytokines responsible for the effects of PC-3 cells on HBME-1 cells. Cytokine and neutralizing antibody studies were done to further investigate specific angiogenic factors, such as transforming growth factor beta (TGFbeta). TGFbeta RNA and protein were detected by real-time RT-PCR and enzyme-linked immunosorbent assay (ELISA) analysis to measure their production by prostate cancer cell lines. Conditioned media experiments using TGFbeta neutralizing antibodies were used to analyze TGFbeta activation by prostate cancer cells.

RESULTS

PC-3 conditioned media altered the expression of several TGFbeta-regulated or -associated genes in HBME-1 cells. Low concentrations of TGFbeta cytokines inhibited HBME-1 cell growth to a similar level as PC-3 conditioned media and partially induced differentiation. Inhibitors and neutralizing antibodies directed against TGFbeta isoforms and TGFbeta receptor type 2 (TGFbetaRII) reversed the growth inhibition of HBME-1 cells conferred by PC-3 conditioned media. Yet, only TGFbetaRII neutralizing antibodies significantly inhibited HBME-1 differentiation. Also, prostate cancer cell lines produced low levels of TGFbeta RNA and protein, and were shown to activate serum-derived TGFbeta.

CONCLUSIONS

These results suggest that prostate cancer cells mediate growth inhibition and differentiation of bone marrow endothelial cells both through production and activation of TGFbeta as well as alteration of TGFbetaRII-mediated signal transduction. This could contribute to the establishment and growth of bone metastases.

Model of cerebral palsy in the perinatal rabbit

Perinatal brain injury results in one of the highest burdens of disease in view of the lifelong consequences and is of enormous cost to society. This makes it imperative to develop better animal models that mimic the human condition. Many neurodevelopmental deficits, such as cerebral palsy, are believed to be a result of prenatal hypoxia-ischemia in humans. Fetal global hypoxia-ischemia is most commonly a consequence of acute placental insufficiency. Our laboratory has modeled in utero sustained and repetitive hypoxia-ischemia in the pregnant rabbit to mimic the insults of abruptio placenta and labor, respectively. Sustained hypoxia-ischemia at 70% (22 days' gestation) and 79% (25 days' gestation) and repetitive hypoxia-ischemia at 90% gestation (28 days' gestation) caused stillbirths and multiple deficits in the postnatal survivors. The deficits included impairment in multiple tests of spontaneous locomotion, reflex motor activity, motor responses to olfactory stimuli, and the coordination of suck and swallow. Hypertonia was observed in the 22 and 25 days' gestation survivors but not in the 28 days' gestation group. Hypertonic survivors were artificially fed and found to have the motor deficits persist for at least 11 postnatal days. A spectrum of brain abnormalities is found on magnetic resonance imaging. This is the first animal model to mimic cerebral palsy. The findings also suggest a window of vulnerability during brain development when the injury results in hypertonia in newborn pups.

The role of PAF, TLR, and the inflammatory response in neonatal necrotizing enterocolitis

The pathogenesis of neonatal necrotizing enterocolitis remains poorly understood. Recent evidence suggests that PAF (platelet activating factor) and human toll-like receptors (TLRs) contribute to the pro-inflammatory response that is characteristic of NEC pathology. Understanding the regulation of these molecular interactions may provide new approaches for prevention or treatment of this dreaded condition.

Bi-directional interactions of prostate cancer cells and bone marrow endothelial cells in three-dimensional culture

BACKGROUND

Prostate cancer preferentially metastasizes to bone, yet little is known about the cellular and molecular factors that support this growth. Endothelial cells are likely the initial contact for circulating prostate cells entering the bone microenvironment.

METHODS

Using co-culture and conditioned media experiments, we studied cellular and molecular interactions of prostate cancer cells of varying aggressiveness (PC-3 and LNCaP) with bone marrow endothelial (HBME-1) cells in collagen gels.

RESULTS

In co-culture, HBME-1 cells stimulated proliferation ( approximately 90% increase) and migration of the more aggressive PC-3 cell line, while having little effect on LNCaP cell proliferation or migration. Concomitantly, HBME-1 cell growth was inhibited by both PC-3 and LNCaP cells and their conditioned media. Additionally, HBME-1 cells underwent significant morphological changes in co-culture, forming large, branching, cord-like structures, which mimic angiogenesis. Prostate cancer cell conditioned media induced a similar effect on HBME-1 cells. In comparison, conditioned media from PC-3 cells also inhibited growth of non-bone marrow-derived endothelial cells, but did not affect their morphology.

CONCLUSIONS

Significant bi-directional interactions, including secreted factors and direct cellular interactions, exist between bone marrow endothelial cells and highly metastatic prostate cancer cells, and may underlie the propensity for prostate cancer to metastasize to the bone.

Intestinal epithelial apoptosis initiates gross bowel necrosis in an experimental rat model of neonatal necrotizing enterocolitis

The histopathology of necrotizing enterocolitis (NEC) is characterized by destruction of the mucosal layer in initial stages and by transmural necrosis of the intestinal wall in advanced stages of the disease. To test the hypothesis that enhanced epithelial apoptosis is an initial event underlying the gross histologic changes, we analyzed epithelial apoptosis and tissue morphology in an animal model of NEC and evaluated the effect of caspase inhibition on the incidence of experimental NEC in this model. Apoptosis was analyzed with terminal deoxynucleotidyltransferase-mediated dUTP-FITC nick end labeling (TUNEL) staining in intestinal sections and by measuring caspase 3 activity from intestinal lysates of neonatal rats subjected to formula feeding and cold/asphyxia stress (FFCAS) and from mother-fed (MF) controls. Morphologic evaluation was based on hematoxylin and eosin staining of intestinal sections. FFCAS resulted in histologic changes consistent with NEC, which were absent from MF animals. FFCAS was also associated with a significantly increased rate of nuclear DNA fragmentation in the small intestinal epithelium compared with MF. Elevated tissue caspase 3 activity confirmed the presence of apoptosis in samples with increased DNA fragmentation. Analysis of the coincidence of morphologic damage and apoptosis in corresponding tissue sections indicated that apoptosis precedes gross morphologic changes in this model. Furthermore, supplementation of formula with 8 boc-aspartyl(OMe)-fluoromethylketone, a pan-caspase inhibitor, significantly reduced the incidences of apoptosis and experimental NEC. These findings indicate that in neonatal rats FFCAS induces epithelial apoptosis that serves as an underlying cause for subsequent gross tissue necrosis.

Platelet-activating factor-induced apoptosis is blocked by Bcl-2 in rat intestinal epithelial cells

Plateletactivating factor (PAF) is a key mediator in pathogenesis of inflammatory bowel diseases (IBDs) but mechanisms of PAF-induced mucosal injury are poorly understood. To determine whether apoptosis and the Bcl-2-family of apoptosis regulatory gene products play a role in PAF-induced mucosal injury, we stably and conditionally overexpressed bcl-2 in rat small intestinal epithelial cells-6 under the control of a lactose-inducible promoter. Western blot analysis and immuno-histochemistry were used to verify inducible Bcl-2 and to analyze Bcl-2 and a proapoptotic member of the Bcl-2 family, Bax, subcellular distribution. DNA fragmentation was quantified by ELISA, caspase activity was measured by using fluorogenic peptide substrates, and mitochondrial membrane potential was assayed by 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolylcarbocyanine iodide (JC-1) and fluorescence digital imaging. Bcl-2 expression was highly inducible by lactose analog isopropyl-beta-(d)-thiogalactoside (IPTG) and was localized predominantly to mitochondria. In the absence of bcl-2 overexpression and after treatment with PAF, Bax translocated to mitochondria, and mitochondrial membrane potential collapsed within 1 h, followed by caspase-3 activation, which peaked at 6 h with an ensuing DNA fragmentation maximizing at 18 h. After IPTG-induction of bcl-2 expression, PAF failed to induce DNA fragmentation, caspase-3 activation, Bax translocation, or a collapse of mitochondrial membrane potential. These data are the first to show that PAF can activate apoptotic machinery in enterocytes via a mechanism involving Bax translocation and collapse of mitochondrial membrane potential and that both of these events are under control by bcl-2 expression levels. A better understanding of the role of PAF and Bcl-2 family of apoptosis regulators in epithelial cell death might aid design of better therapeutic or preventive strategies for IBDs.

Preterm fetal hypoxia-ischemia causes hypertonia and motor deficits in the neonatal rabbit: a model for human cerebral palsy?

Prenatal hypoxia-ischemia to the developing brain has been strongly implicated in the subsequent development of the hypertonic motor deficits of cerebral palsy (CP) in premature and full-term infants who present with neonatal encephalopathy. Despite the enormous impact of CP, there is no animal model that reproduces the hypertonia and motor disturbances of this disorder. We report a rabbit model of in utero placental insufficiency, in which hypertonia is accompanied by marked abnormalities in motor control. Preterm fetuses (67-70% gestation) were subjected to sustained global hypoxia. The dams survived and gave spontaneous birth. At postnatal day 1, the pups that survived were subjected to a battery of neurobehavioral tests developed specifically for these animals, and the tests were videotaped and scored in a masked manner. Newborn pups of hypoxic groups displayed significant impairment in multiple tests of spontaneous locomotion, reflex motor activity, and the coordination of suck and swallow. Increased tone of the limbs at rest and with active flexion and extension were observed in the survivors of the preterm insult. Histopathological studies identified a distinct pattern of acute injury to subcortical motor pathways that involved the basal ganglia and thalamus. Persistent injury to the caudate putamen and thalamus at P1 was significantly correlated with hypertonic motor deficits in the hypoxic group. Antenatal hypoxia-ischemia at preterm gestation results in hypertonia and abnormalities in motor control. These findings provide a unique behavioral model to define mechanisms and sequelae of perinatal brain injury from antenatal hypoxia-ischemia.

Novel complexes of guanylate cyclase with heat shock protein 90 and nitric oxide synthase

Soluble guanylate cyclase (sGC) is an important downstream intracellular target of nitric oxide (NO) that is produced by endothelial NO synthase (eNOS) and inducible NO synthase (iNOS). In this study, we demonstrate that sGC exists in a complex with eNOS and heat shock protein 90 (HSP90) in aortic endothelial cells. In addition, we show that in aortic smooth muscle cells, sGC forms a complex with HSP90. Formation of the sGC/eNOS/HSP90 complex is increased in response to eNOS-activating agonists in a manner that depends on HSP90 activity. In vitro binding assays with glutathione S-transferase fusion proteins that contain the alpha- or beta-subunit of sGC show that the sGC beta-subunit interacts directly with HSP90 and indirectly with eNOS. Confocal immunofluorescent studies confirm the subcellular colocalization of sGC and HSP90 in both endothelial and smooth muscle cells. Complex formation of sGC with HSP90 facilitates responses to NO donors in cultured cells (cGMP accumulation) as well as in anesthetized rats (hypotension). These complexes likely function to stabilize sGC as well as to provide directed intracellular transfer of NO from NOS to sGC, thus preventing inactivation of NO by superoxide anion and formation of peroxynitrite, which is a toxic molecule that has been implicated in the pathology of several vascular diseases.

Infusion of exogenous platelet-activating factor produces intrauterine growth restriction in the rat

OBJECTIVE

To determine the impact of exogenous platelet-activating factor (PAF) on pregnancy outcome in the rat.

METHODS

Carbamyl-PAF (0.05, 0.5, or 5.0 microg/kg per hour) or vehicle was infused intravenously for 7 days by osmotic pump into timed pregnant rats. Infusion was begun on day 14 of a 22-day gestation. Maternal mean arterial blood pressures were measured on days 1, 4, and 7 of the infusion. On gestational day 21 (PAF infusion day 7), fetal and placental weights and viability were evaluated at hysterotomy. Uterine and placental PAF receptor expression was analyzed by reverse transcription-polymerase chain reaction and agarose gel electrophoresis. Data were analyzed by analysis of variance, chi(2), or the Mann-Whitney U test as appropriate.

RESULTS

Fetal weights were dose-dependently lower than control, by 19% and 35%, respectively, at dosages of 0.5 and 5.0 microg/kg per hour (P < .001) but were not affected at the 0.05 microg/kg per hour dose of carbamyl-PAF. Placental weights were significantly lower at all doses (P < .001). Fetal demise was dose-dependently higher and was significantly different from the control group at the 0.5 and 5.0 microg/kg per hour doses of carbamyl-PAF (P < .0001). Maternal mean arterial pressures were not altered by these doses of carbamyl-PAF. PAF receptors were expressed abundantly in both uterus and placenta.

CONCLUSIONS

Exogenous PAF produces dose-dependent fetal growth restriction in the rat. Placental growth is particularly sensitive to PAF and, coupled with the dose-dependent decline in fetal growth, suggests a dose-dependent decline in function. An elevated level of PAF is detrimental to fetal growth and well-being in the rat.

Platelet-activating factor regulates chloride transport in colonic epithelial cell monolayers

Platelet-activating factor (PAF) has been implicated in the pathogenesis of gastrointestinal diseases such as necrotizing enterocolitis, Crohn's disease, and ulcerative colitis. However, neither the physiologic role of PAF in the intestine, nor the mechanisms by which PAF participates in the pathogenesis of disease are well understood. The aim of the present study was to determine the direct effect of PAF on intestinal epithelial cell ion transport, and to delineate the mechanisms of regulation. Ion transport was evaluated by measuring short circuit current (I(sc)) in HT29-CL19A cell monolayers using Ussing chambers. PAF receptor polarity was assessed using domain-selective biotinylation followed by immunoprecipitation and streptavidin blotting of intact epithelial monolayers. PAF (1-200 microM) stimulated I(sc) that followed the direction of a Cl(-) gradient and was specifically inhibited by the Cl(-) channel blockers glybenclamide, 2,2' iminodibenzoic acid and 4,4' diisothiocyanostilbene-2, 2' disulfonic acid, but was unaffected by the inhibition of prostaglandin synthesis with indomethacin. Stimulated I(sc) was only detected after apical addition of PAF, correlating with the results of biotinylation experiments indicating an exclusive apical polarity of the PAF receptor. PAF receptor antagonists CV6209 and octylonium bromide abolished PAF-stimulated I(sc). Thus, mucosal acting PAF directly and specifically stimulates ion transport via activation of an apical Cl(-) channel in intestinal epithelial cell monolayers independent of prostaglandin biosynthesis.

The role of polyunsaturated fatty acid supplementation in intestinal inflammation and neonatal necrotizing enterocolitis

Dietary polyunsaturated fatty acid (PUFA) supplementation has been shown to reduce the incidence of necrotizing enterocolitis (NEC) in a recent randomized, controlled trial. These compounds are known to modulate the inflammatory cascade and to influence intestinal health in a variety of ways. Although the pathophysiology of NEC is not well understood, recent evidence suggests that platelet-activating factor (PAF) is a key endogenous mediator of intestinal necrosis in animals. Using a neonatal rat model of NEC that includes the key risk factors of asphyxia and formula feeding, we investigated the role of dietary PUFA supplementation on the incidence and pathophysiology of NEC. Our findings suggest that PUFA reduce the incidence of NEC by modulating PAF metabolism and endotoxin translocation.

Effect of polyunsaturated fatty acid (PUFA) supplementation on intestinal inflammation and necrotizing enterocolitis (NEC) in a neonatal rat model

Inasmuch as long-chain polyunsaturated fatty acids (PUFA, metabolites of the essential n-3 and n-6 fatty acids) are known to modulate inflammation, we hypothesized that supplementation of formula with these compounds would prevent necrotizing enterocolitis (NEC) and intestinal inflammation in our neonatal rat model. Newborn rats were stressed with asphyxia and formula feeding, and randomly assigned to control formula, control with PUFA supplementation, and PUFA with nucleotides. Animals were followed for 72--96 h and assessed for death, gross and histologic NEC, intestinal apoptosis, endotoxemia, and intestinal mRNA synthesis of phospholipase A(2)-II (rate-limiting enzyme for platelet activating factor production), platelet activating factor receptor, and inducible nitric oxide synthase. We found that PUFA reduced the incidence of death and NEC compared with the other groups (NEC 8 of 24 versus 17 of 24 control and 13 of 23 PUFA + nucleotides, p < 0.05). Furthermore, PUFA reduced plasma endotoxemia at 48 h (25 +/- 4 EU/mL versus 276 +/- 39 EU/mL in control and 170 +/- 28 EU/mL in PUFA + nucleotide), intestinal phospholipase A(2)-II expression at 24 h, and platelet activating factor receptor expression at 48 h. Formula supplementation had no effect on apoptosis of intestinal epithelium or intestinal inducible nitric oxide synthase expression. Addition of nucleotides with PUFA abrogated the beneficial effects of PUFA on intestinal inflammation. We conclude that PUFA reduces the incidence of NEC and intestinal inflammation in a neonatal rat model.

New concepts in necrotizing enterocolitis

Necrotizing enterocolitis is an overwhelming gastrointestinal emergency that primarily afflicts premature infants born weighing less than 1500 g. Despite years of investigation, the etiology remains unclear, and accepted prevention and treatment strategies are lacking. Studies published over the last year have provided new insight into several aspects of this complex disease. In this review, novel information is presented on (1) the epidemiology; (2) methods of early diagnosis, such as abdominal magnetic resonance imaging; (3) the importance of risk factors, including assessment of feeding strategies and role of bacterial colonization; (4) the pathophysiology, highlighting experimental and clinical trials evaluating the role of inflammatory mediators and growth factors on the disease; (5) preventive strategies, such as anaerobic bacterial supplementation; and (6) surgical interventions, including peritoneal drainage. Understanding some of these important aspects of necrotizing enterocolitis may help improve the outlook of patients with this dreaded disease. Although the incidence of neonatal necrotizing enterocolitis (NEC) and the mortality stemming from this disease have not significantly improved over the last 30 years, there is exciting new information that may significantly improve the outlook of patients with this overwhelming intestinal emergency in the near future.