Placenta growth factor augments airway hyperresponsiveness via leukotrienes and IL-13

Airway hyperresponsiveness (AHR) affects 55%-77% of children with sickle cell disease (SCD) and occurs even in the absence of asthma. While asthma increases SCD morbidity and mortality, the mechanisms underlying the high AHR prevalence in a hemoglobinopathy remain unknown. We hypothesized that placenta growth factor (PlGF), an erythroblast-secreted factor that is elevated in SCD, mediates AHR. In allergen-exposed mice, loss of Plgf dampened AHR, reduced inflammation and eosinophilia, and decreased expression of the Th2 cytokine IL-13 and the leukotriene-synthesizing enzymes 5-lipoxygenase and leukotriene-C4-synthase. Plgf-/- mice treated with leukotrienes phenocopied the WT response to allergen exposure; conversely, anti-PlGF Ab administration in WT animals blunted the AHR. Notably, Th2-mediated STAT6 activation further increased PlGF expression from lung epithelium, eosinophils, and macrophages, creating a PlGF/leukotriene/Th2-response positive feedback loop. Similarly, we found that the Th2 response in asthma patients is associated with increased expression of PlGF and its downstream genes in respiratory epithelial cells. In an SCD mouse model, we observed increased AHR and higher leukotriene levels that were abrogated by anti-PlGF Ab or the 5-lipoxygenase inhibitor zileuton. Overall, our findings indicate that PlGF exacerbates AHR and uniquely links the leukotriene and Th2 pathways in asthma. These data also suggest that zileuton and anti-PlGF Ab could be promising therapies to reduce pulmonary morbidity in SCD.

Peroxisome proliferator-activated receptor-α-mediated transcription of miR-301a and miR-454 and their host gene SKA2 regulates endothelin-1 and PAI-1 expression in sickle cell disease

Endothelin-1 (ET-1) and plasminogen activator inhibitor-1 (PAI-1) play important roles in pulmonary hypertension (PH) in sickle cell disease (SCD). Our previous studies show higher levels of placenta growth factor (PlGF) in SCD correlate with increased plasma levels of ET-1, PAI-1, and other physiological markers of PH. PlGF-mediated ET-1 and PAI-1 expression occurs via activation of hypoxia-inducible factor-1α (HIF-1α). However, relatively little is understood regarding post-transcriptional regulation of PlGF-mediated expression of ET-1 and PAI-1. Herein, we show PlGF treatment of endothelial cells reduced levels of miR-301a and miR-454 from basal levels. In addition, both miRNAs targeted the 3'-UTRs of ET-1 and PAI-1 mRNAs. These results were corroborated in the mouse model of SCD [Berkeley sickle mice (BK-SS)] and in SCD subjects. Plasma levels of miR-454 in SCD subjects were significantly lower compared with unaffected controls, which correlated with higher plasma levels of both ET-1 and PAI-1. Moreover, lung tissues from BK-SS mice showed significantly reduced levels of pre-miR-301a and concomitantly higher levels of ET-1 and PAI-1. Furthermore, we show that miR-301a/miR-454 located in the spindle and kinetochore-associated protein-2 (SKA2) transcription unit was co-transcriptionally regulated by both HIF-1α and peroxisome proliferator-activated receptor-α (PPAR-α) as demonstrated by SKA2 promoter mutational analysis and ChIP. Finally we show that fenofibrate, a PPAR-α agonist, increased the expression of miR-301a/miR-454 and SKA2 in human microvascular endothelial cell line (HMEC) cells; the former were responsible for reduced expression of ET-1 and PAI-1. Our studies provide a potential therapeutic approach whereby fenofibrate-induced miR-301a/miR-454 expression can ameliorate PH and lung fibrosis by reduction in ET-1 and PAI-1 levels in SCD.

Peroxisome proliferator-activated receptor-α-mediated transcription of miR-199a2 attenuates endothelin-1 expression via hypoxia-inducible factor-1α

Endothelin-1, a potent vasoconstrictor, plays an important role in pulmonary hypertension (PH) in sickle cell disease (SCD). Our previous studies show that higher levels of placenta growth factor (PlGF), secreted by erythroid precursor cells, correlate with increased plasma levels of endothelin-1 (ET-1) and other functional markers of PH in SCD. PlGF-mediated ET-1 expression occurs via activation of hypoxia-inducible factor-1α (HIF-1α). However, relatively less is understood regarding how PlGF-mediated expression of HIF-1α and its downstream effector ET-1 are post-transcriptionally regulated. Herein, we show that PlGF treatment of endothelial cells resulted in reduced levels of miR-199a2, which targeted the 3'-UTR of HIF-1α mRNA and concomitantly led to augmented ET-1 expression. Plasma levels of miR-199a2 in SCD subjects were significantly lower with reciprocally high levels of plasma ET-1, unlike unaffected controls. This observation provided a molecular link between miR-199a2 and high levels of ET-1 in SCD. Furthermore, we show that miR-199a2 located in the DNM3os transcription unit was co-transcriptionally regulated by peroxisome proliferator-activated receptor α (PPARα). Binding of the latter to PPARα cis-elements in the promoter of DNM3os was demonstrated by promoter mutational analysis and ChIP. Additionally, we show that fenofibrate, a PPARα agonist, increased the expression of miR-199a2 and DNM3os; the former was responsible for reduced expression of HIF-1α and ET-1. In vivo studies of fenofibrate-fed Berkeley sickle mice resulted in increased levels of miR-199a2 and reduced levels of ET-1 in lung tissues. Our studies provide a potential therapeutic approach whereby fenofibrate-induced miR-199a2 expression can ameliorate PH by reduction of ET-1 levels.

Angiogenic growth factors augment K-Cl cotransporter expression in erythroid cells via hypoxia-inducible factor-1α

The potassium chloride cotransporters (KCC) family of proteins are widely expressed and are involved in the transepithelial movement of potassium and chloride ions and the regulation of cell volume. KCC activity is high in reticulocytes, and contributes to the dehydration of sickle red blood cells. Because plasma levels of both vascular endothelial growth factor (VEGF) and placental growth factor (PlGF) are elevated in sickle cell individuals, and VEGF has been shown to increase KCC expression in other cells, we hypothesized that VEGF and PlGF influence KCC expression in erythroid cells. Both VEGF and PlGF treatment of human erythroid K562 cells increased both mRNA and protein levels of KCC1, KCC3b, and KCC4. VEGF- and PlGF-mediated cellular signaling involved VEGF-R1 and downstream effectors, specifically, PI-3 kinase, p38 MAP kinase, mTOR, NADPH-oxidase, JNK kinase, and HIF-1α. VEGF and PlGF-mediated transcription of KCC3b and KCC4 involved hypoxia response element (HRE) motifs in their promoters, as demonstrated by promoter analysis, EMSA and ChiP. These results were corroborated in vivo by adenoviral-mediated overexpression of PlGF in normal mice, which led to increased expression of mKCC3 and mKCC4 in erythroid precursors. Our studies show that VEGF and PlGF regulate transcription of KCC3b and KCC4 in erythroid cells via activation of HIF-1α, independent of hypoxia. These studies provide novel therapeutic targets for regulation of cell volume in RBC precursors, and thus, amelioration of dehydration in RBCs in sickle cell disease.

Abstract B214: Antagonizing CBP/beta-catenin signaling-enhanced radiation sensitivity and altered epithelial-mesenchymal transition markers in head and neck squamous cell carcinoma

Introduction: Survivin is often overexpressed in many types of cancers. An elevated survivin expression level in cancers is correlated with enhanced proliferative index, reduced apoptosis levels, and resistant to chemotherapy and radiation therapy. In addition, cancers often have elevated levels of S100A4 expression, which is known to be involved in metastasis. Metastasis has been linked with the ability of cancer cells to undergo epithelial-mesenchymal transition (EMT). Both survivin and S100A4 are known to be highly expressed in the head and neck cancers(HNC), which is the 6th most common cancer in the world and its 5-year survival rate is often less than 50%. ICG-001, developed by Michael Kahn, is a novel small molecule inhibitor of Wnt signaling. Previous studies have shown that ICG-001 inhibits CBP/beta-catenin interaction and its down-stream target genes, including survivin and S100A4. The purpose of this study is to examine the effect of this small molecule inhibitor in head and neck squamous cell carcinoma (HNSCC), which constitutes more than 90% of all HNC, and radiation resistance and metastasis are the main cause of a poor prognosis.

Experimental Procedures: Three HNSCC cell lines (USC-001, SCC-71, and SCC-15) were used in this study. Expression of survivin, cyclin-D1, S100A4, and E-cadherin were analyzed by realtime qRT-PCR. Survivin expression is further analyzed by western blotting and immunohistochemistry. Survivin and Wnt/b-catenin promoter activities were analyzed by survivin-luciferase and TOPFLASH assays, respectively. Viable cells were determined by trypan blue exclusion assay and WST-1 assay. Dead cells were determined by Sytox-green/Hoechst staining. Caspase activity was determined by caspase-6 assay.

Summary of results: Our in-vitro data showed that ICG-001 treatment (5, 10, and 25uM) reduced viable HNSCC cells and Ki67positive cells as much as 50%, in a dose-dependent manner. Western blotting, RT-PCR, immnohistochemistry and survivin-promotor analysis showed that survivin expression level was significantly reduced by ICG-001 treatment. Moreover, Wnt/b-catenin promoter activity was reduced by ICG-001. In addition, ICG-001 treatment significantly downregulated S100A4(mesenchymal marker) expression and upregulated E-cadherin (epithelial cell marker) expression level in all of the cell lines we tested. Pre-treatment with ICG-001 enhanced radiation induced cell death in vitro, determined by WST-1 and Sytox-Green/Hoechst assays. In order to delineate the molecular mechanisms of ICG-001 coupled radiation-mediated cell death, caspase activity was measured. Our preliminary results showed that Caspase-6 activity was enhanced in a dose dependent manner in ICG-001 pre-treated, radiation-treated cells.

Conclusion: Antagonizing CBP/b-catenin signaling by ICG-001 induced anti-proliferative effect in HNSCC and could enhance radiation sensitivity in vitro, possibly by inducing apoptosis due to a reduced survivin expression. Moreover, the small molecule inhibitor may reduce EMT process by reducing S100A4 expression levels. Modulating downstream target genes of CBP/b-catenin signaling by the small molecule inhibitor ICG-001 may be a powerful tool to enhance radiation sensitivity and to reduce metastatic potential in HNSCC.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr B214.

15th International Symposium on Cells of the Hepatic Sinusoid, 2010

This is a meeting report of the presentations given at the 15th International Symposium on Cells of the Hepatic Sinusoid, held in 2010. The areas covered include the contributions of the various liver cell populations to liver disease, molecular and cellular targets involved in steatohepatitis, hepatic fibrosis and cancer and regenerative medicine. In addition to a review of the science presented at the meeting, this report provides references to recent literature on the topics covered at the meeting.

Involvement of miR-30c and miR-301a in immediate induction of plasminogen activator inhibitor-1 by placental growth factor in human pulmonary endothelial cells

PAI-1 (plasminogen activator inhibitor-1) is a key physiological inhibitor of fibrinolysis. Previously, we have reported PlGF (placental growth factor)-mediated transcriptional up-regulation of PAI-1 (SERPINE1) mRNA expression via activation of HIF-1α (hypoxia-inducible factor-1α) and AP-1 (activator protein-1) in HPMVECs (human pulmonary microvascular endothelial cells), which resulted in elevated PAI-1 in humans with SCA (sickle cell anaemia). In the present study, we have identified the role of post-transcriptional mechanism(s) of PlGF-mediated accumulation of PAI-1 mRNA in HPMVECs by examining the role of microRNAs (miRNAs/miRs) in PlGF-induced PAI-1 mRNA stability. Our results show reduced expression of miR-30c and miR-301a, but not of miR-99a, in response to PlGF, which have evolutionarily conserved binding sites in the 3'-UTR (3'-untranslated region) of PAI-1 mRNA. Transfection of anti-miR-30c or anti-miR-301a oligonucleotides resulted in increased PAI-1 mRNA levels, which were increased further with PlGF stimulation. Conversely, overexpression of pre-miR-30c or pre-miR-301a resulted in an attenuation of PlGF-induced PAI-1 mRNA and protein levels. Luciferase reporter assays using wild-type and mutant 3'-UTR constructs confirmed that the PAI-1 3'-UTR is indeed a direct target of miR-30c and miR-301a. Finally, plasma levels of miR-30c and miR-301a were significantly down-regulated in patients with SCA compared with normal controls. These results provide a post-transcriptional regulatory mechanism of PlGF-induced PAI-1 elevation.

Ethanol-induced HO-1 and NQO1 are differentially regulated by HIF-1alpha and Nrf2 to attenuate inflammatory cytokine expression

Oxidative stress plays an important role in alcohol-induced inflammation and liver injury. Relatively less is known about how Kupffer cells respond to oxidative stress-induced expression of heme oxygenase-1 (HO-1) and NAD(P)H:quinone oxidoreductase (NQO1) to blunt inflammation and liver injury. We showed that Kupffer cells from ethanol-fed rats and ethanol-treated rat Kupffer cells and THP-1 cells displayed increased mRNA expression of HO-1, NQO1, and hypoxia-inducible factor-1α (HIF-1α). Our studies showed that silencing with HIF-1α and JNK-1 siRNAs attenuated ethanol-mediated mRNA expression of HO-1, but not NQO1, whereas Nrf2 siRNA attenuated the mRNA expression of both HO-1 and NQO1. Additionally, JunD but not JunB formed an activator protein-1 (AP-1) oligomeric complex to augment HO-1 promoter activity. Ethanol-induced HO-1 transcription involved antioxidant response elements, hypoxia-response elements, and an AP-1 binding motif in its promoter, as demonstrated by mutation analysis of the promoter, EMSA, and ChIP. Furthermore, livers of ethanol-fed c-Jun(fl/fl) mice showed reduced levels of mRNA for HO-1 but not of NQO1 compared with ethanol-fed control rats, supporting the role of c-Jun or the AP-1 transcriptional complex in ethanol-induced HO-1 expression. Additionally, attenuation of HO-1 levels in ethanol-fed c-Jun(fl/fl) mice led to increased proinflammatory cytokine expression in the liver. These results for the first time show that ethanol regulates HO-1 and NQO1 transcription by different signaling pathways. Additionally, up-regulation of HO-1 protects the liver from excessive formation of inflammatory cytokines. These studies provide novel therapeutic targets to ameliorate alcohol induced inflammation and liver injury.

Placenta growth factor-induced early growth response 1 (Egr-1) regulates hypoxia-inducible factor-1alpha (HIF-1alpha) in endothelial cells

Leukotrienes, the lipid inflammatory products derived from arachidonic acid, are involved in the pathogenesis of respiratory and cardiovascular diseases and reactive airway disease in sickle cell disease. Placenta growth factor (PlGF), elaborated from erythroid cells, increased the mRNA expression of 5-lipoxygenase and 5-lipoxygenase-activating protein (FLAP) in human pulmonary microvascular endothelial cells. PlGF-induced both promoter activity and mRNA expression of hypoxia-inducible factor-1alpha (HIF-1alpha), which was abrogated by early growth response-1 (EGR-1) small interfering RNA. PlGF showed a temporal reciprocal relationship in the mRNA levels of EGR-1 and NAB2, the latter a repressor of Egr-1. Moreover, Nab2, but not mutant Nab2, significantly reduced promoter activity and mRNA expression of HIF-1alpha and also reduced expression of the HIF-1alpha target gene FLAP. Furthermore, overexpression of Egr-1 led to increased promoter activities for both HIF-1alpha and FLAP in the absence of PlGF. Additionally, the Egr-1-mediated induction of HIF-1alpha and FLAP promoters was reduced to basal levels by EGR-1 small interfering RNA. The binding of Egr-1 to HIF-1alpha promoter was corroborated by electrophoretic mobility shift assay and chromatin immunoprecipitation assay, which showed increased Egr-1 binding to the HIF-1alpha promoter in response to PlGF stimulation. These studies provide a novel mechanism for PlGF-mediated regulation of HIF-1alpha via Egr-1, which results in increased FLAP expression. This study provides a new therapeutic target, namely Egr-1, for attenuation of elevated leukotriene levels in patients with sickle cell disease and other inflammatory diseases.

Placenta growth factor (PlGF), a novel inducer of plasminogen activator inhibitor-1 (PAI-1) in sickle cell disease (SCD)

Sickle cell disease (SCD) is characterized by a prothrombotic state. Plasminogen activator inhibitor-1 (PAI-1) is known to modulate fibrinolysis, lung injury/fibrosis, and angiogenesis. However, its role in SCD is less understood, and the molecular mechanisms underlying increased PAI-1 are unknown. Herein, we show a novel link between PAI-1 and sickle erythropoiesis. Plasma PAI-1 levels were high in SCD patients at steady state and in two humanized sickle mouse models, with increased PAI-1 immunolabeling in sickle mouse lung, bronchial epithelial cells, alveolar macrophages, and pulmonary microvascular endothelial cells. Placenta growth factor (PlGF), released at high levels by sickle erythroblasts, induced PAI-1 expression in primary human pulmonary microvascular endothelial cells and monocytes through activation of c-Jun N-terminal kinase (JNK), NADPH oxidase, and hypoxia-inducible factor-1alpha (HIF-1alpha). Analysis of the human PAI-1 promoter revealed this induction was mediated by hypoxia-response element (HRE)-1, HRE-2, and distal activator protein (AP-1) sites. We also identify the involvement of c-Jun, c-Jun/c-Fos, and JunD, but not JunB, in binding with AP-1 sites of the PAI-1 promoter upon PlGF induction. Consistent with these findings, levels of PAI-1 were low in PlGF knock-out mice and sickle-PlGF knock-out mice; overexpression of PlGF in normal mice increased circulating PAI-1. In conclusion, we identify a novel mechanism of PAI-1 elevation in SCD.

Hypoxia-mediated expression of 5-lipoxygenase-activating protein involves HIF-1alpha and NF-kappaB and microRNAs 135a and 199a-5p

Hypoxia occurs in a number of pathological states, such as pulmonary, hematological, and cardiovascular disorders. In this study, we examined the molecular mechanism by which hypoxia contributes to increased leukotriene formation. Our studies showed hypoxia augmented the expression of 5-lipoxygenase activating protein (FLAP), a key enzyme in leukotriene formation, in both human pulmonary microvascular endothelial cells and a transformed human brain endothelial cell line. Hypoxia-induced FLAP mRNA expression involved activation of NADPH-oxidase, PI-3 kinase, mitogen-activated protein kinase, NF-kappaB, and hypoxia-inducible factor (HIF)-1alpha. Hypoxia-induced FLAP promoter activity was attenuated on mutation of hypoxia-response elements (HREs) and NF-kappaB binding motif in the FLAP promoter. Hypoxia also augmented binding of HIF-1alpha to HREs in FLAP promoter as demonstrated by EMSA with nuclear extracts. Furthermore, chromain immunoprecipitation analysis showed HIF-1alpha bound to HREs in native chromatin obtained from hypoxia-treated cells. Next, we examined the role of HIF-1alpha regulated microRNAs on FLAP expression. Our studies showed decreased expression of miR-135a and miR-199a-5p in response to hypoxia. However, overexpression of anti-miR-135a and anti-miR-199a-5p oligonucleotides led to a several fold increased FLAP mRNA and protein expression. These studies demonstrate for the first time that hypoxia-mediated FLAP expression is regulated by HREs and NF-kappaB site in its promoter, and negatively regulated by miR-135a and miR-199a-5p, which target the 3'-UTR of FLAP mRNA. An understanding of these regulatory pathways provides new avenues to ameliorate leukotriene formation and hence reactive airway disease, and inflammation in individuals who have sickle cell disease.

Hypoxia-mediated expression of 5-lipoxygenase-activating protein involves HIF-1alpha and NF-kappaB and microRNAs 135a and 199a-5p

Hypoxia occurs in a number of pathological states, such as pulmonary, hematological, and cardiovascular disorders. In this study, we examined the molecular mechanism by which hypoxia contributes to increased leukotriene formation. Our studies showed hypoxia augmented the expression of 5-lipoxygenase activating protein (FLAP), a key enzyme in leukotriene formation, in both human pulmonary microvascular endothelial cells and a transformed human brain endothelial cell line. Hypoxia-induced FLAP mRNA expression involved activation of NADPH-oxidase, PI-3 kinase, mitogen-activated protein kinase, NF-kappaB, and hypoxia-inducible factor (HIF)-1alpha. Hypoxia-induced FLAP promoter activity was attenuated on mutation of hypoxia-response elements (HREs) and NF-kappaB binding motif in the FLAP promoter. Hypoxia also augmented binding of HIF-1alpha to HREs in FLAP promoter as demonstrated by EMSA with nuclear extracts. Furthermore, chromain immunoprecipitation analysis showed HIF-1alpha bound to HREs in native chromatin obtained from hypoxia-treated cells. Next, we examined the role of HIF-1alpha regulated microRNAs on FLAP expression. Our studies showed decreased expression of miR-135a and miR-199a-5p in response to hypoxia. However, overexpression of anti-miR-135a and anti-miR-199a-5p oligonucleotides led to a several fold increased FLAP mRNA and protein expression. These studies demonstrate for the first time that hypoxia-mediated FLAP expression is regulated by HREs and NF-kappaB site in its promoter, and negatively regulated by miR-135a and miR-199a-5p, which target the 3'-UTR of FLAP mRNA. An understanding of these regulatory pathways provides new avenues to ameliorate leukotriene formation and hence reactive airway disease, and inflammation in individuals who have sickle cell disease.

Ethanol-induced expression of ET-1 and ET-BR in liver sinusoidal endothelial cells and human endothelial cells involves hypoxia-inducible factor-1alpha and microrNA-199

Chronic alcohol consumption leads to inflammation and cirrhosis of the liver. In this study, we observed that liver sinusoidal endothelial cells (LSEC) derived from ethanol-fed rats showed several fold increases in the mRNA expression of endothelin-1 (ET-1), hypoxia-inducible factor-1alpha (HIF-1alpha), and inflammatory cytochemokines compared with control rat LSEC. We also observed the same results in acute ethanol-treated LSEC from control rats and human dermal microvascular endothelial cells. Ethanol-mediated ET-1 expression involved NADPH oxidase and HIF-1alpha activation. Furthermore, ethanol increased the expression of the ET-1 cognate receptor ET-BR in Kupffer cells and THP-1 monocytic cells, which also involved HIF-1alpha activation. Promoter analysis and chromatin immunoprecipitation showed that hypoxia response element sites in the proximal promoter of ET-1 and ET-BR were required for the binding of HIF-1alpha to up-regulate their expression. We showed that microRNAs, miR-199 among several microRNAs, attenuated HIF-1alpha and ET-1 expression, while anti-miR-199 reversed the effects, suggesting that ethanol-induced miR-199 down-regulation may contribute to augmented HIF-1alpha and ET-1 expression. Our studies, for the first time to our knowledge, show that ethanol-mediated ET-1 and ET-BR expression involve HIF-1alpha, independent of hypoxia. Additionally, ethanol-induced ET-1 expression in rat LSEC is regulated by miR-199, while in human endothelial cells, ET-1 expression is regulated by miR-199 and miR-155, indicating that these microRNAs may function as novel negative regulators to control ET-1 transcription and, thus, homeostatic levels of ET-1 to maintain microcirculatory tone.

Ethanol augments RANTES/CCL5 expression in rat liver sinusoidal endothelial cells and human endothelial cells via activation of NF-kappa B, HIF-1 alpha, and AP-1

Chronic alcohol consumption leads to liver inflammation and cirrhosis. Alcoholic liver disease patients have increased levels of hepatic RANTES/CCL5. However, less is known about the molecular mechanisms for ethanol-induced RANTES up-regulation. In this study, we observed that liver sinusoidal endothelial cells derived from ethanol-fed rats (E-rLSECs) showed severalfold increases in RANTES and hypoxia-inducible factor 1alpha (HIF-1alpha) mRNAs compared with control rLSECs (C-rLSECs). Similar effects were seen in acute ethanol treatment of isolated rLSECs and human dermal microvascular endothelial cells. Ethanol-induced RANTES mRNA expression required ethanol metabolism, p38 MAPK, HIF-1alpha, and JNK-2, but not JNK-1. EMSA experiments showed increased HIF-1alpha binding to wild-type hypoxia response elements (HREs; -31 to -9 bp) within the RANTES promoter in response to ethanol. RANTES promoter analysis showed that cis elements proximal to the transcription start site, HRE-1 (nt -22 to -19), HRE-2 (nt -32 to -29), and AP-1 (nt -250 to -244) were required for ethanol-mediated RANTES expression. These results were corroborated by chromatin immunoprecipitation assays showing augmented HIF-1alpha binding to HRE-1. Additionally, promoter analysis revealed c-Jun, c-Jun/c-Fos, and JunD, but not JunB, bound to the AP-1 site of the RANTES promoter. Ethanol-mediated activation of NF-kappaB led to HIF-1alpha activation and concomitant RANTES expression. Plasma of ethanol-fed c-Jun(flox/flox)-Mx-1-Cre mice showed attenuated levels of RANTES compared with ethanol-fed control mice, supporting the role of c-Jun in ethanol-induced RANTES expression. Our studies showed that ethanol-mediated RANTES/CCL5 expression occurs via HIF-1alpha activation independently of hypoxia. The identification of HIF-1alpha and AP-1 in ethanol-induced RANTES expression provides new strategies to ameliorate ethanol-induced inflammatory responses.

Phosphate-buffered saline-based nucleofection of primary endothelial cells

Although various nonviral transfection methods are available, cell toxicity, low transfection efficiency, and high cost remain hurdles for in vitro gene delivery in cultured primary endothelial cells. Recently, unprecedented transfection efficiency for primary endothelial cells has been achieved due to the newly developed nucleofection technology that uses a combination of novel electroporation condition and specific buffer components that stabilize the cells in the electrical field. Despite superior transfection efficiency and cell viability, high cost of the technology has discouraged cardiovascular researchers from liberally adopting this new technology. Here we report that a phosphate-buffered saline (PBS)-based nucleofection method can be used for efficient gene delivery into primary endothelial cells and other types of cells. Comparative analyses of transfection efficiency and cell viability for primary arterial, venous, microvascular, and lymphatic endothelial cells were performed using PBS. Compared with the commercial buffers, PBS can support equally remarkable nucleofection efficiency to both primary and nonprimary cells. Moreover, PBS-mediated nucleofection of small interfering RNA (siRNA) showed more than 90% knockdown of the expression of target genes in primary endothelial cells. We demonstrate that PBS can be an unprecedented economical alternative to the high-cost buffers or nucleofection of various primary and nonprimary cells.

A Novel Role of Hypoxia-Inducible Factor in Cobalt Chloride- and Hypoxia-Mediated Expression of IL-8 Chemokine in Human Endothelial Cells

Tissue hypoxemia is common in several pathological diseases, including vaso-occlusion in sickle cell disease and myocardial infarction. One finds increased presence of leukocytes during lung injury and at sites of inflammation in vascular endothelium. In this study, we used human pulmonary microvascular endothelial cells and human dermal microvascular endothelial immortalized cell line to delineate the cellular signaling mechanism of hypoxia- and CoCl2 (a mimetic of hypoxia)-induced IL-8 expression, and the latter's role in chemotaxis of polmorphonuclear neutrophils. We show that hypoxia- and CoCl2-induced IL-8 mRNA and protein expression involved activation of PI3K/Akt and p38 MAPK, but not MEK kinase. Analysis of some transcription factors associated with IL-8 promoter revealed that hypoxia and CoCl2 increased DNA-binding activity of hypoxia-inducible factor-1alpha (HIF-1alpha), NF-kappaB, and AP-1. In addition, we show that hypoxia- and CoCl2-induced IL-8 expression requires activation of HIF as demonstrated by the following: 1) EMSA; 2) transfection studies with IL-8 promoter reporter constructs with mutation in HIF-1alpha binding site; 3) attenuation of IL-8 expression by both HIF-1alpha small interfering RNA and R59949; 4) augmentation of IL-8 expression by either transfection with HIF-prolyl hydroxylase-2 small interfering RNA or overexpression of HIF-1alpha; and 5) chromatin immunoprecipitation analysis. Moreover, conditioned medium from hypoxia-treated endothelial cells augmented chemotaxis of neutrophils, due to release of IL-8. These data indicate that hypoxia-induced signaling in vascular endothelium for transcriptional activation of IL-8 involves PI3K/Akt, p38 MAPK, and HIF-1alpha. Pharmacological agents, which inhibit HIF-1alpha, may possibly ameliorate inflammation associated with hypoxia in pathological diseases.

Mechanism of amyloid peptide induced CCR5 expression in monocytes and its inhibition by siRNA for Egr-1

In Alzheimer's disease (AD), one finds increased presence of monocytes/macrophages and activated microglial cells in the brain. Immunohistochemical studies show increased expression of chemokine receptor 5 (CCR5) on reactive microglia associated with amyloid deposits in AD, suggesting that CCR5 may play a role in the regulation of the immune response in AD. In this study, we used peripheral blood monocytes and human monocytic THP-1 cell line as a model of microglia to delineate the cellular signaling mechanism of Aβ-induced CCR5 expression and the latter's role in the chemotaxis of monocytes. We observed that Aβ peptides at pathophysiological concentrations (125 nM) increased CCR5 mRNA and cell surface protein expression. The cellular signaling involved activation of c-Raf, ERK-1/ERK-2, and c-Jun NH2-terminal kinase. Analysis of some transcription factors associated with CCR5 promoter revealed that Aβ increased DNA binding activity of Egr-1 and AP-1. In addition, we show that CCR5 promoter contains an Egr-1 like consensus sequence GCGGGGGTG as demonstrated by 1) electrophoretic mobility shift assay, 2) transfection studies with truncated CCR5 gene promoter construct, and 3) chromatin immunoprecipitation analysis. Moreover, transfection of Egr-1 siRNA, but not of scrambled Egr-1 siRNA, in THP-1 cells resulted in >75% reduction in both Aβ-mediated CCR5 expression and concomitant chemotaxis to its ligands. We suggest that inhibition of Egr-1 by either Egr-1 siRNA or pharmacological agents may reduce activation of monocytes/microglia and possibly ameliorate the inflammation and progression of AD.

L-glutamine therapy reduces endothelial adhesion of sickle red blood cells to human umbilical vein endothelial cells

Background

We have previously demonstrated that therapy with orally administered L-glutamine improves nicotinamide adenosine dinucleotide (NAD) redox potential of sickle red blood cells (RBC). On further analysis of L-glutamine therapy for sickle cell anemia patients, the effect of L-glutamine on adhesion of sickle RBC to human umbilical vein endothelial cells (HUVEC) was examined.

Methods

The first part of the experiment was conducted with the blood samples of the 5 adult sickle cell anemia patients who had been on L-glutamine therapy for at least 4 weeks on a dosage of 30 grams per day compared to those of patient control group. In the second part of the experiment 6 patients with sickle cell anemia were studied longitudinally. Five of these patients were treated with oral L-glutamine 30 grams daily and one was observed without treatment as the control. t-test and paired t-test were used for determination of statistical significance in cross-sectional and longitudinal studies respectively.

Results

In the first study, the mean adhesion to endothelial cells with the autologous plasma incubated cells were 0.97 ± 0.45 for the treated group and 1.91 ± 0.53 for the nontreated group (p < 0.02). Similarly with lipopolysaccharide (LPS) incubated cells the mean adhesion to endothelial cells were 1.39 ± 0.33 for the treated group and 2.80 ± 0.47 for the untreated group (p < 0.001). With the longitudinal experiment, mean decrease in the adhesion to endothelial cells was 1.13 ± 0.21 (p < 0.001) for the 5 treated patients whereas the control patient had slight increase in the adhesion to endothelial cells.

Conclusion

In these studies, oral L-glutamine administration consistently resulted in improvement of sickle RBC adhesion to HUVEC. These data suggest positive physiological effects of L-glutamine in sickle cell disease.

Curcumin, the active constituent of turmeric, inhibits amyloid peptide-induced cytochemokine gene expression and CCR5-mediated chemotaxis of THP-1 monocytes by modulating early growth response-1 transcription factor

Epidemiological studies show reduced risk of Alzheimer's disease (AD) among patients using non-steroidal inflammatory drugs (NSAID) indicating the role of inflammation in AD. Studies have shown a chronic CNS inflammatory response associated with increased accumulation of amyloid peptide and activated microglia in AD. Our previous studies showed that interaction of Abeta1-40 or fibrilar Abeta1-42 caused activation of nuclear transcription factor, early growth response-1 (Egr-1), which resulted in increased expression of cytokines (TNF-alpha and IL-1beta) and chemokines (MIP-1beta, MCP-1 and IL-8) in monocytes. We determined whether curcumin, a natural product known to have anti-inflammatory properties, suppressed Egr-1 activation and concomitant expression of cytochemokines. We show that curcumin (12.5-25 microm) suppresses the activation of Egr-1 DNA-binding activity in THP-1 monocytic cells. Curcumin abrogated Abeta1-40-induced expression of cytokines (TNF-alpha and IL-1beta) and chemokines (MIP-1beta, MCP-1 and IL-8) in both peripheral blood monocytes and THP-1 cells. We found that curcumin inhibited Abeta1-40-induced MAP kinase activation and the phosphorylation of ERK-1/2 and its downstream target Elk-1. We observed that curcumin inhibited Abeta1-40-induced expression of CCR5 but not of CCR2b in THP-1 cells. This involved abrogation of Egr-1 DNA binding in the promoter of CCR5 by curcumin as determined by: (i) electrophoretic mobility shift assay, (ii) transfection studies with truncated CCR5 gene promoter constructs, and (iii) chromatin immunoprecipitation analysis. Finally, curcumin inhibited chemotaxis of THP-1 monocytes in response to chemoattractant. The inhibition of Egr-1 by curcumin may represent a potential therapeutic approach to ameliorate the inflammation and progression of AD.

Mechanism of monocyte activation and expression of proinflammatory cytochemokines by placenta growth factor

Monocytes from patients with sickle cell disease (SCD) are in an activated state. However, the mechanism of activation of monocytes in SCD is not known. Our studies showed that placenta growth factor (PlGF) activated monocytes and increased mRNA levels of cytokines (tumor necrosis factor-alpha [TNF-alpha] and interleukin-1beta [IL-1beta]) and chemokines (monocyte chemotactic protein-1 [MCP-1], IL-8, and macrophage inflammatory protein-1beta [MIP-1beta]) in both normal monocytes and in the THP-1 monocytic cell line. This increase in mRNA expression of cytochemokines was also reflected in monocytes derived from subjects with SCD. We studied the PlGF-mediated downstream cellular signaling events that caused increased transcription of inflammatory cytochemokines and chemotaxis of THP-1 monocytes. PlGF-mediated cytochemokine mRNA and protein expression was inhibited by PD98059 and wortmannin, inhibitors of mitogen-activated protein kinase kinase (MAPK/MEK) kinase and phosphatidylinositol-3 (PI3) kinase, respectively, but not by SB203580, a p38 kinase inhibitor. PlGF caused a time-dependent transient increase in phosphorylation of extracellular signal-regulated kinase-1/2 (ERK-1/2), which was completely inhibited by wortmannin, indicating that activation of PI3 kinase preceded MEK activation. PlGF also induced transient phosphorylation of AKT. MEK and PI3 kinase inhibitors and antibody to Flt-1 abrogated PlGF-induced chemotaxis of THP-1 monocytes. Overexpression of a dominant-negative AKT or a dominant-negative PI3 kinase p85 subunit in THP-1 monocytes attenuated the PlGF-mediated phosphorylation of ERK-1/2, cytochemokine secretion, and chemotaxis. Taken together, these data show that activation of monocytes by PlGF occurs via activation of Flt-1, which results in activation of PI3 kinase/AKT and ERK-1/2 pathways. Therefore, we propose that increased levels of PlGF in circulation play an important role in the inflammation observed in SCD via its effects on monocytes.

Placenta growth factor activates monocytes and correlates with sickle cell disease severity

Sickle cell disease (SCD) results in chronic hypoxia and secondarily increased erythropoietin concentrations. Leukocytosis and activated monocytes are also observed in SCD in absence of infection or vaso-occlusion (steady state), the reasons for which are unknown. We found that erythroid cells produced placenta growth factor (PlGF), an angiogenic growth factor belonging to the vascular endothelial growth factor (VEGF) family, and its expression was induced in bone marrow CD34+ progenitor cells in the presence of erythropoietin. Furthermore, the steady state circulating PlGF levels in subjects with severe SCD (at least 3 vaso-occlusive crises [VOCs] per year) were 18.5 +/- 1.2 pg/mL (n = 9) compared with 15.5 +/- 1.2 pg/mL (n = 13) in those with mild SCD (fewer than 3 VOCs per year) and 11.3 +/- 0.7 pg/mL (n = 9) in healthy controls (P <.05), suggesting a correlation between PlGF levels and SCD severity. In addition, PlGF significantly increased mRNA levels of the proinflammatory cytochemokines interleukin-1beta, interleukin-8, monocyte chemoattractant protein-1, and VEGF in peripheral blood mononuclear cells (MNCs) of healthy subjects (n = 4; P <.05). Expression of these same cytochemokines was significantly increased in MNCs from subjects with SCD at steady state (n = 14), compared with healthy controls. Of the leukocyte subfractions, PlGF stimulated monocyte chemotaxis (P <.05, n = 3). Taken together, these data show for the first time that erythroid cells intrinsically release a factor that can directly activate monocytes to increase inflammation. The baseline inflammation seen in SCD has always been attributed to sequelae secondary to the sickling phenomenon. We show that PlGF contributes to the inflammation observed in SCD and increases the incidence of vaso-occlusive events.

Amyloid peptide-induced cytokine and chemokine expression in THP-1 monocytes is blocked by small inhibitory RNA duplexes for early growth response-1 messenger RNA

In Alzheimer's disease (AD) one finds increased deposition of A beta and also an increased presence of monocytes/macrophages in the vessel wall and activated microglial cells in the brain. AD patients show increased levels of proinflammatory cytokines by activated microglia. Here we used a human monocytic THP-1 cell line as a model for microglia to delineate the cellular signaling mechanism involved in amyloid peptides (A beta(1-40) and A beta(1-42))-induced expression of inflammatory cytokines and chemokines. We observed that A beta peptides at physiological concentrations (125 nM) increased mRNA expression of cytokines (TNF-alpha, and IL-1 beta) and chemokines (monocyte chemoattractant protein-1 (MCP-1), IL-8, and macrophage inflammatory protein-1 beta (MIP-1 beta)). The cellular signaling involved activation of c-Raf, extracellular signal-regulated kinase-1 (ERK-1)/ERK-2, and c-Jun N-terminal kinase, but not p38 mitogen-activated protein kinase. This is further supported by the data showing that A beta causes phosphorylation of ERK-1/ERK-2, which, in turn, activates Elk-1. Furthermore, A beta mediated a time-dependent increase in DNA binding activity of early growth response-1 (Egr-1) and AP-1, but not of NF-kappa B and CREB. Moreover, A beta-induced Egr-1 DNA binding activity was reduced >60% in THP-1 cells transfected with small interfering RNA duplexes for Egr-1 mRNA. We show that A beta-induced expression of TNF-alpha, IL-1 beta, MCP-1, IL-8, and MIP-1 beta was abrogated in Egr-1 small inhibitory RNA-transfected cells. Our results indicate that A beta-induced expression of cytokines (TNF-alpha and IL-1 beta) and chemokines (MCP-1, IL-8, and MIP-1 beta) in THP-1 monocytes involves activation of ERK-1/ERK-2 and downstream activation of Egr-1. The inhibition of Egr-1 by Egr-1 small inhibitory RNA may represent a potential therapeutic target to ameliorate the inflammation and progression of AD.

Absorption of intact albumin across rat alveolar epithelial cell monolayers

Transport characteristics of intact albumin were investigated using primary cultured rat alveolar epithelial cell monolayers. The apical-to-basolateral (ab) flux of intact fluorescein isothiocyanate (FITC)-labeled albumin (F-Alb) is greater than basolateral-to-apical (ba) flux at the same upstream [F-Alb]. Net absorption of intact F-Alb occurs with half-maximal concentration of approximately 1.6 microM and maximal transport rate of approximately 0.15 fmol.cm(-2).s(-1). At 15 and 4 degrees C, both ab and ba F-Alb fluxes are not different from zero, collapsing net absorption. The presence of excess unlabeled albumin (but not other macromolecule species) in either the apical or basolateral fluid significantly reduces both ab and ba unidirectional F-Alb fluxes. Photoaffinity labeling of apical cell membranes revealed an approximately 60-kDa protein that exhibits specificity for albumin. These data indicate that net absorption of intact albumin takes place via saturable receptor-mediated transcellular endocytotic processes recognizing albumin, but not other macromolecules, that may play an important role in alveolar homeostasis in the mammalian lung.

Effect of endothelial cell polarity on beta-amyloid-induced migration of monocytes across normal and AD endothelium

During normal aging and amyloid beta-peptide (Abeta) disorders such as Alzheimer's disease (AD), one finds increased deposition of Abeta and activated monocytes/microglial cells in the brain. Our previous studies show that Abeta interaction with a monolayer of normal human brain microvascular endothelial cells results in increased adherence and transmigration of monocytes. Relatively little is known of the role of Abeta accumulated in the AD brain in mediating trafficking of peripheral blood monocytes (PBM) across the blood-brain barrier (BBB) and concomitant accumulation of monocytes/microglia in the AD brain. In this study, we showed that interaction of Abeta(1--40) with apical surface of monolayer of brain endothelial cells (BEC), derived either from normal or AD individuals, resulted in increased transendothelial migration of monocytic cells (HL-60 and THP-1) and PBM. However, transmigration of monocytes across the BEC monolayer cultivated in a Transwell chamber was increased 2.5-fold when Abeta was added to the basolateral side of AD compared with normal individual BEC. The Abeta-induced transmigration of monocytes was inhibited in both normal and AD-BEC by antibodies to the putative Abeta receptor, receptor for advanced glycation end products (RAGE), and to the endothelial cell junction molecule, platelet-endothelial cell adhesion molecule-1 (PECAM-1). We conclude that interaction of Abeta with the basolateral surface of AD-BEC induces cellular signaling, promoting transmigration of monocytes from the apical to basolateral direction. We suggest that Abeta in the AD brain parenchyma or cerebrovasculature initiates cellular signaling that induces PBM to transmigrate across the BBB and accumulate in the brain.

Gp120 activates children's brain endothelial cells via CD4

Encephalopathy represents a common and serious manifestation of HIV-1 infection in children, but its pathogenesis is unclear. We demonstrated that gp120 activated human brain microvascular endothelial cells (HBMEC) derived from children in up-regulating ICAM-1 and VCAM-1 expression, IL-6 secretion and increased monocyte transmigration across monolayers. Another novel observation was our demonstration of CD4 in isolated HBMEC and on microvessels of children's brain cryosections. Gp120-induced monocyte migration was inhibited by anti-gp120 and anti-CD4 antibodies. This is the first demonstration that gp120 activates HBMEC via CD4, which may contribute to the development of HIV-1 encephalopathy in children.

beta-amyloid-induced migration of monocytes across human brain endothelial cells involves RAGE and PECAM-1

In patients with amyloid beta-related cerebrovascular disorders, e.g. , Alzheimer's disease, one finds increased deposition of amyloid peptide (Abeta) and increased presence of monocyte/microglia cells in the brain. However, relatively little is known of the role of Abeta in the trafficking of monocytes across the blood-brain barrier (BBB). Our studies show that interaction of Abeta(1-40) with monolayer of human brain endothelial cells results in augmented adhesion and transendothelial migration of monocytic cells (THP-1 and HL-60) and peripheral blood monocytes. The Abeta-mediated migration of monocytes was inhibited by antibody to Abeta receptor (RAGE) and platelet endothelial cell adhesion molecule (PECAM-1). Additionally, Abeta-induced transendothelial migration of monocytes were inhibited by protein kinase C inhibitor and augmented by phosphatase inhibitor. We conclude that interaction of Abeta with RAGE expressed on brain endothelial cells initiates cellular signaling leading to the transendothelial migration of monocytes. We suggest that increased diapedesis of monocytes across the BBB in response to Abeta present either in the peripheral circulation or in the brain parenchyma may play a role in the pathophysiology of Abeta-related vascular disorder.

Stimulation of macrophages by retinal proteins: production of reactive nitrogen and oxygen metabolites

PURPOSE

In previous work, it has been shown that in experimental autoimmune uveitis, the peroxynitrite-mediated protein nitration product nitrotyrosine was localized in the degenerating photoreceptors. Subsequently, phagocyte-generated inducible nitric oxide synthase (iNOS) was also found to localize, primarily in the outer retina and to a lesser extent in the anterior segments. This study was intended to determine whether retinal soluble proteins such as S-antigen and interphotoreceptor retinoid-binding protein (IRBP) play a role in the induction of *NO and superoxide by a macrophage cell line and by rat and rabbit peritoneal macrophages.

METHODS

Cells from the murine macrophage cell line RAW 264.7 and rat and rabbit peritoneal macrophages were incubated in the presence of retinal soluble proteins. The nitrite level in the cultured supernatant was evaluated for *NO production using the Griess reaction. Activation of nuclear transcription factor kappaB (NF-kappaB) was determined by electrophoretic mobility shift assay. Superoxide production was measured by superoxide dismutase-inhibitable reduction of cytochrome C.

RESULTS

Both S-antigen and IRBP induced significant, dose-dependent nitrite production in RAW 264.7 and rat peritoneal macrophages. Induction of iNOS by retinal proteins was inhibited by the iNOS-specific inhibitor aminoguanidine and the tyrosine kinase inhibitor genistein. This iNOS induction was accompanied by the activation of NF-kappaB. S-antigen also induced superoxide production in rabbit peritoneal macrophages, but not in RAW 264.7.

CONCLUSIONS

These results show that soluble retinal proteins significantly induce *NO and superoxide production by macrophages. Increased production of reactive oxygen species by macrophages in the presence of these soluble retinal proteins in vivo may accelerate photoreceptor degeneration in uveitis.

Cobalt chloride-induced signaling in endothelium leading to the augmented adherence of sickle red blood cells and transendothelial migration of monocyte-like HL-60 cells is blocked by PAF-receptor antagonist

In response to hypoxia, sickle red blood cells (SS RBC) and leukocytes exhibit increased adherence to the vascular endothelium, while diapedesis of leukocytes through the blood vessel increases. However, the cellular signaling pathway(s) caused by hypoxia is poorly understood. We utilized CoCl2 as a mimetic molecule for hypoxia to study cellular signaling pathways. We found that in human umbilical vein endothelial cells (HUVEC), CoCl2 at 2 mM concentration induced the surface expression of a subset of CAMs (VCAM-1) and activation of transcription factor NF-kappaB in the nuclear extracts of HUVEC. Furthermore, CoCl2 also caused time-dependent tyrosine phosphorylation of mitogen-activated protein (MAP) kinase isoform ERK2 without significantly affecting ERK1, indicating ERK2 is the preferred substrate for upstream kinase of the MAPK pathway. Inhibitors of MAP kinase (PD98059) or platelet-activating factor (PAF)- receptor antagonist (CV3988) inhibited the CoCl2-induced NF-kappaB activation and VCAM-1 expression. Augmented expression of VCAM-1 led to increased SS RBC adhesion, inhibitable by a VCAM-1 antibody. Additionally, CoCl2 caused a two- to threefold increase in the rate of transendothelial migration of monocyte-like HL-60 cells and a twentyfold increase in phosphorylation of platelet endothelial cell adhesion molecules (PECAM-1). The transendothelial migration of monocytes was inhibited by an antibody to PECAM-1. Both phosphorylation of PECAM-1 and transendothelial migration of monocytes in response to CoCl2 were inhibited by protein kinase inhibitor (GF109203X) and augmented by protein phosphatase inhibitor (Calyculin A). Our data suggests that CoCl2-induced cellular signals directing increased expression of VCAM-1 in HUVEC involve downstream activation of MAP kinase and NF-kappaB, while the phosphorylation of PECAM-1 occurs as a result of activation of PKC. We conclude that PAF-receptor antagonist inhibits the CoCl2- or hypoxia-induced increase in the adhesion of SS RBC, PECAM-1 phosphorylation, and the concomitant transendothelial migration of monocytes.

Interaction of sickle erythrocytes with endothelial cells in the presence of endothelial cell conditioned medium induces oxidant stress leading to transendothelial migration of monocytes

The abnormal adherence of sickle red blood cells (SS RBC) to endothelial cells has been thought to contribute to vascular occlusion, a major cause of morbidity in sickle cell disease (SCD). We determined whether the interaction of SS RBC with cultured endothelial cells induced cellular oxidant stress that would culminate in expression of cell adhesion molecules (CAMs) involved in the adhesion and diapedesis of monocytes and the adherence of SS reticulocytes. We showed that the interaction of SS RBC at 2% concentration in the presence of multimers of von Willebrand factor (vWf), derived from endothelial cell-derived conditioned medium (E-CM) with cultured human umbilical vein endothelial cells (HUVEC), resulted in a fivefold increased formation of thiobarbituric acid-reactive substances (TBARS) and activation of the transcription factor NF-kB, both indicators of cellular oxidant stress. Normal RBC show none of these phenomena. The oxidant stress-induced signaling resulted in an increased surface expression of a subset of CAMs, ICAM-1, E-selectin, and VCAM-1 in HUVEC. The addition of oxygen radical scavenger enzymes (catalase, superoxide dismutase) and antioxidant (probucol) inhibited these events. Additionally, preincubation of HUVEC with a synthetic peptide Arg-Gly-Asp (RGD) that prevents vWf-mediated adhesion of SS RBC reduced the surface expression of VCAM-1 and NF-kB activation. Furthermore, SS RBC-induced oxidant stress resulted in a twofold increase in the transendothelial migration of both monocyte-like HL-60 cells and human peripheral blood monocytes, and approximately a sixfold increase in platelet-endothelial cell adhesion molecule-1 (PECAM-1) phosphorylation, each of which was blocked by protein kinase C inhibitor and antioxidants. These results suggest that the adherence/contact of SS RBC to endothelial cells in large vessel can generate enhanced oxidant stress leading to increased adhesion and diapedesis of monocytes, as well as heightened adherence of SS reticulocytes, indicating that injury/activation of endothelium can contribute to vaso-occlusion in SCD.

Endotoxin-induced migration of monocytes and PECAM-1 phosphorylation are abrogated by PAF receptor antagonists

The trafficking of monocytes across the endothelial lining of the blood vessel increases in response to bacterial infection at sites of inflammation. However, the molecular events involved in the diapedesis of monocytes in response to endotoxin are not completely understood. Our studies revealed that signaling by lipopolysaccharide (LPS) in human umbilical vein endothelial cells (HUVEC) resulted in a threefold increase in the transendothelial migration of monocyte-like HL-60 cells and a sevenfold increase in the phosphorylation of platelet endothelial cell adhesion molecule-1 (PECAM-1). The transmigration induced by LPS was inhibited by an antibody to PECAM-1. Both the phosphorylation of PECAM-1 and transendothelial migration of monocytes were inhibited by a platelet-activating factor (PAF) receptor antagonist, indicating the autocrine effect of PAF in these events. Treatment of HUVEC with LPS caused a fourfold increase in PAF receptor mRNA expression that was completely blocked by the PAF receptor antagonist. We conclude that PAF, generated by HUVEC in response to LPS or gram-negative bacterial infection, acts in an autocrine manner, causing PECAM-1 phosphorylation and thus the transendothelial migration of monocytes.

Oxidant stress-induced transendothelial migration of monocytes is linked to phosphorylation of PECAM-1

Reactive oxygen species (ROS) are believed to cause vascular injury in the pathophysiology of atherosclerosis, diabetes, and vasoocclusion in sickle cell disease. Studies have shown that ROS causes increased adhesion of monocytes and neutrophils to the endothelium. We investigated the effects of tert-butylhydroperoxide (t-BuOOH), an inducer of oxidant stress, to determine the cellular signaling pathway leading to the transendothelial migration of polymorphonuclear leukocytes. Our studies revealed that signaling by t-BuOOH in human umbilical vein endothelial cells (HUVECs) causes a twofold increase in the transendothelial migration of monocyte-like HL-60 cells and a fivefold increase in platelet endothelial cell adhesion molecule-1 (PECAM-1) phosphorylation. The transmigration induced by t-BuOOH was inhibited by an antibody to PECAM-1. These events were inhibited by antioxidants and inhibitors of protein kinase C, p21ras and glutathione synthesis. However, treatment of HUVECs with the phosphatase inhibitor calyculin A augmented the t-BuOOH-mediated transendothelial migration of monocytes and PECAM-1 phosphorylation. Our results suggest that oxidative stress can induce the transendothelial migration of monocytes as a result of phosphorylation of PECAM-1, a crucial event in the diapedesis of leukocytes during pathophysiology of vascular diseases.

Diabetic RBC-induced oxidant stress leads to transendothelial migration of monocyte-like HL-60 cells

Red blood cells (RBC) from patients with diabetes mellitus exhibit an increased propensity to adhere to cultured human umbilical vein endothelial cells (HUVEC) as a result of interaction of advanced glycation end products with their counter receptors, contributing to the pathogenesis of vascular complications. We determined whether the interaction of diabetic RBC with HUVEC induced cellular oxidant stress that would culminate in adherence and diapedesis of monocytes, these being initiating events in endothelial injury and atherogenesis. We show that the adherence of diabetic RBC (2% hematocrit), but not normal RBC, to HUVEC results in a fourfold increase in the production of lipid peroxides. Furthermore, diabetic RBC-induced oxidant stress causes a sixfold increase in platelet endothelial cell adhesion molecule-1 (PECAM-1) phosphorylation and doubles transendothelial migration of monocyte-like HL-60 cells; both are blocked by antioxidants and protein kinase C (PKC) inhibitors. Our results show that the adherence of diabetic RBC to endothelial cells initiates a cascade of cellular events resulting in PKC activation, causing PECAM-1 phosphorylation and concomitant transendothelial migration of monocytes. The increased diapedesis of monocytes, brought about by the interaction of diabetic RBC across vascular endothelium, may play an important role in accelerated atherosclerosis and cardiovascular disease in diabetics.

Hypoxia induces PECAM-1 phosphorylation and transendothelial migration of monocytes

Polymorphonuclear neutrophils (PMN) adhere to the vascular endothelium under hypoxic conditions, causing microvascular injury. The molecular mechanism of hypoxia-induced adhesion of PMN to and diapedesis through the vascular endothelium is poorly understood. We examined the effects of hypoxia on the transendothelial migration of monocytes. Exposure of human umbilical vein endothelial cells (HUVEC) cultured in Transwell chambers under low oxygen tension (3% O2 compared with 21% O2) resulted in an increased rate of migration of both monocyte-like HL-60 cells and human peripheral blood monocytes. Migration was inhibited by addition of an antibody to platelet endothelial cell adhesion molecule-1 (PECAM-1), a protein kinase C (PKC) inhibitor, or a platelet-activating factor (PAF)-receptor antagonist. In HUVEC, hypoxic conditions (1, 3, 5, and 14% O2) increased the phosphorylation of PECAM-1. The extent of phosphorylation of PECAM-1 was inversely related to the concentration of oxygen to which HUVEC were exposed. Hypoxia-induced phosphorylation of PECAM-1 was inhibited by either a PKC inhibitor or a PAF-receptor antagonist, indicating the involvement of hypoxia-induced release of PAF in both PKC activation and the concomitant phosphorylation of PECAM-1. These results were substantiated by the findings that treatment of HUVEC with 100 nM PAF under normoxic conditions augmented 11.8-fold the phosphorylation of PECAM-1 and twofold increase in the transendothelial migration of monocyte-like HL-60 cells. We conclude that PAF, produced by cultured endothelial cells in response to hypoxia, acts in an autocrine fashion to activate PKC, causing PECAM-1 phosphorylation and thus the transendothelial migration of monocytes.

Glucose-induced transmigration of monocytes is linked to phosphorylation of PECAM-1 in cultured endothelial cells

The adherence of circulating monocytes to the endothelium, their migration into the subendothelium, and the subsequent formation of foam cells are initial events in the pathogenesis of atherosclerosis. However, the effect of hyperglycemia on the transendothelial migration of monocytes is not known. Exposure of human umbilical vein endothelial cells (HUVEC) cultured in a Transwell chamber to 25 mM D-glucose (a concentration representing a hyperglycemic state) for 2 h resulted in a twofold increase in the migration of vitamin D3-differentiated monocyte-like HL-60 cells. The migration was inhibited by addition of either an antibody to platelet-endothelial cell adhesion molecule-1 (PECAM-1) or a protein kinase C inhibitor, GF-109203X. In HUVEC, high concentrations of D-glucose (25 mM), but not of other sugars such as L-glucose, 2-deoxyglucose, D-galactose, or D-mannitol, caused a sevenfold increase in the phosphorylation of PECAM-1 as a result of activation of protein kinase C. The 25 mM D-glucose-induced PECAM-1 phosphorylation and transmigration of monocyte-like HL-60 cells were further increased by treatment of HUVEC with the phosphatase inhibitor calyculin A. These results suggest that direct phosphorylation of PECAM-1 in response to elevated glucose promotes transendothelial migration of monocytes, contributing to accelerated atherogenesis in diabetics.

Lipoxygenase metabolites induced expression of adhesion molecules and transendothelial migration of monocyte-like HL-60 cells is linked to protein kinase C activation

Studies have shown that, among lipoxygenase metabolites examined, 15(S)-hydroperoxy-5,8,11,13-eicosa-tetraenoic acid (15[S]-HPETE), at micromolar concentrations, selectively causes injury to cultured endothelial cells. We investigated whether physiologically relevant concentrations of lipoxygenase metabolites affected the expression of cell adhesion molecules (CAMs) involved in the adhesion of leukocytes and/or the accumulation of leukocytes in the vascular endothelium, these being the initial events in endothelial cell injury. Among lipoxygenase metabolites, 15(S)-HPETE and 12(S)-HETE, at nanomolar concentrations, induced surface expression of a subset of cell adhesion molecules (CAM), ICAM-1, ELAM-1, and VCAM-1, in human umbilical vein endothelial cells (HUVEC), which is associated with an increased binding activity of the transcription factor, NF-kappa B, to the consensus motif common to the CAM genes in the HUVEC nuclear extracts. Furthermore, 15(S)-HPETE (1 nM) caused a threefold increase in the rate of transendothelial migration of vitamin D3-differentiated HL-60 monocyte-like cells and showed a thirtyfold increase in the phosphorylation of PECAM-1, an adhesion molecule involved in endothelial cell-cell adhesion. Both an antibody to PECAM-1 and the protein kinase C inhibitor, GF 109203X, reduced 15(S)-HPETE-induced transmigration of monocyte-like HL-60 cells by approximately 75% and 85%, respectively. Treatment of HUVEC with a phosphatase inhibitor, calyculin A, augmented both the phosphorylation of PECAM-1 and transmigration of monocyte-like HL-60 cells induced by 15(S)-HPETE. Our results show that 15(S)-HPETE, at physiological concentrations, induced activation of protein kinase C in HUVEC and leads to the phosphorylation of PECAM-1, thus facilitating the migration of monocyte-like HL-60 cells across the endothelial cell monolayer. It is suggested that phosphorylation/dephosphorylation events in PECAM-1 are important in regulating the trafficking of monocytes across the endothelial cell monolayer.

Sickle erythrocytes adhere to polymorphonuclear neutrophils and activate the neutrophil respiratory burst

The vasoocclusive process in patients with sickle cell disease (SCD) is complex and involves interactions among sickle erythrocytes (SS-RBC), vascular endothelium, and plasma and cellular components. The role of neutrophils (PMN) in vasoocclusion has not been examined. Patients with SCD appear to have chronically activated PMN. Because the first step in PMN activation is particle recognition, we explored whether normal PMN recognize SS-RBC and whether this recognition results in PMN monolayers, significantly more SS-RBC adhered to the PMN than did normal erythrocytes (AA-RBC; P < .001). Preincubation of erythrocytes with autologous plasma significantly increased the adherence of SS-RBC to PMN but had no effect on AA-RBC (P < .001). When adhesion of density fractionated SS-RBC was performed, dense SS-RBC showed greater adherence to the PMN monolayers than did light SS-RBC (P < .001). To determine mechanisms of this adhesion, IgG and Arg-Gly-Asp-Ser (RGDS) receptor sites on PMN were saturated. IgG inhibited adherence of dense SS-RBC, whereas RGDS inhibited adherence in both fractions, although to a greater extent in the light fraction. We measured SS-RBC activation of PMN by incubating SS-RBC with 2', 7'-Dichloro-fluroescin Diacetate (DCF)-labeled PMN. Incubation of PMN with SS-RBC resulted in a significant increase in fluorescence compared to AA-RBC. We show here that PMN recognize SS-RBC through multiple mechanisms and that this recognition results in activation of PMN. These findings contribute to the understanding of vasoocclusive crisis in patients with SCD and may have therapeutic implications.

Cigarette smoke condensate-induced adhesion molecule expression and transendothelial migration of monocytes

Cigarette smoking is clearly linked with increased incidence of atherosclerosis and cardiovascular disease. The adherence of blood monocytes to the endothelium, followed by their migration beneath the endothelium, are initiating events in the formation of foam cells, promoting atherogenesis. We show that cigarette smoke condensate (CSC)-induced surface expression of a subset of cell adhesion molecules (CAM) [intercellular adhesion molecule 1 (ICAM-1), endothelial leukocyte adhesion molecule 1 (ELAM-1), and vascular cell adhesion molecule 1 (VCAM-1)] in human umbilical vein endothelial cells (HUVEC) is associated with an increase in the binding activity of nuclear transcription factor NF-kappa B to the consensus motif common to the CAM genes. Furthermore, CSC (25 microgram/ml) both increases the rate of transendothelial migration of vitamin D3-differentiated monocyte-like cells across the HUVEC monolayer by 200% and causes an approximately 10-fold increases in the phosphorylation of platelet endothelial CAM (PECAM-1), an adhesion molecule located at intercellular junctions and involved in endothelial cell-cell adhesion. Our results show that CSC-induced activation of protein kinase C in endothelial cells initiates a signaling pathways, leading to heightened binding of NF-kappa B to specific DNA sequences, which in turn increases surface expression of the subset of CAMs. Furthermore, our studies demonstrate a link between the phosphorylation of PECAM-1 and the migration of blood monocytes across vascular endothelium.

Mechanism of cigarette smoke condensate induced adhesion of human monocytes to cultured endothelial cells

Cigarette smoking is ranked among the leading risk factors in the etiology of atherosclerotic vascular disease. The mechanisms, however, that link cigarette smoking to increased incidence of atherosclerosis are not understood. The adherence of circulating monocytes to the endothelium, migration into the subendothelium, and subsequent formation of foam cells are principal initial events in the development of atherosclerosis. We therefore determined whether cigarette smoke caused increased adherence of monocytes to endothelial cells and the cellular mechanism of this increased adherence. Cigarette smoke condensate (CSC), the particulate fraction of cigarette smoke derived from 2R1 standard research cigarettes, at a concentration of 25-30 micrograms/ml (average yield of CSC is 26.1 mg/cigarette), augmented (70-90%) basal adherence of human peripheral blood monocytes to a cultured monolayer of endothelial cells derived from bovine aorta (BAEC) and human umbilical vein (HUVEC). There was a concomitant increase in the expression of CD11b ligand on the surface of monocytes as determined by flow cytometry, utilizing FITC conjugated Mab MO-1 (CD11b). However, nicotine (1-15 micrograms/ml) and cadmium sulfate (10 micrograms/ml), constituents of CSC, individually or in combination had no effect either on CD11b expression or adherence of monocytes to endothelial cells. Treatment of HUVEC with CSC for 60 min also resulted in an increased expression of ICAM-1 and ELAM-1 as determined by mean fluorescence intensity of ICAM-1 and ELAM-1 labeled cells in flow cytometric analysis. The CSC induced expression of CD11b in monocytes was optimal at 25-30 min and was inhibited by protein kinase C inhibitors, staurosporine and H-7, and also by baicalein, a lipoxygenase inhibitor. Similarly, CSC induced ICAM-1 and ELAM-1 expression in HUVEC was inhibited by protein kinase C inhibitors. CSC stimulated the adherence of human monocytes but not the monocytic cell lines HL-60, U937, and THP-1 to endothelial cells. The CSC stimulated adherence of human monocytes was inhibited (80%) by MAb to CD11b and 50% by Mab to ICAM-1 and ELAM-1. These results suggest that cigarette smoke particulate constituents activate protein kinase C, leading to increased surface expression of adhesive ligand CD11b on peripheral blood monocytes and counter receptor(s) ICAM-1 and ELAM-1 in endothelial cells. The expression of ligand and counter receptor leads to potentiated adherence of monocytes to endothelial cells, an initial event in the pathogenesis of cigarette smoke induced inflammatory response in the vessel wall.

Management of secondary pupillary membrane in aphakia (YAG discission vs parsplana membranectomy)

Forty aphakic eyes, with secondary pupillary membranes, underwent pars plana membranectomy and YAG laser discission randomly. Visual improvement was similar in both the groups. IOP remained low for a week in pars-plana membranectomy while it transiently increased following YAG laser discission Complications like anterior chamber reaction, corneal edema and CME were more after pars plana membranectomy than in YAG laser discission. In membranes thicker than 1.2 mm, only pars plana membranectomy is recommended.

Glucose induces lipid peroxidation and inactivation of membrane-associated ion-transport enzymes in human erythrocytes in vivo and in vitro

Erythrocytes of diabetic subjects (non-insulin dependent) were found to have eight- to ten-fold higher levels of endogenously formed thiobarbituric acid reactive malonyldialdehyde (MDA), thirteen-fold higher levels of phospholipid-MDA adduct, 15-20% reduced Na(+)-K(+)-ATPase activity with unchanged Ca+2-ATPase activity, as compared with the erythrocytes from normal healthy individuals. Incubation of normal erythrocytes with elevated concentrations (15-35 mM) of glucose, similar to that present in diabetic plasma, led to the increased lipid peroxidation, phospholipid-MDA adduct formation, reduction of Na(+)-K(+)-ATPase (25-50%) and Ca+2-ATPase (50%) activities. 2-doxy-glucose was 80% as effective as glucose in the lipid peroxidation and lipid adduct formation. However, other sugars, such as fructose, galactose, mannose, fucose, glucosamine and 3-O-methylmannoside, and sucrose, tested at a concentration of 35 mM, resulted in reduced (20-30%) lipid peroxidation without the formation of lipid-MDA adduct. Kinetic studies show that reductions in Na(+)-K(+)-ATPase and Ca+2-ATPase activities precede the lipid peroxidation as the enzyme inactivation occur within 30 min of incubation of erythrocytes with high concentration (15-35 mM) of glucose, while lipid peroxidation product, MDA appears at 4 hr and lipid-MDA adducts at 8 hr. The lipoxygenase pathway inhibitors, 5,8,11-eicosatriynoic acid and Baicalein (5,6,7-trihydroxyflavone), reduced the glucose-induced lipid peroxidation by 30% and MDA-lipid adduct formation by 26%. Indomethacin, a cyclooxygenase pathway inhibitor, had no discernible effect on the lipid peroxidation in erythrocytes. However, the inhibitors of lipid peroxidation, 3-phenylpyrazolidone, metyrapone, and the inhibitors of lipoxygenase pathways did not ablate the glucose-induced reduction of Na(+)-K(+)-ATPase and Ca+2-ATPase activities in erythrocytes. Erythrocytes produce 15-HETE (15-hydroxy-eicosatetraenoic acid), which is augmented by glucose. These results suggest that the formation of lipoxygenase metabolites potentiate the glucose-induced lipid peroxidation and that the inactivation of Na(+)-K(+)-ATPase and Ca+2-ATPase occurs as a result of non-covalent interaction of glucose with these enzymes.

Argon laser iridoplasty: a primary mode of therapy in primary angle closure glaucoma

Argon laser iridoplasty was performed in 40 eyes of 33 patients of primary angle closure glaucoma. There were 12 male and 21 female patients. The mean ages of the male and female patients were 51 years and 48.4 years respectively. Forty eyes were divided into two groups. Group I consisted of ten eyes of subacute angle closure glaucoma and group II included thirty eyes of chronic angle closure glaucoma. Argon laser iridoplasty was performed with Coherent 9000 model using laser settings of spot size 200 micron, duration 0.2 second and power 0.7 watt. A total of 80 spots were applied over 360 degree circumference. The intraocular pressure control (below 22 mm Hg) was achieved after iridoplasty in all the eyes (100%) in group I, where as in group II the intraocular pressure was controlled in 70% eyes. The follow up period varied from 3 months to one year with a mean of eight months. The success rate with iridoplasty was directly related to the extent of peripheral anterior synechiae, optic disc cupping and presence of visual field changes.

Conjunctival microbial flora in leprosy

Conjunctival sacs of seventy one leprosy patients, paramedical and medical personnel working in a leprosy home were cultured. None of these eyes had any pathology in the outer eye. Surprisingly, 46.2% of the eyes which showed a positive culture carried accepted pathogens; Staphylococcus aureus being the commonest. Determining the preoperative bacterial flora and their elimination before undertaking intraocular surgery is recommended.

Heterotypic and homotypic cell-cell adhesion molecules in endothelial cells

Sickle red blood cells display an abnormal propensity to adhere to cultured bovine aortic endothelial cells when compared to normal red blood cells. The adherence was potentiated three-fold by endothelial cell derived conditioned medium, enriched in multimers of von Willebrand factor. Such adherence was ablated by 80% by either the synthetic peptide (RGDS) or antibody to GPIIb/IIIa, indicating the presence of RGD peptide recognition domain/receptor in either endothelial cells or sickle cells or both. The adherence was also inhibited by 70% by phosphatidylserine, but not by other phospholipids, indicating the presence of putative receptors for this phospholipid in endothelial cells. The labeling of cultured bovine aortic endothelial cells with monoclonal antibodies revealed the localization of MAB D2 to regions of cell-cell contact. The antigen on endothelial cells which cross-reacts with this antibody has a Mr of 130,000. The addition of such an antibody during the plating of endothelial cells disrupted monolayer formation. It appears that a 130-kDa polypeptide antigen in endothelial cells which is recognized by MAB D2, may be a cell-cell adhesion molecule.

Conjunctival microbial flora in leprosy

Conjunctival sacs of seventy-one leprosy patients, paramedical and medical personnel working in a Leprosy Home were cultured. None of these eyes had any pathology of the outer eye. Surprisingly, 46.2% of the culturally positive eyes carried accepted pathogens, Staphylococcus aureus being the commonest. Determining the preoperative bacterial flora and their elimination before undertaking intraocular surgery is recommended.

Topical silver sulphadiazine--a new drug for ocular keratomycosis

The efficacy of silver sulphadiazine in human keratomycosis has not been evaluated so far. Encouraged by the success of an earlier experimental trial, a prospective, controlled, randomised double masked clinical study was designed to evaluate the efficacy of 1% silver sulphadiazine ophthalmic ointment in 20 eyes of mycotic keratitis. Miconazole 1% was used for comparative evaluation in another 20 eyes. Silver sulphadiazine had a higher success rate (80% vs 55%) than miconazole. It had broad antifungal activity and was found to be effective in fusarium keratitis. Absence of side effects, economy, and its efficacy in deeper and extensive lesions were additional advantages. It is concluded from this study that silver sulphadiazine is a safe and effective broad spectrum antifungal agent which can be used for the treatment of human keratomycosis.

Sickling-induced binding of immunoglobulin to sickle erythrocytes

Previously we demonstrated that sickle erythrocytes sedimenting at high densities after gradient centrifugation contain higher levels of surface immunoglobulin bound in vivo in comparison to low-density erythrocytes from the same patient. The present study examines the possibility that binding of autologous IgG to sickle erythrocytes may be associated with the sickling phenomenon. In the present study we subjected low-density erythrocytes to prolonged sickling under nitrogen in the presence of platelet-poor autologous plasma with added glucose for 24 hours (37 degrees C). After reoxygenation IgG bound in vitro was quantified by a nonequilibrium 125iodinated protein A-binding assay and by flow cytometry. Results show that sickle erythrocytes incubated under nitrogen bound significantly (P less than .001) more IgG, 439 +/- 41, molecules of IgG per cell (mean +/- SD) compared with sickle cells incubated under oxygenation (227 +/- 12 molecules of IgG per red cell) or compared with 196 +/- 26 molecules IgG per cell for untreated sickle cells. In contrast, normal erythrocytes incubated in autologous plasma exhibited no detectable IgG binding in vitro under either oxygenation or deoxygenation. Flow cytometry shows that deoxygenation of sickle cells generated a two-to-sixfold increase in the subpopulation of brightly fluorescent IgG-positive cells in comparison to oxygenated sickle cells and a 13.5% +/- 3.1% (mean +/- SD) increase in median fluorescence intensity for fluorescein isothiocyanate-labeled deoxygenated sickled cells compared with labeled oxygenated sickle cells. Our studies demonstrate that prolonged sickling will induce in vitro binding of autologous IgG to sickle erythrocytes. These findings indicate that sickle erythrocytes may be unique when compared with erythrocytes from other nonimmunologic hemolytic anemias or senescent red cells in that the primary events producing surface antigens recognized by autoantibody may include the sickling process. These findings also suggest that sickling in vivo may generate membrane alterations in sickle erythrocytes that lead to cumulative binding of autoantibody in vivo.

Alterations in organization of phospholipids in erythrocytes as factor in adherence to endothelial cells in diabetes mellitus

Erythrocytes from patients with diabetes mellitus exhibit increased adherence to cultured human vascular endothelial cells. We investigated the alterations in erythrocyte surface characteristics that may contribute to their abnormal adherence. The organization of phospholipids in the lipid bilayer, as determined by phospholipase A2 treatment and chemical labeling with fluorescamine and trinitrobenzene sulfonic acid (TNBS), is altered in erythrocytes from diabetic patients. Specifically, 12-18% of phosphatidylserine in diabetic erythrocytes (n = 25) is accessible to phospholipase A2 hydrolysis and TNBS labeling, compared to none in normal subjects. These results suggest either a loss in lipid asymmetry or in vivo destabilization of erythrocyte membranes in diabetic patients, causing increased accessibility to phospholipase A2 degradation. The dye merocyanine 540 (MC-540), which is sensitive to the packing of lipids in the bilayer of the membrane, revealed more binding and fluorescence in erythrocytes from diabetic patients than in those from normal subjects. On flow cytometric analysis, 64.5 +/- 17.0% red blood cells (RBCs) in diabetic patients, compared to 35.1 +/- 25.9% RBCs in normal subjects, showed positive MC-540 binding, indicating significant (P less than .001) differences in the packing of lipids in the external leaflet of the bilayer. The results of our study suggest that a loss of lipid asymmetry and/or less ordered packing in the outer leaflet of the diabetic erythrocyte membrane may be responsible for the increased propensity of erythrocytes to adhere to vascular endothelium.

Effect of cell shape, membrane deformability and phospholipid organization on phosphate-calcium-induced fusion of erythrocytes

Fusion of bovine and goat erythrocytes was studied using the phosphate-calcium protocol. Both bovine and goat red cells are resistant to fusion with phosphate and calcium, under conditions that promote fusion of normal human erythrocytes. Fusion resistance is not related to decreased (5%) membrane deformability of erythrocytes of these species, since chicken erythrocytes which are 40% less deformable than human erythrocytes undergo fusion with efficiency similar to human red blood cells. Incorporation of either phosphatidylcholine or phosphatidylserine into bovine erythrocytes mediated by lipid exchange/transfer protein, caused fusion of these erythrocytes. Fluorescence analysis of merocyanine 540 dye labeled erythrocytes, by flow cytometry, showed that the frequency of cells which exhibit dye binding was much less (35%) in dimyristoylphosphatidylcholine (DMPC) incorporated compared to untreated bovine erythrocytes (80%), indicating that incorporation of DMPC caused closed packing of lipids in the external leaflet of the bilayer. These studies show that fusion of bovine erythrocytes, mediated by phosphate and calcium, has a requirement for either specific phospholipids such as phosphatidylcholine, phosphatidylserine, or closed packing of lipids in the external leaflet of the bilayer.