Atherosclerotic aortic gangliosides enhance integrin-mediated platelet adhesion to collagen

Brain-derived gangliosides prime human platelet aggregation and induce platelet-leukocyte aggregate formation

BACKGROUND

Platelet activation and interaction with leukocytes are crucial in inflammation. Gangliosides, sialic acid-containing glycosphingolipids, have been linked to different inflammatory conditions related to cardio- and neurodegenerative disorders. The role of gangliosides in platelet and leukocyte function, although reported, still needs further investigation.

OBJECTIVES

We aimed to study the role of gangliosides in platelet activation and platelet-leukocyte interaction in vitro.

METHODS

Platelet activation was studied through aggregometry in platelet-rich plasma from apparently healthy human volunteers. Signaling protein phosphorylation was analyzed by immunoblotting. Platelet P-selectin expression and platelet-leukocyte aggregate formation were measured by flow cytometry.

RESULTS

The gangliosides monosialoganglioside GM1, disialoganglioside GD1a, and trisialoganglioside GT1b did not induce by themselves any platelet aggregation. Conversely, when preincubated with platelets, they potentiate platelet aggregation induced by submaximal adenosine diphosphate and collagen concentrations and increased P-selectin expression. Incubation of platelets with free sialic acid and the soluble part of monosialoganglioside GM1 induced a similar potentiating effect on platelet aggregation but not on platelet P-selectin expression. Consistently, analyzing the signaling protein phosphorylation, only the entire gangliosides activated extracellular stimuli-responsive kinase 1/2 suggesting that a complete ganglioside is crucial for its action on platelets. Both the priming effect on platelet aggregation and ERK1/2 activation were prevented by aspirin. Moreover, incubation of citrated whole blood with gangliosides induced platelet-leukocyte aggregate formation accompanied by increased expression of granulocyte and monocyte CD11b compared with untreated blood, suggesting a primary leukocyte activation.

CONCLUSION

Gangliosides may act in vitro both on platelet and leukocyte activation and on their interaction. The observed effects might contribute to inflammatory processes in clinical conditions.

Enhanced Anti-Atherosclerotic Efficacy of pH-Responsively Releasable Ganglioside GM3 Delivered by Reconstituted High-Density Lipoprotein

Recently, the atheroprotective role of endogenous GM3 and an atherogenesis-inhibiting effect of exogenous GM3 suggested a possibility of exogenous GM3 being recruited as an anti-atherosclerotic drug. This study seeks to endow exogenous GM3 with atherosclerotic targetability via reconstituted high-density lipoprotein (rHDL), an atherosclerotic targeting drug nanocarrier. Unloaded rHDL, rHDL loaded with exogenous GM3 at a low concentration (GM3_L-rHDL), and rHDL carrying GM3 at a relatively high concentration (GM3_H-rHDL) were prepared and characterized. The inhibitory effect of GM3-rHDL on lipid deposition in macrophages was confirmed, and GM3-rHDL did not affect the survival of red blood cells. In vivo experiments using ApoE^-/- mice fed a high fat diet further confirmed the anti-atherosclerotic efficacy of exogenous GM3 and demonstrated that GM3 packed in HDL nanoparticles (GM3-rHDL) has an enhanced anti-atherosclerotic efficacy and a reduced effective dose of GM3. Then, the macrophage- and atherosclerotic plaque-targeting abilities of GM3-rHD, most likely via the interaction of ApoA-I on GM3-rHDL with its receptors (e.g., SR-B1) on cells, were certified via a microsphere-based method and an aortic fragment-based method, respectively. Moreover, we found that solution acidification enhanced GM3 release from GM3-rHDL nanoparticles, implying the pH-responsive GM3 release when GM3-rHDL enters the acidic atherosclerotic plaques from the neutral blood. The rHDL-mediated atherosclerotic targetability and pH-responsive GM3 release of GM3-rHDL enhanced the anti-atherosclerotic efficacy of exogenous GM3. The development of the GM3-rHDL nanoparticle may help with the application of exogenous GM3 as a clinical drug. Moreover, the data imply that the GM3-rHDL nanoparticle has the potential of being recruited as a drug nanocarrier with atherosclerotic targetability and enhanced anti-atherosclerotic efficacy.

Molecular recognition of sialoglycans by streptococcal Siglec-like adhesins: toward the shape of specific inhibitors

Streptococcus gordonii and Streptococcus sanguinis, commensal bacteria present in the oral cavity of healthy individuals, upon entry into the bloodstream can become pathogenic, causing infective endocarditis (IE). Sialic acid-binding serine-rich repeat adhesins on the microbial surface represent an important factor of successful infection to cause IE. They contain Siglec-like binding regions (SLBRs) that variously recognize different repertoires of O-glycans, with some strains displaying high selectivity and others broader specificity. We here dissect at an atomic level the mechanism of interaction of SLBR-B and SLBR-H from S. gordonii with a multivarious approach that combines NMR spectroscopy and computational and biophysical studies. The binding pockets of both SLBRs are broad enough to accommodate extensive interactions with sialoglycans although with key differences related to strain specificity. Furthermore, and significantly, the pattern of interactions established by the SLBRs are mechanistically very different from those reported for mammalian Siglecs despite them having a similar fold. Thus, our detailed description of the binding modes of streptococcal Siglec-like adhesins sparks the development of tailored synthetic inhibitors and therapeutics specific for Streptococcal adhesins to counteract IE, without impairing the interplay between Siglecs and glycans.

We here present a detailed molecular description of sialoglycans recognition by Siglec-like adhesins from S. gordonii opening the venue for the design of specific inhibitors to influence the propensity of streptococci to cause infective endocarditis.

Effects of Long-Term Calcium Supplementation on Rats Bone Mineral Density and Cardiovascular Based on Metabonomics

Calcium supplements were necessary for those people with low calcium intake and high risk of osteoporosis. Recent cohort studies have shown that long-term calcium supplements may raise the risk of cardiovascular disease, but its mechanism is still unclear. In this study, metabonomics were employed to evaluate the changes of metabolism in rats with long-term calcium supplementation and further seek the potential markers of cardiovascular risk. SD rats were divided into two groups including normal control group (calcium intake, 0.50 g/kg bw) and high calcium supplement group (calcium intake, 2.50 g/kg bw). After 6 mo, the cardiovascular system and bone mineral density were observed. UPLC-MS was used to analyze serum metabonomics in rats. The results showed that the contents of total cholesterol and low-density lipoprotein cholesterol in the high calcium group were significantly higher than those in normal control group (p<0.05). The interventricular septum thickness (IVS), left ventricular mass (LVM), left ventricular posterior wall thickness (LVPW) in the high calcium group were higher than those in normal control group (p<0.05). Serum metabonomics analysis showed that there were persistent changes in many metabolites such as sphingosine and its derivatives (p<0.01) in the comparison between the high calcium group and the normal group. These results indicated that long term calcium supplementation can lead to dyslipidemia in rats, such as the rise of cholesterol and low-density lipoprotein, which might induce myocardial hypertrophy. Long-term calcium supplementation can cause the changes of the amount of sphingosine and its derivatives in the body, which many have potential risk to cardiovascular diseases such as myocardial hypertrophy and atherosclerosis.

Fresh evidence for major brain gangliosides as a target for the treatment of Alzheimer's disease

Although it was suggested that gangliosides play an important role in the binding of amyloid fragments to neuronal cells, the exact role of gangliosides in Alzheimer's disease (AD) pathology remains unclear. To understand the role of gangliosides in AD pathology in vivo, we crossed st3gal5-deficient (ST3^-/-) mice that lack major brain gangliosides GM1, GD1a, GD3, GT1b, and GQ1b with 5XFAD transgenic mice that overexpress 3 mutant human amyloid proteins AP695 and 2 presenilin PS1 genes. We found that ST3^-/- 5XFAD mice have a significantly reduced burden of amyloid depositions, low level of neuroinflammation, and did not exhibit neuronal loss or synaptic dysfunction. ST3^-/- 5XFAD mice performed significantly better in a cognitive test than wild-type (WT) 5XFAD mice, which was comparable with WT nontransgenic mice. Treatment of WT 5XFAD mice with the sialic acid-specific Limax flavus agglutinin resulted in substantial improvement of AD pathology to a level of ST3^-/- 5XFAD mice. Thus, our findings highlight an important role for gangliosides as a target for the treatment of AD.

Platelets mediate protective neuroinflammation and promote neuronal plasticity at the site of neuronal injury

It is generally accepted that inflammation within the CNS contributes to neurodegeneration after traumatic brain injury (TBI), but it is not clear how inflammation is initiated in the absence of infection and whether this neuroinflammation is predominantly beneficial or detrimental. We have previously found that brain-enriched glycosphingolipids within neuronal lipid rafts (NLR) induced platelet degranulation and secretion of neurotransmitters and pro-inflammatory factors. In the present study, we compared TBI-induced inflammation and neurodegeneration in wild-type vs. St3gal5 deficient (ST3^-/-) mice that lack major CNS-specific glycosphingolipids. After TBI, microglial activation and CNS macrophage infiltration were substantially reduced in ST3^-/- animals. However, ST3^-/- mice had a larger area of CNS damage with marked neuronal/axonal loss. The interaction of platelets with NLR stimulated neurite growth, increased the number of PSD95-positive dendritic spines, and intensified neuronal activity. Adoptive transfer and blocking experiments provide further that platelet-derived serotonin and platelet activating factor plays a key role in the regulation of sterile neuroinflammation, hemorrhage and neuronal plasticity after TBI.

GD3 ganglioside-enriched extracellular vesicles stimulate melanocyte migration

Melanomas often accumulate gangliosides, sialic acid-containing glycosphingolipids found in the outer leaflet of plasma membranes, as disialoganglioside G_D3 and its derivatives. Here, we have transfected the G_D3 synthase gene (ST8Sia I) in a normal melanocyte cell line in order to evaluate changes in the biological behavior of non-transformed cells. G_D3-synthase expressing cells converted G_M3 into G_D3 and accumulated both G_D3 and its acetylated form, 9-O-acetyl-G_D3. Melanocytes were rendered more migratory on laminin-1 surfaces. Cell migration studies using the different transfectants, either treated or not with the glucosylceramide synthase inhibitor d-1-threo-1-phenyl-2-palmitoylamino-3-pyrrolidino-1-propanol (PPPP), allowed us to show that while G_M3 is a negative regulator of melanocyte migration, G_D3 increases it. We showed that gangliosides were shed to the matrix by migrating cells and that G_D3 synthase transfected cells shed extracellular vesicles (EVs) enriched in G_D3. EVs enriched in G_D3 stimulated cell migration of G_D3 negative cells, as observed in time lapse microscopy studies. Otherwise, EVs shed by G_M3^+veG_D3^-ve cells impaired migration and diminished cell velocity in cells overexpressing G_D3. The balance of antimigratory G_M3 and promigratory G_D3 gangliosides in melanocytes could be altered not only by the overexpression of enzymes such as ST8Sia I, but also by the horizontal transfer of ganglioside enriched extracellular vesicles. This study highlights that extracellular vesicles transfer biological information also through their membrane components, which include a variety of glycosphingolipids remodeled in disease states such as cancer.

Platelets recognize brain-specific glycolipid structures, respond to neurovascular damage and promote neuroinflammation

Platelets respond to vascular damage and contribute to inflammation, but their role in the neurodegenerative diseases is unknown. We found that the systemic administration of brain lipid rafts induced a massive platelet activation and degranulation resulting in a life-threatening anaphylactic-like response in mice. Platelets were engaged by the sialated glycosphingolipids (gangliosides) integrated in the rigid structures of astroglial and neuronal lipid rafts. The brain-abundant gangliosides GT1b and GQ1b were specifically recognized by the platelets and this recognition involved multiple receptors with P-selectin (CD62P) playing the central role. During the neuroinflammation, platelets accumulated in the central nervous system parenchyma, acquired an activated phenotype and secreted proinflammatory factors, thereby triggering immune response cascades. This study determines a new role of platelets which directly recognize a neuronal damage and communicate with the cells of the immune system in the pathogenesis of neurodegenerative diseases.

Ganglioside GD3 enhances adhesion signals and augments malignant properties of melanoma cells by recruiting integrins to glycolipid-enriched microdomains

Ganglioside GD3 is widely expressed in human malignant melanoma cell lines and tumors. Previously, we reported that GD3+ cells show stronger tyrosine phosphorylation of focal adhesion kinase (FAK), p130(Cas), and paxillin when treated with fetal calf serum than GD3- cells. In this study, we analyzed the changes in the signals mediated by the interaction between integrins and extracellular matrices (ECM) to clarify how GD3 enhances cell signals in the vicinity of the cell membrane. An adhesion assay with a real time cell electronic sensing system revealed that GD3+ cells had stronger adhesion to all extracellular matrices examined. In particular, GD3+ cells attached more strongly to collagen type I and type IV than controls. Correspondingly, they showed stronger tyrosine phosphorylation of FAK and paxillin during adhesion to collagen type I. In the floating pattern of detergent extracts, a high level of integrin beta1 was found in glycolipid-enriched microdomain (GEM)/rafts in GD3+ cells before adhesion, whereas a smaller amount of integrin beta1 was detected in the GEM/rafts of controls. Some phosphorylated forms of FAK as well as total FAK were found in GEM/rafts during cell adhesion only in GD3+ cells. Another signal consisting of integrin-linked kinase/Akt was also activated during adhesion more strongly in GD3+ cells than in controls. In double stained GD3+ cells, GD3 and integrin beta1 co-localized at the focal adhesion with a punctate pattern. All these results suggested that integrins assembled and formed a cluster in GEM/rafts, leading to the enhanced signaling and malignant properties under GD3 expression.

The possible contribution of a general glycosphingolipid transporter, GM2 activator protein, to atherosclerosis

We previously found that oxidized low-density lipoprotein (LDL) elevated the expression of mRNA of GalNAcbeta1-4[NeuNAcalpha2-3]Galbeta1-4Glc-Cer (GM2) ganglioside activator protein, in human monocyte-derived macrophages. Recently, GM2 activator protein has become known as a general glycosphingolipid transporter as well as a specific cofactor for the hydrolysis of GM2 ganglioside by lysosomal beta-hexosaminidase A. Accumulation of glycosphingolipids has been observed in the serum or aorta of atherosclerotic model animals and humans. The proliferation of aortic smooth muscle cells, elevation of LDL uptake by macrophages, interfering LDL clearance by the liver, and enhancement of platelet adhesion to collagen have been proposed as the underlying mechanisms of glycosphingolipid-mediated atherogenesis. The GM2 activator protein can bind, solubilize and transport a broad spectrum of lipid molecules, indicating that GM2 activator protein may function as a general intra- and inter-cellular lipid transport protein. Collectively, elevated levels of GM2 activator protein in the aorta may be another feature of human atherosclerosis.

Inhibition of atherosclerosis by the serine palmitoyl transferase inhibitor myriocin is associated with reduced plasma glycosphingolipid concentration

Glycosphingolipids (GSL) have been implicated as potential atherogenic lipids. Inhibition of hepatic serine palmitoyl transferase (SPT) reduces plasma sphingomyelin (SM) levels in the absence of changes in cholesterol or triglyceride (TG) concentration and this leads to a reduction of atherosclerosis in apolipoprotein-E gene knockout (apoE(-/-)) mice. The possibility that the reduced atherosclerosis resulting from SPT inhibition is associated with decreases in plasma GSL concentration has not been examined and was the primary aim of this investigation. We show that intraperitoneal delivery of the SPT inhibitor myriocin for 9 weeks inhibits atherosclerosis in apoE(-/-) mice fed a high fat diet. Lesion inhibition was most pronounced at the aortic arch and distal sites of the thoracic and abdominal aorta. There was also a trend towards a reduction in lesion area at the aortic root. Myriocin treatment resulted in significant reductions in both plasma SM and GSL concentration of 42% and 25%, as assessed by enzymatic and HPLC methods, respectively. Moreover, SM and GSL concentrations were significantly correlated, indicating that SPT inhibition suppresses the synthesis of both these sphingolipids concomitantly. The inhibition of atherosclerosis induced by myriocin was not associated with changes in plasma cholesterol or TG concentrations or lipoprotein profiles as determined by FPLC. These data indicate that therapeutic reduction of plasma SM and/or GSL concentrations may offer a novel treatment for atherosclerosis.

Gangliosides promote platelet adhesion and facilitate neuroblastoma cell adhesion under dynamic conditions simulating blood flow

BACKGROUND

Aberrant gangliosides are produced and shed by some tumors into the extracellular milieu. Their concentration is related to disease progression in children with neuroblastoma and in experimental models. The mechanism for this tumor promoting effect is not known.

PURPOSE

Here, we investigated the effect of gangliosides on platelet and tumor cell adhesion under shear forces simulating venous and arterial flow.

RESULTS

High shear force increased platelet adhesion 2.5-fold compared to low force. Pre-incubation of platelets with gangliosides increased adhesion at low shear to a level comparable to high shear alone. The addition of gangliosides to platelets perfused at high shear did not further increase adhesion. LAN1 neuroblastoma cells are adherent to collagen in static assays. No effect of either shear or gangliosides was observed on cell adhesion under dynamic conditions. However, when perfused in the presence of platelets, an increase in binding of tumor cells was observed at both shear forces compared to cells alone.

CONCLUSIONS

These results demonstrate that shear and gangliosides increase dynamic platelet adhesion to collagen. In addition, platelets facilitate tumor cell binding. Therefore, by acting as a mediator of platelet activation, gangliosides may promote blood borne metastasis by increasing platelet binding to the vessel wall and in turn facilitate tumor cell arrest in circulation.

The glycosphingolipid, lactosylceramide, regulates beta1-integrin clustering and endocytosis

Glycosphingolipids are known to play roles in integrin-mediated cell adhesion and migration; however, the mechanisms by which glycosphingolipids affect integrins are unknown. Here, we show that addition of the glycosphingolipid, C8-lactosylceramide (C8-LacCer), or free cholesterol to human fibroblasts at 10 degrees C causes the formation of glycosphingolipid-enriched plasma membrane domains as shown by visualizing a fluorescent glycosphingolipid probe, BODIPY-LacCer, incorporated into the plasma membrane of living cells. Addition of C8-LacCer or cholesterol to cells initiated the clustering of beta1-integrins within these glycosphingolipid-enriched domains and the activation of the beta1-integrins as assessed using a HUTS antibody that only binds activated integrin. On warming to 37 degrees C, beta1-integrins were rapidly internalized via caveolar endocytosis in cells treated with C8-LacCer or cholesterol, whereas little beta1-integrin was endocytosed in untreated fibroblasts. Incubation of cells with C8-LacCer or cholesterol followed by warm-up caused src activation, a reorganization of the actin cytoskeleton, translocation of RhoA GTPase away from the plasma membrane as visualized using total internal reflection fluorescence microscopy, and transient cell detachment. These studies show that LacCer can regulate integrin function both by modulating integrin clustering in microdomains and by regulating integrin endocytosis via caveolae. Our findings suggest the possibility that aberrant levels of glycosphingolipids found in cancer cells may influence cell attachment events by direct effects on integrin clustering and internalization.

Platelet alpha2beta1 integrin activation: contribution of ligand internalization and the alpha2-cytoplasmic domain

The alpha2beta1 integrin is a major collagen receptor on platelets. Although it has been proposed that alpha2beta1, like alphaIIbbeta3, undergoes agonist-induced activation, neither the potential contributions of alpha2beta1 receptor/ligand internalization to the increase in ligand binding nor the roles of the alpha2 and beta1 cytoplasmic domains in activation of this integrin have been previously explored. Activation of alpha2beta1 was assessed with fluorescein isothiocyanate-labeled soluble type I collagen binding to platelets by flow cytometry. Although collagen internalization in response to agonist activation of platelets was significant, agonist-induced collagen binding still occurred under conditions that block internalization, with minimal changes in cell surface alpha2beta1 expression. Introduction of cell-permeable peptides containing the alpha2 cytoplasmic tail, and especially the membrane proximal KLGFFKR domain, induced alpha2beta1 activation in resting platelets, whereas a cell-permeable peptide containing the beta1 cytoplasmic tail was without effect. Thus, collagen binding to stimulated platelets is increased due to alpha2beta1 activation, in addition to internalization, and the GFFKR motif appears to play an important role in the activation process.

Gangliosides regulate tumor cell adhesion to collagen

The ability of tumor cells to adhere to extracellular matrix proteins is critical for migration and invasion. The factors that regulate tumor cell adhesion are poorly characterized. Gangliosides promote platelet adhesion and may also play a role in the adhesion of other cell types. We hypothesized that pharmacological depletion of membrane gangliosides from adherent cells would abrogate adhesion to collagen and promote migration and invasion. To test these hypotheses, LA-N1 neuroblastoma cells, which avidly adhere to collagen and are rich with membrane gangliosides (43.69 nmol/10(8) cells), were cultured in the presence of D-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol-HCl. Endogenous gangliosides were reduced by 98% (0.76 nmol/10(8) cells) and adhesion to collagen decreased by 67%. There were no changes in cell morphology, viability, proliferation rate or apoptosis. Pre-incubation of ganglioside-depleted cells in conditioned medium from control cells restored adhesion to collagen (0.45 +/- 0.002), comparable to that of control cells (0.49 +/- 0.035). Similarly, pre-incubation of ganglioside-depleted cells with purified GD2 completely restored adhesion in a concentration-dependent manner. When LA-N1 cells were cultured with retinoic acid, a biological response modifier known to increase endogenous gangliosides, adhesion to collagen increased. Next, we questioned whether changes in adhesion would be reflected as changes in migration and invasion. Cells depleted of endogenous cellular gangliosides migrated more than control cells. Finally, control cells replete with their endogenous gangliosides demonstrated less invasive potential than control cells. The data demonstrate that endogenous tumor gangliosides increase neuroblastoma cell adhesion to collagen and reduce migration and invasion in vitro.

L- and D-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (PDMP) inhibit neurite outgrowth from SH-SY5Y cells

Gangliosides and extracellular matrix molecules influence neurite outgrowth, but the combinatorial effects of these endogenous agents on outgrowth are unclear. Exogenous gangliosides inhibit neurite outgrowth from SH-SY5Y cells stimulated with platelet-derived growth factor-BB, and different isoforms of the ceramide analog threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (PDMP) stimulate (L-PDMP) or inhibit (D-PDMP) glycosphingolipid biosynthesis. In this study, we determined whether altering the endogenous ganglioside levels with PDMP in SH-SY5Y cells regulates neurite outgrowth on the outgrowth-supporting extracellular matrix molecule, laminin. In cells stimulated with 20 ng/ml platelet-derived growth factor-BB to promote outgrowth, we used image analysis to evaluate neurite outgrowth from SH-SY5Y cells grown on endogenous matrix or laminin and exposed to L- or D-PDMP. Both L- and D-PDMP decreased neurite initiation (the number of neurites/cell, the percent of neurite-bearing cells), elongation (the length of the longest neurite/cell, the total neurite length/cell), and branching (the number of branch points/neurite) from SH-SY5Y cells on endogenous matrix or laminin in a dose-dependent manner in serum-free or serum-containing medium. The inhibitory effects of each PDMP isoform were reversible. Inhibition of neurite outgrowth by L-PDMP could be mimicked by addition of exogenous gangliosides or C2-ceramide. Our analyses of neurite outgrowth in SH-SY5Y cells, a model of developing or regenerating noradrenergic neurons, demonstrate that increasing or decreasing endogenous ganglioside levels decreases neurite outgrowth. These results may indicate that SH-SY5Y cells undergo tight regulation by gangliosides, possibly through modulation of growth/trophic factor- and/or extracellular matrix-activated signaling cascades.

Sialyltransferase activity of human plasma and aortic intima is enhanced in atherosclerosis

Sialyltransferase activity has been determined in membrane preparations containing the Golgi apparatus that were isolated from atherosclerotic and normal human aortic intima as well as in plasma of patients with documented atherosclerosis and healthy donors by measuring the transfer of N-acetylneuraminic acid (NeuAc) from CMP-NeuAc to asialofetuin. The asialofetuin sialyltransferase activity was found to be 2 times higher in the atherosclerotic intima as compared to the normal intima and 2-fold higher in patients' plasma than in that from healthy donors. The mean values of the apparent Michaelis constant (K(m)) for the sialylating enzyme for both tissues did not differ and were close for the intima and plasma. In contrast, the maximal velocity (V(max)) was 2 times higher for the atherosclerotic intima than for the normal intima and 3 times higher for patients' plasma than for that of the donors. These results suggest that the activity of asialofetuin sialyltransferases of aortal intima is enhanced in atherosclerosis as is the secretion of their soluble forms into patients' plasma.

Anti-human skeletal muscle glycolipid antibodies in unstable angina

BACKGROUND

We studied whether the level of anti-skeletal muscle glycolipid antibodies (AGA), a marker of acute rejection in heart transplantation, may be associated with an adverse prognosis in unstable angina.

METHODS AND RESULTS

The in-hospital evolution of 50 patients with unstable angina (Braunwald class III B) was assessed. We determined the incidence of death, myocardial infarction, and refractory angina. Blood was collected at admission and 24 hours later for determination of AGA levels by enzyme-linked immunosorbent assay. Twenty-three patients showed a decrease in the AGA level at 24 hours after admission. Ten in-hospital cardiac events occurred in these patients (43.4%) as compared with 4 (14.8%) in the 27 patients who did not show a decrease (P =.025). In patients with previous myocardial infarction (n = 26), the AGA assay was a powerful predictor of outcome. In this subgroup, 66.6% of patients who had decreased AGA levels (8 of 12) had cardiac events as compared with 14.2% (2 of 14) of those who did not have that decrease (P =.001).

CONCLUSIONS

We conclude that a decrease of AGA levels 24 hours after admission is associated with a complicated in-hospital course. This finding may provide new insights in the phenomenon of plaque instability involved in the development of acute coronary syndromes.

Integrins alpha2beta1 and alpha4beta1 can mediate SA11 rotavirus attachment and entry into cells

Most mammalian rotaviruses contain tripeptide amino acid sequences in outer capsid proteins VP4 and VP7 which have been shown to act as ligands for integrins alpha2beta1 and alpha4beta1. Peptides containing these sequences and monoclonal antibodies directed to these integrins block rotavirus infection of cells. Here we report that SA11 rotavirus binding to and infection of K562 cells expressing alpha2beta1 or alpha4beta1 integrins via transfection is increased over virus binding to and infection of cells transfected with alpha3 integrin or parent cells. The increased binding and growth were specifically blocked by a monoclonal antibody to the transfected integrin subunit but not by irrelevant antibodies. In our experiments, integrin activation with phorbol ester did not affect virus binding to cells. However, phorbol ester treatment of K562 parent and transfected cells induced endogenous gene expression of alpha2beta1 integrin, which was detectable by flow cytometry 16 h after treatment and quantitatively correlated with the increased level of SA11 virus growth observed after this time. Virus binding to K562 cells treated with phorbol ester 24 h previously and expressing alpha2beta1 was elevated over binding to control cells and was specifically blocked by the anti-alpha2 monoclonal antibody AK7. Virus growth in alpha4-transfected K562 cells which had also been induced to express alpha2beta1 integrin with phorbol ester occurred at a level approaching that in the permissive MA104 cell line. We therefore have demonstrated that two integrins, alpha2beta1 and alpha4beta1, are capable of acting as cellular receptors for SA11 rotavirus.