Carbohydrate sulfotransferases in lymphocyte homing

Sulfation is a critical modification in many instances of biological recognition. Early work in lymphocyte homing indicated that the endothelial ligands for L-selectin depended upon sulfation modifications. Subsequent studies showed that the two specific modifications, Gal-6-SO4 and GlcNAc-6-SO4, were present on actual biological ligands. Recently, a family of carbohydrate sulfotransferases capable of generating these modifications has been identified at the molecular level. Reconstitution experiments implicate members of this family as critical participants in lymphocyte homing.

Breathlessness in humans activates insular cortex

Dyspnea (shortness of breath, breathlessness) is a major and disabling symptom of heart and lung disease. The representation of dyspnea in the cerebral cortex is unknown. In the first study designed to explore the central neural structures underlying perception of dyspnea, we evoked the perception of severe 'air hunger' in healthy subjects by restraining ventilation below spontaneous levels while holding arterial oxygen and carbon dioxide levels constant. PET revealed that air hunger activated the insular cortex. The insula is a limbic structure also activated by visceral stimuli, temperature, taste, nausea and pain. Like dyspnea, such perceptions underlie behaviors essential to homeostasis and survival.

The brain-heart axis in the perception of cardiac pain: the elusive link between ischaemia and pain

Angina pectoris is a common symptom and one that can have profound implications for the patient. However, it correlates poorly with the extent of myocardial ischaemia and with prognosis. In order to understand more fully the heterogeneity of the experience of chest pain, we have adopted the technique of functional neuroimaging, where positron emission tomography is used to measure regional cerebral blood flow as an index of regional neuronal activation, during myocardial ischaemia in patients with coronary artery disease. We have been able to delineate those brain areas that are involved in the perception of angina: the hypothalamus, periaquaductal grey, thalami and bilaterally the prefrontal cortex and in the left the inferior anterocaudal cingulate cortex. By studying patients with silent myocardial ischaemia, we have established that the silence is not merely a matter of impaired afferent signalling resulting from autonomic neuropathy, but that it is associated with a failure of transmission of signals from the thalamus to the frontal cortex. At the other end of the spectrum, we have studied patients with syndrome X, a condition of chest pain with ischaemic-like stress electrocardiography (ECG) but entirely normal coronary angiogram; (on the basis of our own and other data we consider an ischaemic aetiology to be most unlikely in this condition). In syndrome X, distinct patterns of cerebral activation were found with characteristic activation of the right anterior insula at its junction with the frontal operculum. In conclusion, we present a unified view of the cerebral handling of afferent signals from the heart throughout this spectrum of experience of chest pain, a view that accounts for the clinical features of the patients studied.

Vascular endothelial junction-associated molecule, a novel member of the immunoglobulin superfamily, is localized to intercellular boundaries of endothelial cells

During the process of lymphocyte homing to secondary lymphoid organs, such as lymph nodes and tonsils, lymphocytes interact with and cross a specialized microvasculature, known as high endothelial venules. There is a great deal of information available about the first steps in the homing cascade, but molecular understanding of lymphocyte transmigration through the intercellular junctions of high endothelial venules is lacking. In analyzing expressed sequence tags from a cDNA library prepared from human tonsillar high endothelial cells, we have identified a cDNA encoding a novel member of the immunoglobulin superfamily. The protein, which we have termed VE-JAM ("vascular endothelial junction-associated molecule"), contains two extracellular immunoglobulin-like domains, a transmembrane domain, and a relatively short cytoplasmic tail. VE-JAM is prominently expressed on high endothelial venules but is also present on the endothelia of other vessels. Strikingly, it is highly localized to the intercellular boundaries of high endothelial cells. VE-JAM is most homologous to a recently identified molecule known as Junctional Adhesion Molecule, which is concentrated at the intercellular boundaries of both epithelial and endothelial cells. Because the Junctional Adhesion Molecule has been strongly implicated in the processes of neutrophil and monocyte transendothelial migration, an analogous function of VE-JAM during lymphocyte homing is plausible.

Identification of endoglycan, a member of the CD34/podocalyxin family of sialomucins

CD34 and podocalyxin are structurally related sialomucins, which are expressed in multiple tissues including vascular endothelium and hematopoietic progenitors. These glycoproteins have been proposed to be involved in processes as diverse as glomerular filtration, inhibition of stem cell differentiation, and leukocyte-endothelial adhesion. Using homologies present in the cytoplasmic tails of these proteins, we have identified a novel member of this family, which we designate endoglycan. This protein shares a similar overall domain structure with the other family members including a sialomucin domain, but also possesses an extremely acidic amino-terminal region. In addition, endoglycan contains several potential glycosaminoglycan attachment sites and is modified with chondroitin sulfate. Endoglycan mRNA and protein were detected in both endothelial cells and CD34(+) bone marrow cells. Thus, CD34, podocalyxin, and endoglycan comprise a family of sialomucins sharing both structural similarity and sequence homology, which are expressed by both endothelium and multipotent hematopoietic progenitors. While the members of this family may perform overlapping functions at these sites, the unique structural features of endoglycan suggest distinct functions for this molecule.

Measurement of myocardial blood flow with positron emission tomography before and after transmyocardial laser revascularization

BACKGROUND

Transmyocardial laser revascularization (TMLR) has been proposed for treatment of refractory angina. It has been hypothesized that transmural left ventricular channels created by laser improve myocardial blood flow (MBF) in the treated zones. We aimed to assess the effect of TMLR on MBF and coronary vasodilator reserve (CVR).

METHODS AND RESULTS

We measured MBF by means of PET with (15)O-labeled water in 7 patients with refractory angina, Canadian Cardiovascular Society (CCS) class 3.6+/-0.5, on 3 occasions: before and at 7.5+/-2.8 weeks (FU-1) and 34.6+/-4.7 weeks (FU-2) after TMLR performed with a synchronized, high-powered CO(2) laser. In each study, MBF was measured at rest and during maximal intravenous dobutamine. CVR was computed as dobutamine divided by resting MBF. After TMLR, CCS class was 2.2+/-1.7 at FU-1 and 2.4+/-1 at FU-2 (P=0.04 versus pre-TMLR). Resting MBF in both lasered and nonlasered regions was unchanged after TMLR. Dobutamine MBF at baseline was 1.45+/-0.52 and 1.55+/-0.52 mL. min(-1). g(-1) in lasered and nonlasered regions, respectively (P=NS). At FU-1, dobutamine MBF in nonlasered regions had increased significantly to 1.89+/-0.82 mL x min(-1) x g(-1) (P<0.05) and was higher than in lasered regions (1.51+/-0.61 mL x min(-1) x g(-1); P<0.05 versus nonlasered). At FU-2, dobutamine MBF in nonlasered regions was still higher than in lasered regions (1.56+/-0.54 versus 1.21+/-0.44 mL x min(-1) x g(-1); P<0.01). CVR was comparable in nonlasered and lasered regions at baseline and FU-1, whereas it was higher in nonlasered regions at FU-2 (1.86+/-0.67 versus 1.53+/-0.72 mL x min(-1) x g(-1); P<0.05).

CONCLUSIONS

TMLR has been shown to reduce angina in severely diseased patients. The results of our study do not support the hypothesis that the symptomatic benefit of TMLR can be ascribed to improved myocardial perfusion or CVR in lasered areas.

Effect of alpha1-adrenoceptor blockade on coronary vasodilator reserve in cardiac syndrome X

We sought to test the response of the coronary microcirculation to alpha-adrenoceptor blockade in patients with syndrome X (angina, ischemia-like stress electrocardiogram, and a normal coronary arteriogram). The response of the microcirculation was assessed by quantification of coronary vasodilator reserve (the ratio of hyperemic to resting myocardial blood flow). We investigated 28 patients with syndrome X [18 women, age 54.4 (7.6) years]. Myocardial blood flow was measured at rest and after dipyridamole by using positron emission tomography with H(2)15O. The measurements were made before and after treatment for 10 days with doxazosin (1 mg o.d. for 3 days, followed by 2 mg o.d. for 7 days) or a matched placebo, similarly administered. Patients were randomized to alpha1-blockade or to placebo in double-blind fashion. No significant differences were demonstrable between syndrome X patients treated with doxazosin and those receiving placebo, with respect to resting myocardial blood flow, myocardial blood flow after dipyridamole, or coronary vasodilator reserve (the ratio of the latter two). In addition, no relations were demonstrable among myocardial blood flow, coronary vasodilator reserve, development of chest pain after dipyridamole, or development of ischemia-like ECG changes. Doxazosin had no effect on the perception of chest pain after dipyridamole. No differences were found between the effects of alpha1-blockade with doxazosin or those of placebo with respect to myocardial blood flow in syndrome X. The values obtained for myocardial blood flow and coronary vasodilator reserve for the patients were within the normal range. The data do not support the case for alpha1-mediated vasoconstriction having an etiologic role in the chest pain of syndrome X.

Cloning and characterization of a mammalian N-acetylglucosamine-6-sulfotransferase that is highly restricted to intestinal tissue

Using the sequences of a galactose 6-O-sulfotransferase and an N-acetylglucosamine 6-O-sulfotransferase as probes in an EST approach, we have identified a highly related cDNA in human and an apparent orthologue in mouse. The cDNAs predict type II transmembrane proteins that constitute new members of the Gal/GalNAc/GlcNAc 6-O-sulfotransferase (GST) family. Members of this family have previously been implicated in the sulfation of GAG chains within proteoglycans and the sulfation of O-linked chains within sialomucin ligands for l-selectin. Expression of the newly identified cDNA in COS cells led to the addition of sulfate to C-6 of GlcNAc in an acceptor glycoprotein. The tissue expression of transcripts corresponding to the cDNA was highly restricted to the small intestine and colon in humans. Based on these characteristics, the novel sulfotransferase is designated I-GlcNAc6ST for intestinal GlcNAc 6-O-sulfotransferase.

Painful stimulation suppresses joint inflammation by inducing shedding of L-selectin from neutrophils

Although the inflammatory response is essential for protecting tissues from injury and infection, unrestrained inflammation can cause chronic inflammatory diseases such as arthritis, colitis and asthma. Physiological mechanisms that downregulate inflammation are poorly understood. Potent control might be achieved by regulating early stages in the inflammatory response, such as accumulation of neutrophils at the site of injury, where these cells release chemical mediators that promote inflammatory processes including plasma extravasation, bacteriocide and proteolysis. To access an inflammatory site, neutrophils must first adhere to the vascular endothelium in a process mediated in part by the leukocyte adhesion molecule L-selectin. This adhesion is prevented when L-selectin is shed from the neutrophil membrane. Although shedding of L-selectin is recognized as a potentially important mechanism for regulating neutrophils, its physiological function has not been demonstrated. Shedding of L-selectin may mediate endogenous downregulation of inflammation by limiting neutrophil accumulation at inflammatory sites. Here we show that activation of nociceptive neurons induces shedding of L-selectin from circulating neutrophils in vivo and that this shedding suppresses an ongoing inflammatory response by inhibiting neutrophil accumulation. These findings indicate a previously unknown mechanism for endogenous feedback control of inflammation. Failure of this mechanism could contribute to the etiology of chronic inflammatory disease.

Fractalkine, a CX3C chemokine, is expressed by dendritic cells and is up-regulated upon dendritic cell maturation

The lone CX3C chemokine, fractalkine (FK), is expressed in a membrane-bound form on activated endothelial cells and mediates attachment and firm adhesion of T cells, monocytes and NK cells. We now show that FK is associated with dendritic cells (DC) in epidermis and lymphoid organs. In normal human skin, dual-color fluorescence microscopy co-localized FK expression with Langerhans cells expressing CD1a. In tonsil, FK-positive DC expressed CD83, a marker for mature DC. Human and murine cultured DC up-regulated FK mRNA expression with maturation. Furthermore, CD40 ligation, but not TNF-alpha or lipopolysaccharide treatment, of activated, migratory DC that had migrated from skin explants resulted in a 2.5-fold increase of surface expression of FK without significant alterations of expression of CD80, CD86, CD54 or MHC class II. Since FK mediates adhesion of T cells to activated endothelial cells, the increased expression of FK during DC maturation (and particularly by CD40 ligation) may play a role in the ability of T cells and mature DC to form conjugates and engage in cell-cell communication.

Separate oligosaccharide determinants mediate interactions of the low-molecular-weight salivary mucin with neutrophils and bacteria

The low-molecular-weight human salivary mucin (MG2) coats oral surfaces, where it is in a prime location for governing cell adhesion. Since oligosaccharides form many of the interactive facets on mucin molecules, we examined MG2 glycosylation as it relates to the molecule's adhesive functions. Our previous study of MG2 oligosaccharide structures showed that the termini predominantly carry T, sialyl-T, Lewisx (Lex), sialyl Lex (sLex), lactosamine, and sialyl lactosamine determinants [Prakobphol, A., et al. (1998) Biochemistry 37, 4916-4927]. In addition, we showed that sLex determinants confer L-selectin ligand activity to this molecule. Here we studied adhesive interactions between MG2 and cells that traffic in the oral cavity: neutrophils and bacteria. Under flow conditions, neutrophils tethered to MG2-coated surfaces at forces between 1.25 and 2 dyn/cm2, i.e., comparable to the shear stress generated at the tooth surface by salivary flow ( approximately 0.8 dyn/cm2). MG2 was also found in association with neutrophils isolated from the oral cavity, evidence that the cells interact with this mucin in vivo. Since MG2 serves as an adhesion receptor for bacteria, the MG2 saccharides that serve this function were also identified. Seven of 18 oral bacteria strains that were tested adhered to MG2. Importantly, six of these seven strains adhered via T antigen, sialyl-T antigen, and/or lactosamine sequences. No adherence to Lex and sLex epitopes was detected in all the strains that were tested. Together, these results suggest that distinct subsets of MG2 saccharides function as ligands for neutrophil L-selectin and receptors for bacterial adhesion, a finding with interesting implications for both oral health and mucin function.

Sulfotransferases of two specificities function in the reconstitution of high endothelial cell ligands for L-selectin

L-selectin, a lectin-like receptor, mediates rolling of lymphocytes on high endothelial venules (HEVs) in secondary lymphoid organs by interacting with HEV ligands. These ligands consist of a complex of sialomucins, candidates for which are glycosylation- dependent cell adhesion molecule 1 (GlyCAM-1), CD34, and podocalyxin. The ligands must be sialylated, fucosylated, and sulfated for optimal recognition by L-selectin. Our previous structural characterization of GlyCAM-1 has demonstrated two sulfation modifications, Gal-6-sulfate and GlcNAc-6-sulfate in the context of sialyl Lewis x. We now report the cloning of a Gal-6-sulfotransferase and a GlcNAc-6-sulfotransferase, which can modify GlyCAM-1 and CD34. The Gal-6-sulfotransferase shows a wide tissue distribution. In contrast, the GlcNAc-6-sulfotransferase is highly restricted to HEVs, as revealed by Northern analysis and in situ hybridization. Expression of either enzyme in Chinese hamster ovary cells, along with CD34 and fucosyltransferase VII, results in ligand activity, as detected by binding of an L-selectin/IgM chimera. When coexpressed, the two sulfotransferases synergize to produce strongly enhanced chimera binding.

Parametric polar maps of regional myocardial beta-adrenoceptor density

Quantification of myocardial beta-adrenoceptor density (Bmax) is of interest in cardiac diseases in which altered function of the sympathetic nervous system is thought to play a pathophysiological role. PET provides an unrivaled means of taking regional measurements of cardiac microcirculatory function, tissue metabolism and autonomic nervous system activity. Measurements in small regional areas may be biased because of increased noise levels. This study examined the parametric polar map approach for the regional quantification of Bmax.

METHODS

Dynamic PET with parametric polar map imaging was performed in 10 healthy volunteers and 4 patients with hypertrophic cardiomyopathy using (S)-[11C]-(4-(3-tertiarybutylamino-2-hydroxypropoxy)-benzidimaz ole-2)-on hydrochloride (CGP)-12177 and a double-injection protocol. Time-activity curves were corrected for partial volume, spill-over and wall motion effects. The mean Bmax of the left ventricle was calculated in two ways. First, the average time-activity curve of all segments, having the highest achievable signal-to-noise ratio, was used to calculate Bmax(mTAC) (the myocardial beta-adrenoceptor density of the left ventricle calculated using the average time-activity curve). The bias in Bmax(mTAC) introduced by noise is minimal. Second, an estimate of whole-heart receptor density was calculated using the polar map method by averaging the values of Bmax obtained for 576 individual segments. In these calculations, three different filters (3 x 5, 3 x 9 and 3 x 13 segments) were used to smooth the time-activity curves before calculating Bmax. Mean values of whole-left-ventricular receptor density obtained by averaging regional values using the different filters (Bmax(PMF1/2/3)) were compared with Bmax(mTAC) to assess bias introduced by the polar map approach. Segments with a calculated Bmax outside the range 0.1-50 pmol/g were considered unreliable and were excluded from the analysis.

RESULTS

The differences between the two methods of calculating Bmax were small (7.8%, 4.8% and 3.2%, with the three filters, respectively). Reliable results were obtained in >95% of the segments and in 9 volunteers and all 4 patients.

CONCLUSION

When using PET for the quantification of beta-adrenoceptor density, the regional variation in Bmax can be reliably assessed using the parametric polar map approach.

GlyCAM-1 supports leukocyte rolling in flow: evidence for a greater dynamic stability of L-selectin rolling of lymphocytes than of neutrophils

L-selectin plays a major role in leukocyte traffic through lymph node high endothelial venules (HEV). We have investigated the role of GlyCAM-1, a major L-selectin ligand produced by HEV, in mediating leukocyte rolling under in vitro flow conditions. Purified GlyCAM-1 was found to support tethering and rolling in physiological shear flow of both human and murine L-selectin expressing leukocytes at an efficiency comparable to the HEV-derived L-selectin ligands termed peripheral node addressin (PNAd). Major dynamic differences between L-selectin rolling of peripheral blood T lymphocytes and neutrophils expressing similar L-selectin level were observed on GlyCAM-1. Lymphocytes established slower and more shear resistant rolling than neutrophils and could roll on GlyCAM-1 at shear stresses lower than the threshold values required for L-selectin-mediated neutrophil rolling. Notably, high stability of L-selectin rolling of lymphocytes requires intact cellular energy, although initial lymphocyte tethering to L-selectin ligands is energy-independent. By contrast, L-selectin mediated rolling of neutrophils is insensitive to energy depletion. The distinct dynamic behavior and energy-dependence of L-selectin rolling in different leukocytes suggest that L-selectin adhesiveness in shear flow is regulated in a cell-type specific manner. The greater stability of L-selectin rolling of lymphocytes on surface-adsorbed GlyCAM-1 may contribute to their selective recruitment at peripheral lymph nodes.

A high endothelial cell-derived chemokine induces rapid, efficient, and subset-selective arrest of rolling T lymphocytes on a reconstituted endothelial substrate

The homing of lymphocytes to secondary lymphoid organs is thought to involve the action of chemokines. Secondary lymphoid-tissue chemokine (SLC), a high endothelial venule (HEV)-associated chemokine, has emerged as a candidate for participating in this process. We now show that immobilized SLC strongly induces beta2 integrin-mediated binding of T lymphocytes of naive phenotype and B lymphocytes to ICAM-1 under static conditions. This effect is not mediated by beta2 integrin affinity modulation, because SLC does not elicit a beta2 integrin activation epitope (mAb24) on naive T lymphocytes. In a parallel plate flow chamber, lymphocytes rolling via L-selectin are rapidly arrested through beta2 integrins in a pertussis toxin-sensitive manner on a substrate consisting of L-selectin ligands (peripheral lymph node addressins) together with ICAM-1 and SLC. Naive T lymphocytes are arrested on the HEV substrate with sixfold higher efficiency than memory cells. Neutrophils roll, but are not arrested by SLC, whereas they respond to immobilized IL-8 with rapid arrest. Thus, our artificial HEV system recapitulates critical features of lymphocyte interactions with HEV in vivo. These observations strongly point to the participation of SLC in homing of lymphocytes to secondary lymphoid organs.

Normal values for left ventricular volumes obtained using gated PET

BACKGROUND

Accurate assessment of left ventricular (LV) volumes provides important insights into myocardial function, being particularly important for diseases of the heart in which there is progressive dilatation of the LV, such as remodeling after myocardial infarction. We have recently validated a method for measuring LV volumes using gated positron emission tomography (PET) with oxygen-15 labeled carbon monoxide (C15O). The present study was performed to establish normal values for LV volumes, in absolute units, using this technique.

METHODS

Forty subjects [21 males and 19 females; age 49 +/- 13 years (mean +/- SD), range 24-80; body surface area (BSA) range 1.50-2.18 m2] were studied. End diastolic (EDV) and end systolic volumes (ESV) were calculated by determining the edge of the end diastolic and end systolic blood pool images (obtained using PET with C15O) and summing the volume of the voxels comprising the blood pool.

RESULTS

For the overall study population, EDV was 109 +/- 20 ml and ESV 37 +/- 12 ml. When stratified according to gender, these values were: in males, EDV was 117 +/- 18 ml and ESV 42 +/- 18 ml; in females, EDV was 100 +/- 19 ml and ESV 32 +/- 8 ml. The differences between gender groups (EDV: p = 0.0027, ESV: p = 0.0029) were eliminated when volumes were corrected for BSA.

CONCLUSIONS

These data will form a database of normal values for comparison with pathological conditions of the heart. PET quantification of LV volumes offers a means of measurement of function using an imaging modality that can also assess regional myocardial perfusion and metabolism during the same study session.

Pitfalls in the economic evaluation of thrombolysis in myocardial infarction. The impact of national differences in the cost of thrombolytics and of differences in the efficacy across patient subgroups

BACKGROUND

The economic evaluation of the results of the Global Utilization of Streptokinase and Tissue Plasminogen Activator for Occluded Coronary Artery (GUSTO) trial found that recombinant tissue plasminogen activator is more cost-effective than streptokinase for the treatment of acute myocardial infarction.

AIM

We evaluated the impact on a cost effectiveness analysis, of the differences in the cost of thrombolytics among countries and of differences in efficacy across patient subgroups.

METHODS

We considered the crude costs of streptokinase and recombinant tissue plasminogen activator in Germany, Italy, the United Kingdom, and the United States of America, and the 30-day mortality found in the GUSTO trial. We calculated the incremental costs for each life saved when streptokinase is substituted by recombinant tissue plasminogen activator. We also calculated the incremental costs for each life saved for two protocols implying a selective use of streptokinase and recombinant tissue plasminogen activator (age-selective protocol: recombinant tissue plasminogen activator in patients < or = 75 years, streptokinase in older patients; site-selective protocol: recombinant tissue plasminogen activator in anterior acute myocardial infarction, streptokinase in non-anterior acute myocardial infarction).

RESULTS

The incremental costs for each life saved when streptokinase is substituted by recombinant tissue plasminogen activator in all GUSTO patients vary greatly among countries: the incremental costs for each life saved are 31%, 45%, and 97% higher in Germany, Italy, and the United States of America compared to the United Kingdom. The use of a site-selective protocol implies a halved cost-effectiveness ratio compared to the use of recombinant tissue plasminogen activator in all cases of acute myocardial infarction.

CONCLUSIONS

(1) The cost-efficacy of recombinant tissue plasminogen activator vs streptokinase in acute myocardial infarction varies greatly among countries due to differences in the cost of drugs. (2) A selective use of thrombolytics for some sites of infarction is more cost-effective than the exclusive use of recombinant tissue plasminogen activator.

Identification of an N-acetylglucosamine-6-0-sulfotransferase activity specific to lymphoid tissue: an enzyme with a possible role in lymphocyte homing

BACKGROUND

The leukocyte adhesion molecule L-selection participates in the initial attachment of blood-borne lymphocytes to high endothelial venules (HEVs) during lymphocyte homing to secondary lymphoid organs, and contributes to leukocyte adhesion and extravasation in HEV-like vessels at sites of chronic inflammation. The L-selection ligands on lymph mode HEVs are mucin-like glycoproteins adorned with the unusual sulfated carbohydrate epitope, 6-sulfo sialyl Lewis x. Sulfation of this epitope on the N-acetylglucosamine (GlcNAc) residue confers high-avidity L-selection binding, and is thought to be restricted in the vasculature to sites of sustained lymphocyte recruitment. The GlcNAc-6-0 sulfotransferase that installs the sulfate ester may be a key modulator of lymphocyte recruitment to secondary lymphoid organs and sites of chronic inflammation and is therefore a potential target for anti-inflammatory therapy.

RESULTS

A GlcNAc-6-0-sulfotransferase activity was identified within porcine lymph nodes and characterized using a rapid, sensitive, and quantitative assay. We synthesized two unnatural oligosaccharide substrates, GlcNAc beta 1-->6Gal alpha-R and Gal beta 1-->4GlcNAc beta 1-->6Gal alpha-R, that incorporate structural motifs from the native L-selection ligands into an unnatural C-glycosyl hydrocarbon scaffold. The sulfotransferase incorporated greater than tenfold more sulfate into the disaccharide than the trisaccharide, indicating a requirement for a terminal GlcNAc. Activity across tissues was highly restricted to the HEVs within peripheral lymph node.

CONCLUSIONS

The restricted expression of the GlcNAc-6-0-sulfotransferase activity to lymph node HEVs strongly suggestions a role in the biosynthesis of L-selection ligands. In addition, similar sulfated epitopes are known to be expressed on HEV-like vessels of chronically inflamed tissues; indicating that this sulfotransferase may also contribute to inflammatory lymphocyte recruitment. We identified a concise disaccharide motif, GlcNAc beta 1-->6Gal alpha-R, that preserved both recognition and specificity determinants for the GlcNAc-6-0-sulfotransferase. The absence of activity on the trisaccharide Gal beta 1-->6Gal alpha-R indicates a requirement for a substrate with a terminal GlcNAc residue, suggesting that sulfation precedes further biosynthetic assembly of L-selection ligands.

Measurement of myocardial blood flow with oxygen-15 labelled water: comparison of different administration protocols

Positron emission tomography (PET) in conjunction with C15O2 or H215O can be used to measure myocardial blood flow (MBF) and tissue fraction (TF), i.e. the fraction of the tissue mass in the volume of the region of interest. However, with C15O2 inhalation, the tissue fraction in the septum is overestimated. Bolus injection of H215O together with arterial cannulation gives very precise results but is invasive. The purpose of this study was to develop a method which circumvents these problems. A four-parameter model with parameters for MBF, TF and spill-over fractions from both left and right ventricular cavities was developed. This method was compared with a three-parameter model (no right ventricular cavity spill-over) in both septal and non-septal regions of interest for three different administration protocols: bolus injection of H215O, infusion of H215O and inhalation of C15O2. It was found that MBF can be measured with intravenous administration of H215O without the requirement for arterial cannulation. The four-parameter protocol with bolus injection was stable in clinical studies. The four-parameter model proved essential for the septum, where it gave highly significantly better fits than did the three-parameter model (P<0.00003 in each of 15 subjects). Administration of H215O together with this four-parameter model also circumvented the problem of overestimation of TF in the septum seen with C15O2 inhalation. In addition, the radiation dose of H215O protocols is lower than that of C15O2 inhalation. Using a left atrial input curve instead of a left ventricular cavity input curve gave the same mean MBF and TF.

Identification of podocalyxin-like protein as a high endothelial venule ligand for L-selectin: parallels to CD34

The leukocyte adhesion molecule, L-selectin, mediates the recruitment of lymphocytes to secondary lymphoid organs via interactions with specific ligands presented on high endothelial venules (HEV). Although the HEV-derived ligands for L-selectin are still incompletely defined, they share a common sialomucin-like structure which is thought to present clustered oligosaccharides to the lectin domain of L-selectin. Podocalyxin-like protein (PCLP) is a transmembrane sialomucin that is similar in structure to the well-characterized L-selectin ligand CD34. PCLP has been shown previously to be expressed on the foot processes of podocytes in the kidney glomerulus as well as on vascular endothelium at some sites. We have determined that PCLP is present on HEV, where it binds to both recombinant L-selectin and the HEV-specific monoclonal antibody MECA-79. Furthermore, purified HEV-derived PCLP is able to support the tethering and rolling of lymphocytes under physiological flow conditions in vitro. These results suggest a novel function for PCLP as an adhesion molecule and allow the definition of conserved structural features in PCLP and CD34, which may be important for L-selectin ligand function.

Human low-molecular-weight salivary mucin expresses the sialyl lewisx determinant and has L-selectin ligand activity

Previously we showed that the low-molecular-weight mucin (MG2, encoded by MUC7), a major component of human submandibular/sublingual saliva, is a bacterial receptor that coats the tooth surface. Here we tested the hypothesis that the structure of its carbohydrate residues contains important information about its function. Purified MG2 (Mr 120 000) was digested with trypsin, and the resulting Mr 90 000 fragment, which carried primarily O-linked oligosaccharides, was subjected to reductive beta-elimination. The released oligosaccharides were characterized by using nuclear magnetic resonance spectroscopy and mass spectrometry. Of the 41 different structures we detected, the most prominent included NeuAcalpha2-->3Galbeta1-->3GalNAc-ol (sialyl-T antigen), Galbeta1-->4(Fucalpha1-->3)GlcNAcbeta1-->6(Galbeta1 -->3)GalNAc-ol [type 2 core with Lewisx (Lex) determinant], and NeuAcalpha2-->3Galbeta1-->4(Fucalpha1-->3)GlcNAcbet a1-->6(Galbeta1--> 3) GalNAc-ol [type 2 core with sialyl Lex (sLex) determinant]. We also detected di-, tri-, and pentasaccharides with one sulfate group. Lex, sLex, and related sulfated structures are ligands for selectins, adhesion molecules that mediate leukocyte trafficking. Therefore, we investigated whether MG2 was a selectin ligand. In an enzyme-linked immunosorbent assay, L-selectin chimeras interacted with immobilized MG2 in a Ca2+-dependent manner. L-Selectin chimeras also bound to MG2 immobilized on nitrocellulose. Together, these results suggest that the saccharides that MG2 carries could specify some of its important functions, which may include mediating leukocyte interactions in the oral cavity.

Regional myocardial blood flow redistribution as a cause of postprandial angina pectoris

BACKGROUND

Postprandial angina pectoris has been recognized for more than two centuries and can be identified in up to 10% of patients with chronic ischemic heart disease. Redistribution of myocardial blood flow, from a region supplied by a severely stenotic coronary artery to those supplied by less diseased or normal vessels, is a potential mechanism of postprandial angina.

METHODS AND RESULTS

To test this hypothesis, we have determined the effects of a standard liquid meal on whole heart and regional myocardial blood flow, measured by means of dynamic positron emission tomography (PET) with 15O-labeled water in 14 patients with a reproducible history of postprandial angina and 7 matched control subjects. The standard liquid meal precipitated angina pectoris in all patients. Baseline whole heart blood flow was similar and increased normally after the meal in patients (0.97+/-0.14 to 1.14+/-0.25 mL.min(-1).g(-1), P<.04) as in control subjects (0.92+/-0.12 to 1.02+/-0.13 mL.min(-1).g(-1), P<.02). In contrast, the coefficient of variation of blood flow increased significantly after the standard liquid meal in patients (34+/-9%, P<.05 versus baseline) but not in control subjects (17+/-7%, P=NS versus baseline). In patients, analysis of regional myocardial blood flow demonstrated decreased myocardial blood flow in territories supplied by stenotic arteries (1.01+/-0.35 to 0.76+/-0.27 mL.min(-1).g(-1), P<.03), but there was an increase in blood flow in territories supplied by normal arteries (0.89+/-0.16 to 1.34+/-0.25 mL.min(-1).g(-1), P<.001) after the meal.

CONCLUSIONS

The standard liquid meal induced angina pectoris in patients with coronary artery disease. Although whole heart blood flow increased appropriately for the greater cardiac work, there was a redistribution of regional blood flow from territories supplied by severely stenosed coronary arteries to those supplied by less diseased or normal arteries. This redistribution may be the cause of myocardial ischemia in postprandial angina.

Affinity and kinetic analysis of L-selectin (CD62L) binding to glycosylation-dependent cell-adhesion molecule-1

The selectin family of cell adhesion molecules mediates the tethering and rolling of leukocytes on blood vessel endothelium. It has been postulated that the molecular basis of this highly dynamic adhesion is the low affinity and rapid kinetics of selectin interactions. However, affinity and kinetic analyses of monomeric selectins binding their natural ligands have not previously been reported. Leukocyte selectin (L-selectin, CD62L) binds preferentially to O-linked carbohydrates present on a small number of mucin-like glycoproteins, such as glycosylation-dependent cell adhesion molecule-1 (GlyCAM-1), expressed in high endothelial venules. GlyCAM-1 is a soluble secreted protein which, following binding to CD62L, stimulates beta2-integrin-mediated adhesion of lymphocytes. Using surface plasmon resonance, we show that a soluble monomeric form of CD62L binds to purified immobilized GlyCAM-1 with a dissociation constant (Kd) of 108 microM. CD62L dissociates from GlyCAM-1 with a very fast dissociation rate constant (>/=10 s-1) which agrees well with the reported dissociation rate constant of CD62L-mediated leukocyte tethers. The calculated association rate constant is >/=10(5) M-1 s-1. At concentrations just above its mean serum level (approximately 1.5 microg/ml or approximately 30 nM), GlyCAM-1 binds multivalently to immobilized CD62L. It follows that soluble GlyCAM-1 may cross-link CD62L when it binds to cells, suggesting a mechanism for signal transduction.