Glycation impairs high-density lipoprotein function

AIMS/HYPOTHESIS

To examine the effects of incubation of high-density lipoprotein (HDL) under hyperglycaemic conditions on several functions of HDL in vitro.

METHODS

Human HDL (5 mg protein) was incubated for 1 week at 37 degrees C in the presence or absence of 25 mmol/l glucose. Additional samples of human HDL were incubated in butylated hydroxytoluene to control for oxidation.

RESULTS

High-density lipoprotein incubated for 1 week in 25 mmol/l glucose had significant increases in the glycation product, fructoselysine and in the advanced glycation end product, N epsilon-(carboxymethyl)-lysine. High-density lipoprotein apolipoprotein AI and AII concentrations were not altered but glycated HDL had a 65% reduction in paraoxonase enzymatic activity. Glycated HDL did not inhibit monocyte adhesion to human aortic endothelial cells in response to oxidised low-density lipoprotein in vitro (43 +/- 4 monocytes bound vs 21 +/- 2 monocytes for control HDL, p < 0.0001). Hepatic lipase-mediated non-esterified fatty acid release from HDL lipids was enhanced in glycated HDL compared with control HDL (25 +/- 1 vs 16 +/- 1 nmol non-esterified fatty acid hydrolysed/min, respectively, p < 0.0001). Direct glycation of purified paraoxonase protein by incubation in 25 mmol/l glucose caused a 40% reduction in enzymatic activity. This glycated paraoxonase did not inhibit monocyte adhesion to human aortic endothelial cells in vitro (68 +/- 3 monocytes vs 49 +/- 2 monocytes bound for control paraoxonase, respectively, p < 0.001). We also measured a 40% reduction in paraoxonase activity in patients with Type II (non-insulin-dependent) diabetes mellitus and documented coronary artery disease compared with non-diabetic subjects, p < 0.0001.

CONCLUSIONS/INTERPRETATION

Alterations in function of HDL caused by exposure to hyperglycaemic conditions could contribute to the accelerated atherosclerosis observed in Type II diabetes.

Somatostatin receptor subtype 2A expression in the rat retina

Somatostatin is mainly expressed by sparsely occurring amacrine and interplexiform cells in the retina. In this study, we characterized the expression and cellular localization of one of the somatostatin subtype (sst) receptors, sst2A, in the rat retina. The presence of sst2A receptor messenger RNA in retinal extracts was demonstrated by reverse transcription-polymerase chain reaction using specific primers to detect the sst2 receptor and its isoforms, sst2A and sst2B. Specific sst2A receptor immunoreactivity was mainly localized to the plasma membrane of several neuronal cell types. In the outer retina, immunoreactivity was localized to cone photoreceptors, horizontal cells, and rod and cone bipolar cells. Double-label experiments showed the co-localization of sst2A receptor and protein kinase C (alpha and beta), a rod bipolar cell marker, and of sst2A receptor and Calbindin-D28k, a horizontal cell marker. In the inner retina, sst2A receptor immunoreactivity occurred in tyrosine hydroxylase-positive amacrine cells; most were of medium to large size. These findings indicate that somatostatin may act at a distance, in a paracrine manner, on several cell types that express the sst2A receptor, and therefore exert a broad modulatory influence on both scotopic and photopic visual pathways.

Hypothermia decreases excitatory neurotransmitter release in bacterial meningitis in rabbits

The excitatory neurotransmitters glutamate (GLU) and aspartate (ASP) are involved in the pathogenesis of neuronal injury in meningitis. Based on past findings that the induction of moderate hypothermia (32-34 degrees C) attenuates the release of GLU in ischemic brain injury, this study was designed to detect if the application of moderate hypothermia decreases the release of excitatory amino acids (EAA) from brain tissue of animals with bacterial meningitis. Also examined was whether meningitis induces the expression of 72-kDa heat shock protein (HSP 70) in the cerebellum and how hypothermia affects it, for induction of HSP 70 has been used as a sensitive marker of neuronal stress in other forms of brain injury. Meningitis was induced by injecting Group B Streptococcus (GBS) into the cisterna magnae of rabbits. Antibiotic treatment began 16 h later. At this time the animals were anesthetized, instrumented, and randomized to normothermic (Nor) or hypothermic (Hy) conditions. Temperatures were strictly regimented for the following 10 h while maintaining stable cardiorespiratory parameters. Cerebrospinal fluid (CSF) samples were then withdrawn to measure concentrations of bacteria, protein, and amino acids. Meningitis causes CSF contents of GLU and ASP to increase significantly. Hypothermia treated animals demonstrated a 40-50% reduction in CSF GLU and ASP. Meningitis induced the expression of HSP 70 in the cerebellum while hypothermic animals experienced a significant decrease HSP 70 induction. These data demonstrate that hypothermia produces an attenuation of the release of excitatory neurotransmitters in meningitis and suggest that this treatment may attenuate neuronal stress.

Expression of cholecystokinin A receptors in neurons innervating the rat stomach and intestine

BACKGROUND & AIMS

Two distinct receptors, cholecystokinin (CCK)-A and CCK-B, mediate CCK effects in the digestive system. The aim of this study was to elucidate the cellular sites of expression of CCK-A receptor in the rat stomach and small intestine.

METHODS

We developed and characterized an antibody to the N-terminal region (LDQPQPSKEWQSA) of rat CCK-A receptor and used it for localization studies with immunohistochemistry.

RESULTS

Specificity of the antiserum was demonstrated by (1) detection of a broad band at 85-95 kilodaltons in Western blots of membranes from CCK-A receptor CHO-transfected cells; (2) cell surface staining of CCK-A receptor-transfected cells, (3) translocation of CCK-A receptor immunostaining in CCK-A receptor-transfected cells after exposure to CCK; and (4) abolition of tissue immunostaining by preadsorbtion of the antibody with the peptide used for immunization. CCK-A receptor immunoreactivity was localized to myenteric neurons and to fibers in the muscle and mucosa. In the stomach, myenteric neurons and mucosal fibers were abundant. Many CCK-A receptor myenteric neurons contained the inhibitory transmitter vasoactive intestinal polypeptide, and some were immunoreactive for the excitatory transmitter substance P. Subdiaphragmatic vagotomy reduced the density of CCK-A receptor fibers in the gastric mucosa by approximately 50%, whereas celiac/superior mesenteric ganglionectomy had no detectable effect on fiber density.

CONCLUSIONS

CCK-A receptor is expressed in functionally distinct neurons of the gastrointestinal tract. CCK-A receptor may mediate reflexes stimulated by CCK through the release of other transmitters from neurons bearing the receptor.

Differential inhibition of insulin and islet amyloid polypeptide secretion by intraislet somatostatin in the isolated perfused human pancreas

Islet amyloid polypeptide (IAPP) and insulin are co-stored and generally secreted in parallel; however, studies have demonstrated that the IAPP/insulin molar secretory ratio may be altered in response to certain stimuli. Because we previously demonstrated that intraislet somatostatin is an inhibitory regulator of basal insulin secretion in the isolated perfused human pancreas, this study was designed to determine the relative influence on the regulation of IAPP versus insulin secretion. Single-pass perfusion was performed in pancreata obtained from cadaveric organ donors with continuous perfusion of a modified Krebs media with the glucose level maintained at constant 3.9 mM. Intraislet somatostatin was immunoneutralized by the infusion of either a highly sensitive monoclonal somatostatin antibody (SAb) or its FAb fragment (SFAb). Sequential test periods separated by basal periods were performed by infusion of either of the following: glucose, SAb, SFAb, or appropriate controls. IAPP/insulin molar secretory ratio decreased by 33% in response to infusion of either SAb or the SFAb, respectively (p < 0.01), and decreased by 67% in response to glucose infusion (p < 0.01). An alteration of the IAPP/insulin secretory ratio is seen in response to infusion of exogenous glucose or in response to the neutralization of intraislet somatostatin.

Market factors and the availability of community pharmacies

The purpose of this study was to examine the relationships between the availability of community pharmacies and 4 types of market factors. A composite data set was created that linked, at the county level, data on: (1) type and number of pharmacies; (2) population characteristics; (3) payer variables; (4) health care system factors; and (5) competitive factors. In this exploratory study, secondary data were used to assess the association between the availability of community pharmacies and the influence of market factors. To assess the market influences on availability of community pharmacies, 2 regressions were performed. In 1 model, the number of community pharmacies per 10,000 population was the dependent variable, whereas the dependent variable in the other regression was the proportion of independently owned community pharmacies. The independent variables in each regression were the market factors--population characteristics, payer variables, health care system factors, and competitive variables. Squared terms were included for 8 of 15 market factors to account for nonlinearities in the relationships. Multiple market factors were correlated with both the number of community pharmacies and the proportion of independently owned pharmacies in an area. Several of the relationships were not linear and changed direction within the range of data. Counties with either a low or a high percentage of elderly people had fewer pharmacies and a lower proportion of independently owned pharmacies compared with counties with a moderate percentage of elderly people. Counties that were scarcely or highly rural had fewer community pharmacies but a higher proportion of independently owned pharmacies than counties that were moderately rural. Areas with a greater percentage of the population earning less than the poverty level had more pharmacies, especially independently owned ones. Fewer community pharmacies were found in areas with higher health maintenance organization penetration rates. The number of hospital admissions was positively associated with the number of pharmacies but negatively associated with the proportion of independently owned pharmacies. The availability of community pharmacies varies across the country. In light of the trend toward fewer independently owned pharmacies, potential problems in accessing pharmacy services could develop in certain areas, including those that are highly rural and those with a high percentage of people earning less than the poverty level. Future research and policy issues are identified.

Rhinovirus-16 colds in healthy and in asthmatic subjects: similar changes in upper and lower airways

Rhinovirus (RV) infections appear to precipitate most asthma exacerbations. To investigate whether RV-16 induces different inflammatory changes in upper and lower airways of asthmatic and healthy subjects, we inoculated 10 nonatopic healthy and 11 atopic asthmatic adults with 2,000 TCID50 RV-16. Subjects recorded symptoms and peak flow daily; and they underwent spirometry, methacholine challenge (PC20), nasal lavage, and sputum induction at baseline and on Days 2, 4, 15, and 29 d after inoculation. One asthmatic subject developed an exacerbation requiring prednisone treatment 5 d after inoculation. The cold symptom severity (Jackson score) did not differ between groups. During the cold, asthma symptoms increased slightly from baseline in the asthmatic group; and PC20 decreased in the healthy group. However, peak flow, bronchodilator use, and spirometry did not change in either group. At baseline, asthmatics had higher neutrophils, eosinophils, and interleukin (IL)-6 in nasal lavage. After inoculation, both groups developed significant increases in nasal neutrophils, IL-6 and IL-8, and modest increases in sputum neutrophils and IL-6, but not IL-8. However, these changes did not differ between groups. IL-5, interferon-gamma, and RANTES were detected only in nasal lavages from two asthmatic subjects, who had the most severe colds. IL-11 was not detected in any sample. We conclude that inflammatory responses of upper and lower airways during RV-16 colds are similar in asthmatic and healthy subjects, and that RV-16 infection is not by itself sufficient to provoke clinical worsening of asthma.

Hepatic triglyceride lipase promotes low density lipoprotein receptor-mediated catabolism of very low density lipoproteins in vitro

We demonstrate here that hepatic triglyceride lipase (HTGL) enhances VLDL degradation in cultured cells by a LDL receptor-mediated mechanism. VLDL binding at 4 degrees C and degradation at 37 degrees C by normal fibroblasts was stimulated by HTGL in a dose-dependent manner. A maximum increase of up to 7-fold was seen at 10 microg/ml HTGL. Both VLDL binding and degradation were significantly increased (4-fold) when LDL receptors were up-regulated by treatment with lovastatin. HTGL also stimulated VLDL degradation by LDL receptor-deficient FH fibroblasts but the level of maximal degradation was 40-fold lower than in lovastatin-treated normal fibroblasts. A prominent role for LDL receptors was confirmed by demonstration of similar HTGL-promoted VLDL degradation by normal and LRP-deficient murine embryonic fibroblasts. HTGL enhanced binding and internalization of apoprotein-free triglyceride emulsions, however, this was LDL receptor-independent. HTGL-stimulated binding and internalization of apoprotein-free emulsions was totally abolished by heparinase indicating that it was mediated by HSPG. In a cell-free assay HTGL competitively inhibited the binding of VLDL to immobilized LDL receptors at 4 degrees C suggesting that it may directly bind to LDL receptors but may not bind VLDL particles at the same time. We conclude that the ability of HTGL to enhance VLDL degradation is due to its ability to concentrate lipoprotein particles on HSPG sites on the cell surface leading to LDL receptor-mediated endocytosis and degradation.

Trafficking of proteinase-activated receptor-2 and beta-arrestin-1 tagged with green fluorescent protein. beta-Arrestin-dependent endocytosis of a proteinase receptor

Proteases cleave proteinase-activated receptors (PARs) to expose N-terminal tethered ligands that bind and activate the cleaved receptors. The tethered ligand, once exposed, is always available to interact with its binding site. Thus, efficient mechanisms must prevent continuous activation, including receptor phosphorylation and uncoupling from G-proteins, receptor endocytosis, and lysosomal degradation. beta-Arrestins mediate uncoupling and endocytosis of certain neurotransmitter receptors, which are activated in a reversible manner. However, the role of beta-arrestins in trafficking of PARs, which are irreversibly activated, and the effects of proteases on the subcellular distribution of beta-arrestins have not been examined. We studied trafficking of PAR2 and beta-arrestin1 coupled to green fluorescent protein. Trypsin induced the following: (a) redistribution of beta-arrestin1 from the cytosol to the plasma membrane, where it co-localized with PAR2; (b) internalization of beta-arrestin1 and PAR2 into the same early endosomes; (c) redistribution of beta-arrestin1 to the cytosol concurrent with PAR2 translocation to lysosomes; and (d) mobilization of PAR2 from the Golgi apparatus to the plasma membrane. Overexpression of a C-terminal fragment of beta-arrestin-319-418, which interacts constitutively with clathrin but does not bind receptors, inhibited agonist-induced endocytosis of PAR2. Our results show that beta-arrestins mediate endocytosis of PAR2 and support a role for beta-arrestins in uncoupling of PARs.

Substance P-induced trafficking of beta-arrestins. The role of beta-arrestins in endocytosis of the neurokinin-1 receptor

Agonist-induced redistribution of G-protein-coupled receptors (GPCRs) and beta-arrestins determines the subsequent cellular responsiveness to agonists and is important for signal transduction. We examined substance P (SP)-induced trafficking of beta-arrestin1 and the neurokinin-1 receptor (NK1R) in KNRK cells in real time using green fluorescent protein. Green fluorescent protein did not alter function or localization of the NK1R or beta-arrestin1. SP induced (a) striking and rapid (<1 min) translocation of beta-arrestin1 from the cytosol to the plasma membrane, which preceded NK1R endocytosis; (b) redistribution of the NK1R and beta-arrestin1 into the same endosomes containing SP and the transferrin receptor (2-10 min); (c) prolonged colocalization of the NK1R and beta-arrestin1 in endosomes (>60 min); (d) gradual resumption of the steady state distribution of the NK1R at the plasma membrane and beta-arrestin1 in the cytosol (4-6 h). SP stimulated a similar redistribution of immunoreactive beta-arrestin1 and beta-arrestin2. In contrast, SP did not affect Galphaq/11 distribution, which remained at the plasma membrane. Expression of the dominant negative beta-arrestin319-418 inhibited SP-induced endocytosis of the NK1R. Thus, SP induces rapid translocation of beta-arrestins to the plasma membrane, where they participate in NK1R endocytosis. beta-Arrestins colocalize with the NK1R in endosomes until the NK1R recycles and beta-arrestins return to the cytosol.

An immunohistochemical marker for Wallerian degeneration of fibers in the central and peripheral nervous system

This work was prompted by the accidental observation that a newly developed, affinity purified polyclonal antibody against the C-terminus of the neuropeptide tyrosine (NPY) Y1-receptor protein decorates degenerating fibers in the central nervous system (CNS). This staining did not appear in control animals in which the antibody marked perikarya and dendrites at previously described locations [X. Zhang, L. Bao, Z.-Q. Xu, J. Kopp, U. Arvidsson, R. Elde, T. Hökfelt, Localization of neuropeptide Y Y1-receptors in the rat nervous system with special reference to somatic receptors on small dorsal root ganglion neurons, Proc. Natl. Acad. Sci. USA 91 (1994) 11738-11742]. Three models of experimental lesions were studied: sciatic nerve transection, spinal cord transection and parietal cortex thermocoagulation. In each model, animals were divided in groups (n=2) and processed for indirect immunofluorescence at different time intervals up to 28 days post-lesion (PL) (see below). All three experimental lesions produced a very intense immunolabeling of fibers in the projection pathways of the lesioned structures, strongly reminding of Wallerian degeneration (WD). In the sciatic nerve, the staining first appeared on day 1 PL, was strongly increased on day 3 PL, then declined after 7 days and had almost completely disappeared after 14 days. In the CNS, the staining appeared later and was first observed on day 3 PL and remained for a longer period, thus showing different time courses in the brain and spinal cord as compared to the sciatic nerve. The labeling was completely abolished, both in the CNS and in the sciatic nerve, by pre-incubation of the Y1-R antibody with the immunogenic peptide at a dilution of 10-6 M. The appearance of the staining and its time course strongly suggest that the process was related to degenerating axons. Although the protein actually detected remains to be determined, it is suggested that the staining ability of this antibody could be used as a positive marker of axonal degeneration following experimental or naturally occurring lesions of the nervous system.

Gelatinase-A (MMP-2), gelatinase-B (MMP-9) and membrane type matrix metalloproteinase-1 (MT1-MMP) are involved in different aspects of the pathophysiology of malignant gliomas

Matrix metalloproteinases (MMPs) have been implicated as important factors in gliomas since they may both facilitate invasion into the surrounding brain and participate in neovascularization. We have tested the hypothesis that deregulated expression of gelatinase-A or B, or an activator of gelatinase-A, MT1-MMP, may contribute directly to human gliomas by quantifying the expression of these MMPs in 46 brain tumour specimens and seven control tissues. Quantitative RT-PCR and gelatin zymography showed that gelatinase-A in glioma specimens was higher than in normal tissue; these were significantly elevated in low grade gliomas and remained elevated in GBMs. Gelatinase-B transcript and activity levels were also higher than in normal brain and more strongly correlated with tumour grade. We did not see a close relationship between the levels of expression of MT1-MMP mRNA and amounts of activated gelatinase-A. In situ hybridization localized gelatinase-A and MT1-MMP transcripts to normal neuronal and glia, malignant glioma cells and blood vessels. In contrast, gelatinase-B showed a more restricted pattern of expression; it was strongly expressed in blood vessels at proliferating margins, as well as tumour cells in some cases. These data suggest that gelatinase-A, -B and MT1-MMP are important in the pathophysiology of human gliomas. The primary role of gelatinase-B may lie in remodelling associated with neovascularization, whereas gelatinase-A and MT1-MMP may be involved in both glial invasion and angiogenesis. © 1999 Cancer Research Campaign

Gelatinase-A (MMP-2), gelatinase-B (MMP-9) and membrane type matrix metalloproteinase-1 (MT1-MMP) are involved in different aspects of the pathophysiology of malignant gliomas

Matrix metalloproteinases (MMPs) have been implicated as important factors in gliomas since they may both facilitate invasion into the surrounding brain and participate in neovascularization. We have tested the hypothesis that deregulated expression of gelatinase-A or B, or an activator of gelatinase-A, MT1-MMP, may contribute directly to human gliomas by quantifying the expression of these MMPs in 46 brain tumour specimens and seven control tissues. Quantitative RT-PCR and gelatin zymography showed that gelatinase-A in glioma specimens was higher than in normal tissue; these were significantly elevated in low grade gliomas and remained elevated in GBMs. Gelatinase-B transcript and activity levels were also higher than in normal brain and more strongly correlated with tumour grade. We did not see a close relationship between the levels of expression of MT1-MMP mRNA and amounts of activated gelatinase-A. In situ hybridization localized gelatinase-A and MT1-MMP transcripts to normal neuronal and glia, malignant glioma cells and blood vessels. In contrast, gelatinase-B showed a more restricted pattern of expression; it was strongly expressed in blood vessels at proliferating margins, as well as tumour cells in some cases. These data suggest that gelatinase-A, -B and MT1-MMP are important in the pathophysiology of human gliomas. The primary role of gelatinase-B may lie in remodelling associated with neovascularization, whereas gelatinase-A and MT1-MMP may be involved in both glial invasion and angiogenesis.

Intracisternal TRH analog increases gastrin release and corpus histidine decarboxylase activity in rats

Thyrotropin-releasing hormone (TRH) acts in brain stem nuclei to induce vagally mediated stimulation of gastric secretion. The effects of intracisternal injection of the TRH analog RX-77368 on plasma gastrin levels and corpus histidine decarboxylase (HDC) activity were studied in 48-h fasted conscious rats. RX-77368 (25-100 ng) increased plasma gastrin levels by threefold at 30 min, which remained significantly higher than control at 2 and 4 h postinjection. Corpus HDC activity began to increase at 2 h and reached a peak at 4 h postinjection with a 21-fold maximum response observed at 50 ng. Morphological changes in the appearance of corpus HDC-immunoreactive cells correlated well with HDC activity. Pretreatment with gastrin monoclonal antibody completely prevented RX-77368 stimulatory effects on HDC activity. Atropine significantly attenuated gastrin increase at 30 min by 26%. These results indicated that in conscious fasted rats, TRH analog acts in the brain to increase corpus HDC activity in the enterochromaffin-like cells, which involves gastrin release stimulated by central TRH analog.

Characterization of Moraxella (Branhamella) catarrhalis lbpB, lbpA, and lactoferrin receptor orf3 isogenic mutants

Pathogenic members of the family Neisseriaceae produce specific receptors to acquire iron from their host's lactoferrin and transferrin. Recently, putative Moraxella catarrhalis lactoferrin receptor genes and a third open reading frame (lbpB, lbpA, and orf3) were cloned and sequenced. We describe the preliminary characterization of isogenic mutants deficient in LbpB, LbpA, or Orf3 protein.

Intestinal fat-induced inhibition of meal-stimulated gastric acid secretion depends on CCK but not peptide YY

Fat in small intestine decreases meal-stimulated gastric acid secretion and slows gastric emptying. CCK is a mediator of this inhibitory effect (an enterogastrone). Because intravenously administered peptide YY (PYY) inhibits acid secretion, endogenous PYY released by fat may also be an enterogastrone. Four dogs were equipped with gastric, duodenal, and midgut fistulas. PYY antibody (anti-PYY) at a dose of 0.5 mg/kg or CCK-A receptor antagonist (devazepide) at a dose of 0.1 mg/kg was administered alone or in combination 10 min before the proximal half of the gut was perfused with 60 mM oleate or buffer. Acid secretion and gastric emptying were measured. We found that 1) peptone-induced gastric acid secretion was inhibited by intestinal fat (P < 0.0001), 2) inhibition of acid secretion by intestinal fat was reversed by CCK-A receptor antagonist (P < 0.0001) but not by anti-PYY, and 3) slowing of gastric emptying by fat was reversed by CCK-A antagonist (P < 0. 05) but not by anti-PYY. We concluded that inhibition of peptone meal-induced gastric acid secretion and slowing of gastric emptying by intestinal fat depended on CCK but not on circulating PYY.

Endogenous glucocorticoids released during acute toxic liver injury enhance hepatic IL-10 synthesis and release

Endogenous glucocorticoids are known to play a role in the regulation of the inflammatory response possibly by modulating pro- and anti-inflammatory cytokine expression. We examined endogenous glucocorticoid secretion, hepatic damage, tumor necrosis factor-alpha (TNF-alpha), and interleukin-10 (IL-10) mRNA expression and release in rats treated with carbon tetrachloride (CCl4) after treatment with vehicle or a glucocorticoid receptor antagonist (RU-486). Rats treated with CCl4 demonstrated striking elevations of plasma corticosterone levels. Inhibition of endogenous glucocorticoid activity by pretreatment with the glucocorticoid receptor antagonist RU-486 resulted in augmented CCl4-mediated hepatotoxicity, as reflected by histology and serum transaminase levels, which were independent of alterations in serum TNF-alpha levels or hepatic mRNA expression. CCl4 treatment resulted in enhanced hepatic IL-10 mRNA expression and elevated serum IL-10 levels, which were markedly attenuated by glucocorticoid receptor blockade. In summary, significant endogenous glucocorticoid release occurs during acute toxic liver injury in the rat and suppresses the inflammatory response independent of effects on TNF-alpha but possibly by upregulating hepatic IL-10 production.

The pituitary adenylate cyclase activating polypeptide type 1 receptor (PAC1-R) is expressed on gastric ECL cells: evidence by immunocytochemistry and RT-PCR

The current study was undertaken to determine the presence and distribution of PAC1-Rs within the gastric mucosa. Polyclonal antibodies to the carboxyl terminus of the rat PAC1-R were generated and shown to be specific against the PAC1-R expressed in NIH 3T3 cells. Western blot analysis using isolated (approximately 85% pure) ECL cell membranes identified a 48 kD protein consistent with the calculated molecular mass of the cloned PAC1-R. RT/PCR performed using specific primers for the PAC1-R confirmed the presence of splice variants of the rat PAC1-R, but not VPAC1-R or VPAC2-R. These data provide the first direct evidence for the existence of functional PACAP Type I receptors on ECL cells of the gastric mucosa and suggest a potential role for PACAP in the stimulation of gastric acid secretion and in the regulation of the growth of ECL cells.

Subdomain chimeras of hepatic lipase and lipoprotein lipase. Localization of heparin and cofactor binding

To specify and localize carboxyl-terminal domain functions of human hepatic lipase (HL) and human lipoprotein lipase (LPL), two subdomain chimeras were created in which portions of the carboxyl-terminal domain were exchanged between the two lipases. The first chimera (HL-LPLC1) was composed of residues 1-344 of human HL, residues 331-388 of human LPL, and residues 415-476 of human HL. The second chimera (HL-LPLC2) consisted of just two segments, residues 1-414 of human HL and residues 389-448 of human LPL. These chimeric constructs effectively divided the HL C-terminal domain into halves, with corresponding LPL sequences either in the first or second portion of that domain. Both chimeras were lipolytically active and hydrolyzed triolein emulsions to a similar extent compared with native HL and LPL. Heparin-Sepharose chromatography demonstrated that HL-LPLC1 and HL-LPLC2 eluted at 0.80 and 1.3 M NaCl, respectively, elution positions that corresponded to native HL and LPL. Hence, substitution of LPL sequences into the HL carboxyl-terminal domain resulted in the production of functional lipases, but with distinct heparin binding properties. In addition, HL-LPLC2 trioleinase activity was responsive to apoC-II activation, although the -fold stimulation was less than that observed with native LPL. Moreover, an apoC-II fragment (residues 44-79) was specifically cross-linked to LPL and HL-LPLC2, but not to HL or HL-LPLC1. Finally, both chimeras hydrolyzed phospholipid with a specific activity similar to that of HL, which was unaffected by the presence of apoC-II. These findings indicated that in addition to a region found within the amino-terminal domain of LPL, apoC-II also interacted with the last half of the carboxyl-terminal domain (residues 389-448) to achieve maximal lipolytic activation. In addition, the relative heparin affinity of HL and LPL was determined by the final 60 carboxyl-terminal residues of each enzyme.

Bacterial lactoferrin receptors

Lactoferrin is thought to play a pivotal role in prevention of infection in the host and its ability to sequester iron from potential pathogens has been considered an important component of its antimicrobial function. A number of bacterial species in the Neisseriaceae have developed a mechanism for acquiring iron directly from this host glycoprotein which involves surface receptors capable of specifically binding lactoferrin. Initial attempts at identifying the receptor proteins in Neisseria and Moraxella species using affinity isolation with immobilized lactoferrin under high stringency conditions presumptively identified a single 100 kDa receptor protein, LbpA (formerly Lbp1). Under modified affinity isolation conditions a second 84 kDa lactoferrin binding protein was isolated and had been presumptively identified as LbpB. This protein was not isolated from a CopB-ve isogenic mutant of Moraxella catarrhalis, indicating that it was in fact CopB. However, another lactoferrin binding protein isolated under high stringency conditions, that comigrated with LbpA in most, but not all, M. catarrhalis strains, was identified by convalescent antisera. Its biochemical properties suggested that it indeed was LbpB. The identity of these proteins was confirmed by preparing isogenic mutants with the lbpA and lbpB genes. Growth studies with isogenic mutants deficient in LbpB, LbpA, CopB or FbpA were performed to evaluate their role in iron acquisition from lactoferrin. LbpA and FbpA were essential for this process, supporting prior models of the iron acquisition pathway. LbpB was not essential which is remniscent of studies with the bacterial transferrin receptors. The isogenic CopB-ve isogenic mutants were deficient in iron acquisition from both transferrin and lactoferrin, suggesting that it is a key component in both pathways. A model providing an alternate explanation of the data is presented. The role and surface accessibility of the lactoferrin receptor proteins suggests that they might be useful vaccine antigens and the preferentially reactivity of convalescent antisera with LbpB suggests that it may be the prime candidate.

Substance P (neurokinin-1) receptor is a marker of human mucosal but not peripheral mononuclear cells: molecular quantitation and localization

Reciprocal communication between the immune system and the neuroendocrine system is mediated via a common chemical language of shared ligands and receptors. The neuropeptide substance P (SP) has been implicated as a mediator of immunomodulation. The evidence for substance P receptors on human lymphocytes is, however, controversial. The aims of the present study are to investigate substance P receptor (SPR) expression in human peripheral and mucosal mononuclear cells and to identify cellular sites of expression in human colonic mucosa. Using reverse-transcriptase PCR, we demonstrate that PBMC isolations are negative for SPR mRNA expression, whereas lamina propria mononuclear cell (LPMC) isolations express on average eight SPR mRNA transcripts per cell. In situ hybridization performed on surgically resected colonic tissue confirms the expression of SPR mRNA in LPMC in vivo. SPR mRNA signal was detected in LPMC, lymphoid follicles, and epithelium. The complementary technique of immunohistochemistry gave a similar distribution of SPR expression that colocalized with CD45 immunoreactivity. Dual-fluorochrome flow cytometry revealed SPR expression by CD4, CD45RO, CD45RA, CD8, CD19, and CD14 LPMC subsets, but not PBMC. Our findings suggest that SPR expression is distinctive of human colonic mucosal mononuclear cells and support a direct role for SP in mucosal immunomodulation.

Galanin inhibition of enterochromaffin-like cell function

BACKGROUND & AIMS

Galanin, a 29-amino acid neuropeptide found in the gastric mucosa, inhibits basal and pentagastrin-stimulated acid secretion. Its cellular target is unknown. The aim of this study was to determine whether galanin inhibits Ca2+ signaling and histamine release in enterochromaffin-like (ECL) cells.

METHODS

Isolated rat ECL cells were purified to 85% homogeneity by a combination of elutriation, density gradient centrifugation, and 48-hour culture. Intracellular calcium concentration ([Ca2+]i) was determined using video imaging with Fura-2 in a 37 degreesC superfusion chamber. Histamine was measured by radioimmunoassay.

RESULTS

Reverse-transciption polymerase chain reaction of the ECL cell RNA showed a galanin type I receptor subtype. Galanin inhibited gastrin, Bay K8644, and K+ depolarization-induced calcium mobilization and entry as well as reduced basal calcium levels. Pretreatment with pertussis toxin decreased the effect of galanin. Galanin inhibited basal and gastrin-stimulated histamine release by approximately 60% with a median effective concentration of 1.10(-10) mol/L. The inhibitory actions of galanin on histamine release and Ca2+ influx could be reduced by a galanin antagonist, galantide.

CONCLUSIONS

Galanin's inhibition of acid secretion can be explained in part by inhibition of calcium signaling and histamine release from the ECL cells due to activation of a Gi,o protein-coupled receptor.