Immunotherapy with oral administration of humanized anti-CD3 monoclonal antibody: a novel gut-immune system-based therapy for metaflammation and NASH.

The immune system plays a role in the pathogenesis of non-alcoholic steatohepatitis (NASH) underlying hepatocyte injury and fibrosis progression at all disease stages. Oral administration of anti-CD3 monoclonal antibody (mAb) has been shown in preclinical studies to be an effective method for systemic immune modulation and alleviates immune-mediated disorders without T cell depletion. In the present review, we summarize the concept of the oral administration of humanized anti-CD3 mAb in patients with NASH and discuss the potential of this treatment to address the current requirements of treatments for NASH. Recently published preclinical and clinical data on oral administration of anti CD3 are discussed. Human trials have shown that the oral administration of anti-CD3 in healthy volunteers, patients with chronic hepatitis C virus (HCV) infection and patients with NASH and type 2 diabetes is safe and well tolerated, as well as biologically active. Oral anti-CD3 induces regulatory T cells, suppresses the chronic inflammatory state associated with NASH and exerts a beneficial effect on clinically relevant parameters. Foralumab is a fully human anti-CD3 mAb that has recently been shown to exert a potent anti-inflammatory effect in humanized mice. It is being developed for treatment of NASH and primary biliary cholangitis (PBC). Oral administration of anti CD3 may provide an effective therapy for patients with NASH.

Uroguanylin treatment suppresses polyp formation in the Apc(Min/+) mouse and induces apoptosis in human colon adenocarcinoma cells via cyclic GMP.

The enteric peptides, guanylin and uroguanylin, are local regulators of intestinal secretion by activation of receptor-guanylate cyclase (R-GC) signaling molecules that produce cyclic GMP (cGMP) and stimulate the cystic fibrosis transmembrane conductance regulator-dependent secretion of Cl- and HCO3-. Our experiments demonstrate that mRNA transcripts for guanylin and uroguanylin are markedly reduced in colon polyps and adenocarcinomas. In contrast, a specific uroguanylin-R-GC, R-GCC, is expressed in polyps and adenocarcinomas at levels comparable with normal colon mucosa. Activation of R-GCC by uroguanylin in vitro inhibits the proliferation of T84 colon cells and elicits profound apoptosis in human colon cancer cells, T84. Therefore, down-regulation of gene expression and loss of the peptides may interfere with renewal and/or removal of the epithelial cells resulting in the formation of polyps, which can progress to malignant cancers of the colon and rectum. Oral replacement therapy with human uroguanylin was used to evaluate its effects on the formation of intestinal polyps in the Min/+ mouse model for colorectal cancer. Uroguanylin significantly reduces the number of polyps found in the intestine of Min/+ mice by approximately 50% of control. Our findings suggest that uroguanylin and guanylin regulate the turnover of epithelial cells within the intestinal mucosa via activation of a cGMP signaling mechanism that elicits apoptosis of target enterocytes. The intestinal R-GC signaling molecules for guanylin regulatory peptides are promising targets for prevention and/or therapeutic treatment of intestinal polyps and cancers by oral administration of human uroguanylin.

Purification and characterization of a lymph node sulfotransferase responsible for 6-O-sulfation of the galactose residues in 2'-fucosyllactose and other sialyl LewisX-related sugars.

A microsomal galactose-6-O-sulfotransferase (Gal-6-O-Stase) from porcine lymph nodes, able to transfer the sulfate group from adenosine 3'-phosphate 5'-phosphosulphate (PAPS) onto 2'-fucosyllactose (2'-FL) and other sialyl LewisX (sLex)-related sugars, has been purified and characterized. The enzyme was purified to about 35,000-fold by a combination of conventional and affinity chromatographic steps. The purified enzyme preparation exhibited two protein bands at around 80-90 and 170 kDa on 7.5% SDS-PAGE under reducing conditions. Both of these protein bands always comigrated in the gel when peak fractions containing Gal-6-O-Stase activity from the 3',5'-ADP-agarose column were subjected to 6% SDS-PAGE under reducing conditions. These protein bands also showed similar binding patterns to WGA (wheat germ agglutinin), Con A (concanvalin A), and EBA (elderberry agglutinin). Similarly, when the enzyme preparation after the hydroxylapatite step was photolabeled with 8-azido-[32P]-PAPS, both 80-90 and 170 kDa protein bands were labeled in a specific manner. These results suggest a possible association of these two protein bands with the enzyme activity. The carbohydrate substrate specificity of this enzyme suggests that it is well suited to catalyze the sulphonation at the C-6 position of the galactose residues of oligosaccharides that are structurally similar to sLex. Furthermore, a survey of several porcine organs revealed that this enzyme was selectively expressed in lymphoid tissues such as lymph nodes (peripheral and mesenteric) and spleen. These findings suggest that this enzyme may be involved in the assembly of 3'-sialyl-6'-sulfo Lewisx, the major capping group of HEV-ligands for L-selectin.

Isolation and characterization from porcine serum of a soluble sulfotransferase responsible for 6-O-sulfation of the galactose residue in 2'-fucosyllactose: implications in the synthesis of the ligand for L-selectin.

A soluble sulfotransferase from porcine serum which catalyzes the transfer of sulfate from adenosine 3'-phosphate 5'-phosphosulphate (PAPS) to 2'-fucosyllactose (2'-FL) was purified 36,333-fold using a combination of conventional and affinity chromatographic steps. The purified enzyme preparation after non-denaturing discontinuous-PAGE exhibited a molecular mass of about 80 kDa by reducing SDS-PAGE. However, when a partially purified enzyme preparation was subjected to gel filtration on Sephacryl S-300, the enzyme activity eluted in the void volume, which indicated that the native enzyme existed as an oligomer. The purified enzyme showed Km values of 9.15 microM for PAPS and 15.38 mM for 2'-FL at the optimum pH value of 7.4. The substrate specificity of the purified enzyme was evaluated with various sugars that are structurally similar to sialyl LewisX (sLeX). Results indicated that 3'-sialyllactose and lactose were efficient acceptors of sulfation, whereas 6'-sialyllactose and 6'-sialyllactosamine were poor substrates for this sulfotransferase. Further, the reaction product analysis revealed that the sulfate substitution, when using 2'-FL as the substrate, was at the C-6 position of the galactose residue. Coincidentally, a similar enzyme activity was also found in porcine lymphoid tissues such as, lymph nodes (peripheral and mesenteric) and spleen. Collectively, these findings suggest that this enzyme might be involved in the synthesis of the ligand for L-selectin.

Sulfation and sialylation requirements for a glycoform of CD34, a major endothelial ligand for L-selectin in porcine peripheral lymph nodes.

Leukocyte recruitment from blood into peripheral lymph nodes is controlled in part by a specific interaction of lymphocyte-associated L-selectin with endothelial cell receptors known as peripheral addressins. In murine lymph nodes, two peripheral addressins have been identified, Gly-CAM-1, a 50 kDa molecule that also appears as a secreted form in plasma, and CD34, a 90 kDa membrane-associated sialomucin. A predominant 105 kDa CD34 mucin-like protein has also been identified in human tonsil as peripheral addressin. We have identified a 120 kDa sialomucin as the predominant peripheral addressin in porcine lymph nodes. Validation of the 120 kDa porcine molecule as a peripheral addressins was based on its ability to bind MECA-79, a monoclonal antibody previously used to isolate peripheral addressins from mouse and human tissues, and to bind an L-selectin-Fc chimera (LS-Fc). The binding with LS-Fc was abolished in the presence of fucoidin, a sulfated polysaccharide known to inhibit L-selectin-receptor interactions. To address the possibility that the 120 kDa ligand may contain common recognition determinants for MECA-79 and L-selectin, the requirements for sialylation and sulfation were compared. Whereas desialylation of 120 kDa ligand drastically reduced its binding to LS-Fc, this treatment appeared to enhance the binding of 120 kDa ligand to MECA-79. In contrast, the binding of both MECA-79 and LS-Fc to 120 kDa ligand was drastically reduced when de novo sulfation of this ligand was reduced by including chlorate, a metabolic inhibitor of sulfation, in the culture media. N-Terminal amino acid sequences of the porcine 120 kDa protein revealed homology with human CD34. Taken together, these findings suggest that the porcine 120 kDa peripheral addressin is an L-selectin-binding glycoform of CD34.

An enzymatic procedure for the preparation and purification of 3'-phosphoadenosine 5'-phospho-[35S]sulfate ([35S]PAPS): applications in syntheses of 8-azido and 8-bromo derivatives of [35S]PAPS.

This paper describes a rapid and an efficient procedure for the enzymatic synthesis of 3'-phosphoadenosine 5'-phospho[35S]sulfate ([35S]PAPS). [35S]PAPS was synthesized by incubating ATP and a carrier-free [35S]-Na2(35)SO4 with ATP sulfurylase, a recombinant APS kinase and inorganic pyrophosphatase. The transfer of 35SO4 group from [35S]Na2SO4 to [35S]PAPS proceeded more efficiently in the presence of an ATP-regenerating system composed of pyruvate kinase and phosphoenol pyruvate. About 90% of the radioactivity present in the starting material [35S]Na2SO4 was transferred to [35S]PAPS within a 2-h reaction incubation. The reaction products were applied to a Mono Q column, and [35S]PAPS was eluted by a step-wise gradient of triethylamine bicarbonate buffer (pH 7.5). Under these conditions, [35S]PAPS eluted as a sharp peak at 0.7 M triethylammonium bicarbonate and it was very well separated from other contaminants. The purified [35S]PAPS (yield 85%, purity > 95%) was functional in donating sulfate to an oligosaccharide acceptor in a standard sulfotransferase reaction. The enzymatic procedure described above was particularly useful for the synthesis of [35S]PAPS at a wide range of concentrations and specific activities (up to 1500 Ci/mmol). This generally useful approach was also found to be successful in the syntheses of 8-azido and 8-bromo derivatives of [35S]PAPS. Applications of these two derivatives of PAPS, for purification and identification of sulfotransferases, have also been discussed.

Polysulfated derivatives of beta-cyclodextrin and myo-inositol as potent inhibitors of the interaction between L-selectin and peripheral addressin: implying a requirement for highly clustered sulfate groups.

We have utilized an in vitro assay that measures the binding of an L-selectin-human Fc chimera (LS-Fc) to [35S]sulfate labelled peripheral addressin (PNAd), a 120 kDa glycoprotein ligand for L-selectin in porcine lymph nodes, to evaluate inhibitory properties of a small group of sulfated derivatives of beta-cyclodextrin (beta-CD), sLe(x) and myo-inositol to their non-sulfated counterparts were studied. We found that hepta-sulfated beta-CD (IC50 = 0.2 mM) strongly inhibited the binding of L-selectin to PNAd. In contrast, the monosulfated beta-CD was a poor inhibitor, displaying < 10% inhibition at 0.5 mM and beta-CD was not active as an inhibitor. Similarly, inositol hexakissulfate, a compound containing six sulfate groups on the inositol ring displayed an inhibition of about 61% at 0.5 mM concentration, whereas the non-sulfated myoinositol was not inhibitory. These findings provide evidence that clustering of sulfate groups enhances affinity of molecules for binding to L-selectin.

Enzymatic synthesis of a 6'-sulphated sialyl-Lewisx which is an inhibitor of L-selectin binding to peripheral addressin.

A sulphated form of sialyl-Lewisx, NeuAc alpha 2-3Gal beta 1-4(Fuc alpha 1-3)GlcNAc6OSO3 beta 1-3Gal, was synthesized enzymatically from a precursor disaccharide, GlcNAc6OSO3 beta 1-3Gal, using sequential steps involving beta 1,4-galactosyltransferase, alpha 2,3-trans-sialidase and recombinant alpha 1,3-fucosyltransferase, respectively. Successful enzymatic fucosylation at the 3 position of the GlcNAc6OSO3 residue demonstrated that fucosyltransferase are capable of generating, in situ, sulphated sialyl Lewisx structures containing sulphate at the 6 position of GlcNAc. The sulphated sialyl-Lewisx pentasaccharide produced by this procedure inhibited binding of a soluble form of L-selectin to 35SO4-labelled peripheral addressin with an IC50 of 0.8 mM, whereas sialyl-Lewisx tetrasaccharide was a weaker inhibitor, displaying an IC50 of 3.2 mM. Hemmerich and Rosen (Biochemistry, 33, 4820-4829, 1994) recently reported the presence of Gal beta 1-4GlcNAcO6SO3 structures on murine peripheral addressin Sgp50, in addition to sialyl Lewisx structures sulphated at the 6-O-galactose position. Based on our data, we suggest that sialyl Lewisx sulphated at the 6-O-GlcNAc position may also exist on receptors and function as a ligand for L-selectin.

Glucosidase I, a transmembrane endoplasmic reticular glycoprotein with a luminal catalytic domain.

We have analyzed the functional domain structure of rat mammary glucosidase I, an enzyme involved in N-linked glycoprotein processing, using biochemical and immunological approaches. The enzyme contains a high mannose type sugar chain that can be cleaved by endo-beta-N-acetyl-D-glucosaminidase H without significantly affecting the catalytic activity. Based on trypsin digestion pattern and the data on membrane topography, glucosidase I constitutes a single polypeptide chain of 85 kDa with two contiguous domains: a membrane-bound domain that anchors the protein to the endoplasmic reticulum and a luminal domain. A catalytically active 39-kDa domain could be released from membranes by limited proteolysis of saponin-permeabilized membranes with trypsin. This domain appeared to contain the active site of the enzyme and had the ability to bind to glucosidase I-specific affinity gel. Phase partitioning with Triton X-114 indicated the amphiphilic nature of the native enzyme, consistent with its location as an integral membrane protein, whereas the 39-kDa fragment partitioned in the aqueous phase, a characteristic of soluble polypeptide. These results indicate that glucosidase I is a transmembrane protein with a luminally oriented catalytic domain. Such an orientation of the catalytic domain may facilitate the sequential processing of asparagine-linked oligosaccharide, soon after its transfer en bloc by the oligosaccharyl transferase complex in the lumen of endoplasmic reticulum.

Studies on hormonal modulation of asparagine-linked glycoprotein biosynthesis in explant cultures of rat mammary gland.

Glucosidase I has been purified to homogeneity and polyclonal antibodies against the enzyme have been prepared. The anti-glucosidase I antibodies recognized a single band of 85 kDa on western blot at a dilution as high as 1:2000 and also inhibited the enzyme activity, suggesting the specificity of the antibodies. Con A-Sepharose binding experiment indicates that this enzyme itself is a high mannose type N-linked glycoprotein. The increase in the electrophoretic mobility of 85 kDa band following digestion with endoglycosidase H and F strengthened this observation. The presence of any O-linked sugar attached covalently to glucosidase I could not be detected by binding assays with O-linkage specific biotinylated lectins. The studies on developmental regulation suggest that the synthesis of glucosidase I is modulated with the ontogeny of the gland. Lactogenic hormones, viz. insulin, hydrocortisone and prolactin, appeared to regulate the synthesis of glucosidase I. The possible role of these hormones in the overall regulation of protein N-glycosylation has been discussed.

Photoaffinity labeling of glucosyltransferase of the dolichol cycle from rat mammary gland.

UDP-Glc:dolichol phosphate glucosyltransferase from lactating rat mammary gland has been partially purified by a combination of (NH4)2SO4 fractionation, gel filtration, ion-exchange chromatography on DEAE-TSK, and affinity chromatography. The partially purified enzyme exhibited several protein bands when examined by 10% sodium dodecyl sulfate-polyacrylamide gel electrophoresis under reducing conditions; among these, a 35-kDa polypeptide was quite prominent and appeared to be enriched during purification. Photoaffinity labeling of the partially purified enzyme preparation with 5-azido-[beta-32P]UDP-Glc identified a 35-kDa polypeptide. Labeling of a solubilized enzyme preparation from crude and stripped microsomes also revealed a 35-kDa band on 10% sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Photoinsertion of the probe in this polypeptide is enhanced by the presence of dolichol phosphate and Mg2+. Competition studies with UDP-Glc, UDP-glucuronic acid, other sugar nucleotides, and Glc-1-phosphate provide evidence to validate the specificity of photoaffinity labeling. These studies indicate that this 35-kDa polypeptide is involved in the synthesis of dolichol-P-Glc in rat mammary tissue. The possibility that this polypeptide may represent glucosyltransferase has been discussed.

Developmental regulation of glucosidase I, an enzyme involved in the processing of asparagine-linked glycoproteins in rat mammary gland.

Glucosidase I involved in the processing of N-linked glycoproteins was purified to homogeneity from the lactating rat mammary gland. The purified enzyme exhibited a single band at 85 kDa on 10% sodium dodecyl sulfate-polyacrylamide gel electrophoresis under reducing conditions. Polyclonal antibodies raised against the enzyme recognized a similar band on Western blots and also inhibited the enzyme activity. The enzyme levels gradually increased until the midlactation stage and thereafter declined sharply during the period of postlactation. A similar profile of the levels of immunoreactive glucosidase I was observed. These findings suggest that the accumulation of glucosidase I is modulated as a function of gland ontogeny. The results on hormonal regulation of glucosidase I indicate that the synthesis of the enzyme is stimulated by a combination of insulin, hydrocortisone, and prolactin; additionally, epidermal growth factor may play a role in this regulation. The above observation was substantiated by immunoprecipitation of [35S]methionine-labeled microsomal extracts with anti-glucosidase I antibodies. The immunoprecipitation of soluble extracts from [35S]methionine-labeled tissue with anti-rat alpha-lactalbumin antibodies indicates that these hormones not only stimulate the synthesis of alpha-lactalbumin but also play an important role in its glycosylation.

Purification and characterization of UDP-N-acetyl-D-glucosamine:dolichol phosphate N-acetyl-D-glucosamine-1-phosphate transferase involved in the biosynthesis of asparagine-linked glycoproteins in the mammary gland.

The GlcNAc-1-P-transferase that initiates the dolichol cycle for the biosynthesis of asparagine-linked glycoproteins has been purified from the lactating bovine mammary gland. After solubilization from microsomes with 0.25% Nonidet P-40, the enzyme activity was stabilized with 20% glycerol, 20 micrograms/ml phosphatidylglycerol, 5 microM dolichol phosphate, and 2.5 microM UDP-GlcNAc. The purification protocol involved (NH4)2SO4 precipitation, gel filtration on Sephacryl S-300, DEAE-TSK, and hydroxylapatite chromatography. The purified enzyme was devoid of several readily detectable glycosyltransferases of the dolichol cycle. It showed two bands (A, 50 kDa and B, 46 kDa) on sodium dodecyl sulfate-polyacrylamide gel electrophoresis after either Coomassie Blue or silver staining. Antisera (anti-A and anti-B) raised against individual bands A and B inhibited the enzyme activity in solubilized microsomes. Each of the partially purified antibodies recognizes both bands A and B on Western blots of the enzyme; with the solubilized microsomes, the antibodies also recognize an additional polypeptide of approximately 70 kDa. When radioiodinated microsomes were immunoprecipitated with anti-B and subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis, again bands of 46, 50, and 70 kDa were observed. The peptide mapping of 50 and 46 kDa bands of the purified enzyme by chemical cleavage with N-chlorosuccinimide gave similar fragmentation patterns. The results indicate that either 70 kDa band is a precursor form of the enzyme or this polypeptide, representing the native enzyme or its subunit, is proteolyzed to smaller, enzymatically active peptide(s) of 50 and 46 kDa during purification despite the inclusion of several inhibitors against serine-proteases in all buffers used for tissue homogenization and enzyme purification. A number of properties of the purified enzyme, including its specific activation by Man-P-Dol were also characterized.

Purification and characterization of glucosidase I involved in N-linked glycoprotein processing in bovine mammary gland.

Glucosidase I, the first enzyme involved in the post-translational processing of N-linked glycoproteins, was purified to homogeneity from the lactating bovine mammary tissue. The enzyme was extracted by differential treatment of the microsomal fraction with Triton X-100 and Lubrol PX. The solubilized enzyme was subjected to affinity chromatography on Affi-Gel 102 with N-5-carboxypentyldeoxynojirimycin as ligand and DEAE-Sepharose CL-6B chromatography. Purified glucosidase I shows a molecular mass of 320-330 kDa by gel filtration on Sephacryl S-300. SDS/polyacrylamide-gel electrophoresis under reducing conditions indicates a single band of approx. 85 kDa, indicating that the native enzyme is probably a tetrameric protein. Several criteria, including pH optimum of 6.6-7.0, specific hydrolytic action towards Glc3Man9GlcNAc2, to release the terminally alpha-1,2-linked glucosyl residue, and total lack of activity towards Glc1Man9GlcNAc2 and Glc2Man9GlcNAc2 saccharides, which are the biological substrates for processing glucosidase II, and 4-methylumbelliferyl alpha-D-glucopyranoside show the non-lysosomal origin and the processing-specific role of the purified enzyme. The enzyme does not require any metal ions for its activity. Hg2+, Ag+ and Cu2+ are potent inhibitors of the enzyme; this inhibition can be reversed by adding an excess of dithiothreitol. Among the saccharides tested, kojibiose (Glc alpha 1----2Glc) was inhibitory to the enzyme. Polyclonal antibodies raised against the enzyme in rabbit were found to be specific for glucosidase I, as revealed by Western-blot analysis and by immunoadsorption with Protein A-Sepharose. Anti-(glucosidase I) antibodies were cross-reactive towards a similar antigen in solubilized microsomal preparations from liver, mammary gland and heart from the bovine, guinea pig, rat and mouse.

Purification and characterization of glucosidase II involved in N-linked glycoprotein processing in bovine mammary gland.

Glucosidase II is an endoplasmic-reticulum-localized enzyme that cleaves the two internally alpha-1,3-linked glucosyl residues of the oligosaccharide Glc alpha 1----2Glc alpha 1----3Glc alpha 1----3Man5-9GlcNAc2 during the biosynthesis of asparagine-linked glycoproteins. We have purified this enzyme to homogeneity from the lactating bovine mammary gland. The enzyme is a high-mannose-type asparagine-linked glycoprotein with a molecular mass of approx. 290 kDa. Upon SDS/polyacrylamide-gel electrophoresis under reducing conditions, the purified enzyme shows two subunits of 62 and 64 kDa, both of which are glycosylated. The pH optimum is between 6.6 and 7.0. Specific polyclonal antibodies raised against the bovine mammary enzyme also recognize a similar antigen in heart, liver and the mammary gland of bovine, guinea pig, rat and mouse. These antibodies were used to develop a sensitive enzyme-linked immunosorbent assay for glucosidase II.