Major histocompatibility class I molecules present Urtica dioica agglutinin, a superantigen of vegetal origin, to T lymphocytes

Inhibitory potency of the nettle lectin on neovascularization: a biomolecule for carbohydrate-mediated targeting of angiogenesis

BACKGROUND

Current angiogenesis inhibitors target cellular vascularization processes, including proliferation, migration, and tube formation. In this study, we investigated the impact of Urtica dioica agglutinin (UDA) on the cellular vascularization process.

METHODS AND RESULTS

Various concentrations of UDA were applied to normal (HUVEC, MCF-10 A, and HDF from humans, and L-929 from mice) and cancer (A431 and U87 from humans, and 4T1 from mice) cell lines at different times. The MTT, cell migration assay, differentiation of endothelial cells, expression of VEGF-A/VEGF-R2, and integrin α2 were evaluated. The MTT results demonstrated that UDA was non-toxic to normal cells while inhibiting the growth of neoplastic cells. The migratory capacity of HUVECs and U87 glioblastoma cells was inhibited by UDA in the wound repair model. This lectin inhibited HUVEC-induced vessel sprouting in the collagen-cytodex matrix. In addition, UDA treatment reduced VEGF-integrin cross-talk in HUVECs, confirming the anti-angiogenic activity of this molecule.

CONCLUSIONS

Based on our findings, UDA may have an effect on cancer cell proliferation and vascularization events while causing minimal toxicity to normal cells via binding glyco-conjugates containing GlcNAc/man oligomers like EGFR. This is a blue clue for the angiogenesis-related therapeutic importance of UDA.

The effect of nettle (Urtica dioica) supplementation on the glycemic control of patients with type 2 diabetes mellitus: A systematic review and meta-analysis

Type 2 diabetes mellitus (T2DM) is a major health problem, worldwide, that is associated with increased morbidity and mortality. Several randomized controlled clinical trials (RCTs) have investigated the effect of nettle (Urtica dioica) supplementation on markers of glycemic status in patients with T2DM, with conflicting results. Therefore, the present study assessed the effect of nettle on some glycemic parameters in patients with T2DM. A comprehensive search was conducted in PubMed, Scopus, Cochrane Library, and Web of Science, from database inception up to June 2019, to identify RCTs investigating the effect of nettle supplementation on glycemic markers, including fasting blood sugar (FBS) concentrations, insulin levels, homeostasis model assessment-estimated insulin resistance index, and glycosylated hemoglobin percentage in adults with T2DM. The Cochrane Collaboration tool was used to assess the methodological quality of the included studies. Results of this meta-analysis were reported based on the random effects model. Eight RCTs, comprising 401 participants, were included in the present systematic review and meta-analysis. Based on the Cochrane Collaboration risk of bias tool, five studies were considered as good quality, one was fair, and two studies were poor, respectively. The results of the meta-analysis revealed a significant reduction in FBS concentrations (weighted mean difference [WMD]: -18.01 mg/dl, 95% confidence interval [CI]: -30.04 to -5.97, p < .001, I² = 94.6%) following nettle supplementation. However, no significant reduction was observed in insulin levels (WMD: 0.83 Hedges' g, 95% CI: -0.26 to 1.92, p = .13, I² = 89.4%), homeostasis model assessment-estimated insulin resistance index (WMD: -0.22, 95% CI: -0.83 to 0.40, p = .49, I² = 69.2%), or glycosylated hemoglobin percentage (WMD: -0.77%, 95% CI: -1.77 to 0.22, p = .12, I² = 83.0%). The findings of the present study suggest that nettle supplementation may be effective in controlling FBS for T2DM patients. However, further studies are needed to confirm the veracity of these results.

Combining 3D structure with glycan array data provides insight into the origin of glycan specificity

Defining how a glycan-binding protein (GBP) specifically selects its cognate glycan from among the ensemble of glycans within the cellular glycome is an area of intense study. Powerful insight into recognition mechanisms can be gained from 3D structures of GBPs complexed to glycans; however, such structures remain difficult to obtain experimentally. Here an automated 3D structure generation technique, called computational carbohydrate grafting, is combined with the wealth of specificity information available from glycan array screening. Integration of the array data with modeling and crystallography allows generation of putative co-complex structures that can be objectively assessed and iteratively altered until a high level of agreement with experiment is achieved. Given an accurate model of the co-complexes, grafting is also able to discern which binding determinants are active when multiple potential determinants are present within a glycan. In some cases, induced fit in the protein or glycan was necessary to explain the observed specificity, while in other examples a revised definition of the minimal binding determinants was required. When applied to a collection of 10 GBP-glycan complexes, for which crystallographic and array data have been reported, grafting provided a structural rationalization for the binding specificity of >90% of 1223 arrayed glycans. A webtool that enables researchers to perform computational carbohydrate grafting is available at www.glycam.org/gr (accessed 03 March 2016).

Proteins that bind high-mannose sugars of the HIV envelope

A broad range of proteins bind high-mannose carbohydrates found on the surface of the envelope protein gp120 of the human immunodeficiency virus and thus interfere with the viral life cycle, providing a potential new way of controlling HIV infection. These proteins interact with the carbohydrate moieties in different ways. A group of them interacts as typical C-type lectins via a Ca2+ ion. Another group interacts with specific single, terminal sugars, without the help of a metal cation. A third group is involved in more intimate interactions, with multiple carbohydrate rings and no metal ion. Finally, there is a group of lectins for which the interaction mode has not yet been elucidated. This review summarizes, principally from a structural point of view, the current state of knowledge about these high-mannose binding proteins and their mode of sugar binding.

Modulatory effect of Urtica dioica L. (Urticaceae) leaf extract on biotransformation enzyme systems, antioxidant enzymes, lactate dehydrogenase and lipid peroxidation in mice

The effects of two doses (50 and 100 mg/kg body wt given orally for 14 days) of an ethanol-water (80%-20%) extract of Urtica dioica L. and butylated hydroxyanisole (BHA) were investigated, for phase I and phase II enzymes, antioxidant enzymes, lactate dehydrogenase, lipid peroxidation and sulfhydryl groups in the liver of Swiss albino mice (8-9 weeks old). A modulatory effect of two doses and BHA was also observed for the activities of glutathione S-transferase, DT-diaphorase, superoxide dismutase and catalase in the kidney, lung and forestomach, as compared with the control group. The activities of cytochrome b5 (cyt b5), NADH-cytochrome b5 reductase (cyt b5 R), glutathione S-transferase (GST), DT-diaphorase (DTD), glutathione peroxidase (GPx), glutathione reductase (GR), superoxide dismutase (SOD) and catalase (CAT) showed a significant increase in the liver at both dose levels of extract. Both extract-treated showed significantly lower activity of cytochrome P450 (cyt P450), lactate dehydrogenase (LDH), NADPH-cytochrome P450 reductase (cyt P450 R), total sulfhydryl groups (T-SH), nonprotein sulfhydryl groups (NP-SH) and protein-bound sulfhydryl groups (PB-SH). BHA-treated Swiss albino mice showed a notable increase in levels of cyt b5, DTD, T-SH, PB-SH, GPx, GR, and SOD in the liver while, LDH, cyt P450, cyt P450 R, Cyt b5 R, GST, NP-SH, and CAT levels were reduced significantly as compared to control values. The extract was effective in inducing GST, DTD, SOD and CAT activity in the forestomach and SOD and CAT activity in the lung at both dose levels. BHA-treated Swiss albino mice induced DTD, GST and all antioxidative parameters in the kidney, lung and forestomach.

Survey of the 1999 surface plasmon resonance biosensor literature

The application of surface plasmon resonance biosensors in life sciences and pharmaceutical research continues to increase. This review provides a comprehensive list of the commercial 1999 SPR biosensor literature and highlights emerging applications that are of general interest to users of the technology. Given the variability in the quality of published biosensor data, we present some general guidelines to help increase confidence in the results reported from biosensor analyses.

Crystal structure of Urtica dioica agglutinin, a superantigen presented by MHC molecules of class I and class II

BACKGROUND

Urtica dioica agglutinin (UDA), a monomeric lectin extracted from stinging nettle rhizomes, is specific for saccharides containing N-acetylglucosamine (GlcNAc). The lectin behaves as a superantigen for murine T cells, inducing the exclusive proliferation of Vbeta8.3(+) lymphocytes. UDA is unique among known T cell superantigens because it can be presented by major histocompatibility complex (MHC) molecules of both class I and II.

RESULTS

The crystal structure of UDA has been determined in the ligand-free state, and in complex with tri-acetylchitotriose and tetra-acetylchitotetraose at 1.66 A, 1.90 A and 1.40 A resolution, respectively. UDA comprises two hevein-like domains, each with a saccharide-binding site. A serine and three aromatic residues at each site form the principal contacts with the ligand. The N-terminal domain binding site can centre on any residue of a chito-oligosaccharide, whereas that of the C-terminal domain is specific for residues at the nonreducing terminus of the ligand. We have shown previously that oligomers of GlcNAc inhibit the superantigenic activity of UDA and that the lectin binds to glycans on the MHC molecule. We show that UDA also binds to glycans on the T cell receptor (TCR).

CONCLUSIONS

The presence of two saccharide-binding sites observed in the structure of UDA suggests that its superantigenic properties arise from the simultaneous fixation of glycans on the TCR and MHC molecules of the T cell and antigen-presenting cell, respectively. The well defined spacing between the two binding sites of UDA is probably a key factor in determining the specificity for Vbeta8.3(+) lymphocytes.

Cross-linking staphylococcal enterotoxin A bound to major histocompatibility complex class I is required for TNF-alpha secretion

The mechanism of how superantigens function to activate cells has been linked to their ability to bind and cross-link the major histocompatibility complex class II (MHCII) molecule. Cells that lack the MHCII molecule also respond to superantigens, however, with much less efficiency. Therefore, the purpose of this study was to confirm that staphylococcal enterotoxin A (SEA) could bind the MHCI molecule and to test the hypothesis that cross-linking SEA bound to MHCII-deficient macrophages would induce a more robust cytokine response than without cross-linking. We used a capture enzyme-linked immunosorbent assay and an immunprecipitation assay to directly demonstrate that MHCI molecules bind SEA. Directly cross-linking MHCI using monoclonal antibodies or cross-linking bound SEA with an anti-SEA antibody or biotinylated SEA with avidin increased TNF-alpha and IL-6 secretion by MHCII(-/-) macrophages. The induction of a vigorous macrophage cytokine response by SEA/anti-SEA cross-linking of MHCI offers a mechanism to explain how MHCI could play an important role in superantigen-mediated pathogenesis.