Decoding glycans: deciphering the sugary secrets to be coherent on the implication

Neoteric techniques, skills, and methodological advances in glycobiology and glycochemistry have been instrumental in pertinent discoveries to pave way for a new era in biomedical sciences. Glycans are sugar-based polymers that coat cells and decorate majority of proteins, forming glycoproteins. They are also found deposited in extracellular spaces between cells, attached to soluble signaling molecules, and are key players in several biological processes including regulation of immune responses and cell–cell interactions. Laboratory manipulations of protein, DNA and other macromolecules celebrate the accelerated research in respective fields, but the same seems unlikely for the complex sugar polymers. The structural complex polymers are neither synthesized using a known template nor are dynamically stable with respect to a cell''s metabolic rate. What is more, sugar isomers—structurally distinct molecules with the same chemical formula—can be employed to construct varied glycans, but are almost impossible to tell apart based on molecular weight alone. The apparent lack of a glycan alphabet further reflects on an enduring question: how little do we know about the sugars? Evidently, glycan-based therapeutic potentials and glycomimetics are propitious advances for the future that have not been well exploited, and with a few conspicuous anomalies. Here, we contour the most notable contributions to enhance our ability to utilize the complex glycans as therapeutics. Diagnostic strategies concerning recurrent diseases and headways to address the challenges are also discussed.

A glycan toolbox for pathogenic and cancerous interventions. The review article sheds light on the sweet secrets of this complex structure.

The decisive contribution of carbohydrates in proliferation of cells, signaling, structure, and morphology, alongside several diseases, has incentivized multitudinous endeavors to provide glycan-based remedies. Glycans are chains of monosaccharide units, varying in length from a few sugars to several hundreds. The astonishingly complex carbohydrate polymers form the most abundant family of organic molecules on the planet.^1,2 Glycans are a vital class of biological molecules that compasses spectra of functions including growth, development, maintenance, and survival of an organism. They are key players in nearly every domain of physiology and etiology of almost every disease. Glycans coat the outermost surfaces of cells and secreted macromolecules, found in extracellular compartments and are prodigiously variegated. Differences in monosaccharide constituents, bonding between different monosaccharide units, anomeric states, branched structures, and several substitutions in linkage to the aglycon part are responsible for the diversification.³ Complex glycans are statutory for protein folds in polypeptide chains synthesized afresh, and influence the stability, solubility and trafficking of the terminal glycoprotein. About 1% of the human genome is devoted to the enzyme-catalyzed synthesis and allocation of glycans, and most of human proteins and lipids are believed to be post-translationally remoulded by glycans by a process called glycosylation.^4–6 Major types of glycosylation seen in mammals are illustrated in Fig. 1. Inadequacy in glycosylation in humans and its relation to several diseases trace back to their role in the storage of tremendous amount of biological data. Glycosylation in proteins encompasses the inclusion of O-linked glycans, N-linked glycans, mucopolysaccharides, phosphorylated glycans, glycosylphosphatidylinositol anchors to peptide backbones as well as tryptophan residues undergoing C-mannosylation. Glycolipids are molecules composed of a glycan linked to a lipid ceramide; this type of glycoconjugate includes glycosphingolipids.Open in a separate windowFig. 1Major types of glycosylation and glycans in mammals. Glycans on mammalian cell surfaces are composed of 10 kinds of monosaccharides: glucose (Glc), galactose (Gal), mannose (Man), fucose (Fuc), N-acetylglucosamine (GlcNAc), N-acetylgalactosamine (GalNAc), xylose (Xyl), glucuronic acid (GlcA), iduronic acid (IdA), and sialic acid (Sia), which are connected via glycosyltransferase (GT)-catalyzed substitution from nucleotide pyrophosphate.The biological role of glycans is categorized into: (1) structural and modulatory functions involving storage of nutrients and sequestration; (2) explicit identification by other molecules, specifically glycan-binding proteins; and (3) molecular mimicry of host glycans. Glycan-binding proteins are classified into intrinsic glycan-binding proteins and extrinsic glycan-binding proteins. The intrinsic functionalities are involved in direct cellular interactions, that is, recognition of extracellular glycan molecules from the same organism. The extrinsic functionalities are involved in the recognition of glycans from another organism, which constitute microbial adhesins, agglutinins, or toxins, and few arbitrate to form symbiotic relationships or host defense.^7,8 This has empowered more prominent proficiency in the distinguishing proof, synthesis and assessment of peculiar glycan epitopes present on a surfeit of pathogens and cancerous cells. Glycans and glycan-binding proteins on the host cell are utilized by microbes to attach and invade the host cells, as carbon sources and toxins. Moreover, host glycans can be modified by the bacterial glycosyltransferases and glycosidases as a major share of the pathogenic procedure.⁹ Glycan coatings on the envelope of viruses are eminent for the evasion of the immunological surveillance of the host.^10,11The comprehensive grasp on genotype, which, in turn, controls the phenotype, was plausible with the discovery of structure–activity relationships of nucleic acids and proteins. Thereafter, the biological and biochemical knowledge was successfully translated into drug discovery endeavors. Even though the changes in the expression of glycans concerning cell conditions have been broadly acknowledged, progression in the sub-atomic premise of glycan functions has been fairly moderate compared with similar investigations of proteins and nucleic acids.¹² This slow progress is partly due to the fact that the biosynthesis of glycans, unlike other biopolymers, is not template-driven and that the molecular basis governing glycan functions is not yet fully understood, presumably as a denouement of the huge structural complexity and heterogeneity of glycans. Howbeit, cloning of enzymes required for the synthesis of glycans, as well as elaborating the mechanism of action and substrate specificity, has now helped in the high-throughput analysis of a range of complex glycan structures. Glycomics have acquired appreciable heed. Innumerable genetic knock-out experiments have further enhanced our knowledge by scrutinizing at the organism level, the impingement on biosynthesis and/or catabolism of complex glycans. The loss-of-function studies utilizing gene knock-outs have bestowed significant structure-work associates for both complexes and linear polysaccharide units.^2,13 Analysis of structural properties of individual glycans, distribution on cells or tissues and relationship with each other, and interactions with proteins and lipids foster a large volume of information, and result high-performance computing, overarching information, and data extraction. Several academicians and commercial organizations are involved in the integration of diversified data by utilizing various tools and instruments to develop novel searchable bioinformatics platforms. Some examples of the databases reported in the past few years are Glycostore,¹⁴ Glyco3D,¹⁵ GlyMDB,¹⁶ GLAD,¹⁷ UniLectin web platform,¹⁸ Carbohydrate structure database,¹⁹ UniCorn,²⁰ UniCarbKB,²¹ and Kegg glycan.²² Computational data will aid in the progression of glycoanalytics to high-throughput utilization and quicker determination of new drug–disease relationships.     

Temporal variation of the leak pressure of uncuffed endotracheal tubes following pediatric intubation: an observational study

Purpose

Uncuffed endotracheal tubes are still preferred over cuffed tubes in certain situations in pediatric anesthesia. Inaccurately sized uncuffed endotracheal tubes may lead to inadequate ventilation or tracheal mucosal damage during anesthesia. Endotracheal tube size in children is usually assessed by measuring the audible leak pressure; if the fit of the tube and the leak pressure decrease significantly with time, reintubation during surgery as a result of inability to ventilate effectively may be challenging, and could lead to patient morbidity. There is no evidence to indicate whether leak pressure increases or decreases with time following endotracheal intubation with uncuffed tubes in children.

Methods

We measured leak pressure for 30 min following tracheal intubation in 46 ASA I children age 0–7 years after excluding factors known to modify leak pressure.

Results

The largest mean change in leak pressure occurred between time points 0 and 15 min, an increase of 3.5 cmH₂O. Endotracheal tube size and type of procedure were associated with the leak pressure. In the final linear mixed model, there were no statistically significant variations in leak pressure over time (P = 0.129) in this group of children.

Conclusions

We did not identify a consistent change in leak pressure within 30 min following tracheal intubation with uncuffed endotracheal tubes in this group of children.     

Neo-innervation of a bioengineered intestinal smooth muscle construct around chitosan scaffold

Neuromuscular disorders of the gut result in disturbances in gastrointestinal transit. The objective of this study was to evaluate the neo-innervation of smooth muscle in an attempt to restore lost innervation. We have previously shown the potential use of composite chitosan scaffolds as support for intestinal smooth muscle constructs. However, the constructs lacked neuronal component. Here, we bioengineered innervated colonic smooth muscle constructs using rabbit colon smooth muscle and enteric neural progenitor cells. We also bioengineered smooth muscle only tissue constructs using colonic smooth muscle cells. The constructs were placed next to each other around tubular chitosan scaffolds and left in culture. Real time force generation conducted on the intrinsically innervated smooth muscle constructs showed differentiated functional neurons. The bioengineered smooth muscle only constructs became neo-innervated. The neo-innervation results were confirmed by immunostaining assays. Chitosan supported (1) the differentiation of neural progenitor cells in the constructs and (2) the neo-innervation of non-innervated smooth muscle around the same scaffold.     

3D Ultrasound Strain Imaging of Puborectalis Muscle

The female pelvic floor (PF) muscles provide support to the pelvic organs. During delivery, some of these muscles have to stretch up to three times their original length to allow passage of the baby, leading frequently to damage and consequently later-life PF dysfunction (PFD). Three-dimensional (3D) ultrasound (US) imaging can be used to image these muscles and to diagnose the damage by assessing quantitative, geometric and functional information of the muscles through strain imaging. In this study we developed 3D US strain imaging of the PF muscles and explored its application to the puborectalis muscle (PRM), which is one of the major PF muscles.     

Cannula dacryocystorhinostomy: a simple,innovative and cost-effective method of lacrimal surgery

To compare our innovative, cost-effective method of lacrimal surgery with other methods. A prospective cohort study. The study included 80 eyes of 80 consecutive patients who presented to our clinic between January 2009 and December 2011. The patients underwent surgery using a new technique with a specially designed cannula and were followed according to our protocol. Patency on irrigation. Of the 80 cases enrolled, the procedure was successful in 52.5 % with a mean follow-up of 247.2 days. The success rate was significantly affected by the preoperative conditions (p = 0.001) and follow-up duration (p = 0.006). This simple innovative technique was cost-effective and the results were comparable with those of other techniques.