Expedient Synthesis of Core Disaccharide Building Blocks from Natural Polysaccharides for Heparan Sulfate Oligosaccharide Assembly

Multifaceted Heparin: Diverse Applications beyond Anticoagulant Therapy

Heparin, a naturally occurring polysaccharide, has fascinated researchers and clinicians for nearly a century due to its versatile biological properties and has been used for various therapeutic purposes. Discovered in the early 20th century, heparin has been a key therapeutic anticoagulant ever since, and its use is now implemented as a life-saving pharmacological intervention in the management of thrombotic disorders and beyond. In addition to its known anticoagulant properties, heparin has been found to exhibit anti-inflammatory, antiviral, and anti-tumorigenic activities, which may lead to its widespread use in the future as an essential drug against infectious diseases such as COVID-19 and in various medical treatments. Furthermore, recent advancements in nanotechnology, including nano-drug delivery systems and nanomaterials, have significantly enhanced the intrinsic biofunctionalities of heparin. These breakthroughs have paved the way for innovative applications in medicine and therapy, expanding the potential of heparin research. Therefore, this review aims to provide a creation profile of heparin, space for its utilities in therapeutic complications, and future characteristics such as bioengineering and nanotechnology. It also discusses the challenges and opportunities in realizing the full potential of heparin to improve patient outcomes and elevate therapeutic interventions.

Bioengineered heparin: Advances in production technology

Heparin, a highly sulfated glycosaminoglycan, is considered an indispensable anticoagulant with diverse therapeutic applications and has been a mainstay in medical practice for nearly a century. Its potential extends beyond anticoagulation, showing promise in treating inflammation, cancer, and infectious diseases such as COVID-19. However, its current sourcing from animal tissues poses challenges due to variable structures and adulterations, impacting treatment efficacy and safety. Recent advancements in metabolic engineering and synthetic biology offer alternatives through bioengineered heparin production, albeit with challenges such as controlling molecular weight and sulfonation patterns. This review offers comprehensive insight into recent advancements, encompassing: (i) the metabolic engineering strategies in prokaryotic systems for heparin production; (ii) strides made in the development of bioengineered heparin; and (iii) groundbreaking approaches driving production enhancements in eukaryotic systems. Additionally, it explores the potential of recombinant Chinese hamster ovary cells in heparin synthesis, discussing recent progress, challenges, and future prospects, thereby opening up new avenues in biomedical research.

Sulfation of Heparan and Chondroitin Sulfate Ligands Enables Cell-Specific Homing of Nanoprobes

Demystifying the sulfation code of glycosaminoglycans (GAGs) to induce precise homing of nanoparticles in tumor cells or neurons influences the development of a potential drug- or gene-delivery system. However, GAGs, particularly heparan sulfate (HS) and chondroitin sulfate (CS), are structurally highly heterogeneous, and synthesizing well-defined HS/CS composed nanoparticles is challenging. Here, we decipher how specific sulfation patterns on HS and CS regulate receptor-mediated homing of nanoprobes in primary and secondary cells. We discovered that aggressive cancer cells such as MDA-MB-231 displayed a strong uptake of GAG-nanoprobes compared to mild or moderately aggressive cancer cells. However, there was no selectivity towards the GAG sequences, thus indicating the presence of more than one form of receptor-mediated uptake. However, U87 cells, olfactory bulb, and hippocampal primary neurons showed selective or preferential uptake of CS-E-coated nanoprobes compared to other GAG-nanoprobes. Furthermore, mechanistic studies revealed that the 4,6-O-disulfated-CS nanoprobe used the CD44 and caveolin-dependent endocytosis pathway for uptake. These results could lead to new opportunities to use GAG nanoprobes in nanomedicine.

Synthesis of a Systematic 64-Membered Heparan Sulfate Tetrasaccharide Library

Heparan sulfate (HS) has multifaceted biological activities. To date, no libraries of HS oligosaccharides bearing systematically varied sulfation structures are available owing to the challenges in synthesizing a large number of HS oligosaccharides. To overcome the obstacles and expedite the synthesis, a divergent approach was designed, where 64 HS tetrasaccharides covering all possible structures of 2-O-, 6-O- and N-sulfation with the glucosamine-glucuronic acid-glucosamine-iduronic acid backbone were successfully produced from a single strategically protected tetrasaccharide intermediate. This extensive library helped identify the structural requirements for HS sequences to have strong fibroblast growth factor-2 binding but a weak affinity for platelet factor-4. Such a strategy to separate out these two interactions could lead to new HS-based potential therapeutics without the dangerous adverse effect of heparin-induced thrombocytopenia.

Design and Synthesis of 6-O-Phosphorylated Heparan Sulfate Oligosaccharides to Inhibit Amyloid β Aggregation

Dysregulation of amyloidogenic proteins and their abnormal processing and deposition in tissues cause systemic and localized amyloidosis. Formation of amyloid β (Aβ) fibrils that deposit as amyloid plaques in Alzheimer's disease (AD) brains is an earliest pathological hallmark. The polysulfated heparan sulfate (HS)/heparin (HP) is one of the non-protein components of Aβ deposits that not only modulates Aβ aggregation, but also acts as a receptor for Aβ fibrils to mediate their cytotoxicity. Interfering with the interaction between HS/HP and Aβ could be a therapeutic strategy to arrest amyloidosis. Here we have synthesized the 6-O-phosphorylated HS/HP oligosaccharides and reported their competitive effects on the inhibition of HP-mediated Aβ fibril formation in vitro using a thioflavin T fluorescence assay and a tapping mode atomic force microscopy.

From Cancer to COVID-19: A Perspective on Targeting Heparan Sulfate-Protein Interactions

Heparan sulfate (HS) is a complex, polyanionic polysaccharide ubiquitously expressed on cell surfaces and in the extracellular matrix. HS interacts with numerous proteins to mediate a vast array of biological and pathological processes. Inhibition of HS-protein interactions is thus an attractive approach for new therapeutic development for cancer and infectious diseases, including COVID-19; however, synthesis of well-defined native HS oligosaccharides remains challenging. This has aroused significant interest in the development of HS mimetics which are more synthetically tractable and have fewer side effects, such as undesired anticoagulant activity. This account provides a perspective on the design and synthesis of different classes of HS mimetics with useful properties, and the development of various assays and molecular modelling tools to progress our understanding of their interactions with HS-binding proteins.

Developments in the Chemical Synthesis of Heparin and Heparan Sulfate

Heparin and heparan sulfate represent key members of the glycosaminoglycan family of carbohydrates and underpin considerable repertoires of biological importance. As such, their efficiency of synthesis represents a key requirement, to further understand and exploit the H/HS structure-to-biological function axis. In this review we focus on chemical approaches to and methodology improvements for the synthesis of these essential sugars (from 2015 onwards). We first consider advances in accessing the heparin-derived pentasaccharide anticoagulant fondaparinux. This is followed by heparan sulfate targets, including key building block synthesis, oligosaccharide construction and chemical sulfation techniques. We end with a consideration of technological improvements to traditional, solution-phase synthesis approaches that are increasingly being utilised.

Synthesis of L-hexoses: an Update

Over the years, carbohydrates have increasingly become an important class of compounds contributing significantly to the target specific drug discovery and vaccine development. Several oligosaccharides contain L-hexoses that are biologically relevant as therapeutic and diagnostic tools. Since, L-hexoses and deoxy L-hexoses are not readily available in large amount and pure form, attention is drawn towards development of cost effective and high yielding synthetic routes for their procurement. In this review we give an update on the recent developments in strategies for synthesis of L-hexoses and deoxy L-hexoses.