Macromolecular assemblies of complex polysaccharides with galectin-3 and their synergistic effects on function

Synthetic and plant-derived multivalent galactans as modulators of cancer-associated galectins-3 and -9

Galectins are β-galactoside-binding proteins with numerous functions. Some of them are involved in proliferation and metastasis of cancer, making them promising therapeutic targets. As different plant glycans have been shown to bind to galectins, plant saccharides might be potential galectin inhibitors. To produce plant galactans rich in galactose and smaller in size, we degraded arabinogalactan-proteins from Echinacea purpurea and Zostera marina as well as arabinogalactan from larch. As galectin (Gal)-3 and -9 both have been described to be involved in cancer development, we quantified the binding capacities of the different galactans to both galectins by biolayer-interferometry. Our results revealed that all plant-derived galactans and Yariv reagents with terminal galactose and lactose residues bind to Gal-3 in micromolar ranges. Surprisingly, only the higher charged galactans from Zostera marina showed affinity to Gal-9. Investigations of two different pancreatic cancer cell lines (Panc1 and Panc89) and different cell variants thereof revealed that Gal-3 was expressed by both cell lines with a significantly higher Gal-3 level in Panc1 cells compared to Panc89 cells. Conversely, Gal-9 was only detected in Panc89 cells. The findings revealed that galactans are promising sources to develop galectin antagonists and plant galactans from different species express specificities for distinct galectins.

A homogalacturonan-rich pectic polysaccharide isolated from Lonicera japonica Thunb. modulates galectin-4-mediated bioactivity and anti-hepatocellular carcinoma activity

L. japonica is a traditional Chinese medicine with dual-use properties. Herein, a HG-rich pectic polysaccharide, WLJP-03A, was purified from the dried flowers of L. japonica, which composed of Rha (5 %), GalA (60 %), Gal (5 %), and Ara (30 %), with a molecular weight of 28.1 kDa. WLJP-03A could be defined as an HG backbone with α-(1 → 3,5)-linked and α-(1 → 5)-linked arabinan, β-(1 → 3,6)-linked and β-(1 → 3)-linked galactan, and type II arabinogalactan side chains. Its interaction with two truncated structural domain proteins of galectin-4 (Gal-4) revealed stronger binding of WLJP-03A to Gal-4C (MIC = 15 μg/mL) than to Gal-4N (MIC = 62 μg/mL), indicating that WLJP-03A mainly interacted with the C-terminal CRD to inhibit the biological activity of Gal-4. Furthermore, in vitro antitumor assays showed that WLJP-03A could inhibit the cellular proliferation and migration of HCCLM3 cells induced by Gal-4. These results provide new insights into the structure-activity relationship between L. japonica polysaccharide and Gal-4.

A novel pectin-like polysaccharide from Crocus sativus targets Galectin-3 to inhibit hepatic stellate cells activation and liver fibrosis

Liver fibrosis may lead to cirrhosis and even cancer without effective clinical medicine available. Previous studies demonstrated that galactan-containing pectins or pectin-like polysaccharides might target Galectin-3 (Gal-3) to impede fibrosis. This research aims to discover novel pectin-like galactan to interfere with fibrosis for potential new drug development. Thus, we purify a novel homogeneous Rhamnogalacturonan-I like polysaccharide with galactan input, XHH2, from the Crocus sativus flower. XHH2 (MW: 35.7 kDa) consists of rhamnose, galacturonic acid, galactose, and arabinose in ratios of 6.6: 6.1: 25.2: 12.1. The backbone of XHH2 comprises 1, 3, 6-Gal and 1, 3, 4-GalA, with branches at O-3 of 1, 3, 6-Gal and O-4 of 1, 3, 4-GalA. O-3 branches include 1, 3-Gal, 1, 4-Gal, 1, 6-Gal, T-Gal, and T-Glc, while O-4 branches consist of 1, 2, 4-Rha, 1, 4-GalA, 1, 5-Ara, T-Ara, T-Gal, and T-α-HexA. Surface plasmon resonance measurement shows that XHH2 binds to both Gal-3 and integrin β1 to block Gal-3/integrin β1 interaction. Mechanism studies further suggest that XHH2 inactivates hepatic stellate cells (HSCs) via disturbing the Gal-3/Integrin-β1/FAK pathway to alleviate liver injury and fibrosis in vitro & in vivo. XHH2 shows a favorable drug safety in the acute toxicity test of oral administration of XHH2 in mice. Overall, XHH2 is an active ingredient against liver fibrosis by targeting the interaction between Gal-3 and Integrin-β1.

Galectins and Host-Pathogen Interactions: The roles in viral infections

Galectins, a family of carbohydrate-binding proteins, play crucial roles in the host-virus interaction landscape. This review explores the multifaceted contributions of endogenous galectins to various stages of the viral lifecycle, including attachment, replication, assembly, and release of progeny virions. Recent studies have indicated that viral infections can induce the expression and secretion of specific galectins, with elucidated signaling pathways in some cases, enhancing our understanding of their regulatory mechanisms. While many studies have focused on the effects of exogenous recombinant galectins, there is growing interest in the intrinsic functions of endogenous galectins, particularly through genetic alterations in cellular models. This review highlights the need for further research to uncover the complex roles of galectins in modulating viral infections and emphasizes their potential as therapeutic targets in the fight against viral diseases. Understanding these interactions could pave the way for novel strategies to enhance host defense mechanisms and mitigate viral pathogenesis.

CH-π Interactions Are Required for Human Galectin-3 Function

Glycan-binding proteins, or lectins, recognize distinct structural elements of polysaccharides, to mediate myriad biological functions. Targeting glycan-binding proteins involved in human disease has been challenging due to an incomplete understanding of the molecular mechanisms that govern protein-glycan interactions. Bioinformatics and structural studies of glycan-binding proteins indicate that aromatic residues with the potential for CH-π interactions are prevalent in glycan-binding sites. However, the contributions of these CH-π interactions to glycan binding and their relevance in downstream function remain unclear. An emblematic lectin, human galectin-3, recognizes lactose and N-acetyllactosamine-containing glycans by positioning the electropositive face of a galactose residue over the tryptophan 181 (W181) indole forming a CH-π interaction. We generated a suite of galectin-3 W181 variants to assess the importance of these CH-π interactions to glycan binding and function. As determined experimentally and further validated with computational modeling, variants with smaller or less electron-rich aromatic side chains (W181Y, W181F, W181H) or sterically similar but nonaromatic residues (W181M, W181R) showed poor or undetectable binding to lactose and attenuated ability to bind mucins or agglutinate red blood cells. The latter functions depend on multivalent binding, highlighting that weakened CH-π interactions cannot be overcome by avidity. Two galectin-3 variants with disrupted hydrogen bonding interactions (H158A and E184A) showed similarly impaired lactose binding. Molecular simulations demonstrate that all variants have decreased binding orientation stability relative to native galectin-3. Thus, W181 collaborates with the endogenous hydrogen bonding network to enhance binding affinity for lactose, and abrogation of these CH-π interactions is as deleterious as eliminating key hydrogen bonding interactions. These findings underscore the critical roles of CH-π interactions in carbohydrate binding and lectin function and will aid the development of novel lectin inhibitors.

Dietary fiber as a wide pillar of colorectal cancer prevention and adjuvant therapy

Colorectal cancer is the third most incident and second most lethal type of cancer worldwide. Lifestyle and dietary patterns are the key factors for higher disease development risk. The dietary fiber intake from fruits and vegetables, mainly formed by food hydrocolloids, can help to lower the incidence of this type of neoplasia. Different food polysaccharides have applications in anti-tumoral therapy, such as coadjuvant to mainstream drugs, carriage-like properties, or direct influence on tumoral cells. Some classes include inulin, β-glucans, pectins, fucoidans, alginates, mucilages, and gums. Therefore, it is fundamental to discuss colorectal cancer mechanisms and the roles played by different polysaccharides in intestinal health. Genetic, environmental, and immunological modulation of mutated pathways regarding colorectal cancer has been explored before. Microbial diversity, byproduct formation (primarily short-chain fatty acids), inflammatory profile control, and tumoral mutated pathways regulation are thoroughly explored mechanisms by which dietary fiber sources influence a healthy gut ambiance.

Breaking barriers: How modified citrus pectin inhibits galectin-8

Inhibition of galectin-3-mediated interactions by modified citrus pectin (MCP) could affect several rate-limiting steps in cancer metastasis, but the ability of MCP to antagonize galectin-8 function remains unknown. We hypothesized that MCP could bind to galectin-8 in addition to galectin-3. In this study, a combination of gradual ethanol precipitation and DEAE-Sepharose Fast Flow chromatography was used to isolate several fractions from MCP. The ability of these fractions to antagonize galectin-8 function was studied as well as the primary structure and initial structure-function relationship of the major active component MCP-30-3. The results showed that MCP-30-3 (168 kDa) was composed of Gal (13.8%), GalA (63.1%), GlcA (13.0%), and Glc (10.1%). MCP-30-3 could specifically bind to galectin-8, with an MIC value of 0.04 mg mL-1. After MCP-30-3 was hydrolyzed by β-galactosidase or pectinase, its binding activity was significantly reduced. These results provide new insights into the interaction between MCP structure and galectin function, as well as the potential utility in the development of functional foods.

Pectin: Health-promoting properties as a natural galectin-3 inhibitor

Galectin-3 has a variety of important pathophysiological significance in the human body. Much evidence shows that the abnormal expression of galectin-3 is related to the formation and development of many diseases. Pectin is mostly obtained from processed citrus fruits and apples and is a known natural inhibitor of galactin-3. A large number of peels produced each year are discarded, and it is necessary to recycle some of the economically valuable active compounds in these by-products to reduce resource waste and environmental pollution. By binding with galectin-3, pectin can directly reduce the expression level of galectin-3 on the one hand, and regulate the expression level of cytokines by regulating certain signaling pathways on the other hand, to achieve the effect of treating diseases. This paper begins by presenting an overview of the basic structure of pectin, subsequently followed by a description of the structure of galectin-3 and its detrimental impact on human health when expressed abnormally. The health effects of pectin as a galectin-3 inhibitor were then summarized from the perspectives of anticancer, anti-inflammatory, ameliorating fibrotic diseases, and anti-diabetes. Finally, the challenges and prospects of future research on pectin are presented, which provide important references for expanding the application of pectin in the pharmaceutical industry or developing functional dietary supplements.

Ultrasound-assisted enzymatic extraction, structural characterization, and anticancer activity of polysaccharides from Rosa roxburghii Tratt fruit

In this work, Rosa roxburghii Tratt fruit polysaccharides (RPs) were extracted by ultrasound-assisted enzymatic method. The highest extraction yield of RPs was 4.78 ± 0.10 % under the optimal extraction conditions. Two purified fractions named RP1 and RP3 were obtained and systematically characterized by a combination strategy of FT-IR, monosaccharide composition, molecular weight distribution, methylation and 2D NMR spectroscopy analyses. Structural analysis showed that the main chain of RP1 was composed of rhamnogalacturonan type I (RG-I), while the side chains were rich in arabinogalactan and galactose. RP3 was composed of long homogalacturonan (HG) backbone interspersed with alternating sequences of RG-I domains, with galactose and arabinose side chains. RP1 and RP3 induced apoptosis of MCF-7 cells in a dose dependent manner in vitro especially for RP1, and had no effect on L929 cells. Furthermore, the possible anticancer mechanisms were revealed, and results suggested that RP1 induced apoptosis through ROS-dependent pathway and mitochondrial pathway. The results of this work not only provided an efficient extraction method and theoretical basis for the application of RPs, but also may contribute to develop novel functional foods or pharmaceutical products for the prevention and treatment of human breast cancer disease.

Harnessing the power of mollusc lectins as immuno-protective biomolecules

The rapid advancement of molecular research on macromolecules has contributed to the discovery of 'Lectin', a carbohydrate-binding protein which specifically interacts with receptors on the surface of glycans and regulates various cellular activities thereby stimulating immunological functions. Considering the wide variety of sources and immunological significance, research has led to the discovery of lectins in invertebrate molluscs. Such lectins in molluscs mediate active immune response as they lack adaptive immunity. Phylum Mollusca is identified with different types of lectins such as C-lectin, Galectin, P-lectin, I-lectin, and H-lectin, along with other immunologically significant lectin molecules such as F- lectin, R-lectin, ficolins, chitinase like lectin etc., all of these with specific ligand binding and structural diversity. Molluscan C-type lectins are the most functional ones that increase the activity of phagocytic cells through specific carbohydrate binding of antigenic ligands and haemocyte adhesion thereby enhancing the immune response. Helix pomatia agglutinin and Helix aspersa agglutinin are the two H-lectins that were identified within molluscs that could even target cancer-progressing cells through specific binding. Also, these lectins identified in molluscs are proven to be efficient in antibacterial and immunomodulatory functions. These insights attract researchers to identify novel lectins in molluscs and their characterization that play a key role in protection against diseases. This review discusses the structural features of mollusc lectins, their specific binding, molecular interactions and their immunological applications.

Heterologous Interactions with Galectins and Chemokines and Their Functional Consequences

Extra- and intra-cellular activity occurs under the direction of numerous inter-molecular interactions, and in any tissue or cell, molecules are densely packed, thus promoting those molecular interactions. Galectins and chemokines, the focus of this review, are small, protein effector molecules that mediate various cellular functions-in particular, cell adhesion and migration-as well as cell signaling/activation. In the past, researchers have reported that combinations of these (and other) effector molecules act separately, yet sometimes in concert, but nevertheless physically apart and via their individual cell receptors. This view that each effector molecule functions independently of the other limits our thinking about functional versatility and cooperation, and, in turn, ignores the prospect of physiologically important inter-molecular interactions, especially when both molecules are present or co-expressed in the same cellular environment. This review is focused on such protein-protein interactions with chemokines and galectins, the homo- and hetero-oligomeric structures that they can form, and the functional consequences of those paired interactions.

The model polysaccharide potato galactan is actually a mixture of different polysaccharides

Commercially-supplied potato galactan (PG) is widely used as a model polysaccharide in various bioactivity studies. However, results using this galactan are not always consistent with the stated composition. Here, we assessed its composition by fractionating this commercial PG and purified its primary components: PG-A, PG-B and PG-Cp with weight-averaged molecular weights of 430, 93, and 11.3 kDa, respectively. PG-Cp consists of free β-1,4-galactan chains, whereas PG-A and PG-B are type I rhamnogalacturonans with long β-1,4-galactan side chains of up to 80 Gal residues and short β-1,4-galactan side chains of 0 to 3 Gal residues that display a "trees in lawn" pattern. Structures of these polysaccharides correlate well with their activities in terms of galectin-3 binding and gut bacterial growth assays. Our study clarifies the confusion related to commercial PG, with purified fractions serving as better model polysaccharides in bioactivity investigations.

Targeting galectin-driven regulatory circuits in cancer and fibrosis

Galectins are a family of endogenous glycan-binding proteins that have crucial roles in a broad range of physiological and pathological processes. As a group, these proteins use both extracellular and intracellular mechanisms as well as glycan-dependent and independent pathways to reprogramme the fate and function of numerous cell types. Given their multifunctional roles in both tissue fibrosis and cancer, galectins have been identified as potential therapeutic targets for these disorders. Here, we focus on the therapeutic relevance of galectins, particularly galectin 1 (GAL1), GAL3 and GAL9 to tumour progression and fibrotic diseases. We consider an array of galectin-targeted strategies, including small-molecule carbohydrate inhibitors, natural polysaccharides and their derivatives, peptides, peptidomimetics and biological agents (notably, neutralizing monoclonal antibodies and truncated galectins) and discuss their mechanisms of action, selectivity and therapeutic potential in preclinical models of fibrosis and cancer. We also review the results of clinical trials that aim to evaluate the efficacy of galectin inhibitors in patients with idiopathic pulmonary fibrosis, nonalcoholic steatohepatitis and cancer. The rapid pace of glycobiology research, combined with the acute need for drugs to alleviate fibrotic inflammation and overcome resistance to anticancer therapies, will accelerate the translation of anti-galectin therapeutics into clinical practice.

Inhibition of galectins in cancer: Biological challenges for their clinical application

Galectins play relevant roles in tumor development, progression and metastasis. Accordingly, galectins are certainly enticing targets for medical intervention in cancer. To date, however, clinical trials based on galectin inhibitors reported inconclusive results. This review summarizes the galectin inhibitors currently being evaluated and discusses some of the biological challenges that need to be addressed to improve these strategies for the benefit of cancer patients.

Structural Characteristic and In-Vitro Anticancer Activities of Dandelion Leaf Polysaccharides from Pressurized Hot Water Extraction

Dandelion (Taraxacum mongolicum Hand.-Mazz.) is a medicinal and edible plant. Dandelion has great development value for its health promoting benefits; additionally, Dandelion grows almost anywhere in the world. In this study, we report the structural characteristics and anti-cancer activity of novel dandelion leaf polysaccharides extracted by pressurized hot water extraction at 120 °C (DLP120) with Mw relative to dextran of 1.64 × 10⁶ Da. Structural analysis indicated that DLP120 is a complex polysaccharide composed of pectin and arabinogalactan. It was mainly composed of arabinose (32.35 mol%) and galactose (44.91 mol%). The main glycosidic linkages of DLP120 were 4-β-D-Galp, 4-α-D-GalpA, T-β-D-Galp, 5-α-L-Araf, 3,5-α-L-Araf, and T-α-L-Araf. In vitro, DLP120 inhibited HepG2 cell proliferation in a dose-dependent manner by inducing cell apoptosis. Cell cycle detection results revealed that DLP120 mainly arrests the cell cycle in S phase. Cells treated with DLP120 displayed obvious apoptotic morphology, including cell volume shrinks and cytoskeleton breaks down. In short, DLP120 has potential as an anti-cancer agent.

Synergistic Hypolipidemic Effects and Mechanisms of Phytochemicals: A Review

Hyperlipidemia, a chronic disorder of abnormal lipid metabolism, can induce obesity, diabetes, and cardiovascular and cerebrovascular diseases such as coronary heart disease, atherosclerosis, and hypertension. Increasing evidence indicates that phytochemicals may serve as a promising strategy for the prevention and management of hyperlipidemia and its complications. At the same time, the concept of synergistic hypolipidemic and its application in the food industry is rapidly increasing as a practical approach to preserve and improve the health-promoting effects of functional ingredients. The current review focuses on the effects of single phytochemicals on hyperlipidemia and its mechanisms. Due to the complexity of the lipid metabolism regulatory network, the synergistic regulation of different metabolic pathways or targets may be more effective than single pathways or targets in the treatment of hyperlipidemia. This review summarizes for the first time the synergistic hypolipidemic effects of different combinations of phytochemicals such as combinations of the same category of phytochemicals and combinations of different categories of phytochemicals. In addition, based on the different metabolic pathways or targets involved in synergistic effects, the possible mechanisms of synergistic hypolipidemic effects of the phytochemical combination are illustrated in this review. Hence, this review provides clues to boost more phytochemical synergistic hypolipidemic research and provides a theoretical basis for the development of phytochemicals with synergistic effects on hyperlipidemia and its complications.

The Use of Endo-Cellulase and Endo-Xylanase for the Extraction of Apple Pectins as Factors Modifying Their Anticancer Properties and Affecting Their Synergy with the Active Form of Irinotecan

Pectin constitutes an essential component of dietary fiber. Modified pectins from various sources possess potent anticancer and immunomodulatory activities. In this study, two pectins isolated from apple pomace by Trichoderma enzyme treatment, PX (with endo-xylanase) and PCX (with both endo-cellulase and endo-xylanase), were studied in colon cancer cell lines (HCT 116, Caco-2, and HT-29). Both pectins reduced colon cancer cell viability, induced apoptosis, and increased intracellular amounts of reactive oxygen species. Additionally, synergy between pectin and an active form of irinotecan, SN-38, in all aspects mentioned above, was discovered. This drug is a common component of cytotoxic combinations recommended as treatment for colon cancer patients. PX and PCX demonstrated significant anti-inflammatory activity in lipopolysaccharide-stimulated cells. Interaction of apple pectins with galectin-3 and Toll-like Receptor 4 (TLR4) was suggested to be responsible for their anticancer and anti-inflammatory effect. Since PCX was more active than PX in almost all experiments, the role of the enzyme used to obtain the pectin for its biological activity was discussed. It was concluded that co-operation between both enzymes was needed to obtain the molecule of the most beneficial properties. The low molecular mass of PCX together with a high proportion of rhamnogalacturonan I (RG I) regions seemed to be crucial for its superior activity.

Structural features and anticancer mechanisms of pectic polysaccharides: A review

The anticancer activity of pectic polysaccharides (PPs) was proved by numerous studies, and which also indicated that the bioactivity of PPs was closely related to its complicated structures. Based on the summary and analysis about structure characteristics and corresponding enzymatic process of the reported PPs, the anticancer mechanism and related structural features were systematically clarified. It was found that not only the direct effects on the cancer cells by proliferation inhibition or apoptosis, but also the regulation of immune system, gut microbiota and gut metabolism as indirect effects, jointly played important roles in the anticancer of PPs. Nevertheless, during the study of PPs as promising anticancer components, the exact structure-function relationship, digestion process in vivo, and comprehensive action mechanism are still not well understanding. With the unveiling of the proposed issues, it is believed that PPs are promising to be exploited as effective cancer therapy/adjunctive therapy drugs or functional foods.

The Complex Biological Effects of Pectin: Galectin-3 Targeting as Potential Human Health Improvement?

Galectin-3 is the only chimeric representative of the galectin family. Although galectin-3 has ubiquitous regulatory and physiological effects, there is a great number of pathological environments where galectin-3 cooperatively participates. Pectin is composed of different chemical structures, such as homogalacturonans, rhamnogalacturonans, and side chains. The study of pectin's major structural aspects is fundamental to predicting the impact of pectin on human health, especially regarding distinct molecular modulation. One of the explored pectin's biological activities is the possible galectin-3 protein regulation. The present review focuses on revealing the structure/function relationship of pectins, their fragments, and their biological effects. The discussion highlighted by this review shows different effects described within in vitro and in vivo experimental models, with interesting and sometimes contradictory results, especially regarding galectin-3 interaction. The review demonstrates that pectins are promissory food-derived molecules for different bioactive functions. However, galectin-3 inhibition by pectin had been stated in literature before, although it is not a fully understood, experimentally convincing, and commonly agreed issue. It is demonstrated that more studies focusing on structural analysis and its relation to the observed beneficial effects, as well as substantial propositions of cause and effect alongside robust data, are needed for different pectin molecules' interactions with galectin-3.

Anti-Cancer Pectins and Their Role in Colorectal Cancer Treatment

A class of plant polysaccharides, pectin is known to display several medicinal properties including in cancer. There is some evidence that pectin from some fruits can reduce the severity of colorectal cancer (CRC) due to its antiproliferative, anti-inflammatory, antimetastatic and pro-apoptotic properties. Pectin fermentation in the colon induces antiproliferative activity via butyrate. Research also showed that pectin acts as a potent inducer of programmed cell death and cell-cycle arrest, thereby selectively targeting cancer cells. Pectin can limit oxidative stress to maintain cellular homeostasis while increasing reactive oxygen species damage to activate cancer cell death. Pectin regulates various signaling cascades, e.g., signal transduction and transcriptional activator and mitogen-activated protein kinase signaling, that contribute to its anticancer activity. By curbing inflammation-activated signaling and bolstering immune-protective mechanisms pectin can eradicate CRC. Due to its chemical structure, pectin can also inhibit galectin-3 and suppress tumor growth and metastasis. Prior reports also suggested that pectin is beneficial to use alongside the CRC standard care. Pectin can increase sensitivity to conventional CRC drugs, alleviate unwanted side effects and reduce drug resistance. Although some preclinical studies are promising, early clinical trials are showing some evidence for pectin's efficacy in tumor growth inhibition and preventing metastasis in some cancers; however, the clinical use of pectin in CRC therapy is not yet well established. Further studies are needed to confirm the efficacy of pectin treatment as a valid clinical therapy for CRC in humans.

Degraded Arabinogalactans and Their Binding Properties to Cancer-Associated Human Galectins

Galectins represent β-galactoside-binding proteins with numerous functions. Due to their role in tumor progression, human galectins-1, -3 and -7 (Gal-1, -3 and -7) are potential targets for cancer therapy. As plant derived glycans might act as galectin inhibitors, we prepared galactans by partial degradation of plant arabinogalactan-proteins. Besides commercially purchased galectins, we produced Gal-1 and -7 in a cell free system and tested binding capacities of the galectins to the galactans by biolayer-interferometry. Results for commercial and cell-free expressed galectins were comparable confirming functionality of the cell-free produced galectins. Our results revealed that galactans from Echinacea purpurea bind to Gal-1 and -7 with K_D values of 1–2 µM and to Gal-3 slightly stronger with K_D values between 0.36 and 0.70 µM depending on the sensor type. Galactans from the seagrass Zostera marina with higher branching of the galactan and higher content of uronic acids showed stronger binding to Gal-3 (0.08–0.28 µM) compared to galactan from Echinacea. The results contribute to knowledge on interactions between plant polysaccharides and galectins. Arabinogalactan-proteins have been identified as a new source for production of galactans with possible capability to act as galectin inhibitors.

Targeting galectins in T cell-based immunotherapy within tumor microenvironment

Over the past few years, tumor immunotherapy has emerged as an innovative tumor treatment and owned incomparable advantages over other tumor therapy. With unique complexity and uncertainty, immunotherapy still need helper to apply in the clinic. Galectins, modulated in tumor microenvironment, can regulate the disorders of innate and adaptive immune system resisting tumor growth. Considering the role of galectins in tumor immunosuppression, combination therapy of targeted anti-galectins and immunotherapy may be a promising tumor treatment. This brief review summarizes the expression and immune functions of different galectins in tumor microenvironment and discusses the potential value of anti-galectins in combination with checkpoint inhibitors in tumor immunotherapy.

Synergistic anti-inflammatory effects of different polysaccharide components from Xylaria nigripes

Nondigestible polysaccharides are essential nutrients, which are also important bioactive constituents of mushrooms. This study aimed to investigate the physicochemical properties and anti-inflammatory effects of different polysaccharide components of Xylaria nigripes in lipopolysaccharides (LPS)-induced RAW264.7 macrophages. Results showed that X. nigripes nondigestible polysaccharide (XN) possessed a molecular weight of 910.7 kDa and mainly composed of glucose; it effectively suppressed NO, TNF-α, and IL-6 production. Based on molecular weight, two bioactive polysaccharide components (F1 and F2) were isolated from XN. F1 was a glucan with high molecular weight (885.2 kDa), whereas F2 was a low molecular weight heteropolysaccharide (24.5 kDa) composing of glucose, mannose, and galactose. F1 showed stronger inhibitory effects on NO, TNF-α, and IL-6 production than F2, however, its inhibitory effects were weaker than XN. Further analysis demonstrated that the combined treatment of F1 and F2 exhibited anti-inflammatory activity as good as XN, and they possessed synergistic effects on inhibiting pro-inflammatory mediator production. PRACTICAL APPLICATIONS: Polysaccharides are essential nutrients, and are major bioactive constituents of mushrooms. This study isolated two bioactive polysaccharide components from Xylaria nigripes, namely F1 and F2. F1 was a high molecular weight glucan, whereas F2 was a low molecular weight heteropolysaccharide. F1 showed stronger anti-inflammatory activity than F2, but was weaker than their combined treatment (F1 + F2). Different polysaccharide components were shown to possess synergistic anti-inflammatory effects, suggesting their importance in the formulation of polysaccharide-based products.

The purification of pectin from commercial fruit flours results in a jaboticaba fraction that inhibits galectin-3 and colon cancer cell growth

Fruits are a prime source of nutrients, bioactive compounds, and dietary fibers. Some products available on the Brazilian market use fruit by-products and claim to have useful effects on human health due to their dietary fiber content. The study aimed to extract and purify the total (28-47 w/w yield) and soluble dietary fiber (4-7 w/w yield) from jaboticaba, papaya, and plum commercial flours sold in Brazil and to study the in vitro biological effects of the fractions. The purified water-soluble fractions consisted mainly of pectin-derived oligosaccharides (5-15 KDa molecular weight) with a negligible content of polyphenols, protein, ashes, and starch. Jaboticaba sample was 95% galacturonic acid while plum and papaya samples were 40% galacturonic acid and 40% galactose (mol%), approximately. The samples were tested for recombinant human galectin-3 inhibition and changes in the cell viability of human colorectal cancer cells. Only the jaboticaba sample inhibited galectin-3 and decreased HCT116 cell viability after 48 h of treatment (p ≤ 0.01) while the plum sample decreased the cell viability after 24 h treatment (p ≤ 0.05). The results obtained in this study demonstrate the relationship between the structure of the soluble fibers extracted from jaboticaba flour and the possible beneficial effects of their consumption.

Topsy-turvy binding of negatively charged homogalacturonan oligosaccharides to galectin-3

Galectin-3 is crucial to many physiological and pathological processes. The generally accepted dogma is that galectins function extracellularly by binding specifically to β(1→4)-galactoside epitopes on cell surface glycoconjugates. Here, we used crystallography and NMR spectroscopy to demonstrate that negatively charged homogalacturonans (HG, linear polysaccharides of α(1→4)-linked-D-galacturonate (GalA)) bind to the galectin-3 carbohydrate recognition domain. The HG carboxylates at the C6 positions in GalA rings mandate that this saccharide bind galectin-3 in an unconventional, "topsy-turvy" orientation that is flipped by about 180o relative to that of the canonical β-galactoside lactose. In this binding mode, the reducing end GalA β-anomer of HGs takes the position of the nonreducing end galactose residue in lactose. This novel orientation maintains interactions with the conserved tryptophan and seven of the most crucial lactose-binding residues, albeit with different H-bonding interactions. Nevertheless, the HG molecular orientation and new interactions have essentially the same thermodynamic binding parameters as lactose. Overall, our study provides structural details for a new type of galectin-sugar interaction that broadens glycospace for ligand binding to Gal-3 and suggests how the lectin may recognize other negatively charged polysaccharides like glycoaminoglycans (e.g. heparan sulfate) on the cell surface. This discovery impacts on our understanding of galectin-mediated biological function.

Modified citrus pectins by UV/H2O2 oxidation at acidic and basic conditions: Structures and in vitro anti-inflammatory, anti-proliferative activities

Two modified citrus pectins, MCP4 and MCP10, were prepared by UV/H₂O₂ treatment at pH 4 and pH 10, respectively, and their structures were characterized. MCP10 had a rhamnogalacturonan-I (RG-I) enriched backbone with a high degree of branching (DB ∼61 %) and a low methoxylation degree (24 %). MCP4 had a homogalacturonan enriched backbone with a high degree (46 %) of methoxylation and a low DB (∼41 %) of RG-I branches. MCP10 exhibited a higher anti-inflammatory activity than MCP4 in suppressing the NF-κB expression and the production of pro-inflammatory factors TNF-α and IL-1β of THP-1 cells stimulated by lipopolysaccharide. MCP10 also showed a stronger inhibitory effect on Caco-2 cell proliferation. The stronger bioactivities of MCP10 may be attributable to the abundant branches and the proper length of terminal galactan residues attached to the RG-I domain.

NMR-based insight into galectin-3 binding to endothelial cell adhesion molecule CD146: Evidence for noncanonical interactions with the lectin's CRD β-sandwich F-face

Galectin-3 (Gal-3) binds to cell adhesion glycoprotein CD146 to promote cytokine secretion and mediate endothelial cell migration. Here, we used Nuclear Magnetic Resonance (NMR) 15N-Heteronuclear Single Quantum Coherence (HSQC) spectroscopy to investigate binding between 15N-labeled Gal-3 and the extracellular domain (eFL) of purified CD146 (five Ig-like ectodomains D1-D5) and a shorter, D5-deleted version of CD146 (D1-D4). Binding of Gal-3 and its carbohydrate recognition domain (CRD) to CD146 D1-D4 is greatly reduced vis-à-vis CD146 eFL, supporting the proposal of a larger number of glycosylation sites on D5. Even though the canonical sugar-binding β-sheet S-face (β-strands 1, 10, 3, 4, 5, 6) of the Gal-3 β-sandwich is involved in interactions with CD146 (e.g. N-linked glycosylation sites), equivalent HSQC spectral perturbations at residues on the opposing Gal-3 F-face β-sheet (β-strands 11, 2, 7, 8, 9) indicate involvement of the Gal-3 F-face in binding CD146. This is supported by the observation that addition of lactose, while significantly attenuating Gal-3 binding (primarily with the S-face) to CD146 eFL, does not abolish it. Bio-Layer Interferometry studies with Gal-3 F-face mutants yield KD values to demonstrate a significant decrease (L203A) or increase (V204A, L218A, T243A) in net binding to CD146 eFL compared to wild type Gal-3. However, HSQC lactose titrations show no highly significant effects on sugar binding to the Gal-3 CRD S-face. Overall, our findings indicate that Gal-3 binding to CD146 is more involved than simple interactions with β-galactoside epitopes on the cell receptor, and that there is a direct role for the lectin's CRD F-face in the CD146 binding process.

Phytochemicals and Gastrointestinal Cancer: Cellular Mechanisms and Effects to Change Cancer Progression

Gastrointestinal (GI) cancer is a prevailing global health disease with a high incidence rate which varies by region. It is a huge economic burden on health care providers. GI cancer affects different organs in the body such as the gastric organs, colon, esophagus, intestine, and pancreas. Internal and external factors like smoking, obesity, urbanization, genetic mutations, and prevalence of Helicobacter pylori and Hepatitis B and Hepatitis C viral infections could increase the risk of GI cancer. Phytochemicals are non-nutritive bioactive secondary compounds abundantly found in fruits, grains, and vegetables. Consumption of phytochemicals may protect against chronic diseases like cardiovascular disease, neurodegenerative disease, and cancer. Multiple studies have assessed the chemoprotective effect of selected phytochemicals in GI cancer, offering support to their potential towards reducing the pathogenesis of the disease. The aim of this review was to summarize the current knowledge addressing the anti-cancerous effects of selected dietary phytochemicals on GI cancer and their molecular activities on selected mechanisms, i.e., nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), detoxification enzymes, adenosine monophosphate activated protein kinase (AMPK), wingless-related integration site/β-catenin (wingless-related integration site (Wnt) β-catenin, cell apoptosis, phosphoinositide 3-kinases (PI3K)/ protein kinase B AKT/ mammalian target of rapamycin (mTOR), and mitogen-activated protein kinase (MAPK). In this review phytochemicals were classified into four main categories: (i) carotenoids, including lutein, lycopene, and β-carotene; (ii) proanthocyanidins, including quercetin and ellagic acid; (iii) organosulfur compounds, including allicin, allyl propyl disulphide, asparagusic acid, and sulforaphane; and (iv) other phytochemicals including pectin, curcumins, p-coumaric acid and ferulic acid. Overall, phytochemicals improve cancer prognosis through the downregulation of β-catenin phosphorylation, therefore enhancing apoptosis, and upregulation of the AMPK pathway, which supports cellular homeostasis. Nevertheless, more studies are needed to provide a better understanding of the mechanism of cancer treatment using phytochemicals and possible side effects associated with this approach.

Plant-derived saccharides and their inhibitory potential on metastasis associated cellular processes of pancreatic ductal adenocarcinoma cells

This study intends to investigate the inhibitory potential of different plant derived saccharides on cell migration and adhesion of pancreatic ductal adenocarcinoma (PDAC) cells to microvascular liver endothelium, particularly considering the role of transmembranous galectin-3. PDAC cell lines PancTu1 and Panc1 were characterized by considerable (transmembranous) galectin-3 (Gal3) expression. SiRNA mediated Gal3 knockdown as well as treatment with differentially processed pectins and arabinogalactan-proteins (AGPs) did not impact on cell migration of either PDAC cell line. In contrast, Gal3 knockdown reduced adhesion of PDAC cells to the liver endothelial cell line TMNK-1 being more pronounced in Panc1 cells. Similarly, plant derived substances did not impact cell adhesion of PancTu1 cells while partially hydrolyzed citrus pectin (MCP), pectinase-treated MCP (MCP_Pec) and partially hydrolized AGP (AGP_TFA) clearly diminished adhesive properties of Panc1 cells. MCP_Pec or AGP_TFA could not further intensify the adhesion reducing effect of galectin-3 knockdown, indicating that these plant derived polysaccharides are able to inhibit PDAC cell adhesion to liver endothelial cells in a galectin-3 dependent manner. Overall, these data suggest an inhibitory potential of plant derived processed saccharides which have undergone chemical modification in impairing PDAC cell adhesion to liver endothelium.

Rethinking the impact of RG-I mainly from fruits and vegetables on dietary health

Rhamnogalacturonan I (RG-I) pectin is composed of backbone of repeating disaccharide units →2)-α-L-Rhap-(1→4)-α-D-GalpA-(1→ and neutral sugar side-chains mainly consisting of arabinose and galactose having variable types of linkages. However, since traditional pectin extraction methods damages the RG-I structure, the characteristics and health effects of RG-I remains unclear. Recently, many studies have focused on RG-I, which is often more active than the homogalacturonan (HG) portion of pectic polysaccharides. In food products, RG-I is common to fruits and vegetables and possesses many health benefits. This timely and comprehensive review describes the many different facets of RG-I, including its dietary sources, history, metabolism and potential functionalities, all of which have been compiled to establish a platform for taking full advantage of the functional value of RG-I pectin.

Ingestion of Non-digestible Carbohydrates From Plant-Source Foods and Decreased Risk of Colorectal Cancer: A Review on the Biological Effects and the Mechanisms of Action

The hypothesis that links the increase in the intake of plant-source foods to a decrease in colorectal cancer (CRC) risk has almost 50 years. Nowadays, systematic reviews and meta-analysis of case-control and cohort studies confirmed the association between dietary patterns and CRC risk, in which the non-digestible carbohydrates (NDC) from plant-source foods are known to play beneficial effects. However, the mechanisms behind the physicochemical properties and biological effects induced by NDC on the decrease of CRC development and progression remain not fully understood. NDC from plant-source foods consist mainly of complex carbohydrates from plant cell wall including pectin and hemicellulose, which vary among foods in structure and in composition, therefore in both physicochemical properties and biological effects. In the present review, we highlighted the mechanisms and described the recent findings showing how these complex NDC from plant-source foods are related to a decrease in CRC risk through induction of both physicochemical effects in the gastrointestinal tract, fermentation-related effects, and direct effects resulting from the interaction between NDC and cellular components including toll-like receptors and galectin-3. Studies support that the definition of the structure-function relationship-especially regarding the fermentation-related effects of NDC, as well as the direct effects of these complex carbohydrates in cells-is crucial for understanding the possible NDC anticancer effects. The dietary recommendations for the intake of NDC are usually quantitative, describing a defined amount of intake per day. However, as NDC from plant-source foods can exert effects that vary widely according to the NDC structure, the dietary recommendations for the intake of NDC plant-source foods are expected to change from a quantitative to a qualitative perspective in the next few years, as occurred for lipid recommendations. Thus, further studies are necessary to define whether specific and well-characterized NDC from plant-source foods induce beneficial effects related to a decrease in CRC risk, thereby improving nutritional recommendations of healthy individuals and CRC patients.

Galectin-3 binds selectively to the terminal, non-reducing end of β(1→4)-galactans, with overall affinity increasing with chain length

Galactans are linear polysaccharides of β(1→4)-linked galactose residues. Although they can antagonize galectin function, the nature of their binding to galectins needs to be better defined to develop them as drugs. Here, we investigated interactions between galectin-3 (Gal-3) and a series of galactans ranging in weight average molecular weight from 670 to 7550 Da. 15N-1H HSQC NMR studies with 15N-labeled Gal-3 carbohydrate recognition domain (CRD) indicate that each of these galactans interacts primarily with residues in β-strands 4, 5 and 6 on the canonical, β-galactoside sugar binding S-face. Although these galactans also bind to full length Gal-3 (CRD plus N-terminal tail) to the same extent, it appears that binding to the S-face attenuates interactions between the CRD F-face and N-terminal tail, making interpretation of site-specific binding unclear. Following assignment of galactan 13C and 1H resonances using HSQC, HMBC and TOCSY experiments, we used 13C-1H HSQC data to demonstrate that the Gal-3 CRD binds to the terminal, non-reducing end of these galactans, regardless of their size, but with binding affinity increasing as the galactan chain length increases. Overall, our findings increase understanding as to how galactans interact with Gal-3 at the non-reducing, terminal end of galactose-containing polysaccharides as found on the cell surface.

Analysis of pectin from Panax ginseng flower buds and their binding activities to galectin-3

Water-soluble pectic polysaccharides isolated from Panax ginseng flower buds (WGFPA) were completely fractionated into six homogeneous fractions (WGFPA-1a, WGFPA-2a, WGFPA-3a, WGFPA-1b, WGFPA-2b and WGFPA-3b) by a combination of ion-exchange and size exclusion chromatographies. Monosaccharide composition, enzymatic hydrolysis and ¹³C nuclear magnetic resonance (NMR) spectra analysis were combined to characterize their structural features. Furthermore, the interactions between these polysaccharides and galectin-3 were evaluated by biolayer interferometry assay. The results showed that WGFPA-1a, WGFPA-2a and WGFPA-3a were rhamnogalacturonan I (RG-I) type pectin with abundant side chains, including α-L-1,5-arabinan, β-D-1,4-galactan, arabinogalactan I (AG-I) and arabinogalactan II (AG-II), exhibiting strong binding activities to galectin-3 with apparent KD values 4.9 μM, 0.71 μM and 0.24 μM, respectively. WGFPA-1b, WGFPA-2b and WGFPA-3b were homogalacturonan (HG) type pectin covalently linked with different ratios of rhamnogalacturonan II (RG-II) domains, showing weaker or no interactions with galectin-3. This study provides useful structural information for further investigation on the structure-activity relationship of ginseng flower buds pectin.

CD146 interacts with galectin-3 to mediate endothelial cell migration

Here, we investigated the role of the cell membrane protein CD146 in galectin-3-mediated endothelial cell migration at the molecular level. Our results show that knocking down CD146 significantly attenuates galectin-3-mediated cell migration. Pull-down assays, gel filtration, and biolayer interferometry further demonstrate that galectin-3 binds to the CD146 ectodomain (eFL) with a K_D of ~1.1 μm. To identify the galectin-3-binding site, we used mass spectrometry to show that CD146 eFL has four N-glycosites, with PNGase F treatment indicating that N-glycans define the binding epitope. Galectin-3 likely interacts with Domain 5 on CD146 eFL, because it contains poly-N-acetyllactosamine sites, and deletion of this domain significantly reduces binding. Overall, our findings provide a better understanding of how galectin-3 interacts with cell membrane receptors to mediate endothelial cell migration.

Galectins at a glance

Galectins are carbohydrate-binding proteins that are involved in many physiological functions, such as inflammation, immune responses, cell migration, autophagy and signalling. They are also linked to diseases such as fibrosis, cancer and heart disease. How such a small family of only 15 members can have such widespread effects remains a conundrum. In this Cell Science at a Glance article, we summarise recent literature on the many cellular activities that have been ascribed to galectins. As shown on the accompanying poster, these include carbohydrate-independent interactions with cytosolic or nuclear targets and carbohydrate-dependent interactions with extracellular glycoconjugates. We discuss how these intra- and extracellular activities might be linked and point out the importance of unravelling molecular mechanisms of galectin function to gain a true understanding of their contributions to the physiology of the cell. We close with a short outlook on the organismal functions of galectins and a perspective on the major challenges in the field.