Unveiling the sugary secrets of plasmodium parasites

Plasmodium parasites cause malaria disease, one of the leading global health burdens for humanity, infecting hundreds of millions of people each year. Different glycans on the parasite and the host cell surface play significant roles in both malaria pathogenesis and host defense mechanisms. So far, only small, truncated N- and O-glycans have been identified in Plasmodium species. In contrast, complex glycosylphosphatidylinositol (GPI) glycolipids are highly abundant on the parasite's cell membrane and are essential for its survival. Moreover, the parasites express lectins that bind and exploit the host cell surface glycans for different aspects of the parasite life cycle, such as adherence, invasion, and evasion of the host immune system. In parallel, the host cell glycocalyx and lectin expression serve as the first line of defense against Plasmodium parasites and directly dictate susceptibility to Plasmodium infection. This review provides an overview of the glycobiology involved in Plasmodium-host interactions and its contribution to malaria pathogenesis. Recent findings are presented and evaluated in the context of potential therapeutic exploitation

Semi- and fully synthetic carbohydrate vaccines against pathogenic bacteria : recent developments

The importance of vaccine-induced protection was repeatedly demonstrated over the last three decades and emphasized during the recent COVID-19 pandemic as the safest and most effective way of preventing infectious diseases. Vaccines have controlled, and in some cases, eradicated global viral and bacterial infections with high efficiency and at a relatively low cost. Carbohydrates form the capsular sugar coat that surrounds the outer surface of human pathogenic bacteria. Specific surface-exposed bacterial carbohydrates serve as potent vaccine targets that broadened our toolbox against bacterial infections. Since first approved for commercial use, antibacterial carbohydrate-based vaccines mostly rely on inherently complex and heterogenous naturally derived polysaccharides, challenging to obtain in a pure, safe, and cost-effective manner. The introduction of synthetic fragments identical with bacterial capsular polysaccharides provided well-defined and homogenous structures that resolved many challenges of purified polysaccharides. The success of semisynthetic glycoconjugate vaccines against bacterial infections, now in different phases of clinical trials, opened up new possibilities and encouraged further development towards fully synthetic antibacterial vaccine solutions. In this mini-review, we describe the recent achievements in semi- and fully synthetic carbohydrate vaccines against a range of human pathogenic bacteria, focusing on preclinical and clinical studies

Lectin-mediated bacterial modulation by the intestinal nematode Ascaris suum

Ascariasis is a global health problem for humans and animals. Adult Ascaris nematodes are long-lived in the host intestine where they interact with host cells as well as members of the microbiota resulting in chronic infections. Nematode interactions with host cells and the microbial environment are prominently mediated by parasite-secreted proteins and peptides possessing immunomodulatory and antimicrobial activities. Previously, we discovered the C-type lectin protein AsCTL-42 in the secreted products of adult Ascaris worms. Here we tested recombinant AsCTL-42 for its ability to interact with bacterial and host cells. We found that AsCTL-42 lacks bactericidal activity but neutralized bacterial cells without killing them. Treatment of bacterial cells with AsCTL-42 reduced invasion of intestinal epithelial cells by Salmonella. Furthermore, AsCTL-42 interacted with host myeloid C-type lectin receptors. Thus, AsCTL-42 is a parasite protein involved in the triad relationship between Ascaris, host cells, and the microbiota

Sialylated N-glycans mediate monocyte uptake of extracellular vesicles secreted from Plasmodium falciparum-infected red blood cells

Glycoconjugates on extracellular vesicles (EVs) play a vital role in internalization and mediate interaction as well as regulation of the host immune system by viruses, bacteria, and parasites. During their intraerythrocytic life-cycle stages, malaria parasites, Plasmodium falciparum (Pf) mediate the secretion of EVs by infected red blood cells (RBCs) that carry a diverse range of parasitic and host-derived molecules. These molecules facilitate parasite-parasite and parasite-host interactions to ensure parasite survival. To date, the number of identified Pf genes associated with glycan synthesis and the repertoire of expressed glycoconjugates is relatively low. Moreover, the role of Pf glycans in pathogenesis is mostly unclear and poorly understood. As a result, the expression of glycoconjugates on Pf-derived EVs or their involvement in the parasite life-cycle has yet to be reported. Herein, we show that EVs secreted by Pf-infected RBCs carry significantly higher sialylated complex N-glycans than EVs derived from healthy RBCs. Furthermore, we reveal that EV uptake by host monocytes depends on N-glycoproteins and demonstrate that terminal sialic acid on the N-glycans is essential for uptake by human monocytes. Our results provide the first evidence that Pf exploits host sialylated N-glycans to mediate EV uptake by the human immune system cells

Enhanced microbial bile acid deconjugation and impaired ileal uptake in pregnancy repress intestinal regulation of bile acid synthesis

Pregnancy is associated with progressive hypercholanemia, hypercholesterolemia, and hypertriglyceridemia, which can result in metabolic disease in susceptible women. Gut signals modify hepatic homeostatic pathways, linking intestinal content to metabolic activity. We sought to identify whether enteric endocrine signals contribute to raised serum bile acids observed in human and murine pregnancies, by measuring fibroblast growth factor (FGF) 19/15 protein and mRNA levels, and 7α-hydroxy-4-cholesten-3-one. Terminal ileal farnesoid X receptor (FXR)-mediated gene expression and apical sodium bile acid transporter (ASBT) protein concentration were measured by qPCR and western blotting. Shotgun whole-genome sequencing and ultra-performance liquid chromatography tandem mass spectrometry were used to determine the cecal microbiome and metabonome. Targeted and untargeted pathway analyses were performed to predict the systemic effects of the altered metagenome and metabolite profiles. Dietary CA supplementation was used to determine whether the observed alterations could be overcome by intestinal bile acids functioning as FXR agonists. Human and murine pregnancy were associated with reduced intestinal FXR signaling, with lower FGF19/15 and resultant increased hepatic bile acid synthesis. Terminal ileal ASBT protein was reduced in murine pregnancy. Cecal bile acid conjugation was reduced in pregnancy because of elevated bile salt hydrolase-producing Bacteroidetes. CA supplementation induced intestinal FXR signaling, which was not abrogated by pregnancy, with strikingly similar changes to the microbiota and metabonome as identified in pregnancy. Conclusion: The altered intestinal microbiota of pregnancy enhance bile acid deconjugation, reducing ileal bile acid uptake and lowering FXR induction in enterocytes. This exacerbates the effects mediated by reduced bile acid uptake transporters in pregnancy. Thus, in pregnant women and mice, there is reduced FGF19/15-mediated hepatic repression of hepatic bile acid synthesis, resulting in hypercholanemia

Visible-light mediated oxidative ring expansion of anellated cyclopropanes to fused endoperoxides with antimalarial activity

A visible light mediated ring expansion of readily available carbo- and heterocyclic anellated cyclopropanes by molecular oxygen at ambient pressure has been developed. Tolerating a variety of functional groups, the reaction yields fused 1,2-dioxolanes, which were tested for antimalarial activity given their close analogy to the active principle of approved drugs such as artemisinin

Total synthesis of D-glycero-D-mannno-heptose 1β, 7-bisphosphate with 3-O-amyl amine linker and its monophosphate derivative

D-Glycero-D-mannno-heptose 1β, 7-bisphosphate (HBPβ) is an important intermediate for constructing the core structure of Gram-negative bacterial lipopolysaccharides and was reported as a pathogen-associated molecular pattern (PAMP) that regulates immune responses. HBPβ with 3-O-amyl amine linker and its monophosphate derivative D-glycero-D-mannno-heptose 7-phosphate (HP) with 1α-amyl amine linker have been synthesized as candidates for immunity study of HBPβ. The O3-amyl amine linker of heptose was installed by dibutyltin oxide-mediated regioselective alkylation under fine-tuned protecting condition. The stereoselective installation of 1β-phosphate ester was achieved by NIS-mediated phosphorylation at low temperature. The strategy for installation of 3-O-amyl amine linker onto HBP derivative can be expanded to the syntheses of other conjugation-ready carbohydrates bearing anomeric phosphoester

Imaging keratan sulfate in ocular tissue sections by immunofluorescence microscopy and LA-ICP-MS

Carbohydrate-specific antibodies can serve as valuable tools to monitor alterations in the extracellular matrix resulting from pathologies. Here, the keratan sulfate-specific monoclonal antibody MZ15 was characterized in more detail by immunofluorescence microscopy as well as laser ablation ICP-MS using tissue cryosections and paraffin-embedded samples. Pretreatment with keratanase II prevented staining of samples and therefore demonstrated efficient enzymatic keratan sulfate degradation. Random fluorescent labeling and site-directed introduction of a metal cage into MZ15 were successful and allowed for a highly sensitive detection of the keratan sulfate landscape in the corneal stroma from rats and human tissue

Generation of glycan-specific nanobodies

The development of antibodies that target specific glycan structures on cancer cells or human pathogens poses a significant challenge due to the immense complexity of naturally occurring glycans. Automated glycan assembly enables the production of structurally homogeneous glycans in amounts that are difficult to derive from natural sources. Nanobodies (Nbs) are the smallest antigen-binding domains of heavy-chain-only antibodies (hcAbs) found in camelids. To date, the development of glycan-specific Nbs using synthetic glycans has not been reported. Here, we use defined synthetic glycans for alpaca immunization to elicit glycan-specific hcAbs, and describe the identification, isolation, and production of a Nb specific for the tumor-associated carbohydrate antigen Globo-H. The Nb binds the terminal fucose of Globo-H and recognizes synthetic Globo-H in solution and native Globo-H on breast cancer cells with high specificity. These results demonstrate the potential of our approach for generating glycan-targeting Nbs to be used in biomedical and biotechnological applications