Tailoring Trehalose for Biomedical and Biotechnological Applications

Targeting Mycobacterium tuberculosis Persistence through Inhibition of the Trehalose Catalytic Shift

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb), is the leading cause of death worldwide by infectious disease. Treatment of Mtb infection requires a six-month course of multiple antibiotics, an extremely challenging regimen necessitated by Mtb's ability to form drug-tolerant persister cells. Mtb persister formation is dependent on the trehalose catalytic shift, a stress-responsive metabolic remodeling mechanism in which the disaccharide trehalose is liberated from cell surface glycolipids and repurposed as an internal carbon source to meet energy and redox demands. Here, using a biofilm-persister model, metabolomics, and cryo-electron microscopy (EM), we found that azidodeoxy- and aminodeoxy-d-trehalose analogues block the Mtb trehalose catalytic shift through inhibition of trehalose synthase TreS (Rv0126), which catalyzes the isomerization of trehalose to maltose. Out of a focused eight-member compound panel constructed by chemoenzymatic synthesis, the natural product 2-trehalosamine exhibited the highest potency and significantly potentiated first- and second-line TB drugs in broth culture and macrophage infection assays. We also report the first structure of TreS bound to a substrate analogue inhibitor, obtained via cryo-EM, which revealed conformational changes likely essential for catalysis and inhibitor binding that can potentially be exploited for future therapeutic development. Our results demonstrate that inhibition of the trehalose catalytic shift is a viable strategy to target Mtb persisters and advance trehalose analogues as tools and potential adjunctive therapeutics for investigating and targeting mycobacterial persistence.

Immune Targeting of Mycobacteria through Cell Surface Glycan Engineering

Mycobacteria and other organisms in the order Mycobacteriales cause a range of significant human diseases, including tuberculosis, leprosy, diphtheria, Buruli ulcer, and non-tuberculous mycobacterial (NTM) disease. However, the intrinsic drug tolerance engendered by the mycobacterial cell envelope undermines conventional antibiotic treatment and contributes to acquired drug resistance. Motivated by the need to augment antibiotics with novel therapeutic approaches, we developed a strategy to specifically decorate mycobacterial cell surface glycans with antibody-recruiting molecules (ARMs), which flag bacteria for binding to human-endogenous antibodies that enhance macrophage effector functions. Mycobacterium-specific ARMs consisting of a trehalose targeting moiety and a dinitrophenyl hapten (Tre-DNPs) were synthesized and shown to specifically incorporate into outer-membrane glycolipids of Mycobacterium smegmatis via trehalose metabolism, enabling recruitment of anti-DNP antibodies to the mycobacterial cell surface. Phagocytosis of Tre-DNP-modified M. smegmatis by macrophages was significantly enhanced in the presence of anti-DNP antibodies, demonstrating proof-of-concept that our strategy can augment the host immune response. Because the metabolic pathways responsible for cell surface incorporation of Tre-DNPs are conserved in all Mycobacteriales organisms but absent from other bacteria and humans, the reported tools may be enlisted to interrogate host-pathogen interactions and develop immune-targeting strategies for diverse mycobacterial pathogens.

Chemical approaches to unraveling the biology of mycobacteria

Mycobacterium tuberculosis (Mtb), perhaps more than any other organism, is intrinsically appealing to chemical biologists. Not only does the cell envelope feature one of the most complex heteropolymers found in nature1 but many of the interactions between Mtb and its primary host (we humans) rely on lipid and not protein mediators.2,3 Many of the complex lipids, glycolipids, and carbohydrates biosynthesized by the bacterium still have unknown functions, and the complexity of the pathological processes by which tuberculosis (TB) disease progress offers many opportunities for these molecules to influence the human response. Because of the importance of TB in global public health, chemical biologists have applied a wide-ranging array of techniques to better understand the disease and improve interventions.

Dietary Trehalose as a Bioactive Nutrient

Trehalose is a naturally occurring, non-reducing disaccharide comprising two covalently-linked glucose molecules. It possesses unique physiochemical properties, which account for multiple biological roles in a variety of prokaryotic and eukaryotic organisms. In the past few decades, intensive research on trehalose has uncovered its functions, and extended its uses as a sweetener and stabilizer in the food, medical, pharmaceutical, and cosmetic industries. Further, increased dietary trehalose consumption has sparked research on how trehalose affects the gut microbiome. In addition to its role as a dietary sugar, trehalose has gained attention for its ability to modulate glucose homeostasis, and potentially as a therapeutic agent for diabetes. This review discusses the bioactive effects of dietary trehalose, highlighting its promise in future industrial and scientific contributions.

Trehalose-Grafted Glycopolymer: Synthesis via the Staudinger Reaction and Capture of Mycobacteria

A new trehalose-grafted poly(2-hydroxyethyl methacrylate) (HEMA) glycopolymer was synthesized via the perfluorophenyl azide (PFPA)-mediated Staudinger reaction between poly(HEMA-co-HEMA-PFPA) and a diphenylphosphine-derivatized trehalose. The reaction occurred rapidly at room temperature without the use of any catalyst, giving the trehalose glycopolymers over 68% yield after 1 h. The grafting density of trehalose can be controlled by the copolymer composition in poly(HEMA-co-HEMA-PFPA), resulting in 6.1% (TP1) or 37% (TP2) at 10:1 and 1:1 HEMA/HEMA-PFPA feed ratio, respectively. The trehalose glycopolymer was covalently attached on glass slides or silicon wafers using a thin film of poly(HEMA-co-HEMA-PFPA) as the adhesion layer, achieved through the C-H insertion reaction of the photogenerated singlet perfluorophenyl nitrene. To demonstrate the ability of the trehalose glycopolymer to capture mycobacteria, arrays of the trehalose glycopolymer were fabricated and treated with Mycobacterium smegmatis. Results from the optical, fluorescence, and scanning electron microscopy showed that mycobacteria were indeed captured on the trehalose glycopolymer. The amount of mycobacteria captured increased with the percent trehalose in the trehalose glycopolymer and also with the concentration of the trehalose glycopolymer. In addition, the captured bacteria could be visualized by the naked eye under the illumination of a hand-held UV lamp.

Potential Properties of Natural Nutraceuticals and Antioxidants in Age-Related Eye Disorders

Eye health is crucial, and the onset of diseases can reduce vision and affect the quality of life of patients. The main causes of progressive and irreversible vision loss include various pathologies, such as cataracts, ocular atrophy, corneal opacity, age-related macular degeneration, uncorrected refractive error, posterior capsular opacification, uveitis, glaucoma, diabetic retinopathy, retinal detachment, undetermined disease and other disorders involving oxidative stress and inflammation. The eyes are constantly exposed to the external environment and, for this reason, must be protected from damage from the outside. Many drugs, including cortisonics and antinflammatory drugs have widely been used to counteract eye disorders. However, recent advances have been obtained via supplementation with natural antioxidants and nutraceuticals for patients. In particular, evidence has accumulated that polyphenols (mostly deriving from Citrus Bergamia) represent a reliable source of antioxidants able to counteract oxidative stress accompanying early stages of eye diseases. Luteolin in particular has been found to protect photoreceptors, thereby improving vision in many disease states. Moreover, a consistent anti-inflammatory response was found to occur when curcumin is used alone or in combination with other nutraceuticals. Additionally, Coenzyme Q10 has been demonstrated to produce a consistent effect in reducing ocular pressure, thereby leading to protection in patients undergoing glaucoma. Finally, both grape seed extract, rich in anthocyanosides, and polynsatured fatty acids seem to contribute to the prevention of retinal disorders. Thus, a combination of nutraceuticals and antioxidants may represent the right solution for a multi-action activity in eye protection, in association with current drug therapies, and this will be of potential interest in early stages of eye disorders.

Design and Synthesis of Visible-Light-Responsive Azobenzene Building Blocks for Chemical Biology

Tetra-ortho-fluoro-azobenzenes are a class of photoswitches useful for the construction of visible-light-controlled molecular systems. They can be used to achieve spatio-temporal control over the properties of a chosen bioactive molecule. However, the introduction of different substituents to the tetra-fluoro-azobenzene core can significantly affect the photochemical properties of the switch and compromise biocompatibility. Herein, we explored the effect of useful substituents, such as functionalization points, attachment handles, and water-solubilizing groups, on the photochemical properties of this photochromic system. In general, all the tested fluorinated azobenzenes exhibited favorable photochemical properties, such as high photostationary state distribution and long half-lives, both in organic solvents and in water. One of the azobenzene building blocks was functionalized with a trehalose group to enable the uptake of the photoswitch into mycobacteria. Following metabolic uptake and incorporation of the trehalose-based azobenzene in the mycobacterial cell wall, we demonstrated photoswitching of the azobenzene in the isolated total lipid extract.

Identification of the Toxic Compounds in Camellia oleifera Honey and Pollen to Honey Bees (Apis mellifera)

Identifying the components of Camellia oleifera honey and pollen and conducting corresponding toxicological tests are essential to revealing the mechanism of Camellia oleifera toxicity to honey bees. In this research, we investigated the saccharides and alkaloids in honey, nectar, and pollen from Camellia oleifera, which were compared with honey, nectar, and pollen from Brassica napus, a widely planted flowering plant. The result showed that melibiose, manninotriose, raffinose, stachyose, and lower amounts of santonin and caffeine were found in Camellia oleifera nectar, pollen, and honey but not in B. napus nectar, pollen, and honey. Toxicological experiments indicated that manninotriose, raffinose, and stachyose in Camellia oleifera honey are toxic to bees, while alkaloids in Camellia oleifera pollen are not toxic to honey bees. The toxicity mechanism of oligosaccharides revealed by temporal metabolic profiling is that oligosaccharides cannot be further digested by honey bees and thus get accumulated in honey bees, disturbing the synthesis and metabolism of trehalose, ultimately causing honey bee mortality.

AuCl3-Catalyzed Hemiacetal Activation for the Stereoselective Synthesis of 2-Deoxy Trehalose Derivatives

A new practical, catalytic, and highly stereoselective method for directly accessing 1,1-α,α'-linked 2-deoxy trehalose analogues via AuCl₃-catalyzed dehydrative glycosylation using hemiacetal glycosyl donors and acceptors is described. The method relies on the chemoselective Brønsted acid-type activation of tribenzylated 2-deoxy hemiacetals in the presence of other less reactive hemiacetals.

Rediscovery of 4-Trehalosamine as a Biologically Stable, Mass-Producible, and Chemically Modifiable Trehalose Analog

Nonreducing disaccharide trehalose is used as a stabilizer and humectant in various products and is a potential medicinal drug, showing curative effects on the animal models of various diseases. However, its use is limited as it is hydrolyzed by trehalase, a widely expressed enzyme in multiple organisms. Several trehalose analogs are prepared, including a microbial metabolite 4-trehalosamine, and their high biological stability is confirmed. For further analysis, 4-trehalosamine is selected as it shows high producibility. Compared with trehalose, 4-trehalosamine exhibits better or comparable protective activities and a high buffer capacity around the neutral pH. Another advantage of 4-trehalosamine is its chemical modifiability: simple reactions produce its various derivatives. Labeled probes and detergents are synthesized in one-pot reactions to exemplify the feasibility of their production, and their utility is confirmed for their respective applications. The labeled probes are used for mycobacterial staining. Although the derivative detergents can be effectively used in membrane protein research, long-chain detergents show 1000-3000-fold stronger autophagy-inducing activity in cultured cells than trehalose and are expected to become a drug lead and research reagent. These results indicate that 4-trehalosamine is a useful trehalose substitute for various purposes and a material to produce new useful derivative substances.

Chemical Reporters for Bacterial Glycans: Development and Applications

Bacteria possess an extraordinary repertoire of cell envelope glycans that have critical physiological functions. Pathogenic bacteria have glycans that are essential for growth and virulence but are absent from humans, making them high-priority targets for antibiotic, vaccine, and diagnostic development. The advent of metabolic labeling with bioorthogonal chemical reporters and small-molecule fluorescent reporters has enabled the investigation and targeting of specific bacterial glycans in their native environments. These tools have opened the door to imaging glycan dynamics, assaying and inhibiting glycan biosynthesis, profiling glycoproteins and glycan-binding proteins, and targeting pathogens with diagnostic and therapeutic payload. These capabilities have been wielded in diverse commensal and pathogenic Gram-positive, Gram-negative, and mycobacterial species─including within live host organisms. Here, we review the development and applications of chemical reporters for bacterial glycans, including peptidoglycan, lipopolysaccharide, glycoproteins, teichoic acids, and capsular polysaccharides, as well as mycobacterial glycans, including trehalose glycolipids and arabinan-containing glycoconjugates. We cover in detail how bacteria-targeting chemical reporters are designed, synthesized, and evaluated, how they operate from a mechanistic standpoint, and how this information informs their judicious and innovative application. We also provide a perspective on the current state and future directions of the field, underscoring the need for interdisciplinary teams to create novel tools and extend existing tools to support fundamental and translational research on bacterial glycans.

PPE51 mediates uptake of trehalose across the mycomembrane of Mycobacterium tuberculosis

The disaccharide trehalose is essential for viability of Mycobacterium tuberculosis, which synthesizes trehalose de novo but can also utilize exogenous trehalose. The mycobacterial cell wall encompasses two permeability barriers, the cytoplasmic membrane and the outer mycolic acid-containing mycomembrane. The ABC transporter LpqY-SugA-SugB-SugC has previously been demonstrated to mediate the specific uptake of trehalose across the cytoplasmic membrane. However, it is still unclear how the transport of trehalose molecules across the mycomembrane is mediated. In this study, we harnessed the antimycobacterial activity of the analogue 6-azido trehalose to select for spontaneous resistant M. tuberculosis mutants in a merodiploid strain harbouring two LpqY-SugA-SugB-SugC copies. Mutations mediating resistance to 6-azido trehalose mapped to the proline-proline-glutamate (PPE) family member PPE51 (Rv3136), which has recently been shown to be an integral mycomembrane protein involved in uptake of low-molecular weight compounds. A site-specific ppe51 gene deletion mutant of M. tuberculosis was unable to grow on trehalose as the sole carbon source. Furthermore, bioorthogonal labelling of the M. tuberculosis Δppe51 mutant incubated with 6-azido trehalose corroborated the impaired internalization. Taken together, the results indicate that the transport of trehalose and trehalose analogues across the mycomembrane of M. tuberculosis is exclusively mediated by PPE51.

Microbial trehalose boosts the ecological fitness of biocontrol agents, the viability of probiotics during long-term storage and plants tolerance to environmental-driven abiotic stress

Despite the impressive gain in agricultural production and greater availability of food, a large portion of the world population is affected by food shortages and nutritional imbalance. This is due to abiotic stresses encountered by plants as a result of environmental-driven perturbations, loss of viability of starter cultures (probiotics) for functional foods during storage as well as the vulnerability of farm produce to postharvest pathogens. The use of compatible solutes (e.g., trehalose, proline, etc.) has been widely supported as a solution to these concerns. Trehalose is one of the widely reported microbial- or plant-derived metabolites that help microorganisms (e.g., biocontrol agents, probiotics and plant growth-promoting bacteria) and plants to tolerate harsh environmental conditions. Due to its recent categorization as generally regarded as safe (GRAS), trehalose is an essential tool for promoting nutrition-sensitive agriculture by replacing the overuse of chemical agents (e.g., pesticides, herbicides). Therefore, the current review evaluated the progress currently made in the application of trehalose in sustainable agriculture. The challenges, opportunities, and future of this biometabolite in food security were highlighted.

Sustainability in Heritage Wood Conservation: Challenges and Directions for Future Research

Conserving the world’s cultural and natural heritage is considered a key contributor to achieving the targets set out in the United Nation’s Sustainable Development Goals, yet how much attention do we pay to the methods we use to conserve and protect this heritage? With a specific focus on wooden objects of cultural heritage, this review discusses the current state-of-the-art in heritage conservation in terms of sustainability, sustainable alternatives to currently used consolidants, and new research directions that could lead to more sustainable consolidants in the future. Within each stage a thorough discussion of the synthesis mechanisms and/or extraction protocols, particularly for bio-based resources is provided, evaluating resource usage and environmental impact. This is intended to give the reader a better understanding of the overall sustainability of each different approach and better evaluate consolidant choices for a more sustainable approach. The challenges facing the development of sustainable consolidants and recent research that is likely to lead to highly sustainable new consolidant strategies in the future are also discussed. This review aims to contribute to the ongoing discussion of sustainable conservation and highlight the role that consolidants play in truly sustainable heritage conservation.

Metabolic Labeling of Live Mycobacteria with Trehalose-Based Probes

The mycobacterial cell envelope includes a unique outer membrane, also known as the mycomembrane, which is the major defense barrier that confers intrinsic drug tolerance to Mycobacterium tuberculosis (Mtb) and related bacteria. The mycomembrane is typified by long-chain mycolic acids that are esterified to various acceptors, including: (1) trehalose, forming trehalose mono- and di-mycolate; (2) arabinogalactan, forming arabinogalactan-linked mycolates; and (3) in some species, protein serine residues, forming O-mycoloylated proteins. Synthetic trehalose and trehalose monomycolate analogs have been shown to specifically and metabolically incorporate into mycomembrane components, facilitating their analysis in native contexts and opening new avenues for the specific detection and therapeutic targeting of mycobacterial pathogens in complex settings. This chapter highlights trehalose-based probes that have been developed to date, briefly discusses their applications, and describes protocols for their use in mycobacteria research.

Trehalose-based neuroprotective autophagy inducers

A small set of trehalose-centered putative autophagy inducers was rationally designed and synthesized, with the aim to identify more potent and bioavailable autophagy inducers than free trehalose, and to acquire information about their molecular mechanism of action. Several robust, high yield routes to key trehalose intermediates and small molecule prodrugs (2-5), putative probes (6-10) and inorganic nanovectors (12a - thiol-PEG-triazole-trehalose constructs 11) were successfully executed, and compounds were tested for their autophagy-inducing properties. While small molecules 2-11 showed no pro-autophagic behavior at sub-millimolar concentrations, trehalose-bearing PEG-AuNPs 12a caused measurable autophagy induction at an estimated 40 μM trehalose concentration without any significant toxicity at the same concentration.

Mechanistic differences in the effects of sucrose and sucralose on the phase stability of lysozyme solutions

The effect of two disaccharide analogues, sucrose and sucralose, on the phase stability of aqueous lysozyme solutions has been addressed from a mechanistic viewpoint by a combination of experiment and molecular dynamics (MD) simulations. The influence of the added low molecular weight salts (NaBr, NaI and NaNO₃) was considered as well. The cloud-point temperature measurements revealed a larger stabilizing effect of sucralose. Upon increasing sugar concentration, the protein solutions became more stable and differences in the effect of sucralose and sucrose amplified. It was confirmed that the addition of either of the two sugars imposed no secondary structure changes of the lysozyme. Enthalpies of lysozyme-sugar mixing were exothermic and a larger effect was recorded for sucralose. MD simulations indicated that acidic, basic and polar amino acid residues play predominant roles in the sugar-protein interactions, mainly through hydrogen bonding. Such sugar mediated protein-protein interactions are thought to be responsible for the biopreserative nature of sugars. Our observations hint at mechanistic differences in sugar-lysozyme interactions: while sucrose does not interact directly with the protein's surface for the most part (in line with the preferential hydration hypothesis), sucralose forms hydrogen bonds with acidic, basic and polar amino acid residues at the lysozyme's surface (in line with the water replacement hypothesis).

Molecular cloning and biochemical characterization of a trehalose synthase from Myxococcus sp. strain V11

The tresI gene of Myxococcus sp. strain V11 was cloned, and found to encode a trehalose synthase comprising 551 amino acids. The deduced molecular weight of the encoded TreS I protein 64.7 kDa and the isoelectric point (pI) was predicted to be 5.6. The catalytic cleft consists of the Asp202-Glu244-Asp310 catalytic triad and additional conserved residues. The recombinant (His)₆-tag enzyme was expressed in Escherichia coli BL21(DE3) and purified by Ni²⁺-affinity chromatography, resulting in a specific activity of up to 172.7 U/mg. TLC and HPLC results confirmed that rTreS I can convert maltose into trehalose, with a yield of 61%. The K_M and V_max values of recombinant TreS I for maltose were 0.62 mM and 25.5 mM min^-1 mg^-1 protein, respectively. TreS I was optimally active at 35° and stable at temperatures of <25 °C. TreS I was stable within a narrow range of pH values, from 6.0 to 7.0. The enzymatic activity was slightly stimulated by Mg²⁺ and strongly inhibited by Fe³⁺, Co²⁺ and Cu²⁺. TreS I was also strongly inhibited by SDS and weakly by EDTA and TritonX-100.

The role of chemoenzymatic synthesis in advancing trehalose analogues as tools for combatting bacterial pathogens

Trehalose, a disaccharide of glucose, is increasingly recognized as an important contributor to virulence in major bacterial pathogens, such as Mycobacterium tuberculosis, Clostridioides difficile, and Burkholderia pseudomallei. Accordingly, bacterial trehalose metabolic pathways that are not present in humans have gained traction as targets for antibiotic and diagnostic development. Toward this goal, trehalose can be modified through a combination of rational design and synthesis to produce functionalized trehalose analogues, which can be deployed to probe or inhibit bacterial trehalose metabolism. However, the unique α,α-1,1-glycosidic bond and C2 symmetry of trehalose make analogue synthesis via traditional chemical methods very challenging. We and others have turned to the creation of chemoenzymatic synthesis methods, which in principle allow the use of nature's trehalose-synthesizing enzymes to stereo- and regioselectively couple simple, unprotected substrates to efficiently and conveniently generate trehalose analogues. Here, we provide a contextual account of our team's development of a trehalose analogue synthesis method that employs a highly substrate-tolerant, thermostable trehalose synthase enzyme, TreT from Thermoproteus tenax. Then, in three vignettes, we highlight how chemoenzymatic synthesis has accelerated the development of trehalose-based imaging probes and inhibitors that target trehalose-utilizing bacterial pathogens. We describe the role of TreT catalysis and related methods in the development of (i) tools for in vitro and in vivo imaging of mycobacteria, (ii) anti-biofilm compounds that sensitize drug-tolerant mycobacteria to clinical anti-tubercular compounds, and (iii) degradation-resistant trehalose analogues that block trehalose metabolism in C. difficile and potentially other trehalose-utilizing bacteria. We conclude by recapping progress and discussing priorities for future research in this area, including improving the scope and scale of chemoenzymatic synthesis methods to support translational research and expanding the functionality and applicability of trehalose analogues to study and target diverse bacterial pathogens.

Microbial and metabolic impacts of trehalose and trehalose analogues

Trehalose is a disaccharide and fasting-mimetic that has been both canonized and vilified for its putative cardiometabolic and microbial effects. Trehalose analogues are currently under development to extend the key metabolic therapeutic actions of trehalose without adversely affecting host microbial communities. In the current study, we contrast the extent to which trehalose and its degradation-resistant analogue, lactotrehalose (LT), modulate microbial communities and host transcriptomic profiles. We demonstrate that trehalose and LT each exert adaptive metabolic and microbial effects that both overlap and diverge. We postulate that these effects depend both upon compound stability and bioavailability, and on stereospecific signal transduction. In context, the data suggest that trehalose is unlikely to be harmful, and yet it harbors unique effects that are not yet fully replicated by its analogues. These compounds are thus valuable probes to better define trehalose structure-function, and to offer as therapeutic metabolic agents.

Validamycin A Delays Development and Prevents Flight in Aedes aegypti (Diptera: Culicidae)

Trehalose is a disaccharide that is the major sugar found in insect hemolymph fluid. Trehalose provides energy, and promotes growth, metamorphosis, stress recovery, chitin synthesis, and insect flight. The hydrolysis of trehalose is under the enzymatic control of the enzyme trehalase. Trehalase is critical to the role of trehalose in insect physiology, and is required for the regulation of metabolism and glucose generation. Trehalase inhibitors represent a novel class of insecticides that have not been fully developed. Here, we tested the ability of trehalose analogues to function as larvacides or adulticides in an important disease vector-Aedes aegypti. We show that validamycin A, but not 5-thiotrehalose, delays larval and pupal development and prevents flight of adult mosquitoes. Larval mosquitoes treated with validamycin A were hypoglycemic and pupae had increased levels of trehalose. Treatment also skewed the sex ratio toward male mosquitoes. These data reveal that validamycin A is a mosquito adulticide that can impair normal development of an important disease vector.

Increasing storage stability of freeze-dried plasma using trehalose

Preservation of blood plasma in the dried state would facilitate long-term storage and transport at ambient temperatures, without the need of to use liquid nitrogen tanks or freezers. The aim of this study was to investigate the feasibility of dry preservation of human plasma, using sugars as lyoprotectants, and evaluate macromolecular stability of plasma components during storage. Blood plasma from healthy donors was freeze dried using 0-10% glucose, sucrose, or trehalose, and stored at various temperatures. Differential scanning calorimetry was used to measure the glass transition temperatures of freeze-dried samples. Protein aggregation, the overall protein secondary structure, and oxidative damage were studied under different storage conditions. Differential scanning calorimetry measurements showed that plasma freeze-dried with glucose, sucrose and trehalose have glass transition temperatures of respectively 72±3.4°C, 46±11°C, 15±2.4°C. It was found that sugars diminish freeze-drying induced protein aggregation in a dose-dependent manner, and that a 10% (w/v) sugar concentration almost entirely prevents protein aggregation. Protein aggregation after rehydration coincided with relatively high contents of β-sheet structures in the dried state. Trehalose reduced the rate of protein aggregation during storage at elevated temperatures, and plasma that is freeze- dried plasma with trehalose showed a reduced accumulation of reactive oxygen species and protein oxidation products during storage. In conclusion, freeze-drying plasma with trehalose provides an attractive alternative to traditional cryogenic preservation.

Trehalose for Ocular Surface Health

Trehalose is a natural disaccharide synthesized in various life forms, but not found in vertebrates. An increasing body of evidence demonstrates exceptional bioprotective characteristics of trehalose. This review discusses the scientific findings on potential functions of trehalose in oxidative stress, protein clearance, and inflammation, with an emphasis on animal models and clinical trials in ophthalmology. The main objective is to help understand the beneficial effects of trehalose in clinical trials and practice, especially in patients suffering from ocular surface disease. The discussion is supplemented with an overview of patents for the use of trehalose in dry eye and with prospects for the 2020s.

Lactotrehalose, an Analog of Trehalose, Increases Energy Metabolism Without Promoting Clostridioides difficile Infection in Mice

BACKGROUND & AIMS

Trehalose is a disaccharide that might be used in the treatment of cardiometabolic diseases. However, trehalose consumption promotes the expansion of Clostridioides difficile ribotypes that metabolize trehalose via trehalose-6-phosphate hydrolase. Furthermore, brush border and renal trehalases can reduce the efficacy of trehalose by cleaving it into monosaccharides. We investigated whether a trehalase-resistant analogue of trehalose (lactotrehalose) has the same metabolic effects of trehalose without expanding C difficile.

METHODS

We performed studies with HEK293 and Caco2 cells, primary hepatocytes from mice, and human intestinal organoids. Glucose transporters were overexpressed in HEK293 cells, and glucose tra2nsport was quantified. Primary hepatocytes were cultured with or without trehalose or lactotrehalose, and gene expression patterns were analyzed. C57B6/J mice were given oral antibiotics and trehalose or lactotrehalose in drinking water, or only water (control), followed by gavage with the virulent C difficile ribotype 027 (CD027); fecal samples were analyzed for toxins A (ToxA) or B (ToxB) by enzyme-linked immunosorbent assay. Other mice were given trehalose or lactotrehalose in drinking water for 2 days before placement on a chow or 60% fructose diet for 10 days. Liver tissues were collected and analyzed by histologic, serum biochemical, RNA sequencing, autophagic flux, and thermogenesis analyses. We quantified portal trehalose and lactotrehalose bioavailability by gas chromatography mass spectrometry. Fecal microbiomes were analyzed by 16S ribosomal RNA sequencing and principal component analyses.

RESULTS

Lactotrehalose and trehalose each blocked glucose transport in HEK293 cells and induced a gene expression pattern associated with fasting in primary hepatocytes. Compared with mice on the chow diet, mice on the high-fructose diet had increased circulating cholesterol, higher ratios of liver weight-to-body weight, hepatic lipid accumulation (steatosis), and liver gene expression patterns of carbohydrate-responsive de novo lipogenesis. Mice given lactotrehalose while on the high-fructose diet did not develop any of these features and had increased whole-body caloric expenditure compared with mice given trehalose or water and fed a high-fructose diet. Livers from mice given lactotrehalose had increased transcription of genes that regulate mitochondrial energy metabolism compared with liver from mice given trehalose or controls. Lactotrehalose was bioavailable in venous and portal circulation and fecal samples. Lactotrehalose reduced fecal markers of microbial branched-chain amino acid biosynthesis and increased expression of microbial genes that regulate insulin signaling. In mice given antibiotics followed by CD027, neither lactotrehalose nor trehalose increased levels of the bacteria or its toxin in stool-in fact, trehalose reduced the abundance of CD027 in stool. Lactotrehalose and trehalose reduced markers of inflammation in rectal tissue after CD027 infection.

CONCLUSIONS

Lactotrehalose is a trehalase-resistant analogue that increases metabolic parameters, compared with trehalose, without increasing the abundance or virulence of C difficile strain CD027. Trehalase-resistant trehalose analogues might be developed as next-generation fasting-mimetics for the treatment of diabetes and nonalcoholic fatty liver disease.

Autophagy Function and Regulation in Kidney Disease

Autophagy is a dynamic process by which intracellular damaged macromolecules and organelles are degraded and recycled for the synthesis of new cellular components. Basal autophagy in the kidney acts as a quality control system and is vital for cellular metabolic and organelle homeostasis. Under pathological conditions, autophagy facilitates cellular adaptation; however, activation of autophagy in response to renal injury may be insufficient to provide protection, especially under dysregulated conditions. Kidney-specific deletion of Atg genes in mice has consistently demonstrated worsened acute kidney injury (AKI) outcomes supporting the notion of a pro-survival role of autophagy. Recent studies have also begun to unfold the role of autophagy in progressive renal disease and subsequent fibrosis. Autophagy also influences tubular cell death in renal injury. In this review, we reported the current understanding of autophagy regulation and its role in the pathogenesis of renal injury. In particular, the classic mammalian target of rapamycin (mTOR)-dependent signaling pathway and other mTOR-independent alternative signaling pathways of autophagy regulation were described. Finally, we summarized the impact of autophagy activation on different forms of cell death, including apoptosis and regulated necrosis, associated with the pathophysiology of renal injury. Understanding the regulatory mechanisms of autophagy would identify important targets for therapeutic approaches.

Trehalose-cored amphiphiles for membrane protein stabilization: importance of the detergent micelle size in GPCR stability

Despite their importance in biology and medicinal chemistry, structural and functional studies of membrane proteins present major challenges. To study diverse membrane proteins, it is crucial to have the correct detergent to efficiently extract and stabilize the proteins from the native membranes for biochemical/biophysical downstream analyses. But many membrane proteins, particularly eukaryotic ones, are recalcitrant to stabilization and/or crystallization with currently available detergents and thus there are major efforts to develop novel detergents with enhanced properties. Here, a novel class of trehalose-cored amphiphiles are introduced, with multiple alkyl chains and carbohydrates projecting from the trehalose core unit are introduced. A few members displayed enhanced protein stabilization behavior compared to the benchmark conventional detergent, n-dodecyl-β-d-maltoside (DDM), for multiple tested membrane proteins: (i) a bacterial leucine transporter (LeuT), (ii) the R. capsulatus photosynthetic superassembly, and (iii) the human β2 adrenergic receptor (β2AR). Due to synthetic convenience and their favourable behaviors for a range of membrane proteins, these agents have potential for membrane protein research. In addition, the detergent property-efficacy relationship discussed here will guide future design of novel detergents.

Using trehalose to prevent and treat metabolic function: effectiveness and mechanisms

PURPOSE OF REVIEW

Trehalose is a disaccharide with manifold industrial, commercial and biomedical uses. In the decade following its initial definition as an autophagy-inducing agent, significant advances have been realized in regard to the applicable clinical and preclinical contexts in which trehalose can be deployed. Moreover, the mechanisms by which trehalose exerts its metabolic effects are only beginning to gain clarity. In this review, we will highlight the most recent advances regarding the effectiveness and mechanisms of trehalose actions in metabolic disease, and discuss barriers and opportunities for this class of compounds to advance as a clinical therapeutic.

RECENT FINDINGS

Trehalose reduced cardiometabolic disease burden in diet-induced and genetic models of atherosclerosis, dyslipidemia, hepatic steatosis and insulin tolerance and glucose tolerance. The mechanism by which these effects occurred were pleiotropic, and involved activation of fasting-like processes, including autophagic flux and transcription factor EB. These mechanisms depend heavily on route of administration and disease-specific context. Host and microbial trehalase activity is likely to influence trehalose efficacy in a tissue-dependent manner.

SUMMARY

Trehalose and its analogues are promising cardiometabolic therapeutic agents with pleiotropic effects across tissue types. It is likely that we are only beginning to uncover the broad efficacy and complex mechanisms by which these compounds modulate host metabolism.

Degradation-resistant trehalose analogues block utilization of trehalose by hypervirulent Clostridioides difficile

Trehalose is used as an additive in thousands of foods, cosmetics, and pharmaceutical products, and it is being investigated as a therapeutic for multiple human diseases. However, its ability to be used as a carbon source by microbes is a concern, as highlighted by the recent finding that trehalose can be metabolized by and potentially enhance the virulence of epidemic Clostridioides difficile. Here, we show that trehalose analogues designed to resist enzymatic degradation are incapable of being used as carbon sources by C. difficile. Furthermore, we demonstrate that trehalose analogues, but not the known trehalase inhibitor validamycin A, inhibit native trehalose utilization by hypervirulent C. difficile. Thus, degradation-resistant trehalose analogues are valuable as trehalase inhibitors and as surrogates for or co-additives with trehalose in applications where enzymatic breakdown is a concern.

Hepatic arginase 2 (Arg2) is sufficient to convey the therapeutic metabolic effects of fasting

Caloric restriction and intermittent fasting are emerging therapeutic strategies against obesity, insulin resistance and their complications. However, the effectors that drive this response are not completely defined. Here we identify arginase 2 (Arg2) as a fasting-induced hepatocyte factor that protects against hepatic and peripheral fat accumulation, hepatic inflammatory responses, and insulin and glucose intolerance in obese murine models. Arg2 is upregulated in fasting conditions and upon treatment with the hepatocyte glucose transporter inhibitor trehalose. Hepatocyte-specific Arg2 overexpression enhances basal thermogenesis, and protects from weight gain, insulin resistance, glucose intolerance, hepatic steatosis and hepatic inflammation in diabetic mouse models. Arg2 suppresses expression of the regulator of G-protein signalling (RGS) 16, and genetic RGS16 reconstitution reverses the effects of Arg2 overexpression. We conclude that hepatocyte Arg2 is a critical effector of the hepatic glucose fasting response and define a therapeutic target to mitigate the complications of obesity and non-alcoholic fatty liver disease.

Fasting is known for its beneficial effects on obesity and diabetes-related health complications. Here Zhang et al. show that fasting induces expression of arginase-2 (Arg2) in the liver, and that hepatic Arg2, by suppressing the expression of the regulator of G-protein signalling 16, recapitulates the positive effects of fasting in obesity and diabetes.

Artificial Fusion of mCherry Enhances Trehalose Transferase Solubility and Stability

LeLoir glycosyltransferases are important biocatalysts for the production of glycosidic bonds in natural products, chiral building blocks, and pharmaceuticals. Trehalose transferase (TreT) is of particular interest since it catalyzes the stereo- and enantioselective α,α-(1→1) coupling of a nucleotide sugar donor and monosaccharide acceptor for the synthesis of disaccharide derivatives. Heterologously expressed thermophilic trehalose transferases were found to be intrinsically aggregation prone and are mainly expressed as catalytically active inclusion bodies in Escherichia coli To disfavor protein aggregation, the thermostable protein mCherry was explored as a fluorescent protein tag. The fusion of mCherry to trehalose transferase from Pyrobaculum yellowstonensis (PyTreT) demonstrated increased protein solubility. Chaotropic agents like guanidine or the divalent cations Mn(II), Ca(II), and Mg(II) enhanced the enzyme activity of the fusion protein. The thermodynamic equilibrium constant, K _eq, for the reversible synthesis of trehalose from glucose and a nucleotide sugar was determined in both the synthesis and hydrolysis directions utilizing UDP-glucose and ADP-glucose, respectively. UDP-glucose was shown to achieve higher conversions than ADP-glucose, highlighting the importance of the choice of nucleotide sugars for LeLoir glycosyltransferases under thermodynamic control.IMPORTANCE The heterologous expression of proteins in Escherichia coli is of great relevance for their functional and structural characterization and applications. However, the formation of insoluble inclusion bodies is observed in approximately 70% of all cases, and the subsequent effects can range from reduced soluble protein yields to a complete failure of the expression system. Here, we present an efficient methodology for the production and analysis of a thermostable, aggregation-prone trehalose transferase (TreT) from Pyrobaculum yellowstonensis via its fusion with mCherry as a thermostable fluorescent protein tag. This fusion strategy allowed for increased enzyme stability and solubility and could be applied to other (thermostable) proteins, allowing rapid visualization and quantification of the mCherry-fused protein of interest. Finally, we have demonstrated that the enzymatic synthesis of trehalose from glucose and a nucleotide sugar is reversible by approaching the thermodynamic equilibrium in both the synthesis and hydrolysis directions. Our results show that uridine establishes an equilibrium constant which is more in favor of the product trehalose than when adenosine is employed as the nucleotide under identical conditions. The influence of different nucleotides on the reaction can be generalized for all LeLoir glycosyltransferases under thermodynamic control as the position of the equilibrium depends solely on the reaction conditions and is not affected by the nature of the catalyst.

A FRET-Based Fluorogenic Trehalose Dimycolate Analogue for Probing Mycomembrane-Remodeling Enzymes of Mycobacteria

The mycobacterial outer membrane, or mycomembrane, is essential for the viability and virulence of Mycobacterium tuberculosis and related pathogens. The mycomembrane is a dynamic structure, whose chemical composition and biophysical properties can change during stress to give an advantage to the bacterium. However, the mechanisms that govern mycomembrane remodeling and their significance to mycobacterial pathogenesis are still not well characterized. Recent studies have shown that trehalose dimycolate (TDM), a major glycolipid of the mycomembrane, is broken down by the mycobacteria-specific enzyme TDM hydrolase (Tdmh) in response to nutrient deprivation, a process which appears to modulate the mycomembrane to increase nutrient acquisition, but at the expense of stress tolerance. Tdmh activity thus balances the growth of M. tuberculosis during infection in a manner that is contingent upon host immunity. Current methods to probe Tdmh activity are limited, impeding the development of inhibitors and the investigation of the role of Tdmh in bacterial growth and persistence. Here, we describe the synthesis and evaluation of FRET-TDM, which is a fluorescence-quenched analogue of TDM that is designed to fluoresce upon hydrolysis by Tdmh and potentially other trehalose ester-degrading hydrolases involved in mycomembrane remodeling. We found that FRET-TDM was efficiently activated in vitro by recombinant Tdmh, generating a 100-fold increase in fluorescence. FRET-TDM was also efficiently activated in the presence of whole cells of Mycobacterium smegmatis and M. tuberculosis, but the observed signal was predominantly Tdmh-independent, suggesting that physiological levels of Tdmh are low and that other mycobacterial enzymes also hydrolyze the probe. The latter notion was confirmed by employing a native protein gel-based fluorescence assay to profile FRET-TDM-activating enzymes from M. smegmatis lysates. On the other hand, FRET-TDM was capable of detecting the activity of Tdmh in cells when it was overexpressed. Together, our data demonstrate that FRET-TDM is a convenient and sensitive in vitro probe of Tdmh activity, which will be beneficial for Tdmh enzymatic characterization and inhibitor screening. In more complex samples, for example, live cells or cell lysates, FRET-TDM can serve as a tool to probe Tdmh activity at elevated enzyme levels, and it may facilitate the identification and characterization of related hydrolases that are involved in mycomembrane remodeling. Our study also provides insights as to how the structure of FRET-TDM or related fluorogenic probes can be optimized to achieve improved specificity and sensitivity for detecting mycobacteria.

Rethinking Carbohydrate Synthesis: Stereoretentive Reactions of Anomeric Stannanes

In this Concept article, recent advances are highlighted in the synthesis and applications of anomeric nucleophiles, a class of carbohydrates in which the C1 carbon bears a carbon-metal bond. First, the advantages of exploiting the carboanionic reactivity of carbohydrates and the methods for the synthesis of mono- and oligosaccharide stannanes are discussed. Second, recent developments in the glycosyl cross-coupling method resulting in the transfer of anomeric configuration from C1 stannanes to C-aryl glycosides are reviewed. These highly stereoretentive processes are ideally suited for the preparation of carbohydrate-based therapeutics and were demonstrated in the synthesis of antidiabetic drugs. Next, the application of the glycosyl cross-coupling method to the preparation of Se-glycosides and to glycodiversification of small molecules and peptides are highlighted. These reactions proceed with exclusive anomeric control for a broad range of substrates and tolerate carbohydrates with free hydroxyl groups. Taken together, anomeric nucleophiles have emerged as powerful tools for the synthesis of oligosaccharides and glycoconjugates and their future applications will open new possibilities to incorporate saccharides into small molecules and biologics.

Chemoenzymatic radiosynthesis of 2-deoxy-2-[18F]fluoro-d-trehalose ([18F]-2-FDTre): A PET radioprobe for in vivo tracing of trehalose metabolism

Trehalose analogues bearing fluorescent and click chemistry tags have been developed as probes of bacterial trehalose metabolism, but these tools have limitations with respect to in vivo imaging applications. Here, we report the radiosynthesis of the ¹⁸F-modified trehalose analogue 2-deoxy-2-[¹⁸F]fluoro-d-trehalose ([¹⁸F]-2-FDTre), which in principle can be used in conjunction with positron emission tomography (PET) imaging to allow in vivo imaging of trehalose metabolism in various contexts. A chemoenzymatic method employing the thermophilic TreT enzyme from Thermoproteus tenax was used to rapidly (15-20 min), efficiently (70% radiochemical yield; ≥ 95% radiochemical purity), and reproducibly convert the commercially available radiotracer 2-deoxy-2-[¹⁸F]fluoro-d-glucose ([¹⁸F]-2-FDG) into the target radioprobe [¹⁸F]-2-FDTre in a single step; both manual and automated syntheses were performed with similar results. Cellular uptake experiments showed that radiosynthetic [¹⁸F]-2-FDTre was metabolized by Mycobacterium smegmatis but not by various mammalian cell lines, pointing to the potential future use of this radioprobe for selective PET imaging of infections caused by trehalose-metabolizing bacterial pathogens such as M. tuberculosis.

Chemoenzymatic Synthesis of Trehalosamine, an Aminoglycoside Antibiotic and Precursor to Mycobacterial Imaging Probes

Trehalosamine (2-amino-2-deoxy-α,α-d-trehalose) is an aminoglycoside with antimicrobial activity against Mycobacterium tuberculosis, and it is also a versatile synthetic intermediate used to access imaging probes for mycobacteria. To overcome inefficient chemical synthesis approaches, we report a two-step chemoenzymatic synthesis of trehalosamine that features trehalose synthase (TreT)-catalyzed glycosylation as the key transformation. Soluble and recyclable immobilized forms of TreT were successfully employed. We demonstrate that chemoenzymatically synthesized trehalosamine can be elaborated to two complementary imaging probes, which label mycobacteria via distinct pathways.

Hit Generation in TB Drug Discovery: From Genome to Granuloma

Current tuberculosis (TB) drug development efforts are not sufficient to end the global TB epidemic. Recent efforts have focused on the development of whole-cell screening assays because biochemical, target-based inhibitor screens during the last two decades have not delivered new TB drugs. Mycobacterium tuberculosis (Mtb), the causative agent of TB, encounters diverse microenvironments and can be found in a variety of metabolic states in the human host. Due to the complexity and heterogeneity of Mtb infection, no single model can fully recapitulate the in vivo conditions in which Mtb is found in TB patients, and there is no single “standard” screening condition to generate hit compounds for TB drug development. However, current screening assays have become more sophisticated as researchers attempt to mirror the complexity of TB disease in the laboratory. In this review, we describe efforts using surrogates and engineered strains of Mtb to focus screens on specific targets. We explain model culture systems ranging from carbon starvation to hypoxia, and combinations thereof, designed to represent the microenvironment which Mtb encounters in the human body. We outline ongoing efforts to model Mtb infection in the lung granuloma. We assess these different models, their ability to generate hit compounds, and needs for further TB drug development, to provide direction for future TB drug discovery.

The trehalose-specific transporter LpqY-SugABC is required for antimicrobial and anti-biofilm activity of trehalose analogues in Mycobacterium smegmatis

Mycobacteria, including the bacterial pathogen that causes human tuberculosis, possess distinctive pathways for synthesizing and utilizing the non-mammalian disaccharide trehalose. Trehalose metabolism is essential for mycobacterial viability and has been linked to in vitro biofilm formation, which may bear relevance to in vivo drug tolerance. Previous research has shown that some trehalose analogues bearing modifications at the 6-position inhibit growth of various mycobacterial species. In this work, 2-, 5-, and 6-position-modified trehalose analogues were synthesized using our previously reported one-step chemoenzymatic method and shown to inhibit growth and biofilm formation in the two-to three-digit micromolar range in Mycobacterium smegmatis. The trehalose-specific ABC transporter LpqY-SugABC was essential for antimicrobial and anti-biofilm activity, suggesting that inhibition by monosubstituted trehalose analogues requires cellular uptake and does not proceed via direct action on extracellular targets such as antigen 85 acyltransferases or trehalose dimycolate hydrolase. Although the potency of the described compounds in in vitro growth and biofilm assays is moderate, this study reports the first trehalose-based mycobacterial biofilm inhibitors and reinforces the concept of exploiting unique sugar uptake pathways to deliver inhibitors and other chemical cargo to mycobacteria.