pH sensing at the intersection of tissue homeostasis and inflammation

Imine Crosslinked, Injectable, and Self-Healing Fucoidan Hydrogel with Immunomodulatory Properties

Biomaterials with inherent anti-inflammatory properties and the ability to foster a pro-regenerative environment hold significant promise for enhancing cell transplantation and tissue regeneration. Fucoidan, a sulfated polysaccharide with well-documented immune-regulatory and antioxidant capabilities, offers strong potential for creating such biomaterials. Yet, there is a lack of engineered fucoidan hydrogels that are injectable and provide tunable physicochemical properties. In this study, the ability of fucoidan to undergo periodate-mediated oxidation is leveraged to introduce aldehydes into backbone (oxidized fucoidan, OFu), enabling the formation of reversible, imine-crosslinks with amine-containing molecules such as gelatin. The imine-crosslinked OFu-gelatin hydrogel provided excellent control over gelation rate and mechanical properties. Counter-intuitively, OFu-gelatin hydrogel exhibited excellent long-term stability (≥28 days), even though imine crosslinks are known to be relatively less stable. Moreover, the OFu-gelatin hydrogels are self-healing, injectable, and biocompatible, supporting cell culture and encapsulation. Furthermore, fucoidan hydrogels displayed immune-modulatory properties both in vitro and in vivo. This innovative injectable fucoidan hydrogel presents a versatile platform for applications in tissue engineering and regenerative medicine.

Stimuli-Responsive Nanomedicines for the Treatment of Non-cancer Related Inflammatory Diseases

Nanomedicines offer a means to overcome the limitations associated with traditional drug dosage formulations by affording drug protection, enhanced drug bioavailability, and targeted drug delivery to affected sites. Inflamed tissues possess unique microenvironmental characteristics (including excessive reactive oxygen species, low pH levels, and hypoxia) that stimuli-responsive nanoparticles can employ as triggers to support on-demand delivery, enhanced accumulation, controlled release, and activation of anti-inflammatory drugs. Stimuli-responsive nanomedicines respond to physicochemical and pathological factors associated with diseased tissues to improve the specificity of drug delivery, overcome multidrug resistance, ensure accurate diagnosis and precision therapy, and control drug release to improve efficacy and safety. Current stimuli-responsive nanoparticles react to intracellular/microenvironmental stimuli such as pH, redox, hypoxia, or specific enzymes and exogenous stimuli such as temperature, magnetic fields, light, and ultrasound via bioresponsive moieties. This review summarizes the general strategies employed to produce stimuli-responsive nanoparticles tailored for inflammatory diseases and all recent advances, reports their applications in drug delivery, and illustrates the progress made toward clinical translation.

Cu(OH)2 nanopesticide induced liver dysfunction in mice by targeting lipoylated tricarboxylic acid cycle proteins via ferredoxin 1

Copper hydroxide [Cu(OH)2] nanopesticide is an emerging agrochemical known for its ability to mitigate bacterial and fungal damage to host organisms. However, its environmental exposure and potential toxicological effects have garnered significant attention. The liver is regarded as the primary organ for copper storage and utilization within the body. Here, the potential hepatic dyshomeostasis and metabolic dysfunction resulting from exposure to Cu(OH)2 nanopesticide for a month were investigated using the C57BL/6 mouse model. The findings demonstrated that Cu(OH)2 nanopesticide induced damage to the core functions of the mouse liver, evidenced by an impaired tissue microstructure, attenuated biochemical function, as well as disturbed bile acid synthesis and energy metabolism. The regulatory manner of Cu(OH)2 nanopesticide on the lipoylated proteins in the tricarboxylic acid (TCA) cycle by targeting ferredoxin 1 (FDX1) and its associated lipoic acid and iron-sulfur pathways, also shared genetic characteristics with the recently identified cuproptosis mechanism, providing a deeper understanding of the hepatoxic effects induced by this copper nanopesticide. These findings contribute valuable data for evaluating the hepatotoxicity of Cu(OH)2 nanopesticide, and further research into the molecular mechanisms is anticipated to enhance the identification of therapeutic targets for hepatic diseases related to copper metabolism.

Unraveling the proton-sensing mechanisms of G protein-coupled receptors: Insights from cryogenic electron microscopy studies

In this issue, Guo et al.1 and Chen et al.2 resolved the cryo-EM structures of G protein-coupled receptor (GPR) 4 and GPR68, unveiling that histidine protonation initiates conformational rearrangements and dictates G protein coupling bias, illuminating pH-sensing mechanisms.

Proton perception and activation of a proton-sensing GPCR

Maintaining pH at cellular, tissular, and systemic levels is essential for human health. Proton-sensing GPCRs regulate physiological and pathological processes by sensing the extracellular acidity. However, the molecular mechanism of proton sensing and activation of these receptors remains elusive. Here, we present cryoelectron microscopy (cryo-EM) structures of human GPR4, a prototypical proton-sensing GPCR, in its inactive and active states. Our studies reveal that three extracellular histidine residues are crucial for proton sensing of human GPR4. The binding of protons induces substantial conformational changes in GPR4's ECLs, particularly in ECL2, which transforms from a helix-loop to a β-turn-β configuration. This transformation leads to the rearrangements of H-bond network and hydrophobic packing, relayed by non-canonical motifs to accommodate G proteins. Furthermore, the antagonist NE52-QQ57 hinders human GPR4 activation by preventing hydrophobic stacking rearrangement. Our findings provide a molecular framework for understanding the activation mechanism of a human proton-sensing GPCR, aiding future drug discovery.

Acidosis-induced p38-kinase activation triggers an IL-6-mediated crosstalk of renal proximal tubule cells with fibroblasts leading to their inflammatory response

BACKGROUND

Local interstitial acidosis in chronic kidney disease (CKD) induces inflammatory responses and dedifferentiation of proximal tubule cells (PTCs), disrupting cellular crosstalk through cytokine and COX-2 metabolite secretion. This promotes a switch to an inflammatory fibroblast phenotype, further exacerbating inflammation and PTC dedifferentiation. p38-signaling and downstream transcription factors, including P-CREB and c-fos, contribute to these responses. This study investigates the impact of acidosis on inflammatory responses in PTCs and fibroblasts, focusing on cellular crosstalk and the role of p38-signaling.

METHODS

HK-2 (human PTCs) and CCD-1092Sk (human fibroblasts) were exposed to acidic or control media in mono- and coculture for 30 min, 3 h, or 48 h. Protein expression of IL-6, phosphorylated (P-) and total CREB, P- and total SRF, c-fos, and P- and total p38 was analyzed by western blot. IL-6 secretion was measured using ELISA. The impact of p38 and IL-6 receptor activity was assessed by pharmacological intervention.

RESULTS

In coculture, acidosis initially caused a transient decrease in IL-6 secretion but significantly increased IL-6 levels after 48 h. Acidosis induced intracellular IL-6 expression in HK-2 cells within 3 h independent of culture conditions, with sustained IL-6 protein increase after 48 h only in coculture. Acidosis also enhanced P-CREB and c-fos expression in coculture during the first 3 h. Regardless of culture conditions, acidosis increased IL-6, c-fos, and P-SRF expression in CCDSK cells after 48 h. P-CREB and COX-2 expression were elevated in CCDSK in coculture. Acidosis-mediated effects on IL-6, P-CREB, and P-SRF expression were p38-dependent in both cell lines. Finally, we assessed the pH-dependency of IL-6 action and found that IL-6 addition increased COX-2 expression via the IL-6 receptor in acidic but not control media. Thus, acidosis enhances IL-6 secretion and potentiates its receptor-mediated biological effects.

CONCLUSION

This study identifies IL-6 as a key mediator of tubule-fibroblast crosstalk in an acidic milieu, promoting inflammatory processes. Acidosis induces IL-6 expression, secretion, and biological effects, with p38 kinase as a crucial mediator. If validated in vivo, these findings could enhance understanding of CKD and support early interventions.

A Novel pH-Responsive Baicalein@Chitosan Hydrogel for the Topical Treatment of Herpes Simplex Virus Type 1 Skin Infections: Therapeutic Potential and Mechanisms

Herpes simplex virus type 1 (HSV-1) is a prevalent human pathogen primarily transmitted through skin-to-skin contact. Traditional antiviral drugs like acyclovir (ACV) have limitations due to viral resistance and side effects, necessitating the development of alternative therapeutic strategies. Drug-loaded hydrogels have emerged as a promising approach for managing various skin infections. Considering the low-pH microenvironment following HSV-1 infection, a pH-responsive baicalein@chitosan (B@C) hydrogel is developed for the topical treatment of HSV-1 skin infections. This hydrogel is synthesized by incorporating baicalein, a natural flavonoid, into a chitosan matrix modified with 4-formylphenylboronic acid and protocatechualdehyde to achieve potent anti-HSV-1 activity and pH-responsiveness. In vitro results demonstrated the hydrogel's pH-dependent inhibitory effect on HSV-1 infections, including ACV-resistant strains. Subsequent investigations confirmed its efficacy in multiple murine infection models. Mechanistically, the B@C hydrogel inhibited viral replication by modulating the phosphorylation of inhibitor of nuclear factor kappa-B kinase subunit beta, promoted collagen synthesis, and decreased reactive oxygen species generation. Ultra-high-performance liquid chromatography-tandem mass spectrometry analysis revealed a sustained release of baicalein from the hydrogel, ensuring long-term drug retention in HSV-1-infected skin tissues. Collectively, these findings suggest that the B@C hydrogel holds significant potential for the therapeutic management of HSV-1 skin infections.

Structural Impact of 3-methylcytosine Modification on the Anticodon Stem-loop of a Neuronally-enriched Arginine tRNA

All tRNAs undergo a series of chemical modifications to fold and function correctly. In mammals, the C32 nucleotide in the anticodon loop of tRNA-Arg-CCU and UCU is methylated to form 3-methylcytosine (m3C). Deficiency of m3C in arginine tRNAs has been linked to human neurodevelopmental disorders, indicating a critical biological role for m3C modification. However, the structural repercussions of m3C modification are not well understood. Here, we examine the structural effects of m3C32 modification on the anticodon stem loop (ASL) of human tRNA-Arg-UCU-4-1, a unique tRNA with enriched expression in the central nervous system. Optical melting experiments demonstrate that m3C modification can locally disrupt nearby base pairing within the ASL while simultaneously stabilizing the ASL electrostatically, resulting in little net change thermodynamically. The isoenergetic nature of the C32-A38 pair versus the m3C32-A38 pair may help discriminate against structures not adopting canonical C32-A38 pairings, as most other m3C pairings are unfavorable. Furthermore, multidimensional NMR reveals that after m3C modification there are changes in hairpin loop structure and dynamics, the structure of A37, and the neighboring A31-U39 base pair. However, these structural changes after modification are made while maintaining the shape of the C32-A38 pairing, which is essential for efficient tRNA function in translation. These findings suggest that m3C32 modification could alter interactions of tRNA-Arg isodecoders with one or more binding partners while simultaneously maintaining the tRNA's ability to function in translation.

Layered Double Hydroxide Reshapes the Immune Microenvironment of Rheumatoid Arthritis through Small Mothers against Decapentaplegic 5

Persistent synovitis is a pivotal pathological feature of rheumatoid arthritis (RA). However, the current rheumatoid drugs are accompanied by severe side effects and have limited anti-inflammatory capabilities. In this work, we designed a bioactive material-folic acid modified layered double hydroxides (FA-LDH), aiming at targeting M1 macrophages and modulating macrophage repolarization. The in vitro experiment showed that FA-LDH mitigated the release of proinflammatory cytokines and promoted the expression of M2 macrophage markers. In terms of the action mechanism, FA-LDH modulated the nucleocytoplasmic transport of the small mothers against decapentaplegic 5 (Smad5) protein by adjusting the pH within the immune microenvironment. Subsequently, relying on the interaction between phospho-Smad5 (pSmad5) and p65, the nuclear factor kappa B signaling pathway was down-regulated through inhibiting nuclear transport of p65. Additionally, FA-LDH exhibited excellent targeting capability toward M1 macrophages and strong accumulation capacity in inflamed joints. In vivo experiment showed that FA-LDH could relieve swelling of limbs, reduce the infiltration of inflammatory cells, and protect joint cartilage and subchondral bone structure in collagen-induced arthritis mice. In summary, this work introduces a strategy for utilizing bioactive FA-LDH in the treatment of RA, highlighting the potential of FA-LDH to alleviate inflammation and reshape the immune microenvironment through the pSmad5/p65 axis.

Lysosomes in the immunometabolic reprogramming of immune cells in atherosclerosis

Lysosomes have a central role in the disposal of extracellular and intracellular cargo and also function as metabolic sensors and signalling platforms in the immunometabolic reprogramming of macrophages and other immune cells in atherosclerosis. Lysosomes can rapidly sense the presence of nutrients within immune cells, thereby switching from catabolism of extracellular material to the recycling of intracellular cargo. Such a fine-tuned degradative response supports the generation of metabolic building blocks through effectors such as mTORC1 or TFEB. By coupling nutrients to downstream signalling and metabolism, lysosomes serve as a crucial hub for cellular function in innate and adaptive immune cells. Lysosomal dysfunction is now recognized to be a hallmark of atherogenesis. Perturbations in nutrient-sensing and signalling have profound effects on the capacity of immune cells to handle cholesterol, perform phagocytosis and efferocytosis, and limit the activation of the inflammasome and other inflammatory pathways. Strategies to improve lysosomal function hold promise as novel modulators of the immunoinflammatory response associated with atherosclerosis. In this Review, we describe the crosstalk between lysosomal biology and immune cell function and polarization, with a particular focus on cellular immunometabolic reprogramming in the context of atherosclerosis.

The epidermal lipid-microbiome loop and immunity: Important players in atopic dermatitis

BACKGROUND

The promotion of epidermal barrier dysfunction is attributed to abnormalities in the lipid-microbiome positive feedback loop which significantly influences the imbalance of the epithelial immune microenvironment (EIME) in atopic dermatitis (AD). This imbalance encompasses impaired lamellar membrane integrity, heightened exposure to epidermal pathogens, and the regulation of innate and adaptive immunity. The lipid-microbiome loop is substantially influenced by intense adaptive immunity which is triggered by abnormal loop activity and affects the loop's integrity through the induction of atypical lipid composition and responses to dysregulated epidermal microbes. Immune responses participate in lipid abnormalities within the EIME by downregulating barrier gene expression and are further cascade-amplified by microbial dysregulation which is instigated by barrier impairment.

AIM OF REVIEW

This review examines the relationship between abnormal lipid composition, microbiome disturbances, and immune responses in AD while progressively substantiating the crosstalk mechanism among these factors. Based on this analysis, the "lipid-microbiome" positive feedback loop, regulated by immune responses, is proposed.

KEY SCIENTIFIC CONCEPTS OF REVIEW

The review delves into the impact of adaptive immune responses that regulate the EIME, driving AD, and investigates potential mechanisms by which lipid supplementation and probiotics may alleviate AD through the up-regulation of the epidermal barrier and modulation of immune signaling. This exploration offers support for targeting the EIME to attenuate AD.

A review on polysaccharide-based delivery systems for edible bioactives: pH responsive, controlled release, and emerging applications

pH changes occur during bodily lesions, presenting an opportunity for leveraging pH-responsive delivery systems as signals for a targeted response. This review explores the design and application of pH-responsive delivery systems based on natural polysaccharides for the controlled release of bioactives. The article examines the development of diverse delivery carriers, including nanoparticles, nanofibers, nanogels, core-shell carriers, hydrogels, emulsions as well as liposomes and their capacity to respond to pH variations, enabling the precise and targeted delivery of bioactives within the human body. These polysaccharide-based delivery systems can be made pH-responsive by modulating the charge of polybasic or polyacidic polysaccharides, inducing swelling of the carrier and subsequent release of the encapsulated bioactives. These pH-responsive systems show promise in stabilizing under acidic conditions for enhanced retention in the stomach during oral delivery while also enabling targeted release at low pH sites such as tumors and wounds, thereby accelerating wound healing and aiding in cancer therapy and inflammation treatment. pH can co-respond with a variety of stimuli, including temperature, enzymes and reactive oxygen species, enabling more precise responses to the microenvironment for targeted delivery. It provides solid theoretical foundations for the advancement of personalized nutrition and therapeutics through controlled and responsive release technologies.

Miniaturized Liver Disease Mimics to Gain Insights into MMP Expression during Disease Progression

Nonalcoholic fatty liver disease (NAFLD) encompasses a spectrum of liver conditions, ranging from hepatic steatosis to steatohepatitis, fibrosis, and severe outcomes such as cirrhosis or cancer. The progression from hepatic steatosis to fibrosis involves significant extracellular matrix (ECM) remodeling, characterized by increased collagen deposition and cross-linking of ECM proteins, causing increased tissue stiffness and altered MMP expression patterns. Dysregulated MMP expression and extracellular acidosis are key contributors to NAFLD progression. Unlike other MMPs, which may be relevant only at specific disease stages, MMP-9 serves as a universal marker, allowing for monitoring of its expression in relation to disease states and ECM parameters. Understanding dysregulated MMP-9 expression across different NAFLD stages can provide crucial insights into disease progression and serve as both a diagnostic and a prognostic biomarker, identifying potential therapeutic targets. This study introduces a three-dimensional (3D) collagen/alginate-based liver disease model designed to investigate how matrix collagen content, elasticity, and diseased cell conditions influence MMP expression and pH levels in situ using nanoprobes. The platform offered an understanding of the relationships between these factors and their role in NAFLD progression, offering valuable insights into disease progression and potential resolution. To examine how various physicochemical and biological factors, particularly MMP expression and collagen deposition, drive NAFLD progression, three 3D NAFLD models were developed, simulating healthy (HL), steatotic (SL), and fibrotic (FL) liver matrices. Additionally, the role of collagenase treatment in the FL matrix in enhancing MMP expression and potentially mitigating fibrosis was also explored. By employing dual-sensitive fluorescent nanoprobes to monitor real-time in situ changes in MMP-9 expression and pH levels, this platform offers a novel approach to understanding the in vitro roles of matrix stiffness, collagen deposition, and diseased cell conditions in NAFLD pathogenesis.

pH-dependent cadmium binding to hemoglobin: Implications for human excretion

Half-life of cadmium (Cd) in blood is around 3-4 months, which is much shorter than its half-life in human organs (30 years). Promoting the elimination of Cd from the blood is a crucial step in reducing the body's Cd burden. However, there is currently no effective method available to facilitate this process. In this study, we found that almost all (>98 %) of the Cd in blood samples from occupationally exposed workers was concentrated in blood cells. Hemoglobin (Hb) was identified as the primary Cd-binding protein within these cells. Further investigation revealed that pH, a key regulator of metabolic processes in the blood, played a crucial role in altering the binding capacity of Cd to Hb. We observed that as pH decreased, the binding capacity and the number of available binding sites for Cd on Hb significantly diminished. Cellular experiments confirmed that lower pH can promote the release of Cd from blood cells, facilitating its transfer into the serum. These findings suggested that manipulating blood pH could enhance the rate of Cd excretion from the body, offering a potential strategy for reducing Cd burden.

I-Motif DNA Based Fluorescent Ratiometric Microneedle Sensing Patch for Sensitive Response of Small pH Variations in Interstitial Fluid

Detection of slight pH changes in skin interstitial fluid (ISF) is crucial yet challenging for studying pathological processes and understanding personal health conditions. In this work, we construct an i-motif DNA based fluorescent ratiometric microneedle sensing patch (IFR-pH MN patch) strategy that enables minimally invasive, high-resolution, and sensitive transdermal monitoring of small pH variations in ISF. The IFR-pH MN patch with advanced integration of both ISF sampling and pH sensing was fabricated from the cross-linking of gelatin methacryloyl and methacrylated hyaluronic acid, wrapping with pH-sensitive hairpin-containing i-motif DNA based fluorescent ratiometric probes in the matrix. Because it is mechanically robust for skin penetration and has high swelling ability, the IFR-pH MN patch could be quickly extracted as sufficient liquid from agarose gel (∼56.4 μL in 10 min). Benefiting from conformation changes of the hairpin-containing i-motif DNA under pH variation and ratiometric fluorescence signal readout, the IFR-pH MN patch could quantitate pH over a small range between pH 6.2 and 6.9 with an accuracy of 0.2 pH units in the mimic skin model. Furthermore, in vivo testing on wound and tumor mouse models indicated the ability of the biocompatible IFR-pH MN patch to penetrate the skin for obtaining transdermal pH values, demonstrating the potential applications in monitoring and intervention of pathological states.

Excitation-Dependent pKa Extends the Sensing Range of Fluorescence Lifetime pH Sensors

Biological activity is strongly dependent on pH, which fluctuates within a variety of neutral, alkaline, and acidic local environments. The heterogeneity of tissue and subcellular pH has driven the development of sensors with different pKa values, and a huge assortment of fluorescent sensors have been created to measure and visualize pH in living cells and tissues. In particular, sensors that report based on fluorescence lifetime are advantageous for quantitation. Here, we apply a theoretical framework to derive how the apparent pKa of lifetime-based pH sensors depends on fluorescence excitation wavelength. We demonstrate that theory predicts the behavior of two different fluorescent protein-based pH sensors in solution as proofs-of-concept. Furthermore, we show that this behavior has great practical value in living cells because it extends the sensing range of a single sensor by simply choosing appropriate detection parameters to match the physiological pH range of interest. More broadly, our results show that the versatility of a single lifetime-based sensor has been significantly underappreciated, and our approach provides a means to use a single sensor across a range of pH environments.

Computational investigation of missense somatic mutations in cancer and potential links to pH-dependence and proteostasis

Metabolic changes during tumour development lead to acidification of the extracellular environment and a smaller increase of intracellular pH. Searches for somatic missense mutations that could reveal adaptation to altered pH have focussed on arginine to histidine changes, part of a general arginine depletion that originates from DNA mutational mechanisms. Analysis of mutations to histidine, potentially a simple route to the introduction of pH-sensing, shows no clear biophysical separation overall of subsets that are more and less frequently mutated in cancer genomes. Within the more frequently mutated subset, individual sites predicted to mediate pH-dependence upon mutation include NDST1 (a Golgi-resident heparan sulphate modifying enzyme), the HLA-C chain of MHCI complex, and the water channel AQP-7. Arginine depletion is a general feature that persists in the more frequently mutated subset, and is complemented by over-representation of mutations to lysine. Arginine to lysine balance is a known factor in determining protein solubility, with higher lysine content being more favourable. Proteins with greater change in arginine to lysine balance are enriched for cell periphery location, where proteostasis is likely to be challenged in tumour cells. Somatic missense mutations in a cancer genome number only in the 10s typically, although can be much higher. Whether the altered arginine to lysine balance is of sufficient scale to play a role in tumour development is unknown.

Structural impact of 3-methylcytosine modification on the anticodon stem of a neuronally-enriched arginine tRNA

All tRNAs undergo a series of chemical modifications to fold and function correctly. In mammals, the C32 nucleotide in the anticodon loop of tRNA-Arg-CCU and UCU is methylated to form 3-methylcytosine (m3C). Deficiency of m3C in arginine tRNAs has been linked to human neurodevelopmental disorders, indicating a critical biological role for m3C modification. However, the structural repercussions of m3C modification are not well understood. Here, we examine the structural effects of m3C32 modification on the anticodon stem loop (ASL) of human tRNA-Arg-UCU-4-1, a unique tRNA with enriched expression in the central nervous system. Optical melting experiments demonstrate that m3C modification can locally disrupt nearby base pairing within the ASL while simultaneously stabilizing the ASL electrostatically, resulting in little net change thermodynamically. The isoenergetic nature of the C32 - A38 pair vs the m3C32 - A38 pair may help discriminate against structures not adopting canonical C32 - A38 pairings, as most other m3C pairings are unfavorable. Furthermore, multidimensional NMR reveals that after m3C modification there are changes in hairpin loop structure and dynamics, the structure of A37, and the neighboring A31 - U39 base pair. However, these structural changes after modification are made while maintaining the shape of the C32 - A38 pairing, which is essential for efficient tRNA function in translation. These findings suggests that m3C32 modification could alter interactions of tRNA-Arg isodecoders with one or more binding partners while simultaneously maintaining the tRNA's ability to function in translation.

Self-healing and injectable chitosan/konjac glucomannan hydrogel with pH response for controlled protein release

Dynamic hydrogels with the features of injection, self-healing, and remodeling at the target site have been developed as smart multifunctional biomaterials for drug delivery. However, most self-healing injectable hydrogels are difficult to control protein release after implantation, owing to the deficiency of pH responsiveness, which reduces the bioavailability of proteins. Herein, we propose a facile strategy to endow pH responsiveness into a dynamic hydrogel with both self-healing and injectable capabilities, by crosslinking biomacromolecular backbones via dual pH sensitive dynamic covalent bond. Particularly, oxidized konjac glucomannan (OKGM) can be crosslinked with poly (aspartic hydrazide) (PAHy) and N-carboxyethyl chitosan (CEC) to form dynamic acylhydrazone bonds and imide bonds, respectively, endowing the hydrogel with pH responsiveness and dynamic behaviors. Specifically, PAHy facilitates the formation of acylhydrazone bonds, improving the mechanical properties and pH sensitivity while reducing the degradation behavior of the hydrogels under physiological conditions. Kinetics indicate that the release of bovine serum albumin follows Fick diffusion under different pH conditions. The pH responsive hydrogel with self-healing injectable capabilities has the potential to be used as a controllable and sustain release carrier for protein drugs.

Euterpe oleracea Mart. Bioactive Molecules: Promising Agents to Modulate the NLRP3 Inflammasome

Inflammation is a vital mechanism that defends the organism against infections and restores homeostasis. However, when inflammation becomes uncontrolled, it leads to chronic inflammation. The NLRP3 inflammasome is crucial in chronic inflammatory responses and has become a focal point in research for new anti-inflammatory therapies. Flavonoids like catechin, apigenin, and epicatechin are known for their bioactive properties (antioxidant, anti-inflammatory, etc.), but the mechanisms behind their anti-inflammatory actions remain unclear. This study aimed to explore the ability of various flavonoids (isolated and combined) to modulate the NLRP3 inflammasome using in silico and in vitro models. Computer simulations, such as molecular docking, molecular dynamics, and MM/GBSA calculations examined the interactions between bioactive molecules and NLRP3 PYD. THP1 cells were treated with LPS + nigericin to activate NLRP3, followed by flavonoid treatment at different concentrations. THP1-derived macrophages were also treated following NLRP3 activation protocols. The assays included colorimetric, fluorometric, microscopic, and molecular techniques. The results showed that catechin, apigenin, and epicatechin had high binding affinity to NLRP3 PYD, similar to the known NLRP3 inhibitor MCC950. These flavonoids, particularly at 1 µg/mL, 0.1 µg/mL, and 0.01 µg/mL, respectively, significantly reduced LPS + nigericin effects in both cell types and decreased pro-inflammatory cytokine, caspase-1, and NLRP3 gene expression, suggesting their potential as anti-inflammatory agents through NLRP3 modulation.

Not just sugar: metabolic control of neutrophil development and effector functions

The mammalian immune system is constantly surveying our tissues to clear pathogens and maintain tissue homeostasis. In order to fulfill these tasks, immune cells take up nutrients to supply energy for survival and for directly regulating effector functions via their cellular metabolism, a process now known as immunometabolism. Neutrophilic granulocytes, the most abundant leukocytes in the human body, have a short half-life and are permanently needed in the defense against pathogens. According to a long-standing view, neutrophils were thought to primarily fuel their metabolic demands via glycolysis. Yet, this view has been challenged, as other metabolic pathways recently emerged to contribute to neutrophil homeostasis and effector functions. In particular during neutrophilic development, the pentose phosphate pathway, glycogen synthesis, oxidative phosphorylation, and fatty acid oxidation crucially promote neutrophil maturation. At steady state, both glucose and lipid metabolism sustain neutrophil survival and maintain the intracellular redox balance. This review aims to comprehensively discuss how neutrophilic metabolism adapts during development, which metabolic pathways fuel their functionality, and how these processes are reconfigured in case of various diseases. We provide several examples of hereditary diseases, in which mutations in metabolic enzymes validate their critical role for neutrophil function.

The immunomicrotope of Leishmania control and persistence

Leishmania is an intracellular protozoan transmitted by sand fly vectors; it causes cutaneous, mucocutaneous, or visceral disease. Its growth and survival are impeded by type 1 T helper cell responses, which entail interferon (IFN)-γ-mediated macrophage activation. Leishmania partially escapes this host defense by triggering immune cell and cytokine responses that favor parasite replication rather than killing. Novel methods for in situ analyses have revealed that the pathways of immune control and microbial evasion are strongly influenced by the tissue context, the micro milieu factors, and the metabolism at the site of infection, which we collectively term the 'immunomicrotope'. Understanding the components and the impact of the immunomicrotope will enable the development of novel strategies for the treatment of chronic leishmaniasis.

Recent Advances in Conductive Polymers-Based Electrochemical Sensors for Biomedical and Environmental Applications

Electrochemical sensors play a pivotal role in various fields, such as biomedicine and environmental detection, due to their exceptional sensitivity, selectivity, stability, rapid response time, user-friendly operation, and ease of miniaturization and integration. In addition to the research conducted in the application field, significant focus is placed on the selection and optimization of electrode interface materials for electrochemical sensors. The detection performance of these sensors can be significantly enhanced by modifying the interface of either inorganic metal electrodes or printed electrodes. Among numerous available modification materials, conductive polymers (CPs) possess not only excellent conductivity exhibited by inorganic conductors but also unique three-dimensional structural characteristics inherent to polymers. This distinctive combination allows CPs to increase active sites during the detection process while providing channels for rapid ion transmission and facilitating efficient electron transfer during reaction processes. This review article primarily highlights recent research progress concerning CPs as an ideal choice for modifying electrochemical sensors owing to their remarkable features that make them well-suited for biomedical and environmental applications.

Blood pH Changes in Dental Pulp of Patients with Pulpitis

The severity of pulpitis is a crucial factor in determining the suitable treatment. There are no clear objective indicators to assess the stage of pulp inflammation that could be used in clinical practice. The change in blood pH of the pulp during the inflammatory phase could hypothetically serve as an indicator of the pulp inflammation severity. The aim of this study was to assess the pH values in the pulpal blood of mature teeth in patients with symptomatic pulpitis, in comparison with the healthy controls. The study included patients with symptoms of pulpitis in premolar or molar teeth (Test group; n = 24, mean age 36.04, SD 7.10), and healthy controls (Control group, n = 6, mean age 24.5, SD 5.94) referred for extraction of premolars or third molars, for orthodontic reasons. The pulpal blood was taken at the opening of the endodontic access cavity, and the pH value was measured in both groups. Statistical analysis was performed using the SPSS 27.0 program with a significance level of p ≤ 0.05. The Mann-Whitney test for dependent samples was performed to evaluate the statistical difference between the groups. The patients with symptomatic pulpitis had significantly decreased pulpal blood pH compared to the healthy controls (p ≤ 0.05). The mean pulpal blood pH was 7.27 (SD 0.06) and 7.40 (SD 0.02) in Test and Control groups, respectively. In the Test group, the pulpal blood pH values were significantly lower in the patients who had symptoms for 3 days or more (7.25, SD 0.05) than in those who had symptoms for up to 3 days (7.33, SD 0.03) (p < 0.001). The pH value of the pulpal blood gradually declines in cases of symptomatic pulpitis, along with increasing duration of the symptoms.

3D microscaffolds with triple-marker sensitive nanoprobes for studying fatty liver disease in vitro

Non-alcoholic fatty liver disease (NAFLD) is a heterogeneous condition that encompasses a wide range of liver diseases that progresses from simple hepatic steatosis to the life-threatening state of cirrhosis. However, due to the heterogeneity of this disease, comprehensive analysis of several physicochemical and biological factors that drive its progression is necessary. Therefore, an in vitro platform is required that would enable real-time monitoring of these changes to better understand the progression of these diseases. The earliest stage of NAFLD, i.e. hepatic steatosis, is characterised by triglyceride accumulation in the form of lipid vacuoles in the cytosol of hepatocytes. This fatty acid accumulation is usually accompanied by hepatic inflammation, leading to tissue acidification and dysregulated expression of certain proteases such as matrix metalloproteinases (MMPs). Taking cues from the biological parameters of the disease, we report here a 3D in vitro GelMA/alginate microscaffold platform encapsulating a triple-marker (pH, MMP-3 and MMP-9) sensitive fluorescent nanoprobe for monitoring, and hence, distinguishing the fatty liver disease (hepatic steatosis) from healthy livers on the basis of pH change and MMP expression. The nanoprobe consists of a carbon nanoparticle (CNP) core, which exhibits intrinsic pH-dependent fluorescence properties, decorated either with an MMP-3 (NpMMP3) or MMP-9 (NpMMP9) sensitive peptide substrate. These peptide substrates are flanked with a fluorophore-quencher pair that separates on enzymatic cleavage, resulting in fluorescence emission. The cocktail of these nanoprobes generated multiple fluorescence signals corresponding to slightly acidic pH (blue) and overexpression of MMP-3 (green) and MMP-9 (red) enzymes in a 3D in vitro fatty liver model, whereas no/negligible fluorescence signals were observed in a healthy liver model. Moreover, this platform enabled us to mimic fatty liver disease in a more realistic manner. Therefore, this 3D in vitro platform encapsulating triple-marker sensitive fluorescent nanoprobes would facilitate the monitoring of the changes in pH and MMP expression, thereby enabling us to distinguish a healthy liver from a diseased liver and to study liver disease stages on the basis of these markers.

Control of Inflammatory Response by Tissue Microenvironment

Inflammation is an essential defense response but operates at the cost of normal functions. Whether and how the negative impact of inflammation is monitored remains largely unknown. Acidification of the tissue microenvironment is associated with inflammation. Here we investigated whether macrophages sense tissue acidification to adjust inflammatory responses. We found that acidic pH restructured the inflammatory response of macrophages in a gene-specific manner. We identified mammalian BRD4 as a novel intracellular pH sensor. Acidic pH disrupts the transcription condensates containing BRD4 and MED1, via histidine-enriched intrinsically disordered regions. Crucially, decrease in macrophage intracellular pH is necessary and sufficient to regulate transcriptional condensates in vitro and in vivo, acting as negative feedback to regulate the inflammatory response. Collectively, these findings uncovered a pH-dependent switch in transcriptional condensates that enables environmental sensing to directly control inflammation, with a broader implication for calibrating the magnitude and quality of inflammation by the inflammatory cost.

Role of pH-sensing receptors in colitis

Low pH in the gut is associated with severe inflammation, fibrosis, and colorectal cancer (CRC) and is a hallmark of active inflammatory bowel disease (IBD). Subsequently, pH-sensing mechanisms are of interest for the understanding of IBD pathophysiology. Tissue hypoxia and acidosis-two contributing factors to disease pathophysiology-are linked to IBD, and understanding their interplay is highly relevant for the development of new therapeutic options. One member of the proton-sensing G protein-coupled receptor (GPCR) family, GPR65 (T-cell death-associated gene 8, TDAG8), was identified as a susceptibility gene for IBD in a large genome-wide association study. In response to acidic extracellular pH, GPR65 induces an anti-inflammatory response, whereas the two other proton-sensing receptors, GPR4 and GPR68 (ovarian cancer G protein-coupled receptor 1, OGR1), mediate pro-inflammatory responses. Here, we review the current knowledge on the role of these proton-sensing receptors in IBD and IBD-associated fibrosis and cancer, as well as colitis-associated cancer (CAC). We also describe emerging small molecule modulators of these receptors as therapeutic opportunities for the treatment of IBD.