ZNT5-6 and ZNT7 play an integral role in protein N-glycosylation by supplying Zn2+ to Golgi α-mannosidase II.

The stepwise addition of monosaccharides to N-glycans attached to client proteins to generate a repertoire of mature proteins involves a concerted action of many glycosidases and glycosyltransferases. Here, we report that Golgi α-mannosidase II (GMII), a pivotal enzyme catalyzing the first step in the conversion of hybrid- to complex-type N-glycans, is activated by Zn2+ supplied by the early secretory compartment-resident ZNT5-ZNT6 heterodimers (ZNT5-6) and ZNT7 homodimers (ZNT7). Loss of ZNT5-6 and ZNT7 function results in marked accumulation of hybrid-type and complex/hybrid glycans with concomitant reduction of complex- and high-mannose-type glycans. In cells lacking the ZNT5-6 and ZNT7 functions, the GMII activity is substantially decreased. In contrast, the activity of its homolog, lysosomal mannosidase (LAMAN), is not decreased. Moreover, we show that the growth of pancreatic cancer MIA PaCa-2 cells lacking ZNT5-6 and ZNT7 is significantly decreased in a nude mouse xenograft model. Our results indicate the integral roles of ZNT5-6 and ZNT7 in N-glycosylation and highlight their potential as novel target proteins for cancer therapy.

Natural antisense transcription of presenilin in sea urchin reveals a possible role for natural antisense transcription in the general control of gene expression during development

One presenilin gene (PSEN) is expressed in the sea urchin embryo, in the vegetal pole of the gastrula and then mainly in cilia cells located around the digestive system of the pluteus, as we recently have reported. PSEN expression must be accurately regulated for correct execution of these two steps of development. While investigating PSEN expression changes in embryos after expansion of endoderm with LiCl or of ectoderm with Zn2+ by whole-mount in situ hybridization (WISH) and quantitative PCR (qPCR), we detected natural antisense transcription of PSEN. We then found that Endo16 and Wnt5, markers of endo-mesoderm, and of Hnf6 and Gsc, markers of ectoderm, are also sense and antisense transcribed. We discuss that general gene expression could depend on both sense and antisense transcription. This mechanism, together with the PSEN gene, should be included in gene regulatory networks (GRNs) that theorize diverse processes in this species. We suggest that it would also be relevant to investigate natural antisense transcription of PSEN in the field of Alzheimer's disease (AD) where the role of human PSEN1 and PSEN2 is well known.

Quantitative, in situ visualization of intracellular insulin vesicles in pancreatic beta cells.

Characterizing relationships between Zn2+, insulin, and insulin vesicles is of vital importance to the study of pancreatic beta cells. However, the precise content of Zn2+ and the specific location of insulin inside insulin vesicles are not clear, which hinders a thorough understanding of the insulin secretion process and diseases caused by blood sugar dysregulation. Here, we demonstrated the colocalization of Zn2+ and insulin in both single extracellular insulin vesicles and pancreatic beta cells by using an X-ray scanning coherent diffraction imaging (ptychography) technique. We also analyzed the elemental Zn2+ and Ca2+ contents of insulin vesicles using electron microscopy and energy dispersive spectroscopy (EDS) mapping. We found that the presence of Zn2+ is an important characteristic that can be used to distinguish insulin vesicles from other types of vesicles in pancreatic beta cells and that the content of Zn2+ is proportional to the size of insulin vesicles. By using dual-energy contrast X-ray microscopy and scanning transmission X-ray microscopy (STXM) image stacks, we observed that insulin accumulates in the off-center position of extracellular insulin vesicles. Furthermore, the spatial distribution of insulin vesicles and their colocalization with other organelles inside pancreatic beta cells were demonstrated using three-dimensional (3D) imaging by combining X-ray ptychography and an equally sloped tomography (EST) algorithm. This study describes a powerful method to univocally describe the location and quantitative analysis of intracellular insulin, which will be of great significance to the study of diabetes and other blood sugar diseases.

The Pseudomonas aeruginosa PAO1 metallo flavoprotein d-2-hydroxyglutarate dehydrogenase requires Zn2+ for substrate orientation and activation.

Pseudomonas aeruginosa PAO1 d-2-hydroxyglutarate (D2HG) dehydrogenase (PaD2HGDH) oxidizes D2HG to 2-ketoglutarate during the vital l-serine biosynthesis and is a potential therapeutic target against P. aeruginosa. PaD2HGDH, which oxidizes d-malate as an alternative substrate, has been demonstrated to be a metallo flavoprotein that requires Zn2+ for activity. However, the role of Zn2+ in the enzyme has not been elucidated, making it difficult to rationalize why nature employs both a redox center and a metal ion for catalysis in PaD2HGDH and other metallo flavoenzymes. In this study, recombinant His-tagged PaD2HGDH was purified to high levels in the presence of Zn2+ or Co2+ to investigate the metal's role in catalysis. We found that the flavin reduction step was reversible and partially rate limiting for the enzyme's turnover at pH 7.4 with either D2HG or d-malate with similar rate constants for both substrates, irrespective of whether Zn2+ or Co2+ was bound to the enzyme. The steady-state pL profiles of the kcat and kcat/Km values with d-malate demonstrate that Zn2+ mediates the activation of water coordinated to the metal. Our data are consistent with a dual role for the metal, which orients the hydroxy acid substrate in the enzyme's active site and rapidly deprotonates the substrate to yield an alkoxide species for hydride transfer to the flavin. Thus, we propose a catalytic mechanism for PaD2HGDH oxidation that establishes Zn2+ as a cofactor required for substrate orientation and activation during enzymatic turnover.

Comparative analysis of the physical properties of murine and human S100A7: Insight into why zinc piracy is mediated by human but not murine S100A7.

S100 proteins are a subfamily of EF-hand calcium-binding proteins found primarily in vertebrate animals. They are distinguished by binding of transition metals and functioning in both the intracellular and extracellular milieu. S100A7 functions in the protection of the skin and mucous membranes and is a biomarker in inflammatory skin disease. A recent study of Neisseria gonorrhoeae infection revealed that human but not murine S100A7 could be used to evade host nutritional immunity. To understand the molecular basis for this difference, we carried out a comparative analysis of the physical and structural properties of human and murine S100A7. The X-ray crystal structure of Ca2+-loaded mouse S100A7 (mS100A7) was determined to 1.69 Å resolution, and Ca2+-induced conformational changes were assessed by NMR. Unlike human S100A7 (hS100A7), which exhibits conformational changes in response to binding of Ca2+, no significant changes in mS100A7 were detected. Dynamic light scattering, circular dichroism, and a competition chelator assay were used to compare the Zn2+ affinity and the effects of ion binding on mS100A7 versus hS100A7. Alignment of their sequences revealed a substantial difference in the C-terminal region, which is an important mediator of protein-protein interactions, suggesting a rationale for the specificity of N. gonorrhoeae for hS100A7. These data, along with more detailed analysis of S100A7 sequence conservation across different species, support the proposal that, although hS100A7 is highly conserved in many mammals, the murine protein is a distinct ortholog. Our results highlight the potential limitations of using mouse models for studying bacterial infections in humans.

Uncovering Zn2+ as a cofactor of FAD-dependent Pseudomonas aeruginosa PAO1 d-2-hydroxyglutarate dehydrogenase.

Pseudomonas aeruginosa couples the oxidation of d-2-hydroxyglutarate (D2HG) to l-serine biosynthesis for survival, using d-2-hydroxyglutarate dehydrogenase from P. aeruginosa (PaD2HGDH). Knockout of PaD2HGDH impedes P. aeruginosa growth, making PaD2HGDH a potential target for therapeutics. Previous studies showed that the enzyme's activity increased with Zn2+, Co2+, or Mn2+ but did not establish the enzyme's metal composition and whether the metal is an activator or a required cofactor for the enzyme, which we addressed in this study. Comparable to the human enzyme, PaD2HGDH showed only 15% flavin reduction with D2HG or d-malate. Upon purifying PaD2HGDH with 1 mM Zn2+, the Zn2+:protein stoichiometry was 2:1, yielding an enzyme with ∼40 s-1kcat for d-malate. Treatment with 1 mM EDTA decreased the Zn2+:protein ratio to 1:1 without changing the kinetic parameters with d-malate. We observed complete enzyme inactivation for the metalloapoenzyme with 100 mM EDTA treatment, suggesting that Zn2+ is essential for PaD2HGDH activity. The presence of Zn2+ increased the flavin N3 atom pKa value to 11.9, decreased the flavin ε450 at pH 7.4 from 13.5 to 11.8 mM-1 cm-1, and yielded a charged transfer complex with a broad absorbance band >550 nm, consistent with a Zn2+-hydrate species altering the electronic properties of the enzyme-bound FAD. The exogenous addition of Zn2+, Co2+, Cd2+, Mn2+, or Ni2+ to the metalloapoenzyme reactivated the enzyme in a sigmoidal pattern, consistent with an induced fit rapid-rearrangement mechanism. Collectively, our data demonstrate that PaD2HGDH is a Zn2+-dependent metallo flavoprotein, which requires Zn2+ as an essential cofactor for enzyme activity.

Zn2+ improves sepsis-induced acute kidney injury by upregulating SIRT7-mediated Parkin acetylation.

Zn2+ levels are reported to be correlated with kidney function. We explored the significance of Zn2+ in sepsis-induced acute kidney injury (SI-AKI) through the regulation of sirtuin 7 (SIRT7) activity. The sepsis rat model was established by cecal ligation and perforation (CLP) and intraperitoneally injected with ZnSO4 or SIRT7 inhibitor 97491 (SIRT7i), with renal tubular injury assessed by hematoxylin and eosin staining. In vitro, human renal tubular epithelial cells (HK-2) were induced with lipopolysaccharide to obtain a renal injury cell model, followed by ZnSO4 or SIRT7i and autophagy inhibitor (3-methyladenine) treatment. Interleukin (IL)-1ß, IL-18, reactive oxygen species (ROS), Parkin acetylation level, kidney injury molecule-1 (KIM-1), and neutrophil gelatinase-associated lipocalin (NGAL) expression levels were determined. The renal tubule injury, inflammation condition, and pyroptosis-related and autophagy-related protein levels were assessed. The pyroptosis in kidney tissues and autophagosome formation were observed by transmission electron microscopy. Zn2+ alleviated renal injury in CLP rats and inhibited pyroptosis and its related protein levels by inhibiting SIRT7 activity in septic rat renal tissues. In vitro, Zn2+ increased HK-2 cell viability and reduced KIM-1, NGAL, IL-1ß, IL-18, NLRP3 inflammasome, cleaved caspase-1, gasdermin D-N levels, and pyroptotic cell number. Zn2+ increased autophagosome number and LC3BII/LC3BI ratio and decreased TOM20, TIM23, P62, and mitochondrial ROS levels. Zn2+ increased Parkin acetylation by repressing SIRT7 activity. Inhibiting mitophagy partially averted Zn2+-inhibited NLRP3 inflammasome activation and apoptosis in HK-2 cells. Zn2+ upregulated Parkin acetylation by repressing SIRT7 activity to promote mitophagy and inhibit NLRP3 inflammasome activation and pyroptosis, thus improving SI-AKI.NEW & NOTEWORTHY Zn2+ upregulated Parkin acetylation by repressing sirtuin 7 activity to promote mitophagy and inhibit NLRP3 inflammasome activation and pyroptosis, thus improving sepsis-induced acute kidney injury.

Ionic reverberation modulates the cellular fate of CD8+tissue resident memory T cells (TRMs) in patients with renal cell carcinoma: A novel mechanism.

In metastatic renal cell carcinoma (mRCC), existing treatments including checkpoint inhibitors are failed to cure and/or prevent recurrence of the disease. Therefore, in-depth understanding of tumor tissue resident memory T cells (TRMs) dysfunction are necessitated to enrich efficacy of immunotherapies and increasing disease free survival in treated patients. In patients, we observed dysregulation of K+, Ca2+, Na2+ and Zn2+ ion channels leads to excess infiltration of their respective ions in tumor TRMs, thus ionic gradients are disturbed and cells became hyperpolarized. Moreover, overloaded intramitochondrial calcium caused mitochondrial depolarization and trigger apoptosis of tumor TRMs. Decreased prevalence of activated tumor TRMs reflected our observations. Furthermore, disruptions in ionic concentrations impaired the functional activities and/or suppressed anti-tumor action of circulating and tumor TRMs in RCC. Collectively, these findings revealed novel mechanism behind dysfunctionality of tumor TRMs. Implicating enrichment of activated TRMs within tumor would be beneficial for better management of RCC patients.

A Self-Cascade Oxygen-Generating Nanomedicine for Multimodal Tumor Therapy.

Natural and artificial enzyme oxygen-generating systems for photodynamic therapy (PDT) are developed for tumor treatment, yet they have fallen short of the desired efficacy. Moreover, both the enzymes and photosensitizers usually need carriers for efficient delivery to tumor sites. Here, a self-cascade-enhanced multimodal tumor therapy is developed by ingeniously integrating self-cascade-enhanced PDT with Zn2+-overloading therapy. Manganese-porphyrin (TCPP-Mn) is chosen both as the photosensitizer and catalase (CAT) mimic, which can be encapsulated within glucose oxidase (GOx). Acid-responsive zeolitic imidazolate framework-8 (ZIF-8) is applied as the carrier for TCPP-Mn@GOx (T@G), attaining TCPP-Mn@GOx@ZIF-8 (T@G@Z). T@G@Z demonstrates robust anti-tumor ability as follows: upon the structural degradation of ZIF-8, GOx can mediate the oxidation of glucose and generate hydrogen peroxide (H2O2); TCPP-Mn can catalyze H2O2 into O2 for self-cascade-enhanced PDT; meanwhile, the released Zn2+ can enhance oxidative stress and induce mitochondrial dysfunction by destroying mitochondrial membrane potential; furthermore, immunotherapy can be activated to resist primary tumor and tumor metastasis. The self-cascade-enhanced T@G@Z exhibited its potential application for further tumor management.

Regulation of Zn2+ Solvation Configuration in Aqueous Batteries via Selenium-Substituted Crown Ether Engineering.

The efficient utilization of the metallic Zn in rechargeable aqueous Zn-ion batteries (RAZBs) struggle to suffer from parasitic Zn dendrite formation, hydrogen evolution reactions as well as severe interfacial degradation at high areal capacity loadings. This study thus proposes to employ the modified crown ether as an aqueous electrolyte additive to regulate the Zn2+ desolvation kinetic and facilitates the horizontally oriented (002) deposition of Zn, extending the lifespan of both the symmetric cell and full cell models. Specifically, zincophilic cyano and hydrophobic selenium atoms are incorporated into the crown ether supramolecule to enhance Zn2+ coordination and desolvation capability. The addition of 4-cyanobenzo-21-crown-7-selenium at a low concentration of 0.5 wt.% effectively mitigates hydrogen evolution and Zn corrosion caused by water, promoting the oriented deposition of Zn2+. The Zn||V2O5 full cell prototype, assembled with the areal capacity loadings of 2 mAh cm-2 and N/P ratio of 2.95, exhibits negligible capacity fading at 2.0A g-1 for 300 cycles, highlighting the commercial feasibility of supramolecular macrocycles additive for practical RAZBs applications.

Organic Dye Molecule Intercalated Vanadium Oxygen Hydrate Enables High-Performance Aqueous Zinc-Ion Storage.

Although the layered vanadium oxide-based materials have been considered to be one of the candidates for aqueous Zn-ion batteries (AZIBs), it still faces inevitable challenges of unsatisfactory capacities and sluggish kinetics because of strong electrostatic interactions between Zn-ions and structure lattice. This work addresses the strategy of pre-inserting guest materials to vanadium oxide cathode using different intercalants. To achieve this goal, the small organic dye molecules, methyl orange (MO), and methylene blue (MB) are proposed as the intercalants for vanadium oxygen hydrate (VOH). It has been demonstrated that use of these intercalants can facilitate reaction kinetics between Zn2+ and VOH, leading to an improvement of specific capacity (293 mAh g-1 at 0.3 A g-1 for MO-VOH and 311 mAh g-1 for MB-VOH) compared to VOH, a large enhancement of excellent energy density (237.1 Wh kg-1 for MO-VOH, 232.3 Wh kg-1 for MB-VOH), and a prolong lifespan operation at 3 A g-1 . The mechanism studies suggest that the weakened electrostatic interactions between the Zn-ions and V-O lattice after intercalating organic molecules contribute to boosting the electrochemical performance of AZIBs unveiled by charge density difference and binding energy.

Pre-Intercalation of TMA Cations in MoS2 Interlayers for Fast and Stable Zinc Ion Storage.

Applications of aqueous zinc ion batteries (ZIBs) for grid-scale energy storage are hindered by the lacking of stable cathodes with large capacity and fast redox kinetics. Herein, the intercalation of tetramethylammonium (TMA+) cations is reported into MoS2 interlayers to expand its spacing from 0.63 to 1.06 nm. The pre-intercalation of TMA+ induces phase transition of MoS2 from 2H to 1T phase, contributing to an enhanced conductivity and better wettability. Besides, The calculation from density functional theory indicates that those TMA+ can effectively shield the interactions between Zn2+ and MoS2 layers. Consequently, two orders magnitude high Zn2+ ions diffusion coefficient and 11 times enhancement in specific capacity (212.4 vs 18.9 mAh g‒1 at 0.1 A g‒1) are achieved. The electrochemical investigations reveal both Zn2+ and H+ can be reversibly co-inserted into the MoS2-TMA electrode. Moreover, the steady habitat of TMA+ between MoS2 interlayers affords the MoS2-TMA with remarkable cycling stability (90.1% capacity retention after 2000 cycles at 5.0 A g‒1). These performances are superior to most of the recent zinc ion batteries assembled with MoS2 or VS2-based cathodes. This work offers a new avenue to tuning the structure of MoS2 for aqueous ZIBs.

Two Zn2Cys6-type transcription factors respond to aromatic compounds and regulate the expression of laccases in the white-rot fungus Trametes hirsuta.

White-rot fungi differentially express laccases when they encounter aromatic compounds. However, the underlying mechanisms are still being explored. Here, proteomics analysis revealed that in addition to increased laccase activity, proteins involved in sphingolipid metabolism and toluene degradation as well as some cytochrome P450s (CYP450s) were differentially expressed and significantly enriched during 48 h of o-toluidine exposure, in Trametes hirsuta AH28-2. Two Zn2Cys6-type transcription factors (TFs), TH8421 and TH4300, were upregulated. Bioinformatics docking and isothermal titration calorimetry assays showed that each of them could bind directly to o-toluidine and another aromatic monomer, guaiacol. Binding to aromatic compounds promoted the formation of TH8421/TH4300 heterodimers. TH8421 and TH4300 silencing in T. hirsuta AH28-2 led to decreased transcriptional levels and activities of LacA and LacB upon o-toluidine and guaiacol exposure. EMSA and ChIP-qPCR analysis further showed that TH8421 and TH4300 bound directly with the promoter regions of lacA and lacB containing CGG or CCG motifs. Furthermore, the two TFs were involved in direct and positive regulation of the transcription of some CYP450s. Together, TH8421 and TH4300, two key regulators found in T. hirsuta AH28-2, function as heterodimers to simultaneously trigger the expression of downstream laccases and intracellular enzymes. Monomeric aromatic compounds act as ligands to promote heterodimer formation and enhance the transcriptional activities of the two TFs.IMPORTANCEWhite-rot fungi differentially express laccase isoenzymes when exposed to aromatic compounds. Clarification of the molecular mechanisms underlying differential laccase expression is essential to elucidate how white-rot fungi respond to the environment. Our study shows that two Zn2Cys6-type transcription factors form heterodimers, interact with the promoters of laccase genes, and positively regulate laccase transcription in Trametes hirsuta AH28-2. Aromatic monomer addition induces faster heterodimer formation and rate of activity. These findings not only identify two new transcription factors involved in fungal laccase transcription but also deepen our understanding of the mechanisms underlying the response to aromatics exposure in white-rot fungi.

Synthesis of Fluorescent Pyrazoline Sensors as Versatile Tool for Zinc ion Detection: A Mini-Review.

Zinc ions are one of the 2nd most abundant mineral after iron and it is important for immune system, enzymatic catalysis, DNA synthesis, and maintaining structural integrity in humans. But, monitoring the Zn levels in human body poses more challenges. This review paper investigates (paper from 2010 to 2023) the synthesis of pyrazoline derivatives by different methods, including conventional methods and green chemistry protocol. These Pyrazoline derivatives highlighted for their potential application as chemo-sensor for Zn2+ ions recognition. Pyrazoline compounds exhibit excellent sensitivity & selectivity and emitting blue-light with high quantum yields and electroluminescence, along with a superior limit of detection. These derivatives are stable bioactive molecule, with well-known diverse biological activities. This review not only gives valuable insights into the essential role of Zinc in human physiology but also provides a practical method for accurate Zinc detection in various samples. Which holds the potential for advancements in health diagnostics and environmental monitoring. Because of their significant biological application and selectivity as sensors, researchers have much more attention to prepare green environmentally-friendly pyrazoline derivatives.

A ThT Derivative as Zn2+ Sensor Based on DNA G-quadruplex.

In this report, we developed a sensing strategy based on ThT-E (a ThT derivative) and DNA G-quadruplex for the label-free detection of Zn2+. In the absence of Zn2+, there was a fluorescence enhancement of ThT-E by interaction with human telomere sequence. On the addition of Zn2+, Zn2+ induced a more compact antiparallel G-quadruplex to release ThT-E, resulting in fluorescence quenching. The detection limit was 0.6996 µM, and the fluorescence intensity showed a good linear relationship with the concentration of Zn2+ in the range of 0-10 µM. This sensing strategy which only needs to mix two kinds of materials has the characteristics of label-feel, simple operation, short response time, economical and efficient.

Recent Advances in Organic Small-Molecule Fluorescent Probes for the Detection of Zinc Ions (Zn2+).

Zinc(II) ions (Zn2g) play crucial roles in the growth, propagation, and metabolism of animals, plants, and humans. Abnormal concentrations of Zn2+ in the environment and living organisms pose potential risks to environmental protection and human health. Therefore, it is imperative to develop rapid, reliable and in-situ detection methods for Zn2+ in both environmental and biological contexts. Furthermore, effective analytical methods are required for diagnosing diseases and understanding physiological metabolic mechanisms associated with Zn2+ concentration levels. Organic small-molecule fluorescent probes offer advantages such as fast, reliable, convenient, non-destructive detection capabilities and have significant application potential in Zn2+ detection and bioimaging; thus garnering extensive attention. Over the past two years alone, various organic small-molecule probes for Zn2+ based on different detection mechanisms and fluorophores have been rapidly developed. However, these probes still exhibit several limitations that need further resolution. In light of this context, we provide a comprehensive summary of the detection mechanisms, performance characteristics, and application scope of Zn2+ fluorescence probes since year 2022 while highlighting their advantages. We also propose solutions to address existing issues with these probes and outline future directions for their advancement. This review aims to serve as a valuable reference source offering insights into the development of advanced organic small-molecule-based fluorescence probes specifically designed for detecting Zn2+.

New Fluorescent Dye for the Detection of Zn2+ in Living Cells and Fixed Sections of the Rat Pancreas.

We report the synthesis and characterization of a new 4-methoxyphenyl-2,2'-bipyridine-based ligand, such as 12, bearing dipicolylaminomethyl core as a receptor unit, as a probe for the fluorescence "turn-on" detection of Zn2+. Thus, in the presence of Zn2+ the probe 12 exhibited a fluorescence enhancement with a Stokes shift of ~ 180 nm and photoluminescence quantum yields value of ~ 1.0. In addition, 12 exhibited higher binding constant for Zn2+ (~ 2 × 105 M-1) with the LOD reaching the nanomolar level (~ 0.1 × 10-9 M) compare to the previously reported probe 1. The stoichiometry and structure of the [Zn(12)]2+ and [Zn(1)]2+ complexes were supported by XRD analysis, DFT calculations and 1H NMR experiments. It was postulated that, as a result of binding of Zn2+, the sample exhibited a bright "on" state via the PET-ICT processes. Molecular docking studies and confocal fluorescence microscopy experiments demonstrated that the probe 12 could be used for the fluorescence detection of Zn2+ not only in artificially enriched with zinc salts live cells, but also in fixed tissues with cations are in a bound state. The high binding constant of compound 12 to Zn2+ cation allows it to be used for the accurate localization of pancreatic beta cells (islets of Langerhans).

A Novel Multi-Functional Fluorescence Probe for the Detection of Al3+/Zn2+/Cd2+ and its Practical Applications.

A novel multi-functional fluorescence probe HMIC based on hydrazide Schiff base has been successfully synthesized and characterized. It can distinguish Al3+/Zn2+/Cd2+ in ethanol, in which fluorescence emission with different colors (blue for Al3+, orange for Zn2+, and green for Cd2+) were presented. The limits of detection of HMIC towards three ions were calculated from the titration curve as 7.70 × 10- 9 M, 4.64 × 10- 9 M, and 1.35 × 10- 8 M, respectively. The structures of HMIC and its complexes were investigated using UV-Vis spectra, Job's plot, infrared spectra, mass spectrometry, 1H-NMR and DFT calculations. Practical application studies have also demonstrated that HMIC can be applied to real samples with a low impact of potential interferents. Cytotoxicity and cellular imaging assays have shown that HMIC has good cellular permeability and potential antitumor effects. Interestingly, HMIC can image Al3+, Zn2+ and Cd2+ in the cells with different fluorescence signals.

Paper-based uric acid assay in whole blood samples by Zn2+ protein precipitation and enzyme-free colorimetric detection.

Uric acid (UA) is an important biomarker, as a high concentration in blood can lead to gout and further renal syndrome. Although several point-of-care testing (POCT) devices have been reported to detect UA, there are some limitations such as the requirement for uricase and the complicated pretreatment of serum/plasma samples, which restricts their use at home or in undeveloped areas. In this work, we developed an approach by applying Zn2+ to precipitate proteins and cells in whole blood to avoid interference with the chromogenic reaction. We used carboxymethylcellulose (CMC) to immobilize tetramethylbenzidine (TMB) on a nitrocellulose membrane for colorimetric detection. Using the oxidization properties of H2O2, which turns TMB into oxidized tetramethylbenzidine (TMBox) in the presence of catalyst gold nanoparticles (AuNPs), we successfully constructed an enzyme-free paper-based POCT device using the reduction reaction of UA and TMBox for simple, speedy, and cheap colorimetric detection of UA, achieving a detection time of 8 min, a linear range of 0-150 µg/mL, and an LOD of 25.79 µg/mL. The UA concentration in whole blood samples was further measured and correlated well with the clinical value (R2 = 0.8212). Thus, the proposed assay has the potential for POCT diagnosis, monitoring, and prognosis of diseases related to UA.

Coordination chemistry suggests that independently observed benefits of metformin and Zn2+ against COVID-19 are not independent.

Independent trials indicate that either oral Zn2+ or metformin can separately improve COVID-19 outcomes by approximately 40%. Coordination chemistry predicts a mechanistic relationship and therapeutic synergy. Zn2+ deficit is a known risk factor for both COVID-19 and non-infectious inflammation. Most dietary Zn2+ is not absorbed. Metformin is a naked ligand that presumably increases intestinal Zn2+ bioavailability and active absorption by cation transporters known to transport metformin. Intracellular Zn2+ provides a natural buffer of many protease reactions; the variable "set point" is determined by Zn2+ regulation or availability. A Zn2+-interactive protease network is suggested here. The two viral cysteine proteases are therapeutic targets against COVID-19. Viral and many host proteases are submaximally inhibited by exchangeable cell Zn2+. Inhibition of cysteine proteases can improve COVID-19 outcomes and non-infectious inflammation. Metformin reportedly enhances the natural moderating effect of Zn2+ on bioassayed proteome degradation. Firstly, the dissociable metformin-Zn2+ complex could be actively transported by intestinal cation transporters; thereby creating artificial pathways of absorption and increased body Zn2+ content. Secondly, metformin Zn2+ coordination can create a non-natural protease inhibitor independent of cell Zn2+ content. Moderation of peptidolytic reactions by either or both mechanisms could slow (a) viral multiplication (b) viral invasion and (c) the pathogenic host inflammatory response. These combined actions could allow development of acquired immunity to clear the infection before life-threatening inflammation. Nirmatrelvir (Paxlovid®) opposes COVID-19 by selective inhibition the viral main protease by a Zn2+-independent mechanism. Pending safety evaluation, predictable synergistic benefits of metformin and Zn2+, and perhaps metformin/Zn2+/Paxlovid® co-administration should be investigated.