The carbamido diacetyl reaction: a test for citrulline

Exploring the impact of metabolites function on heart failure and coronary heart disease: insights from a Mendelian randomization (MR) study

BACKGROUND

Heart failure (HF) and coronary heart disease (CHD) are major causes of morbidity and mortality worldwide. While traditional risk factors such as hypertension, diabetes, and smoking have been extensively studied, the role of metabolite functions in the development of these cardiovascular conditions has been less explored. This study employed a Mendelian randomization (MR) approach to investigate the impact of metabolite functions on HF and CHD.

METHODS

To assess the causal impacts of specific metabolite risk factors on HF and CHD, this study utilized genetic variants associated with these factors as instrumental variables. Comprehensive genetic and phenotypic data from diverse cohorts, including genome-wide association studies (GWAS) and cardiovascular disease registries, were incorporated into the research.

RESULTS

Our results encompass 61 metabolic cell phenotypes, with ten providing strong evidence of the influence of metabolite functions on the occurrence of HF and CHD. We found that elevated levels of erucate (22:1n9), lower levels of α-tocopherol, an imbalanced citrulline-to-ornithine ratio, elevated γ-glutamyl glycine levels, and elevated 7-methylguanine levels independently increased the risk of these cardiovascular conditions. These findings were consistent across different populations and robust to sensitivity analyses.

CONCLUSION

This MR study provides valuable insights into the influence of metabolite functions on HF and CHD. However, further investigation is needed to fully understand the precise mechanisms by which these metabolite factors contribute to the onset of these conditions. Such research could pave the way for the development of targeted therapeutic strategies.

Screening of natural inhibitors against peptidyl arginine deiminase 4 from herbal extracts by a high-performance liquid chromatography ultraviolet-visible based method

Peptidyl arginine deiminase 4 (PAD4) is an important biocatalytic enzymes involved in the conversion of protein arginine to citrulline, its dysregulation has a great impact on many physiological processes. Recently, PAD4 has emerged as a potential therapeutic target for the treatment of various diseases including rheumatoid arthritis (RA). Traditional Chinese Medicines (TCMs), also known as herbal plants, have gained great attention by the scientific community due to their good therapeutic performance and far fewer side effects observed in the clinical treatment. However, limited researches have been reported to screen natural PAD4 inhibitors from herbal plants. The color developing reagent (COLDER) or fluorescence based methods have been widely used in PAD4 activity assay and inhibitor screening. However, both methods measure the overall absorbance or fluorescence in the reaction solution, which are easy to be affected by the background interference due to colorful extracts from herbal plants. In this study, a simple, and robust high-performance liquid chromatography ultraviolet-visible (HPLC-UV) based method was developed to determine PAD4 activity. The proposed strategy was established based on COLDER principle, while used hydrophilic l-arginine instead of hydrophobic N-benzoyl-l-arginine ethyl ester (BAEE) as a new substrate to determine PAD4 inhibition activity of herbal extracts. The herbal extracts and PAD4 generated hydrophobic l-citrulline were successfully separated by the HPLC, and the developed method was optimized and validated with a known PAD4 inhibitor (GSK484) in comparison with COLDER assay. The IC50 value of GSK484 measured by HPLC-UV method was 153 nM, and the detection limit of the citrulline was 0.5 nmol, respectively, with a linear range of 0.5 nmol to 20 nmol. The IC50 value of the HPLC-UV method was improved by nearly three times compared with COLDER assay (527 nM), and the results indicated the reliability of PAD4 inhibition via HPLC-UV method. The inhibitory effect against PAD4 were fast and accurately screened for the twenty-four extracts from eight herbs. Among them, Ephedra Herba extracts showed significant inhibitory activity against the PAD4 with the IC50 values of three extracts (ethanol, ethyl acetate and water) ranging from 29.11 μg/mL to 41.36 μg/mL, which may help researchers to discover novel natural compounds holding high PAD4 inhibition activity.

Ameliorative potential role of Rosmarinus officinalis extract on toxicity induced by etoposide in male albino rats

Abstract The present work was showed to assess the effect of administration of rosemary extract on etoposide-induced toxicity, injury and proliferation in male rats were investigated. Forty male albino rats were arranged into four equal groups. 1st group, control; 2nd group, etoposide; 3rd group, co-treated rosemary & etoposide; 4th group, rosemary alone. In comparison to the control group, etoposide administration resulted in a significant increase in serum ALT, AST, ALP, total bilirubin, total protein, and gamma GT. In contrast; a significant decrease in albumin level in etoposide group as compared to G1. G3 revealed a significant decrease in AST, ALT, ALP, total protein and total bilirubin levels and a significant rise in albumin level when compared with G2. Serum levels of urea, creatinine, potassium ions, and chloride ions significantly increased; while sodium ions were significantly decreased in G2 when compared with G1. Also, there was an increase of MDA level for etoposide treated group with corresponding control rats. However, there was a remarkable significant decrease in SOD, GPX and CAT levels in G2 as compared to G1. There was a significant increase in serum hydrogen peroxide (H2O2) and Nitric oxide (NO) levels in group treated with etoposide when compared to control group. It was noticeable that administrated by rosemary alone either with etoposide had not any effect on the levels of H2O2 and Nitric oxide. Serum level of T3 and T4 was significantly increased in etoposide-administered rats in comparison with G1. The administration of rosemary, either alone or with etoposide, increased the serum levels of T3 and T4 significantly when compared to control rats. The gene expression analysis showed significant downregulation of hepatic SOD and GPx in (G2) when compared with (G1). The treatment with rosemary extract produced significant upregulation of the antioxidant enzymes mRNA SOD and GPx. MDA gene was increased in (G2) when contrasted with (G1). Treatment of the etoposide- induced rats with rosemary extract delivered significant decrease in MDA gene expression when compared with etoposide group. Rats treated with etoposide showed significant decline in hepatic Nrf2 protein expression, when compared with G1. While, supplementation of Etoposide- administered rats with the rosemary produced a significant elevation in hepatic Nrf2 protein levels. Additionally, the liver histological structure displayed noticeable degeneration and cellular infiltration in liver cells. It is possible to infer that rosemary has a potential role and that it should be researched as a natural component for etoposide-induced toxicity protection.

Characterizing citrullination by mass spectrometry-based proteomics

Citrullination is an important post-translational modification (PTM) of arginine, known to play a role in autoimmune disorders, innate immunity response and maintenance of stem cell potency. However, citrullination remains poorly characterized and not as comprehensively understood compared to other PTMs, such as phosphorylation and ubiquitylation. High-resolution mass spectrometry (MS)-based proteomics offers a valuable approach for studying citrullination in an unbiased manner, allowing confident identification of citrullination modification sites and distinction from deamidation events on asparagine and glutamine. MS efforts have already provided valuable insights into peptidyl arginine deaminase targeting along with site-specific information of citrullination in for example synovial fluids derived from rheumatoid arthritis patients. Still, there is unrealized potential for the wider citrullination field by applying MS-based mass spectrometry approaches for proteome-wide investigations. Here we will outline contemporary methods and current challenges for studying citrullination by MS, and discuss how the development of neoteric citrullination-specific proteomics approaches still may improve our understanding of citrullination networks. This article is part of the Theo Murphy meeting issue 'The virtues and vices of protein citrullination'.

Post-translational modifications and their implications in cancer

Post-translational modifications (PTMs) are crucial regulatory mechanisms that alter the properties of a protein by covalently attaching a modified chemical group to some of its amino acid residues. PTMs modulate essential physiological processes such as signal transduction, metabolism, protein localization, and turnover and have clinical relevance in cancer and age-related pathologies. Majority of proteins undergo post-translational modifications, irrespective of their occurrence in or after protein biosynthesis. Post-translational modifications link to amino acid termini or side chains, causing the protein backbone to get cleaved, spliced, or cyclized, to name a few. These chemical modifications expand the diversity of the proteome and regulate protein activity, structure, locations, functions, and protein-protein interactions (PPIs). This ability to modify the physical and chemical properties and functions of proteins render PTMs vital. To date, over 200 different protein modifications have been reported, owing to advanced detection technologies. Some of these modifications include phosphorylation, glycosylation, methylation, acetylation, and ubiquitination. Here, we discuss about the existing as well as some novel post-translational protein modifications, with their implications in aberrant states, which will help us better understand the modified sites in different proteins and the effect of PTMs on protein functions in core biological processes and progression in cancer.

Non-Canonical Amino Acids as Building Blocks for Peptidomimetics: Structure, Function, and Applications

This review provides a fresh overview of non-canonical amino acids and their applications in the design of peptidomimetics. Non-canonical amino acids appear widely distributed in nature and are known to enhance the stability of specific secondary structures and/or biological function. Contrary to the ubiquitous DNA-encoded amino acids, the structure and function of these residues are not fully understood. Here, results from experimental and molecular modelling approaches are gathered to classify several classes of non-canonical amino acids according to their ability to induce specific secondary structures yielding different biological functions and improved stability. Regarding side-chain modifications, symmetrical and asymmetrical α,α-dialkyl glycines, Cα to Cα cyclized amino acids, proline analogues, β-substituted amino acids, and α,β-dehydro amino acids are some of the non-canonical representatives addressed. Backbone modifications were also examined, especially those that result in retro-inverso peptidomimetics and depsipeptides. All this knowledge has an important application in the field of peptidomimetics, which is in continuous progress and promises to deliver new biologically active molecules and new materials in the near future.

Selective inhibition of peptidyl-arginine deiminase (PAD): can it control multiple inflammatory disorders as a promising therapeutic strategy?

Peptidyl arginine deiminases (PADs) are a family of post-translational modification enzymes that irreversibly citrullinate (deiminate) arginine residues of protein and convert them to a non-classical amino acid citrulline in the presence of calcium ions. It has five isotypes, such as PAD1, PAD2, PAD3, PAD4, and PAD6, found in mammalian species. It has been suggested that increased PAD expression in various tissues contributes to the development of multiple inflammatory diseases, including rheumatoid arthritis (RA), cancer, diabetes, and neurological disorders. Elevation of PAD enzyme expression depends on several factors like rising intracellular Ca²⁺ levels, oxidative stress, and proinflammatory cytokines. PAD inhibitors originating from natural or synthetic sources can be used as a novel therapeutic approach concerning inflammatory disorders. Here, we review the pathological role of PAD in several inflammatory disorders, factors that trigger PAD expression, epigenetic role and finally, decipher the therapeutic approach of PAD inhibitors in multiple inflammatory disorders.

A new and accessible instrumentation to determine urea in UHT milk using digital image analysis

This research demonstrates the development, optimization and application of a new low-cost detection system, based on digital image analysis, for the detection of urea in ultra-high-temperature (UHT) milk samples. The apparatus built in the laboratory, allows the capture of images through a simple system built by polyvinyl chloride (PVC) tubes, a digital microscope and a peristaltic mini-pump, after the colorimetric reaction between urea and diacetylmonoxime (butane-2,3-dionammonoxime). The red, green and blue (RGB) and hue, saturation and value (HSV) color systems were studied, with the saturation channel of the HSV color system selected as the analytical signal. Subsequently, the experimental chemical conditions were evaluated through multivariate experimental designs and the optimal conditions were defined. The proposed method was validated, and the detection and quantification limits presented by the method were 0.35 mg L^-1 and 0.52 mg L^-1, respectively; precision, ranged between 1.6  and 2.8 %. The results were compared with those obtained using the mid-infrared technique and no statistically significant differences were observed at a 95 % confidence level. The proposed method was applied to eight UHT milk samples that presented urea content ranging from 187 to 386 mg L^-1. The mean values obtained are in agreement with values presented in other studies for the determination of urea in milk. The results indicated that the system described and validated here is promising and can be applied to assess the authenticity and quality of milk.

An Update on Arginase Inhibitors and Inhibitory Assays

Arginase, which converts arginine into ornithine and urea, is a promising therapeutic target. Arginase is involved in cardiovascular diseases, parasitic infections and, through a critical role in immunity, in some cancers. There is a need to develop effective arginase inhibitors and therefore efforts to identify and optimize new inhibitors are increasing. Several methods of evaluating arginase activity are available, but few directly measure the product. Radiometric assays need to separate urea and dying reactions require acidic conditions and sometimes heating. Hence, there are a variety of different approaches available, and each approach has its own limits and benefits. In this review, we provide an update on arginase inhibitors, followed by a discussion on available arginase assays and alternative methods, with a focus on the intrinsic biases and parameters that are likely to impact results.

pH/Acetonitrile-Gradient Reversed-Phase Fractionation of Enriched Hyper-Citrullinated Library in Combination with LC-MS/MS Analysis for Confident Identification of Citrullinated Peptides

Citrullination, the Ca²⁺-driven enzymatic conversion of arginine residues to citrulline, is a posttranslational modification, implicated in several physiological and pathological processes. Several methods to detect citrullinated proteins have been developed, including color development reagent, fluorescence, phenylglyoxal, and antibody-based methods. These methods yet suffer from limitations in sensitivity, specificity, or citrullinated site determination. Mass spectrometry (MS)-based proteomic analysis has emerged as a promising method to resolve these problems. However, due to low abundance of citrullinated proteins and similar MS features to deamidation of asparagine and glutamine, confident identification of citrullinated proteome is challenging. Here, we present a systematic approach to identify a compendium of steps to enhance the number of detected citrullinated residue and implement diagnostic MS feature that allow the confidence of MS-based identifications. Our method is based on the concept of generation of hyper-citrullinated library with high-pH reversed-phase peptide fractionation that allows to enrich in low abundance citrullinated peptides and amplify the effect of charge loss upon citrullination. Application of our approach to complex global citrullino-proteome datasets demonstrates the confident assessment of citrullinated peptides, thereby enhancing the size and functional interpretation of citrullinated proteomes.

Colorimetric determination of urea using diacetyl monoxime with strong acids

Urea is a byproduct of the urea cycle in metabolism and is excreted through urine and sweat. Ammonia, which is toxic at low levels, is converted to the safe storage form of urea, which represents the largest efflux of nitrogen from many organisms. Urea is an important nitrogen source in agriculture, is added to many industrial products, and is a large component in wastewater. The enzyme urease hydrolyzes urea to ammonia and bicarbonate. This reaction is microbially mediated in soils, hydroponic solutions, and wastewater recycling and is catalyzed in vivo in plants using native urease, making measurement of urea environmentally important. Both direct and indirect methods to measure urea exist. This protocol uses diacetyl monoxime to directly determine the concentration of urea in solution. The protocol provides repeatable results and stable reagents with good color stability and simple measurement techniques for use in any lab with a spectrophotometer. The reaction between diacetyl monoxime and urea in the presence of sulfuric acid, phosphoric acid, thiosemicarbazide, and ferric chloride produces a chromophore with a peak absorbance at 520 nm and a linear relationship between concentration and absorbance from 0.4 to 5.0 mM urea in this protocol. The lack of detectable interferences makes this protocol suitable for the determination of millimolar levels of urea in wastewater streams and hydroponic solutions.

Citrulline, Biomarker of Enterocyte Functional Mass and Dietary Supplement. Metabolism, Transport, and Current Evidence for Clinical Use

L-Citrulline is a non-essential but still important amino acid that is released from enterocytes. Because plasma levels are reduced in case of impaired intestinal function, it has become a biomarker to monitor intestinal integrity. Moreover, oxidative stress induces protein citrullination, and antibodies against anti-citrullinated proteins are useful to monitor rheumatoid diseases. Citrullinated histones, however, may even predict a worse outcome in cancer patients. Supplementation of citrulline is better tolerated compared to arginine and might be useful to slightly improve muscle strength or protein balance. The following article shall provide an overview of L-citrulline properties and functions, as well as the current evidence for its use as a biomarker or as a therapeutic supplement.

Citrullination and PAD Enzyme Biology in Type 1 Diabetes - Regulators of Inflammation, Autoimmunity, and Pathology

The generation of post-translational modifications (PTMs) in human proteins is a physiological process leading to structural and immunologic variety in proteins, with potentially altered biological functions. PTMs often arise through normal responses to cellular stress, including general oxidative changes in the tissue microenvironment and intracellular stress to the endoplasmic reticulum or immune-mediated inflammatory stresses. Many studies have now illustrated the presence of 'neoepitopes' consisting of PTM self-proteins that induce robust autoimmune responses. These pathways of inflammatory neoepitope generation are commonly observed in many autoimmune diseases including systemic lupus erythematosus, rheumatoid arthritis, multiple sclerosis, and type 1 diabetes (T1D), among others. This review will focus on one specific PTM to self-proteins known as citrullination. Citrullination is mediated by calcium-dependent peptidylarginine deiminase (PAD) enzymes, which catalyze deimination, the conversion of arginine into the non-classical amino acid citrulline. PADs and citrullinated peptides have been associated with different autoimmune diseases, notably with a prominent role in the diagnosis and pathology of rheumatoid arthritis. More recently, an important role for PADs and citrullinated self-proteins has emerged in T1D. In this review we will provide a comprehensive overview on the pathogenic role for PADs and citrullination in inflammation and autoimmunity, with specific focus on evidence for their role in T1D. The general role of PADs in epigenetic and transcriptional processes, as well as their crucial role in histone citrullination, neutrophil biology and neutrophil extracellular trap (NET) formation will be discussed. The latter is important in view of increasing evidence for a role of neutrophils and NETosis in the pathogenesis of T1D. Further, we will discuss the underlying processes leading to citrullination, the genetic susceptibility factors for increased recognition of citrullinated epitopes by T1D HLA-susceptibility types and provide an overview of reported autoreactive responses against citrullinated epitopes, both of T cells and autoantibodies in T1D patients. Finally, we will discuss recent observations obtained in NOD mice, pointing to prevention of diabetes development through PAD inhibition, and the potential role of PAD inhibitors as novel therapeutic strategy in autoimmunity and in T1D in particular.

Bioorthogonal protein labelling enables the study of antigen processing of citrullinated and carbamylated auto-antigens

Proteolysis is fundamental to many biological processes. In the immune system, it underpins the activation of the adaptive immune response: degradation of antigenic material into short peptides and presentation thereof on major histocompatibility complexes, leads to activation of T-cells. This initiates the adaptive immune response against many pathogens. Studying proteolysis is difficult, as the oft-used polypeptide reporters are susceptible to proteolytic sequestration themselves. Here we present a new approach that allows the imaging of antigen proteolysis throughout the processing pathway in an unbiased manner. By incorporating bioorthogonal functionalities into the protein in place of methionines, antigens can be followed during degradation, whilst leaving reactive sidechains open to templated and non-templated post-translational modifications, such as citrullination and carbamylation. Using this approach, we followed and imaged the post-uptake fate of the commonly used antigen ovalbumin, as well as the post-translationally citrullinated and/or carbamylated auto-antigen vinculin in rheumatoid arthritis, revealing differences in antigen processing and presentation.

Organic bases catalyze the synthesis of urea from ammonium salts derived from recovered environmental ammonia

Ammonia from sewage and livestock manure is a major environmental pollutant. To consume environmental ammonia, we investigated the organic base-catalyzed synthesis of urea. 1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU) catalyzes the conversion of ammonium carbamate to urea in 35% yield at 100 °C. Moreover, DBU also converts other ammonium salts into urea. A mechanism that involves nucleophilic attack of ammonia following ion exchange is proposed.

Probing remote residues important for catalysis in Escherichia coli ornithine transcarbamoylase

Understanding how enzymes achieve their tremendous catalytic power is a major question in biochemistry. Greater understanding is also needed for enzyme engineering applications. In many cases, enzyme efficiency and specificity depend on residues not in direct contact with the substrate, termed remote residues. This work focuses on Escherichia coli ornithine transcarbamoylase (OTC), which plays a central role in amino acid metabolism. OTC has been reported to undergo an induced-fit conformational change upon binding its first substrate, carbamoyl phosphate (CP), and several residues important for activity have been identified. Using computational methods based on the computed chemical properties from theoretical titration curves, sequence-based scores derived from evolutionary history, and protein surface topology, residues important for catalytic activity were predicted. The roles of these residues in OTC activity were tested by constructing mutations at predicted positions, followed by steady-state kinetics assays and substrate binding studies with the variants. First-layer mutations R57A and D231A, second-layer mutation H272L, and third-layer mutation E299Q, result in 57- to 450-fold reductions in k_cat/K_M with respect to CP and 44- to 580-fold reductions with respect to ornithine. Second-layer mutations D140N and Y160S also reduce activity with respect to ornithine. Most variants had decreased stability relative to wild-type OTC, with variants H272L, H272N, and E299Q having the greatest decreases. Variants H272L, E299Q, and R57A also show compromised CP binding. In addition to direct effects on catalytic activity, effects on overall protein stability and substrate binding were observed that reveal the intricacies of how these residues contribute to catalysis.

An Overview of the Intrinsic Role of Citrullination in Autoimmune Disorders

A protein undergoes many types of posttranslation modification. Citrullination is one of these modifications, where an arginine amino acid is converted to a citrulline amino acid. This process depends on catalytic enzymes such as peptidylarginine deiminase enzymes (PADs). This modification leads to a charge shift, which affects the protein structure, protein-protein interactions, and hydrogen bond formation, and it may cause protein denaturation. The irreversible citrullination reaction is not limited to a specific protein, cell, or tissue. It can target a wide range of proteins in the cell membrane, cytoplasm, nucleus, and mitochondria. Citrullination is a normal reaction during cell death. Apoptosis is normally accompanied with a clearance process via scavenger cells. A defect in the clearance system either in terms of efficiency or capacity may occur due to massive cell death, which may result in the accumulation and leakage of PAD enzymes and the citrullinated peptide from the necrotized cell which could be recognized by the immune system, where the immunological tolerance will be avoided and the autoimmune disorders will be subsequently triggered. The induction of autoimmune responses, autoantibody production, and cytokines involved in the major autoimmune diseases will be discussed.

Glutathione Supplementation of Parenteral Nutrition Prevents Oxidative Stress and Sustains Protein Synthesis in Guinea Pig Model

Peroxides contaminating parenteral nutrition (PN) limit the use of methionine as a precursor of cysteine. Thus, PN causes a cysteine deficiency, characterized by low levels of glutathione, the main molecule used in peroxide detoxification, and limited growth in individuals receiving long-term PN compared to the average population. We hypothesize that glutathione supplementation in PN can be used as a pro-cysteine that improves glutathione levels and protein synthesis and reduces oxidative stress caused by PN. One-month-old guinea pigs (7–8 per group) were used to compare glutathione-enriched to a non-enriched PN, animals on enteral nutrition were used as a reference. PN: Dextrose, amino acids (Primene), lipid emulsion (Intralipid), multivitamins, electrolytes; five-day infusion. Glutathione (GSH, GSSG, redox potential) and the incorporation of radioactive leucine into the protein fraction (protein synthesis index) were measured in the blood, lungs, liver, and gastrocnemius muscle. Data were analysed by ANOVA; p < 0.05 was considered significant. The addition of glutathione to PN prevented the PN-induced oxidative stress in the lungs and muscles and supported protein synthesis in liver and muscles. The results potentially support the recommendation to add glutathione to the PN and demonstrate that glutathione could act as a biologically available cysteine precursor.

Exceptionally versatile – arginine in bacterial post-translational protein modifications

Post-translational modifications (PTM) are the evolutionary solution to challenge and extend the boundaries of genetically predetermined proteomic diversity. As PTMs are highly dynamic, they also hold an enormous regulatory potential. It is therefore not surprising that out of the 20 proteinogenic amino acids, 15 can be post-translationally modified. Even the relatively inert guanidino group of arginine is subject to a multitude of mostly enzyme mediated chemical changes. The resulting alterations can have a major influence on protein function. In this review, we will discuss how bacteria control their cellular processes and develop pathogenicity based on post-translational protein-arginine modifications.

Pharmacological targeting of exercise adaptations in skeletal muscle: Benefits and pitfalls

Exercise exerts significant effects on the prevention and treatment of many diseases. However, even though some of the key regulators of training adaptation in skeletal muscle have been identified, this biological program is still poorly understood. Accordingly, exercise-based pharmacological interventions for many muscle wasting diseases and also for pathologies that are triggered by a sedentary lifestyle remain scarce. The most efficacious compounds that induce muscle hypertrophy or endurance are hampered by severe side effects and are classified as doping. In contrast, dietary supplements with a higher safety margin exert milder outcomes. In recent years, the design of pharmacological agents that activate the training program, so-called "exercise mimetics", has been proposed, although the feasibility of such an approach is highly debated. In this review, the most recent insights into key regulatory factors and therapeutic approaches aimed at leveraging exercise adaptations are discussed.

Human Deiminases: Isoforms, Substrate Specificities, Kinetics, and Detection

Peptidylarginine deiminase (PAD) enzymes are of enormous interest in biomedicine. They catalyze the conversion of a positively-charged guanidinium at an arginine side chain into a neutral ureido group. As a result of this conversion, proteins acquire the non-ribosomally encoded amino acid "citrulline". This imposes critical influences on the structure and function of the target molecules. In multiple sclerosis, myelin hyper-citrullination promotes demyelination by reducing its compaction and triggers auto-antibody production. Immune responses to citrulline-containing proteins play a central role in the pathogenesis of autoimmune diseases. Moreover, auto-antibodies, specific to citrullinated proteins, such as collagen type I and II and filaggrin, are early detectable in rheumatoid arthritis, serving as diagnostic markers of the disease. Despite their significance, little is understood about the role in demyelinating disorders, diversified cancers, and auto-immune diseases. To impart their biological and pathological effects, it is crucial to better understand the reaction mechanism, kinetic properties, substrate selection, and specificities of peptidylarginine deiminase isoforms.Many aspects of PAD biochemistry and physiology have been ignored in past, but, herein is presented a comprehensive survey to improve our current understandings of the underlying mechanism and regulation of PAD enzymes.

Effect of variable water intake as mediated by dietary potassium carbonate supplementation on rumen dynamics in lactating dairy cows

Water is a critical nutrient for dairy cows, with intake varying with environment, production, and diet. However, little work has evaluated the effects of water intake on rumen parameters. Using dietary potassium carbonate (K2CO3) as a K supplement to increase water intake, the objective of this study was to evaluate the effect of K2CO3 supplementation on water intake and on rumen parameters of lactating dairy cows. Nine ruminally cannulated, late-lactation Holstein cows (207±12d in milk) were randomly assigned to 1 of 3 treatments in a replicated 3×3 Latin square design with 18-d periods. Dietary treatments (on a dry matter basis) were no added K2CO3 (baseline dietary K levels of 1.67% dietary K), 0.75% added dietary K, and 1.5% added dietary K. Cows were offered treatment diets for a 14-d adaption period followed by a 4-d collection period. Ruminal total, liquid, and dry matter digesta weights were determined by total rumen evacuations conducted 2h after feeding on d 4 of the collection period. Rumen fluid samples were collected to determine pH, volatile fatty acids, and NH3 concentrations, and Co-EDTA was used to determine fractional liquid passage rate. Milk samples were collected twice daily during the collection period. Milk, milk fat, and protein yields showed quadratic responses with greatest yields for the 0.75% added dietary K treatment. Dry matter intake showed a quadratic response with 21.8kg/d for the 0.75% added dietary K treatment and 20.4 and 20.5kg/d for control and the 1.5% added dietary K treatment, respectively. Water intake increased linearly with increasing K2CO3 supplementation (102.4, 118.4, and 129.3L/d) as did ruminal fractional liquid passage rate in the earlier hours after feeding (0.118, 0.135, and 0.141 per hour). Total and wet weights of rumen contents declined linearly and dry weight tended to decline linearly as dietary K2CO3 increased, suggesting that the increasing water intake and fractional liquid passage rate with increasing K2CO3 increased the overall ruminal turnover rate. Ruminal ammonia concentrations declined linearly and pH increased linearly as K supplementation increased. As a molar percentage of total volatile fatty acids, acetate increased linearly as dietary K increased, though propionate declined. Increasing dietary K2CO3 and total K in the diets of lactating dairy cows increased water consumption and modified ruminal measures in ways suggesting that both liquid and total ruminal turnover were increased as both water and K intake increased.

Demonstration of extracellular peptidylarginine deiminase (PAD) activity in synovial fluid of patients with rheumatoid arthritis using a novel assay for citrullination of fibrinogen

Introduction

Members of the peptidylarginine deiminase (PAD) family catalyse the posttranslational conversion of peptidylarginine to peptidylcitrulline. Citrullination of proteins is well described in rheumatoid arthritis (RA), and hypercitrullination of proteins may be related to inflammation in general. PAD activity has been demonstrated in various cell lysates, but so far not in synovial fluid. We aimed to develop an assay for detection of PAD activity, if any, in synovial fluid from RA patients.

Methods

An enzyme-linked immunosorbent assay using human fibrinogen as the immobilized substrate for citrullination and anti-citrullinated fibrinogen antibody as the detecting agent were used for measurement of PAD activity in synovial fluid samples from five RA patients. The concentrations of PAD2 and calcium were also determined.

Results

Approximately 150 times lower levels of recombinant human PAD2 (rhPAD2) than of rhPAD4 were required for citrullination of fibrinogen. PAD activity was detected in four of five synovial fluid samples from RA patients and correlated with PAD2 concentrations in the samples (r = 0.98, P = 0.003). The calcium requirement for half-maximal activities of PAD2 and PAD4 were found in a range from 0.35 to 1.85 mM, and synovial fluid was found to contain sufficient calcium levels for the citrullination process to occur.

Conclusions

We present an assay with high specificity for PAD2 activity and show that citrullination of fibrinogen can occur in cell-free synovial fluid from RA patients.

Immune response to chemically modified proteome

Both enzymatic and nonenzymatic PTMs of proteins involve chemical modifications. Some of these modifications are prerequisite for the normal functioning of cell, while other chemical modifications render the proteins as "neo-self" antigens, which are recognized as "non-self" leading to aberrant cellular and humoral immune responses. However, these modifications could be a secondary effect of autoimmune diseases, as in the case of type I diabetes, hyperglycemia leads to protein glycation. The enigma of chemical modifications and immune response is akin to the "chick-and-egg" paradox. Nevertheless, chemical modifications regulate immune response. In some of the well-known autoimmune diseases such as rheumatoid arthritis, systemic lupus erythematosus, and multiple sclerosis, chemically modified proteins act as autoantigens forming immune complexes. In some instances, chemical modifications are also involved in regulating immune response during pathogen infection. Further, the usefulness of proteomic analysis of immune complexes is briefly discussed.

Methods for the detection of peptidylarginine deiminase (PAD) activity and protein citrullination

The post-translational conversion of peptidylarginine to peptidylcitrulline, a process also known as citrullination, is catalyzed by the enzyme family of peptidylarginine deiminases (PADs) and has been demonstrated to be involved in many physiological processes, including the regulation of gene expression. In addition, citrullination has been shown to be associated with several diseases, such as cancer, multiple sclerosis, rheumatoid arthritis, and Alzheimer's disease. To get more insight into the role of PAD enzymes and citrullination in both health and disease, experimental strategies to study PAD activity and to characterize citrullinated proteins in complex biological samples are crucial. Here, we describe the chemical, proteomic and antibody-based procedures that are currently available and discuss their applicability for the analysis of complex samples. The methods that have been developed can be used to provide more insight in the substrate specificity of PAD enzymes. Because the evidence that PADs play a pathophysiological role in the diseases mentioned above is increasing, they become attractive targets for therapeutic interventions. More knowledge of PAD specificity and the availability of reliable, high-throughput assays for PAD activity will facilitate the development of highly specific PAD inhibitors.

A colorimetric assay optimization for high-throughput screening of dihydroorotase by detecting ureido groups

Dihydroorotase (DHOase) is the third enzyme in the de novo pyrimidine biosynthesis pathway and is a potential new antibacterial drug target. No target-based high-throughput screening (HTS) assay for this enzyme has been reported to date. Here, we optimized two colorimetric-based enzymatic assays that detect the ureido moiety of the DHOase substrate, carbamyl-aspartate (Ca-asp). Each assay was developed in a 40-μl assay volume using 384-well plates with a different color mix, diacetylmonoxime (DAMO)-thiosemicarbazide (TSC) or DAMO-antipyrine. The sensitivity and color interference of both color mixes were compared in the presence of common HTS buffer additives, including dimethyl sulfoxide, reducing agents, detergents, and bovine serum albumin. DAMO-TSC (Z'-factors 0.7-0.8) was determined to be superior to DAMO-antipyrine (Z'-factors 0.5-0.6) with significantly less variability within replicates. An HTS pilot screening with 29,552 compounds from four structurally diverse libraries confirmed the quality of our newly optimized colorimetric assay with DAMO-TSC. This robust method has no heating requirement, which was the main obstacle to applying previous assays to HTS. More important, this well-optimized HTS assay for DHOase, the first of its kind, should make it possible to screen large-scale compound libraries to develop new inhibitors against any enzymes that produce ureido functional groups.

Effect of exposure to solid wastes in relation to employment duration on some important markers of health and disease in waste management workers of Ogun State in southwest Nigeria

Waste management workers (WMWs) around the world are at risk of work-related health disorders. The influence of employment duration on individuals occupationally exposed to solid waste was investigated in this study. The study comprised (n = 280) 180 WMWs and 100 controls. Employment duration was obtained from questionnaire survey and categorized into three groups: group I (0.5-2 years), group II (>2-4 years) and group III (>4-6 years). Blood sample (10 ml) was collected from the antecubital vein of subjects for analysis. WMWs exhibited significantly (p < 0.001) elevated inflammatory markers (erythrocyte sedimentation rate (ESR), C-reactive protein (CRP) and ceruloplasmin (Cp)) relative to control. While Cp increased, ESR and CRP decreased with increasing WMWs' employment duration. Alteration in oxidant/antioxidant markers was characterized by significant (p < 0.001) decrease in ferric-reducing ability of plasma (FRAP) and catalase activity together with marked (p < 0.01) elevation of thiobarbituric acid reactive substances (TBARS) and uric acid (UA). TBARS, UA and FRAP increased while catalase decreased with WMWs' employment duration. In addition, WMWs exhibited significantly (p < 0.01) elevated immunoglobulin A (IgA) and IgG, which also increased and decreased, respectively, with job duration. The significantly (p < 0.01) decreased haemoglobin and haematocrit levels as well as the significantly (p < 0.001) elevated total leukocytes in WMWs increased with employment duration. Alanine aminotransferase increased and albumin decreased significantly (p < 0.05) in WMWs, and these changes also increased and decreased, respectively, with job duration. Data suggest that levels of alteration of important systemic markers of health/disease are related to WMWs' employment or exposure duration.

A capacitive biosensor for ultra-trace level urea determination based on nano-sized urea-imprinted polymer receptors coated on graphite electrode surface

A novel urea biosensor based on capacitive detection was developed using nano-sized molecularly imprinted polymers (nano-MIP). The sensitive layer was created by casting a thin layer of poly (vinyl chloride) (PVC)/nano-MIP composite on a graphite electrode surface. Cyclic voltammetry and impedance spectroscopy were used to monitor the electrode surface modification. The insulating properties of the layer were studied in the presence of K3Fe(CN)6/K4Fe(CN)6 redox couple by AC impedance measurements. The proposed capacitive sensor exhibited good selectivity for urea, compared to the chemicals with high resemblance to urea. The repeatability of the senor was found to be satisfactory. Very wide dynamic linear range (1×10(-11)-1×10(-4)M) as well as an ultra-trace detection limit equal to 5 picomolar was obtained for the sensor. The relevant experiments indicated satisfactory repeatability and reproducibility for the developed sensor. The results from sample analysis confirmed the applicability of the MIP-based sensor to quantitative analysis of urea in real samples.

The levels of inflammatory markers and oxidative stress in individuals occupationally exposed to municipal solid waste in Ogun State, South West Nigeria

Airway inflammation and related respiratory complaints are common symptoms among waste management workers (WMWs). This study investigated the relationship between exposure to municipal solid waste (MSW) and the levels of inflammatory markers and oxidative stress among WMW of Ogun State, South West Nigeria. A total of 280 subjects consisting of 180 WMW and 100 controls were recruited. Ten millilitres of blood were collected from antecubital vein of the subjects for analysis. Results reveal that exposure to MSW is associated with systemic inflammation and oxidative stress. Significant ( p < 0.001) elevation of ceruloplasmin (Cp) and C-reactive protein was associated with marked decreases in superoxide dismutase ( p < 0.01), catalase ( p < 0.001), and glutathione ( p < 0.05) and significant ( p < 0.001) increases in malondialdehyde (MDA) and uric acid when compared with control. Haematological disorders include significant ( p < 0.05) decreases in haemoglobin, packed cell volume, and mean corpuscular volume and significant ( p < 0.01) increase in total leucocyte count. Apart from decreased albumin ( p < 0.05) and elevated aspartate aminotransferase ( p < 0.05) activity observed in WMW, other markers of hepatic (alanine aminotransferase, alkaline phosphatase, total cholesterol and triglycerides) and renal (urea and creatinine) functions did not change significantly ( p > 0.05) when compared with the control. A positive correlation between leucocytes ( r = 0.195, p < 0.01), Cp ( r = 0.210, p < 0.01) and job duration and between Cp and MDA ( r = 0.200, p < 0.01) and Cp and leucocytes ( r = 0.260, p < 0.001) were observed in WMW. Overall, exposure to MSW predisposes to systemic inflammation and oxidative stress and Cp may be a useful biomarker for monitoring health status of Nigerian WMWs.

The role of anti-cyclic citrullinated peptide antibody in periodontal disease

The anti-Cyclic Citrullinated Peptide Antibodies (anti-CCP) are produced locally in the inflamed synovium of Rheumatoid arthritis (RA) patients, suggesting that citrullinated proteins are located in the inflamed synovium. In scientific literature were find periodontal bacterial DNA in serum and synovial fluid of RA with PD patients. RA and adult periodontitis share common pathogenetic mechanisms and immunologic and pathological findings RA. One oral pathogen strongly implicated in the pathogenesis of periodontal disease (PD), Porphyromonas. gingivalis, possesses a unique microbial enzyme, peptidylarginine deiminase (PAD), the human equivalent of which has been identified as a susceptibility factor for RA. Under this point of view, we speculate about the presence of anti-CCP antibodies in sera of PD with RA patients. We conducted this study to evaluate and compare the diagnostic and predictive utility of anti-CCP antibodies in patients with PD and patients with PD and RA. Anti-CCP antibody was not found in 21 sera (U/ml<10), included RA controls, while only 1 patient with chronic PD and probing depth of 7,1 mm was identified positive for anti-CCP (22.2 U/ml). Our data do not support a role for anti-CCP in diagnoses of periodontal disease.

Synthesis of Isocyanic Acid from Nitric Oxide over Palladium and Iridium Catalysts

A novel and convenient synthesis of isocyanic acid (HNCO) and its trimer isocyanuric acid has been obtained by the conversion of nitric oxide (NO). Nitric oxide, carbon monoxide, and hydrogen mixed in helium at the level of 0.3 to 5 percent reacted over iridium and palladium catalysts at 280 degrees to 450 degrees C to form HNCO in 60 to 75 percent yield. Major side products were ammonium cyanate at low temperature and ammonia or nitrogen at high temperature. Total conversion of nitrogen from NO to NCO reached 73 percent over palladium and 86 percent over iridium.

Preparation of molecularly imprinted polymer containing selective cavities for urea molecule and its application for urea extraction

A new molecularly imprinted polymer material having urea molecule selective cavities was introduced. Urea was properly dissolved in acetonitrile in the presence of an acidic functional monomer. Molecularly imprinted polymers with different compositions were examined and the roper formulation was selected. It was shown that the MIP had a considerable selectivity for urea in comparison to similar compounds such as thiourea and hydroxyurea. The obtained polymer was used as an adsorber for solid phase extraction (SPE) of urea in the aqueous samples. The extracted urea was determined by using a spectrophotometric method. Different parameters of SPE were optimized and the developed procedure was used for urea determination in real samples. The calibration graph of the method was linear in the range of 0.6-8.3 micromol L(-1). The detection limit was calculated to be 0.14 micromol L(-1).