Kinetic, thermodynamic and statistical studies on the inhibition of adenosine deaminase by aspirin and diclofenac

Understanding the mode of inhibition and molecular interaction of taxifolin with human adenosine deaminase

Adenosine deaminase is a zinc⁺² dependent key enzyme of purine metabolism which irreversibly converts adenosine to inosine and form ammonia. Overexpression of adenosine deaminase has been linked to a variety of pathophysiological conditions such as atherosclerosis, hypertension, and diabetes. In the case of a cell-mediated immune response, ADA is thought to be a marker, particularly in type II diabetes. Deoxycoformycin is the most potent ADA inhibitor that has been discovered so far, but it has several drawbacks, including being toxic and having poor pharmacokinetics. Taxifolin, a flavonoid derived from plants, was discovered to be a potent inhibitor of the human ADA (hADA) enzyme in the current study. Taxifolin bound at the active site of human ADA and showed fifty percent inhibition at a concentration of 400 µM against the enzyme. To better understand the interactions between taxifolin and human ADA, docking and molecular dynamic simulations were performed. In-silico studies using autodock revealed that taxifolin bound in the active site of human ADA with a binding energy of -7.4 kcal mol ^-1 and a theoretical Ki of 3.7 uM. Comparative analysis indicated that taxifolin and deoxycoformycin share a common binding space in the active site of human ADA and inhibit its catalytic activity similarly. The work emphasises the need of employing taxifolin as a lead chemical in order to produce a more precise and effective inhibitor of the human ADA enzyme with therapeutic potential.Communicated by Ramaswamy H. Sarma.

A Capstone Laboratory theme investigating properties of non-steroidal anti-inflammatory drugs and their solubilization by cationic surfactant micelles

Research experience is becoming an increasingly crucial element of today's undergraduate science curriculum. In recent years, the establishment of the Course-Based Undergraduate Research Experience Network (CUREnet) has provided a framework for the development of courses aiming to cultivate students' proficiency in undergraduate research techniques while fostering scientific curiosity in a laboratory setting. Capstone Laboratory is one such course that was designed to provide second-year pre-medical students at Weill Cornell Medicine-Qatar with exposure to laboratory techniques to develop their repertoire of research skills. For the past 3 years, Capstone Laboratory has incorporated a project-based learning component involving non-steroidal anti-inflammatory drugs (NSAIDs). The research element of the NSAID-surfactant theme investigated the partitioning of various drugs into cationic surfactant micelles. Structural elements and enzyme inhibition characteristics of NSAIDs were also investigated, while integrating principles of biochemistry, general chemistry, and experimental organic chemistry. By studying drug properties in these contexts, students integrate their learning and develop skills needed for the study and practice of medicine.

Therapeutic Perspectives of Adenosine Deaminase Inhibition in Cardiovascular Diseases

Adenosine deaminase (ADA) is an enzyme of purine metabolism that irreversibly converts adenosine to inosine or 2'deoxyadenosine to 2'deoxyinosine. ADA is active both inside the cell and on the cell surface where it was found to interact with membrane proteins, such as CD26 and adenosine receptors, forming ecto-ADA (eADA). In addition to adenosine uptake, the activity of eADA is an essential mechanism that terminates adenosine signaling. This is particularly important in cardiovascular system, where adenosine protects against endothelial dysfunction, vascular inflammation, or thrombosis. Besides enzymatic function, ADA protein mediates cell-to-cell interactions involved in lymphocyte co-stimulation or endothelial activation. Furthermore, alteration in ADA activity was demonstrated in many cardiovascular pathologies such as atherosclerosis, myocardial ischemia-reperfusion injury, hypertension, thrombosis, or diabetes. Modulation of ADA activity could be an important therapeutic target. This work provides a systematic review of ADA activity and anchoring inhibitors as well as summarizes the perspectives of their therapeutic use in cardiovascular pathologies associated with increased activity of ADA.

Adenosine deaminase inhibition

Adenosine deaminase is a critical enzyme in purine metabolism that regulates intra and extracellular adenosine concentrations by converting it to inosine. Adenosine is an important purine that regulates numerous physiological functions by interacting with its receptors. Adenosine and consequently adenosine deaminase can have pro or anti-inflammatory effects on tissues depending on how much time has passed from the start of the injury. In addition, an increase in adenosine deaminase activity has been reported for various diseases and the significant effect of deaminase inhibition on the clinical course of different diseases has been reported. However, the use of inhibitors is limited to only a few medical indications. Data on the increase of adenosine deaminase activity in different diseases and the impact of its inhibition in various cases have been collected and are discussed in this review. Overall, the evidence shows that many studies have been done to introduce inhibitors, however, in vivo studies have been much less than in vitro, and often have not been expanded for clinical use.

Role of Copper in the Onset of Alzheimer's Disease Compared to Other Metals

Alzheimer's disease (AD) is a neurodegenerative disorder that is characterized by amyloid plaques in patients' brain tissue. The plaques are mainly made of β-amyloid peptides and trace elements including Zn2+, Cu2+, and Fe2+. Some studies have shown that AD can be considered a type of metal dyshomeostasis. Among metal ions involved in plaques, numerous studies have focused on copper ions, which seem to be one of the main cationic elements in plaque formation. The involvement of copper in AD is controversial, as some studies show a copper deficiency in AD, and consequently a need to enhance copper levels, while other data point to copper overload and therefore a need to reduce copper levels. In this paper, the role of copper ions in AD and some contradictory reports are reviewed and discussed.

Development of quantitative structure activity relationship (QSAR) model for disinfection byproduct (DBP) research: A review of methods and resources

Quantitative structure-activity relationship (QSAR) models are tools for linking chemical activities with molecular structures and compositions. Due to the concern about the proliferating number of disinfection byproducts (DBPs) in water and the associated financial and technical burden, researchers have recently begun to develop QSAR models to investigate the toxicity, formation, property, and removal of DBPs. However, there are no standard procedures or best practices regarding how to develop QSAR models, which potentially limit their wide acceptance. In order to facilitate more frequent use of QSAR models in future DBP research, this article reviews the processes required for QSAR model development, summarizes recent trends in QSAR-DBP studies, and shares some important resources for QSAR development (e.g., free databases and QSAR programs). The paper follows the four steps of QSAR model development, i.e., data collection, descriptor filtration, algorithm selection, and model validation; and finishes by highlighting several research needs. Because QSAR models may have an important role in progressing our understanding of DBP issues, it is hoped that this paper will encourage their future use for this application.

High-sensitivity capillary electrophoresis method for monitoring purine nucleoside phosphorylase and adenosine deaminase reactions by a reversed electrode polarity switching mode

A simple, efficient, and highly sensitive in-line CE method was developed for the characterization and for inhibition studies of the nucleoside-metabolizing enzymes purine nucleoside phosphorylase (PNP) and adenosine deaminase (ADA) present in membrane preparations of human 1539 melanoma cells. After filling the running buffer (50 mM borate buffer, 100 mM SDS, pH 9.10) into a fused-silica capillary (50 cm effective length × 75 μm), a large sample volume was loaded by hydrodynamic injection (5 psi, 36 s), followed by the removal of the large plug of sample matrix from the capillary using polarity switching (-20 kV). The current was monitored and the polarity was reversed when 95% of the current had been recovered. The separation of the neutral analytes (nucleosides and nucleobases) was performed by applying a voltage of 15 kV. An about 10-fold improvement of sensitivity for the five investigated analytes (adenosine, inosine, adenine, hypoxanthine, xanthine) was achieved by large-volume stacking with polarity switching when compared with CE without stacking. For inosine and adenine detection limits as low as 60 nM were achieved. To the best of our knowledge, this represents the highest sensitivity for nucleoside and nucleobase analysis using CE with UV detection reported so far. The Michaelis-Menten constants (K(m)) for PNP and ADA and the inhibition constants (K(i)) for standard inhibitors determined with the new method were consistent with literature data.

Functional variability of the adenosine A3 receptor (ADORA3) gene polymorphism in aspirin-induced urticaria

BACKGROUND

To improve understanding of aspirin hypersensitivity, this study focused on adenosine as a noncyclooxygenase target molecule of aspirin. Adenosine may affect the release of histamine from cutaneous mast cells through a mechanism mediated by the adenosine A3 receptor.

OBJECTIVES

To investigate the genetic contribution of adenosine A3 receptor gene (ADORA3) polymorphisms in the pathogenesis of aspirin-induced urticaria (AIU) in a case-control association study in a Korean population.

METHODS

A case-control association study was performed in 385 patients with AIU and 213 normal controls from a Korean population. The functional variability of genetic polymorphisms in the ADORA3 gene was analysed in in vitro studies that included a luciferase reporter assay and an electrophoretic mobility shift assay (EMSA), and ex vivo studies that included real-time polymerase chain reaction for mRNA expression in peripheral blood mononuclear cells and a histamine release assay.

RESULTS

A significant association of ADORA3 promoter polymorphism at -1050G/T was found with the phenotype of AIU. Patients with AIU showed higher frequency of the haplotype, ht1 (T(-1050) C(-564) ), compared with normal healthy controls. Moreover, ht1 (TC) was found to be a high-transcript haplotype by the luciferase activity assay, and a -564C allele-specific DNA binding protein was found by EMSA. Increased basophil histamine release was noted in subjects who had the high-transcript haplotype, ht1 (TC).

CONCLUSION

These results suggest that the high-transcript haplotype, ht1 (TC), of the ADORA3 gene may contribute to the development of cutaneous hyper-reactivity to aspirin, leading to the clinical presentation of AIU.

Expression, purification and kinetic characterization of His-tagged glyceraldehyde-3-phosphate dehydrogenase from Trypanosoma cruzi

Trypanosomes are flagellated protozoa responsible for serious parasitic diseases that have been classified by the World Health Organization as tropical sicknesses of major importance. One important drug target receiving considerable attention is the enzyme glyceraldehyde-3-phosphate dehydrogenase from the protozoan parasite Trypanosoma cruzi, the causative agent of Chagas disease (T. cruzi Glyceraldehyde-3-phosphate dehydrogenase (TcGAPDH); EC 1.2.1.12). TcGAPDH is a key enzyme in the glycolytic pathway of T. cruzi and catalyzes the oxidative phosphorylation of D-glyceraldehyde-3-phosphate (G3P) to 1,3-bisphosphoglycerate (1,3-BPG) coupled to the reduction of oxidized nicotinamide adenine dinucleotide, (NAD(+)) to NADH, the reduced form. Herein, we describe the cloning of the T. cruzi gene for TcGAPDH into the pET-28a(+) vector, its expression as a tagged protein in Escherichia coli, purification and kinetic characterization. The His(6)-tagged TcGAPDH was purified by affinity chromatography. Enzyme activity assays for the recombinant His(6)-TcGAPDH were carried out spectrophotometrically to determine the kinetic parameters. The apparent Michaelis-Menten constant (K(M)(app)) determined for D-glyceraldehyde-3-phosphate and NAD(+) were 352±21 and 272±25 μM, respectively, which were consistent with the values for the untagged enzyme reported in the literature. We have demonstrated by the use of Isothermal Titration Calorimetry (ITC) that this vector modification resulted in activity preserved for a higher period. We also report here the use of response surface methodology (RSM) to determine the region of optimal conditions for enzyme activity. A quadratic model was developed by RSM to describe the enzyme activity in terms of pH and temperature as independent variables. According to the RMS contour plots and variance analysis, the maximum enzyme activity was at 29.1°C and pH 8.6. Above 37°C, the enzyme activity starts to fall, which may be related to previous reports that the quaternary structure begins a process of disassembly.

Identification and localization of the bilitranslocase homologue in white grape berries (Vitis vinifera L.) during ripening

A homologue of the mammalian bilirubin transporter bilitranslocase (BTL) (TCDB 2.A.65.1.1), able to perform an apparent secondary active transport of flavonoids, has previously been found in carnation petals and red grape berries. In the present work, a BTL homologue was also shown in white berries from Vitis vinifera L. cv. Tocai/Friulano, using anti-sequence antibodies specific for rat liver BTL. This transporter, similarly to what found in red grape, was localized in the first layers of the epidermal tissue and in the vascular bundle cells of the mesocarp. In addition, a strong immunochemical reaction was detected in the placental tissue and particularly in peripheral integuments of the seed. The protein was expressed during the last maturation stages in both skin and pulp tissues and exhibited an apparent molecular mass of c. 31 kDa. Furthermore, the transport activity of such a carrier, measured as bromosulphophthalein (BSP) uptake, was detected in berry pulp microsomes, where it was inhibited by specific anti-BTL antibodies. The BTL homologue activity exhibited higher values, for both K(m) and V(max), than those found in the red cultivar. Moreover, two non-pigmented flavonoids, such as quercetin (a flavonol) and eriodictyol (a flavanone), inhibited the uptake of BSP in an uncompetitive manner. Such results strengthen the hypothesis that this BTL homologue acts as a carrier involved also in the membrane transport of colourless flavonoids and demonstrate the presence of such a carrier in different organs and tissues.

A survey of the year 2007 literature on applications of isothermal titration calorimetry

Elucidation of the energetic principles of binding affinity and specificity is a central task in many branches of current sciences: biology, medicine, pharmacology, chemistry, material sciences, etc. In biomedical research, integral approaches combining structural information with in-solution biophysical data have proved to be a powerful way toward understanding the physical basis of vital cellular phenomena. Isothermal titration calorimetry (ITC) is a valuable experimental tool facilitating quantification of the thermodynamic parameters that characterize recognition processes involving biomacromolecules. The method provides access to all relevant thermodynamic information by performing a few experiments. In particular, ITC experiments allow to by-pass tedious and (rarely precise) procedures aimed at determining the changes in enthalpy and entropy upon binding by van't Hoff analysis. Notwithstanding limitations, ITC has now the reputation of being the "gold standard" and ITC data are widely used to validate theoretical predictions of thermodynamic parameters, as well as to benchmark the results of novel binding assays. In this paper, we discuss several publications from 2007 reporting ITC results. The focus is on applications in biologically oriented fields. We do not intend a comprehensive coverage of all newly accumulated information. Rather, we emphasize work which has captured our attention with originality and far-reaching analysis, or else has provided ideas for expanding the potential of the method.

Effect of cardiovascular drugs on adenosine deaminase activity

OBJECTIVE

Adenosine deaminase catalyzes the conversion of adenosine and deoxyadenosine to inosine and deoxyinosine, respectively. Because raising adenosine concentration can affect several physiological processes we studied the effect of a selection of cardiological drugs on adenosine deaminase activity in red blood cells and rabbit plasma after 21 days administration.

METHODS AND RESULTS

We determined the activity of adenosine deaminase isoenzymes (ADA(1) and ADA(2)). Simvastatin, aspirin, metoprolol, and isosorbide mononitrate significantly decreased plasma total adenosine activity (by 50%, 34%, 29%, and 19%, respectively; P < .05 to P < .001) mainly by decreasing the activity of ADA(2).

CONCLUSIONS

As a consequence of decreased ADA(2) activity , the half-life of adenosine will be lengthened. This may, at least in part, explain some of the beneficial effects of analyzed drugs. Our results might be clinically relevant in patients with coronary artery disease, acute coronary syndromes, heart failure, or stroke where the investigated drugs are commonly used. However, our results should be confirmed in large studies in humans.