Purification and characterization of intestinal adenosine deaminase from mice

Quercetin mitigates rheumatoid arthritis by inhibiting adenosine deaminase in rats

Rheumatoid arthritis (RA) is a chronic inflammatory joint disease characterized by synovial proliferation and bone destruction. Adenosine deaminase (ADA) is a key inflammatory enzyme that increases joint stiffness and pain in RA. In this study, we evaluated the in-silico, and in vivo inhibitory effect of quercetin isolated from Egyptian Fenugreek on ADA enzyme activity. We also determined the combinatorial effect of quercetin on methotrexate mediated anti-inflammatory efficacy and toxicity. In-silico molecular docking was conducted and confirmed in an in vivo RA rat model. The results showed that the inhibition constant of quercetin on joint ADA by docking and in-vitro was 61.9 and 55.5 mM, respectively. Therefore, quercetin exhibits anti-inflammatory effect in a rat RA model as evidenced by reducing the specific activity of ADA in joint tissues, lower jaw volume, enhance body weight, downregulate ADA gene expression, reduce levels of RA cytokines interleukin-1^β, interleukin-6, tumor necrosis factor-α, also, rheumatoid factor, C-reactive protein, and anti-cyclic citrullinated peptide RA biomarker levels. These findings demonstrate that the purified quercetin has a promising anti-inflammatory effect against RA disease through its inhibitory effects on the ADA enzyme. Furthermore, isolated quercetin improved the anti-inflammatory efficacy of methotrexate, reduced its toxic effects by increasing antioxidant enzymes and reducing oxidative stress.

Biochemical characterization of adenosine deaminase (CD26; EC 3.5.4.4) activity in human lymphocyte-rich peripheral blood mononuclear cells

The conversion of adenosine to inosine is catalyzed by adenosine deaminase (ADA) (EC 3.5.4.4), which has two isoforms in humans (ADA1 and ADA2) and belongs to the zinc-dependent hydrolase family. ADA modulates lymphocyte function and differentiation, and regulates inflammatory and immune responses. This study investigated ADA activity in lymphocyte-rich peripheral blood mononuclear cells (PBMCs) in the absence of disease. The viability of lymphocyte-rich PBMCs isolated from humans and kept in 0.9% saline solution at 4-8°C was analyzed over 20 h. The incubation time and biochemical properties of the enzyme, such as its Michaelis-Menten constant (Km) and maximum velocity (Vmax), were characterized through the liberation of ammonia from the adenosine substrate. Additionally, the presence of ADA protein on the lymphocyte surface was determined by flow cytometry using an anti-CD26 monoclonal human antibody, and the PBMCs showed long-term viability after 20 h. The ADA enzymatic activity was linear from 15 to 120 min of incubation, from 2.5 to 12.5 µg of protein, and pH 6.0 to 7.4. The Km and Vmax values were 0.103±0.051 mM and 0.025±0.001 nmol NH3·mg-1·s-1, respectively. Zinc and erythro-9-(2-hydroxy-3-nonyl) adenine (EHNA) inhibited enzymatic activity, and substrate preference was given to adenosine over 2'-deoxyadenosine and guanosine. The present study provides the biochemical characterization of ADA in human lymphocyte-rich PBMCs, and indicates the appropriate conditions for enzyme activity quantification.

Adenosine Receptors As Drug Targets for Treatment of Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a clinical condition characterized by pulmonary arterial remodeling and vasoconstriction, which promote chronic vessel obstruction and elevation of pulmonary vascular resistance. Long-term right ventricular (RV) overload leads to RV dysfunction and failure, which are the main determinants of life expectancy in PAH subjects. Therapeutic options for PAH remain limited, despite the introduction of prostacyclin analogs, endothelin receptor antagonists, phosphodiesterase type 5 inhibitors, and soluble guanylyl cyclase stimulators within the last 15 years. Through addressing the pulmonary endothelial and smooth muscle cell dysfunctions associated with PAH, these interventions delay disease progression but do not offer a cure. Emerging approaches to improve treatment efficacy have focused on beneficial actions to both the pulmonary vasculature and myocardium, and several new targets have been investigated and validated in experimental PAH models. Herein, we review the effects of adenosine and adenosine receptors (A₁, A_2A, A_2B, and A₃) on the cardiovascular system, focusing on the A_2A receptor as a pharmacological target. This receptor induces pulmonary vascular and heart protection in experimental models, specifically models of PAH. Targeting the A_2A receptor could potentially serve as a novel and efficient approach for treating PAH and concomitant RV failure. A_2A receptor activation induces pulmonary endothelial nitric oxide synthesis, smooth muscle cell hyperpolarization, and vasodilation, with important antiproliferative activities through the inhibition of collagen deposition and vessel wall remodeling in the pulmonary arterioles. The pleiotropic potential of A_2A receptor activation is highlighted by its additional expression in the heart tissue, where it participates in the regulation of intracellular calcium handling and maintenance of heart chamber structure and function. In this way, the activation of A_2A receptor could prevent the production of a hypertrophic and dysfunctional phenotype in animal models of cardiovascular diseases.

Impact of ectonucleotidases in autonomic nervous functions

Adenine and uracil nucleotides play key functions in the autonomic nervous system (ANS). For instance, ATP acts as a neurotransmitter, co-transmitter and neuromodulator in the ANS. The purinergic system encompasses (1) receptors that respond to extracellular purines, which are designated as P1 and P2 purinoceptors, (2) purine release and uptake, and (3) a cascade of enzymes that regulate the concentration of purines near the cell surface. Ectonucleotidases and adenosine deaminase (ADA) are enzymes responsible for the hydrolysis of ATP (and other nucleotides such as ADP, UTP, UDP, AMP) and adenosine, respectively. Accordingly, these enzymes are expected to play an important role in the control of neuro-effector transmission in tissues innervated by both the sympathetic and parasympathetic divisions of the ANS. Indeed, ectonucleotidases have the ability to either terminate P2 receptor responses initiated by nucleoside triphosphates (ATP and UTP), and/or to favor the activation of ADP (e.g. P2Y1,12,13) and UDP (e.g. P2Y6) and/or adenosine (P1) specific receptors. In addition, ectonucleotidases can also importantly protect some P2 receptors from desensitization (e.g. P2X1, P2Y1). In this review, we present the (putative) roles of ectonucleotidases and ADA in the ANS with a focus on their regulatory activity at neuro-effector junctions in the following tissues: heart, vas deferens, urinary bladder, salivary glands, blood vessels and the intestine. We also present their implication in nociceptive transmission.

Adenine aminohydrolase from Leishmania donovani: unique enzyme in parasite purine metabolism

Adenine aminohydrolase (AAH) is an enzyme that is not present in mammalian cells and is found exclusively in Leishmania among the protozoan parasites that infect humans. AAH plays a paramount role in purine metabolism in this genus by steering 6-aminopurines into 6-oxypurines. Leishmania donovani AAH is 38 and 23% identical to Saccharomyces cerevisiae AAH and human adenosine deaminase enzymes, respectively, catalyzes adenine deamination to hypoxanthine with an apparent K(m) of 15.4 μM, and does not recognize adenosine as a substrate. Western blot analysis established that AAH is expressed in both life cycle stages of L. donovani, whereas subcellular fractionation and immunofluorescence studies confirmed that AAH is localized to the parasite cytosol. Deletion of the AAH locus in intact parasites established that AAH is not an essential gene and that Δaah cells are capable of salvaging the same range of purine nucleobases and nucleosides as wild type L. donovani. The Δaah null mutant was able to infect murine macrophages in vitro and in mice, although the parasite loads in both model systems were modestly reduced compared with wild type infections. The Δaah lesion was also introduced into a conditionally lethal Δhgprt/Δxprt mutant in which viability was dependent on pharmacologic ablation of AAH by 2'-deoxycoformycin. The Δaah/Δhgprt/Δxprt triple knock-out no longer required 2'-deoxycoformycin for growth and was avirulent in mice with no persistence after a 4-week infection. These genetic studies underscore the paramount importance of AAH to purine salvage by L. donovani.

Kinetic characterization and gene expression of adenosine deaminase in intact trophozoites of Trichomonas vaginalis

Trichomonas vaginalis is a parasite that resides in the human urogenital tract and causes trichomonosis, the most prevalent nonviral sexually transmitted disease. Nucleoside triphosphate diphosphohydrolase (NTPDase), which hydrolyzes extracellular di- and triphosphate nucleotides, and ecto-5'-nucleotidase, which hydrolyzes AMP, have been characterized in T. vaginalis. The aim of this study was to characterize the adenosine deaminase (ADA) activity in intact trophozoites of T. vaginalis. A strong inhibition in adenosine deamination was observed in the presence of calcium and magnesium, which was prevented by EDTA. The apparent K(M) value for adenosine was 1.13 ± 0.07mM. The calculated V(max) was 2.61 ± 0.054 nmol NH(3) min(-1) mg(-1) protein. Adenosine deamination was inhibited in the presence of erythro-9-(2-hydroxy-3-nonyl)adenine. Semi-quantitative reverse transcriptase-PCR experiments were performed and both ADA-related genes ada(125) and ada(231) mRNA were expressed, although ada(231) in higher quantity when compared with the ada(125) : α-tubulin ratio. Furthermore, a phylogenetic analysis showed that the T. vaginalis sequences formed a clade with Entamoeba histolytica and Dictyostelium discoideum sequences, and it strongly suggests homologous functions in the T. vaginalis genome. The presence of ADA activity in T. vaginalis may be important to modulate the adenosine/inosine levels during infection and, consequently, to maintain the anti-inflammatory properties through different nucleoside-signalling mechanisms.

Rapid determination of adenosine deaminase kinetics using fast-scan cyclic voltammetry

Adenosine deaminase is an enzyme involved in purine metabolism and its inhibitors are used as anticancer and antiviral drugs. In this study, we show that fast-scan cyclic voltammetry at carbon-fiber microelectrodes can be used to study the kinetics of adenosine deaminase by electrochemically monitoring decreases in adenosine concentration. Buffer and salt concentrations were shown to affect the enzyme kinetics and the inhibition by erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA) and deoxycoformycin (DCF). In a Tris buffer containing salts that mimic cerebrospinal fluid, EHNA and DCF showed non-competitive inhibition with a K(i) of 1.7 +/- 0.6 nM and 1.2 +/- 0.2 nM, respectively. However, removing the divalent cations from the Tris buffer caused the inhibition to be competitive and reduced the K(i) for DCF by two orders of magnitude. In phosphate-buffered saline, the K(i) was 1.0 +/- 0.2 nM for EHNA and 3.6 +/- 0.3 pM for DCF, similar to literature values. Adenosine deaminase was also competitively inhibited by AgNO(3), showing it is susceptible to silver toxicity. Caffeine was found to increase adenosine deaminase activity. This is a fast, easy method for screening drug effects on enzyme kinetics and could be applied to other enzymatic reactions where there is a significant difference in the electroactivity of the reactant and product.

Kinetic characterization of adenosine deaminase activity in zebrafish (Danio rerio) brain

Adenosine deaminase (ADA; EC 3.5.4.4) activity is responsible for cleaving adenosine to inosine. In this study we described the biochemical properties of adenosine deamination in soluble and membrane fractions of zebrafish (Danio rerio) brain. The optimum pH for ADA activity was in the range of 6.0-7.0 in soluble fraction and reached 5.0 in brain membranes. A decrease of 31.3% on adenosine deamination in membranes was observed in the presence of 5 mM Zn(2+), which was prevented by 5 mM EDTA. The apparent K(m) values for adenosine deamination were 0.22+/-0.03 and 0.19+/-0.04 mM for soluble and membrane fractions, respectively. The apparent V(max) value for soluble ADA activity was 12.3+/-0.73 nmol NH(3) min(-1) mg(-1) of protein whereas V(max) value in brain membranes was 17.5+/-0.51 nmol NH(3) min(-1) mg(-1) of protein. Adenosine and 2'-deoxyadenosine were deaminated in higher rates when compared to guanine nucleosides in both fractions. Furthermore, a significant inhibition on adenosine deamination in both soluble and membrane fractions was observed in the presence of 0.1 mM of erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA). The presence of ADA activity in zebrafish brain may be important to regulate the adenosine/inosine levels in the CNS of this species.

AMINOHYDROLASES ACTING ON ADENINE, ADENOSINE AND THEIR DERIVATIVES

BACKGROUND

Adenine and adenosine-acting aminohydrolases are important groups of enzymes responsible for the metabolic salvage of purine compounds. Several subclasses of these enzymes have been described and given current knowledge of the full genome sequences of many organisms, it is possible to identify genes encoding these enzymes and group them according to their primary structure.

METHODS AND RESULTS

This article is a short overview of the enzymes classified as adenine and adenosine deaminase. It summarises knowledge of their occurrence, genetic basis and their catalytic and structural properties.

CONCLUSIONS

These enzymes are constitutive components of purine metabolism and their impairment may cause serious medical disorders. In humans, adenosine deaminase deficiency is linked to severe combined immunodeficiency and as such the enzyme has been approved for the first gene therapy trial. The role of these enzymes in plants is unclear, since the activity was has not been detected in extracts and putative genes have not been yet cloned and analyzed. A literature search and amino acid identity comparison show that Ascomycetes contain only adenine deaminase, but not adenosine deaminase, despite the fact that corresponding genes are annotated in databases as the adenosine cleaving enzymes because they share the same conserved domain.

The purine metabolism of human erythrocytes

This review summarizes currently available information about a crucial part of erythrocyte metabolism, that is, purine nucleotide conversions and their relationships with other conversion pathways. We describe the cellular resynthesis, interconversion, and degradation of purine compounds, and also the regulatory mechanisms in the conversion pathways. We also mention purine metabolism disorders and their clinical consequences. The literature is fragmentary because studies have concentrated only on selected aspects of purine metabolism; hence the need for a synthetic approach.

Adenosine deaminase from camel tick Hyalomma dromedarii: purification and characterization

Adenosine deaminase is involved in purine metabolism and is a key enzyme for the control of the cellular levels of adenosine. Adenosine deaminase activity showed significant changes during embryogenesis of the camel tick Hyalomma dromedarii. From the elution profile of chromatography on DEAE-sepharose, three forms of enzyme (ADAI, ADAII and ADAIII) were separated. ADAII was purified to homogeneity after chromatography on Sephacryl S-200. The molecular mass of adenosine deaminase ADAII was 42 kDa for the native enzyme and represented a monomer of 42 kDa by SDS-PAGE. The enzyme had a pH optimum at 7.5 and temperature optimum at 40 degrees C with heat stability up to 40 degrees C. ADAII had a K (m) of 0.5 mM adenosine with higher affinity toward deoxyadenosine and adenosine than other purines. Ni(2+), Ba(2+), Zn(2+), Li(2+), Hg(2+) and Mg(2+) partially inhibited the ADAII. Mg(2+) was the strongest inhibitor by 91% of the enzyme's activity.

Binding Properties of Adenosine Deaminase Interacted with Theophylline

Thermodynamic studies were carried out to evaluate the binding of theophylline on adenosine deaminase (ADA) in 50 mM sodium phosphate buffer pH 7.5, at 300 K, using isothermal titration calorimetry (ITC). A simple method for determination of binding isotherm in the drug--ADA interaction was applied using ITC data. ADA has two binding sites for theophylline, which show positive cooperativity in its sites. The intrinsic association equilibrium constants are 6 and 52 mM(-1) in the first and second binding sites, respectively. Hence, occupation of the first site has produced an appreciable enhancement by 8.7 of the binding affinity of the second site. The molar enthalpies of binding are -12.2 and -14.9 kJ/mol in the first and second binding sites, respectively.

Purification and characterization of adenosine deaminase from camel skeletal muscle

Adenosine deaminase was purified (780-fold) from skeletal muscle of camel (Camelus Dormedarius) to homogeneity level by using DEAE Sephadex chromatography, ammonium sulfate precipitation, gel filtration and ion exchange chromatography. The enzyme appeared to be monomeric with subunit molecular weight of 43kDa and isoelectric point of 4.85. The enzyme showed specificity for adenosine and exhibited Michaelis-Menten Kinetics with kappa(cat) of 1112.41 min(-1) and K(m) of 14.7 microM at pH 7.5. The pH and temperature optima for enzyme activity were 7-7.5 and 25 degrees C, respectively. Free energy (DeltaG*), enthalpy (DeltaH*) and entropy (DeltaS*) of activation for denaturation of adenosine deaminase at 50 degrees C were 88.94, 99.65 kJmol(-1) and 33.16 Jmol(-1), respectively. The purified enzyme had half-lives of 636 and 61 min at 25 and 50 degrees C, respectively. The activation energy for catalysis of camel skeletal muscle adenosine deaminase was 9.13 kJmol(-1). Free energy (DeltaG#), enthalpy (DeltaH#) and entropy (DeltaS#) of activation for hydrolysis of adenosine deaminase at 25 degrees C were 50.35, 6.65 kJmol(-1) and -146.62 Jmol(-1), respectively. Purine riboside inhibited the enzyme competitively with K(i) of 16 microM.