[Criteria for evaluation of functional importance of endogenous analogues of pharmacological regulators]

Some criteria for the evaluation of the functional importance of endogenous analogues of pharmacological drugs are proposed. For endogenous regulators, these include opposite changes in their content in opposite (patho)physiological states, accompanied by corresponding changes in the functional activity of enzymes sensitive to changes in their level; regulation of target enzymes by physiological concentrations of such endogenous compounds. The applicability of these criteria has been demonstrated using tribulin, the endogenous family of inhibitors of monoamine oxidases.

Ubiquitin-protein ligase parkin and its role in the development of Parkinson’s disease

Parkin is a protein encoded by the corresponding parkin gene. It exhibits ubiquitin-protein ligase activity. In this review, we analyze domain structure, substrate specificity, subcellular localization of parkin, and regulation of its activity. Then we discuss data on the effects of various mutations in the parkin gene on structure and functions of this protein and results obtained with parkin knock-out animals. Better understanding of parkin biochemistry, its compartmentalization, functions, and altered functions would help the development of new approaches for the treatment of both inherited and sporadic cases of Parkinson's disease.

[Interaction of pyruvate kinase with isatin and deprenyl]

The glycolytic enzyme, pyruvate kinase, exhibits moderate affinity [3H]isatin binding (KD approximately 10 microM), which is inhibited by ATP (IC50 25 microM) and deprenyl (IC50 5 microM). Interaction of pyruvate kinase with isatin and its inhibition by ATP and deprenyl has also been confirmed using an independent biosensor technique and immobilized isatin analogue, aminoisatin. This effect has some specificity because the enzyme, creatine phosphokinase, does not exhibit specific isatin-binding. It is suggested that interaction of pyruvate kinase with isatin may reflect some non-glycolytic functions of this enzyme.

[The role of ceruloplasmin in neoplastic processes]

Ceruloplasmin (CP) is a copper containing oxidase of human plasma alpha 2-globulin fraction. The review summarizes literature data on biological role of CP under normal conditions and during development of malignant tumor. This protein may be involved both into antitumor deference and also into metastasizing process. Although CP has already been employed into intensive therapy of oncologic patients all mechanisms underlying its biological activity remain to be clarified.

[The effect of long-term administration of isatin and himantan to mice on sensitivity of brain monoamine oxidase B to inhibition by deprenyl in vivo and in vitro]

Chronic administration of a low dose of reversible monoamine oxidase (MAO) B inhibitors isatin or himantane (20 mg/kg) to mice during 21 day did not influence the enzyme activity assayed in isolated brain mitochondria. However in vivo sensitivity of brain MAO B to irreversible mechanism-based inhibitor deprenyl injected to animals right after the last administration of the reversible inhibitor sharply decreased. This suggests accumulation of these compounds (or their metabolites?) in the brain accompanied by increased protection of active site of MAO B against specific irreversible inhibitor. deprenyl. In vitro inhibition of MAO B activity in mitochondria isolated from brain of mice treated with isatin or himantane was somewhat higher than in control mitochondria. The latter suggests that long-term treatment of animals with reversible easily dissociating inhibitors may influence regulatory properties of MAO B.

Nonselective inhibition of monoamine oxidases A and B by activators of soluble guanylate cyclase

Several activators of soluble guanylate cyclase were investigated as potential inhibitors of rat liver mitochondrial monoamine oxidases (MAO) A and B. They all fitted into the previously designed "molds" of substrate-inhibitor binding sites of these enzymes. However, only two of them, NO donors (7-nitro-benzotetrazine-1,3-dioxide (7-NBTDO) and benzodifuroxan), caused nonselective inhibition of MAO A and MAO B with IC(50) values of 1.3-1.6 and 6.8-6.3 microM, respectively. The inhibitory effect on both MAO A and MAO B was reduced by mitochondria wash suggesting reversible mode of the enzyme inhibition. There was no correlation between potency of MAO inhibition and activation of human platelet soluble guanylate cyclase. The NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (carboxy-PTIO) had no effect on the manifestation of MAO inhibition by benzodifuroxan and 7-NBTDO; however, at 50 microM concentration carboxy-PTIO caused potent inhibition of MAO A with minor effect on MAO B activity. The data suggest that nonselective inhibition of MAO A and MAO B by benzodifuroxan and 7-NBTDO can be attributed to the properties of the chemical structures of these compounds. The results of the present study demonstrate a real possibility for the development of a new generation of effective reversible nonselective MAO inhibitors exhibiting equal inhibitory activity with respect to both MAO A and MAO B.

Novel Pyridazino[4,3-b]indoles with Dual Inhibitory Activity against Mycobacterium tuberculosis and Monoamine Oxidase

Tuberculosis is one of the most common infectious diseases known to man. About 37% of the world's population (about 1.86 billion people) are infected with Mycobacterium tuberculosis. According to the World Health Organization, every year approximately 8 million people develop active tuberculosis and almost 2 million of those die from the disease. The incidence of multidrug-resistant tuberculosis (MDR-TB) is increasing. The present drug regimen for treating tuberculosis has been in existence for 30 years. New drugs that will shorten total treatment duration, improve the treatment of MDR-TB, and address latent tuberculosis are the most urgent need of tuberculosis control programs. A new series of synthetic 3-amino-4-arylpyridazino[4,3-b]indoles (pyridazinoindoles) were identified as inhibitors of Mycobacterium tuberculosis. The design, synthesis, and antimycobacterial activity of these compounds are described. While the most active compounds are still not comparable to the front-line drugs rifampicin and isoniazid, they do show promise. Most of the pyridazinoindoles with appreciable antituberculosis activity also inhibit monoamine oxidase, suggestive of a novel inhibitory effect on mycobacterial redox reactions.

Computer Modelling and Visualization of Active Site of Monoamine Oxidases

In spite of significant progress in MAO research culminating in the crystallization of the MAO B, many structure-functional aspects of these enzymes still require better characterization. Computer modelling of the substrate/inhibitory binding region of the active site includes consensus overlay of several series of fully reversible and/or tightly bound inhibitors onto a rigid referent inhibitor(s). The shape of resultant mould obviously reflects spatial characteristic features of the substrate/inhibitor binding region. The comparison of the active site mould of MAO B with its crystal structure revealed correctness of this approach. The resultant moulds may be effectively used for virtual screening of molecular databases for new lead-structures. Using this approach we have found several selective MAO A inhibitors in databases and these compounds have never been tested for MAO inhibitory activity.

Tribulin and Endogenous MAO-Inhibitory Regulation In Vivo

Tribulin is the name given to a family of endogenous nonpeptide substances which inhibit monoamine oxidase (MAO) and benzodiazepine binding. It is widely distributed in mammalian tissues and body fluids, and exhibit some species and tissue variations. Several components selectively inhibiting MAO A, MAO B, central and peripheral benzodiazepine binding (tribulins A, B, BZc and BZp, respectively) have been recognised. Tribulin A represents some tissue-specific metabolites of trace amines, whereas isatin is the major component of tribulin B. Tribulin content increases in brain under conditions of stress and anxiety and is reduced under sedation. Changes in tribulin content in the brain are accompanied by corresponding changes in the content of monoamines and their acidic metabolites, and also by altered susceptibility of MAO to specific mechanism-based inhibitors. This suggests that tribulin is involved in MAO inhibitory regulation in vivo.

[Glycerol-3-phosphate dehydrogenase--cytosolic isatin-binding protein]

Isatin is an endogenous indole widely distributed in mammalian tissues and body fluids. The presence of isatin-binding proteins has been recognised in particulate and soluble fractions of various organs and tissues. However, identified targets of isatin action (monoamine oxidase, natriuretic peptide receptor type A and soluble NO-stimulated guanylate cyclase) cannot account for all biological activity of this compound. Highly purified glycerol-3-phosphate dehydrogenase (GPDH) from rabbit muscle effectively interacts with the isatin analogue immobilised on the cuvette of IAsys optical biosensor. This effect was specific because the other NAD-dependent cytosolic enzyme purified from rabbit muscle, lactate dehydrogenase failed to interact with the immobilised isatin analogue. Replacement of the cuvette medium for washing buffer did not cause total dissociation of GPDH-isatin complexes. This suggests involvement of several types of enzyme-isatin interaction including tight binding. Low (10 microM) and high (100 microM) concentrations of isatin caused different effects on GPDH activity: the former significantly increased apparent Km for NAD, whereas the latter decreased apparent Vmax and increased Km.

[Effect of a new antiparkinsonian drug himantane on monoamine oxidase activity]

N-2(adamantyl)hexamethyleneimine hydrochloride (hemantane) is a new potential antiparkinsonian drug targeted at several neurochemical systems. The drug exhibits the properties of a low-affinity noncompetitive blocker of the ion channels of glutamate NMDA receptors. Hemantane increases the content of dopamine in the striatum, while decreasing the level of dopamine metabolite dioxyphenylacetic acid (DOPAC). Investigation of the drug interaction with monoamine oxidases (MAOs) of the A and B types in vitro showed that hemantane acts as a weak competitive inhibitor of MAO-B (Ki = 470 +/- 70 microM) and partly protected MAO-B from irreversible inhibition by selegiline (deprenyl), while virtually not influencing the activity of MAO-A. Administered to C57BL6 mice (20-100 mg/kg), hemantane did not influence the activity of MAO-B measured in isolated cerebral mitochondria. At the same time, hemantane administered in combination with deprenyl significantly reduced activity of the latter drug and caused pronounced irreversible inhibition of mitochondrial MAO-B (comparable with the effect of deprenyl introduced alone). Therefore, inhibition of MAO-B may contribute to the spectrum of neurochemical activity of hemantane.

Computer visualisation of the active site of monoamine oxidase-A by means of selective inhibitors

Computer visualisation of the active site of monoamine oxidase (MAO) is based on an assumption that the specific and reversible interaction of a ligand (substrate or inhibitor) with the substrate-binding region of the active site requires shape complementarity. The size of the ligand must allow its accommodation at the substrate-binding region. Analysis of the MAO-inhibitory activity of rigid analogues of isatin and pirlindole revealed a dependence between three-dimensional linear sizes of these molecules and the efficacy of inhibition of both MAO-A and MAO-B. However, flexible molecules did not exhibit any dependence between linear sizes and MAO-B inhibitory potency, possibly because they folded into compact structures could fit into the substrate-binding pocket of MAO-B. 'Moulding' of the substrate/inhibitor binding region by superposition of effective MAO-A inhibitors from various groups of chemicals allowed the shape of substrate/inhibitor binding region to be visualised. 'Removal of contents' from this mould yielded a cavity, which corresponded to the shape of substrate/inhibitor binding region. Such cavity can be used to evaluate the most probable positions known inhibitors take in binding to it. The docking procedure can also be used for searching molecular databases for new inhibitors. Pilot experiments revealed that relatively rigid compounds, which did not fit to this cavity, were poor inhibitors of MAO-A.

[Effect of oxidized indoles on monoamine oxidase activity in the rat brain mitochondria]

There is increasing evidence, that oxidized indoles, isatin, 5-hydroxyoxindole, 2-oxindole, play important regulatory functions in the brain. Isatin and 5-hydroxyoxindole share some common regulatory properties in cell cultures (Cane et al., 2000, BBRC, 276, 379), however, their effects on brain mitochondrial monoamine oxidases, a potential target for their action, have not been compared yet. Isatin acted as a rather selective monoamine oxidase B inhibitor, whereas 5-hydroxyoxindole was more selective monoamine oxidase A inhibitor, but it was less potent than that of 5-hydroxyisatin, a synthetic analogue of isatin.

[Study of the tissue and subcellular distribution of isatin-binding proteins with optical biosensor]

An original method for the integral evaluation of tissue and subcellular distribution of isatin binding proteins has been developed. This method is based on continuous monitoring of changes of optical characteristics that accompany complex formation between a ligand (immobilized on dextran bed of IAsys biosensor cell) and its soluble receptor. Solubilisation of tissue preparations and subcellular fractions with detergent (1% Triton X-100) is the important preconditions for the applicability of this method. The immobilisation of 5-aminoisatin was achieved by peptide bond formation between amino group of this isatin analogue and carboxyl group of the dextran bed of the biosensor cell. Addition of Triton X-100 treated preparations of membrane and soluble fractions of rat brain, liver, heart, and kidneys to the biosensor cell resulted in appearance of the characteristic response, indicating complex formation with the immobilised isatin analogue. The magnitude and a shape of kinetic curve vary in these samples. Isatin binding proteins predominated in membrane fractions of brain, liver and heart preparations whereas in the kidneys the highest isatin-binding response was detected in the soluble fraction. The distribution of isatin binding sites in the particulate fraction reduced in the following order: brainstem > brain hemispheres = cerebellum > heart > kidneys > liver. In the soluble fraction there was different rank of isatin binding activity: kidneys > heart > brainstem = brain hemispheres > liver > cerebellum. Liver outer mitochondrial membranes are characterised by the higher isatin-binding than mitochondria. Treatment of mitochondria with clorgyline and deprenyl, specifically inhibiting MAO A and B, respectively, significantly reduced the magnitude of the biosensor response and changed the shape of the kinetic curve. These data are consistent with the notion that within mitochondria MAOs are the major targets of isatin.

[Modeling of monoamine oxidase B active site by computer moulding]

Using previously developed approach for active site modelling of enzymes with unknown spatial structure (Veselovsky et al., Biochemistry (Moscow), 65, 1072-1079) substrate/inhibitor binding site of monoamine oxidase B was designed by means of computer moulding. This mould corresponds to the shape and volume size of selective substrates and inhibitors of this enzyme. Active site moulds of monoamine oxidases A and B exhibit significant differences in these parameters. The correctness of the resultant model of monoamine oxiadse B active site was validated by using three compounds which were not employed in the training sets. Weak inhibitors were not accommodated in the mould whereas their "flexible" analogues exhibitng rather potent inhibition are readily accommodated in this mould. This suggests that our mould reflects some important spatial features of monoamine oxidase B active site. This mould can be employed for screening of new perspective inhibitior of monoamine oxidase B and pilot evaluation of their monoamine oxidase B inhibitory activity.

Induction of tolerance to lipopolysaccharide and mycobacterial components in Chinese hamster ovary/CD14 cells is not affected by overexpression of Toll-like receptors 2 or 4

Down-regulation of cell surface expression of Toll-like receptor (TLR) 4 following LPS stimulation has been suggested to underlie endotoxin tolerance. In this study, we examined whether overexpression of TLR2 or TLR4 would affect the ability of cells to become tolerant to LPS or the mycobacterial components, arabinose-capped lipoarabinomannan (LAM) and soluble tuberculosis factor (STF). To this end, Chinese hamster ovary/CD14 cells stably transfected with a NF-kappaB-dependent reporter construct, endothelial leukocyte adhesion molecule CD25 (the 3E10 clone), were engineered to overexpress either human TLR2 or TLR4. Transfected TLRs exhibited proper signaling functions, as evidenced by increased LPS responsiveness of 3E10/TLR4 cells and acquisition of sensitivity to TLR2-specific ligands upon transfection of TLR2 into TLR2-negative 3E10 cells. Pretreatment of cells with LPS, LAM, or STF did not modulate TLR2 or TLR4 cell surface expression. Following LPS exposure, 3E10, 3E10/TLR2, and 3E10/TLR4 cells exhibited comparable decreases in LPS-mediated NF-kappaB activation and mitogen-activated protein (MAP) kinase phosphorylation. Likewise, LPS pretreatment profoundly inhibited LPS-induced NF-kappaB translocation in Chinese hamster ovary cells that concomitantly overexpressed human TLR4 and myeloid differentiation protein-2 (MD-2), but failed to modulate TLR4 or MD-2 cell surface expression. Pretreatment of 3E10/TLR2 cells with LAM or STF decreased their NF-kappaB responses induced by subsequent stimulation with these substances or LPS. Conversely, prior exposure of 3E10/TLR2 cells to LPS led to hyporesponsiveness to LPS, LAM, and STF, indicating that LPS and mycobacterial products induce cross-tolerance. Thus, tolerance to LPS and mycobacterial components cannot be attributed solely to a decrease in TLR/MD-2 expression levels, suggesting inhibition of expression or function of other signaling intermediates.

The effect of ethanol consumption on the sensitivity of rat brain monoamine oxidases to the inhibition by pargyline in vivo and in vitro

The effect of ethanol consumption on the sensitivity of rat brain mitochondrial monoamine oxidases to the inhibition by pargyline in vivo and in vitro was investigated. Administration of pargyline (10 mg/kg, s.c.) produced significantly higher inhibition of MAO-A in alcoholised rats, whereas MAO-B inhibition did not differ from that observed in control animals. The concentration-response curve for the inhibition of brain mitochondrial MAO-A and MAO-B by pargyline in vitro did not reveal higher sensitivity of MAO from alcoholised rats to pargyline. This probably means that more pronounced inhibition by pargyline of brain MAO-A in alcoholised rats in vivo can be attributed to decreased content of compounds reversibly interacting with the its catalytic site. Taking into consideration some ethanol-induced decrease of brain tribulin content we suggest that the reduced level of endogenous inhibitors (tribulin components?) may have some importance in the development of alcoholism.

Selective inhibitors and computer modelling of the active site of monoamine oxidase

MAO inhibitors can be employed for computer modelling of the active site of MAO A and B. Competitive fully reversible MAO inhibitors with rigid structure and limited number of conformers are preferential compounds for these studies. Among various isatin analogues with nearllanar structure selective MAO B inhibitors fit to 3D box of 8.5x5.1x1.8 A, whereas 3D box of 14.2x5.6x1.8 A accommodates selective MAO A inhibitors. Validity of these data was tested using a series of pyrazinocarbazoles, analogues of short-acting antidepressant pirlindole. Rigid analogues exhibiting potent and selective inhibition of MAO A have 3D size limits of 13x7x4.4 A. Flexible analogues also demonstrated potent inhibition of MAO B and in contrast to rigid analogues their inhibitory activity did not show any dependence on 3D sizes. 3D-QSAR with CoMFA of isatin and pirlindole analogues of MAO A and B revealed differences in the models of MAO A and B.

Different sensitivity of mitochondrial and cytosolic monoamine oxidases to in vivo but not in vitro inhibition by specific irreversible inhibitors

The sensitivity of mitochondrial and cytosolic monoamine oxidase (MAO) activities to inhibition by specific irreversible inhibitors was investigated. There were no significant differences in the sensitivity of MAO A and MAO B activities of these fractions to selective inhibitors. However, in vivo administration of pargyline caused a much more potent inhibition of cytosolic MAO than the mitochondrial enzymes. This suggests that cytosolic MAO activity does not represent an artifact (e.g. a product of proteolytic degradation) appearing after tissue homogenisation. The higher sensitivity of cytosolic MAO to inhibitors also points to different routes for pargyline to inhibit MAO in these subcellular fractions.

An approach for visualization of the active site of enzymes with unknown three-dimensional structures

A new approach for virtual characterization of the active site structure of enzymes with unknown three-dimensional (3D) structure has been proposed. It includes analysis of data on enzyme interaction with reversible competitive inhibitors, their 3D structures and moulding of the substrate-binding region. The superposition of ligands in biologically active conformations allows to determine the shape and dimension of the active site cavity accommodating these compounds. Monoamine oxidase A (MAO-A), a "typical" enzyme with unknown spatial organisation, was used to test this method. The correctness of such approach was validated by the analysis of HIV protease interaction with its inhibitors using 3D structures of their complexes. Mould of the substrate/inhibitor binding site can be used for the visualization of this binding site and for searching new ligands in molecular databases.

[Effect of isatin on the electrical activity in the rat hippocampus cells]

In vitro superfusion of rat hippocampal slices with isatin changed the population spikes. Isatin perfusion produced two clear effects. 50 microM isatin it increased the amplitude of the population spike in the CA1 evoked by stimulation of stratum radiatum. This effect was readily reversible. 100 microM isatin decreased the population spike amplitude with minimal effect on its latency. High initial response were more suppressed. This effect on the population spike amplitude was not eliminated even after 1 h of washing with saline. The data obtained suggest that isatin-induced electrophysiological changes are involved into the anticonvulsant effect of isatin.

The stimulating effects of ethanol consumption on synthesis of rat brain monoamine oxidases and their sensitivity to the irreversible inhibitor, pargyline

Administration of a large dose of pargyline (60mg/kg) caused total irreversible inhibition of brain monoamine oxidases (MAOs) in both control and alcoholised rats. During the first 50h the recovery of brain MAO-A (but not MAO-B) activity occurred faster in the alcoholised rats. A low dose of pargyline (10mg/kg) produced significantly higher inhibition of MAO-A in the alcoholised rats, whereas the degree of MAO-B inhibition was the same in both groups. Brain MAOs of control and alcoholised rats exhibited similar sensitivity to pargyline in vitro. Since chronic ethanol feeding reduced the content of reversible endogenous MAO inhibitor, tribulin, higher pargyline-induced inhibition of MAO-A in alcoholised rats may stem from a tribulin deficit. The data obtained suggest that chronic ethanol consumption increases turnover of MAO-A molecules in the brain and reduces the content of endogenous MAO(A) inhibitors.

Inhibition of LPS-induced cytokines by Bcl-xL in a murine macrophage cell line

The antiapoptotic molecule Bcl-xL has been implicated in the differentiation and survival of activated macrophages in inflammatory conditions. In this report, the role of Bcl-xL in LPS-induced cytokine gene expression and secretion was studied. Bcl-xL-transfected RAW 264 macrophages were protected from gliotoxin-induced apoptosis, indicating the presence of functional Bcl-xL. Overexpression of Bcl-xL in this macrophage cell line was also associated with a marked inhibition of LPS-induced TNF-alpha, JE/monocyte chemoattractant protein 1, and macrophage inflammatory protein 2 secretion. Inhibition of LPS-induced cytokine secretion was paralleled by a decrease in levels of steady-state mRNA for the above cytokines and for IL-1beta. Decreased production of TNF-alpha in Bcl-xL transfectants was not due to increased mRNA degradation, as the mRNA half-lives were the same in Bcl-xL transfectants and control macrophages. Although the composition of NF-kappaB complexes detected by EMSA and supershift analysis in nuclear lysates derived from Bcl-xL transfectants and control cells was indistinguishable, LPS-induced inhibitory kappaBalpha degradation, as well as NF-kappaB binding and AP-1 activation, were slightly decreased by ectopic expression of Bcl-xL. More strikingly, LPS-induced phosphorylation of p38 mitogen-activated protein kinase and c-Jun N-terminal kinase was strongly repressed by Bcl-xL overexpression, offering a possible mechanism for the inhibition of LPS-induced cytokine production. These data provide the first evidence for a novel role for Bcl-xL as an anti-inflammatory mediator in macrophages.