[Pathogenetic basis of optic nerve atrophy in methanol poisoning]

Optic nerve atrophy is a pathomorphological consequence of diseases of the peripheral neuron of the visual pathway, manifested as atrophy of nerve fibers of varying severity. The toxic effect of methanol is mainly associated with formic acid and formaldehyde, which suppress the cytochrome system, inhibit oxidative phosphorylation, and thereby cause a deficiency of adenosine triphosphoric acid, to which brain and retinal tissues are especially susceptible. When formiate accumulates, tissue respiration is disrupted, leading to pronounced tissue hypoxia. As a result of such methanol metabolism, metabolic acidosis occurs. Tissue hypoxia develops in the first few hours as a result of the action of formic acid on the respiratory enzyme chain at the cytochrome oxidase level. Hypoxia and, as a consequence, a decrease in energy supply lead to a disruption of biological oxidation and the development of apoptosis in the optic nerve fibers. Understanding the process of optic nerve atrophy development at the pathogenetic level in methyl alcohol intoxication will help make a correct early diagnosis and prescribe timely treatment.

[DNA Probes for Analysis of the Activity of Key Enzymes of the Base Excision DNA Repair Pathway in Human Cells]

The important role of DNA damage in the occurrence of various diseases, including cancer, has led to study of the mechanisms of genetic information stability, that have been carried out since the discovery of DNA repair systems. The question of the relationship between the accumulation of DNA damage, disorders in DNA repair pathways, and increased risk of disease development is still relevant. Over the past few years, significant efforts have been made to develop methods for analyzing the activity of DNA repair enzymes in human cells. In this work, we developed fluorescent DNA probes that allow us to determine the activity of key enzymes of base excision DNA repair in cell extracts, namely the DNA glycosylases UNG2, SMUG1, MBD4, TDG, AAG, NEIL1, NTHL1, and OGG1 and the AP endonuclease APE1. The sensitivity of DNA probes was determined on pure enzyme preparations. Determination of the activity of repair enzymes in cell extracts of the human ovarian tumor lines TOV112, 79, OVCAR3, MESOV, SCOV3, and TOV21 revealed significant variability in the level of enzyme activity in these cell lines. These results may become a test system platform for analyzing the activity of the base excision DNA repair system in the human body.

[Comparative Analysis of Family A DNA-Polymerases as a Searching Tool for Enzymes with New Properties]

DNA polymerases catalyze DNA synthesis during DNA replication, repair, and recombination. A number of DNA polymerases, such as the Taq enzyme from Thermus aquaticus, are used in various applications of molecular biology and biotechnology, in particular as DNA amplification tools. However, the efficiency of these enzymes depends on factors such as DNA origin, primer composition, template length, GC-content, and the ability to form stable secondary structures. These limitations in the use of currently known DNA polymerases lead to the search for new enzymes with improved properties. This review summarizes the main structural and molecular-kinetic features of the functioning of DNA-polymerases belonging to structural family A, including Taq polymerase. A phylogenetic analysis of these enzymes was carried out, which made it possible to establish a highly conserved consensus sequence containing 62 amino acid residues distributed over the structure of the enzyme. A comparative analysis of these amino acid residues among poorly studied DNA-polymerases revealed 7 enzymes that potentially have the properties necessary for use in DNA amplification.

[Stroke in children: experience of the Center for the Treatment of Cerebrovascular Diseases in Children and Adolescents in Moscow]

OBJECTIVE

To analyze the work of the Center for the Treatment of Cerebrovascular Pathology in Children and Adolescents, operating on the basis of the Morozov Children's City Clinical Hospital of the Moscow Health Department for the period 2018-2021 and to assess the peculiarities of organizing the provision of specialized care to children and adolescents with acute cerebrovascular accident (ACA).

MATERIAL AND METHODS

Annual reports of the Center for the period 2018-2021; included children and adolescents aged 1 month to 17 years 11 months 29 days, with new onset ischemic stroke (IS) and hemorrhagic stroke (HS), cerebral venous thrombosis (sinus thrombosis), confirmed clinically and radiologically.

RESULTS

Statistical data on stroke and organization of care for children with this pathology in Moscow are presented. The incidence of IS in Moscow for the period 2018-2021 ranged from 1.6 to 2.5 per 100.000 children, HI - from 2.35 to 3.3 per 100.000, sinus thrombosis from 0.5 to 1.38 per 100.000. When assessing the main etiological factors of stroke in The Center for International Pediatric Stroke Research categories, we noted a prevalence of chronic head and neck diseases (20-37%) and chronic systemic conditions (conditions or diseases with known changes in coagulation or vascular structure, including connective tissue dysplasia, genetic, hematological, inflammatory or diseases of the immune system) (15-20%). In addition, data on reperfusion therapy carried out at the Center are presented. From 2018 (first thrombolysis was performed) to 2021, 7.3-14.7% of all patients with IS underwent thrombolysis.

CONCLUSION

The experience of functioning of the Center for the Treatment of Cerebrovascular Pathology in Children and Adolescents has shown that the creation of such centers in the regions of the Russian Federation is relevant, but requires taking into account the characteristics of the pediatric population when organizing their work.

Detection of Anthracnose in Strawberry and Methods of Etiological Diagnosis

Anthracnose of strawberry caused by Colletotrichum fungi is a dangerous disease associated with serious damage in berry plantations. Colletotrichum nymphaeae, C. lineola, and C. godetiae have been found in Russian and international planting material of strawberry plants. The cultural and morphological characteristics are described for the isolates and nucleotide ITS1-5.8S-ITS2 sequences of fragments received are identified. It is shown that the fragments of glyceraldehyde 3-phosphate dehydrogenase and actin genes can be used to efficiently differentiate the C. lineola species from the closely related С. dematium. Two diagnostic test systems for acutatum complex identification are compared. The studied test systems do not demonstrate any false-positive results; the prepared set of С. acutatum complex-RT (ZAO Sintol) shows specificity only for the C. nymphaeae and C. fioriniae species and turned out to be nonspecific to the C. godetiae species included in the acutatum complex. The test system elaborated by Garrido et al. is found to be highly sensitive and specific to the target species of the acutatum complex.

The impact of image orientation on distribution of visual fixations while solving simple cognitive problems

Optimization of the educational process, including distance learning, requires orderly arrangement of the information presented, which translates into the need to factor in oculomotor reactions accompanying the search for solutions to simple cognitive tasks. This need supports the relevance of the present study, which aimed to investigate the age-dependent parameters of the oculomotor reactions occurring in solving a simple cognitive task. The sample included 97 persons, 47 males and 50 females, ages 21 to 36. For the purpose of rating the oculomotor reactions, the sample was divided into age groups: 21–26 years (n = 34); 27–32 years (n = 29); 33–36 years (n = 34). The methodology that governed the rating procedures was developed by the authors of the study and relied on the Tobii EyeX eye tracking hardware and software solution (GazeControl software). The study revealed a significant correlation between orientation of the image (presentation angle) and distribution of the visual fixations: regardless of the image presentation angle and its properties (schematic monochrome or full color image), the fixations tend to fall predominantly into the top and left parts of the image (the first quadrant). Other findings include a) a significant dependence of the capability to solve simple cognitive tasks and recognize the contents of the image on the spatial orientation of the presented stimuli, and b) the number of errors made in image contents recognition increasing with age, this dependence being significant and observed for both the schematic monochrome image (p1 = 0.014; p2 = 0.016; p3 = 0.014) and the full-color image (p1 = 0.015; p2 = 0.015; p3 = 0.017). The researchers have also identified the significant angles of rotation of the presented face images that stably caused recognition errors.

Consolidation and reconsolidation of visual and semantic memory in Parkinson’s disease

Cognitive and mnestic impairments have a significant negative impact on the quality of parkinsonian patients’ life. Memory impairment causes changes in the mechanisms of information processing. The aim of this study was to investigate the characteristics of transformations undergone by memorized visual and semantic content during memory consolidation and reconsolidation in patients with Parkinson’s disease. The study was conducted on 32 male patients with PD (ICD code: G20). Among the patients, 9 had rigidity/bradykinesia-d ominant PD, 11 had tremor-dominant PD, and 12 suffered from a mixed type of PD. Short-term memory span was assessed using the 10 words and the visual memory tests proposed by Luria. As stimulus materials we used a symbolic representation of the old Greek letter resembling an owl and a translated excerpt from a Canadian aboriginal epic. Regardless of the PD form, the quality of the memorized information was either altered or completely lost. The mechanisms underlying such transformations differed quantitively depending on the PD form. Transformation of the memorized information occurred in the conditions of both incidental and deliberate memorization and was represented by distortions (substitution of the original content with confabulations) and simplifications of the structural and semantic organization. We consolidated significantly lesser amount of auditory verbal (р = 0.018) and visual (p = 0.029) information. This trend was consistent with the pronounced distortion of content during its retrieval.

Pre-Steady-State Kinetics of the SARS-CoV-2 Main Protease as a Powerful Tool for Antiviral Drug Discovery

The design of effective target-specific drugs for COVID-19 treatment has become an intriguing challenge for modern science. The SARS-CoV-2 main protease, M^pro, responsible for the processing of SARS-CoV-2 polyproteins and production of individual components of viral replication machinery, is an attractive candidate target for drug discovery. Specific M^pro inhibitors have turned out to be promising anticoronaviral agents. Thus, an effective platform for quantitative screening of M^pro-targeting molecules is urgently needed. Here, we propose a pre-steady-state kinetic analysis of the interaction of M^pro with inhibitors as a basis for such a platform. We examined the kinetic mechanism of peptide substrate binding and cleavage by wild-type M^pro and by its catalytically inactive mutant C145A. The enzyme induces conformational changes of the peptide during the reaction. The inhibition of M^pro by boceprevir, telaprevir, GC-376, PF-00835231, or thimerosal was investigated. Detailed pre-steady-state kinetics of the interaction of the wild-type enzyme with the most potent inhibitor, PF-00835231, revealed a two-step binding mechanism, followed by covalent complex formation. The C145A M^pro mutant interacts with PF-00835231 approximately 100-fold less effectively. Nevertheless, the binding constant of PF-00835231 toward C145A M^pro is still good enough to inhibit the enzyme. Therefore, our results suggest that even noncovalent inhibitor binding due to a fine conformational fit into the active site is sufficient for efficient inhibition. A structure-based virtual screening and a subsequent detailed assessment of inhibition efficacy allowed us to select two compounds as promising noncovalent inhibitor leads of SARS-CoV-2 M^pro.

Common Kinetic Mechanism of Abasic Site Recognition by Structurally Different Apurinic/Apyrimidinic Endonucleases

Apurinic/apyrimidinic (AP) endonucleases Nfo (Escherichia coli) and APE1 (human) represent two conserved structural families of enzymes that cleave AP-site–containing DNA in base excision repair. Nfo and APE1 have completely different structures of the DNA-binding site, catalytically active amino acid residues and catalytic metal ions. Nonetheless, both enzymes induce DNA bending, AP-site backbone eversion into the active-site pocket and extrusion of the nucleotide located opposite the damage. All these stages may depend on local stability of the DNA duplex near the lesion. Here, we analysed effects of natural nucleotides located opposite a lesion on catalytic-complex formation stages and DNA cleavage efficacy. Several model DNA substrates that contain an AP-site analogue [F-site, i.e., (2R,3S)-2-(hydroxymethyl)-3-hydroxytetrahydrofuran] opposite G, A, T or C were used to monitor real-time conformational changes of the tested enzymes during interaction with DNA using changes in the enzymes’ intrinsic fluorescence intensity mainly caused by Trp fluorescence. The extrusion of the nucleotide located opposite F-site was recorded via fluorescence intensity changes of two base analogues. The catalytic rate constant slightly depended on the opposite-nucleotide nature. Thus, structurally different AP endonucleases Nfo and APE1 utilise a common strategy of damage recognition controlled by enzyme conformational transitions after initial DNA binding.

Mutational and Kinetic Analysis of APE1 Endoribonuclease Activity

Human apurinic/apyrimidinic endonuclease 1 (APE1) participates in the DNA repair system. It is believed that the main biological function of APE1 is Mg²⁺-dependent hydrolysis of AP-sites in DNA. On the base of structural data, kinetic studies, and mutation analysis, the key stages of APE1 interaction with damaged DNA were established. It has been shown recently that APE1 can act as an endoribonuclease that catalyzes mRNA hydrolysis at certain pyrimidine–purine sites and thus controls the level of certain transcripts. In addition, the presence of Mg²⁺ ions was shown to be not required for the endoribonuclease activity of APE1, in contrast to the AP-endonuclease activity. This indicates differences in mechanisms of APE1 catalysis on RNA and DNA substrates, but the reasons for these differences remain unclear. Here, the analysis of endoribonuclease hydrolysis of model RNA substrates with wild type APE1 enzyme and its mutant forms Y171F, R177F, R181A, D210N, N212A, T268D, M270A, and D308A, was performed. It was shown that mutation of Asn212, Asp210, and Tyr171 residues leads to the decrease of AP-endonuclease activity while endoribonuclease activity is retained. Also, T268D and M270A APE1 mutants lose specificity to pyrimidine–purine sequences. R177F and R181A did not show a significant decrease in enzyme activity, whereas D308A demonstrated a decrease of endoribonuclease activity.

[Mutational and Kinetic Analysis of APE1 Endoribonuclease Activity]

Human apurinic/apyrimidinic endonuclease 1 (APE1) participates in the DNA repair system. It is believed that the main biological function of APE1 is Mg^(2+)-dependent hydrolysis of AP-sites in DNA. On the base of structural data, kinetic studies, and mutation analysis, the key stages of APE1 interaction with damaged DNA were established. It has been shown recently that APE1 can act as an endoribonuclease that catalyzes mRNA hydrolysis at certain pyrimidine-purine sites and thus controls the level of certain transcripts. In addition, the presence of Mg^(2+) ions was shown to be not required for the endoribonuclease activity of APE1, in contrast to the AP-endonuclease activity. This indicates differences in mechanisms of APE1 catalysis on RNA and DNA substrates, but the reasons for these differences remain unclear. Here, the analysis of endoribonuclease hydrolysis of model RNA substrates with wild type APE1 enzyme and its mutant forms Y171F, R177F, R181A, D210N, N212A, T268D, M270A, and D308A, was performed. It was shown that mutation of Asn212, Asp210, and Tyr171 residues leads to the decrease of AP-endonuclease activity while endoribonuclease activity is retained. Also, T268D and M270A APE1 mutants lose specificity to pyrimidine-purine sequences. R177F and R181A did not show a significant decrease in enzyme activity, whereas D308A demonstrated a decrease of endoribonuclease activity.

[Efficiency of RNA Hydrolysis by Binase from Bacillus pumilus: The Impact of Substrate Structure, Metal Ions, and Low Molecular Weight Nucleotide Compounds]

Binase is an extracellular guanyl-preferring ribonuclease from Bacillus pumilus. The main biological function of binase is RNA degradation with the formation of guanosine-2',3'-cyclic phosphate and its subsequent hydrolysis to 3'-phosphate. Extracellular RNases are believed to be key agents that affect the functional activity of the body, as they directly interact with epithelial and immune cells. The biological effects of the enzyme may consist of both direct RNA degradation, and the accumulation of 2',3'-cGMP in the human body. In this work, we have performed a comparative analysis of the cleavage efficiency of model RNA substrates, i.e., short hairpin structures that contain guanosine at various positions. It has been shown that the hydrolysis efficiency of the model RNA substrates depends on the position of guanosine. We have also demonstrated the influence of various divalent metal ions and low molecular weight nucleotide compounds on the binase-catalyzed endoribonucleolytic reaction.

Lesion Recognition and Cleavage of Damage-Containing Quadruplexes and Bulged Structures by DNA Glycosylases

Human telomeres as well as more than 40% of human genes near the promoter regions have been found to contain the sequence that may form a G-quadruplex structure. Other non-canonical DNA structures comprising bulges, hairpins, or bubbles may have a functionally important role during transcription, replication, or recombination. The guanine-rich regions of DNA are hotspots of oxidation that forms 7,8-dihydro-8-oxoguanine, thymine glycol, and abasic sites: the lesions that are handled by the base excision repair pathway. Nonetheless, the features of DNA repair processes in non-canonical DNA structures are still poorly understood. Therefore, in this work, a comparative analysis of the efficiency of the removal of a damaged nucleotide from various G-quadruplexes and bulged structures was performed using endonuclease VIII-like 1 (NEIL1), human 8-oxoguanine-DNA glycosylase (OGG1), endonuclease III (NTH1), and prokaryotic formamidopyrimidine-DNA glycosylase (Fpg), and endonuclease VIII (Nei). All the tested enzymes were able to cleave damage-containing bulged DNA structures, indicating their important role in the repair process when single-stranded DNA and intermediate non–B-form structures such as bubbles and bulges are formed. Nevertheless, our results suggest that the ability to cleave damaged quadruplexes is an intrinsic feature of members of the H2tH structural family, suggesting that these enzymes can participate in the modulation of processes controlled by the formation of quadruplex structures in genomic DNA.

Activity of Human Apurinic/Apyrimidinic Endonuclease APE1 Toward Damaged DNA and Native RNA With Non-canonical Structures

The primary role of apurinic/apyrimidinic (AP) endonuclease APE1 in human cells is the cleavage of the sugar phosphate backbone 5' to an AP site in DNA to produce a single-strand break with a 5'-deoxyribose phosphate and 3'-hydroxyl end groups. APE1 can also recognize and incise some damaged or modified nucleotides and possesses some minor activities: 3'-5' exonuclease, 3'-phosphodiesterase, 3'-phosphatase, and RNase H. A molecular explanation for the discrimination of structurally different substrates by the single active site of the enzyme remains elusive. Here, we report a mechanism of target nucleotide recognition by APE1 as revealed by the results of an analysis of the APE1 process involving damaged DNA and native RNA substrates with non-canonical structures. The mechanism responsible for substrate specificity proved to be directly related to the ability of a target nucleotide to get into the active site of APE1 in response to an enzyme-induced DNA distortion.

The Role of Active-Site Plasticity in Damaged-Nucleotide Recognition by Human Apurinic/Apyrimidinic Endonuclease APE1

Human apurinic/apyrimidinic (AP) endonuclease APE1 hydrolyzes phosphodiester bonds on the 5′ side of an AP-site, and some damaged nucleotides such as 1,N6-ethenoadenosine (εA), α-adenosine (αA), and 5,6-dihydrouridine (DHU). To investigate the mechanism behind the broad substrate specificity of APE1, we analyzed pre-steady-state kinetics of conformational changes in DNA and the enzyme during DNA binding and damage recognition. Molecular dynamics simulations of APE1 complexes with one of damaged DNA duplexes containing εA, αA, DHU, or an F-site (a stable analog of an AP-site) revealed the involvement of residues Asn229, Thr233, and Glu236 in the mechanism of DNA lesion recognition. The results suggested that processing of an AP-site proceeds faster in comparison with nucleotide incision repair substrates because eversion of a small abasic site and its insertion into the active site do not include any unfavorable interactions, whereas the insertion of any target nucleotide containing a damaged base into the APE1 active site is sterically hindered. Destabilization of the α-helix containing Thr233 and Glu236 via a loss of the interaction between these residues increased the plasticity of the damaged-nucleotide binding pocket and the ability to accommodate structurally different damaged nucleotides. Nonetheless, the optimal location of εA or αA in the binding pocket does not correspond to the optimal conformation of catalytic amino acid residues, thereby significantly decreasing the cleavage efficacy for these substrates.

Substrate specificity of human apurinic/apyrimidinic endonuclease APE1 in the nucleotide incision repair pathway

Human apurinic/apyrimidinic (AP) endonuclease APE1 catalyses the hydrolysis of phosphodiester bonds on the 5′ side of an AP-site (in the base excision repair pathway) and of some damaged nucleotides (in the nucleotide incision repair pathway). The range of substrate specificity includes structurally unrelated damaged nucleotides. Here, to examine the mechanism of broad substrate specificity of APE1, we performed pulsed electron–electron double resonance (PELDOR) spectroscopy and pre-steady-state kinetic analysis with Förster resonance energy transfer (FRET) detection of DNA conformational changes during DNA binding and lesion recognition. Equilibrium PELDOR and kinetic FRET data revealed that DNA binding by APE1 leads to noticeable damage-dependent bending of a DNA duplex. Molecular dynamics simulations showed that the damaged nucleotide is everted from the DNA helix and placed into the enzyme’s binding pocket, which is formed by Asn-174, Asn-212, Asn-229, Ala-230, Phe-266 and Trp-280. Nevertheless, no damage-specific contacts were detected between these amino acid residues in the active site of the enzyme and model damaged substrates containing 1,N6-ethenoadenosine, α-adenosine, 5,6-dihydrouridine or F-site. These data suggest that the substrate specificity of APE1 is controlled by the ability of a damaged nucleotide to flip out from the DNA duplex in response to an enzyme-induced DNA distortion.

Roles of Active-Site Amino Acid Residues in Specific Recognition of DNA Lesions by Human 8-Oxoguanine-DNA Glycosylase (OGG1)

Human 8-oxoguanine-DNA glycosylase (hOGG1) possesses very high specificity for 8-oxoguanine (oxoG), even though this damaged base differs from normal guanine by only two atoms. Our aim was to determine the roles of certain catalytically important amino acid residues in the hOGG1 enzymatic pathway and describe their involvement in the mechanism of DNA lesion recognition. Molecular dynamic simulation and pre-steady-state fluorescence kinetics were performed to analyze the conformational behavior of wild-type hOGG1 and mutants G42S, D268A, and K249Q, as well as damaged and undamaged DNA. A loss of electrostatic interactions in the K249Q mutant leads to the disruption of specific contacts in the active site of the enzyme and the loss of catalytic activity. The absence of residue Asp-268 abrogates the ability of the enzyme to fully flip out the oxoG base from the double helix, thereby disrupting proper positioning of the damaged base in the active site. Furthermore, substitution of Gly-42 with Ser, which forms a damage-specific H-bond with the N7 atom of the oxoG base, creates a stable H-bond between N7 of undamaged G and Oγ of Ser-42. Nevertheless, positioning of the undamaged base in the active site is unsuitable for catalytic hydrolysis of the N-glycosidic bond.

Kinetic Features of 3'-5' Exonuclease Activity of Human AP-Endonuclease APE1

Human apurinic/apyrimidinic (AP)-endonuclease APE1 is one of the key enzymes taking part in the repair of damage to DNA. The primary role of APE1 is the initiation of the repair of AP-sites by catalyzing the hydrolytic incision of the phosphodiester bond immediately 5' to the damage. In addition to the AP-endonuclease activity, APE1 possesses 3'-5' exonuclease activity, which presumably is responsible for cleaning up nonconventional 3' ends that were generated as a result of DNA damage or as transition intermediates in DNA repair pathways. In this study, the kinetic mechanism of 3'-end nucleotide removal in the 3'-5' exonuclease process catalyzed by APE1 was investigated under pre-steady-state conditions. DNA substrates were duplexes of deoxyribonucleotides with one 5' dangling end and it contained a fluorescent 2-aminopurine residue at the 1st, 2nd, 4th, or 6th position from the 3' end of the short oligonucleotide. The impact of the 3'-end nucleotide, which contained mismatched, undamaged bases or modified bases as well as an abasic site or phosphate group, on the efficiency of 3'-5' exonuclease activity was determined. Kinetic data revealed that the rate-limiting step of 3' nucleotide removal by APE1 in the 3'-5' exonuclease process is the release of the detached nucleotide from the enzyme's active site.

Pre-steady-state kinetic analysis of damage recognition by human single-strand selective monofunctional uracil-DNA glycosylase SMUG1

In all organisms, DNA glycosylases initiate base excision repair pathways resulting in removal of aberrant bases from DNA. Human SMUG1 belongs to the superfamily of uracil-DNA glycosylases catalyzing the hydrolysis of the N-glycosidic bond of uridine and uridine lesions bearing oxidized groups at C5: 5-hydroxymethyluridine (5hmU), 5-formyluridine (5fU), and 5-hydroxyuridine (5hoU). An apurinic/apyrimidinic (AP) site formed as the product of an N-glycosylase reaction is tightly bound to hSMUG1, thus inhibiting the downstream action of AP-endonuclease APE1. The steady-state kinetic parameters (k_cat and K_M; obtained from the literature) correspond to the enzyme turnover process limited by the release of hSMUG1 from the complex with the AP-site. In the present study, our objective was to carry out a stopped-flow fluorescence analysis of the interaction of hSMUG1 with a DNA substrate containing a dU:dG base pair to follow the pre-steady-state kinetics of conformational changes in both molecules. A comparison of kinetic data obtained by means of Trp and 2-aminopurine fluorescence and Förster resonance energy transfer (FRET) detection allowed us to elucidate the stages of specific and nonspecific DNA binding, to propose the mechanism of damaged base recognition by hSMUG1, and to determine the true rate of the catalytic step. Our results shed light on the kinetic mechanism underlying the initiation of base excision repair by hSMUG1 using the "wedge" strategy for DNA lesion search.

New oligonucleotide derivatives as unreactive substrate analogues and potential inhibitors of human apurinic/apyrimidinic endonuclease APE1

Human apurinic/apyrimidinic endonuclease APE1 is one of the key enzymes of the base excision DNA repair system. The main biological function of APE1 is the hydrolysis of the phosphodiester bond on the 5'-side of an apurinic/apyrimidinic site (AP-site) to give the 5'-phosphate and 3'-hydroxyl group. It has long been known that AP-sites have mutagenic and cytotoxic effects and their accumulation in DNA is a potential hazard to the cell lifecycle. The structural and biochemical studies of APE1 are complicated by its high catalytic activity towards the AP-site and its cyclic or acyclic analogues. This work has focussed on the design, synthesis and analysis of oligonucleotide derivatives as potentially unreactive APE1 substrates. We have shown that the replacement of oxygen atoms in the phosphate group on the 5'-side from the AP-site analogue tetrahydrofuran (F) considerably decreases the rate of enzymatic hydrolysis of modified oligonucleotides. We have calculated that a N3'-P5' phosphoramidate linkage is hydrolysed about 30 times slower than the native phosphodiester bond while phosphorothioate or primary phosphoramidate linkages are cleaved more than three orders of magnitude slower. The value of IC50 of the oligonucleotide duplex containing a primary phosphoramidate linkage is 2.5 × 10(-7) M, which is in accordance with the APE1 association constant of DNA duplexes containing AP-sites. Thus, it is demonstrated that oligonucleotide duplexes with chemical modifications could be used as unreactive substrates and potential competitive inhibitors of APE1.

Pre-steady state kinetics of DNA binding and abasic site hydrolysis by tyrosyl-DNA phosphodiesterase 1

Tyrosyl-DNA phosphodiesterase 1 (Tdp1) processes DNA 3'-end-blocking modifications, possesses DNA and RNA 3'-nucleosidase activity and is also able to hydrolyze an internal apurinic/apyrimidinic (AP) site and its synthetic analogs. The mechanism of Tdp1 interaction with DNA was analyzed using pre-steady state stopped-flow kinetics with tryptophan, 2-aminopurine and Förster resonance energy transfer fluorescence detection. Phosphorothioate or tetramethyl phosphoryl guanidine groups at the 3'-end of DNA have been used to prevent 3'-nucleosidase digestion by Tdp1. DNA binding and catalytic properties of Tdp1 and its mutants H493R (Tdp1 mutant SCAN1) and H263A have been compared. The data indicate that the initial step of Tdp1 interaction with DNA includes binding of Tdp1 to the DNA ends followed by the 3'-nucleosidase reaction. In the case of DNA containing AP site, three steps of fluorescence variation were detected that characterize (i) initial binding the enzyme to the termini of DNA, (ii) the conformational transitions of Tdp1 and (iii) search for and recognition of the AP-site in DNA, which leads to the formation of the catalytically active complex and to the AP-site cleavage reaction. Analysis of Tdp1 interaction with single- and double-stranded DNA substrates shows that the rates of the 3'-nucleosidase and AP-site cleavage reactions have similar values in the case of single-stranded DNA, whereas in double-stranded DNA, the cleavage of the AP-site proceeds two times faster than 3'-nucleosidase digestion. Therefore, the data show that the AP-site cleavage reaction is an essential function of Tdp1 which may comprise an independent of AP endonuclease 1 AP-site repair pathway.

The formation of catalytically competent enzyme-substrate complex is not a bottleneck in lesion excision by human alkyladenine DNA glycosylase

Human alkyladenine DNA glycosylase (AAG) protects DNA from alkylated and deaminated purine lesions. AAG flips out the damaged nucleotide from the double helix of DNA and catalyzes the hydrolysis of the N-glycosidic bond to release the damaged base. To understand better, how the step of nucleotide eversion influences the overall catalytic process, we performed a pre-steady-state kinetic analysis of AAG interaction with specific DNA-substrates, 13-base pair duplexes containing in the 7th position 1-N6-ethenoadenine (εA), hypoxanthine (Hx), and the stable product analogue tetrahydrofuran (F). The combination of the fluorescence of tryptophan, 2-aminopurine, and 1-N6-ethenoadenine was used to record conformational changes of the enzyme and DNA during the processes of DNA lesion recognition, damaged base eversion, excision of the N-glycosidic bond, and product release. The thermal stability of the duplexes characterized by the temperature of melting, T_m, and the rates of spontaneous opening of individual nucleotide base pairs were determined by NMR spectroscopy. The data show that the relative thermal stability of duplexes containing a particular base pair in position 7, (T_m(F/T) < T_m(εA/T) < T_m(Hx/T) < T_m(A/T)) correlates with the rate of reversible spontaneous opening of the base pair. However, in contrast to that, the catalytic lesion excision rate is two orders of magnitude higher for Hx-containing substrates than for substrates containing εA, proving that catalytic activity is not correlated with the stability of the damaged base pair. Our study reveals that the formation of the catalytically competent enzyme-substrate complex is not the bottleneck controlling the catalytic activity of AAG.

Effects of mono- and divalent metal ions on DNA binding and catalysis of human apurinic/apyrimidinic endonuclease 1

Here, we used stopped-flow fluorescence techniques to conduct a comparative kinetic analysis of the conformational transitions in human apurinic/apyrimidinic endonuclease 1 (APE1) and in DNA containing an abasic site in the course of their interaction. Effects of monovalent (K(+)) and divalent (Mg(2+), Mn(2+), Ca(2+), Zn(2+), Cu(2+), and Ni(2+)) metal ions on DNA binding and catalytic stages were studied. It was shown that the first step of substrate binding (corresponding to formation of a primary enzyme-substrate complex) does not depend on the concentration (0.05-5.0 mM) or the nature of divalent metal ions. In contrast, the initial DNA binding efficiency significantly decreased at a high concentration (5-250 mM) of monovalent K(+) ions, indicating the involvement of electrostatic interactions in this stage. It was also shown that Cu(2+) ions abrogated the DNA binding ability of APE1, possibly, due to a strong interaction with DNA bases and the sugar-phosphate backbone. In the case of Ca(2+) ions, the catalytic activity of APE1 was lost completely with retention of binding potential. Thus, the enzymatic activity of APE1 is increased in the order Zn(2+) < Ni(2+) < Mn(2+) < Mg(2+). Circular dichroism spectra and calculation of the contact area between APE1 and DNA reveal that Mg(2+) ions stabilize the protein structure and the enzyme-substrate complex.

[STUDY OF THE EFFICACY OF REGULATION OF THE BLOOD SERUM PHYSICOCHEMICAL PARAMETERS IN CHILDREN WITH DYSFUNCTION OF PHYSIOLOGICAL SYSTEMS]

The physicochemical parameters of blood serum (osmolality, concentration of several ions, total protein, glucose) were studied in 200 children of different age with various forms of pathology. The variability of each parameter was calculated. A high level of stability of the parameters studies was revealed in healthy children and in children with dysfunction of various systems (disease of the respiratory system, gastrointestinal tract, renal and urinary tract, nervous and endocrine systems). However, estimation of their coefficients of variation showed significant individual deviations of these parameters from the average value of the examined patients. This fact reflects the extent of efficacy of activity of different organs and regulatory systems under pathological processes. Combination of clinical and ontogenetic methods of evolutionary physiology in this study opens new possibilities for understanding the nature of regulation of water-salt balance in humans and points out to the expedience of using these approaches in the practical medicine.

Conformational Dynamics of DNA Repair by Escherichia coli Endonuclease III

Escherichia coli endonuclease III (Endo III or Nth) is a DNA glycosylase with a broad substrate specificity for oxidized or reduced pyrimidine bases. Endo III possesses two types of activities: N-glycosylase (hydrolysis of the N-glycosidic bond) and AP lyase (elimination of the 3'-phosphate of the AP-site). We report a pre-steady-state kinetic analysis of structural rearrangements of the DNA substrates and uncleavable ligands during their interaction with Endo III. Oligonucleotide duplexes containing 5,6-dihydrouracil, a natural abasic site, its tetrahydrofuran analog, and undamaged duplexes carried fluorescent DNA base analogs 2-aminopurine and 1,3-diaza-2-oxophenoxazine as environment-sensitive reporter groups. The results suggest that Endo III induces several fast sequential conformational changes in DNA during binding, lesion recognition, and adjustment to a catalytically competent conformation. A comparison of two fluorophores allowed us to distinguish between the events occurring in the damaged and undamaged DNA strand. Combining our data with the available structures of Endo III, we conclude that this glycosylase uses a multistep mechanism of damage recognition, which likely involves Gln(41) and Leu(81) as DNA lesion sensors.

Pre-steady-state kinetic and structural analysis of interaction of methionine γ-lyase from Citrobacter freundii with inhibitors

Methionine γ-lyase (MGL) catalyzes the γ-elimination of l-methionine and its derivatives as well as the β-elimination of l-cysteine and its analogs. These reactions yield α-keto acids and thiols. The mechanism of chemical conversion of amino acids includes numerous reaction intermediates. The detailed analysis of MGL interaction with glycine, l-alanine, l-norvaline, and l-cycloserine was performed by pre-steady-state stopped-flow kinetics. The structure of side chains of the amino acids is important both for their binding with enzyme and for the stability of the external aldimine and ketimine intermediates. X-ray structure of the MGL·l-cycloserine complex has been solved at 1.6 Å resolution. The structure models the ketimine intermediate of physiological reaction. The results elucidate the mechanisms of the intermediate interconversion at the stages of external aldimine and ketimine formation.

Pre-steady-state fluorescence analysis of damaged DNA transfer from human DNA glycosylases to AP endonuclease APE1

BACKGROUND

DNA glycosylases remove the modified, damaged or mismatched bases from the DNA by hydrolyzing the N-glycosidic bonds. Some enzymes can further catalyze the incision of a resulting abasic (apurinic/apyrimidinic, AP) site through β- or β,δ-elimination mechanisms. In most cases, the incision reaction of the AP-site is catalyzed by special enzymes called AP-endonucleases.

METHODS

Here, we report the kinetic analysis of the mechanisms of modified DNA transfer from some DNA glycosylases to the AP endonuclease, APE1. The modified DNA contained the tetrahydrofurane residue (F), the analogue of the AP-site. DNA glycosylases AAG, OGG1, NEIL1, MBD4(cat) and UNG from different structural superfamilies were used.

RESULTS

We found that all DNA glycosylases may utilise direct protein-protein interactions in the transient ternary complex for the transfer of the AP-containing DNA strand to APE1.

CONCLUSIONS

We hypothesize a fast "flip-flop" exchange mechanism of damaged and undamaged DNA strands within this complex for monofunctional DNA glycosylases like MBD4(cat), AAG and UNG. Bifunctional DNA glycosylase NEIL1 creates tightly specific complex with DNA containing F-site thereby efficiently competing with APE1. Whereas APE1 fast displaces other bifunctional DNA glycosylase OGG1 on F-site thereby induces its shifts to undamaged DNA regions.

GENERAL SIGNIFICANCE

Kinetic analysis of the transfer of DNA between human DNA glycosylases and APE1 allows us to elucidate the critical step in the base excision repair pathway.

Thermodynamics of the DNA damage repair steps of human 8-oxoguanine DNA glycosylase

Human 8-oxoguanine DNA glycosylase (hOGG1) is a key enzyme responsible for initiating the base excision repair of 7,8-dihydro-8-oxoguanosine (oxoG). In this study a thermodynamic analysis of the interaction of hOGG1 with specific and non-specific DNA-substrates is performed based on stopped-flow kinetic data. The standard Gibbs energies, enthalpies and entropies of specific stages of the repair process were determined via kinetic measurements over a temperature range using the van’t Hoff approach. The three steps which are accompanied with changes in the DNA conformations were detected via 2-aminopurine fluorescence in the process of binding and recognition of damaged oxoG base by hOGG1. The thermodynamic analysis has demonstrated that the initial step of the DNA substrates binding is mainly governed by energy due to favorable interactions in the process of formation of the recognition contacts, which results in negative enthalpy change, as well as due to partial desolvation of the surface between the DNA and enzyme, which results in positive entropy change. Discrimination of non-specific G base versus specific oxoG base is occurring in the second step of the oxoG-substrate binding. This step requires energy consumption which is compensated by the positive entropy contribution. The third binding step is the final adjustment of the enzyme/substrate complex to achieve the catalytically competent state which is characterized by large endothermicity compensated by a significant increase of entropy originated from the dehydration of the DNA grooves.

[Genetic ecological monitoring in human populations: heterozygosity, mtDNA haplotype variation, and genetic load]

Yu. P. Altukhov suggested that heterozygosity is an indicator of the state of the gene pool. The idea and a linked concept of genetic ecological monitoring were applied to a new dataset on mtDNA variation in East European ethnic groups. Haplotype diversity (an analog of the average heterozygosity) was shown to gradually decrease northwards. Since a similar trend is known for population density, interlinked changes were assumed for a set of parameters, which were ordered to form a causative chain: latitude increases, land productivity decreases, population density decreases, effective population size decreases, isolation of subpopulations increases, genetic drift increases, and mtDNA haplotype diversity decreases. An increase in genetic drift increases the random inbreeding rate and, consequently, the genetic load. This was confirmed by a significant correlation observed between the incidence of autosomal recessive hereditary diseases and mtDNA haplotype diversity. Based on the findings, mtDNA was assumed to provide an informative genetic system for genetic ecological monitoring; e.g., analyzing the ecology-driven changes in the gene pool.

[Incretory function of the kidney]

Participation of kidney in maintenance of constancy of parameters of the organism internal medium is connected with formation in it of physiologically active substances. They are components of systems of regulation of water-salt balance, arterial pressure, blood coagulation, erythropoiesis. Mechanisms of normalization by kidney of concentration of hormones in blood and of modulation of action of hormones are analyzed.

[Diabetes mellitus: renal osmoregulating function]

AIM

To evaluate the kidney status from osmotic urine concentration in different stages of diabetes mellitus (DM) to define whether not only glomeruli and proximal tubules, but also renal medullary substance structures are involved into the pathological process, as well as their reaction to endogenous vasopressin production.

SUBJECTS AND METHODS

Forty patients with a 1-to-28-year history of DM, including 18 with diabetic nephropathy, 10 with chronic renal failure, and 22 without diabetic nephropathy, were examined. Urine and blood osmolality were determined and renal osmoregulating function was estimated.

RESULTS

Decreased glomerular filtration rate was found in relation to the duration of DM. The osmolality of nocturnal urine samples tended to diminish during short-term deprivation depending on the duration of DM. Increased diuresis in DM was shown to correlate with the higher reabsorption of osmotically free water.

CONCLUSION

Diminished renal concentrating capacity in DM appears to depend on evolving renal failure rather than vasopressin resistance. The application of a new approach, by calculating the clearance of sodium-free water, suggests that its increased reabsorption favors normalization of serum osmolality in hyperglycemia.

[Single-stranded DNA modification by an oligonucleotide-phthalocyanine Fe(II) conjugate: kinetic regulation and mechanism]

Catalytic oxidative modification of single-stranded DNA with hydrogen peroxide and molecular oxygen in the presence of a conjugate containing an oligonucleotide complementary to the DNA fragment and tetra-4-carboxyphthalocyanine Fe(II) was studied. The conjugate examined was found to be active in the reaction of oxidative DNA cleavage in the presence of hydrogen peroxide, like earlier studied oligonucleotide conjugates containing tetra-4-carboxyphthalocyanine Co(II) and 2,4-di-[2-(2-hydroxyethyl)]deuteroporphyrin IX Fe(III) metallocomplexes generating active oxygen forms. The new conjugate was more active in the case of oxidation with molecular oxygen. Kinetic regularities and optimal regimes of DNA oxidation with hydrogen peroxide were found.

DNA-binding and oxidative properties of cationic phthalocyanines and their dimeric complexes with anionic phthalocyanines covalently linked to oligonucleotides

Design of chemically modified oligonucleotides for regulation of gene expression has attracted considerable attention over the past decades. One actively pursued approach involves antisense or antigene oligonucleotide constructs carrying reactive groups, many of these based on transition metal complexes. The complexes of Fe(II) and Co(II) with phthalocyanines are extremely good catalysts of oxidation of organic compounds with molecular oxygen and hydrogen peroxide. The binding of positively charged Fe(II) and Co(II) phthalocyanines with single- and double-stranded DNA was investigated. It was shown that these phthalocyanines interact with nucleic acids through an outside binding mode. The site-directed modification of single-stranded DNA by O2 and H2O2 in the presence of dimeric complexes of negatively and positively charged Fe(II) and Co(II) phthalocyanines was investigated. These complexes were formed directly on single-stranded DNA through interaction between negatively charged phthalocyanine in conjugate and positively charged phthalocyanine in solution. The resulting oppositely charged phthalocyanine complexes showed significant increase of catalytic activity compared with monomeric forms of phthalocyanines Fe(II) and Co(II). These complexes catalyzed the DNA oxidation with high efficacy and led to direct DNA strand cleavage. It was determined that oxidation of DNA by molecular oxygen catalyzed by complex of Fe(II)-phthalocyanines proceeds with higher rate than in the case of Co(II)-phthalocyanines but the latter led to a greater extent of target DNA modification.

[Role of V1- and V2-receptors in mechanism of physiological paradox--an increase of reabsorption of the solute free water and simultaneous rise of diuresis]

In experiments on non-anesthetized rats with administration into stomach of water (5 ml/100 g body mass) direct correlation has been found between an increase of diuresis and excretion of solute free water (r = 0.98, p < 0.01), while after injection to these animals of 5 x 10(-11) M arginine-vasotocin - between an increase of diuresis and simultaneous rise reabsorption of solute free water (r = 0.8, p < 0.01). The rise of diuresis after the vasotocin injection is due to inhibition of sodium re- absorption, with the solute excretion fraction increasing from 2.6 +/- 0.2 % to 11.9 +/- 1.2, p < 0.001. A similar physiological paradox - an increase of diuresis with the simultaneous increase of reabsorption of solute free water - has been revealed at night hours in children with tendency for nocturnal enuresis (r = 0.64, p < 0.01). Mechanism responsible for this phenomenon consists in a rise of diuresis due to a decrease of sodium ion reabsorption in the ascending Henle loop limb. A problem is discussed of the homeostatic significance of a decrease of sodium reabsorption combined with an increase of solute-free water reabsorption; it is suggested that this phenomenon is based on a redistribution of reabsorption inside the nephron - a decrease of ion and water reabsorption in the initial parts of the nephron distal segment and an increase of solute free water reabsorption with the antidiuretic hormone-stimulated high osmotic permeability of terminal parts of renal tubules. An intraperitoneal injection of V1-anatagonist (OPC-21268) decreased the natriuretic component of response to arginine-vasotocin, while injection of V2-antagonist (OPC-31260) eliminated the antidiuretic component.

Kinetic study of DNA modification by phthalocyanine derivative of the oligonucleotide

Design of chemically modified oligonucleotides for regulation of gene expression has attracted considerable attention over the last decades. One actively pursued approach involves antisense or antigene constructs carrying reactive groups, many of these based on transition metal complexes. The complexes of Co(II) with phthalocyanines are extremely good catalysts of oxidation of organic compounds with molecular oxygen and hydrogen peroxide. In this study, we have investigated the kinetics and thermodynamics of sequence-specific modification of DNA with deoxyribooligonucleotide linked to Co(II)-tetracarboxyphthalocyanine (PtcCo(II)) in the presence of H(2)O(2).

[Cations in the human blood serum]

The review summarizes data (more than 450 references) on concentration of human serum cations (Na+, K+, Ca2+, and Mg2+) and human blood serum osmolality depending on age, diverse physiological and pathological states, and action of physiologically active substances. There are summarized data of many thousand measurements of physicochemical parameters of the blood serum, the mean values of osmolality and cation concentrations in healthy people are calculated. The values are kept at a stable level throughtout the entire life since the moment of birth; in many cases they are maintained by regulatory systems within the normal limits and during various physiological and pathological states. There are formulated the main types of the states characterized by deviations from norm of physicochemical parameters of the internal medium fluids.

[Physiological analysis of plasma hypo-osmolality in pneumonia]

AIM

To study the physiological mechanisms of plasma hypoosmolality in patients with pneumonia and on this basis to elaborate principles of therapy for this condition.

MATERIALS AND METHODS

52 individuals of different age, including 26 patients with pneumonia, were examined. Osmolality, the concentrations of ions of sodium, potassium, magnesium, and creatinine were measured in the serum.

RESULTS

The patients with pneumonia were found to have osmolality, hyponatremia in combination with severe hypodiuresis, high urinary osmotic pressure and intensive reabsorption of osmotically free water in the kidney, which leads to blood dilution. As hypoosmolality usually causes higher diuresis and decreased urinary osmolality; hypodiuresis with high urinary osmolality in pneumonia is indicative of effective renal performance and its altered regulation evidently due to the hypersecretion of vasopressin or to the decreased formation of a number of autacoids in the kidney.

CONCLUSION

Blood hypoosmolality and hyponatremia in the examined patients result from inadequate blood osmolality and high urinary osmotic concentrating. The principles of this condition in pneumonia are discussed and aquaretics are proposed for use as pathogenetic therapy.

Study of the role of prostaglandin E2 in urine flow regulation in chronic renal failure

OBJECTIVE

This study was carried out to investigate the role of prostaglandin E2 in the regulation of urine flow and ion excretion in patients with chronic renal failure.

MATERIAL AND METHODS

Twenty patients with chronic renal failure (CRF) and 13 healthy people were studied. CRF develops as a terminal stage of glomerulonephritis, pyelonephritis or polycystic renal disease. Osmolality and sodium, potassium, magnesium, calcium and creatinine concentrations were measured in urine and blood serum. Urine prostaglandin E2 was determined using kits for imminoenzyme analysis.

RESULTS

The average creatinine clearance was 19.9 +/- 6.3 ml/min, but it varied from 30 to 10 ml/min in different patients. In patients with CRF a correlation was revealed between diuresis and Na excretion (r = 0.78, p < 0.001) and between Na excretion and PGE2 excretion (r = 0.65, p < 0.001), a correlation that lacking in the healthy subject. A correlation was also found between diuresis and Mg excretion (r = 0.68, p < 0.001) and between Mg excretion and Na excretion (r = 0.83, p < 0.001) in patients with CRF but not in healthy subject.

CONCLUSION

It is suggested that in patients with CRF who experience a decrease in the glomerular filtration rate (to 75-90% of the normal value) the increase in urine flow is due to prostaglandin-dependent inhibition of ion reabsorption in the thick ascending limb of the loop of Henle.

[Mechanism f kidney participation in maintaining osmotic and ion homeostasis in chronic renal failure]

In examination of patients with chronic renal failure (CRF) at glomerular filtration rate below 30 ml/min and blood serum ion concentration within limits of normal values hyperosmia has been found. Under the natural regimen essential differences have been revealed neither in variation limits of renal excretion of ions nor osmotically active substances in CRF patients as compared with healthy controls. Diuresis correlated with renal excretion of osmotically active substances. It is shown that a decrease in reabsorption of osmotically active substances depends on secretion and excretion of prostaglandin E2. A suggestion is made about the role of prostaglandins in regulation of renal tubular function at terminal CRF stages.

Possible role of prostaglandins in pathogenesis of nocturnal enuresis in children

OBJECTIVE

To compare excretion of ions and prostaglandins by the kidney in children with noctural enuresis.

MATERIAL AND METHODS

Thirty-two children with primary nocturnal enuresis and 23 normal children were examined. Osmolality and sodium and potassium concentrations were measured in their urine and blood serum. Prostaglandins E2, E1, and F2alpha were determined using kits for immunoenzyme analysis. Luminal and contraluminal prostaglandin secretions were studied in frog urinary bladder.

RESULTS

Children with nocturnal enuresis have increased nocturnal diuresis and renal sodium excretion, but no increase was found in excretion of prostaglandins E2, E1, and F2alpha. Administration of sodium diclofenac before bed-time eliminated episodes of nocturnal enuresis in 37% of children; intranasal administration of Adiuretin SD had a positive effect in 69% of enuretics. In children with nocturnal enuresis there is a correlation between renal excretion of PGE2 and sodium ions; this correlation is absent in the control group children, and disappears in enuretics treated with desmopressin. To evaluate the representativeness of the data on prostaglandin secretions to urine as compared with their release to extracellular fluid, experiments on frog urinary bladder were performed: a correlation was found between prostaglandin secretion to the urinary bladder lumen and to the extracellular fluid.

CONCLUSIONS

The results of the study suggest that changes in renal function are due not to a higher secretion of prostaglandins in nocturnal enuresis but to the relative dominance of their effect as compared with other physiologically active substances that simultaneously act on renal tubular cells.

Nocturnal enuresis: correction of renal function by desmopressin and diclofenac

Sixty-two children with nocturnal enuresis (43 boys, 19 girls aged 6-15 years) were treated with either desmopressin (Adiuretin-SD) (n = 32) or sodium diclofenac (n = 30). Desmopressin was effective in 85% of children and diclofenac in 33%. In children with primary nocturnal enuresis, the glomerular filtration rate was normal, whereas diuresis and solute excretion during the night were increased. Compared with healthy children, the nightly excretion of sodium was elevated by 43.7% and magnesium by 58.4%. A high correlation was found between the free water reabsorption and solute clearance (P < 0.001) in children with nocturnal enuresis. Changes in kidney function in nocturnal enuresis appear to be due to a decrease in the water and ion reabsorption in the thick ascending limb of Henle's loop because of a changed regulation of ion transport in this part of the nephron. Administration of desmopressin or a decrease in prostaglandin production after diclofenac administration restores the ion and water transport in the kidney, which results in the disappearance of nocturnal enuresis. The results indicate a role of changes in regulation of ion transport in renal tubules in the pathogenesis of one of the forms of primary nocturnal enuresis.

Defect of osmoregulatory renal function in nocturnal enuresis

Renal function was studied in 62 children with primary nocturnal enuresis (PNE) and in 20 healthy children aged 6-15 years. During the night, children with PNE exhibited an increase in diuresis, free water reabsorption and solute excretion (including sodium and magnesium) in comparison to controls. Intranasal administration of Adiuretin-SD (10.5-24.5 micrograms) in the evening reduced diuresis and ion excretion to normal levels. During the treatment, 61% of the children became completely dry and, in 24% of the children, the number of wet nights was reduced by 50%. It is suggested that in the pathogenesis of PNE, the decrease in ion reabsorption in the thick ascending Henle's loop--resulting in a greater load of tubular fluid in the collecting ducts, an elevation of diuresis and increases in free water reabsorption and solute excretion--plays the leading role in disturbing renal function. Treatment of PNE with desmopressin is pathogenically justified, as it eliminates the principal defect of renal tubular function.

Osmoregulatory function of the kidney in enuretic children

Twenty children with primary nocturnal enuresis and 20 healthy children of the same age and sex were studied. Natural urination was used for the 24-h urine collection. It was found that urine osmolality and free water reabsorption during the night did not differ statistically significantly between the enuretic children and the healthy. The increased diuresis in the enuretic children was caused by a higher excretion of the osmotically active solutes, including sodium. Use of desmopressin reduced diuresis and natriuresis to normal levels. It is suggested that the main role in the pathogenesis of the studied form of nocturnal enuresis is played by a decrease in ion reabsorption, probably in the thick ascending Henle loop, which facilitates the increase in diuresis and occurrence of nocturnal enuresis.

[Nocturnal enuresis as a manifestation of autocoidosis]

The study entered 30 children with nocturnal enuresis and 20 healthy controls aged 6-15 years. The enuretic children had a higher night diuresis and free water reabsorption; there was an increase in nocturnal excretion of sodium, calcium and magnesium ions. Before going to bed the patients received diclofenac-sodium. Inhibition of cyclooxygenase and decrease of prostaglandin production led to normalization of diuresis and natriuresis, elimination of nocturnal enuresis episodes. The evidence has been obtained that nocturnal enuresis is accompanied by an increased production of autocoids in the thick ascending Henle loop and, as a result, of an increase in saluresis and diuresis. It is suggested that there is a form of nocturnal diuresis which depends on a local hyperproduction of autocoids. The problem of autocoids role in the internal medicine is discussed.