Оксидативні пошкодження ДНК

Проаналізовано деякі характеристики основних типів оксидативних пошкоджень ДНК: модифікації азотистих основ та дезоксирибози, одноланцюгові та дволанцюгові розриви, апуринові/апіримідинові сайти, міжвалентні взаємодії ДНК з білками. Наведено хімічну структуру найдослідженіших форм оксидативних пошко...

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Date:2007
Main Authors: Скрипник, Н.В., Маслова, О.О.
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Language:Ukrainian
Published: Інститут молекулярної біології і генетики НАН України 2007
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Online Access:https://nasplib.isofts.kiev.ua/handle/123456789/157527
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Cite this:Оксидативні пошкодження ДНК / Н.В. Скрипник, О.О. Маслова // Біополімери і клітина. — 2007. — Т. 23, № 3. — С. 202-214. — Бібліогр.: назв. — укр., англ.

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spelling nasplib_isofts_kiev_ua-123456789-1575272025-02-09T12:55:34Z Оксидативні пошкодження ДНК Оксидативные повреждения ДНК Oxidative DNA damage Скрипник, Н.В. Маслова, О.О. Матеріали семінару Проаналізовано деякі характеристики основних типів оксидативних пошкоджень ДНК: модифікації азотистих основ та дезоксирибози, одноланцюгові та дволанцюгові розриви, апуринові/апіримідинові сайти, міжвалентні взаємодії ДНК з білками. Наведено хімічну структуру найдослідженіших форм оксидативних пошкоджень ДНК. Зазначено найпоширеніші генотоксичні агенти (активні форми кисню, вільні радикали, алкілуючі чинники). Розглянуто сучасні методи якісних і кількісних досліджень пошкоджень ДНК. Several characteristics of the basic types of oxidative DNA damage are analysed in the present work. They are as follows base and sugar modifications lesions, single-strand and double-strand breaks, apurinic/apyrimidinic sites and DNA-proteins cross-links. The chemical structure of the most investigated types of oxidative DNA damage is shown. The most common genotoxic agents (reactive oxygen species, free radicals, alkylating agents) are also discussed. The methods of identification and measurement of oxidative DNA damage are considered. Проанализированы некоторые характеристики основных типов оксидативных повреждений ДНК: модификации азотистых оснований и дезоксирибозы, одноцепочечные и двухцепочечные разрывы, апуриновые/апиримидиновые сайты, межвалентные взаимодействия ДНК с белками. Приведена химическая структура наиболее изученных форм оксидативных повреждений ДНК. Указаны самые распространeнные генотоксические факторы (активные формы кислорода, свободные радикалы, алкилирующие агенты). Рассмотрены современные методики качественных и количественных исследований повреждений ДНК. 2007 Article Оксидативні пошкодження ДНК / Н.В. Скрипник, О.О. Маслова // Біополімери і клітина. — 2007. — Т. 23, № 3. — С. 202-214. — Бібліогр.: назв. — укр., англ. 0233-7657 DOI: http://dx.doi.org/10.7124/bc.000766 https://nasplib.isofts.kiev.ua/handle/123456789/157527 577.21+575.857 uk Біополімери і клітина application/pdf application/pdf Інститут молекулярної біології і генетики НАН України
institution Digital Library of Periodicals of National Academy of Sciences of Ukraine
collection DSpace DC
language Ukrainian
topic Матеріали семінару
Матеріали семінару
spellingShingle Матеріали семінару
Матеріали семінару
Скрипник, Н.В.
Маслова, О.О.
Оксидативні пошкодження ДНК
Біополімери і клітина
description Проаналізовано деякі характеристики основних типів оксидативних пошкоджень ДНК: модифікації азотистих основ та дезоксирибози, одноланцюгові та дволанцюгові розриви, апуринові/апіримідинові сайти, міжвалентні взаємодії ДНК з білками. Наведено хімічну структуру найдослідженіших форм оксидативних пошкоджень ДНК. Зазначено найпоширеніші генотоксичні агенти (активні форми кисню, вільні радикали, алкілуючі чинники). Розглянуто сучасні методи якісних і кількісних досліджень пошкоджень ДНК.
format Article
author Скрипник, Н.В.
Маслова, О.О.
author_facet Скрипник, Н.В.
Маслова, О.О.
author_sort Скрипник, Н.В.
title Оксидативні пошкодження ДНК
title_short Оксидативні пошкодження ДНК
title_full Оксидативні пошкодження ДНК
title_fullStr Оксидативні пошкодження ДНК
title_full_unstemmed Оксидативні пошкодження ДНК
title_sort оксидативні пошкодження днк
publisher Інститут молекулярної біології і генетики НАН України
publishDate 2007
topic_facet Матеріали семінару
url https://nasplib.isofts.kiev.ua/handle/123456789/157527
citation_txt Оксидативні пошкодження ДНК / Н.В. Скрипник, О.О. Маслова // Біополімери і клітина. — 2007. — Т. 23, № 3. — С. 202-214. — Бібліогр.: назв. — укр., англ.
series Біополімери і клітина
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AT maslovaoo oksidativnyepovreždeniâdnk
AT skripniknv oxidativednadamage
AT maslovaoo oxidativednadamage
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fulltext Oxidative DNA dam age N. V. Skrypnyk, O. O. Maslova Na tional Taras Shevchenko Uni ver sity of Kyiv, 64, Volodymyrska street, 01033 Kyiv, Ukraine. skrypnyk@i.com.ua Sev eral char ac ter is tics of the ba sic types of ox i da tive DNA dam age are ana lysed in the pres ent work. They are as fol lows: base and sugar mod i fi ca tions le sions, sin gle-strand and dou ble-strand breaks, apurinic/apyrimidinic sites and DNA-pro teins cross-links. The chem i cal struc ture of the most in ves ti gated types of ox i da tive DNA dam age is shown. The most com mon genotoxic agents (re ac tive ox y gen spe cies, free rad i cals, alkylating agents) are also dis cussed. The meth ods of iden ti fi ca tion and mea sure ment of ox i da tive DNA dam age are con sid ered. Key words: ox i da tive stress, DNA dam age, genotoxic agents In tro duc tion. A vast num ber of dif fer ent types of DNA dam age take place in the cell at nor mal con di - tions. How ever, a strict bound ary line has to be drawn be tween DNA dam ages at nor mal con di tions and ar ti fi - cial dam ages oc cur ring in the vial. DNA dam ages may oc cur due to var i ous chem i cal and phys i cal agents of exo gen ic or endogenic or i gin. Exo gen ic agents, ca pa ble of dam ag ing DNA struc ture, in clude the fol low ing: ion iz ing ra di a tion, ul tra-vi o let ra di a tion, some med i ca tions, stain ing agents, etc. Endogenic DNA dam ag ing agents, i.e. ac tive forms of ox y gen and ni tro gen, free rad i cals, methylating agents, even at nor mal met a bolic con di tions form a sig nif i cant num ber of DNA dam ag ing fac tors. All these com po si - tions cause the dam age of DNA as a re sult of re ac tions of alkylation, hy dro ly sis, and ox i da tion, and re quire rep a ra tion. At the same time sin gle- and dou ble-strand breaks, base drop-out sites (AP-sites), base and sugar mod i fi ca tions le sions, intervalent in ter ac tion with pro - teins (cross-links) are formed. Some of the men tioned dam ages may be re paired and some of them may not. It is ev i dent that such struc tural changes will in flu ence the func tions of DNA. Mean while, there is al ways a cer - tain level of mod i fied DNA in the cell [1–5]. Cur rent re view pres ents the in for ma tion on ox i da - tive DNA dam ages only, oc cur ring both dur ing nor mal me tab o lism and ox i da tive stress con di tions. The range of these dam ages is rather wide (it in cludes ni tro gen bases mod i fi ca tions, changes in deoxyribose struc ture, chain breaks), there fore, talk ing about ox i da tive DNA dam ages, they have to be con sid ered as a com plex of dif fer ent dam ages, caused by the group of par tic u lar agents [1–5]. Types of ox i da tive DNA dam ages and the groups of agents which cause them. DNA dam ages oc cur as a re sult of a se ries of chem i cal re ac tions, i.e. redoxreaction, alkylation, hy dro ly sis, etc. The cells al - ways dem on strate a bal anced level of DNA dam age. The level of DNA dam ages, which ex ceeds the norm 10-100 times, and not the pres ence of a cer tain type of dam age, is con sid ered to be the patho log i cal con di tion in dex [1–6]. 202 ISSN 0233-7657. Biopolymers and cell. 2007. Vol. 23. ISS 3. Translated from Ukrainian. Ó N. V. SKRYPNYK, O. O. MASLOVA, 2007 Ox i da tive DNA dam ages are nu mer ous in the course of ox i da tive stress un der the in flu ence of free rad i cals and other ac tive forms of ox y gen [1–7]. Free rad i cals, which con tain un paired elec trons, are dan ger - ous and sur pris ingly re ac tion-ca pa ble com pounds. They are formed through out the time of met a bolic trans for ma tions in mi to chon dria, endoplasmic re tic u - lum, etc. Re gard less of the short half life time (1 nsec for OH·-rad i cal), free rad i cals are of sig nif i cant in flu - ence on macromolecules of the or gan ism [2, 8]. Sim ple cal cu la tions re veal that at the dif fu sion level of 500 m/sec and the size of the mol e cule with an ex ited atom or an ex ited chem i cal group of 0.5 nm, in 10-9 sec a free rad i cal can cover the dis tance of 0.5·1012 nm, which is ~1000 of its di am e ters [9]. Free rad i cals also in clude some ac tive forms of ox y gen (AFO), ni tro gen (AFN), lipid rad i cals (per ox ide – ROO·, alkoxyl RO·, etc), as well as some semiquinones (·QH). In ter act ing with a DNA mol e cule, free rad i cals may be come the rea son of chain breaks and mod i fi ca tion of bases and deoxyribose [2, 5]. AFOs rep re sent rather a wider col lec tion, com pared to free rad i cals, as this group in cludes not only free rad - i cals of ox y gen (superoxide-an ion O2 - and hydroxyl-rad i cal OH·) but also hy dro gen per ox ide, sin - glet ox y gen (with elec tron of sin glet con di tion, 1O2, com pared to nor mal, the trip let one), ozone, and some “non-clas si cal” AFOs [1, 5, 7]. These com pounds are ca pa ble of caus ing the larg est group of dam ages – the changes in struc ture of ni tro gen bases, deoxyribose, sin gle- and dou ble-strand breaks, intermolecular cross-links. All these dam ages are con sid ered as the ox i da tive stress in di ces, which have the neg a tive in flu - ence on the cell, as well as on the whole or gan ism [1–7]. The big gest con tri bu tion into the endogenic for ma - tion of ac tive forms of ox y gen is made by mitochondrial re spi ra tory chain (that is why mi to chon drial DNA is of - ten se lected to be the ob ject of ox i da tive dam age in ves ti - ga tions), the sys tem of cytochrome P-450 in the endoplasmic re tic u lum, and â-ox i da tion of fatty ac ids. These com pounds are formed in the course of other met - a bolic re ac tions as well, and some cells of im mune sys - tem (macrophages, neu tro phils, and eosinophils) neu - tral ize allogenic agents by AFOs. Exo gen ic stimu la tors of AFO for ma tion may also in clude UV rays, ion iz ing ra di a tion, and some chem i cal com pounds [1, 5, 6, 8]. On en ter ing the or gan ism, the ox y gen mol e cule has to trans - form into wa ter, by means of con nec tion of 4 elec trons and 4 pro tons, how ever, even at nor mal con di tions, 5% of ox y gen con nects not 4, but 1, 2, or 3 elec trons, which re sults in the for ma tion of AFOs, i.e. free super ox - ide-an ion O2 -, hy dro gen per ox ide (H2O2) and the most ef fec tive hydroxyl-rad i cal (OH·) (Fig.1) [8, 10]. Hy dro gen per ox ide is of low reactional ca pa bil ity, but in the pres ence of met als of al tered va lence (iron, cop per) it takes part in, so called, Fenton’s re ac tion [11]: Fe2+ + H2O2 ® Fe3+ + ·OH + OH- One more re ac tion is Harber-Weiss’ re ac tion, ac - com pa nied by the for ma tion of a sig nif i cant amount of OH-rad i cals: ·O2 - + H2O2 ® O2 + ·OH + OH- At nor mal con di tions, per ox ides are neu tral ized by en zy matic sys tems (superoxide dismutase, glutathione-peroxidase, catalase, peroxidase) and ox i - da tive stress pro tec tion is pro vided by the com plex of nat u ral an ti ox i dants, such as tocopherol, ferritin, ca rot - en oids, ascor bic and uric ac ids, etc [13]. OH-rad i cals in ter act with deoxyribose with a sub - se quent for ma tion of var i ous de riv a tives (erythrose, 2-deoxy-tetrodialdose (Fig.2)) and chain breaks, while OXIDATIVE DNA DAM AGE 203 Fig.1 AFO for ma tion dur ing four-elec tron ox y gen res to ra - tion in the cell their in ter ac tion with all types of ni trog e nous bases re - sults in the for ma tion of hun dreds of in ter me di ate prod - ucts [2]. Due to in sta bil ity of the ma jor ity of formed in ter - me di ate prod ucts the bio chem i cal specificities of only some of them were de fined clearly. The main forms of ox i da tive dam ages of ni trog e nous bases are shown in Fig. 3 [1, 5]. The vast ma jor ity of dam ages, caused by OH-rad i - cals, were stud ied in vi tro and in vivo us ing g-ir ra di a tion [1, 3]. Hydroxyl-rad i cal is ca pa ble of rip ping of the hy - dro gen atom from thy mine methyl group and from each one of C-H bonds of 2'-deoxyribose [1]. Cou pling of dou ble bounds in the bases is char ac ter ized by spe cific ve loc ity con stant of 3-10·109 M–1·sec–1 and hy dro gen atom rip ping ve loc ity was shown to be 2·109 M–1·sec–1. C4-C5 is OH-rad i cal sen si tive in py rimi dines whereas C4, C5, C8 – in pur ines. The at tack of hydroxyl-rad i cal re sults in dif fer ent mod i fi ca tions of py rim i dine bases, i.e. for ma tion of 5-OHdU (Fig.3, b), 5-OHdC (Fig.3, d), uracyl gly col (Fig. 3, e), thy mine gly col (Fig. 3, f) and some other com pounds [1–7]. The in ter ac tion of OH-rad i cal with pur ines also leads to some changes – the for ma tion of formamidopyrimidine (Fapy), 8-oxoguanine (8-OHdG) (Fig. 3, a) (ba sic ox i da tive stress marker in vi tro and in vivo), 8-hydroxideoxyadenosine (8-OHdA) (Fig. 3, c), etc. Fapy is an open imidazole cir cle gua nine 2,6-diamine-4-hydroxy-5N-methyl-formamidopyrimi dine (Fapy-G) (Fig. 3, g) and 4,6-diamino-5-formamidopyrimidine (Fapy-A) (Fig. 3, h) [1]. The for ma tion of 8-OHdG or al most equiv a lent 8-oxo-7,8-dihydroguanine (8-oxo-G) is the most com - mon re sult of ox i da tive dam ages. All these com pounds turn eas ily into one an other, thus, they are usu ally called 8-oxo-G. The quan ti ta tive anal y sis of 8-oxo-G is most com monly car ried out in or der to de ter mine the level of ox i da tive stress. It co mes from high con tents of these com pounds in the cells as well as the pres ence of a large amount of rel a tively ob jec tive re search meth ods [1–7]. The whole se ries of com mer cial kits for quan ti - ta tive anal y sis have been de vel oped now a days [1, 4, 14, 15]. Glycols and hy drates of cy to sine lead to transversion as a re sult of aminogroup rip ping more of - ten, com pared to nor mal cy to sine [1, 16]. Ad di tional com pounds of ni trog e nous bases with OH-rad i cal is the group of com pounds hav ing oxi dis ing/reductive am - biv a lence and ca pa ble of be ing a part of com plex re ac - tions [1]. Some mod i fied bases be come free rad i cals and re - sult in chain re ac tions. For in stance, cy to sine rad i cals C5-OH-6-peroxile and C6-OH-5 are in volved in the for ma tion of 4-amino-5-hydroxy-2,6(1H,5H)-py rim i - dine dion and 4-amino-6-hydroxy-2,5(1H,6H)-py rim i - dine dion [1, 3, 5]. DNA in ter act ing with ozone, sin glet ox y gen and other AFK, also re sults in the for ma tion of a se ries of ni tro gen bases de riv a tives [3, 4]. Of ten ni tro gen ox ide (NO) is formed in the cell out of arginine ac com pa nied by NO-synthetase. Its [arginine] in ter ac tion with DNA re sults in deaminization of bases and oc cur rence of tran si tions [6]. Hypochlorite (ClO–) in duces the dam age spec trum, sim i lar to the ef fect of sin glet ox y gen [3, 4]. Ul tra-vi o let light in duces the for ma tion of so called py rim i dine dimers of two types (Fig. 4) [17, 18]. Vis i ble light brings up the re ac tions, iden ti cal to those caused by sin glet ox y gen and flu o rine re ac tions of type I (con nected with the ef fect of photo sensitizers, e.g. hematoporphyrin, ri bo fla vin, meth y lene blue, etc) [3, 4]. How ever, sim i lar re ac tions are dif fer ent from those caused by OH-rad i cal, which causes al most equal amounts of breaks, AP-sites and dif fer ent mod i fi ca - tions of bases. Mean while, sin glet ox y gen and the ma - jor ity of photosensitizers lead to dam ages, ba si cally, sen si tive to the ef fect of en zyme of ex ci sion re pair of formamidopyrimidine-DNA-glycosylase, 8-oxo-G and formamidopyridines [3, 4, 18, 19]. A sig nif i cant num ber of ox y gen ac tive forms ap - pears dur ing the in flam ma tory pro cesses, which is the SKRYPNYK N. V., MASLOVA O. O. 204 Fig.2 Deoxyribose de riv a tives, formed as a re sult of hydroxyl rad i - cal at tack re sult of the ac tiv ity of cells of im mune sys tem. NADN-oxidase en zymes and myeloperoxidase, which form OH-rad i cals and hypochlorite, which, in a turn, are in volved in elim i na tion of allogenic agents, take an ac tive part in the pro cesses of ac ti va tion of macrophages. There fore, the ox i da tive stress is con sid - ered to be one of the in di ca tors of chronic in flam ma - tions [1, 6, 10]. The intervalent in ter ac tions of nu cleic ac ids and pro - teins rep re sent one more type of free rad i cals-in duced dam ages (es pe cially, by hydroxyl rad i cal and malondialdehyde) [1, 2]. The most vivid ex am ples of this group are thy mine-ty ro sine and thy mine-lysine in ter ac - tions. Thy mine is also ca pa ble of in ter act ing with glyc - erol, alanine, valine, leucine, isoleucine, and threonine. Some times cy to sine in ter acts with ty ro sine [2]. DNA alkylation is the pro cess of spon ta ne ous (with out any in ter fer ence from the en zy matic sys tems of or gan ism) bind ing of alkyl group in cer tain po si tion of the ni trog e nous base [20]. Alkyl group may be OXIDATIVE DNA DAM AGE 205 Fig.3 The most com mon mod i fi ca - tions of ni trog e nous bases as a re - sult of AFO ef fect shifted in the form of car ban ion, carbcation or free rad i - cal. Alkylating agents com prise rather a large group of com pounds ca pa ble of dam ag ing the struc ture of macromolecules. They can also bind alkylating side groups (methyl, ethyl, propyl, butyl groups, etc). Alkylating fac tors are clas si fied ac cord ing to the type of the trans ferred group, and also ac cord ing to the num - ber of such groups (mono-, bi-func tional, etc agents). The most com mon to be bound are the methyl groups [20-23]. DNA alkylation is not the sub ject of cur rent re search, how ever, some of its ba sic fea tures are go ing to be pre sented, as ox i da tive stress re sults in in crease in DNA dam ages by other agents as well [5]. Alkylating agents can be of exogenic and endogenic or i gin. Exo gen ic ones in clude epoxides, â-lac tones, diazocompounds (dia zo me thane (CH2N=N), nitrocompounds (N-methyl-N-ni tro-N- nitrosoguanidine CH3N(NO)C(=NH)NHNO2), etc). The lat ter is con sid ered to be one of the most dan ger ous exo gen ic alkylating agents, at the same time, S-adenosylmethionine is one of the most dan ger ous ones among endogenic alkylating agents. Some of the agents have been used as anti-tu mour drugs [20]. O6-methylguanine, O4-alkylthymine, 3-methyladenin, 7-methylguanine, and 7-ethylguanine, ca pa ble of bind ing thy mine (Fig. 5), are con sid ered as the most com mon prod ucts of alkylation of ni trog e nous bases [20]. N-1, N-2, N-3, N-7, O-6 gua nine, N-1, N-3, N-6, N-7 ad e nine, N-3, N-4 O-2 cy to sine, and N-3, O-2, O-4 SKRYPNYK N. V., MASLOVA O. O. 206 Fig.4 UV-formed prod ucts: a – cyclobutane dimers, b – 6-4-dimers, c – thy mine-thy mine dimers thy mine are the sites, alkylation of which may re sult in mu ta tions (Fig. 6) [21-23]. The specificities of DNA alkylation are de scribed in some re views [24, 25]. The hy dro ly sis-caused dam ages re sult in sev eral types of dam ages: deaminization, depurination, and depyrimidination, i.e. the for ma tion of lost bases sites (AP-sites) [1, 20]. Ura cil is formed as a re sult of loss of the amino group out of cy to sine (Fig.7), xanthine out of gua nine, and hypoxanthine out of ad e nine [16]. Deaminization of cy to sine and its de riv a tives is con sid ered to be the most dan ger ous one. Thy mine is formed as a re sult of deaminization of 5-methylcytosine (Fig.8) [20]. The ap pear ance of AP-sites is rather a com mon group of dam ages. Pu rine bases are lost eas ier than py - rim i dine ones. These kinds of pro cess of ten take place in brain, heart, liver, in tes ti nal ca nal, and not so of ten – in kid neys and lungs. Also AP-sites ap pear as a re sult of the ef fect of rep a ra tion en zymes. For in stance, glykolases cut out the mod i fied base af ter the ap pear - ance of AP-site. The rea son of their for ma tion is the hy - dro ly sis of N-glycosyl bonds as well as the at tack of free rad i cals in po si tions 1', 2' or 4' of deoxyribose (Fig.9) [5, 26, 27]. Meth ods of quan ti ta tive and qual i ta tive anal y ses of DNA dam ages. The meth ods of in ves ti ga tion of ox i - da tive, as well as other DNA dam ages may be di vided into two groups. The first group in cludes the meth ods, ap pli ca tion of which re quires hy dro ly sis of mol e cules, the sec ond one in cludes the meth ods used to study the whole mol e cule [5, 7, 13, 17]. In or der to per form flu o res cent, chro mato graphic and some ra dio log i cal in ves ti ga tions, DNA has to be prior chem i cally or en zy mat i cally hy dro lysed. The larg est sub group is the group of chro mato graphic meth - ods, the most ef fec tive one among which is the method of high res o lu tion liq uid chro ma tog ra phy, com bined with elec tro chem i cal de tec tion (HPLC-ECD), as well as the method of gas chro ma tog ra phy with mass-spec - trom e try (GC/MS) [3, 5, 7, 13, 17, 28]. The ap pli ca tion of the sec ond group of meth ods re - quires some spe cial en zymes [3, 5]. Af ter the en zy - matic treat ment, the ma te rial is ana lysed us ing sin gle cell gel-elec tro pho re sis (SCGE), method of al ka line elu tion [29] etc. OXIDATIVE DNA DAM AGE 207 Fig.5 The for ma tion of hy dro gen bonds be tween elec tron-neu tral 7-ethylguanine and thy mine Fig.6 Sites of pos si ble alkylation of ni trog e nous bases (cir cled) Fig.7 Deaminization of cy to sine with uracyl for ma tion The ap pli ca tion of such en zymes as formamidopyrimidine-N-glycosylase (fpg), as well as its eukaryotic homo logues (par tic u larly, hOGG1), and endonuclease III is rather pop u lar [30-33]. There is a whole se ries of com mer cial kits for de ter min ing the DNA dam ages us ing the en zymes. Bac te rial glycolases are the most com monly used, how ever, some man u fac - tur ers sup ply their kits with hu man and yeast homo - logues of these en zymes [17, 31]. fpg is a very con ve - nient ap pli ca tion-wise en zyme, which con sists of 269 amino acid res i dues and its mo lec u lar weight is 30.2 kDa. Pro tein cod ing gene con sists of 807 pairs of nu - cleo tides. fgp re cog nises 8-oxo-G, formamidopyrimidines (pur ines with open imidazole cir cle and) is ca pa ble of cut ting out AP-sites, i.e. is of lyase ac tiv ity. fgp is max i mally ac tive at pH val ues in the range of 6.5 to 8.5 and fpg does not re quire two-va - lence cat ions [30, 33]. The method of comet tar get ing con sists in the as - sess ment of the de gree of DNA dam age, based on the cor re la tion of the length of the “tail”, which is formed dur ing the move ment of the dam aged nu cleic acid re - gions dur ing elec tro pho re sis, and the di am e ter of the nu cleus, where un dam aged DNA is con cen trated [13]. Flu o res cent dyes, i.e. acridine or ange, ethidium bro - mide, propidium bro mide, and the most re cent one SYBR®Green, are used for visu ali sa tion [34]. Com plete DNA is ana lysed by im mu no log i cal meth ods as well. These meth ods in clude ELISA tests (e.g. ARP-test), ra dio-im mune anal y sis, and Im mune slot blot method, all of them are rather con ve nient, al - though, not sen si tive enough for qual i ta tive anal y sis [16, 17, 35]. The meth ods used to study the dam ages of ge netic ma te rial, ac cord ing to the type of in ter fer ence, are clas - si fied into in va sive and non-in va sive (the lat ter in clude the de ter mi na tion of the amounts of dam aged DNAs in urine) [17, 26, 36]. The se lec tion of meth ods which are the most ra tio - nal to be used for study ing DNA dam ages is a very dif - fi cult task. The search for the most ad e quate method has been in pro cess for sev eral de cades, how ever, the prob lem re mains un solved. The dif fer ence be tween the re sults, ob tained us ing sev eral dif fer ent meth ods, is amaz ing [17]. Thus, the data ob tained us ing GC/MS, re veal the level of 8-OHdG in the cells to be at the hun - dreds of res i dues per 106 of nor mal guanines. HPLC-ECD al lowed ob tain ing the re sult be ing at ~5–50 res i dues per 106 of guanines. The en zy matic re - search us ing fpg and sub se quent ap pli ca tion of meth ods SKRYPNYK N. V., MASLOVA O. O. 208 Fig.8 re ac tions of methylation and fur ther deaminization of cy - to sine of comet tar get ing or alkylating un twist ing re vealed 0.5 of 8-OHdG res i due per 106 of guanines [3, 13, 17, 28, 37, 38]. Pre sented dis ar range ments of the re sults are ex plained by the ap pear ance of artefacts in the course of in ves ti ga tion, re lated to the prep a ra tion of the ma te rial, DNA iso la tion, etc. Be sides, the state of the in ves ti - gated mol e cule de pends on the pres ence of cer tain en - zymes, endonucleases in par tic u lar [3, 28, 37, 38]. The method of quan ti ta tive poly mer ase chain re ac - tion (Q-PCR) has be come pop u lar in the re cent years. This method is based on the ca pa bil ity of some forms of DNA dam ages to block rep li ca tion, de creas ing the am - pli fi ca tion ef fi ciency [7, 37]. Some qual i ta tive data are pre sented in lit er a ture sources. The num ber of events, ca pa ble of pro vok ing a de struc tive in flu ence on the ge netic ma te rial of cells var ies, ac cord ing to dif fer ent data, from 74,000 to 500,000 per twenty-four hours [28]. It is known that the for ma tion of 8-OHdG, or al most iden ti cal to it 8-oxo-G, is the most com mon re sult of ox i da tive dam - age (from 7,500 to 200,000 mod i fi ca tions of the cell per day) [16, 28]. The fre quency of 7-methylguanine for - ma tion in the cell is app. 4,000 events per day. 3-methyladenine is con sid ered to be one of the most com mon mod i fied bases with high for ma tion fre quency (sev eral hun dreds events per day) [39]. The ap pear ance of AP-sites is one of the most wide-spread forms of dam age – around 200,000 bases are lost a day. Some data pres ent the level of spon ta ne ous depurination at nor mal con di tions to be at 10,000 bases per day [27]. A se ries of prob lems does arise when the num ber of cer tain dam ages (8-oxo-G, for ex am ple) has been es ti - mated. A num ber of works with ar ti fi cially syn the sised oligonucleotides with a known amount of 8-oxo-G were car ried out [17]. The re sults ob tained dem on strate that HPLC method un der es ti mates the level of dam ages de tected sig nif i cantly. The in ves ti ga tions which in - volved phe nol for pro tein pu ri fi ca tion, re vealed the op - po site re sults, i.e. sig nif i cant over es ti ma tion, as it is com monly-known, phe nol is ca pa ble of dam ag ing nu - cleic ac ids. The ap pli ca tion of so dium io dide re vealed the lack of 8-oxo-G, which may be ex plained by the ca - pa bil ity of so dium to re pair the dam ages [3, 13, 17, 40]. Some sci en tists con sider the de ter mi na tion of the DNA dam ages in the in tact cells to be the best way to avoid the afore men tioned prob lems. Im mu no log i cal meth ods are suit able for these pur poses, al though, the use of an ti bod ies is rather ef fi cient for visu ali sa tion of dam ages, yet it re mains semi-quan ti ta tive one. The method of comet tar get ing is a con ve nient method, but the ap pli ca tion of this method un der es ti mates the amounts of 8-oxo-G as well. Pos si bly it is due to the fact that the en zymes do not reach the chromatin “depths” and two closely lo cated dam ages may be cut out as one. One more pop u lar method is the method of GC/MS, but it has ear lier been men tioned to over es ti - mate the quan ti ta tive in di ces [7, 17, 28, 40, 41]. There - fore, now a days nei ther one of known meth ods pro vides cor rect data on the num bers of DNA dam ages due to sig nif i cant dis ar range ments of the re sults, which leads to the use of com par a tive anal y sis, re gard less of the in - di ca tion of ex act nu mer i cal val ues [7, 13, 17, 28]. It is wor thy to be noted that to day spe cial at ten tion is paid to the study ing of the dam ages of mi to chon drial OXIDATIVE DNA DAM AGE 209 Fig.9 Scheme of pos si ble AP-site DNA. The de gree of its (mi to chon drial DNA) ox i da tive dam age can be in ter preted as the in dex of or gan ism age. How ever, on the other hand, the iso la tion of mi to chon - drial DNA as such is ac com pa nied by sig nif i cant ox i da - tive dam age, which over es ti mates the in di cated level of mi to chon drial dam ages es sen tially [37, 38, 40, 42]. There fore, there are no clear data on the num ber of 8-oxo-G as well as other mod i fi ca tions in nor mal young, age ing, or sick cell at the mo ment. All the re sults may be con sid ered to be of rel a tive cor rect ness due to the ab - sence of one and com mon re cal cu la tion co ef fi cient for the num ber of dam ages. The dif fi culty of ob tain ing quan ti ta tive data is ac com pa nied by the fact that ex act num bers of dam ages in the cell un der the in flu ence of a cer tain agent may be ob served at the mo ment of the ef - fect of this agent only, as the rep a ra tion sys tems are work ing con stantly. Thus, the meth ods of study ing DNA are be ing im proved and mod i fied with the pur pose of achiev ing higher lev els of their sen si tiv ity, as well as of max i mal de creas ing the level of dam ages in the course of pre lim i nary treat ment of the ma te rial and elim i na tion of artefacts [1, 3, 5, 7, 17, 28]. Of ten there is a ques tion, aris ing in the course of de ter min ing cer tain dam ages, ox - i da tive ones, for in stance, oc cur ring in the cell – Is DNA dam age a rea son or a con se quence? Main tain ing the in teg rity of ge nome is the mo ment of spe cial im por tance for proper func tion ing of or gan - isms, which is com pli cated by the pres ence of the whole se ries of var i ous fac tors, ca pa ble of loos en ing the ge - nome con sis tency. A num ber of works are ded i cated to the bi o log i cal con se quences and the im por tance of ox i da tive dam ages of DNA, how ever, the pres ent re view shall pres ent only some of gen eral no tions. The prob lem of ox i da tive stress is con sid ered to be one of the most cur rent bi o log i cal prob lems in the course of the re cent de cades. The dam ages of the ge - netic ma te rial, oc cur ring as a re sult of the ef fect of ac - tive ox y gen forms on DNA, are con sid ered to be one of the con stit u ent parts of this no tion [1–7, 17]. The ques tion of the role of ox i da tive dam age of DNA in the pro cesses of mu ta gen e sis, carcinogenesis, and age ing, at tract the most of at ten tion now a days [1–7, 12, 13]. A se ries of pub li ca tions have been ded i cated to the in ves ti ga tion of free-rad i cal the ory of age-re lated changes in the or gan ism. Un for tu nately, the ap pli ca - tion of var i ous meth ods of quan ti ta tive anal y sis of ox i - da tive stress mark ers (e.g. 8-OHdG) pro vides dif fer ent re sults [1, 7, 17, 28]. How ever, ev i dent is the fact that some mod i fi ca tions re sult in mu ta tions, stim u late carcinogenesis, ac ti vat ing proto-onco genes and in hib it - ing can cer-suppressors, in flu ence the reg u la tion of cell cy cle, the course of tran scrip tion and rep li ca tion pro - cesses, and par tic i pate in the de vel op ment of age ing pro cesses [1, 3, 7, 43]. It is also known that some DNA dam ages oc cur in the cases of car dio vas cu lar dis eases, ner vous sys tem dis eases etc. One of the hy poth e ses of age ing is the hy poth e sis of in hib ited rep a ra tion sys tem with the course of time (age ing), which re sults in ac cu - mu la tion of er rors in DNA [1–8, 32]. As of to day, there is not a sin gle doubt that chem i - cal re or gani sa tion of DNA may re sult in sig nif i cant changes, i.e. tran si tions, transversions, and de le tions [1, 3, 4]. It has been dis cov ered that the high est mutagenic ca pac ity is spe cific to O6-methylguanine and O4-alkylthymine [20–22]. 8-oxo-G is also a mutagen and, as a part of nucleoside triphosphate, it is mounted into DNA on the op po site side to ad e nine on the DNA tem plate, re sult ing in G:C®T:A transversions [1–7]. How ever, 8-oxo-G does not block rep a ra tion and tran scrip tion and has no in flu - ence on the cell cy cle [3], op po site to thy mine gly col, a rather com mon dam age, which hin ders the rep li ca - tion and is con sid ered to be po ten tially le thal for the cell [1]. Formamidopyrimidines have got the ca pac ity to block polymerases as well [1, 4]. Deaminization of 5-methylcytosine is of mutagenic na ture, which re sults in the for ma tion of T:G pair [1, 20]. Be sides mutagenic ca pac ity, dam ages of DNA ac ti vate the pro cess of malignization of cells [1, 6, 12, 44]. Carcinogenesis may take place in two pos si ble sce nar ios – some DNA dam - ages are ca pa ble of ac ti vat ing proto-onco genes, p21, c-myc, c-Ha-ras, in par tic u lar, or in hibit can cer-sup pres - sor genes, e.g. p53, Rb [43, 45, 46]. Valid data tes ti fy ing to the pres ence of 8-OHdG sur plus in vivo in ras-onco - gene and can cer-sup pres sor gene p53 in cases of lung, liver, and in tes tine can cer have been ob tained [47–51]. Breast can cer has been proven to be con nected with the ac cu mu la tion of DNA dam ages due to ox i da tion and alkylation [52]. The link be tween the amounts of ox i - da tive dam ages of DNA due to age ing and pros tate can - cer has been re vealed [53]. SKRYPNYK N. V., MASLOVA O. O. 210 There are two known types of ef fect of mod i fied DNA on cell cy cle – the ac cel er at ing one, caus ing malignization, and the de cel er at ing one, re sult ing in apoptosis [1, 42, 54]. It has to be em pha sized spe cif i cally that the works of the last three years re veal a grow ing num ber of ox i - da tive dam ages of DNA in the course of in flam ma tory pro cesses. As a re sult, a clear cause-and-ef fect con nec - tion be tween the con di tion of the cell and the con di tion of its ge netic ma te rial is ev i dent [1, 5, 6, 28]. The pro cesses of age ing are gen er ally re lated to both pro grammed events and ac cu mu la tion of er rors. Free-rad i cal the ory of age ing, or ox i da tive stress the - ory, is con sid ered to be the most pop u lar one as it in - cludes the pro vi sions at tempt ing to ex plain pro gram - ma bil ity and ac cu mu la tion of er rors [42]. Ac cord ing to the given the ory in the course of the life of or gan ism (even at nor mal me tab o lism) a great num ber of free rad - i cals are formed, which in clude ac tive forms of ox y gen, caus ing the dam age of bi o log i cal macromolecules with sub se quent dis or der ing of reg u la tory pro cesses [1, 15, 40, 42, 44]. The hy poth e sis of pos si ble role of free rad i - cals in the pro cesses of age ing has been pro posed by Garman in the 1950s. In 1990 the pos si bil ity of ef fect of DNA ox i da tion on the pro cess of age ing has been de - fined clearly [36, 40]. The re sults ob tained dem on - strated a 2-3 times in crease in 8-oxo-G amount in ex - per i men tal rats. How ever, these re sults turned out to be not per sua sive enough, leav ing the room for doubts due to the fact that the in ves ti ga tion was car ried out on DNA, iso lated by us ing phe nol, and as a re sult the oc - cur rence of artefacts was highly pos si ble [1, 3, 7]. Some sci en tists con sider the in ves ti ga tion of DNA, iso - lated us ing so dium io dide to be more con vinc ing. This method al lows ob tain ing more ac cu rate re sults with out any ad di tional dam ages [14, 17]. Ac cord ing to these data, the level of ox i da tive dam ages of DNA in ro dents in creases sig nif i cantly with age (from 3 8-OHdG res i - dues per 108 res i dues in young mice to 8 per 108 res i - dues in the old ones) [7, 14, 17, 31, 42]. A sig nif i cant num ber of works are ded i cated to the com par i son of the amounts of dam aged DNA in mitochondrias and nu cleus, as mi to chon drial DNAs are con sid ered to be the place of ac cu mu la tion of er rors [37, 38]. The pro cess of DNA alkylation is con sid ered to be rather dan ger ous – it can re sult in mu ta tions and de vel op ment of tu mours. 3-methyladenine in flu ences the pro cess of rep li ca tion, O6-methylguanine and O4-alkylthymine are con sid ered to be of mutagenic or i - gin, and 7-methylguanine is con sid ered to be a rel a - tively harm less com pound (which can be ex plained by in suf fi cient in for ma tion on its specificities) [20, 22, 26]. How ever, the thought does ex ist that methylation of cy to sine may be con sid ered a norm (as one of epigenetic mech a nisms). This is sue is a topic for a ded i - cated dis cus sion, which has a sig nif i cant num ber of works de voted to [55-57]. The most com mon place for methylation in hu man adult so matic cells is CpG-re - gions (app. 70% of them are meth yl ated), at the same time, so called, non-CpG-methylation, is ob served in em bry onic stem cells. At early stages of de vel op ment (from cell fer til iza tion to the stage of eight cells) eukaryotic ge nome is non-meth yl ated. Start ing from the stage of eight cells and to morula methylation de novo takes place. At the stage of blastula the pro cesses of methylation, which pro vide epigenetic re-pro gram - ming, are com pleted [55-57]. The is sue of rep a ra tion is not the topic of cur rent re - view, yet it has no be noted that the pres ence of sys tems of ef fec tive rep a ra tion of DNA dam ages proper pro - vides the sta ble con di tion of the cell. The is sue of rep a - ra tion was re viewed in de tail in nu mer ous pub li ca tions [26, 32]. The rep a ra tion of the bulk of DNA dam ages is re - lated to the pres ence of base ex ci sion re pair (BER) and nu cle o tide ex ci sion re pair (NER) [20, 26]. The first type of re pair is fast and rel a tively sim ple, at the same time it re quires the pres ence of sev eral groups of en - zymes, namely, glykolases, endonucleases, exonucleases, polymerases, and lyases. It is wor thy to be no ticed that the elim i na tion of dam aged re gions takes place in a short time – some data show that hu man lung ep i the lium cell is ca pa ble of get ting rid of dam ag - ing mod i fi ca tions in 8–65 min (de pend ing on the form of dam age) [7]. BER is con sid ered to be the main type of cor rec tion of er rors, formed as a re sult of alkylation and ox i da tion of DNA. The de fects of BER lead to ge - nome in sta bil ity and in flu ence the cell cy cle, which re - sults in carcinogenesis or apoptosis [1, 26, 32]. NER pro vides neu tral iza tion of er rors in the re gion of sev eral nu cleo tides (elim i na tion of cyclobutane OXIDATIVE DNA DAM AGE 211 dimers, intermolecular cross-links, etc). This type of rep a ra tion re quires more time and is con di tioned by the ac tiv ity of more than 20 dif fer ent types of en zymes. NER can be di vided into two sub types, i.e. global ge - nome re pair and tran scrip tion-re lated rep a ra tion. Var i - ous dis eases, e.g. xeroderma, trichothiodystrophy, Cockayne’s syn drome, are of ten to oc cur dur ing NER dis or ders [1, 7, 20, 26, 32]. The mod i fi ca tions, formed as a re sult of alkylation, are re paired with highly-spe cial ised en zymes of alkyltransferases [26]. The re pair of prod ucts of deaminization of ni trog e - nous bases is con sid ered to be im por tant as well. The tran si tions, which oc cur due to these dam ages, are re - vealed dur ing he red i tary dis eases, plac ing this group of mod i fi ca tions among the most dan ger ous ones. The en - zymes, ca pa ble of cor rect ing the dam ages, caused by deaminization, are as fol lows: T:G DNA-glycosylase, uracyl-DNA- glycosylase etc. [20, 26]. Yet the part of dam ages may be cor rected by di rect elim i na tion of chem i cal groups. Thus, the ex ci sion of O6-methylguanine is pos si ble with the en zyme of nar - row sub strate spec i fic ity – MGMT – O6-methylguanine-DNA-methyltransferase [23, 26]. The cor rec tion of sites of lost bases is per formed by AP-endonucleases [27]. Dou ble strand dam ages of DNA are of ex treme im - por tance. These dam ages re sult in le thal con se quences for the cell. Dou ble strand DNA dam ages take place when the mol e cules are over-loaded with var i ous dam - aged com po nents, which hap pen to oc cur un der the in - flu ence of a strong de struc tive agent, ir ra di a tion, for in - stance. These dam ages are very hard to be cor rected [20, 26, 32]. The ma jor ity of DNA dam ages formed in the cell can be re paired. How ever, their over-ac cu mu la tion may re sult in ir re vers ible changes, le thal case in par tic - u lar [1, 7, 26, 58, 59]. Fi nally we have to men tion that the ab sence of clear quan ti ta tive, and some times qual i ta tive, re sults brings up the ne ces sity of de tailed in ves ti ga tion on this prob - lem. The se lec tion of ap pro pri ate method, which in - cludes the fac tors of the form of dam age and the type of the in ves ti gated cells is the is sue of spe cial im por tance. Some forms of dam ages have not been stud ied well-enough due to their bio chem i cal specificities, whereas some – due to their in sig nif i cant quan ti ties in the cells [1–7]. It should be taken into ac count also that, as it fol lows from the com mon prac tice, the re sults, ob - tained dur ing the in ves ti ga tion of the iso lated DNA and of the ge netic ma te rial from in tact cells, might dif fer sig nif i cantly. Be sides, DNA dam ages, de fined in the cells in deed are the part of bal anced damageability of ge nome. Only a small num ber of works pres ent the in - for ma tion on the dam ages in dy nam ics. All quan ti ta - tive de ter mi na tions of DNA mod i fi ca tions pres ent their con stant level of some sort. The pro cess of ac cu mu la - tion of dam ages is the re sult of misbalance in dam - age/re pair ra tio [1, 7]. There is al most no doubt in re gards to that fact that hav ing ob tain ing data on the DNA con di tion, it is pos si - ble to make a con clu sion on func tional con di tion of the cell. The stud ies on the specificities of DNA dam ages will also pro vide better un der stand ing of carcinogenesis and age ing. Í. Â. Ñêðèï íèê, Î. À. Ìàñ ëî âà Îêñè äà òèâ íûå ïî âðåæ äå íèÿ ÄÍÊ Ðå çþ ìå Ïðî à íà ëè çè ðî âà íû íå êî òî ðûå õà ðàê òå ðèñ òè êè îñíîâ íûõ òè - ïîâ îêñè äà òèâ íûõ ïî âðåæ äå íèé ÄÍÊ: ìî äè ôè êà öèè àçî òèñ - òûõ îñíî âà íèé è äåç îêñè ðè áî çû, îä íî öå ïî ÷å÷ íûå è äâóõ öå ïî ÷å÷ íûå ðàç ðû âû, àïó ðè íî âûå/àïè ðè ìè äè íî âûå ñàé òû, ìåæ âà ëåí òíûå âçà è ìî äå éñòâèÿ ÄÍÊ ñ áåë êà ìè. Ïðè âå äå íà õè - ìè ÷åñ êàÿ ñòðóê òó ðà íà è áî ëåå èç ó÷åí íûõ ôîðì îêñè äà òèâ íûõ ïî âðåæ äå íèé ÄÍÊ. Óêà çà íû ñà ìûå ðàñ ïðîñ òðàíe ííûå ãå íî - òîê ñè ÷åñ êèå ôàê òî ðû (àê òèâ íûå ôîð ìû êèñ ëî ðî äà, ñâî áîä - íûå ðà äè êà ëû, àë êè ëè ðó þ ùèå àãåí òû). Ðàñ ñìîò ðå íû ñî âðå ìåí íûå ìå òî äè êè êà ÷åñ òâåí íûõ è êî ëè ÷åñ òâåí íûõ èñ ñëå - äî âà íèé ïîâðåæäåíèé ÄÍÊ. Êëþ ÷å âûå ñëî âà: îêñè äà òèâ íûé ñòðåññ, ïî âðåæ äå íèÿ ÄÍÊ, ãå íî òîê ñè ÷åñ êèå àãåí òû. REFERENCES 1. Cooke M. S., Evans M. D., Dizdaroglu M., Lunec J. 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