**2. Oxidative damage of DNA in the striatum from patients with neurodegenerative diseases**

It is widely recognized that 8-oxo-7,8-dihydro-2′-deoxyguanosine (8-oxo-dG) and 8-oxo-7,8-dihydroguanosine (8-oxo-G) may act as biomarkers of oxidative damage to DNA and RNA, respectively [1]. Studies by Li et al. have reported the levels of DNA adducts in the caudate and putamen of the disease groups and age-matched controls [21]. Compared to controls, remarkable reductions in DNA

**209**

**Figure 1.**

*The Striatal DNA Damage and Neurodegenerations DOI: http://dx.doi.org/10.5772/intechopen.93706*

ization by VMAT2 [28].

oxidation adducts were observed in the caudate of PD and DLB brains, including males and females. However, in the caudate of AD brains, these levels were elevated. This finding was especially pronounced for male AD patients, as adduct levels were 36% elevated compared to controls (**Figure 1**). The concentrations of 8-oxo-dG in the putamen of the disease groups were similar to the controls. Comparing between caudate and putamen, there were impressive elevations in adduct levels in the caudate, especially for the AD brains. These data indicate that the caudate is more

RNA bases are more exposed and vulnerable to oxidative damage than DNA as they are not protected by hydrogen bonding and specific proteins. RNA oxidation has been described as a "steady-state" marker of oxidative lesions [22]; however, DNA oxidation has been believed to be a historical marker of oxidative damage during disease pathogenesis and aging progression [23]. Increased 8-OHdG levels have been documented in PD patients [24–26], but as shown in **Figure 1**, a noticeable reduction of DNA oxidation adducts in the caudate was observed in the late-stage LBD brains. It was not unique; the urinary concentration of 8-OHdG in the MFB 6-hydroxydopamine lesion model started to elevate at day 3 with a significant increase to day 7 and gradually back to baseline at day 42 [27]. The increased 8-oxodG levels in the caudate of AD brains connected with the increase in dopamine levels of the same cases. These phenomena are most likely due to the Fenton reactions taking place—in response to dopamine release and dopamine compartmental-

*8-oxo-dG levels in the caudate and putamen of patients with diseases (PD: n = 10, PDD: n = 7, DLB: n = 10, and AD: n = 26) and age-matched controls (n = 10). Values shown are means ± SEM as the concentration of 8-oxo-7,8-dihydro-2*′*-deoxyguanosine (8-oxo-dG) (pg) per total DNA (μg). (a) Female and (b) male.*

vulnerable to DNA damage than the putamen in advanced AD patients.

*The Striatal DNA Damage and Neurodegenerations DOI: http://dx.doi.org/10.5772/intechopen.93706*

*DNA - Damages and Repair Mechanisms*

brains.

disease (LBD) [12].

age at the onset of diseases.

generative patients will be presented.

**neurodegenerative diseases**

lateral sclerosis (ALS) [4–9]. The elevated DNA strand breaks and the decreased DNA double-strand breaks (DSBs) repair proteins have been described in AD

Striatal dopaminergic dysfunction probably is involved in both AD and LBD, while degeneration of nigrostriatal dopaminergic neurons is the classic pathology of PD; striatal dopaminergic dysfunction may also promote the motor manifestations of AD. The striatum consists of several subregions—caudate and putamen. The caudate nucleus is essential in many behaviors, including procedural learning and working memory; the dorsal posterior putamen receives its primary input from the motor and sensorimotor cortices and regulates the motor circuits [13–15]. Dopamine generates hydroxyl radical (•OH) through Fenton reactions in the presence of iron, which is believed to be responsible for the oxidative damage to lipids, proteins, and DNA in living cells and dopaminergic neurons [16]. Besides, as a chelator, dopamine can form different complexes with Fe(II) and Fe(III), decreasing catalytic productions of ROS [17]. Dopamine compartmentalization has been described by the vesicular monoamine transporter 2 (VMAT2)—correlates with dopaminergic neurons' vulnerability in Parkinsonism neurodegeneration [18]. There are close interactions among oxidative damage and dopamine concentration, and the antioxidant role of VMAT2 should be given more attention. Oxidative stress induced by genetics has been linked to the Y-chromosome gene products that modulate dopamine biosynthesis and motor function [19]. Further, DNA damage is associated with acceleration of the rate of aging, causing a variety of early symptoms such as gray hair, kidney disease, cataracts, osteoporosis, and neuronal atrophy [20]—factors which determine the health or disease people's life span and

Therefore, it is clear that there is an appreciable need for a better understanding of the correlations between oxidative damage and neurodegenerations. In this chapter, the striatal DNA damage was first focused, and its brain region concentrations in neurodegenerative diseases will be discussed with parallel changes of dopamine levels and VMAT2 densities. Moreover, original data on the association among striatal DNA damages, sex, life span, and the age of onset of diseases in neurode-

**2. Oxidative damage of DNA in the striatum from patients with** 

It is widely recognized that 8-oxo-7,8-dihydro-2′-deoxyguanosine (8-oxo-dG) and 8-oxo-7,8-dihydroguanosine (8-oxo-G) may act as biomarkers of oxidative damage to DNA and RNA, respectively [1]. Studies by Li et al. have reported the levels of DNA adducts in the caudate and putamen of the disease groups and age-matched controls [21]. Compared to controls, remarkable reductions in DNA

Additionally, the increase in β-amyloid (Aβ) and neurofibrillary tangles (NFTs) is closely linked to decreased oxidative damage—an early event in AD that decreases with disease progression [10]. What is more, the lesions to mitochondrial, a major source of ROS, have been reported in the PD cases, and mitochondrial dysfunctions have been associated with the disease pathophysiology. Historically, the first investigation involving mitochondria in PD relates to the observation that the presence of an impairment of complex I in the different forms of PD and Parkinsonism [11]. Dementia with Lewy bodies (DLB), Parkinson disease dementia (PDD), and PD have been aggregated conceptually as Lewy body

**208**

oxidation adducts were observed in the caudate of PD and DLB brains, including males and females. However, in the caudate of AD brains, these levels were elevated. This finding was especially pronounced for male AD patients, as adduct levels were 36% elevated compared to controls (**Figure 1**). The concentrations of 8-oxo-dG in the putamen of the disease groups were similar to the controls. Comparing between caudate and putamen, there were impressive elevations in adduct levels in the caudate, especially for the AD brains. These data indicate that the caudate is more vulnerable to DNA damage than the putamen in advanced AD patients.

RNA bases are more exposed and vulnerable to oxidative damage than DNA as they are not protected by hydrogen bonding and specific proteins. RNA oxidation has been described as a "steady-state" marker of oxidative lesions [22]; however, DNA oxidation has been believed to be a historical marker of oxidative damage during disease pathogenesis and aging progression [23]. Increased 8-OHdG levels have been documented in PD patients [24–26], but as shown in **Figure 1**, a noticeable reduction of DNA oxidation adducts in the caudate was observed in the late-stage LBD brains. It was not unique; the urinary concentration of 8-OHdG in the MFB 6-hydroxydopamine lesion model started to elevate at day 3 with a significant increase to day 7 and gradually back to baseline at day 42 [27]. The increased 8-oxodG levels in the caudate of AD brains connected with the increase in dopamine levels of the same cases. These phenomena are most likely due to the Fenton reactions taking place—in response to dopamine release and dopamine compartmentalization by VMAT2 [28].

#### **Figure 1.**

*8-oxo-dG levels in the caudate and putamen of patients with diseases (PD: n = 10, PDD: n = 7, DLB: n = 10, and AD: n = 26) and age-matched controls (n = 10). Values shown are means ± SEM as the concentration of 8-oxo-7,8-dihydro-2*′*-deoxyguanosine (8-oxo-dG) (pg) per total DNA (μg). (a) Female and (b) male.*

## **3. Interactions between oxidative damage and dopamine in the striatum of patients with neurodegenerative diseases**

There are three biologically critical free radicals in our body, O2 •−, •OH, and NO• , mainly produced through Fenton oxidative reaction. Fenton reactions are catalytic oxidation reactions starting with transition metal ions, either iron or copper, and yielding both the hydroxyl radical (•OH) and higher oxidation states of the iron [29].

$$\text{Fe}^{2+} + \text{H}\_{2}\text{O}\_{2} \rightarrow \text{Fe}^{3+} + \text{'OH} + \text{OH}^{-} \tag{1}$$

$$\text{Fe}^{3+} + \text{H}\_{\text{z}}\text{O}\_{\text{z}} \rightarrow \text{Fe}^{2+} + \text{'OOH} + \text{H}^\* \tag{2}$$

The relatively large amount of hydroxyl radical attacks adjacent to mitochondrial DNA strands and cytoplasmic RNA single-strands consequently produce an amount of oxidative adducts [29]. It is also critical to note that dopamine is metabolized enzymatically to produce a mass of H2O2 and, ultimately, dihydroxyphenylacetate, conversely promoting the dopaminergic exposure neurons to oxidative lesions. Put it another way, dopamine and related catechol are vulnerable molecules that can oxidize in the presence of transition metals to yield O2 − , playing an essential role in nucleic oxidation as a major ROS source. O2 − , a product of catechol autoxidation, can reversely oxidize catechol [30]. Either spontaneously or enzymatically, O2 − can yield H2O2 and then •OH in the presence of transition metals [11]. The imbalance between clearance and generation of ROS promotes progressive dysfunction or increased death of dopaminergic neurons. Also, dopamine affects as a good metal chelator and electron donor and is capable of capturing iron and manganese [17]. Fe3+ has been reported as a catalyst for autoxidation of dopamine via the following mechanism [31]:

This mechanism can be proved further by a significant negative correlation between dopamine levels and 8-oxo-dG levels in the caudate of AD patients (**Figure 2**). Combined with a significant negative correlation between 8-oxo-dG levels and VMAT2 density in the same brain area from AD cases (**Figure 3**), these results are most likely owning to Fenton oxidation reactions taking place in the caudate from AD brains, which was believed to be a response to dopamine concentration and dopamine compartmentalization by VMAT2. As shown in **Figure 2**, dopamine concentrations in the caudate and putamen of disease patients and controls did not significantly differ. However, there were trends of decreasing and increasing dopamine levels in the LBD and AD patients, especially for the female cohorts.

**211**

**Figure 2.**

*The Striatal DNA Damage and Neurodegenerations DOI: http://dx.doi.org/10.5772/intechopen.93706*

oxidation in the same brain area of PD cases [11].

PD has been described to be associated with both increased levels of nigral iron—a catalytic agent for yielding •OH—and enhanced Mn superoxide dismutase activity. As the midbrain levels of reduced glutathione were diminished, there was evidence of increased oxidative damage in the midbrain of PD patients, including not only lipid peroxidation, protein oxidation, oxidation of DNA, but also catechol

As shown in **Figure 3**, similar changes in VMAT2 density in the caudate and putamen are in line with the 8-oxo-dG and dopamine levels of the same cohorts. Compared to the controls, lower VMAT2 binding levels were found in the caudate from both female and male LBD cases. Diversely, a significant increase in VMAT2 density in female and male AD patients was observed. We can see significant negative correlations between 8-oxo-dG levels and VMAT2 density in the caudate (*r*s = −0.451, *p* = 0.027) and putamen (*r*s = −0.516, *p* = 0.024) of AD patients, as well as in the caudate (*r*s = −0.683, *p* = 0.042) of PD patients. It might give

*Concentration of dopamine in the caudate and putamen from patients with diseases (PD: n = 10, PDD: n = 7, DLB: n = 10, and AD: n = 26) and age-matched controls (n = 10). (A) Female and (B) male. The values shown are means ± SEM. (C) Concentration of dopamine versus level of 8-oxo-dG in the caudate from diseases brains, significant association was observed only in the AD group (p = 0.026); concentration of dopamine versus VMAT2 expression in the putamen from diseases brains, significant association was observed only in* 

*DLB group (p = 0.050). rs, the Spearman's rank correlation coefficient.*

*The Striatal DNA Damage and Neurodegenerations DOI: http://dx.doi.org/10.5772/intechopen.93706*

*DNA - Damages and Repair Mechanisms*

NO•

of the iron [29].

mechanism [31]:

**of patients with neurodegenerative diseases**

oxidize in the presence of transition metals to yield O2

nucleic oxidation as a major ROS source. O2

**3. Interactions between oxidative damage and dopamine in the striatum** 

, mainly produced through Fenton oxidative reaction. Fenton reactions are catalytic oxidation reactions starting with transition metal ions, either iron or copper, and yielding both the hydroxyl radical (•OH) and higher oxidation states

+ +− + →++ • Fe H O Fe OH OH 2 3

+ ++ + →+ + • Fe H O Fe OOH H 3 2

The relatively large amount of hydroxyl radical attacks adjacent to mitochondrial DNA strands and cytoplasmic RNA single-strands consequently produce an amount of oxidative adducts [29]. It is also critical to note that dopamine is metabolized enzymatically to produce a mass of H2O2 and, ultimately, dihydroxyphenylacetate, conversely promoting the dopaminergic exposure neurons to oxidative lesions. Put it another way, dopamine and related catechol are vulnerable molecules that can

−

can reversely oxidize catechol [30]. Either spontaneously or enzymatically, O2

yield H2O2 and then •OH in the presence of transition metals [11]. The imbalance between clearance and generation of ROS promotes progressive dysfunction or increased death of dopaminergic neurons. Also, dopamine affects as a good metal chelator and electron donor and is capable of capturing iron and manganese [17]. Fe3+ has been reported as a catalyst for autoxidation of dopamine via the following

This mechanism can be proved further by a significant negative correlation between dopamine levels and 8-oxo-dG levels in the caudate of AD patients (**Figure 2**). Combined with a significant negative correlation between 8-oxo-dG levels and VMAT2 density in the same brain area from AD cases (**Figure 3**), these results are most likely owning to Fenton oxidation reactions taking place in the caudate from AD brains, which was believed to be a response to dopamine concentration and dopamine compartmentalization by VMAT2. As shown in **Figure 2**, dopamine concentrations in the caudate and putamen of disease patients and controls did not significantly differ. However, there were trends of decreasing and increasing dopamine levels in the LBD and AD patients,

2 2 (1)

2 2 (2)

−

•−, •OH, and

, playing an essential role in

− can

, a product of catechol autoxidation,

There are three biologically critical free radicals in our body, O2

**210**

especially for the female cohorts.

PD has been described to be associated with both increased levels of nigral iron—a catalytic agent for yielding •OH—and enhanced Mn superoxide dismutase activity. As the midbrain levels of reduced glutathione were diminished, there was evidence of increased oxidative damage in the midbrain of PD patients, including not only lipid peroxidation, protein oxidation, oxidation of DNA, but also catechol oxidation in the same brain area of PD cases [11].

As shown in **Figure 3**, similar changes in VMAT2 density in the caudate and putamen are in line with the 8-oxo-dG and dopamine levels of the same cohorts. Compared to the controls, lower VMAT2 binding levels were found in the caudate from both female and male LBD cases. Diversely, a significant increase in VMAT2 density in female and male AD patients was observed. We can see significant negative correlations between 8-oxo-dG levels and VMAT2 density in the caudate (*r*s = −0.451, *p* = 0.027) and putamen (*r*s = −0.516, *p* = 0.024) of AD patients, as well as in the caudate (*r*s = −0.683, *p* = 0.042) of PD patients. It might give

#### **Figure 2.**

*Concentration of dopamine in the caudate and putamen from patients with diseases (PD: n = 10, PDD: n = 7, DLB: n = 10, and AD: n = 26) and age-matched controls (n = 10). (A) Female and (B) male. The values shown are means ± SEM. (C) Concentration of dopamine versus level of 8-oxo-dG in the caudate from diseases brains, significant association was observed only in the AD group (p = 0.026); concentration of dopamine versus VMAT2 expression in the putamen from diseases brains, significant association was observed only in DLB group (p = 0.050). rs, the Spearman's rank correlation coefficient.*

evidence that the reduction of vesicular storage increased dopamine release and then was conductive to produce hydrogen peroxide from MAO-catalyzed dopamine metabolism [32].

To better understand the correlations between oxidative damage and dopamine storage abilities, the spatial control of dopamine by VMAT2 and the antioxidation role of VMAT2 should be further elucidated. Bearing in mind the portrayal of oxidative lesions in the pathogenesis of PD, packing of cytosolic dopamine into synaptic vesicles by VMAT2 inhibits its autoxidation and the subsequent degeneration of dopaminergic neurons [33]. This theory conforms to the negative correlations observed between oxidative damage and VMAT2 density in striatum of both AD and PD patients. Reduced dopamine levels attenuated its uptake and transport functions by changing dopamine turnover. Thus,

#### **Figure 3.**

*Quantitative autoradiographic analysis of VMAT2 density (fmol/mg) in the caudate and putamen from patients with diseases (PD: n = 10, PDD: n = 7, DLB: n = 10, and AD: n = 26) and age-matched controls (n = 10). (A) Female and (B) male. The values shown are means ± SEM. Statistical significance between two disease groups are indicated with brackets and corresponding p-values. A p value of <0.05 was considered significant: \* indicates p < 0.05 versus the controls. (C) Density of VMAT2 as concentration of 8-oxo-dG in the caudate and putamen from AD brains (p = 0.027 and p = 0.024, respectively) as well as that in the caudate from PD brains (p = 0.042). Rs, the Spearman's rank correlation coefficient.*

**213**

**Figure 4.**

*(p = 0.020).*

*The Striatal DNA Damage and Neurodegenerations DOI: http://dx.doi.org/10.5772/intechopen.93706*

cantly with the gradual loss in dopamine cells [19].

dopamine pool [32].

systems [40–42].

VMAT2 expression correlates with the severity of Parkinsonism and cognitive impairment in DLB [18, 34]. The inhibition of dopamine metabolism by MAO-B attenuates hydrogen peroxide production, as a two-edged sword, it also increases the risk of dopamine autoxidation and subsequent augmentation of the cytosolic

**4. The interactions between oxidative damage in the striatum, sex, life span, and the age of onset of diseases in neurodegenerative patients**

Many neurological diseases show significant sex differences in their susceptibility, severity, and progression [35, 36]. Specifically, a male bias has been found for disorders such as PD and attention-deficit hyperactivity disorder (ADHD), both of which are associated with abnormal levels of dopamine [37–39]. Considerable studies have supported the hypothesis that gonadal sex steroid hormones, especially estrogen, act as protectors in females by modulating dopamine release, metabolism, and dopamine receptors' activity. However, there is numerous evidence that genetic factors, especially sex-specific genes, influence either healthy or diseased dopamine

As shown in **Figure 4**, Kendall's tau\_b analysis revealed a significant positive correlation between sex and 8-oxo-dG levels in the caudate of PD cases. The result indicates that there is a sex difference concerning DNA damage in late-stage PD patients. Postmortem brain studies have revealed that the expression of PD-related genes in the substantia nigra pars compact (SNc), such as α*-synuclein* and *PINK-1*, is higher in men than women [43]. Sex-chromosome genes are critically involved, particularly the sex-determining region of the Y chromosome (*SRY*) gene [44]. The dopaminergic toxin, 6-hydroxydopamine (6-OHDA), has been described to significantly elevate *SRY* mRNA expression in human male dopamine cells, accompanied by an increase in the expression of GADD45γ, a DNA damage-inducible factor gene and a known *SRY* regulator. Interestingly, SRY upregulation initiated by dopamine cell damage is a protective response in males; however, the effect diminishes signifi-

DNA damage may be unique in its ability to promote multiple symptoms associated with old age. Exposure of rodents to ionizing radiation leads to the premature

*Kendall's tau\_b analysis of the correlation between sex and 8-oxo-dG levels in the caudate from PD brains* 

*The Striatal DNA Damage and Neurodegenerations DOI: http://dx.doi.org/10.5772/intechopen.93706*

*DNA - Damages and Repair Mechanisms*

mine metabolism [32].

evidence that the reduction of vesicular storage increased dopamine release and then was conductive to produce hydrogen peroxide from MAO-catalyzed dopa-

To better understand the correlations between oxidative damage and dopamine storage abilities, the spatial control of dopamine by VMAT2 and the antioxidation role of VMAT2 should be further elucidated. Bearing in mind the portrayal of oxidative lesions in the pathogenesis of PD, packing of cytosolic dopamine into synaptic vesicles by VMAT2 inhibits its autoxidation and the subsequent degeneration of dopaminergic neurons [33]. This theory conforms to the negative correlations observed between oxidative damage and VMAT2 density in striatum of both AD and PD patients. Reduced dopamine levels attenuated its uptake and transport functions by changing dopamine turnover. Thus,

*Quantitative autoradiographic analysis of VMAT2 density (fmol/mg) in the caudate and putamen from patients with diseases (PD: n = 10, PDD: n = 7, DLB: n = 10, and AD: n = 26) and age-matched controls (n = 10). (A) Female and (B) male. The values shown are means ± SEM. Statistical significance between two disease groups are indicated with brackets and corresponding p-values. A p value of <0.05 was considered significant: \* indicates p < 0.05 versus the controls. (C) Density of VMAT2 as concentration of 8-oxo-dG in the caudate and putamen from AD brains (p = 0.027 and p = 0.024, respectively) as well as that in the caudate* 

*from PD brains (p = 0.042). Rs, the Spearman's rank correlation coefficient.*

**212**

**Figure 3.**

VMAT2 expression correlates with the severity of Parkinsonism and cognitive impairment in DLB [18, 34]. The inhibition of dopamine metabolism by MAO-B attenuates hydrogen peroxide production, as a two-edged sword, it also increases the risk of dopamine autoxidation and subsequent augmentation of the cytosolic dopamine pool [32].
