The interactions of dopamine and oxidative damage in the striatum of patients with neurodegenerative diseases

Abstract

The striatum with a number of dopamine containing neurons, receiving projections from the substantia nigra and ventral tegmental area; plays a critical role in neurodegenerative diseases of motor and memory function. Additionally, oxidative damage to nucleic acid may be vital in the development of age-associated neurodegeneration. The metabolism of dopamine is recognized as one of the sources of reactive oxygen species through the Fenton mechanism. The proposed interactions of oxidative insults and dopamine in the striatum during the progression of diseases are the hypotheses of most interest to our study. This study investigated the possibility of significant interactions between these molecules that are involved in the late-stage of Alzheimer's disease (AD), Parkinson disease (PD), Parkinson disease dementia, dementia with Lewy bodies, and controls using ELISA assays, autoradiography, and mRNA in situ hybridization assay. Interestingly, lower DNA/RNA oxidative adducts levels in the caudate and putamen of diseased brains were observed with the exception of an increased DNA oxidative product in the caudate of AD brains. Similar changes were found for dopamine concentration and vesicular monoamine transporter 2 densities. We also found that downstream pre-synaptic dopamine D1 Receptor binding correlated with dopamine loss in Lewy body disease groups, and RNA damage and β-site APP cleaving enzyme 1 in the caudate of AD. This is the first demonstration of region-specific alterations of DNA/RNA oxidative damage which cannot be viewed in isolation, but rather in connection with the interrelationship between different neuronal events; chiefly DNA oxidative adducts and density of vesicular monoamine transporter 2 densities in AD and PD patients.

Keywords: Alzheimer's disease; Lewy body diseases; dopamine; oxidative damage; striatum.

Figure 1

8‐oxo‐dG levels in the caudate and putamen from patients with diseases [Parkinson disease (PD): n = 10, Parkinson disease dementia (PDD): n = 7, dementia with Lewy bodies (DLB): n = 10, Alzheimer's disease (AD): n = 26] and age‐matched controls (n = 10). Value shown are means ± SEM as the concentration of 8‐oxo‐7,8‐dihydro‐2'‐deoxyguanosine (8‐oxo‐dG) (pg) per total DNA (µg). A p value of < 0.05 was considered significant. The only statistical significance is between the PD vs AD (p = 0.0039) as demonstrated with the bracket.

Figure 2

8‐oxo‐7,8‐dihydroguanosine (8‐oxo‐G) levels in the caudate and putamen from patients with diseases [Parkinson disease (PD): n = 10, Parkinson disease dementia (PDD): n = 7, dementia with Lewy bodies (DLB): n = 10, Alzheimer's disease (AD): n = 26] and age‐matched controls (n = 10). Value shown are means ± SEM as the concentration of 8‐oxo‐G (pg) per total RNA (µg). A p value of < 0.05 was considered significant: ** indicates p < 0.01, **** indicates p < 0.0001, vs. the controls. Significant differences between two non‐control groups are indicated with brackets and corresponding p‐values [Putamen: PD vs AD (p = 0.0086), PDD vs AD (p = 0.0162), DLB vs AD (p = 0.002)].

Figure 3

(a) Concentration of dopamine in the caudate and putamen from patients with diseases [Parkinson disease (PD): n = 10, Parkinson disease dementia (PDD): n = 7, dementia with Lewy bodies (DLB): n = 10, Alzheimer's disease (AD): n = 26] and age‐matched controls (n = 10). Value shown are means ± SEM. (b) Concentration of dopamine vs level of 8‐oxo‐7,8‐dihydro‐2'‐deoxyguanosine (8‐oxo‐dG) in the caudate from diseases brains, significantly association was observed only in AD group (p = 0.026). (c) Concentration of dopamine vs vesicular monoamine transporter 2 (VMAT2) expression in the putamen from diseases brains, significantly association was observed only in DLB group (p = 0.050). r _s, the Spearman's rank correlation coefficient.

Figure 4

Quantitative autoradiographic analysis of vesicular monoamine transporter 2 (VMAT2) density in the caudate and putamen from patients with diseases [Parkinson disease (PD): n = 10, Parkinson disease dementia (PDD): n = 7, dementia with Lewy bodies (DLB): n = 10, Alzheimer's disease (AD): n = 26] and age‐matched controls (n = 10). (a) Quantitative analysis of the VMAT2 density (fmol/mg) in the caudate and putamen from subjects. Value shown are means ± SEM. Statistical significances between two disease groups are indicated with brackets and corresponding p‐values (p < 0.0001 were found for PD vs AD, PDD vs AD, and DLB vs AD in the caudate, as well as PD vs AD in the putamen). (b) Autoradiograms show total binding of 4 nmol/L [³H]DTBZ (Panel b top row) and non‐specific binding in the presence of 1 µM S(‐)‐tetrabenazine (Panel b bottom row) in the striatal regions of 5 representative subjects. The numbers 1 and 2 designate the following regions: caudate (1) and putamen (2). (c) [³H]Microscale standards (ranging from 0 to 36.3 nCi/mg) were also counted. (d) Density of VMAT2 as concentration of 8‐oxo‐7,8‐dihydro‐2'‐deoxyguanosine (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). r _s, the Spearman's rank correlation coefficient.

Figure 5

Quantitative autoradiographic analysis of dopamine D1 receptor (D1R) density in the caudate and putamen of patients with diseases [Parkinson disease (PD): n = 10, Parkinson disease dementia (PDD): n = 7, dementia with Lewy bodies (DLB): n = 10, Alzheimer's disease (AD): n = 26] and age‐matched controls (n = 10). (a) Quantitative analysis of the D1R density (fmol/mg) in the caudate and putamen of subjects. Value shown are means ± SEM. Statistical significances between two disease groups are indicated with brackets and corresponding p‐values [Caudate: PD vs AD (p = 0.0021); Putamen: PD vs AD (p = 0.0005), PDD vs AD (p = 0.0004), DLB vs AD (p = 0.0041)]. A p value of < 0.05 was considered significant: ** indicates p < 0.01, *** indicates p < 0.001, vs. the controls. (b) Autoradiograms show total binding of 1.5 nM [³H]SCH23390 (Panel b top row) and non‐specific binding in the presence of 1 µM (+) butaclamol (Panel b bottom row) in the striatal regions of the same 5 representative subjects. The numbers 1 and 2 designate the following regions: caudate (1) and putamen (2). (c) [³H]Microscale standards (ranging from 0 to 36.3 nCi/mg) were also counted.

Figure 6

RNAscope in situ hybridization (ISH) analysis of β‐site APP cleaving enzyme 1 (BACE1) transcriptional expression in the caudate and putamen from patients with Alzheimer's disease (AD) (n = 10) and age‐matched controls (n = 10). (a) RNAscope in situ hybridization (ISH) labeling for BACE1 mRNA in the caudate and putamen from the AD subject included in the previous group of 5 representative subjects. Scale bar in the whole slide section: 10 mm. Scale bar in the high magnification mode β‐amyloid plaque and NFT sections: 500 µm. Rectangle drawn in the whole slide section is magnified to highlight AB plaques and labeled as AD putamen image directly to the right. The numbers 1 and 2 designate the following regions: caudate (1) and putamen (2). (b) Positive cells (red with arrow pointing to them) in the caudate and putamen of AD and control subjects with scale bar: 100 µm. (c) semi‐quantitative regional analysis of ISH signal in region of interest, the signals were quantified as the average red dots count per mm². Value shown are means ± SEM. T‐test was used. A p value of < 0.05 was considered significant, * indicates p < 0.05 vs. the controls. (d) BACE1 mRNA expression as density of dopamine D1 receptor in the caudate and putamen from patients with AD and age‐matched controls. r _s, the Spearman's rank correlation coefficient. The only significant correlation was in the caudate of the AD group (p = 0.02).

Figure 7

Data analysis of all assay results of the caudate and putamen of the Alzheimer's disease (AD) cases chosen for β‐site APP cleaving enzyme 1 mRNA analysis (n = 10) and age‐matched controls (n = 10). (a) Oxidative damage of nucleic acid in the caudate and putamen from 10 AD cases and age‐matched controls. A p value of < 0.05 was considered significant: *indicates p < 0.05 vs. the controls. (b) Biological consequence of oxidative damage to dopamine system in the caudate and putamen from 10 AD cases and age‐matched controls. A p value of < 0.05 was considered significant,  **indicates p < 0.01 and ****indicates p < 0.0001 vs. the controls. (c) Density of vesicular monoamine transporter 2 (VMAT2) and DNA oxidative adducts levels (r _s = −0.678, p = 0.015), density of VMAT2 and RNA oxidative adducts levels (r _s = −0.717, p = 0.030), as well as density of dopamine D1 receptor and RNA oxidative adducts levels (r _s = −0.750, p = 0.020) in the caudate from 10 AD cases. r _s, the Spearman's rank correlation coefficient.