Possible neuroprotective effects of rasagiline in Alzheimer’s disease: a SPECT study

Abstract

Background

The current lack of effective treatments for Alzheimer’s disease (AD) and the rapidly increasing burden of the disease highlight the urgent need to find new treatments. Despite accumulating evidence of the beneficial effects of rasagiline in neurodegenerative diseases such as Parkinson’s disease, the effects of rasagiline on the brains of patients with AD have not been elucidated.

Purpose

To examine the effects of rasagiline on regional cerebral flow (rCBF) in patients with AD using single photon emission computed tomography (SPECT).

Material and Methods

Among 22 patients with AD, 11 patients received adjunctive rasagiline at 1 mg/day in conjunction with acetylcholinesterase inhibitors (AChEI); 11 patients were only treated with AChEI for about 1.6 years. All patients underwent brain technetium-99m hexamethylpropylene amine oxime SPECT scans and clinical assessments at baseline and follow-up visits. Annual percent changes in rCBF were compared between the groups in a voxel-wise manner.

Results

SPECT analysis revealed that the rasagiline-treated group showed more increased rCBF in the cingulate gyrus, inferior frontal gyrus, putamen, and thalamus compared to the comparison group (P < 0.005).

Conclusion

We demonstrated that adjunctive rasagiline treatment may have beneficial effects on brain perfusion in patients with AD, suggesting potential neuroprotective effects.

Keywords

Alzheimer’s disease rasagiline single photon emission computed tomography regional cerebral blood flow

Introduction

Alzheimer’s disease (AD), which is the most common type of dementia, is characterized by memory loss, cognitive impairment, and personality disorders as well as diffuse structural abnormalities in the brains. In addition to classical neuropathological features such as amyloid plaques and neurofibrillary tangles, AD is associated with a reduction of regional cerebral blood flow (rCBF) in multiple brain regions. It has been thought that early diagnosis, management, and intervention of AD would have great potential to prevent cognitive decline that is severe enough to interfere with patients’ daily lives. Many clinical attempts have been made to prevent the clinical progressive cognitive decline of AD, but the results have been largely unsuccessful (1). Moreover, the currently available medical therapies including acetylcholinesterase inhibitors and antipsychotics are symptomatic treatments and no disease-modifying therapy has been established (2,3). Therefore, there is a high priority for finding a therapy that slows, stops, or reverses the progression of the disease.

Rasagiline [N-propargyl-1(R)-aminoindan] is a selective, irreversible, second-generation monoamine oxidase type B (MAO-B) inhibitor (4). Rasagiline suppresses neurotoxin and oxidative stress-induced membrane permeabilization in isolated mitochondria, but the mechanism has not been fully clarified (5). It has been suggested that rasagiline may have neuroprotective effects that are independent of MAO-B inhibition (6 –8).

Functional neuroimaging such as positron emission tomography (PET) and single photon emission computed tomography (SPECT) has been widely used for diagnosis, evaluation of treatment effects, and monitoring disease progression. Moreover, functional neuroimaging has advantages of detecting subtle changes before appearance of behavioral or clinical signs (9). Taken together, despite accumulating evidence for the neuroprotective properties of rasagiline and the widespread use of functional neuroimaging in neurodegenerative diseases, the effects of rasagiline in AD have not been elucidated. Therefore, the aim of the present study was to examine the effects of rasagiline on rCBF in patients with AD using perfusion SPECT.

Material and Methods

Participants

Eleven patients (7 women, 4 men; mean age = 75.8 ± 2.9 years) with probable AD were recruited. The clinical diagnosis of AD was made according to the Diagnostic and Statistical Manual of Mental Disorders-IV (DSM-IV) criteria (10) and the National Institute of Neurological and Communicative Disorders and Stroke and the Alzheimer’s Disease and Related Disorders Association (NINCDS-ADRDA) criteria (11). Patients were excluded from the study if they had a history of head trauma, epilepsy, stroke, mixed or vascular dementia, and other neurological or psychiatric disorders. Eleven age- and sex-matched patients with probable AD (7 women, 4 men; mean age = 76.1 ± 2.1 years) who did not receive rasagiline treatment were included in the comparison group. All patients underwent SPECT scans and clinical assessments at baseline and follow-up visits; the mean follow-up period was 1.6 ± 0.7 years.

All procedures were performed in accordance with the ethical standards of the Institutional Review Board of the Incheon St. Mary’s Hospital and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.

Administration of rasagiline

All participants were being treated with donepezil, an acetylcholinesterase inhibitor (AChEI), at the time of the study and the dosage remained unchanged throughout the study. In the rasagiline group, ten patients were treated with 5 mg/day of donepezil and one patient was treated with 10 mg/day. In the comparison group, eight patients were treated with 5 mg/day of donepezil and two patients were treated with 10 mg/day. Participants in the rasagiline group received add-on rasagiline at a dose of 1 mg daily. Safety was assessed by examining the incidence of adverse events and the results of physical examinations, vital signs, electrocardiography, and laboratory tests.

SPECT acquisition and analysis

Brain SPECT scans were acquired approximately 40 min after the intravenous injection of 555–740 MBq of technetium-99m hexamethylpropylene amine oxime (^99mTc-HMPAO) using a dual-head gamma camera (Discovery NM630, GE Healthcare, Milwaukee, WI, USA). Patients were supine with their eyes open during the scans. Images were acquired by rotating the gamma camera twice clockwise and counterclockwise in a total of 720° with 6° at a rate of 12 s per frame. Continuous transaxial brain images were reconstructed in a 128 × 128 matrix with a pixel size of 1.95 × 1.95 mm (field of view = 250 mm, slice thickness = 2.08 mm) and a 20% symmetric energy window at 140 keV using the ordered-subset expectation maximization (OSEM) algorithm (6 iterations and 10 subsets) and a Butterworth filter (cut-off frequency of 0.5 cycles/pixel and power of 10.0) to reduce noise.

All SPECT images were preprocessed and analyzed using Statistical Parametric Mapping 12 (SPM; Wellcome Department of Cognitive Neurology, London, UK). The images were first spatially normalized to the SPM SPECT template using the “Old Normalize” function. After spatial normalization, the images were re-sliced with a voxel size of 2.0 ×2.0 × 2.0 mm and scaled to the mean intensity of the cerebellum (12,13) using the MarsBar toolbox (14) and Automated Anatomical Labeling atlas (15). For each patient, maps of annual percent change of rCBF were created as follows:

\frac{Follow - up map - Baseline map}{Baseline map} \times \frac{100}{Interscan time (years)}

Finally, all images were smoothed with a 12-mm full-width half-maximum Gaussian kernel.

Group differences in rCBF at baseline and differences in annual percent change of rCBF during the follow-up period were examined using a voxel-by-voxel t-test in SPM. Baseline age, sex, and years of education were included as covariates for all analyses. The voxel-wise significance threshold was set at P < 0.005 with a minimum cluster size of 100 contiguous voxels.

Clinical assessment

Clinical assessment including a detailed medical history and neurological examination was conducted by board-certified neurologists. Cognitive status and dementia severity were assessed using the Mini-Mental State Examination (MMSE) (16) and the Clinical Dementia Rating (CDR) scale (17), respectively.

Statistical analysis

Independent t-test and Fisher’s exact test were used to compare the differences in demographic and clinical characteristics between the groups. The significance level was set at P < 0.05. All statistical analyses were performed using STATA 13 (Stata Corp., College Station, TX, USA).

Results

Demographic and clinical characteristics

Demographic and clinical characteristics of the rasagiline and comparison groups are summarized in Table 1. There were no significant differences between the two groups on key baseline variables including age (P = 0.93), sex (P = 1.00), years of education (P = 0.36), baseline MMSE score (P = 0.96), baseline CDR score (P = 0.59), and interval between the baseline and follow-up visits (P = 0.76). No significant difference was found in the mean annual change of MMSE score between the groups (P = 0.45). All patients in the rasagiline group remained stable at the same CDR score at follow-up, whereas two patients in the comparison group went from 0.5 to 1.0 at follow-up.

Table 1.

Demographic and clinical characteristics of the participants.

Characteristics	Rasagiline group (n = 11)	Comparison group (n = 11)	Test statistics
Age (years)	75.8 ± 2.9	76.1 ± 2.1	t = 0.09, P = 0.93
Sex (M:F)	4: 7	4: 7
Education (years)	4.1 ± 1.0	5.6 ± 1.3	t = 0.93, P = 0.36
Baseline MMSE score	20.6 ± 1.2	20.7 ± 1.5	t = 0.05, P = 0.96
Baseline CDR			P = 0.59*
0.5	10	8
1.0	1	2
2.0	0	1
Interval between baseline and follow-up (years)	1.6 ± 0.9	1.5 ± 0.6	t = –0.31, P = 0.76

Values are given as n or mean ± SD.

*Fisher’s exact test.

CDR, Clinical Dementia Rating; MMSE, Mini-Mental State Examination.

SPECT results

Between-group comparison on baseline SPECT scans revealed that there were no significant differences in rCBF between the groups at baseline, adjusted for age, sex, and education. The voxel-by-voxel t-test of the annual percent change maps of rCBF showed that there were relatively higher rates of signal increase in the right anterior cingulate gyrus (P < 0.001), bilateral posterior cingulate gyrus (P < 0.001), bilateral putamen (left, P < 0.001; right, P = 0.001), right thalamus (P = 0.001), and right inferior frontal gyrus (P = 0.001), whereas no relatively higher rate of signal reduction was observed in the rasagiline group compared with the comparison group, after controlling for age, sex, and education (Tables 2 and 3, Fig. 1).

Table 2.

Group differences of the annual percent change in regional cerebral blood flow.

Region	t	P	Coordinates* (x, y, z)	Cluster size (voxels)
Rasagiline group > Comparison group
Posterior cingulate gyrus	5.05	<0.001	0, –46, 34	279
Right anterior cingulate gyrus	4.45	<0.001	6, 36, 8	359
Left putamen	4.33	<0.001	–32, –12, 4	276
Left putamen	3.99	<0.001	–20, 18, –8	280
Right putamen	3.92	0.001	16, 8, –6	107
Right thalamus	3.89	0.001	12, –20, 8	421
Right inferior frontal gyrus	3.68	0.001	46, 38, 2	139
Rasagiline group < Comparison group
None

*The coordinates refer to the Montreal Neurological Institute coordinate system.

Table 3.

Mean annual percent change of regional cerebral blood flow in significant clusters between the groups.

	Rasagiline group (n = 11)	Comparison group (n = 11)
Posterior cingulate gyrus	2.0 ± 3.2	–2.6 ± 2.9
Right anterior cingulate gyrus	4.2 ± 3.6	–3.0 ± 4.8
Left putamen	2.0 ± 2.5	–1.8 ± 2.8
Left putamen	3.0 ± 4.2	–2.1 ± 2.8
Right putamen	3.1 ± 4.2	–2.1 ± 2.8
Right thalamus	3.0 ± 5.1	–3.1 ± 3.8
Right inferior frontal gyrus	3.1 ± 3.2	–1.8 ± 3.2

Values are given as mean ± SD.

Fig. 1.

Annual percent changes in rCBF between the groups. Images depict the brain areas of relatively higher rate of signal increase in rCBF in the rasagiline group compared to the comparison group, adjusting for age, sex, and education. Images are displayed in neurological convention. Color bar represents the voxel-level t-values. rCBF, regional cerebral blood flow.

Discussion

The present study reports for the first time the improvement of cerebral regional function in patients with AD after rasagiline treatment using perfusion SPECT. In particular, we found that the rasagiline-treated group showed more increased rCBF in the cingulate gyrus and right inferior frontal gyrus, regions that are often implicated in AD, compared to the control group. Considering that a global reduction of cerebral perfusion is the natural course of the disease (18), our findings suggest that the treatment with rasagiline may have beneficial effects on cerebral perfusion in patients with AD.

The cingulate cortex is well-known to be affected in early AD (19,20). Several previous studies have demonstrated regional atrophy of the middle cingulate gyrus or the dorsal/caudal anterior cingulate cortex in patients with early AD, suggesting that this region may be a diagnostic marker for early AD (19,21). Moreover, decreased resting state functional connectivity between the precuneus and dorsal anterior cingulate cortex in patients with AD suggests disruptions of the default mode network in AD (22). Furthermore, one study reported increased rCBF in the middle cingulate cortex and posterior cingulate cortex after donepezil treatment in patients with mild AD (23). According to other reports, the right inferior frontal gyrus is also shown to be activated across a wide variety of task demands, including attentional reorienting and shifting, and is often co-activated with the parietal cortex in neuroimaging studies of executive function (24 –26). Namely, there is evidence of an important role of the right inferior frontal gyrus in attention and executive functions in patients with AD. Taken together, the increased perfusion in the regions that are implicated in the pathophysiology of AD indicates positive effects of rasagiline on cerebral function in patients with AD, suggesting potential neuroprotective effects.

Rasagiline has been shown to have a broad neuroprotective activity against a variety of neurotoxins in neuronal cell cultures and in animal models of neurodegenerative disease (27). For instance, rasagiline reduced the infarct volume in a focal ischemia model in rats and prevented 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced neurotoxicity in mice (28,29). In addition, rasagiline suppresses the cell death cascade initiated by Bcl-2 family pro-apoptotic mitochondrial proteins and caspase-3, preventing the decline in mitochondrial membrane potential, and the nuclear translocation of gyceraldehyde-3-phosphate dehydrogenase (GAPDH) and DNA fragmentation (30 –32). Moreover, another study reported that rasagiline suppresses neurotoxin- and oxidative stress-induced membrane permeabilization in isolated mitochondria by regulating the mitochondrial permeability transition pore (5). Rasagiline inhibited mitochondrial Ca2⁺ efflux through the mitochondrial permeability transition pore dose dependently. Ca2⁺ efflux was confirmed as the initial signal in mitochondrial apoptotic cascade, and the suppression of Ca2⁺ efflux may account for the neuroprotective function of rasagiline (33,34).

The present study has some limitations. First, the study includes a relatively small sample size. Second, despite the improvement in cerebral perfusion in the rasagiline group, no significant changes in the clinical measures were observed. A comprehensive neuropsychological battery may have been useful in detecting subtle changes and providing additional information. Third, we used the cerebellum as a normalization reference region because it has been suggested that cerebellum is one of the regions least affected by AD pathology and the pons is susceptible to random noise due to its small size (12,13,35). Nevertheless, other imaging methods such as [¹⁵O]-water PET or arterial spin labeling that quantify absolute rCBF are warranted in future studies. Lastly, as glutathione is involved in intracellular conversion and retention of ^99mTc-HMPAO, there may have been some interaction between MAO inhibition and glutathione availability (36). Further studies are needed to better understand the molecular mechanisms underlying the effects of rasagiline.

In conclusion, the present study is the first to examine the effects of rasagiline on cerebral perfusion in patients with AD. We demonstrated that rasagiline treatment combined with AChEI improves cerebral perfusion in the inferior frontal gyrus and cingulate gyrus. These results may indicate positive effects of rasagiline on brain functions in AD. Future studies with larger samples are necessary to confirm our findings and to examine associations between changes in cerebral perfusion and those in clinical symptoms after rasagiline treatment in AD.

Footnotes

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The authors received the following financial support for the research, authorship, and/or publication of this article: This research was supported by grants from Institute of Information & Communications Technology Planning & Evaluation (2020-0-00238) and the National Research Foundation of Korea (2020R1C1C1007254) funded by the Korean government, and a Grant of Translational R&D Project through Institute for Bio-Medical convergence, Incheon St. Mary’s Hospital, The Catholic University of Korea.

ORCID iD

Yong-An Chung

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