A Retrospective Study on the Benefits of Combined Citicoline,Memantine,and Acetylcholinesterase Inhibitor Treatments in Older Patients Affected with Alzheimer’s Disease

INTRODUCTION

Alzheimer’s disease (AD) is the most common cause of dementia, accounting for an estimated 60%to 80%of cases. The Alzheimer’s Association estimates that 81%of people who have AD are 75 years or older. Official records indicate a 71%increase in deaths due to AD from 2000 to 2013 [1, 2].

Therapeutic strategies must take into account the characteristics of elderly people, who often have somatic comorbidities. Only a careful evaluation of the associated somatic diseases, taking into account drugs safety indexes and tolerability, can lead to per-sonalized treatment in order to maximize drug efficacy, minimize adverse drug reactions, and optimize quality of life [3]. To date, the acetylcholinesterase inhibitors (AChEIs), donepezil, rivastigmine, and galantamine, and the N-methyl-D-aspartate (NMDA) receptor antagonist, memantine, are indicated for the treatment of mild to moderate AD. Several clinical trials or long-term observational studies investigated the use of combined treatment with memantine and AChEIs, highlighting that this therapeutic strategy produces consistent benefits, that are sustained or even increased over time, and that generally overcome the effectiveness of treatment with AChEIs alone [4–9]. As known, memantine and AChEIs tar-get two different pathological pathways, the dysfu-nctional glutamatergic and cholinergic transmitter systems, respectively and CDP–Choline though an increase in acetylcholine intrasynaptic levels. Thus, their complementary activity may produce effects greater than either drug individually.

Pharmacokinetic/pharmacodynamic studies indicated a lack of interaction between memantine and AChEIs, suggesting that they can be safely and eff-ectively used in combination [10, 11]. CDP-choline (cytidine-5^′-diphosphate choline) is a mononucleotide composed of ribose, cytosine, pyrophosphate, and choline. In both animals and humans, citicoline proved neuroprotective properties, much more evident than when it is used for a long time and is eff-ective in different patterns of cognitive impairment [12–15]. Indeed, citicoline can have beneficial effects in both degenerative and vascular cognitive decline; it works through an increase in acetylcholine intrasynaptic levels and promoting phospholipid synthesis, cellular function, and neuronal repair. Moreover, it is able to inhibit apoptosis associated with cerebral ischemia and several models of neurodegeneration. Some previous studies have already highlighted that citicoline alone and combined treatment of citicoline and one or more AChEIs are effective in mixed dementia (MD) and in AD, by slowing down cognitive impairment progression versus AChEIs alone [16, 17]. Recently, citicoline and memantine has been proven to be more advantageous and effective when compared with memantine alone in AD patients [18].

The aim of the present study was to evaluate the effectiveness and safety of oral citicoline sodium salt (1000 mg/day) plus memantine and AChEIs (at the maximum tolerated dosage) in AD patients, when compared with combined treatment with memantine and an AChEI. It was called CITIMEA, that is CITIcoline plus MEmantine and Acetylcholinesterase inhibitor.

MATERIALS AND METHODS

This was a retrospective multi-centric case-control study enrolling 170 consecutive patients aged 65 years old or older (34.11%men), affected with AD and visited in Italian Centers for Cognitive disorders and Dementia, between January 1, 2014 and De-cember 31, 2019. AD was diagnosed according to standard research criteria [19]. In short, AD diagnosis was confirmed by a combination of clinical and neuropsychological evaluation (assessing different cognitive areas, such as memory, language, and constructional praxis), and brain imaging (3T magnetic resonance imaging [MRI] and, if needed, positron emission tomography [PET]) [20]. Treatment was usually supervised by a family member or a caregiver. Memantine and AChEI were used at the maximum tolerated dose. Previous treatment with other cholinergic precursors (i.e., choline alphoscerate, choline bitartrate, L-alpha-glycerophosphorylethanolamine) or other nootropics (such as homotaurine) was an exclusion criteria.

81 patients (47,65%) took oral citicoline sodium salt 1000 mg/day, memantine, and an AChEI (case-group); 89 patients (52.35%) memantine and an AC-hEI (donepezil, rivastigmine, or galantamine) (con-trol-group). Visits were performed at baseline (T0), after 6 (T1), and after 12 (T2) months. Patients (or their legal representatives) signed informed con-sent forms at baseline. Cognitive functions were assessed by Mini-Mental State Examination (MMSE) [21]. The Activities of Daily Living (ADL) and the Instrumental Activities of Daily Living (IADL) scales were used in the assessment of the level of independence in daily self-care activities. The ADL scale is based on six items (bathing, dressing, toileting, transferring, eating, and the use of incontinence materials), with a score ranging from 0 (total independence) to 6 (total dependence) [22]. IADL total score range from 0 to 8, a score of 8 corresponding to the highest level of independence in all eight items (eating, dressing, sphincter control, house work, cooking, using telephone, using money, outside mo-vement) [23]. The Cumulative Illness Rating Scale (CIRS) was used for the assessment of comorbidities and their impact. In line with CIRS, clinicians rate the degree of impairment in 13 body organ sys-tems (cardiac, endocrine/metabolic, upper gastroint-estinal, lower gastrointestinal, genitourinary, hepatic, musculoskeletal, neurologic, ophthalmologic/otolar-yngologic, psychiatric, renal, respiratory, and vascular) rated from 0 (no impairment) to 4 (extremely severe) [24]. Mood was assessed by Geriatric Depression Scale-Short form (GDS-S) [25]. In the GDS-S, users’ answer was in a “Yes/No” format, with 15 items chosen from the GDS long form. Among these items, 10 of them indicate the presence of depression when answered positively, and 5 are indicative of depression when answered negatively. This form can be filled out in approximately 5 to 7 minutes, making it ideal for older people having difficulty to concentrate for longer periods of time. Psychiatric symptoms were assessed by the Neuropsychiatric Inventory (NPI) scale [26]. NPI is based on an interview of the caregivers and evaluates 12 psychiatric symptoms (delusions, hallucinations, depressed mood, anxiety, agitation, euphoria, apathy, irritability, disinhibition, aberrant motor behavior, night-time behavior disturbances, and eating behavior changes), for which the frequency is rated 1-3 and the severity is rated 1-3 (with higher numbers indicating greater frequency and severity). A total score for each symptom is obtained by multiplying the frequency by the severity.

Donepezil tablets were administered orally (5–10 mg/day); rivastigmine was administered through transdermal patches (4.6–9.5–13.3 mg/day); exten-ded-release galantamine capsules were administe-red orally (8–16–24 mg/day). Adverse events were reported at any follow-up visit.

The primary outcome was to assess whether a combined treatment of citicoline, memantine, and AChEI slow cognitive impairment. The secondary outcomes were to assess: a) the effects of combined treatment on ADL, IADL, GDS, and NPI scores; b) safety and adverse drug reactions; c) the possible interactions of citicoline, memantine, and AChEIs with other drugs. The research was in accordance with Italian req-uirements and conformed to the principles embo-died in the 1964 Declaration of Helsinki (http://www.wma.net), as well as to the International Ethical Gu-idelines for Biomedical Research Involving Human Subjects and the International Guidelines for Eth-ical Review for Epidemiological Studies (http://www.cioms.ch). The ethical committee was involved and no objections were raised.

RESULTS

The main characteristics of the enrolled patients are listed in Table 1. No significant differences were present at baseline regarding age, gender, education, MMSE, ADL, IADL, CIRS, GDS, and NPI. Mean MMSE score was 14.61±2.79. In the case- and in control groups, we compared the main variables over the assessment scheduled time (T0, T1, and T2). Regarding the MMSE scores, no statistically significant difference was found at T0 and T1 (T0: case 14.88±2.95; controls: 14.37±2.63; p = NS - T1: case 14.95±2.63; controls: 14.19±2.81; p = NS). The MMSE total score was statistically higher at T2 in the case group (15.09±3.00) than in the control group (14.03±2.92) with p = 0.022) (Table 2). In the case group, a statistically significant increasing trend was found between T0 and T2 (14.88±2.95 versus 15.09±0; p = 0.040; Table 3). On the contrary, in the control group, the decrease in the MMSE total scores was statistically significant between T0 and T2 (14.37±2.63 versus 14.03±2.92; p =  0.024; Table 3).

Moreover, we compared MMSE scores in the case group in order to assess the possible differences among the three different AChEIs, and no statistically significant difference was found.

Among the side effects observed in patients treated with combined treatment, we recorded agitation in two patients, gastric intolerance in two patients, and restlessness in one patient (Table 4). All these adverse events were self-limiting and treatment interruption was never necessary.

DISCUSSION

To the best of our knowledge, the CITIMEA study was the first in which a combined therapy with citicoline, memantine, and an AChEI was used. The results of this observational retrospective multicentric study showed that this association therapy is effective on cognitive functions in elderly patients with AD. Instead, we found no significant improvements on the ADL, IADL, GDS, and NPI total scores. The case-group patients had a significant increase in MMSE total score, and statistically significant differences compared to the control-group patients were found after 12 months of treatment. It is common knowledge that the best benefits are usually observed only after prolonged administration of citicoline, as also confirmed, for instance, by the Citicholinage study in which the usefulness on cognitive functions of adding citicoline to memantine was observed only after nine months of treatment [17]. In partic-ular, in our study, the MMSE total score increased by 0.21 points after twelve months of treatment. The clinical relevance of this statistically significant increase is that in AD patients, the MMSE total score at 12 months worsens in absence of therapy. Moreover, in previously published studies, such as the CITIMEM and the CITIRIVAD studies evaluating the effectiveness of combined therapy in AD patients, it had been reported that adding citicoline to an AChEI resulted in improvement in MMSE, whereas none of the AChEI by itself was able to stop MMSE worsening. In short, in the CITIRIVAD study, citicoline plus rivastigmine was more effective than rivastigmine alone [16]; in the CITIMEM study citicoline plus memantine was more effective than memantine alone [18]. In these two studies the increase of the MMSE total score, expressed in absolute terms, was always very low, confirming that the usefulness for adding citicoline consisted essentially in slowing disease progression. On the other hand, the effectiveness of citicoline as adding drug is well clear when the MEMAGE is compared to the CITIMEA study. In 2014, some investigators reported that in 240 AD patients followed for six months, combined therapy of memantine and an AChEI was more effective on cognitive functions than AChEI alone, but only between month 3 and month 6. No statistically significant differences were found comparing the MMSE total scores at baseline and after six months. In the MEMAGE study, citicoline was not used [9].

As already highlighted, in our study no statistically significant improvement on ADL, IADL, GDS, and NPI total scores was reported. The lack of such improvement is constant in all of the published studies, that evaluated the effectiveness of a combination therapy in AD patients.

It is a common knowledge that there is a weak-to-moderate inverse relationship between performance on the MMSE and ADL/IADLs, such that AD pati-ents with lower MMSE scores are more likely to have impairment in ADL/IADLs. Besides, the MMSE visuospatial and executive domains are considered the most predictive of functional ability. The neurobiology underlying ADL and IADL disruptions is still unclear. For instance, some investigators hypothesized that complex activities of daily living are related to specific regional neurodegeneration [27]. The lack of these evaluations in our study can be a limit.

Citicoline is converted into cytidine plus choline inside the organism [15]. Choline is required to tran-sport fats in and out of cells, and is a precursor both of acetylcholine, the neurotransmitter required for several brain functions including learning and memory, and phosphatidylcholine, a major constituent of all biological membranes [27, 29]. The most pro-nounced benefits of treatment with citicoline are probably due to the activation of biosynthesis of pho-spholipids in neuronal membranes, the increase in brain metabolism, and the neuroprotective effects during hypoxia and ischemia [30]. On the other hand, phospholipids are the essential constituents of cell membranes and of primary importance in mai-ntaining homeostasis, activity of membrane associated enzymes, coupling of receptor and intracellular signaling, and nerve impulse conduction. The synthesis of 80%of central nervous system phospholipids can be controlled by altering the concentration of citicoline [31]. Lastly, citicoline is an α7 nicotinic acetylcholine receptor (α7 nAChR) agonist [32]. The possibility that the effectiveness of CDP-choline may be linked to sirtuin 1 (SIRT1) expression is an interesting working hypothesis. Sirtuins are nicotinamide adenine dinucleotide (NAD)-dependent pro-tein deacetylases, that are known to have protective effects against several age-related diseases, such as cancer, diabetes, cardiovascular and neurodegenerative diseases [33]. In experimental studies, citicoline proved to increase SIRT1 protein expression [34], and SIRT1 can also activate the transcription of the so-called “good secretase” that is ADAM10, the most important enzyme with alpha-secretase activity for proteolytic processing of the amyloid-beta protein precursor, and increases its RNA and protein levels [35]. To date, the effect of citicoline on SIRT1 in humans is still debated.

Our study has limitations that should be addressed. The observational retrospective design rises some important limitations, such as the open-label design, the lack of a control group, and the pre-selection of patients as potential allocation bias that could have excluded patients potentially difficult to treat. On the other hand, the numerical representativeness of the sample was fully respected, and the CITIMEA study is a unique study.

CONCLUSIONS

In view of the currently limited therapeutic app-roaches, the search for strategies proven to strengthen and maximize the available drugs can result in effective and safe therapeutic responses for both the patient and the caregivers.

The CITIMEA study suggests that association of citicoline, memantine, and AChEIs may represent an option to prolong or even potentiate the beneficial effects of cholinergic therapies in AD patients. Indeed, this triple association proved to be advantageous in terms of cognitive performances versus patients treated with memantine plus AChEIs alone, without significant adverse reactions.