Pharmacological Potential of Cilostazol for Alzheimer's Disease

Inhibition of amyloid beta oligomer accumulation by NU-9: A unifying mechanism for the treatment of neurodegenerative diseases

Protein aggregation is a hallmark of neurodegenerative diseases, which connects these neuropathologies by a common phenotype. Various proteins and peptides form aggregates that are poorly degraded, and their ensuing pathological accumulation underlies these neurodegenerative diseases. Similarities may exist in the mechanisms responsible for the buildup of these aggregates. Therefore, therapeutics designed to treat one neurodegenerative disease may be beneficial to others. In ALS models, the compound NU-9 was previously shown to block neurodegeneration produced by aggregation-inducing mutations of SOD-1 and TDP-43 [B. Genç et al., Clin. Transl. Med. 11, e336 (2021)]. Here, we report that NU-9 also prevents the accumulation of amyloid beta oligomers (AβOs), small peptide aggregates that are instigators of Alzheimer's disease neurodegeneration [M. Tolar et al., Int. J. Mol. Sci. 22, 6355 (2021)]. AβO buildup was measured by immunofluorescence imaging of cultured hippocampal neurons exposed to exogenous monomeric Aβ. In this model, AβO buildup occurs via cathepsin L- and dynamin-dependent trafficking. This is prevented by NU-9 through a cellular mechanism that is cathepsin B- and lysosome-dependent, suggesting that NU-9 enhances the ability of endolysosomal trafficking to protect against AβO buildup. This possibility is strongly supported by a quantitative assay for autophagosomes that shows robust stimulation by NU-9. These results contribute additional understanding to the mechanisms of protein aggregation and suggest that multiple neurodegenerative diseases might be treatable by targeting common pathogenic mechanisms responsible for protein aggregation.

Target the Heart: a new axis of Alzheimer's disease prevention

Cyclosporine A and other calcineurin inhibitors have been identified as prospective treatments for preventing Alzheimer's disease. Utilizing a neural network model, Z-LaP Tracker, we previously found that calcineurin inhibitors elicit a unique behavioral profile in zebrafish larvae characterized by increased activity, acoustic hyperexcitability, and reduced visually guided behaviors. Screening a large library of FDA-approved drugs using Z-LaP Tracker revealed a cluster of 65 drugs demonstrating a cyclosporine A-like behavioral profile. 14 of these drugs were heart medications, including angiotensin receptor blockers, beta-blockers, alpha-adrenergic receptor antagonists, and a statin. This suggests some heart medications may be effective in preventing or ameliorating Alzheimer's disease pathology. Other studies have shown that many of these 14 drugs directly or indirectly inhibit the calcineurin-NFAT pathway, alike cyclosporine A. Dual administration of the heart medications with cyclosporine A in Z-LaP Tracker revealed synergistic effects: lower doses of each heart medication could be delivered in conjunction with a lower dose of cyclosporine A to evoke a similar or larger behavioral effect than higher doses of each drug independently. This indicates that co-administering a low dose of cyclosporine A with select cardiac drugs could be a potentially effective treatment strategy for Alzheimer's disease and cardiovascular dysfunction, while mitigating side effects associated with higher doses of cyclosporine A. Given that heart disease precedes Alzheimer's disease in many patients, physicians may be able to create a treatment regimen that simultaneously addresses both conditions. Our results suggest that cyclosporine A combined with simvastatin, irbesartan, cilostazol, doxazosin, or nebivolol are the most promising candidates for future exploration.

Cilostazol counteracts mitochondrial dysfunction in hepatic encephalopathy rat model: Insights into the role of cAMP/AMPK/SIRT1/ PINK-1/parkin hub and p-CREB /BDNF/ TrkB neuroprotective trajectory

A devasting stage of chronic hepatic dysfunction is strictly correlated with neurological impairment, signifying hepatic encephalopathy (HE). HE is a multifactorial condition; therefore, hyperammonemia, oxidative stress, neuroinflammation, and mitochondrial dysfunction interplay in HE's progressive development. Cilostazol (Cilo) has shown promising neuroprotective and hepatoprotective effectiveness in different neuronal and hepatic disorders; however, its efficiency against HE hasn't yet been explored. This study aimed to investigate the protective role of Cilo against thioacetamide (TAA)-induced HE in rats targeting mitochondrial dysfunction via modulation of Adenosine monophosphate-activated protein kinase (AMPK)/Silent information regulator 1 (SIRT1) dependent pathways. Rats were allocated into three groups: the normal control group, the TAA group received (100 mg/kg, three times per week, for six weeks) to induce HE, and the Cilo group received (Cilo 100 mg/kg/day for six weeks, oral gavage) concurrently with TAA. Cilo counteracted HE indicated in the enhancement of cognitive impairment and the motor performance of rats (P < 0.0001), modulation AMPK/SIRT1signaling pathway causing reduction of NF-kB p65 (P < 0.0001) evoked inflammation along with histopathological alterations and glial fibrillary acidic protein (GFAP) immunoreactivity (P < 0.0001), restoration nuclear factor E2-related factor 2 (Nrf2) (P < 0.0001) antioxidant effects, reduction of Bax and elevation of Bcl2 immunoreactivity (P < 0.0001) in addition to boosting mitochondrial biogenesis by upregulation of PTEN-induced kinase-1 (PINK-1)/Parkin (P < 0.0001)and restoration of Brain-derived neurotrophic factor (BDNF) (P = 0.0002)/tropomyosin-related kinase B (TrkB) (P < 0.0001)/cAMP response element-binding (CREB) (P < 0.0001) neuroprotective axis. Collectively, Cilo activates the SIRT1 trajectory to abridge mitochondrial dysfunction invigorated in the HE rat model via restoration of mitochondrial hemostasis.

Recent pharmacological insights on abating toxic protein species burden in neurological disorders: Emphasis on 26S proteasome activation

Protein homeostasis (proteostasis) refers to the plethora of mechanisms that safeguard the proper folding of the newly synthesized proteins. It entails various intricately regulated cues that demolish the toxic protein species to prevent their aggregation. The ubiquitin-proteasome system (UPS) is recognized as a salient protein degradation system, with a substantial role in maintaining proteostasis. However, under certain circumstances the protein degradation capacity of the UPS is overwhelmed, leading to the accumulation of misfolded proteins. Several neurodegenerative disorders, such as Alzheimer's disease, Parkinson's disease, Huntington disease, and amyotrophic lateral sclerosis are characterized with the presence of protein aggregates and proteinopathy. Accordingly, enhancing the 26S proteasome degradation activity might delineate a pioneering approach in targeting various proteotoxic disorders. Regrettably, the exact molecular approaches that enhance the proteasomal activity are still not fully understood. Therefore, this review aimed to underscore several signaling cascades that might restore the degradation capacity of this molecular machine. In this review, we discuss the different molecular components of the UPS and how 26S proteasomes are deleteriously affected in many neurodegenerative diseases. Moreover, we summarize different signaling pathways that can be utilized to renovate the 26S proteasome functional capacity, alongside currently known druggable targets in this circuit and various classes of proteasome activators.

A Long-Acting Lyotropic Liquid Crystalline Implant Promotes the Drainage of Macromolecules by Brain-Related Lymphatic System in Treating Aged Alzheimer's Disease

Numerous evidence has demonstrated that the brain is not an immune-privileged organ but possesses a whole set of lymphatic transport system, which facilitates the drainage of harmful waste from brains to maintain cerebral homeostasis. However, as individuals age, the shrinkage and dysfunction of meningeal and deep cervical lymphatic networks lead to reduced waste outflow and elevated neurotoxic molecules deposition, further inducing aging-associated cognitive decline, which act as one of the pathological mechanisms of Alzheimer's disease. Consequently, recovering the function of meningeal and deep cervical lymph node (dCLNs) networks (as an important part of the brain waste removal system (BWRS)) of aged brains might be a feasible strategy. Herein we showed that the drug brain-entering efficiency was highly related to administration routes (oral, subcutaneous, or dCLN delivery). Besides, by injecting a long-acting lyotropic liquid crystalline implant encapsulating cilostazol (an FDA-approved selective PDE-3 inhibitor) and donepezil hydrochloride (a commonly used symptomatic relief agent to inhibit acetylcholinesterase for Alzheimer's disease) near the deep cervical lymph nodes of aged mice (about 20 months), an increase of lymphatic vessel coverage in the nodes and meninges was observed, along with accelerated drainage of macromolecules from brains. Compared with daily oral delivery of cilostazol and donepezil hydrochloride, a single administered dual drugs-loaded long-acting implants releasing for more than one month not only elevated drug concentrations in brains, improved the clearing efficiency of brain macromolecules, reduced Aβ accumulation, enhanced cognitive functions of the aged mice, but improved patient compliance as well, which provided a clinically accessible therapeutic strategy toward aged Alzheimer's diseases.

Sex Differences in the Preventive Effect of Cardiovascular and Metabolic Therapeutics on Dementia

Dementia is a clinical syndrome characterized by progressive impairment of cognitive and functional abilities. As currently applied treatments for dementia can only delay the progression of dementia and cannot fundamentally cure it, much attention is being paid to reducing its incidence by preventing the associated risk factors. Cardiovascular and metabolic diseases are well-known risk factors for dementia, and many studies have attempted to prevent dementia by treating these risk factors. Growing evidence suggests that sex-based factors may play an important role in the pathogenesis of dementia. Therefore, a deeper understanding of the differences in the effects of drugs based on sex may help improve their effectiveness. In this study, we reviewed sex differences in the impact of therapeutics targeting risk factors for dementia, such as cardiovascular and metabolic diseases, to prevent the incidence and/or progression of dementia.

Antiplatelet drugs: Potential therapeutic options for the management of neurodegenerative diseases

The blood platelet plays an important role but often remains under-recognized in several vascular complications and associated diseases. Surprisingly, platelet hyperactivity and hyperaggregability have often been considered the critical risk factors for developing vascular dysfunctions in several neurodegenerative diseases (NDDs) like Alzheimer's disease, Parkinson's disease, Huntington's disease, and multiple sclerosis. In addition, platelet structural and functional impairments promote prothrombotic and proinflammatory environment that can aggravate the progression of several NDDs. These findings provide the rationale for using antiplatelet agents not only to prevent morbidity but also to reduce mortality caused by NDDs. Therefore, we thoroughly review the evidence supporting the potential pleiotropic effects of several novel classes of synthetic antiplatelet drugs, that is, cyclooxygenase inhibitors, adenosine diphosphate receptor antagonists, protease-activated receptor blockers, and glycoprotein IIb/IIIa receptor inhibitors in NDDs. Apart from this, the review also emphasizes the recent developments of selected natural antiplatelet phytochemicals belonging to key classes of plant-based bioactive compounds, including polyphenols, alkaloids, terpenoids, and flavonoids as potential therapeutic candidates in NDDs. We believe that the broad analysis of contemporary strategies and specific approaches for plausible therapeutic treatment for NDDs presented in this review could be helpful for further successful research in this area.

Blood-brain crosstalk: the roles of neutrophils, platelets, and neutrophil extracellular traps in neuropathologies

Systemic inflammation, neurovascular dysfunction, and coagulopathy often occur concurrently in neuropathologies. Neutrophils and platelets have crucial synergistic roles in thromboinflammation and are increasingly suspected as effector cells contributing to the pathogenesis of neuroinflammatory diseases. In this review, we summarize the roles of platelet-neutrophil interactions in triggering complex pathophysiological events affecting the brain that may lead to the disruption of brain barriers, infiltration of toxic factors into the parenchyma, and amplification of neuroinflammation through the formation of neutrophil extracellular traps (NETs). We highlight the clinical significance of thromboinflammation in neurological disorders and examine the contributions of damage-associated molecular patterns (DAMPs) derived from platelets and neutrophils. These DAMPs originate from both infectious and non-infectious risk factors and contribute to the activation of inflammasomes during brain disorders. Finally, we identify knowledge gaps in the molecular mechanisms underlying neurodegenerative disease pathogenesis and emphasize the potential of interventions targeting platelets and neutrophils to treat neuroinflammatory diseases.

Constituent isoflavones of Puerariae radix as a potential neuroprotector in cognitive impairment: Evidence from preclinical studies

With the increasing aging population worldwide, the incidence of senile cognitive impairment (CI) is increasing, posing a serious threat to the health of elderly persons. Despite developing new drugs aimed at improving CI, progress in this regard has been insufficient. Natural preparations derived from plants have become an unparalleled resource for developing new drugs. Puerariae radix (PR) has a long history as Chinese herbal medicine. PR is rich in various chemical components such as isoflavones, triterpenes, and saponins. The isoflavones (puerarin, daidzein, formononetin, and genistein) exhibit potential therapeutic effects on CI through multiple mechanisms. Relevant literature was organized from major scientific databases such as PubMed, Elsevier, SpringerLink, ScienceDirect, and Web of Science. Using "Puerariae radix," "Pueraria lobata," "isoflavones," "puerarin," "antioxidant," "daidzein," "formononetin," "genistein," "Alzheimer"s disease," and "vascular cognitive impairment" as keywords, the relevant literature was extracted from the databases mentioned above. We found that isoflavones from PR have neuroprotective effects on multiple models of CI via multiple targets and mechanisms. These isoflavones prevent Aβ aggregation, inhibit tau hyperphosphorylation, increase cholinergic neurotransmitter levels, reduce neuroinflammation and oxidative stress, improve synaptic plasticity, promote nerve regeneration, and prevent apoptosis. PR has been used as traditional Chinese herbal medicine for a long time, and its constituent isoflavones exert significant therapeutic effects on CI through various neuroprotective mechanisms. This review will contribute to the future development of isoflavones present in PR as novel drug candidates for the clinical treatment of CI.

Cilostazol as adjunctive therapy in treatment of children with autism spectrum disorders: a double-blind and placebo-controlled randomized trial

We aimed to evaluate cilostazol therapeutic effects on aberrant behaviors of autism spectrum disorder (ASD) children and its safety profile in a double-blind, randomized clinical trial. Sixty-six children with confirmed ASD were allocated to receive either daily 50-mg cilostazol (increased to 100 mg/day after 2 weeks) or matched placebo in addition to risperidone. The Aberrant Behavior Checklist-Community Edition (ABC-C) scale and a checklist of probable adverse effects were used to assess the behavioral outcomes and safety profile at weeks 0, 5, and 10 of the study. Sixty-one participants, with comparable baseline characteristics, completed the trial. Unlike other ABC-C subscales, repeated-measures analysis showed significant effect for time × treatment interaction in the hyperactivity subscale ( P = 0.047; partial eta squared = 0.06). We used the median value for the baseline score hyperactivity subscale [median (interquartile range) = 31 (24-37)] to stratify participants to higher hyperactivity and lower hyperactivity subgroups and found that only participants with higher hyperactivity benefit from cilostazol adjunctive therapy ( P = 0.028; partial eta squared = 0.14). Cilostazol could be considered as a safe agent with beneficial effects on hyperactivity in children with ASD and higher levels of hyperactivity.

Cognitive effects of cilostazol in Alzheimer's dementia patients with peripheral arterial occlusive disease: A case-control study

AIM

Alzheimer's dementia (AD) is a slowly progressing neurodegenerative disease, characterized by beta-amyloid deposition and neurofibrillary tangles. Peripheral atherosclerosis may deteriorate these processes via endothelial cell dysfunction and microvascular impairment. Cilostazol - a phosphodiesterase 3 inhibitor - is a standard treatment for peripheral arterial occlusive disease and a potential treatment for preserving cognitive function in AD patients. We aimed to determine whether cilostazol is beneficial in AD patients with peripheral arterial occlusive disease by evaluating Cognitive Abilities Screening Instrument (CASI) domains.

METHODS

We conducted a retrospective case-control study of 62 AD patients in Taiwan. Thirty-one patients had peripheral arterial occlusive disease and were receiving cilostazol plus acetylcholinesterase inhibitors (AchEIs) or N-methyl d-aspartate antagonists, whereas 31 others were receiving AchEIs. Therapeutic responses were measured using neuropsychological assessments. The CASI was administered at baseline and 12 months later; different domains were analyzed between the groups using univariate and multivariate analyses.

RESULTS

Age, sex, education duration, ApoE ε4 gene status, and initial Mini-Mental State Examination scores were not different between the two groups. Except for fluency, no CASI domains showed a statistical difference between the groups. A significant difference was observed in category fluency (P = 0.010). In the logistic regression analysis, after adjusting for covariate effects, category fluency still showed a significant difference between the groups (P = 0.013).

CONCLUSIONS

In AD patients with peripheral arterial occlusive disease who have received Food and Drug Administration-approved pharmacotherapy, cilostazol, as an antiplatelet, may help to preserve general cognitive function, with significant preservation in category fluency. Geriatr Gerontol Int 2023; 23: 194-199.

Potential role of IP3/Ca2+ signaling and phosphodiesterases: Relevance to neurodegeneration in Alzheimer's disease and possible therapeutic strategies

Despite large investments by industry and governments, no disease-modifying medications for the treatment of patients with Alzheimer's disease (AD) have been found. The failures of various clinical trials indicate the need for a more in-depth understanding of the pathophysiology of AD and for innovative therapeutic strategies for its treatment. Here, we review the rational for targeting IP3 signaling, cytosolic calcium dysregulation, phosphodiesterases (PDEs), and secondary messengers like cGMP and cAMP, as well as their correlations with the pathophysiology of AD. Various drugs targeting these signaling cascades are still in pre-clinical and clinical trials which support the ideas presented in this article. Further, we describe different molecular mechanisms and medications currently being used in various pre-clinical and clinical trials involving IP3/Ca⁺² signaling. We also highlight various isoforms, as well as the functions and pharmacology of the PDEs broadly expressed in different parts of the brain and attempt to unravel the potential benefits of PDE inhibitors for use as novel medications to alleviate the pathogenesis of AD.

LigAdvisor: a versatile and user-friendly web-platform for drug design

Although several tools facilitating in silico drug design are available, their results are usually difficult to integrate with publicly available information or require further processing to be fully exploited. The rational design of multi-target ligands (polypharmacology) and the repositioning of known drugs towards unmet therapeutic needs (drug repurposing) have raised increasing attention in drug discovery, although they usually require careful planning of tailored drug design strategies. Computational tools and data-driven approaches can help to reveal novel valuable opportunities in these contexts, as they enable to efficiently mine publicly available chemical, biological, clinical, and disease-related data. Based on these premises, we developed LigAdvisor, a data-driven webserver which integrates information reported in DrugBank, Protein Data Bank, UniProt, Clinical Trials and Therapeutic Target Database into an intuitive platform, to facilitate drug discovery tasks as drug repurposing, polypharmacology, target fishing and profiling. As designed, LigAdvisor enables easy integration of similarity estimation results with clinical data, thereby allowing a more efficient exploitation of information in different drug discovery contexts. Users can also develop customizable drug design tasks on their own molecules, by means of ligand- and target-based search modes, and download their results. LigAdvisor is publicly available at https://ligadvisor.unimore.it/.

Discovery and Validation of Key Biomarkers Based on Immune Infiltrates in Alzheimer's Disease

BACKGROUND

As the most common neurodegenerative disease, Alzheimer's disease (AD) leads to progressive loss of cognition and memory. Presently, the underlying pathogenic genes of AD patients remain elusive, and effective disease-modifying therapy is not available. This study explored novel biomarkers that can affect diagnosis and treatment in AD based on immune infiltration.

METHODS

The gene expression profiles of 139 AD cases and 134 normal controls were obtained from the NCBI GEO public database. We applied the computational method CIBERSORT to bulk gene expression profiles of AD to quantify 22 subsets of immune cells. Besides, based on the use of the Least Absolute Shrinkage Selection Operator (LASSO), this study also applied SVM-RFE analysis to screen key genes. GO-based semantic similarity and logistic regression model analyses were applied to explore hub genes further.

RESULTS

There was a remarkable significance in the infiltration of immune cells between the subgroups. The proportions for monocytes, M0 macrophages, and dendritic cells in the AD group were significantly higher than those in the normal group, while the proportion of some cells was lower than that of the normal group, such as NK cell resting, T-cell CD4 naive, T-cell CD4 memory activation, and eosinophils. Additionally, seven genes (ABCA2, CREBRF, CD72, CETN2, KCNG1, NDUFA2, and RPL36AL) were identified as hub genes. Then we performed the analysis of immune factor correlation, gene set enrichment analysis (GSEA), and GO based on seven hub genes. The AUC of ROC prediction model in test and validation sets were 0.845 and 0.839, respectively. Eventually, the mRNA expression analysis of ABCA2, NDUFA2, CREBRF, and CD72 revealed significant differences among the seven hub genes and then was confirmed by RT-PCR.

CONCLUSION

A model based on immune cell infiltration might be used to forecast AD patients' diagnosis, and it provided a new perspective for AD treatment targets.

Memory Enhancers for Alzheimer's Dementia: Focus on cGMP

Cyclic guanosine-3',5'-monophosphate, better known as cyclic-GMP or cGMP, is a classical second messenger involved in a variety of intracellular pathways ultimately controlling different physiological functions. The family of guanylyl cyclases that includes soluble and particulate enzymes, each of which comprises several isoforms with different mechanisms of activation, synthesizes cGMP. cGMP signaling is mainly executed by the activation of protein kinase G and cyclic nucleotide gated channels, whereas it is terminated by its hydrolysis to GMP operated by both specific and dual-substrate phosphodiesterases. In the central nervous system, cGMP has attracted the attention of neuroscientists especially for its key role in the synaptic plasticity phenomenon of long-term potentiation that is instrumental to memory formation and consolidation, thus setting off a "gold rush" for new drugs that could be effective for the treatment of cognitive deficits. In this article, we summarize the state of the art on the neurochemistry of the cGMP system and then review the pre-clinical and clinical evidence on the use of cGMP enhancers in Alzheimer's disease (AD) therapy. Although preclinical data demonstrates the beneficial effects of cGMP on cognitive deficits in AD animal models, the results of the clinical studies carried out to date are not conclusive. More trials with a dose-finding design on selected AD patient's cohorts, possibly investigating also combination therapies, are still needed to evaluate the clinical potential of cGMP enhancers.

Therapeutic Strategies to Reduce the Toxicity of Misfolded Protein Oligomers

The aberrant aggregation of proteins is implicated in the onset and pathogenesis of a wide range of neurodegenerative disorders, including Alzheimer’s and Parkinson’s diseases. Mounting evidence indicates that misfolded protein oligomers produced as intermediates in the aggregation process are potent neurotoxic agents in these diseases. Because of the transient and heterogeneous nature of these elusive aggregates, however, it has proven challenging to develop therapeutics that can effectively target them. Here, we review approaches aimed at reducing oligomer toxicity, including (1) modulating the oligomer populations (e.g., by altering the kinetics of aggregation by inhibiting, enhancing, or redirecting the process), (2) modulating the oligomer properties (e.g., through the size–hydrophobicity–toxicity relationship), (3) modulating the oligomer interactions (e.g., by protecting cell membranes by displacing oligomers), and (4) reducing oligomer toxicity by potentiating the protein homeostasis system. We analyze examples of these complementary approaches, which may lead to the development of compounds capable of preventing or treating neurodegenerative disorders associated with protein aggregation.

Repurposed agents in the Alzheimer's disease drug development pipeline

BACKGROUND

Treatments are needed to address the growing prevalence of Alzheimer's disease (AD). Clinical trials have failed to produce any AD drugs for Food and Drug Administration (FDA) approval since 2003, and the pharmaceutical development process is both time-consuming and costly. Drug repurposing provides an opportunity to accelerate this process by investigating the AD-related effects of agents approved for other indications. These drugs have known safety profiles, pharmacokinetic characterization, formulations, doses, and manufacturing processes.

METHODS

We assessed repurposed AD therapies represented in Phase I, Phase II, and Phase III of the current AD pipeline as registered on ClinicalTrials.gov as of February 27, 2020.

RESULTS

We identified 53 clinical trials involving 58 FDA-approved agents. Seventy-eight percent of the agents in trials had putative disease-modifying mechanisms of action. Of the repurposed drugs in the pipeline 20% are hematologic-oncologic agents, 18% are drugs derived from cardiovascular indications, 14% are agents with psychiatric uses, 12% are drug used to treat diabetes, 10% are neurologic agents, and the remaining 26% of drugs fall under other conditions. Intellectual property strategies utilized in these programs included using the same drug but altering doses, routes of administration, or formulations. Most repurposing trials were supported by Academic Medical Centers and were not funded through the biopharmaceutical industry. We compared our results to a European trial registry and found results similar to those derived from ClinicalTrials.gov.

CONCLUSIONS

Drug repurposing is a common approach to AD drug development and represents 39% of trials in the current AD pipeline. Therapies from many disease areas provide agents potentially useful in AD. Most of the repurposed agents are generic and a variety of intellectual property strategies have been adopted to enhance their economic value.

Phosphodiesterase Inhibitors for Alzheimer's Disease: A Systematic Review of Clinical Trials and Epidemiology with a Mechanistic Rationale

BACKGROUND

Preclinical studies, clinical trials, and reviews suggest increasing 3',5'-cyclic adenosine monophosphate (cAMP) and 3',5'-cyclic guanosine monophosphate (cGMP) with phosphodiesterase inhibitors is disease-modifying in Alzheimer's disease (AD). cAMP/protein kinase A (PKA) and cGMP/protein kinase G (PKG) signaling are disrupted in AD. cAMP/PKA and cGMP/PKG activate cAMP response element binding protein (CREB). CREB binds mitochondrial and nuclear DNA, inducing synaptogenesis, memory, and neuronal survival gene (e.g., brain-derived neurotrophic factor) and peroxisome proliferator-activated receptor-γ coactivator-1α (PGC1α). cAMP/PKA and cGMP/PKG activate Sirtuin-1, which activates PGC1α. PGC1α induces mitochondrial biogenesis and antioxidant genes (e.g.,Nrf2) and represses BACE1. cAMP and cGMP inhibit BACE1-inducing NFκB and tau-phosphorylating GSK3β.

OBJECTIVE AND METHODS

We review efficacy-testing clinical trials, epidemiology, and meta-analyses to critically investigate whether phosphodiesteraseinhibitors prevent or treat AD.

RESULTS

Caffeine and cilostazol may lower AD risk. Denbufylline and sildenafil clinical trials are promising but preliminary and inconclusive. PF-04447943 and BI 409,306 are ineffective. Vinpocetine, cilostazol, and nicergoline trials are mixed. Deprenyl/selegiline trials show only short-term benefits. Broad-spectrum phosphodiesterase inhibitor propentofylline has been shown in five phase III trials to improve cognition, dementia severity, activities of daily living, and global assessment in mild-to-moderate AD patients on multiple scales, including the ADAS-Cogand the CIBIC-Plus in an 18-month phase III clinical trial. However, two books claimed based on a MedScape article an 18-month phase III trial failed, so propentofylline was discontinued. Now, propentofylline is used to treat canine cognitive dysfunction, which, like AD, involves age-associated wild-type Aβ deposition.

CONCLUSION

Phosphodiesterase inhibitors may prevent and treat AD.

Cilostazol protects against acetic acid-induced colitis in rats: Possible role for cAMP/SIRT1 pathway

The phosphodiesterase-3 inhibitor, cilostazol has been recently shown to protect against chemically induced colitis in animal models. However, whether cyclic adenosine monophosphate (cAMP) contributes to the anti-inflammatory activity of cilostazol in colitis is still unknown. In the current study, we investigated the role of cAMP/silent information regulator-1 (SIRT-1) pathway in the protective effect of cilostazol using rat model of acetic acid-induced colitis. Upregulation of SIRT1 activity and expression has been recently shown to protect against chemically induced colitis. Our results demonstrated that cilostazol alleviated the histopathological changes associated with acetic acid-induced colitis. Interestingly, pre-administration of cilostazol increased cAMP concentration and SIRT1 expression in colonic mucosa to levels similar to that observed in control animals without induction of colitis. In addition, cilostazol inhibited the SIRT1 targets; NF-κB, Akt and MAPK inflammatory pathways as demonstrated by suppression of acetic acid-induced upregulation of NF-κB activity, p-AKT levels and the expression of p38 MAPK. NF-κB activity and the levels of p-AKT, tumor necrosis factor α (TNF-α), interleukin-1β (IL-1β) were similar in rats pretreated with cilostazol prior to induction of colitis and the control rats without colitis. Furthermore, cilostazol reduced acetic acid-induced oxidative stress and apoptosis. In conclusion, the protective effect of cilostazol against acetic acid-induced colitis may be attributed to activation of SIRT1 expression by cAMP. SIRT1 is suggested to contribute to cilostazol-induced suppression of NF-κB, Akt and MAPK inflammatory pathways, oxidative stress and apoptosis.

Potential Therapeutic Approaches for Cerebral Amyloid Angiopathy and Alzheimer's Disease

Cerebral amyloid angiopathy (CAA) is a cerebrovascular disease directly implicated in Alzheimer’s disease (AD) pathogenesis through amyloid-β (Aβ) deposition, which may cause the development and progression of dementia. Despite extensive studies to explore drugs targeting Aβ, clinical benefits have not been reported in large clinical trials in AD patients or presymptomatic individuals at a risk for AD. However, recent studies on CAA and AD have provided novel insights regarding CAA- and AD-related pathogenesis. This work has revealed potential therapeutic targets, including Aβ drainage pathways, Aβ aggregation, oxidative stress, and neuroinflammation. The functional significance and therapeutic potential of bioactive molecules such as cilostazol and taxifolin have also become increasingly evident. Furthermore, recent epidemiological studies have demonstrated that serum levels of a soluble form of triggering receptor expressed on myeloid cells 2 (TREM2) may have clinical significance as a potential novel predictive biomarker for dementia incidence. This review summarizes recent advances in CAA and AD research with a focus on discussing future research directions regarding novel therapeutic approaches and predictive biomarkers for CAA and AD.