Ocular biomarkers of Alzheimer's disease

Tools and Biomarkers for the Study of Retinal Ganglion Cell Degeneration

The retina is part of the central nervous system, its analysis may provide an idea of the health and functionality, not only of the retina, but also of the entire central nervous system, as has been shown in Alzheimer’s or Parkinson’s diseases. Within the retina, the ganglion cells (RGC) are the neurons in charge of processing and sending light information to higher brain centers. Diverse insults and pathological states cause degeneration of RGC, leading to irreversible blindness or impaired vision. RGCs are the measurable endpoints in current research into experimental therapies and diagnosis in multiple ocular pathologies, like glaucoma. RGC subtype classifications are based on morphological, functional, genetical, and immunohistochemical aspects. Although great efforts are being made, there is still no classification accepted by consensus. Moreover, it has been observed that each RGC subtype has a different susceptibility to injury. Characterizing these subtypes together with cell death pathway identification will help to understand the degenerative process in the different injury and pathological models, and therefore prevent it. Here we review the known RGC subtypes, as well as the diagnostic techniques, probes, and biomarkers for programmed and unprogrammed cell death in RGC.

Plumula Nelumbinis: A review of traditional uses, phytochemistry, pharmacology, pharmacokinetics and safety

ETHNOPHARMACOLOGICAL RELEVANCE

Plumula Nelumbinis, the green embryo of the mature seeds of Nelumbo nucifera Gaertn, has a medical history of over 400 years. It is widely used for clearing the heart and heat, calming the mind, and promoting astringent essence and hemostasis in traditional Chinese medicine. Moreover, it usually dual use as food and medicine. This review aimed to evaluate the therapeutic potential of Plumula Nelumbinis by summarizing its botany, traditional uses, phytochemistry, pharmacology, pharmacokinetics and safety.

METHODS

This review summarized published studies on Plumula Nelumbinis in the Chinese Pharmacopoeia and literature databases including PubMed, Web of Science, Baidu Scholar, Wiley and China Knowledge Resource Integrated Database (CNKI), and limits the different research articles in botany, traditional uses, phytochemistry, pharmacology, pharmacokinetics and safety about Plumula Nelumbinis.

RESULTS

Plumula Nelumbinis is used to treat hypertension, arrhythmia, severe aplastic anemia, insomnia, encephalopathy and gynecological disease in traditional Chinese medicine and clinical studies. More than 130 chemicals have been isolated and identified from Plumula Nelumbinis, including alkaloids, flavonoids, polysaccharides and volatile oil. In addition, pharmacological effects, such as protective effects against cardiovascular diseases, neurological diseases, lung and kidney injury, anti-inflammatory and anticancer activities, were also evaluated by in vitro and in vivo studies. Moreover, the potential signaling pathways regulated by Plumula Nelumbinis in cardiovascular and neurological diseases and perspectives on Plumula Nelumbinis research were discussed.

CONCLUSION

Plumula Nelumbinis, a commonly used Chinese medicine, has a variety of traditional and modern therapeutic uses. Some traditional uses, especially the treatment of cardiovascular and neurological diseases, have been verified by pharmacological investigation. However, the pharmacological molecular mechanisms, pharmacokinetics and toxicology of Plumula Nelumbinis are still incomplete. In the future, a series of systematic studies on active compounds identification, pharmacological mechanism clarification, quality and safety evaluation are necessary.

Visual Abnormalities Associate With Hippocampus in Mild Cognitive Impairment and Early Alzheimer's Disease

Background and Objective: Alzheimer's disease (AD) has been shown to affect vision in human patients and animal models. This study was conducted to explore ocular abnormalities in the primary visual pathway and their relationship with hippocampal atrophy in patients with AD and mild cognitive impairment (MCI). The aim of this study was to investigate the potential value of ocular examinations as a biomarker during the AD progression. Methods: Patients with MCI (n = 23) or AD (n = 17) and age-matched cognitively normal controls (NC; n = 19) were enrolled. Pattern visual-evoked potentials (PVEP), flash electroretinogram (FERG) recordings and optical coherence tomography (OCT) were performed for all participants. Hippocampal volumes were measured by 3T magnetic resonance imaging. Cognitive function was assessed by Mini Mental State Examination (MMSE), Montreal Cognitive Assessment (MoCA) and Alzheimer's Disease Assessment Scale-cognitive subscale (ADAS-cog). Pearson correlation was employed to analyze the potential associations between ocular abnormalities and hippocampal volumes. Hierarchical regression models were conducted to determine associations between cognitive performances and ocular abnormalities as well as hippocampal volumes after adjusting for confounding factors including age, sex, cognitive reserve, and APOE4 status. Results: PVEP amplitude of P100 waveform was significantly decreased in AD patients compared to MCI and normal individuals. In FERG test, delayed latencies of rod response, rod cone response and 3.0 flicker time were found in cognitively impaired groups, indicating dysfunctions of both the rod and cone systems in the disease progression. OCT test revealed reduced macular retinal nerve fiber layer (m-RNFL) thickness in MCI and AD patients, which significantly correlated with brain structure of hippocampus particularly vulnerable during the progression of AD. Interestingly, P100 amplitude showed a significant association with hippocampal volumes even after adjusting confounding factors including age, sex, and cognitive reserve. Hierarchical regression analysis further demonstrated that m-RNFL thickness, as well as hippocampal volumes, significantly associated with ADAS-cog scores. Conclusion: P100 amplitude and m-RNFL thickness showed significant correlations with brain structure involved in AD-related neurodegeneration, and therefore proved to be potential indicators of brain imaging pathologies.

Annexins in Glaucoma

Glaucoma is one of the leading causes of irreversible visual loss, which has been estimated to affect 3.5% of those over 40 years old and projected to affect a total of 112 million people by 2040. Such a dramatic increase in affected patients demonstrates the need for continual improvement in the way we diagnose and treat this condition. Annexin A5 is a 36 kDa protein that is ubiquitously expressed in humans and is studied as an indicator of apoptosis in several fields. This molecule has a high calcium-dependent affinity for phosphatidylserine, a cell membrane phospholipid externalized to the outer cell membrane in early apoptosis. The DARC (Detection of Apoptosing Retinal Cells) project uses fluorescently-labelled annexin A5 to assess glaucomatous degeneration, the inherent process of which is the apoptosis of retinal ganglion cells. Furthermore, this project has conducted investigation of the retinal apoptosis in the neurodegenerative conditions of the eye and brain. In this present study, we summarized the use of annexin A5 as a marker of apoptosis in the eye. We also relayed the progress of the DARC project, developing real-time imaging of retinal ganglion cell apoptosis in vivo from the experimental models of disease and identifying mechanisms underlying neurodegeneration and its treatments, which has been applied to the first human clinical trials. DARC has potential as a biomarker in neurodegeneration, especially in the research of novel treatments, and could be a useful tool for the diagnosis and monitoring of glaucoma.

Pharmacological benefits of neferine - A comprehensive review

This article recapitulates the existing in vitro and in vivo studies focusing on the effects of neferine-an alkaloid derivative of lotus plant, in various disease models and its effects on key signaling molecules. The review also compiles a large number of research studies that demonstrate methods for isolation and extraction, biosynthetic pathway, pharmacological activity and mode of action of neferine and their underlying mechanisms at cellular level. Neferine is a unique bis-benzylisoquinoline alkaloid that possesses a number of therapeutic effects such as anti-cancer, anti-diabetic, anti-aging, anti-microbial, anti-thrombotic, anti-arrhythmic, anti-inflammatory and even anti-HIV. It also enhances the anti-cancer properties of other anti-cancer drugs like cisplatin, adriamycin, taxol, etc. It is also reported to reverse chemo-resistance and enhance sensitivity of the cancer cells towards anti-cancer drugs. The underlying mechanisms for its activities mainly include apoptosis, autophagy and G1 arrest. Neferine protects them against the effect of drugs like cisplatin. The therapeutic properties of neferine is widely diverse, while it shows toxicity to cancer it also shows cyto-protective effects against cardio-vascular diseases, pulmonary disease, and is also effective against Alzheimer's disease and elicits anti-oxidative effect in many cellular systems. This article thus is the first ever attempt to review the therapeutic activities of neferine established in in vitro and in vivo models and to compile all the fragmented data available on the omnipotent activities of neferine.

Change in retinal structural anatomy during the preclinical stage of Alzheimer's disease

INTRODUCTION

We conducted a 27-month longitudinal study of mid-life adults with preclinical Alzheimer's disease (AD), using spectral domain optical coherence tomography to compare changes in volume and thickness in all retinal neuronal layers to those of age-matched healthy control subjects.

METHODS

Fifty-six older adults (mean age = 65.36 years) with multiple risk factors for AD completed spectral domain optical coherence tomography retinal imaging and cognitive testing at baseline. Twenty-seven months later, they completed the same examinations and an 18F-florbetapir positron emission tomography imaging study.

RESULTS

Compared to healthy control subjects, those in the preclinical stage of AD showed a significant decrease in macular retinal nerve fiber layer (mRNFL) volume, over a 27-month follow-up interval period, as well as a decrease in outer nuclear layer and inner plexiform layer volumes and thickness in the inferior quadrant. However, only the mRNFL volume was linearly related to neocortical positron emission tomography amyloid standardized uptake value ratio after controlling for any main effects of age (R2 = 0.103; ρ = 0.017). Furthermore, the magnitude of mRNFL volume reduction was significantly correlated with performance on a task of participants' abilities to efficiently integrate visual and auditory speech information (McGurk effect).

DISCUSSION

We observed a decrease in mRNFL, outer nuclear layer, and inner plexiform layer volumes, in preclinical AD relative to controls. Moreover, the largely myelinated axonal loss in the RNFL is related to increased neocortical amyloid-β accumulation after controlling for age. Volume loss in the RNFL, during the preclinical stage, is not related to performance on measures of episodic memory or problem solving. However, this retinal change does appear to be modestly related to relative decrements in performance on a measure of audiovisual integration efficiency that has been recently advanced as a possible early cognitive marker of mild cognitive impairment.

Cognitive functions and normal tension glaucoma

Purpose:

Only a few studies have analyzed the potential link between glaucoma and cognitive function impairment. They have found controversial results. This study aims to perform quick cognitive function assessment with clock drawing test (CDT) using two different scoring systems and compare between normal tension glaucoma (NTG) and cataract patients.

Methods:

Totally, 30 NTG and 30 patients with cataracts were included in a prospective, pilot study. The predrawn circle was given, and patients were asked to draw the clock showing a time of 11:10. The test was evaluated using two methods – Freund method using a 7-point scoring scale (optimal cutoff ≤4) and Rakusa using a 4-point scoring scale (optimal cutoff ≤3). The level of significance was set at P < 0.05.

Results:

CDT result was significantly better in cataract group than in NTG group: 3.5 (2) versus 2 (2) by Freund, (P = 0.003) and 6.5 (1) versus 4.5 (2.75) by Rakusa, respectively (P = 0.004). Sixty percent (n = 18) of NTG group and 10% (n = 3) of cataract group patients completed the CDT in the specific picture manner (the short hand on 11 and the long hand between 11 and 12), (P = 0.001).

Conclusions:

Lower CDT results were seen in NTG patients according to two different scoring systems. NTG patients showed a specific manner of drawing. Further prospective studies are needed to investigate the CDT reliability as fast screening test of cognitive function impairment in glaucoma patients.

Can the retina be used to diagnose and plot the progression of Alzheimer's disease?

Alzheimer's disease (AD) is a neurodegenerative disease and the most common cause of senile dementia. It impairs the quality of life of a person and their family, posing a serious economic and social threat in developed countries. The fact that the diagnosis can only be definitively made post-mortem, or when the disease is fairly advanced, presents a serious problem if novel therapeutic interventions are to be devised and used early in the course of the disease. There is therefore a pressing need for more sensitive and specific diagnostic tests with which we can detect AD in the preclinical stage. The tau proteins and beta-amyloid proteins start to accumulate 20 years before the symptoms begin to manifest. Detecting them in the preclinical stage would be a potential breakthrough in the management of AD. A high degree of clinical suspicion is needed to correlate problems in cognition with the changes in the eye, particularly the retina, pupil and ocular movements, so that the disease can be detected early and managed in the prodromal phase. In this systematic review, we ask the question whether the retina can be used to make a specific and early diagnosis of AD.

Absence of Alzheimer Disease Neuropathologic Changes in Eyes of Subjects With Alzheimer Disease

Alzheimer disease (AD) is the most common cause of dementia in the elderly, and is characterized by extracellular deposition of β-amyloid and intracellular accumulation of hyperphosphorylated tau protein in the brain. These pathologic findings are identified postmortem. Various visual deficits in AD have been reported and there have been conflicting reports, through imaging and pathology studies, regarding the presence of changes in the globe that mirror Alzheimer changes in the brain. Moreover, both macular degeneration and glaucoma have been variously characterized as having AD-related features. We examined one or both eyes from 19 autopsy cases, 17 of which had varying degrees of AD-related changes, and 2 of which were age-matched controls. Three cases had glaucoma and 4 had macular degeneration. Immunohistochemistry for tau, β-amyloid, TDP-43, ubiquitin, and α-synuclein showed no evidence of inclusions, deposits or other protein accumulation in any case, in any part of the globe. This finding suggests that regardless of the severity of changes seen in the brain in AD, there are no similar changes in the globe.

Glaucoma: the retina and beyond

Over 60 million people worldwide are diagnosed with glaucomatous optic neuropathy, which is estimated to be responsible for 8.4 million cases of irreversible blindness globally. Glaucoma is associated with characteristic damage to the optic nerve and patterns of visual field loss which principally involves the loss of retinal ganglion cells (RGCs). At present, intraocular pressure (IOP) presents the only modifiable risk factor for glaucoma, although RGC and vision loss can continue in patients despite well-controlled IOP. This, coupled with the present inability to diagnose glaucoma until relatively late in the disease process, has led to intense investigations towards the development of novel techniques for the early diagnosis of disease. This review outlines our current understanding of the potential mechanisms underlying RGC and axonal loss in glaucoma. Similarities between glaucoma and other neurodegenerative diseases of the central nervous system are drawn before an overview of recent developments in techniques for monitoring RGC health is provided, including recent progress towards the development of RGC specific contrast agents. The review concludes by discussing techniques to assess glaucomatous changes in the brain using MRI and the clinical relevance of glaucomatous-associated changes in the visual centres of the brain.

Translational biomarkers: from discovery and development to clinical practice

The refinement of disease taxonomy utilizing molecular phenotypes has led to significant improvements in the precision of disease diagnosis and customization of treatment options. This has also spurred efforts to identify novel biomarkers to understand the impact of therapeutically altering the underlying molecular network on disease course, and to support decision-making in drug discovery and development. However, gaps in knowledge regarding disease heterogeneity, combined with the inadequacies of surrogate disease model systems, make it challenging to demonstrate the unequivocal association of molecular and physiological biomarkers to disease pathology. This article will discuss the current landscape in biomarker research and highlight strategies being adopted to increase the likelihood of transitioning biomarkers from discovery to medical practice to enable more objective decision making, and to improve health outcome.

Advances in retinal ganglion cell imaging

Glaucoma is one of the leading causes of blindness worldwide and will affect 79.6 million people worldwide by 2020. It is caused by the progressive loss of retinal ganglion cells (RGCs), predominantly via apoptosis, within the retinal nerve fibre layer and the corresponding loss of axons of the optic nerve head. One of its most devastating features is its late diagnosis and the resulting irreversible visual loss that is often predictable. Current diagnostic tools require significant RGC or functional visual field loss before the threshold for detection of glaucoma may be reached. To propel the efficacy of therapeutics in glaucoma, an earlier diagnostic tool is required. Recent advances in retinal imaging, including optical coherence tomography, confocal scanning laser ophthalmoscopy, and adaptive optics, have propelled both glaucoma research and clinical diagnostics and therapeutics. However, an ideal imaging technique to diagnose and monitor glaucoma would image RGCs non-invasively with high specificity and sensitivity in vivo. It may confirm the presence of healthy RGCs, such as in transgenic models or retrograde labelling, or detect subtle changes in the number of unhealthy or apoptotic RGCs, such as detection of apoptosing retinal cells (DARC). Although many of these advances have not yet been introduced to the clinical arena, their successes in animal studies are enthralling. This review will illustrate the challenges of imaging RGCs, the main retinal imaging modalities, the in vivo techniques to augment these as specific RGC-imaging tools and their potential for translation to the glaucoma clinic.