Current Topics in Medicinal Chemistry - Volume 16, Issue 5, 2016

Recently, formaldehyde (FA), existing in a number of different cells including neural cells, was found to affect age-related cognitive impairment. Oral administration of methanol (the metabolic precursor of FA) triggers formation of senile plaques (SPs) and Tau hyperphosphorylation in the brains of monkeys with memory decline. Intraperitoneal injection of FA leads to hyperphosphorylation of Tau in wild-type mouse brains and N2a cells through activation of glycogen synthase kinase-3β (GSK-3β). Furthermore, formaldehyde at low concentrations can directly induce Tau aggregation and amyloid β (Aβ) peptide deposits in vitro. Formaldehyde-induced Tau aggregation is implicated in cytotoxicity and neural cell apoptosis. Clarifying how FA triggers Aβ deposits and Tau hyperphosphorlyation will not only improve our understanding of the molecular and cellular mechanisms of age-related cognitive impairment but will also contribute to the ongoing investigation of alternate targets for new drugs. Here, we review the role of FA, particularly that of endogenous origin, in protein aggregation and as a potential drug intervention in the development of agerelated cognitive impairment.

Sporadic Alzheimer's disease (AD) is caused by multiple etiological factors, among which impaired brain insulin signaling and decreased brain glucose metabolism are important metabolic factors. Contrary to previous belief that insulin would not act in the brain, studies in the last three decades have proven important roles of insulin and insulin signaling in various biological functions in the brain. Impaired brain insulin signaling or brain insulin resistance and its role in the molecular pathogenesis of sporadic AD have been demonstrated. Thus, targeting brain insulin signaling for the treatment of cognitive impairment and AD has now attracted much attention in the field of AD drug discovery. This article reviews recent studies that target brain insulin signaling, especially those investigations on intranasal insulin administration and drugs that improve insulin sensitivity, including incretins, dipeptidyl peptidase IV inhibitors, thiazolidinediones, and metformin. These drugs have been previously approved for the treatment of diabetes mellitus, which could expedite their development for the treatment of AD. Although larger clinical trials are needed for validating their efficacy for the treatment of cognitive impairment and AD, results of animal studies and clinical trials available to date are encouraging.

Alzheimer’s disease (AD) is the most prevalent human neurodegenerative disease. Disturbances of brain glucose uptake, glucose tolerance, glucose utilization and of the insulin/insulin receptor signaling cascade are thought to be key features of the pathophysiology of AD. Changes in energy homeostasis in the brain and in the periphery dramatically influence the proliferation of adult neural stem cells and neurogenesis in the hippocampus. Recent findings suggest that adult neurogenesis is altered in the hippocampus of AD patients and in various animal models of AD. Several factors associated with the pathogenesis of AD are also known to be involved in the regulation of adult neurogenesis. Understanding the mechanisms underlying these changes at different stages of AD could provide insights into its pathogenesis, contribute to identifying biomarkers of early AD, and supply fundamental knowledge that will allow novel therapeutic approaches to treating AD by intervening in adult neurogenesis. In this review we provide an overview of the connections between energy metabolism, adult neurogenesis and AD.

Carbonylation due to oxidation and glycation is an important biochemical cause of degenerative diseases and aging. While the enigma of aging is understood as a result of molecular dysfunction due to the failure of maintenance systems, a brief history of the interpretation of aging mechanisms and the exact biochemistry connecting entropy and biological aging is addressed. Lipofuscin formation mechanisms resulting in irreparable accumulative changes represent the most important aging- related alterations of entropy increase in biological kingdom, which is very different from the damage-based “aging” process of inorganic materials. A fifth level of aging mechanism investigations that highlights the importance of functional groups of biochemistry, the “missing codes” of life science, is put forward in this review. Significance and validities of such ‘life codes’ in biology beyond genomic and proteomic concepts has also been clarified. An open-minded consideration of functional groups of biomolecules, such as carbonyl groups, may help to explain the mechanisms of fatigue and sleep in terms of neurobiochemistry and biological pharmaco-medicine.

Background: Ginkgo biloba is a natural medicine used for cognitive impairment and Alzheimer’s disease. The objective of this review is to explore the effectiveness and safety of Ginkgo biloba in treating mild cognitive impairment and Alzheimer’s disease. Methods: Electronic search was conducted from PubMed, Cochrane Library, and four major Chinese databases from their inception up to 1st December, 2014 for randomized clinical trials on Ginkgo biloba in treating mild cognitive impairment or Alzheimer’s disease. Meta-analyses were performed by RevMan 5.2 software. Results: 21 trials with 2608 patients met the inclusion criteria. The general methodological quality of included trials was moderate to poor. Compared with conventional medicine alone, Ginkgo biboba in combination with conventional medicine was superior in improving Mini-Mental State Examination (MMSE) scores at 24 weeks for patients with Alzheimer’s disease (MD 2.39, 95% CI 1.28 to 3.50, P<0.0001) and mild cognitive impairment (MD 1.90, 95% CI 1.41 to 2.39, P<0.00001), and Activity of Daily Living (ADL) scores at 24 weeks for Alzheimer’s disease (MD -3.72, 95% CI -5.68 to -1.76, P=0.0002). When compared with placebo or conventional medicine in individual trials, Ginkgo biboba demonstrated similar but inconsistent findings. Adverse events were mild. Conclusion: Ginkgo biloba is potentially beneficial for the improvement of cognitive function, activities of daily living, and global clinical assessment in patients with mild cognitive impairment or Alzheimer’s disease. However, due to limited sample size, inconsistent findings and methodological quality of included trials, more research are warranted to confirm the effectiveness and safety of ginkgo biloba in treating mild cognitive impairment and Alzheimer’s disease.

Background: There is no curative treatment for Alzheimer’s disease (AD). Ginseng is widely used in the treatment of AD in Asian countries. Objective: To evaluate the effectiveness and safety of ginseng for AD. Methods: We searched seven main databases for randomized clinical trials (RCTs) on ginseng for AD from their inception to December 2014. The Cochrane risk of bias tool was used to assess the methodological quality. We used RevMan 5.2 to synthesize the results. Results: Four RCTs involving 259 participants were identified for this systematic review. The methodological quality of included studies was not promising. All comparisons were made between combined treatment (ginseng plus conventional treatment) versus conventional treatment. The results of meta-analyses and several individual studies showed that the effectiveness of combined treatment was inconsistent as measured by MMSE, ADAS-cog, ADAS-noncog, and CDR. No studies reported the outcomes of quality of life (QoL). The current data did not report serious adverse events. Conclusion: This review showed that the effects of ginseng on AD were still inconclusive. The main limitations of the available studies were small sample sizes, poor methodological qualities and no placebo controls. Larger, well-designed studies are needed to test the effect of ginseng on AD in the future.

Alzheimer’s disease (AD) is a multifactorial complex disease. The pathogenesis of AD is very complicated, and involves the β-amyloid (Aβ) cascade, tau hyperphosphorylation, neuroinflammation, oxidative stress, mitochondrial dysfunction, reduced levels of neurotrophic factors, and damage and loss of synapses as well as cholinergic neurons. The multi-target characteristics of traditional Chinese medicine (TCM) may be advantageous over single-target drugs in the treatment of complex diseases. These drugs have therefore attracted more attention in the research and development of AD therapies. This review describes advances made in experimental studies of TCM for AD treatment. It discusses research, from our group and other laboratories, on TCM compound drugs (Shenwu capsule) and approximately 10 Chinese medicinal herb extracts (tetrahydroxystilbene glucoside, epimedium flavonoid, icariin, cornel iridoid glycoside, ginsenoside, puerarin, clausenamide, huperzine A, and timosaponins).

γ-secretase is a membrane-embedded aspartyl protease carrying out cleavage of more than 100 single transmembrane-spanning proteins, including APP, Notch, N-cadherin, etc. Its subunit, presenilin (PS) is the catalytic component, of which mutations are a major cause of early onset familial Alzheimer disease (FAD). These mutations lead to an increase in the production of the highly amyloidogenic Aβ42 isoform. Drugs aimed at γ-secretase are now considered to be promising therapeutic targets for AD. γ-secretase inhibitors (GSIs) were first introduced into clinical trials due to their efficacy in lowering Aβ production, but later were found to cause severe adverse events due to their blockage of the Notch signaling process. γ-secretase modulators (GSMs) were developed to modulate γ-secretase activity by selectively targeting Aβ42 reduction over the Notch pathway, which have been shown to have less side effects. Although clinical studies show that none of the GSIs or GSMs have been proven to be fully effective, they shed light on the physiological role of γ-secretase and PS in AD development. At the same time, natural products, due to their structural diversity and pleiotropic profile, can modulate γ-secretase activity in a dose-dependent manner, broadening our vision of drug development. With the structural information of γ-secretase released recently, we speculate there will be an explosion of γ-secretase modulators targeting not only the proteolysic center but also the interaction of its different components.

Both Docosahexaenoic acid (DHA) and Phosphatidylcholine (PC) have been shown to halt the pathogenesis of Alzheimer disease (AD) and vascular dementia. This study aimed to investigate the role of DHA-containing PC (DHA-PC) in the improvement of Aβ25-35-induced cognitive deficits in rats. Aβ25-35-induced AD rats were treated for 30 days with DHA-PC, which was extracted from Sthenoteuthis oualaniensis spawns. Cognitive improvement of the AD rats was detected using the Morris water maze (MWM). The results demonstrated that DHA-PC could improve the learning and memory abilities of AD rats in a dose-dependent pattern. Further analyses showed that expression of phosphorylated tau decreased, and the neuronal morphology recovered in brains of DHA-PC-treated AD rats, as compared with mock-treated AD rats. In addition, DHAPC treatment increased the activity of GSH-Px and SOD in the cortex and hippocampus of AD rats. Taken together, these data suggest that DHA-PC is able to improve the cognitive deficits in AD rats, probably through decreasing the phosphorylation of tau in the cortex and hippocampus CA1 area, and increasing the GSH-Px and SOD activities in the brain of AD rats.

Levetiracetam is a homologue of piracetam with an a-ethyl side-chain substitution and it is a Food and Drug Administration (FDA) approved antiepileptic drug. Recently, several studies have found that levetiracetam was able to reduce seizure frequency in epileptic seizures patients without affecting their cognitive functions. In the present review, the effects of levetiracetam on cognitive improvement were summarized in epileptic seizures patients with or without Alzheimer's disease (AD), high-grade glioma (HGG) patients and amnestic mild cognitive impairment (aMCI) patients. In addition, levetiracetam was observed to improve the cognitive deficits in normal aged animals and the transgenic animal models with AD, suggesting that levetiracetam may be a better choice for the prevention or treatment of AD.

Alzheimer’s disease is the most common type of dementia in the aging population worldwide. The etiology and treatment of Alzheimer’s disease are still not very clear. Finding a new treatment is urgent due to the increasing population aging. Acupuncture has been practicing in China for more than 3000 years and reported to be beneficial in treating cognitive impairment of Alzheimer’s disease. This paper reviews the recent development on the effect of acupuncture on Alzheimer’s disease in animal-based researches. It is suggested that acupuncture improves cognitive function of Alzheimer’s disease by regulating glucose metabolism, enhancing neurotransmission as well as reducing oxidative stress, Aβ protein deposition, and neuronal apoptosis. However, it is still difficult to clarify which specific signaling pathway contributes to the acupuncture effect. Better designed studies are recommended to investigate the effects of acupuncture on Alzheimer’s disease.