Genetic variants conferring susceptibility to Alzheimer's disease in the general population; do they also predispose to dementia in Down's syndrome

From the Bush to the Brain: Preclinical Stages of Ethnobotanical Anti-Inflammatory and Neuroprotective Drug Discovery-An Australian Example

The Australian rainforest is a rich source of medicinal plants that have evolved in the face of dramatic environmental challenges over a million years due to its prolonged geographical isolation from other continents. The rainforest consists of an inherent richness of plant secondary metabolites that are the most intense in the rainforest. The search for more potent and more bioavailable compounds from other plant sources is ongoing, and our short review will outline the pathways from the discovery of bioactive plants to the structural identification of active compounds, testing for potency, and then neuroprotection in a triculture system, and finally, the validation in an appropriate neuro-inflammatory mouse model, using some examples from our current research. We will focus on neuroinflammation as a potential treatment target for neurodegenerative diseases including multiple sclerosis (MS), Parkinson's (PD), and Alzheimer's disease (AD) for these plant-derived, anti-inflammatory molecules and highlight cytokine suppressive anti-inflammatory drugs (CSAIDs) as a better alternative to conventional nonsteroidal anti-inflammatory drugs (NSAIDs) to treat neuroinflammatory disorders.

Pharmacological considerations for treating neuroinflammation with curcumin in Alzheimer's disease

Prof. Dr. Peter Riederer, the former Head of the Neurochemistry Department of the Psychiatry and Psychotherapy Clinic at the University of Würzburg (Germany), has been one of the pioneers of research into oxidative stress in Parkinson's and Alzheimer's disease (AD). This review will outline how his scientific contribution to the field has opened a new direction for AD treatment beyond "plaques and tangles". In the 1990s, Prof. Riederer was one of the first scientists who proposed oxidative stress and neuroinflammation as one of the major contributors to Alzheimer's disease, despite the overwhelming support for the "amyloid-only" hypothesis at the time, which postulated that the sole and only cause of AD is β-amyloid. His group also highlighted the role of advanced glycation end products, sugar and dicarbonyl-derived protein modifications, which crosslink proteins into insoluble aggregates and potent pro-inflammatory activators of microglia. For the treatment of chronic neuroinflammation, he and his group suggested that the most appropriate drug class would be cytokine-suppressive anti-inflammatory drugs (CSAIDs) which have a broader anti-inflammatory action range than conventional non-steroidal anti-inflammatory drugs. One of the most potent CSAIDs is curcumin, but it suffers from a variety of pharmacokinetic disadvantages including low bioavailability, which might have tainted many human clinical trials. Although a variety of oral formulations with increased bioavailability have been developed, curcumin's absorption after oral delivery is too low to reach therapeutic concentrations in the micromolar range in the systemic circulation and the brain. This review will conclude with evidence that rectally applied suppositories might be the best alternatives to oral medications, as this route will be able to evade first-pass metabolism in the liver and achieve high concentrations of curcumin in plasma and tissues, including the brain.

Effects of a solid lipid curcumin particle formulation on chronic activation of microglia and astroglia in the GFAP-IL6 mouse model

Chronic glial activation is characterized by increased numbers of activated glial cells, secreting free radicals and cytotoxic cytokines, subsequently causing neuronal damage. In order to investigate the anti-inflammatory activity of Longvida^® Optimised Curcumin (LC), we fed 500 ppm of LC to 2-month-old wild type and GFAP-IL6 mice for 6 months. LC feeding led to a significant reduction in the number of Iba-1⁺ microglia by 26% in the hippocampus and by 48% in the cerebellum, GFAP⁺ astrocytes by 30%, and TSPO⁺ cells by 24% in the hippocampus and by 31% in the cerebellum of the GFAP-IL6 mice. The morphology of the cells was assessed and LC significantly decreased the dendritic length of microglia and the convex area, convex perimeter, dendritic length, nodes and number of processes of astrocytes in the hippocampus while decreasing the soma area and perimeter in the cerebellum, in LC-fed GFAP-IL6 mice. In addition, LC feeding increased pre- and postsynaptic protein levels and improved balance measured by Rotarod. Together, these data suggest that LC is able to attenuate the inflammatory pathology and ameliorate neurodegeneration and motor deficits in GFAP-IL6 mice. For patients with neuro-inflammatory disorders, LC might potentially reverse the detrimental effects of chronic glial activation.

Down Syndrome, Ageing and Epigenetics

During the past decades, life expectancy of subjects with Down syndrome (DS) has greatly improved, but age-specific mortality rates are still important and DS subjects are characterized by an acceleration of the ageing process, which affects particularly the immune and central nervous systems. In this chapter, we will first review the characteristics of the ageing phenomenon in brain and in immune system in DS and we will then discuss the biological hallmarks of ageing in this specific population. Finally, we will also consider in detail the knowledge on epigenetics in DS, particularly DNA methylation.

Targeting Inflammatory Pathways in Alzheimer's Disease: A Focus on Natural Products and Phytomedicines

Studies of the brains of Alzheimer's disease (AD) patients have revealed key neuropathological features, such as the deposition of aggregates of insoluble amyloid-β (Aβ) peptides and neurofibrillary tangles (NFTs). These pathological protein deposits, including Aβ peptides (which form senile plaques) and hyperphosphorylated tau (which aggregates into NFTs), have been assumed to be 'the cause of AD'. Aβ has been extensively targeted to develop an effective disease-modifying therapy, but with limited clinical success. Emerging therapies are also now targeting further pathological processes in AD, including neuroinflammation. This review focuses on the inflammatory and oxidative stress-related changes that occur in AD, and discusses some emerging anti-inflammatory natural products and phytomedicines. Many of the promising compounds are cytokine-suppressive anti-inflammatory drugs (CSAIDs), which target the proinflammatory AP1 and nuclear factor-κB signalling pathways and inhibit the expression of many proinflammatory cytokines, such as interleukin (IL)-1, IL-6, tumour necrosis factor-α, or nitric oxide produced by inducible nitric oxide synthase. However, many of these phytomedicines have not been tested in rigorous clinical trials in AD patients. It is not yet clear if the active compounds reach an effective concentration in the brain (due to limited bioavailability) or if they can slow down AD progression in long-term trials. The authors suggest that it is crucial for both the pharmacological and complementary medicine industries to conduct and fund those studies to significantly advance the field.

Candidate gene analysis for Alzheimer's disease in adults with Down syndrome

Individuals with Down syndrome (DS) overexpress many genes on chromosome 21 due to trisomy and have high risk of dementia due to the Alzheimer's disease (AD) neuropathology. However, there is a wide range of phenotypic differences (e.g., age at onset of AD, amyloid β levels) among adults with DS, suggesting the importance of factors that modify risk within this particularly vulnerable population, including genotypic variability. Previous genetic studies in the general population have identified multiple genes that are associated with AD. This study examined the contribution of polymorphisms in these genes to the risk of AD in adults with DS ranging from 30 to 78 years of age at study entry (N = 320). We used multiple logistic regressions to estimate the likelihood of AD using single-nucleotide polymorphisms (SNPs) in candidate genes, adjusting for age, sex, race/ethnicity, level of intellectual disability and APOE genotype. This study identified multiple SNPs in APP and CST3 that were associated with AD at a gene-wise level empirical p-value of 0.05, with odds ratios in the range of 1.5-2. SNPs in MARK4 were marginally associated with AD. CST3 and MARK4 may contribute to our understanding of potential mechanisms where CST3 may contribute to the amyloid pathway by inhibiting plaque formation, and MARK4 may contribute to the regulation of the transition between stable and dynamic microtubules.

Medicinal Plants of the Australian Aboriginal Dharawal People Exhibiting Anti-Inflammatory Activity

Chronic inflammation contributes to multiple ageing-related musculoskeletal and neurodegenerative diseases, cardiovascular diseases, asthma, rheumatoid arthritis, and inflammatory bowel disease. More recently, chronic neuroinflammation has been attributed to Parkinson's and Alzheimer's disease and autism-spectrum and obsessive-compulsive disorders. To date, pharmacotherapy of inflammatory conditions is based mainly on nonsteroidal anti-inflammatory drugs which in contrast to cytokine-suppressive anti-inflammatory drugs do not influence the production of cytokines such as tumour necrosis factor-α or nitric oxide. However, their prolonged use can cause gastrointestinal toxicity and promote adverse events such as high blood pressure, congestive heart failure, and thrombosis. Hence, there is a critical need to develop novel and safer nonsteroidal anti-inflammatory drugs possessing alternate mechanism of action. In this study, plants used by the Dharawal Aboriginal people in Australia for the treatment of inflammatory conditions, for example, asthma, arthritis, rheumatism, fever, oedema, eye inflammation, and inflammation of bladder and related inflammatory diseases, were evaluated for their anti-inflammatory activity in vitro. Ethanolic extracts from 17 Eucalyptus spp. (Myrtaceae) were assessed for their capacity to inhibit nitric oxide and tumor necrosis factor-α production in RAW 264.7 macrophages. Eucalyptus benthamii showed the most potent nitric oxide inhibitory effect (IC₅₀  5.57 ± 1.4 µg/mL), whilst E. bosistoana, E. botryoides, E. saligna, E. smithii, E. umbra, and E. viminalis exhibited nitric oxide inhibition values between 7.58 and 19.77 µg/mL.

Novel promising therapeutics against chronic neuroinflammation and neurodegeneration in Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder, characterized by deposition of amyloid plaques and neurofibrillary tangles, as well as microglial and astroglial activation, and, finally, leading to neuronal dysfunction and death. Current treatments for AD primarily focus on enhancement of cholinergic transmission. However, these treatments are only symptomatic, and no disease-modifying drug is available for the treatment of AD patients. This review will provide an overview of the antioxidant, anti-inflammatory, anti-amyloidogenic, neuroprotective, and cognition-enhancing effects of a variety of nutraceuticals including curcumin, apigenin, docosahexaenoic acid, epigallocatechin gallate, α-lipoic acid and resveratrol and their potential for AD prevention and treatment. We suggest that therapeutic use of these compounds might lead to a safe strategy to delay the onset of AD or slow down its progression. The continuing investigation of the potential of these substances is necessary as they are promising compounds to yield a possible remedy for this pervasive disease.

Curcumin and Apigenin - novel and promising therapeutics against chronic neuroinflammation in Alzheimer's disease

Alzheimer's disease is a progressive neurodegenerative disorder, characterized by deposition of amyloid beta, neurofibrillary tangles, astrogliosis and microgliosis, leading to neuronal dysfunction and loss in the brain. Current treatments for Alzheimer's disease primarily focus on enhancement of cholinergic transmission. However, these treatments are only symptomatic, and no disease-modifying drug is available for Alzheimer's disease patients. This review will provide an overview of the proven antioxidant, anti-inflammatory, anti-amyloidogenic, neuroprotective, and cognition-enhancing effects of curcumin and apigenin and discuss the potential of these compounds for Alzheimer's disease prevention and treatment. We suggest that these compounds might delay the onset of Alzheimer's disease or slow down its progression, and they should enter clinical trials as soon as possible.