A Diet Enriched in Palmitate and Deficient in Linoleate Exacerbates Oxidative Stress and Amyloid-β Burden in the Hippocampus of 3xTg-AD Mouse Model of Alzheimer’s Disease

Phytochemicals targeting Alzheimer's disease via the AMP-activated protein kinase pathway, effects, and mechanisms of action

Alzheimer's disease (AD), characterized by cognitive dysfunction and other behavioral abnormalities, is a progressive neurodegenerative disease that occurs due to aging. Currently, effective drugs to mitigate or treat AD remain unavailable. AD is associated with several abnormalities in neuronal energy metabolism, such as decreased glucose uptake, mitochondrial dysfunction, and defects in cholesterol metabolism. Amp-activated protein kinase (AMPK) is an important serine/threonine protein kinase that regulates the energy status of cells. AMPK is widely present in eukaryotic cells and can sense and regulate energy metabolism to maintain energy supply and demand balance, making it a promising target for energy metabolism-based AD therapy. Therefore, this review aimed to discuss the molecular mechanism of AMPK in the pathogenesis of AD to provide a theoretical basis for the development of new anti-AD drugs. To review the mechanisms of phytochemicals in the treatment of AD via AMPK pathway regulation, we searched PubMed, Google Scholar, Web of Science, and Embase databases using specific keywords related to AD and phytochemicals in September 2023. Phytochemicals can activate AMPK or regulate the AMPK pathway to exert therapeutic effects in AD. The anti-AD mechanisms of these phytochemicals include inhibiting Aβ aggregation, preventing Tau hyperphosphorylation, inhibiting inflammatory response and glial activation, promoting autophagy, and suppressing anti-oxidative stress. Additionally, several AMPK-related pathways are involved in the anti-AD mechanism, including the AMPK/CaMKKβ/mTOR, AMPK/SIRT1/PGC-1α, AMPK/NF-κB/NLRP3, AMPK/mTOR, and PERK/eIF2α pathways. Notably, urolithin A, artemisinin, justicidin A, berberine, stigmasterol, arctigenin, and rutaecarpine are promising AMPK agonists with anti-AD effects. Several phytochemicals are effective AMPK agonists and may have potential applications in AD treatment. Overall, phytochemical-based drugs may overcome the barriers to the effective treatment of neurodegenerative diseases.

Palmitate and glucose increase amyloid precursor protein in extracellular vesicles: Missing link between metabolic syndrome and Alzheimer's disease

The metabolic syndrome (MetS) and Alzheimer's disease share several pathological features, including insulin resistance, abnormal protein processing, mitochondrial dysfunction and elevated inflammation and oxidative stress. The MetS constitutes elevated fasting glucose, obesity, dyslipidaemia and hypertension and increases the risk of developing Alzheimer's disease, but the precise mechanism remains elusive. Insulin resistance, which develops from a diet rich in sugars and saturated fatty acids, such as palmitate, is shared by the MetS and Alzheimer's disease. Extracellular vesicles (EVs) are also a point of convergence, with altered dynamics in both the MetS and Alzheimer's disease. However, the role of palmitate- and glucose-induced insulin resistance in the brain and its potential link through EVs to Alzheimer's disease is unknown. We demonstrate that palmitate and high glucose induce insulin resistance and amyloid precursor protein phosphorylation in primary rat embryonic cortical neurons and human cortical stem cells. Palmitate also triggers insulin resistance in oligodendrocytes, the supportive glia of the brain. Palmitate and glucose enhance amyloid precursor protein secretion from cortical neurons via EVs, which induce tau phosphorylation when added to naïve neurons. Additionally, EVs from palmitate-treated oligodendrocytes enhance insulin resistance in recipient neurons. Overall, our findings suggest a novel theory underlying the increased risk of Alzheimer's disease in MetS mediated by EVs, which spread Alzheimer's pathology and insulin resistance.

Type 2 Diabetes and Alzheimer's Disease: The Emerging Role of Cellular Lipotoxicity

Type 2 diabetes (T2D) and Alzheimer's diseases (AD) represent major health issues that have reached alarming levels in the last decades. Although growing evidence demonstrates that AD is a significant comorbidity of T2D, and there is a ~1.4-2-fold increase in the risk of developing AD among T2D patients, the involvement of possible common triggers in the pathogenesis of these two diseases remains largely unknown. Of note, recent mechanistic insights suggest that lipotoxicity could represent the missing ring in the pathogenetic mechanisms linking T2D to AD. Indeed, obesity, which represents the main cause of lipotoxicity, has been recognized as a major risk factor for both pathological conditions. Lipotoxicity can lead to inflammation, insulin resistance, oxidative stress, ceramide and amyloid accumulation, endoplasmic reticulum stress, ferroptosis, and autophagy, which are shared biological events in the pathogenesis of T2D and AD. In the current review, we try to provide a critical and comprehensive view of the common molecular pathways activated by lipotoxicity in T2D and AD, attempting to summarize how these mechanisms can drive future research and open the way to new therapeutic perspectives.

Oxidative stress, the immune response, synaptic plasticity, and cognition in transgenic models of Alzheimer disease

INTRODUCTION

Worldwide, approximately 50 million people have dementia, with Alzheimer disease (AD) being the most common type, accounting for 60%-70% of cases. Given its high incidence, it is imperative to design studies to expand our knowledge about its onset and development, and to develop early diagnosis strategies and/or possible treatments. One methodological strategy is the use of transgenic mouse models for the study of the factors involved in AD aetiology, which include oxidative stress and the immune response.

DEVELOPMENT

We searched the PubMed, Scopus, and Google Scholar databases for original articles and reviews published between 2013 and 2019. In this review, we address two factors that have been studied independently, oxidative stress and the immune response, in transgenic models of AD, and discuss the relationship between these factors and their impact on the loss of synaptic and structural plasticity, resulting in cognitive impairment.

CONCLUSION

This review describes possible mechanisms by which oxidative stress and the immune response participate in the molecular, cellular, and behavioural effects of AD, observing a close relationship between these factors, which lead to cognitive impairment.

Fatty Acids: An Insight into the Pathogenesis of Neurodegenerative Diseases and Therapeutic Potential

One of the most common lipids in the human body is palmitic acid (PA), a saturated fatty acid with essential functions in brain cells. PA is used by cells as an energy source, besides being a precursor of signaling molecules and protein tilting across the membrane. Although PA plays physiological functions in the brain, its excessive accumulation leads to detrimental effects on brain cells, causing lipotoxicity. This mechanism involves the activation of toll-like receptors (TLR) and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) pathways, with the consequent release of pro-inflammatory cytokines, increased production of reactive oxygen species (ROS), endoplasmic reticulum (ER) stress, and autophagy impairment. Importantly, some of the cellular changes induced by PA lead to an augmented susceptibility to the development of Alzheimer's and Parkinson´s diseases. Considering the complexity of the response to PA and the intrinsic differences of the brain, in this review, we provide an overview of the molecular and cellular effects of PA on different brain cells and their possible relationships with neurodegenerative diseases (NDs). Furthermore, we propose the use of other fatty acids, such as oleic acid or linoleic acid, as potential therapeutic approaches against NDs, as these fatty acids can counteract PA's negative effects on cells.

Saikosaponin-D Mitigates Oxidation in SH-SY5Y Cells Stimulated by Glutamate Through Activation of Nrf2 Pathway: Involvement of PI3K

Alzheimer's disease (AD) is a typical neurodegenerative disease. Well-established studies have shown an elevated level of ROS (reactive oxygen species) that induces oxidative stress in AD. Saikosaponin-D exhibited significant therapeutic effects on neurodegenerative diseases. However, its in-depth molecular mechanisms against neurotoxicity remain not fully uncovered. Herein, the possible protective effects of saikosaponin-D on glutamate-induced neurotoxicity in SH-SY5Y cells and the underlying mechanism were elucidated. Saikosaponin-D pretreatment could ameliorate glutamate-induced cytotoxicity according to MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay and depress apoptosis according to Hoechst 33,342 staining and Annexin V-FITC/PI double staining in SH-SY5Y cells. Additionally, saikosaponin-D administration suppressed oxidative stress in response to glutamate indicated by diminished intracellular ROS formation and reduced MDA (malondialdehyde) content in SH-SY5Y cells. These phenomena, appeared to correlate with the recovered cellular antioxidant enzyme activities and inducted HO-1 (heme oxygenase-1) expression accompanying the nuclear translocation of Nrf2 conduct by saikosaponin-D preconditioning which had been altered by glutamate, were correlated with its neuroprotective. Furthermore, addition of LY294002, a selective inhibitor of PI3K (phosphatidylinositol 3 kinase), blocked saikosaponin-D-caused Nrf2 nuclear translocation and reversed the protection of saikosaponin-D against glutamate in SH-SY5Y cells. Moreover, saikosaponin-D exhibited antioxidant potential with high free radical-scavenging activity as confirmed by a DPPH (2,2-diphenyl-1-picrylhydrazyl) and TEAC (Trolox equivalent antioxidant capacity) in a cell-free system in vitro. Taken together, our results indicated that saikosaponin-D enhanced cellular antioxidant capacity through not only intrinsic free radical-scavenging activity but also induction of endogenous antioxidant enzyme activities and HO-1 expression mediated, at least in part, by activating PI3K and subsequently Nrf2 nuclear translocation, thereby protecting the SH-SY5Y cells from glutamate-induced oxidative cytotoxicity. In concert, these data raise the possibility that saikosaponin-D may be an attractive candidate for prevention and treatment of AD and other diseases related to oxidation in the future.

Oxidative stress, the immune response, synaptic plasticity, and cognition in transgenic models of Alzheimer disease

INTRODUCTION

Worldwide, approximately 50 million people have dementia, with Alzheimer disease (AD) being the most common type, accounting for 60%-70% of cases. Given its high incidence, it is imperative to design studies to expand our knowledge about its onset and development, and to develop early diagnosis strategies and/or possible treatments. One methodological strategy is the use of transgenic mouse models for the study of the factors involved in AD aetiology, which include oxidative stress and the immune response.

DEVELOPMENT

We searched the PubMed, Scopus, and Google Scholar databases for original articles and reviews published between 2013 and 2019. In this review, we address 2 factors that have been studied independently, oxidative stress and the immune response, in transgenic models of AD, and discuss the relationship between these factors and their impact on the loss of synaptic and structural plasticity, resulting in cognitive impairment.

CONCLUSION

This review describes possible mechanisms by which oxidative stress and the immune response participate in the molecular, cellular, and behavioural effects of AD, observing a close relationship between these factors, which lead to cognitive impairment.

Elevated Plasma Free Fatty Acid Susceptible to Early Cognitive Impairment in Type 2 Diabetes Mellitus

BACKGROUND

Elevated free fatty acid (FFA) induces lipotoxicity, attributed to diabetes and cognitive decline. Sterol regulatory element-binding protein-1c (SREBP-1c) regulates lipid metabolism.

OBJECTIVE

We investigated the roles of FFA in mild cognitive impairment (MCI) of type 2 diabetes mellitus (T2DM) patients and determine its association with rs11868035 polymorphism.

METHODS

We recruited 191 Chinese T2DM patients into two groups through Montreal Cognitive Assessment. Demographic and clinical data were collected, multiple domain cognitive functions were tested, plasma FFA levels were measured through ELISA, and SREBP-1c rs11868035 genotype was detected using the Seqnome method.

RESULTS

In comparison with the healthy-cognition group (n = 128), the MCI group (n = 63) displayed lower glucose control (p = 0.012) and higher plasma FFA level (p = 0.021), which were independent risk factors of MCI in T2DM patients in multivariate regression analysis (OR = 1.270, p = 0.003; OR = 1.005, p = 0.036). Additionally, the plasma FFA levels of MCI patients were positively correlated with Stroop color word test-C time scores (r = 0.303, p = 0.021) and negatively related to apolipoprotein A1 levels (r = -0.311, p = 0.017), which are associated positively with verbal fluency test scores (r = 0.281, p = 0.033). Both scores reflected attention ability and executive function. Moreover, the G allele carriers of rs11868035 showed higher digit span test scores than non-carriers in T2DM patients (p = 0.019) but without correlation with plasma FFA levels.

CONCLUSION

In T2DM, elevated plasma level of FFA, when combined with lower apolipoprotein A1 level portends abnormal cholesterol transport, were susceptible to early cognitive impairment, especially for attention and execution deficits. The G allele of SREBP-1c rs11868035 may be a protective factor for memory.