Alzheimer's disease, cholesterol, and statins: the junctions of important metabolic pathways

Gut microbiota-host lipid crosstalk in Alzheimer's disease: implications for disease progression and therapeutics

Trillions of intestinal bacteria in the human body undergo dynamic transformations in response to physiological and pathological changes. Alterations in their composition and metabolites collectively contribute to the progression of Alzheimer's disease. The role of gut microbiota in Alzheimer's disease is diverse and complex, evidence suggests lipid metabolism may be one of the potential pathways. However, the mechanisms that gut microbiota mediate lipid metabolism in Alzheimer's disease pathology remain unclear, necessitating further investigation for clarification. This review highlights the current understanding of how gut microbiota disrupts lipid metabolism and discusses the implications of these discoveries in guiding strategies for the prevention or treatment of Alzheimer's disease based on existing data.

Protein lipidation in health and disease: molecular basis, physiological function and pathological implication

Posttranslational modifications increase the complexity and functional diversity of proteins in response to complex external stimuli and internal changes. Among these, protein lipidations which refer to lipid attachment to proteins are prominent, which primarily encompassing five types including S-palmitoylation, N-myristoylation, S-prenylation, glycosylphosphatidylinositol (GPI) anchor and cholesterylation. Lipid attachment to proteins plays an essential role in the regulation of protein trafficking, localisation, stability, conformation, interactions and signal transduction by enhancing hydrophobicity. Accumulating evidence from genetic, structural, and biomedical studies has consistently shown that protein lipidation is pivotal in the regulation of broad physiological functions and is inextricably linked to a variety of diseases. Decades of dedicated research have driven the development of a wide range of drugs targeting protein lipidation, and several agents have been developed and tested in preclinical and clinical studies, some of which, such as asciminib and lonafarnib are FDA-approved for therapeutic use, indicating that targeting protein lipidations represents a promising therapeutic strategy. Here, we comprehensively review the known regulatory enzymes and catalytic mechanisms of various protein lipidation types, outline the impact of protein lipidations on physiology and disease, and highlight potential therapeutic targets and clinical research progress, aiming to provide a comprehensive reference for future protein lipidation research.

Evaluation and targeting of amyloid precursor protein (APP)/amyloid beta (Aβ) axis in amyloidogenic and non-amyloidogenic pathways: A time outside the tunnel

In Alzheimer disease (AD), amyloid precursor protein (APP) and production of amyloid beta (Aβ) which is generated by amyloidogenic pathway is implicated in neurotoxicity and neuronal cell deaths. However, physiological Aβ level is essential to improves neuronal survival, attenuates neuronal apoptosis and has neuroprotective effect. In addition, physiological APP level has neurotrophic effect on the central nervous system (CNS). APP has a critical role in the brain growth and development via activation of long-term potentiation (LTP) and acceleration of neurite outgrowth. Moreover, APP is cleaved by α secretase to form a neuroprotective soluble APP alpha (sAPPα) in non-amyloidogenic pathway. Consequently, this mini-review purposes to highlight the possible beneficial role of APP and Aβ. In addition, this mini-review discussed the modulation of APP processing and Aβ production.

Cholesterol-dependent amyloid β production: space for multifarious interactions between amyloid precursor protein, secretases, and cholesterol

Amyloid β is considered a key player in the development and progression of Alzheimer's disease (AD). Many studies investigating the effect of statins on lowering cholesterol suggest that there may be a link between cholesterol levels and AD pathology. Since cholesterol is one of the most abundant lipid molecules, especially in brain tissue, it affects most membrane-related processes, including the formation of the most dangerous form of amyloid β, Aβ42. The entire Aβ production system, which includes the amyloid precursor protein (APP), β-secretase, and the complex of γ-secretase, is highly dependent on membrane cholesterol content. Moreover, cholesterol can affect amyloidogenesis in many ways. Cholesterol influences the stability and activity of secretases, but also dictates their partitioning into specific cellular compartments and cholesterol-enriched lipid rafts, where the amyloidogenic machinery is predominantly localized. The most complicated relationships have been found in the interaction between cholesterol and APP, where cholesterol affects not only APP localization but also the precise character of APP dimerization and APP processing by γ-secretase, which is important for the production of Aβ of different lengths. In this review, we describe the intricate web of interdependence between cellular cholesterol levels, cholesterol membrane distribution, and cholesterol-dependent production of Aβ, the major player in AD.

Structural diversity, hypothetical biosynthesis, chemical synthesis, and biological activity of Ganoderma meroterpenoids

Covering: 2018 to 2022Meroterpenoids found in fungal species of the genus Ganoderma and known as Ganoderma meroterpenoids (GMs) are substances composed of a 1,2,4-trisubstituted benzene and a polyunsaturated side chain. These substances have attracted the attention of chemists and pharmacologists due to their diverse structures and significant bioactivity. In this review, we present the structures and possible biosynthesis of representative GMs newly found from 2018 to 2022, as well as chemical synthesis and biological activity of some interesting GMs. We propose for the first time a plausible biosynthetic pathway for GMs, which will certainly motivate further research on the biosynthetic pathway in Ganoderma species, as well as on chemical synthesis of GMs as important bioactive compounds for the purpose of drug development.

Association Between Dietary and Serum Cholesterol and Cognitive Function Among the U.S. Elderly from NHANES 2011-2014

BACKGROUND

The association between dietary or serum cholesterol and cognitive performance in older adults has not been well-established.

OBJECTIVE

This study aimed to investigate the potential association between dietary or serum cholesterol and cognitive performance in the elderly population.

METHODS

A cross-sectional analysis was conducted using data from the National Health and Nutrition Examination Survey (NHANES) 2011-2012 and 2013-2014. Diet and supplement cholesterol was estimated based on two non-consecutive 24-hour dietary recalls. Cognitive function was assessed using various statistical tests. Poor cognitive performance was defined as scores below the lowest quartile within age groups. Regression models were adjusted for demographic factors, and subgroup analyses were performed for non-Hispanic White (NHW) and non-Hispanic Black (NHB) individuals.

RESULTS

Among 759 participants aged 60 years and above, dietary cholesterol was only associated with dietary saturated fatty acids and serum high-density lipoprotein cholesterol. There was no evidence of an association between dietary cholesterol and cognitive function, except for NHB individuals, where dietary cholesterol showed a positive correlation with cognitive function. In the overall sample and NHW participants, there were consistent positive associations between serum total cholesterol and cognitive performance across statistical tests, while such associations were rare among NHB individuals. Although not statistically significant, NHB individuals had higher dietary/supplementary/total cholesterol intake compared with NHW individuals.

CONCLUSION

Within the normal range, increasing serum cholesterol may be a potential factor to prevent or relieve cognitive dysfunction. However, ethnic differences should be taken into account when considering the association between cholesterol and cognitive performance.

Cholesterol as a key player in amyloid β-mediated toxicity in Alzheimer’s disease

Alzheimer’s disease (AD) is a neurodegenerative disorder that is one of the most devastating and widespread diseases worldwide, mainly affecting the aging population. One of the key factors contributing to AD-related neurotoxicity is the production and aggregation of amyloid β (Aβ). Many studies have shown the ability of Aβ to bind to the cell membrane and disrupt its structure, leading to cell death. Because amyloid damage affects different parts of the brain differently, it seems likely that not only Aβ but also the nature of the membrane interface with which the amyloid interacts, helps determine the final neurotoxic effect. Because cholesterol is the dominant component of the plasma membrane, it plays an important role in Aβ-induced toxicity. Elevated cholesterol levels and their regulation by statins have been shown to be important factors influencing the progression of neurodegeneration. However, data from many studies have shown that cholesterol has both neuroprotective and aggravating effects in relation to the development of AD. In this review, we attempt to summarize recent findings on the role of cholesterol in Aβ toxicity mediated by membrane binding in the pathogenesis of AD and to consider it in the broader context of the lipid composition of cell membranes.

Regulation of cholesterol homeostasis in health and diseases: from mechanisms to targeted therapeutics

Disturbed cholesterol homeostasis plays critical roles in the development of multiple diseases, such as cardiovascular diseases (CVD), neurodegenerative diseases and cancers, particularly the CVD in which the accumulation of lipids (mainly the cholesteryl esters) within macrophage/foam cells underneath the endothelial layer drives the formation of atherosclerotic lesions eventually. More and more studies have shown that lowering cholesterol level, especially low-density lipoprotein cholesterol level, protects cardiovascular system and prevents cardiovascular events effectively. Maintaining cholesterol homeostasis is determined by cholesterol biosynthesis, uptake, efflux, transport, storage, utilization, and/or excretion. All the processes should be precisely controlled by the multiple regulatory pathways. Based on the regulation of cholesterol homeostasis, many interventions have been developed to lower cholesterol by inhibiting cholesterol biosynthesis and uptake or enhancing cholesterol utilization and excretion. Herein, we summarize the historical review and research events, the current understandings of the molecular pathways playing key roles in regulating cholesterol homeostasis, and the cholesterol-lowering interventions in clinics or in preclinical studies as well as new cholesterol-lowering targets and their clinical advances. More importantly, we review and discuss the benefits of those interventions for the treatment of multiple diseases including atherosclerotic cardiovascular diseases, obesity, diabetes, nonalcoholic fatty liver disease, cancer, neurodegenerative diseases, osteoporosis and virus infection.

The Role of Lipid Rafts and Membrane Androgen Receptors in Androgen’s Neurotoxic Effects

Sex differences have been observed in multiple oxidative stress–associated neurodegenerative diseases. Androgens, such as testosterone, can exacerbate oxidative stress through a membrane androgen receptor (mAR), AR45, localized to lipid rafts in the plasma membrane. The goal of this study is to determine if interfering with mAR localization to cholesterol-rich lipid rafts decreases androgen induced neurotoxicity under oxidative stress environments. We hypothesize that cholesterol-rich caveolar lipid rafts are necessary for androgens to induce oxidative stress generation in neurons via the mAR localized within the plasma membrane. Nystatin was used to sequester cholesterol and thus decrease cholesterol-rich caveolar lipid rafts in a neuronal cell line (N27 cells). Nystatin was applied prior to testosterone exposure in oxidatively stressed N27 cells. Cell viability, endocytosis, and protein analysis of oxidative stress, apoptosis, and mAR localization were conducted. Our results show that the loss of lipid rafts via cholesterol sequestering blocked androgen-induced oxidative stress in cells by decreasing the localization of mAR to caveolar lipid rafts.

Protective effect of rosuvastatin pretreatment against acute myocardial injury by regulating Nrf2, Bcl-2/Bax, iNOS, and TNF-α expressions affecting oxidative/nitrosative stress and inflammation

Cardiovascular disorders are the leading cause of death globally. Rosuvastatin is a member of statins (inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A reductase) with many pleiotropic properties. This study investigated cardioprotective effects of rosuvastatin in isoprenaline-induced myocardial injury. Male rats were given rosuvastatin (1, 5, or 10 mg/kg, oral) daily for 1 week and on seventh and eighth day isoprenaline (150 mg/kg, subcutaneous) was given to induce cardiac injury. On ninth day, rats were euthanized and different samples were harvested for analysis. Isoprenaline administration resulted in increased cardiac mass, increased cardiac injury marker levels (cTnI, CK-MB, ALT, and AST), increased lipid/protein oxidation, and increased cardiac nitrite levels. It also decreased superoxide dismutase, CAT, GST, and glutathione reductase activities, and total antioxidant activity. Isoprenaline also increased TNF-α and IL-6 levels. Decreased mRNA expression of Nrf2 and Bcl-2 along with increased mRNA expression of Bax, eNOS and iNOS genes was observed in isoprenaline treated animals. Histopathological evaluations of rosuvastatin pre-treated groups showed reduction of myocardial necrosis. Pretreatment with rosuvastatin (5 and 10 mg/kg) reduced many of these pathological changes. The current study showed that rosuvastatin significantly reduces myocardial injury induced by isoprenaline.

((±)-Spiroganoapplanin A, a complex polycyclic meroterpenoid dimer from Ganoderma applanatum displaying the potential against Alzheimer’s disease

A pair of meroterpenoid dimers, (±)-spiroganoapplanain A (1) represents a new subtype of Ganoderma meroterpenoid dimers with a 6/5/5/6/5/6 hexacyclic system were isolated from Ganoderma applanatum. Their structures were determined...

Simvastatin Prevents Neurodegeneration in the MPTP Mouse Model of Parkinson's Disease via Inhibition of A1 Reactive Astrocytes

Emerging evidence indicates that A1 reactive astrocytes play crucial roles in the pathogenesis of Parkinson's disease (PD). Thus, development of agents that could inhibit the formation of A1 reactive astrocytes could be used to treat PD. Simvastatin has been touted as a potential neuroprotective agent for neurologic disorders such as PD, but the specific underlying mechanism remains unclear. The 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of PD and primary astrocytes/neurons were prepared to investigate the effects of simvastatin on PD and its underlying mechanisms in vitro and in vivo. We show that simvastatin protects against the loss of dopamine neurons and behavioral deficits in the MPTP mouse model of PD. We also found that simvastatin suppressed the expression of A1 astrocytic specific markers in vivo and in vitro. In addition, simvastatin alleviated neuron death induced by A1 astrocytes. Our findings reveal that simvastatin is neuroprotective via the prevention of conversion of astrocytes to an A1 neurotoxic phenotype. In light of simvastatin favorable properties, it should be evaluated in the treatment of PD and related neurologic disorders characterized by A1 reactive astrocytes.

Statin exposure and the risk of dementia in individuals with hypercholesterolaemia

OBJECTIVES

This study aimed to examine the association between statin exposure and dementia risk in individuals with hypercholesterolaemia using data from the NHIS-HEALS database between 2002 and 2015.

METHODS

Subjects were classified into statin exposure and statin nonexposure groups according to medication possession ratio. Dementia was defined as those with primary diagnostic dementia codes such as F00-F03, G30, G31.1, G31.9 or G31.82. Cox proportional hazards regression models were adopted after stepwise adjustment for confounders to investigate the prospective association between statin exposure and dementia risk.

RESULTS

During the follow-up period (median follow-up 11.7 years), 711 cases of dementia occurred, accounting for 11.5% of the total study population (statin exposure group, 8.2%; statin nonexposure group, 12.9%). Compared to the statin nonexposure group, fully adjusted hazard ratios (HRs) (95% confidence intervals [CIs]) for overall dementia in the statin exposure group were 0.63 (0.43-0.91) and 0.62 (0.50-0.78) in men and women, respectively. Compared to the statin nonexposure group, the HRs (95% CIs) for Alzheimer's disease and related dementia, vascular dementia and other types of dementia in the statin exposure group were 0.54 (0.32-0.91), 2.45 (0.69-8.68) and 0.59 (0.32-1.07), respectively, in men and 0.53 (0.38-0.73), 1.29 (0.42-3.96) and 0.70 (0.51-0.96), respectively, in women.

CONCLUSIONS

Hypercholesterolaemic individuals exposed to statin had a lower risk of overall dementia and Alzheimer's disease and related dementia in both sexes, and a lower risk of other types of dementia in women, than subjects who were not exposed to statins.

Lipid rafts and neurodegeneration: structural and functional roles in physiologic aging and neurodegenerative diseases

Lipid rafts are small, dynamic membrane areas characterized by the clustering of selected membrane lipids as the result of the spontaneous separation of glycolipids, sphingolipids, and cholesterol in a liquid-ordered phase. The exact dynamics underlying phase separation of membrane lipids in the complex biological membranes are still not fully understood. Nevertheless, alterations in the membrane lipid composition affect the lateral organization of molecules belonging to lipid rafts. Neural lipid rafts are found in brain cells, including neurons, astrocytes, and microglia, and are characterized by a high enrichment of specific lipids depending on the cell type. These lipid rafts seem to organize and determine the function of multiprotein complexes involved in several aspects of signal transduction, thus regulating the homeostasis of the brain. The progressive decline of brain performance along with physiological aging is at least in part associated with alterations in the composition and structure of neural lipid rafts. In addition, neurodegenerative conditions, such as lysosomal storage disorders, multiple sclerosis, and Parkinson's, Huntington's, and Alzheimer's diseases, are frequently characterized by dysregulated lipid metabolism, which in turn affects the structure of lipid rafts. Several events underlying the pathogenesis of these diseases appear to depend on the altered composition of lipid rafts. Thus, the structure and function of lipid rafts play a central role in the pathogenesis of many common neurodegenerative diseases.jlr;61/5/636/F1F1f1.

Dysfunction of ABC transporters at the blood-brain barrier: Role in neurological disorders

ABC (ATP-binding cassette) transporters represent one of the largest and most diverse superfamily of proteins in living species, playing an important role in many biological processes such as cell homeostasis, cell signaling, drug metabolism and nutrient uptake. Moreover, using the energy generated from ATP hydrolysis, they mediate the efflux of endogenous and exogenous substrates from inside the cells, thereby reducing their intracellular accumulation. At present, 48 ABC transporters have been identified in humans, which were classified into 7 different subfamilies (A to G) according to their phylogenetic analysis. Nevertheless, the most studied members with importance in drug therapeutic efficacy and toxicity include P-glycoprotein (P-gp), a member of the ABCB subfamily, the multidrug-associated proteins (MPRs), members of the ABCC subfamily, and breast cancer resistance protein (BCRP), a member of the ABCG subfamily. They exhibit ubiquitous expression throughout the human body, with a special relevance in barrier tissues like the blood-brain barrier (BBB). At this level, they play a physiological function in tissue protection by reducing or limiting the brain accumulation of neurotoxins. Furthermore, dysfunction of ABC transporters, at expression and/or activity level, has been associated with many neurological diseases, including epilepsy, multiple sclerosis, Alzheimer's disease, and amyotrophic lateral sclerosis. Additionally, these transporters are strikingly associated with the pharmacoresistance to central nervous system (CNS) acting drugs, because they contribute to the decrease in drug bioavailability. This article reviews the signaling pathways that regulate the expression and activity of P-gp, BCRP and MRPs subfamilies of transporters, with particular attention at the BBB level, and their mis-regulation in neurological disorders.

Rosuvastatin and retinoic acid may act as 'pleiotropic agents' against β-adrenergic agonist-induced acute myocardial injury through modulation of multiple signalling pathways

Cardiovascular disorders constitute the principal cause of deaths worldwide and will continue as the major disease-burden by the year 2060. A significant proportion of heart failures occur because of use and misuse of drugs and most of the investigational agents fail to achieve any clinical relevance. Here, we investigated rosuvastatin and retinoic acid for their "pharmacological pleiotropy" against high dose β-adrenergic agonist (isoproterenol)-induced acute myocardial insult. Rats were pretreated with rosuvastatin and/or retinoic acid for seven days and the myocardial injury was induced by administering isoproterenol on the seventh and eighth day. After induction, rats were anaesthetized for electrocardiography, then sacrificed and different samples were collected/stored for various downstream assays. Myocardial injury with isoproterenol resulted in increased cardiac mass, decreased R-wave amplitude, increased QRS and QT durations; elevated levels of cardiac markers like cTnI, CK-MB, ALT and AST; increased lipid peroxidation, protein carbonylation and tissue nitric oxide levels; decreased endogenous antioxidants like SOD, CAT, GR, GST, GPx and total antioxidant activity; increased inflammatory markers like TNF-α and IL-6; decreased the mRNA expression of Nrf2 and Bcl-2; increased the mRNA expression of Bax, eNOS and iNOS genes. Pretreatment with rosuvastatin and/or retinoic acid mitigated many of the above biochemical and pathological alterations. Our results demonstrate that rosuvastatin and retinoic acid exert cardioprotective effects and may act as potential agents in the prevention of β-adrenergic agonist-induced acute myocardial injury in rats. Cardioprotective potential of rosuvastatin and retinoic acid could be attributed to their influence on the redox pathways, immunomodulation, membrane stability, Nrf2 preservation, iNOS and Bax expression levels. Thus, they may act directly or indirectly at various steps, the breakpoints, in the pathophysiological cascade responsible for cardiac injury. Our study gives insights about the pharmacological pleiotropism of rosuvastatin and retinoic acid.

Development of AD-Like Pathology in Skeletal Muscle

Effective therapeutic strategy against Alzheimer's disease (AD) requires early detection of AD; however, clinical diagnosis of Alzheimer's disease (AD) is not precise and a definitive diagnosis of AD is only possible via postmortem examination for AD pathological hallmarks including senile plaques composed of Aβ and neuro fibrillary tangles composed of phosphorylated tau. Although a variety of biomarker has been developed and used in clinical setting, none of them robustly predicts subsequent clinical course of AD. Thus, it is essential to identify new biomarkers that may facilitate the diagnosis of early stages of AD, prediction of subsequent clinical course, and development of new therapeutic strategies. Given that pathological hallmarks of AD including Aβaccumulation and the presence of phosphorylated tau are also detected in peripheral tissues, AD is considered a systemic disease. Without the protection of blood-brain barrier, systemic factors can affect peripheral tissues much earlier than neurons in brain. Here, we will discuss the development of AD-like pathology in skeletal muscle and the potential use of skeletal muscle biopsy (examination for Aβaccumulation and phosphorylated tau) as a biomarker for AD.

Biocatalyzed Synthesis of Statins: A Sustainable Strategy for the Preparation of Valuable Drugs

Statins, inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, are the largest selling class of drugs prescribed for the pharmacological treatment of hypercholesterolemia and dyslipidaemia. Statins also possess other therapeutic effects, called pleiotropic, because the blockade of the conversion of HMG-CoA to (R)-mevalonate produces a concomitant inhibition of the biosynthesis of numerous isoprenoid metabolites (e.g., geranylgeranyl pyrophosphate (GGPP) or farnesyl pyrophosphate (FPP)). Thus, the prenylation of several cell signalling proteins (small GTPase family members: Ras, Rac, and Rho) is hampered, so that these molecular switches, controlling multiple pathways and cell functions (maintenance of cell shape, motility, factor secretion, differentiation, and proliferation) are regulated, leading to beneficial effects in cardiovascular health, regulation of the immune system, anti-inflammatory and immunosuppressive properties, prevention and treatment of sepsis, treatment of autoimmune diseases, osteoporosis, kidney and neurological disorders, or even in cancer therapy. Thus, there is a growing interest in developing more sustainable protocols for preparation of statins, and the introduction of biocatalyzed steps into the synthetic pathways is highly advantageous—synthetic routes are conducted under mild reaction conditions, at ambient temperature, and can use water as a reaction medium in many cases. Furthermore, their high selectivity avoids the need for functional group activation and protection/deprotection steps usually required in traditional organic synthesis. Therefore, biocatalysis provides shorter processes, produces less waste, and reduces manufacturing costs and environmental impact. In this review, we will comment on the pleiotropic effects of statins and will illustrate some biotransformations nowadays implemented for statin synthesis.

A Review on the Relationship between Tocotrienol and Alzheimer Disease

Alzheimer’s disease (AD) is plaguing the aging population worldwide due to its tremendous health care and socioeconomic burden. Current treatment of AD only offers symptomatic relief to patients. Development of agents targeting specific pathologies of AD is very slow. Tocotrienol, a member of the vitamin E family, can tackle many aspects of AD, such as oxidative stress, mitochondrial dysfunction and abnormal cholesterol synthesis. This review summarizes the current evidence on the role of tocotrienol as a neuroprotective agent. Preclinical studies showed that tocotrienol could reduce oxidative stress by acting as a free-radical scavenger and promoter of mitochondrial function and cellular repair. It also prevented glutamate-induced neurotoxicity in the cells. Human epidemiological studies showed a significant inverse relationship between tocotrienol levels and the occurrence of AD. However, there is no clinical trial to support the claim that tocotrienol can delay or prevent the onset of AD. As a conclusion, tocotrienol has the potential to be developed as an AD-preventing agent but further studies are required to validate its efficacy in humans.

Resveratrol Intervenes Cholesterol- and Isoprenoid-Mediated Amyloidogenic Processing of AβPP in Familial Alzheimer's Disease

Deterioration of cholesterol metabolism has recently been a frontier subject of investigation in the field of Alzheimer's disease (AD). Though amyloid-β protein precursor (AβPP) primes the pathological cascade, changes in cholesterol levels and its intermediates, geranyl geranyl pyrophosphate and farnesyl pyrophosphate, is expected to have a different consequence on AβPP processing and amyloid-β (Aβ) generation. However, the use of statins (HMG-COA reductase inhibitor) has been widely implicated in slowing down the pathogenic progression of AD, while the epidemiological reports on its biological effect remains controversial. Considering this fact, the choice of drug that could maintain cholesterol homeostasis without altering its biosynthesis may yield a better therapeutic efficacy on AD. Thus, the present study focused on determining the influence of cholesterol and isoprenoids on amyloidogenic-cleavage of AβPP, in addition to resveratrol as a potent therapeutic drug in CHO-APPswe cell lines. High levels of cholesterol were found to enhance the maturation of AβPP and altered the expression and subcellular localization of ADAM10, BACE1, and PS1 thereby promoting Aβ generation, whereas high isoprenoids increased both maturation as well as amyloidogenic-cleavage of AβPP, which was evident through β-CTF production. Interestingly, the therapeutic efficacy of resveratrol maintained cholesterol homeostasis and reduced the amyloidogenic burden through its ability to enhance SIRT1 expression and thereby regulating differential expression of AD determinants.

Loss-of-Function PCSK9 Mutations Are Not Associated With Alzheimer Disease

BACKGROUND

Hypercholesterolemia is a major risk factor for the late-onset form of Alzheimer disease (AD). Loss-of-function (LOF) mutations of PCSK9 and PCSK9 inhibitors lower low-density lipoprotein cholesterol (LDL-C) and have been associated with a reduced risk of cardiovascular disease. The aim of this study was to examine the effect of PCSK9 LOF variants on risk and age of onset of AD.

METHODS

A total of 878 participants (410 controls and 468 AD cases) from the Quebec Founder Population were included in the study.

RESULTS

Fifty-four (6.2%) participants carried the R46L mutation, whereas 226 (26.2%) participants carried the InsLEU mutation. There was no protective or no deleterious effect of carrying PCSK9 LOF mutations on AD prevalence nor on age of onset, even when stratified by apolipoprotein E epsilon 4 genotype or by gender.

CONCLUSION

Our data indicate that carrying PCSK9 LOF mutations has a neutral effect on neurocognitive health and the prevalence of AD.

Alpha-Secretase ADAM10 Regulation: Insights into Alzheimer's Disease Treatment

ADAM (a disintegrin and metalloproteinase) is a family of widely expressed, transmembrane and secreted proteins of approximately 750 amino acids in length with functions in cell adhesion and proteolytic processing of the ectodomains of diverse cell-surface receptors and signaling molecules. ADAM10 is the main α-secretase that cleaves APP (amyloid precursor protein) in the non-amyloidogenic pathway inhibiting the formation of β-amyloid peptide, whose accumulation and aggregation leads to neuronal degeneration in Alzheimer’s disease (AD). ADAM10 is a membrane-anchored metalloprotease that sheds, besides APP, the ectodomain of a large variety of cell-surface proteins including cytokines, adhesion molecules and notch. APP cleavage by ADAM10 results in the production of an APP-derived fragment, sAPPα, which is neuroprotective. As increased ADAM10 activity protects the brain from β-amyloid deposition in AD, this strategy has been proved to be effective in treating neurodegenerative diseases, including AD. Here, we describe the physiological mechanisms regulating ADAM10 expression at different levels, aiming to propose strategies for AD treatment. We report in this review on the physiological regulation of ADAM10 at the transcriptional level, by epigenetic factors, miRNAs and/or translational and post-translational levels. In addition, we describe the conditions that can change ADAM10 expression in vitro and in vivo, and discuss how this knowledge may help in AD treatment. Regulation of ADAM10 is achieved by multiple mechanisms that include transcriptional, translational and post-translational strategies, which we will summarize in this review.

Inhibition of Cholesterol Biosynthesis Reduces γ-Secretase Activity and Amyloid-β Generation

Amyloid-β (Aβ) is one of major molecules contributing to the pathogenesis of Alzheimer's disease (AD). Aβ is derived from amyloid-β protein precursor (AβPP) through sequential cleavages by β- and γ-secretases. Regulation of these components is thought to be an important factor in Aβ generation during the pathogenesis of AD. AβPP, β-secretase, and γ-secretase reside in lipid rafts, where cholesterol regulates the integrity and flexibility of membrane proteins and Aβ is generated. However, the relationship between cholesterol and Aβ generation is controversial. In this study, we aimed to elucidate the direct effects of cholesterol depletion on AβPP processing using AY9944, which blocks the last step of cholesterol biosynthesis and thus minimizes the unknown side effects of upstream inhibitors, such as HMG-CoA reductase inhibitors. Treatment with AY9944 decreased γ-secretase activity and Aβ generation. These results suggested that changes in membrane composition by lowering cholesterol with AY9944 affected γ-secretase activity and Aβ generation, which is associated with AD pathogenesis.

Wheelchair use and lipophilic statin medications may influence bone loss in chronic spinal cord injury: findings from the FRASCI-bone loss study

We identified a protective bone effect at the knee with lipophilic statin use in individuals with chronic spinal cord injury. Lipophilic statin users gained bone at the knee compared to non-users and wheelchair users lost bone compared to walkers. Ambulation and or statins may be effective osteogenic interventions in chronic spinal cord injury (SCI).

INTRODUCTION

SCI increases the risk of osteoporosis and low-impact fractures, particularly at the knee. However, during the chronic phase of SCI, the natural history and factors associated with longitudinal change in bone density remain poorly characterized. In this study, we prospectively assessed factors associated with change in bone density over a mean of 21 months in 152 men and women with chronic SCI.

METHODS

A mixed model procedure with repeated measures was used to assess predictors of change in bone mineral density (PROC MIXED) at the distal femur and proximal tibia. Factors with a p value of <0.10 in the univariate mixed models, as well as factors that were deemed clinically significant (gender, age, and walking status), were assessed in multivariable models. Factors with a p value of ≤0.05 were included in the final model.

RESULTS

We found no association between bone loss and traditional osteoporosis risk factors, including age, gender, body composition, or vitamin D level or status (normal or deficient). In both crude and fully adjusted models, wheelchair users lost bone compared to walkers. Similarly, statin users gained bone compared to nonusers.

CONCLUSIONS

The statin finding is supported by reports in the general population where statin use has been associated with a reduction in bone loss and fracture risk. Our results suggest that both walking and statins may be effective osteogenic therapies to mitigate bone loss and prevent osteoporosis in chronic SCI. Our findings also suggest that loss of mechanical loading and/or neuronal factors contribute more to disuse osteoporosis than traditional osteoporosis risk factors.

Global gene expression changes in the prefrontal cortex of rabbits with hypercholesterolemia and/or hypertension

Although many studies have identified a link between hypercholesterolemia or hypertension and cognitive deficits, till date, comprehensive gene expression analyses of the brain under these conditions is still lacking. The present study was carried out to elucidate differential gene expression changes in the prefrontal cortex (PFC) of New Zealand white rabbits exposed to hypercholesterolemia and/or hypertension with a view of identifying gene networks at risk. Microarray analyses of the PFC of hypercholesterolemic rabbits showed 850 differentially expressed genes (DEGs) in the cortex of hypercholesterolemic rabbits compared to controls, but only 5 DEGs in hypertensive rabbits compared to controls. Up-regulated genes in the PFC of hypercholesterolemic rabbits included CIDEC, ODF2, RNASEL, FSHR, CES3 and MAB21L3, and down-regulated genes included FAM184B, CUL3, LOC100351029, TMEM109, LOC100357097 and PFDN5. Comparison with our previous study on the middle cerebral artery (MCA) of the same rabbits showed many differentially expressed genes in common between the PFC and MCA, during hypercholesterolemia. Moreover, these genes tended to fall into the same functional networks, as revealed by IPA analyses, with many identical node molecules. These include: proteasome, insulin, Akt, ERK1/2, histone, IL12, interferon alpha and NFκB. Of these, PSMB4, PSMD4, PSMG1 were chosen as representatives of genes related to the proteasome for verification by quantitative RT-PCR. Results indicate significant downregulation of all three proteasome associated genes in the PFC. Immunostaining showed significantly increased number of Aβ labelled cells in layers III and V of the cortex after hypercholesterolemia and hypertension, which may be due to decreased proteasome activity and/or increased β- or γ-secretase activity. Knowledge of altered gene networks during hypercholesterolemia and/or hypertension could inform our understanding of the link between these conditions and cognitive deficits in vascular dementia or Alzheimer's disease.

Recent progress in repositioning Alzheimer's disease drugs based on a multitarget strategy

Alzheimer's disease (AD) is a serious progressive neurological disorder, characterized by impaired cognition and profound irreversible memory loss. The multifactorial nature of AD and the absence of a cure so far have stimulated medicinal chemists worldwide to follow multitarget drug-design strategies based on repositioning approved drugs. This review describes a summary of recently published works focused on tailoring new derivatives of US FDA-approved acetylcholinesterase inhibitors, in addition to huperzine (a drug approved in China), either by hybridization with other pharmacophore elements (to hit more AD targets), or by combination of two FDA-approved drugs. Besides the capacity for improving the cholinergic activity, these polyfunctional derivatives are also able to tackle other important neuroprotective properties, such as anti-β-amyloid aggregation, scavenging of radical oxygen species, modulation of redox-active metals or inhibition of monoamine oxidase, thereby resulting in potentially novel and more effective therapeutics for the treatment of AD.

Bile Acid Modifications at the Microbe-Host Interface: Potential for Nutraceutical and Pharmaceutical Interventions in Host Health

Bile acids have emerged as important signaling molecules in the host, as they interact either locally or systemically with specific cellular receptors, in particular the farnesoid X receptor (FXR) and TGR5. These signaling functions influence systemic lipid and cholesterol metabolism, energy metabolism, immune homeostasis, and intestinal electrolyte balance. Through defined enzymatic activities, the gut microbiota can significantly modify the signaling properties of bile acids and therefore can have an impact upon host health. Alterations to the gut microbiota that influence bile acid metabolism are associated with metabolic disease, obesity, diarrhea, inflammatory bowel disease (IBD), Clostridium difficile infection, colorectal cancer, and hepatocellular carcinoma. Here, we examine the regulation of this gut-microbiota-liver axis in the context of bile acid metabolism and indicate how this pathway represents an important target for the development of new nutraceutical (diet and/or probiotics) and targeted pharmaceutical interventions.

Synthesis of Denosomin-Vitamin D3 Hybrids and Evaluation of Their Anti-Alzheimer's Disease Activities

As an extension of previously conducted studies on developing an anti-Alzheimer's disease agent, denosomin (1-deoxy-24-norsominone, an artificial inducer of neurite elongation), derivatives were designed and synthesized based on the hypothesis that our denosomin would exhibit axonal extension activity via a 1,25D(3)-membrane-associated, rapid response steroid-binding protein (1,25D(3)-MARRS) pathway. The biological assay revealed that the hybridization of characteristic δ-lactone in denosomin and the triene moiety in VD(3) was effective to enhance the nerve re-extension activity in amyloid β (Aβ)-damaged neurons.

The FDA-approved natural product dihydroergocristine reduces the production of the Alzheimer's disease amyloid-β peptides

Known γ-secretase inhibitors or modulators display an undesirable pharmacokinetic profile and toxicity and have therefore not been successful in clinical trials for Alzheimer's disease (AD). So far, no compounds from natural products have been identified as direct inhibitors of γ-secretase. To search for bioactive molecules that can reduce the amount of amyloid-beta peptides (Aβ) and that have better pharmacokinetics and an improved safety profile, we completed a screen of ~400 natural products by using cell-based and cell-free γ-secretase activity assays. We identified dihydroergocristine (DHEC), a component of an FDA- (Food and Drug Administration)-approved drug, to be a direct inhibitor of γ-secretase. Micromolar concentrations of DHEC substantially reduced Aβ levels in different cell types, including a cell line derived from an AD patient. Structure-activity relationship studies implied that the key moiety for inhibiting γ-secretase is the cyclized tripeptide moiety of DHEC. A Surface Plasmon Resonance assay showed that DHEC binds directly to γ-secretase and Nicastrin, with equilibrium dissociation constants (Kd) of 25.7 nM and 9.8 μM, respectively. This study offers DHEC not only as a new chemical moiety for selectively modulating the activity of γ-secretase but also a candidate for drug repositioning in Alzheimer's disease.

Berberine Reduces Neurotoxicity Related to Nonalcoholic Steatohepatitis in Rats

Berberine is a plant alkaloid that has several pharmacological effects such as antioxidant, antilipidemic, and anti-inflammatory effects. Nonalcoholic steatohepatitis (NASH) triggers different aspects of disorders such as impaired endogenous lipid metabolism, hypercholesterolemia, oxidative stress, and neurotoxicity. In this study, we examined the mechanism by which NASH induces neurotoxicity and the protective effect of berberine against both NASH and its associated neurotoxicity. NASH induced rats showed significant impairments in lipid metabolism with increased serum triglycerides, cholesterol, and low-density lipoprotein (LDL). The NASH induced group also demonstrated a significant oxidative stress which is characterized by increased TBARs level and decreased antioxidant capacity such as GSH and SOD levels. Moreover, the NASH induction was associated with inflammation which was demonstrated by increased TNFα and nitric oxide levels. Hyperglycemia and hyperinsulinemia were observed in the NASH induced group. Also, our results showed a significant increase in the expression of the acetylcholine esterase (AChE) and amyloid beta precursor protein (AβPP). These changes were significantly correlated with decreased insulin degrading enzyme (IDE) and beta-amyloid40 (Aβ 40) and increased beta-amyloid42 (Aβ 42) in the hippocampal region. Daily administration of berberine (50 mg/kg) for three weeks ameliorated oxidative stress, inflammation, hyperlipidemia, hyperglycemia, hyperinsulinemia, and the observed neurotoxicity.

Understanding the cholesterol metabolism-perturbing effects of docosahexaenoic acid by gas chromatography-mass spectrometry targeted metabonomic profiling

PURPOSE

Over the past few decades, docosahexaenoic acid (DHA) has gained special attention for management of cholesterol-associated metabolic disorders and neurodegenerative diseases such as Alzheimer's disease (AD) owing to its neuroprotective, anti-inflammatory and hypolipidemic properties. Several epidemiological studies have reported the effect of DHA in reducing the risk of developing AD by lowering cholesterol. Hypercholesterolemia is a pro-amyloidogenic factor influencing the enzymatic processing of amyloid-β precursor protein (AβPP) to toxic β-amyloid. However, the mechanism by which DHA modulates the cholesterol pathway has not been established. Thus, the objective of this study was to investigate the mechanism of regulation of cholesterol metabolism by DHA in an AβPP₆₉₅ overexpressing AD cell model.

METHODS

A gas chromatography/mass spectrometry method was developed and validated for the targeted profiling of 11 cholesterol metabolites in DHA-treated Chinese hamster ovary wild-type (CHO-wt) and AβPP₆₉₅ overexpressing (CHO-AβPP₆₉₅) cells. The differential metabolite profiles between DHA- and vehicle-treated groups were further analyzed using fold change values of the ratio of concentration of metabolites in CHO-AβPP₆₉₅ to CHO-wt cells. Effect of DHA on key rate-limiting enzymatic activities within the cholesterol pathway was established using biochemical assays.

RESULTS

Our results showed that DHA reduced the levels of key cholesterol anabolites and catabolites in CHO-AβPP₆₉₅ cells as compared to CHO-wt cells. Further enzymatic studies revealed that the cholesterol-lowering effect of DHA was mediated by regulating HMG-CoA reductase and squalene epoxidase enzyme activities.

CONCLUSION

We demonstrate for the first time the dual effects of DHA in inhibiting HMG-CoA reductase and squalene epoxidase and modulating the sterol biosynthesis axis of the cholesterol pathway in AβPP₆₉₅ overexpressing AD. Our novel findings underscore the potential of DHA as a multi-target hypocholesterolemic agent for the prophylaxis of AD and other cholesterol-associated diseases.

Cholesterol, statins, and dementia: what the cardiologist should know

Alzheimer dementia (AD) is an important clinical problem that appears to be closely tied to comorbid cardiovascular disease, making it a relevant topic for the clinical cardiologist. Determinants of cardiovascular health, especially midlife dyslipidemia, are associated with an increased risk of dementia based on molecular and epidemiologic data. Given the potential role of dyslipidemia in the development of dementia, statins have been investigated as potential therapeutic options to slow or prevent disease. This review discusses the role of dyslipidemia and other cardiovascular risk factors in the pathogenesis of AD, with a focus on the existing evidence for the use of statin medications in the treatment and prevention of AD from observational studies and randomized clinical trials. Clinical questions for the practicing cardiologist are addressed.

Human isoprenoid synthase enzymes as therapeutic targets

In the human body, the complex biochemical network known as the mevalonate pathway is responsible for the biosynthesis of all isoprenoids, which consists of a vast array of metabolites that are vital for proper cellular functions. Two key isoprenoids, farnesyl pyrophosphate (FPP) and geranylgeranyl pyrophosphate (GGPP) are responsible for the post-translational prenylation of small GTP-binding proteins, and serve as the biosynthetic precursors to numerous other biomolecules. The down-stream metabolite of FPP and GGPP is squalene, the precursor to steroids, bile acids, lipoproteins, and vitamin D. In the past, interest in prenyl synthase inhibitors focused mainly on the role of the FPP in lytic bone diseases. More recently pre-clinical and clinical studies have strongly implicated high levels of protein prenylation in a plethora of human diseases, including non-skeletal cancers, the progression of neurodegenerative diseases and cardiovascular diseases. In this review, we focus mainly on the potential therapeutic value of down-regulating the biosynthesis of FPP, GGPP, and squalene. We summarize the most recent drug discovery efforts and the structural data available that support the current on-going studies.

Interaction of Alzheimer's β-amyloid peptides with cholesterol: mechanistic insights into amyloid pore formation

Brain cholesterol plays a critical role in Alzheimer's disease and other neurodegenerative diseases. The molecular mechanisms linking cholesterol to neurotoxicity have remained elusive for a long time, but recent data have allowed the identification of functional cholesterol-binding domains in several amyloidogenic proteins involved in neurodegenerative diseases, including Alzheimer's disease. In this review, we analyze the cholesterol binding properties of β-amyloid (Aβ) peptides and the impact of these interactions on amyloid pore formation. We show that although the cholesterol-binding domains of Aβ peptides and of transmembrane precursor C99 are partially overlapping, they involve distinct amino acid residues, so that cholesterol has a greater affinity for Aβ than for C99. Synthetic 22-35 and 25-35 fragments of Aβ retained the ability of the full-length peptide 1-42 to bind cholesterol and to form zinc-sensitive, calcium-permeable amyloid pores in cultured neural cells. Studies with mutant peptides allowed the identification of key residues involved in cholesterol binding and channel formation. Cholesterol promoted the insertion of Aβ in the plasma membrane, induced α-helical structuration, and forced the peptide to adopt a tilted topology that favored the oligomerization process. Bexarotene, an amphipathic drug currently considered as a potential candidate medication for the treatment of neurodegenerative diseases, competed with cholesterol for binding to Aβ and prevented oligomeric channel formation. These studies indicate that it is possible to prevent the generation of neurotoxic oligomers by targeting the cholesterol-binding domain of Aβ peptides. This original strategy could be used for the treatment of Alzheimer's and other neurodegenerative diseases that involve cholesterol-dependent toxic oligomers.

Transient dynamics of Aβ contribute to toxicity in Alzheimer's disease

The aggregation and deposition of the amyloid-β peptide (Aβ) in the brain has been linked with neuronal death, which progresses in the diagnostic and pathological signs of Alzheimer’s disease (AD). The transition of an unstructured monomeric peptide into self-assembled and more structured aggregates is the crucial conversion from what appears to be a harmless polypeptide into a malignant form that causes synaptotoxicity and neuronal cell death. Despite efforts to identify the toxic form of Aβ, the development of effective treatments for AD is still limited by the highly transient and dynamic nature of interconverting forms of Aβ. The variability within the in vivo “pool” of different Aβ peptides is another complicating factor. Here we review the dynamical interplay between various components that influence the heterogeneous Aβ system, from intramolecular Aβ flexibility to intermolecular dynamics between various Aβ alloforms and external factors. The complex dynamics of Aβ contributes to the causative role of Aβ in the pathogenesis of AD.

Lipidomics of Alzheimer’s disease

Alzheimer’s disease (AD) is a progressive brain disease that leads to an irreversible loss of neurons and cognition. It is the most common cause of dementia and can be considered as a major public health problem. At the histological level, AD is characterized by senile plaques and neurofibrillary tangles. Numerous studies involving genomic, transcriptomic and proteomic approaches have been published in order to understand the molecular mechanisms involved in AD, and to find new biomarkers. Metabolomics, and in particular lipidomics, have recently offered new possibilities due to the development of robust and sensitive analytical methods, such as LC–MS. This review aims to illustrate how lipidomics can help understand the biological mechanisms inherent to AD and how lipids can be considered as relevant biomarkers of AD at early stages.

Altered Cholesterol Intracellular Trafficking and the Development of Pathological Hallmarks of Sporadic AD

Compared to the rare familial early onset Alzheimer's disease (AD) that results from gene mutations in AbPP and presenilin-1, the pathogenesis of sporadic AD is much more complex and is believed to result from complex interactions between nutritional, environmental, epigenetic and genetic factors. Among those factors, the presence APOE4 is still the single strongest genetic risk factor for sporadic AD. However, the exact underlying mechanism whereby apoE4 contributes to the pathogenesis of sporadic AD remains unclear. Here, we discuss how altered cholesterol intracellular trafficking as a result of apoE4 might contribute to the development of pathological hallmarks of AD including brain deposition of amyloid beta (Ab), neurofibrillary tangles, and synaptic dysfunction.

Role of LDL cholesterol and endolysosomes in amyloidogenesis and Alzheimer's disease

The pathogenesis of late-onset sporadic Alzheimer's disease (AD) is believed to result from complex interactions between nutritional, environmental, epigenetic and genetic factors. Among those factors, altered circulating cholesterol homeostasis, independent of the APOE genotype, continues to be implicated in brain deposition of amyloid beta protein (Aβ) and the pathogenesis of AD. It is believed that trafficking of amyloid beta precursor protein (AβPP) into endolysosomes appears to play a critical role in determining amyloidogenic processing of AβPP because this is precisely where two enzymes critically important in AβPP metabolism are located; beta amyloid converting enzyme (BACE-1) and gamma secretase enzyme. We have shown that elevated levels of LDL cholesterol promote AβPP internalization, disturb neuronal endolysosome structure and function, and increase Aβ accumulation in neuronal endolysosomes. Here, we will further discuss the linkage between elevated levels of LDL cholesterol and AD pathogenesis, and explore the underlying mechanisms whereby elevated levels of plasma LDL cholesterol promote amyloidogenesis.

Statins more than cholesterol lowering agents in Alzheimer disease: their pleiotropic functions as potential therapeutic targets

Alzheimer disease (AD) is a progressive neurodegenerative disorder characterized by severe cognitive impairment, inability to perform activities of daily living and mood changes. Statins, long known to be beneficial in conditions where dyslipidemia occurs by lowering serum cholesterol levels, also have been proposed for use in neurodegenerative conditions, including AD. However, it is not clear that the purported effectiveness of statins in neurodegenerative disorders is directly related to cholesterol-lowering effects of these agents; rather, the pleiotropic functions of statins likely play critical roles. The aim of this review is to provide an overview on the new discoveries about the effects of statin therapy on the oxidative and nitrosative stress levels as well as on the modulation of the heme oxygenase/biliverdin reductase (HO/BVR) system in the brain. We propose a novel mechanism of action for atorvastatin which, through the activation of HO/BVR-A system, may contribute to the neuroprotective effects thus suggesting a potential therapeutic role in AD and potentially accounting for the observation of decreased AD incidence with persons on statin.