Decreased prevalence of Alzheimer disease associated with 3-hydroxy-3-methyglutaryl coenzyme A reductase inhibitors

Intracerebral propagation of Alzheimer's disease: strengthening evidence of a herpes simplex virus etiology

BACKGROUND

A faulty human protein, abnormally phosphorylated tau, was recently publicized to spread "like a virus" from neuron to neuron in Alzheimer's patients' brains. For several decades, we have been amassing arguments showing that herpes simplex virus type 1 (HSV-1), not p-tau, propagates this interneuronal, transsynaptic pathologic cascade.

METHODS

We reiterate convincing data from our own (and other) laboratories, reviewing the first anatomic foothold neurofibrillary tangles gain in brainstem and/or entorhinal cortex; the chronic immunosurveillance cellularity of the trigeminal ganglia wherein HSV-1 awakens from latency to reactivate; the inabilities of p-tau protein's physical properties to promote it to jump synapses; the amino acid homology between human p-tau and VP22, a key target for phosphorylation by HSV serine/threonine-protein kinase UL13; and the exosomic secretion of HSV-1-infected cells' L-particles, attesting to the cell-to-cell passage of microRNAs of herpesviruses.

RESULTS

The now-maturing construct that reactivated HSV-1 best accounts for the intracerebral propagation of AD changes in the human brain should at last seem highly attractive. This hypothesis might even explain statins' apparent mechanism in some studies for lowering AD incidence.

CONCLUSION

Provided that funding agencies will quickly ignite a new realm of investigation, the rejuvenated enthusiasm for testing this optimistic construct holds incalculable potential for rapid, efficacious clinical application, through already available and relatively safe antiviral therapeutics.

Atorvastatin attenuates the production of IL-1β, IL-6, and TNF-α in the hippocampus of an amyloid β1-42-induced rat model of Alzheimer's disease

Background and aim

Amyloid-beta (Aβ) peptide is reported to initiate flexible inflammation in the hippocampus of the human brain in Alzheimer’s disease (AD). The present study aimed to investigate the possible effects of atorvastatin on the production of inflammation cytokines in the hippocampus and the potential impacts on behavioral ability, in an AD model.

Methods

We firstly established AD rat models using intracerebroventricular injection of Aβ1-42. A Morris water maze was also performed to determine the spatial learning and memory ability in the AD models. Intracellular staining of interleukin (IL)-1β, IL-6, and tumor necrosis factor alpha was determined using immunohistochemical staining at 6 hours and day 7 after the injection of Aβ.

Results

The escape latency of the atorvastatin-treated AD group (5 mg/kg/d) was significantly shorter than that of AD group on day 3 (41 ± 1.05 seconds versus 47 ± 1.05 seconds, P < 0.01) and day 4 (34 ± 1.25 seconds versus 43 ± 1.01 seconds, P < 0.01) after the beginning of the training. Furthermore, the atorvastatin-treated AD group displayed a significant higher mean number of annulus crossings than did the AD group (2.9 ± 0.5 versus 2.4 ± 0.9, P < 0.05). Fewer injured nerve cells and proliferated glial cells were also demonstrated in the atorvastatin-treated AD group than in the AD group. Of great importance, we demonstrated that IL-1β, IL-6, and tumor necrosis factor alpha were significantly decreased in the atorvastatin-treated AD group than that in the AD group.

Conclusion

Atorvastatin might attenuate the damage of nerve cells and improve learning and memory ability by inhibiting inflammatory response in the progression of AD.

Brain insulin dysregulation: implication for neurological and neuropsychiatric disorders

Arduous efforts have been made in the last three decades to elucidate the role of insulin in the brain. A growing number of evidences show that insulin is involved in several physiological function of the brain such as food intake and weight control, reproduction, learning and memory, neuromodulation and neuroprotection. In addition, it is now clear that insulin and insulin disturbances particularly diabetes mellitus may contribute or in some cases play the main role in development and progression of neurodegenerative and neuropsychiatric disorders. Focusing on the molecular mechanisms, this review summarizes the recent findings on the involvement of insulin dysfunction in neurological disorders like Alzheimer's disease, Parkinson's disease and Huntington's disease and also mental disorders like depression and psychosis sharing features of neuroinflammation and neurodegeneration.

A review of the potential therapeutic role of statins in the treatment of Alzheimer's disease: current research and opinion

Alzheimer's disease is one of the most prevalent neurodegenerative disorders. However, there is no current treatment, which definitively influences disease progression over a sustained period. Numerous studies linking an increase in serum cholesterol, mainly during midlife, with the pathogenic process of Alzheimer's disease have been published. Therefore, the role of statins as a therapy in this disorder may be of great interest. The aim of the present review is to summarize of the role of statins in the treatment of Alzheimer's disease.

Cholesterol homeostasis: a key to prevent or slow down neurodegeneration

Neurodegeneration, a common feature for many brain disorders, has severe consequences on the mental and physical health of an individual. Typically human neurodegenerative diseases are devastating illnesses that predominantly affect elderly people, progress slowly, and lead to disability and premature death; however they may occur at all ages. Despite extensive research and investments, current therapeutic interventions against these disorders treat solely the symptoms. Therefore, since the underlying mechanisms of damage to neurons are similar, in spite of etiology and background heterogeneous, it will be of interest to identify possible trigger point of neurodegeneration enabling development of drugs and/or prevention strategies that target many disorders simultaneously. Among the factors that have been identified so far to cause neurodegeneration, failures in cholesterol homeostasis are indubitably the best investigated. The aim of this review is to critically discuss some of the main results reported in the recent years in this field mainly focusing on the mechanisms that, by recovering perturbations of cholesterol homeostasis in neuronal cells, may correct clinically relevant features occurring in different neurodegenerative disorders and, in this regard, also debate the current potential therapeutic interventions.

Statins reduce amyloid β-peptide production by modulating amyloid precursor protein maturation and phosphorylation through a cholesterol-independent mechanism in cultured neurons

Statins, 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors, have been reported to attenuate amyloid-β peptide (Aβ) production in various cellular models. However, the mechanisms by which statins affect neuronal Aβ production have not yet been clarified. Here, we investigated this issue in rat primary cortical neurons using two statins, pitavastatin (PV) and atorvastatin (AV). Treatment of neurons with 0.2-2.5 μM PV or AV for 4 days induced a concentration- and time-dependent reduction in the secretion of both Aβ40 and Aβ42. Moreover, Western blot analyses of cell lysates showed that treatment with PV or AV significantly reduced expression levels of the mature form of amyloid precursor protein (APP) and Thr668-phosphorylated APP (P-APP), but not immature form of APP; the decreases in P-APP levels were more notable than those of mature APP levels. The statin treatment did not alter expression of BACE1 (β-site APP-cleaving enzyme 1) or γ-secretase complex proteins (presenilin 1, nicastrin, APH-1, and PEN-2). In neurons overexpressing APP via recombinant adenoviruses, PV or AV similarly reduced Aβ secretion and the levels of mature APP and P-APP. Statins also markedly reduced cellular cholesterol content in neurons in a concentration-dependent manner. Co-treatment with mevalonate reversed the statin-induced decreases in Aβ secretion and mature APP and P-APP levels, whereas co-treatment with cholesterol did not, despite recovery of cellular cholesterol levels. Finally, cell-surface biotinylation experiments revealed that both statins significantly reduced the levels of cell-surface P-APP without changing those of cell surface mature APP. These results suggest that statins reduce Aβ production by selectively modulating APP maturation and phosphorylation through a mechanism independent of cholesterol reduction in cultured neurons.

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

Recent years have seen a significant increase in published data supporting the positive effects of statins on neurodegenerative diseases, in particular on Alzheimer's disease. Statins show neuroprotective activity by a combination of different cellular and systemic mechanisms that are based on the inhibition of the biosynthesis of cholesterol and isoprenoid by-products. The promising results obtained in vivo and in epidemiological studies are generally not in accordance with those of placebo-controlled randomized clinical trials. Nevertheless, these results make statins valuable assets for disease prevention rather than therapeutic agents for use when disease symptoms are already displayed. Thus, the modulation of midlife cholesterol and/or statin administration prior to the appearance of dementia or cognitive impairment may have a better long-term outcome.

A modern understanding of the traditional and nontraditional biological functions of angiotensin-converting enzyme

Angiotensin-converting enzyme (ACE) is a zinc-dependent peptidase responsible for converting angiotensin I into the vasoconstrictor angiotensin II. However, ACE is a relatively nonspecific peptidase that is capable of cleaving a wide range of substrates. Because of this, ACE and its peptide substrates and products affect many physiologic processes, including blood pressure control, hematopoiesis, reproduction, renal development, renal function, and the immune response. The defining feature of ACE is that it is composed of two homologous and independently catalytic domains, the result of an ancient gene duplication, and ACE-like genes are widely distributed in nature. The two ACE catalytic domains contribute to the wide substrate diversity of ACE and, by extension, the physiologic impact of the enzyme. Several studies suggest that the two catalytic domains have different biologic functions. Recently, the X-ray crystal structure of ACE has elucidated some of the structural differences between the two ACE domains. This is important now that ACE domain-specific inhibitors have been synthesized and characterized. Once widely available, these reagents will undoubtedly be powerful tools for probing the physiologic actions of each ACE domain. In turn, this knowledge should allow clinicians to envision new therapies for diseases not currently treated with ACE inhibitors.

Atorvastatin stimulates neuroblastoma cells to induce neurite outgrowth by increasing cellular prion protein expression

Recently, 3-hydroxy-3-methyl glutaryl coenzyme A (HMG-CoA) reductase inhibitors were reported to induce neurite outgrowth in vitro. However, the mechanism underlying this effect remains unclear. Cellular prion protein (PrP(C)) is a ubiquitous glycoprotein present on the surfaces of various cells, including neurons, and is suggested to be involved in neurite outgrowth. Therefore, the present study aimed to determine whether PrP(C) mediates neurite outgrowth induced by HMG-CoA reductase inhibitors. Atorvastatin, a strong HMG-CoA reductase inhibitor, induced neurite outgrowth and increased PrP(C) levels in Neuro2a cells in a time- and dose-dependent manner. PrP(C) mRNA expression was also increased by atorvastatin. Farnesol, a non-sterol mevalonate derivative, attenuated the atorvastatin-induced neurite outgrowth and increase in PrP(C). Neuro2a cells overexpressing PrP(C) showed a remarkable enhancement of atorvastatin-induced neurite outgrowth compared with mock cells transfected with empty pCI-neo vector. These findings suggest that PrP(C) contributes, at least in part, to atorvastatin-induced neurite outgrowth. This phenomenon may be included among the mechanisms underlying decreased risk of Alzheimer's disease in patients treated with HMG-CoA reductase inhibitors.

Dysregulation of cholesterol balance in the brain: contribution to neurodegenerative diseases

Dysregulation of cholesterol homeostasis in the brain is increasingly being linked to chronic neurodegenerative disorders, including Alzheimer’s disease (AD), Huntington’s disease (HD), Parkinson’s disease (PD), Niemann-Pick type C (NPC) disease and Smith-Lemli Opitz syndrome (SLOS). However, the molecular mechanisms underlying the correlation between altered cholesterol metabolism and the neurological deficits are, for the most part, not clear. NPC disease and SLOS are caused by mutations in genes involved in the biosynthesis or intracellular trafficking of cholesterol, respectively. However, the types of neurological impairments, and the areas of the brain that are most affected, differ between these diseases. Some, but not all, studies indicate that high levels of plasma cholesterol correlate with increased risk of developing AD. Moreover, inheritance of the E4 isoform of apolipoprotein E (APOE), a cholesterol-carrying protein, markedly increases the risk of developing AD. Whether or not treatment of AD with statins is beneficial remains controversial, and any benefit of statin treatment might be due to anti-inflammatory properties of the drug. Cholesterol balance is also altered in HD and PD, although no causal link between dysregulated cholesterol homeostasis and neurodegeneration has been established. Some important considerations for treatment of neurodegenerative diseases are the impermeability of the blood-brain barrier to many therapeutic agents and difficulties in reversing brain damage that has already occurred. This article focuses on how cholesterol balance in the brain is altered in several neurodegenerative diseases, and discusses some commonalities and differences among the diseases.

Lipid metabolism and neuroinflammation in Alzheimer's disease: a role for liver X receptors

Liver X receptors (LXR) are nuclear receptors that have emerged as key regulators of lipid metabolism. In addition to their functions as cholesterol sensors, LXR have also been found to regulate inflammatory responses in macrophages. Alzheimer's disease (AD) is a neurodegenerative disease characterized by a progressive cognitive decline associated with inflammation. Evidence indicates that the initiation and progression of AD is linked to aberrant cholesterol metabolism and inflammation. Activation of LXR can regulate neuroinflammation and decrease amyloid-β peptide accumulation. Here, we highlight the role of LXR in orchestrating lipid homeostasis and neuroinflammation in the brain. In addition, diabetes mellitus is also briefly discussed as a significant risk factor for AD because of the appearing beneficial effects of LXR on glucose homeostasis. The ability of LXR to attenuate AD pathology makes them potential therapeutic targets for this neurodegenerative disease.

Low-density lipoprotein receptor-related protein 1: a physiological Aβ homeostatic mechanism with multiple therapeutic opportunities

Low-density lipoprotein receptor-related protein-1 (LRP1) is the main cell surface receptor involved in brain and systemic clearance of the Alzheimer's disease (AD) toxin amyloid-beta (Aβ). In plasma, a soluble form of LRP1 (sLRP1) is the major transport protein for peripheral Aβ. LRP1 in brain endothelium and mural cells mediates Aβ efflux from brain by providing a transport mechanism for Aβ across the blood-brain barrier (BBB). sLRP1 maintains a plasma 'sink' activity for Aβ through binding of peripheral Aβ which in turn inhibits re-entry of free plasma Aβ into the brain. LRP1 in the liver mediates systemic clearance of Aβ. In AD, LRP1 expression at the BBB is reduced and Aβ binding to circulating sLRP1 is compromised by oxidation. Cell surface LRP1 and circulating sLRP1 represent druggable targets which can be therapeutically modified to restore the physiological mechanisms of brain Aβ homeostasis. In this review, we discuss how increasing LRP1 expression at the BBB and liver with lifestyle changes, statins, plant-based active principles and/or gene therapy on one hand, and how replacing dysfunctional plasma sLRP1 on the other regulate Aβ clearance from brain ultimately controlling the onset and/or progression of AD.

The link between altered cholesterol metabolism and Alzheimer's disease

Alzheimer's disease (AD), the most common form of dementia, is characterized by the progressive loss of neurons and synapses, and by extracellular deposits of amyloid-β (Aβ) as senile plaques, Aβ deposits in the cerebral blood vessels, and intracellular inclusions of hyperphosphorylated tau in the form of neurofibrillary tangles. Several mechanisms contribute to AD development and progression, and increasing epidemiological and molecular evidence suggests a key role of cholesterol in its initiation and progression. Altered cholesterol metabolism and hypercholesterolemia appear to play fundamental roles in amyloid plaque formation and tau hyperphosphorylation. Over the last decade, growing evidence supports the idea that cholesterol oxidation products, known as oxysterols, may be the missing link between altered brain cholesterol metabolism and AD pathogenesis, as their involvement in neurotoxicity, mainly by interacting with Aβ peptides, is reported.

Regulation of cerebral cholesterol metabolism in Alzheimer disease

Alzheimer disease (AD) is an age-related neurodegenerative disorder that manifests as a progressive loss of memory and deterioration of higher cognitive functions. Alzheimer disease is characterized by accumulation in the brain of the β-amyloid peptide generated by β- and γ-secretase processing of amyloid precursor protein. Epidemiological studies have linked elevated plasma cholesterol and lipoprotein levels in midlife with AD development. Cholesterol-fed animal models exhibit neuropathologic features of AD including accumulation of β-amyloid peptide. Specific isoforms of the cholesterol transporter apolipoprotein E are associated with susceptibility to AD. Although multiple lines of evidence indicate a role for cholesterol in AD, the exact impact and mechanisms involved remain largely unknown. This review summarizes the current state of our knowledge of the influence of cholesterol and lipid pathways in AD pathogenesis in vitro and in vivo.

Restoration of dietary-fat induced blood-brain barrier dysfunction by anti-inflammatory lipid-modulating agents

BACKGROUND

Several studies have identified use of non-steroidal-anti-inflammatory drugs and statins for prevention of dementia, but their efficacy in slowing progression is not well understood. Cerebrovascular disturbances are common pathological feature of Alzheimer's disease. We previously reported chronic ingestion of saturated fatty acids (SFA) compromises blood-brain barrier (BBB) integrity resulting in cerebral extravasation of plasma proteins and inflammation. However, the SFA-induced parenchymal accumulation of plasma proteins could be prevented by co-administration of some cholesterol lowering agents. Restoration of BBB dysfunction is clinically relevant, so the purpose of this study was to explore lipid-lowering agents could reverse BBB disturbances induced by chronic ingestion of SFA's.

METHODS

Wild-type mice were fed an SFA diet for 12 weeks to induce BBB dysfunction, and then randomised to receive atorvastatin, pravastatin or ibuprofen in combination with the SFA-rich diet for 2 or 8 weeks. Abundance of plasma-derived immunoglobulin-G (IgG) and amyloid-β enriched apolipoprotein (apo)-B lipoproteins within brain parenchyme were quantified utilising immunofluorescence microscopy.

RESULTS

Atorvastatin treatment for 2 and 8 weeks restored BBB integrity, indicated by a substantial reduction of IgG and apo B, particularly within the hippocampus. Pravastatin, a water-soluble statin was less effective than atorvastatin (lipid-soluble). Statin effects were independent of changes in plasma lipid homeostasis. Ibuprofen, a lipid-soluble cyclooxygenase inhibitor attenuated cerebral accumulation of IgG and apo B as effectively as atorvastatin. Our findings are consistent with the drug effects being independent of plasma lipid homeostasis.

CONCLUSION

Our findings suggest that BBB dysfunction induced by chronic ingestion of SFA is reversible with timely introduction and sustained treatment with agents that suppress inflammation.

Role of cholesterol in APP metabolism and its significance in Alzheimer's disease pathogenesis

Alzheimer's disease (AD) is a complex multifactorial neurodegenerative disorder believed to be initiated by accumulation of amyloid β (Aβ)-related peptides derived from proteolytic processing of amyloid precursor protein (APP). Research over the past two decades provided a mechanistic link between cholesterol and AD pathogenesis. Genetic polymorphisms in genes regulating the pivotal points in cholesterol metabolism have been suggested to enhance the risk of developing AD. Altered neuronal membrane cholesterol level and/or subcellular distribution have been implicated in aberrant formation, aggregation, toxicity, and degradation of Aβ-related peptides. However, the results are somewhat contradictory and we still do not have a complete understanding on how cholesterol can influence AD pathogenesis. In this review, we summarize our current understanding on the role of cholesterol in regulating the production/function of Aβ-related peptides and also examine the therapeutic potential of regulating cholesterol homeostasis in the treatment of AD pathology.

Treatment of cognitive impairment in Alzheimer's disease

In Alzheimer's disease, cognition now responds to several drugs. Anticholinesterases target the acetylcholine deficit. In mild-to-moderate Alzheimer's disease, they all provide significant benefit versus placebo on the Alzheimer's Disease Assessment ScheduleCognitive Section (ADAS-Cog), Side effects, in 5% to 15% of cases, include nausea, vomiting, diarrhea, anorexia, and dizziness. Tacrine, the leading anticholinesterase, caused frequent hepatic enzyme elevation and was withdrawn; once-daily donepezil spares the liver and improves global measures of change in severe dementia; rivasiigmine is indicated in comorbid vascular disease; while galaniamine modulates the cerebral nicotinic acetylcholine receptors that potentiate the response to acetylcholine. Alternative agents include the N-methyl-D-aspartate (NMDA) receptor antagonist, memaniine, licensed in Europe for moderately severe to severe Alzheimer's disease; it acts on a different neurotransmitter system present in 70% of neurons, protecting against pathologic glutamergic activation while preserving or even restoring physiologic glutamergic activation. The clinician's armamentarium in AD has never been greater.

Therapeutic approaches to age-associated neurocognitive disorders

The United Nations projects that the number of individuals with dementia in developed countries alone will be approximately 36,7 million by the year 2050. International recognition of the significant emotional and economic burden of Alzheimer's disease has been matched by a dramatic increase in the development of pharmacological and nonpharmacological approaches to this illness in the past decade. Changing demographics have underscored the necessity to develop similar approaches for the remediation of the cognitive impairment associated with more benign syndromes, such as mild cognitive impairment (MCI) and age-associated cognitive decline (AACD). The present article aims to provide an overview of the most current therapeutic approaches to age-associated neurocognitive disorders. Additionally, it discusses the conceptual and methodological issues that surround the design, implementation, and interpretation of such approaches.

Therapeutic interventions targeting Beta amyloid pathogenesis in an aging dog model

Aged dogs and humans share complex cognitive and pathological responses to aging. Specifically, dogs develop Alzheimer's Disease (AD) like beta-amyloid (Aβ) that are associated with cognitive deficits. Currently, therapeutic approaches to prevent AD are targeted towards reduced production, aggregation and increased clearance of Aβ. The current review discusses cognition and neuropathology of the aging canine model and how it has and continues to be useful in further understanding the safety and efficacy of potential AD prevention therapies targeting Aβ.

The effect of HMG-CoA reductase inhibitors on cognition in patients with Alzheimer's dementia: a prospective withdrawal and rechallenge pilot study

BACKGROUND

Statins are well-known for their cardiovascular benefits. However, the cognitive effects of statins are not well understood. We hypothesized that individuals with preexisting dementia would be more vulnerable to statin-related cognitive effects.

OBJECTIVE

The aim of this study was to evaluate the impact on cognition of 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitor (statin) discontinuation and rechallenge in individuals with Alzheimer's dementia (AD) on statins at baseline.

METHODS

A 12-week prospective, open-label study was conducted in a geriatric clinic setting. Eighteen older subjects underwent a 6-week withdrawal phase of statins followed by a 6-week rechallenge. The primary outcome measure was cognition, measured by the Mini-Mental State Examination (MMSE); secondary outcome measures were the Consortium to Establish a Registry for Alzheimer's Disease (CERAD) neuropsychological battery, Activities of Daily Living (ADL) scale, Instrumental ADL (IADL) scale, and fasting cholesterol. The change in outcome measures was assessed using repeated-measures ANOVA and paired t tests.

RESULTS

At the end of the intervention, there was a significant difference across time for MMSE score (P = 0.018), and total cholesterol (P = 0.0002) and a trend toward change across time for ADL (P = 0.07) and IADL (P = 0.06) scale scores. Further analyses using paired t tests indicated improvement in MMSE scores (Δ1.9 [3.0], P = 0.014) with discontinuation of statins and a decrease in MMSE scores (Δ1.9 [2.7], P = 0.007) after rechallenge. Total cholesterol increased with statin discontinuation (P = 0.0003) and decreased with rechallenge (P = 0.0007). The CERAD score did not show a change across time (P = 0.31). There was a trend toward improvement in ADL (P = 0.07) and IADL (P = 0.06) scale scores with discontinuation of statins, but no change with rechallenge.

CONCLUSIONS

This pilot study found an improvement in cognition with discontinuation of statins and worsening with rechallenge. Statins may adversely affect cognition in patients with dementia.

Statins, risk of dementia, and cognitive function: secondary analysis of the ginkgo evaluation of memory study

BACKGROUND

Lipid-lowering medications (LLMs) and especially statin drugs can delay cognitive decline and dementia onset in individuals with and without mild cognitive impairment (MCI) at baseline.

METHODS

A longitudinal, observational study was conducted of 3069 cognitively healthy elderly patients (≥75 years of age) who were enrolled in the Ginkgo Evaluation of Memory Study. The primary outcome measure was the time to adjudicated all-cause dementia and Alzheimer dementia (AD). The secondary outcome measure was the change in global cognitive function over time measured by scores from the Modified Mini-Mental State Exam (3MSE) and the cognitive subscale of the AD Assessment Scale (ADAS-Cog).

RESULTS

Among participants without MCI at baseline, the current use of statins was consistently associated with a reduced risk of all-cause dementia (hazard ratio [HR], 0.79; 95% confidence interval [95% CI], 0.65-0.96; P = .021) and AD (HR, 0.57; 95% CI, 0.39-0.85; P = .005). In participants who initiated statin therapy, lipophilic statins tended to reduce dementia risk more than nonlipophilic agents. In contrast, there was no significant association between LLM use (including statins), dementia onset, or cognitive decline in individuals with baseline MCI. However, in individuals without MCI at baseline, there was a trend for a neuroprotective effect of statins on cognitive decline.

CONCLUSIONS

Statins may slow the rate of cognitive decline and delay the onset of AD and all-cause dementia in cognitively healthy elderly individuals, whereas individuals with MCI may not have comparable cognitive protection from these agents. However, the results from this observational study need to be interpreted with caution and will require confirmation by randomized clinical trials stratifying treatment groups based on MCI status at baseline.

Statins have therapeutic potential for the treatment of Alzheimer's disease, likely via protection of the neurovascular unit in the AD brain

Structural and functional abnormalities in the neurovascular unit (NVU) have been recently observed in Alzheimer's disease (AD). Statins, which are used clinically for reducing cholesterol levels, can also exert beneficial vascular actions, improve behavioral memory and reduce senile plaque (SP). Thus, we examined cognitive function, the serum level of lipids, senile plaque (SP), and the protective effects of statins on NVU disturbances in a mouse AD model. Amyloid precursor protein (APP) transgenic (Tg) mice were used as a model of AD. Atorvastatin (30 mg/kg/day, p.o.) or pitavastatin (3mg/kg/day, p.o.) were administered from 5 to 20 months of age. These 2 statins improved behavioral memory and reduced the numbers of SP at 15 and 20 M without affecting serum lipid levels. There was a reduction in immunopositive staining for N-acetyl glucosamine oligomer (NAGO) in the endothelium and in collagen IV in the APP vehicle (APP/Ve) group, with collagen IV staining most weakest near SP. There was also an increase in intensity and numbers of glial fibrillary acidic protein (GFAP) positive astrocytes, particularly around the SP, where MMP-9 was more strongly labeled. Double immunofluorescent analysis showed that astrocytic endfeet had detached from the capillary endothelium in the APP/Ve group. Overall, these data suggest that statins may have therapeutic potential for AD by protecting NVU.

Adult Changes in Thought study: dementia is an individually varying convergent syndrome with prevalent clinically silent diseases that may be modified by some commonly used therapeutics

The Adult Changes in Thought (ACT) study is a longitudinal population-based prospective cohort study of brain aging and incident dementia in the Seattle metropolitan area. Observational studies using autopsies from ACT indicate that dementia is a convergent syndrome that commonly derives from Alzheimer's disease (AD), microvascular brain injury (mVBI), and Lewy body disease (LBD), and that these diseases have prevalent subclinical forms that also are commonly co-morbid. The existence of subclinical diseases highlights potential opportunities to intervene before the development of clinically apparent impairments. Our observations suggest that some such interventions already may exist to suppress processes of AD (statin therapy) or mVBI (treatment of hypertension). Reduced burden of LBD is associated with cigarette smoking; although smoking is not recommended as an intervention, these exposure data may provide clues to alternative neuroprotective mechanisms. Self reported anti-oxidant supplementation was without apparent effect in this cohort on indices of AD, mVBI, or LBD. Continued observational studies of brain aging will provide further insight into the convergent complexity of the dementia syndrome and its subclinical forms as well as highlight potential interventions that will require validation in clinical trials.

Age-dependent rescue by simvastatin of Alzheimer's disease cerebrovascular and memory deficits

Alzheimer's disease (AD) is now established as a progressive compromise not only of the neurons but also of the cerebral vasculature. Increasing evidence also indicates that cerebrovascular dysfunction may be a key or an aggravating pathogenic factor in AD, emphasizing the importance to properly control this deficit when aiming for effective therapy. Here, we report that simvastatin (3-6 months, 40 mg/kg/d) completely rescued cerebrovascular reactivity, basal endothelial nitric oxide synthesis, and activity-induced neurometabolic and neurovascular coupling in adult (6 months) and aged (12 months) transgenic mice overexpressing the Swedish and Indiana mutations of the human amyloid precursor protein (AD mice). Remarkably, simvastatin fully restored short- and long-term memory in adult, but not in aged AD mice. These beneficial effects occurred without any decreasing effect of simvastatin on brain amyloid-β (Aβ) levels or plaque load. However, in AD mice with recovered memory, protein levels of the learning- and memory-related immediate early genes c-Fos and Egr-1 were normalized or upregulated in hippocampal CA1 neurons, indicative of restored neuronal function. In contrast, the levels of phospholipase A2, enkephalin, PSD-95, synaptophysin, or glutamate NMDA receptor subunit type 2B were either unaltered in AD mice or unaffected by treatment. These findings disclose new sites of action for statins against Aβ-induced neuronal and cerebrovascular deficits that could be predictive of therapeutic benefit in AD patients. They further indicate that simvastatin and, possibly, other brain penetrant statins bear high therapeutic promise in early AD and in patients with vascular diseases who are at risk of developing AD.

Accumulation of exogenous amyloid-beta peptide in hippocampal mitochondria causes their dysfunction: a protective role for melatonin

Amyloid-beta (Aβ) pathology is related to mitochondrial dysfunction accompanied by energy reduction and an elevated production of reactive oxygen species (ROS). Monomers and oligomers of Aβ have been found inside mitochondria where they accumulate in a time-dependent manner as demonstrated in transgenic mice and in Alzheimer's disease (AD) brain. We hypothesize that the internalization of extracellular Aβ aggregates is the major cause of mitochondrial damage and here we report that following the injection of fibrillar Aβ into the hippocampus, there is severe axonal damage which is accompanied by the entrance of Aβ into the cell. Thereafter, Aβ appears in mitochondria where it is linked to alterations in the ionic gradient across the inner mitochondrial membrane. This effect is accompanied by disruption of subcellular structure, oxidative stress, and a significant reduction in both the respiratory control ratio and in the hydrolytic activity of ATPase. Orally administrated melatonin reduced oxidative stress, improved the mitochondrial respiratory control ratio, and ameliorated the energy imbalance.

Prediction of drug-target interactions and drug repositioning via network-based inference

Drug-target interaction (DTI) is the basis of drug discovery and design. It is time consuming and costly to determine DTI experimentally. Hence, it is necessary to develop computational methods for the prediction of potential DTI. Based on complex network theory, three supervised inference methods were developed here to predict DTI and used for drug repositioning, namely drug-based similarity inference (DBSI), target-based similarity inference (TBSI) and network-based inference (NBI). Among them, NBI performed best on four benchmark data sets. Then a drug-target network was created with NBI based on 12,483 FDA-approved and experimental drug-target binary links, and some new DTIs were further predicted. In vitro assays confirmed that five old drugs, namely montelukast, diclofenac, simvastatin, ketoconazole, and itraconazole, showed polypharmacological features on estrogen receptors or dipeptidyl peptidase-IV with half maximal inhibitory or effective concentration ranged from 0.2 to 10 µM. Moreover, simvastatin and ketoconazole showed potent antiproliferative activities on human MDA-MB-231 breast cancer cell line in MTT assays. The results indicated that these methods could be powerful tools in prediction of DTIs and drug repositioning.

Sterol lipid metabolism in down syndrome revisited: down syndrome is associated with a selective reduction in serum brassicasterol levels

Over the past 15 years, insights into sterol metabolism have improved our understanding of the relationship between lipids and common conditions such as atherosclerosis and Alzheimer's Disease (AD). A better understanding of sterol lipid metabolism in individuals with Down Syndrome (DS) may help elucidate how this population's unique metabolic characteristics influence their risks for atherosclerosis and AD. To revisit the question of whether sterol lipid parameters may be altered in DS subjects, we performed a pilot study to assess traditional serum sterol lipids and lipoproteins, as well as markers of sterol biosynthesis, metabolites, and plant sterols in 20 subjects with DS compared to age-matched controls. Here we report that the levels of nearly all lipids and lipoproteins examined are similar to control subjects, suggesting that trisomy 21 does not lead to pronounced general alterations in sterol lipid metabolism. However, the levels of serum brassicasterol were markedly reduced in DS subjects.

How statins could be evaluated successfully in clinical trials for Alzheimer's disease?

Over the last decade, a large number of experimental observations have suggested a relationship between alterations in cholesterol homeostasis and Alzheimer's disease (AD). Moreover, epidemiological studies have pointed an association between statin treatment and a decrease in the risk of having AD. For these reasons, a large number of clinical trials have been carried out to determine whether the statins can prevent the progression of AD. However, these studies did not provide clear evidence for the therapeutic efficacy in AD. We consider that there are a number of explanations for this failure that may provide guidance for selecting and clinically developing statins with therapeutic efficacy in AD.

Alzheimer's disease: redox dysregulation as a common denominator for diverse pathogenic mechanisms

Alzheimer's disease (AD) is the most common cause of dementia and a progressive neurodegeneration that appears to result from multiple pathogenic mechanisms (including protein misfolding/aggregation, involved in both amyloid β-dependent senile plaques and tau-dependent neurofibrillary tangles), metabolic and mitochondrial dysfunction, excitoxicity, calcium handling impairment, glial cell dysfunction, neuroinflammation, and oxidative stress. Oxidative stress, which could be secondary to several of the other pathophysiological mechanisms, appears to be a major determinant of the pathogenesis and progression of AD. The identification of oxidized proteins common for mild cognitive impairment and AD suggests that key oxidation pathways are triggered early and are involved in the initial progression of the neurodegenerative process. Abundant data support that oxidative stress, also considered as a main factor for aging, the major risk factor for AD, can be a common key element capable of articulating the divergent nature of the proposed pathogenic factors. Pathogenic mechanisms influence each other at different levels. Evidence suggests that it will be difficult to define a single-target therapy resulting in the arrest of progression or the improvement of AD deterioration. Since oxidative stress is present from early stages of disease, it appears as one of the main targets to be included in a clinical trial. Exploring the articulation of AD pathogenic mechanisms by oxidative stress will provide clues for better understanding the pathogenesis and progression of this dementing disorder and for the development of effective therapies to treat this disease.

Upstream transcription factor 1 (USF1) polymorphisms associate with Alzheimer's disease-related neuropathological lesions: Tampere Autopsy Study

The apolipoprotein E (APOE) gene associates with Alzheimer's disease (AD) and cholesterol levels. Upstream transcription factor 1 (USF1) regulates lipid metabolism genes, including APOE, and the AD Aβ-precursor protein. We investigated associations between 6 haplotype-tagging USF1 single-nucleotide polymorphisms (and haplotypes) and AD-related neuropathological lesions [senile plaques (SP), neurofibrillary tangles (NFT) ] in an autopsy series comprising 603 cases (ages 0-97, mean 62 years, 215 women) that died out-of-hospital. In age- and APOE-adjusted analyses, the minor G-allele of rs2774276, previously linked to elevated cholesterol, associated with late-stage burnt out SP among women and early non-neuritic SP among men. The G-allele of the previously unreported rs10908821 showed significant risk of having SP, especially neuritic and burnt out SP, among women but not men. USF1 haplotype GCGCAC carriers (risk alleles of rs2774276 and rs10908821) associated with SP risk, especially neuritic and late-stage burnt out SP, among women but not men. Younger CCGCAC carriers (risk allele of rs2774276 and protective of rs10908821) were more likely to have non-neuritic and diffuse SP. Conversely, USF1 CCGCAC haplotype carriers had lower NFT prevalence among 65+ year-olds. These results suggest USF1 has an independent but gender- and age-associated effect on AD-related brain lesion development.

Selective liver X receptor modulators (SLiMs): what use in human health?

Liver X receptors (LXR) are members of the nuclear receptor family. As activated transcription factors, their putative association with human diseases makes them promising pharmacological targets because of the large potential to develop ligands. LXR are mainly considered as intracellular cholesterol "sensors" whose activation leads to decreased plasma cholesterol. They also modulate numerous physiological functions: fatty acid synthesis and metabolism, glucose homeostasis, steroidogenesis, immunity, and neurological homeostasis. LXR-deficiency in mouse results in several phenotypes mimicking pathological conditions in humans. This review will be focused on the various natural and synthetic LXR agonists and antagonists. Putative clinical targets including atherosclerosis, diabetes, Alzheimer's disease, skin disorders, and cancer will be covered.

Is statin-associated cognitive impairment clinically relevant? A narrative review and clinical recommendations

OBJECTIVE

To explore the impact of statin use on cognition.

DATA SOURCES

A literature search was performed using MEDLINE (1950-November 2011), EMBASE (1980-November 2011), and the Cochrane Library (1960-November 2011) using the search terms "cognition/drug effects," "delirium, dementia, amnestic, cognitive disorders/chemically induced," "memory disorders/chemically induced," "hydroxymethylglutaryl-CoA reductase inhibitors/adverse effects," and "hydroxymethylglutaryl-CoA reductase inhibitors." A bibliographic search on included references was also conducted.

STUDY SELECTION AND DATA EXTRACTION

Studies were included for analysis if they were conducted in humans and examined the impact of statin use on cognition as either a primary or secondary endpoint; case reports and case series were also included for analysis.

DATA SYNTHESIS

Reports of statin-associated cognitive impairment were found primarily in observational studies (eg, case reports/series). One randomized controlled trial demonstrated that simvastatin impaired some measures of cognition compared to placebo. Conversely, in the majority of randomized controlled trials and observational studies, statins were found to have either a neutral or beneficial effect on cognition. Preliminary data suggest that statins that are less lipophilic (ie, pravastatin and rosuvastatin) may be less likely to contribute to cognitive impairment due to limited penetration across the blood-brain barrier. These drugs would be a logical alternative in cases where cognitive impairment secondary to another statin is suspected.

CONCLUSIONS

Despite several reports of statin-associated cognitive impairment, this adverse effect remains a rare occurrence among the totality of the literature. If statin-associated cognitive impairment is suspected, a trial discontinuation can reveal a temporal relationship. Switching from lipophilic to hydrophilic statins may resolve cognitive impairment. The vascular benefits and putative cognitive benefits outweigh the risk of cognitive impairment associated with statin use; therefore, the current evidence does not support changing practice with respect to statin use, given this adverse effect.

Isoprenoids and related pharmacological interventions: potential application in Alzheimer's disease

Two major isoprenoids, farnesyl pyrophosphate and geranylgeranyl pyrophosphate, serve as lipid donors for the posttranslational modification (known as prenylation) of proteins that possess a characteristic C-terminal motif. The prenylation reaction is catalyzed by prenyltransferases. The lipid prenyl group facilitates to anchor the proteins in cell membranes and mediates protein-protein interactions. A variety of important intracellular proteins undergo prenylation, including almost all members of small GTPase superfamilies as well as heterotrimeric G protein subunits and nuclear lamins. These prenylated proteins are involved in regulating a wide range of cellular processes and functions, such as cell growth, differentiation, cytoskeletal organization, and vesicle trafficking. Prenylated proteins are also implicated in the pathogenesis of different types of diseases. Consequently, isoprenoids and/or prenyltransferases have emerged as attractive therapeutic targets for combating various disorders. This review attempts to summarize the pharmacological agents currently available or under development that control isoprenoid availability and/or the process of prenylation, mainly focusing on statins, bisphosphonates, and prenyltransferase inhibitors. Whereas statins and bisphosphonates deplete the production of isoprenoids by inhibiting the activity of upstream enzymes, prenyltransferase inhibitors directly block the prenylation of proteins. As the importance of isoprenoids and prenylated proteins in health and disease continues to emerge, the therapeutic potential of these pharmacological agents has expanded across multiple disciplines. This review mainly discusses their potential application in Alzheimer's disease.

Combined treatment of Aβ immunization with statin in a mouse model of Alzheimer's disease

We evaluated the therapeutic efficacy of combined treatment of Aβ-immunization with simvastatin in an Alzheimer mouse model at age 22 months. DNA prime-adenovirus boost immunization induced modest anti-Aβ titers and simvastatin increased the seropositive rate. Aβ-KLH was additionally administered to boost the titers. Irrespective of simvastatin, the immunization did not decrease cerebral Aβ deposits but increased soluble Aβ and tended to exacerbate amyloid angiopathy in the hippocampus. The immunization increased cerebral invasion of leukocytes and simvastatin counteracted the increase. Thus, modest anti-Aβ titers can increase soluble Aβ and simvastatin may reduce inflammation associated with vaccination in aged Alzheimer mouse models.

Effects of the antioxidant baicalein on the pharmacokinetics of nimodipine in rats: a possible role of P-glycoprotein and CYP3A4 inhibition by baicalein

The reduced bioavailability of nimodipine after oral administration might not only be due to the metabolizing enzyme cytochrome P450 3A4(CYP3A4) but also to the P-glycoprotein efflux transporter in the small intestine. The aim of this study was to investigate the effects of baicalein on the pharmacokinetics of nimodipine in rats. The effect of baicalein on P-glycoprotein and CYP3A4 activity was evaluated. A single dose of nimodipine was administered intravenously (3 mg/kg) and orally (12 mg/kg) to rats in the presence and absence of baicalein (0.4, 2 and 8 mg/kg). Baicalein inhibited CYP3A4 enzyme activity in a concentration-dependent manner, with a 50% inhibition concentration (IC(50)) of 9.2 μM. In addition, baicalein significantly enhanced the cellular accumulation of rhodamine-123 in MCF-7/ADR cells overexpressing P-glycoprotein. Baicalein significantly altered the pharmacokinetics of orally administered nimodipine. Compared to the oral control group given nimodipine alone, the area under the plasma concentration-time curve (AUC(0-∞)) and the peak plasma concentration (C(max)) of nimodipine significantly increased (p < 0.05 for 2 mg/kg; p < 0.01 for 8 mg/kg). Consequently, the absolute bioavailability of nimodipine in the presence of baicalein (2 and 8 mg/kg) was 31.0-35.3%, which was significantly enhanced (p < 0.05 for 2 mg/kg; p < 0.01 for 8 mg/kg) compared to the oral control group (22.3%). Moreover, the relative bioavailability of nimodipine was 1.39- to 1.58-fold greater than that of the control group. The pharmacokinetics of intravenous nimodipine were not affected by baicalein in contrast to those of oral nimodipine. Baicalein significantly enhanced the oral bioavailability of nimodipine, which may be mainly due to inhibition of the CYP3A4-mediated metabolism of nimodipine in the small intestine and/or in the liver and the inhibition of the P-glycoprotein efflux pump in the small intestine by baicalein. The increase in oral bioavailability of nimodipine in the presence of baicalein should be taken into consideration as a potential drug interaction between nimodipine and baicalein.

Dual effects of statins on Aβ metabolism: upregulation of the degradation of APP-CTF and Aβ clearance

BACKGROUND/AIMS

Retrospective cohort studies have suggested that statin users have a lower prevalence of dementia. On the other hand, a randomized controlled study failed to show beneficial effects on the cognitive decline in Alzheimer's disease (AD). However, a prospective cohort study demonstrated that users of statins had a lower incidence of AD. One possible interpretation might be that statins could prevent or delay the onset of AD, but not slow cognitive decline once the disease has set in. Given that statins could prevent or delay the onset of AD, what is the responsible mechanism?

METHODS

We investigated the effect of fluvastatin on Aβ metabolism at a clinically relevant dose in mice.

RESULTS

Fluvastatin reduced the brain Aβ level by increased trafficking of the carboxyl terminal fragment of the amyloid precursor protein (APP-CTF), which was mediated by inhibition of protein isoprenylation. Moreover, the statin reduced the brain Aβ level through enhanced Aβ clearance mediated by upregulation of low-density lipoprotein receptor-related protein 1 (LRP-1) expression. The statin increased LRP-1 expression, mediated by inhibition of protein isoprenylation.

CONCLUSION

Statins might prevent the onset of AD through reduced Aβ production by enhancement of APP-CTF degradation and/or upregulation of Aβ clearance. We also showed that promotion of APP-CTF degradation and upregulation of Aβ clearance could be modified by a drug, suggesting possible mechanistic targets for disease-modifying drugs.

Statins and therapy of Alzheimer's disease: questions of efficacy versus trial design

Recent trials of statins produced no benefit for subjects with Alzheimer's disease. These negative studies add to a growing list of negative clinical trials. These data point to a need for reevaluating the pathophysiology of late-onset Alzheimer's disease. Late-onset Alzheimer's disease might result from the cumulative effects of at least four different factors: β-amyloid accumulation, cardiovascular disease, aging and the associated loss of synaptic plasticity, and inflammation. Successful therapy of subjects with overt dementia might require approaches targeting all four pathophysiological domains.

Alzheimer's Disease: APP, Gamma Secretase, APOE, CLU, CR1, PICALM, ABCA7, BIN1, CD2AP, CD33, EPHA1, and MS4A2, and Their Relationships with Herpes Simplex, C. Pneumoniae, Other Suspect Pathogens, and the Immune System

Alzheimer's disease susceptibility genes, APP and gamma-secretase, are involved in the herpes simplex life cycle, and that of other suspect pathogens (C. pneumoniae, H. pylori, C. neoformans, B. burgdorferri, P. gingivalis) or immune defence. Such pathogens promote beta-amyloid deposition and tau phosphorylation and may thus be causative agents, whose effects are conditioned by genes. The antimicrobial effects of beta-amyloid, the localisation of APP/gamma-secretase in immunocompetent dendritic cells, and gamma secretase cleavage of numerous pathogen receptors suggest that this network is concerned with pathogen disposal, effects which may be abrogated by the presence of beta-amyloid autoantibodies in the elderly. These autoantibodies, as well as those to nerve growth factor and tau, also observed in Alzheimer's disease, may well be antibodies to pathogens, due to homology between human autoantigens and pathogen proteins. NGF or tau antibodies promote beta-amyloid deposition, neurofibrillary tangles, or cholinergic neuronal loss, and, with other autoantibodies, such as anti-ATPase, are potential agents of destruction, whose formation is dictated by sequence homology between pathogen and human proteins, and thus by pathogen strain and human genes. Pathogen elimination in the ageing population and removal of culpable autoantibodies might reduce the incidence and offer hope for a cure in this affliction.

Statins in unconventional secretion of insulin-degrading enzyme and degradation of the amyloid-β peptide

Population-based studies demonstrated that statins might decrease the risk of developing Alzheimer's disease (AD). Statins inhibit the 3-hydroxy-3-methyl-glutaryl-coenzyme-A reductase and thereby de novo synthesis of cholesterol. Cell culture and animal studies indicated that cholesterol affects the proteolytic processing of the amyloid precursor protein and the generation of amyloid-β (Aβ). Recently, we have demonstrated that statins can also stimulate the degradation of Aβ. The statin-induced clearance of Aβ could be attributed to increased release of the insulin-degrading enzyme (IDE) via an exosome-related unconventional secretory pathway. Interestingly, this statin-induced secretion of exosome-associated IDE was independent of cellular cholesterol concentrations, but rather caused by impairment of isoprenoid biosynthesis and protein prenylation. We further identified a new hexapeptide sequence in the C-terminal region of IDE, named the SlyX motif that is critically involved in IDE secretion. Taken these findings together, the increased clearance of Aβ by stimulated secretion of IDE might contribute to the protective effects of statins against AD.