Statins: drugs for Alzheimer’s disease?

Statins Use in Alzheimer Disease: Bane or Boon from Frantic Search and Narrative Review

Alzheimer’s disease (AD) was used to describe pre-senile dementia to differentiate it from senile dementia, which develops in the adult age group of more than 65 years. AD is characterized by the deposition of amyloid beta (Aβ) plaque and tau-neurofibrillary tangles (TNTs) in the brain. The neuropathological changes in AD are related to the deposition of amyloid plaques, neurofibrillary tangles, and progression of neuroinflammation, neuronal mitochondrial dysfunction, autophagy dysfunction, and cholinergic synaptic dysfunction. Statins are one of the main cornerstone drugs for the management of cardiovascular disorders regardless of dyslipidemia status. Increasing the use of statins, mainly in the elderly groups for primary and secondary prevention of cardiovascular diseases, may affect their cognitive functions. Extensive and prolonged use of statins may affect cognitive functions in healthy subjects and dementia patients. Statins-induced cognitive impairments in both patients and health providers had been reported according to the post-marketing survey. This survey depends mainly on sporadic cases, and no cognitive measures were used. Evidence from prospective and observational studies gives no robust conclusion regarding the beneficial or detrimental effects of statins on cognitive functions in AD patients. Therefore, this study is a narrative review aimed with evidences to the beneficial, detrimental, and neutral effects of statins on AD.

Computational studies on statins photoactivity

Statins are popular drugs widely prescribed to control hypercholesterolaemia and to prevent cardiovascular diseases. Synthetic statins constitute a group of pharmaceuticals which are very sensitive to exposure to light in both UVA and UVB ranges. Light, by causing drugs degradation, can essentially change their pharmaceutical properties leading even to the loss of therapeutic activity and/or to the formation of deleterious photoproducts. Drugs which exhibit photochemical reactivity may elicit undesired adverse effects. A detailed understanding of mechanisms involved in molecular basis of these effects origin is very important for evaluating the photobiological risk associated with therapy in which drugs prone to exposure to light are involved. In this work we critically discussed finding regarding the mechanisms of synthetic statins phototransformation. We showed inconsistency of some previously reported facts and revised earlier presented studies. We also completed the lack of information on pitavastatin photobehaviour. This all together resulted in proposal of new schemes for the statins photodecomposition. We reviewed data derived from both experimental and computational methods. Studies of photochemical problems by the use of theoretical methods enable getting insight into areas of some fascinating events that experimental techniques can touch only indirectly. Besides effect of light, phenomenon of statins’ sensitivity to pH and resulting implications were discussed. Statins undergo pH-dependent interconversion between their pharmacologically active hydroxy acid and inactive lactone forms, and it was shown that for both forms, drugs’ interactions should be considered. Knowledge of the statins interconversion mechanisms is important for understanding how differences in the structures of their molecules can affect the drugs’ activity.

Selected LDLR and APOE Polymorphisms Affect Cognitive and Functional Response to Lipophilic Statins in Alzheimer's Disease

Effects of statins over clinical changes in Alzheimer's disease (AD) are usually non-significant, but epistatic interactions between genetic variants involved in cholesterol metabolism could be important for such effects. We aimed to investigate whether LDLR single-nucleotide polymorphisms rs11669576 (LDLR8), rs5930 (LDLR10), and rs5925 (LDLR13) are associated with cognitive and functional changes in AD, while also considering APOE haplotypes and lipid-lowering treatment with lipophilic statins for stratification. Consecutive outpatients with late-onset AD were screened with cognitive tests, while caregivers scored functionality and caregiver burden, with prospective neurotranslational correlations documented for 1 year. For 179 patients, minor allele frequencies were 0.078 for rs11669576-A (14.5% heterozygotes), 0.346 for rs5930-A (42.5% heterozygotes), and 0.444 for rs5925-C (56.4% heterozygotes), all in Hardy-Weinberg equilibrium; 134 patients had hypercholesterolemia, and 133 used lipophilic statins. Carriers of rs11669576-G had faster cognitive decline, while functional decline was slower for carriers of rs11669576-A who used lipophilic statins. APOE-ε4 carriers who also carried rs5930-AA had improved caregiver burden, while carriers of haplotypes that included rs5930-AG had worse cognitive and functional outcomes, though carriers of the A allele of rs5930 had better cognitive and functional response to lipophilic statins. APOE-ε4 non-carriers who carried rs5925-TT had slower cognitive decline, while lipophilic statins protected carriers of the other genotypes. We preliminarily conclude that reportedly protective variants of LDLR and APOE against risk of AD also slowed cognitive decline, regardless of cholesterol variations, while therapy with lipophilic statins might benefit carriers of specific genetic variants.

Emerging Alternative Proteinases in APP Metabolism and Alzheimer's Disease Pathogenesis: A Focus on MT1-MMP and MT5-MMP

Processing of amyloid beta precursor protein (APP) into amyloid-beta peptide (Aβ) by β-secretase and γ-secretase complex is at the heart of the pathogenesis of Alzheimer’s disease (AD). Targeting this proteolytic pathway effectively reduces/prevents pathology and cognitive decline in preclinical experimental models of the disease, but therapeutic strategies based on secretase activity modifying drugs have so far failed in clinical trials. Although this may raise some doubts on the relevance of β- and γ-secretases as targets, new APP-cleaving enzymes, including meprin-β, legumain (δ-secretase), rhomboid-like protein-4 (RHBDL4), caspases and membrane-type matrix metalloproteinases (MT-MMPs/η-secretases) have confirmed that APP processing remains a solid mechanism in AD pathophysiology. This review will discuss recent findings on the roles of all these proteinases in the nervous system, and in particular on the roles of MT-MMPs, which are at the crossroads of pathological events involving not only amyloidogenesis, but also inflammation and synaptic dysfunctions. Assessing the potential of these emerging proteinases in the Alzheimer’s field opens up new research prospects to improve our knowledge of fundamental mechanisms of the disease and help us establish new therapeutic strategies.

HMG-CoA reductase promotes protein prenylation and therefore is indispensible for T-cell survival

Statins are a well-established family of drugs that lower cholesterol levels via the competitive inhibition of the enzyme 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGCR). In addition, the pleiotropic anti-inflammatory effects of statins on T cells make them attractive as therapeutic drugs in T-cell-driven autoimmune disorders. Since statins do not exclusively target HMGCR and thus might have varying effects on different cell types, we generated a new mouse strain allowing for the tissue-specific deletion of HMGCR. Deletion of HMGCR expression in T cells led to a severe decrease in their numbers with the remaining cells displaying an activated phenotype, with an increased proportion of regulatory T cells (T_regs) in particular. However, deletion of HMGCR specifically in T_regs resulted in severe autoimmunity, suggesting that this enzyme is also essential for the maintenance of T_regs. We were able to prevent the death of HMGCR-deficient lymphocytes by the addition of either the direct metabolite of HMGCR, namely mevalonate, or the downstream metabolite geranylgeranyl pyrophosphate, which is essential for protein prenylation. However, the addition of cholesterol, which is the final product of the mevalonate pathway, did not inhibit cell death, indicating that protein prenylation rather than the cholesterol biosynthesis pathway is indispensible for T-cell survival.

Evidence for benefit of statins to modify cognitive decline and risk in Alzheimer's disease

Background

Despite substantial research and development investment in Alzheimer’s disease (AD), effective therapeutics remain elusive. Significant emerging evidence has linked cholesterol, β-amyloid and AD, and several studies have shown a reduced risk for AD and dementia in populations treated with statins. However, while some clinical trials evaluating statins in general AD populations have been conducted, these resulted in no significant therapeutic benefit. By focusing on subgroups of the AD population, it may be possible to detect endotypes responsive to statin therapy.

Methods

Here we investigate the possible protective and therapeutic effect of statins in AD through the analysis of datasets of integrated clinical trials, and prospective observational studies.

Results

Re-analysis of AD patient-level data from failed clinical trials suggested by trend that use of simvastatin may slow the progression of cognitive decline, and to a greater extent in ApoE4 homozygotes. Evaluation of continual long-term use of various statins, in participants from multiple studies at baseline, revealed better cognitive performance in statin users. These findings were supported in an additional, observational cohort where the incidence of AD was significantly lower in statin users, and ApoE4/ApoE4-genotyped AD patients treated with statins showed better cognitive function over the course of 10-year follow-up.

Conclusions

These results indicate that the use of statins may benefit all AD patients with potentially greater therapeutic efficacy in those homozygous for ApoE4.

Impact of lifestyle-related disease on conversion and reversion in patients with mild cognitive impairment: after 12 months of follow-up

OBJECTIVE

The objective of the study is to investigate whether the lifestyle-related disease (LSRD) hypertension, type II diabetes mellitus, and lipid abnormality are associated with conversion and reversion in patients with mild cognitive impairment (MCI) over 12 months of follow-up.

METHODS

One hundred and thirteen patients with MCI were prospectively enrolled and longitudinally assessed. Methods used include mini-mental state examination, the Japanese version of the cognitive subscale of the Alzheimer's Disease Assessment Scale, the Clinical Dementia Rating, the Frontal Assessment Battery, the Neuropsychiatric Inventory, magnetic resonance imaging, and quantitative single-photon emission computed tomography. In addition, laboratory examinations of glucose and lipids were also performed. All measurements were performed at first intake and again at the end of the 12-month follow-up. Conversion was identified as a change in Clinical Dementia Rating from 0.5 to 1 and reversion as a change from 0.5 to 0.

RESULTS

Patients with MCI with reversion had lower comorbid lipid abnormality at baseline and higher cognitive and behaviour function across the 12-month follow-up compared with those with no change or conversion. Patients without comorbid LSRD had lower systolic pressure and lower glucose and triglyceride levels at baseline, as well as less cognitive decline compared with other groups across the follow-up period.

CONCLUSIONS

The absence of lipid abnormality at baseline may contribute to reversion in patients with MCI. The presence of multiple LSRD was associated with cognitive decline. Our results highlight the contribution of multiple LSRD on increasing conversion and decreasing reversion in patients with MCI. Copyright © 2015 John Wiley & Sons, Ltd.

Upstream and downstream processing of lovastatin by Aspergillus terreus

The present study describes the enhanced production and purification of lovastatin by Aspergillus terreus in submerged batch fermentation. The enhancement of lovastatin production from A. terreus was attempted by random mutagenesis using ultraviolet radiations and nitrous acid. UV mutants exhibited increased efficiency for lovastatin production as compared with nitrous acid mutants. Among all the mutants developed, A. terreus UV-4 was found to be the hyper producer of lovastatin. This mutant gave 3.5-fold higher lovastatin production than the wild culture of A. terreus NRRL 265. Various cultural conditions were also optimized for hyper-producing mutant strain. 5 % glucose as carbon source, 1.5 % corn steep liquor as nitrogen source, initial pH value of 6, 120 h of incubation period, and 28 °C of incubation temperature were found as best parameters for higher lovastatin production in shake flasks. Production of lovastatin by wild and mutant strains of A. terreus was also scaled up to laboratory scale fermentor. The fermentation process was conducted at 28 °C, 200 rpm agitation, and 1vvm air flow rate without pH control. After the optimization of cultural conditions in 250 ml Erlenmeyer flasks and scaling up to laboratory scale fermentor, the mutant A. terreus UV-4 gave eightfold higher lovastatin production (3249.95 μg/ml) than its production by wild strain in shake flasks. Purification of lovastatin was carried out by solvent extraction method which yielded 977.1 mg/l of lovastatin with 98.99 % chromatographic purity and 26.76 % recovery. The crystal structure of lovastatin was determined using X-ray diffraction analysis which is first ever reported.

Atorvastatin Protects NSC-34 Motor Neurons Against Oxidative Stress by Activating PI3K, ERK and Free Radical Scavenging

Although statins, or hydroxymethylglutaryl coenzyme A (HMG-Co A) reductase inhibitors, are generally used to decrease levels of circulating cholesterol, they have also been reported to have neuroprotective effects through various mechanisms. However, recent results have indicated that they may be harmful in patients with amyotrophic lateral sclerosis (ALS). In this study, we investigate whether atorvastatin protects motor neuron-like cells (NSC-34D) from oxidative stress. To evaluate the effects of atorvastatin or hydrogen peroxide or both on NSC-34D cells, the cells were treated with various combinations of these agents. To evaluate the viability of the cells, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays and trypan blue staining were performed. Levels of free radicals and intracellular signaling proteins were evaluated using the fluorescent probe 2',7'-dichlorodihydrofluorescein diacetate (DCFH-DA) and Western blotting, respectively. Atorvastatin protected NSC-34D cells against oxidative stress in a concentration-dependent manner. This neuroprotective effect of atorvastatin was blocked by LY294002, a phosphatidylinositol 3-kinase (PI3K) inhibitor and by FR180204, a selective extracellular signal-related kinase (ERK) inhibitor. Atorvastatin treatment increased the expression levels of p85αPI3K, phosphorylated Akt, phosphorylated glycogen synthase kinase-3β, phosphorylated ERK, and Bcl-2, which are proteins related to survival. Furthermore, atorvastatin decreased the levels of cytosolic cytochrome C, Bax, cleaved caspase-9, and cleaved caspase-3, which are associated with death in oxidative stress-injured NSC-34D cells. We conclude that atorvastatin has a protective effect against oxidative stress in motor neurons by activating the PI3K and ERK pathways as well as by scavenging free radicals. These findings indicate that statins could help protect motor neurons from oxidative stress.

Hyperlipidemia and statins affect neurological outcome in lumbar spine injury

The disabling pathophysiologic effects of lipid and neuroprotective effects of statins have recently been demonstrated for acute spinal cord injuries in animal models. This large scale population-based study aimed to investigate the effect hyperlipidemia and the use of statins in patients with lumbar spine injury. The National Health Insurance Research Database of Taiwan was used to identify patients with lumbar spine injury. A total of 2844 patients were grouped into three: no hyperlipidemia, hyperlipidemia using low-dose of statins (≤90 of the defined daily dosage (DDD)), and severe hyperlipidemia using high-dose of statins (>90 DDD). A Cox multiple regression model was used to compare the incidence rates of disability among the three groups. The results showed that patients with hyperlipidemia appeared a higher risk of permanent disability (adjusted HR = 1.38, p = 0.28). In subgroup analysis, patients with severe hyperlipidemia had a higher risk of disability (adjusted HR = 3.1, p < 0.004), whereas hyperlipidemia using low-dose statins had a similar risk of permanently disability (adjusted HR = 0.83, p = 0.661). Hyperlipidemia adversely affected the neurological outcomes of lumbar spinal injury. Statins may have the potential to reverse this higher risk of disability. However, this beneficiary effect of statins only existed in patients using a lower dose (≤90 DDD).

Apolipoprotein E receptor pathways in Alzheimer disease

Alzheimer disease (AD) is the most common neurodegenerative disease affecting millions of patients worldwide. According to the amyloid cascade hypothesis, the formation of neurotoxic oligomers composed of amyloid-β (Aβ) peptides is the main mechanism that causes synaptic dysfunction and, eventually, neuronal cell death in this condition. Intriguingly, apolipoprotein E (apoE), the most important genetic risk factor for sporadic AD, emerges as a key factor that contributes to many aspects of the amyloid cascade including the clearance of Aβ from brain interstitial fluid and the ability of this peptide to form neurotoxic oligomers. Central to the activity of apoE in the healthy and in the diseased brain are apoE receptors that interact with this protein to mediate its multiple cellular and systemic effects. This review describes the molecular interactions that link apoE and its cellular receptors with neuronal viability and function, and how defects in these pathways in the brain promote neurodegeneration. For further resources related to this article, please visit the WIREs website.

CONFLICT OF INTEREST

The authors have declared no conflicts of interest for this article.

Statins, Bcl-2, and apoptosis: cell death or cell protection?

Statins have proven their effectiveness in the treatment of cardiovascular disease. This class of drugs has also attracted attention as a potential treatment for dissimilar diseases such as certain types of cancers and neurodegenerative diseases. What appears to be a contradiction is that, in the case of cancer, it has been suggested that statins increase apoptosis and alter levels of Bcl-2 family members (e.g., reduce Bcl-2 and increase Bax), whereas studies mainly using noncancerous cells report opposite effects. This review examined studies reporting on the effects of statins on Bcl-2 family members, apoptosis, cell death, and cell protection. Much, but not all, of the evidence supporting the pro-apoptotic effects of statins is based on data in cancer cell lines and the use of relatively high drug concentrations. Studies indicating an anti-apoptotic effect of statins are fewer in number and generally used much lower drug concentrations and normal cells. Those conclusions are not definitive, and certainly, there is a need for additional research to determine if statin repositioning is justified for noncardiovascular diseases.

Ayurvedic medicinal plants for Alzheimer's disease: a review

Alzheimer's disease is an age-associated, irreversible, progressive neurodegenerative disease that is characterized by severe memory loss, unusual behavior, personality changes, and a decline in cognitive function. No cure for Alzheimer's exists, and the drugs currently available to treat the disease have limited effectiveness. It is believed that therapeutic intervention that could postpone the onset or progression of Alzheimer's disease would dramatically reduce the number of cases in the next 50 years. Ayurvedic medicinal plants have been the single most productive source of leads for the development of drugs, and over a hundred new products are already in clinical development. Indeed, several scientific studies have described the use of various Ayurvedic medicinal plants and their constituents for treatment of Alzheimer's disease. Although the exact mechanism of their action is still not clear, phytochemical studies of the different parts of the plants have shown the presence of many valuable compounds, such as lignans, flavonoids, tannins, polyphenols, triterpenes, sterols, and alkaloids, that show a wide spectrum of pharmacological activities, including anti-inflammatory, anti-amyloidogenic, anti-cholinesterase, hypolipidemic, and antioxidant effects. This review gathers research on various medicinal plants that have shown promise in reversing the Alzheimer's disease pathology. The report summarizes information concerning the phytochemistry, biological, and cellular activities and clinical applications of these various plants in order to provide sufficient baseline information that could be used in drug discovery campaigns and development process, thereby providing new functional leads for Alzheimer's disease.

Microbial production and biomedical applications of lovastatin

Lovastatin is a potent hypercholesterolemic drug used for lowering blood cholesterol. Lovastatin acts by competitively inhibiting the enzyme, 3-hydroxy-3-methylglutaryl coenzyme A reductase involved in the biosynthesis of cholesterol. Commercially lovastatin is produced by a variety of filamentous fungi including Penicillium species, Monascus ruber and Aspergillus terreus as a secondary metabolite. Production of lovastatin by fermentation decreases the production cost compared to costs of chemical synthesis. In recent years, lovastatin has also been reported as a potential therapeutic agent for the treatment of various types of tumors and also play a tremendous role in the regulation of the inflammatory and immune response, coagulation process, bone turnover, neovascularization, vascular tone, and arterial pressure. This review deals with the structure, biosynthesis, various modes of fermentation and applications of lovastatin.

Alzheimer's disease: brain expression of a metabolic disorder?

Alzheimer's disease (AD) is the most common form of dementia and is of rapidly increasing health, social and economic impact. Recent evidence suggests a strict link between metabolic disorders and AD. In the last decade much attention has focused specifically on the connection between dysfunction of lipid metabolism and AD. Here we discuss aspects of lipid regulation, including changes in cholesterol levels, function of apolipoproteins and leptin, and how these relate to AD pathogenesis. Despite the vast literature available, many aspects still need clarification. Nevertheless, the route is already delineated to directly connect aspects of lipid regulation to AD. This could represent a starting point to identify novel potential targets for a preventive and/or treatment strategy of the disease.

Statins and neuroprotection: a prescription to move the field forward

There is growing interest in the use of statins, HMG-CoA reductase inhibitors, for treating specific neurodegenerative diseases (e.g., cerebrovascular disease, Parkinson's disease, Alzheimer's disease, multiple sclerosis) and possibly traumatic brain injury. Neither is there a consensus on the efficacy of statins in treating the aforementioned diseases nor are the mechanisms of the purported statin-induced neuroprotection well-understood. Part of the support for statin-induced neuroprotection comes from studies using animal models and cell culture. Important information has resulted from that work but there continues to be a lack of progress on basic issues pertaining to statins and brain that impedes advancement in understanding how statins alter brain function. For example, there are scant data on the pharmacokinetics of lipophilic and hydrophilic statins in brain, statin-induced neuroprotection versus cell death, and statins and brain isoprenoids. The purpose of this mini-review will be to examine those aforementioned issues and to identify directions of future research.

Simvastatin stimulates production of the antiapoptotic protein Bcl-2 via endothelin-1 and NFATc3 in SH-SY5Y cells

The use of statins for the prevention or treatment of different neurodegenerative diseases has generated considerable interest albeit with some controversy. Mechanisms of statin-induced neuroprotection are not well understood. Recently, we reported that simvastatin stimulated neuronal gene expression and protein levels of the major antiapoptotic protein Bcl-2 in vivo and in vitro; suppression of Bcl-2 in SH-SY5Y cells reduced simvastatin neuroprotection; effects were independent of cholesterol and other products of the 3-hydroxy-3-methylglutaryl-CoA reductase pathway. Endothelin-1 (ET-1) can increase Bcl-2 abundance via the transcription factor nuclear factor of activated thymocytes (NFATc), and simvastatin was reported to increase ET-1 gene expression. We tested the hypothesis that simvastatin stimulation of Bcl-2 involves up-regulation of ET-1 and binding of NFATc to Bcl-2 promoter sites in SH-SY5Y human neuroblastoma cells. Simvastatin increased both intracellular and secreted ET-1 protein levels. Exogenous ET-1 increased Bcl-2 protein abundance, which was inhibited by ET-1 receptor antagonists. Simvastatin increased translocation of NFATc3 to the nucleus while reducing nuclear NFATc1 and having no effect on NFATc4. Endothelin-1 also increased NFATc3 levels in the nucleus, and this increase was inhibited by ET-1 receptor antagonists. Treatment of cells with simvastatin stimulated binding of NFATc3 to the Bcl-2 promoter. We report novel findings showing that up-regulation of Bcl-2 by simvastatin involves ET-1 and the transcription factor NFATc3. Discovering how statins can selectively alter a specific NFATc isoform that leads to an increase in an antiapoptotic protein will provide a new approach to understanding statin-induced neuroprotection and conditions outside the brain in which apoptosis contributes to pathophysiology.

Modulation of cholesterol, farnesylpyrophosphate, and geranylgeranylpyrophosphate in neuroblastoma SH-SY5Y-APP695 cells: impact on amyloid beta-protein production

There is keen interest in the role of the isoprenoids farnesylpyrophosphate (FPP) and geranylgeranylpyrophosphate (GGPP) in protein prenylation and cell function in Alzheimer's disease (AD). We recently reported elevated FPP and GGPP brain levels and increased gene expression of FPP synthase (FPPS) and GGPP synthase (GGPPS) in the frontal cortex of AD patients. Cholesterol levels and gene expression of 3-hydroxy-3-methylglutaryl-coenzyme A reductase were similar in AD and control samples, suggesting that homeostasis of FPP and GGPP but not cholesterol is specifically targeted in brain tissue of AD patients (Neurobiol Dis 2009 35:251-257). In the present study, it was determined if cellular levels of FPP, GGPP, and cholesterol affect beta-amyloid (Abeta) abundance in SH-SY5Y cells, expressing human APP695. Cells were treated with different inhibitors of the mevalonate/isoprenoid/cholesterol pathway. FPP, GGPP, cholesterol, and Abeta(1-40) levels were determined, and activities of farnesyltransferase and geranylgeranyltransferase I were measured. Inhibitors of different branches of the mevalonate/isoprenoid/cholesterol pathway as expected reduced cholesterol and isoprenoid levels in neuroblastoma cells. Abeta(1-40) levels were selectively reduced by cholesterol synthesis inhibitors but not by inhibitors of protein isoprenylation, indicating that changes in cholesterol levels per se and not isoprenoid levels account for the observed modifications in Abeta production.

Isoprenoids, small GTPases and Alzheimer's disease

The mevalonate pathway is a crucial metabolic pathway for most eukaryotic cells. Cholesterol is a highly recognized product of this pathway but growing interest is being given to the synthesis and functions of isoprenoids. Isoprenoids are a complex class of biologically active lipids including for example, dolichol, ubiquinone, farnesylpyrophosphate (FPP) and geranylgeranyl pyrophosphate (GGPP). Early work had shown that the long-chain isoprenoid dolichol is decreased but that dolichyl phosphate and ubiquinone are elevated in brains of Alzheimer's disease (AD) patients. Until recently, levels of their biological active precursors FPP and GGPP were unknown. These short-chain isoprenoids are critical in the post-translational modification of certain proteins which function as molecular switches in numerous signaling pathways. The major protein families belong to the superfamily of small GTPases, consisting of roughly 150 members. Recent experimental evidence indicated that members of the small GTPases are involved in AD pathogenesis and stimulated interest in the role of FPP and GGPP in protein prenylation and cell function. A straightforward prediction derived from those studies was that FPP and GGPP levels would be elevated in AD brains as compared with normal neurological controls. For the first time, recent evidence shows significantly elevated levels of FPP and GGPP in human AD brain tissue. Cholesterol levels did not differ between AD and control samples. One obvious conclusion is that homeostasis of FPP and GGPP but not of cholesterol is specifically targeted in AD. Since prenylation of small GTPases by FPP or GGPP is indispensable for their proper function we are proposing that these two isoprenoids are up-regulated in AD resulting in an over abundance of certain prenylated proteins which contributes to neuronal dysfunction.

Increased membrane cholesterol might render mature hippocampal neurons more susceptible to beta-amyloid-induced calpain activation and tau toxicity

A growing body of evidence suggests that beta-amyloid (Abeta), the main component of senile plaques, induces abnormal posttranslational processing of the microtubule-associated protein tau. We have recently described that, in addition to increasing tau phosphorylation, Abeta enhanced calpain activity leading to the generation of a toxic 17 kDa tau fragment in cultured hippocampal neurons. How aging, the greatest Alzheimer's disease (AD) risk factor, might regulate this proteolytic event remains unknown. In this study, we assessed the susceptibility of cultured hippocampal neurons to Abeta-dependent 17 kDa tau production at different developmental stages. Our results revealed that mature neurons were more susceptible to Abeta-induced calpain activation leading to the generation of this fragment than young neurons. In addition, the production of this fragment correlated with a decrease in cell viability in mature hippocampal neurons. Second, we determined whether membrane cholesterol, a suspect player in AD, might mediate these age-dependent differences in Abeta-induced calpain activation. Filipin staining and an Amplex Red cholesterol assay showed that mature neuron membrane cholesterol levels were significantly higher than those detected in young ones. Furthermore, decreasing membrane cholesterol in mature neurons reduced their susceptibility to Abeta-dependent calpain activation, 17 kDa tau production, and cell death, whereas increasing membrane cholesterol in young neurons enhanced these Abeta-mediated cellular processes. Finally, fura-2 calcium imaging indicated that membrane cholesterol alterations might change the vulnerability of cells to Abeta insult by altering calcium influx. Together these data suggested a potential role of cholesterol in linking aging to Abeta-induced tau proteolysis in the context of AD.

Plasma lipoprotein beta-amyloid in subjects with Alzheimer's disease or mild cognitive impairment

BACKGROUND

Plasma amyloid beta-peptide (Abeta) can compromise the blood-brain barrier, contributing to cerebrovascular alterations and amyloid angiopathy in Alzheimer's disease (AD). The objectives of this study were to investigate the distribution of lipoprotein-bound plasma-Abeta isoforms.

METHODS

This involved a case-control study of subjects with AD or amnestic mild cognitive impairment (MCI) versus controls. Lipoprotein Abeta distribution was determined in fasted plasma. For assessment of chylomicron homeostasis in the postabsorptive state, subjects were bled 4 h after a low-fat meal. The main outcome measures were plasma lipoprotein Abeta isoform distribution and lipid homeostasis.

RESULTS

We found the majority of plasma Abeta to be associated with triglyceride-rich lipoproteins (TRLs) encompassing chylomicrons, VLDL and IDL. For all lipoprotein groups, Abeta1-40 was the predominant isoform, accounting for approximately 50% of the total. Thereafter, equivalent amounts of the isoforms 1-42, 2-40, 1-38, 1-37 and 1-39 were found. Abeta1-37, Abeta1-38 and Abeta2-40 isoforms were significantly enriched within the TRL fraction of AD/MCI subjects and similar trends were observed for isoforms Abeta1-39, Abeta1-40 and Abeta1-42. Lipoprotein-Abeta was inversely associated with plasma total- and LDL cholesterol. AD/MCI subjects were not dyslipidaemic, however, there was evidence of accumulation of chylomicrons in the postabsorptive state.

CONCLUSIONS

Our data show that Abeta was found to be associated with plasma lipoproteins, especially those enriched with triglyceride. We find that Abeta may be increased in normolipidaemic AD subjects, commensurate with possible disturbances in postprandial lipoprotein homeostasis.

Apolipoprotein E and cholesterol in aging and disease in the brain

Cholesterol can be detrimental or vital, and must be present in the right place at the right time and in the right amount. This is well known in the heart and the vascular system. However, in the CNS cholesterol is still an enigma, although several of its fundamental functions in the brain have been identified. Brain cholesterol has attracted additional attention owing to its close connection to ApoE, a key polymorphic transporter of extracellular cholesterol in humans. Indeed, both cholesterol and ApoE are so critical to fundamental activities of the brain, that the brain regulates their synthesis autonomously. Yet, similar control mechanisms of ApoE and cholesterol homeostasis may exist on either sides of the blood-brain barrier. One indication is that the APOE ε4 allele is associated with hypercholesterolemia and a proatherogenic profile on the vascular side and with increased risk of Alzheimer's disease on the CNS side. In this review, we draw attention to the association between cholesterol and ApoE in the aging and diseased brain, and to the behavior of the ApoE4 protein at the molecular level. The attempt to correlate in vivo and in vitro observations is challenging but crucial for developing future strategies to address ApoE-related aberrations in cholesterol metabolism selectively in the brain.

Biological consequences of statins in Candida species and possible implications for human health

The statins, simvastatin and atorvastatin are the most widely prescribed drugs. Statins lower cholesterol levels through their action on HMG-CoA (3-hydroxy-3-methylglutaryl-CoA) reductase, an essential enzyme for the biosynthesis of cholesterol. Fungal HMG-CoA reductases are also inhibited by statins, resulting in reduced levels of ergosterol (the fungal equivalent of cholesterol) and concomitant growth inhibition. This effect occurs in a range of fungal species and possibly affects fungal colonization of people on statin therapy. Furthermore, it may suggest that statins could have a role in new antifungal therapies. Possibly associated with the reduction in ergosterol levels, statins also inhibit respiratory growth. In the yeast, Candida glabrata, passage with statins dramatically increased the frequencies of petite mutants that were devoid of mitochondrial DNA, suggesting that statins caused a defect in the maintenance of mitochondrial DNA. These observations in C. glabrata may provide further insights into side effects of statins in humans undergoing treatment for hypercholesterolaemia. In addition, C. glabrata may be highly useful for the preliminary screening of agents to reduce statin side effects.

Fatty acids, lipid metabolism and Alzheimer pathology

Alzheimer's disease is the most common form of dementia in the elderly. The cause of Alzheimer's disease is still unknown and there is no cure for the disease yet despite 100 years of extensive research. Cardiovascular risk factors such as high serum cholesterol, presence of the Apolipoprotein epsilon4 (APOE epsilon4) allele and hypertension, play important roles in the development of Alzheimer's disease. We postulate that a combination of diet, lifestyle, vascular, genetic, and amyloid related factors, which enhance each other's contribution in the onset and course of Alzheimer's disease, will be more likely the cause of the disease instead of one sole mechanism. The possibility that the risk for Alzheimer's disease can be reduced by diet or lifestyle is of great importance and suggests a preventative treatment in Alzheimer's disease. Because of the great importance of lipid diets and metabolism in preventative treatment against both Alzheimer's disease and cardiovascular disease, long-chain polyunsaturated fatty acids from fish oil, ApoE genotype and cholesterol metabolism in correlation with Alzheimer's disease will be reviewed.

Comparison of biochemical effects of statins and fish oil in brain: the battle of the titans

Neural membranes are composed of glycerophospholipids, sphingolipids, cholesterol and proteins. The distribution of these lipids within the neural membrane is not random but organized. Neural membranes contain lipid rafts or microdomains that are enriched in sphingolipids and cholesterol. These rafts act as platforms for the generation of glycerophospholipid-, sphingolipid-, and cholesterol-derived second messengers, lipid mediators that are necessary for normal cellular function. Glycerophospholipid-derived lipid mediators include eicosanoids, docosanoids, lipoxins, and platelet-activating factor. Sphingolipid-derived lipid mediators include ceramides, ceramide 1-phosphates, and sphingosine 1-phosphate. Cholesterol-derived lipid mediators include 24-hydroxycholesterol, 25-hydroxycholesterol, and 7-ketocholesterol. Abnormal signal transduction processes and enhanced production of lipid mediators cause oxidative stress and inflammation. These processes are closely associated with the pathogenesis of acute neural trauma (stroke, spinal cord injury, and head injury) and neurodegenerative diseases such as Alzheimer disease. Statins, the HMG-CoA reductase inhibitors, are effective lipid lowering agents that significantly reduce risk for cardiovascular and cerebrovascular diseases. Beneficial effects of statins in neurological diseases are due to their anti-excitotoxic, antioxidant, and anti-inflammatory properties. Fish oil omega-3 fatty acids, eicosapentaenoic acid and docosahexaenoic acid, have similar anti-excitotoxic, antioxidant and anti-inflammatory effects in brain tissue. Thus the lipid mediators, resolvins, protectins, and neuroprotectins, derived from eicosapentaenoic acid and docosahexaenoic acid retard neuroinflammation, oxidative stress, and apoptotic cell death in brain tissue. Like statins, ingredients of fish oil inhibit generation of beta-amyloid and provide protection from oxidative stress and inflammatory processes. Collective evidence suggests that antioxidant, anti-inflammatory, and anti-apoptotic properties of statins and fish oil contribute to the clinical efficacy of treating neurological disorders with statins and fish oil. We speculate that there is an overlap between neurochemical events associated with neural cell injury in stroke and neurodegenerative diseases. This commentary compares the neurochemical effects of statins with those of fish oil.

Regulation of central nervous system cholesterol homeostasis by the liver X receptor agonist TO-901317

The nuclear oxysterol receptors known as liver X receptors (LXR) are responsible for regulating genes involved in cholesterol homeostasis. Two subtypes exist, LXR-alpha and LXR-beta, both of which are expressed in the central nervous system (CNS). Activation of LXR causes an increase in mechanisms involved in cholesterol efflux, including ATP-binding cassette transporters (ABC)-A1 and ABC-G1. Although LXR agonists have been found to induce gene expression for ABC-A1 and ABC-G1 in the CNS, no functional response has been recorded. In this study, we show that an LXR agonist (TO-901317) increases protein levels of the cholesterol transporters ABC-A1 and ABC-G1, as well as the cholesterol chaperone protein apolipoprotein E (apoE). These changes are associated with a decrease in cholesterol levels from isolated cortical synaptosomal plasma membranes. LXR activation occurs in response to increased cholesterol levels in cells. However, while data exists on how LXR alter cholesterol efflux, there is no data on whether these receptors alter production of cholesterol. We found that TO-901317 increases HMG-CoA reductase activity, the rate-limiting step of cholesterol production in vivo. This finding was duplicated in an in vitro system. Although high concentrations (>1 microM) of TO-901317 were required to induce HMG-CoA reductase activity, these changes only occurred in the presence of apolipoprotein AI, suggesting that cholesterol efflux is required for this effect to occur. These data show that the LXR agonist TO-901317 is capable of reducing cholesterol in neurons of the CNS.

Effects of statins on cognitive function in patients with Alzheimer's disease in galantamine clinical trials

BACKGROUND AND OBJECTIVE

A number of reports have been published on the possible involvement of changes in brain cholesterol metabolism in the origin of Alzheimer's disease (AD) and the potential for influencing these changes by administration of HMG-CoA reductase inhibitors ('statins'). The aim of this study was to evaluate a potential association between use of statins and maintenance of cognitive function in patients with AD in galantamine clinical trials.

METHOD

A post hoc analysis was conducted on data pooled from three double-blind, placebo-controlled, clinical trials of galantamine in patients with AD. Patients were divided into four treatment groups: statin plus galantamine (n = 42), statin alone (n = 50), galantamine alone (n = 614) or neither galantamine nor statin (n = 619).

RESULTS

Galantamine was associated with a significant beneficial effect on cognitive status (p < 0.001). The association of use of statins with changes in cognitive status was not significant (p = 0.083). There was no significant interaction between the effects on cognition of statins and galantamine (p = 0.183) and no statistically significant changes in adverse effect rates were observed.

CONCLUSION

These findings suggest the need for larger long-term trials to confirm or refute possible effects of statins on cognitive function and the potential interaction of statins with acetylcholinesterase inhibitors in the treatment of AD.

Memantine in the treatment of mild-to-moderate Alzheimer's disease

Memantine is the first and only medication that has been approved by European, US and Canadian regulatory agencies for the treatment of moderate-to-severe Alzheimer's disease (AD). It is an NMDA receptor antagonist that works to prevent excitotoxicity and cell death, which are mediated by the excessive influx of calcium during a sustained release of glutamate. Preclinical studies of memantine reveal that it has the potential to improve memory and learning processes after impairment has occurred, as well as to prevent further neuronal damage. Although memantine has been considered for the treatment of earlier AD, it has not yet been approved for this. Randomized controlled trials of memantine in the treatment of mild-to-moderate AD have demonstrated small treatment effects in measures of cognition, global assessment and behavior favoring the use of memantine. However, the differences between treatment groups were not consistently significant. Two ongoing long-term trials are further investigating the efficacy of memantine in the treatment of mild-to-moderate AD.

Bcl-2 upregulation and neuroprotection in guinea pig brain following chronic simvastatin treatment

The present study determined if chronic simvastatin administration in vivo would provide neuroprotection in brain cells isolated from guinea pigs after challenge with the Bcl-2 inhibitor HA 14-1 or the NO donor sodium nitroprusside (SNP). Bcl-2 levels were significantly increased in brains of simvastatin-treated guinea pigs while levels of the pro-apoptotic protein Bax were significantly reduced. The ratio of Bax/Bcl-2, being a critical factor of the apoptotic state of cells, was significantly reduced in simvastatin-treated animals. Cholesterol levels in the brain remained unchanged in the simvastatin group. Brain cells isolated from simvastatin-treated guinea pigs were significantly less vulnerable to mitochondrial dysfunction and caspase-activation. These results provide new insight into potential mechanisms for the protective actions of statins within the CNS where programmed cell death has been implicated.

Memantine in the treatment of Alzheimer’s disease

Memantine is a moderate-affinity glutamate antagonist that primarily takes action at the N-methyl-D-aspartate receptor site. It has US FDA and European Medicines Agency approval for the treatment of moderate-to-severe Alzheimer’s disease. Memantine replaces Mg2+ at the N-methyl-D-aspartate receptor, blocking pathological glutamate activity but allowing normal glutamate action at this site. Consequently, calcium homeostasis is better maintained, reducing slow after hyperpolarization and preventing neuronal excitotoxicity and cell death. Clinical trials have shown that memantine is generally safe and well tolerated, and have provided evidence for its efficacy as assessed by cognitive, behavioral, functional and global measures. It has also been shown to be well tolerated and effective in the treatment of moderate-to-severe Alzheimer’s disease when patients received previous and ongoing treatment with donepezil. The tolerability and efficacy of memantine is under continued investigation in milder Alzheimer’s disease and other forms of dementia.

Alzheimer disease--no target for statin treatment. A mini review

Nosologically, Alzheimer disease (AD) is not a single disorder. A minority of around 400 families worldwide can be grouped as hereditary in origin, whereas the majority of all Alzheimer cases (approx. 25 million worldwide) are sporadic in origin. In the pathophysiology of the latter type, a number of susceptibility genes contribute to the disease among which are allelic abnormalities of the apolipoprotein E4 gene pointing to a link between disturbed cholesterol metabolism and sporadic AD. Cholesterol is a main component of membrane composition enriched in microdomains and is functionally linked to the proteolytic processing of amyloid precursor protein (APP). In sporadic AD, a marked diminution of both membrane phospholipids and cholesterol has been found. Evidence has been provided that high plasma cholesterol may protect from AD. In contrast to these well documented abnormalities observed in AD patients, it was assumed that an elevated cholesterol concentration might favour the generation of beta-amyloid and, thus, AD. However, a series of in vitro-and in vivo-studies did not provide evidence for the assumption that an enhanced cholesterol concentration increased betaA4-production. A harsh reduction of membrane cholesterol only caused a "beneficial" effect of APP metabolism. However, this experimentally induced condition may not be compatible to sporadic AD. The application of statins in sporadic AD did not yield results to assume that this therapeutic strategy may prevent or treat successfully sporadic AD.

Oxidative stress and neurodegeneration: where are we now?

The brain and nervous system are prone to oxidative stress, and are inadequately equipped with antioxidant defense systems to prevent 'ongoing' oxidative damage, let alone the extra oxidative damage imposed by the neurodegenerative diseases. Indeed, increased oxidative damage, mitochondrial dysfunction, accumulation of oxidized aggregated proteins, inflammation, and defects in protein clearance constitute complex intertwined pathologies that conspire to kill neurons. After a long lag period, therapeutic and other interventions based on a knowledge of redox biology are on the horizon for at least some of the neurodegenerative diseases.

The 3-hydroxy-3-methylglutaryl co-enzyme A reductase inhibitor pravastatin enhances neurite outgrowth in hippocampal neurons

Epidemiological studies demonstrate a relationship between statin [3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor] usage and reduced risk of developing Alzheimer's disease. To determine whether statins affect neuronal development, we treated cultured rat hippocampal neurons with pravastatin. After 4-48 h of treatment, pravastatin significantly increased the number of neurites produced by each cell and caused a corresponding increase in levels of the membrane phospholipid phosphatidylcholine. Pravastatin treatment also significantly increased neurite length and branching but did not affect cellular cholesterol levels. Co-incubation with mevalonate, but not cholesterol, abolished the stimulatory effect of pravastatin on neurite outgrowth. Treatment of neurons with isoprenoids also abolished the effect of pravastatin on neurite growth, suggesting that pravastatin may stimulate neuritogenesis by preventing isoprenylation of signaling molecules such as the Rho family of small GTPases. A specific inhibitor of geranylgeranylation, but not farnesylation, mimicked the stimulatory effect of pravastatin on neuritogenesis. Pravastatin treatment significantly decreased levels of membrane-associated RhoA. These data suggest that pravastatin treatment increases neurite outgrowth and may do so via inhibiting the activity of geranylgeranylated proteins such as RhoA.

Does cholesterol act as a protector of cholinergic projections in Alzheimer's disease?

The relationship between Alzheimer's disease (AD) and progressive degeneration of the forebrain cholinergic system is very well established, whereas mechanisms linking this disease with cholesterol, apolipoprotein E (apoE) phenotype, and amyloid precursor protein (APP) metabolism have not been fully elucidated even though there is a plethora of publications separately on each of these issues. The intention of this hypothesis is to unify knowledge coming from all of these areas. It is based on an assumption that the process of APP hypermetabolism is a neuroprotective response for age-related cholinergic deterioration. In some individuals this initially positive process becomes highly overregulated by genetic or/and epigenetic risk factors and after many years of accumulations lead eventually to AD. I hypothesise that neuroprotective role of APP-hypermetabolism might be related to enrichment of neuronal membranes (lipid rafts in particular) in cholesterol in order to compensate for decrease in presynaptic cholinergic transmission and/or AD-related decrease in cholesterol levels. The above is consistent with findings indicating that activity of both muscarinic and nicotinic cholinergic receptors is correlated in a positive manner with cholesterol plasmalemmal content. Briefly – APP metabolism together with transport of cholesterol in apoE containing lipoproteins seem to play a key role in mobilising cholesterol into neuronal membranes.